SEISMIC ARRAYS FOR THE IMAGING OF ALLUVIAL DEPOSITS AND MONITORING ENGINEERING SYSTEMS

Abstract

As part of the PoroTomo Project, active and passive seismic data were collected with a three component seismometer array in order to image petrophysical properties of a 1500-m by 500-m by 400-m volume in a geothermal field at Brady Hot Springs, Nevada. We intended to use the arrival of multiple phases including P, S, and surface waves to invert for the distribution of petrophysical parameters, including Young’s modulus, shear modulus, Poisson’s ratio, density and porosity with an expected resolution of 50 m or better at a depth of 200 m. Since the determination of arrival times of S-waves is challenging, we implemented an analysis based on polarized particle motion to assess the arrivals of different phases. The methodology included rotation, filtering, cross-correlation, and stacking of waves generated by a vibroseis truck and captured by a the Nodal seismograph array. The determination of body and surface wave travel times were made by the changes in the obtained particle velocity polarization caused by the anisotropy and heterogeneity of the formation. In spite of these challenges, the obtained results provide a robust and tested methodology to determine arrival times of different phases. These arrival times could then be fed into neural network algorithm to provide a larger dataset and be used for overall inversion of P- and S-wave travel time tomographic images