Integrating geophysical methods to study subsurface features of the Snake River Plain, Idaho

Abstract

Structural complexities and evolution of the Snake River Plain (SRP) and the role of extension in its formation have been a topic of scientific discussion for decades. Recent oil and natural gas exploration that is taking place on the Western Snake River Plain (WSRP) is another important factor in the need for a detailed scientific study of the area. In this research, we are addressing some of these issues by focusing on the WSRP, using a pre-existing gravity and magnetic database compiled through a community effort. These data are available at the Pan American Center for Environmental Studies (http://research.utep.edu/paces ). In the regional context of the SRP, the Complete Bouguer Anomaly (CBA) varies by about 210 mGal along its axis. For gravity processing, we used upward continuation filters to delineate features by wavelength. Total Magnetic Intensity (TMI) data were also analyzed. TMI values range over 600 nT with much more complex and erratic magnetic signatures that arise from the shallow flood basalts and rhyolite deposits within the region. We used total horizontal derivative and tilt derivative filters for further processing of the magnetic data. We are able to identify the major structural components in the area using gravity and magnetic data. The bounding normal faults of the WSRP are well observed. CBA values along the SRP show that the western and central sections of the SRP have higher gravity anomaly values than the eastern sections and the Yellowstone (YS) area. We used forward gravity modeling of the subsurface structures across the WSRP, starting from the High Lava Plains on the southwest to the Idaho Batholith on the northeast. From the model, we observed that the Moho depth increases northeastward and varies between 35 and 43 km along the profile. These results match with receiver function Moho depth estimates from the EarthScope USArray. We used borehole data and shallow seismic survey results to constrain the upper 5 km of the model along the profile. A number of normal faults that form a series of grabens and half grabens were also modeled beneath the WSRP. On the southwest part of the WSRP profile, the Oregon-Idaho grabens that separate the WSRP from the High Lava Plains is also modeled.