Fundamental solutions for a fluid‐saturated,transversely isotropic,poroelastic solid

The fundamental solutions were obtained for step‐like point forces acting in three orthogonal directions and an instantaneous fluid point source in a fluid‐saturated, porous, infinite solid of transversely isotropic elasticity and permeability. After expressing the governing equations in the form of matrix in the Laplace space, we employed Kupradze's method together with the triple Fourier transforms. This method reduces the simultaneous partial differential equations with respect to three displacement components and a pore fluid pressure to a differential equation in terms of only one potential scalar function, which can be operationally solved in the transformed space. After the Laplace inversion of the potential, the residue theorem was applied to its Fourier inverse transform with respect to one of the transformation variables. The Fourier transforms with respect to two other variables were rewritten into the Hankel transforms. Copyright © 2002 John Wiley & Sons, Ltd.     

岩体初始地应力场分析方法研究

初始地应力场是影响岩土工程稳定性的重要因素之一,如何合理地模拟初始地应力场一直是岩体力学中的重要研究课题。以国内某大型水利水电工程构筑区域实测空间地应力资料为基础,以边界位移为控制对象,采用有限元（无界元）方法对工程区大范围内的岩体初始地应力场进行了分析和研究。尝试在实际边界上满足无穷远处位移为0的模型边界上引入了无界单元,实测点上的应力拟合结果有较明显的改善,这表明所采用的方法是切实可行和有效的。     

泉州台763长周期地震仪的震相记录特征

76 3长周期地震仪 1 997年起取代基式仪 ,承担我国一类合网对国内外地震的监测和对外观测资料交换任务。本文介绍了我台 76 3长周期地震仪的震相记录特征 ,有利于台站对震相的分析 ,提高对外资料交换和大震速报水平。     

Local magnetic field measurements and fault creep observations on the San Andreas fault

Simultaneous creep and magnetic field records have been obtained for more than 60 episodic creep events since early 1974, no clear magnetic transients or offsets, as suggested by Breiner and Kovach (1968), are observed at or up to several days before the occurrence times of these events. Although some patterns of creep onset times at adjacent stations over periods of weeks to months appear to correspond to some periods of longer term change in local magnetic field, these changes do not always occur and other groups of creep events have no corresponding changes in local magnetic field. Changes in stress related to the surface expression of episodic fault creep on the San Andreas fault can be estimated from dislocation models fit to observations of simultaneous strains and tilts at points near the fault. These stress values are generally less than 1 bar. For these stress levels and with the apparent limited extent of surface failure, tectonomagnetic models of creep events indicate that simultaneous observations of related magnetic field variations at detectable levels of a gamma or so are unlikely. Slip at greater depth may occur more smoothly and would load the near-surface material to failure. These data also argue against large-scale dilatant cracking occurring along the region of the fault presently monitored.     

基于包络的汶川大地震高频地震波辐射区域反演及近场加速度合成

合理地估计汶川破坏区域的地震动有助于地震灾害的研究.通过利用芦山地震记录建立的加速度包络衰减关系和汶川地震近场30个台站的加速度包络,基于线源模型,采用差分进化方法反演了汶川地震断层面上高频 (＞1 Hz) 辐射区域分布.结果表明:断层面上高频辐射分布很不均匀,辐射较强的区域主要位于:(1) 产生较大地表破裂的映秀、北川和南坝区域;(2) 映秀和北川等凹凸体的周边区域,包括震中东北侧60~90 km区域、北川和南坝东北侧30 km处;(3) 断层破裂停止的东北端约30 km长的区域.其中,破裂贯穿到地表的映秀、北川和南坝是低频和高频辐射都很强的区域.对于无观测记录场点,选择其临近且场地条件类似的台站加速度提取平稳随机过程,结合高频辐射分布和衰减关系得到的包络,合成了加速度时程,可为汶川地震结构震害分析提供地震动输入.      

Complex seismic signatures and narrow azimuthal study of Hindukush earthquakes

About eighty earthquakes, exclusively from the Hindukush region, which were recorded at Gauribidanur seismic array (GBA) have been used in the present study. Short periodP-wave recordings upto 36 seconds were processed using adaptive cross-correlation filtering technique. The main objective of this exercise was to examine the signal complexities and seismic ray direction anomalies of these earthquakes which have identical epicentral distances and a narrow azimuthal range from GBA but different focal depths from 10 to 240 km. Slowness anomalies of the order of 1–4 sec/deg and azimuthal anomalies upto 6° have been found in this case. These deviations have been attributed to the upper mantle region between source and the receiver. Analysis of the data reveals that most of the events occurring at shallower depths had complex signatures as compared to the deeper events. The structure near the source region, complicated source functions and scattering confined to the crust-upper mantle near source are mainly responsible for complexity of the observed signals as the transmission path of the ray tubes from turning point to the recording stations is practically the same.     

Vortex Motion of the Crust Deformation in the Tibetan Plateau and Its Foreland

VORTEX MOTION OF THE CRUST DEFORMATION IN THE TIBETAN PLATEAU AND ITS FORELANDFromtheresultsofthecooperativeprojectbetweenChengduInstituteofGeologyandMineralResources andMassachusettsInstituteofTechnology     

Relative teleseismic travel-time residuals, North Island, New Zealand, and their relation to upper-mantle structure

Relative travel-time residuals computed from clear P-wave arrivals at fourteen seismograph stations in the North Island, New Zealand, from five deep-focus events in the Banda Sea region, show large spatial variations of up to 3 sec. The variations can be explained by higher than normal velocities in the oceanic lithosphere which is underthrust to depths of 350 km beneath the North Island. After correction for crustal structure, the residuals imply an average P-wave velocity about 11% higher than in the surrounding mantle. The lack of suitable source events at azimuths other than northwest prevents a more detailed investigation by this means.     

Energy flux of strong earthquakes

In this paper, the energy flux of strong earthquakes at a station is determined considering the progressive rupture of a fault as the source of earthquakes. It is found that the motion of the source and the relative position of the station with respect to the fault are important in determining the energy density, the energy flux and the duration of the earthquake at this station. There is a “sphere of influence” beyond which the source may be assumed to be stationary. The analytical results are in good agreement with those of the 5 strong motion records obtained very near the fault from the Parkfield event of 27th June, 1966. 21 strong motion records are studied for energy densities at the stations from which a magnitude-energy relationship is obtained which agrees closely with other existing relationships.     

The earthquake swarm of December 2007 in the Mila region of northeastern Algeria

In December 2007, the Mila region of northeastern Algeria experienced thousands of microearthquakes (0.8????Md????3.9) recorded by eight temporary stations, in addition to permanent stations. Most of the events were too small to be located precisely, but a set of 122 precisely located events shows an alignment of epicenters, extending mainly in a horizontal band at about 1?C2?km depth in a NNW?CSSE direction and concentrated in a small area, 3?km southeast of Jebel Akhal, a small rocky hill between the Beni Haroun dam/reservoir and the Oued Athmania reservoir. The reservoirs are connected by pipelines, and a pumping station ensures water can be transferred between them at transient pressures of up to 80?bars. During the pumping in 2007, only 45?% of the transferred water (~600,000?m³ per day) was recovered at the Oued Athmania reservoir, and a large amount of the slightly pressurized water leaked through defective joints in a tunnel that passes through the Jebel. This water penetrated deeply into the soil with the assistance of preexisting fractures, faults, and karsts. Nine days after the first pumping started, a local increase in pore fluid pressures at shallow depths triggered seismicity southeast of Jebel Akhal, where the faults were probably close to failure. The focal mechanisms show a near vertical N?CS strike-slip fault plane under regional NW?CSE tectonic compression. One of the fault plane solutions is consistent with the NNW?CSSE direction along which the seismic events are aligned. Furthermore, a long-term comparison of the seismic activity in the region versus water levels behind the dam and the pumping of water shows that the earthquake swarm was a one-off event related to the pumping operation.     

Moment Tensor Solutions of some Selected Local Events: Implications towards the Present-day Tectonics of the Kachchh Rift zone

The Kachchh rift zone of the northwestern India lies near to the India-Arabia and the India-Eurasia plate boundaries, which has experienced many devastating earthquakes in the past, namely the 1819 Allah Bund earthquake, the 1956 Anjar earthquake and the 2001 Bhuj earthquake. These earthquakes claimed the lives of about 17,000 people. To understand the current seismo-tectonic scenario, moment tensor inversion on the broadband data of fourteen Kachchh events of M_w 3.5–4.6 (during 2009–2015) from 5–12 three-component seismograph stations of the National Geophysical Research Institute (NGRI), Hyderabad, India was applied. Here deviatoric moment tensor inversion of multiple point sources (10–20s) for regional (or local) earthquakes, developed by Zahradnik et al. (2005) was used. The study reveals that modeled focal mechanisms range between reverse and normal oblique strikeslip while no pure normal dip-slip mechanism is found. However, only four out of fourteen events show oblique normal faulting with a minor strike-slip component. Thus, the modeling proposed in this study suggests that the oblique-reverse strike-slip, reverse and strike-slip type focal mechanisms are found to be dominant in the Kachchh rift zone. This observation indicates that the region is presently under compression.     

相位加权叠加方法在探测鄂尔多斯东南缘地壳结构中的应用

本文利用在鄂尔多斯东南缘地区宽频带流动地震台阵记录的远震数据,提取各台站的接收函数,并利用相位加权方 法进行单台多震叠加、H -κ叠加以及共转换点叠加,获得了研究区莫霍过渡带的深度及其变化趋势。研究结果显示,莫霍的 深度由鄂尔多斯块体往东南方向逐渐变浅,在不同区域莫霍具有不同的特征：鄂尔多斯的莫霍深度在42~38 km;渭河-山 西地堑的莫霍出现约3 km的上隆;熊耳-伏牛山的莫霍深度在35~33 km;河淮盆地的莫霍形态比较复杂。相位加权叠加方 法能有效地压制相关性不好的噪音,在部分受噪音及沉积层多次波干扰的台站记录中,对突出莫霍的转换波Ps震相有很大 的帮助。     

Earthquake source model using strong motion displacement as response of finite elastic media

The strong motion displacement records available during an earthquake can be treated as the response of the earth as the a structural system to unknown forces acting at unknown locations. Thus, if the part of the earth participating in ground motion is modelled as a known finite elastic medium, one can attempt to model the source location and forces generated during an earthquake as an inverse problem in structural dynamics. Based on this analogy, a simple model for the basic earthquake source is proposed. The unknown source is assumed to be a sequence of impulses acting at locations yet to be found. These unknown impulses and their locations are found using the normal mode expansion along with a minimization of mean square error. The medium is assumed to be finite, elastic, homogeneous, layered and horizontal with a specific set of boundary conditions. Detailed results are obtained for Uttarkashi earthquake. The impulse locations exhibit a linear structure closely associated with the causative fault. The results obtained are shown to be in good agreement with reported values. The proposed engineering model is then used to simulate the acceleration time histories at a few recording stations. The earthquake source in terms of a sequence of impulses acting at different locations is applied on a 2D finite elastic medium and acceleration time histories are found using finite element methods. The synthetic accelerations obtained are in close match with the recorded accelerations.     

Infinite elements in a poroelastodynamic FEM

An infinite element is presented to treat wave propagation problems in unbounded saturated porous media. The porous media is modeled by Biot's theory. Conventional finite elements are used to model the near field, whereas infinite elements are used to represent the behavior of the far field. They are constructed in such a way that the Sommerfeld radiation condition is fulfilled, i.e. the waves decay with distance and are not reflected at infinity. To provide the wave information the infinite elements are formulated in Laplace domain. The time domain solution is obtained by using the convolution quadrature method as the inverse Laplace transformation. The temporal behavior of the near field is calculated using standard time integration schemes, e.g. the Newmark method. Finally, the near and far field are combined using a substructure technique for any time step. The accuracy as well as the necessity of the proposed infinite elements, when unbounded domains are considered, is demonstrated by different examples. Copyright © 2010 John Wiley & Sons, Ltd.     

涡动相关仪观测数据的处理与质量评价研究

涡动相关仪能够较准确地直接测量地表—大气间的湍流交换,在世界范围内得到了广泛的应用。但它的使用是有条件限制的,如果不进行必要的修正,得到的通量就可能有较大的误差。以密云观测站一年的涡动相关仪观测数据为例进行分析。结果表明：野点值剔除、坐标旋转以及超声温度订正对地表感热、潜热等通量的测量结果影响均在±1%之内,但坐标旋转对动量通量影响较大,必须对潜热和CO2通量进行空气密度效应订正;湍流谱在惯性副区基本满足-2/3次方定律,协谱基本满足-4/3次方定律。经过对观测数据的筛选和处理后,约75%的观测数据质量较好,2%的数据需要剔除。通量贡献源区分析表明,全天和白天均有超过70%的通量源区落在感兴趣区域内,超过90%的通量贡献最大点落在感兴趣区域内。     

从德令哈地震分析青藏高原北缘东段的深部构造活动

在祁连山南北布设的10台REFTEK宽频地震仪器记录到了2003年4月发生在仪器台阵范围内的6．7级地震及其数十次余震,提供了研究青藏高原北缘深部构造的新资料,对3级以上震源的定位和震源机制研究结果表明,柴达木盆地北缘逆冲左行走滑断裂东段的宗务隆山逆冲断裂在南北挤压作用下引发了此次地震活动,是陆陆碰撞和内陆俯冲的结果,青藏高原北缘的走滑断裂在浅部呈缓倾斜,深部往往以较陡的产状向下延伸。震源区的构造分析证实了印度板块岩石圈的超深俯冲作用对高原北缘的影响,受南北向应力作用影响形成的走滑断裂近东西向的位移目前仍很剧烈。     

Near-surface Geothermal Gradient Observation and Geothermal Analyses in the Xianshuihe Fault Zone, Eastern Tibetan Plateau

The Xianshuihe fault(XSHF) zone, characterized by intense tectonic activity, is located at the southwest boundary of the Bayan Har block, where several major earthquakes have occurred, including the 2008 Wenchuan and the 2013 Lushan earthquakes. This study analysed underground temperature sequence data for four years at seven measuring points at different depths(maximum depth: 18.9 m) in the southeastern section of the XSHF zone. High-frequency atmospheric noise was removed from the temperature sequences to obtain relatively stable temperature fields and heat fluxes near the measurement points. Our measurements show that the surrounding bedrock at(the seven stations distributed in the fault zone) had heat flux values range from-41.0 to 206 m W/m~2, with a median value of 54.3 m W/m~2. The results indicate a low heat flux in the northern section of DaofuKangting and a relatively high heat flux in the southern section of Kangting, which is consistent with the temperature distributions of the hot springs near the fault. Furthermore, our results suggest that the heat transfer in this field results primarily from stable underground heat conduction. In addition, the underground hydrothermal activity is also an obvious factor controlling the geothermal gradient.     

利用全站仪激光对点器对井下投点的方法

竖井联系测量中,利用全站仪进行竖井投点,在近井点设站,罐笼与井壁间隙处选两个临时点,测出两点坐标。分别在两个临时点摆站,利用全站仪激光对点器将其点位在罐笼与井壁间隙中间投于井下。实践证明全站仪激光对点器对井下投点的方法投点方法简便,点位选择灵活,不需要多余记算,不用添置专用仪器,是行之有效的测量方法。     

Flow and high sediment yield from the Huangfuchuan watershed

This study deals with general features of sediment transport in the Huangfuchuan river, an important branch river of the Yellow river, draining the Loess Plateau in China. The long-term precipitation records at 3 climate stations near the watershed have been used to assess the changes in precipitation in this region. By introducing metrics for runoff and sediment transport, long-term observations on discharge and sediment concentration at the Huangfuchuan gauging station on the Huangfuchuan river have been used to assess the changes in runoff and sediment transport in the Huangfuchuan River compared with those at the Toudaoguai and Fugu gauging stations on the Yellow river. It is found that both runoff and sediment metrics have a clearly downward trend. From July to August, the long-term sediment transport modulus at the Huangfuchuan gauging station is much higher than those at the Toudaoguai and Fugu stations on the Yellow river. The long-term average sediment transport modulus at the Huangfuchuan gauging station are high, ranging from 14000. t/(km² y) but decreasing to 5900 t/(km² y) over the last 10 years. Additionally, analyses on grain size distribution of suspended load in the Huangfuchuan and Yellow river have been conducted.     

High velocity anomaly beneath the Deccan volcanic province: Evidence from seismic tomography

Analysis of teleseismicP-wave residuals observed at 15 seismograph stations operated in the Deccan volcanic province (DVP) in west central India points to the existence of a large, deep anomalous region in the upper mantle where the velocity is a few per cent higher than in the surrounding region. The seismic stations were operated in three deployments together with a reference station on precambrian granite at Hyderabad and another common station at Poona. The first group of stations lay along a west-northwesterly profile from Hyderabad through Poona to Bhatsa. The second group roughly formed an L-shaped profile from Poona to Hyderabad through Dharwar and Hospet. The third group of stations lay along a northwesterly profile from Hyderabad to Dhule through Aurangabad and Latur. Relative residuals computed with respect to Hyderabad at all the stations showed two basic features: a large almost linear variation from approximately +1s for teleseisms from the north to—1s for those from the southeast at the western stations, and persistance of the pattern with diminishing magnitudes towards the east. Preliminary ray-plotting and three-dimensional inversion of theP-wave residual data delineate the presence of a 600 km long approximately N−S trending anomalous region of high velocity (1–4% contrast) from a depth of about 100 km in the upper mantle encompassing almost the whole width of the DVP. Inversion ofP-wave relative residuals reveal the existence of two prominent features beneath the DVP. The first is a thick high velocity zone (1–4% faster) extending from a depth of about 100 km directly beneath most of the DVP. The second feature is a prominent low velocity region which coincides with the westernmost part of the DVP. A possible explanation for the observed coherent high velocity anomaly is that it forms the root of the lithosphere which coherently translates with the continents during plate motions, an architecture characteristic of precambrian shields. The low velocity zone appears to be related to the rift systems (anomaly 28, 65 Ma) which provided the channel for the outpouring of Deccan basalts at the close of the Cretaceous period.