Stochastic Inversions for Source, Path, and Site Parameters from West Texas Earthquakes

ABSTRACT This study utilizes recorded ground motions from West Texas to evaluate the source, path, and site effects in this region. We analyze the Fourier amplitude spectra from 354 earthquakes in the Delaware basin recorded by the TexNet seismic network at 49 sites. The magnitudes of the earthquakes range from ∼3.0 to 5.0, with hypocentral distances up to 300 km. Using a Bayesian parametric inversion on 6479 records, we simulate the spectra as a combination of source, path, and site effects from a stochastic point-source model. The inverted moment magnitudes were comparable to the catalog moment magnitudes, and the stress parameter (Δσ) ranged from 5 to 134 bar, increasing with magnitude. The geometrical spreading was characterized by a smooth bilinear function, yielding a near-field γ of 1.15 and a frequency-dependent quality factor of Q=837·f0.59. The inverted site amplification functions revealed six distinct clusters of response, with three clusters located in the western part of the study area and the other three scattered to the east. The inverted high-frequency decay parameter (κ0) ranged from 0.005 to 0.056 s, with no clear relationship to shear-wave velocity but systematic variation with cluster and location. Correlation between parameters was observed, but only the prior distribution of Δσ strongly influenced the other inverted parameters.