Earthquake gates, recurrence intervals and expected magnitude range for strike-slip faults

Michael E. Oskin, Alba M. Rodriguez Padilla, & Wing Yee Winnie Lau

Published September 10, 2023, SCEC Contribution #12847, 2023 SCEC Annual Meeting Poster #164

We combine recurrence information from long paleoseismic records with analysis of mapped surface ruptures to estimate the range of earthquake sizes produced by strike-slip faults. Long earthquake recurrence records (n>8 events) from strike-slip faults are well described by a Weibull distribution, with hazard increasing in proportion to time raised to a power, k. Most sites exhibit k~0.5, which we interpret as a result of smaller, partial-length ruptures interrupting progress to a system-spanning event. The exception is the Alpine fault of New Zealand, with much more regular recurrence and k~2. Earthquake surface-rupture maps reveal that discontinuities, such as bends and stepovers, are present at all scales. These act as earthquake gates, each with a probability of stopping an earthquake rupture related to its geometry. We cast the expected range of earthquake event sizes as a probability distribution controlled by the number and effectiveness of the gates along its rupture length. The lower bound of this distribution is controlled by the minimum event magnitude with surface rupture, and the upper bound is limited by the length of the fault system. The width of this range controls the frequency of events passing through a paleoseismic site. Earthquake recurrence on the northern San Andreas fault, southern San Andreas Fault, and San Jacinto fault are all consistent with a wide range of rupture length and sizes, from M~6.5 to system-spanning events exceeding M7.8. The longer mean recurrence of the Alpine fault, relative to its slip rate, is consistent with a narrow magnitude range with events M≥7.8. Overall, our analysis suggests, with the exception of the Alpine fault, that the large strike-slip faults with long earthquake records analyzed for this study should not exhibit characteristic earthquake size or recurrence. Instead, most-strike-slip faults host a range of event sizes, and as result exhibit a wide range of recurrence intervals between surface-rupturing events.

Key Words
paleoseismology, earthquake gates, earthquake magnitude

Citation
Oskin, M. E., Rodriguez Padilla, A. M., & Lau, W. (2023, 09). Earthquake gates, recurrence intervals and expected magnitude range for strike-slip faults. Poster Presentation at 2023 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Forecasting and Predictability (EFP)