Spatiotemporal Patterns and Predictability of Shallow Slow Slip Sequences on Superstition Hills Fault

Zhenyu Kang, & Junle Jiang

In Preparation September 30, 2026, SCEC Contribution #15670

Crustal faults host different modes of movement that vary with time, depth, and lateral distance. While earthquakes impose predominant threats, slow slip on shallow faults redistributes stress and incurs persistent damage to nearby infrastructure. The Superstition Hills Fault (SHF) in southern California is an active strike-slip fault that exhibits both seismic and aseismic behaviors at different depths, including long-term plate loading below the locking depth, coseismic slip at the seismogenic depth, and quasi-steady creep and slow slip events (SSEs) within the shallow sedimentary layer. Here, we study the SSE behavior on the SHF in 2017 and over the past four decades to reveal the spatiotemporal patterns and predictability of the SSEs. The SSE in August 2017 was recorded by one GNSS station and Interferometric Synthetic Aperture Radar (InSAR) of Sentinel-1A/B satellites but has not yet been investigated in detail. We utilize the time-dependent InSAR displacement field to invert for the finite-fault slip distribution on the SHF using least-squares and Bayesian approaches. Then we compile the earthquakes and SSEs history on SHF to compare the spatial distribution of transient slip amplitudes, as well as cumulative slip history in the seismogenic layer and the sedimentary layer at different along-fault locations. The slip amplitudes of SSEs are spatially variable within the same event and across different events. The SSEs occur every several years, with a maximum amplitude of 20-40 mm, equivalent to earthquakes of moment magnitude of 4-4.5. The SSEs triggered by nearby earthquakes in 1999 and 2010 appear to have shorter durations and recurrence intervals compared to spontaneously initiated events in 2006, 2017, and 2023. The shallow slip deficit left by the 1987 M 6.6 Superstition Hills earthquake has been largely accommodated by decades of quasi-static creep and SSEs. Local slip history across the northern and southern fault segments is not simply time- or slip-predictable, suggesting that the initiation styles, finite dimensions, and spatial variability of SSEs inherently complicate fault slip evolution. While SSEs release the shallow strain intermittently, their decadal behavior may influence and portend future earthquake ruptures.

Citation
Kang, Z., & Jiang, J. (2026). Spatiotemporal Patterns and Predictability of Shallow Slow Slip Sequences on Superstition Hills Fault. Journal of Geophysical Research: Solid Earth, (in preparation).