Earthquake source processes are described based on friction laws on faults, bulk constitutive behavior of the surrounding medium, and the stress state of an intricate fault network, including off-fault damage. The combination of these components forms a dynamic earthquake rupture model that accounts for the seismological, geodetic, and geological observations, as well as enables estimation of the earthquake energy budget. While such models help clarify key factors characterizing earthquake source processes, trade-offs among these factors often prevent identifying the dominant physical mechanism. For example, enhanced near-field high-frequency radiation can be attributed to fault roughness, structural heterogeneity, or coseismic off-fault damage (Okubo et al., 2019), each of which can produce similar observational signatures.

To mitigate the modeling uncertainties, information available from laboratory experiments can be utilized, such as fault geometry, bulk elastic properties, stress state, and frictional conditions. Here, I demonstrate this concept through a laboratory study aimed at controlling the size and location of earthquake source patches on a laboratory fault (Okubo et al., in revision). This approach provides a predetermined source configuration that can be incorporated into a dynamic rupture model. Circular gouge patches as earthquake sources were placed on a 4-meter-long laboratory fault in a large-scale biaxial apparatus, generating microearthquakes during the evolution of preslip or afterslip on the entire fault in stick-slip experiments. Acoustic emission waveforms carefully corrected for instrumental response and attenuation suggest that these earthquake clusters exhibit non-self-similar scaling. Using the controlled source geometry and the observed source parameters, we developed a dynamic rupture model that is quantitatively consistent with laboratory observations. Although this model is not a unique solution for explaining the observed non-self-similar scaling, given the limited information available to fully resolve the rupture process even under laboratory conditions, it complements previously proposed models for non-self-similar earthquakes and provides a useful basis for interpreting natural earthquakes.

Close integration of experiments and modeling is key to updating previous findings by addressing limitations in existing modeling frameworks. Large-scale experiments allow for spatially dense measurement arrays relative to the characteristic length scales of dynamic ruptures. Models quantitatively constrained by these high-quality measurements help clarify the details in source processes and play an important role in determining which observables, and at what resolution, are required to effectively monitor faulting activity.

How to cite: Okubo, K.: Advancing Knowledge of Earthquake Source Processes Through Dynamic Rupture Modeling with Natural and Laboratory Observables, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14630, https://doi.org/10.5194/egusphere-egu26-14630, 2026.

EGU26-14630

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In Gutenberg’s era, earthquakes were understood primarily as phenomena involving the release and propagation of seismic wave energy. Since the 1960s, seismic wave radiation has been explained by fault slip, and various characteristics of earthquakes have been successfully described by slip processes governed by friction laws on fault surfaces. As a result, the view that “earthquakes are fault slip” became widely accepted, and earthquake size is now usually represented not by radiated seismic energy but by seismic moment, a measure of fault slip. However, while earthquakes certainly involve fault slip, it is incorrect to assume that all fault slip represents an earthquake.

The discovery and increasing understanding of slow earthquakes in recent decades have made it necessary to reconsider a fundamental question: What exactly is an earthquake? What distinguishes slow earthquakes from regular earthquakes? Under what conditions does this distinction arise? Do regular earthquakes begin in a universal manner? Addressing such questions leads to a view of earthquakes as a coupled process of rock fracture and wave radiation that cascades through hierarchical heterogeneities spanning a wide range of spatial and temporal scales. I aim to discuss approaches for understanding—and ultimately forecasting—such complex, multiscale phenomena.

How to cite: Ide, S.: Rethinking Earthquakes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4764, https://doi.org/10.5194/egusphere-egu26-4764, 2026.

EGU26-4764

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