Group B, Poster #062, Stress and Deformation Over Time (SDOT)

Characteristic Slow‐Slip Events on the Superstition Hills Fault

Ellis J. Vavra, Yuri Fialko, Thomas K. Rockwell, Roger Bilham, Petra Stepancikova, Jakub Stemberk, Petr Taborik, & Josef Stemberk
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Poster Presentation

2024 SCEC Annual Meeting, Poster #062, SCEC Contribution #14010 VIEW PDF
Multiple decades of observations have documented a wide range of slip behavior along the Superstition Hills Fault (SHF) at the southern end of the San Jacinto Fault Zone in Southern California. The SHF experienced a notable M 6.6 earthquake in 1987, which was followed by rapid shallow afterslip. Background quasi-steady creep on the SHF has been punctuated by dynamically triggered and apparently spontaneous slow slip events (SSEs) both prior to and following the 1987 earthquake. Following a 13 year period of minimal creep, a large SSE was detected by local creepmeters in May 2023. Over 25 mm of slip was recorded over 16-19 May 2023, with subsequent slip pulses bringing the total to 41 mm over... the following months. Analysis of interferometric synthetic aperture radar (InSAR) data indicates that the event initiated on the northern portion of the fault, prior to detection by the creepmeters, and subsequently propagated north and south over the following days. Fault offsets obtained from both field and InSAR measurements illuminate a skewed, bi-modal surface rupture. Slip on the southern section of the fault was approximately twice as large as that on the northern section. In addition, slip on the southern section is highly localized (< 100 m), while the northern section is characterized by distributed deformation over a ~500-1200 m zone. Kinematic slip models obtained from inversions of InSAR data constrain the depth extent of slip to 2-4 km; while the entire event is confined to the shallow sedimentary layer, there are additional systematic contrasts in slip depth between the northern and southern halves of the fault. Comparisons of the slip models and surface offsets reveal a remarkable similarity between the 2023 SSE and past events occurring in 1999, 2006, and 2010, which indicates that the SHF exhibits at least one style of characteristic rupture. Our updated time-averaged rates of shallow creep along the SHF implies that the long-term fault slip rate is underestimated, which is consistent with previous work that has suggested the SHF is structurally connected to the main San Jacinto Fault strand.
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Citation: Vavra, E. J., Fialko, Y., Rockwell, T. K., Bilham, R., Stepancikova, P., Stemberk, J., Taborik, P., & Stemberk, J. (2024, 09). Characteristic Slow‐Slip Events on the Superstition Hills Fault. Poster Presentation at 2024 SCEC Annual Meeting.
Relevant SCEC Themes:
Improving Observations and Closing Data Gaps