Introduction

While helioseismologists routinely crosscorrelate stochastic acoustic noise to produce time-distance curves Duvall et al. (1993) that look like active-source seismograms, terrestrial geophysicists have had less success. Baskir and Weller (1975) describe the first published attempt to use passive seismic energy to image subsurface reflectivity. They briefly describe crosscorrelating long seismic records to produce correlograms that could be processed, stacked and displayed as conventional seismic data. Unfortunately their field tests seem to have been inconclusive. Cole (1995) crosscorrelated data collected using a 4000 channel 2-D field array on Stanford campus. Unfortunately again, possibly due to the short (20 minute) records or bad coupling between the geophones and the dry California soil, his results were also disappointing.

In this paper we present results from a small environmental-scale passive 3-D survey, recorded in Long Beach, California. In total, about four hours of 60-channel passive data were recorded and processed. Although no clear reflection events are visible, a coherent dispersive ground-roll event is visible, and the correlograms do resemble active source seismograms.