Locally and remotely triggered aseismic slip on the central San Jacinto Fault near Anza, CA, from joint inversion of seismicity and strainmeter data

Abstract

We study deep aseismic slip along the central section of the San Jacinto Fault, near the Anza Seismic Gap, in southern California. Elevated strain rates following the remote Mw7.2, 4 April 2010 El Mayor‐Cucapah and the local Mw5.4, 7 July 2010 Collins Valley earthquakes were recorded by Plate Boundary Observatory borehole strainmeters near Anza and were accompanied by vigorous aftershock sequences. We introduce a method to infer the distribution of triggered aseismic slip from combined seismicity and geodetic data, based on a rate‐and‐state friction model that maps observed changes in seismicity rates into stress changes. We invert for the cumulative slip in the 10 day period following each main shock. Synthetic tests show that the effect of aftershock interactions on the inferred slip distribution is negligible. The joint data set is more consistent with a model in which aseismic slip on a principal fault triggers seismicity on adjacent faults than with one in which aseismic slip and seismicity are coplanar. Our results indicate that aseismic slip primarily occurs along the rim of two seismicity clusters adjacent to Anza Gap, as well as beneath the Anza Gap itself, at depths larger than 10 km. The triggered aseismic slip generated by the two main shocks has little overlap, a pattern also found in sequences of large earthquakes occurring on a same fault. Stresses inferred from seismic activity leading to the Collins Valley main shock suggest that this earthquake was triggered by stresses imposed by the El Mayor‐Cucapah remote‐triggered aseismic slip, which persisted for more than 2 months.

Constitutive Law for Earthquake Production Based on Rate‐and‐State Friction: Dieterich 1994 Revisited

“…Most applications have considered simple stressing, such as a step change in shear stress due to a large earthquake. Some studies have looked at more complicated stressing histories and shown the model to be consistent with observations or independent data sets such as geodetic data (e.g., Dieterich et al, ; Green et al, ; Inbal et al, ; Segall et al, ; Ziv, ). However, as was previously mentioned, there is still need for further verification.…”

“…This was also investigated by Helmstetter and Shaw () who found an analytical expression that maps seismicity rate and cumulative number of events to stress change. A number of observational studies have utilized this result (e.g., Inbal et al, ; Savage, ) since seismicity rate and cumulative number of events can be estimated directly from data. Spatially heterogeneous stresses were explored by Helmstetter and Shaw (), who related the p value of Omori's law to stress heterogeneity.…”

Constitutive Law for Earthquake Production Based on Rate‐and‐State Friction: Theory and Application of Interacting Sources

“…However, here source interactions have been taken into account. In application of the Dieterich theory for joint inversion the role of earthquake interactions and secondary events is often cited (e.g., Inbal et al, ; Segall et al, ) as an element of uncertainty in determining the applied stress field. Equation provides a possible resolution as it allows us to separate the externally applied stress field and the changes that occur through source interactions.…”

“…However, in many applications of the Dieterich theory the cumulative number of events (or seismicity rate) is not simulated. Instead, observed seismicity rate and cumulative number of events are used to extract the changes in stress (e.g., Dieterich et al, 2000;Helmstetter & Shaw, 2009;Inbal et al, 2017;Ziv, 2012).…”

Strong Hydro‐Related Localized Long‐Period Crustal Deformation Observed in the Plate Boundary Observatory Borehole Strainmeters

“…In addition, rainfall and barometric pressure are measured at all the strainmeters, and pore pressure at some of the strainmeters in Cascadia and California. Since installation in 2005, strain signals related to many geophysical phenomena are observed in the strainmeters, including tide (Hodgkinson et al, ; Lu & Wen, ; Roeloffs, ), earthquake (Barbour et al, ; Inbal et al, ; Roeloffs, ), aseismic creep (Inbal et al, ; Langbein, ; Roeloffs, ), episodic tremor and slip (Dragert & Wang, ; Hawthorne & Rubin, ; K. Wang et al, ), groundwater extraction (Barbour & Wyatt, ), and lake seiche (Luttrell et al, ).…”