结构型式对寒区高铁路基冻结特征影响试验研究

哈尔滨至大连客运专线是我国在中-深季节冻土地区设计、建造和运营的第一条高速铁路,其独特的工程地质条件以及在低温环境下线路的苛刻要求引发的工程需求对寒区路基的稳定性问题提出了新的严峻挑战。通过在不同冻深区选择典型性路基断面,以用来监测路基的稳定性和冻结特征。并通过对运营后第1个冻融期内的监测数据分析发现,路基的结构型式对寒区高铁路基的冻结特征有着显著的差别性影响和制约作用。结果表明：对比路堑段的中部及其临近路堑进出口处的路堤段,路堤段存续有较长时间和较厚的冻结夹层,其堑-堤地温差值也随着纬度的增加而增加。同时发现在4月份的路基中存在有一定厚度的高温冻结夹层。而同一区域内,路堑的最大冻结深度要较路堤的冻结深度浅20～50 cm,但相反的是,路堑的最大变形却较路堤的要大2～5 mm,这种差值越向北越明显。同时在春融期内,路堑段的冻深变化速率在0上下剧烈波动,此时变形产生了突变式上升,而路堤段的冻深变化速率却在负值区内变化,变形并未发生明显的突变。     

排桩支护基坑的一种桩身位移及内力解析法推导及其应用

选取某一支护面上的任意一根桩为研究对象,设置一道支撑（或锚索或锚杆）及开挖至坑底,建立其受力平衡方程和位移协调方程。通过圈梁的协调作用,将研究对象扩大到整个支护面,推导出能够同时考虑开挖过程、支撑设置以及桩-土-圈梁共同作用的支护面位移和受力方程组,利用FORTRAN语言编制的程序求解,可计算出开挖至坑底工况下圈梁、桩身任一截面的内力、水平位移。通过算例计算圈梁（桩顶）的位移与监测位移及部分桩的内力,与文献[1]方法计算的内力进行对比分析,验证文中方法的合理与可行性。     

汶川地震同震形变场的GPS和InSAR邻轨平滑校正与断层滑移精化反演

为克服InSAR观测汶川地震同震形变场的邻轨不连续问题,提出联合GPS观测值与邻轨平滑约束的同震位移校正方法,采用GPS观测形变去除PALSAR轨道误差引入的残留平地相位,基于形变平滑条件校正邻轨干涉相位的不连续性.ALOS/PALSAR干涉处理结果表明,校正后同震形变场的准确度与平滑性得以显著提高,InSAR高相干点残差达3.6 cm,校正后精度提高约60%,低相干点精度提高约40%,校正后形变场的邻接平滑因子标准差减小约33%,验证了轨道误差校正与邻轨平滑约束方法的准确性与可靠性.进一步基于弹性半空间位错模型的断层滑移反演结果表明,断层滑移主要分布于映秀、北川和青川地区,集中于地壳深度0~16 km范围,最大滑动量（位于北川县城）约为9.0 m,GPS反演模型残差为5.5 cm,InSAR反演模型残差达9.2 cm,InSAR反演精度约有30%的显著提高,由模型反演计算得到的地震矩为8.0469×10²⁰ N·m.     

InSAR约束下的2008年汶川地震同震和震后形变分析

2008年5月12日,青藏高原东缘的龙门山断裂带上发生了M_w7.9级汶川地震.本文通过分析覆盖汶川地震震中区域的ALOS/PALSAR像对的方位向偏移量来选择无明显电离层扰动影响的像对进行干涉处理,获取了高精度、连续的InSAR地表形变场.在此基础上,结合高精度GPS同震形变数据,采用同震、黏弹性松弛震后形变联合反演模型同时确定了汶川地震的同震滑动分布和龙门山地区的流变结构参数.研究结果表明,汶川地震是一个断层破裂非常复杂的地震事件,其中,北川段、岳家山段、虹口段和汉旺段的滑动以逆冲为主,而青川段以右旋走滑为主.滑动主要发生在10 km深度以上的区域,最大滑动量位于虹口段的东北端,达10.7 m.地震释放的总能量为9.28×10²⁰ N·m（M_w7.91）,与地震学的结果一致.联合反演模型确定的龙门山地区中下地壳的黏性系数为2×10¹⁸ Pa·s,为青藏高原东部地区的黏性系数提供了一个可靠的下限值.如果有更长时间的震后形变观测时间序列,将为该区域提供更为可靠的流变结构.     

基于PSInSAR技术的长白山天池火山形变监测

将PSInSAR技术引入长白山天池火山的形变监测,获取了1992—1998年和2007—2010年2个时段的火山形变信息。结果显示:天池火山在这2个时段内整体抬升,1992—1998年火山较为活跃,雷达视线向平均形变速率为6mm/a,2007—2010年火山活动趋于平缓,雷达视线向平均形变速率为3mm/a;结合水准和GPS数据分析,发现火山口区域地表抬升明显,远离火山口处较为稳定。文中PSInSAR结果与水准数据能较好地吻合,且在空间上有较大覆盖范围,能更直观地反映火山地表的形变特征。     

Plio-Quaternary paleostresses in the Atlantic passive margin of the Moroccan Meseta: Influence of the Central Rif escape tectonics related to Eurasian-African plate convergence

The Atlantic Moroccan Meseta margin is affected by far field recent tectonic stresses. The basement belongs to the variscan orogen and was deformed by hercynian folding and metamorphism followed by a post-Permian erosional stage, producing the flat paleorelief of the region. Tabular Mesozoic and Mio-Plio-Quaternary deposits locally cover the Meseta, which has undergone recent uplift, while north of Rabat the subsidence continues in the Gharb basin, constituting the foreland basin of the Rif Cordillera.The Plio-Quaternary sedimentary cover of the Moroccan Meseta, mainly formed by aeolian and marine terraces deposits, is affected by brittle deformations (joints and small-scale faults) that evidence that this region – considered up to date as stable – is affected by the far field stresses. Striated faults are recognized in the oldest Plio-Quaternary deposits and show strike-slip and normal kinematics, while joints affect up to the most recent sediments.Paleostress may be sorted into extensional, only affecting Rabat sector, and three main compressive groups deforming whole the region: (1) ENE–WSW to ESE–WNW compression; (2) NNW–SSE to NE–SW compression and (3) NNE–SSW compression. These stresses can be attributed mainly to the NW–SE oriented Eurasian-African plate convergence in the western Mediterranean and the escape toward the SW of the Rif Cordillera. Local paleostress deviations may be related to basement fault reactivation. These new results reveal the tectonic instability during Plio-Quaternary of the Moroccan Meseta margin in contrast to the standard passive margins, generally considered stable.     

Kinematic model of crustal deformation of Fenwei basin,China based on GPS observations

Using high precision GPS data for the period of 1999–2007 from the China Crustal Movement Observation Network, we have constructed a plate kinematic model of crustal deformation of Fenwei basin, China. We have examined different kinematic models that can fit the horizontal crustal deformation of the Fenwei basin using three steps of testing. The first step is to carry out unbiasedness and efficiency tests of various models. The second step is to conduct significance tests of strain parameters of the models. The third step is to examine whether strain parameters can fully represent the deformation characteristics of the 11 tectonic blocks over the Fenwei basin. Our results show that the degree of rigidity at the Ordos, Hetao, Yinshan and South China blocks is significant at the 95% confidence level, indicating the crustal deformation of these blocks can be represented by a rigid block model without the need to consider differential deformation within blocks. We have demonstrated that homogeneous strain condition is suitable for the Yinchuan basin but not for other 6 blocks. Therefore, inhomogeneous strains within blocks should be considered when establishing the crustal deformation model for these blocks. We have also tested that not all of the quadratic terms of strain parameters are needed for the Yuncheng-Linfen block. Therefore, four kinds of elastic kinematic models that can best represent the detailed deformation characteristics of the 11 blocks of Fenwei basin are finally obtained. Based on the established model, we have shown that the current tectonic strain feature of the Fenwei basin is mainly characterized by tensile strain in the NW–SE direction, and the boundaries betweem the Ganqing and Ordos blocks and the Shanxi graben possess the maximum shear strain. A comparison between our results and past geological and geophysical investigations further confirms that the model established in this paper is reasonable.     

Basin evolution associated to curved thrusts: The Prerif Ridges in the Volubilis area (Rif Cordillera,Morocco)

The Volubilis Basin is located between two structural arcs formed by the Prerif Ridges that developed during and after sedimentation. The arcs correspond with W- to WSW-verging anticline culminations, limited, to the north by a NE-SW strike-slip lateral ramp. Sedimentary infill took place during two stages of ridge formation and propagation. The first stage occurred in the Middle Miocene-early Tortonian and was determined by the deposition of the Nappe Prérifaine in the northern part of the basin, and continental and marine sediments over the Prerif Ridges. The second one, Late Miocene in age (Tortonian–Messinian), corresponds to the sedimentation of calcarenites and bioclastic limestones at the basin edges, with a lateral transition to white and blue marls toward the center of the basin. There is clear evidence of synsedimentary deformation, suggesting the interaction of sedimentation and tectonics. Geophysical data allow us to characterize the stratigraphic architecture of the Volubilis Basin and the geometry of the top of the Paleozoic basement. An approximately N–S Tortonian–Messinian asymmetric depocenter is located close to the front of the eastern arc. This research illustrates the nucleation, progressive thrust bending and segmentation, and the propagation of folds interacting with sedimentation. Thrust nucleation agrees with Paleozoic basement highs under the detachment surface. The progressive development of these tectonic structures conditioned the formation, segmentation and final continentalization of the Volubilis Basin, which can be considered as a piggy-back basin.     

Deformation characterization of a regional thrust zone in the northern Rif (Chefchaouen,Morocco)

This paper provides the structural analysis of the Chefchaouen area in the northern Rif. Here the Dorsale Calcaire superposes, by means of an excellently exposed thrust fault, onto the Predorsalian succession in turn tectonically covering the Massylian Unit. Hanging wall carbonates of the Dorsale Calcaire Unit form a WSW-verging regional fold with several parasitic structures, deformed by late reverse faults in places indicating an ENE vergence. A 200 m thick shear zone characterizes the upper part of the Predorsalian succession, located at footwall of the Dorsale Calcaire Unit. Here the dominantly pelitic levels are highly deformed by (i) C′ type shear bands indicating a mean WSW tectonic transport and (ii) conjugate extensional shear planes marking an extension both orthogonal and parallel to the shear direction. The Massylian Unit is characterized by a strain gradient increasing toward the tectonic contact with the overlying Predorsalian succession, where the dominantly pelitic levels are so highly deformed so as appearing as a broken formation. Such as the previous succession, conjugate extensional shear bands and normal faults indicate a horizontal extension parallel to the thrust front synchronous with the mainly WSW-directed overthrusting. The whole thrust sheet pile recorded a further shortening, characterized by a NW–SE direction, expressed by several reverse and thrust faults and related folds. Finally strike-slip and normal faults were the last deformation structures recorded in the analyzed rocks. A possible tectonic evolution for these successions is provided. In the late Burdigalian, the Dorsale Calcaire Unit tectonically covered the Predorsalian succession and together the Massylian Unit. The latter two successions were completely detached from their basement and accreted in the orogenic wedge within a general NE–SW shortening for the analyzed sector of the northern Rif. At lithosphere scale the thrust front migration was driven by roll back and slab tear mechanisms producing a synchronous arching and related counterclockwise rotation of the tectonic prism along the African margin. Radial displacement involved extension parallel to the thrust front well-recorded in the analyzed rocks. The NE–SW shortening, probably acting in the Tortonian–Pliocene interval, was related to the final compression of the Rif Chain resulting in out-of-sequence thrusts affecting the whole orogenic belt.     

GNSS在断层形变研究中的应用

Great earthquakes often occur along or near active fault belts. Thus, monitoring and research on fault deformation are quite important. Methods such as short-leveling, short- baseline and integrated monitoring profile across fault belts have been used to monitor fault activities for many years. GNSS observations are mainly used to obtain the horizontal velocity field in large areas and to study the activities and deformation of major blocks. GNSS technology has been used to monitor and study the deformation of faults from a different aspects, In this paper, some applications and new explorations of GNSS are discussed. They are： （1） Research and monitoring of strike-slip activities of faults with GNSS. （2） Research and monitoring of vertical activities of faults with GNSS. （3） Investigating the laws of deformation of blocks on the sides of fault zone and setting up strain models to deduce the activities and deformation of faults with respective models and compare the deduced results with the actual measurements across fault. It is concluded that a larger discrepancy between the deduced and the observed deformation indicates a stronger interaction between the blocks, which can be important for predicting the location of a strong earthquake and assessing seismic hazard, as well as the seismicity trend.