The Oaxaca gap: A case history

An attempted use of seismic gap observations to predict a large earthquake in Oaxaca, Mexico is discussed. The observations were initially published in a scientific journal and were subsequently distorted by noncientists, who predicted a major earthquake and tsunami to take place at Pinotepa Nacional, Oaxaca on 23 April 1978. Public reactions and property losess sustained by individuals and communities were comparable to those expected from an actual earthquake. A revision of epicenter locations from the NOAA data file revealed that a number of earthquakes did occur in the alleged gap but had been excluded because their reported focal depth was in excess of 60 km. It is shown that the probability that the number of earthquakes in two consecutive time intervals of a stationary Poisson process differs by an amount which would be reported as a seismic gap is of the order of 5% or more for Oaxaca. This means that spurious seismic gaps would be observed in one out of 20 data runs. The possibility of detecting a true interval of abnormal quiescence in a random earthquake sequence appears to be fairly remote in this case.     

态矢量--分析地震活动性的一种新方法

态矢量来源于统计物理学，是一种对连续场进行粗粒化描述的方法。现移植到地震学中用以定量地刻画地震活动性的演化，取得较好的结果。作者分析研究了几个著名震例(海城地震、唐山地震、昆仑山口西地震)，发现地震前其态矢量均有显著的变化，因此认为它可能是大地震的一种前兆，而用之于地震预报。     

地震活动性研究及其应用于地震预测的一些问题

依据20世纪上半叶的强震资料对全球地震活动性进行的研究结果显示，强震活动呈带状分布，其实质是揭示了全球大尺度地壳介质的非均匀性。地震带与板块的活动密不可分，对认识板块活动做出了应有的贡献。基于悠久的历史地震资料和地质构造活动特征划分了20多条地震带，这是对大陆内部地壳介质非均匀性的一种认识，也是统计预测方法的基础之一。     

Study of the Seismicity of Strong Earthquakes in the Yunnan Area

INTRODUCTIONYunnanis located in the east margin of the collision zone between the India Plate and theEurasian Plate on the Chinese Continent , where crustal movement is violent and moderate-strongearthquakes are frequent withlarge magnitudes and wide distributions .It is also a place of particularinterest to geo-science researchers both at home and abroad. Since 1970 , 8 earthquakes withmagnitude 7·0 have occurred here .It is a perfect site to study seismicity.Whether or not seismicit…     

2010年太康ML5.0级地震前地震活动特征

通过对2010年10月24日太康ML5.0级地震前的资料进行回顾研究,认为在这次地震前,存在区域中等地震活动增强、ML≥2.0级弱震空区、弱震条带、地震平静及霍山地震后窗口高频次异常等异常图象.它又一次为该区对中等地震的监测预报积累了资料.     

库玛断裂带强震活动与地震空区研究

库玛断裂带作为青藏高原内部的一条强地震活动带, 1900年以来发生过3次7级地震,其中2次7级大震前均出现5级以上地震的背景空区,表明背景空区对该带大震具有中长期预报意义。最近一次背景空区业已形成,并出现与之配套的孕震空区,其演化图像符合强震孕育模式。研究发现,库玛断裂带中段M_L 3以上地震空区,对共和7级强震及周边200 km的强震有前兆意义。     

1999年5月17日万宁近海MS4.8级地震

对１９９９年５月１７日万宁近海Ｍｓ４．８级地震进行了总结。分析认为,这次地震属孤立型,发震断层为ＮＥ向的兴隆－龙滚断裂和琼东南海断裂之间的次一级断裂,具有走滑特征。地震前存在３个月无ＭL≥３．０级地震的异常平静、低b值、应变释放加速、缺震、地震频度地ＣＬ高值以及琼中地磁台Ｚ分量“双低点”等前兆异常现象。地震前有不同程度的中期和短期预报。     

Most likely locations of large earthquakes in the Kanto and Tokai areas, Japan, based on the local recurrence times

We examined the hypothesis that minima in local recurrence time, T_L, or equivalently maxima in local probability, P_L, may map asperities in the Kanto and Tokai areas of Japan, where the earthquake catalog of the National Research Institute for Earth Science and Disaster Prevention (NIED) is complete at the M=1.5 (M1.5) level. We mapped T_L (P_L) based on the a- and b-values of the nearest earthquakes within 20 km of every node of a grid spaced 0.01° for M7 target events. Only earthquakes within the top 33 km were used. The b-values increase strongly with depth, in several areas. Therefore, some of the T_L (P_L) anomalies are not revealed if data from the entire crustal seismogenic zone are mixed. Thus, we mapped T_L (P_L) separately for the top 15 km and the rest of the depth range, as well as for the entire seismogenic crust. The resulting T_L- and P_L-maps show that approximately 12% of the total area shows anomalously short recurrence times. Out of six shallow target events with M≥6.5 and which occurred since 1890, five are located within the anomalous areas with T_L <450 years. We interpret this to mean that areas with anomalously short T_L map asperities, which are more likely than other areas to generate future target events. The probability that this result is due to chance is vanishingly small. The great Kanto rupture of 1923 appears to have initiated in the most significant asperity we mapped in the study area. One anomaly is located in the northeastern part of the area of the proposed future rupture of the Tokai earthquake, and another one at its southwestern corner. The absolute values of T_L calculated are uncertain because they depend on the size of the volume used for the calculation.     

再论MDCB地震监测仪的映震效果

分析了 Ｍ Ｄ Ｃ Ｂ 型地震监测仪在廊坊连续４２ 个月观测期间, 所记录的类地应力值、８ 方位异常值和异常频度等１４ 种电磁波地震前兆异常参数的动态趋势、方向性反映、临震变化与一定范围内一定强度地震的对应关系, 并得出了电磁波前兆异常参数与地震数量关系的初步结果。     

Seismic quiescence precursory to a past and a future Kurile island earthquake

A systematic search was made for seismicity rate changes in the segment of the Kurile island arc from 45°N to 53°N by studying the cumulative seismicity of shallow (h100 km) earthquakes within 11 overlapping volumes of radius 100 km for the time period 1960 through beginning of 1978. We found that in most parts of this island arc and most of the time the seismicity rate as obtained from the NOAA catalogue and not excluding any events is fairly constant except for increased seismicity in the mid 1960s in the southern portion due to the great 1963 mainshock there, and for seismicity quiescence during part of the time period studied within two well defined sections of the arc. The first of these is a volume of 100 km radius around a 1973 (M _s =7.3) mainshock within which the seismicity rate was demonstrated at the 99% confidence level to have been lower by 50% during 2100 days (5.75 years) before this mainshock. The second volume of seismic quiescence coincides with the 400 km long north Kuriles gap. In this gap the seismicity rate is shown (at the 99% confidence level) to be lower by 50% from 1967 to present (1978), in comparison with the rate within the gap befor 1967, as well as with the rate surrounding the gap. We propose that the anomalously low seismicity rate within the Kuriles gap is a precursor to a great earthquake, the occurrence time of which was estimated by the following preliminary relation between precursory quiescence time and source dimensionT=190L ^0.545. We predict that an earthquake with source length of 200–400 km (M>8) will occur along the north Kurile island arc between latitude 45.5°N and 49.2°N at a time between now and 1994.     

Anomalous seismicity prior to rock bursts: Implications for earthquake prediction

Anomalous seismicity changes (increase followed by a decrease) were recorded prior to three moderate rock bursts in the Star mine, Burke, Idaho. In each case, based upon the anomalous seismicity behavior, miners were evacuated or were prohibited from entering active mine stopes that were located in the immediate vicinity of the seismicity buildup prior to the bursts. Analyses of pre- and post-seismic activity are interpreted in terms of, and shown to be consistent with, the inclusion theory of failure. Implications of these observational results for the problem of rock bursts and earthquake prediction are discussed.     

Seismicity characteristics of a potentially active Quaternary volcano: The Tatun Volcano Group, northern Taiwan

The Tatun Volcano Group (TVG) is located at the northern tip of Taiwan, near the capital Taipei and close to two nuclear power plants. Because of lack of any activity in historical times it has been classified as an extinct volcano, even though more recent studies suggest that TVG might have been active during the last 20 ka. In May 2003 a seismic monitoring project at the TVG area was initiated by deploying eight three-component seismic stations some of them equipped with both short-period and broadband sensors. During the 18 months observation period local seismicity mainly consisted of high frequency earthquakes either occurring as isolated events, or as a continuous sequence in the form of spasmodic bursts. Mixed and low frequency events were also present during the same period, even though they occurred only rarely. Arrival times from events with clear P-/S-wave phases were inverted in order to obtain a minimum 1D velocity model with station corrections. Probabilistic nonlinear earthquake locations were calculated for all these events using the newly derived velocity model. Most high frequency seismicity appeared to be concentrated near the areas of hydrothermal activity, forming tight clusters at depths shallower than 4 km. Relative locations, calculated using the double-difference method and utilising catalogue and cross-correlation differential traveltimes, showed insignificant differences when compared to the nonlinear probabilistic locations. In general, seismicity in the TVG area seems to be primarily driven by circulation of hydrothermal fluids as indicated by the occurrence of spasmodic bursts, mixed/low frequency events and a b-value (1.17 ± 0.1) higher than in any other part of Taiwan. These observations, that are similar to those reported in other dormant Quaternary volcanoes, indicate that a magma chamber may still exist beneath TVG and that a future eruption or period of unrest should not be considered unlikely.     

与香港地区地震危险性相关的汶川地震灾害调查的五点认识

在2008年汶川地震灾害凋查和认识的基础上,研究了与香港地区地震危险性相关的五点认识.香港地区虽然有较大断裂,但是它的断裂处于较为完整的花岗岩和火山岩岩体中,深部不具备产储大型高压人然气囊,因此,它不具备发生中强地震的充分条件.香港地区的岩石类型、周边和内部海水体、周边岛屿和建筑楼顶水体的均有利于抗震减灾.     

A preliminary study on the relationship between precipitation and large earthquakes in Southern California

By comparing seasonal rainfall data from the past 90 years with the occurrence of large (M6) earthquakes along an arid stretch of the San Andreas fault system in southern California, certain correlations have been observed. Most large earthquakes are preceded by a pattern consisting of a few years of below normal precipitation (drought) terminated by one or more consecutive seasons of heavy (above normal) rainfall. While this drought-above normal rainfall cycle can be seen at times other than prior to major earthquakes, it precedes, to varying degrees, all of the twelve M6 events. This new precursor evidence, when combined with other premonitory signals, may offer a helpful diagnostic measure that could be useful in earthquake prediction in arid regions.     

地震前驱波观测与研究进展

前驱波的研究,可能成为未来地震预测和理论研究的一个突破点。列举了国内外前驱波观测事实,综述了近年来国内地震工作者对前驱波进行的实验和理论研究。     

江苏省盐城地区地震活动特征及震灾分析

对盐城地区地震活动概况进行了背景性分析,从该地区地震地质构造背景人手,阐述了影响盐城地区地震活动的主要断裂构造．对研究区域内的地震活动空间、时问分布特征进行了探讨,并分析了盐城地区的地震灾害特点。     

前兆场稳定度Dk在中强地震前兆资料分析中的应用

提出了前兆场稳定度的概念,利用前兆场稳定度的方法对中强地震前豫鲁冀交界区不同台站和不同手段的前兆观测数据进行分析。结果表明,在１９８３年１１月７日山东菏泽Ｍs５ ．９级和１９８５年１１月３０日河北任县Ｍs５．０级地震前１４个月内,前兆场稳定度有低值异常显示,并且异常幅度越来越大,地震后恢复到正常值。     

Anomalous crustal strain prior to the 1923 Kanto,Japan, earthquake as deduced from analysis of old triangulation data

Horizontal earth's strains preceding the Kanto, Japan, earthquake of 1, September 1923, are deduced from the analysis of the old triangulation data. The anomalous strains that are several times larger than usual tectonic strain are found in the western part of Tokyo Bay, Sagamihara district, Japan for the observational period 1882/91–1898/1910, while any significant strain is not revealed in the other region of the Kanto district. The Kanto district was surveyed twice during the period 1883/85–1890/92 in the west and during the period 1890/92–1897/99 in the east respectively. The polarity of the detected anomalous strains, the directions and the signs of the principal strains, are quite the same as those of the postseismic crustal strains during the period 1924–74, and are reversed as compared to the coseismic one.The Philippine Sea plate thrusts under the South Kanto district with N25°W direction and pulls down the land during the interseismic period. The aseismic reverse faulting would begin several decades before the 1923 Kanto earthquake along the deep interface between the Asian plate and the convergent Philippine Sea plate. The down-going along the locked part of the interface would be accelerated, thus the compressional stress on the earth's surface might be concentrated over the deep fault plane together with the acceleration of the subsidence at the tip of the peninsula close to the Sagami trough.     

Instability model for recurring large and great earthquakes in southern California

The locked section of the San Andreas fault in southern California has experienced a number of large and great earthquakes in the past, and thus is expected to have more in the future. To estimate the location, time, and slip of the next few earthquakes, an earthquake instability model is formulated. The model is similar to one recently developed for moderate earthquakes on the San Andreas fault near Parkfield, California. In both models, unstable faulting (the earthquake analog) is caused by failure of all or part of a patch of brittle, strain-softening fault zone. In the present model the patch extends downward from the ground surface to about 12 km depth, and extends 500 km along strike from Parkfield to the Salton Sea. The variation of patch strength along strike is adjusted by trial until the computed sequence of instabilities matches the sequence of large and great earthquakes sincea.d. 1080 reported by Sieh and others. The last earthquake was theM=8.3 Ft. Tejon event in 1857. The resulting strength variation has five contiguous sections of alternately low and high strength. From north to south, the approximate locations of the sections are: (1) Parkfield to Bitterwater Valley, (2) Bitterwater Valley to Lake Hughes, (3) Lake Hughes to San Bernardino, (4) San Bernardino to Palm Springs, and (5) Palm Springs to the Salton Sea. Sections 1, 3, and 5 have strengths between 53 and 88 bars; sections 2 and 4 have strengths between 164 and 193 bars. Patch section ends and unstable rupture ends usually coincide, although one or more adjacent patch sections may fail unstably at once. The model predicts that the next sections of the fault to slip unstably will be 1, 3, and 5; the order and dates depend on the assumed length of an earthquake rupture in about 1700.     

基于“区域-时间-长度算法”分析川滇地区强震前地震活动性变化*

本文基于“区域-时间-长度算法”(Region-Time-Length algorithm)回顾性检验了1976年以来发生在川滇地区的6个M_S7.0以上和23个M_S6.0~6.9地震前地震活动性变化。M_S7.0以上强震前,5例检测到地震活动平静异常,仅1例检测到地震活动增强;M_S6.0~6.9地震前,12例检测到平静,11例检测到地震活动增强。以上异常大部分出现于震前0.5~2.5a,持续0.5~2a。另外,发生在云南普洱地区的4个MS6.0以上地震震前都检测到平静异常;发生在北纬22.7°~31.0°N,99.6°~102.5°E范围内的17个地震,13例于震前检测到平静异常。以上研究对更好地认识川滇地区地震孕育过程和发震前兆提供了一些参考。