Elucidating the Mead Slope Fault with Drone-Sourced Imagery and Dems

Session: Cryptic Faults: Assessing Seismic Hazard on Slow Slipping, Blind or Distributed Fault Systems [Poster]
Type: Poster
Date: 4/28/2020
Time: 08:00 AM
Room: Ballroom
Description: 

The Mead Slope fault (MSF) poses a significant seismic hazard for the growing populations of the Las Vegas area and Hoover Dam. The MSF is a slow slipping NE-SW trending Quaternary fault located along the eastern shore of Lake Mead and is difficult to access. The MSF had been previously mapped, however the fault’s slip rate, as well as the age and size of past surface-rupturing earthquakes remained unknown. We used high-resolution DEMs generated from multiple drone flights and ground-control points and aerial imagery to map the fault in detail. We determined that the fault consists of two main strands, both offsetting Quaternary alluvial fan remnants. The northwestern strand offsets late to latest Pleistocene fan deposits, as well as relatively young tributary gravel deposits exposed below a wave-cut bench associated with past high levels of Lake Mead. Examination of this exposure revealed 3 identifiable surface ruptures, with the latest two events occurring within the last ~23k yr. We collected 3 OSL samples to date the sediments that will help to constrain the earthquake ages, as well as 18 ³He cosmogenic surface rock samples to date various Quaternary landforms displaced by the fault. Sampling efforts for the cosmogenic dates were focused on early to middle Pleistocene landforms due to the high age inheritance of the younger fan surfaces. We estimate the slip rate to range from 0.06mm/yr to 0.15mm/yr based on amount of offset of Qi3-4 channels and the correlation of the soil ages from the wave cut exposure.

Presenting Author: Jeri Y. Ben-Horin

Authors