Holocene Earthquake History of the Meers Fault, Oklahoma: Refining Rupture Length Estimates From Subtle Tectonic Geomorphology and Modern Paleoseismology

Session: Cryptic Faults: Assessing Seismic Hazard on Slow Slipping, Blind or Distributed Fault Systems
Type: Oral
Date: 4/28/2020
Time: 04:45 PM
Room: 240
Description: 

Characterizing the frequency and size (displacement and rupture length) of large earthquakes on intraplate faults is critical to improve seismic hazard models for the Central and Eastern United States. The WNW-trending, left-lateral Meers fault in southwestern Oklahoma is the only mapped Quaternary-active fault in the state, but its late Quaternary rupture history remains poorly understood. Previous paleoseismic studies reported at least two surface deforming earthquakes in the last 2,900 years (Crone and Luza, 1990). We analyzed high-resolution topography derived from lidar and balloon-based photogrammetry to map cryptic tectonic geomorphic evidence of recent coseismic surface deformation and coupled this mapping with paleoseismic trenching. We mapped subtle monoclinal folding of Holocene deposits ~6 km farther to the WNW than previously-mapped Holocene traces, corroborated by new paleoseismic trench evidence of at least two north-side-up Holocene folding events. Surface deformation transitions towards the ESE from folding above a blind fault to discrete surface rupture, coincident with an along-strike change in bedrock lithology. New OxCal modeling of earthquake ages from two previous paleoseismic trenches (Crone and Luza, 1990) combined with results from our three paleoseismic trenches, one of which is the re-excavation and resampling of an earlier trench, suggest that at least four, possibly five, surface-deforming earthquakes have occurred in the last ~7,000 years. These observations indicate at least two different along-strike slip distribution scenarios and at least two different rupture lengths. Our results demonstrate non-characteristic, multi-mode strain release through partially blind fault rupture in this intraplate setting and will help refine future seismic hazard models and maps.

Presenting Author: Scott E. K. Bennett

Authors