High Resolution Seismic Velocity Structure in the Reno Basin from Ambient Noise Recorded by a Variety of Seismic Instruments

Abstract

Geothermal prospects may be located in regions characterized by low seismic activity, thus leading to difficulty in estimation of an accurate seismic velocity model. Estimation of velocity models in the upper 5 km of the crust using ambient noise is an inexpensive alternative to active experiments. In the Reno Basin, we are testing a transportable and cost-effective ambient seismic noise processing methodology (when compared to active source experiments) to estimate a high resolution shallow seismic velocity model. A gap exists for demonstrated extraction of Green’s Functions (with Rayleigh waves as the most prominent arrivals) from ambient noise between short and long inter-station distances. In other words, noise-extracted Rayleigh waves are currently sampling less than 0.2 km from the surface, or more than 10 km deep. Also, recent studies demonstrate that ambient noise is effective in exploration seismology for retrieving first-arrival reflections. However, this possibility was not yet demonstrated for inter-station distance larger than several tens on meters. We investigate the possibility of extraction of first arrival reflections and of surface waves from ambient noise Green’s Functions (GF’s). For this purpose, we use a variety of available instruments in a 60 km x 60 km area in the Reno Basin and innovative adaptations of array and network signal processing techniques. We investigate recovery of GF’s from ambient noise for pairs of different instruments: 1) digital narrow-band seismometer recordings (for instance, S-13 seismometer), 2) analog narrow-band seismometer recordings, digitized after transmission, 3) digital accelerometer recordings; 4) digital broadband instruments, including USArray stations and 5) seismic exploration geophones. Each of these instrument classes presents its own problems for GF recovery and requires appropriate processing. We have developed cross-correlation software to take advantage of all types of instruments in our recording archive and thus enlarge the number of paths for which GF’s can be recovered. With a set of traditional inversion programs, we invert the Green’s functions for seismic velocity structure in the Reno Basin.