Propagating creep events on the Superstition Hills and Imperial faults measured by InSAR, GNSS, and creepmeters

Kathryn Materna, Sarah E. Minson, Danielle Lindsay, Roland Bürgmann, Brendan W. Crowell, & Roger Bilham

Published September 10, 2023, SCEC Contribution #13130, 2023 SCEC Annual Meeting Poster #151

Transient creep events in the upper 2-4 kilometers of the crust provide an opportunity to probe the mechanical properties of faults. Aseismic creep episodes represent frictional instabilities in that they slip much faster than the long-term plate rate, but they are also much slower than regular earthquakes – they produce displacements of only a few centimeters over multiple days and they do not produce seismic waves. Many creep events have been observed with creepmeters on faults around the world; however, the spatio-temporal evolution of these events, which is key to their dynamics, is still poorly understood. In the spring of 2023, the Superstition Hills fault and the Imperial fault in southern California each experienced large transient slip events. With a mix of complementary geodetic observations (sub-daily GNSS, frequent satellite radar acquisitions, and creepmeters with high temporal sampling), these recent transient motions were captured in unprecedented detail. The observations from southern California show that in both creep events, slip initiated in one part of the fault and propagated along-strike over 1-2 weeks. The Superstition Hills creep event propagated bilaterally from its initiation point in a pulse-like manner. Based on the combined InSAR, GNSS, and creepmeter observations, the propagation velocity is about 10 km/day, similar to along-strike propagation velocities of slow slip events observed in subduction zones. We calculate the total moment released in both creep events and model the depth of slip, which occurs from a few km depth to ~15 m below the surface for the majority of the rupture. These events reveal that fault slip in the upper 2-4 kilometers of the crust in the Imperial Valley does not obey classical rate-and-state friction laws and instead requires additional fault-frictional properties, such as slip in a dilatant-strengthening or a poroelastic medium.

Key Words
slow slip event, superstition hills fault

Citation
Materna, K., Minson, S. E., Lindsay, D., Bürgmann, R., Crowell, B. W., & Bilham, R. (2023, 09). Propagating creep events on the Superstition Hills and Imperial faults measured by InSAR, GNSS, and creepmeters. Poster Presentation at 2023 SCEC Annual Meeting.

Related Projects & Working Groups
Stress and Deformation Over Time (SDOT)