SCEC Award Number 14086 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title A High-Resolution Study of Microearthquakes on the San Andreas Fault at SAFOD
Name Organization
Charles Sammis University of Southern California
Other Participants Danielle Sumy, Fred Aminzadeh
SCEC Priorities 4a, 6d, 2b SCEC Groups FARM, Seismology, EFP
Report Due Date 03/15/2015 Date Report Submitted N/A
Project Abstract
The objectives of this project are to analyze data from a dense, near-fault temporary borehole array deployed within the San Andreas Fault Observatory at Depth (SAFOD) main borehole by Paulsson Geophysical Services (PGS) between late April to early May 2005. Our primary goal is to produce a catalog that can be used to extend spatial and temporal earthquake statistics to very small events within the SAF fault zone. Toward this end we have achieved the following milestones:
1) Surface seismic data has been downloaded onto our dedicated computer (Berkeley HRSN and the EarthScope-funded PASO experiments).
2) Paulsson’s VSP borehole data has been organized on the new computer (3 TB raw data).
3) Utility code written to read the Paulsson VSP data (continuous data in 16 second chunks in industry SEG2 format).
4) The entire data volume has been plotted with preliminary seismic signal processing.
5) We have made preliminary comparisons of surface array versus downhole array for same earthquakes.
6) A template-matching method for event detection was coded and rejected.
7) We have coded and tested a kertosis statistical method for event detection and time picking which looks promising.
We are running a bit behind on processing the catalog because the co-PI on this project left her post-doctoral position to accept a job with IRIS. The work is being pursued by a graduate student (Robert Walker) who will complete the catalog and subsequent temporal and spatial analysis for his Ph.D. thesis project.
Intellectual Merit Our catalog will be used to address the following SCEC scientific objectives: (4a) detailed geologic, seismic, geodetic, and hydrologic investigations of fault complexities at Special Fault Study Areas and other important regions, (6d) measurement of earthquakes with unprecedented station density using emerging sensor technologies, and (2b) improve descriptions of the spatiotemporal behavior of triggered and/or clustered earthquakes
Broader Impacts This project supported a Post Doctoral Researcher (Danielle Sumy) who has moved on in her seismological career. It also supported the Ph.D. project of Rober Walker who is continuing this line of research. A better understanding of the physics of earthquakes and its application to public policy is a primary goal of the SCEC community.
Exemplary Figure Figure 3: (a) 47 events reported in the USGS catalog near the SAFOD drill site. Most events occur along the SAF (thick dotted white line). Earthquakes are color-coded by time, where blue is earlier and red is later. (b) Preliminary locations of 100 earthquakes analyzed by PGS. Note the location of the array (vertical seismic profile (VSP)), denoted with a black line with respect to the SAF. The earthquakes are scaled by magnitude, where the largest detected in both catalogs is M2.77. Green colored earthquakes have a down (dilational) first-motion, while red colored earthquakes have an up (compressional) first-motion, consistent with Pacific plate motion.