Unraveling the apparent magnitude threshold of remote earthquake triggering using full wavefield surface wave simulation

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Abstract

[1] Empirical studies with earthquake catalogs suggest that large events (M > 5) are rarely triggered in significant numbers by passing surface waves at remote distances from main shocks. Triggered, small (M < 5) earthquakes are routinely associated with the passage of surface waves from large (M > 7) main shocks. Since large earthquakes involve larger rupture areas, we study the spatial and temporal characteristics of dynamic stress change for clues. Using a 3D finite element method, we model the complete wavefield from the 2002 M= 7.9 Denali earthquake recorded near the Wasatch Front in Utah, where details about triggered seismicity are known. In particular, we load our model with a displacement seismogram to acquire a time series of the stress change tensor and model failure of a representative normal fault based on these stress changes. We note that the stress-change regime varies rapidly between favoring strike-slip, thrust, and normal faulting, with durations lasting ∼1–4 s. We find that these stress regimes usually affect only some fraction of a fault surface at any given time. Stress amplitudes also vary, meaning that ideal conditions for triggering are short-lived and spatially limited. Stress conditions can also rapidly reverse to regimes that inhibit slip. Given these stressing conditions, we conclude that it may be difficult for a larger rupture area to experience the temporally and spatially coherent stress change necessary to develop into a large magnitude earthquake.

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