Synthesis of fault geometry, seismicity, and deep structural fabric to constrain Community Fault (CFM) and Rheology (CRM) Models

Vera Schulte-Pelkum, & Deborah Kilb

Published August 13, 2021, SCEC Contribution #11340, 2021 SCEC Annual Meeting Poster #006 (PDF)

We combine newly available southern California data sets to provide constraints for refinement of the SCEC Community Fault Model (CFM) as well as development of the Community Rheology Model (CRM). We compare data from (1) the recently released CFM 5.3, (2) receiver function imaging of faults and intracrustal tectonic structural grain, and (3) refined earthquake catalogs (GrowClust and QTM). We use comparisons and synthesis of these data sets to define fault and shear zone geometries within and below the seismogenic zone to develop constraints for shear zones and block rheology for the CRM. Our work leverages recent receiver function results using azimuthal harmonic arrivals to image the depth, amplitude, and strike of conversions from contrasts in dipping foliation and dipping contrasts between isotropic bodies. Unlike splitting methods, this receiver function approach is sensitive to narrow shear zones and dipping contrasts rather than bulk properties and is thus particularly well suited to mapping shear zones, dipping faults, and tectonic boundaries. We highlight general parallelism of receiver function-derived crustal fabric strikes with strikes of nearby faults in the CFM. We also find multiple instances of alignment of receiver function-derived strikes with planar features delineated in relocated seismicity. A particular strength of this comparative approach is the extension of surface constraints to depth, including below the seismogenic zone past the brittle-viscous transition. For example, lower crustal distributed fabric in the southern Sierra Nevada parallels exhumed ductile fabric aligning with the reactivated Kern Canyon Fault. We also find near-fault structure imaged by data from dense station deployments along the San Jacinto fault and the San Andreas Fault near Parkfield showing deep pervasive fault-parallel fabric, as well as fine structure of the Ridgecrest and Coso areas with orthogonal features in seismicity and receiver function imaging. In fact, in most of southern California deep distributed fabric aligns with past tectonics. Therefore, for a CRM, we discourage attempting to define individual shear zone geometries and instead favor an approach that defines anisotropy of viscosity in lithospheric blocks.

Key Words
CFM, CRM, faults, receiver functions, seismicity, shear zones

Citation
Schulte-Pelkum, V., & Kilb, D. (2021, 08). Synthesis of fault geometry, seismicity, and deep structural fabric to constrain Community Fault (CFM) and Rheology (CRM) Models. Poster Presentation at 2021 SCEC Annual Meeting.

Related Projects & Working Groups
SCEC Community Models (CXM)