芦山地震的震源断层及在应急救援中应用的可能性

芦山地震之后,岩崩灾害造成交通断绝,通往极重灾区乡镇的道路只有一条窄路;而极灾区仅仅限于5个乡镇,坍塌的楼房等大型废墟不多,大量投入的大型器械和运输车阻碍交通,成为救灾的瓶颈。在情况不明的条件下,军政领导应急过度在所难免。不能忽视,地震初期地震系统提供的信息存在不确定性：2min地震基本参数速报的震级偏低很多;震区构造研究程度低,对主震的发震构造有不同认识,经现场考察之后提出发生在盲断裂的判断;     

构造"稳定"区强震长期预测的简便途径--以张北地震为例

作为强震长期预测基础的地震带、潜在震源区的划分,仍然依据地震构造类比和地震活动重复两原则。现有的强震长期预测方法在构造“稳定”区,即没有活动构造、没有历史地震(包括古地震)资料的条件下,无能为力。通过张北地震资料的分析,高精度地震定位并结合波形数据反演震源机制的结果表明：在稳定而统一的构造应力场的作用下,沿其最大剪切应力方向上的小地震集中成带,并且持续活动、震源机制的优势取向与应力场吻合,小震带便可以看作属于现今活动的震源断层,在地震长期预测工作中可以作为划分潜在震源区的依据。构造“稳定”区发生的强震属于新破裂。     

地块活动与成组地震关系的初步探讨

中国大陆构造的成块性与中国地震活动的成组性构成中国地震构造和地震活动的一个突出现象．本文在前人对中国大陆地震成组划分的结果和地块划分方案的基础上,研究了中国大陆地块与成组地震活动之间的关系,发现大部分强震分布于地块边界断层上,成组地震的孕育和发生与块体活动有关．由成组地震震中分布图表现出来的地块活动方式主要有４种:单缝式活动型、单地块活动型、多地块活动型和地块内部活动型．地块活动频度以单缝式活动型为最高,在成组地震中则以单地块活动型为多．大陆内部各地块的活动性有差别,东部比较活跃的地块有太行山和华北平原地块,西部比较活跃的地块有川滇和昆仑-松潘地块．      

Fault plane solutions in Sichuan-Yunnan rhombic block and their dynamic implications

Harvard Centroid Moment Tensor (CMT) solutions for earthquakes from 1977 to 2004 showed that the stress fields are obviously different in northwestern Sichuan sub-block (NWSSB), western parts of Central Yunnan sub-block (CYSB) and eastern part of CYSB. The characteristics of the mean stress fields in these three regions are obtained by fitting to CMT solutions. The stress state in NWSSB is characterized by its sub-horizontal tensile principal axis of stress (T axis) in roughly N-S direction and west dipping compressive principal axis of stress (P axis); the one in western part of CYSB is characterized by its ENE dipping T axis and sub-horizontal medium prin-cipal axis of stress (B axis) in roughly N-S direction; the one in eastern part of CYSB is characterized by its sub-horizontal P axis in roughly NNW-SSE direction and sub-horizontal T axis in roughly WSW-ENE direction. Finite element method simulation clearly shows that the Indian Plate imposes great extrusion on Sichuan-Yunnan rhombic block (SYRB) near Assam massif. The value of the simulated compressive principal stress decreases with the distance from Assam massif. The simulated directions of the T axes in SYRB form annular distribution encir-cling Assam. For a homogeneous elastic medium with free boundary conditions on the top and bottom surfaces as well as the displacement boundary conditions derived from the GPS observations on the lateral boundaries, the computation results are consistent with the Harvard CMT solutions in NWSSB and western part of CYSB, while inconsistent with the Harvard CMT solutions in eastern part of CYSB. The inconsistency in eastern part of CYSB can be reduced when it includes inhomogeneous elastic media. The stress states in NWSSB and western part of CYSB revealed by the Harvard CMT solutions are not local, which are mainly controlled by the boundary force on the whole region. On the other hand, the stress state in eastern part of CYSB given by the Harvard CMT solutions is local, which may be affected by local topography, material inhomogeneity, and the drag force underneath.     

首都圈平均波速比分析

首都圈数字地震台网覆盖京、津和河北中部,其中自2002年5月—2003年12新记录1级以上地震1186个,台站记录的纵、横波到时差约2~25 s。选取被5个以上台站所记录到的地震,震中位于网内或者网缘附近,计算其平均波速比。分析认为:(1)通过HYPODD修订震源位置,绝大多数震源深度在8~10 km,平均波速比所反映的是地壳上层的状态。(2)无论是从较长的时间尺度还是从较大的空间范围来看,平均波速比值都是非常稳定的。(3)平均波速比的可靠性有赖于较多的台站数目,以满足拟合精度的要求。少数台站的测定结果往往伴随较大的误差,单一地震的平均波速比值大幅度的涨落,不宜表征地壳介质性质的改变。     

Consistent CMT solutions from Harvard University before great earthquakes in Kurile Islands and its significance for earthquake prediction

Introduction In the development of seismic science,the improvement of observational instruments is prone to produce new parameters and promote rapid growth of seismology.For example,after the global digital seismograph network is established,some studies that could not be made or easily made in the past are now being carried out successively.As a result,analytical studies based on digital data have been made one after another and digital seismology has formed.Up to now,Harvard University has …     

Some evidences for earthquake occurrence in the shallow crust in some areas of North China and Southwest China

IntroductionThe hypocentral location parameters (the longitude and latitude of epicenter and the focal depth) are important fundamental data for the study of seismology and the earth interior physics. To locate the seismic source precisely is the basis for the study of seismicity patterns, relation between earthquake and active structures, engineering seismology, etc (WANG, et al, 1995). Among these parameters, the precise measurement of focal depth is closely related to the correct understa…     

伽师强震群序列的破列特征

分析了伽师强震群序列中13次5级以上地震的震源机制解资料，其中有8个走滑型地震、5个倾滑型地震。走滑型地震的北北西向节面与Ms≥5．0级地震震中分布的斜列线一致，伽师强震群序列可能是北北西向右旋走滑断层及与其斜交的张性正断层共同作用的结果。     

Study on S wave velocity structure beneath part stations in Shanxi Province

Introduction Shanxi uplift area is bounded by Ordos block to the west, Taihang Mountain front fault zone to the east. On the north side, it is also adjoined with Yinshan fold belt and Hetao-Baotou fault depression basin accompanied with its southern active ruptures, as well as on the south side, connected to Weihe fault depression basin accompanied with large ruptures on the northern margin of Qinling fold belt. The interior of the Shanxi uplift area, with complicated tectonic structures, …     

河北张北地震区活动断裂的探测与研究

1998年1月10日河北张北6．2级地震是河北省张家口坝上稳定地区的一次罕见的破坏性地震。震区被晚第三纪玄武岩覆盖，地面未发现第四纪活动断裂。为了研究震区地表活动断层，利用电磁波探测技术，以玄武岩底界面深度的变化来分析张北震区活动断裂，为此，在河北张北6．2级地震Ⅷ度区范围进行了3条剖面探测，解释结果表明，震区存在北西向、北东向、北北东向3组第四纪活动断裂，张北6．2级地震发生在3组断裂的交汇区附近。