Application of pattern recognition algorithm in the seismic belts of Indian convergent plate margins — M8 algorithm

The seismicity associated with the convergence of the Indian and Eurasian plates, from 1964 to August 1990 was scanned using the M8 algorithm with a view to identify the times of increased probabilities (TIPs) of the earthquakes of magnitudes greater or equal to 6·4 that occurred during the period from 1970 to August 1990. 23 out of 28 earthquakes (M ? 6·4) have been predicted. These were preceded by specific activation of the earthquake flow which was picked up by the M8 algorithm. The earthquake of August 1988 in the Himalaya could not be predicted, the other four unpredictable earthquakes occurred in the early dates of the catalogue (1970–1971) and hence their TIPs could not be diagnosed. Two current alarms are diagnosed, one in the Indo-Burmese arc and the other in the Hindukush-Pamir region. The algorithm provides the correlation between the earthquakes and their area of activation (both in time as well as in space) which, when compared with the local geology, may help to comment on the present day status of the seismic features on the surface.     

Application of pattern recognition algorithm in the seismic belts of Indian convergent plate margin — CN algorithm

The earthquake catalogue from 1964 to August 1991 is used to identify the times of increased probabilities (TIPs) of the earthquake mainshocks of magnitudes greater than or equal to 6·4 and are associated with the Indian convergent plate margins, in retrospect. In Pakistan and Indo-Burma regions, the analysis was repeated for magnitude threshold 6·2 and 7·0 respectively. All the earthquakes (except one in the Hindukush region and one in Indo-Burmese region) in Pakistan, Hindukush-Pamir, Himalaya and Indo-Burmese regions were preceded by the special activation and hence were predicted. Approximately 23 ± 10% of the total time (1970 to August 1991) is occupied by the TIPs in all the regions. The reasons for failure to predict the two earthquakes in these regions are discussed. Our analysis gives a better picture of the regionalization and the size of the space-time volume for the preparation of an earthquake. The high success ratio of the algorithm proves that it can be applied in this territory for further prediction in the real time, without any significant changes in its parameters.     

Simulation of Paleotectonic Stress Fields and Distribution Prediction of Tectonic Fractures at the Hudi Coal Mine, Qinshui Basin

Study on tectonic fractures based on the inversion of tectonic stress fields is an effective method. In this study, a geological model was set up based on geological data from the Hudi Coal Mine, Qinshui Basin, a mechanical model was established under the condition of rock mechanics and geostress, and the finite element method was used to simulate the paleotectonic stress field. Based on the Griffith and Mohr-Coulomb criterion, the distribution of tectonic fractures in the Shanxi Formation during the Indosinian, Yanshanian, and Himalayan period can be predicted with the index of comprehensive rupture rate. The results show that the acting force of the Pacific Plate and the India Plate to the North China Plate formed the direction of principal stress is N-S, NW-SE, and NE-SW, respectively, in different periods in the study area. Changes in the direction and strength of the acting force led to the regional gradients of tectonic stress magnitude, which resulted in an asymmetrical distribution state of the stress conditions in different periods. It is suggested that the low-stress areas are mainly located in the fault zones and extend along the direction of the fault zones. Furthermore, the high-stress areas are located in the junction of fold belts and the binding site of multiple folds. The development of tectonic fractures was affected by the distribution of stress intensity and the tectonic position of folds and faults, which resulted in some developed areas with level Ⅰ and Ⅱ. There are obvious differences in the development of tectonic fractures in the fold and fault zones and the anticline and syncline structure at the same fold zones. The tectonic fractures of the Shanxi Formation during the Himalayan period are more developed than those during the Indosinian and Yanshanian period due to the superposition of the late tectonic movement to the early tectonic movement and the differences in the magnitude and direction of stress intensity.     

库车坳陷新生代构造应力场恢复

库车坳陷的构造变形及演化与南天山造山带的发育密切相关。库车坳陷新近纪以来的喜马拉雅晚期构造运动最为强烈,形成了天山山前大型冲断带,并造就了现今的构造格局。通过对库车坳陷北部构造样式的识别及各种应力场指示标志的测量、统计和构造解析,对野外获得的应力场指示标志划分了期次,认为喜马拉雅晚期应力场标志为近南北向挤压。结合库车坳陷区域构造要素,如地质体几何形态、边界条件、岩石力学参数等,运用弹性力学有限元数值模拟的方法获得了喜马拉雅晚期库车坳陷的区域应力场。模拟结果表明,库车坳陷喜马拉雅晚期最大主压应力方向为近南北向,与古应力场标志拟合较高,可以为库车坳陷裂缝预测和评价提供依据,对勘探开发有应用价值。     

The influence of neo-tectonics on river patterns in Bangladesh; a preliminary study based on Landsat MSS imagery

Bangladesh is part of the active foredeep depression south of the Himalayan collision zone, bordering the Indian plate. Seismic activity is common both in the mountain chain and in the Ganga plain reaching into the basin of the Bay of Bengal and forming the counterpart of the uplifted Himalayan chain. Erosion, sedimentation, river migration and transport within the Jamuna (Brahmaputra) river system are therefore not only controlled by processes on the Earth's surface, but are also the result of a balance between fast and continuing deposition versus geological subsidence and uplift. An attempt is made to correlate the behaviour of the Jamuna river to neo-tectonic movements, as interpreted from Landsat MSS imagery using available literature. From the imagery, covering the period 1976 to 1987, supervised and unsupervised classifications of bands 5 and 7 were made. The 1978 and 1986 images revealed the most useful classifications and yielded pronounced differences in colour variation for visual interpretations of geological lineaments and terrain units. The Jamuna riverbed can be divided into compartments, limited by faults.     

滇西时代不明变质岩系的解体和时代厘定

建立在岩石组合、变质、变形、碎屑组分和同位素年代学基础上的研究成果表明,滇西时代不明变质岩系是两个时代不同的构造岩片,分别相当于中元古界崇山群和二叠系吉东龙组,二者是喜山期构造混杂带的重要组成部分。崇山群在晚元古时期(727～956 Ma)发生区域性的动热变质作用,加里东时期(397 Ma)又叠加了一次变质作用。吉东龙组中有喜山期(32 Ma)变质作用的叠加。     

Tree-Ring-Based Spring Temperature Patterns over the Past Four Centuries in Western Himalaya

A network of 12 tree-ring width chronologies of Himalayan cedar (Cedrus deodara) from the western Himalayan region, India, has been used to reconstruct mean spring (March–May) temperature variations back to A.D. 1600. The most conspicuous feature of the temperature reconstruction is the long-term cooling trend since the late 17th century that ended early in the 20th century. The warmest 30-yr mean for the 20th century was recorded during 1945–1974. However, this warming, in the context of the past four centuries is well within the range of natural variability, since warmer springs of greater magnitude occurred in the later part of the 17th century (1662–1691).     

Largest earthquake in Himalaya: An appraisal

The largest earthquake (Mw 8.4 to 8.6) in Himalaya reported so far occurred in Assam syntaxial bend in 1950. However, some recent studies have suggested for earthquake of magnitude M_w 9 or more in the Himalayan region. In this paper, we present a detailed analysis of seismological data extending back to 1200 AD, and show that earthquake in Himalayan region may not be expected to be as large as those of subduction zones. Also, there appears to be a lateral variation in the earthquake magnitude, being lesser in the western syntaxial bend when compared close to the eastern syntaxial bend. This is attributed to the difference in the plate boundary scenario; dominance of strike-slip and thrusting along the western syntaxis as against thrusting and remnant subduction along the eastern syntaxis.     

Earthquake triggered landslide–Indian scenario

Landslide initiation due to earthquake is one of the most prevalent seismic hazard, which claims hundreds of lives in the Himalayan mountainous terrains of India. Number of landslides, maximum distance from the epicentre and total landslide area/volume are correlatable with earthquake magnitudes. Application of globally accepted earthquake triggered landslide parameter models do not match well with published data for the Himalayan earthquake triggered landslides. Considering the incompleteness of landslide inventories for most of the Himalayan earthquakes, development of regression equations show that in the Himalayan environment, landslide may trigger even with imperciptable earthquakes affecting longer distances having earthquake magnitude of more than 8 M with potential to affect more areas than the global expectations.     

Estimation of earthquake hazard parameters for incomplete and uncertain data files

The maximum likelihood estimation of earthquake hazard parameters (maximum regional magnitudem _max, activity rate λ, and theb parameter in the Gutenberg-Richter distribution) is extended to the cases of incomplete and uncertain data. The method accepts mixed data containing only large (extreme) events and a variable quality of complete data with different threshold magnitude values. Uncertainty of earthquake magnitude is specified by two values, the lower and upper magnitude limits. It is assumed that such an interval contains the real unknown magnitude. The proposed approach allows the combination of different quality catalog parts, e.g. those where the assignment of magnitude is questionable and those with magnitudes precisely determined. As an illustration of the method, the seismic hazard analysis for western Norway and adjacent sea area (4–8°E, 58–64°N) is presented on the basis of the strongest earthquakes felt during the period 1831–1889 and three complete catalog parts, covering the period 1890–1987.     

准噶尔盆地西南缘构造模式、演化及其油气

通过地震勘探、钻井、地面地质资料综合分析,列出了6点依据,认为,盆地南缘西部构造特征是3个深浅层次的北凸孤形滑脱体。它们分别为燕山和喜山运动由南向北的侧向挤压造就而成。圈闭的含油气性,总的说来西段较东段好。     

云南兰坪盆地中部白垩系沉积环境及区域构造意义

云南兰坪盆地在白垩纪的演化为其喜马拉雅期的大规模成矿起到了铺垫作用。前人对该时期的沉积相分析较为笼统,一定程度上影响了对盆地演化、盆地性质及成矿方面的深入理解。在兰坪盆地中部开展了实测剖面和路线调查等工作,认为兰坪盆地的白垩系分为扇三角洲-湖泊和辫状河三角洲-残余河湖2个沉积体系,盆地性质应属断陷盆地。结合对特提斯洋演化过程的认识,认为早白垩世兰坪盆地继承了中侏罗世—晚侏罗世沉降的构造背景,早白垩世末中特提斯洋的闭合中断了盆地的沉降作用,晚白垩世新特提斯洋的北向俯冲导致了中生代兰坪盆地演化的终止。结合区域矿产资料,认为早白垩世成矿元素已有初步富集,并为喜马拉雅期成矿提供了必要的矿源层、建造水、运移通道及成矿定位空间。研究可为兰坪盆地的演化过程提供新的实证资料。     

Detection,characterization, and analysis of land subsidence in Nairobi using InSAR

Natural Hazards - Himalayan mountains are one of the most seismo-tectonically active zones on the surface of the earth. Recurring moderate and high magnitude earthquakes are not uncommon in this...     

喜马拉雅淡色花岗岩带伟晶岩的富铍成矿特点及向更高处找锂

喜马拉雅淡色花岗岩作为新识别的稀有金属成矿区带,已发现以Be-Nb-Ta(Sn-W)组合为主矿化且已形成大型矿床,如错那洞,但仅在为数不多的几处伟晶岩见到锂辉石,尚未发现工业锂矿床。因此,有必要剖析该区伟晶岩成矿(尤其Be同Li的对比)特点、条件及可能潜力,并与国内其他稀有金属矿带进行对比分析,从而推动喜马拉雅伟晶岩稀有金属矿床尤其是锂矿的发现。该区伟晶岩母体淡色花岗岩与华南稀有金属矿化花岗岩类似,显示高的分异程度但较窄的演化区间,并且熔体具有高的Li浓度。在印亚大陆碰撞带复杂的构造-变质-深熔作用下产生了多期次的岩浆活动,尤其新喜马拉雅期巨量的岩浆可为伟晶岩的形成、远距离迁移分异及成矿提供有利的热和物质基础。基于含Li伟晶岩形成于"远"母体、"高"海拔的特点,提出区域构造层位的上部或更高海拔地区以及淡色花岗岩岩体外侧远端的围岩内将可能是含锂伟晶岩的就位空间与找矿重点地段。     

Deformation and displacement fields of the Himalayan arc,seismicity and large earthquake hazards in its eastern segment and vicinity

The Himalayan arc is a type of plate margin similar to an island arc and is a world-famous region of tectonic and seismic activities, where a series of large earthquakes have occurred in historical time. In this paper, the vertical deformation and horizontal displacement fields of the Himalayan arc are theoretically derived from the viewpoint of the collision between the Indian and Eurasian plates. In the light of the observed data, the seismicity, earthquake focal mechanism, seismotectonic and geomorphological features of the arc and its vicinity are reasonably explained. The characteristics of seismicity and the possibility of earthquakes with magnitude above 8 occurring in this region in the future are studied.     

珠穆朗玛峰地区侏罗纪沉积环境

珠峰地区(指北喜马拉雅断裂以南的吉隆～岗巴一带。该地区侏罗纪地层分布广泛,发育也较完全,其中以聂拉木县古错剖面出露最好。笔者认为,侏罗纪时珠峰地区属与印度板块毗连的被动大陆边缘(冒地槽)环境。地层层序较完全,沉积类型多样,厚度大,相变快,反映了当时板块扩张作用的影响,并造成了当时该区构造运动比较活跃的沉积作用背景。     

喜马拉雅山脉近期上升的探讨

喜马拉雅山脉是地球上最高、最长大和最年青的山脉之一。它以宏伟的规模和巨大的海拔高度强烈地影响着我国西藏地区以至亚洲中部自然环境的变化。自1949年中华人民共和国成立以来,在毛主席和党中央的关怀下,曾对珠穆朗玛峰及邻近地区进行过多次考察。在无产阶级文化大革命的1966-1968年,又进行了珠峰地区多学科的科学考察。     

世界自然遗产黄龙钙华景观的地质分析

四川省松潘县黄龙是世界自然遗产,以秀美的自然景色、巨型的钙华堆积闻名于世.黄龙所处的岷山地区位于喜马拉雅期是构造活动地区,更新世以来不断隆起,成为现代隆起高山区.在更新世,山岳冰川广布全区,进入全新世,区内发育现代冰川,因而留下了冰蚀地貌和大量冰积物.黄龙的钙华来源于大气降水下渗形成的喀斯特水,该地下水以断层泉方式转为地表迳流,在沿沟向下流动过程中形成了钙华堆积,正是这种不断变化的钙华堆积呈现出绚丽的钙华风貌.钙华的堆积地貌有钙华池、钙华滩和钙华瀑布,溶蚀地貌有钙华洞穴,其钙华景观至今仍是处于不断变化中.     

Clustering of Earthquake Events in the Himalaya - Its Relevance to Regional Tectonic Set-up

The earthquake events of Himalaya of magnitude ≥5.0 from the time window 1905–2000 are statistically analysed. The inter-event time between earthquakes shows Hurst phenomena of temporal clustering which are spatially located in five distinct domains along the Himalayan fold-thrust belt. Out of these, two domains, one around Uttaranchal-Nepal border and the other around Nepal-Sikkim border reveal maximum number of temporal clusters and thus considered as seismically most potential zones of the Himalaya. Both these zones are located at the interface of the orthogonally disposed major tectonic discontinuities of the Peninsular Shield and Himalayan fold-thrust belt. Such zones are geologically most favourable locales for strain accumulation during later-tectonic movement. Statistical analysis points towards a probability of recurrence of seismic events in near future in these two zones. However, validity of such statistical results can be ascertained by detailed geological and geophysical modelling of the terrain.     

Evaluating the effects of ground motion parameters on response spectra in Uttarakhand Himalayas,India

Uttarakhand, a state of India, is located in seismically active Himalayan region and in the proximity of plate boundaries. The effects of important ground motion parameters like magnitude, distance, and local geology and site conditions on acceleration response spectra are examined in Uttarakhand Himalayas in this work. A total of 447 strong ground motion histories (horizontal and vertical) from 42 earthquakes were selected. The results show that the shape of the acceleration response spectra is influenced by the local site conditions and regional geology. The studies are carried out for two categories of sites, i.e., rock sites and soft soil sites. The maximum average horizontal spectral amplification for rock sites is 2.7 at 0.1 s, while for soft soil sites, it is found to be 3.2 at 0.2 s. In the same way, the maximum average vertical spectral amplification for rock is found to be 2.7 at 0.1 s, while for soft soil, it is found to be 2.95 at 0.1 s. The average spectral amplification in vertical component also shifts from low period (rock) to high period (soft soil). The level of spectra increases with decrease in distance for rock sites as well as soft soil sites. When comparing different magnitude earthquakes in different geological conditions, the response spectra are found to follow each other up to 0.04 s, while for period greater than 0.04 s, the spectra of higher magnitude earthquake is observed on the higher side. For soft soil sites, spectra from different magnitude earthquakes are observed to follow each other up to 0.1 s, beyond which they get separated.