SCEC Award Number 14152 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Toward Integrating Models Of Stress From Multiple Physical Processes, Timescales, And Spatial Scales In Southern California
Investigator(s)
Name Organization
Karen Luttrell Louisiana State University Bridget Smith-Konter The University of Texas at El Paso David Sandwell University of California, San Diego
Other Participants graduate research assistant
SCEC Priorities 2d, 1b SCEC Groups SDOT, Geodesy, EFP
Report Due Date 03/15/2015 Date Report Submitted N/A
Project Abstract
 The goal of this research has been to integrate three CSM stress models (individually contributed to previous CSM workshops by Yang, Luttrell, and Smith-Konter), each estimating a different component of stress due to a different set of physical processes with a different set of physical assumptions acting over different spatial and temporal scales.
First, we have completed an estimate of minimum differential stress magnitude throughout Southern California based on a force balance analysis between the stress state indicated by topography and gravity data and that observed in focal mechanism data. We estimate the stress field across southern California must have a differential stress magnitude of at least 60 MPa at seismogentic depth in order to maintain the stress orientation inferred from focal mechanism observations in the presence of the observed rugged topography.
Second, using a simple homogeneous driving stress field, calculated stress due to rugged topography, and models of stress accumulation rate due to locked fault segments throughout southern California, we have identified the fault loading time on each modeled segment that best brings the simple forward model in line with the stress orientation indicated by focal mechanisms. Along the main San Andreas fault segments, this loading time is estimated to be ~4000 years, an order of magnitude larger than either the time since last rupture or the expected recurrence interval, possibly indicating incomplete crustal stress release over the timescale of a single earthquake cycle.
Intellectual Merit These findings directly support an important objective of the CSM community, to synthesize the insights offered by diverse contributed models in order to gain a more holistic understanding of the 4D stress field and to be better situated to present a community-endorsed stress model to the broader SCEC community. Though this problem represents a considerable challenge, the work presented here, along with parallel work from other CSM colleagues, comprises deliberate progress toward that goal.
Broader Impacts Award support has been used to support LSU Undergraduate Research Assistant Madeline Myers in her work interpreting stress field orientation, its sensitivity to stress perturbations of a well-constrained magnitude, and the implications for the seismic behavior of nearby faults. In particular, we note that Myers was able to present her work on this project at the 2014 Fall AGU meeting, and will be a co-author on the resulting manuscript to be submitted later this year.
Exemplary Figure Figure 2: (a) Mean misfit between in situ stress orientation (from focal mechanisms) and scaled in situ stress with modeled topography stress. Misfit function is one minus the mean of the tensor dot product between the two stress fields, such that a value of 0 indicates a perfect fit and a value of 1 indicates complete non-correlation. For 95% misfit reduction, regional differential stress must be > 60 MPa. (b) Contours of mean misfit over southern California region, as a function of tectonic principal stress magnitudes. Inset indicates misfit associated with different SHmax orientations. Smallest tectonic stress field that achieves 99% misfit reduction includes 40 MPa compression at 9ºEofN and 45 MPa extension at 99ºEofN.