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Persistent earthquake clusters and gaps from slip on irregular faults

December 9, 2007

Earthquake-producing fault systems like the San Andreas fault in California show self-similar structural variation1; earthquakes cluster in space, leaving aseismic gaps between clusters. Whether gaps represent overdue earthquakes or signify diminished risk is a question with which seismic-hazard forecasters wrestle1,2,3,4,5. Here I use spectral analysis of the spatial distribution of seismicity along the San Andreas fault (for earthquakes that are at least 2 in magnitude), which reveals that it obeys a power-law relationship, indicative of self-similarity in clusters across a range of spatial scales. To determine whether the observed clustering of earthquakes is the result of a heterogeneous stress distribution, I use a finite-element method to simulate the motion of two rigid blocks past each other along a model fault surface that shows three-dimensional complexity on the basis of mapped traces of the San Andreas fault. The results indicate that long-term slip on the model fault generates a temporally stable, spatially variable distribution of stress that shows the same power-law relationship as the earthquake distribution. At the highest rates of San Andreas fault slip (40 mm yr−1), stress patterns produced are stable over a minimum of 25,000 years before the model fault system evolves into a new configuration. These results suggest that although gaps are not immune to rupture propagation they are less likely to be nucleation sites for earthquakes.

Publication Year 2008
Title Persistent earthquake clusters and gaps from slip on irregular faults
DOI 10.1038/ngeo.2007.36
Authors Tom Parsons
Publication Type Article
Publication Subtype Journal Article
Series Title Nature Geoscience
Index ID 70217330
Record Source USGS Publications Warehouse
USGS Organization Pacific Coastal and Marine Science Center