考虑地震位错引起的大地水准面形变的源参数反演

本文首先讨论了地震位错引起的参考系,即大地水准面形变问题.给出了位错引起的大地水准面高和垂线偏差的变化,以及大地水准面高随位错面倾角变化等数值结果.在进一步考虑大地水准面形变的条件下,给出用表面视位移和重力变化资料反演位错模型参数的处理方法,以及用于确定唐山地震源参数和大地水准面高的变化的实例.研究结果表明,在使用大地测量资料进行地震位错模型参数反演时,考虑大地水准面形变不仅在理论上更加严格,而且在实际应用中也确有意义.      

不同产状断层错动的地表重力变化和形变

根据点源位错引起的地表重力变化和形变的理论公式,应用数值算法求得半无限空间任意产状断层位错在地表的重力变化和形变．计算结果表明,产状和位错方式是决定断层的地表重力和形变效应的基本因素．铲式断层活动的地表重力和形变效应与矩形断层相比有显著差异．断层位错引起的重力变化、垂直形变、视垂直形变的图象特征相似．根据重力变化和形变的特殊图象特征,有可能从观测资料中提取断层活动引起的重力变化和形变信息,判识和估计发震断层的几何学和运动学特征．      

由近断层强震记录得到的断层位错过程对管道的影响分析

在近些年的几次大地震中,例如,汶川地震和集集地震等,获得了不少近断层乃至断层上的加速度强震记录.这些近断层加速度强震记录对研究近断层的地震动特征(如速度脉冲、方向性效应)、震源机制等具有重要的意义.通过对断层附近的加速度记录进行2次积分,并经过适当基线校正后得到断层位错时程,发现其位移峰值往往大于断层的永久位移量.而目前埋地管道在断层位错下的反应分析方法一般直接输入的是断层的永久位移量.     

球形地球模型的地震位错理论及其应用

地震位错理论是研究地震断层滑动与地球物理场变化之间关系的理论,是震源机制、地球内部构造、地震预测等基本地球物理问题与大地测量、地球物理观测数据之间的联系纽带。被广泛使用的半无限空间介质模型的位错理论,由于其几何模型的限制,在地震变形和地球动力学等应用研究中会导致一定程度的误差。此外,现代大地测量技术可以在全球和区域尺度上精确地观测地震变形,亟需一个适用于全球地震变形研究的地震位错理论。为此,本团队基于球形地球模型,经过多年系统性研究,建立了地震位错理论新体系。所构建的球形地球模型的地震位错理论,促进了全球地震变形和地球动力学变化的研究,是近年来地球物理学领域取得的重要理论进展之一。本文简要地介绍了国内球形地球模型地震位错理论的发展及其应用研究。首先,介绍了弹性球形地球模型、三维不均匀地球模型和黏弹地球模型的位错理论;其次,介绍球形地球模型的位错理论在地球动力学变化研究、断层与地下介质结构反演和地震大地测量学研究方面的相关应用;最后,对球形地球模型的位错理论的发展方向作出展望。      

汶川地震发震构造及同震模型研究

正在前人研究的基础上,收集了相对丰富的GPS、In SAR、强震动等同震观测数据,借助重新构建的发震断层模型开展了汶川地震同震位错分布的反演工作,分析了位错分布特征及可能的影响因素,并就目前汶川同震模型研究中存在的一些争议进行了讨论分析。首先,基于汶川余震序列重新定位数据,综合区域地质剖面、速度成像、大地电磁测深、物探剖面等资料,以地表破裂分布为断层浅部约束,通过多剖面断层解译,我们获得了相对精细     

活动断层运动的重力场反演

阐述了断层错动引起地表地表重力变化的基本原理,给出了弹性半无限空间点源位错到矩形位错引起的重力变化的基本解析式,并将结论推广到多个断层,介绍了利用重力变化反演断层运动的基本思路。以滇西实验场作为实用实例,对１９９６年２月丽江７．１级地震发生前后场区内的活动断层运动进行了演算,给出了断层位位移解,并与已有资料相比较,结果基本一致,但误差分析结果表明本文错模型还有待于改善。     

沿走滑活动断层的基岩河道系统位错——以青藏高原东部为例

河流位错是沿走滑活动断层的重要构造地貌之一。然而,由于河流复杂的自然形态、沿走滑断层容易发生河流袭夺等因素,使得利用河流形态来判断走滑断层的滑动方向、位错量等存在一定的困难。文中系统介绍了利用基岩河道系统位错对沿走滑断层的河流位错地貌进行分析的方法。系统水系位错是构造过程和地表过程沿走滑活动断层相互作用的结果,是穿过走滑活动断层的河流累积位错量的同时在溯源侵蚀作用下向上游方向增长的现象。对青藏高原东部甘孜-玉树、鲜水河、昆仑东段3条走滑断裂带的河流位错地貌进行的解译、测量和统计表明,沿3条断裂带都发育系统水系位错,河流从源头到断层的上游长度(L)越长,其累积的位错量(D)越大,两者之间存在线性相关关系D=a·L。为研究青藏高原东部构造地貌演化过程中走滑断裂带的作用提供了重要依据。     

关于有限断层计算模型的研究——考虑位错时、空不均匀分布的滑动时间函数

断层面上某一点的滑动时间函数需要用三个参数来表达:断层的平均位错量、上升时间和破裂传播的时间延迟。本文基于有限断层模型,根据断层面上每个子源的位错量时、空不均匀分布特征,采用Brune模型系统确定了相应滑动时间函数的三个参数,构建了位错量呈时、空不均匀分布的有限断层滑动模型。该方法可以表现破裂面上断层位错量在时间和空间上分布的不均匀特征,既能够表现震源的复杂性同时又能够简化震源模型的构建过程,为考虑断层附近的强地震动数值模拟计算提供了有效的途径。     

利用震后黏弹性位错理论研究苏门答腊地震(M_w9.3)的震后重力变化

本文利用2003—2011年的GRACE RL05数据提取了苏门答腊地震(Mw9.3)引起的震后重力变化,发现断层两侧震后重力变化速率存在明显差异,断层下盘总体变化率为0.55μGal/yr,断层上盘为0.16μGal/yr.基于子断层叠加的编程思想,本文将Tanaka的黏弹球体位错理论配套计算程序(简称黏弹位错程序)加以改造,克服了其近场计算精度不足(甚至错误)的缺陷,可用来研究大地震引起的近场震后位移与重力变化.本文利用改造后的黏弹位错程序计算了2004年苏门答腊地震(Mw9.3)产生的同震重力变化,计算结果在空间分布和量级上均与利用弹性位错程序计算获得的结果一致,验证了我们对黏弹位错程序进行改造的正确性.最后,结合GRACE卫星观测数据,本文利用Tanaka的黏弹位错理论研究了苏门答腊地区的地幔黏性因子.结果表明,该地区地幔黏滞性具有显著的横向差异,当发震断层上下两盘的地幔黏滞性系数分别取8×1018 Pa·s和1×1018 Pa·s时,模拟的震后重力变化在总体空间分布和变化趋势上与GRACE卫星观测结果更接近.     

球体位错理论计算程序的总体设计与具体实现

本文详细介绍了球体位错理论计算程序的总体设计思想、 各类配套文件的具体内涵以及各类输出文件的物理含义, 同时介绍了程序的使用方法和注意事项, 为读者独立使用该程序提供参考。 球体位错理论计算程序主要由三部分组成: ① 位错格林函数计算程序, 基于具体的球对称地球模型提供离散的二维格林函数数值框架; ② 积分计算程序, 对离散的格林函数数值框架进行双二次样条插值运算, 并对四类独立位错源对应的格林函数进行适当组合, 从而计算出任意位置任意类型震源在地表产生的同震变形(含位移、 应变、 重力变化和大地水准面变化); ③ 辅助文件, 用于提供发震断层模型和计算点位信息。 一般情况下, 读者不需要理解位错格林函数计算程序和积分计算程序, 只需要对辅助文件提供的信息进行针对性改动, 就可以计算目标地震在目标观测站引起的同震变形。     

On Gravity Inversion for Point Mass Anomalies by Means of the Truncated Geoid

The physical meaning of the truncated geoid, which is defined by the convolution of gravity anomalies with the Stokes function on a spherical cap of specified radius, has been studied by the authors. They investigated its relation to the density distribution, generating the surface gravity, and its potential use in inversion. Some progress results for simulated studies on point mass anomalies are presented. The behavior of the truncated geoid is controlled by the radius of the integration domain, hereinafter referred to as the truncation parameter, which is treated as a free parameter. The change of the truncated geoid in response to the change of the truncation parameter was studied in the context of the simulated mass distributions. By means of such computer simulations we have managed to demonstrate the clear sensitivity of the truncated geoid to the depths, in addition to the horizontal positions, of point mass anomalies generating the synthetic surface gravity. The objective of this paper is to illustrate, with the help of computer simulation as the method of our study, the contribution of the truncated geoid to the solution of the gravimetric inverse problem. Further work towards employing the truncated geoid in gravity exploration is being conducted.     

Point Mass Method Applied to the Regional Gravimetric Determination of the Geoid

The determination of the local gravity field by means of the point mass inversion method can be performed as an alternative to conventional numerical methods, such as the least-squares collocation. Based on the first derivative of the inverse-distance Newtonian potential for the representation of the gravity anomaly data, it is possible to compute any wavelength component of the geoid in planar approximation with sufficient accuracy. In order to exemplify the theoretical concept, two applications are presented of the computation of two different wavelength components of the geoid, the long wavelength component in a local solution and the short wavelength component in a regional solution. The results are compared with corresponding least-squares collocation solutions, using a global geopotential model to remove and to restore the long wavelength component.     

Local geoid determination based on airborne gravity data

A mathematical model used for determination of a local geoid model by combining airborne gravity disturbances and the Earth Gravitational Model 2008 (EGM08) is shortly reviewed. The precision of the estimated local geoid model of Taiwan is tested by its comparison with the “real” geoid at Global Satellite Navigation Systems (GNSS)/levelling points. The same comparison at GNSS/levelling points is done for the geoid evaluated only by using EGM08. Conclusions concerning a rate of improvement of the “global” geoid from EGM08 using the “local” geoid from airborne gravity data are presented.     

Modelling the fine-structure of the geoid: Methods,data requirements and some results

The requirements for precise geoid models on local and regional scales have increased in recent years, primarily due to the ongoing developments in height determination by GPS on land, but also due to oceanographic requirements in using satellite altimetry for recovering dynamic sea-surface topography. Suitable methods for geoid computations from gravity data include Stokes integration, FFT methods, and least-squares collocation. Especially the FFT methods are efficient in handling large amounts of gravity data, and new variants of the methods taking earth curvature rigorously into account provide attractive methods for obtaining continental-scale, high-resolution geoid models. The accuracy of such models may be from 2–5 cm locally, to 50–100 cm on regional scales, depending on gravity data coverage, long wave-length gravity field errors, and datum problems. When approaching the cm-level geoid basic geoid definition questions (geoid or quasigeoid?) become very significant, especially in rugged areas. In the paper the geoid modelling methods and problems are reviewed, and some investigations on local data requirements for cm-level geoid prediction are presented. Some actual results are presented from Scandinavia, where a recent regional high-resolution geoid model yields apparent accuracies of 2–10 cm over GPS baselines of 50 to 2000 km.     

Comparison of the qualities of recent global and local gravimetric geoid models in Iran

A number of regional gravimetric geoid models have recently been determined for the Iran area, and a common problem is to select the best model, e.g. for engineering applications. A related problem is that in order to improve the local geoid models, the selection of the best Global Geopotential Model (GGM) model for the region is essential, to be used in a combined solution from GGM and local gravimetric data. We discuss these problems by taking advantage of 260 GPS/levelling points as an external tool for validation of different global and local geoid models in the absolute and relative senses. By using relative comparisons of the height differences between precise levelling and GPS/geoid models we avoid possible unknown systematic effects between the different types of observables.The study shows that the combination of the newly released GRACE model (GGM02C) with EGM96 geoid model fits the GPS/levelling data in Iran with the best absolute and relative accuracy among the GGMs. Among the local geoid models, the newly gravimetric geoid model IRG04 agrees considerably better with GPS/levelling than any of the other recent local geoid models. Its rms fit with GPS/levelling is 55 cm. Hence, we strongly recommend the use of this new model in any surveying engineering or GPS/levelling projects in the area.     

Transformation between gravimetric and GPS/levelling-derived geoids using additional gravity information

The transformation from the gravimetric to the GPS/levelling-derived geoid using additional gravity information for the covariance function of geoid height differences has been investigated in a test area in south-western Canada. A “corrector surface” model, which accounts for datum inconsistencies, long-wavelength geoid errors, vertical network distortions and GPS errors, has been constructed using least-squares collocation. The local covariance function of geoid height differences is usually obtained from residual values between the GPS/levelling and gravimetric geoid heights after the elimination of all known systematic distortions. If additional gravity data (in the form of gravity anomalies) are available, the covariance function of geoid height differences can be determined by the following steps: (1) transforming the GPS/levelling-derived geoid heights into gravity anomalies; (2) forming differences between the computed in step 1 and given gravity anomalies; (3) determining the parameters of the local covariance function of the gravity anomaly differences; (4) constructing an analytical covariance model for the geoid height differences from the covariance function of the gravity anomaly differences using the parameters derived in step 3. The advantage of the proposed method stems from the great number of gravity data used to derive the empirical covariance function. A comparison with the least-squares adjustment shows that the standard deviation of the residuals of the predicted geoid height differences with respect to the control point values decreases by 2.4 cm.     

青藏地区大地水准面形态及其与构造动力学的关系

利用密合法求解青藏地区大地水准面模型，研究青藏地区大地水准面主要特征及其与该区内部构造和活动的相关性．表明青藏地区大地水准而异常与青藏高原隆起的形状极为相似，大地水准面整体负异常与下地幔相关，形状起伏与上地幔相对应，岩石层反映的大地水准而异常与青藏高原活动构造有较好的对应关系．     

Detection of Local Geoid Deformations by Gravity Disturbances from GPS/Gravimetric Observations

This paper deals with a method for detection of local geoid deformations; as a consequence, the methods main application concerns geoid adjustment to GPS/levelling points. This is based on the fact that these points should present no local geoid deformation to avoid errors in the adjustments. These type of miscalculations would lead to an incorrect adjustment and result in further errors in subsequent studies with GPS in the proximity at the point with local deformation.The method proposed is based on predictions of gravity disturbance from geoid undulations using Poisson integral with modified kernel, and its comparison with the gravity disturbance from GPS and gravimetric observations.The use of gravity disturbance instead of gravity anomalies has been chosen since gravity disturbance is a quantity derived from GPS and not from levelling. The loss of accuracy arising with a local height reference system is therefore theoretically avoided as far as the differences in geodetic reference systems regarding positions of gravity measurements and coefficients of the global models are accounted for.Extended numerical tests using computed geoidal undulations and the corresponding gravity disturbances obtained from the geopotential model GPM98cr computed up to degree 720 illustrate the validity of the proposed method and its usefulness as local geoid deformations detection tool.Finally, the method is tested using real GPS/Gravimetric data and geoid models IBERGEO95 and EGG97 with good results.     

基于有限元方法的陆海大地水准面衔接

大陆上用重力数据和GPS水准数据确定(似)大地水准面,海洋上用卫星测高数据确定(似)大地水准面.由于沿海地区和近岸海域往往缺少完好的重力数据,近岸海域卫星测高数据质量相对较差,两类大地水准面在陆海相接区域精度偏低且存在拼合差.纯几何方法拟合陆海局部区域大地水准面,不能顾及大地水准面的物理特性,拟合结果不稳定.顾及到大地水准面的物理特性,依据其在局部所应满足的数学物理方程,拟合陆海局部区域大地水准面问题,转化为Laplace第一边值问题.讨论了有限元法衔接陆海局部区域大地水准面的数学思想,给出了相应的数学模型.     

应用GPS/重力数据确定(似)大地水准面

作为GPS/重力边值问题理论及方法的应用,本文在对GPS/重力方法确定（似）大地水准面的原理进行简要介绍与分析的基础上,利用收集到的N区的702个GPS重力数据以及52个高精度的GPS水准数据,计算出该区域的似大地水准面. 通过拟合法和系统差直接改正法进行的精度分析表明,应用GPS/水准方法确定的该地区似大地水准面的精度达到厘米级.