Over the past two decades, these approaches have led to fascinating discoveries, from earthquake processes and subduction dynamics to mantle plumes, mid-ocean ridges, transform faults, thermal heterogeneity, and volatile cycling. They also reveal exciting new opportunities to study oceanographic, biological, and environmental processes. Yet challenges remain: large-scale deployments are costly and logistically complex, data sharing and best practices are often limited, and many valuable data sets remain inaccessible for years, reducing the long-term impact of these community investments.
This session invites contributions from the global community on the full spectrum of amphibian geophysics: from instrument development, experiment design, and novel analysis methods (e.g. machine learning, data fusion, cross-disciplinary approaches) to new scientific results. We particularly encourage submissions that integrate different types of amphibian instrumentation and highlight the role of ocean observations in advancing our understanding of both the oceans and the Earth’s deep interior.
We are also delighted to announce an invited speaker, presenting on their recent work on large-scale OBS experiments such as Santorini and the Galápagos (title to be confirmed).
Orals: Fri, 8 May, 16:15–18:00 | Room K2
Amphibian geophysical experiments are transforming our ability to image Earth’s interior beneath the oceans, yet only a limited number of deployments have been designed at the scale and density required to address specific scientific questions from the crust to the mantle. In this invited talk, I synthesize results from two large ocean-bottom seismometer (OBS) experiments, at Santorini and the Galápagos, that demonstrate a range of science questions, spatial scales, depth ranges, and physical targets.
To image magma transport throughout the entire crust at an arc volcano, the PROTEUS experiment deployed a uniquely dense amphibian short-period array of 89 OBS and 65 land stations at the Santorini-Kolumbo volcanic system. The design combined active-source and passive seismic observations to resolve crustal magma plumbing and volcanic structure at kilometer-scale resolution. The data revealed the depth, volume, and melt extent of shallow magma accumulation beneath the Santorini caldera and demonstrated that caldera-collapse structures formed during the Late Bronze Age Plinian eruption continue to control present-day magma recharge, including the 2011-2012 and 2024-2025 inflation episodes. Imaging further showed how the evolution of regional extension during the Neogene to Quaternary formed a complex of faulted basins. This tectonic system has interacted with magmatism, influencing magma pathways, storage geometry, and anisotropic crustal structure.
A key advance was the discovery of a small, high–melt-fraction magma chamber beneath the adjacent Kolumbo volcano at ~2–4 km depth using full-waveform inversion; an approach enabled by the first use of dense source–receiver coverage at a volcanic system. The smaller size of this eruptible magma reservoir meant it could not be detected using traditional travel-time tomography. More recent tomography leverages the large aperture of the array to extend the velocity structure to greater depths, revealing a mid-crustal magma storage region (8-15 km depth) laterally offset from both Santorini and Kolumbo, as well as deep accumulation of mafic–ultramafic material that thickens the crust beneath Santorini. This crustal framework is central to interpreting the February 2025 seismic swarm, whose migration pattern is consistent with a substantial magma intrusion interacting with extensional faulting.
In contrast, the Marine IGUANA experiment was designed to address mantle-scale questions, including plume-ridge interaction and lithosphere-asthenosphere coupling beneath the Galápagos. These questions require broad spatial coverage and long-duration recordings of natural earthquakes, motivating a 15-month deployment of 53 broadband OBS spanning a ~650 × 800 km region around the archipelago and the nearby Galápagos Spreading Center. Preliminary results reveal low-velocity mantle structures in both P- and S-waves associated with hot plume material, high-velocity material consistent with foundering lithosphere, and plume transport to both the eastern and western Galápagos spreading centers. In addition, spatial variations in seismic anisotropy indicate mantle flow due to absolute plate motion that is modified by the mantle plume.
Together, these experiments illustrate how science-driven experimental design enables insights into processes ranging from crustal magma systems to mantle dynamics, highlighting the power of dense, large-aperture amphibian OBS arrays to address Earth science questions across different scales.
How to cite: Hooft, E. and the PROTEUS team & Marine IGUANA team: Imaging Crustal Magma Systems and Mantle Dynamics with Large Amphibian OBS Arrays, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6002, https://doi.org/10.5194/egusphere-egu26-6002, 2026.
In April 2024, a major submarine eruption occurred at the I1 segment of the Southeast Indian Ridge (SEIR), near Amsterdam Island in the southern Indian Ocean (see Royer et al., EGU26-GD5.1 and Olive et al., EGU26-GD5.1). Luckily, the OHA-GEODAMS Autonomous Hydrophone (AuH) network had been deployed a few weeks before the event and efficiently monitored the eruptive event. This work presents results from this hydroacoustic monitoring together with an innovative automatic cataloging pipeline that allowed to obtain a full spatio-temporal coverage of the event.
Thanks to the low attenuation of low-frequency hydroacoustic waves, hydroacoustics is known to be an efficient way to monitor earthquake swarms. In this case, the GEODAMS network efficiently monitored the eruptive swarm and detected both direct (P- and S-phases) and indirect (T-phases) seismic waves, as well as H-waves generated by interactions between lava and seawater.
During the first weeks of hydroacoustic activity, more than 500 T-waves and 200 H-waves were detected and their sources located. This enabled a precise relocation of the early swarm of strong, teleseismically-recorded earthquakes (Mw~5) that had been registered in the ISC and GCMT catalogs. It also enabled the detection of smaller events that had been missed by land stations. However, this initial analysis relied on manual annotation, a process that is particularly time-consuming and hinders the possibility to build reliable and near-exhaustive catalogs over extended time periods. To overcome this limitation, a fully automated cataloging pipeline was developed (Raumer et al., 2024 & 2025), enabling systematic detection, association, and location of hydroacoustic signals associated with the swarm. This methodology enabled us to estimate key parameters of the eruptive dynamics, such as the precise timing of sequential dyking events, and subsequent lava outpouring, which was later revealed by diachronous seafloor mapping. Moreover, the seismological catalog showed to be complementary with vertical deformation measurements (detailed in Ballu et al., EGU26-SM3.2).
Beyond its own geodynamical significance, the 2024 I1 eruption constitutes a relevant case study to demonstrate the strong potential of an automated approach for hydroacoustic earthquake monitoring. Future applications of this generic methodology should enable the extraction of geodynamical insights from past and potentially large-scale AuH observatories.
Raumer et al. (2024). Seismica. doi: 10.26443/seismica.v3i2.1344
Raumer et al. (2025). Geochem., Geophys., Geosys. doi: 10.1029/2025GC012572
How to cite: Raumer, P.-Y., Royer, J.-Y., Sara, B., Lise, R., Jean-Arthur, O., Valérie, B., Anne, B., and Edgar, L. and the OHA-GEODAMS Scientific party: Making Hydrophones Speak: Semi-Automated Hydroacoustic Monitoring of a Seafloor Spreading Event, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5145, https://doi.org/10.5194/egusphere-egu26-5145, 2026.
Seafloor quartz-resonant pressure gauges manufactured by Paroscientific have long been used to measure vertical seafloor deformation, yet the gauge-specific drift characteristics continue to hinder the precise identification of geodetic and oceanic signals. Recent self-calibrating pressure gauge designs address this limitation by housing an internal reference pressure standard that can be isolated from ambient seawater. Scheduled valve operations switch between ambient and reference pressures, thereby enabling in situ drift calibrations that are isolated from oceanographic variability and seafloor deformation. We evaluate four designs of self-calibrating pressure gauges. The University of Washington (UW) A-0-A, commercial Sonardyne Fetch AZA, and commercial RBR BPRzero use the internal pressure of the instrument housing, measured by a barometer, as a reference. In contrast, the Scripps Institution of Oceanography Cabled Self-Calibrating Pressure Recorder (CSCPR) uses a piston-cylinder system to generate a controlled reference pressure near ambient pressure reading. A-0-A, Fetch AZA, and CSCPR instruments are deployed at 1500 m depth on Axial Seamount at the Central Caldera site of the Ocean Observatories Initiative Regional Cabled Array. Additionally, a Fetch AZA is deployed at 400 m depth on the Barkley Canyon, and a BPRzero is deployed at 2200 m depth on the Endeavour segment on the Ocean Networks Canada NEPTUNE cabled observatory.
At Axial Seamount, the instruments are within 50 m of one another and are adjacent to a conventional pressure gauge in a bottom pressure and tilt (BOTPT) instrument that has been deployed since 2014 and is well aged, with a small drift rate inferred from repeated mobile pressure recorder surveys. Assuming ocean-derived pressure fluctuations and volcanic deformation are spatially coherent across all sensors, each self-calibrating gauge is evaluated by (i) comparing its data with the BOTPT and other gauges to quantify post-calibration residuals, and (ii) assessing internal consistency for the UW A-0-A and CSCPR, which have two pressure gauges inside each unit. Our comparison shows that the self-calibrating pressure gauges generally agree within ±1.0 hPa/year (or 1.0 cm/year of water column height change) over multiple years of deployment. The one exception is the UW A-0-A system. Early in two deployments (2019-2022 and 2024-present), its two gauges are inconsistent with one another and other instruments by up to several hPa, but this bias diminishes within a year, and the records converge. We are evaluating the cause of this transient behavior by analyzing A-0-A calibration sequences. At Barkley Canyon and the Endeavour segment, we evaluate Fetch AZA and BPRzero in the same manner as at Axial Seamount, using several co-sited gauges within 3 km. Both commercial gauges agree with the independent co-sited gauge within ±1.0 hPa/year after applying drift corrections. Comparing data from co-sited sensors enables us to investigate the subtle features of each sensor's performance. All designs demonstrate the potential to reduce instrumental drift to less than 1.0 cm/year. Further evaluation across a wider range of ambient conditions and deployment configurations is warranted.
How to cite: Dobashi, Y., Wilcock, W., Manalang, D., Smith, K., Dentoni, L., Zumberge, M., Sasagawa, G., Cook, M., Sullivan, C., Nooner, S., Chadwick, W., Beeson, J., Heesemann, M., and Schlesinger, A.: Evaluation of Self-Calibrating Pressure Gauges for Seafloor Geodesy: Instrument Comparison at Axial Seamount, Barkley Canyon, and the Endeavour Segment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15728, https://doi.org/10.5194/egusphere-egu26-15728, 2026.
Underwater passive acoustics enables the detection of a wide range of sounds from diverse sources, including seismic T-waves. To locate these events, hydrophone arrays are deployed, requiring arrivals to be identified across multiple synchronized sensors. While manual picking is reliable, it is labor-intensive, time-consuming, and prone to human bias. Automated picking using neural networks significantly increases the number of detected events but introduces challenges such as false positives. The next challenge is to associate detections of the same events to locate their source by trilateration.
The recently published TAPAAS algorithm (Raumer et al., 2025) generates candidate associations for these detections. However, among the produced candidates, there is a substantial number of overlapping and subsets of detections leading to different event locations. Relying solely on least-squares cost or RMSE is insufficient to address these conflicts. To overcome this, we developed a systematic approach combining relocation and a graph-based review of conflicting events, which we validated using synthetic event datasets.
When applied to real data from OHASISBIO and CTBTO arrays of hydrophones in the Indian Ocean, our method successfully built comprehensive catalogs of events. In addition, with a sufficient number of hydrophones (> 4), it is possible to check and improve the instrument synchronization. Generally, autonomous instruments are synchronized with a GNSS clock at deployment and upon recovery, allowing to measure the clock drift (~1-2s/yr); but when hydrophones run out of battery before recovery, the final time information is lost (i.e. drift unknonw). We also found that, sometimes, real-time hydrophone clocks are reset. Our approach allowed us to identify and determine these unknown clock drifts or clock offsets, then correct the arrival-times, and iteratively improve the trilateration.
Raumer et al. (2025). Geochem., Geophys., Geosyst. https://doi.org/10.1029/2025GC012572
How to cite: Safran, R., Raumer, P.-Y., Bazin, S., Briais, A., and Royer, J.-Y.: A Graph-Based Approach for Resolving Conflicts in Underwater Acoustic Event Association for Systematic and Improved Trilateration, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3816, https://doi.org/10.5194/egusphere-egu26-3816, 2026.
It is well known that seismic and electromagnetic experiments provide complementary information regarding lithology and fluid content. There are many published examples where marine seismic and electromagnetic experiments have been conducted on the same geological target and their results combined to provide new insights, and a few where such pairs of experiments have been conducted on coincident profiles. For both techniques, normally the most time-consuming and therefore most expensive component is seabed instrument deployment and recovery. In 2023 we conducted a novel experiment that involved acquisition of both seismic and electromagnetic data using seafloor instruments equipped with both types of sensor that therefore only needed to be deployed once. We deployed 35 Scripps instruments equipped with orthogonal horizontal electrodes, orthogonal horizontal coil magnetometers and 14 instruments from the UK Ocean Bottom Instrumentation Facility equipped with orthogonal horizontal electrodes, three-component fluxgate magnetometers, hydrophones and short-period three-component geophone packages. These instruments were deployed for c. two weeks at c. 4-km intervals along a transect across the continent-ocean transition southwest of the UK. During this time, we shot two different airgun sources and then conducted a controlled source electromagnetic (CSEM) experiment by towing Southampton’s deep-towed electromagnetic transmitter along the transect. Our transect coincided with a pre-existing seismic reflection profile collected with a 10-km streamer as part of an Irish government project (covering part of the transect) and a new profile with a 2-km streamer acquired during a test cruise by the National Oceanography Centre in 2024 (covering the remainder of the transect).
The resulting rich dataset allows a variety of analyses, some of which are only made possible by the multiphysics acquisition. Electromagnetic sensors are normally located by acoustic triangulation; these locations can be improved by using the airgun shots. The fluxgate magnetometers can be used as compasses to orient both the electromagnetic sensors and the horizontal geophones. At crustal level, the seismic and CSEM experiments allow us to obtain coincident P-wave velocity and resistivity models at similar resolution. Magnetotelluric data provide constraints on the mantle lithosphere and the lithosphere-asthenosphere boundary. Our seismic experiment is not designed to image at these depths, but there are some constraints from teleseismic events such as the 8th September Morocco earthquake, which is well recorded across our array. Additional constraints may come from ambient noise cross-correlation of hydrophone data, which extend to 10-12 s period. Airgun shots and the Morocco earthquake are well recorded by magnetometer channels and our electromagnetic transmitter is well recorded by geophone channels; these coupled signals may yield further complementary information about Earth structure.
How to cite: Minshull, T., Bayrakci, G., Constable, S., and Ivey, K. and the UK Ocean Bottom Instrumentation Facility: On the value of multiphysics instrumentation on the seafloor , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12651, https://doi.org/10.5194/egusphere-egu26-12651, 2026.
The Lower St. Lawrence Seismic Zone, a paleorift zone in Quebec, is one of the most seismically active areas in eastern Canada. It underlies the St. Lawrence Estuary, which is itself an important habitat for endangered baleen whales. Between 2023 and 2025, we carried out two deployments of an amphibious seismic network with eight broadband ocean-bottom seismometers (OBS) and four coastal stations to monitor earthquakes and baleen whales. The OBS were deployed via free-fall; we present the required preliminary analysis including 1) clock-drift calculation using ambient noise cross-correlation, 2) tilt estimation using transfer functions, and 3) horizontal-component orientation using passing ships as a noise source.
We apply machine learning pickers in combination with probabilistic earthquake phase association to construct an earthquake catalogue. Initial results indicate a detection rate of roughly twice that of the Canadian National Earthquake Database, although some detections may be rock blasts. Fin and blue whale calls are monitored using their characteristic internote intervals. An increase in vocal activity of both species is observed between the first (2023-24) and second (2024-25) deployments, despite the second being shorter in duration and missing the typically active month of October. In terms of per-OBS averages, fin whale activity increased from 63 active days to 97, and the number of detected calls per active day increased from 270 to 960, whereas blue whales remained more consistent in terms of active days (83 to 76) but the number of calls per active day increased from 106 to 173.
How to cite: Sirati, E., Plourde, A., Liu, Y., Chien, J., Darbyshire, F., Nedimović, M., and Zhang, M.: The Lower St. Lawrence Seismic Zone Ocean Bottom Seismometer Deployment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15093, https://doi.org/10.5194/egusphere-egu26-15093, 2026.
The İzmit Basin, located at the easternmost part of the Sea of Marmara, constitutes a key segment of the North Anatolian Fault system where the main fault strand bifurcates into northern and southern branches. This structurally complex transition zone is characterized by interacting fault segments and distributed deformation, making it a critical area for investigating microseismic activity. The dataset analyzed in this study was acquired by an ocean-bottom seismometer (OBS) deployment in the İzmit Basin. Eight OBS stations equipped with 4.5 Hz geophones were deployed in September 2023 and recovered in July 2024, providing approximately 10 months of continuous three-component seismic recordings. The instruments recorded data at a sampling rate of 100 samples per second, enabling the detection of local microearthquakes with magnitudes down to approximately M 0.2.
Initial earthquake locations reveal dense microseismic activity distributed along both the northern and southern branches of the North Anatolian Fault, as well as within intervening fault segments and fracture zones connecting these branches. These preliminary patterns highlight active deformation within the basin but exhibit significant scatter in both epicentral location and hypocentral depth, primarily due to velocity-model uncertainties and sediment effects inherent to offshore OBS observations. Reliable earthquake locations, in both horizontal and vertical dimensions, are critical for resolving fault-specific seismicity patterns and for investigating depth-dependent variations in seismic parameters, such as b-values. To improve location accuracy, events were refined using VELEST (Kissling et al., 1994), which iteratively optimizes a one-dimensional P- and S-wave velocity model and relocates earthquakes by minimizing travel-time residuals.
The initial VELEST velocity models display substantial scatter at shallow depths, particularly within the upper 0–5 km, reflecting strong sediment-related velocity uncertainties typical of offshore OBS observations. Following iterative relocation and velocity model optimization, the final VELEST solutions show clear convergence of both P- and S-wave velocities. The most pronounced improvement is observed within the 3–12 km depth range, corresponding to the main seismogenic layer. At depths around 10 km, the optimized models yield Vp values of approximately 5.8–6.2 km/s and Vs values of approximately 3.3–3.6 km/s, consistent with previous studies in the Marmara region and indicating a physically meaningful, data-driven velocity structure. The VELEST-based iterative velocity model optimization substantially reduces velocity uncertainty within the seismogenic depth range (approximately 5–15 km), leading to improved hypocentral depth and overall location reliability. The refined locations delineate coherent patterns of microseismic activity along the fault branches and connecting structures, providing a high-resolution view of seismic deformation in the İzmit Basin.
How to cite: Ergün, Dr. T., Meral Özel, N., Yamamoto, Y., Takahashi, N., Polat, R., Teoman, U. M., Turhan, F., Dindar, A. A., Kaneda, Y., and Aitaro, K.: High Resolution Microseismicity in the İzmit Basin-Sea of Marmara from OBS Data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10836, https://doi.org/10.5194/egusphere-egu26-10836, 2026.
Developed after the breakup of Gondwana in the Early Cretaceous, the southeastern margin of Brazil comprises a large, economically important hydrocarbon province that includes two of the world’s most prolific offshore sedimentary basins: Santos and Campos. At the same time, this passive margin hosts the country's main offshore seismic zone, characterised by frequent small-magnitude earthquakes and occasional larger events (M ≥ 4.8), occurring on average every 20-25 years, mostly within the extended and submerged continental crust. The larger events include the 1955 Vitória earthquake (mb 6.1), the 1939 Tubarão earthquake (mb 6.0), the 1972 Campos earthquake (M 4.8), the 1990 Porto Alegre earthquake (mR 5.2), and the 2008 São Vicente earthquake (mR 5.2). Due to insufficient instrumentation, limited to a few distant and unevenly distributed coastal stations of the Brazilian Seismographic Network (RSBR), and the low frequency of larger events, both the origin of this seismic activity and the risk it poses to key offshore infrastructure remain poorly understood. To better understand the processes related to the seismic activity in southeastern Brazil, the Brazilian Seismographic Network at the Sea Project (RSBR-Mar) intends to improve coverage by deploying: i - six temporary broadband coastal stations; ii - five Ocean Bottom Seismometers (OBSs); and iii - eight Mobile Earthquake Recorder in Marine Areas by Independent Divers (MERMAIDs) between São Paulo and Espírito Santo states. To date, two temporary land stations have been installed in Espírito Santo in June 2025. During a cruise mission between late September and early October 2025, we deployed all five OBSs and eight MERMAIDs. The OBSs will be recovered by September 2026, after one year of data acquisition, at which time the batteries will be replaced and the OBSs redeployed for an additional year. MERMAIDs periodically surface and establish satellite communication, allowing them to send important data back to us, collected during each operational cycle. To date, we have collected 50 waveforms detected by the MERMAIDs. Although MERMAIDs were originally designed to record high-quality P-waveforms for teleseismic tomography, rather than to detect small local events, we will explore this possibility by requesting data stored in their one-year internal storage. If successful, MERMAIDs could improve the localisation of earthquakes recorded in continuous records from land stations and OBSs. First, we plan to automatically detect and locate earthquakes in continuous seismograms from land stations and OBSs using machine-learning-based algorithms (e.g., LOC-FLOW, MALMI). These preliminary locations allow us to identify which data windows to request for each MERMAID. Then, we can relocate the small earthquakes with the acoustic data. Finally, relocation methods may help us to delineate possible seismogenic offshore structures (e.g., HypoDD).
How to cite: Leite Neto, G., Nascimento, A., Coelho, D., Fontes, S., Maurício, Í., Alfonzo, A., Chaves, C., Bianchi, M., do Nascimento, A., França, G., and Rocha, M.: The RSBR-Mar Project: Monitoring Offshore Small-Magnitude Earthquakes in Southeastern Brazil with Marine and Land-Based Instrumentation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21055, https://doi.org/10.5194/egusphere-egu26-21055, 2026.
Posters on site: Fri, 8 May, 08:30–10:15 | Hall X1
The SEASMO (SEismo-Acoustic Submarine Mediterranean Observatory) platform represents a major technological advancement in deep-sea multidisciplinary monitoring. Situated in the Ionian Sea at a depth of 3,450 meters, approximately 80 km SE offshore from Portopalo di Capo Passero, Sicily, the observatory was successfully deployed in October 2024 as part of the “Marine Hazard” project. Having now surpassed its first year of continuous operation, SEASMO has established itself as a cornerstone of real-time scientific data acquisition and environmental risk mitigation within the Mediterranean basin.
This sophisticated facility is the result of a strategic collaboration between the National Institute for Nuclear Physics (INFN) and the National Institute of Geophysics and Volcanology (INGV). The platform leverages the world-class deep-sea neutrino telescope KM3NeT/IDMAR infrastructure, utilizing two primary 100 km electro-optical cables to provide robust connectivity. This high-bandwidth link connects a submarine network of junction boxes equipped with Remotely Operated Vehicle (ROV) mateable wet connectors to an onshore laboratory, ensuring a stable power supply and instantaneous telemetry for uninterrupted data transfer.
A key feature of SEASMO is its complete integration into global and national monitoring frameworks. It is officially registered in the International Federation of Digital Seismograph Networks (FDSN) database under the station code MHPPL, operating as part of the KM3NeT Seismic Network (K3). Beyond its registration, the station’s data stream is directly integrated into the INGV seismic monitoring system, significantly extending the reach of the national seismic network into the offshore environment. Furthermore, the observatory is currently being incorporated into the operational workflow of the Tsunami Alert Center (CAT-INGV), providing essential offshore data that enhances the accuracy and timeliness of natural hazard alerts for the region. This latter is particularly important given that some of the most damaging historical earthquakes in the Mediterranean realm were generated by offshore active faults located close to the Sicilian coastline, including the “1693 Val di Noto earthquake” and the “1908 Messina earthquake” (M > 7). Nonetheless, the observatory is also located close to the poorly constrained Ionian Subduction Zone, whose potential to generate subduction-related megathrust earthquakes remains unclear.
The scientific payload of the station is specifically designed for high-resolution environmental and geodynamic characterization. Central to its mission is a 120-second broadband Ocean Bottom Seismometer (OBS) and a high-resolution hydrophone, capable of detecting frequencies with a 12.8 kHz bandwidth down to 1 Hz. This combination allows for the precise monitoring of seismic activity and the characterization of both natural and anthropogenic acoustic sources, providing critical insights into the impact of human activities on marine ecosystems. Additionally, the suite includes a Conductivity, Temperature, and Depth (CTD) sensor for tracking physical-chemical shifts in the water column, as well as detecting high-resolution temporal sea-level anomalies.
Throughout its operation, SEASMO has demonstrated the reliability of its automated data-processing routines, providing 24/7 real-time monitoring of the deep Mediterranean and offering a unique window into its geodynamics and acoustic soundscape, with considerable implications for marine science and hazard prevention.
How to cite: Sciré Scappuzzo, S. and the SEASMO Team: Introducing SEASMO: SEismo-Acoustic Submarine Mediterranean Observatory, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7119, https://doi.org/10.5194/egusphere-egu26-7119, 2026.
Researchers continue to intensify their focus on the seafloor to gain a deeper understanding of the Earth's structure, tectonic processes, and potential hazards through the acquisition of ocean-bottom seismic (OBS) data. However, the unique challenges of deep-sea environments require innovative, purpose-built engineering solutions and robust manufacturing techniques to safeguard data quality, data completeness and system reliability, while meeting scientific objectives and optimizing ease of deployment. A range of cabled and autonomous ocean bottom sensing solutions is now available, supporting the global community’s study of underwater ground motion, its dynamic properties, and natural or triggered events on the seafloor.
This poster presentation provides a comprehensive overview of the engineering challenges in the domain of OBS platforms, highlighting the advancements in technology and capability solutions that the Nanometrics team has developed to address those challenges for various configurations and use cases. With proven technologies such as integrated kinematic gimbals for levelling at all landing tilt angles, an integrated MEMS gyrocompass for precise orientation, and designs certified for deployment depths of up to 6,000 m, this poster will demonstrate that seamless multidisciplinary data collection across diverse marine environments is now more accessible than ever before. Recent technological advances include customer deliveries of both SMART cable seismic instrumentation and an integrated Cabled OBS observatory, expanding options to support a wide range of application-driven sensing instruments and dataloggers. This continuous innovation aims to facilitate further understanding of the dynamic properties in these challenging deep ocean environments.
How to cite: Jusko, M., Allardice, S., Somerville, T., Bainbridge, G., and Perlin, M.: Ocean-Bottom Seismology: Next-Generation Technology Solutions for Marine Monitoring, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5534, https://doi.org/10.5194/egusphere-egu26-5534, 2026.
Transfer function techniques are commonly used to remove tilt and compliance noise from broadband ocean bottom seismometers (BBOBS), particularly at periods longer than 10 s. Temporary deployments and cabled observatory installations utilizing BBOBS have increased in the past several years and involved a variety of different organizations globally. Furthermore, techniques utilizing non-traditional approaches, such as short-period ambient noise and the expanded use of horizontal-component seismic data, have also expanded. Here we present updates to the Automated Tilt and Compliance Removal (ATaCR) package, designed to help users both assess and remove noise from BBOBS projects. In particular, we have improved flexibility and assessment metrics to better meet the variety of approaches necessary for modern analyses. Notable additions include: (1) summary figures assessing tilt properties; (2) improved phase analyses to discriminate between microseismic and other sources of noise; (3) expanded flexibility to incorporate a variety of data and metadata, such as quality control metrics, and instrument handedness; (4) generalized TF removal algorithm to allow exploration of non-traditional correction sequences; (5) transfer function workflows for ambient noise imaging.
How to cite: Janiszewski, H., Russell, J., Audet, P., and Wu, Y.: Updates to and New Applications of the ATaCR Package for Tilt and Compliance Removal, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14832, https://doi.org/10.5194/egusphere-egu26-14832, 2026.
The North Sea is transitioning from a hydrocarbon province to a wind-turbine and CO2-sequestration hotspot. The latter activity needs assurance that the CO2 is kept within the envisioned subsurface containers. Microseismic monitoring is one of the methods to track the movement of the injected CO2. Additionally, the North Sea experiences both tectonic earthquakes and events that are related to gas production. To sufficiently detect, locate and characterize the different events, onshore sensors do not suffice. The seismic network thus needs to be expanded into the sea. The dynamic marine environment, characterized by shallow water, active sand dynamics, and diverse marine life, makes it unfavourable for standard seismological deployments.
In this work, we report a series of experiments toward deploying a seismometer in the Dutch North Sea. The experiments were conducted at shallow water depth (~2m) near the NIOZ harbour at Texel Island and at ~10m depth in the Wadden Sea. We have chosen to deploy a broadband seismometer, so that the acquired data is not only useful for local monitoring, but also for crustal studies using teleseismic earthquakes and teleseisms. We tested two designs, one with a sea-bottom seismometer and the other with a posthole one. Furthermore, we developed a full prototype for a stand-alone station setup, which has been tested in the Wadden Sea. The sea-bottom seismometer performed well at long periods > 10s, while the posthole version showed a higher signal-to-noise ratio at shorter periods, making it more stable for local seismicity detection and localisation. Due to active sand dynamics, the sea-bottom sensor showed a higher temporal variation with the sensors' masses, requiring mass balancing more frequently than the posthole version. The posthole sensor remained clean, whereas the sea-bottom sensor acted as a reef for all kinds of marine life.
How to cite: Fadel, I., Akinremi, S., de Laat, J. I., Schmidt-Aursch, M. C., Thomas, C., and Ruigrok, E.: Towards permanent seismological monitoring in the Dutch North Sea: Progress and early results, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20259, https://doi.org/10.5194/egusphere-egu26-20259, 2026.
Real-time seismic monitoring infrastructure requires permanent power and data transmission and therefore largely relies on land-based seismological stations. As a result, regional seismic monitoring of marine regions remains challenging with respect to event detection thresholds and hypocentral location accuracy. Particular challenges in seismic event monitoring in Northern Germany are the occurrence of both natural and anthropogenic events in the southern Baltic Sea and therefore the discrimination of event source types and, for tectonic events, hypocentral depth determination of earthquakes in the wider Tornquist zone region. Beyond that, seismic monitoring gained in recent years importance as an additional tool to monitor critical infrastructure as well as controlled and uncontrolled detonations of unexploded ordnance (UXO).
Recent advances in both offshore infrastructure and seismic offshore instrumentation systems provide a realistic opportunity to facilitate deployments of continuous, real-time ocean-bottom seismometers to significantly improve monitoring capabilities in offshore regions.
In summer 2025, we deployed a three component, cabled broad band Ocean Bottom Seismometer (Trillium Compact OBS) at the Darss Sill in the western Baltic Sea. At the site, the permanent MARNET monitoring station, operated by the Leibniz Institute of Baltic Sea Research in Warnemünde on behalf of the Federal Maritime and Hydrographic Agency (BSH) provides the infrastructure for a prototype deployment of a real-time OBS system. Seismic data is transmitted in near real-time to the data center at Kiel University and included in the real-time monitoring system. Over the past months, the OBS installation has been continuously improved, to enhance the data quality. The MARNET station also records oceanographic, biological and meteorological parameters that can be used to improve our understanding of ocean generated microseism with in situ data. While models and theories exist for microseism generation in the deep ocean, its generation mechanisms in coastal areas is still an open question.
We present first data observations and correlations and discuss challenges and opportunities for future offshore seismological monitoring in Northern Germany coastal region.
How to cite: Wiesenberg, L., Weidle, C., Mars, R., Schönke, M., Uhlmann, S., and Meier, T.: A cabled, real time ocean bottom seismometer in the western Baltic Sea, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11722, https://doi.org/10.5194/egusphere-egu26-11722, 2026.
Autonomous free-fall ocean-bottom seismometers (OBS) offer flexible deployment and redeployment options. The Güralp Aquarius operates at any orientation without a gimbal and can wirelessly transmit state-of-health (SOH) and seismic data to the surface via an integrated acoustic modem. This enables monitoring and partial real-time data transmission without offshore cabling, reducing logistical complexity while maintaining data accessibility. These capabilities make Aquarius well suited to OBS pool operations, including the National Facility for Seismic Imaging in Canada, one of the most recent large-scale OBS pools to become operational worldwide. In contrast, cabled observatory systems provide continuous, high-resolution real-time data via direct connections to onshore infrastructure. The Güralp Orcus is a compact underwater seismic station integrating a broadband seismometer and strong-motion accelerometer in a single package. The slimline Güralp Maris offers additional flexibility, using the same omnidirectional sensor as Aquarius and supporting deployment on the seabed or within narrow-diameter subsea boreholes. Both systems are deployed globally within multidisciplinary observatories, including the Neptune array operated by Ocean Networks Canada.
SMART Cables represent a promising pathway to expanding cabled ocean observatory networks at significantly reduced cost. By combining seismology, oceanography, and telecommunications within a single system, large-scale monitoring networks can be developed through shared logistics and funding across industries. Güralp has demonstrated this approach through a successful wet demonstration in the Ionian Sea, conducted in collaboration with the Istituto Nazionale di Geofisica e Vulcanologia (INGV), representing the first practical deployment of this technology. Future projects will leverage low-power, low-volume sensor and data acquisition designs to support both commercial SMART cable initiatives and science-driven observatories.
How to cite: Lindsey, J., Watkiss, N., Calver, J., Kerkenyakova, A., Kitka, K., Hill, P., and Restelli, F.: Güralp Ocean Bottom Monitoring Solutions: Autonomous Nodes, Cabled Observatories and SMART Cables, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11873, https://doi.org/10.5194/egusphere-egu26-11873, 2026.
In the last years, fibre optic sensing methods, in particular Distributed Acoustic Sensing (DAS), have been experimentally demonstrated to be suitable for monitoring Earth System parameters in submarine cables. The SUBMERSE project (SUBMarinE cables for ReSearch and Exploration) aims to develop blueprints for using telecommunication fibre optic cables as sensors by attaching fibre optic interrogators at selected landing stations, also building a data infrastructure for both temporary storage of full resolution data and permanent archival of reduced data sets.
We analyse data from interrogating the East/West oriented Ionian Submarine System cable from both end points, i.e., Preveza, Greece, and Crotone, Italy, along the same fibre. This cable is located to the north of the Kefalonia Transform Zone. This fault zone marks the western termination of the Hellenic subduction system and is one of the most active seismic zones in Greece, with large damaging earthquakes above M > 6 occurring every few years on average.
In addition to acquiring the full large dataset, decimated channels (~100 in each case) acted as virtual seismic stations offshore, acquired at the NOA datacenter for realtime monitoring purposes. We explored various approaches to automated phase picking and magnitude determination on a reduced data set as well as the full resolution data. We also consider other test sites on the Ellalink cable branches extending from Sines in southern Portugal and from Madeira.
In order to support these and other acquisitions, we have developed a range of tools that can be deployed at future sites. We have enabled real-time streaming of DAS data following the standard Seedlink protocol, which allows straightforward integration into existing workflows at earthquake observatories. We have developed an automated, machine-learning-based algorithm for analysing earthquake waveforms and assembled a benchmark data set of earthquake recordings from DAS cables worldwide with labels of P and S arrival times that can serve to further refine machine learning and other automated analysis approaches. Finally, leveraging the Xdas platform (Trabattoni et al. 2025), we have extended the popular SeisBench platform (Woollam et al, 2022) for machine learning in seismology with the ability to efficiently process dense DAS datasets with algorithms/machine learning models operating across either single or multiple channels.
How to cite: Tilmann, F., Evangelidis, C., Fountoulakis, I., Xiao, H., Münchmeyer, J., Heinloo, A., Strollo, A., Hillmann, L., Morten, J. P., Poggi, V., Parolai, S., Loureiro, A., Custodio, S., and Atherton, C.: Establishing continuous seismic monitoring by DAS interrogation of submarine telecommunication cables in Europe with the SUBMERSE consortium: tools and use cases, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19750, https://doi.org/10.5194/egusphere-egu26-19750, 2026.
Distributed Acoustic Sensing (DAS) enables broadband strain measurements with exceptional spatial and temporal resolution, effectively transforming fibre-optic cables into dense sensor arrays. Its ability to operate continuously and cost-effectively in challenging environments makes DAS a powerful tool for geophysical, seismological, and oceanographic research. However, the lack of adequate transfer functions linking DAS strain measurements to true ground motion remains a key limitation for its reliable use in quantitative seismic analysis.
Project ECHO (Earthquakes, Currents, Hydroacoustics, and Oceanography) addresses this limitation by establishing local, empirically derived transfer functions for the GeoLab fibre. By deploying a suite of collocated reference instruments along the cable track, the project will characterize the contributions of ground motion, temperature, pressure, and oceanographic processes to the measured DAS strain, and also quantify cross-sensitivities between these parameters.
To constrain strain and ground motion, two ocean-bottom seismometers equipped with additional pressure and temperature sensors will be deployed at water depths exceeding 2000 m, complemented by a land-based seismic station. Oceanographic variability will be monitored using acoustic Doppler current profilers (ADCPs) and conductivity, temperature, depth (CTD) sensors. Hydrophones will serve as an independent reference for calibrating the DAS response to underwater acoustic signals, including marine mammal vocalizations and anthropogenic sound sources, with complementary confirmation of low frequency signals from the ocean-bottom seismometers.
Expected outcomes include segment-specific DAS transfer functions, a DAS-derived seismic catalogue, detection and classification of marine mammals from their vocalizations, the development of DAS-based proxies for sea-state variability, and an assessment of the feasibility of shear-wave splitting analysis given the existing cable geometry. Together, these results will advance understanding of regional seismicity, ocean dynamics from the coastal zone to the deep basin, and underwater acoustics, while substantially enhancing the scientific utility and applicability of DAS in Earth and marine sciences.
The richness of the multi-parameter datasets acquired within ECHO create significant opportunities for interdisciplinary collaboration, providing a unique framework for joint studies across seismology, physical oceanography, marine ecology, and fibre-optic sensing. This integrated approach is intended to foster collaboration within the broader scientific community and to stimulate the development of novel methodologies and applications beyond the immediate scope of the project.
All datasets generated by ECHO will be released under F.A.I.R. principles at the conclusion of the project.
This work is supported by the ECHO project (DOI: 10.54499/2024.13655.PEX), ARDITI - Agência Regional para o Desenvolvimento da lnvestigação, Tecnologia e lnovação, the SUBMERSE EU project (GA 101095055), and FCT, I.P./MCTES through national funds (PIDDAC): LA/P/0068/2020 (DOI:10.54499/LA/P/0068/2020), UID/50019/2025 (DOI: 10.54499/UID/50019/2025), UID/PRR2/50019/2025 (DOI: 10.54499/UID/PRR/50019/2025).
How to cite: Loureiro, A., Schlaphorst, D., Corela, C., Matias, L. M., Peliz, Á., Ferreira, R., Pereira, A., and Reis, J.: ECHO project: Multi-parameter calibration of the GeoLab DAS fibre, Madeira, Portugal, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7689, https://doi.org/10.5194/egusphere-egu26-7689, 2026.
In northern Macaronesia in the Atlantic the Azores, Canaries and Madeira are three mantle upwelling surface expressions. While Madeira and the Canaries are located on old oceanic crust as intraplate hotspots (~135 Ma and 150-180 Ma), the Azores result from interaction between a hotspot and the Mid-AtlanticRidge and sit on younger crust (<50 Ma). Mantle upwellings can influence the subsurface discontinuity structure, including shallow crustal contributions, in an area that reaches beyond the locations of the islands into the offshore oceanic subsurface. Therefore, an observation of seismic crust and upper mantle properties in the whole region is key to understanding mantle dynamics and its effect on volcanism.
Since seismic stations are mostly found on land, offshore seismic measurements are more challenging and globally sparse. From 2021 to 2022 an OBS network was deployed in the oceanic region of northern Macaronesia by the UPFLOW project. This deployment enables, for the first time in this region, the investigation of discontinuity variations over a broad offshore area and their comparison with land-station observations from the islands.
With P-S receiver functions we obtain high-resolution point measurements of the Moho and further intercrustal and upper mantle discontinuities beneath 43 stations. We use frequencies of 0.4 to 3 Hz, but add higher frequency ranges to investigate the robustness. Furthermore, we compare frequency- and time-domain deconvolution techniques. Moho depths vary between 5 to 12 km, in some places over short length-scales, which could be linked to melt generation and composition changes. The crustal structure is more complex around the Azores region, reflecting the complex dynamics around the mantle upwellings. Oceanic noise levels, shallow subsurface structure, and thick sediments – particularly in the southeastern part of the region – pose additional challenges by causing receiver-function polarity flips and less well-defined converted-phase arrivals, which complicate interpretation.
This contributes to projects AMULETO (2022.06660.CEECIND) and GEMMA (DOI:10.54499/PTDC/CTA-GEO/2083/2021). This work is supported by FCT, I.P./MCTES through national funds (PIDDAC): LA/P/0068/2020 - https://doi.org/10.54499/LA/P/0068/2020 , UID/50019/2025, https://doi.org/10.54499/UID/PRR/50019/2025, UID/PRR2/50019/2025.
How to cite: Schlaphorst, D., Silveira, G., Ferreira, A., Dias, N., and Miranda, M.: Moho Discontinuity Structure using Data from Land Stations and a Broad Atlantic OBS Network – Potential and Challenges, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13683, https://doi.org/10.5194/egusphere-egu26-13683, 2026.
As part of the ERC (European Research Council)-funded UPFLOW project (2021–2027), we conducted the largest passive seafoor seismic experiment to date in the Atlantic, focusing on the Azores-Madeira-Canary Islands region, a unique setting with multiple unresolved upwellings. Between June 2021 and August 2022, we deployed 50 and recovered 49 ocean bottom seismometers (OBSs) across a ~1,000×2,000 area with ~110–160 km spacing. The data reveal a wealth of good quality seismic signals, enabling detailed imaging of mantle upwellings and opening avenues for interdisciplinary research in marine biology and oceanography.
We present our ongoing UPFLOW 3-D mantle model series, which uses a combination of massive global seismic datasets (millions of body wave travel-times, multimode surface wave dispersion data) with tens of thousands of measurements from UPFLOW's OBS waveforms. Various modelling approaches are used ranging from computationally efficient ray theory-based global inversions to finite-frequency and waveform approaches. We invert for a range of model parameters including shear- and P-wave speed, as well as for radial anisotropy.
Our images show complex 3-D structures from the upper mantle to the lowermost mantle. We also observe lateral links between low velocity anomalies beneath the Canary, Azores and Madeira Islands associated with positive radial anisotropy anomalies, which possibly indicate plume ponding and horizontal mantle flow. Moreover, low-velocity anomalies right beneath the Azores appear not to extend into the lower mantle; instead, they seem to spread laterally and connect to the lower mantle beneath the center of our study region. We discuss the resolution of our images and well as their scope and geodynamical implications.
How to cite: Ferreira, A. M., Harris, K., Witek, M., Chang, S.-J., Veisi, M., Tsekhmistrenko, M., and Miranda, M.: UPFLOW 3-D mantle tomography from crust to core, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15079, https://doi.org/10.5194/egusphere-egu26-15079, 2026.
Macquarie Island is a small sliver of uplifted oceanic crust and mantle lying between New Zealand and Antarctica, near the middle of the Macquarie Ridge Complex (MRC) - a transpressional plate boundary that divides the Australian and Pacific plates. Evidence for subduction initiation has previously been found at both extremities of the MRC, yet subsurface information on its central portion near Macquarie Island remains limited. In this study, we extract teleseismic waveform data from ocean bottom seismometers (OBSs) deployed around Macquarie Island between October 2020 and November 2021 in conjunction with a small number of temporary land stations and the permanent MCQ station in order to perform teleseismic tomography across the region. We apply a denoising scheme (ATaCR) to help extract as much usable data as possible from the noisy OBS recordings to produce a denoised dataset, which we intend on using to image subcrustal features in order to better understand the nature of this plate boundary.
How to cite: Li, Y., Rawlinson, N., Lü, C., O'Hara, T., Winder, T., Tkalcic, H., Coffin, M., and Stock, J.: Investigating the nature of the Australian/Pacific plate boundary beneath Macquarie Island using teleseismic tomography, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13418, https://doi.org/10.5194/egusphere-egu26-13418, 2026.
The Macquarie Ridge Complex (MRC), situated at the the boundary between the Australian, Macquarie, and Pacific plates south of New Zealand, is presently understood to be a primarily transform boundary that originated as a mid-ocean ridge. Although the northern (Puysegur) and southern (Hjort) sections of the MRC are considered to be initiating subduction, the tectonic activity along its central portions (Macquarie and McDougall segments) remains ambiguous.
Macquarie Island is situated on the central segments of the MRC. The region is characterized by exceptionally rugged topography, a feature that can indicate the incipient subduction. Furthermore, the MRC has produced some of the most powerful intra-oceanic strike-slip earthquakes on record. Such significant seismic events in this area pose a potential tsunami hazard. Consequently, despite its isolation, detailed geophysical studies are warranted, which led to our deployment of an integrated network of ocean bottom seismometers (OBSs) and seismometers on the island (Tkalčić et al., 2020; 2021). The primary aim of our research is therefore to employ seismological methods to advance the comprehension of the tectonic development of the Australian-Macquarie-Pacific plate boundary.
From 2020 to 2021, we installed a network comprising five land-based stations and 27 ocean bottom seismometers on and around Macquarie Island along the MRC in the Southern Ocean. Utilizing data from the successfully retrieved OBSs and island stations, including the permanent station MCQ, we applied an adjoint waveform tomography technique to surface waves (5-20 s period) extracted from ambient seismic noise. This process, conducted over five iterations, yielded a 3-D model of S-wave velocity for the crust and uppermost mantle. Our starting 3-D model incorporated accurate bathymetry, a water layer, and an optimized 1-D velocity structure. For the seismic wavefield simulations required in the inversion, we employed the spectral element method with Specfem3D_Cartesian (Komatitsch and Tromp, 1999). The resulting S-wave velocity model shows a marked velocity increase at crustal and uppermost mantle depths, between 7 and 12 kilometers. The presence of relatively high S-wave velocities (>3.8 km/s) in the shallow lithosphere aligns with upper mantle rocks being located at unusually shallow depths along the ridge. The extensive distribution of this high-velocity material suggests that the uppermost lithosphere has not undergone significant deformation during the process of obduction.
Reference
Tkalčić, H., Eakin, C., Rawlinson, N., Coffin, M. F., & Stock, J. (2020) Macquarie Ridge [Data set]. AusPass: The Australian Passive Seismic Server. https://doi.org/10.7914/SN/3F_2020
Tkalčić, H., Eakin, C., Coffin, M. F., Rawlinson, N. & Stock, J. (2021) Deploying a submarine seismic observatory in the Furious Fifties, Eos, 102, https://doi.org/10.1029/2021EO159537
Komatitsch, D., & Tromp, J. (1999). Introduction to the spectral element method for three-dimensional seismic wave propagation. Geophysical Journal International, 139(3), 806-822. https://doi.org/10.1046/j.1365-246x.1999.00967.x
How to cite: Tkalčić, H., Wei, Z., and Pham, T.-S. and the MRC Team: The Central Macquarie Ridge Complex in 3D from Adjoint Waveform Tomography Using Ambient Seismic Noise, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21714, https://doi.org/10.5194/egusphere-egu26-21714, 2026.
The Queen Charlotte Triple Junction (QCTJ) is a complex plate boundary offshore British Columbia, Canada, linking the Cascadia subduction zone, the Queen Charlotte transform fault, and the Juan de Fuca Ridge through the Revere–Dellwood fault (RDF) system. This region accommodates marked changes in plate motion and deformation style over short spatial scales, yet its offshore structure and seismicity remain poorly constrained due to distant land-based seismic coverage. The Pacific Coast Seismic Assessment for Faults and Earthquakes (PACSAFE) is a multi-year Canadian ocean-bottom seismometer (OBS) program designed to resolve this plate-boundary transition through dense, multi-deployment offshore monitoring.
During Leg 1 (October 2023-July 2024), 26 broadband OBS from the National Facility for Seismological Investigations (Dalhousie University) were deployed across the QCTJ and adjacent segments of the RDF and Explorer Ridge, and continental shelf break. During the deployment, two of these instruments located along the continental shelf break as well as one on the RDF prematurely released from the sea floor. All remaining 23 instruments were successfully recovered. Clock drift corrections were applied by the NFSI technical team, then orientations of all instruments were computed using local and teleseismic waveforms. We then applied a deep-learned based approach to phase picking, utilizing the OBSTransformer on the 3-component data, resulting in ~1.23 million P phases and ~3.11 million S phases. These arrivals were associated and located using the maximum likelihood approach, to generate a catalog of ~11,000 events. These events were then reduced using additional quality control parameters, and double-difference relocated using both pick times and waveform cross correlations. The resulting relocated catalog contains more than 5,000 of the most robustly relocated events.
The catalog reveals dense, previously unobserved microseismicity that delineates near-vertical fault strands, fault-perpendicular seismicity lineations associated with the Revere-Dellwood transform and multiple seismicity strands associated with the northern Explorer ridge and transform system. Seismicity extends from near the seafloor to ~20 km depth, with most activity concentrated between 5 and 10 km. We provide new observations with unprecedented constraints on deformation and plate-boundary partitioning within the QCTJ. Ongoing analyses of focal mechanisms, seismicity, and tectonic context will further refine models of seismic and tsunami hazard for Canada’s Pacific margin.
How to cite: Schaeffer, A. and Bostock, M. and the PACSAFE Team: High-resolution seismicity and fault imaging of the Queen Charlotte Triple Junction region from the PACSAFE Leg1 ocean-bottom seismometer network, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15321, https://doi.org/10.5194/egusphere-egu26-15321, 2026.
The Blanco transform fault system (BTFS) represents an evolving transform plate boundary in the Northeast Pacific Ocean. Its seismic behavior was captured with a dense network of 54 ocean-bottom seismometers (OBS) operated for one year. We created a high-resolution earthquake catalog based on different machine-learning onset pickers. The high-resolution seismicity catalog has 12,708 events outlining the current deformation and stress release. Seismicity indicates seismic and aseismic fault patches or segments, as well as complex along-strike and off-axis deformation, step-overs, and internal faulting within pull-apart basins. Along simple linear fault strands, earthquakes are localized within 2 km of the seafloor expression of the fault. By applying cross-correlation techniques, we identified bursts and repeaters along the BTFS. Most bursts have interevent times of less than five minutes. Repeaters are predominantly found in the west of the BTFS and along the Gorda Depression, and to a smaller extent beneath the eastern Blanco Ridge. Slip rates estimated from repeaters exceed the geological slip rate by approximately 4 times, suggesting small seismic patches that release their slip every ~4 years. Along the BTFS, fault coupling varies between fully locked and creeping. Local earthquake tomography shows elevated vp/vs values exceeding 2, suggesting significant serpentinization from seawater entering the transform faults, the oceanic crust, and the mantle. The study shows how modern machine learning pickers applied to OBS data yield essential insights into the physics of faulting along major plate boundary faults in time and space, including the partitioning of deformation between seismic and aseismic slip.
How to cite: Lange, D., Ren, Y., and Grevemeyer, I.: Seismicity, Repeating Earthquakes,and Tomographic Imaging of the Blanco Transform Fault System, Northeast Pacific, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21326, https://doi.org/10.5194/egusphere-egu26-21326, 2026.
Seafloor sediment layers strongly influence seismic signals recorded by ocean-bottom seismometers through reverberations, velocity reduction, and waveform amplification. These effects can significantly bias seismic observations, limiting investigations of the oceanic crust and mantle. While direct drilling and active-source seismic surveys provide robust constraints on sediment structure, they are not always feasible in areas instrumented solely with passive seafloor seismometers. In this study, we estimate Rayleigh-wave ellipticity from both ambient seismic noise and earthquake recordings using a polarization-based H/V approach that isolates elliptically polarized Rayleigh waves. Rayleigh-wave ellipticity derived from OBS data shows clear correlations with water depth and sediment thickness. The combined ellipticity curves are inverted using the Neighbourhood Algorithm to constrain crustal shear-wave velocity structure beneath the OBS stations. Our inversion results indicate sedimentary cover thicker than ~2 km beneath the Madeira region, closer to the continent, whereas relatively thin sediment layers are observed near the Azores region. The resulting crustal thickness and shear-wave velocity models across the Azores–Madeira–Canaries region provide a useful reference for future seismic investigations in this region, including studies based on the UPFLOW data.
How to cite: Kim, T., Ferreira, A. M. G., Jones, G. A., and Chang, S.-J.: Constraining shallow S-wave velocity structure beneath the Azores–Madeira–Canaries region from Rayleigh-wave ellipticity analysis using UPFLOW data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15400, https://doi.org/10.5194/egusphere-egu26-15400, 2026.
Oceanic transform faults (OTFs) are a major type of plate boundary on Earth. They are segmented into seismic and aseismic sections, with large earthquakes clustering on individual seismic segments. Some OTF segments even produce quasi-periodic large earthquakes, a behavior that is rarely observed on continental faults. Despite their remote locations, OTFs therefore provide a unique natural laboratory for understanding earthquake processes and faulting mechanisms.
Because OTFs are located on the seafloor, their internal structure and the ways in which they accommodate plate motion remain poorly understood. Over the past two decades, several ocean-bottom seismometer (OBS) experiments have been conducted along OTFs. Microseismicity recorded by these experiments has revealed important and sometimes surprising properties, including the behavior of aseismic sections and deep-penetrating seismicity that has changed our understanding of OTF rheology. To further resolve fault structure and slip behavior, we need earthquake catalogs with both high-resolution locations and high completeness, so that we can interpret fault geometry and identify transient slip processes.
In recent years, machine-learning phase pickers have been increasingly applied to OBS data, greatly improving the efficiency of earthquake detection. However, major challenges remain in building high-quality catalogs, including uncertainties in phase picking, limitations of location algorithms, and the effects of station spacing and velocity models. In this study, we systematically evaluate key components of the data-processing workflow that control catalog quality, including the performance of different phase pickers, the impact of station coverage and velocity models, and the behavior of different earthquake location methods. We also discuss strategies for building multi-tier catalogs that balance location accuracy and catalog completeness, providing datasets that are suitable for both structural interpretation and studies of fault slip behavior.
How to cite: Gong, J.: Microseismicity Detection and Location along Oceanic Transform Faults, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18632, https://doi.org/10.5194/egusphere-egu26-18632, 2026.
Vertical ground deformation is a key parameter to document magmatic or tectonic processes occurring below the surface, such as magma movement, tectonic strain build-up or seismic rupture. When occurring underwater, vertical deformation can be quantified using ocean bottom pressure gauges. Although these gauges have an intrinsic resolution sufficient to document sub centimeter movements, the identification and precise quantification of vertical displacements face several challenges due to instrumental drift modeling, ocean dynamics or instrumental artefacts or orientation related sensitivity.
In 2024 and 2025, in the framework of the GEODAMS project (see related presentations Royer et al. and Olive et al., in session EGU26-GD5.1), we carried out repeated bathymetric surveys and deployed an A0A gauge - a bottom pressure recorder with a built-in drift controlling system - along with networks of seafloor acoustic transponders and moored hydrophones (Raumer et al., EGU26-SM3.2). This experiment allowed us to detect and characterize a major magmato-tectonic event which, luckily, occurred 2 months after the initial bathymetric survey and instrument installation. The detailed description of this unique event will be given in the presentation by Royer et al. (EGU26-GD5.1).
Our presentation will focus on the interpretation of the recorded pressure variations to derive a chronicle of vertical deformation, before, during and after the magmato-tectonic event. Although the instrument recorded a spectacular total subsidence close to 4 meters, the precise quantification of the deformation through the submarine eruption requires a precise modeling of the instrumental drift and changes in calibration parameters, which may be affected by likely changes in gauge orientation induced by the seafloor deformation.
How to cite: Ballu, V., Testut, L., Dausse, D., Royer, J.-Y., Olive, J.-A., Tranchant, Y.-T., Joyard, R., Laurent, A., Bazin, S., Retailleau, L., Briais, A., Raumer, P.-Y., and Lenhof, E. and the OHA-GEODAMS: Challenges and rewards: a chronicle of vertical displacements during a seafloor spreading event at the Southeast Indian Ridge, from a seafloor pressure A0A recorder, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9061, https://doi.org/10.5194/egusphere-egu26-9061, 2026.
The global transition toward renewable energy has accelerated the deployment of offshore wind farms, where reliable mapping of the shallow subsurface is crucial for wind-turbine foundation design and installation. Detecting shallow structures and their lateral variability in marine sediments helps reduce geotechnical uncertainties related to subsoil heterogeneity, which strongly influence construction risks, performance, and costs. Among geophysical methods, Direct Current (DC) resistivity surveys are effective for lithological and structural characterization; however, their offshore application remains strongly limited by two main factors: current leakage into the highly conductive seawater column and the resulting reduction in apparent resistivity (ρₐ) sensitivity to seabed targets.
We present a marine acquisition enhancement technique that deploys an electrically insulating sheet directly above the electrode cable placed on the seafloor—a previously patented concept—to restrict vertical current leakage and promote lateral current diffusion along the seabed, thereby increasing electrical interaction with subsurface formations.
A numerical parametric study was conducted using the finite element method (COMSOL Multiphysics), followed by a comparison between insulated marine models and equivalent terrestrial reference models without seawater. The analysis investigated the effects of: (1) seawater depth (Wd) = 1–60 m, (2) seawater-to-subformation resistivity contrast (Cr) = 1.5–100, (3) Wenner electrode spacing (a) = 2–30 m, and (4) insulation width (L) = 1–100 m, symmetrically covering 30 electrodes with 2 m spacing (Fig. 1a).
For Cres = 1.5, conventional marine acquisition without insulation produces large ρₐ errors relative to the terrestrial reference (Fig. 1b), exceeding 20% at small spacings (a = 2–6 m) in shallow water (Wd = 1 m), and remaining between 50% and 60% for most spacings when Wd increases to 28–60 m. The insulating sheet significantly enhances sensitivity: in shallow water (Wd = 1 m), long sheets (L = 60–100 m) as well as intermediate coverage (L = 30 m) reduce ρₐ errors to less than 2% over the entire spacing range (a = 2–30 m), closely reproducing the terrestrial response. Shorter sheets (L ≤ 10 m) still reduce errors to below 10% at intermediate to large spacings.
As water depth increases (Wd = 28–60 m), resistivity recovery becomes partial: even long sheets reduce ρₐ errors to approximately 10% at a = 30 m, compared to more than 50% without insulation. The effectiveness of leakage control also decreases geometrically at larger spacings, where errors tend to stabilize or slightly increase. Furthermore, when Cres increases to 10, relative errors rise for all sheet lengths, reaching approximately 15% at a = 30 m even for L = 60–100 m. This behavior is attributed to stronger lateral current diffusion within the subsurface, which diminishes the influence of insulation on current pathways.
This comparative analysis confirms that seafloor insulation systematically improves ρₐ sensitivity relative to conventional marine acquisition, particularly for larger insulation coverage. The proposed technique provides an effective solution for enhancing shallow structural detection in offshore DC resistivity surveys and offers quantitative guidelines for optimized survey design in offshore wind-turbine foundation site investigations.
How to cite: Tartoussi, N., Palma Lopes, S., and Leparoux, D.: Enhancement of Apparent Resistivity Sensitivity in Offshore DC Surveys Using Local Seafloor Insulation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19552, https://doi.org/10.5194/egusphere-egu26-19552, 2026.
