SCEC Award Number 18119 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Imaging Fault Structures Near the Imperial Fault in the All American Canal
Name Organization
Valerie Sahakian University of Oregon Neal Driscoll University of California, San Diego
Other Participants Will include 2 students from UCSD for fieldwork, and 2 students from UO for fieldwork
SCEC Priorities 1a, 3a, 5c SCEC Groups Geology, FARM, CXM
Report Due Date 03/15/2020 Date Report Submitted 02/23/2021
Project Abstract
We employed an acoustic high-resolution, shallow imaging technique (CHIRP) in the All American Canal (AAC) by the US-Mexico border to provide direct constraints on near-surface splays of the Imperial Fault (IF), and other structures to its west. The Imperial Fault is a high slip-rate fault within the context of Southern California tectonics, yet there are few paleoseismic studies due to agricultural obfuscation of surface faulting. Our goal was to directly image near-surface structures on and near the IF to understand better local fault interactions, and direct future paleoseismic studies for improved slip rates. Current results have shown some shallow deformation near the area of the mapped IF surface trace, as well as offset strata and significant distributed deformation in an area approximately 10 to 23km west of the mapped IF trace. We interpret that this corresponds to deformation associated with the northern extension of the Michoacán fault, as well as structures associated with a stepover between the Michoacán and Dixieland Faults.
Intellectual Merit Our findings are:
• We image deformation of strata due to the Imperial Fault, both in the shallow surface
and below ∼ 15m depth.
• We resolve significant deformation (∼4.5m) near the northward extension of the Michoacán fault, corresponding with lineaments of seismicity and structures proposed by Magistrale [2002] and Lindsey and Fialko [2016].
• We see offset strata, and significant and distributed deformation in an area approximately 10 - 23km west of the Imperial Fault, between the Michoacán and Dixieland faults, likely due to shallow deformation within the transtensional stepover.
Broader Impacts The results from this work suggest that surface faulting or shallow deformation may be more distributed in this region than is represented in hazard models. Shallow constraints like those provided by our data will be helpful in a number of ways. They will allow future workers to target ideal locations for further studies such as trenching, to obtain direct geologic slip rate estimates on these fault zones. They will also help in defining fault structures in the region besides the IF to include in modeling studies. Additionally, this work will contribute to our understanding of the interactions between faults in this region and how they may impact estimates of seismic hazard.
Exemplary Figure Figure 6, top