SCEC Award Number 11151 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Observational and Theoretical Investigations of the Spatio-temporal Behavior of Spontaneous Tremor near the San Jacinto Fault in Rate-and-state Models
Investigator(s)
Name Organization
Jean Paul Ampuero California Institute of Technology
Other Participants Asaf Inbal, Yingdi Luo
SCEC Priorities A4, A10, A11 SCEC Groups FARM, Seismology
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
 This project aimed at investigating the relations between spatio-temporal properties of tectonic tremors and fault heterogeneities through observational and theoretical approaches. The observational component consisted of a search for spontaneous tremors near the Anza gap of the San Jacinto fault. Initial analysis of three years of waveform data from the Anza and PBO seismic networks was complemented with field experiments based on small-aperture seismic arrays. We detected several periods of transients containing repeating waveforms with spectra strongly peaked between 3 and 4 Hz. We determined that these transients are associated with cultural activity, mainly freight train traffic along the Coachella Valley. Our results place bounds on the capability to detect spontaneous tremors in southern California with current instrumentation. The theoretical component of this project aimed at developing a model of tremor activity based on the collective behavior of fault asperities mediated by transient creep. We conducted integrated simulations of slow slip and tremor swarms that reproduce the observed diversity of tremor migration patterns. Our model provides a mechanical connection between speed and orientation of tremor swarms and the distribution of slip velocity within the underlying slow slip pulse. We identified tremor properties that are robust to uncertainties in the characteristics of fault heterogeneities. Predicted relations between slow slip rate and the response of tremor activity to oscillatory loadings provide a framework to interpret observations of variable tidal sensitivity of tremors near Parkfield. Our modeling results highlight the potential role of tremors as a monitor for aseismic transients.
Intellectual Merit This research addresses a priority objective of FARM to understand implications of slow events and non-volcanic tremors for constitutive properties of faults and overall seismic behavior, and that of CDM to investigate possible causes and effects of transient slip. Slow slip and tremors, one of the most intriguing discoveries of the last decade in Earth sciences, has been the target of many observational studies but modeling studies are still needed. Spontaneous tremor has not been documented yet in southern California. The data analysis developed here will guide future efforts to detect tremor activity in southern California. The model developed here provides a framework to unify a diversity of tremor observations and to relate them to the mechanical properties of faults and their heterogeneity near brittle-ductile transition zones. Our models contribute to the physical basis of using tremors as a monitor for aseismic transients.
Broader Impacts The project provided training and research opportunities for two graduate students in Caltech. The observational activities involved other SCEC researchers (Jamie Steidl, UCSB) and SCEC PBIC instrumentation. Open source software for quasi-dynamic earthquake simulation was produced and is now available online.
Exemplary Figure Figure 3.
Top: spatio-temporal distribution of tremor activity during an ETS event in Cascadia (Houston et al, 2011). The light blue arrow shows the large scale slow migration. The zoom (right) shows some rapid tremor reversals (dark blue arrow). Bottom: similar plot derived from the results of a simulation of asperities interacting through transient creep, showing also slow migration and RTRs (Luo and Ampuero, 2011).