Mercury indicating inflow zones and ruptures along the Wenchuan Ms 8.0 earthquake fault

During the Wenchuan Fault Scientific Drilling Project,we determined the values of total mercury(HgT)and gaseous elemental mercury(GEM) from drilled cores and drilling mud,respectively.Geochemical analysis shows HgT values ranging from 0.24 to 6.45 ng/g for the Penguan complex and from 2.90 to 137.54 ng/g for T3 sediment.The average levels of HgT for the Penguan complex and T3 sediments are 1.81 ± 0.26 ng/g and23.96 ± 4.80 ng/g,respectively.Major anomalous peaks of HgT appear at depth of 614,731,993 and 1,107 m,which correspond to the long-term high seismic activity during crustal deformation in response to tectonic stresses.Gaseous elemental mercury dissolved in drilling mud was also analyzed.We found fluid inflow zones with high GEM at depths of 590-750 m,suggesting that fluid-filled ruptures exist in the LMS fault zone.It indicates that mercury provides geochemical evidence for inflow zones and ruptures/fault zones in the Wenchuan Ms 8.0 earthquake fault.

Deformation of the Most Recent Co-seismic Surface Ruptures Along the Garzê–Yushu Fault Zone(Dangjiang Segment)and Tectonic Implications For the Tibetan Plateau

The Garzê–Yushu strike-slip fault in central Tibet is the locus of strong earthquakes（M 〉 7）. The deformation and geometry of the co-seismic surface ruptures are reflected in the surface morphology of the fault and depend on the structure of the upper crust as well as the pre-existing tectonics. Therefore, the most recent co-seismic surface ruptures along the Garzê–Yushu fault zone（Dangjiang segment） reveal the surface deformation of the central Tibetan Plateau. Remote sensing images and field investigations suggest a 85 km long surface rupture zone（striking NW-NWW）, less than 50 m wide, defined by discontinuous fault scarps, right-stepping en echelon tensional cracks and left-stepping mole tracks that point to a left-lateral strike-slip fault. The gullies that cross fault scarps record systematic left-lateral offsets of 1.8 m to 5.0 m owing to the most recent earthquake, with moment magnitude of about M 7.5, in the Dangjiang segment. Geological and geomorphological features suggest that the spatial distribution of the 1738 co-seismic surface rupture zone was controlled by the pre-existing active Garzê–Yushu fault zone（Dangjiang segment）. We confirm that the Garzê–Yushu fault zone, a boundary between the Bayan Har Block to the north and the Qiangtang Block to the south, accommodates the eastward extrusion of the Tibetan Plateau and generates strong earthquakes that release the strain energy owing to the relative motion between the Bayan Har and Qiangtang Blocks.

Late Quaternary Activity and Strong Earthquake Recurrence Interval along the North Segment of the Longling-Ruili Fault

According to field investigation and interpretation of remote sensing images,the north segment of the Longling-Ruili fault is a Holocene dextral strike-slip fault with a small amount of normal faulting.Based on large-scale geological mapping at some typical locations and quantitative geomorphologic deformation measurement and dating analysis,this fault is a Holocene active fault.The strike-slip rate of the Longling-Ruili fault is 2.2 ~2.5mm / a and vertical slip rate is 0.6mm /a since the late Pleistocene epoch.The strike-slip rate of the Longling-Ruili fault is 1.8~3.0mm /a and vertical slip rate is 0.5mm /a since the Holocene epoch.Based on the Poisson model,lognormal model and BPT model,the occurrence probability of strong earthquakes in 50 years is estimated to be 6.32%,0.08%and 0.05%,respectively.Then,a 1.82% probability of occurrence of characteristic earthquake for the north segment of the Longling-Ruili fault is obtained by setting a weight of 0.28,0.36 and 0.36 to the Poisson model,lognormal model and BPT model,respectively.

Numerical Simulation of Annual Change Patterns of Contemporary Tectonic Stress-Strain Field of the Chinese Mainland

Based on the active crustal block structures, the Holocene active faults and the wave velocity structures with a resolution of 1°×1°, a two-dimensional finite element model for the tectonic stress-strain field of the Chinese mainland is constructed in the paper. Using GPS measurements, the velocity boundary conditions for the model are deduced, then, the annual change patterns of the present-day stress-strain field of the Chinese mainland are simulated. The results show that (1) the general pattern of the recent tectonic deformation in the Chinese mainland is governed by the interactions of its surrounding plates, of which, the Indian Plate plays a major role. There is a NNE-directed velocity distribution in the west of the Chinese mainland. The maximum slip rate appears at the collision boundary. The north-directed components decrease, while the east-directed components increase gradually from south to north and from west to east. In the east part, there is a general east-directed movement, with a certain amount of south-directed components. (2) The present-day tectonic stress field in the Chinese mainland has undergone the process of enhancement in recent years, and this process presents a general pattern of radiating eastwards from the Qinghai-Xizang (Tibet) Plateau as the center. The general pattern is similar to the ambient tectonic stress field, indicating the inheritance of contemporary tectonic deformation on the Chinese mainland. (3) The maximum principal strain presents an obvious pattern of being high in the west and low in the east. The tectonic movement in the west is stronger than that in the east. Large active faults are all located in the high-value zones of maximum principal strain. However, the magnitude of strain is smaller in the interior of the active crustal blocks, which are enclosed by these faults. (4) The stress-strain field of the Sichuan-Yunnan region is unique. It may not be governed by collision of plates alone but a combination of the movement of peripheral active blocks, material flow in the lower crust or upper mantle and special tectonic geometry (such as the eastern Himalayan syntax) as well.

中国大陆地壳应力环境基础数据库

本文介绍了国际上有关地应力环境研究与数据库建设的相关情况;重点阐述了“中国大陆地壳应力环境基础数据库”的构成,包括基本数据类型、数据来源以及数据覆盖范围等基本情况;阐述了本数据库管理系统的基本设计思想、主要功能及其特色;扼要介绍了以数据库资料为基础开展了中国大陆构造应力分区以及应力场的数值模拟研究成果。

内昆线天星场至仙水段构造应力场分析

一、引言内昆线(内江—昆明铁路选线)位于四川盆地西南缘至云贵高原的过渡地带。所经地区主要为低山峡谷,中、高山峡谷和高原低山丘陵地区,其中天星场—仙水段地形、地貌和地质构造条件最为复杂。为了解天星场—仙水段场区的构造稳定性和为铁路选线的勘测设计提供有关地应力参数,开展了利用断层滑动矢量反演构造应力张量,并结合水压致裂应力测量结果,进行场区构造应力场综合研究。

大青山地区构造应力场与构造活动方式及地震活动特点

一、引言构造运动是地壳应力的一种表现形式。构造的形成与演变,是构造应力场在时间和空间上变化与作用的结果。断裂活动的几何形态、活动性质及强度和地震活动都与构造应力场息息相关。本文通过大青山山前活动断裂填图,根据断裂的运动学特征、活动性质、地震活动和形变场特点综合分析了断裂带附近的构造应力场。大青山山前断裂是河套断陷带中呼包断陷盆地的北缘断裂,位于内蒙地轴南侧。从本区构造的演变来看,构造活动具有不同的特点。

Dynamic mechanisms of earthquake-triggered landslides

Earthquake-triggered landslides usually cause great disasters,and yet their dynamic mechanisms remain poorly understood.This paper will derive a general conceptual landslide model from the geometric and kinematic features of the most landslide masses triggered by the 2008 Wenchuan earthquake.Kinematic characteristics and dynamic processes are simulated here by means of finite element method(FEM)based on the dynamic process of the discontinuous deformable body.The calculated results presented the whole course of landslide motion,and displayed some typical kinematic characteristics such as initiation,sliding,ejection,collision,flying in the air,and climbing of landslides.The simulation result also shows that,under combined seismic inertial forces and gravity,landslides will start to slip once it overcomes the friction between the sliding mass and slip-bed,then it will move from slow to fast along the slippery bed until it ejects from the slip-bed.Moreover,the high frequencies and serious damages by landslides in the Wenchuan earthquake are caused by the strong ground motion on the mountain slopes in and around the epicenter that was dramatically amplified owing to both resonances produced by the seismic event and topographical amplification by seismic motion.In addition,the modeling results suggest that the direction,amplitude,frequency,and duration of strong ground motion have a great influence on the stability of landslide mass.Therefore,the study helps us better understand dynamic mechanism of landslides,seismic hazard assessment,and dynamic earthquake triggering.

六盘山东麓断裂带应力场变化的初步研究

一、引言随着对活动断裂研究的逐步深入,断裂活动动力学环境的研究越来越引起人们的关注。本文是在对断裂几何结构、运动特征调查的基础上,利用断裂带的断裂擦痕资料反演及对附近变质岩石进行岩组分析等方法,以试图再现断裂活动和岩石最后变形时的应力状态,乃至推测出六盘山东麓断裂带的动力学环境。