A shallow seismic reflection survey in basalts of the Snake River Plain, Idaho

Abstract

The objective of this feasibility study was to determine if the seismic reflection method could help to optimize placement of water‐quality monitoring wells near a radioactive storage facility. Seismic reflections from depths less than 30 m were recorded along a 500 m long line over a basalt, rhyolite, and sedimentary sequence in the Snake River Plain. Some shallow reflections at 40 to 50 ms on the field files are of exceptional quality with frequency exceeding 150 Hz. Reflections and refractions from selected seismograms along the line possess vastly different normal‐moveout (NMO) and apparent velocities as well as wavelet characteristics. Extreme variations in quality, seismic character, and reflector geometries observed on seismograms give the appearance of varying geologic settings and are uncommon for such short distances. Severe surgical muting was necessary for accurate velocity and statics analyses. The seismic reflection data show apparent structural lows in a sedimentary layer sandwiched between basalt flows. Interpreted structural lows must be verified by drilling before a monitoring plan can be fully developed. Similar shallow reflection surveys could also be used to improve deeper conventional seismic data in this and other basaltic terrain.