Characteristic Slow-Slip Events on the Superstition Hills Fault,
Southern California
Abstract
The Superstition Hills Fault (SHF) exhibits a rich spectrum of slip
modes, including M 6+ earthquakes, afterslip, quasi-steady creep, and
both triggered and spontaneous slow slip events (SSEs). Following 13
years of quiescence, creepmeters recorded 25 mm of slip during 16-19 May
2023. Additional sub-events brought the total slip to 41 mm. The event
nucleated on the northern SHF in early-May and propagated bi-laterally
at rates on the order of kilometers per day. Surface offsets reveal a
bi-modal slip distribution, with slip on the northern section of the
fault being less localized and lower amplitude compared to the southern
section. Kinematic slip models confirm systematic variations in the slip
distribution along-strike and with depth and suggest that slip is
largely confined to the shallow sedimentary layer. Observations and
models of the 2023 SSE bear a strong similarity to previous slip
episodes in 1999, 2006, and 2010, suggesting a characteristic behavior.