Reconciling seismicity and geodetic locking depths on the Anza section of the San Jacinto fault. Issue 20 (21st October 2016)

• Record Type: Journal Article
• Authors: Jiang, Junle; Fialko, Yuri
• Is Part Of: Geophysical research letters. Volume 43:Issue 20(2016)
• Page Start: 10, 663
• Page End: 10, 671
• Publication Date: 2016-10-21
• Subjects: fault mechanics -- rate‐and‐state friction -- earthquake rupture -- geodetic locking -- seismicity -- aseismic transients; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2016GL071113
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Observations from the Anza section of the San Jacinto Fault in Southern California reveal that microseismicity extends to depths of 15–18 km, while the geodetically determined locking depth is less than ~10 km. This contrasts with observations from other major faults in the region and also with predictions of fault models assuming a simple layered distribution of frictional properties with depth. We suggest that an anomalously shallow geodetic fault locking may result from a transition zone at the bottom of seismogenic layer with spatially heterogeneous frictional properties. Numerical models of faults that incorporate stochastic heterogeneity at transitional depths successfully reproduce the observed depth relation between seismicity and geodetic locking, as well as complex spatiotemporal patterns of microseismicity with relatively scarce repeating earthquakes. Our models predict propagation of large earthquakes to the bottom of the transition zone, and ubiquitous aseismic transients below the locked zone, potentially observable using high‐precision geodetic techniques. Key Points: A transition zone with heterogeneous frictional properties may explain microseismicity much below the geodetic locking depth Large earthquakes can penetrate beyond the geodetic locking depth to the deepest extent of seismicity, with complexity in downdip ruptures Our model predicts deep aseismic transients that can be potentially detected by modern geodetic techniques