SCEC Award Number 17161 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Understanding strain accumulation and transfer between the SSAF, San Gorgonio Pass, and the ECSZ Part II. Geologic and geodetic observations along faults of the Eastern Transverse Ranges, Joshua Tree National Park, CA
Investigator(s)
Name Organization
Katherine Guns University of Arizona Richard Bennett University of Arizona Kimberly Blisniuk San Jose State University
Other Participants Undergraduate Student Researcher/Intern (1)
SCEC Priorities 1a, 3a, 3c SCEC Groups SAFS, Geodesy, Geology
Report Due Date 06/15/2018 Date Report Submitted 06/30/2018
Project Abstract
 Better characterizing the distribution of strain around the southern San Andreas Fault in southern California is a critical because this section of the fault system is at least 100 years overdue for a major surface-rupturing earthquake. At the moment, as the fault system moves north into San Gorgonio Pass, it breaks into several smaller fault strands, each of which appear to accommodate much smaller amounts of slip and strain than the main fault to the south. With our present knowledge, this means that some amount of strain is missing from our strain budgets. The goal of this project is to determine the amount of strain that may be transferred to the Eastern California Shear Zone through block rotation facilitated along faults of the Eastern Transverse Ranges (ETR) within Joshua Tree National Park. This funded project is testing the block rotation and strain transfer hypothesis by: (1) Characterizing the recent Quaternary displacements and ages of offset geomorphic features along two of the West trending left lateral faults in Joshua Tree National Park through field mapping, geomorphological surface characterization and 10Be surface exposure dating, (2) Collecting and processing new campaign geodetic position estimates at all 12 stations in the University of Arizona-run Joshua Tree Integrative Geodetic Network (JOIGN) to estimate a new velocity field in the region. We present our current status of mapping interpretations for our three sites along the Blue Cut Fault and one site along the Smoke Tree Wash Fault.
Intellectual Merit This work will improve upon the existing broad scale geologic and geodetic estimates of slip along faults in Southern California, thereby addressing SCEC5 Scientific Priority 1.a. The collection of geodetic data and the integration of updated geologic and geodetic data into elastic fault block modeling, and will additionally address Priorities 3.a. and 3.e. Furthermore, this proposed work will add valuable new data for the SCEC Community Geodetic Model (CGM) and the Community Fault Model (CFM). Understanding slip rates along faults in the ETR will help us to better determine and understand slip rates along the SSAF in this region, which are vital to producing earthquake rupture models for an event propagating along this zone. The work proposed herein will also build upon ongoing research by Dr. Robert Powell and collaborators who are actively working on geologic slip rate estimates on the Pinto Mountain fault, another ETR fault that could contribute to the overall slip rate budget of the region.
Broader Impacts A section of this SCEC Award was earmarked for undergraduate student salary for a field assistant, and has been used to pay University of Arizona undergraduate Maria Snyder, a female Geosciences major, for her time and efforts assisting Graduate Student Guns in the field. During the course of two field seasons (January and May 2018), Ms. Snyder has learned how to complete a tectonic geomorphic map (using the full range of surface characteristics), how to efficiently and safely carry out desert based field work (in the winter and summer) and she has learned the fundamental considerations and pitfalls of how to run a GPS campaign for data, including how to do basic troubleshooting. She is now going on to take more field-based classes (Structural Geology and Stratigraphy) based on her enjoyment of research fieldwork. Beyond just preparing her for further education in the Geosciences, Ms. Snyder has received an inside look into the world of field research, and is interested to continue into research based work.
Another section of this SCEC award is set to pay the summer salary of Graduate Student Guns, who is working on mapping interpretations and reconstructions under the guidance and supervision of Co-PI Blisniuk, and who is working on GPS data processing under the supervision of PI Bennett. She is honing her mapping skills both in the field and in ArcGIS (as well as GMT), and is learning the ins and outs of GPS data processing through GAMIT/GLOBK (as well as all kinds of troubleshooting tips). Ms. Guns will continue to work on these project goals throughout the summer months.
Additionally, our planned GPS campaign will involve the participation of 4-5 undergraduate students and 3-4 graduate students who will learn how to (1) locate a remote campaign GPS measurement site using a handheld GPS and orienteering skills, (2) set up and take down campaign GPS equipment, (3) complete safe and efficient fieldwork.
Last but not least, because this project takes place entirely within Joshua Tree National Park, we have strengthened an ongoing partnership between the University of Arizona and the National Park Service and we plan to continue this relationship going forward.
Exemplary Figure Figure 2. Mapping Interpretation for Blue Cut Site #1, near Cholla Gardens in Joshua Tree National Park as mapped by Graduate Student Guns and Co-PI Blisniuk; We interpret six units of preserved alluvial or debris flow sediments at this site, four of which have been clearly left-laterally or normally offset (Qf1, Qf1a, Qf2, Qf3). Blue stars indicate preliminary 10Be surface exposure dating samples collected and processed through an Awards for Geochronology Student Research (AGeS) Program grant awarded to Graduate Student Guns, while white stars indicate samples that have been collected for future processing. LiDAR from NCALM Seed Proposal Program awarded to Graduate Student Guns.