SCEC Award Number 11079 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Steady and time-dependent block models for California
Name Organization
Robert McCaffrey Portland State University
Other Participants
SCEC Priorities A2, A7, A1 SCEC Groups CDM, Geodesy, SHRA
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
The purpose of the project was to contribute to UCERF3 by utilizing GPS data from California to constrain fault slip rates and off-fault strain rates. The PI joined a working group of geologists and geophysicists to this end. He specifically used a block model derived by the group and processed it through his software (tDEFNODE). The goal was to provide a range of geodetic fault slip rates allowed by the data for input into a UCERF3 logic tree. From the results of five modeling techniques, the PI ran a ‘grand inversion’, that is, inverting the predicted slip rates of the methods for a single set of slip rates and internal strain rates. The inversion was done within a block model framework in order to provide a weighted average of the results but subject to kinematic consistency of the deformation. The results provided estimates of long-term slip rates on over 1000 fault segments in California. These were provided to be carried on to the next stage of UCERF3 and inclusion in the logic tree.
To address the role of transient deformation in GPS velocities, the PI started time-dependent block modeling of GPS time series in California. The transient motions embedded in the models to date include post-seismic fault slip, post-seismic mantle relaxation and volcanic sources. The aim is to provide a better assessment of fault slip rates by taking into account the sources of non-linearity in the GPS time series.
Intellectual Merit The work contributed to the seismic hazard assessment for California by supplying fault slip rate estimates to be used in UCERF3 logic tree. The comparison of five modeling techniques helped us understand the variability of the results arising from different physical assumptions. Development of time-dependent inversions will help uncover the long-term motions currently masked by transient signals.
Broader Impacts The software tDEFNODE was improved by this work and continues to be made available freely to researchers. The group meetings included young, starting researchers who contributed to and benefited from the discussions.
Exemplary Figure Fig. 2. Estimates of strike-slip (Vss) and fault-normal (Vnorm) components of faulting on block-bounding faults. Positive values are right-lateral for strike-slip and extension for fault-normal.