Tom Parsons
2008
<p><span>Earthquake-producing fault systems like the San Andreas fault in California show self-similar structural variation</span><sup><a id="ref-link-section-d71288e263" title="Kagan, Y. Y. & Knopoff, L. Spatial distribution of earthquakes: The two-point correlation function. Geophys. J. R. Astron. Soc. 62, 303–320 (1980)." href="https://www.nature.com/articles/ngeo.2007.36#ref-CR1" data-track="click" data-track-action="reference anchor" data-track-label="link" data-test="citation-ref" aria-label="Reference 1" data-mce-href="https://www.nature.com/articles/ngeo.2007.36#ref-CR1">1</a></sup><span>; 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 wrestle</span><sup><a id="ref-link-section-d71288e267" title="Kagan, Y. Y. & Knopoff, L. Spatial distribution of earthquakes: The two-point correlation function. Geophys. J. R. Astron. Soc. 62, 303–320 (1980)." href="https://www.nature.com/articles/ngeo.2007.36#ref-CR1" data-track="click" data-track-action="reference anchor" data-track-label="link" data-test="citation-ref" aria-label="Reference 1" data-mce-href="https://www.nature.com/articles/ngeo.2007.36#ref-CR1">1</a>,<a id="ref-link-section-d71288e270" title="McCann, W. R., Nishenko, S. P., Sykes, L. R. & Krause, J. Seismic gaps and plate tectonics: Seismic potential for major boundaries. Pure Appl. Geophys. 117, 1082–1147 (1979)." href="https://www.nature.com/articles/ngeo.2007.36#ref-CR2" data-track="click" data-track-action="reference anchor" data-track-label="link" data-test="citation-ref" aria-label="Reference 2" data-mce-href="https://www.nature.com/articles/ngeo.2007.36#ref-CR2">2</a>,<a id="ref-link-section-d71288e273" title="Nishenko, S. P. Circum-Pacific seismic potential—1989–1999. Pure Appl. Geophys. 135, 169–259 (1991)." href="https://www.nature.com/articles/ngeo.2007.36#ref-CR3" data-track="click" data-track-action="reference anchor" data-track-label="link" data-test="citation-ref" aria-label="Reference 3" data-mce-href="https://www.nature.com/articles/ngeo.2007.36#ref-CR3">3</a>,<a id="ref-link-section-d71288e276" title="Kagan, Y. Y. & Jackson, D. D. Seismic gap hypothesis: Ten years after. J. Geophys. Res. 96, 21419–21429 (1991)." href="https://www.nature.com/articles/ngeo.2007.36#ref-CR4" data-track="click" data-track-action="reference anchor" data-track-label="link" data-test="citation-ref" aria-label="Reference 4" data-mce-href="https://www.nature.com/articles/ngeo.2007.36#ref-CR4">4</a>,<a id="ref-link-section-d71288e279" title="Rong, Y., Jackson, D. D. & Kagan, Y. Y. Sesimic gaps and earthquakes, J. Geophys. Res. 108 (2003) (doi:10.1029/2002JB002334)." href="https://www.nature.com/articles/ngeo.2007.36#ref-CR5" data-track="click" data-track-action="reference anchor" data-track-label="link" data-test="citation-ref" aria-label="Reference 5" data-mce-href="https://www.nature.com/articles/ngeo.2007.36#ref-CR5">5</a></sup><span>. 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</span><sup>−1</sup><span>), 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.</span></p>
application/pdf
10.1038/ngeo.2007.36
en
Springer
Persistent earthquake clusters and gaps from slip on irregular faults
article