“帕克菲尔德圣安德烈斯断层深部探测计划”——井下主动源监测中观测到的震前波速变化
摘要
测量活动地震断裂带内的应力变化是地震学的长期努力目标。途径之一是探测地震波速度的应力依赖性。在"圣安德烈斯断层深部探测计划"主动源钻井试验中,我们探测了波速随应力的变化。文中认为应用该技术的确可以测量应力变化。在两个多月的试验中,观测到剪切波沿固定路径上的传播时间(几个毫秒)与气压变化之间呈现出很好的负相关性。我们还观测到两处明显的走时偏离异常,与观测期间发生的两次地震事件密切相关,而这两次地震均在SAFOD产生了较大的同震应力变化。走时异常分别发生在两次地震事件的前10h和前2h,可能与早期实验室研究发现的破裂前应力导致的裂纹特性变化有关[1,2]。
引文
[1]Brace W F,Paulding B W,Scholz C H.Dilatancy in the fracture of crystalline rocks.J.Geophys.Res.,1966,71:3939-3953
[2]Scholz C H.Microfracturing and the inelastic deformation of rock I:Compression.J.Geophys.Res.,1968,73:1417-1432
[3]Birch F.The velocity of compressional waves in rocks to10kilobars,part1.J.Geophys.Res.,1960,65:1083-1102
[4]Birch F.The velocity of compressional waves in rocks to10kilobars,part2.J.Geophys.Res.,1961,66:2199-2224
[5]Nur A and Simmons G.The effect of saturation on velocity in low porosity rocks.Earth Planet.Sci.Lett.,1969(7):183-193
[6]Walsh J B.The effect of cracks on the compressibility of rock.J.Geophys.Res.,1965,70:381-389
[7]Nur A.Effects of stress on velocity anisotropy in rocks with cracks.J.Geophys.Res.,1971,76:2022-2034
[8]O’Connell R J and Budiansky B.Seismic velocities in dry and saturated cracked solids.J.Geophys.Res.,1974,79:5412-5426
[9]De Fazio TL,Aki Kand Alba,J.Solid earth tide and observed change in the in situ seismic velocity.J.Geo-phys.Res.,1973,78:1319-1322
[10]Reasenberg P and Aki K.A precise,continuous measurement of seismic velocity for monitoring in situ stress.J.Geophys.Res.,1974,79:399-406
[11]Leary P C,Malin P E,Phinny R A,et al.Systematic monitoring of millisecond traveltime variations near Palmdale,California.J.Geophys.Res.,1979,84:659-666
[12]Yamamura K.Long-term observation of in situ seismic velocity and attenuation.J.Geophys.Res.,2003,108:doi:10.1029/2002JB002005
[13]Silver P G,Daley TM,Niu F et al.Active source monitoring of crosswell seismic traveltime for stress-in-duced changes.Bull.Seismol.Soc.Am.,2007,97:281-293
[14]Aki K,Richards P G.Quantitative Seismology(Freeman,New York,1980)
[15]Abercrombie R E.Earthquake source scaling relationships from21to5MLusing seismogramsrecorded at2.5-kmdepth.J.Geophys.Res.,1995,100:24015-24036
[16]Rubin A M,Gillard D.Aftershock asymmetry/rupture directivity among central San Andreas fault microearth-quakes.J.Geophys.Res.,2000,105:19095-19109
[17]Segall P,Jonsson S,Agustsson K.When is the strain in the meter the same as the strain in the rock?Geo-phys.Res.Lett,2003,30:doi:10.1029/2003GL017995
[18]Unsworth M,Bedrosian P,Eisel M,et al.Along strike variations in the electrical structure of the San Andreas Fault at Parkfield,California.Geophys.Res.Lett.,2000,27:3021-3024
[2]Scholz C H.Microfracturing and the inelastic deformation of rock I:Compression.J.Geophys.Res.,1968,73:1417-1432
[3]Birch F.The velocity of compressional waves in rocks to10kilobars,part1.J.Geophys.Res.,1960,65:1083-1102
[4]Birch F.The velocity of compressional waves in rocks to10kilobars,part2.J.Geophys.Res.,1961,66:2199-2224
[5]Nur A and Simmons G.The effect of saturation on velocity in low porosity rocks.Earth Planet.Sci.Lett.,1969(7):183-193
[6]Walsh J B.The effect of cracks on the compressibility of rock.J.Geophys.Res.,1965,70:381-389
[7]Nur A.Effects of stress on velocity anisotropy in rocks with cracks.J.Geophys.Res.,1971,76:2022-2034
[8]O’Connell R J and Budiansky B.Seismic velocities in dry and saturated cracked solids.J.Geophys.Res.,1974,79:5412-5426
[9]De Fazio TL,Aki Kand Alba,J.Solid earth tide and observed change in the in situ seismic velocity.J.Geo-phys.Res.,1973,78:1319-1322
[10]Reasenberg P and Aki K.A precise,continuous measurement of seismic velocity for monitoring in situ stress.J.Geophys.Res.,1974,79:399-406
[11]Leary P C,Malin P E,Phinny R A,et al.Systematic monitoring of millisecond traveltime variations near Palmdale,California.J.Geophys.Res.,1979,84:659-666
[12]Yamamura K.Long-term observation of in situ seismic velocity and attenuation.J.Geophys.Res.,2003,108:doi:10.1029/2002JB002005
[13]Silver P G,Daley TM,Niu F et al.Active source monitoring of crosswell seismic traveltime for stress-in-duced changes.Bull.Seismol.Soc.Am.,2007,97:281-293
[14]Aki K,Richards P G.Quantitative Seismology(Freeman,New York,1980)
[15]Abercrombie R E.Earthquake source scaling relationships from21to5MLusing seismogramsrecorded at2.5-kmdepth.J.Geophys.Res.,1995,100:24015-24036
[16]Rubin A M,Gillard D.Aftershock asymmetry/rupture directivity among central San Andreas fault microearth-quakes.J.Geophys.Res.,2000,105:19095-19109
[17]Segall P,Jonsson S,Agustsson K.When is the strain in the meter the same as the strain in the rock?Geo-phys.Res.Lett,2003,30:doi:10.1029/2003GL017995
[18]Unsworth M,Bedrosian P,Eisel M,et al.Along strike variations in the electrical structure of the San Andreas Fault at Parkfield,California.Geophys.Res.Lett.,2000,27:3021-3024
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