Shallow Deformation Features of the Imperial Fault System from Subsurface Imaging

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: 

Accommodating 30 – 45 mm/yr of slip and hosting two >M6 earthquakes in the past century, the Imperial Fault (IF) is a large player in Southern California’s fault system. Despite its contribution to regional seismic hazard and Pacific/North American plate boundary motion, both the IF system and its interactions with other faults are not as well-understood as other regional faults. Seismicity studies identify event concentrations on a linear structure ~10km west of the main trace of the IF. In addition, a geodetic investigation reveals deformation west of the main trace of the IF, best fit by a fault structure with a slip rate of ~15 mm/yr, possibly accommodating a portion of the IF’s slip rate. It is difficult to obtain a full picture of this system and the interaction between structures, as we lack shallow subsurface geologic and imaging data. Only 5 paleoseismic sites have been trenched along the IF, none of which yield a direct slip rate due to the absence of observable piercing points along the fault.

To fill this gap, we collected high-resolution subsurface seismic data within the All American Canal in the Imperial Valley, in 2019. These data focus on the mapped IF trace and suggested westward fault trace by the US-Mexico border. With an acoustic compressed high intensity radar pulse (CHIRP) system, we imaged shallow deformation near the region proposed to accommodate slip west of the IF. This deformation occurs as close as 10km west of the IF and some of the most prominent shallow displacement occurs ~20km west of the IF. The deformed reflectors are observed ~25m below the canal bed in some places, near the depth resolution of our dataset. Here, we will show these findings, faulting interpretations and implications for tectonics in the region. These data may be useful to support or direct future paleoseismic and geophysical studies along this fault trace and to understand better the interactions between the IF system and other fault system in the region.

Presenting Author: Valerie J. Sahakian

Authors