Moment Tensor Solutions of Earthquakes in the Indian Ocean from Surface Waves and their Tectonic Implications

—Rayleigh and Love waves generated by sixteen earthquakes which occurred in the Indian Ocean and were recorded at 13 WWSSN stations of Asia, Africa and Australia are used to determine the moment tensor solution of these earthquakes. A combination of thrust and strike-slip faulting is obtained for earthquakes occurring in the Bay of Bengal. Thrust, strike slip or normal faulting (or either of the combination) is obtained for earthquakes occurring in the Arabian Sea and the Indian Ocean. The resultant compressive and tensional stress directions are estimated from more than 300 centroid moment tensor (CMT) solution of earthquakes occurring in different parts of the Indian Ocean. The resultant compressive stress directions are changing from north-south to east-west and the resultant tensional stress directions from east-west to north-south in different parts of the Indian Ocean. The results infer the counterclockwise movement of the region (0°–33°S and 64°E–94°E), stretching from the Rodriguez triple junction to the intense deformation zone of the central Indian Ocean and the formation of a new subduction zone (island arc) beneath the intense deformation zone of the central Indian Ocean and another at the southern part of the central Indian basin. The compressive stress direction is along the ridge axis and the extensional stress manifests across the ridge axis. The north-south to northeast-south west compression and east-west to northwest-southeast extension in the Indian Ocean suggest the northward underthrusting of the Indian plate beneath the Eurasian plate and the subduction beneath the Sunda arc region in the eastern part. The focal depth of earthquakes is estimated to be shallow, varying from 4 to 20 km and increasing gradually in the age of the oceanic lithosphere with the focal depth of earthquakes in the Indian Ocean.     

Moment Magnitude (M W) and Local Magnitude (M L) Relationship for Earthquakes in Northeast India

An attempt has been made to examine an empirical relationship between moment magnitude (M _W) and local magnitude (M _L) for the earthquakes in the northeast Indian region. Some 364 earthquakes that were recorded during 1950–2009 are used in this study. Focal mechanism solutions of these earthquakes include 189 Harvard-CMT solutions (M _W?≥?4.0) for the period 1976–2009, 61 published solutions and 114 solutions obtained for the local earthquakes (2.0?≤?M _L?≤?5.0) recorded by a 27-station permanent broadband network during 2001–2009 in the region. The M _W–M _L relationships in seven selected zones of the region are determined by linear regression analysis. A significant variation in the M _W–M _L relationship and its zone specific dependence are reported here. It is found that M _W is equivalent to M _L with an average uncertainty of about 0.13 magnitude units. A single relationship is, however, not adequate to scale the entire northeast Indian region because of heterogeneous geologic and geotectonic environments where earthquakes occur due to collisions, subduction and complex intra-plate tectonics.     

青藏高原震源分布与板块运动

本文分析了青藏高原及其邻区大量近期地震的震源深度分布资料,发现中源地震不仅分布在众所周知的兴都库什和印缅山弧一带,而且在印度洋板块与欧亚板块汇聚带印度河-雅鲁藏布江以南,以及欧亚板块内部的帕米尔、西昆仑、柴达木和天山南缘一带也有中源地震分布,它们构成了这一地区三条向南倾斜的震源带。 这些中源地震震源带的存在表明,向北运动的印度次大陆与亚洲大陆碰撞以后,印度次大陆北缘本身并没有消减,而是迫使亚洲大陆通过三条向南倾斜的岩石层消减带产生了大规模的消减作用。 中源地震在平面上分布的不连续性,揭示了这一地区的许多条走滑断层的现代活动。这些走滑断层的巨大位移显示了青藏高原内部各块体之间的横向运动也是很可观的。 最后,提出了亚洲大陆多条南倾消减带的形成和发展模式。     

Anelasticity of the crust and upper mantle beneath north and central India from the inversion of observed Love and Rayleigh wave attenuation data

The fundamental mode Love and Rayleigh waves generated by earthquakes occurring in Kashmir, Nepal Himalaya, northeast India and Burma and recorded at Hyderabad, New Delhi and Kodaikanal seismic stations are analysed. Love and Rayleigh wave attenuation coefficients are obtained at time periods of 15–100 seconds, using the spectral amplitude of these waves for 23 different paths along northern (across Burma to New Delhi) and central (across Kashmir, Nepal Himalaya and northeast India to Hyderabad and Kodaikanal) India. Love wave attenuation coefficients are found to vary from 0.0003 to 0.0022 km^–1 for northern India and 0.00003 km^–1 to 0.00016 km^–1 for central India. Similarly, Rayleigh wave attenuation coefficients vary from 0.0002 km^–1 to 0.0016 km^–1 for northern India and 0.00001 km^–1 to 0.0009 km^–1 for central India. Backus and Gilbert inversion theory is applied to these surface wave attenuation data to obtainQ ^–1 models for the crust and uppermost mantle beneath northern and central India. Inversion of Love and Rayleigh wave attenuation data shows a highly attenuating zone centred at a depth of 20–80 km with lowQ for northern India. Similarly, inversion of Love and Rayleigh wave attenuation data shows a high attenuation zone below a depth of 100 km. The inferred lowQ value at mid-crustal depth (high attenuating zone) in the model for northern India can be by underthrusting of the Indian plate beneath the Eurasian plate which has caused a low velocity zone at this shallow depth. The gradual increase ofQ ^–1 from shallow to deeper depth shows that the lithosphere-asthenosphere boundary is not sharply defined beneath central India, but rather it represents a gradual transformation, which starts beneath the uppermost mantle. The lithospheric thickness is 100 km beneath central India and below that the asthenosphere shows higher attenuation, a factor of about two greater than that in the lithosphere. The very lowQ can be explained by changes in the chemical constitution taking place in the uppermost mantle.     

俯冲带地震动特征及其衰减规律探讨

随着我国南海不断开发建设,海洋工程的抗震问题日益受到重视.我国南海东部区域位于大陆板块与海洋板块共同作用的俯冲带地区,地震活动频繁,震级较大,潜在地震对南海开发建设有重要影响.为了研究俯冲带地震的地震动特征及其衰减规律,本文基于实际俯冲带地震数据,并结合数值模拟方法,分析和探讨了俯冲带板内、板缘地震与浅地壳地震的地震动特征和衰减规律的差异.研究结果表明:俯冲带地震动存在区域性差异,在地震动衰减特征方面,同一区域的俯冲带板缘地震要比浅地壳地震衰减慢,俯冲带板内地震要比浅地壳地震衰减得快;数值模拟分析不同深度海水对海底地震动的影响表明,海底地震动水平分量几乎不受海水介质的影响,但是竖向分量随海水深度的增加有减小的趋势.最终,基于数值模拟和经验关系的混合方法建立了南海俯冲带地震动衰减关系模型,其结果可为海域区划等相关研究和海域工程建设提供参考.     

Global tectonics and the plate motion obtained from the ITRF97 station velocity vectors

~~Global tectonics and the plate motion obtained from the ITRF97 station velocity vectors@马宗晋 @任金卫 @张进~~     

Attenuation of seismic waves from moderate earthquakes of the Vrancea zone

The paper presents results of studying the attenuation of ground accelerations from earthquakes of the Vrancea with magnitudes less that 6.0 at distance greater than 300 km in a narrow sector located northeast of the focal region, within the limits of which are located acting and planned nuclear power plants (NNPs). Attenuation of peak ground accelerations in individual sections along the Vrancea–IRIS OBN station path is approximated by individual functions. It is shown that for a rough estimation of the seismic effect of earthquakes from the Vrancea zone it is acceptable to use the empirical relationship obtained by F.F. Aptikaev. For a more accurate estimate, it needs to be modified by adding a constant, whose value depends on the specific conditions of the NPP sites. It is shown that the results of data analysis on moderate earthquakes can be extrapolated to an earthquake with the maximum possible magnitude for the Vrancea zone and used to estimate the maximum seismic effects at the sites of operating and planned NPPs.     

西北太平洋俯冲带日本本州至中国东北段应力场反演

本研究基于Global CMT提供的1196个1976年11月—2017年1月MW4.6地震矩心矩张量解,对西北太平洋俯冲带日本本州至中国东北段的应力场进行反演计算,得到了从浅表到深部俯冲带应力状态的完整分布.结果显示:俯冲带浅表陆壳一侧应力场呈现水平挤压、垂向拉伸状态,洋壳一侧的应力状态则相反,即近水平拉张、近垂向压缩.沿着俯冲板片向下,应力主轴逐渐向俯冲板片轮廓靠拢,其中位于双地震层(120km深度附近)之上的部分,主张应力轴沿俯冲板片轮廓展布而又比其更为陡倾;双地震层内的应力模式同典型I型双层地震带内的应力模式一致,即上层沿俯冲板片轮廓压缩、下层沿俯冲板片轮廓拉伸;双地震层之下,应力模式逐步转变为主压应力轴平行于俯冲板片轮廓.通观所研究的整个俯冲系统,水平面内主压和主张应力轴基本保持了与西北太平洋板片俯冲方向上的一致性,同经典俯冲板片的应力导管模型所预言的俯冲带应力模式相符;而主张应力轴在俯冲板片表面之下的中源地震深度范围内转向海沟走向,或许同研究区域横跨日本海沟与千岛海沟结合带,改变的浅部海沟形态致使完整俯冲板片下部产生横向变形有关.     

The geometry of the Burmese-Andaman subducting lithosphere

The gross seismotectonic features for the Burmese-Andaman arc system which defines the northeast margin of the Indian plate are rather well known but variations in the subduction zone geometry along and across the arc and fault pattern within the subducting Indian plate have not been studied. Present workaims to study these by using seismicity data whose results are presented in the form of: (a) Lithospheric across-the-arc sections at about every 100–120 km (approximately one degree latitude apart) covering the 3500 km longBurmese-Andaman arc system, (b) a structure contour map showing the depth tothe top surface of the seismically active lithosphere and (c) interpretationof focal mechanism solutions for 148 Benioff zone earthquakes. Both penetrationdepth and the dip of the Benioff zone vary considerably along the arc in correspondence to the curvature of the fold-thrust belt which varies from concave to convex in different sectors of the arc. Several extensive `Hinge faults' that abut at high angles to the arc orientation, are inferred from aninterpretation of the structure contour map. Active nature of the hinge faultsis established in several areas by their association with earthquakes andcorroborated through fault plane solutions. At shallow level of the Benioffzone along these faults, focal mechanism solutions display left lateral strikeslip movement while at deeper levels reverse fault solutions are common.     

Simulations of Seismic Hazard for the Pacific Northwest of the United States from Earthquakes Associated with the Cascadia Subduction Zone

-- We investigate the impact of different rupture and attenuation models for the Cascadia subduction zone by simulating seismic hazard models for the Pacific Northwest of the U.S. at 2% probability of exceedance in 50 years. We calculate the sensitivity of hazard (probabilistic ground motions) to the source parameters and the attenuation relations for both intraslab and interface earthquakes and present these in the framework of the standard USGS hazard model that includes crustal earthquakes. Our results indicate that allowing the deep intraslab earthquakes to occur anywhere along the subduction zone increases the peak ground acceleration hazard near Portland, Oregon by about 20%. Alternative attenuation relations for deep earthquakes can result in ground motions that differ by a factor of two. The hazard uncertainty for the plate interface and intraslab earthquakes is analyzed through a Monte-Carlo logic tree approach and indicates a seismic hazard exceeding 1 g (0.2 s spectral acceleration) consistent with the U.S. National Seismic Hazard Maps in western Washington, Oregon, and California and an overall coefficient of variation that ranges from 0.1 to 0.4. Sensitivity studies indicate that the paleoseismic chronology and the magnitude of great plate interface earthquakes contribute significantly to the hazard uncertainty estimates for this region. Paleoseismic data indicate that the mean earthquake recurrence interval for great earthquakes is about 500 years and that it has been 300 years since the last great earthquake. We calculate the probability of such a great earthquake along the Cascadia plate interface to be about 14% when considering a time-dependent model and about 10% when considering a time-independent Poisson model during the next 50-year interval.     

中国大陆西部及周边地区地震活动特征的研究

探讨了中国周缘板块的联合作用对中国大陆地震的控制和影响，进一步研究了中国大陆西部及周边地区的地震活动特征。结果发现，该区域的地震活动除了有高潮和低潮的轮回特征外，还有相互消长的关系，并且地震相互消长有一个特定的比例。这一特点，对于中国大陆强震活动主体区的预测，尤其是对地震高潮期的结束时间提供了一个判据。     

青藏高原吉隆-鲁谷(Hi-Climb)层析成像与印藏碰撞的消减作用

利用中美合作Hi-Climb项目北段吉隆-鲁谷剖面的天然地震探测数据,拾取2004～2005年期间5级以上地震事件的P波与4级以上地震的Pn波震相的走时,通过多震相层析成像反演获得青藏高原腹地的地下500 km以上的P波速度扰动结构.结果表明雅江地区为北向倾斜的低速扰动,班公-怒江断裂下方存在向南俯冲并被印度板块俯冲挤压而回折的高速体,建立了印度板块在冈底斯地块下方拆沉并被雅江低速体穿越的构造样式.说明印度板块俯冲在到达班公-怒江缝合带之前已经开始消减,与拆沉位置对比发现,印度板块的前锋深部呈现多期多级次特征,并受到地幔热循环作用的影响.     

Seismotectonics of the Himalaya and its vicinity from centroid-moment tensor (CMT) solution of earthquakes

The centroid-moment tensor solutions of more than 300 earthquakes that occurred in the Himalayas and its vicinity regions during the period of 1977–1996 are examined. The resultant seismic moment tensor components of these earthquakes are estimated. The Burmese arc region shows prominent east–west compression and north–south extension with very little vertical extension. Northeast India and Pamir–Hindu Kush regions show prominent vertical extension and east–west compression. The Indian plate is subducting eastward beneath the northeast India and Burmese arc regions. The overriding Burmese arc has overthrust horizontally with the underthrusting Indian plate at a depth of 20–80 km and below 80 km depth, it has merged with the Indian plate making “Y” shape structure and as a result the aseismic zone has been formed in the region lying between 26°N–28°N and 91.5°E–94°E at a depth of 10–50 km. Similarly, the Indian plate is underthrusting in the western side beneath the Pamir–Hindu Kush region and the overriding Eurasian plate has overthrust it to form a “Y” shape structure at a depth of 10–40 km and below 60 km depth, it has merged with the Indian plate and both the plates are subducting below 60–260 km depth. Further south, the overriding Eurasian plate has come in contact with the Indian plate at a depth of 20–60 km beneath northwest India and Pakistan regions with left lateral strike slip motion.     

Response spectral attenuation relationships for Singapore and the Malay Peninsula due to distant Sumatran‐fault earthquakes

As part of the effort to assess the seismic hazards of Singapore and the Malay Peninsula, representative ground motion prediction models have to be established. Seven existing attenuation relationships developed for shallow crustal earthquakes in stable continent and active tectonic regions are examined, and they are found to consistently over‐predict the ground motions of Sumatran‐fault earthquakes recently recorded in Singapore. This may be attributed to the differences in the regional crustal structures and distance ranges considered. Since the number of recorded ground motions in the region is very limited, a new set of attenuation relationships is derived based on synthetic seismograms. The uncertainties in rupture parameters, such as stress drop, focal depth, dip and rake angles, are defined according to the regional geological and tectonic settings as well as the ruptures of previous earthquakes. Ground motions are simulated for earthquakes with Mw ranging from 4.0 to 8.0, within a distance range from 174 to 1379km. Besides magnitude and distance, source‐to‐station azimuth is found to influence the amplitudes of the ground motions simulated. Thus, the azimuth is taken as an independent variable in the derived ground motion attenuation relationships. The Sumatran‐fault segments that have the potential to generate a specified level of response spectral accelerations in Singapore and Kuala Lumpur are identified based on the newly derived ground motion models. Copyright © 2003 John Wiley & Sons, Ltd.     

Oblique Plate Convergence in the Indo-Burma (Myanmar) Subduction Region

— The Indo-Burma (Myanmar) subduction boundary is highly oblique to the direction of relative velocity of the Indian tectonic plate with respect to the Eurasian plate. The area includes features of active subduction zones such as a Wadati-Benioff zone of earthquakes, a magmatic arc, thrust and fold belts. It also has features of oblique subduction such as: an arc-parallel strike-slip fault (Sagaing Fault) that takes up a large fraction of the northward component of motion and a buttress (the Mishmi block) that resists the motion of the fore-arc sliver. In this paper, I have examined the seismicity, slip vectors and principal axes of the focal mechanisms of the earthquakes to look for features of active subduction zones and for evidence of slip partitioning as observed in other subduction zones. The data set consists of Harvard CMT solutions of 89 earthquakes (1977–1999 with 4.8≦̸Mw≦̸7.2 and depths between 3–140 km). Most of these events are shallow and intermediate depth events occurring within the Indian plate subducting eastward beneath the Indo-Burman ranges. Some shallow events within the fore-arc region have arc-parallel Paxes, reflecting buttressing of the fore-arc sliver at its leading edge. Some of the shallowest events have nearly E-W oriented P axes which might account for recent folding and thrusting. Examination of earthquake slip vectors in this region shows that the slip vector azimuths of earthquakes in the region between 20°–26°N are rotated towards the trench normal, which is an indication of partial partitioning of the oblique convergence. It is seen that all aspects of seismicity, including the paucity of shallow underthrusting earthquakes and the orientation of P axes, are consistent with oblique convergence. The conclusions of this paper are consistent with recent geological studies and interpretations such as the coexistence of eastward subduction, volcanic activity and transcurrent movement through mid-Miocene to Quaternary period.     

Historical seismicity near Chagos: a complex deformation zone in the equatorial Indian Ocean

Over the last twenty years, Chagos Bank has a seismicity rate disproportionate to its supposed intraplate location. Earthquake relocation also shows a high seismicity rate in pre-WWSSN time (1912–1963), with seven events located off of the Central Indian Ridge, including large events in 1912 (M = 6.8) and 1944 (M = 7.2). This study uses the moment variance technique, a systematic search for the mechanism which best fits P, PP, SH, Love and Rayleigh amplitudes, to determine the focal mechanisms of two pre-WWSSN earthquakes. A test with a recent event of known mechanism demonstrates that accurate focal parameter determination is possible even when only a few good records are available. Moment variance analysis shows a thrust faulting mechanism for the 1944 event, northeast of Chagos Bank near the Chagos-Laccadive ridge, and a strike-slip focal mechanism for a smaller 1957 event west of Chagos Bank. The 1944 event, one of the largest oceanic “intraplate” earthquakes known (moment 1.4 × 10²⁷ dyne-cm), indicates that the Chagos seismicity reflects not an isolated occurrence of normal faulting as previously thought, but rather regional tectonic deformation extending northeast of Chagos Bank and including thrust, normal and strike-slip events. This seismicity and previously studied seismicity near the Ninetyeast Ridge and Central Indian Basin suggest a broad zone of deformation stretching across the equatorial Indian Ocean. This zone contains all known magnitude seven oceanic “intraplate” earthquakes not associated with subduction zones or continental margins, suggesting that elsewhere such extensive deformation occurs only along plate boundaries. This study proposes that a slow, diffuse plate boundary extends east from the Central Indian Ridge to the Ninetyeast Ridge and north to the Sumatra Trench. A recent plate motion study confirms this boundary and suggests that it separates the Australian plate from a single Indo-Arabian plate.     

2008年新疆乌恰6.8级地震序列震源特征及帕米尔东北缘应力场研究

本文使用新疆区域数字地震台站记录的宽频带长周期数字波形资料,在时间域反演了2008年10月5日新疆乌恰6.8级地震的强余震及其周围先后发生的52次中等强度地震的矩张量解,结合Harvard大学在该区域的地震矩张量结果,研究了帕米尔东北缘的应力场分区特征.研究结果显示,位于印度板块向欧亚板块推挤的前缘及向北凸出的弧型构造的最北缘的卡兹克阿尔特弧形活动褶皱-逆断裂带,以逆冲推覆活动为主,并有部分走滑类型的地震,基本不存在正断层类型的地震;该弧型构造近东西走向的顶部(文中的西区)与其北西走向的东侧(文中的东区)的局部应力场最大主压应力方向不同,分别为NW、NNE方向,显示出在承受印度板块向欧亚板块俯冲作用的同时,东区也更多的受到了塔里木块体顺时针旋转作用的影响.位于帕米尔陆内俯冲和变形作用强烈、碰撞造成深源地震带东段的南区,地震以走滑错动为主, 逆断、正断层都有,显示出相对复杂的应力状态.位于帕米尔高原内部的西区和南区的应力场最大主压应力方向一致,由北向南,由最大主压应力轴接近水平,过渡为最大主张应力轴接近水平,一定程度揭示了板块俯冲的状态.结合南区和西区的地震深度差异及机制解中断层面的倾角,推测在中帕米尔的东部,由北向南的板块俯冲至150~170km深度,俯冲角度为60°左右.     

南海、中印半岛及其邻近地区的地震活动及应力状态

研究了南海、中印半岛及邻区的地震分布,地震主要集中在板块的边界。此外,一些浅震主要集中在缅甸西部和中缅边界。研究了Benioff带的形态。在爪哇海沟、菲律宾海沟,两板块耦合得不好;在缅甸山弧、安达曼-尼科巴岛弧下,俯冲的印度板块向NNE运动。由震源机制解及断层运动推断,主压应力方向在缅泰西部为NNE,在南海为NNW或S-N,与板块相互作用密切相关。      

EFFECT OF TSUNAMIS GENERATED IN THE MANILA TRENCH ON CHINA MAINLAND

Tsunami is one of the most devastating natural coastal disasters. Most of large tsunamis are generated by submarine earthquakes occurring in subduction zones. Tsunamis can also be triggered by volcano eruptions and large landslides. There are many records about "sea-overflow" in Chinese ancient books, which are not proved to be tsunamis. Tectonics and historical records analysis are import to forecast and prevention of tsunami. Consider the tectonic environment of the China sea, the possibility of huge damage caused by the offshore tsunami is very small. And the impact of the ocean tsunami on the Bohai sea, the Yellow sea, and the East China sea is also small. But in the South China Sea, the Manila subduction zone has been identified as a high hazardous tsunamigenic earthquake source region. No earthquake larger than M_W7.6 has been recorded in the past 100a in this region, suggesting a high probability for larger earthquakes in the future. If a tsunamigenic earthquake were to occur in this region in the near future, a tragedy with the magnitude similar to the 2004 Indian Ocean tsunami could repeat itself. In this paper, based on tectonics and historical records analysis, we have demonstrated that potential for a strong future earthquake along the Manila subduction zone is real. Using a numerical model, we have also shown that most countries in the South China Sea will be affected by the tsunamis generated by the future earthquake. For China, it implies that the maximum wave height over 4.0 meter on China mainland, especially the Pearl River Estuary. But the island, local relief maybe influence the maximum wave. But it takes nearly 3 hours to attack China mainland, if there is the operational tsunami warning system in place in this region, should be greatly reduced losses. And the simulated results are conformable to historical records. It indicates that the tsunami hazards from Manila trench to China mainland worthy of our attention and prevention.     

Seismicity,earthquake mechanisms and tectonics along the Himalayan mountain range and vicinity

The historical as well as recent seismicity data and the focal mechanism solutions for 48 earthquakes determined from the observations of world-wide standardized stations network (WWSSN) records, were used to investigate the tectonics of the Himalayan mountain system and vicinity. Seismicity maps of the region showing large earthquakes (magnitude 7.0 and above, and damaging earthquakes that caused fatalities) from the earliest time through 1976, and instrumentally located earthquakes for the period January 1963–March 1974 are presented. Eleven of these earthquakes are estimated to be of magnitude 8.0 and above. The earthquake epicenters generally follow the trend of the mountains with greatest concentrations of seismic activity occurring along the Hindu Kush and Pamir mountain ranges, and near the Quetta, Kashmir and Assam syntaxes. Throughout Tibet, however, the distribution of epicenters is rather irregular and no clear trends are apparent. Two aseismic lineaments, one west of the Sulaiman Range and the other in the Assam Valley, are identified. Also, seismic activity in the vicinity of the Counter Thrust (Indus-Tsangpo suture zone) is rather small. Based on the identification of these aseismic lineaments and from a consideration of the geometry and kinematics of the continental collision model, a hypothesis for the origin of the Himalayan syntaxes is presented.Focal mechanism solutions confirm northward underthrusting of the Indian Plate along the Main Boundary Thrust and Main Central Thrust system, and eastward underthrusting along the Burmese Arc. Fault-plane solutions indicate left-lateral motion along the Kirthar-Sulaiman Range, right-lateral motion along the Karakoram Fault, left-lateral motion along the eastern extremity of the Himalayan flank of the Assam syntaxis, and right-lateral motion along the northern part of the Naga Hill flank of the syntaxis. These observations are in agreement with the expected sense of lateral (parallel to the collision boundary) mass movement for the continental collision model. Focal mechanism solutions for three earthquakes in east Afghanistan show NW-SE compression. A near-vertical orientation of the axes of tension in the solutions for two earthquakes in the Hindu Kush region is consistent with the sinking of a remnant slab of oceanic lithospere. Normal fault-plane solutions showing NW-SE extension for two events near Gatok, Tibet, and for the recent Kinnaur earthquake are interpreted to indicate a possible subsurface northern continuation of the Aravalli Range of Peninsular India, and its involvement in the tectonic framework of the region. Focal mechanism solutions of three earthquakes near the southern edge of the Shillong Plateau suggest block uplift of the plateau as a horst along the Dauki Fault. The solution for one earthquake near the Yunnan Graben shows NE-SW extension.