Maps of recent vertical crustal movements in Romania: Similarities and differences

A new map of recent crustal vertical movements (RCVM) in Romania, on the basis of high-precision geodetical measurements by the repeated levelling method, had become necessary firstly as a consequence of the great seismic event of March 4, 1977 with foci under the Vrancea Region (the most important seismic zone in the country) and secondly because many years had passed since the previous edition.Certainly, there are similitudes and differences between the two editions, and the authors will try to put these into evidence and explain them.The general view of the major geological units of Romania in both maps is the same: the mountain regions being zones of more or less continuous uplift, the plains showing subsidence movements and the plateau regions presenting a relative stability. Some modifications became apparent owing to the improvement of the national geodetical network on which the repeated levelling measurements were performed and following the choice of the Harbour of Constanţa as the fundamental point.     

Coseismic vertical deformation of the MS8.0 Wenchuan earthquake from repeated levelings and its constraint on listric fault geometry

The devastating M_S8.0 Wenchuan earthquake ruptured two large parallel thrust faults along the middle segment of the Longmenshan thrust belt. Preseismic and postseismic leveling data indicated the hanging wall of the YingxiuBeichuan-Nanba thrust fault mainly presented coseismic uplift with respect to the reference point at Pingwu county town, and the observed maximum uplift of 4.7 m is located at Beichuan county (Qushan town) which is about 100 m west of the fault scarp. The foot wall of the Yingxiu-Beichuan-Nanba thrust fault mainly showed subsidence with maximum subsidence of 0.6 m near the rupture. By employing a listric dislocation model, we found that the fault geometry model of exponential dip angle δ= 88°?×1-exp(-9/h) with depth of 18 km and uniform thrust-slip of 5.6 m could fit the observed coseismic vertical deformation very well, which verifies the listric thrust model of the Longmenshan orogenic zone.

     

The regularity of vertical crustal movements of the western slopes of the Peter the Great Range

The results of relevellings made in 1948 and 1969–1975 along the Obi-Hingou profile, which is a part of the Garm test area, are analysed. Different characteristics of slow movements in the separate parts of the levelling line divided by faults were obtained by using the displacement velocities of the Earth's surface in each separate section of the profile (from the results of repeated levellings). The uplift of the Peter the Great Range is determined against the background of subsidence in the Tadjik Depression. The exact values of maximum displacements ( ≈ 7 mm ) were determined and the radius of the deformation zone (12–13 km) was established for earthquakes with M = 4.5–5.     

Relation of surface movements in West Bohemia to earthquake swarms

GPS observations in the Western Bohemia/Vogtland earthquake swarm region revealed indications of horizontal displacements of low amplitude, and no clear long-term trend in 1993–2007. On the other hand, in 1998–2001 there was relatively significant active movement along NNE-SSW oriented line that we called the “Cheb-Kraslice GPS Boundary” (ChKB), identical with an important limitation of earthquake activity. The most impressive were dextral (right-lateral) movements in the 1998–1999 period followed by reverse sinistral (left-lateral) movements in 1999–2000 that correlate with prevailing motion defined by fault plane solutions of the Autumn 2000 earthquake swarm. Before the February 2004 micro-swarm, two points located on opposite sides of the Mariánské Lázně fault showed extension in the order of about 7 mm in the same NNE-SSW direction of ChKB. The new NOKO permanent GPS station in Novy Kostel showed the peak-to-peak vertical changes up to 10 mm before and during the February 2007 micro-swarm. Annual precise levelling campaigns in the local network around Novy Kostel revealed regular vertical displacements during the 1994, 1997 and 2000 earthquake swarms. The points around the Novy Kostel seismological station showed uplift during the active periods, including the micro-swarm February 2004. However, no such indication was observed on levelling points in the period of the February 2007 swarm. Long-term vertical displacements depend on the same direction NNE-SSW (ChKB) as the GPS displacements. Both geodetic techniques have revealed oscillating displacements, GPS horizontal, and levelling vertical, rather than any long-term trends in the study period 1993–2007. The displacements exhibited significant spatial and temporal relation to tectonic activity (earthquake swarms) including their coincidence with the seismologically determined sense of motion along the fault plane during earthquakes.     

GEOMETRY AND DEFORMATION TRANSFORMATION OF THE XIMALIN FAULT

The Ximalin fault is the northwest section of the Ximalin-Shuiquan fault, which is part of the north-edge fault zone of the Yanghe Basin, located in the conjunction of the Zhangjiakou-Bohai fault zone and Shanxi fault-depression basin, and its structural geometry and deformation characteristics can facilitate the research on the interaction of the two tectonic belts. In this paper, data of geological surveys and geophysical exploration are used to study this fault exhaustively, concerning its geometry, structural features and activity as well as its relationship with adjacent faults and rule in the deformation transform of the north-edge fault zone of the Yanghe Basin. The results show that the Ximalin Fault is a strike-slip feature with thrust component. Its vertical slip rates are 0.17mm/a and 0.25~0.38mm/a, and the horizontal slip rate is 0.58~0.67mm/a and 0.50mm/a during the late Middle Pleistocene and Holocene, respectively. It is formed alternately by the NW-trending main faults and secondary NE-trending faults, of which the former is characterized by high-angle reverse with sinistral strike-slip, and the latter shows normal faulting. The two sets of structures have specific structural geometry relations, and the motion manners and deformation characteristics match each other. During the active process of the north-edge fault of the Yanghe Basin, the NW trending Ximalin fault played a role similar to a transform fault in deformation change and stress transfer, and its sinistral strike slip activity accommodated the NE trending normal faulting at the both ends.     

中国东南地区地壳垂直形变基本特征

本文利用现有的Ⅰ、Ⅱ等多期水准复测成果,编制了我国东南地区垂直形变图。按区内垂直形变特征划分为三大区,南、北以上升为主,中部呈现大面积下降。文中还应用区内近期跨断裂测量资料,综合分析区域现代构造活动特点,并对区域构造应力场的变化进行了讨论     

Coseismic vertical deformation of the M_S8.0 Wenchuan earthquake from repeated levelings and its constraint on listric fault geometry

The devastating MS8.0 Wenchuan earthquake ruptured two large parallel thrust faults along the middle segment of the Longmenshan thrust belt.Preseismic and postseismic leveling data indicated the hanging wall of the YingxiuBeichuan-Nanba thrust fault mainly presented coseismic uplift with respect to the reference point at Pingwu county town, and the observed maximum uplift of 4.7 m is located at Beichuan county(Qushan town)which is about 100 m west of the fault scarp.The foot wall of the Yingxiu-Beichuan-Nan...     

Recent crustal movement studies at seiyal area, northwest of aswan Lake, Egypt

A local geodetic network of 20 points was established in 1988 around the Seiyal fault for monitoring lateral movements. Two levellinglines, crossing the fault, were prepared for monitoring vertical movements. The initial horizontal geodetic measurements were carried out in March 1989. The measurements were repeated twice a year. The initial vertical geodetic measurements (levelling) were carried out in November 1989 and repeated in November 1990.Four horizontal geodetic measurements and two levelling measurements were analysed. The results revealed remarkable horizontal and vertical changes during the period of measurement.     

Vertical movements on the territory of Tallinn

Studies based on repeat levelling performed in the city of Tallinn show local earth surface deformations in the area of ancient valleys buried under quaternary sediments. Until 1964, the highest rate of sinking (up to 30 mm/year) was observed in the area south of Tallinn Old Port until Liivalaia Street. The maps of vertical movements drawn up on the basis of earlier levelling data indicate local sinking in the region of the city centre since 1951. From 1964 onwards, the intensity of the sinking has been steadily decreasing. The data obtained from the latest levelling works show that the sinking of the area under study has stopped or reversed into rising (up to +0.4 mm per year). Sinking of Tallinn is connected with the geological structure and ground water level.     

基于地热钻孔资料探讨北京黄庄-高丽营断裂的构造活动特征

根据地热深井的地层资料,绘制了横穿黄庄-高丽营断裂带的地质剖面图,对断裂带的深部构造特点进行了探讨。结合已有研究成果分析,发现黄庄-高丽营断裂曾经至少有过4次正、逆构造转换,具有反复震荡性。认为断裂的成因是区域板块开裂,后由于板块间的水平运动方向多次转变,形成拉张与挤压的反复转变,不断产生上盘的下降及逆冲运动,而呈现出构造活动的反复震荡特征,分析认为其断裂形成时代约在1.6～1.4亿年间的晚侏罗世(J_3)。后来岩体的活动产生局部挤压和抬升,使得南、北两端上盘活动受限,产生掀斜抬升现象;而中段断块的活动自由度相对更大,根据水准监测当前中段上盘平均每年下降3 mm左右。结合构造特征及历史地震结果分析,认为应当注重对断裂带两侧板块的水平运移状况加以监测。     

甘加盆地西缘断裂带发现新活动证据

甘加盆地位于西秦岭北缘断裂带西端,盆地西缘发育了三条近南北向的断层(东支、中支、西支),表现为西高东低的弧形地貌阶梯带.基于高分辨率卫星遥感影像解译、地质地貌调查、UAV航拍测量、剖面清理与14 C测年等工作,对甘加盆地西缘断裂带进行综合研究,发现该断裂带第四纪晚期有新活动.断层新活动在地貌上表现为不同级别的断层陡坎、...     

张家口-宣化盆地断裂特征与活动性研究

运用地质地貌调查、地球物理勘探和年代测定等方法,对张家口—宣化盆地的四条主要断裂(张家口断裂、万全断裂、洗马林—水泉断裂和洋河断裂)的空间展布特征和活动性进行分析和研究,获得其活动时代、活动速率等参数。研究表明:上述断裂第四纪期间持续活动,以脆性变形为特征;总体上NW向断裂以高角度的正(或逆)倾滑断层为主,NE或NEE向的断裂以高角度的正断层为主;盆地内活动断裂总体来说活动强烈,多处可见断裂正断运动及左旋走滑运动的地质剖面,早更新世以来单条断层的平均垂直活动速率大于0.07~0.30mm/a,总垂直活动速率可能达到1.33mm/a。     

华北地区跨断层垂直形变分区特征及其对块体划分的意义

对 70年代以来的华北地区跨断层形变测量资料进行了分区研究。按构造单元将华北地区的跨断层测量台站或测点分为五组 :山西带、郯庐带、阴山 -燕山带西段、阴山 -燕山带东段和首都圈。对 80项实测资料的计算结果表明 ,华北地区断层垂直活动平均年速率为 0 335mm/a ,但各分区之间的断层活动速率值相差很大。山西断陷带的断层形变速率最高 ,是华北地区最重要的活动块体边界 ;其它构造带的断层形变速率都比较低     

Geodetic measurements on the Asal Rift (Djibouti): Twelve years of observations

The resurvey of both a geodetic network and a levelling net was carried out in June 1981, 8 months after the M_s = 7.3 El Asnam earthquake of 10 October 1980. Previous seismological and neotectonic studies indicate that this event results from a north-east-trending overthrust complex fault of about 40-km length, which shows at least three principal segments with slightly different directions.Vertical movements, evaluated by means of a trigonometric levelling method show an uplift of the thrust fault of about 5 m and a depression of the southeastern edge of about 1 m. These movements are progressively attenuated away from the fault trace (see fig. 1). Horizontal movements have been evaluated by a classical first-order triangulation method. (see fig. 2 and table 1).The resulting mean strain tensors, calculated for different triangles of the geodetic network, indicate a shortening of about 2.50 m which is consistent with the SE-NW direction of compression determined from neotectonic evaluations and focal mechanisms (see fig. 3). Dislocation models are used to explain and discuss the observed deformations in the light of the seismological data and the observed ground breakages. Five segments are required to explain both horizontal and vertical deformations. The magnitude of vertical displacement (about 6 m) at the junction between the southwest and the central segments of the fault argues for the breaking of this area during the main shock and for a slip vector of about 8 m, at least in the central segment.In such circumstances where the first field observations show that a strong coseismic movement has taken place, the best methodology to be used seems to be:

• - to resurvey as quickly as possible the widest acceptable zone of the old existing geodetic network, without special attention paid to the precision of these measurements.

• - to set up as soon as possible a small aperture geodetic network of high accuracy in order to monitor the possible postseismic readjustments.

For vertical movements, trigonometric leveling using reciprocal zenith measurements with two high-precision theodolites and EDM appears to be far the best solution. It is much quicker than classical leveling and it can afford the same precision if necessary. In our case, the precision was not critical, so that long ranges (up to 1500 m) between stations were used when necessary.     

FAULT GEOMETRY DEFINED BY MULTIPLE REMOTE SENSING IMAGES INTERPRETATION AND FIELD VERIFICATION: A CASE STUDY FROM SOUTHERN GUANGGAISHAN- DIESHAN FAULT,WESTERN QINLING

The NE margin of Tibetan plateau outspreads northeastward in late Cenozoic. The west Qinling locates at intervening zone among Tibetan plateau, Sichuan Basin and Ordos block, and is bounded by East Kunlun Fault in the southwest, the north margin of West Qinling Fault in the northeast, and the Longmen Shan Fault in the southeast. The west Qinling has been experiencing intense tectonic deformation since late Cenozoic, accompanying by uplift of mountains, downward incision of rivers, frequent moderate-strong earthquakes, vertical and horizontal motion of secondary faults, and so on. A series of "V-shape" faults are developed in the transfer zone between East Kunlun Fault and north margin of West Qinling Fault. The NWW-NW striking faults include Tazang Fault, Bailongjiang Fault, Guanggai Shan-Die Shan Fault, and Lintan-Dangchang Fault; EW-NEE-NE striking faults include Ha'nan-Qingshanwan-Daoqizi Fault, Wudu-Kangxian Fault, Liangdang-Jiangluo Fault, and Lixian-Luojiapu Fault. Among them, the Southern Guanggai Shan-Die Shan Fault (SGDF)is one of the principle branch which accommodates strain partitioning between the East Kunlun Fault and the north margin of west Qinling Fault. Although some works have been done and published, the geometry of SGDF is still obscure due to forest cover, bad traffic, natural and manmade reworks. In this paper, we collected remote sensing images with various resolutions, categories, imaging time. The selected images include composite map of Landsat image (resolution is 28.5m among 1984-1997, and 14.5m among 1999-2003), Landsat-8 OLI image (15/30m), Gaofen-1 (2m/8m), Pleiades (0.5m/2m), DEM (~25m)and Google Earth image (submeter resolution). After that, we reinforced tectonic information of those images by Envi5.2 software, then we interpreted SGDF from those images. As indoor interpretation fulfilled, we testified indoor interpretation results through geomorphological and geological investigation. Finally, we got fault distribution of SGDF. Conclusions are as follows:First, remote sensing image selection and management is crucial to indoor interpretation, and image resolution is the only factor we commonly consider before, however, things have changed in places where there is complex weather and dense vegetation. Image categories, imaging time and bands selected for compositing in pretreatment and etc. should all be taken into consideration for better interpretation. Second, SGDF distributes from Lazikou town in the west, extending through Pingding town, Zhou County, Huama town, then terminating at Majie town of Wudu district in the east, the striking direction is mainly NWW, and it could be roughly divided into 3 segments:Lazikou-Heiyusi segment, Pingding-Huama segment, and Huama-Majie segment, with their length amounting to 47km, 32.5km, 47km, respectively. The arrangement pattern between Lazikou-Heiyusi segment and Pingding-Huama segment is right-stepping, and the arrangement pattern is left-stepping bending between Pingding-Huama segment and Huama-Majie segment. Third, SGDF controlled magnificent macro-topography, such as fault cliff, fault facet, which often constitute the boundary of intermontane basins or erosional surfaces to west of Minjiang River. Micro-geomorphic expressions were severely eroded and less preserved, including fault scarps, fault troughs, sinistral offset gullies and geomorphic surfaces. Finally, SGDF mainly expresses left-lateral dominated motion, only some short branch faults with diverting striking direction exhibit vertical dominated motion. The left-lateral dominated component with little vertical motion of SGDF is consistent with regional NWW-striking faults as Tazang Fault, Bailongjiang Fault and Lintan-Dangchang Fault, also in coincidence with regional boundary faults such as east Kunlun Fault and north margin of west Qinling Fault, illustrating regional deformation field is successive in west Qinling, and NWW striking faults show good inheritance and transitivity on differential slip rate between east Kunlun Fault and west Qinling Fault. The geometry of SGDF makes quantitative studies possible, and also provides scientific basis for keeping construction away from fault traces.     

The character and extent of seismic deformation in the focal zone of gazli earthquakes of 1976 and 1984,M>7.0

With objective of investigating the peculiarities of seismic process development and seismotectonic deformation character in the focal area of the Gazli earthquakes of 1976 (7.0<M<7.3) and 1984 (M=7.2), a local seismic network was installed. For the field observation period (May to June, 1991) more than 400 events with magnitudes –0.2<M<4.5 were recorded by at least 6 stations.Isometric presentation of earthquake hypocenters distribution allows us to define the depth and dipping planes orientation of seismoactive faults of the region.The focal mechanisms of 35 earthquakes for the period 1979–1988,M>2.8, connected to a gas extraction regime period, and 75 events 1<M<4.3 for the 1991 period (gas storage regime) are used to analyze the dynamics of seismotectonic deformation processes (SDP) in this region. It has been ascertained, that the earth's crust in the Gazli region is subject to complicated deformation processes, particularly below 4 km depth. The predominant kind of deformation is compression. Vertical velocities of deformation show uplift of most of the region during the period of field work. The maximum velocity of vertical deformations for the Gazli structure isV=0.41 mm/year. The comparison of the vertical velocities' displacements due to seismic flow with recent tectonic movements of the earth's crust has revealed their direct relation and high percentage of seismic flow contribution to the tectonic movement. The results obtained testify that the active seismic processes in the Gazli region are connected not as much as the residual stress release in the focal zone of the earthquakes 05. 1976 and 1984,M>7.0 but rather with the influence of the gas reservoir exploitational regime on the rocks with different rheologic properties.     

Vertical Displacements in the Nový Kostel Seismoactive Area

Since 1994 annual campaigns of precise levelling have been performed on the network established in the surroundings of Nový Kostel. The network covers the most dynamic part of the West Bohemia seismoactive region with a total of 70 points in 1999. The measurements are connected to a reference point of the national levelling system and to our GPS-gravity network. It was proved by the error and confidence level of the data that small displacements of three and more millimetres can be recognised. The data analysis showed that all points could be divided into several groups according to temporal changes of height. Mutual comparison of these changes enabled to detect both general and very local short-term movements. It appeared that, in general, the involved part of the mountain block is subsiding relative to the Cheb basin. This is in contradiction to the recent uplift of the Kruné hory Mts. The correlation between vertical displacements and earthquake swarms was examined with the conclusion that during a swarm period the movements have special homogeneous pattern, contrary to inter-periods. The division line of different displacements (a fault zone) for the swarms 1994 and 1997 was determined.     

山西活动断陷带主要断层垂直形变分段特征

断层运动方式与滑动速率是断层活动性研究和地震危险性判定的重要参数。本文基于山西断陷带多年积累的跨断层水准观测资料,在处理与重构的基础上采用断层活动性分析方法,基于构造分区给出各构造区主要断层现今运动特征。结果表明,山西断陷带主要断层在观测期内以继承性正断运动为主,各盆地断层运动特征具有显著差异,表现为南、北两段的垂直活动量明显大于中段,其中,忻定盆地累积变化量值最小。从断层垂直活动速率来看,五台山断裂、系舟山山前断裂、唐河断裂和霍山山前断裂跨断层测段活动速率明显低于全区水平;受长期构造应力加载及区域中强地震影响,各时段断层运动也存在差异变化,下达枝、亭旨头、太原、广胜寺等部分跨断层测段表现出明显的断层逆继承运动、断层相对闭锁等特征。     

苏鲁皖豫地区垂直形变的构造背景分析

本文利用1953—1955年,1976—1980年两期精密水准测量成果编绘的垂直形变图,在苏鲁皖豫地区形变的构造背景作了初步分析。认为区内存在着郯庐带临沂—嘉山段和豫鲁交界两个构造形变异常区。全区形变主要受北西西、北西和北东向断裂控制。郯庐带的现今运动具有明显的分段特征     

涉县盆地控盆构造晚第四纪活动特征

涉县断裂为太行山隆起区内涉县盆地的控盆构造,走向由NE转为近EW向,倾向NW/N,中部在井店东被EW向断裂错断,是控制涉县盆地的一组断裂。本文采用地质地貌调查、河流阶地分析和地质测年等方法,研究了涉县断裂晚第四纪活动特征。研究发现,涉县断裂带由多组断裂构成,带宽约200m,在清漳河两侧表现为山前的陡崖地貌、基岩破碎变形带,具有正断兼走滑特征,在基岩变形带上部发育走向NNE向和NWW向次级滑动面,次级滑动面错断第四系黄土,最新活动到晚更新世;断裂在盆地区通过,地表形成低缓陡坎,断裂错断Q2-3地层,表现为上陡下缓的正断层。通过对涉县断裂两侧清漳河河流阶地、夷平面和地层年龄综合分析,估算涉县断裂晚更新世以来平均垂直滑动速率为0.06～0.08mm/a,中更新世以来平均垂直滑动速率为0.22～0.34mm/a,垂直差异活动主要发生于中更新世期间。