2-D crustal structure of Changbaishan-Tianchi volcanic region determined by seismic traveltime inversion

2-D velocity structure and tectonics of the crust and upper mantle is revealed by inversion of seismic refraction and wide-angle reflection traveltimes acquired along the profile L1 in the Changbaishan-Tianchi volcanic region. It is used in this study that seismic traveltime inversion for simultaneous determination of 2-D velocity and interface structure of the crust and upper mantle. The result shows that, under Changbaishan-Tianchi crater, there exists a low-velocity body in the shape of an inverted triangle, and the crustal reflecting boundaries and Moho all become lower by a varying margin of 2-6 km, forming a crustal root which is assumed to be the Changbaishan-Tianchi volcanic system. Finally, we make a comparison between our 2-D velocity model and the result from the studies by using trial-and-error forward modeling with SEIS83.

Inversions for MT data in 2D symmetrical anisotropic media

In the paper, a 2D symmetrical anisotropic medium whose strike agrees with one of the horizontal principal axes is considered to develop a corresponding inversion technique. In the specified conditions, if we assume an equivalent conductivity anisotropy in both the vertical and dipping directions, i.e., σzz=σyy, the differential equations obtained are formally the same as that for TE and TM modes in the 2D isotropic geoelectrical media. The same inversion technique as that in the 2D isotropic media can be employed to obtain the anisotropic conductivities. It means that the TE and TM inversion results in the isotropic media can be respectively thought as the resistivities in the two principal directions of the symmetrically anisotropic media, which has offered a new approach and a theoretical guidance for interpreting magnetotelluric data. And the inversion technique developed here is used to test the magnetotelluric data in the area of Tianzhu and Yongdeng in Gansu Province, so that the crust anisotropic geoelectrical structures in this region can be obtained.

Application effect of high-density electrical method on detecting artificial filling layer: A case study of Chengjiangshan area of Huaibei City

High-density electrical method has been proved to be an effective method for probing shallow sedimentary layers.It is principally used to identify the boundary between the Quaternary soil layer and bedrock according to the vertical change of apparent resistivity.However,the artificial filling layer has the characteristics of heterogeneity and high porosity,which makes it challenging to detect the artificial filling layer by high-density electrical method.The key to solve this problem is to detect the difference of conductivity between the filling layer and the underlying bedrock.This paper takes the land in Chengjiangshan area of Huaibei City,Anhui Province as the detection target.On the basis of fully analyzing the physical properties of the artificial filling layer,two-dimensional high-density electrical survey and inversion are used to define the thickness of the artificial filling layer.The research shows that the highdensity resistivity method has obvious advantages in delineating the distribution of bedrock and the thickness of the filling layer,and the reliability of the high-density electrical method in the detection of the artificial filling layer,and delineates the scope of the filling layer is verified by the borehole data.

新疆玛纳斯大震区地壳深部的电性结构

对玛纳斯大震区新近观测的大地电磁测深数据进行了处理，得到视电阻率曲线、阻抗相位曲线、二维偏离度、主轴方位角和地磁实感应矢量。然后对所有测点的资料进行了二维自动反演解释。结果表明，沿剖面的地壳浅部可划分为５个区段，沿剖面的深部可划分为３个区段，各区段的接触边界由断层或深断裂带组成。沿测线沉积盖层最大深度达１２ｋｍ左右；测线南段存在壳内低阻体。这些解释结果与地质及其它资料吻合较好。玛纳斯７．７级地震发生在地壳电性结构发生明显变化的接触带附近。

二维对称各向异性介质大地电磁反演

考虑一种二维构造走向与一水平各向异性主方向一致的对称各向异性介质.在这种特殊情况下,若假设电导率沿垂向和倾向表现相同的各向异性,即σzz=σyy,则得到形式完全等同于各向同性情形TE和TM极化方程的微分方程.因此,就可用各向同性完全相同的反演方法,获得二维各向异性介质的电导率.亦即各向同性介质的TE和TM极化反演结果,可以解释为对称各向异性介质两主方向上的电阻率.这为MT解释提供了新的解释途径及其理论依据.最后用由此发展起来的各向异性介质反演方法,对甘肃天祝永登一带大地电磁资料进行了反演试验。

宁洱地震区深部电性结构及发震构造初析(一)

在2007年6月3日宁洱6.4级地震区进行了宽频带(1000～1/4096Hz)大地电磁观测,采用了远参考道技术和Robust技术对观测数据进行了处理,分析了视电阻率和相位曲线、二维偏离度及区域电性结构方向,采用非线性共扼梯度(NLCG)二维反演技术对实测资料进行了反演,得到了与实测曲线拟合程度较高的反演模型。从二维解释结果可以看出:横向上,以12号测点为界,明显地划分为2个不同的电性分区,推测存在具一定延伸的断裂构造。纵向上,30km深度以上大致可分为4个电性层:1)中、新生代盆地沉积层(Mz—Cz),厚约1km。2)古生代沉积层(Pz),厚约5km。3)壳内高导层(HCL)。4)中、下地壳(MLC)。其中壳内高导层埋深在12号点左右存在较大的差异,推测在12—13号点下高导层顶部存在壳内的滑脱构造。宁洱地震震源深度为5km,文中所推测的滑脱构造位于这一层位上。认为该滑脱构造为本次地震的发震构造。

用地震走时反演长白山天池火山地区的二维地壳结构

应用一种同时获得地壳上地幔二维速度结构和界面形态的地震走时反演算法 ,对在长白山天池火山区L1 剖面获得的人工地震折射和宽角反射走时数据进行反演 ,得到了该剖面的地壳上地幔二维速度结构和构造 .结果表明 :长白山天池火山口下方中下地壳存在一倒三角状的低速体 ,壳内反射界面和莫霍面一致呈下凹形态 ,幅度 2～ 6km不等 ,形成一个地壳根 ,推测是长白山天池火山系统 .

1966年邢台6.8级地震的深部结构背景

根据“八五”期间邢台地震区深部地球物理方法的综合探测研究成果，依据P波、S波联合解释和二维密度反演，并结合浅部构造和三维应力场数值模拟计算等资料，进行综合分析研究。以1966年邢台6．8级地震为例，揭示了邢台地震区的孕震发震过程。邢台地震区的深部结构和介质结构：①中、下地壳内分布有北东向高角度深断裂，深断裂两侧出现明显的波速比异常。②中地壳有低速高导层和密度不均匀异常。③上地壳底部有滑脱构造带，浅部为束鹿断凹。

一种连续模型二维地电构造大地电磁测深反演方法

本文是出一种连续模型二维地电构造的大地电磁测深资料的反演方法。首先,定义了二维反演问题的目标函数为F[λ]=sum form i=1 to M×N再给出两种不同极化方式反演问题的 Frechet 导函数。H 极化时的 Frechet 导函数为1/2QE 极化时的 Frechet 导函数为1/2Q然后用正则化了的广义逆方法求解上述两个线性积分方程。数值计算表明反演方法是稳定而有效的。