Systematic detection and correction of instrumental time shifts using
crosscorrelations of ambient seismic noise
Abstract
Timing errors are a notorious problem in seismic data acquisition and
processing. We present a technique that allows such time shifts to be
detected and corrected in a systematic fashion. The technique relies on
virtual-source surface-wave responses retrieved through the
crosscorrelation of ambient seismic noise. In particular, it relies on
the theoretical time-symmetry of these time-averaged receiver-receiver
crosscorrelations. By comparing the arrival time of the surface waves at
positive time to the arrival time of the surface waves at negative time
for a large a number of receiver-receiver pairs, relative timing errors
can be determined in a least-squared sense. The time-symmetry of the
receiver-receiver crosscorrelations, however, is contingent on a uniform
surface-wave (noise) illumination pattern. In practice, the illumination
pattern is often not uniform. We therefore show that weighting different
receiver-receiver pairs differently in the inversion allows timing
errors to be determined more accurately. The weights are based on the
susceptibility of different receiver pairs to illumination-related
travel-time errors. The proposed methodology is validated using both
synthetic data and field data. The field data consists of recordings of
ambient seismic noise by an array of stations centered around the tip of
the Reykjanes peninsula, southwest Iceland (some of these stations
exhibit time shifts of an unknown nature).