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911.
912.
天山地区地质构造复杂,地震活动频繁,其壳幔变形和深部结构一直受到学者们的高度关注.然而,由于天山地区地震台站资料较少,致使壳幔变形研究结果与解释存在诸多争议.本研究利用在天山地区（40°N-46°N,78°E-92°E）新布设的11个流动宽频带地震台站和该地区39个固定台站的观测资料,采用接收函数与面波联合反演方法,获得了研究区地壳厚度及壳幔S波速度结构.反演结果显示天山地区（41.5°N-44°N,78°E-88°E）平均地壳厚度为56 km,塔里木盆地（40°N-41.5°N,79°E-90°E）、准噶尔盆地（44°N-46°N,82°E-90°E）和吐鲁番盆地（42°N-43°N,88°E-90°E）具有较厚的沉积层,地壳平均厚度为43 km、53 km和46 km,整体表现为天山厚、盆地相对较薄的特征;在研究区南天山的最高峰（42°N,80.5°E）及北天山的最高峰（43.5°N,86°E）附近,中下地壳存在较厚的低速层,我们认为在强烈挤压作用下低速、低强度的中下地壳强烈变形可能是导致该区域快速隆升的主要原因.在研究区中部,位于塔里木盆地与准噶尔盆地之间的天山地区,中下地壳及上地幔均存在低速层,且盆地莫霍面向天山倾斜明显.结合前人的研究成果推测,在南北向构造挤压应力作用下,塔里木盆地与准噶尔盆地发生了向天山造山带方向的双向壳幔层间插入俯冲.在研究区东部,塔里木盆地东北缘与天山东部接触带的地壳内没有明显的低速层,推测应处在早期挤压变形状态,该区域的壳幔边界为缓变的速度梯度带,可能与上地幔热物质侵入或渗透有关. 相似文献
913.
It is widely accepted that ductility design improves the seismic capacity of structures worldwide. Nevertheless, inelastic deformation allows serious damage to occur in structures. Previous studies have shown that a certain level of postyield stiffness may reduce both the peak displacement and residual deformation of a structure. In recent years, several high-strength elastic materials, such as fiber-reinforced polymer (FRP) and high-strength steel bars, have been developed. Application of these materials can easily provide a structure with a much higher and more stable postyield stiffness. Many materials, members, and structures that incorporate both high-strength elastic materials and conventional materials show significant postyield hardening (PYH) behaviors. The significant postyield stiffness of PYH structures can help effectively reduce both peak and residual deformations, providing a choice when designing resilient structures. However, the findings of previous studies of structures with elastic-perfectly plastic (EPP) behavior or small postyield stiffness may not be accurate for PYH structures. The postyield stiffness of a structure must be considered an important primary structural parameter, in addition to initial stiffness, yielding strength, and ductility. In this paper, extensive time history and statistical analyses are carried out for PYH single–degree-of-freedom (SDOF) systems. The mean values and coefficients of variation of the peak displacement and residual deformation are obtained and discussed. A new R-μp-T-α relationship and damage index for PYH structures are proposed. A theoretical model for the calculation of residual deformation is also established. These models provide a basis for developing the appropriate seismic design and performance evaluation procedures for PYH structures. 相似文献
914.
结构面对于黑方台台塬斜坡变形破坏的影响研究成果较多,但以单方面研究为主,较少进行系统研究,因此通过对黑方台台塬结构面类型及其组合特征以及斜坡变形破坏类型和特征的分析可知:研究区结构面类型主要包括节理裂隙、层面、接触面、断层和临空面,结构面组合类型分2大类8小类,各类型具有自身的结构特征和分布特征;结构面及其组合对黑方台台塬斜坡变形破坏类型选择和空间分布选择控制效应明显,特别是对滑坡类型选择和空间分布的影响。 相似文献
915.
为了研究降雨对定点形变观测的影响,在了解呼和浩特地震台形变观测环境后,分析了伸缩仪、水管倾斜仪和垂直摆倾斜仪的观测数据质量,统计了降雨量和各仪器分量的变化,并进行了相关分析,得到不同形变仪器测项数据变化幅度对降雨量的响应函数,结果显示两者间呈较好的线性相关。 相似文献
916.
强震震前(preseismic)动力学过程的研究对于地震预测具有十分重要的意义,但由于观测资料的限制,目前对强震前孕震区力学状态及其演化过程的认识还非常有限.2011年日本东北9.0特大地震(Tohoku-Oki)发生在GPS观测台站最为密集的地区,为研究特大地震震间(interseismic)与震前的变形状态提供了难得的机会.文中将利用日本东北大地震之前连续的GPS观测资料,分别计算震间与震前的速度场与变形场.通过对比分析发现,日本东北地区(Tohoku)震前的应变状态与震间的有很大的不同,震间的变形主要受到太平洋板块向日本海沟北西西向的俯冲挤压作用所控制,其主压应变以近东西向压缩为主,日本东北地区的运动方向与太平洋板块的运动方向大体一致.但是,临近地震前(震前)日本东北地区的运动方向发生了很大变化,震前30天的连续GPS观测结果显示,速度场的优势方向经常变换,间歇性地出现与太平洋板块运动方向相反的情况.这意味着震前孕震区的力学状态发生了很大的改变.这种变化可能与震前破裂成核或慢滑移及慢地震等过程有关,这些过程将加速或促进大地震的发生,从而为大地震的发生准备了力学条件.值得特别强调的是,这些现象都是可以通过直接观测能够发现的大地震之前的异常现象.由此可见,加密GPS站点进行连续观测,寻找震前变形异常区以及探索异常的物理机制对于地震预测预报有重要的科学意义. 相似文献
917.
COSEISMIC DISPLACEMENT FIELD OF THE WENCHUAN EARTHQUAKE DERIVED FROM STRONG MOTION RECORDS AND APPLICATION IN SLIP INVERSION 
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下载免费PDF全文 The development of high-rate GNSS seismology and seismic observation methods has provided technical support for acquiring the near-field real-time displacement time series during earthquake. But in practice, the limited number of GNSS continuous stations hardly meets the requirement of near-field quasi-real-time coseismic displacement observation, while the macroseismographs could be an important complement. Compared with high-rate GNSS, macroseismograph has better sensitivity, higher resolution(100~200Hz)and larger dynamic range, and the most importantly, lower cost. However, baseline drift exists in strong-motion data, which limits its widespread use. This paper aims to prove the feasibility and reliability of strong motion data in acquiring seismic displacement sequences, as a supplement to high-rate GNSS.
In this study, we have analyzed the strong-motion data of Wenchuan MS8.0 earthquake in Longmenshan fault zone, based on the automatic scheme for empirical baseline correction proposed by Wang et al., which fits the uncorrected displacement by polynomial to obtain the fitting parameters, and then the baseline correction is completed in the velocity sequence. Through correction processing and quadratic integration, the static coseismic displacement field and displacement time series are obtained. Comparison of the displacement time series from the strong motions with the result of high-rate GPS shows a good coincidence. We have worked out the coseismic displacement field in the large area of Wenchuan earthquake using GPS data and strong motion data. The coseismic displacement fields calculated from GPS and strong motions are consistent with each other in terms of magnitude, direction and distribution patterns. High-precision coseismic deformation can provide better data constraint for fault slip inversion. To verify the influence of strong-motion data on slip distribution in Wenchuan earthquake, we used strong motion, GPS and InSAR data to estimate the stress drop, moment magnitude and coseismic slip model, and our results agreed with those of the previous studies. In addition, the inversion results of different data are different and complementary to some extent. The use of strong-motion data supplements the slip of the fault in the 180km segment and the 270~300km segment, thus making the inversion results of fault slip more comprehensive.
From this result, we can draw the following conclusions:1)Based on the robust baseline correction method, the use of strong motion data, as an important complement to high-rate GNSS, can obtain reliable surface displacement after the earthquake. 2)The strong motion data provide an effective method to study the coseismic displacement sequence, the surface rupture process and quick seismogenic parameters acquisition. 3)The combination of multiple data can significantly improve the data coverage and give play to the advantages of different data. Therefore, it is suggested to combine multiple data(GPS, strong motion, InSAR, etc.)for joint inversion to improve the stability of fault slip model. 相似文献
918.
919.
The Longmenshan fault, which defines the eastern edge of the Tibetan Plateau, is one of the steepest margins of the plateau with a sharp elevation drop of about 4 km over a distance less than 100 km across the Longmenshan fault. The mechanism which is responsible for controlling and maintaining the elevation difference is highly debated. Using multiple observations including seismic velocity model, Moho depth, effective elastic thickness of the lithosphere, we conducted a quantitative study for elucidating the contributions from crust and lithospheric mantle by an integrated analysis of lithospheric isostasy and flexure. It is shown that the topography of the Longmenshan fault is supported by both lithospheric isostasy and flexure statically, and lower crustal channel flow and mantle convection dynamically. Different mechanisms have different weights for contribution to the topography of the Songpan-Ganzi block and the Sichuan Basin. The static and dynamic support contribute roughly the same to the topographic difference of ~4 km between the two sides of the Longmenshan fault. The static topographic difference of ~2 km is mainly resulted from the lithospheric isostasy, while the dynamic one of ~2 km is contributed by the uprising of the accumulated material in the lower crust beneath the Songpan-Ganzi block and the downward drag force caused by the upper mantle convection under the Sichuan Basin. It is thus suggested that the lower crustal flow and upper mantle convection are dynamic forces which should be taken into account in the studies on the dynamics in the Longmenshan and surrounding regions. 相似文献
920.