芦山地震前后次声波及重力波信号分析
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摘要
2013年4月20日芦山地震(MS7.0)发生前后,位于三峡库区的次声监测阵列记录下了一系列的次声波与重力波信号。文中首先对不同类型的地震次声波以及重力波做出概念上的区分,然后处理、分析采集到的信号,一一判定信号的类型,厘清次声信号、重力波信号与地震事件间的联系。文中讨论了次声压和大地垂直起伏运动之间的线性耦合,使用简正波叠加的方式生成了仿真地震波,并与次声波进行比较,判定4月20日接收到的地震次声波为本地次声波,次声波形与大地垂直运动速率的波形具有极高的相关度。文中还使用基于S变换的时频分析、基于互相关系数的时差计算以及三角阵定向等方法,对4月18日及22日接收到的重力波做了来波定向。经计算,4月22日来波方向约为254.3°,波速约为9m/s,关联度最强的地震事件为21日凌晨发生的芦山地震余震(MS4.9),三角阵对芦山地震震中的反方位角为267.7°,方位角误差为13.4°;18日来波方向约为220.2°,波速约为28m/s,关联度最强的地震事件为4月17日发生的云南大理地震(MS5.1)及其余震,三角阵对此震中的反方位角为244.7°,方位角误差为24.5°。
A couple of days before and after the Lushan earthquake(MS7.0)occurred on April 20,2013,atmospheric pressure perturbations were observed in the Three Gorges Reservoir Area by several infrasound monitors,installed by the Three Gorges Research Center for Geo-hazard.Among the observations,local infrasound and very low frequency gravity waves can be clearly identified.We generated synthetic seismic waves in order to compare it to the air pressure changes,testing the ground-to-air coupling near the infrasound monitor,and found that the correlation between the local infrasound and the vertical movement velocity of the ground is high.We also calculated the azimuth of the gravity wave sources on the basis of a triangle monitor array.The results show that one of the aftershocks(MS4.9)of the Lushan earthquake is the most relevant event to the gravity waves received on April 22,the wave propagation velocity is 9m/s,the calculated azimuth of the wave source is 254.3°,giving a deviation of 13.4°to the practical epicenter azimuth.The Dali earthquake(MS5.1)in Yunan province occurred on April 17is the most relevant event to the gravity waves received on April 18,the wave propagation velocity is about 28m/s,the calculated azimuth of the wave source is 220.2°,giving a deviation of 24.5°to the practical epicenter azimuth.
A couple of days before and after the Lushan earthquake(MS7.0)occurred on April 20,2013,atmospheric pressure perturbations were observed in the Three Gorges Reservoir Area by several infrasound monitors,installed by the Three Gorges Research Center for Geo-hazard.Among the observations,local infrasound and very low frequency gravity waves can be clearly identified.We generated synthetic seismic waves in order to compare it to the air pressure changes,testing the ground-to-air coupling near the infrasound monitor,and found that the correlation between the local infrasound and the vertical movement velocity of the ground is high.We also calculated the azimuth of the gravity wave sources on the basis of a triangle monitor array.The results show that one of the aftershocks(MS4.9)of the Lushan earthquake is the most relevant event to the gravity waves received on April 22,the wave propagation velocity is 9m/s,the calculated azimuth of the wave source is 254.3°,giving a deviation of 13.4°to the practical epicenter azimuth.The Dali earthquake(MS5.1)in Yunan province occurred on April 17is the most relevant event to the gravity waves received on April 18,the wave propagation velocity is about 28m/s,the calculated azimuth of the wave source is 220.2°,giving a deviation of 24.5°to the practical epicenter azimuth.
引文
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[16]潘黎黎,曾佐勋,王杰.芦山地震(MS7.0)及玉树地震(MS5.2)震前次声波异常信号分析[J].地学前缘,2013,20(6):73-79.
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[19]Watada S,Kunugi T,Hirata K,et al.Atmospheric pressure change associated with the 2003Tokachi-Oki earthquake[J].Geophysical Research Letters,2006,33:L24306.doi:10.1029/2006GL027967.
[2]杨训仁.大气声学[M].2版.北京:科学出版社,2007:18-22.
[3]Beer T.Atmospheric Waves[M].London:Adam Hilger,1975.
[4]谢金来,谢照华.1993年7月2日日本北海道地震次声波[J].声学学报,1996,21(1):55-61.
[5]Le Pichon A,Guilbert J,ValléM,et al.Infrasonic imaging of the Kunlun Mountains for the great 2001China earthquake[J].Geophysical Research Letters,2003,30(15):1814,doi:10.1029/2003GL017581.
[6]Landès M,Ceranna L,Le Pichon A,et al.Localization of microbarom sources using the IMS infrasound network[J].Journal of Geophysical Research,2013,117:D06102,doi:10.1029/2011JD016684.
[7]苏伟,楼海,袁松湧,等.云南腾冲火山区地震/次声台阵建设[J].国际地震动态,2010(5):26-32.
[8]Le Pichon A,Herry P,Mialle P,et al.Infrasound associated with the 2004-2005large Sumatra earthquakes and tsunami[J].Geophysical Research Letters,2005,32:L19802,doi:10.1029/2005GL023893.
[9]Mikumo T,Shibutani T,Le Pichon A,et al.Low-frequency acoustic-gravity waves from coseismic vertical deformation associated with the 2004Sumatra-Andaman earthquake(MW=9.2)[J].Journal of Geophysical Research,2008,113:B12402,doi:10.1029/2008JB005710.
[10]胡心康,石金瑞,任建国.大气中一种压力波动与地震关系的初步探索[J].地球物理学报,1980,23(4):450-458.
[11]李钧之,夏雅琴,陈维生.近几年日本强地震的临震前兆信息[J].北京工业大学学报,1995,21(4):1-12.
[12]苏昉,田维.2000年4—5月强地震的前兆次声波测量研究[C]∥中国地震学会第八次学术大会论文摘要集.北京:地震出版社,2000.
[13]林琳,杨亦春.大气中一种低频次声波观测研究[J].声学学报,2010,35(2):200-207.
[14]夏雅琴,崔晓艳,李均之,等.震前次声波异常信号的研究[J].北京工业大学学报,2011,37(3):463-469.
[15]吕君,郭泉,冯浩楠,等.北京地震前的异常次声波[J].地球物理学报,2012,55(10):3379-3385.
[16]潘黎黎,曾佐勋,王杰.芦山地震(MS7.0)及玉树地震(MS5.2)震前次声波异常信号分析[J].地学前缘,2013,20(6):73-79.
[17]Cansi Y.An automatic seismic event processing for detection and location:The P.M.C.C.method[J].Geophysical Research Letters,1995,22(9):1021-1024.
[18]陈兴钩,林景荣,雷英果,等.利用台风次声波确定台风方位的计算方法[J].华侨大学学报,1980(1):11-23.
[19]Watada S,Kunugi T,Hirata K,et al.Atmospheric pressure change associated with the 2003Tokachi-Oki earthquake[J].Geophysical Research Letters,2006,33:L24306.doi:10.1029/2006GL027967.
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