Abstract
SUMMARY Correlations of the ambient seismic field recorded by seismic stations carry information about the wave propagation between the stations. They also contain information about the ambient field—both the source of the ambient field, and sources of scattering that contribute to it. The waves that comprise the ambient field are subject to scattering due to the heterogeneous Earth, which can generate supplementary arrivals on the correlation functions. We use these effects to locate sources of signals linked to scattering. For this analysis, we use correlation functions computed from continuous signals recorded between 2013 and 2015 by a line of seismic stations in Central California. We identify spurious arrivals on the Vertical to Vertical and Transverse to Transverse correlation functions and use array analysis to map the source of scattering, which is linked to strong structural variations in the Coast ranges and at the border of the Great Valley.
Highlights
The seismic ambient field and the correlation functions derived from it have been used widely and successfully in a variety of contexts: from imaging the structure of the Earth to monitoring its evolution with time
Several high resolution 3-D tomography analyses were performed on Central California data sets in the Parkfield earthquake, using ambient noise correlations, earthquakes, control shots, quarry blasts and/or low-frequency earthquake observations (Zeng et al 2016; Lippoldt et al 2017; Zeng & Thurber 2019)
Correlation functions computed between seismic stations contain information about the propagation between those stations and information about the ambient field surrounding the stations
Summary
The seismic ambient field and the correlation functions derived from it have been used widely and successfully in a variety of contexts: from imaging the structure of the Earth to monitoring its evolution with time. The extracted velocity is still correct (Fig. 3d) for both arrivals on the causal and anticausal parts, and for end fire lobes with and without the added sources This simple test agrees with different studies that have shown that a heterogeneous source distribution can still lead to a correct extraction of wave speed and arrival time, which would not lead to biased tomographic results (e.g. Yao & Van Der Hilst 2009; Tsai 2009). The line of stations installed in California is a good case study because it crosses several prominent structural boundaries at nearly right angles
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