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Wasatch Fault Zone Paleoseismic Rupture Models

Description: 

The Wasatch fault zone (WFZ), which forms the approximate eastern limit of Basin and Range Province extension in Utah, has long been evaluated through the lens of fault segmentation, which impacts estimates of earthquake rupture length, recurrence, magnitude, and probability. We evaluate this assumption using WFZ paleoseismic data, including 87 earthquakes younger than 7 ka identified at 28 sites along the 290-km-long Holocene trace. Using the temporal overlap of these earthquakes, we generate four non-unique rupture models that capture a range of plausible rupture behavior. Two end-member modes use overlapping site earthquakes to generate (1) minimum-length (≤50-km) and (2) maximum-length rupture models, which include the most spatially limited (n=30) and longest-possible (n=22) ruptures, respectively. (3) A structural model is similar to (2) but with ruptures trimmed or extended to geometric complexities (n=26). (4) A segmented model includes ruptures that are largely restricted to the most prominent structural complexities along strike (n=26). These models yield consistent rupture extents in the youngest portion of the paleoseismic record (<1ka) and diverge with age as timing uncertainty increases and the completeness of the record decreases. Across the models, rupture lengths vary from 12 to 154 km (mean of 45 ± 20 km). Although some ruptures appear to terminate at or near structural complexities, spatially variable ruptures that cross typical segmentation boundaries are the norm. We evaluate seismic moment release over time, spatial and temporal patterns of recurrence, and aperiodicity implied by these rupture models. We also compare our results with an inversion-based rupture forecast using geometric plausibility filters to determine multi-fault ruptures. Our results improve understanding of how earthquake cycles manifest on long normal faults and will inform time-dependent earthquake probability calculations for the Wasatch Front region.

Session: Temporally Variable Records of Earthquake Behavior and Considerations for Seismic Hazard Analyse [Poster]

Type: Poster

Date: 4/17/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Christopher

Student Presenter: No

Invited Presentation: 

Poster Number: 31

Authors