前兆逆向追踪法与台湾地震前兆

用前兆逆向追踪法研究台湾东部地区大地震前兆, 讨论适合该地区地震链和中期图象的参数,确定地震链的中期图象阈值. 将线性判别方法应用于地震链的中期图象,给出一种探索大地震前兆的途径. 数据分析结果表明,这种途径可降低对该地区大地震的虚报率; 前兆逆向追踪法在台湾地区是适用的.      

Statistical property of candidate earthquake precursors and its apparent focal mechanism dependence

Statistical properties of reported earthquake precursors show apparent focal mechanism dependence. Intensity of anomaly is described by the ‘anomaly ratio’ as defined by the number of stations/items reporting anomalies before the target earthquake over the number of stations/items in operation around the target earthquake. Variation of the ‘anomaly ratio’ with the magnitude of the target earthquake was studied for dip-slip earthquakes all over China, strike-slip earthquakes in eastern China, and strike-slip earthquakes in western China, respectively. It is observed that for strike-slip earthquakes, the ‘anomaly ratio’ increases linearly with the magnitude of the target earthquake, while earthquakes in eastern China and western China have different slopes. For dip-slip earthquakes, however, the ‘anomaly ratio’ has no statistically significant change with the magnitude of the target earthquake. Limited data imply that the ‘anomaly ratio’ seems proportional to the apparent stress of the target earthquake. The result might be heuristic for the analysis of candidate earthquake precursors. Foundation item: National Natural Science Foundation of China (40274013) and MOST Project (2001BA601B02). Contribution No.04FE1020, Institute of Geophysics, China Earthquake Administration.     

Intermediate-term seismic precursors for some coupled subduction zones

The paper discusses model results and then reviews observational data concerning some aspects of the mechanics of mature seismic gaps in coupled subduction zones. The concern is with space-and time-varying stresses, as signalled by the presence and mechanisms of earthquakes in the outer-rise zones adjacent to main thrust areas of large subduction events, and down-dip from such areas, in the downgoing slab. Observations are shown to be consistent with the expectation that in mature seismic gaps, as a result of interplate boundary locking in presence of sustained gravitational driving forces, at least the deeper portions of the ocean plate in the outer-rise zones are under increased compression, and the downgoing slab is under increased tension. The observational data cover two cases of closed seismic gaps, namely the region of the Chilean Valparaiso earthquake of March 3, 1985, and the earthquake of October 4, 1983. Four other cases concern still to-be-closed gaps in northern Chile and along the coast of Guatemala, and also the Kurile Islands Trench gap and the northern New Hebrides gap. It is concluded that the intermediate-term precursor, consisting of a combination of compressional outer-rise earthquake(s) and tensional intermediate-depth, intra-plate events in the downgoing slab, which mechanically signals the latter part of the earthquake cycle, could be useful in evaluating the maturity, and hence great earthquake potential of a seismic gap.     

华安汰内井水氡对闽台地震的映震特征差异性分析

通过华安汰内井水氡对1987年以来福建地区M_L4.5以上地震、 台湾地区M_S7.0以上地震的映震特征分析, 认为该井水氡对福建和台湾地区地震的映震特征具有一定的差异性, 其差异性表现为对福建地区的地震, 其异常特征一般表现为突跳及振荡, 且异常多发生在震前20天左右, 同时异常持续的时间也较短; 对台湾地区的地震, 其异常特征表现为高值异常且异常持续时间长, 异常多发生在震前11个月左右。 据此可以在华安汰内井水氡发生异常时对未来的发震地点做出较为准确的判断。     

Possible creep-related tilt precursors obtained in the Central Apennines (Italy) and in the Southern Caucasus (Georgia)

Daily averaged tilt component data from two sites of the Central Apennines (Italy) and of the Southern Caucasus (Georgia), respectively, revealed intermediate-term tilts as possible precursors to earthquakes (M=3.0÷4.7) which occurred in the above-mentioned seismic areas within a distance of 50 km from the sites. A good temporal correlation as well as a fair spatial correspondence between these residual tilts (with amplitude and duration of some microradians and months, respectively) and main shocks were pointed out, by removing both secular trends and seasonal thermoelastic effects from the raw tilts. An attempt was made to justify the above-mentioned results, based on the assumption that the observed intermediate-term preseismic tilts are the manifestation of aseismic creep episodes of comparable duration in the fault materials of thrust faults close to the tilt sites. The mechanism refers to a strain field slowly propagating from the preparation focal area to the tilt site, through crustal blocks separated by weak transition zones. This propagation is thought to be the cause of the local aseismic fault slip recorded by the tiltmeters. Previously, both discrete structures and strain propagation effects were revealed in the Central Apennines and are thought also to exist in the Southern Caucasus. As in the past, the rheological properties of fault materials are revealed as viscoelastic ones. In fact, creep equations obtained by applying several viscoelastic models on our data, proved to fit quite well some of the observed tilt precursors, producing viscosity and rigidity values very similar to those reported in literature.Professor Petr Viktorovich Manjgaladze died during the writing of this paper     

Reverse Tracing of Precursors Applied to the Annual Earthquake Forecast: Retrospective Test of the Annual Consultation in the Sichuan-Yunnan Region of Southwest China

An Annual Consultation on the Likelihood of Earthquakes is regularly undertaken in continental China. It is a special kind of intermediate-term medium-range earthquake forecast and a practical service provided by seismological communities within the capability of modern seismology. One of the problems the Annual Consultation encounters is its false alarm rate, which has been higher than expected and has caused numerous controversies on the methodology and significance of the Annual Consultation. To tackle this problem we use the concept of reverse tracing of precursors (RTP) to analyze the long-term seismic activity in the alarm regions, or regions thought to have increased probability of earthquakes, as identified by the Annual Consultation. We apply the Pattern Informatics (PI) and relative intensity (RI) algorithms to the long-term estimation of seismic hazard in the RTP analysis. A retrospective study of the Sichuan-Yunnan region of southwest China, using the data from 1990 to 2003, shows that, by choosing the threshold proportion of overlapped areas between the long-term estimates and the Annual Consultation, the RTP analysis can correctly remove some of the false-alarm regions from the “black list’ and thus reduce the false-alarm rate of the Annual Consultation, without reducing the hit rate. Remarkably, the RTP approach, although originally proposed for short-term earthquake predictions, seems able to contribute to the Annual Consultation as well.     

台湾地区地震的空间关联维特征与构造环境研究

采用关联维方法对台湾地区地震活动的空间特征进行了研究。先利用 10 0a来台湾的地震目录计算各个地震区、带的关联维数 ,将地震空间分布的分形特征定量表达出来 ,然后综合分析地震空间分布的关联维数和孕震构造环境之间的关系 ,得出了以下结论 :1)台湾东、西部地震区由于地震属于不同的大地构造单元 ,因此关联维数有较大的差异 ;2 )在各地震区内部的各个地震带由于板块构造、地壳结构、活断层分布上的差异 ,而具有与其构造特征相对应的关联维数 ;3)各地震带内部的各个不同的部位又由于不同的构造应力场 ,而导致地震分布上出现不同的丛集性 ,表现为不同的关联维数。这些结论充分说明通过关联维分析所得到的地震活动的空间图像与地震活动所代表的不同地质构造背景有着良好的对应关系     

华南地区地震活动特征与台湾强震影响

以M_S5.5以上地震是否发生为标记, 划分华南地区的活跃和平静时段, 结果显示与华南地区2级以上地震频次的应力调制时间过程变化趋势有很好的一致性。 另外, 在活跃和平静时段华南地区的震级频次特点显著不同。 华南地区在中强震发生前有4级左右地震频繁活动和小震群频发的特点。 华南地区的中强震与云南地区7级地震的发生相关。 统计20世纪以来台湾强震与华南中强震的对应关系, 台湾西带6级强震后1年内华南中强震的对应率近0.5, 地区影响似有由东至西逐渐减弱的趋势。 台湾7级地震后2年内华南中强震的对应率只有0.3, 对应地区除台湾海峡、 福建和广东东部地震外, 也有几次对应广西和北部湾地区的地震, 与6级相比, 台湾7级强震影响范围大。     

台湾及东部海域强震活动性研究及其对大陆强震的预测意义

研究了 1900年以来台湾及东部海域强震 (M≥ 7)时空分布特征,收集和测定了 1933年以来强震震源机制解。 结果表明,台湾及东部海域存在 3个强震活动带及 4个活跃时段。 29个强震震源机制解较好地反映了 3个地震活动带的区域应力场特征和力源。 研究认为,台湾及东部海域自 1986年开始的第四活跃时段与大陆地区强震活动的第五活跃期有同期活动特点。 据推测,我国大陆和台湾的强震活动可能还要持续一段时间。     

Research on the Algorithm CN Applied to Prediction of 23 Strong Earthquakes in China

This paper researches TIP before 23 strong earthquakes occurring in the eastern part and the southern and northern zones of the western part of China and their nearby areas in recent decades.The results show that 18 strong earthquakes occurred within the diagnosed TIP.The TIP precaution occupies about 30% of the total space-time domain which we researched,indicating quite good results of intermediate-term prediction of earthquakes.The algorithm CN can thus be used as an intermediate-term prediction method for strong earthquakes.     

一种评估地震前兆可信度的方法

本文提出了一种可以对地震前兆的可信度进行评估的方法. 通过对前兆信息的抽取、各类非地震干扰的识别、前兆与地震事件在时间和空间的相关性分析以及前兆的随机检验等一系列手段来评估前兆信息的真伪,提高地震前兆信息的显著性和可信度. 该方法及思路也可为其他非地震前兆的可信度评估所借鉴. 作为一个具体的例子,本文利用日本气象厅的地震目录以及能定量描述地震活动的时、空、强信息演化特征的RTL(Region_Time_Length)方法对2000年10月6日在日本鸟取县西部发生的73级地震前周围地区近26年的地震活动进行了系统的研究,得到了可能的地震活动前兆信息,并采用本文提出的方法对该前兆进行了评估,证实了上述前兆的显著性和可信性.     

Induced seismicity in large-scale mining in the kola peninsula and monitoring to reveal informative precursors

Large volumes of rock mass, mined-out and moved within these deposits, resulted in irreversible changes in the geodynamic regime in the upper earth's crust of the adjacent territory. These changes manifest themselves in a more frequent occurrence of such intensive dynamic phenomena as tectonic rock bursts due to fault movement adjacent to the area which is mined-out and man-made earthquakes which sharply decrease mining safety and result in great material losses.To develop the prediction techniques of such phenomena, a monitoring system is created, based on the program of the Kola Complex of geodynamic measuring stations. Most of this system is realized in the region of the Khibiny apatite mines. The system provides regional seismological monitoring, local prediction of seismicity in separate areas of a rock mass and, determination of stress and strain in rock masses, local geophysical monitoring over the state of rocks in a rock mass as well as physical and mathematical modelling of geodynamic processes in the upper earth's crust.The investigations have resulted in the distinguishing of some regularities in manifestations of induced seismicity and tectonic rock bursts and in the determination of strain precursors of intensive seismic events in the Khibiny mines.The mechanism is provided by the induced seismicity which resulted from the anthropogenic impact on the geological medium. A geodynamic monitoring complex is described, which is used to reveal the precursors of powerful seismic eventsin situ, and monitoring results are shown, obtained in the Kola Complex of geodynamic stations. Methods of preventing tectonic rock bursts and induced earthquakes are presented.     

福建台网接入台湾台站对定位台湾中深源地震精度影响分析

福建台网负责监测中国台湾地区地震。对于中深源地震使用何种定位方法能获得较好的地震参数,这直接影响到地震定位精度。利用JOPENS系统中交互分析软件MSDP提供的定位方法,对同一地震进行两次定位,即不使用和使用接入的台湾台站,将福建台网得出的两次结果与中国台湾公布的地震参数进行对比,分析定位精度,进而找出适用于台湾地区中深源地震的定位方法,以便进一步判断在地震速报中使用这些台站进行辅助定位的可行性,并给出相关的操作方法及建议。     

基于sP前驱震相叠加研究南美中部地区岩石圈-软流圈边界形态

岩石圈-软流圈边界（lithosphere-asthenosphere boundary）是上地幔内具有负速度梯度的地震波速度界面.对俯冲带区域LAB开展地震学探测有助于进一步认识岩石圈和软流圈的相互作用以及与板块俯冲有关的地球动力学过程.本文收集了2006-2012年发生于南美中部地区4个深源地震的垂向宽频带波形资料,利用线性倾斜叠加处理得到了相对走时-慢度域的灰度图,并成功提取了sP在LAB底反射的前驱震相s_LABP.基于改进的一维速度模型IASP91-SA计算得出了6个s_LABP震相反射点的水平分布,并划分为西部（Ⅰ）和东部（Ⅱ）分区：分区Ⅰ内LAB深度位于60~63 km,平均深度为61 km,起伏为3 km;分区Ⅱ内LAB深度位于78~82 km,平均深度为80 km,起伏为4 km.研究结果显示南美中部地区LAB深度自西向东呈变大的趋势,这可能反映了大陆岩石圈受改造程度的差异.我们推测在靠近海沟的地区,软流圈内部分熔融程度较高且熔体较为富集,对大陆岩石圈的侵蚀作用较强;在远离海沟的地区,软流圈内部分熔融程度降低且熔体分布减少,对大陆岩石圈的侵蚀作用减弱.

     

日本东北地区双震带高精度重定位研究

日本所在的西太平洋地区是世界上中深源地震发生最为频繁的地区. 早期研究已表明, 日本东北地区下方的中深源地震呈双层分布. 为进一步分析该双震带的空间分布特征, 本文通过方法测试证明了采用球坐标系下的三维射线追踪法改进后的双差定位法进行地震重定位的精确性和有效性, 对使用该方法进行重定位前、 后各方向上的误差进行了分析, 并确定了最佳的定位参数. 在此基础上, 对日本东北地区的中深源地震进行了高精度重定位, 并对重定位得到的震源位置进行了空间拟合, 其结果表明地震呈明显的双层分布, 且与西太平洋俯冲板块几近平行. 本文研究结果对揭示双震带中地震的发震机理以及俯冲板块内的精细结构均具有重要意义.      

震兆信息的遥联性讨论

在2004年12月26日印尼苏门答腊以北近海发生MS8.7两次大地震之前,华北地区小震日频次演变出现了类似震兆的信息。采用“震情三分律”的方法处理了华北地区小震活动的数据,分析认为成组震兆的出现与大震之间的遥联性绝不只是一种小区域性的现象,而是一种大范围的普遍现象,大地震是全球性的震动,其震动遥联性的显示,就必然是跨越全球性的。讨论这种现象的物理意义目的在于识别和判断这种震兆的特性,对本区今后的地震活动趋势预测工作有所借鉴。     

Tracing the Forecast of Earthquakes Based on the Seismicity Characteristics of the Chi-Chi Strong Earthquake Swarm Sequence

The data of earthquakes with M≥3.0 during the 7 years from September 21, 1993 to September 20, 2000 recorded by the Taiwan Central Weather Bureau (CWB) show that there were 6 types of clear characteristics of seismicity during the Chi-Chi strong earthquake swarm of September 21. These 6 types of characteristics are (1) foreshock types, (2) seismic gaps, (3) seismic bands, (4) clustering activity of foreshocks and signal shock, (5) quiescence before the main shock and (6) secondary aftershocks in the aftershock sequence. Using the procedures for analyzing the yearly strong earthquake tendency, further tracing based on the earthquake sequence characteristics, and taking the Chi-Chi earthquake sequence as an example, tracing analysis of the earthquake tendency was attempted using the shorter time range of monthly rather than in a yearly time scale. An attempt was made to establish the procedures for tracing analysis of shallow-focus earthquakes in the seismic belt of western Taiwan. It is hoped that this can provide an analystical method for approaching the short-imminent time scale of seismometry-based earthquake forecasting.     

中国大陆地震灾害分区人员死亡评估模型研究

针对现阶段地震人员死亡评估模型在评估特定区域地震时评估结果误差较大的问题,结合中国地震灾害特点、人口分布情况等,将中国大陆划分为西北、西南和大陆东部三个地区,并对各区域按照人口密度进行分级。采用多元非线性回归方法,选取震中烈度、震区面积、抗震设防烈度参数建立分区域的地震灾害人员死亡评估模型。研究结果表明,该模型在西北、西南地区的验证结果较好,适用于中国地震灾害情况,可以用于震后快速盲评估,在一定程度上能够避免评估不同震级、相同震中烈度和人口密度的地震时,出现相同结果的情况;虽然该模型在震例较少的大陆东部地区以及城市直下型地震中评估结果需要进一步改进,但为解决特定区域地震死亡评估中误差较大问题提供了思路,能够为震后应急指挥和救援提供数据参考。     

我国地震预报研究近十年的发展与展望

简要回顾了我国地震预报的发展过程，并着重对最近10年（尤其是90年代以来）的地震预报研究进展作了较系统的阐述．主要分为：（1）大地震震源区地壳细结构和介质物性的探测研究；（2）地震和前兆数字化观测技术的研制；（3）地震短临预报方法及其判据、指标的研究；（4）地震序列类型和震后趋势早期应用判断方法及其指标的研究；（5）华北北部地震短临预报方法、前兆综合解释模型与短临预报综合判别系统的研究；（6）地震预报新技术、新方法的探索；（7）地震中长期预报研究及我国近期（10年左右尺度）地震重点监视防御区的确定；（8）板内地震孕育发生的物理模型及前兆场物理解释的探索研究．最后还对我国地震预报的未来发展进行了展望．     

Searching for an Earthquake Precursor—A Case Study of Precursory Swarm as a Real Seismic Pattern Before Major Shocks

A long-range correlation between earthquakes is indicated by some phenomena precursory to strong earthquakes. Most of the major earthquakes show prior seismic activity that in hindsight seems anomalous. The features include changes in regional activity rate and changes in the pattern of small earthquakes, including alignments on unmapped linear features near the (future) main shock. It has long been suggested that large earthquakes are preceded by observable variations in regional seismicity. Studies on seismic precursors preceding large to great earthquakes with M ≥ 7.5 were carried out in the northeast India region bounded by the area 20°–32°N and 88°–100°E using the earthquake database from 1853 to 1988. It is observed that all earthquakes of M ≥ 7.5, including the two great earthquakes of 1897 and 1950, were preceded by abnormally low anomalous seismicity phases some 11–27 years prior to their occurrence. On the other hand, precursory time periods ranged from 440 to 1,768 days for main shocks with M 5.6–6.5 for the period from 1963 to 1988. Furthermore, the 6 August, 1988 main shock of M 7.5 in the Arakan Yoma fold belt was preceded by well-defined patterns of anomalous seismicity that occurred during 1963–1964, about 25.2 years prior to its occurrence. The pattern of anomalous seismicity in the form of earthquake swarms preceding major earthquakes in the northeast India region can be regarded as one of the potential seismic precursors. Database constraints have been the main barrier to searching for this precursor preceding smaller earthquakes, which otherwise might have provided additional information on its existence. The entire exercise indicates that anomalous seismicity preceding major shocks is a common seismic pattern for the northeast India region, and can be employed for long-range earthquake prediction when better quality seismological data sets covering a wide range of magnitudes are available. Anomalous seismic activity is distinguished by a much higher annual frequency of earthquake occurrence than in the preceding normal and the following gap episodes.