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A Preliminary Study on the Phenomenon of Microseismic Fluctuations before Impending Strong Earthquake
YANG Liming1,2, HAO Zhen1, WANG Jianjun1, ZHANG Shuzhen1, YAO Jiajun3, DONG Lei4
1.Lanzhou Institute of Seismology, CEA, Lanzhou 730000, China;2.Qinghai Earthquake Agency, Xining 810001, China;3.Geophysical Exploration Center, CEA, Zhengzhou 450002, China;4.Chongqing Earthquake Agency, Chongqing 401147, China
摘要:
Based on repeated comparison studies of broadband digital seismic records before the Wenchuan MS8.0, Yushu MS7.1 and Qingchuan MS5.4 earthquakes, the possible microseismic fluctuations before impending earthquakes were preliminarily identified. In order to verify and test this phenomenon, a real-time tracking technical system was established by using continuous waveform records of more than 200 wide-band digital seismic stations in regional networks such as Gansu, Qinghai, Sichuan, Yunnan and Tibet. Through real-time tracking and dynamic monitoring of 24 earthquakes with M ≥ 5.0 occurring in the Qinghai-Tibetan block during the period of 2012-2014 and the observations of stations in some non-seismic areas, the reproducibility and objectivity of the impending earthquake phenomenon were verified. The main characteristics of the microseismic fluctuation phenomena immediately preceding the strong earthquakes are as follows:(1) the spectrum range is wider, the dominant frequency is 11-16Hz, and the spectrum shape is more regular; (2) it appears 6-24 days before the earthquake, averaging about 15 days; (3) it is possible to be recorded by the stations within the epicenter distance of 50km, and the stations with the epicenter distance of more than 50km generally cannot record it; (4) this phenomenon is directional, i.e. the direction in which the activity degree, N-value, varies significantly may be related to the location of the seismic source, the seismogenic fault and the distribution of aftershocks of the strong earthquake. The preliminary study shows that the impending-earthquakes microseismic phenomena may be related to the pre-activity, micro-vibration and micro-rupture in the source region in the imminent stage, or the micro-activity and micro-rupture associated with the active tectonics.
关键词:  Impending microseisms  Dominant frequency  11-16Hz  Space-time characteristics  Pre-activity of source area
DOI:10.19743/j.cnki.0891-4176.201903008
分类号:
基金项目:This project sponsored by Application of Digital Seismic Technology in Short- and Medium-term Prediction of Strong Earthquakes:a Special Topic of the Twelfth "Five-year Plan" Chinese Science and Technology Support Plan(2012BAK19B02-01).
A Preliminary Study on the Phenomenon of Microseismic Fluctuations before Impending Strong Earthquake
YANG Liming1,2, HAO Zhen1, WANG Jianjun1, ZHANG Shuzhen1, YAO Jiajun3, DONG Lei4
1.Lanzhou Institute of Seismology, CEA, Lanzhou 730000, China;2.Qinghai Earthquake Agency, Xining 810001, China;3.Geophysical Exploration Center, CEA, Zhengzhou 450002, China;4.Chongqing Earthquake Agency, Chongqing 401147, China
Abstract:
Based on repeated comparison studies of broadband digital seismic records before the Wenchuan MS8.0, Yushu MS7.1 and Qingchuan MS5.4 earthquakes, the possible microseismic fluctuations before impending earthquakes were preliminarily identified. In order to verify and test this phenomenon, a real-time tracking technical system was established by using continuous waveform records of more than 200 wide-band digital seismic stations in regional networks such as Gansu, Qinghai, Sichuan, Yunnan and Tibet. Through real-time tracking and dynamic monitoring of 24 earthquakes with M ≥ 5.0 occurring in the Qinghai-Tibetan block during the period of 2012-2014 and the observations of stations in some non-seismic areas, the reproducibility and objectivity of the impending earthquake phenomenon were verified. The main characteristics of the microseismic fluctuation phenomena immediately preceding the strong earthquakes are as follows:(1) the spectrum range is wider, the dominant frequency is 11-16Hz, and the spectrum shape is more regular; (2) it appears 6-24 days before the earthquake, averaging about 15 days; (3) it is possible to be recorded by the stations within the epicenter distance of 50km, and the stations with the epicenter distance of more than 50km generally cannot record it; (4) this phenomenon is directional, i.e. the direction in which the activity degree, N-value, varies significantly may be related to the location of the seismic source, the seismogenic fault and the distribution of aftershocks of the strong earthquake. The preliminary study shows that the impending-earthquakes microseismic phenomena may be related to the pre-activity, micro-vibration and micro-rupture in the source region in the imminent stage, or the micro-activity and micro-rupture associated with the active tectonics.
Key words:  Impending microseisms  Dominant frequency  11-16Hz  Space-time characteristics  Pre-activity of source area