SCEC Award Number 17094 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Searching for the deep seismic activity in the roots of the San Andreas Fault
Name Organization
Lingsen Meng University of California, Los Angeles Paul Davis University of California, Los Angeles
Other Participants Graduate student Tian Feng
SCEC Priorities 1d, 3a, 3d SCEC Groups SAFS, FARM, Seismology
Report Due Date 06/15/2018 Date Report Submitted 06/15/2018
Project Abstract
Slow slip events and tremors have begun to reshape our understanding on how locked zones in subduction zones are loaded. The Tohoku earthquake is thought to be triggered by the stress transfer from the precursory slow slip events. It is thus essential to monitor the slow-slip and tectonic tremors which potentially shed light on the probability of imminent large earthquakes. In the last decades, development of dense seismic networks has enabled rapid progresses in a broad spectrum of seismological studies. Particularly, a dense small-scale array that composed of ~ 5000 vertical Geophone sensors enables the detection of tremor-like events deeper than 20 km on the Newport Inglewood fault beneath Long Beach, CA. In this proposal, we seek to answer the question as to how common is this phenomenon on S. California faults. In our initial effort, we first determine if tremor-like events occur beneath the San Jacinto Fault and the San Andreas Fault. We detect 57 and 1549 new events in Carrizo Plain and San Jacinto, respectively, using Neighboring Station Coherence method. After removing signals from non-seismic sources, we confirm 8 and 120 events as earthquakes in Carrizo Plain and San Jacinto respectively. We are able to determine their location and magnitude using seismic array analysis. But the determination of the focal depth is challenging due to the low SNR of the depth phases and insensitivity of the S-P time to depth. In the future work, we will try to use 3D Back-Projection method to determine the micro-seismicity depth.
Intellectual Merit Our research test and develop methods for detecting micro-earthquakes and discriminate them from other natural and artificial acoustic events. The capability of detecting and mapping these new events is crucial to understand the seismogenic depth in the San Andreas fault. Our initial results showed a potential of detecting more events than the routine catalog, and we are currently working to locate and determine their focal depths. The results can potentially improve the assessment of local seismic hazards, which will benefit SCEC information and techniques in seismic hazard, earthquake engineering, risk analysis, and ultimately loss mitigation.
Broader Impacts Our SCEC project supported one graduate student in UCLA (Tian Feng), who is working on various technologies to detect and monitor microseismic events. In addition, our projects provide research and educational opportunities for summer undergraduate student interns at UCLA. UCLA undergraduate students from groups underrepresented in the Earth sciences (female and/or minority) participated in related projects and are trained with the latest techniques for signal processing and seismic imaging.
Exemplary Figure
Figure 12: Recorded (green circles) events by USGS at San Jacinto from 15th to 27th May 2014. The red circles denote the new events detected by this project. The blue triangle represents the dense seismic array.