Understanding interaction of small repeating earthquakes through models of rate-and-state faults
Abstract
Due to their short recurrence times and known locations, small repeating earthquakes are widely used to study earthquake physics. Some of the repeating sequences are located close to each other and appear to interact. For example, the "San Francisco" (SF) and "Los Angeles" (LA) repeating sequences, which are targets of the San Andreas Fault Observatory at Depth (SAFOD), have a lateral separation of less than 70 m. The LA events tend to occur within 24 hours after the SF events, suggesting a triggering effect. Our goal is to study interaction of repeating earthquakes in the framework of rate-and-state fault models, in which repeating earthquakes occur on velocity-weakening patches embedded into a larger velocity-strengthening fault area. Such models can reproduce behavior of isolated repeating earthquake sequences, in particular, the scaling of their moment versus recurrence time and the response to accelerated postseismic creep (Chen and Lapusta, 2009; Chen et al., 2010). Our studies of the interaction of seismic events on two patches show that a variety of interesting behaviors. As expected based on intuition prior studies (e.g., Kato, JGR, 2004; Kaneko et al., Nature Geoscience, 2010), the two patches behave independently when they are far apart and rupture together if they are next to each other. In the intermediate range of distances, we observe triggering effects, with ruptures on the two patches clustering in time, but also other patterns, including supercycles that alternate between events that rupture a single asperity and events that rupture both asperities at the same time. When triggering occurs, smaller events tend to trigger larger events, since the nucleation of smaller events tends to be more frequent. To overcome such a pattern, and have larger events trigger smaller events as observed for the SF-LA interaction, the patch for the smaller event needs to be of the order of the nucleation size, so that the smaller event has difficulty nucleating by itself, without the external trigger. Our simulations show that, in addition to static and dynamic stress changes that a seismic event on one patch creates on the other patch, the interaction also occurs through accelerated post-seismic slip between the two patches. For a wide range of model parameters, such accelerated aseismic slip seems to be an important, and perhaps determining, factor, as triggered events nucleate shortly after the postseismic slip front created by the event on one patch reaches the other patch. We will report on the results of our current work aimed at quantifying the relative importance of the three triggering mechanisms and their effect on the degree of interaction.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.S21B2494C
- Keywords:
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- 7209 SEISMOLOGY / Earthquake dynamics;
- 7223 SEISMOLOGY / Earthquake interaction;
- forecasting;
- and prediction;
- 7250 SEISMOLOGY / Transform faults