Using a Time‐Based Subarray Method to Extract and Invert Noise‐Derived Body Waves at Long Beach, California

Abstract

The reconstruction of body waves from the cross‐correlation of random wavefields has recently emerged as a promising approach to probe the fine‐scale structure of the Earth. However, because of the nature of the ambient noise field, the retrieval of body waves from seismic noise recordings is highly challenging and has only been successful in a few cases. Here, we use seismic noise data from a 5,200‐node oil‐company survey to reconstruct body waves and determine the velocity structure beneath Long Beach, California. To isolate the body wave energy from the ambient noise field, we divide the entire survey into small‐aperture subarrays and apply a modified double‐beamforming scheme to enhance coherent arrivals within the cross‐correlated waveforms. The resulting beamed traces allow us to identify clear refracted P waves traveling between different subarray pairs, which we then use to construct a high‐resolution 3D velocity model of the region. The inverted velocity model reveals velocity variations of the order of 3% and strong lateral discontinuities caused by the presence of sharp geologic structures such as the Newport‐Inglewood fault (NIF). Additionally, we show that the resolution that is achieved through the use of high‐frequency body waves allows us to illuminate small geometric variations of the NIF that were previously unresolved with traditional passive imaging methods.

High‐Resolution Ambient Noise Imaging of Geothermal Reservoir Using 3C Dense Seismic Nodal Array and Ultra‐Short Observation

“…The radial component of the modeled P ‐wave amplitudes is significantly stronger than the vertical component (Figure 7c), confirming the assumption of observation of P‐ wave energy on the radial component of the interferograms. These observations suggest that double‐beamforming techniques might be useful for isolating the body wave energy from the ambient noise field and enhancing P first arrivals for body wave tomography (Castellanos et al., 2020; Nakata et al., 2016).…”

The Fine‐Scale Structure of Long Beach, California, and Its Impact on Ground Motion Acceleration

“…Fortunately, during their time of operation, these instruments recorded continuously and, therefore, not only captured the active source component of the surveys, but also several passive sources including the ambient noise field. This last characteristic of the experiments allows us to move beyond the focus of traditional petroleum seismology and use this type of instrumentation to investigate local microseismicity (e.g., Li et al., 2018), the mechanics of active fault zones (e.g., Inbal et al., 2016), and the structure of the deeper crust (e.g., Castellanos et al., 2020; Clayton, 2020; Lin et al., 2013; Nakata et al., 2015).…”

The fine-scale structure of Long Beach, California, and its impact on ground motion acceleration

“…Fortunately, during their time of operation, these instruments recorded continuously and, therefore, not only captured the active source component of the surveys, but also several passive sources including the ambient noise field. This last characteristic of the experiments allows us to move beyond the focus of traditional petroleum seismology and use this type of instrumentation to investigate local microseismicity (e.g., Li et al, 2018), the mechanics of active fault zones (e.g., Inbal et al, 2016), and the structure of the deeper crust (e.g., Lin et al, 2013;Nakata et al, 2015;Castellanos et al, 2020;Clayton, 2020).…”