THE ROCK VALLEY DIRECT COMPARISON (RV/DC) EXPERIMENT: AN OVERVIEW

In 1993, a shallow earthquake sequence occurred in Rock Valley, Nevada National Security Site in southern Nevada. The largest event, M3.7, was followed by eleven M>2 events ranging in depth from 1-3 km. All events were well constrained due to the deployment of seismic stations that occurred early in the sequence. Comparison of these shallow earthquakes to nearby historic nuclear tests identified gaps in our ability to discriminate these event types. To understand the physics of shallow earthquakes, the Rock Valley Direct Comparison Experiment was conceived. We will conduct two chemical explosions at similar hypocenters to the earthquake sequence to compare the discrimination features between these types of events. We have systematically relocated the 1993 events, varying velocity models and codes, but using a common pick data set to choose the experiment borehole. Three additional boreholes are planned and will be instrumented to obtain microseismicity data, sample fault properties, and record the chemical explosions. We are in the process of installing a dense seismic network, including re-occupying stations that recorded the 1993 earthquakes. In addition, we are conducting geophysical and geologic studies such as controlled-source surveys with an Accelerated Weight Drop source, installing new Geodetic stations, geologic mapping, gravity mapping, material properties testing, and UAS collections over the Testbed. To visualize the Testbed, a 3D geologic framework model (GFM) has been developed that incorporates the geologic and geophysical data. The GFM can also be used to output numerical meshes for the modeling and simulation efforts. We expect this unprecedented data set will address seismic waveform differences between earthquake and underground explosion sources.