Seismic Hazard Inferred from Tectonics: California

Peter Bird, & Zhen Liu

Published 2007, SCEC Contribution #926

In this paper we propose simple methods for estimating long-term average seismicity of any region, based on a local kinematic model of surface velocities and an existing global calibration of plate-boundary seismicity. We apply the method to California and obtain a long-term forecast of seismicity that exceeds the levels seen in several 20th-century catalogs.

This contribution is the third in a series describing a project informally known as Seismic Hazard Inferred from Tectonics (SHIFT). Its goal is to realize the promise of plate tectonic theory to provide long-term seismicity forecasts (and, eventually, seismic hazard forecasts) more reliable than those based primarily on local instrumental and/or historic records. Bird (2003) reviewed the literature on plate tectonics, assembling model PB2002 consisting of 52 plates and 13 orogens, with every plate-boundary step (great-circle arc between digitized points) classified as one of seven types. Bird and Kagan (2004) used this model to assign 95% of shallow earthquakes to appropriate plate boundaries and to estimate the seismicity parameters (width, productivity, spectral slope, corner magnitude, and coupled thickness) for each boundary type. Here we propose simple hypotheses predicting the long-term shallow seismicity produced by any geometry of tectonic faults (and/or zones of distributed anelastic straining) by treating each fault or region as a small sample of the most appropriate type of plate boundary. This is consistent with the observation that the distribution of plate sizes obeys a power law (Bird 2003; Sornette and Pisarenko 2003), so that the number of plates is uncountable, and it may even be difficult to defend a fundamental distinction between plate boundaries and plate interiors in some cases.

Bird, P., & Liu, Z. (2007). Seismic Hazard Inferred from Tectonics: California. Seismological Research Letters, 78(1), 37-48. doi: 10.1785/gssrl.78.1.37.