青藏高原东缘新构造及其对汶川地震的控制作用

基于卫星遥感图像解译、地形起伏度分析和地面调查资料,论述了青藏高原东缘构造地貌格局、新构造演化阶段和活动断裂特征,提出青藏高原东缘不同地块在晚新生代时期有序的向东挤出过程,并划分为4个阶段：中新世早期川滇地块向北东挤出、中新世晚期川滇地块的再次强烈向东挤出、上新世至早中更新世时期川青地块的向东挤出、晚更新世以来最新构造变动阶段,青藏高原东缘地貌边界带也经历了由西向东、由南向北的有规律的迁移过程。基于活动构造的最新研究成果和现今GPS测量成果,阐述了东昆仑岷山龙门山走滑逆冲断裂系统的运动学特征。根据地震破裂构造的实地调查,分析了汶川地震的地表破裂行为,提出了汶川地震的发震构造模型。研究认为,青藏高原东部地区NW向楔状条块向东运动速度的一半被鲜水河断裂及其北西延伸的构造带所吸收,而龙门山构造带向东运动受阻于四川盆地之下扬子刚性地块,使得龙门山断裂带处在低应变、高应力环境下,因长期应力应变累积而导致向西陡倾的断裂带突然向东逆冲运动而释放能量。汶川强震发生的深部机理值得深入研究。     

应对云南地震中国地质科学院启动重大地质灾害应急机制

正2014年8月3日16时30分,云南省昭通市鲁甸县发生里氏6.5级地震,震中坐标:北纬27.1°,东经103.3°。鲁甸地震发生之后,中国地质科学院立即组织专家分析地震地质背景与发展趋势。王小烈书记指示启动重大地质灾害应急机制,董树文副院长迅速组织地质力学研究所相关专家进行会商。该次地震发生在扬子地块与川滇菱形地块的边界断裂小江断裂带的东侧,震源机制为走滑型破裂地     

青藏高原向东挤出的变形响应及南北地震带构造组成

受青藏高原物质在南北挤压下向东逸出的影响 ,四川地块、鄂尔多斯地块、川滇地块和滇西地块均发生了不同性质的变形响应。根据航磁异常揭示的四川、鄂尔多斯盆地基底构造样式和滇西地区的地质构造研究结果 ,在主要由变质褶皱基底组成的四川地块发生平行龙门山断层的逆冲推覆 ,基底岩石发生递进褶皱缩短的同时 ,由华北变质结晶基底组成的鄂尔多斯地块在前期逆冲推覆构造的基础上 ,结晶基底沿一系列近东西向左行走滑断层向东错移。滇西和川滇地块则分别沿金沙江—红河断裂 (2 0Ma前后 )和鲜水河—小江断裂 (5Ma前后 )发生了大规模的左行位移。发生在滇西、川滇、四川和鄂尔多斯地块上的最新构造变动叠加或改造了先存构造 ,并且表现为从南向北、由盖层向基底发展的趋势 ,变形程度自西向东减弱 ,反映了青藏高原持续同构造伸展作用的边缘和远程效应。青藏高原东缘多层次、多阶段的现今构造变动引发的地震活动组成了宏观的南北地震带。     

青藏高原东南缘川滇地块古近纪沉积地层古地磁分析及其构造意义

针对中国西部及中亚地区以红色陆相沉积岩为主的白垩纪—新生代地层中普遍存在古地磁数据磁倾角偏低的现象,对青藏高原东南缘川滇地块中部大姚地区古近纪陆相红层进行了磁倾角偏低研究。实验结果表明,川滇地块内部古近纪陆相红层古地磁数据不存在明显的磁倾角偏低的现象。结合前人对川滇地块内部古地磁数据及周缘新生代走滑断裂的活动演化历史研究,确定川滇地块自中中新世以来川滇地块内部表现为刚性旋转,楚雄地区则发生局部构造旋转叠加。     

青藏高原东北缘大陆岩石圈现今变形和位移

川青地块在地貌上为川西高原,亦是青藏高原东北边缘最重要的构造单元。新的GPS监测资料表明,在欧亚框架内,川青地块及其邻近的龙门山带和华南地块西缘的地壳运动水平速度,具有自西向东由25.66mm/a递变下降到6.99mm/a的总趋势。速度矢量表现出顺时针涡旋转动。川青地块内具有局部应变积累的非均一的区域剪切。横切鲜水河断裂带中段新的GPS测量结果揭示,两侧地块间的平均左旋滑动速率约8mm/a;由于局部应变积累,断裂系南西侧的主断裂的移动速率为9.3mm/a,其间为拉分盆地和小的横向伸展断裂。鲜水河断裂系的左旋断裂滑动作用,调节了川青地块与川滇地块之间的相对运动。     

青藏高原东北缘大陆岩石圈现今变形和位移

川青地块在地貌上为川西高原,亦是青藏高原东北边缘最重要的构造单元.新的GPS监测资料表明,在欧亚框架内,川青地块及其邻近的龙门山带和华南地块西缘的地壳运动水平速度,具有自西向东由25.66 mm/a递变下降到6.99 mm/a的总趋势.速度矢量表现出顺时针涡旋转动.川青地块内具有局部应变积累的非均一的区域剪切.横切鲜水河断裂带中段新的GPS测量结果揭示,两侧地块间的平均左旋滑动速率约8mm/a;由于局部应变积累,断裂系南西侧的主断裂的移动速率为93mm/a,其间为拉分盆地和小的横向伸展断裂.鲜水河断裂系的左旋断裂滑动作用,调节了川青地块与川滇地块之间的相对运动.     

青藏高原东南缘德钦- 中甸断裂中北段活动性及地震危险性评估

青藏高原的隆升和向东挤出使得青藏高原内部和周缘形成一系列强烈变形的次级块体,川滇地块是其中变形最为活跃的地块。德钦 中甸断裂是川滇地块的西边界断裂之一,晚第四纪以来断裂主要表现为右旋滑动,同时发育倾滑分量。在奔子栏镇 瓦卡镇以南至中甸一带,断层发育明显的正倾滑分量,在奔子栏镇 瓦卡镇以北则发育明显的逆倾滑分量。奔子栏镇一带是断层运动特征的改变部位,也是断层宏观走向改变的部位,这些特征表明奔子栏镇更是德钦 中甸走滑断裂的枢纽部位。研究表明德钦 中甸断裂在奔子栏镇附近的古地震平均复发周期为11. 35±2. 4ka,长期滑动速率1. 3~1. 7mm/a。按照构造类比原则,奔子栏镇是德钦 中甸断裂的地震成核部位,其潜在震级下限不会低于M7,潜在地震烈度下限不会低于Ⅹ度。     

中国大陆及其邻区强震活动与活动地块关系研究

从活动地块假说出发 ,在活动地块研究的基础上 ,探讨了中国大陆及邻区活动地块与强震活动的关系。研究指出 ,主要构造变形和强烈地震大都发生在活动地块边界。在占总面积 17%的活动地块边界上 ,集中了全部的 8级以上巨大地震和 86 %的 7级以上大地震 ,其释放能量占全部总能量的 95 %以上 ,表明中国大陆及其邻区活动地块边界带控制了绝大部分的强地震。从活动地块的整体来看 ,强震活动不仅显示出显著的韵律性特征 ,而且其高、低起伏基本上与中国大陆地区一致 ,只是强震活跃时段有时稍长于中国大陆。各轮回强震活动都有各自活动的主体地区 ,反映了不同活跃期内地块的不同活动方式。文中还从现今地壳运动角度 ,讨论了活动地块运动速率与强地震活动水平之间的可能联系。     

青藏高原东北缘大陆岩石圈现今变形和位移

川青地块在地貌上为川西高原，亦是青藏高原东北边缘最重要的构造单元。新的GPS监测资料表明，在欧亚框架内，川青地块及其邻近的龙门山带和华南地块西缘的地壳运动水平速度，具有自西向东由25．66mm／a递变下降到6．99mm／a的总趋势。速度矢量表现出顺时针涡旋转动。川青地块内具有局部应变积累的非均一的区域剪切。横切鲜水河断裂带中段新的GPS量结果揭示，两侧地块间的平均左旋滑动速率约8mm／a；由于局部应变积累，断裂系南西侧的主断裂的移动速率为9．3mm／a，其间为拉分盆地和小的横向伸展断裂。鲜水河断裂系的左旋断裂滑动作用，调节了川青地块与／11滇地块之间的相对运动。     

2021年5月21日漾濞MS6.4地震的发震断层及其破裂特征: 地震序列的重定位分析结果

据中国地震台网测定，2021年5月21日21时48分在云南省大理州漾濞县发生M_S6.4地震，及时查明此次地震的发震构造及震源破裂特征，可为认识该区孕震条件和判别未来强震危险性提供关键依据。采用双差定位方法对漾濞地震序列进行重新定位，得到3863次地震事件的精确震源位置。结果显示:漾濞地震序列整体呈北西—南东向分布，长约25 km；整体走向135°；M_S6.4主震震中位置为25.688°N，99.877°E；震源深度约9.6 km。综合地震序列深度剖面和震源机制解结果可知，发震断层应为北西走向、整体向西南方向陡倾的右旋走滑断层，倾角具有自北西向南东逐渐变缓的趋势。进一步分析地震序列的时空演化过程发现，该地震具有典型的"前震-主震-余震型"地震序列活动特点，其破裂过程主要包括3个阶段。破裂成核阶段:首先在发震断层10~12 km深度处相对脆弱部位产生小尺度破裂，之后失稳加速破裂，发生M_S5.6地震；主震破裂阶段:在构造应力场持续加载和周围小尺度破裂的共同影响下，促使浅部较高强度断层闭锁区破裂，形成M_S6.4主震；尾端拉张破裂阶段:主震破裂向东南扩展过程中，在东南端形成与之呈马尾状斜交的、具有正断性质的次级破裂，并产生M_S5.2余震。而且此次地震还在源区北东侧触发了北北东向的左旋走滑破裂。综合分析认为，漾濞地震是兰坪-思茅地块内部北西向草坪断裂在近南北向区域应力挤压作用下发生右旋走滑运动的结果，具有明显的新生断裂特征。近年来兰坪-思茅地块内部一系列中强地震的发生表明，青藏高原物质向东南持续挤出的过程中，遇到该地块的阻挡，正在导致地块内部早期断层贯通形成新的活动断裂。因此，川滇地块西南边界带上或相邻地块内部老断层的复活和新生断裂的产生是区域中强地震危险性分析评价中值得关注的重要课题，同时建议需重视未来该区中强地震进一步向东南和向北的迁移或扩展的可能性。      

地震勘探技术新进展——中国地球物理学会年会地震新技术简介

2006年10月中旬在成都召开了中国地球物理学会年会,这次年会对几十个地球物理学术理论与其应用领域进行了学术交流,其中一些地震勘探新技术,值得从事煤炭地震勘探的同行们借鉴,如饱和激发、山地高精度定位、精细表层调查等复杂山地地震采集技术,振幅补偿、叠前时间偏移、层析静校正等资料处理技术,三维地震数据可视化解释技术以及基于CMP理论的横向分辨率控制方法等.     

Appearance of the Coast Effect in Tectonic Deformations Due to Magnetic Storms

Doklady Earth Sciences - The records from fifty-eight identical broadband seismic stations located in different regions of the world have been studied from the strong geomagnetic storm of October...     

Observations from the 12 October 1992 Dahshour earthquake in Egypt

An earthquake of local magnitude 5.3 (duration magnitudeM _d ) on the Richter Scale occurred at Dahshour, 18 km south of Cairo, Egypt, on Monday, 12 October 1992 at 3:09 pm (local time). Numerous aftershocks followed the main event during the following weeks with magnitude up to 4.3. The earthquake occurred in an area that has had no recent seismic activity, and affected many cities in Egypt. Many buildings and monuments were severely damaged or collapsed. Modern concrete skeletal structures suffered minor nonstructural damage. Earthquake physical damage was estimated at about one billion U.S. Dollars. The severity of the damage was mainly due to poor construction materials and detailing, aging, inferior workmanship, and inadequate maintenance. Egypt was generally considered to be an area of moderate seismic activity. In 1989, earthquake provisions were first introduced in the Egyptian Code of Practice for Reinforced Concrete Structures only. The earthquake clearly showed the urgent need for an assessment and rehabilitation program to mitigate seismic risk hazard in existing structures. In addition, future development planning, and earthquake preparedness strategies should implement lessons learned from the event. In this paper, an overview discussion about the observations from the 12 October earthquake is presented.     

Pushover and nonlinear time history analysis evaluation of a RC building collapsed during the Van (Turkey) earthquake on October 23, 2011

The nonlinear seismic behavior of a collapsed reinforced concrete (RC) residential building in the city of Van in Turkey is investigated by the static pushover and nonlinear time history analyses. The selected RC structure was designed according to the 1975 version of Turkish Earthquake Code (TEC-1975). The building had experienced heavy damage, and it was demolished in the Van earthquake on October 23, 2011. The 2007 version of Turkish Earthquake Code (TEC-2007) is considered for the assessing seismic performance evaluation of the selected RC building. The RC structure presents collapse performance level under the earthquake loads. Besides, the analytical solutions show that different performance levels for the sections are obtained from the pushover and nonlinear time history methods.     

Landslides and other surface effects induced by the 1997 Umbria–Marche seismic sequence

This paper both describes and discusses landslides and other ground effects induced by the September–October 1997 seismic sequence, which struck the Umbria and Marche regions (Central Italy). Three main events occurred on 26 September at 00:33 and 09:40 GMT, and 14 October with magnitude M_w equal to 5.8, 6.0 and 5.4, respectively; furthermore hundreds of minor but significant events were also recorded. The authors examined an area of some 700 km² around the epicentre (Colfiorito). Primary and secondary effects were observed, including surface faulting phenomena, landslides, ground fractures, compaction and various hydrological phenomena. Surface evidence of faulting reactivation was found along the well-known capable faults, to a total length of ca. 30 km. Landslides, which were the most recurrent among the phenomena induced, consisted mainly of rock falls and subordinately of rotational and translational slides, which were generally mobilised by the inertia forces during the seismic motion. The percentage of reactivated old landslides decreased as the distance from the epicentral zone increased; a similar decrease had been observed for the 1980 Irpinia earthquake (Southern Italy). The ground fracture distribution was consistent with the regional structural setting and the general pattern of macroseismic field. Numerous episodes of hydrological changes were observed within the most severely damaged area. All this evidence confirms the relevance of the study of ground surface effects for achieving a more complete evaluation of seismic hazard.     

Continued seismic activity at the Koyna reservoir site, India

Following the impounding of the Shivaji Sager Lake in 1962, tremors became prevalent in the Koyna region, considered previously to be aseismic. During ensuing years the tremor frequency appears to have been dependent on the rate of increase of water level, maximum water level reached, and the period for which high levels were retained. This culminated in a burst of seismic activity from September 1967 to January 1968 following the record water levels in the reservoir and included the earthquake of September 13, 1967 with magnitude 5.5 and the damaging December 10, 1967 earthquake of magnitude 6.0. During the next five years water levels were kept low and no significant earthquakes occurred subsequent to the October 29, 1968 earthquake of magnitude 5.

The reservoir was filled to maximum capacity during September 1973 and this was followed by a conspicuous increase in seismic activity which included an earthquake of magnitude 5.1 on October 17, 1973. However, seismic activity during 1973 was much less severe than that of 1967. This relative decrease in seismicity may indicate that (a) the “threshhold level” for relatively large magnitude earthquakes had increased; (b) a major portion of the accumulated strains had been released; and/or (c) the importance of the longer period of high loading in 1967. Similar observations have been made at other seismically active reservoir sites.     

Source mechanism and parameters of the 19 October 2012 earthquake,northern Egyptian continental margin

The 19 October 2012 earthquake (M _L = 5.1) occurred in the northern continental margin of Egypt within the Nile Cone at latitude 32.35° N and longitude 31.27° E. The quake was felt over a wide area in north Egypt and East Mediterranean countries, but no casualties have been reported. This area had experienced the large earthquake (Ms = 6.7) of 12 September 1955. The fault plane solution of the 19 October 2012 earthquake is here presented based on the digital seismograms recorded by the Egyptian National Seismological Network (ENSN) and other regional seismic stations. The analysis is carried out using the well-known techniques of first motion polarities of P-wave and the amplitude ratios of P-, SH-, and SV-waves with lower hemisphere projection. The fault plane solution based on the first P-wave onset demonstrates a left lateral strike-slip faulting mechanism, while the solution based on both P-wave polarities and amplitude ratios of P-, SH-, and SV-waves reveals a reverse fault with strike-slip component trending NW–SE to NE–SW, in conformity with the N–S compression along the Hellenic Arc convergence zone. Following the Brune’s model, the source dynamic parameters for the 19 October 2012 earthquake are estimated as corner frequency = 1.47 Hz, fault radius = 0.7 km, stress drop = 22.1 MPa, seismic moment = 2.80E + 16 Nm, and moment magnitude M _w = 4.9. These parameters may provide important quantitative information for the seismic hazard assessment studies.     

The 2012/2014 swarmquakes of Jaen,Spain: a working hypothesis involving hydroseismicity associated with the hydrologic cycle and anthropogenic activity

A total of 2,300 swarmquake-type seisms have been striking the Torreperogil–Sabiote Hill (TSH) in southern Spain (Jaen) from October 2012 to the present, involving a major seismic crisis with six subseries until May 2013 (TSH seismic series, TSHS), followed by seven final series (FS). Two mild premonitory events occurred nearby in 2010–2011. Several evidences suggest cause–effect relationships between water and seismicity at the TSH: (1) The characteristics of seisms with a vast majority of ill-defined shallow/small events, spatial/temporal variations of the better constrained diffuse swarmquakes, increasing seismic velocities preceding stronger events, marked periodicities, abundant hydro-tremors, etc. (2) A series of spatial/temporal relationships between water and seismicity: Time lags between rainfall/reservoir peaks and seismic peaks; spatial links between swarmquakes and several factors (underground hydrogeology, reservoirs, etc.); etc. (3) From May 2013 to January 2014 evolution of rainfall and FS seismicity declined drastically at the same time. We suggest a hydroseismic hypothesis for TSH swarmquakes resulting from a complex series of cumulative factors: (1) A million-years natural setting involving geological, hydrogeological, geomorphological and tectonic elements. (2) A decades-long series of natural and anthropogenic factors are as follows: the 2012/2013 meteorological change, the massive overexploitation of the confined aquifers and alternating impoundment/emptying of the Giribaile reservoir.     

浅层地震勘探震源性状探讨

该文通过某浅层地震勘探工程在不同的场地条件下采用的几种震源方式所得到的资料,探讨震源的性状和使用。