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 Yingxiu-Beichuan-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.

Response of vertical deformation on faults to remote strong earthquakes

Vertical coseismic deformation on non-causative fault caused by remote strong earthquakes （epicentral distance ≥1 500 km, Ms≥7.0） are observed by fault-monitoring instruments of new type during recent two years. The monitoring result shows, delay time, maximum amplitude and duration of vertical deformation on the non-causative fault have remarkable close relationship with earthquakes magnitude and epicentral distance. The delay time of vertical coseismic deformation have positive linear relationship with epicentral distance. The velocity of coseismic deformation is 5.5 km/s, close to the velocity of surface wave in granite. The logarithms of maximum amplitude of coseismic deformation and epicentral distance have remarkable linear relationship with magnitude. The greater the magnitude and the closer the epicentral distance are, the bigger the maximum amplitude of coseismic deformation on non-causative fault will be. Relative to the epicentral distance, the magnitude is the most important factor to the duration of coseismic vertical deformation on the non-causative fault. Stronger earthquake causes longer vibration duration of coseismic deformation. The experiential equation of co-seismic deformation faults obtained by this work is significant on the coseismic deformation research.

Late Cretaceous Transpressional Fault System: A Case Study of the Yishu Fault Belt, Shandong Province, Eastern China

On the basis of field observations of the structures of three profiles from the Linshu region, deformation characteristics and the tectonic background of the Yishu fault belt in the Late Cretaceous–Early Cenozoic have been discussed in detail.Three structural profiles, whose deformations consist mainly of earlier transpressional faults and later normal faults, were developed for the Mengtuan Formation of the Lower Cretaceous Dasheng Group.Typical positive flower structures, duplex structures, and break-through faults were found in these profiles.On the basis of analyses of the structural deformation and previous geochronological studies, it was concluded that the earlier transpressional faults of the profiles were triggered by the sinistral transpression of the Yishu fault belt in the Late Cretaceous–Early Paleogene, and that the later normal faults, formed during the Late Paleogene–Neogene extension, truncated the earlier transpressional faults.With consideration of the tectonic evolution of the Tan-Lu fault belt and the different drift directions of the Pacific plate since the Cretaceous, we suggest that the major tectonic events of the Late Cretaceous–Neogene in eastern China were mainly controlled by the subduction of the Pacific plate.

Vertical Differential Structural Deformation of the Main Strike-slip Fault Zones in the Shunbei Area,Central Tarim Basin:Structural Characteristics,Deformation Mechanisms,and Hydrocarbon Accumulation Significance

Vertical differential structural deformation(VDSD),one of the most significant structural characteristics of strike-slip fault zones(SSFZs)in the Shunbei area,is crucial for understanding deformation in the SSFZ and its hydrocarbon accumulation significance.Based on drilling data and high-precision 3-D seismic data,we analyzed the geometric and kinematic characteristics of the SSFZs in the Shunbei area.Coupled with the stratification of the rock mechanism,the structural deformations of these SSFZs in different formations were differentiated and divided into four deformation layers.According to comprehensive structural interpretations and comparisons,three integrated 3-D structural models could describe the VDSD of these SSFZs.The time-space coupling of the material basis(rock mechanism stratification),changing dynamic conditions(e.g.,changing stress-strain states),and special deformation mechanism of the en echelon normal fault array uniformly controlled the formation of the VDSD in the SSFZs of the Shunbei area.The VDSD of the SSFZs in this area controlled the entire hydrocarbon accumulation process.Multi-stage structural superimposing deformation influenced the hydrocarbon migration,accumulation,distribution,preservation,and secondary adjustments.

Vertical deformation of the fault-crossing network around Baotou,observed by GPS

GPS data and precise leveling data of seismic network profiles across the fault in Baotou in 2006, 2009 and 2011 were processed and analyzed to test the feasibility of using GPS technology for fault-crossing vertical deformation monitoring. The results showed that high precision cross-fauh vertical deformation measurements can be obtained using appropriate GPS data processing strategies.

Vertical deformation and tectonic activity in Tianjin area

Vertical deformation in Tianjin area during 1992 -2008 was calculated from leveling data. The effect of large surface subsidence caused by extensive groundwater pumping was removed by fitting the data along each survey line with a polynomial function. The results are fitted with crustal blocks individually in this area. Vertical deformation rates are mapped, vertical rates of the main fault zones were calculated, and the activities of the blocks and fault zones were investigated. The observed vertical deformation shows that some of the blocks tilted and some blocks rose or subsided as a whole. The vertical rates at fault zones in the area vary within the range of 0. 13-0. 48 mm/a,with an average value of 0.29 mm/a.

Current tectonic deformation and seismogenic characteristics along the northeast margin of Qinghai -Xizang block

Based on the data from repeated precise leveling and across-fault deformation measurements carried out in recent 30 years and the analyzed results from GPS observations made in recent years along the northeastern margin of Qinghai-Xizang block, and combined with the geological structures and seismic activities, some characteristics in regional tectonic deformation and strong earthquake development are studied and approached preliminarily. The results show that: a) The space-time distribution of current tectonic deformation in this area is inhomogeneous with relatively intensive tectonic deformation in the vicinity of main boundary faults and weak deformation in the farther areas. The intensity of vertical differential movement and the deformation status vary with time, and the horizontal movement and deformation are characterized by apparent compression and strike-slip. b) The tectonic stress field generated by the NE-trending continuous compressive movement of Qinghai-Xizang block due to the northward press and collision of India plate is the principal stress for the tectonic deformation and earthquake development in this area. The evolution of space-time distribution of tectonic deformation and seismicity is closely related to the block activity and dynamic evolution of regional tectonic stress field. c) The vertical deformation uplift and high-gradient deformation zones and the obvious fault deformation anomaly appeared along the boundaries of tectonic blocks can be considered as the indicators of hindered block motion and intensified tectonic stress field for strong earthquake development. Usually, the above-mentioned phenomena would be followed by the seismicity of M6.0, but the earthquake might not occur in the place with the maximum movement. The zones with the fault deformation anomaly characterized by tendencious accumulation acceleration turning and the surrounding areas might be the positions for accumulation of strain energy and development and occurrence of strong earthquakes.

RECENT TECTONIC DEFORMATION ANOMALY AND EARTHQUAKES IN GANSU-NINGXIA-QINGHAI AREA

By processing and analyzing geodetic data of vertical deformation, fault deformation and horizontal deformation by GPS in Gansu Ningxia Qinghai area and by comparing them with geological structures and many medium to strong earthquake activities in this area, some features of recent tectonic deformation anomaly and the development of medium to strong earthquakes are studied. The results show that: ①Near the main faults tectonic deformations are relatively large. The amount of vertical movement and the deformation status evolve with time. The horizontal movement and deformation show obvious compressional strike slip character. ②The dominant stress of tectonic deformation and seismic development in this area comes from the persistent northeastward compression of Qinghai Tibet block;The time spatial distribution evolution of tectonic deformation and seismic activities are closely related to dynamic evolution of block motion and regional tectonic stress field. ③The abnormal uplift and high gradient deformation belts and remarkable fault deformation anormaly on the borders of regional tectonic blocks are indicators of developing moderate to strong earthquakes but earthquakes may not necessarily take place in the position of maxium deformation, it usually occurred in the region where fault deformation anormaly shows “trend accumulation acceleration turn ” variation character or nearby. On the basis of above study, a preliminary prediction for strong earthquake risk in this area is given.

断层破碎带形态对隧道围岩变形影响研究

断层破碎带具有围岩破碎、强度低等特点,极易引起隧道围岩发生大变形,进而诱发工程灾害。因此,依托重庆市郊铁路璧铜线云雾山隧道工程,采用PLAXIS3D数值分析软件,建立了隧道穿越不同形态断层破碎带计算模型。计算结果表明:断层破碎带倾角和厚度对隧道围岩变形影响显著,断层走向线与隧道轴线夹角对隧道围岩变形影响较小。随着断层破碎带倾角的增大,受断层破碎带影响的范围明显缩小,隧道围岩竖向和水平位移值均逐渐减小,且当断层破碎带倾角为90°时,受断层破碎带影响的范围最小;随着断层破碎带厚度的增大,受断层破碎带影响的范围随之增大,围岩的竖向和水平位移值均逐渐增大,且当断层破碎带厚度为22 m时达到最大值。隧道正交穿越断层破碎带薄弱处时,围岩变形控制效果会更好。该研究成果可为山岭隧道穿越断层破碎带设计与施工提供一定的参考。

沂沭断裂带垂直形变与断层活动特征分析

利用跨断层短水准资料分析了沂沭断裂带断层活动特征 ,结果表明 :NNE向的沂沭断裂带与NW向断裂活动性质有所不同 ,沂沭断裂带主要为压性逆断活动 ,北西向断裂带为张性正断活动 ,与地质考察结果基本一致。此外 。

山东安丘地区软土震陷及地震产生的土层构造新启示

通过地震调查、土工试验和14C测年,从沂沭断裂地震带安丘地区的全新世中—晚期湖沼相软土中,识别出了软土震陷灾害现象和地震产生的软土沉陷向斜褶曲、小尺度同震断层、狭缩–膨胀构造和震裂缝等共生土层变形构造,其中,软土沉陷向斜是直接反应震陷灾害的纵向土层变形。小尺度同震断层是地震产生的小断层,发育在沉陷向斜之下,其垂向延长0.5~1.8 m。沉陷向斜随着同震断层的产生而初现;又紧随断层向深部延伸而向下发展。地震振动使饱和软土发生触变,土质点从沉陷向斜的转折端向两翼发生流动,在此过程中,附加地震应力不断作用,结果形成了窄而深的沉陷向斜。软土震陷最大深度为1.08 m,平均震陷深度为0.68 m。推断当时的地震烈度达到Ⅷ度、震级超过M6。测得淤泥质土的14C年龄为3901±33a B.P.,该地震事件约发生公元前19世纪。同震断层是形成震陷的重要诱导因素,这为认识软土震陷的形成机理提供了新资料;也为防治或减轻软土震陷的危害提出了新启示。因此,应重视软土下伏土层可能产生同震断层的隐患。

汶川8.0级地震前后地壳垂直形变分析

利用汶川8.0级地震周边区域水准、跨断裂水准资料,分析了汶川Ms8.0地震前后的地壳垂直形变。结果表明:震前,区域垂直形变表现出某种阶段性,升降差异运动由剧烈向减弱变化,龙门山断裂活动也由活跃向闭锁转换;震后,地震影响主要沿龙门山断裂带向北东方向扩展,余震区附近同震形变显著。

沂沭断裂带及附近地区垂直形变特征分析

利用小波变换分析方法提取沂沭断裂带及其分支断裂跨断层流动短水准和长水准趋势变化成分,计算分析不同断裂的垂直形变速率和受力状态,结果表明:沂沭断裂带及其北西向分支断裂近期垂直形变速率均较小,没有明显的速率异常和受力状态改变;同一断裂具有分段和分时活动特征,断裂活动性质与地质考察结果基本一致;大部分水准观测场地在1995年苍山5.2级、2011年日本9.0级地震前后断裂垂直形变速率和受力方式发生了变化;山东近几年出现的跨断层水准异常基本结束,仅存的冯家坊子水准异常存在一定干扰,沂沭断裂带及附近地区近期发生强震的形变背景尚不明显。

地壳垂直形变速率梯度、断层形变速率变化与强震危险区研究

应用最新的全国垂直形变速率图和各地区不同年代的形变（速率）图，编绘了相应的形变速率梯度图，计算了若干跨断层测量台、点资料的低通滤波残差及其一阶和二阶差分。结合在相应空间和时间域内所发生的强震，讨论了地壳形变与强震的关系，探讨了用大地形变测量方法划定近期（１—３年或稍长一点时间）强震危险区的判据，得到了一些有意义的结果。

东昆仑山断裂带及昆仑山口西8.1级地震垂直形变研究

沿格尔木—五道梁公路测线 1979,2 0 0 1年的 2期水准观测资料表明 :1)东昆仑山及可可西里地区现今相对于柴达木盆地仍在发生继承性的隆升运动。 1979— 2 0 0 1年期间 ,昆仑山口主峰一带相对于格尔木约上升了 2 80mm ,上升速率高达 15mm/a ;五道梁相对于格尔木上升了约 2 10mm ,上升速率约 10mm/a。 2 )昆仑山口至五道梁之间的可可西里地区 ,在相对于柴达木盆地以 7mm/a的速度整体抬升的同时 ,还相对于南、北两侧的五道梁和昆仑山隆起区以 3～ 7mm/a的速度下沉。 3)格尔木—五道梁剖面垂直形变整体符合俯冲 -逆掩地壳增厚模式 ,其中 ,沿西大滩断裂、中昆仑山断裂和昆仑山北缘断裂带的逆冲推覆运动 ,占了整个东昆仑山现今构造隆起的大部分 ,其逆冲推覆运动有自南向北衰减的特点。 4 )地质调查结果表明 ,沿 2 0 0 1年 11月 14日昆仑山口西MS8.1地震 35 0km的左旋破裂带 ,可以划分出若干个不均匀错动段 ,错动量最大可达 6m ,最小只有 2m。基于Okada (1985 )位错模型的理论计算结果表明 ,地震断层不均匀左旋错动可以在昆仑山口破裂带南北两侧产生 10 0多毫米的差异性垂直位移。 1979— 2 0 0 2年实测垂直位移中 ,西大滩断裂谷地水准点的异常上升、昆仑山口测点的异常下降等都与发震断层的不均匀错动密切相?

断层垂向封闭油气性研究方法及其应用

断层面除受上覆地层重力的作用外，还要受到区域主压应力的作用。在考虑断层面所受上覆沉积物重力和区域主压应力作用的基础上，通过对断层垂向封闭性主要影响因素（断层面压力和断移地层性质）的深入分析，根据泥质岩塑性变形所需要的最小压力，利用断层面压力大小，探讨了断层垂向封闭油气性的研究方法，并将其应用于松辽盆地北部三肇凹陷汪家屯气田Ｗ１、Ｗ２、Ｗ３、Ｗ４断层和长春岭背斜带三站气田Ｓ１、Ｓ２、Ｓ３、Ｓ４断层的垂向封闭天然气的研究中，其研究结果与二个气田的实际地地质条件相吻合，表明该方法用于断层垂向封闭油气性研究是可行的。

天津地区的垂直形变与构造活动研究

根据1992—2008年的水准观测资料计算结果,研究了天津地区的地面垂直升降变化。使用多项式函数对每条测线上的漏斗进行了计算,排除因开采地下水造成的沉降干扰,对所得结果分块拟合,绘制了垂直形变速度图,并计算了主要活动断裂带的垂直活动速率,在此基础上研究了天津地区的块体和断裂带的现今活动性。研究结果表明：垂直形变反映出天津地壳块体有的为掀斜活动,有的为整体性上升或者下降;块体的垂直变化差异幅度亦有大有小,活动程度亦存在差别;本区断裂的垂直活动速率在0.13-0.48 mm/a,平均速率为0.29 mm/a。

早寒武世初期沂沭断裂带地震效应

早寒武世初期,随着从古沂沭海峡向西海侵的发展,鲁西地区沉积了厚度不等的主要由砂岩、泥岩和碳酸盐岩组成的滨海、潟湖及浅海相沉积,其层位属下寒武统底部的李官组和朱砂洞组。在它们沉积过程中,沂沭断裂带正发生着伴有频繁海底地震的构造裂陷活动,使海底沉积物在自沂沭断裂带向西200 km范围内产生了不同的地震效应,形成了各种地震成因的同沉积变形构造。发育在朱砂洞组中的地震效应记录除有少量半固结沉积物的脆性变形外,主要是液化底劈、碳酸盐灰泥火山、液化脉、液化角砾岩、震褶曲、粒序断层和硅质脉等软沉积物变形;李官组中既有含滑塌褶曲、负载构造、球—枕构造等震滑塌堆积,也有震浊积岩。由海底地震效应记录所反映的震级为5～8.9级。这些证据表明沂沭断裂带在早寒武世初期发生了强构造活动。从海底工程地质的角度来分析,上述地震效应是地震对海底沉积层的破坏形式,这为认识海底工程地基岩土层的地震破坏提供了直观的资料。

苍山5.2级地震的地形变特征及机制

运用新方法对苍山地震前后的形变资料进行了异常识别，重点分析形变异常的变化特征及机制。结果显示：①苍山地震是大面积应力积累、调整的结果；②以外围区100～200km中短及短期异常为主，而震中100km内的近源区异常并不显著；③进入短期的异常标志是中短期异常出现转折或反向。

青藏块体东北缘现今构造形变与蕴震特征

利用青藏块体东北缘近 3 0年的精密水准网、跨断层形变测量网复测资料 ,以及近年来GPS观测分析结果 ,结合地质构造与地震活动 ,初步研究和探讨了区域构造形变与强震蕴育的一些特征 .结果表明 :1本区现今构造形变时空分布很不均匀 :主要边界断裂附近构造形变相对强烈 ,远离则衰减 .垂直差异运动强度和变形状态随时间演变 ,水平运动与变形呈明显的挤压走滑特征 ;2印度板块的北推碰撞引起的青藏块体持续 NE向挤压运动所产生的构造应力场 ,是本区构造形变与地震蕴育的主控应力 .构造形变及地震活动的时空分布演化 ,与块体活动及区域构造应力场动态演化密切相关 ;3构造块体边界地带出现的垂直形变异常隆起与高梯度形变带 ,以及显著地断层形变异常 ,是块体运动受阻、构造应力场强化而蕴育强震的一个标志 ,往往伴随有 6级左右及以上强震活动 ,但地震并不一定发生在运动幅度最大的部位 .断层形变异常呈现“趋势积累—加速—转折”变化特征的地段及附近 ,往往是应变能积累。