Abstract

AbstractThe style of convective force transmission to plates and strain‐localization within and underneath plate boundaries remain debated. To address some of the related issues, we analyze a range of deformation indicators in southern California from the surface to the asthenosphere. Present‐day surface strain rates can be inferred from geodesy. At seismogenic crustal depths, stress can be inferred from focal mechanisms and splitting of shear waves from local earthquakes via crack‐dependent seismic velocities. At greater depths, constraints on rock fabrics are obtained from receiver function anisotropy, Pn and P tomography, surface wave tomography, and splitting of SKS and other teleseismic core phases. We construct a synthesis of deformation‐related observations focusing on quantitative comparisons of deformation style. We find consistency with roughly N‐S compression and E‐W extension near the surface and in the asthenospheric mantle. However, all lithospheric anisotropy indicators show deviations from this pattern. Pn fast axes and dipping foliations from receiver functions are fault‐parallel with no localization to fault traces and match post‐Farallon block rotations in the Western Transverse Ranges. Local shear wave splitting orientations deviate from the stress orientations inferred from focal mechanisms in significant portions of the area. We interpret these observations as an indication that lithospheric fabric, developed during Farallon subduction and subsequent extension, has not been completely reset by present‐day transform motion and may influence the current deformation behavior. This provides a new perspective on the timescales of deformation memory and lithosphere‐asthenosphere interactions.

Highlights

  • Southern California hosts one of the world's best-instrumented and most thoroughly studied transform plate boundaries, yet questions as to how surface deformation transitions to convective flow and deformation at depth remain

  • Constraints on rock fabrics are obtained from receiver function anisotropy, Pn and P-to-S conversion (Ps) tomography, surface wave tomography, and splitting of SKS and other teleseismic core phases

  • Surface instantaneous strain as well as focal mechanisms are as expected for the present transform motion, an alignment that is borne out on smaller scales for most faults in the area besides those recently affected by major earthquakes (Becker et al, 2005)

Read more

Summary

Introduction

Southern California hosts one of the world's best-instrumented and most thoroughly studied transform plate boundaries, yet questions as to how surface deformation transitions to convective flow and deformation at depth remain. Present-day transform motion is accommodated on the San Andreas Fault (SAF) (Figure 1). H. Hearn, 2019; Meade & Hager, 2005; Y. Zeng & Shen, 2016, 2017).

Methods
Results
Discussion
Conclusion
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call