The Balei earthquake of 6 January 2006 (Mw = 4.5): a rare case of seismic activity in eastern Transbaikalia

The Balei earthquake of 6 January 2006 (M_w = 4.5) was felt over a large part of Transbaikalia. Judging by its updated source parameters (earthquake mechanism, seismic moment, and moment magnitude), the event was generated by the Balei–Darasun fault reactivated in the Cenozoic. Exhaustive macroseismic evidence has been collected for the first time from the study area. The reported results fill up the gap in the seismological knowledge of eastern Transbaikalia and can be used for seismic risk mapping and earthquake prediction.     

The South Australian earthquake of January 7, 1971 and aftershocks

A moderately large earthquake (for South Australia) with magnitude ML = 4.6 occurred in the mid‐north near Spalding on January 7, 1971 (January 6, G.M.T.). It caused minor damage and was felt up to 80 km from the epicentre. Four aftershocks were located and another four events are inferred to have been associated with this sequence.     

青藏高原昆仑—汶川地震系列与巴颜喀喇断块的最新活动

青藏高原是中国最主要的地震活动区之一。最近十多年来,在青藏高原中部连续发生了1997年西藏玛尼Ms7.5级地震、2001年青海昆仑山Ms8.1级地震、2008年3月新疆于田Ms7.3级地震和5月四川汶川Ms8.0级地震及2010年青海玉树Ms7.1级地震,它们相继发生于青藏断块区巴颜喀喇断块四周边界活动断裂带上,是该断块最新活动的结果。发生于断块南北边界断裂上的3次地震都是走滑断裂错动的结果,发生在断块东南端的汶川地震则是挤压逆冲断裂的产物,而西北端的于田地震则呈现出张性特征,它们共同反映青藏断块区巴颜喀喇条状断块向东南方向滑动的最新活动。自1900年以来,青藏断块区和巴颜喀喇断块的强震活动表现出多期活动和区域性转移的特征,20世纪早期Ms7.0级以上强地震活动的主体地区在青藏断块区北部边界构造带,中期转移到高原南部喜马拉雅板块边界构造带和断块区南部断块,最近十多年来则在巴颜喀喇断块及周缘边界断裂上活动。青藏高原这种块体活动和地震活动与澳大利亚-印度板块对亚洲大陆的推挤作用相关,因而,青藏高原和巴颜喀喇断块的强震活动与澳-印板块边界苏门答腊强震活动相对应。目前苏门答腊地区强震活动仍在继续,因此,近期对巴颜喀喇断块及青藏高原南部地区的强震活动和强震危险性仍需加以注意。     

Seismotectonic significance of the 29 January 1989 Etne earthquake, SW Norway

The integrated analysis of geological, seismological and field observations with lineament data derived from satellite images allows the identification of a possible seismogenic fault zone for an earthquake which occurred near Etne in southwestern Norway, on 29 February 1989. The hypocentre of the earthquake was located at the mid-crust at a depth of 13.8±0.9 km which is typical of small intraplate earthquakes. The Etne earthquake occurred as a result of normal faulting with a dextral strike-slip component on a NW–SE trending fault. Available geological and lineament data indicate correlation of the inferred seismogenic fault with the NW–SE trending Etne fault zone. An aeromagnetic anomaly related to the Etne fault zone forms a regional feature intersecting both Precambrian basement and allochthonous Caledonian rocks. Based on these associations the occurrence of the Etne event is ascribed to the reactivation of a zone of weakness along the Etne fault zone. Slope-instabilities developed in the superficial deposits during the Etne event demonstrate the existence of potentially hazardous secondary-effects of such earthquakes even in low seismicity areas such as southwestern Norway.     

沂沭断裂带北段东支断裂的浅部构造特征及活动性

沂沭断裂带北段即潍坊市朱里以北的隐伏构造区,其主要隐伏活动断裂对第四系的发育具有控制作用。沂沭断裂带的活动性具有东强西弱的特点,其东支主干断裂是新构造运动强活动带,对地震的发生具有控制作用。莱州湾地区所开展的1∶5万区域地质调查、工程地质调查,通过大量的地面调查、物探、钻探等工作,对沂沭断裂带北段安丘-莒县断裂、昌邑-大店断裂的空间分布及活动性进行了深入调查研究,结果表明:两条主干断裂呈NNE向大致平行展布延伸,进入莱州湾海域,其中昌邑-大店断裂活动性质表现为走滑为主兼具逆冲运动,倾角近直立,倾向大致以东冢村北为界,由南段的倾向东转为北段的倾向西,该断裂最晚活动时代为晚更新世。安丘-莒县断裂控制了新生代地层的空间分布,新生代以来活动方式以向西正断为主,错断全新世地层并造成地表建筑物的开裂,目前仍处于活动期。本次调查首次确定了昌邑潜凸起的存在,该凸起位于断裂带北段东支两条主断裂之间,凸起区第四系厚度明显变薄,局部基岩出露;以柳疃断裂为界,北段潜凸区第四系下伏地层为新近纪明化镇组、馆陶组;南段潜凸区第四系下伏地层为新近纪八亩地组、牛山组,古近纪朱碧店组和白垩纪红土崖组。昌邑潜凸起区的发现对于莱州湾南岸水文地质、工程地质调查研究工作具有重要意义。     

新疆东准噶尔萨尔托海石英二长闪长岩岩体形成时代及构造环境

新疆东准噶尔萨尔托海石英二长闪长岩体属于晚古生代额尔齐斯构造-岩浆带。通过对萨尔托海石英二长闪长岩体的岩相学,主量、微量和稀土元素岩石地球化学特征及LA-ICP-MS锆石U-Pb年龄研究,认为萨尔托海石英二长闪长岩属于偏铝质、高钾钙碱质的镁质花岗岩类;富集大离子亲石元素(LILE,如Rb、Ba),亏损高场强元素(HFSE,如Ta、Nb、Hf和Ti),轻稀土元素富集,轻、重稀土元素分馏程度较高,负Eu异常不明显,表明形成于早二叠世(277.4±5.1Ma)后碰撞阶段的板内构造环境中。     

汶川地震假玄武玻璃的特征、成因及其构造意义

富流体的断层泥是浅部地震断层带中的特征岩石。一般认为,地震过程中摩擦热会导致粒间孔隙流体热膨胀增压,形成同震断层弱化（热增压机制）,从而抑制摩擦熔融的发生。然而我们研究发现,在2008年汶川大地震（M_W 7.9）中断层浅部发生了摩擦熔融。汶川地震发生一年后,我们在汶川地震断裂带科学钻探项目一号钻孔（WFSD-1）732.6m深处的断层泥中发现了厚度约2mm的假玄武玻璃（凝固的摩擦熔融物）。该假玄武玻璃形成的位置极浅,且产生于非固结的、富流体的断层泥中。从岩心来看,断层面可见镜面构造和同震擦痕。微构造分析显示,该假玄武玻璃主要由石英碎屑和由长石与黏土矿物熔融的非晶质基质组成,基质中发育众多不规则的微裂隙,并可见流动构造。化学成分分析显示,其基质富Ba且被重晶石（BaSO₄）小细脉切割,为同震及震后流体存在的证据。由于假玄武玻璃在流体存在的条件下会快速蚀变,且龙门山地区大地震复发周期为3000~6000年,因而这些完全未被蚀变的新鲜假玄武玻璃可能是最近一次大地震,即2008年汶川大地震的产物。针对钻孔中断层泥进行的高速摩擦试验,证实了在钻孔732m深度发生地震滑动的条件下确实会产生假玄武玻璃。因此WFSD-1钻孔732.6m的假玄武玻璃被认为是汶川地震的产物,代表了汶川地震主滑动带位置。这是首次在自然界中发现浅部含水断层泥摩擦熔融形成假玄武玻璃的实例,不仅对认识汶川大地震的发震机制、断层强度、应力迁移与破裂传播具有重要意义,而且有助于我们认识断裂带内浅部脆性区域的力学属性、岩石变形环境和变形机制,促进对地震滑动机制和破裂过程的认识。

     

Geoseismological investigation of the January 26, 2001 Bhuj earthquake in western peninsular India

Of the intraplate seismic events, the January 26, 2001 Bhuj earthquake (Mw 7.7) would be remembered as one of the deadliest, in which 13,805 human lives were lost, 0.177 million injured and a total of 1,205,198 houses were fully or partly damaged in 16 districts of Gujarat state with an estimated overall loss of Rs. 284, 23 million. The brunt of the calamity was borne by five districts, namely Kachchh, Ahmadabad, Rajkot, Jamnagar and Surendranagar, where 99?% of the total casualties and damage occurred. In the neighbouring parts of Sindhh Province of Pakistan, 40 human casualties were reported, and some buildings cracked in the Karachi city as well. In the Kachchh district of Gujarat state, the telecommunication links and power supply were totally disrupted, road and rail links partially impaired and water supply snapped at many places. The Bhuj airbase had to be closed for some time due to damage to the infrastructure. The macroseismic survey carried out by the Geological Survey of India in an area as large as 1.2 million?sq?km indicated an epicentral intensity as high as X on the MSK scale in an area of 780?sq?km in the central part of Kachchh rift basin. Apart from damages to civil structures, the January 26 earthquake induced conspicuous terrain deformation in the form of liquefaction features, structural ground deformation and low-order slope failures that were mainly prevalent within the higher intensity isoseists. Liquefaction occurred in an area of about 50,000?sq?km. The extensive plains of Rann of Kachchh, the marshy tracts of the Little Rann and the shallow groundwater table zones of Banni Land provided the most conducive geotechnical environments for the development of seismites. The liquefaction activity was profuse in seismic intensity zones X and IX, widespread in intensity VIII, subdued in intensity VII and stray in intensity VI. The common forms of liquefaction were sand blows/boils, ground fissures, craters, lateral spreading and slumping. Ground deformation of tectonic origin was witnessed in the epicentral tract. Such features, though much less subdued in comparison with the 1819 large earthquake (Mw 7.8) in region, occurred along the Kachchh Mainland fault (KMF) and along a transverse lineament, referred to as Manfara?CKharoi fault. The manifestations were in the form of fractures, displacement of strata, linear subsidence, upheaval, formation of micro-basins/micro-ridges, ripping off of rock surface, and at places violent forms of liquefaction. The localities where coseismic deformations were observed include Bodhormora, Sikra, Vondh, Chobari, Manfara and Kharoi. The 2001 event has demonstrated the role of local geology in influencing the ground motion characteristics and, therefore, the hazard estimation.     

The identification and use of petrophysical anomalies to forecast the mineralization at the Antey uranium deposit (Southwestern Trans-Baikal Region)

The determination of petrophysical parameters in conjunction with the geological, structural, mineralogical, and petrographic study of rocks is necessary to assess the localization conditions of uranium–molybdenum ore, the processing prospects, and the extent of mineralization at the Antey vein–stockwork deposit, which is the Russia’s largest, confined to the granitoid basement of the Streltsovo Caldera in the Southeastern Trans-Baikal Region.     

构造体制转折是岩石圈尺度的行为

试将华北中生代的构造-岩浆演化划分为3个阶段早中生代岩石圈结构的深部调整和底侵作用;中晚侏罗世的断块差异隆升和火山喷发;早白垩世的地壳伸展和岩石圈减薄.据此说明构造体制转折是一个渐变的过程,其动力来源应与岩石圈地幔乃至软流圈的运动相联系.因此,转折的过程应从深部开始,不同深度的响应必然有一个滞后效应.构造体制转折的标志也应是多方面的,其构造格局的转化是首位的,而且应从全球角度探讨它们的背景.     

Fault-plane solution and tectonic implications of the Pattan, Pakistan earthquake of December 28, 1974

A large destructive earthquake occurred on December 28, 1974 on the western bank of the Indus River near the village of Pattan. The earthquake reportedly killed 5,300 persons, injured 17,000 and left 60,000 people homeless. A seismicity map of the region is presented for the period January, 1963, to March, 1974 on a Mercator projection. Two main linear trends are recognized on the epicenter map. The northwest trend, beginning at 32.3°N, 76.6°E terminates at the southwest alignment of epicenters beginning at 36.0°N, 73.5°E and ending at 33.0°N, 71.0°E. The Pattan earthquake occurred near the junction of the two linear trends. A fault-plane solution for this earthquake has been determined from an analysis of teleseismic P-wave first-motion and S-wave polarization data. The strike and dip of the two nodal planes are N65°E, 68°SE and N50°E, 23°NW, respectively. The solution is compatible with and indicates underthrusting of the Indian plate in this region in the NNW direction along a thrust zone striking northeast.     

The age and tectonic setting of the Lukinda dunite-gabbro-anorthosite massif in the east of the Selenga-Stanovoi superterrane,Central Asian Fold Belt

Results of integrated ⁴⁰Ar/³⁹Ar, Rb-Sr, and Sm-Nd geochronological studies of the Lukinda dunite-troctolite-gabbro-anorthosite massif in the northeast of the Selenga-Stanovoi superterrane, Central Asian Fold Belt, are presented. It is shown that this massif is much younger than formerly thought: 249 ± 14 to 251 ± 15 Ma vs. Paleoproterozoic. This date of magmatism corresponds to one of the stages of the formation of the Selenga-Vitim belt, which ranks among the largest Phanerozoic volcanoplutonic belts in Central Asia.     

Coseismic slip distribution of the 14 January 2021 Mamuju-Majene,Sulawesi, earthquake derived from GPS data

Natural Hazards - The 14 January 2021 Mw 6.2 Mamuju-Majene earthquake occurred in West Sulawesi, Indonesia, preceded by three earthquakes with Mw 5.7, Mw 5.2 and Mw 4.3. The fault responsible for...     

The Gornozavodsk earthquake of August 17(18), 2006, in the south of Sakhalin Island

The August 17 (18), 2006, Gornozavodsk earthquake (M_w = 5.6) in the southwestern part of Sakhalin was preceded by a number of anomalous seismological and geophysical phenomena. The extensive data recorded by a network of digital seismic stations make it possible to track the aftershock dynamics of the process within 24 hours after the main event. The paper describes various manifestations of the earthquake.     

The effects of a large destructive local earthquake on earthquake preparedness as assessed by an earthquake preparedness scale

A multi-act scale for measuring the earthquake preparedness of individuals and small businesses was developed and used to assess the earthquake preparedness and the perceived difficulty of becoming prepared for earthquakes of 291 University of Southern California undergraduate students approximately 3 weeks prior to the 5.9 magnitude Whittier Narrows earthquake on 1 October 1987. These data were then compared with similar information collected over a 2 1/2 month period following the earthquake from randomly selected samples of subjects that had participated in the original survey. In one case, levels of preparedness of a single group were measured at approximately 2 week intervals (the repeated measures study). In a second case, this information was collected at different points in time following the earthquake from different groups of subjects (the between groups study). Results indicated an initial increase in earthquake preparedness which was significant for subjects in the repeated measures group and which approached significance for subjects in the between groups. This increase in preparedness was maintained for subjects in the repeated measure study but gradually declined to pre-earthquake levels for subjects in the between subjects study. Subjects in the repeated measures study also perceived earthquake preparedness as a significantly less difficult task following the earthquake. Level of perceived difficulty continued to decline over the 2 1/2 month study period. Declines in perceived difficulty for the between subjects study were more erratic, and were only approximately 1/3 of that for the repeated measures group at the end of 2 1/2 months.     

从德令哈地震分析青藏高原北缘东段的深部构造活动

在祁连山南北布设的10台REFTEK宽频地震仪器记录到了2003年4月发生在仪器台阵范围内的6．7级地震及其数十次余震,提供了研究青藏高原北缘深部构造的新资料,对3级以上震源的定位和震源机制研究结果表明,柴达木盆地北缘逆冲左行走滑断裂东段的宗务隆山逆冲断裂在南北挤压作用下引发了此次地震活动,是陆陆碰撞和内陆俯冲的结果,青藏高原北缘的走滑断裂在浅部呈缓倾斜,深部往往以较陡的产状向下延伸。震源区的构造分析证实了印度板块岩石圈的超深俯冲作用对高原北缘的影响,受南北向应力作用影响形成的走滑断裂近东西向的位移目前仍很剧烈。