Seismic activity at the Changbaishan Tianchi volcano in the summer of 2002

The level of seismicity in the Changbaishan Tianchi volcano has been increased obviously since the June of 2002. In this paper, the seismic activity of the Changbaishan Tianchi volcano is studied by using the data recorded at 15 broad-band portable seismographs operating in the volcanic region in summer of 2002. The result shows that the average rate of seismicity is more than 30 events per day in this area during summer of 2002. Most earthquakes occur-red in two areas, southwest and northeast of the Tianchi caldera. The focal depths are shallow, and usually less than 5km from surface. The b values of events occurred in southwest and northeast areas are quite different from each other. Seismic spectral and time spectral analyses show that the events occurred in the summer of 2002 are all of volcano-tectonic earthquakes. The obvious 2Hz low frequency component in seismic records at stations HSZ and DZD is mainly caused by local variations of media and low velocity fault zones near the two stations. We infer that the large number of earthquakes and earthquake swarms occurred in summer of 2002 might be caused by local faulting induced by deep volcanic activities.