SCEC Award Number 16121 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Reconciling seismic and geodetic locking depths on the Anza segment of the San Jacinto Fault
Investigator(s)
Name Organization
Yuri Fialko University of California, San Diego
Other Participants Junle Jiang - postdoc
SCEC Priorities 1b, 3c, 4a SCEC Groups FARM, SDOT
Report Due Date 03/15/2017 Date Report Submitted 04/07/2017
Project 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 that exhibit a general agreement between the seismic and geodetic locking depths, and also with predictions of models of faults that obey rate and state friction with simple layered distribution of friction properties with depth. We suggest that an anomalously shallow geodetic fault locking may result from a transition zone between the locked and creeping fault sections with spatially heterogeneous distribution of 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 spatio-temporal patterns of microseismicity with relatively scarce repeating earthquakes. Our models suggest propagation of large earthquakes to the bottom of the transition zone, and ubiquitous aseismic transients in the transition zone, potentially observable using high-precision geodetic techniques.
Intellectual Merit This project offered an explanation for an apparent discrepancy between the seismologically and geodetically inferred locking depths on the Anza section of the San Jacinto fault, the most seismically active fault in Southern California. It advanced our understanding of fault behavior and relationships between seismicity and surface deformation, and contributed to several research objectives of SCEC4, including: focused laboratory, numerical, and geophysical studies of the character of the lower crust, its rheology, stress state, and expression in surface deformation; formulation of theoretical and numerical models of specific fault resistance mechanisms for seismic radiation and rupture propagation, including interaction with fault roughness and damage-zone properties; and detailed geologic, seismic, geodetic, and hydrologic investigations of fault complexities at Special Fault Study Areas and other important regions.
Broader Impacts The proposed models can be applied to other active faults in Southern California where the geodetically inferred locking depth is shallower than the depth extent of seismicity (one notable example is the Imperial fault). This project provided training and partial support for one post-doctoral scholar (Junle Jiang). The PI (Fialko) used results of this study in a graduate class taught at SIO.
Exemplary Figure Figure 3
Credits: Junle Jiang and Yuri Fialko, SIO/UCSD