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1.
地震波泊松比蕴涵着丰富的地质信息,根据泊松比可以识别地壳岩石的基性程度,进而分析地球动力学与成矿背景。本文搜集整理了国家地震科学数据共享中心等数据平台自20世纪80年代至2017年底的天然地震震相资料,经过数据筛选,得到华南研究区内M≥2.0级地震事件11410个。通过最小二乘法拟合数据的走时-震中距关系直线方程,得到Pg波平均波速6.11 km/s,Sg波平均波速3.60 km/s,首波Pn波平均波速8.06 km/s,Sn波平均波速4.59 km/s。在此基础上,求得华南地壳平均波速比Vp/Vs为1.697,由公式计算得到华南地壳的平均泊松比为0.234,壳幔界面附近的平均波速比Vp/Vs为1.756,计算得到壳幔界面附近的平均泊松比为0.260。走时反演给出的泊松比结果显示扬子地块、华夏地块以及东南沿海地壳的物性差异。华夏地块与扬子地块之间存在大面积的低泊松比异常区,与江南造山带存在良好的对应关系;而东南沿海、钦杭成矿带泊松比明显较高,解释为幔源物质注入地壳的结果。 相似文献
2.
羊场磷矿是近年来在云南评价确认的沉积大型磷矿床,磷矿体赋存于下寒武统梅树村组碳酸盐岩-泥质碎屑岩沉积中部的一套含磷岩系中,呈层状、似层状展布于羊场背斜两翼,其产状与地层产状基本一致,含矿岩性为含磷白云岩、磷质岩、磷块岩、硅质岩建造。通过分析该矿床矿体特征和梅树村组磷块岩的主微量元素组成,研究了羊场磷矿的地球化学特征及其沉积环境。结果表明,羊场磷矿磷块岩具有富钙（w（CaO）=42.07%~45.01%）、磷（w（P2O5）=27.66%~39.25%）和贫硅（w（SiO2）=8.27%~15.40%）的特征;w（P2O5）与w（CaO）呈较好的正相关关系,与w（MgO）呈负相关关系,与w（Al2O3）呈较明显的负相关关系。矿石的w（Th）/w（U）值小于1、Pb （亲硫元素）和Sr富集（Pb平均富集系数16.66,Sr平均富集系数1.17）特征表明,羊场磷矿可能是热水沉积成矿与生物成矿双重作用的结果;微量元素特征值反映,羊场磷矿形成于深海到浅海的变化环境,为海相沉积型磷块岩,沉积时水体呈还原环境。 相似文献
3.
邹家山矿床位于赣杭构造火山岩铀成矿带与大王山-于山花岗岩型铀成矿带的复合叠加部位。矿体产于下白垩统鹅湖岭组上段碎斑熔岩和打鼓顶组上段流纹英安岩中,呈脉状、细脉状,主要受NE向邹家山-石洞断裂带控制。围岩蚀变主要为萤石化、伊利石化、黄铁矿化、绿泥石化、碳酸盐化等。文章通过野外地质调查、地球化学分析、电子探针分析及矿物自动定量分析等方法,对该矿床超常富集铀矿石中Ti的赋存特征展开研究,结果表明,超常富集铀矿石中w（TiO2）和w（U）特征与前人研究的w（TiO2）和w（U）呈非线性正相关的结果不同。超常富集铀矿石中平均w（TiO2）仅是围岩的1.90倍,而平均w（U）却是围岩的565倍,TiO2与U相比富集程度并不高。元素相关性研究发现超常富集铀矿石中w（TiO2）与w（U）呈中度负相关,与易形成络阴离子的F、S、P2O5含量关系不明显,而w（U）与F、S、P2O5含量呈正相关,说明成矿环境中U与Ti物理化学性质差别较大,物质来源可能不同。超常富集铀矿石中Ti主要赋存于钛铀矿中。钛铀矿呈自形-半自形,大小约1~75 μm,大量分布于白云石、铁白云石等边缘。钛铀矿既包裹着早期的沥青铀矿,又被晚期的沥青铀矿包裹。经研究分析认为,铀矿石中Ti主要来源于赋矿围岩中的黑云母蚀变,胶体TiO2矿物对U的强吸附性有利于钛铀矿的形成,并促使U在地球化学障处超常富集。但铀成矿后期,热液中Ti几乎耗尽,钛铀矿不再新增,伴随成矿环境的改变,部分钛铀矿缓慢溶蚀以及被新形成的沥青铀矿交代,引起Ti流失,导致超常富集铀矿石中w（U）与w（TiO2）为中度负相关。 相似文献
4.
破火山内出露的火山岩与浅成侵入岩为硅质岩浆演化研究提供了一个重要窗口，从而备受关注。小雄破火山内的火山-侵入杂岩是中国东南沿海晚白垩世岩浆活动的典型代表，包括小雄组火山岩（K2x）与两类侵入岩（花岗斑岩、正长斑岩）。本文以小雄火山-侵入杂岩为研究对象，开展了系统的锆石U-Pb年代学、岩石学和地球化学研究，旨在深入探讨破火山内火山岩与侵入岩之间的成因联系和岩浆演化过程。系统的LA-ICP-MS 锆石U-Pb年代学研究表明，小雄组火山岩形成于98~88Ma，并具有多期次喷发的特点，可分为下段、中段和上段，年龄分别为98~96Ma（K2x1）、95~92Ma（K2x2）、~ 88Ma（K2x3）。小雄花岗斑岩形成年龄为90Ma；正长斑岩形成稍晚，约88Ma。与下段流纹质玻屑凝灰岩的Nd-Hf同位素组成[εNd（t）=-8.3~-7.2， εHf（t）=-11.8~-7.2]相比，中段流纹岩要更为亏损[εNd（t）=-5.84~-5.32， εHf（t）=-10.1~-0.5]。研究表明，小雄组流纹质火山岩的母岩浆可能起源于发生在深部岩浆房中渐进的壳幔相互作用，中段流纹岩的源区混入了更多的亏损幔源组分。中段流纹岩与花岗斑岩具有相似的Nd-Hf同位素组成，以及 "互补"的微量元素地球化学特征，由发生在浅部岩浆房的分离结晶作用和堆晶作用所制约。值得注意的是，正长斑岩与花岗斑岩并不存在直接的成因演化关系，两者应是不同的起源。不同的正长斑岩岩株具有高度一致的结晶年龄、微量元素特征以及Nd-Hf同位素组成，以上特征均表明小雄破火山内的正长斑岩具有相同的起源。正长斑岩母岩浆起源于富集岩石圈地幔的部分熔融，岩浆源区混入了来自亏损的软流圈地幔组分，其地球化学成分变化主要受"普通辉石+磷灰石+钛铁矿"的分离结晶所控制。 相似文献
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闪叶石族矿物是富含Sr、Na、Ca和Ba等的钛硅酸盐矿物的总称,迄今共有19个矿物种,其中的氟闪叶石矿物首次发现于巴西Serrote山碱性岩中。本文利用电子探针和X射线衍射仪等分析测试手段,从化学成分和晶体结构等方面对产出于中国辽宁赛马碱性岩体中的闪叶石族矿物进行了详细的矿物学特征研究,发现其中常呈柱状、针状和纤维状集合体产出的闪叶石的晶体化学式为(Sr1.00Na1.00)Σ2.00Ti2(Na1.98Sr0.33Mn0.26K0.12Mg0.10Ca0.09Ba0.05)Σ2.93(Ti0.69Fe3+0.33Al0.02)Σ1.04(Si3.80O14) O2(F1.16OH0.84)Σ2.00,属于单斜晶系,空间群为C2/m,晶胞参数a=19.271 9(8) Å,b=7.077 9(3) Å, c=5.388 2(2) Å, β=96.780(2)°, V=729.84(5) Å3, Z=2。上述矿物学特征均与巴西发现的新矿物氟闪叶石的矿物学特征一致,表明赛马碱性岩体产出的氟闪叶石堪称该矿物种在中国的首次发现。不仅如此,赛马碱性岩体也有闪叶石产出,而且,迄今已发现多个新矿物,寓示该岩体仍有良好的新矿物发现前景。 相似文献
6.
觉学红层滑坡发育于向斜北东翼形成的反向坡，是近年来依托川藏交通廊道沿线灾害地质调查在新厘定的“藏东昌都红层区”发现的典型红层滑坡。为厘定其成因，以基础地质为切入点，进行了详实的地质调查与分析。结果表明，滑坡区地层岩性主要为中侏罗统东大桥组(J2d)紫红色、灰色薄层泥岩、粉砂质泥岩夹中-厚层砂岩。地层内发育与区域构造活动配套的轴面劈理(S1)、“X”型共轭剪节理(S2、S3)和层间剪切劈理(S4)。文章从沉积环境控制地层岩性及物理力学性质、区域构造演化制约斜坡结构与岩体结构面组合特征和地下水及重力作用加剧斜坡失稳等角度，提出觉学红层滑坡形成于内外地质营力耦合的失稳机理，对区域红层滑坡防治和川藏交通建设具有一定参考价值。 相似文献
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青藏高原的冰碛层与环境 总被引：11，自引：2，他引：11
最近3.4 Ma青藏高原尤其是南部可见七套冰碛层（自新至老M0—M6）,M1—M6上对应发育古土壤MS0—MS5,除M0和MS0外,形成于六次冰期和五次间冰期。通过与黄土高原对比,除M6外,可用黄土-古土壤序列确定它们的年代。分别以M0—M5上的古土壤为标志,算出高原于1.56—1.23 Ma B.P.、平均高程约2500m开始整体隆升、经历时约0.4 Ma的三个阶段,在0.075 MaB.P.已升到4300m,上升速率从2.0、2.5、2.8增至8.7 mm/a,导致冰期雪线升高,冰进范围缩小。冰期和季风气候变化及阶段性隆升共同决定了高原的环境变迁。 相似文献
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Cu在自然界主要以硫化物的形式存在,目前只确定了几种含Cu硫化物的S同位素分馏系数以及黄铜矿的Fe同位素分馏系数,而且不同研究者确定的系数有很大的差别,使得S、Fe同位素在研究铜矿床的形成、演化等方面不能很好地发挥示踪作用。因此,本文基于第一性原理计算确定了0~1 000℃温度范围内主要含Cu硫化物的S同位素简约配分函数比（103lnβ34-32）,以及Cu-Fe硫化物的Fe同位素简约配分函数比（103lnβ57-54）。重S同位素在这些含Cu硫化物中的富集顺序为铜蓝>方黄铜矿>黄铜矿≈黑硫铜镍矿>斑铜矿>辉铜矿,重Fe同位素在Cu-Fe硫化物中的富集顺序为方黄铜矿≈黄铜矿>低温斑铜矿>高温斑铜矿>中温斑铜矿>Cu8Fe4S8（中温斑铜矿的可能变体）。含Cu硫化物的103lnβ34-32与S原子的配位数、金属-S平均键长、S原子形成的所有化学键的平均键长没有明显的相关性,而Cu-Fe硫化物的103lnβ57-54与Fe—S平均键长基本成线性负相关关系。辉铜矿相变引起的S同位素分馏特别大,而斑铜矿相变时产生的S同位素分馏却可以忽略不计。本文的计算结果将会为探讨斑岩铜矿及其它类型的硫化物矿床的成因提供支持。 相似文献
9.
2017年8月8日四川省九寨沟县发生Ms7.0级地震,构造部位处于青藏高原东缘的巴颜喀拉地块东北角,震中位置是岷江断裂、塔藏断裂、虎牙断裂和雪山梁子断裂围闭的空震区。哪条断裂发震,如何界定其与周边活动断裂的关系,与青藏高原东缘近年来发生的大地震是否有成因联系等问题对于理解该区域现今构造活动模式、预判地震发展趋势和部署地震地质灾害防控等工作具有重要意义。利用地震前后两期Sentinel-1合成孔径雷达数据对地表同震形变场进行了InSAR测量,获取了极震区约2000 km2范围内的雷达视线向变形（-13~28 cm）和运动方向,呈现为主动盘单侧走滑兼逆冲的变形模式,结合震源机制、断裂展布、构造背景和近年地震迁移的分析,揭示了控震构造是巴颜喀拉地块北缘边界断裂弧形旋转体系的尾端构造,发震断层是该断裂系中塔藏断裂的南段,并有与虎牙断裂贯通的趋势,因此,应重视本次地震与虎牙断裂之间的空震区未来的强震危险性问题;从区域上看,此次九寨沟地震可能与汶川地震具有一定的时空成因联系,因在巴颜喀拉地块南北边界断裂破裂基本贯通的条件下,2008年汶川地震诱发的东缘中部锁固破裂导致块体加速向东挤出,2013年鲁甸地震又释放了东缘南段挤压构造应力,从而进一步加剧了东北角的应力集中,促使九寨沟地震的发生。 相似文献
10.
【研究目的】川滇黔地区铅锌矿成因具有多样性,特别是与峨眉山玄武岩的关系存在较大的争议,本文从前人关注较少的二叠系碳酸盐岩中的铅锌矿入手,研究成矿物质来源。【研究方法】以云南寻甸县太平子铅锌矿为研究对象,运用S、Pb、C、H、O同位素实验数据及流体包裹体测温等方法,对成矿物质来源及成矿流体特征进行探讨。【研究结果】矿石铅同位素组成比较均一,分布集中,206Pb/204Pb、207Pb/204Pb、208Pb/204Pb的变化范围分别为18.543～18.584、15.646～15.694、38.799～38.958,属于正常普通铅,具壳源特征,主要来源于基底岩石,水岩反应可能使赋矿围岩贡献少量的成矿物质。矿石硫化物δ34S变化范围为-13.6‰～-7.3‰,方铅矿的δ34S高于闪锌矿,硫同位素分馏并未达到平衡,生物成因硫酸盐还原作用（BSR）是还原硫的主要来源。热液方解石δ13CV-PDB范围为3.8‰～4.7‰,δ18OV-SMOW范围为12.0‰～16.7‰,相较于滇东北其他重要的铅锌矿床,具有明显的低δD、高δ18Ofluid特点,成矿流体中的水主要来源于岩浆水和有机水的混合,具有中—高温、低盐度特征。【结论】太平子铅锌矿在成矿物质、流体、成矿温度等均与区域上其他典型铅锌矿有较明显差别,具有典型的岩浆-热液成因特点。 相似文献
11.
在研究分析地震灾区地形地貌、地层岩性、地质构造、气象水文和典型地区滑坡的基础上,采用Newmark斜坡累积位移模型对2015年4月25日尼泊尔M_s8.1级地震诱发的滑坡危险性的空间分布状况进行了快速评估,通过典型地区的滑坡遥感解译结果验证表明评估结果具有较好的可信度,初步反映了尼泊尔地震诱发滑坡危险性分布的基本特征。然后考虑降雨作用对震后滑坡危险性的影响,对地震叠加降雨诱发滑坡危险性分布进行了快速预测。研究结果对地震应急救灾中的地质灾害防灾减灾具有重要的参考意义。 相似文献
12.
Xuanmei Fan Gianvito Scaringi Qiang Xu Weiwei Zhan Lanxin Dai Yusheng Li Xiangjun Pei Qin Yang Runqiu Huang 《Landslides》2018,15(5):967-983
On 8th August 2017, a magnitude Ms 7.0 earthquake struck the County of Jiuzhaigou, in Sichuan Province, China. It was the third Ms ≥?7.0 earthquake in the Longmenshan area in the last decade, after the 2008 Ms 8.0 Wenchuan earthquake and the 2013 Ms 7.0 Lushan earthquake. The event did not produce any evident surface rupture but triggered significant mass wasting. Based on a large set of pre- and post-earthquake high-resolution satellite images (SPOT-5, Gaofen-1 and Gaofen-2) as well as on 0.2-m-resolution UAV photographs, a polygon-based interpretation of the coseismic landslides was carried out. In total, 1883 landslides were identified, covering an area of 8.11 km2, with an estimated total volume in the order of 25–30?×?106 m3. The total landslide area was lower than that produced by other earthquakes of similar magnitude with strike-slip motion, possibly because of the limited surface rupture. The spatial distribution of the landslides was correlated statistically to a number of seismic, terrain and geological factors, to evaluate the landslide susceptibility at regional scale and to identify the most typical characteristics of the coseismic failures. The landslides, mainly small-scale rockfalls and rock/debris slides, occurred mostly along two NE-SW-oriented valleys near the epicentre. Comparatively, high landslide density was found at locations where the landform evolves from upper, broad valleys to lower, deep-cut gorges. The spatial distribution of the coseismic landslides did not seem correlated to the location of any known active faults. On the contrary, it revealed that a previously-unknown blind fault segment—which is possibly the north-western extension of the Huya fault—is the plausible seismogenic fault. This finding is consistent with what hypothesised on the basis of field observations and ground displacements. 相似文献
13.
基于地震滑坡危险性评估的Newmark累积位移模型,利用震前获取的震区地形数据、区域地质资料,结合地震动近实时获取技术,开展了四川九寨沟M_s7.0级地震诱发滑坡的应急快速评估。地震滑坡位移分析结果表明,同震滑坡活动的中—高强度区分布在断层两侧宽约4 km的带状区域内,整体沿北西方向延伸。其中,极震区的丰雪塘、日则和干海子等城镇驻地及附近道路的滑坡强度相对较高;震前、震后影像对比表明九寨沟地震诱发的滑坡类型以浅表型碎屑流及小规模崩塌为主,且同震碎屑流多是在震前已有碎屑流的基础上进一步活动扩展而来,震后汛期泥石流隐患也不容忽视;通过典型地区滑坡位移分析结果与震前、震后影像对比,表明滑坡位移分析结果能够较好的反映同震滑坡的宏观分布特征,但在场地尺度上吻合程度欠佳,后续将通过提升岩性和地形等数据质量进行改进。研究结果可为灾情研判提供宝贵信息,对提高灾害应急救援效率具有重要意义。 相似文献
14.
Preliminary investigation of some large landslides triggered by the 2008 Wenchuan earthquake, Sichuan Province, China 总被引：14，自引：5，他引：9
Fawu Wang Qiangong Cheng Lynn Highland Masakatsu Miyajima Huabin Wang Changgen Yan 《Landslides》2009,6(1):47-54
The M
s 8.0 Wenchuan earthquake or “Great Sichuan Earthquake” occurred at 14:28 p.m. local time on 12 May 2008 in Sichuan Province, China. Damage by earthquake-induced landslides was an important part of the
total earthquake damage. This report presents preliminary observations on the Hongyan Resort slide located southwest of the
main epicenter, shallow mountain surface failures in Xuankou village of Yingxiu Town, the Jiufengchun slide near Longmenshan
Town, the Hongsong Hydro-power Station slide near Hongbai Town, the Xiaojiaqiao slide in Chaping Town, two landslides in Beichuan
County-town which destroyed a large part of the town, and the Donghekou and Shibangou slides in Qingchuan County which formed
the second biggest landslide lake formed in this earthquake. The influences of seismic, topographic, geologic, and hydro-geologic
conditions are discussed. 相似文献
15.
以穿越汶川震区的成兰铁路龙门山关键段为例, 探索提出了强震扰动背景下重大工程场区多尺度滑坡危险性评估方法。利用信息量模型反演评估了汶川地震诱发的同震滑坡空间分布特征, 以此为前提开展了区域和局地两种空间尺度的滑坡危险性预测评估。在区域廊带尺度上, 分别利用可能最大降雨量预测方法和信息量模型, 进行了日超越概率10%的最大降雨量时空分布预测及其诱发滑坡的危险性评估; 同时, 结合地震危险性区划成果, 开展了50年超越概率10%的基本地震动诱发滑坡的危险性评估。在局地场站尺度上, 利用基于崩塌运动过程模拟的Rockfall Analyst软件, 开展了柿子园大桥周边崩塌运动学特征(Runout)模拟和危险性评估。滑坡和崩塌危险性评估的结果分别为铁路规划选线和场站防护设计提供了不同尺度的地质安全依据。 相似文献
16.
Landslide hazards triggered by the 2008 Wenchuan earthquake, Sichuan, China 总被引：35，自引：16，他引：19
The 2008 Wenchuan earthquake (M
s = 8.0; epicenter located at 31.0° N, 103.4° E), with a focal depth of 19.0 km was triggered by the reactivation of the Longmenshan
fault in Wenchuan County, Sichuan Province, China on 12 May 2008. This earthquake directly caused more than 15,000 geohazards
in the form of landslides, rockfalls, and debris flows which resulted in about 20,000 deaths. It also caused more than 10,000
potential geohazard sites, especially for rockfalls, reflecting the susceptibility of high and steep slopes in mountainous
areas affected by the earthquake. Landslide occurrence on mountain ridges and peaks indicated that seismic shaking was amplified
by mountainous topography. Thirty-three of the high-risk landslide lakes with landslide dam heights greater than 10 m were
classified into four levels: extremely high risk, high risk, medium risk, and low risk. The levels were created by comprehensively
analyzing the capacity of landslide lakes, the height of landslide dams, and the composition and structure of materials that
blocked rivers. In the epicenter area which was 300 km long and 10 km wide along the main seismic fault, there were lots of
landslides triggered by the earthquake, and these landslides have a common characteristic of a discontinuous but flat sliding
surface. The failure surfaces can be classified into the following three types based on their overall shape: concave, convex,
and terraced. Field evidences illustrated that the vertical component of ground shaking had a significant effect on both building
collapse and landslide generation. The ground motion records show that the vertical acceleration is greater than the horizontal,
and the acceleration must be larger than 1.0 g in some parts along the main seismic fault. Two landslides are discussed as
high speed and long runout cases. One is the Chengxi landslide in Beichuan County, and the other is the Donghekou landslide
in Qingchuan County. In each case, the runout process and its impact on people and property were analyzed. The Chengxi landslide
killed 1,600 people and destroyed numerous houses. The Donghekou landslide is a complex landslide–debris flow with a long
runout. The debris flow scoured the bank of the Qingjiang River for a length of 2,400 m and subsequently formed a landslide
dam. This landslide buried seven villages and killed more than 400 people. 相似文献
17.
Reconnaissance report on landslide disasters in northeast Japan following the M 9 T��hoku earthquake
Toyohiko Miyagi Daisuke Higaki Hiroshi Yagi Shoji Doshida Noriyuki Chiba Jun Umemura Go Satoh 《Landslides》2011,8(3):339-342
An earthquake of Mw 9.0 struck the Pacific coast in northeast Japan on March 11, 2011 and was followed by a hugely damaging tsunami along 500 km
of the Japanese coastline. An inland aftershock of M. 7.0 occurred on April 11; during which, surface fault ruptures appeared
on land. A large variety of landslide disasters resulted from these earthquakes in various parts of northeastern Honshu, Japan.
The full extent of the landslides is still being determined. This brief report introduces some of the landslide phenomena
so far investigated by the Japanese Landslide Society. These are (1) failure of a water reservoir embankment dam in Sukagawa,
Fukushima prefecture, (2) landslides and surface seismic fault rupture from the April 11 aftershock in Iwaki, Fukushima, (3)
a concentration of surface failures at Matsushima Bay in Miyagi prefecture, and (4) small landslides on modified slopes in
residential areas around Sendai city. 相似文献
18.
Tapas R. Martha Priyom Roy Ritwik Mazumdar K. Babu Govindharaj K. Vinod Kumar 《Landslides》2017,14(2):697-704
High magnitude earthquakes trigger numerous landslides and their occurrences are mainly controlled by terrain parameters. We created an inventory of 15,551 landslides with a total area of 90.2 km2 triggered by the 2015 Mw 7.8 (Gorkha) and Mw 7.3 (Dolakha) earthquakes in Nepal, through interpretation of very high resolution satellite images (e.g. WorldView, Pleiades, Cartosat-1 and 2, Resourcesat-2). Our spatial analysis of landslide occurrences with ground acceleration, slope, lithology and surface defomation indicated ubiquitous control of steep slope on landslides with ground acceleration as the trigger. Spatial distribution of landslides shows increasing frequency away from the Gorkha earthquake epicentre up to 130 km towards east, dropping sharply thereafter, which is an abnormal phenomenon of coseismic landslides. Landslides are laterally concentrated in three zones which matches well with the seismic rupture evolution of Gorkha earthquake, as reported through teleseismic measurements. 相似文献
19.
Abstract: There were huge life and property losses during the Ms8.0 Wenchuan earthquake on May 12, 2008. Strain fluctuation curves were completely recorded at stress observatory stations in the Qinghai-Tibet plateau and its surroundings in the process of the earthquake. This paper introduces the geological background of the Wenchuan earthquake and the profile of in-situ stress monitoring stations. In particular, data of 174 earthquakes (Ms4.0-Ms8.5) were processed and analyzed with various methods, which were recorded at the Shandan station from August 2007 to December 2008. The results were compared with other seismic data, and further analyses were done for the recoded strain seismic waves, co-seismic strain stepovers, pre-earthquake strain valleys, Earth’s free oscillations before and after the earthquake and their physical implications. During the Wenchuan earthquake, the strainmeter recorded a huge extensional strain of 70 seconds, which shows that the Wenchuan earthquake is a rupture process predominated by thrusting. Significant precursory strain anomalies were detected 48 hours, 30 hours, 8 hours and 37 minutes before the earthquake. The anomalies are very high and their forms are very similar to that of the main shock. Similar anomalies can also be found in strain curves of other shocks greater than Ms7.0, indicating that such anomalies are prevalent before a great earthquake. In this paper, it is shown that medium aftershocks (Ms5.5-6.0) can also cause Earth’s free oscillations. Study of free oscillations is of great significance to understand the internal structure of the Earth and focal mechanisms of earthquakes and to recognize slow shocks, thus providing a scientific basis for the prevention and treatment of geological disasters and the prediction of future earthquakes. 相似文献
20.
Landslides triggered by slipping-fault-generated earthquake on a plateau: an example of the 14 April 2010, Ms 7.1, Yushu, China earthquake 总被引：3，自引：1，他引：2
On 14 April 2010 at 07:49 (Beijing time), a catastrophic earthquake with Ms 7.1 struck Yushu County, Qinghai Province, China. A total of 2,036 landslides were interpreted from aerial photographs and satellite images, verified by selected field checking. These landslides cover about a total area of 1.194 km2. The characteristics and failure mechanisms of these landslides are presented in this paper. The spatial distribution of the landslides is evidently strongly controlled by the locations of the main co-seismic surface fault ruptures. The landslides commonly occurred close together. Most of the landslides are small; there were only 275 individual landslide (13.5 % of the total number) surface areas larger than 1,000 m2. The landslides are of various types. They are mainly shallow, disrupted landslides, but also include rock falls, deep-seated landslides, liquefaction-induced landslides, and compound landslides. Four types of factors are identified as contributing to failure along with the strong ground shaking: natural excavation of the toes of slopes, which mean erosion of the base of the slope, surface water infiltration into slopes, co-seismic fault slipping at landslide sites, and delayed occurrence of landslides due to snow melt or rainfall infiltration at sites where slopes were weakened by the co-seismic ground shaking. To analyze the spatial distribution of the landslides, the landslide area percentage (LAP) and landslide number density (LND) were compared with peak ground acceleration (PGA), distance from co-seismic main surface fault ruptures, elevation, slope gradient, slope aspect, and lithology. The results show landslide occurrence is strongly controlled by proximity to the main surface fault ruptures, with most landslides occurring within 2.5 km of such ruptures. There is no evident correlation between landslide occurrences and PGA. Both LAP and LND have strongly positive correlations with slope gradient, and additionally, sites at elevations between 3,800 and 4,000 m are relatively susceptible to landslide occurrence; as are slopes with northeast, east, and southeast slope aspects. Q4 al-pl, N, and T3 kn 1 have more concentrated landslide activity than others. This paper provides a detailed inventory map of landslides triggered by the 2010 Yushu earthquake for future seismic landslide hazard analysis and also provides a study case of characteristics, failure mechanisms, and spatial distribution of landslides triggered by slipping-fault generated earthquake on a plateau. 相似文献