Surface Rupture Effects on Earthquake Moment-Area Scaling Relations
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Empirical earthquake scaling relations play a central role in fundamental studies of earthquake physics and in current practice of earthquake hazard assessment, and are being refined by advances in earthquake source analysis. A scaling relation between seismic moment (M 0) and rupture area (A) currently in use for ground motion prediction in Japan features a transition regime of the form M 0–A 2, between the well-recognized small (self-similar) and very large (W-model) earthquake regimes, which has counter-intuitive attributes and uncertain theoretical underpinnings. Here, we investigate the mechanical origin of this transition regime via earthquake cycle simulations, analytical dislocation models and numerical crack models on strike-slip faults. We find that, even if stress drop is assumed constant, the properties of the transition regime are controlled by surface rupture effects, comprising an effective rupture elongation along-dip due to a mirror effect and systematic changes of the shape factor relating slip to stress drop. Based on this physical insight, we propose a simplified formula to account for these effects in M 0–A scaling relations for strike-slip earthquakes.
KeywordsEarthquake scaling relations surface rupture effects earthquake cycle model rate-and-state friction analytical dislocation model numerical crack model
This study was based on the 2015 research project ‘Improvement for uncertainty of strong ground motion prediction’ by the Nuclear Regulation Authority (NRA), Japan.
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