Joint observation of long period tremor signals with broadband seismometer,tiltmeter and gravimeter

We report here the observation result of joint observation of long period tremor signals with broadband seismome-ter,tiltmeter and gravimeter at the HUST(Huazhong University of Science and Technology)station.The observed data were compared and analyzed.Since 2005,the several tens of abnormal tremor signals which are weak,com-plex and duration of 2 to 3 days have been synchronously recorded by the different instruments.The tremor signals have the periodic domain in the range of 3 to 5 minutes,20 to 30 minutes and even more than 1 hour.The observa-tion shows such tremors are a physical existence.The analysis indicates that a part of the tremors caused by the typhoon from the western Pacific Ocean.These tremors have a close relationship with wind velocity of typhoon and distance between the typhoon center and the station.Except these,the cause of others is still unclear.

This paper reports the result of a joint observation of long period seismic signals with broadband digital seismometer, tiltmeter and gravimeter at the HUST station, Wuhan of China. The observed data were compared and analyzed. Since 2005, these different instruments have synchronously recorded several tens of pattern alike, weak abnormal tremor signals, which lasted for two or three days. The signals involve complex components. Our analyzed result indicates that one part of the tremor signals is caused by the typhoon moving to the offshore region of China mainland from western Pacific Ocean. Amplitude of such signal is closely related to the distance between the center of typhoon and the observation station, and to the wide velocity of typhoon. Except for this, we do not know the cause of another kind of abnormal tremor. A spectral analysis shows that the abnormal tremor has the signal components of 3--5 min period, 20--30 min period, and even more than 1 hour period. With these spectrum components we may distinguish the tremor from background noise. The continuous records for a long time confirm the widespread existence of the tremor. But its mechanism needs to be further investigated.