SCEC Award Number 12050 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Paleoseismic investigation along the inferred northernmost extent of the 1857 rupture: Do large southern San Andreas Fault ruptures extend into the creeping section?
Name Organization
Nathan Toke Utah Valley University J Ramon Arrowsmith Arizona State University
Other Participants J. Barrett Salisbury (ASU Ph.D. student with Arrowsmith)
Lawrence Kellum and another student TBD (UVU B.S. students with Toke)
SCEC Priorities 2a, 4c, 4a SCEC Groups SoSAFE, Geology, WGCEP
Report Due Date 03/15/2013 Date Report Submitted N/A
Project Abstract
This research consisted of two components. Component A – test the longevity of the historically-observed aseismic slip release behavior for the central creeping section of the SAF and understand the broader implications for earthquake hazard related to extreme events. Component B – examine size and spatial distribution of right-lateral channel offsets along this portion of the SAF to test the role of climate in the production of characteristically-sized offsets. In 2012, we completed a remote LiDAR survey of 41 right-lateral offsets with less than 30 meters of total displacement, we conducted a field review of roughly half of these offsets, and we conducted a five week paleoseismic investigation of the Dry Lake Valley (DLV) site. Remote LiDAR mapping and field analyses showed a minimum offset along this section of the fault of 2-5 meters. Beyond that minimum length, the offsets do not group into distinct size clusters. Thus, over some time periods channels may form randomly and frequently and during other periods channel incision may cease, resulting in clusters and gaps in the distribution of offset sizes. Trenching at the DLV site revealed many structures consistent with surface manifestations of aseismic slip. This site also revealed evidence for significant ground deformation between 780 and 1031 A.D. This evidence consists of a nearly vertical package of gravel and small boulders that are capped by horizontally-bedded stratigraphy. This paleoseismic result is the focus of our 2013 SCEC proposal which has been approved for funding.
Intellectual Merit This research aims to address a previously unexplored earthquake geology question which has come up in numerical modeling experiments and in UCERF 3 discussions: Do large ruptures penetrate through the creeping section of the San Andreas Fault and is there any geologic evidence for extreme events involving rupture of both the southern and northern San Andreas Fault? It addresses this question by extending the paleoseismic record of the creeping section beyond 1000 years before present at the previously unexplored Dry Lake Valley site. Additionally, this project's focus on the creeping section of the San Andreas demonstrates that over the past one thousand years climatic cycles can control the distribution of geomorphic offsets. This has been a question surrounding the origin of charactistically-sized offsets observed along the southern San Andreas Fault.
Broader Impacts Broader Impacts: Student Training and Mentoring: In addition to the ongoing scientific contributions from this research, this project benefited the educational experience of two graduate students from Arizona State University and twelve undergraduates from Utah Valley University: Arizona State University J. Barrett Salisbury (Ph.D. Student) – Barrett helped lead our preliminary fault strip mapping with N. Toké, paleoseismic site selection, and he led our effort to evaluate geomorphic offsets along the creeping section of the SAF. Tsurue Sato (M.S. Student) – Tsurue led ASU’s participation in the paleoseismic field season, helped rectify photomosiacs, and worked with N. Abueg to run C14 sample analysis at UC Irvine. Utah Valley University Nicole Abueg (B.S. in Geology) – Nicole was a paid research assistant on the project. She helped prepare field logistics, participated in the field work, and took the lead on preparing C14 samples for radiocarbon analyses. She took our samples to UC Irvine where she and T. Sato worked with J. Southon to obtain geochronology constraints for this work. Additionally, along with N. Toké and the other three UVU undergraduates Nicole presented in the UVU Earth Science colloquium. Nicole presented on methods the radiocarbon method and sample analysis. James Anderson (B.S. in Geology) – James volunteered to participate in this project. He first participated in the project as a member of the 2012 UVU Geology field camp, but after the field camp he returned to help with paleoseismic field work. James attended the annual SCEC meeting to help present a poster on our work. Additionally, along with N. Toké and the other three UVU undergraduates James presented in the UVU Earth Science colloquium. Jim presented on methods for distinguishing between ground rupture and aseismic creep in a paleoseismic trench. Lawrence Kellum (B.S. in Geology) – Larry was a paid research assistant on the project. He helped prepare field logistics, participated in field work, and attended the annual SCEC meeting to help present a poster on our work. Additionally, along with N. Toké and the other three UVU undergraduates Larry presented in the UVU Earth Science colloquium. Larry presented on methods of paleoseismic logging. Jeff Selck (Continuing Education in Geology) – Jeff volunteered to participate in this project. He participated in the field work and rectifying photomosiacs following the field season. Additionally, along with N. Toké and the other three UVU students Jeff presented in the UVU Earth Science colloquium. Jeff presented on photo documentation methods. Utah Valley University Field Camp – 9 UVU undergraduates spent six days conducting field work at the Dry Lake Valley Paleoseismic Site. We received land owner permission for the students to do geomorphic strip mapping along a 4km stretch of the fault. They spent two days doing this mapping and 2.5 days doing industry-style paleoseismic logging with a capstone trench party. The UVU Earth Science Department paid for all aspects of these students’ travel expense, but this student benefit would not have been possible without the ongoing SCEC research project. Scientific Presentations: To date, three scientific presentations have directly resulted from this research project. They were presented at the Annual SCEC Meeting, the AGU fall meeting, and the UVU Earth Science Department Colloquium: Toké, N. A., Abueg, N., Anderson, J., Kellum, L., Selck, J., Sato, T., Salisbury, J.B., and Arrowsmith JR., “Recognition of Paleoseismicity along Creeping Faults: Examples from the Dry Lake Valley Site on the central San Andreas” Eos Transactions, American Geophysical Union, Fall Meeting, Abstract T22C-02, San Francisco, California, December 4th, 2012. Toké, N. A., Sato, T., Kellum, L., Abueg, N., Anderson, J., Selck, J., Salisbury, J.B., and Arrowsmith JR., “Preliminary Results from the 2012 Dry Lake Valley Paleoseismic Site on the central Creeping section of the San Andreas Fault.” Annual Southern California Earthquake Center Meeting, Proceedings and Abstracts Vol. 21, Palm Springs, California, September 9-12, 2012. UVU Earth Science Seminar Series “All Quiet on the Western Front? Tales from a trench on the creeping section of the San Andreas Fault.” Presented by Nathan Toké with Larry Kellum, Nicole Abueg, Jim Anderson, and Jeff Selck on November 27th, 2012. Finally, This project was aided in financial support by Utah Valley University (UVU). UVU provided ~$5,700 of additional support through the following programs: 1)The College of Science and Health's Scholarly Activities Committee Awarded all four of UVU's undergraduate research participants $1,000 each which helped pay for student transportation and lodging during our field work. 2)The UVU Department of Earth Science paid for all field camp expenses and provided the project a month long SUV rental and gas (~$1,700) which supported travel for N. Toké, N. Abueg, and L. Kellum throughout the field season.
Exemplary Figure Figure 5: The northwest wall of the 2012 Dry Lake Valley trench (above and below a two meter wide bench). Calibrated radiocarbon ages (colored horizons) show that a sub-vertical gravel package, originating from a buried paleochannel (fault-parallel trench: Figure 1C), was emplaced within the fault zone between 780-1031 A.D. (~1100 years B.P). In 2013, we will slice back this trench to where the paleochannel is cut by the fault. As we do this, we will carefully document the stratigraphic and structural relationships to determine if fault zone emplacement was due to fissure infilling following coseismic rupture or shear and rotation due to prolonged aseismic creep. Minor, oblique-to-the-SAF-trend, faults and fractures were also found throughout the exposures indicating a pervasive overprinting of recent aseismic creep.