Teleseismic P-wave Coda Autocorrelation for Crustal Structure beneath the Bighorn Mountains, Wyoming

The Bighorn Arch Seismic Experiment (BASE) was a combined passive and active source seismic experiment designed to image deep crustal structures and the Moho beneath a basement-involved foreland arch in Wyoming. In the summer of 2010, over 1800 single channel RefTek RT125 'Texan' receivers, with 4.5 Hz vertical component geophones, were deployed at spacings of 100 m to 1 km in a region spanning the Bighorn Arch and the adjacent Bighorn and Powder River Basins and set to record continuously. Forty-three teleseismic events, magnitude 4+, were recorded over approximately a two-week acquisition period. Explosive sources and mine blasts were also recorded during this time period.

We utilize the teleseismic P-wave coda autocorrelation method to explore for deep crustal features and the Moho. Teleseismic P-wave coda autocorrelation can provide complementary constraints on subsurface structures when compared to receiver functions. We use teleseismic events ranging from magnitude 4.2 to 5.6 and epicentral distance 36 to 113 degrees. We calculate an autocorrelation function at each receiver for each teleseismic event and then the autocorrelations of all events at a given receiver are stacked together. Due to the variable signal strengths of different events and the number of seismic stations not being consistent day-to-day during the acquisition period, trace normalization is necessary both pre- and post-stack. We use synthetic seismograms to identify arrival times of simple '2p' reflections and make interpretations about the remaining reflections. The '2p' signal is a first-order multiple that bounces off the free-air interface and the interface of interest and gets its name because it is 2 P-wave legs longer than the direct arrival. We identify a Moho 2p reflection with the autocorrelations and are exploring additional reflections.