On finding and using repeating seismic events in and near China

A comprehensive search for repeating seismic events was performed using cross correlation on waveforms for 17,898 seismic events in and near China reported in the Annual Bulletin of Chinese Earthquakes from 1985 to 2005. We define a repeat as an event pair having a high cross correlation (>= 0.8) for a particular bandwidth (0.5 to 5 Hz) and time window (5 s before P arrival to 40 s after Lg arrival). Such events typically have hypocenters separated by no more than about 1 km. This result enables a determination of median relative location error of around 15 km for global and regional catalogs that locate events in this study one at a time using phase picks. The maximum location error is on the order of hundreds of kilometers. We use nonnormalized cross-correlation values to measure relative amplitudes of event pairs. The standard deviation is about 0.06 magnitude units, much better than the precision of relative magnitudes for doublet events, which we estimate for the Chinese catalog to have a standard deviation of 0.36 magnitude units. Two thousand three hundred and seventy-nine events out of the 17,898 or 13% of the events in this catalog are classified as repeats, with later years showing an increase in the percentage. About half the repeats occur as isolated doublets, the rest as multiplets of three or larger, up to a 92-event multiplet. Most of the events appear to be triggered or are due to some earthquake interaction since their recurrence intervals are significantly shorter than would be estimated from tectonic loading.