泰国北部梅江断裂探槽剖面研究     

韩新民  张建国  毛玉平  杨继武 《地震研究》2001,24(1):61-64

通过详细分析上覆于梅江断裂上全新统地层中三个人工探槽剖面，得出该断裂是一条全新世活动断层，且近3000年以来，至少发生过两次7级左右强烈地震事件的结论性认识。  相似文献   

Anomalous Rayleigh-Wave Propagation Along Oceanic Trench     

Yomogida  Kiyoshi  Okuyama  Riko  Nakanishi  Ichiro 《Studia Geophysica et Geodaetica》2002,46(4):691-710

A clear later phase of amplitude larger than the direct surface wave packet was observed at stations in Hokkaido, Japan, for several events of the December 1991 off-Urup earthquake swarm in the Kuril Islands region. From its particle motion, this phase is likely to be a fundamental Rayleigh wave packet that arrived with an azimuth largely deviated from each great-circle direction. As its origin, Nakanishi (1992) proposed that the sea-trench topography in this area as deep as 10 km may produce a narrow zone of low velocity for Rayleigh waves of periods around 15 sec. Following this idea, we compute ray paths and estimate how Rayleigh waves would propagate if we assume that lateral velocity variations are caused only by seafloor topography. We confirm that thick sea water in the trench indeed produces the phase velocity of Rayleigh waves to be smaller than in a surrounding area by the degree over 100%. Such a low-velocity zone appears only in a period range from 12 to 20 sec. Although this strong low-velocity zone disturbs the direction of Rayleigh wave propagation from its great circle, the overall ray paths are not so affected as far as an epicentre is outside this low-velocity zone, that is, off the trench axis. In contrast, the majority of rays are severely distorted for an event within the low-velocity zone or, in other words, in the neighborhood of the trench axis. For such an event, a part of wave energy appears to be trapped in this zone and eventually propagates outwards due to the curvature or bend of trench geometry, resulting in very late arriving waves of large amplitude with an incident direction clearly different from great circles. This phenomenon is observed only at a very limited period range around 16 sec. These theoretical results are consistent with the above mentioned observation of Nakanishi (1992).  相似文献   

Research on paleoearthquakes in Jiuxian trenches across Nankou-Sunhe fault zone in Changping County of Beijing plain     

江娃利  侯治华  谢新生 《中国科学D辑(英文版)》2002,45(2):160-173

An abundance of the phenomena of tectonic deformation and paleoseismic events of different times and their recurrent interval, as well as coseismic vertical displacements is exposed in Jiuxian trenches across the Nankou-Sunhe fault zone in Changping County. The research result shows three paleoearthquakes occurring during the Holocene. They were dated as 10643 ± 250 a B.P.-9706 ± 1235 a B.P., 7894±150 a B.P.-7640 ± 650 a B.P., and 3987±100 a B.P.-3670 ± 310 a B.P., respectively. The coseismic vertical displacements are 1.0 m, 2.0 m, and 2.0 m, respectively. From a statistical formula of relation between historic earthquake magnitudes and surface seismic dislocations in North China, the magnitudes of these paleoearthquakes are inferred to be in a range from M 7.7 to M 7.9. The research shows that the Holocene fault activity in the plain can be traced in the trenches according to the micro-geomorphic features. Many micro-structural phenomena are also found in these trenches. Identification of the paleoearthquakes in the Nankou-Sunhe fault zone during the Holocene time is of significance for assessment of future seismic risk in Beijing area.  相似文献   

Incipient subduction of the Ontong Java Plateau along the North Solomon trench     

A. Taira  P. Mann  R. Rahardiawan   《Tectonophysics》2004,389(3-4):247

The Ontong Java Plateau (OJP) in the western central Pacific is the largest and thickest oceanic plateau and one of a few oceanic plateaus converging on an island arc (Solomon island arc—SIA). To better understand the evolution of the North Solomon trench (NST), active oblique convergence between the OJP and SIA, and late Neogene development of Malaita accretionary prism (MAP), we present 850 km of multichannel seismic reflection data integrated with 7832 km² of IZANAGI side-scan sonar coverage. We have focussed the study at the transition area between the well-defined northwestern end of the North Solomon trench and a diffusely deformed area where the trench is actively propagating in a northwestward direction. The deeper structure beneath the survey area is discussed by Phinney et al. [Oceanic plateau accretion in the Malaita accretionary prism inferred from multi-channel seismic reflection data, this issue] using deeper penetration, multichannel seismic reflection lines. The serial cross sections provided by multichannel seismic profiling combined with the IZANAGI backscattering imagery provides a time series evolution for the development of the North Solomon trench. The main evolutionary stages include (1) the incipient trench in the northern area marked by a diffuse zone of deformation above a broad arch in the crust. Deeper penetration profiles by Phinney et al. show the bulge is related to a deeper decollement fault that is propagating upward and seaward through the crust. (2) The formation of a continuous thrust front in the central area. Deeper penetration profiles by Phinney et al. show this thrust front is surface expression of the same decollement present at depth to the north. The boundary between the surface trace of the thrust and the diffuse area of deformation in the northern area is inferred as a vertical, high-angle tear fault with left-lateral offset. (3) The formation of a deep, elongate trench which controls gravitationally related slumping and sedimentation around the steep edges of the trench fill basin. The areas to the southeast are those that have undergone convergence for the longest period of time and therefore show better developed trench structures and a reduced width of the MAP. Areas to the northwest have undergone convergence for a shorter period of time and show less developed trench structures and a wide area of the MAP.  相似文献   

Evidence of paleoearthquakes from trench investigations across Pinjore Garden fault in Pinjore Dun, NW Himalaya   总被引：2，自引：0，他引：2  

Javed N. Malik  George Mathew 《Journal of Earth System Science》2005,114(4):387-400

The Pinjore Garden Fault (PGF) striking NNW-SSE is now considered one of the active faults displacing the younger Quaternary surfaces in the piggyback basin of Pinjore Dun. This has displaced the older Kalka and Pinjore surfaces, along with the other younger surfaces giving rise to WSW and SW-facing fault scarps with heights ranging from 2 to 16 m. The PGF represents a younger branch of the Main Boundary Thrust (MBT) system. An ~ 4m wide trench excavated across the PGF has revealed displacement of younger Quaternary deposits along a low angle thrust fault. Either side of the trench-walls reveals contrasting slip-related deformation of lithounits. The northern wall shows displacement of lithounits along a low-angle thrust fault, while the southern wall shows well-developed fault-related folding of thick sand unit. The sudden change in the deformational features on the southern wall is an evidence of the changing fault geometry within a short distance. Out of five prominent lithounits identified in the trench, the lower four units show displacement along a single fault. The basal unit ‘A’ shows maximum displacement of aboutT _o = 2.85 m, unit B = 1.8 m and unit C = 1.45 m. The displacement measured between the sedimentary units and retro-deformation of trench log suggests that at least two earthquake events have occurred along the PGF. The units A and D mark the event horizons. Considering the average amount of displacement during one single event (2 m) and the minimum length of the fault trace (~ 45 km), the behaviour of PGF seems similar to that of the Himalayan Frontal Fault (HFF) and appears capable of producing large magnitude earthquakes.  相似文献   

Pliocene marine deposits at Punta Maldonado, Guerrero state, Mexico     

Edgar Jurez-Arriaga  Ana Luisa Carreo  Jos Luis Snchez Zavala 《Journal of South American Earth Sciences》2005,19(4):537-546

Diverse and abundant Foraminifera and Ostracoda assemblages were recovered from a measured stratigraphic section at Punta Maldonado, Guerrero state, Mexico. The planktonic species indicate an early Pliocene age, between 5.3 and 3.6 Ma; an early late Pliocene (around 2.4 Ma) planktonic assemblage also was recorded from isolated deposits. These ages contradict the Cretaceous–Paleogene age previously assigned to the sedimentary succession at Punta Maldonado. All indicators—benthic assemblages, ichnofacies, lithology, grain size, primary structures, mineralogy, body rock geometry, and facies—suggest deposition in the foreshore and offshore transition zones of a storm-dominated shallow siliciclastic shelf. The Ostracoda and Foraminifera indicate deposition around the outer neritic/upper bathyal boundary, which suggests an uplift of 320–400 m in the area during the Pliocene. This study represents the first report of Pliocene marine rocks in the southwestern coast of Mexico; the data presented contribute to regional geotectonic models.  相似文献   

深基坑支护变形机理及实例分析          下载免费PDF全文

齐亮  刘康和 《探矿工程》2005,32(3):5-8

介绍了深基坑支护变形机理，结合工程实例，根据收集整理的深基坑支护变形监测结果，简述了深基坑支护变形计算中存在的一些问题，并对一些新方法做了简要探讨。  相似文献   

Focal mechanism solutions and its tectonic significance in the trench of the eastern South China Sea   总被引：1，自引：0，他引：1  

朱俊江  丘学林  詹文欢  徐辉龙  孙龙涛 《地震学报(英文版)》2005,18(3):280-289

Introduction South China Sea (SCS) is located in the convergence zone between Euro-Asian plate, Pacific plate (Philippine plate) and Indian plate. Interactions of three plates made the crust of this region suffer tectonic stress in many directions and made the South China Sea be in the complex environ-ment of the tectonic stress. There are four different marginal types in the surrounding of the South China Sea: The tectonic zone of the rifting margin in the north of SCS, the NS direct…  相似文献   

海原断裂高湾子地点三维探槽的开挖与古地震研究   总被引：22，自引：6，他引：22       下载免费PDF全文

冉勇康  焦德成 《地震地质》1997,19(2):2-107

对海原断裂高湾子地点进行大比例尺地质地貌填图和三维探槽开挖，揭示出７次古地震事件，除１９２０年地震外，它们的年龄分别为距今（１０００４±３１９６），（６６８９±１６９），（６１２０±５０５），（４２０８±５７７），（２７６３±３７２）和（１００５±４６５）ａ；重复间隔分别为（３３１５±３２００），（５６１±５３２），（１９２０±７６６），（１４２５±６８６），（１５７８±５９５）和（９８０±４６５）ａ。事件Ⅲ，Ⅳ，Ⅴ，Ⅵ，Ⅶ的水平位移量分别为（５．６±２．３），（１．５±１．１），（１．５±１．１），（２±１）和（７±０．５）ｍ。显示出重复间隔时间的分段性和特征行为的分级性。两次类似１９２０年强度的地震间隔期间，有３次位移量为１～２ｍ的地震发生  相似文献   

Earthquake migration in East Asia mainland (I)—The migration of huge earthquakes and volcanic activity from West Pacific Trench to the Chinese mainland     

Gen-Mo Zhao  Lan-Yu Yao 《地震学报(英文版)》1995,8(4):541-549

The researches in this paper disclose a huge earthquake migration series that lasted more than one century—from the 17th century to the early day of the 18th, transverse migration of huge earthquake from West Pacific trench to the Chinese mainland, lasted about 134 a, the distance is about 2600 km, the velocity is about 19 km/a, and the direction of migration agrees with the direction of plate subduction and vertical to the strike of plate boundary. The migration has two branches. One extends westwards and terminates at the central longitude belt (Helanshan—Liupanshan fault zone) of the Chinese mainland, triggered the strongest seismicity episode in North China, including 4 earthquakes withM ⩾8.0. The other extends northwards, passing through Korea Peninsula, terminates at the north part of Heilongjian Province, and triggered the volcanic eruption activity in Changbaishan and Wudalianchi. The time-space linearity of migration is good. Its velocity is stable and its activity attenuates gradually. It is estimated that it is related with the disturbance of asthenosphere matters caused by the sudden acceleration of the subduction of the trench plate. There are two similar transverse migration series from 1498 to 1556 and from 1843 to 1927, and the velocities are 36.2 and 33.7 km/a respectively.  相似文献