SCEC Award Number 11100 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title High-Resolution Mapping and Analysis of Borderland Faults Using Multibeam Bathymetry Data
Investigator(s)
Name Organization
Monica Kohler University of California, Los Angeles Mark Legg Legg Geophysical
Other Participants Weeraratne, Dayanthie (CSUN - professor)
Shintaku, Natsumi (CSUN - student)
SCEC Priorities A9, A11, C SCEC Groups USR, LAD, Geology
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
 This project involved processing and analyzing new high-resolution swath bathymetry data from Borderland fault structures where seismic hazard is significant but fault mapping lacks detail needed to evaluate seismic potential accurately. In 2010, R/V Melville was used to conduct swath bathymetry surveys of major fault regions to map unknown geometry and rupture extent. We targeted sections of four major fault systems for their active seismicity, large lateral extent, geometric complexity, tsunamigenic potential, and lack of detailed bathymetry data: i) San Clemente fault system within the Inner Borderland focusing on the northern Santa Cruz-Catalina Ridge fault zone; ii) East Santa Cruz Basin fault system (ESCB) in the area where the San Nicolas Island escarpment intersects from the west; iii) Ferrelo fault system along its entire extent in U.S. waters; iv) San Nicolas Island escarpment that represents a major transverse structure and possible segmentation boundary between the ESCB and Ferrelo fault zones. Faults identified from the seafloor morphology were verified in the subsurface using existing seismic reflection data, including USGS and exploration industry multichannel seismic (MCS) profiles, and high-resolution MCS and single-channel data. Mapped fault traces from published sources based on seismic reflection profiles and compiled into the original SCEC fault database were updated to provide more accurate representation of shallow crustal faulting in the Borderland. This study examined the likelihood of multi-segment and multi-fault ruptures on several large offshore faults. The outcome of this work shows great detail at high resolution not before visible and will contribute toward a high-resolution map of offshore southern California fault structures.
Intellectual Merit The goals of this study were to process, image and analyze new multibeam swath bathymetry data, and to contribute the new findings from targeted areas to public databases of seafloor geomorphology and fault structure. Faults identified from the seafloor morphology were verified in the subsurface using existing Borderland seismic reflection data, including USGS and exploration industry multichannel seismic (MCS) profiles in the National Archive of Marine Seismic Surveys, and high-resolution MCS and single-channel data compiled over the past three decades. Mapped fault traces from published sources based on seismic reflection profiles and compiled into the original SCEC fault database were updated to provide more accurate representation of shallow crustal faulting in the Borderland. This study had the direct objective of investigating the likelihood of multi-segment and multi-fault ruptures on several large offshore faults. Of particular interest to the SCEC community is the transition from Neogene transtension to post-Miocene transpression as the plate boundary jumped inland to the Gulf of California creating the major restraining bend on the San Andreas Fault. The outcome of this work shows great detail at high resolution not before visible and will contribute toward a high-resolution map of offshore southern California fault structures.
Broader Impacts Accurate mapping of the major active fault structures and resulting seafloor morphology provides data necessary for understanding the tectonic evolution and earthquake hazard potential of major offshore structures. The products developed here will contribute directly to the Unified Structural Representation. They will improve the Community Fault Model by defining the geometry of faults which are incompletely or inaccurately represented in the current model. The compiled information, including the new high-resolution bathymetry data collected in 2010, will be made available to the SCEC scientific community.
Exemplary Figure Figure 3 (on page 4). Map showing multibeam bathymetry, seismicity and major faults in the Outer Borderland. Earthquakes located by the SCSN are shown, with events that occurred during the deployment of the ocean bottom seismometer (OBS) array are scaled by magnitude. OBS locations are shown by dots-in-circles. The two shaded relief images of bathymetry for the Ferrelo areas are shown with an western sun angle to highlight northwest-trending fault zones.