俯冲带深部应力场的二维粘弹性有限元数值模拟
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摘要
基于粘弹性平面应变有限元数值模拟方法 ,研究了俯冲带深部的应力场特征 .当根据Karato等的研究结果给出俯冲板块的粘度结构时 ,橄榄石—尖晶石相变界面以下中心低粘区两侧出现应力集中区 ,而且其主压应力方向沿俯冲方向走向 .其特征与已有的深源地震主压应力方向沿俯冲方向及深源地震有两个条带的地震观测结果相吻合 .相变过渡区因矿物更小的颗粒粒度而导致的更小的等效粘度对俯冲带深部应力场的影响不大 ;存在和不存在亚稳态橄榄石楔的情况下 ,橄榄石—尖晶石相变过渡区附近都有最大剪应力的最大值出现 ,而其主压应力方向有垂直于橄榄石—尖晶石相变过渡区走向的趋势 ,尚与地震观测资料不符
Using a 2-D plain strain viscoelastic FEM code, we study the characteristics of the stress fields in deep subducting slabs. There are maxima of shear stress at the transition region from olivine to spinel, the direction of the maximum compressional stress of which is roughly along the trend of the phase boundary. When we introduce the new rheology structure given by Karato et al into our computation, two new maxima of shear stress appear just below the olivine-spinel transition zone, which encompass the low viscosity zone below the tip of metastable wedge. It is needed to mention that the directions of the maximum compressional stress of these two regions are all along the dip direction of the subducting slab. This new feature of stress state in the subducting slab reveals a new way to explain the deep seismicity.
Using a 2-D plain strain viscoelastic FEM code, we study the characteristics of the stress fields in deep subducting slabs. There are maxima of shear stress at the transition region from olivine to spinel, the direction of the maximum compressional stress of which is roughly along the trend of the phase boundary. When we introduce the new rheology structure given by Karato et al into our computation, two new maxima of shear stress appear just below the olivine-spinel transition zone, which encompass the low viscosity zone below the tip of metastable wedge. It is needed to mention that the directions of the maximum compressional stress of these two regions are all along the dip direction of the subducting slab. This new feature of stress state in the subducting slab reveals a new way to explain the deep seismicity.
引文
毛兴华,刘亚静,叶国扬,等.2002.俯冲带深部应力场的二维弹性有限元数值模拟[J].地震学报,24(3):
宁杰远,臧绍先.1987.日本本州北部至中国东北地震的深度分布及其应力状态[J].地震地质,9(1):49～61
臧绍先,宁杰远,许立忠.1989.琉球岛弧地区地震分布,Benioff带形态及应力状态[J].地震学报,11(2):113～123
臧绍先,吴忠良,宁杰远.1992.日本海—鄂霍次克海下俯冲带的应力状态及其深部形变[J].地球物理学报,35(5):560～573
臧绍先,宁杰远.1996.西太平洋俯冲带研究及其动力学意义[J].地球物理学报,39(2):188～202
臧绍先,宁杰远,景志成.2001.俯冲带流变性质的研究[J].中国科学(D辑),31(9):705～711
BinaC R.1997.Patterns of deep seismicity reflect buoyancy stresses due to phase transitions[J].GeophysResLett,24:3301～3304
DaviesG F.1980.Mechanics of subducted lithosphere[J].J GeophysRes,85:6304～6318
DevauxJP,FleitoutL,SchubertG,etal.2000.Stressesin a subducting slab in the presence of a metastable olivine wedge[J].J GeophysRes,105:13365～13373
FrostH J,AshbyM F.1982.DeformationMechanismMaps[M].Oxford:PergamonPress,168
FurukawaY.1994.Two types of deep seismicity in subduction slabs[J].GeophysResLett,21:1181～1184
GotoK,HamaguchiH,SuzukiZ.1983.Distribution of stressin descending plate in specialreference to intermediate and deepfocusearthquakes;I,Characteristics of thermal stressdistribution[J].TohokuGeophysJ,29:81～105
GotoK,SuzukiZ,HamaguchiH.1987.Stressdistribution due to olivine-spinelphasetransition in descending plateand deep-focusearthquakes[J].J GeophysRes,92:13811～13820
HelffrichG,BrodholtJ.1991.Relationship of deep seismicity to thethermalstructureof subducted lithosphere[J].Nature,353:252～255
IidakaT,FurukawaY.1994.Double seismic zone for deep earthquakes in theIzu-Bonin subduction zone[J].Science,263:1116～1118
IsacksB,MolnarP.1971.Distribution of stressesin the descending lithospherefrom a globalsurvey of focalmechanism solu-tions of mantle earthquakes[J].RevGeophys,9:103～174
JingZ C,NingJY.2001.A coupled computational scheme on thermal and phase structuresof subducting slabs[J].ChinesePhysicsLetters,18:1297～1300
KaratoS,RiedelM R,YuenD A.2001.Rheological structure and deformation of subducted slabs in the mantle transitionzone:implications for mantle circulation and deep earthquakes[J].PhysEarthPlaneInter,127:83～108
KikuchiM,FukaoY.1987.Inversion of long-periodP-waves from great earthquakes along subduction zones[J].Tectono-physics,144:231～247
KirbyS H,SteinS,OkalE A,etal.1996.Metastable mantle phase transformations and deep earthquakes in subductingoceanic lithosphere[J].RevGeophys,34:261～306
MosenfelderJL,MartonF C,RossIIC R,etal.2001.Experimentalconstraintson the depth of olivine metastability in sub-ducting lithospere[J].PhysEarthPlaneInter,127:165～180
RichterF M.1979.Focal mechanisms and seismic energy release of deep and intermediate earthquakes in theTonga-Ker-madec region and their bearing on the depth extent of mantle flow[J].J GeophysRes,84:6783～6795
RiedelM R,KaratoS.1997.Grain-sizeevolution in subducted oceanic lithosphere associated with the olivine-spinel transfor-mation and its effectson rheology[J].EarthPlanetSci,148:27～43
RubieD C.1993.Mechanisms and kineticsof solid statereconstructivephasetransformationsin theEarth′smantle[A].In:LuthR W ed.ShortCourseH andbook onExperimentsatH igh-PressureandApplicationsto theEarth′sMantle,Vol.21[C].Edmonton:MinrealAssociationCanada,247～303
RubieD C,RossC R.1994.Kineticsof the olivine-spinel constraintsand implications for deep slab processes[J].PhysEarthPlanetInter,86:223～241
SungC M,BurnsR G.1976 a.Kinetics of the olivine-spinel transition:implications to deep-focus earthquake genesis[J].EarthPlanetSciLett,32:165～170
SungC M,BurnsR G.1976 b.Kinetics of the high-pressure phase transformations:implications to the evolution of the o-livine-spinel phase transition in the downgoing lithosphere and its consequences on the dynamics of the mantle[J].Tectonophysics,31:1～32
VassiliouM S,HagerB H.1988.Subduction zone earthquakesand stressin slabs[J].PureApplGeophys,128:547～624
WortelM JR,VlaarN J.1988.Subduction zone seismicity and the thermo-mechanical evolution of downgoing lithosphere[J].PureApplGeophys,128:625～659
YoshiokaS,DaesslerR,YuenD A.1997.Stress field associated with metastable phase transitions in descending slabs anddeep-focus earthquakes[J].PhysEarthPlaneInter,104:345～361
宁杰远,臧绍先.1987.日本本州北部至中国东北地震的深度分布及其应力状态[J].地震地质,9(1):49～61
臧绍先,宁杰远,许立忠.1989.琉球岛弧地区地震分布,Benioff带形态及应力状态[J].地震学报,11(2):113～123
臧绍先,吴忠良,宁杰远.1992.日本海—鄂霍次克海下俯冲带的应力状态及其深部形变[J].地球物理学报,35(5):560～573
臧绍先,宁杰远.1996.西太平洋俯冲带研究及其动力学意义[J].地球物理学报,39(2):188～202
臧绍先,宁杰远,景志成.2001.俯冲带流变性质的研究[J].中国科学(D辑),31(9):705～711
BinaC R.1997.Patterns of deep seismicity reflect buoyancy stresses due to phase transitions[J].GeophysResLett,24:3301～3304
DaviesG F.1980.Mechanics of subducted lithosphere[J].J GeophysRes,85:6304～6318
DevauxJP,FleitoutL,SchubertG,etal.2000.Stressesin a subducting slab in the presence of a metastable olivine wedge[J].J GeophysRes,105:13365～13373
FrostH J,AshbyM F.1982.DeformationMechanismMaps[M].Oxford:PergamonPress,168
FurukawaY.1994.Two types of deep seismicity in subduction slabs[J].GeophysResLett,21:1181～1184
GotoK,HamaguchiH,SuzukiZ.1983.Distribution of stressin descending plate in specialreference to intermediate and deepfocusearthquakes;I,Characteristics of thermal stressdistribution[J].TohokuGeophysJ,29:81～105
GotoK,SuzukiZ,HamaguchiH.1987.Stressdistribution due to olivine-spinelphasetransition in descending plateand deep-focusearthquakes[J].J GeophysRes,92:13811～13820
HelffrichG,BrodholtJ.1991.Relationship of deep seismicity to thethermalstructureof subducted lithosphere[J].Nature,353:252～255
IidakaT,FurukawaY.1994.Double seismic zone for deep earthquakes in theIzu-Bonin subduction zone[J].Science,263:1116～1118
IsacksB,MolnarP.1971.Distribution of stressesin the descending lithospherefrom a globalsurvey of focalmechanism solu-tions of mantle earthquakes[J].RevGeophys,9:103～174
JingZ C,NingJY.2001.A coupled computational scheme on thermal and phase structuresof subducting slabs[J].ChinesePhysicsLetters,18:1297～1300
KaratoS,RiedelM R,YuenD A.2001.Rheological structure and deformation of subducted slabs in the mantle transitionzone:implications for mantle circulation and deep earthquakes[J].PhysEarthPlaneInter,127:83～108
KikuchiM,FukaoY.1987.Inversion of long-periodP-waves from great earthquakes along subduction zones[J].Tectono-physics,144:231～247
KirbyS H,SteinS,OkalE A,etal.1996.Metastable mantle phase transformations and deep earthquakes in subductingoceanic lithosphere[J].RevGeophys,34:261～306
MosenfelderJL,MartonF C,RossIIC R,etal.2001.Experimentalconstraintson the depth of olivine metastability in sub-ducting lithospere[J].PhysEarthPlaneInter,127:165～180
RichterF M.1979.Focal mechanisms and seismic energy release of deep and intermediate earthquakes in theTonga-Ker-madec region and their bearing on the depth extent of mantle flow[J].J GeophysRes,84:6783～6795
RiedelM R,KaratoS.1997.Grain-sizeevolution in subducted oceanic lithosphere associated with the olivine-spinel transfor-mation and its effectson rheology[J].EarthPlanetSci,148:27～43
RubieD C.1993.Mechanisms and kineticsof solid statereconstructivephasetransformationsin theEarth′smantle[A].In:LuthR W ed.ShortCourseH andbook onExperimentsatH igh-PressureandApplicationsto theEarth′sMantle,Vol.21[C].Edmonton:MinrealAssociationCanada,247～303
RubieD C,RossC R.1994.Kineticsof the olivine-spinel constraintsand implications for deep slab processes[J].PhysEarthPlanetInter,86:223～241
SungC M,BurnsR G.1976 a.Kinetics of the olivine-spinel transition:implications to deep-focus earthquake genesis[J].EarthPlanetSciLett,32:165～170
SungC M,BurnsR G.1976 b.Kinetics of the high-pressure phase transformations:implications to the evolution of the o-livine-spinel phase transition in the downgoing lithosphere and its consequences on the dynamics of the mantle[J].Tectonophysics,31:1～32
VassiliouM S,HagerB H.1988.Subduction zone earthquakesand stressin slabs[J].PureApplGeophys,128:547～624
WortelM JR,VlaarN J.1988.Subduction zone seismicity and the thermo-mechanical evolution of downgoing lithosphere[J].PureApplGeophys,128:625～659
YoshiokaS,DaesslerR,YuenD A.1997.Stress field associated with metastable phase transitions in descending slabs anddeep-focus earthquakes[J].PhysEarthPlaneInter,104:345～361
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