SCEC Award Number 15165 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Updated Spatial and Temporal Mapping of the Geomorphic Evolution of Wheeler Ridge and Application to Blind Thrusts in California
Investigator(s)
Name Organization
J Ramon Arrowsmith Arizona State University Duane DeVecchio Arizona State University
Other Participants Emily Kleber, M.S. Candidate
SCEC Priorities 1a, 4c, 4b SCEC Groups Geology, USR, CCSP
Report Due Date 03/15/2016 Date Report Submitted 03/14/2016
Project Abstract
 The objective of this SCEC funding was to update the geologic understanding of Wheeler Ridge, an active blind thrust fault located at the base of the San Joaquin Valley associated with transpression along the “Big Bend” in the San Andreas fault. We used high resolution topography (HRT) from a 2014 airborne survey and SCEC funded geochronology results using Optically Stimulated Luminescence (OSL) along with geologic and geomorphic mapping. Geomorphic and morphologic mapping were used to investigate older surfaces that have been altered by colluvial and alluvial processes. Our findings show different surface responses on the western geomorphic forelimb, where the drainage divide has eroded past the asymmetric anticline axis, and the western geomorphic backlimb. Surface processes on the western geomorphic forelimb are closely associated with the changes in bedrock, structural dip, climate, and mass wasting. These factors determine whether the surface processes are soil dominated, colluvial dominated, or in some intermediate state. This suggests that the forelimb surfaces are not in steady state and the channels and hillslopes are still adjusting to tectonic, climatic, and bed-rock differences along the fold. On the back limb where bedrock is homogeneous and slopes are low-er, drainage morphology indicates surface processes are responding to the eastward decrease in age of initiation of local rock uplift.
Intellectual Merit Wheeler Ridge is a widely cited example of the geomorphic response of a propagating blind thrust fault (Medwedeff, 1992; Keller et al., 1998). Additionally, the Wheeler Ridge-related structures may have been responsible in part for the 3rd largest earthquake in California history (1952 Mw 7.3 Kern County earthquake). This study applies new techniques and data to better constrain this blind thrust fault and tectonic deformation rates, discovering new surface relationships previously not possible with existing data. SCEC funded geochronology has improved the temporal accuracy of surface ages for this classic structure. Initial results indicate a more complicated uplift and incision history and new minimum uplift rates.
Broader Impacts This SCEC funded work has had impacts within the SCEC and broader geologic research community. Within the SCEC community, this study has shown that feldspar grains are excellent chronometers for the southern San Joaquin Valley and rocks initiating from the San Emigdios. In the geologic community, access to the HRT through OpenTopography and exposure from poster presentations at professional meetings has created more exposure for data made available by SCEC funding. Additionally, data from Wheeler Ridge are part of a set of undergraduate exercises aimed for learning about tectonic geomor-phology (http://serc.carleton.edu/getsi/teaching_materials/imaging_active_tectonics/unit2.html).
Exemplary Figure Figure 2. Geomorphic and morphologic map of Wheeler Ridge. Mapping combined previously identified Q-surfaces (Zepeda, 1993; Keller et al., 1998) and morphological mapping techniques (Savigear, 1965). This mapping identifies additional tectonically isolated surfaces in the central and western portions of Wheeler Ridge as well as uplifted terraces in the wind gap and water gap. The map has surface domains mapped on the western geomorphic forelimb, which was used to better understand the role of large landslides in propagating bare-soil surfaces. Morphological surfaces are interpreted propagation surfaces by Keller et al. (1998) and new surfaces identified in this study. The black squared indicate places where OSL samples were collected. Larger black squares show the IRSL age with 2σ error. Smaller black squares are samples that will be proce
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