SCEC Award Number 11104 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Multi-earthquake slip rate, Frazier Mountain paleoseismic site
Name Organization
Kate Scharer Appalachian State University
Other Participants Streig, Ashley (UO graduate student)
SCEC Priorities A1, C, A6 SCEC Groups SoSAFE, Geology, Seismology
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
Like slip per event, multi-earthquake slip rates provide critical data for refining earthquake correlations between paleoseismic sites. We have collected sufficient trenching data on the faulting and geometry of tilted bedding at the Frazier Mountain paleoseismic site (San Andreas fault) to show that the site has been a pull-apart basin for at least the last ~1000 years. We do not, however, have sufficient data to map the evolution of the basin, which we need to calculate robust multi-earthquake slip rates. The goal of this project was to complete a cone penetrometer (CPT) survey of the western portion of the site in order to (1) test the feasibility of this approach at Frazier and (2) add to the 3D database of the site structure without using the destructive and time-consuming process of trenching. The CPT field effort was successful, and we are now integrating the results into our 3D map of the site structure. In order to confidently correlate units the spacing of CPT holes needed to be closer together than we originally planned so the survey extent was smaller than proposed. However, the utility of the data is sufficient that we will be investigating other sources of funds to complete a larger survey at the site. The CPT survey shows that the syncline associated with the Frazier pull-apart has been active for at least 2000 years, and that the location and orientation of the syncline has not changed. As proposed, the CPT survey informed our future excavations and is being incorporated into our 3D database of the site structure.
Intellectual Merit This project represents a small portion of our larger field effort to understand the timing and size of prehistoric earthquakes. Because the instrumental and historical records of large earthquakes are too short to discern fault-specific patterns of rupture timing, size, and extent, field data from paleoseismic studies remain necessary to provide key constraints on fault behavior. These data feed into controversies about strain partitioning in the crust over century to millennial timescales, inform on fault connectivity and crustal behavior, and provide fundamental data for probabilistic seismic hazard assessments.
Broader Impacts The Frazier Mountain paleoseismic site has provided training in field methods for over a dozen undergraduate students and three female graduate students. Training has spanned a wide variety of tasks, from detailed field mapping (1:8), photography, trenching techniques, surveying, modeling data in matlab, and use of GIS and other 3D programs to image the data. The three undergraduate students from Appalachian State University (one male Iraq war veteran, two female) that completed a Senior Honors Thesis based on work and data from the site have gone on to graduate school in the geological sciences.
Exemplary Figure N/A