断层围陷波(Fault zone trapped waves)又称为断层通道波、断层导波、槽波,是波在断层的两个边界内侧多次反射并相干迭加而形成的.围陷波既然是由断层带内低速介质和高速围岩之间的相干多次反射波构成的,那么其振幅和频率就强烈地依赖于断层带内介质的物理性质和断层的几何形态.所以观测、分析和模拟断层围陷波能够确定断层的深部细节.

Three component rotational ground motion is one of the most important point of geophysics research.In this paper, the rotational ground motions with three components were deduced by calculation using records of translational seismographs from explosions.The observational data used are from three shots with explosive charge of 500kg for each and observational distances of 1.8, 2.8, 8.9km respectively.The rotational motions of the array from these three shots were obtained by calculation.The largest peak angular velocities of ground motion are 41.65, 21.98 and 0.29μrads/s respectively, which are quite near the results from international colleagues.How the peak values of the ground motion decay with the epicenter distance is always the focal problem in earthquake engineering.In this paper, the peak angular velocities of ground motion are fit with exponent function, and the decay of peak values with distance is obtained.The main features of the decay curves are as follows: The values decay very fast within 1-3km and slow down gradually beyond 5km.And with the increase of the distance, the curve tends to more and more flat.

According to anti-seismic design criterion for bridges and roads in China, the designed ground motion parameters of bridge design is determined by the probability level of reproduction period T=475 years and 2000 years, probabilistic seismic hazard analysis ( PSHA) is often used for calculating bedrock peak gravity acceleration ( PGA) in similar project. This paper studied a bridge in southern Henan area to calculate the seismic hazard of ground motion parameters. Results show: At the probability reproduction period of T=100 years, 475 years and 2000 years, the bed rock PGA is respectively 12. 7, 31. 6 and 72. 5 gal; corresponding to horizontal designed ground motion PGA of respectively 19. 3 , 45. 7 and 98. 7gal. The studied zone is at 0. 05G zone in 5th generation China Ground Motion Parameters Map, the authors suggests the designed basic PGA be 50gal, which is coherent with calculation results.

利用小波分析处理青藏高原航磁资料,得到多尺度的航磁异常分布图.一阶小波结果反映地壳浅部的构造特征,在第Ⅰ和第Ⅱ缝合带位置,存在多条明显的北西西向弧形构造,由正负相间的磁异常带组成;在格尔木附近第Ⅳ缝合带位置存在近东西向的负磁异常条带.三阶小波结果反映地壳深部的构造特征,在约84°～91°E存在明显的近南北向的负磁异常条带,是研究区主要的深部构造特征.尼泊尔8.1级地震和3次7级强余震发生在近南北向的负磁异常条带的南端.该位置是近东西向的喜马拉雅构造带和近南北向的深部负磁异常条带的交汇部位.总体来说,青藏高原航磁资料揭示的浅部构造为多条近东西走向的带状构造,而深部构造是以近南北走向为主要特征,复杂的立交构造交汇部位是发生尼泊尔8.1级大地震的深部构造背景.

为了研究某些震源区的细结构，可以在震源区周围布设几千米点距的密集临时地震台网，记录近场微震资料。近场资料的特点是震源—接收台站之间的路径较短，接收到的地震波直接反映震源区介质的信息，并且台站之间距离较小且分布较均匀。因此，可以得到精细的震源区成像结果。在唐山至滦县地区布设过由30个台站组成的密集临时地震台网，得到了大量的微震记录。利用地震成像方法对临时地震台网资料做进一步处理，得到唐山震源区的三维地壳速度结构。

断层围陷波的观测特点是利用密集的地震台阵,横跨断层布设测线.可以利用爆炸震源也可以利用余震进行观测,本文分别介绍了实际观测的例子.对大地震破裂带内部的观测,测线位置通常布设在地表破裂带明显、已开挖了地震探槽、断层陡坎出露等地震地质的典型地段.利用爆炸震源激发观测断层围陷波,震源位置应尽量选择在断层带上,震源炸药量大约500kg,测线位置与震源的距离大约5-15km.断层围陷波在新破裂带和老的断层中都能形成和传播,因此该方法可以用于大震破裂带研究,也可以用于城市活断层探测.

利用汶川地震区不同地段的断层围陷波记录,分析了该地震断层的分段性特征.对断层北东段的关庄测线分析研究结果表明:地壳内破碎带的宽度大约160～180 m,地下破碎带的中间与地表破裂的位置对应,并且地下破碎带在断层的两盘边缘较均匀地分布,反映了北东段的断层倾角较陡,近似直立断层.对断层南西段的虹口测线研究结果表明:地壳内破碎带的宽度大约180～200 m,地下破碎带主要分布在地表断层陡坎上盘所对应的地壳内,反映了南西段断层倾角比北东段断层倾角小.本文的研究结果可以为汶川8.0级地震的构造背景研究提供依据.

Trapped waves in different sections of Longmenshan fault belt were observed, and the results show the difference between the northern and southern portions of this fault belt. Guanzhuang and Leigu surveying lines are located at the northern portion of the fault belt, and the result indicates that the width of the rupture zone underground in this area is about 160 – 180m. The center position of rupture zone underground corresponds to the surface breaking trace, and is equally distributed at the edges of the two fault walls. However, Hongkou surveying line is located at the southern portion of the fault belt, and the result indicates that the width of the rupture zone underground in this area is about 180 – 200m. The rupture zone underground is mainly distributed below fault scarp. The Wenchuan Ms8. 0 earthquake and Lushan Ms7. 0 earthquake both occurred at the Longmenshan fault belt. The results will provide information for the structure background of the two violent earthquakes.

Seismic tomography is used for processing the data of temporary seismostations networks in Tangshan region,and the velocity images of upper and mid crust in this earthquake region are obtained.The results show that,in the upper crust image,the velocity of two sides between the Tangshan fault zone are different,where the northwest side is high velocity zone while the southeast side is low and the Tangshan fault is belt with sharp velocity variety.Besides in the mid crust velocity image,it shows that there is low velocity belt near EW strike in the centre of the studied area,and its location and strike are corresponding with the Fengtai-Yejituo fault which is near EW strike and in Tangshan epicenter region,along both of the depth and horizon,sharp velocity variety in crust exsits too.

<正>南北构造带一直是地学界关注的焦点,它是第四纪地壳构造变动十分强烈的地震活动带、地质灾害多发带;也是地壳厚度和重力异常的陡变带,它在东亚大陆动力学研究中占有十分重要的地位。从地震活动性来看,该带有史以来曾发生过多次8级以上大震,是中国大陆地区地震活动水平最高的一个地震带。我们在天水、武都两个8级大震区布设了两条相互垂直的高分辨地震折射剖面以及相应

We used the Pg-wave arrival times from high-resolution active-source seismic sounding to carry out the tomographic job on the northeastern margin of Qinghai-Tibet plateau, that is, the Tianshui-Wudu area in West Qinling, with finite difference forward and least squares inversing algorithm with irregular meshes. The results indicate that the study area has rich and complex fractures, such as the fluctuant basement and the steep faults mostly extending to great depths and cutting through the basement. The low-velocity zone between Lixian and Xihe reflects the existence of Xi-Li sedimentary basin, the basement of which is about 5 km deep. The pronounced changing of the velocity contour on the east of Wushan is consistent with the fold region nearby. The Chengxian basin has a relatively high and gently changing velocity, the basement depth of which is less than 3 km. Near Lixian there is a near north- south fault, and a low-velocity zone exists beneath about 5 km depth in the tomographic profile, which may be the upwelling channel of the deep mantle substance in the Tibetan Plateau.

This article gives a description of our first study on ground rotational motion and its preliminary results. The ground rotational motions around vertical axis were obtained using near-field translational records of a temporal seismic array with observational distances of 1.8 to 2.7 km. The sources used are explosions with explosive of 500 kg for each. Ground rotational velocities were calculated using the space derivatives of the horizontal components of translational velocities from the array. The peak ground rotational velocities (PGRV) are approximately 30 to 57 μrad/s. Our results are very close to those from Wassermann et al. (2009), who used both a seismic array and a rotational sensor to record an explosion in Germany and obtained PGRV values of about 50 μrad/s. Their explosives are 150 kg, only one third of ours, but their observational distance is 250 m, much less than ours.

Trapped waves in the Qingchuan fault zone were observed at Muyu near the northeastern end of the fractured zone of the Wenchuan Ms8. 0 earthquake. The results indicate a fault-zone width of about 200m and a great difference in physical property of the crust on different sides of the fault. The inferred location of crustal changes is consistent with land-form boundary on the surface.

A 2-D model of lithospheric velocity structures in the southern part of the North China Craton was obtained using data from the Zhucheng-Yichuan deep seismic sounding profile. Results show that there are great differences in lithospheric structures between two sides of Taihang Mountain. In the eastern region, the lithosphere is thinner, with a thickness of about 70–80 km, while in the western region, the thickness is 85–120 km. There is a jump of the lithospheric thickness across Taihang Mountain gravity anomaly belt with a magnitude of about 30 km. P wave velocities of the lithospheric mantle and lower crust are lower in the eastern region and higher in the western region. In the eastern region, there are low velocity bodies in the middle and lower crust, while none were found in the western region. These differences indicate that the Taihang Mountain gravity anomaly belt is a belt with a abrupt change of lithospheric thickness and lithological composition. According to the Pm waveform, it can be deduced that the Moho in the eastern region is not a sharp discontinuity, but a complex transitional zone. From a preliminary analysis, it is found that the geothermal mechanical-chemical erosion could be the main mechanism causing the thinning and destruction of the lithosphere beneath the eastern side of Taihang Mountain. In addition, subduction of the Pacific Plate is an important factor which changes the properties of the lithospheric mantle of the North China Craton.

利用诸城-宜川人工地震折射/宽角反射剖面的资料,得到了华北克拉通南部岩石圈二维速度结构.结果表明,太行山东西两侧岩石圈结构存在着巨大的差异.东侧较薄,为70～80 km;西侧较厚,为85～120 km.在太行山重力梯度带附近,岩石圈厚度出现了约30 km的突变.岩石圈地幔和下地壳介质的P波速度值东侧较低,西侧较高.东侧的中下地壳内存在不同尺度的低速体,西侧则尚未发现.这些差异表明,太行山重力梯度带也是一条岩石圈厚度突变带和岩石成分分隔带.根据Pm波的波形特点,推测东部地区的莫霍面不再是一个尖锐的间断面,而是一个复杂的过渡带.初步分析认为,上地幔物质的热机械-化学侵蚀作用是引起太行山东侧岩石圈减薄和破坏的主要机制,太平洋板块俯冲是改变华北克拉通岩石圈地幔性质的重要动力学因素.

Pingtong Town is located on the fractured zone of the Wenchuan 8.0 earthquake, and is seriously damaged by the earthquake. Our observation line is centered at an earthquake exploration trench across the fractured zone in the NW-SE direction, and is about 400 m long. The results reveal trapped waves in the ruptured fault zone of the earthquake, and indicate a great difference in physical property between the media inside and outside the fault zone. The predominant frequency of the fault-zone trapped waves is about 3 – 4 Hz. The wave amplitudes are larger near the exploration trench. The width of the fault zone in the crust at this location is estimated to be 200 m. In some records, the waveforms and the arrival times of S waves are quite different between the two sides of the trench. The place of change coincides with the boundary of uplift at the surface.

<正>2008年5月12日在四川省汶川地区发生了8级特大地震,断裂长度达300 km,地震中最大错位10 m以上,造成震区地面建筑大面积倒塌和大量人员伤亡,并诱发了严重的地质灾害,毁坏了公路、桥梁等交通系统和通讯设施。由于地震的发生和破坏程度与地壳内部断裂构造的形态和分布之间有着密切的关系,因此,尽快确定龙门山断裂带目前的状况,探明各分支断层的位置和几何形态,测定岩体破碎程度和分布范围,为震后灾区恢复重建合理选择提供科学依据,便成了当务之急。

The rupture process of the May 12, 2008 M S 8.0 Wenchuan earthquake was very complex. To study the rupture zones generated by this earthquake, four dense temporary seismic arrays across the two surface breaking traces of the main-shock were deployed in July and recorded a great amount of aftershocks. This paper focuses on the data interpretation of two arrays across the central main fault, the northern array line 1 and southern array line 3. The fault zone trapped waves recorded by the two arrays were used to study the structure of the central main fault and the difference between the northern and southern portions. The results show that the widths of the rupture zone are about 170–200 m and 200–230 m for northern and southern portions respectively. And the corresponding dip angles are 80° and 70°. The seismic velocity inside the fracture zone is about one half of the host rock. By comparison, the northern portion of the rupture zone is slightly narrower and steeper than the southern portion. Besides these differences, one more interesting and important difference is the positions of the rupture zone with respect to surface breaking traces. At the northern portion, the rupture zone is centered at the surface breaking trace, while at the southern portion it is not but is shifted to the northwest. This difference reflects the difference of rupture behaviors between two portions of the central main fault. The width of the rupture zone is smaller than that of M 8.1 Kunlun earthquake though these two earthquakes have almost the same magnitudes. Multiple ruptures may be one factor to cause the narrower rupture zone.

Large property contrasts between materials in a fault zone and the surrounding rock are often produced by repeating earthquakes. Fault zones are usually characterized by fluid concentration, clay-rich fault gouge, increased porosity, and dilatant cracks. Thus, fault zones are thought to have reduced seismic velocities than the surrounding rocks. In this article, we first investigated the synthetic waveforms at a linear array across a vertical fault zone by using 3D finite difference simulation. Synthetic waveforms show that when sources are close to, inside, or below the fault zone, both arrival times and waveforms of P- and S-waves vary systematically across the fault zone due to reflections and transmissions from boundaries of the low-velocity fault zone. The arrival-time patterns and waveform characteristics can be used to determine the fault zone structure. Then, we applied this method to the aftershock waveform data of the 1992 Landers M7.4 and the 2008 Wenchuan (ae +/- a center dot e) M8.0 earthquakes. Landers waveform data reveal a low-velocity zone with a width of approximately 270-370 m, and P- and S-wave velocity reductions relative to the host rock of approximately 35%-60%; Wenchuan waveform data suggest a low-velocity zone with a width of approximately 220-300 m, and P- and S-wave velocities drop relative to the host rock of approximately 55%.

The structure of crust and upper mantle in Tianshui-Wudu strong earthquake region is studied by using DSS data from two cross high resolution refraction /wide angle reflection profiles and corresponding fan profiles.The 2-D result shows that the crust can be vertically divided into two layers:upper crust and lower crust.There exists a low velocity layer in the upper crust with velocity difference of 0.3-0.5 km/s.The depth of Moho is about 46-48 km.There is a strong lateral variation in the lower crust along the NE Tianshui-Wudu profile.And along the NW Chengxian-Wushan profile,there are some evidences showing that the Moho and C discontinuities are changed by substances from the deep layer.The 3-D result shows that there is a fault with near NS strike at the depth of 7-11 km near 105°E.The velocities at the two sides of this fault are quite different:low velocity at the west side and high velocity at the east side.This NS fault is very close to the deep fault of 2-D profile.All the large earthquakes occurred near 105°E and formed a NS belt.