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Geomorphology May Be a Poor Recorder of Slip Distributions From Paleo Surface Ruptures

Description: 

Interpreting the geomorphic record of strike-slip earthquakes to infer slip in past events is complicated by the observed complexities of surface ruptures. Recent earthquakes show that slip variability in a rupture is on the order of 40-50%, distributed deformation is common and spatially variable, and rupture start and end points are not always at obvious section boundaries. Further complicating the record created by each surface rupture is climate’s influence on the landscape. Offset features are modified by geomorphic processes between earthquakes, and the precipitation rate of a region may affect the distribution of offset features preserved along a fault. Here, we explore the limitations of the geomorphic record with offsets from 40 historical surface ruptures and synthetic elliptical and flat slip distributions with 0-50% noise to infer best practices for interpreting slip in past earthquakes (paleo slip distributions). Given typical variability levels of modern surface ruptures and rates of geomorphic change, we find that it is unlikely to accurately reconstruct more than one or two paleo slip distributions from offset geomorphic features except in unique cases. In cases where site-specific conditions or information allow for interpretation of more than two events, extrapolating that information along a fault is not straightforward because on-fault displacement and distributed deformation are often spatially variable. We apply these insights to interpret geomorphic offset data in 2D probability space using a Monte Carlo approach to construct slip distributions with uncertainty bounds. Applying this method to both the recent ruptures and geomorphic offset data for 20 strike-slip faults with evidence of multiple paleo earthquakes, we find that the prevalence of uniform, full-fault ruptures (i.e., the “Characteristic Earthquake Model” of Schwartz and Coppersmith 1984) is likely lower than previously interpreted from geomorphic offset data.

Session: From Earthquakes to Plate Boundaries: Insights Into Fault Behavior Spanning Seconds to Millennia [Poster]

Type: Poster

Date: 4/20/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Nadine Reitman

Student Presenter: No

Invited Presentation: 

Authors