Towards Improved Understanding of Regional Tectonics and Faulting at the Mendocino Triple Junction from Geomorphic Investigation
Hazard associated with the transition from the dextral San Andreas Fault system to the Cascadia subduction zone in the Mendocino triple junction (MTJ) region is complex and in need of ongoing research using up-to-date methods. This area has high rates of seismicity and is characterized by an enigmatic network of faults having some combination of compressional and dextral motion that has been difficult to constrain, perhaps complemented by diffuse shearing and folding. The densely vegetated mountains, river valleys, and coast appear to record strikingly variable patterns of tectonic uplift, subsidence, and fluvial and coastal erosion that cause ongoing drainage divide shifts, unusual stream channel longitudinal profiles, and variable amounts of topographic development. These patterns have also been indicated by geodetic surveys following historic earthquakes. The geomorphic characteristics can be interrogated to understand the regional tectonics, which can in turn be used, in combination with analysis of recently released lidar topographic data, to identify locations of active faulting. We are currently working to generate a suite of catchment erosion rates from cosmogenic isotope inventories within and adjacent to the Mattole and Eel Rivers. We are mapping and dating uplifted fluvial terraces along the Mattole and Eel Rivers, and marine terraces from along the MTJ coast. This is complemented by generation of quantitative landscape metrics including channel steepness index and chi. We are also mapping active fault traces and expanding collaborative work on known high-potential paleoseismic sites. Our long-term objectives include better understanding of the connections between, and geometry of, the San Andreas, Maacama, and Bartlett Springs Faults and the southern Cascadia onshore fault network, better understanding of the linkages between tectonics, stream capture, and critical anadromous fish habitat, and better understanding of how topographic development and fault activity are related, with an eye towards improving hazard models.
Session: Cryptic Faults: Advances in Characterizing Low Strain Rate and Environmentally Obscured Faults - II
Type: Oral
Room: Tubughnenq’ 3
Date: 5/1/2024
Presentation Time: 11:00 AM (local time)
Presenting Author: Stephen DeLong
Student Presenter: No
Additional Authors
Stephen DeLong Presenting Author Corresponding Author sdelong@usgs.gov U.S. Geological Survey |
Jessie Vermeer jvermeer@usgs.gov U.S. Geological Survey |
Jason Patton jason.patton@conservation.ca.gov California Geological Survey |
Brad Sion brad.sion@dri.edu Desert Research Institute |
Morena Hammer mhammer@usgs.gov U.S. Geological Survey |
Charles Trexler ctrexler@usgs.gov U.S. Geological Survey |
Mark Hemphill-Haley mark@humboldt.edu California State Polytechnic University, Humboldt |
Harvey Kelsey hmk1@humbolt.edu California State Polytechnic University, Humboldt |
Tom Leroy toml@pacificwatershed.com Pacific Watershed Associates |
Michelle Robinson micheller@pacificwatershed.com Pacific Watershed Associates, McKinleyville, California, United States |
Robert C McPherson bomac@humboldt.edu California State Polytechnic University, Humboldt, Arcata, California, United States |
Robert McLaughlin rjmcl@usgs.gov U.S. Geological Survey, Moffett Field, California, United States |
Towards Improved Understanding of Regional Tectonics and Faulting at the Mendocino Triple Junction from Geomorphic Investigation
Category
Cryptic Faults: Advances in Characterizing Low Strain Rate and Environmentally Obscured Faults
Description