SCEC Award Number 25253 View PDF
Proposal Category Collaborative Research Project (Multiple Investigators / Institutions)
Proposal Title Analyzing Key Earthquake Questions with Nodal Array of Arrays around the San Jacinto Fault
Investigator(s)
Name Organization
Peter Shearer University of California, San Diego Wenyuan Fan University of California, San Diego John Vidale University of Southern California
SCEC Milestones A2-3 SCEC Groups Seismology, CEM, RC
Report Due Date 03/15/2026 Date Report Submitted 03/31/2026
Project Abstract
 This collaboration between UCSD and USC will analyze data from a unique field experiment of five small-scale nodal arrays, each with 81 three-component sensors, currently deployed around the San Jacinto Fault Zone (SJFZ), which will probe earthquake behavior, the fault zone states, and crustal structure in unprecedented detail. The arrays are operating for four months surrounding a complicated zone of ongoing seismicity that is among the most active in California and hosts occasional tremor and deep slow slip episodes, ensuring a rich dataset for study. These arrays will enable us to detect, locate, and characterize smaller earthquakes than those in any existing catalogs, search for exotic sources using array analyses, and probe fault zone and crustal structures and associated temporal variations using ambient noise techniques. Expanding earthquake catalogs to include smaller events will help refine space-time analyses of seismicity rates, more completely characterize swarms and foreshock sequences, and improve clustered seismicity forecasts. We will measure the noise reduction of a new configuration with an array of compact dense arrays. Our array-based phase picks that will provide a new training dataset for machine learning methods and our micro-earthquake locations will help define 3D geometries for the CFM. The project involves students and postdocs at both UCSD and USC and will coordinate their analyses of the array data to develop shared software and databases. We will try to distribute the raw and processed data through IRIS.
Intellectual Merit Resolving spatial and temporal patterns in seismicity is important for describing the processes that drive earthquake occurrence. Our knowledge of these patterns is limited because earthquake catalogs, even those generated with machine-learning and template-matching methods, are only complete above a threshold magnitude and vast numbers of tiny earthquakes are missed. We are conducting a focused experiment to see whether arrays of nodal instruments in active regions can detect still smaller earthquakes and improve our outstanding of swarms and foreshock occurrence and driving mechanisms.
Broader Impacts The Array of Arrays experiment provided an opportunity for more than 10 students to participate in fieldwork and gain firsthand experience with nodal seismic instrumentation. The project has also enabled one graduate student, Taiga Morioka, to attend the annual meetings of SCEC, AGU, and SSA, contributing to his PhD thesis. In the long run, our research will help improve our understanding of processes that drive earthquake occurrence and may lead to better forecasts of future seismic activity.
Project Participants Peter Shearer, Wenyuan Fan, Dan Hollis, Taiga Morioka, Ian Vandevert, Jeremy Wong (UCSD)
John Vidale, Hao Zhang (USC)
Elizabeth Cochran (USGS)
Exemplary Figure Figure 1. Map of the five arrays (pins) installed in this experiment with M ≥ 1 seismicity in our observation
period as red dots [1]. Pins show the location of the Pinyon Flat Observatory, CVCC, Sky Oaks, Borrego
Valley and Jordan arrays. Pink lines show the fault lines around the SJF. Blue star at the center of the map
shows epicenter of M 3.35 event in Borrego Spring on November 7th, 2024.
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