SCEC Award Number 15179 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Refining the late Quaternary slip rate of the Sierra Madre fault with relative and absolute dating of offset fans
Investigator(s)
Name Organization
Reed Burgette New Mexico State University Katherine Scharer United States Geological Survey
Other Participants Austin Hanson, NMSU M.S. student
SCEC Priorities 1a, 4b, 4c SCEC Groups Geology, SoSAFE, WGCEP
Report Due Date 03/15/2016 Date Report Submitted 03/14/2016
Project Abstract
 The primary goal of this project is to determine the late Quaternary slip rate of the Central Sierra Madre fault (CSMF) through dating of offset alluvial fan and terrace surfaces. We used remote and field geologic and geomorphic mapping to identify offset geomorphic surfaces and identify promising locations for dating the surfaces. We tested a Schmidt hammer as a tool for relative correlation of surfaces and a calibrated dating technique. We collected a suite of nine samples for luminescence dating to complement a suite of 10Be profile samples collected along the CSMF. The luminescence samples are designed to achieve three objectives: (1) directly validate cosmogenic ages from the same sediment, (2) constrain the cover sediment history of gravel deposits analyzed by 10Be surface dating, and (3) determine the age of the youngest offset surface along the CSMF. All nine samples have been prepared, and are being analyzed at the Utah State University Luminescence Lab with the small aliquot IRSL technique. Preliminary IRSL ages from five samples are consistent with the preliminary age estimates we have made with 10Be surface dating. The preliminary IRSL ages tentatively suggest that fine grained sediment covering the gravel sampled for 10Be dating was deposited soon after terrace abandonment and that the younger portions of the current 10Be uncertainty distributions are more likely than the older age ranges. As the IRSL results become complete, we will use this information to better characterize sources of uncertainty in the 10Be dating and develop landform age models consistent with both types of geochronologic data.
Intellectual Merit At a broad scale, this project contributes to understanding how plate boundary zone deformation is partitioned spatially in the western Transverse Ranges. The broader Sierra Madre fault zone is one of the longest continuous structures in the western Transverse Ranges. This reverse fault system cross-cuts major lines of infrastructure leading into the LA area and heavily populated basins lie up-dip of its earthquake source areas. These tectonic and societal factors motivate our study to resolve the spatial distribution of slip rate on this major fault system. Additionally, recent work has suggested that very large prehistoric earthquakes have occurred on faults in the Ventura area, which has motivated the SCEC Special Fault Study Area. Possible scenarios for large slip in Ventura include ruptures that link through the Sierra Madre fault zone, and our work will help evaluate such behavior.
This project is designed to determine slip rates over a latest Quaternary time period that is recorded by a suite of prominent alluvial fan surfaces. This time scale is longer than that recorded by existing trench-based investigations on this fault, but short enough that the slip rates we derive may still be influenced by irregular earthquake recurrence. The rates we estimate here will contribute to understanding the temporal variations in fault slip, when integrated with paleoseismic records and our work in progress on a longer-term Quaternary slip rate for this fault zone.
This SCEC funding has supported collection of luminescence dating to complement terrestrial cosmogenic nuclide and radiocarbon dating of alluvial fan surfaces along the San Gabriel Mountains rangefront. The combination of techniques is giving us an especially strong dataset to resolve the Quaternary history of landforms which have been offset by the Central Sierra Madre fault zone. This will help us resolve epistemic uncertainties inherent in the interpretation of the geochronologic data types, which will contribute to studies elsewhere in southern California, as well as the broader Quaternary neotectonics community.
Broader Impacts This project has directly contributed to the education of one graduate student and one undergraduate intern. The USGS undergraduate intern assisted with the majority of our fieldwork, and gained significant experience in interpreting tectonic geomorphology and sampling for Quaternary dating methods, and assisted with the presentation of results at SCEC and AGU. NMSU graduate student Hanson has had a primary role in the field, lab, and interpretation portions of the project. This SCEC funding enabled him to travel to the USU Luminescence Lab to prepare samples for IRSL dating. This project has also allowed a pre-tenure PI to develop new collaborations with a USGS colleague and other SCEC community members. The ultimate product from this project will be more accurate slip rates for a major fault bounding the LA metropolitan area. Our results will complement the work of other members of the SCEC community investigating the late Quaternary temporal and spatial distribution of deformation and those modeling fault slip rates from geodetic data. Our results will contribute to hazard mitigation when incorporated into future seismic hazard analyses.
Exemplary Figure Figure 2. Geologic and geomorphic map of the Arroyo Seco area showing locations of samples collected for dating. Mapping is modified from Crook et al. (1987), and basemap is shaded relief derived from a USGS 0.5 m resolution lidar digital elevation model. Boxes B-B' and C-C' show locations where we have made preliminary swath profile estimates of vertical separations of terrace surfaces (Hanson et al., 2015).
Credit: Burgette and Scharer, 2016, Refining the late Quaternary slip rate of the Sierra Madre fault with relative and absolute dating of offset fans, Report for SCEC Award #15179.
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