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Stairways to Hazard: Quantifying Geologic Slip Rate Variability Along Low Strain Rate Faults

Session: Cryptic Faults: Assessing Seismic Hazard on Slow Slipping, Blind or Distributed Fault Systems II

Type: Oral

Date: 4/21/2021

Presentation Time: 03:00 PM Pacific

Description: 

Geologic slip rates are time-averaged measurements of earthquake behavior calculated over 10²–10^6--year time scales and thus represent a coarse metric of the rate of strain release along faults. Slip rates are a primary input for seismic hazard analyses, which forecast expected ground shaking in future earthquakes. Despite the importance of this metric in calculating seismic hazard, geologic slip rates are typically low-resolution approximations of potentially complex, high-resolution faulting histories. The issue of simplification is exacerbated when calculating geologic slip rates along low strain rate faults, given that very few earthquake cycles are included in a single slip rate. Averaging over only one or two earthquake cycles, including an open interval, may yield spurious slip-rate estimates. It can also be difficult to quantify the uncertainty in slip rates from short records. We developed a numerical approach that explicitly addresses these issues by constructing models of time-displacement paths (or ‘stairways’) that rely on field-based observations of dated offsets, mean recurrence interval and mean slip per event. We apply this approach to faults in the Basin and Range Province, which are generally characterized by low (<1 mm/yr) slip rates with a limited number of recurrence intervals. This numerical methodology allows us to extrapolate slip rate records further into the past utilizing available field measurements, yielding more robust estimates of geologic slip rates over multiple earthquake cycles. Using numerous simulations of displacement-time paths, we derive a distribution of modeled slip rates constrained by the field observations. Modeled slip rate distributions expand and quantify the uncertainties about these median geologic slip rate values. Slip rate estimates can also be extended into the future to estimate the probability of future events. Results from this work will be considered for use in the geologic deformation model component of the U.S. National Seismic Hazard Model.

Presenting Author: Alexandra E. Hatem

Student Presenter: No

Authors