Title

A Paleoseismic Study Of The Twin Lakes Fault, Mount Hood Fault Zone, Oregon

Date

11-8-2021 2:30 PM

Abstract

Recent geologic mapping on high-resolution topography from lidar has led to the discovery of a zone of active faults on Mount Hood. The Mt. Hood Fault Zone consists of four separate faults, and stretches ~55 km from south to north, and crosses the summit of Mount Hood. The focus of this study is the northern section of Twin Lakes Fault, which lies directly south of Mount Hood and adjacent to OR35 and the White River. Lidar topography reveals the west side down normal displacement on the Twin Lakes fault. The highest tectonic seismicity rates in the Mount Hood area occur along faults that are south of the summit, and suggests the faults are active. This research seeks to further understand the possibility of recent tectonic activity along the Twin Lakes Fault with an in-depth paleoseismic investigation of the study area. Using lidar data in ArcGIS, I have mapped the faults and geology of the study area, measured vertical separation across the fault, and have excavated a paleoseismic trench across the fault, in a small wetland. Our paleoseismic study has revealed sedimentary units offset by the fault, stratigraphic units that postdate the most recent faulting event, and has confirmed the west side down dip normal style of earthquake deformation for the Twin Lakes Fault. For future research, carbon samples from offset stratigraphy have been submitted to constrain the timing of the most recent earthquake. Faults that have generated large earthquakes with Holocene (~11 ka to present) displacement are considered active faults and a seismic hazard. This study provides new age data on the timing of the last large earthquake on the Twin Lakes fault that formed the fault scarp visible in lidar derived topography.

Biographies

Charlie Carr, Geology; Minors: GIS and Geography

Charlie Carr is majoring in geology with minors in Geographic Information Systems and Geography. She is a part of the Active Tectonics Lab at Portland State University. She is a McNair Scholar, President of the Coriba Geology Club, and a part of the Association of Environmental and Engineering Geologists – PSU Student Chapter. Throughout her life, Charlie has shown a passion for increasing public information and education regarding hazard management. She believes that further research and investment into geohazards can make safer, and more resilient, communities. Charlie plans to complete a Ph.D. in Geophysics. In her free time, Charlie enjoys learning about traditional ecological knowledge and political science. She enjoys gardening, kayaking, hiking, and biking with her two children and partner.

Dr. Ashley Strieg, Faculty Mentor, Department of Geology

My research focuses on answering questions about active faults and folds, earthquakes and associated hazards, earthquake frequency and magnitude. I am currently interested in whether recurrence intervals for forearc faults in the Pacific Northwest are intrinsically linked with the long recurrence of Cascadia subduction zone events. I am also currently working with students, DOGAMI, and USGS, to map faults along Mt. Hood with a goal of improving our understanding of the timing and magnitude of past surface rupturing earthquakes along these previously unmapped faults. I use geologic mapping and paleoseismology to answer these questions. I attended University of Oregon for my Ph.D., and received a National Science Foundation Postdoctoral Fellowship in Earth Science prior to arriving at PSU as a faculty member of the Geology Department.

Disciplines

Geology

Persistent Identifier

https://archives.pdx.edu/ds/psu/36206

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Aug 11th, 2:30 PM

A Paleoseismic Study Of The Twin Lakes Fault, Mount Hood Fault Zone, Oregon

Recent geologic mapping on high-resolution topography from lidar has led to the discovery of a zone of active faults on Mount Hood. The Mt. Hood Fault Zone consists of four separate faults, and stretches ~55 km from south to north, and crosses the summit of Mount Hood. The focus of this study is the northern section of Twin Lakes Fault, which lies directly south of Mount Hood and adjacent to OR35 and the White River. Lidar topography reveals the west side down normal displacement on the Twin Lakes fault. The highest tectonic seismicity rates in the Mount Hood area occur along faults that are south of the summit, and suggests the faults are active. This research seeks to further understand the possibility of recent tectonic activity along the Twin Lakes Fault with an in-depth paleoseismic investigation of the study area. Using lidar data in ArcGIS, I have mapped the faults and geology of the study area, measured vertical separation across the fault, and have excavated a paleoseismic trench across the fault, in a small wetland. Our paleoseismic study has revealed sedimentary units offset by the fault, stratigraphic units that postdate the most recent faulting event, and has confirmed the west side down dip normal style of earthquake deformation for the Twin Lakes Fault. For future research, carbon samples from offset stratigraphy have been submitted to constrain the timing of the most recent earthquake. Faults that have generated large earthquakes with Holocene (~11 ka to present) displacement are considered active faults and a seismic hazard. This study provides new age data on the timing of the last large earthquake on the Twin Lakes fault that formed the fault scarp visible in lidar derived topography.