AAPG ACE 2018

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High Resolution Shallow Crustal Imaging Using Passive Seismic Dense Arrays

Abstract

The recent development on passive seismic imaging methods combined with the availability of dense seismic arrays has now opened up many new opportunities on high-resolution shallow crustal imaging. Seismic interferometry and tomography, for example, has been used to extract seismic waves propagating between stations and invert for 3D crustal structure. Receiver function analysis, on the other hand, has been used to investigate dominant structure discontinuities such as the sediment/bedrock interface. In this presentation, I will review the work our group has done on using these methods to image shallow hydrothermal, geothermal, sedimentary, and fault zone structure. In each study, hundreds to thousands of autonomous geophones were deployed and recorded passive seismic signals continuously for up to 35 days. By calculating the cross-correlations between all the background seismic noise recorded, we can extract surface wave signals that are sensitive to structure from surface down to couple kilometer depth. Applying the method to the data collected within the Upper Geyser Basin in Yellowstone, for example, has revealed the hydrothermal reservoir of Old Faithful geyser between 20 and 60 meter depth. Similar method has also been used to construct a 3D crustal velocity model in Long Beach, California, and the model was used to make static correction for the active source experiment. With three-component data, receiver function analysis can be done using teleseismic signals and multi-component deconvolution. With a dense station coverage, coherent shallow crustal interfaces can be tracked and local geology can be interpreted. For example, we observed clear basement dipping at the FORGE geothermal site near Milford, Utah. The ability to image shallow crustal structure using passive signals now provides a new way to explore near surface geology with a much reduced cost.