Physical background on estimating bvalue

ＰｈｙｓｉｃａｌｂａｃｋｇｒｏｕｎｄｏｎｅｓｔｉｍａｔｉｎｇｂｖａｌｕｅＷＥＩＱＩＯＮＧＨＵＡＮＧ（黄玮琼）ＷＥＮＸＩＡＮＧＬＩ（李文香）ＩｎｓｔｉｔｕｔｅｏｆＧｅｏｐｈｙｓｉｃｓ，ＳｔａｔｅＳｅｉｓｍｏｌｏｇｉｃａｌＢｕｒｅａｕ，Ｂｅｉｊｉｎ...     

StudyofCurieisothermalsurfaceinSichuanBasinandtheseismicareaonitswesternmar┐gin

ＳｔｕｄｙｏｆＣｕｒｉｅｉｓｏｔｈｅｒｍａｌｓｕｒｆａｃｅｉｎＳｉｃｈｕａｎＢａｓｉｎａｎｄｔｈｅｓｅｉｓｍｉｃａｒｅａｏｎｉｔｓｗｅｓｔｅｒｎｍａｒ┐ｇｉｎＸＩＡＮＺＨＡＮＧ（张先），ＸＩ－ＦＥＮＧＨＵ（虎喜凤），ＪＩＮＧ－ＸＩＵＳＨＥＮ（沈京秀...     

The numerical method of Fourier eigen transform and its application in seismicity analysis

ＴｈｅｎｕｍｅｒｉｃａｌｍｅｔｈｏｄｏｆＦｏｕｒｉｅｒｅｉｇｅｎｔｒａｎｓｆｏｒｍａｎｄｉｔｓａｐｐｌｉｃａｔｉｏｎｉｎｓｅｉｓｍｉｃｉｔｙａｎａｌｙｓｉｓＢＩＮＧＣＨＥＮ１）（陈兵）ＺＨＩ－ＺＨＥＮＺＨＥＮＧ２）（郑治真）ＺＡＩ－ＳＥＮＪＩＡＮＧ...     

Ambient tectonic shear stress field in Southern California and seismic hazard regions

ＡｍｂｉｅｎｔｔｅｃｔｏｎｉｃｓｈｅａｒｓｔｒｅｓｆｉｅｌｄｉｎＳｏｕｔｈｅｒｎＣａｌｉｆｏｒｎｉａａｎｄｓｅｉｓｍｉｃｈａｚａｒｄｒｅｇｉｏｎｓＰＥＩＳＨＡＮＣＨＥＮ（陈培善）ＬＥＩＸＩＡＯ（肖磊）ＴＯＮＧＸＩＡＢＡＩ（白彤霞）ＪＩＮＣＨ...     

Effects of magnitude accuracy and complete－ness data on seismic hazard parameters

Ｅｆｆｅｃｔｓｏｆｍａｇｎｉｔｕｄｅａｃｃｕｒａｃｙａｎｄｃｏｍｐｌｅｔｅ┐ｎｅｓｄａｔａｏｎｓｅｉｓｍｉｃｈａｚａｒｄｐａｒａｍｅｔｅｒｓＨＵＩ－ＣＨＥＮＧＳＨＡＯ（邵辉成），ＪＩＡ－ＳＨＵＸＩＥ（谢家树），ＰＩＮＧＷＡＮＧ（王平）ａｎｄＹＡ－Ｘ...     

Fractal research of fault gouge

ＦｒａｃｔａｌｒｅｓｅａｒｃｈｏｆｆａｕｌｔｇｏｕｇｅＳＨＵＮ－ＭＥＩＳＨＡＯ（邵顺妹）ａｎｄＪＩＮ－ＣＨＡＮＧＺＯＵ（邹瑾敞）ＥａｒｔｈｑｕａｋｅＲｅｓｅａｒｃｈＩｎｓｔｉｔｕｔｅｏｆＬａｎｚｈｏｕ，ＳｔａｔｅＳｅｉｓｍｏｌｏｇｉｃａｌＢｕｒｅａ...     

Epicentral distribution in 1996

Ｅｐｉｃｅｎｔｒａｌｄｉｓｔｒｉｂｕｔｉｏｎｉｎ１９９６ＰＥＩ－ＳＨＡＮＣＨＥＮ（陈培善）ＩｎｓｔｉｔｕｔｅｏｆＧｅｏｐｈｙｓｉｃｓ，ＳｔａｔｅＳｅｉｓｍｏｌｏｇｉｃａｌＢｕｒｅａｕ，Ｂｅｉｊｉｎｇ１０００８１，ＣｈｉｎａＦｏｒｓｈｏｗｉｎｇｔｈｅｅ...     

A two－dimensional earthquake fault modeling with fractal structure strength distribution

Ａｔｗｏ┐ｄｉｍｅｎｓｉｏｎａｌｅａｒｔｈｑｕａｋｅｆａｕｌｔｍｏｄｅｌｉｎｇｗｉｔｈｆｒａｃｔａｌｓｔｒｕｃｔｕｒｅｓｔｒｅｎｇｔｈｄｉｓｔｒｉｂｕｔｉｏｎＸＩＡＮＧ－ＸＩＯＮＧＣＨＥＮ（陈祥熊）ＳｅｉｓｍｏｌｏｇｉｃａｌＢｕｒｅａｕｏｆＦｕｊｉ...     

Study of a 3-D seismic gap

Ｓｔｕｄｙｏｆａ３ＤｓｅｉｓｍｉｃｇａｐＹＵＡＮＱＩＮＧＺＨＵ１）（朱元清）ＣＯＮＧＪＵＮＸＩＡ１）（夏从俊）ＧＥＴＵＺＵＯＬＩ２）（左力格图）ＨＵＩＭＩＮＬＩ１）（李慧民）１）ＳｅｉｓｍｏｌｏｇｉｃａｌＢｕｒｅａｕｏｆＳｈａｎｇｈａｉ，...     

Parameter sensitivity analyses in seismic hazard

Ｐａｒａｍｅｔｅｒｓｅｎｓｉｔｉｖｉｔｙａｎａｌｙｓｅｓｉｎｓｅｉｓｍｉｃｈａｚ┐ａｒｄＪＩＡＮＷＡＮＧ（王健）ａｎｄＭＥＮＧ－ＴＡＮＧＡＯ（高孟潭）ＩｎｓｔｉｔｕｔｅｏｆＧｅｏｐｈｙｓｉｃｓ，ＳｔａｔｅＳｅｉｓｍｏｌｏｇｉｃａｌＢｕｒｅａｕ，Ｂｅ...     

汤加-克马德克俯冲带现今非均匀应力场特征及其动力学意义

汤加-克马德克俯冲带是太平洋板块向澳大利亚板块俯冲碰撞的动力作用区,是全球俯冲带动力学研究的热点区域.本研究基于EHB地震目录,对汤加-克马德克俯冲带(18.5°S-28.5°S)区域进行平面拟合,得到该范围内俯冲带走向约为196°,倾角约为48°;利用该俯冲带研究区域内Global CMT目录,对不同位置、不同深度进行区域应力张量反演,得到汤加-克马德克俯冲带研究区内精细的应力图像.结果显示:(1) 俯冲带浅部(60~300 km)应力结构非均匀特征明显,主应力轴倾伏角变化多样,并且最大主压应力轴方位在24°S左右发生明显偏转,我们推测这可能与洋底构造路易斯维尔海链俯冲有关;(2)中部(300~500 km)最大主压、主张应力轴由北向南逐渐发生偏转,这可能与由北向南流动的地幔流对俯冲板片产生推挤作用有关,并且这种推挤作用向南逐渐减弱;(3)深部(500~700 km)最大主压应力轴沿俯冲方向分布;(4)本文的结果还发现了主俯冲带深部西侧"偏移"板片与主俯冲带应力结构不同,表明"偏移"板片与主俯冲带是分离的.     

智利三联点南部扩张洋脊俯冲区域岩石层热结构的数值模拟

智利三联点（CTJ）位于纳兹卡板块、南极洲板块与南美板块的交界处,由南极洲—纳兹卡板块之间的智利洋脊俯冲到智利海沟而形成.巴塔哥尼亚板片窗的发展是智利洋脊长期扩张俯冲的结果之一.随着纳兹卡板块的不断东向俯冲,纳兹卡板块范围逐渐变小,CTJ同时向北移动.本文采用数值模拟方法,建立了关于洋脊海沟碰撞的简单二维模型,来研究智利三联点南部扩张洋脊俯冲区域岩石层的热结构.模拟结果表明,洋脊的位置、板块相对汇聚速度及上覆大陆板块的存在均对俯冲区域海洋板块的温度结构有着很大影响,并且大陆板块下方海洋板块温度变化最大的位置距洋脊的水平距离与洋脊到板片窗范围的水平距离两者之间具有较好的一致性.同时,当存在两两板块间的相对汇聚时,洋脊右侧大陆板块下表面的温度升高,俯冲带内海洋板块温度接近于地幔温度.纳兹卡板块以7.8 cm·a^-1的速度急速俯冲于南美板块之下的过程中,同时伴随着智利洋脊的持续扩张俯冲,在智利三联点南部,南美板块之下纳兹卡板块的温度因而可以更快地达到地幔软流层的约1300℃温度,并最终消亡于地幔之中.

     

地幔对流对全球岩石圈应力产生与分布的作用

利用动力学模拟方法研究地幔对流对于大尺度岩石圈内部应力场形成的作用. 地幔物质内部的密度横向非均匀及表面板块运动引起地幔流动,并在岩石圈底部产生一个应力场. 该应力场作为面力将造成岩石圈本身变形,从而产生岩石圈内部的应力分布. 模拟计算结果表明,大部分俯冲带及大陆碰撞带区域应力均呈现挤压特征,如环太平洋俯冲带及印度－欧亚碰撞带等;而东太平洋洋脊、大西洋洋脊及东非裂谷处应力状态均表现为拉张;并且绝大多数热点位置处于应力拉张区域,这与目前对全球构造应力状态的理解是一致的. 计算的岩石圈内部最大水平主压应力的方向与观测表现出相当的一致,其结果总体上吻合得较好,然而在局部区域（例如西北太平洋的俯冲带、青藏高原等地区）存在着较大的差异. 研究表明,地幔对流是造成岩石圈内部大尺度应力状态及分布的一个重要因素.     

智利三联点南部含洋脊海洋板块俯冲过程的数值模拟

“三联点”是全球板块运动系统的重要组成部分.扩张的智利洋脊向南美板块俯冲形成了智利三联点,并造成了智利三联点以南数百千米范围内剧烈的地形变化.智利三联点区域的初始板块俯冲角度、洋脊扩张速率等因素的差异对南美板块岩石层热结构及地形起伏造成了显著影响.本文采用有限差分方法,构建了智利三联点区域洋脊俯冲的二维数值模型,模拟洋脊俯冲的动力学过程,探究扩张洋脊俯冲过程中的岩石层变形机制、地表热流的分布特征及其影响因素.结果表明,与俯冲速率相比,俯冲角度对地表热流的影响相对较大,较小俯冲角度（15°）情况下的计算热流分布与基于观测点的插值数据较为吻合,并且俯冲速率越大,上覆板块岩石层温度异常区的水平长度越大,其距海沟的距离最大可至190 km.我们的模拟结果支持智利三联点南部南极洲板块以低角度俯冲至南美大陆板块下方的观点.

     

西太平洋俯冲带的研究及其动力学意义

讨论了西太平洋俯冲带的分布及特征、西太平洋Ｗａｄａｔｉ－Ｂｅｎｉｏｆｆ带的形态及俯冲带上的应力状态及太平洋板块、菲律宾海板块与欧亚板块之间的相互作用；总结了地震层析成像结果；计算了俯冲板块在地幔中引起的Ｐ波速度异常，提出了俯冲板块与６６０ｋｍ间断面相互作用的４种可能；研究了俯冲板块物理性质的变化、俯冲板块产生的负浮力及其影响因素；提出需要开展俯冲带对东亚大陆构造运动和演化的影响、俯冲带相互关系及演化的研究．     

西太平洋俯冲带的研究及其动力学意义

讨论了西太平洋俯冲带的分布及特征、西太平洋Ｗａｄａｔｉ－Ｂｅｎｉｏｆｆ带的形态及俯冲带上的应力状态及太平洋板块、菲律宾海板块与欧亚板块之间的相互作用;总结了地震层析成像结果;计算了俯冲板块在地幔中引起的Ｐ波速度异常,提出了俯冲板块与６６０ｋｍ间断面相互作用的４种可能;研究了俯冲板块物理性质的变化、俯冲板块产生的负浮力及其影响因素;提出需要开展俯冲带对东亚大陆构造运动和演化的影响、俯冲带相互关系及演化的研究．     

Some consequences of the subduction of young slabs

The negative buoyancy force exerted by a subducting oceanic slab depends on its descent velocity, and strongly on its age. For lithosphere close to thermal equilibrium, this force dominates by a large margin the resisting forces arising from friction on the plate boundary and compositional buoyancy. This may result in oceanward migration of the trench, with associated back-arc spreading. However, the strong age dependence of this force, and of the ridge push mean that a horizontal compressive stress is required to continue subduction if changing plate geometry should bring young lithosphere to the trench. Estimates can be made of the slab age, as a function of descent velocity, at which the driving forces are no longer sufficient to overcome a given resisting force. The transition corresponding to a resisting force of 8 × 10¹² N/m divides regions displaying back-arc extensional tectonics from those displaying compressional tectonics. This is in good agreement with other estimates of the forces resisting slab motion. It is suggested that an increase in the width of — or the shear stress on — the plate boundary, associated with the subduction of lithosphere to the buoyant side of this transition, can result in a compressional stress on the overriding plate which is great enough to account for cordilleran tectonics.The proposed reduction in the one of driving forces of plate motion is still consistent with observations, being compensated by the greaterrelative importance of the push from the ridges.     

汕头－吕宋岛岩石圈速度结构与震源构造──台湾浅滩7．3级地震构造之一

汕头－吕宋岛岩石圈速度结构剖面，划分出华南陆缘古生代陆壳、陆架区晚古生代－中生代陆壳、陆坡带中生代－早第三纪过渡壳、新生代南海海盆洋壳及吕宋岛中生代－新生代岛弧陆壳与东吕宋海槽洋壳等地壳构造组分，并确定了上述地壳构造之间的边界断裂构造及其性质。结合地震震源分布及机制，初步确定了华南陆架盆岭构造带北、南两侧地震构造的控震构造与发震构造性质及其震源力学特征；１）指出１９９４年９月１６日台湾浅滩７．３级地震属于板缘壳幔地震及造成一千公里有感范围的原因；２）马尼拉海沟的海底地堑构造与南海海盆岩石圈地幔上隆是马尼拉海沟俯冲带震源显示正断层性质的原因，且为被动的或转换俯冲带；３）东吕宋海槽仍属于菲律宾海俯冲带性质；吕宋岛东西两侧俯冲带岩石圈板片震源深度的准三层分布，可能表明俯冲带岩石圈板片存在相应的低速滑移层。     

Thermal consequences of the formation of a slab window beneath the Mid-Cretaceous southwest Japan arc: A 2-D numerical analysis

Abstract   The development of voluminous granitic magmatism and widespread high-grade metamorphism in Mid-Cretaceous southwest Japan have been explained by the subduction of a spreading ridge (Kula–Pacific or Farallon–Izanagi plate boundaries) beneath the Eurasian continent and the formation of a slab window. In the present study, the thermal consequences of the formation of a slab window beneath a continental margin are evaluated through a 2-D numerical simulation. The model results are evaluated by comparison with the Mid-Cretaceous geology of southwest Japan. Of particular interest are the absence of an amphibolite- to granulite-facies metamorphic belt near the Wadati–Benioff plane, and significant melting of the lower crustal-mafic rocks sufficient to form a large amount of granitic magma. Because none of the model results simultaneously satisfied these two geological interpretations, it is suggested that subduction of plate boundaries in Mid-Cretaceous southwest Japan was not associated with the opening of a slab window. According to previous studies, and the results of the present study, two different tectonic scenarios could reasonably explain the geological interpretations for Mid-Cretaceous southwest Japan: (i) The spreading ridge did not subduct beneath the Eurasian continent, but was located off the continental margin, implying the continuous subduction of very young oceanic lithosphere; (ii) ridge subduction beneath the continental margin occurred after active spreading had ceased. Consequently, in both tectonic scenarios, the subduction of plate boundaries at the Mid-Cretaceous southwest Japan was not associated with a slab window, but very young (hot) oceanic lithosphere.     

A large normal-fault earthquake at the junction of the Tonga trench and the Louisville ridge

The source mechanism of a large (M_s ? 7.2) earthquake that occurred in the oceanic plate at the junction of the Tonga—Kermadec trench systems with the aseismic Louisville ridge is found by inverting long-period vertical-component Rayleigh waves recorded by the IDA network. The solution is an almost-pure normal fault, on a plane striking roughly parallel to the trench axis, with seismic moment of 1.7 × 10²⁷ dyn cm, and thus is among the ten largest documented shallow normal-fault earthquakes. A point-source depth of 20 km for the event is resolved by modeling teleseismic body waves; the actual rupture may have extended deeper, to 30 or 40 km. The earthquake was a multiple event, consisting of two sources separated by 16 s. A rupture velocity of 3.5 km s^?1 is inferred. The earthquake can be interpreted as tensional failure in the shallow portion of the downgoing plate caused by the gravitational pull of the slab. The Louisville ridge may be creating a local degree of decoupling of the oceanic plate from the overriding plate, and/or a zone of extension within the slab, which could enhance the effect of the gravitational forces in the shallower part of the downgoing plate. In particular, the earthquake could be associated with the break-up of the leading seamount of the ridge, which is currently right at the trench. Alternatively, the earthquake may have been caused by stresses associated with the bending of the plate prior to subduction.