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SCEC2021 Plenary Talk, Seismology

Exploring The Subsurface with Regional DAS Networks: Results from the Imperial Valley Dark Fiber Project

Jonathan Ajo-Franklin, Veronica Rodriguez-Tribaldos, Patrick Dobson, Avinash Nayak, Feng Cheng, Benxin Chi, Todd Wood, Michelle Robertson, Rob Mellors, Cody Rotermund, Bin Dong, John Wu, Christina Morency, Dennise Templeton, & Eric Matzel

Oral Presentation

2021 SCEC Annual Meeting, SCEC Contribution #11238
Recent studies by several research groups have conclusively demonstrated that existing telecommunication infrastructure can be effectively paired with Distributed Acoustic Sensing (DAS) to provide high-density broad band recordings at 10s of km scale. While early results have focused on proof-of-concept demonstrations of this technology combination, our community is now at the point of refining the approach, particularly for regional seismology applications, and tackling high-resolution imaging problems which would be challenging to conduct otherwise. The combination of sensor density and aperture provided by DAS also enables imaging studies which utilize later seismic phases, e.g. coherent scattered events, which are difficult to identify or incorporate with sparse arrays.

We present new results from a long-duration DAS recording effort which exploits a 28 km dark fiber section spanning the active Brawley Seismic Zone (BSZ) in California’s Imperial Valley. This study targets the detection of hidden geothermal resources, the monitoring of existing geothermal production, and the characterization of basin-scale structural features relevant to seismic hazard. The array has been operating since November of 2020 and has recorded several hundred TBs of passive data sampled at 4m and 500 Hz. Using ambient noise surface wave imaging we have identified several zones of low velocity and high seismic scattering, likely related to a regional fault at the southern end of the BSZ. We have also detected a large number of local events, some as small as M1, including the June 2021 Salton Sea swarm. The dense spatial sampling of DAS has allowed us to detect and migrate coherently scattered phases associated with these events to help constrain structures beneath the array. Lastly, the combination of numerous local events and the DAS array aperture have enabled accurate arrival time-picking and body wave tomography to assist in constraining deep S-wave velocity features. Based on these preliminary results, we hope to build enthusiasm for creation of a longer-term DAS-based seismic observatory in the Salton Trough.