汶川大地震宽带地震仪短临异常及成因初探
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摘要
2008年5月12日8.1级汶川大地震发生后,我们对国家测震台网的40台宽频带地震仪在5月7日~5月13日的观测数据进行了分析.结果表明,汶川大地震前有明显的短临异常:各台站在大地震发生前1~3天内不同程度检测到了低频异常颤动,颤动振幅逐渐增大,一直持续到大地震发生,信号周期范围为2~10 s.重力仪和倾斜仪也观测到了这类颤动信号.汶川大地震前的异常颤动信号几乎遍布中国大陆,但在西部较弱,东南部较强,尤其在华南地块靠近菲律宾板块的边界处颤动信号很强.因此我们的初步推测是:异常颤动产生的可能原因是地震爆发前华南地块可能开始了慢滑移,滑移时的摩擦产生低频颤动.
We investigated broadband seismographic waveform data in 7~13 May 2008 from 40 seismic stations of the National Digital Seismograph Network of China(NDSN) after the 12 May 2008 Wenchuan earthquake,showing that obvious precursor was widely detected throughout China.The premonitory phenomena is that tremor amplitudes in the period band of 2~10 s have increased steadily within 1~3 days before the main shock rupture.Anomaly tremors can also be detected by gravimeters and tiltmeters.Tremor signals are widely detected in mainland China,but they are very strong in Southeastern China and weak in Western China.The possible slow slip of South China block before the great Wenchuan earthquake may be the cause of tremors,which is related to some frictional processes of the slow slip.
We investigated broadband seismographic waveform data in 7~13 May 2008 from 40 seismic stations of the National Digital Seismograph Network of China(NDSN) after the 12 May 2008 Wenchuan earthquake,showing that obvious precursor was widely detected throughout China.The premonitory phenomena is that tremor amplitudes in the period band of 2~10 s have increased steadily within 1~3 days before the main shock rupture.Anomaly tremors can also be detected by gravimeters and tiltmeters.Tremor signals are widely detected in mainland China,but they are very strong in Southeastern China and weak in Western China.The possible slow slip of South China block before the great Wenchuan earthquake may be the cause of tremors,which is related to some frictional processes of the slow slip.
引文
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[23]薛光琦,王有学,宿和平.拉萨地体内低速异常成因的探讨—壳内局部熔融的地震层析证据.地球学报,2005,26(5):411~415Xue G Q,Wang Y X,Su H P.Interpretation of the lowvelocity anomaliesin the Lhasa terrain:tomographic evidencefor partial melting in the crust.Acta Geoscientia Sinica(inChinese),2005,26(5):411~415
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[2]郝晓光,许厚泽,郝兴华等.重力高频扰动与地震,地壳形变与地震.2001,21(3):9~13Hao X G,Xu HZ,Hao X H,et al.High-frequency gravitydisturbance before earthquakes.Crustal Deformation andEarthquake(in Chinese),2001,21(3):9~13
[3]郝晓光,胡小刚,许厚泽等.汶川大地震前的重力扰动.大地测量与地球动力学,2008,28(3):129~131Hao X G,Hu XG,Xu HZ,et al.Gravity disturbance beforethe Wenchuan Ms8.0 earthquake.Journal of Geodesy andGeodynamics(in Chinese),2008,28(3):129~131
[4]郝晓光,胡小刚.宽带地震仪资料证实汶川大地震“震前重力扰动”.地球物理学进展,2008,23(4):1332~1335Hao X G,Hu X G.Disturbance before the Wenchuanearthquake by broadband seismometer.Progress inGeophysics(in Chinese),2008,23(4):1332~1335
[5]Wang Q,Zhang P Z,Freymueller J T,et al.Present-daycrustal deformation in China constrained by Global PositionSystem measurements.Science,2001,294(5542):574~577
[6]Zhang P Z,Shen Z,Wang M,et al.Continuous deformationof the Tibetan plateau from global positioning system data.Geology,2004,32(9):809~812
[7]许志琴,李化启,侯立玮等.青藏高原东缘龙门山-锦屏造山带的崛起—大型拆离断层和挤出机制.地质通报,2007,26(10):1262~1276Xu Z Q,Li H Q,Hou L W,et al.Uplift of the Longmen-Jinping orogenic belt along the eastern margin of the Qinghai-Tibet Plateau:Large-scale detachment faulting and extrusionmechanism.Geological Bulletin of China(in Chinese),2007,26(10):1262~1276
[8]Burchfiel B C,Royden L H,van der Hilst R D,et al.Ageological and geophysical context for the Wenchuanearthquake of 12 May 2008,Sichuan,People's Republic ofChina.GSAtoday,2008,18(7):4~11
[9]张培震,徐锡伟,闻学泽等.2008年汶川8.0级地震发震断裂的滑动速率、复发周期和构造成因.地球物理学报,2008,51(4):1066~1073Zhang P Z,Xu X W,Wen X Z,et al.Slip rates andrecurrence intervals of the LongmenShan active fault zone,and tectonic i mplications for the mechanism of the May 12Wenchuan earthquake,Sichuan,China.Chinese J.Geophys.(in Chinese),2008,51(4):1066~1073
[10]Obara K.Nonvolcanic deep tremor associated withsubduction in southwest Japan.Science,2002,296(5573):1679~1681
[11]Rogers G,Dragert H.Episodic Tremor and slip on theCascadia Subduction Zone:The chatter of silent slip.Science,2003,300(5627):1942~1943
[12]Schwartz S Y,Rokosky J M.Slow slip events and seismictremor at circum-Pacific subduction zones.Rev.Geophys.2007,45,RG3004,doi:10.1029/2006RG000208
[13]Shelly D R,Gregory C B,Satoshi I,et al.Low-frequencyearthquakes in Shikoku,Japan,and their relationship toepisodic tremor and slip.Nature,2006,442(7099):188~191
[14]Ide S,Shelly D R,Beroza G C.Mechanism of deep lowfrequency earthquakes:Further evidence that deep non-volcanic tremor is generated by shear slip on the plateinterface.Geophys.Res.Lett.,2007,34,L03308,doi:10.1029/2006GL028890
[15]Shelly D R,Gregory C B,Satoshi I.Non-volcanic tremor andlow-frequency earthquake swarms.Nature,2007,446(7133):305~307
[16]Dragert H.Mediating plate convergence.Science,2007,315(5811):471~472
[17]王妙月.板内地震成因与物理预报.地球物理学报,1994,34(增刊I):208~213Wang M Y.Cause and physical prediction of intraplateearthquakes.Chinese J.Geophys.(in Chinese),1994,34(Suppl.I):208~213
[18]方剑,许厚泽.中国及邻区岩石层密度三维结构.地球物理学进展,1999,14(2):88~93Fang J,Xu H Z.Three di mensional distribution oflithospheric density beneath the China and its adjacentregion.Progress in Geophysics(in Chinese),1999,14(2):88~93
[19]柯小平,王勇,许厚泽等.青藏高原地壳三维密度结构的重力地震联合反演.地球物理学进展,2008(出版中)Ke X P,Wang Y,Xu H Z,et al.The three-di mensionalcrustal density structure of Tibetan plateau from jointinversion of gravity and seismic data.Progressin Geophysics(in Chinese),2008(in press)
[20]Rainer K,James N,Wenjin Z,et al.Evidence fromearthquake data for partially molten crustal layer in SouthernTibet.Science,1996,274(5293):1692~1693
[21]Kind R,Yuan X,Saul J,et al.Seismic i mages of crust andupper mantle beneath Tibet:evidence for Eurasian platesubduction.Science,2002,298(5596):1219~1221
[22]李海鸥,姜枚,王有学等.青藏高原地壳的低速层与部分熔融.物探与化探,2004,28(4):290~293Li H O,Jiang M,Wang Y X,et al.Low-velocitylayers andpartial melting in Qinghai-Tibet plateau.Geophysical andGeochemical Exploration(in Chinese),2004,28(4):290~293
[23]薛光琦,王有学,宿和平.拉萨地体内低速异常成因的探讨—壳内局部熔融的地震层析证据.地球学报,2005,26(5):411~415Xue G Q,Wang Y X,Su H P.Interpretation of the lowvelocity anomaliesin the Lhasa terrain:tomographic evidencefor partial melting in the crust.Acta Geoscientia Sinica(inChinese),2005,26(5):411~415
[24]杨又陵,赵根模,高国英等.2001年11月14日昆仑山口西Ms8.1地震前的缓慢地震事件.国际地震动态,2003,9:1~4Yang Y L,Zhao G M,Gao G Y,et al.The slowearthquakeevent occurring before west to Kunlun Mountain Passearthquake ofMs8.1 on November 14,2001.RecentDevelopmentsin World Seismology(in Chinese),2003,9:1~4
[25]赵根模,杨港生,陈化然.寂静的前震与地震预测.地震,2001,21(1):69~76Zhao G M,Yang G S,Chen H R.Quiescent foreshock andearthquake prediction.Earthquake(in Chinese),2001,21(1):69~76
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