Nodal and Broadband Seismometer Complement to the Imperial Valley Dark Fiber DAS Array

Abstract

Abstract Distributed acoustic sensing (DAS) technology provides the capability to efficiently acquire dense and continuous seismic data on preexisting, unused fiber-optic cables buried in the ground (dark fiber) that were originally deployed for telecommunication. However, these fiber installations typically use existing “right-of-way corridors” along roadways and railway tracks, leading to piecewise linear or quasi-linear seismic receiver geometries, thereby reducing their utility in seismic studies over a broad areal extent. Short-term and dense arrays of seismometers can be deployed to complement dark fiber DAS arrays, leading to improved seismic receiver coverage over a broader area in the vicinity of the DAS array. This study describes the deployment strategies and procedures, data, and metadata of a contemporaneous and complementary network of three temporary broadband seismic stations and 69 nodal seismometers operated in the vicinity of a 27 km long segment of dark fiber DAS array in the Imperial Valley, Southern California. The study area is a sedimentary basin characterized by intense seismicity and faulting in a transtensional tectonic regime, and hosts multiple producing geothermal fields. The broadband stations used direct-burial sensors with a corner period of 120 s and operated continuously for a year from September 2021 to September 2022. The 5 Hz three-component nodal seismometers acquired continuous data for a month approximately from February to March 2022 over a ∼37 km × ∼24 km area, with an average interstation spacing of ∼3 km. Both the broadband and the nodal stations recorded a wealth of ambient seismic noise and high-quality local earthquake data that can be used in a variety of seismological analyses, including local earthquake detection and location, and body-wave and surface-wave tomography.