Shallow Seismicity in the Long Beach–Seal Beach, California Area
Abstract
Seismicity can help to locate fault zones that are often difficult to characterize in densely populated urban areas. In this study, we use three dense nodal arrays consisting of thousands of sensors to detect and locate seismic events in the Long Beach–Seal Beach area of California. Small events can be detected at sufficient signal-to-noise levels during the night, when urban noise is relatively low. We detect and locate >1000 events with ML below 2. Most of the located events are clustered at very shallow depth (0–2 km). The results support previous suggestions that the shallow Newport-Inglewood fault is a wide splayed fault in this area. The seismicity pattern also compares well with some newly identified faults from reflection seismic surveys. The shallow events, which elude detection by the regional seismic network, underscore the complex nature of the faults and their seismic hazard.
Copyright and License
© 2023 Seismological Society of America.
Acknowledgement
The authors thank Signal Hill Petroleum for providing access to the two Long Beach surveys and 3D Seismic Solutions for access to the Seal Beach survey. Dan Hollis and Eric Campbell were key to providing this access. The authors thank Dan Gish and Steve Boljen of 3D Seismic Solutions for providing the seismic cross section and the locations of the faults shown in Figure 5. The authors thank Susan Hough for helpful comments in the article. The authors thank Daniel Trugman and an anonymous reviewer for their insightful comments and advice. This study was supported by the Southern California Earthquake Center (SCEC) Award Number 21034. Part of the material presented in this article was reported as a progress report to SCEC as part of the results of an SCEC award.
Data Availability
The supplemental material for this article contains the following: Figure S1 shows our attempt to use a machine learning–based denoiser before seismicity detection. Figure S2 shows the detected and located daytime events. Figure S3 shows our attempt to determine the focal mechanism of the detected small events. The seismic data used in this study were recorded as part of three exploration surveys. The two surveys in the Long Beach area are property of Signal Hill Petroleum LLC, and permission to use the data must be obtained from them. The survey in the Seal Beach area is managed by 3D Seismic Solutions, and permission to use may be obtained from that company. The seismic catalog produced by this study is available at https://data.caltech.edu/records/5ws5e-ddh43. The fault locations in Figure 1 are publicly available at https://www.usgs.gov/natural-hazards/earthquake-hazards/faults. The software used in this study are publicly available and downloaded from NonLinLoc (https://github.com/alomax/NonLinLoc) and GrowClust (https://github.com/dttrugman/GrowClust). All websites were last accessed in March 2023.
Supplemental Material
Supplementary data (DOCX)
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Additional details
- Southern California Earthquake Center
- 21034
- Available
-
2023-04-05First Online
- Caltech groups
- Division of Geological and Planetary Sciences, Seismological Laboratory
- Publication Status
- Published