DELINEATING NEAR-SURFACE FAULT USING TELESEISMIC RECEIVER FUNCTION ANALYSIS

Teleseismic receiver function (RF) analysis allows to effectively detect impedance contrasts in the subsurface relying on observations of earthquake-generated converted body waves. This technique has traditionally targeted deep Earth structures, such as Moho discontinuity and transition zones, due to the low frequency content of teleseismic waves. There has been significant interest in applying RF analysis for basin-scale seismic characterization, in part aimed to assess its potential for onshore commercial integration as a cost-effective supplement to active-source seismic surveys. Despite limited frequency contents, instrumentations of conventional passive-source experiments possess a number of advantages over those of the active-source surveys. Specifically, the logistics of data acquisition for passive-source experiments are relatively simple, and multicomponent sensors of the conventional broadband seismometers enable effective detection of shear waves, and by extension, anisotropy-related directional variations of observed signals. In this study, we perform teleseismic RF analysis to detect shear wave anisotropy and related symmetry axes orientations in the subsurface beneath western border of the Green River Basin, using an open-source seismic data recorded at 55 closely spaced broadband seismometers of the LaBarge Passive Seismic Experiment (LPSE). The array was deployed over the LaBarge platform between November 2008 to June 2009, traversing a major Paleocene thrust fault (Hogsback Fault) that emplaced Paleozoic carbonate units over Mesozoic siliciclastics. In addition to the isotropic negative signals expected across the interface between the carbonates and the siciliclastics, we also find coincident anisotropic signals that effectively delineate the fault interface. We also observe variable strength and geometry of the observed anisotropy along the array. Significantly, the presence of anisotropy can substantiate and reveal additional interpretable signals that are otherwise disregarded. Finally, the estimated fast axes orientations compare favorably with the bedding orientations of the Madison limestones observed at surface exposures near the fault trace.