不同产状断层错动的地表重力变化和形变

根据点源位错引起的地表重力变化和形变的理论公式,应用数值算法求得半无限空间任意产状断层位错在地表的重力变化和形变．计算结果表明,产状和位错方式是决定断层的地表重力和形变效应的基本因素．铲式断层活动的地表重力和形变效应与矩形断层相比有显著差异．断层位错引起的重力变化、垂直形变、视垂直形变的图象特征相似．根据重力变化和形变的特殊图象特征,有可能从观测资料中提取断层活动引起的重力变化和形变信息,判识和估计发震断层的几何学和运动学特征．      

鲜水河断裂带形变累积率及其效能评价

对沿鲜水河断裂带布设的跨断层形变测点水平形变和垂直形变累积率进行了计算,根据结果分析了该断裂带及其附近区域发生中强地震前的变化特征并对其进行效能评价.其结果表明：在鲜水河断裂带上每次地震前震源体附近断层都有一个形变累积率绝对值减小过程;沿鲜水河断裂带如果形变累积率出现低值异常,则未来1～1.5年左右的时间内其附近区域100～300 km范围内将有5.0级以上地震发生的可能;且垂直形变累积率预报效能优于水平形变。     

运用InSAR技术解算四川长宁MS6.0地震三维形变场及时间序列形变分析

运用升、降轨Sentinel-1A 卫星的差分干涉影像,获取2019-06-17四川宜宾长宁 MS6．0地震的三维同震形变场.在此基础上,以升降轨同震形变数据为约束条件,基于 Okada弹性半空间位错模型反演得到发震断层符合走滑和逆冲特征,断层破裂尺度约为15km×20km,断层滑动角为 44．37°,断层倾角为56．42°,震源深度约为10．2km,矩震级为 M W5．8.最后,采用SBAS-InSAR 技术获取该地区2019-04-05至2019-08-03各时间段的累计形变,结果认为该区域在震前近场形变波动较小,震后一段时间累积形变增长,分析原因可能是余震分布使得地表变化处于不稳定状态.通过与已有研究文献的比较和对该区域断层构造的分析,推测此次长宁地震发震断层由反演出的断层滑动引起,滑动面上缘接近地表,主震引起的次级断层活动触发短期内强余震频发.     

基于InSAR的青海大柴旦地震三维同震形变场获取与震源特征分析

本文利用Envisat ASAR的升、降轨和宽幅数据,通过基于先验知识的最小二乘迭代逼近获取大柴旦2次地震的地表三维同震形变.结果表明,2008年MW6.3地震垂直向形变主要发生在断层南盘,以隆升形变为主,最大隆升量约10cm,北盘沉降量小于等于-1cm.东西向形变在南盘呈向东运动的特征,最大运动量约4cm,北盘向西运动,最大运动量约为-2cm.2009年MW5.8地震垂直向形变显示断层南盘抬升的特征,最大抬升量约27cm,北盘最大沉降量约-3cm.东西向形变表现为南盘向东运动,最大约10cm,北盘向西运动,约为-4cm.可以看出这两次地震均表现为逆冲为主,兼少量左旋走滑的震源特征.视线向结果无法判定同震形变的少量走滑特征,而地表三维分量可以有效地识别出少量左旋还是右旋走滑的震源特性.本文以视线向、垂直向、东西向形变量作为约束条件,利用Okada模型正演了2008年地震同震三维形变场.结果显示,采用逆冲兼少量左旋走滑的发震断层参数,视线向、垂直向、东西向正演结果与观测结果吻合.这也表明采用分解后的地表三维同震形变场可以有效地识别出发震断层的少量左旋走滑特征.     

InSAR技术在青海地区地震中的应用研究

以近年来InSAR技术在地震灾害领域的应用研究为基础,综述了InSAR技术应用于青海地区的研究进展,并利用ALOS PALSAR数据和Sentinel-1A卫星数据对2010年玉树7.1级、2016年门源6.4级、杂多6.2级地震的InSAR数据进行了计算和分析。结果显示:玉树7.1级地震和门源6.4级地震地表形变比较明显。其中,玉树7.1级地震地表形变长轴达60 km,门源6.4级地震地表形变长轴达30 km,杂多6.2级地震地表形变比较模糊,长轴约10 km;干涉条纹与震级、震源深度以及震源机制解性质等都有着明显的相关性,不同性质的地震断层引起的地震破裂在干涉图上呈现出各自不同的特点。     

唐山地震后发震断层和周围地区的地壳形变

介绍了设于唐山地震发震断层地表裂缝的形变台站，在地震后18年间观测到的断层形变．结果表明，发震断层的垂直和水平形变都集中在大震之后的7年之内；1983年是震后形变的转折期．大面积水准显示的形变与断层形变强度定性相符，目前呈现出不易于积累应力的松弛状态，近期不大可能发生较强地震．      

根据地面形变的观测研究1966年邢台地震的震源过程

本文以完整的形式给出拉梅常数不相等情形的半无限弹性介质中任意倾角的矩形滑动断层引起的地震位移场解析表示式。以一些数值结果说明介质的泊松比、断层面的倾角、上界和下界对地面的地震位移场的影响。在比较1966年邢台地震的地形变资料和计算得到的各种走向、倾向、倾角、断层面长度、宽度、震源深度和错距的单个的矩形滑动断层引起的地面位移之后指出,简单的滑动断层错动模式不能同时很好地解释观测到的邢台地震的水平和垂直形变。为了解释观测结果,提出了一个复合的断层模式。这个复合断层模式由六个简单的矩形滑动断层构成。运用网格尝试法,得到了基本上符合观测到的水平和垂直位移场的震源参数。     

芦山MS7.0地震前远、 近场形变 时空演化特征研究

应用芦山M_S7.0地震震中附近跨断层及连续形变观测资料, 分析了芦山地震前不同阶段地形变变化的特点, 讨论了震中附近区域异常时空演化过程. 结果表明: ① 自2013年1月起, 沿鲜水河断裂带一些跨断层基线观测到显著的加速转折变化, 沿安宁河、 则木河断裂带个别场地的跨断层水准基线, 2010年以来出现的巨幅异常等是突出的场兆变化; 沿龙门山断裂带一些水准观测在汶川M_S8.0地震后持续的调整变化具有近震源区变形特征. ② 鲜水河、 龙门山和安宁河3条主要断裂围成的三叉口地区, 地倾斜、 应变、 重力及断层水准和蠕变观测临震前均未有显著的异常变化, GPS水平、 垂直位移年速率最小, 该地区是形变变化或形变异常分布的“空区”. ③ 在对近场与远场多种连续形变数据通过傅里叶变换提取年周期成分后发现, 临震前2—3年近震源区域的地倾斜、 重力年变化幅度不是增大, 而是减小. 芦山M_S7.0地震前观测到的形变前兆现象特征与汶川M_S8.0地震等震前的前兆现象较为接近. 因此, 芦山地震前近震源区及外围形变异常分布特征不是个别的现象.      

1679年三河—平谷大震的地震断裂带

历史的和现今的强震研究事实表明,凡震级大于6(1/2)的地震均会在地表产生明显的错动和变形。对于伴随地震形成的地表形变带的研究,尤其是对地震断层的研究具有重要的意义,因为地震断层可将震源机制、地壳形变、断裂     

2013年芦山MS7.0地震序列断层结构及震源区应力场特征

使用芦山地震序列2013年4月20日至5月20日一个月的地震震相数据和M_S4.0以上地震的波形数据, 通过双差定位方法得到了3398个地震的精定位结果, 利用时间域全波形反演方法得到17个地震的矩张量解。 综合分析地震双差定位结果和芦山地震序列中强地震震源机制解, 发现芦山地震发震构造由主震断层和次级反冲断层组成, 主震断层为一走向北东、 倾向北西、 倾角约为45°的高角度逆冲断层, 次级反冲断层与主震断层走向相同, 倾向相反, 两条断层均未出露地表。 主震和余震震源机制解均为逆冲型, 几乎没有走滑分量。 震源区主压应力方位为北西向, 与发震断层走向近乎垂直。     

The research on relationship between wavelet transform on vertical deformation and moderate earthquakes in hexi region, Gansu Province

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Study of dislocation model and evolution characteristics of vertical deformation field of gonghe M S=6.9 earthquake

The preliminary research results of vertical deformation dislocation model of GongheM _S =6.9 earthquake show that, the causative structure is a hidden fault with strike N60°W, dipping S47°W, which lies near the current subsidence center of Gonghe basin. The rupture length and width are 30km and 14km, the upper and lower bound depth of the fault in width direction are 3km and 17km respectively. The maximum coseismic and preseismic vertical deformation of GongheM _S =6.9 earthquake are 247mm and about 100mm. The reasons why there existed rapid postseismic uplift are also given a tentative discussion. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 289–295, 1993.     

The North-South Seismic Belt:Vertical Deformation Velocity Gradient Research

The vertical deformation gradient can reflect the rate of vertical change in unit distance, and the vertical deformation velocity gradient can reflect the strength of the earth''s crust tectonic activities. In this paper, using long period leveling data combined with GPS data, the vertical deformation gradient values are calculated. Leveling data and GPS data are two different means of monitoring deformation, but the result is approximately the same vertical deformation gradient. The results show that the spatial distribution of the vertical deformation velocity gradient and tectonic distribution has an obvious correlation. The most significant gradient anomalies along the North-South Seismic Belt are Xianshuihe fault, Longmenshan fault and Xiaojiang-Zemuhe fault, while the second gradient anomalies in the northeastern Qinghai-Tibetan plateau are Zhuanglanghe fault and Lenglongling fault. The Menyuan M_S6.4 earthquake in 2016 occurred in this abnormal area. However, according to the vertical deformation high gradient area distribution, there is also the possibility of an earthquake occurrence in the Tianzhu and Jingtai area. The area of convergence of three major fault zones is the strongest tectonically active region of the North-South Seismic Belt.     

Experimental examination on the heterogeneity parameter C v of earthquake precursors

Two rock samples with different structures and materials were deformed under a biaxial loading system, and multipoint strain measurements were performed for each sample. The distribution of strain anomalies during the deformation and the instability process were analyzed by using C _v value put forward by WANG Xiao-qing and CHEN Xue-zhong, et al, a parameter to describe the heterogeneous distribution of earthquake precursors, so as to examine the method of C _v value and to explore its physical meaning experimentally. The result shows that the change of C _v value is correlated to the change of deformation characteristics and is an effective parameter to describe the heterogeneity of precursor distribution. C _v value increases firstly and then decreases before the instability, and the instability occurs when C _v value decreases to the level before increasing. This indicates that C _v value may be a useful parameter for earthquake prediction. Foundation item: Chinese Joint Earthquake Sciences Foundation (9507435).     

Effective relaxation time and viscosity of the earth inferred from the postseismic vertical deformations of the 1990 M S=7.0 Gonghe earthquake

The postseismic vertical deformation rates of the 1990 Gonghe M _S=7.0 earthquake appears to have decreased exponentially. Based on Okada’s coseismic surface displacement solution caused by a uniform fault slip in an elastic homogeneous half space, we derived its postseismic surface displacement by using a single-layer standard linear solid model, and further derived a simplified formula for determining the effective relaxation time and viscosity of the earth, which is independent of the dislocation parameters of the causative fault. From the postseismic vertical deformation of the 1990 Gonghe earthquake, we inferred that the effective relaxation time defined by τ=η/μ is 2.6 years, and the effective viscosity η is about 10¹⁸ Pa · s. This work was supported by Chinese Joint Seismological Science Foundation under the grants 92088 and 196098.     

Response of vertical deformation on faults to remote strong earthquakes

Vertical coseismic deformation on non-causative fault caused by remote strong earthquakes(epicentral distance≥1500 km,MS≥7.0)are observed by fault-monitoring instruments of new type during recent two years.The monitor-ing result shows,delay time,maximum amplitude and duration of vertical deformation on the non-causative faulthave remarkable close relationship with earthquakes magnitude and epicentral distance.The delay time of verticalcoseismic deformation have positive linear relationship with epicentral distance.The velocity of coseismic defor-mation is 5.5 km/s,close to the velocity of surface wave in granite.The logarithms of maximum amplitude of co-seismic deformation and epicentral distance have remarkable linear relationship with magnitude.The greater themagnitude and the closer the epicentral distance are,the bigger the maximum amplitude of coseismic deformationon non-causative fault will be.Relative to the epicentral distance,the magnitude is the most important factor to theduration of coseismic vertical deformation on the non-causative fault.Stronger earthquake causes longer vibrationduration of coseismic deformation.The experiential equation of co-seismic deformation faults obtained by thiswork is significant on the coseismic deformation research.     

GPS测定的四川九寨沟MW6.6地震同震形变

2017年8月8日四川阿坝州九寨沟发生M_W6.6地震,震源机制解显示该地震为左旋走滑型地震。对震中周围的GPS连续站观测资料进行处理,获得高频GPS动态形变和静态同震水平位移。震中100km范围内四川松潘和甘肃武都站观测到1 Hz动态形变。距离震中约69km的松潘站观测的同震水平位移为7.4mm。根据少量的GPS静态同震位移反演的同震破裂模型显示本次地震的最大滑动量为376mm,地震矩为7.25×1018 N·m,等效矩震级为M_W6.6。正演计算的同震三维形变场显示本次地震的最大水平位移可达4~5cm,垂直位移呈四象限分布,最大可达1.5cm,区域内10个流动GPS站可观测到同震形变。     

九寨沟MS7.0地震前地磁异常

分析距离九寨沟M_S7.0地震震中分别为65 km、254 km和238 km的松潘地磁台、成都地磁台和天水地磁台2017年连续观测结果,发现九寨沟地震前,松潘地磁台出现异常变化,主要表现为2017年5月开始,松潘地磁台长时间垂直分量累积变化量达40 nT。短时间内也存在地磁场突变,最高可达10 nT,而成都地磁台和天水地磁台地磁场无明显异常。通过对观测数据的详细检查发现松潘地磁台很多观测日的最后一个观测值与后一观测日的第一个观测值相差超过1 nT,因此认为九寨沟地震前观测数据的异常是由观测系统异常导致。对三个台站地磁场垂直分量日变化的统计分析发现垂直分量在不同时段相关性保持一致,说明地震前短时间内不存在地磁垂直分量的明显异常变化,三个台站地磁场日变化的差异是由地下介质性质不同导致。岩石圈磁场在震中西侧区域出现正负异常交替现象,这可能与九寨沟地震的孕育有关。     

Inversion of normal moveout for monoclinic media1

Multiple vertical fracture sets, possibly combined with horizontal fine layering, produce an equivalent medium of monoclinic symmetry with a horizontal symmetry plane. Although monoclinic models may be rather common for fractured formations, they have hardly been used in seismic methods of fracture detection due to the large number of independent elements in the stiffness tensor. Here, we show that multicomponent wide-azimuth reflection data (combined with known vertical velocity or reflector depth) or multi-azimuth walkaway VSP surveys provide enough information to invert for all but one anisotropic parameters of monoclinic media. In order to facilitate the inversion procedure, we introduce a Thomsen-style parametrization for monoclinic media that includes the vertical velocities of the P-wave and one of the split S-waves and a set of dimensionless anisotropic coefficients. Our notation, defined for the coordinate frame associated with the polarization directions of the vertically propagating shear waves, captures the combinations of the stiffnesses responsible for the normal-moveout (NMO) ellipses of all three pure modes. The first group of the anisotropic parameters contains seven coefficients (ε^(1,2), δ^(1,2,3) and γ^(1,2)) analogous to those defined by Tsvankin for the higher-symmetry orthorhombic model. The parameters ε^(1,2), δ^(1,2) and γ^(1,2) are primarily responsible for the pure-mode NMO velocities along the coordinate axes x₁ and x₂ (i.e. in the shear-wave polarization directions). The remaining coefficient δ⁽³⁾ is not constrained by conventional-spread reflection traveltimes in a horizontal monoclinic layer. The second parameter group consists of the newly introduced coefficients ζ^(1,2,3) which control the rotation of the P-, S₁- and S₂-wave NMO ellipses with respect to the horizontal coordinate axes. Misalignment of the P-wave NMO ellipse and shear-wave polarization directions was recently observed on field data by Pérez et al. Our parameter-estimation algorithm, based on NMO equations valid for any strength of the anisotropy, is designed to obtain anisotropic parameters of monoclinic media by inverting the vertical velocities and NMO ellipses of the P-, S₁- and S₂-waves. A Dix-type representation of the NMO velocity of mode-converted waves makes it possible to replace the pure shear modes in reflection surveys with the PS₁- and PS₂-waves. Numerical tests show that our method yields stable estimates of all relevant parameters for both a single layer and a horizontally stratified monoclinic medium.     

Styles of volcano-induced deformation: numerical models of substratum flexure, spreading and extrusion

The gravitational deformation of volcanoes is largely controlled by ductile layers of substrata. Using numerical finite-element modelling we investigate the role of ductile layer thickness and viscosity on such deformation. To characterise the deformation we introduce two dimensionless ratios; Π_a (volcano radius/ductile layer thickness) and Π_b (viscosity of ductile substratum/failure strength of volcano). We find that the volcanic edifice spreads laterally when underlain by thin ductile layers (Π_a>1), while thicker ductile layers lead to inward flexure (Π_a<1). The deformation style is related to the switch from predominantly horizontal to vertical flow in the ductile layer with increasing thickness (increasing Π_a). Structures produced by lateral spreading include concentric thrust belts around the volcano base and radial normal faulting in the cone itself. In contrast, flexure on thick ductile substrata leads to concentric normal faults around the base and compression in the cone. In addition, we show that lower viscosities in the ductile layer (low Π_b) lead to faster rates of movement, and also affect the deformation style. Considering a thin ductile layer, if viscosity is high compared to the failure strength of the volcano (high Π_b) then deformation is coupled and spreading is produced. However, if the viscosity is low (low Π_b) substratum is effectively decoupled from the volcano and extrudes from underneath it. In this latter case evidence is likely to be found for basement compression, but corresponding spreading features in the volcano will be absent, as the cone is subject to a compressive stress regime similar to that produced by flexure. At volcanoes where basement extrusion is operating, high volcano stresses and outward substratum movement may combine to produce catastrophic sector collapse. An analysis of deformation features at a volcano can provide information about the type of basement below it, a useful tool for remote sensing and planetary geology. Also, knowledge of substratum geology can be used to predict styles of deformation operating at volcanoes, where features have not yet become well developed, or are obscured.