Single-Site Phase Velocity Measurement

Mikumo & Aki attempted to determine phase velocities at a single site using seismometers and strainmeters oriented in the same horizontal direction. For the five earthquakes studied, they found a good agreement with the theoretically predicted velocities for body waves and, in some cases, for surface waves. Rodgers showed that for long periods (> 100 s), horizontal acceleration and tilt cannot easily be separated instrumentally, and King et al. have shown that near-station heterogeneities may result in azimuthal effects not considered by Mikumo & Aki. We rederive the method for single-site phase velocity determinations taking into account both of these effects. Our method uses strain and vertical acceleration measurements because the vertical acceleration record is neither affected by site effects nor contaminated by tilt.