Concrete dams as seismic imaging sources

We obtained noise correlation functions (NCF) in northern Montana from broadband data that include P- and S-wave first arrivals and short-period surface waves for frequencies extending to nearly 15 Hz at offsets of 5-17 km using ambient resonant vibrations of a concrete gravity-arch dam as seismic source. A seismograph operated close to the dam acted as a virtual source with a compact autocorrelation function, making it feasible to use short-duration crosscorrelation time windows to obtain a larger number of NCF stacks with impulsive high-frequency body wave first-arrival from recording durations of a single day to several weeks.