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When Strike-slip Is Not Enough: The Full Kinematics of the Central San Andreas Fault

Description: 

Fault creep rates along the creeping section of the San Andreas fault (SAF) have been measured and modeled since the 1960s. The modeled average creep rates range from 1 to 3 cm/yr depending on the location along strike. However, such estimates mainly focus on the strike-slip component of the fault slip, overlooking the dip-slip counterpart as well as the fault-normal contraction/dilation motion. Regional stress field orientation inferred from local seismicity indicates that the maximum horizontal stress direction is at an acute angle to the central SAF, suggesting that the fault is experiencing large contractional forces. Additionally, local surface uplift and subsidence across the central SAF are also observed in our results. Therefore, we hypothesize that fault slip/creep along the central SAF is a rather complex mechanism, in other words, the complete 3D fault kinematics should exhibit not only the strike-slip component but also the two other orthogonal vectors acting on the fault.
Here, we use UAVSAR and Sentinel-1 datasets to jointly invert for the 3D surface deformation rates around the central San Andreas fault. For the UAVSAR data, we use a set of polynomial functions to correct for erroneous signals that arise from platform instability. Then, we project the horizontal surface deformation rate components to fault-parallel and fault-perpendicular directions. We model the 3D surface deformation rate with Okada’s model, simultaneously solving for the rake angle and the tensile deformation on the fault. Results show that the rake angles vary between 170 and 190 degrees along the fault with the Parkfield segment showing a rather consistent reverse slip sense. In addition to faulting, we also find the tensile deformation can explain the observed surface fault-normal contraction. Possible driving mechanisms of such tensile closing might be due to the regional stress field orientation and/or the internal rotation from shearing.

Session: SSJ-SSOC-SSA Joint Session: From Slow to Fast Earthquakes: Bridging the Spectrum of Fault Slip [Poster]

Type: Poster

Date: 4/16/2026

Presentation Time: 08:00 AM (local time)

Presenting Author: Li-Chieh Lin

Student Presenter: Yes

Invited Presentation: 

Poster Number: 147

Authors