Interesting Regional Seismic Event From Qinghai Province, China

摘要

We anticipate that regional seismology will play a key role in future monitoring for potential underground nuclear tests. Understanding the regional characteristics of wave propagation, including source, path, and site effects, will be required before such monitoring becomes routine. To prepare for such monitoring, we have been studying many seismic events from central Asia recorded at regional distances. Here we report on one particularly interesting event from Qinghai Province, China that provides a good example of why a comprehensive regionalization effort is required for successful monitoring. On December 6, 1997, a seismic event with mb near 4.5 occurred in a mountainous region (over 4000 meters elevation) of the east-central Qinghai Province, China. The event was detected and located by the prototype International Data Centre (pIDC) and by the National Earthquake Information Center (NEIC). Both organizations fixed the depth when estimating the event's location. The pIDC estimated an mb of 4.2 and an MS (using only 2 stations) of 3.4. Using the pIDC mb:MS event screening criteria this event falls within the earthquake population. From the regional waveforms for this event we observe, in general, that signal-to-noise ratios are poor for body waves at frequencies above about 2 Hz, except at stations WMQ (1350 km) and MAKZ (2000 km). Rayleigh and Love waves at periods between about 15 and 25 seconds generally have good signal-to-noise ratios at most regional stations. We merged arrival times from regional stations with times from the NEIC and pIDC bulletins and relocated the event. Our relocation moved the event about 10 km farther south, but we could not constrain depth.