地震动力:由巨观到微观——1999年台湾集集地震
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摘要
决定地震发生时的断层破裂能量和了解一个断层带的孕育与发展都需要地震和地质数据的结合.在一个大地震的发生过程中,藉由地震仪的记录分析,了解地震断层破裂过程中其断层的几何破裂行为及其机制,甚至分析其运动学上的灾害行为.在地震源分析中文章作者将以上行为分析称为地震的巨观分析.而地震的微观分析,则是以探讨当地震断层及破裂前缘持续向前前进时,其所需的破碎能量及其形成的极小颗粒之断层泥的物理化学机制.此断层滑移带中的断层泥之物理机制、化学组成及地震断层滑移带厚度,皆为了解地震滑移时摩擦行为及能量释放的重要参数.地震的巨观及微观行为的结合分析,为地震学上重要的突破,使人们得以进一步了解地震破裂过程中的摩擦行为、温度及压力的变化,并探讨地震时造成的地表位移、速度及加速度行为.但断层滑移带的断层泥并不易获得,除非有清楚的深部断层几何,并能以深钻的方式取得断层泥材料进行分析.1999年7.6级的台湾集集大地震产生地表或近地表8—12m的滑移,此近地表的滑移是钻井容易达成的,因此提供一次难得的机会,得出大地震滑移带的断层泥了解大滑移断层的动力机制.而2008年四川汶川地震为另一了解此巨观与微观机制的地震.
Determining the seismic fracture energy during an earthquake and understanding the associated creation and development of a fault zone requires a combination of both seismological and geological field data.The analysis of earthquake kinematics from seismic waveform data,which we call macroscopic seismology,can help us understand the temporal and spatial slip distribution,and furthermore,the possible associated hazard pattern.The actual thickness of the zone that slips during the rupture of a large earthquake is not known and is a key seismological parameter in understanding energy dissipation,rupture processes and seismic efficiency.This analysis requires the investigation of fault gouge related to an earthquake,and we call it microscopic seismology.The overall understanding of earthquake dynamics requires the integration of macroscopic with microscopic studies.The 1999 magnitude-7.7 earthquake in Chi-Chi,Taiwan,produced a large slip(8 to 12 m) at or near the surface,which was accessible to borehole drilling and provided a rare opportunity to sample a large slip fault.The Taiwan Chelungpu-fault drilling project retrieved samples from the fresh slip zone associated with the 1999 Chi-Chi earthquake.The surface fracture energy estimated from grain sizes in the gouge zone of the fault was directly compared to the seismic fracture energy determined from near-field seismic data.The chemical and physical characteristics of the retrieved core helped us give the constraints on the faulting dynamics as thermal pressurization,which yielded the large slip and slip velocity with less acceleration observed at the northern portion of the fault.The opportunity of linking earthquake studies from the macroscopic to the microscopic is rare and unique.The 2008 Wenchuan earthquake is another possible earthquake for this integrated seismology study.
Determining the seismic fracture energy during an earthquake and understanding the associated creation and development of a fault zone requires a combination of both seismological and geological field data.The analysis of earthquake kinematics from seismic waveform data,which we call macroscopic seismology,can help us understand the temporal and spatial slip distribution,and furthermore,the possible associated hazard pattern.The actual thickness of the zone that slips during the rupture of a large earthquake is not known and is a key seismological parameter in understanding energy dissipation,rupture processes and seismic efficiency.This analysis requires the investigation of fault gouge related to an earthquake,and we call it microscopic seismology.The overall understanding of earthquake dynamics requires the integration of macroscopic with microscopic studies.The 1999 magnitude-7.7 earthquake in Chi-Chi,Taiwan,produced a large slip(8 to 12 m) at or near the surface,which was accessible to borehole drilling and provided a rare opportunity to sample a large slip fault.The Taiwan Chelungpu-fault drilling project retrieved samples from the fresh slip zone associated with the 1999 Chi-Chi earthquake.The surface fracture energy estimated from grain sizes in the gouge zone of the fault was directly compared to the seismic fracture energy determined from near-field seismic data.The chemical and physical characteristics of the retrieved core helped us give the constraints on the faulting dynamics as thermal pressurization,which yielded the large slip and slip velocity with less acceleration observed at the northern portion of the fault.The opportunity of linking earthquake studies from the macroscopic to the microscopic is rare and unique.The 2008 Wenchuan earthquake is another possible earthquake for this integrated seismology study.
引文
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[5]Kanamori H,Heaton T.Geophysical monograph,2000,120:147
[6]Brodsky E,Kanamori H.J.Geophys.Res.,2001,106:16357
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[8]Ma K F,Tanaka H,Song S Ret al.Nature,2006,444:473
[9]Tanaka H,Wang C Y,Chen W Met al.Terr.Atmos.Ocean.,2002,113:227
[10]Wang C Y,Li C L,Yen HY.Geophys.Res.Lett.,2002,29:1790
[11]Tanaka H,Chen W M,Wang C Yet al.Geophys.Res.Lett.,2006,33:L16316
[12]Tanaka H,Chen W M,Kawabata Ket al.Geophys.Res.Lett.,2007,34:L01309
[13]Kano Y,Mori J,Fujio Ret al.Geophys.Res.Lett.,2006,33:L14306
[2]Ji C,Helmberger D Jet al.J.Geophys.Res.,2003,108:2412
[3]Lee S J,Ma K F,Chen H W.J.Geophys.Res.,2006,111:B11308
[4]Lee S J,Chen HW,Ma K F.J.Geophys.Res.,2007,112:B06307
[5]Kanamori H,Heaton T.Geophysical monograph,2000,120:147
[6]Brodsky E,Kanamori H.J.Geophys.Res.,2001,106:16357
[7]Ma K F,Brodsky E E,Mori Jet al.Geophys.Res.Lett.,2003,30:1244
[8]Ma K F,Tanaka H,Song S Ret al.Nature,2006,444:473
[9]Tanaka H,Wang C Y,Chen W Met al.Terr.Atmos.Ocean.,2002,113:227
[10]Wang C Y,Li C L,Yen HY.Geophys.Res.Lett.,2002,29:1790
[11]Tanaka H,Chen W M,Wang C Yet al.Geophys.Res.Lett.,2006,33:L16316
[12]Tanaka H,Chen W M,Kawabata Ket al.Geophys.Res.Lett.,2007,34:L01309
[13]Kano Y,Mori J,Fujio Ret al.Geophys.Res.Lett.,2006,33:L14306
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