福建仙游地震序列的震源机制解

1,209 earthquakes occurred in Xianyou, Fujian from August 4, 2010 to October 4, 2013. The largest earthquake was ML5.0 on September 4, 2013. In order to study the Xianyou earthquake sequence and understand the causative structure and stress field of Xianyou, the focal mechanism solutions of six earthquakes （ ML 〉 3. 5 ） in the Xianyou earthquake sequence are calculated using the broadband digital data of the Fujian Seismic Network with the seismic moment tensor inverse method. The results show that the focal faults of the six earthquakes are similar, which are all strike-slip faults striking to the northwest with high dip angles. The direction of the principal compressive stress axes is near SN, which is different from the stress field of Fujian region. The Xianyou earthquake sequence may have been induced by the stress adjustment after the impoundment of Jinzhong reservoir.     

基于Fatti近似的弹性阻抗方程及反演

用Connolly的弹性阻抗(EI,elastic impedance)公式进行反演只能直接得到纵、横波速度和密度的信息,然后才可间接计算得到纵横波阻抗等其它的参数数据体,这样便增加了一步误差使数据的准确性降低.本文首先针对该方法的这些缺点和不足,提出了以Zoeppritz方程的Fatti近似为基础一种新的弹性阻抗公式,由该公式可得到比用Fatti近似更准确的反射系数,然后对这个公式进行了标准化以实现不同角度的弹性阻抗间量纲的统一,最后用标准化后的公式进行了反演,从反演得到的不同角度的弹性阻抗数据体中可直接提取得到纵横波阻抗数据体.应用实例表明用这种方法提取得到的纵横波阻抗更加稳定、准确,而且能很好地反映储层信息.这种新的方法是对以Connolly公式为基础的传统方法的改进.     

Impedance of flexible suction caissons

The dynamic response of offshore wind turbines is affected by the properties of the foundation and the subsoil. The aim of this paper is to evaluate the dynamic soil–structure interaction of suction caissons for offshore wind turbines. The investigations include evaluation of the vertical and coupled sliding–rocking vibrations, influence of the foundation geometry and examination on the properties of the surrounding soil. The soil is simplified as a homogenous linear viscoelastic material and the dynamic stiffness of the suction caisson is expressed in terms of dimensionless frequency‐dependent coefficients corresponding to different degrees of freedom. The dynamic stiffness coefficients for the skirted foundation are evaluated using a three‐dimensional coupled boundary element/finite element model. Comparisons with known analytical and numerical solutions indicate that the static and dynamic behaviours of the foundation are predicted accurately using the applied model. The analysis has been carried out for different combinations of the skirt length, Poisson's ratio of the subsoil and the ratio of the soil stiffness to the skirt stiffness. Copyright © 2007 John Wiley & Sons, Ltd.     

适于陡坡带砂砾岩体的地震资料叠前时间偏移处理技术

随着勘探程度的不断提高,断陷盆地陡坡带砂砾岩体油气藏成为了重点勘探对象之一,但陡倾角的大断层、非均质性强的砂砾岩体使得常规的叠后偏移成像方法成果难以满足勘探开发的需要.采用叠前时间偏移处理技术,开展针对性的叠前预处理技术、精细的速度模型建立和关键参数的合理选取等研究,三维叠前时间偏移处理较常规三维叠后时间偏移处理获得了较高质量的成像剖面,且输出的道集可以用于砂砾岩体储层描述研究.     

Source Parameters of the Deadly M<Subscript>w</Subscript> 7.6 Kashmir Earthquake of 8 October, 2005

During the last six years, National Geophysical Research Institute, Hyderabad has established a semi-permanent seismological network of 5–8 broadband seismographs and 10–20 accelerographs in the Kachchh seismic zone, Gujarat with a prime objective to monitor the continued aftershock activity of the 2001 M_w 7.7 Bhuj mainshock. The reliable and accurate broadband data for the 8 October M_w 7.6 2005 Kashmir earthquake and its aftershocks from this network as well as Hyderabad Geoscope station enabled us to estimate the group velocity dispersion characteristics and one-dimensional regional shear velocity structure of the Peninsular India. Firstly, we measure Rayleigh-and Love-wave group velocity dispersion curves in the period range of 8 to 35 sec and invert these curves to estimate the crustal and upper mantle structure below the western part of Peninsular India. Our best model suggests a two-layered crust: The upper crust is 13.8 km thick with a shear velocity (Vs) of 3.2 km/s; the corresponding values for the lower crust are 24.9 km and 3.7 km/sec. The shear velocity for the upper mantle is found to be 4.65 km/sec. Based on this structure, we perform a moment tensor (MT) inversion of the bandpass (0.05–0.02 Hz) filtered seismograms of the Kashmir earthquake. The best fit is obtained for a source located at a depth of 30 km, with a seismic moment, Mo, of 1.6 × 10²⁷ dyne-cm, and a focal mechanism with strike 19.5°, dip 42°, and rake 167°. The long-period magnitude (M_A ~ M_w) of this earthquake is estimated to be 7.31. An analysis of well-developed sPn and sSn regional crustal phases from the bandpassed (0.02–0.25 Hz) seismograms of this earthquake at four stations in Kachchh suggests a focal depth of 30.8 km.     

Relation of the Wave-Propagation Metric Tensor to the Curvatures of the Slowness and Ray-Velocity Surfaces

The contravariant components of the wave-propagation metric tensor equal half the second-order partial derivatives of the selected eigenvalue of the Christoffel matrix with respect to the slowness-vector components. The relations of the wave-propagation metric tensor to the curvature matrix and Gaussian curvature of the slowness surface and to the curvature matrix and Gaussian curvature of the ray-velocity surface are demonstrated with the help of ray-centred coordinates.     

Moment-tensor statistics of the 1997 Long Valley microearthquake swarm

Abstract. A simple, fast, moment-tensor inversion method using bandpass-filtered P-amplitudes was used to study the moment-tensor statistics of Long Valley caldera microearthquakes. The events were recorded in the summer of 1997, during a swarm in the caldera. The swarm was associated with geodetic extension, uplift, and subsequent moderate earthquake activity. The moment tensor solutions for 1,993 events were calculated using the new method. The majority of the resulting focal mechanisms appear to be explained in terms of double couple mechanisms. Since some events did exhibit considerable deviation from double-couples, the moment data were studied for their statistical significance. The moments of the actual data were compared to the moments of synthetic data with varying degrees of random noise in their spectra. The results of this study suggested that unless data from more than 20 stations are used and the earthquake epicenter is located inside or very close to the network area, moment-tensor inversion does not correctly resolve the non-double-couple components of microearthquakes. Analysis of the inversion residuals shows that the average noise in the P-wave spectra was close to 20%. The fluctuations of the volumetric components of the moment-tensor are in good agreement with those of the synthetic pure double-couples with 20% of added noise. Thus the moment-tensor statistics suggests that little if any volume change is required to explain the observed seismic energy release in the swarm. However, the statistics do show that a significant compensated-linear-vector-dipole component maybe present in the bulk of the seismicity. Given the network used in this study, such a component could not be precisely resolved for individual earthquakes. This possibility deserves further investigation because of its bearing on the nature of fluid-fault-earthquake processes in swarms.     

Mechanism of the June 4, 2000 Southern Sumatra, Indonesia, earthquake

Introduction The June 4, 2000 southern Sumatra, Indonesia, earthquake (16h28min26.2s UTC, 4.72, 102.09, 33 km, MS=8.0 [IRIS]) occurred under the Indian Ocean, near the Mentawai fault, along the well-known Sumatran subduction zone and the great Sumatran fault, all of which trend northwest-southeast. 1 800 houses were totally destroyed, 10 196 were heavily damaged, and 18 378 were slightly damaged by the earthquake. At least 97 people were killed, 1 900 were injured, and 122 000 were left…     

Rocking response of flexible circular foundations on layered media

The analysis of the response of a flexible circular foundation on layered media due to an arbitrarily distributed vertical loading is presented. The analysis is based on the ‘ring method’ approach, i.e. discretization of the foundation in a set of concentric rings. The arbitrarily distributed loading is expanded in the circumferential direction in a Fourier series. The influence coefficient matrix of soil for each element of the series is evaluated utilizing the stiffness matrix approach. The stiffness matrix of the foundation is obtained from the finite difference energy method approach. Numerical examples illustrate the influence of several soil-foundation parameters on the rocking response of a foundation. Results are presented in terms of displacement and soil reaction distributions and impedance functions point to significantly different responses of flexible and rigid foundations.     

Tectonic analysis of mine tremor mechanisms from the Upper Silesian Coal Basin

Fault network of the Upper Silesian Coal Basin (USCB) is built of sets of strike-slip, oblique-slip and dip-slip faults. It is a typical product of force couple which acts evenly with the parallel of latitude, causing horizontal and anti-clockwise movement of rock-mass. Earlier research of focal mechanisms of mine tremors, using a standard fault plane solution, has shown that some events are related to tectonic directions in main structural units of the USCB. An attempt was undertaken to analyze the records of mine tremors from the period 1992–1994 in the selected coal fields. The digital records of about 200 mine tremors with energy larger than 1×10⁴ J (M _L >1.23) were analyzed with SMT software for seismic moment tensor inversion. The decomposition of seismic moment tensor of mine tremors was segmented into isotropic (I) part, compensated linear vector dipole (CLVD) part and double-couple (DC) part. The DC part is prevalent (up to 70%) in the majority of quakes from the central region of the USCB. A group of mine tremors with large I element (up to 50%) can also be observed. The spatial orientation of the fault and auxiliary planes were obtained from the computations for the seismic moment DC part. Study of the DC part of the seismic moment tensor made it possible for us to separate the group of events which might be acknowledged to have their origin in unstable energy release on surfaces of faults forming a regional structural pattern. The possible influence of the Cainozoic tectonic history of the USCB on the recent shape of stress field is discussed.