地震研究

大震前重力地脉动异常分析^*

(1.甘肃省地震局高台地震台,甘肃高台 734300; 2.甘肃省地震局,甘肃兰州 730000; 3.甘肃省地震局肃南地震台,甘肃肃南 734400)

Analysis on the Abnormalities of Gravity Microtremor before the Strong Earthquakes

YIN Liang¹,YANG Li-ming²,LEI Deng-xue³,LIU Hong-bin¹,ZOU Xiao-bo¹

(1. Gaotai Seismic Station,Earthquake Administration of Gansu Province,Gaotai 734300,Gansu,China)(2. Earthquake Administration of Gansu Province,Lanzhou 730000,Gansu,China)(3. Sunan Seismic Station,Earthquake Administration of Gansu Province,Sunan 734400,Gansu,China)

Keywords：gravity; microtremor; spectrum analysis; earthquake case; earthquake prediction

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参考文献

研究了高台地震台和兰州地震台在2008年5月12日汶川8.0级、2009年8月28日青海海西6.4级、2009年9月30日撒摩亚群岛8.1级地震前重力记录资料脉动幅度及频谱变化,总结了重力地脉动在时间域和频率域上的临震前兆异常特征,发现有与宽带地震仪低频波异常对应的异常信息,即震前时域脉动曲线出现纺锤型或喇叭口形态,0.1～0.14 Hz的频幅最大值在震前几天加速增大直到发震。跟踪地脉动异常变化可以为地震短临预报提供有用信息。

Analyzing the variation of microtremor-amplitude and frequency spectrum of the gravity data recorded by Gaotai Station and Lanzhou Station before the Wenchuan M_S8.0 earthquake on May 12,2008,the Haixi,Qinghai,M_S6.4 earthquake on August 28,2009,and the Samoa Islands M_S8.1 earthquake on September 30,2009,we summarized the characteristics of impending precursors of the gravity data in the time domain and frequency domain. Then we discovered that before the earthquakes,the microtremor curve in the time domain appeared to be spindlelike or bell-mouthed. Further,the amplitude-frequency value in 0.1 Hz～0.14 Hz acceleratedly rose a few days before the earthquakes. Tracking the abnormal variation of the gravity microtremor,we may find the useful information for the short-term earthquake prediction.

引言
1 重力固体潮与正常地脉动
2 震例研究
3 结论与讨论

图1 2008年5月1日兰州台重力地脉动曲线(a)及频谱分析结果(b)(信号长度3 600 s×24 h)<br/>Fig.1 Gravity microtremor records(a)and the results of spectral analysis(b)recorded at Lanzhou Station from May 1, 2008(signal length 3 600 s×24 h)

图1 2008年5月1日兰州台重力地脉动曲线(a)及频谱分析结果(b)(信号长度3 600 s×24 h)
Fig.1 Gravity microtremor records(a)and the results of spectral analysis(b)recorded at Lanzhou Station from May 1, 2008(signal length 3 600 s×24 h)

图2 2008年5月1日兰州台(a)、高台台(b)重力记录滤去固体潮后的地脉动曲线(信号长度24 h)<br/>Fig.2 Gravity microtremor records and the results of spectral analysis recorded at Lanzhou Station(a)and Gaotai station(b)from May 1, 2008(signal length 24 hours)

图2 2008年5月1日兰州台(a)、高台台(b)重力记录滤去固体潮后的地脉动曲线(信号长度24 h)
Fig.2 Gravity microtremor records and the results of spectral analysis recorded at Lanzhou Station(a)and Gaotai station(b)from May 1, 2008(signal length 24 hours)

图3 2008年5月1～12日高台台(a)、兰州台(b)重力地脉动曲线<br/>Fig.3 Gravity microtremor records at Gaotai Station(a)and Lanzhou station(b)from 1 to 12 May, 2008

图3 2008年5月1～12日高台台(a)、兰州台(b)重力地脉动曲线
Fig.3 Gravity microtremor records at Gaotai Station(a)and Lanzhou station(b)from 1 to 12 May, 2008

图4 2008年5月1～13日高台台(a)和兰州台(b)重力地脉动曲线(滤去固体潮成份,<br/>只保留0.08～0.4 Hz的成份)<br/>Fig.4 Gravity microtremor records at Gaotai station(a)and Lanzhou Station(b)from 1 to 13 May, 2008(solid tide filtered out, ingredient in 0.08～0.4 Hz retained)

图4 2008年5月1～13日高台台(a)和兰州台(b)重力地脉动曲线(滤去固体潮成份,
只保留0.08～0.4 Hz的成份)
Fig.4 Gravity microtremor records at Gaotai station(a)and Lanzhou Station(b)from 1 to 13 May, 2008(solid tide filtered out, ingredient in 0.08～0.4 Hz retained)

图5 2008年5月10日13时至12日13时高台台(a)、兰州台(b)重力地脉动频谱变化(0.10～0.14 Hz)<br/>Fig.5 Spectrum changes of gravity microtremor recorded at Gaotai Station(a)and Lanzhou Station(b)from 10 to 12 May, 2008(0.10～0.14 Hz)

图5 2008年5月10日13时至12日13时高台台(a)、兰州台(b)重力地脉动频谱变化(0.10～0.14 Hz)
Fig.5 Spectrum changes of gravity microtremor recorded at Gaotai Station(a)and Lanzhou Station(b)from 10 to 12 May, 2008(0.10～0.14 Hz)

图6 高台重力固体潮曲线(秒值)(a)和重力滤去固体潮汐成份的地脉动曲线(秒值)(b)<br/>Fig.6 Gravity solid tide records recorded at Gaotai Station(second sampling)(a)and gravity microtremor records by filtering out the solid tide(second sampling)(b)

图6 高台重力固体潮曲线(秒值)(a)和重力滤去固体潮汐成份的地脉动曲线(秒值)(b)
Fig.6 Gravity solid tide records recorded at Gaotai Station(second sampling)(a)and gravity microtremor records by filtering out the solid tide(second sampling)(b)

图7 兰州台重力固体潮曲线(秒值)(a)和重力滤去固体潮汐成份的地脉动曲线(秒值)(b)<br/>Fig.7 Gravity solid tide records recorded at Lanzhou Station(second sampling)(a)and gravity microtremor records by filtering out the solid tide(second sampling)(b)

图7 兰州台重力固体潮曲线(秒值)(a)和重力滤去固体潮汐成份的地脉动曲线(秒值)(b)
Fig.7 Gravity solid tide records recorded at Lanzhou Station(second sampling)(a)and gravity microtremor records by filtering out the solid tide(second sampling)(b)

图8 2009年8月24～28日高台台重力地脉动频谱幅度变化(0.10～0.14Hz)<br/>Fig.8 Spectrum changes of gravity microtremor recorded at Gaotai Station from 24 to 28 Aug., 2009(0.10～0.14Hz)

图8 2009年8月24～28日高台台重力地脉动频谱幅度变化(0.10～0.14Hz)
Fig.8 Spectrum changes of gravity microtremor recorded at Gaotai Station from 24 to 28 Aug., 2009(0.10～0.14Hz)

图9 高台台重力固体潮曲线(a)和滤去固体潮成份的地脉动曲线(b)(时段: 2009年9月)<br/>Fig.9 Gravity solid tide records recorded at Gaotai Station(a)and the gravity microtremor records by filters out the solid tide(b)(duration: Sep., 2009)

图9 高台台重力固体潮曲线(a)和滤去固体潮成份的地脉动曲线(b)(时段: 2009年9月)
Fig.9 Gravity solid tide records recorded at Gaotai Station(a)and the gravity microtremor records by filters out the solid tide(b)(duration: Sep., 2009)

图10 2009年9月26～30日高台重力地脉动频谱幅度变化(0.10～0.14 Hz)<br/>Fig.10 Spectrum range changes of gravity microtremor recorded at Gaotai Station from 26 to 30 Sep., 2009(0.10～0.14Hz)

图10 2009年9月26～30日高台重力地脉动频谱幅度变化(0.10～0.14 Hz)
Fig.10 Spectrum range changes of gravity microtremor recorded at Gaotai Station from 26 to 30 Sep., 2009(0.10～0.14Hz)