Geochemical precursors to seismic activity

Studies of earthquake precursory phenomena during the last several decades have found that significant geophysical and geochemical changes can occur prior to intermediate and large earthquakes. Among the more intensely investigated geochemical phenomena have been: (1) changes in the concentrations of dissolved ions and gases in groundwaters and (2) variations in the concentrations of crustal and mantle volatiles in ground gases. The concentration changes have typically showed no conanomalies trend (either increasing or decreasing), and the spatial and temporal distribution of the observed anomalies have been highly variable. As a result, there is little agreement on the physical or chemical processes responsible for the observed anomalies. Mechanisms proposed to account for precursory groundwater anomalies include ultrasonic vibration, pressure sensitive solubility, pore volume collapse, fracture induced increases in reactive surfaces, and aquifer breaching/fluid mixing. Precursory changes in soil gas composition have been suggested to result from pore volume collapse, micro-fracture induced exposure of fresh reactive silicate surfaces, and breaching of buried gas-rich horizons. An analysis of the available field and laboratory data suggests that the aquifer breaching/fluid mixing (AB/FM) model can best account for many of the reported changes in temperature, dissolved ion and dissolved gas concentrations in groundwater. Ultrasonic vibration and pressure sensitive solubility models cannot reasonably account for the geochemical variations observed and, although the pore collapse model could explain some of the observed chemical changes in groundwater and ground gas, uncertainties remain regarding its ability to generate anomalies of the magnitude observed. Other geochemical anomalies, in particular those associated with hydrogen and radon, seem best accounted for by increases in reactive surface areas (IRSA model) that may accompany precursory deformation around the epicenter of an impending earthquake. Analysis of the probable response of these models to the earthquake preparation process, as well as to other environmental factors, suggests that geochemical monitoring programs can provide information that may be valuable in forecasting the probability of an earthquake; however, because of the complexity of the earthquake preparation process, the absolute prediction of seismic events using geochemical methods alone, does not presently appear to be feasible.     

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.     

Nucleation of earthquakes and its implication to precursors

IntroductionIn the middle of 1990s, the argument about nucleation phase occurred. Ellsworth and Beroza(1 995) studied the wave records of 30 earthquake events, which initiated slowly. Ellsworth, et al calledthem as nucleation phase. They discussed the relationship between their moment, duration time andthe relationship with the main shock behind. Scherbaum (1997a, b) proposed his different view andsuggested that some of the recording of the long period initial of seismic wave was misinterpret…     

近期国际地震预测预报研究进展的几个侧面

本文从国际组织、国际计划、科学出版物、主要代表性人物及其学术观点、实际地震预测与地震前兆检验等方面，介绍了20世纪90年代后期以来国际上地震预测预报研究进展的几个侧面，这些进展在一定程度上反映了此间地震预测预报研究从“低谷”走向新的发展的思想脉络。     

静乐井水位前驱波重现性问题探讨

以山西静乐井为研究对象,对井水位前驱波重现性问题进行了探讨。结果表明,相似地震前前驱波起始时间和波动周期在一定范围内具有较强的重现性,其比例可达63.1%;部分相似地震前前驱波的波动形态和幅度也存在一定的相似性,但在研究范围内前驱波各项特征均相似的地震尚未发现,其原因可能与前驱波的成因、传播途径、相似地震的震源区特征等因素有关。     

从卫星观测数据提取地震前兆信息研究中的参考文献

如何从卫星观测数据中提取地震前兆信息,是近年来的一个跨空间物理、地震学和板块构造学等交叉领域的研究焦点,本文收集整理了部分近年来国外学者在该方面研究的论文,以供相关领域研究者参考之用。     

强震前中短期地震活动异常动态图像的表示方法及其预测意义

提出了二个描述中强震发生前中短期阶段地震活动异常时空演经图像的参量σＮ、σＥ。分别将其用于华北地区、新疆地震区及南北地震带,并对其预报效能进行检验,对其异常的空间分布图像与强震发生地震进行了分析,结果表明,该二参量能较好地瓜倾吐夺前中短期阶段孕震区及其周围地区地震活动的异常平静及丛集的现象。二参量异常的时空分布图像上示出在中强震发生前３个月至１年在震中周围地区有明显的异常分布,且随着时间逼近发震时     

张北-尚义地震前地下水物理动态异常与短临预报

张北－尚义地震前塔院、太平庄两井的水位、水温出现明显的中短期异常和短临异常。笔者利用这些异常并结合其它测项的异常,震前曾提出了一定的短临预报意见     

A review of rock mechanics studies in the United States pertinent to earthquake prediction

Premonitory phenomena such as dilatancy, creep, acoustic emission, and changes in seismic velocity and attenuation, electrical resistivity, magnetic moment, and gas emission, which occur before fracture of initially intact rock and before stick-slip on faults or between finely ground surfaces of rock, have been reviewed and discussed in relation to earthquake prediction. This review is restricted to the results of laboratory experiments that have been carried out in the United States of America.     

Aspects regarding the use of the INFREP network for identifying possible seismic precursors

In the last decades, one of the main research directions in identifying seismic precursors involved monitoring VLF (Very Low Frequency) and LF (Low Frequency) radio waves and analysing their propagation characteristics. Essentially this method consists of monitoring different available VLF and LF transmitters from long distance reception points. The received signal has two major components: the ground wave and the sky wave, where the sky wave propagates by reflection on the lower layers of the ionosphere. It is assumed that before and during major earthquakes, unusual changes may occur in the lower layers of the ionosphere, such as the modification of the charged particles number density and the altitude of the reflection zone. Therefore, these unusual changes in the ionosphere may generate unusual variations in the received signal level.The International Network for Frontier Research on Earthquake Precursors (INFREP) was developed starting with 2009 and consists of several dedicated VLF and LF radio receivers used for monitoring various radio transmitters located throughout Europe. The receivers’ locations were chosen so that the propagation path from these VLF/LF stations would pass over high seismicity regions while others were chosen to obtain different control paths.The monitoring receivers are capable of continuously measuring the received signal amplitude from the VLF/LF stations of interest. The recorded data is then stored and sent to an INFREP database, which is available on the Internet for scientific researchers. By processing and analysing VLF and LF data samples, collected at different reception points and at different periods of the year, one may be able to identify some distinct patterns in the envelope of the received signal level over time. Significant deviations from these patterns may have local causes such as the electromagnetic pollution at the monitoring point, regional causes like existing electrical storms over the propagation path or even global causes generated by high-intensity solar flares. As a consequence, classifying these perturbations and minimizing them (when possible) would represent an important step towards identifying significant pattern deviations caused by seismic activities.Taken into consideration some of the issues mentioned above, this paper intends to present some aspects meant to improve the overall performance of the existing INFREP network. The signal-to-noise ratio improvement of the monitoring receiver may be achieved by relocating the antenna (or even the entire monitoring system if possible) in areas with less electromagnetic pollution within the VLF and LF bands. Other solution may involve replacing the existing electric “whip” antennas with magnetic loop antennas.Regarding the measuring method, long-term averaging of the received signal to reduce the electromagnetic noise should be carefully applied. If the averaging time is too long, there is a risk that, during a seismic event, the details of the received signal envelope would be lost. Moreover, this may reduce the possibility of making correlations between the monitored stations and INFREP receivers in case of sudden ERP (Effective Radiated Power) variations of the VLF/LF stations. For the same reason, the time synchronization of the recorded data using (for instance) GPS technology is highly recommended.Other aspects related to the overall performance improvement of the INFREP network consist of monitoring other VLF/LF stations such as the Krasnodar station (south of Russia), part of the ALPHA/RSDN-20 VLF navigation system, or the 77.5 kHz DCF77 time signal transmitter (near Frankfurt am Main, Germany). Moreover, the installation of a new reception point in Romania (near Cluj-Napoca) for monitoring the Vrancea area (within the Carpathians Mountains) and the Adriatic region will provide complementary scientific data within the network.     

Seismicity variations in the Makran region of Pakistan and Iran: Relation to great earthquakes

Teleseismic activity in the Makran region of southeastern Iran and southwestern Pakistan prior to the great earthquake (M_s=8) of 1945 can be characterized in terms of two stages. First, during the period 30 (or more) to 10 years prior to the main event, the frequency of occurrence of moderate to large earthquakes was relatively high in the region between the impending rupture zone and the volcanic arc to the northwest. These events probably occurred near the down-dip limit of seismic activity within the subducted slab. Second, activity was concentrated along the coast during the ten years immediately preceding the great earthquake and most of this activity was confined to the vicinity of the epicenter of the 1945 earthquake. These patterns are similar in some respects to those observed prior to some large earthquakes in other parts of the world.Three observations concerning the pre-1945 seismicity suggest it was associated with the preparation for rupture of the zone that eventually broke during the great earthquake in 1945: (1) The activity before 1945 is located either within the 1945 rupture zone or between this zone and the volcanic arc to the northwest; (2) No activity of similar magnitude and occurrence rate is observed elsewhere along the Makran plate boundary; and (3) The region that was active prior to 1945 has been relatively quiet since the decline in aftershock activity associated with the 1945 shock. The current quiescence may be related to the release of stress during the 1945 earthquake.Recent seismicity in the region west of that affected prior to 1945 suggests that this western region may be the site of the next large earthquake. Events along the coast are grouped at both ends of a seismically quiet zone, producing a distribution similar to the donut pattern identified by Mogi. In addition, one moderate-magnitude earthquake occurred within the subducted slab to the northwest of the donut pattern along the coast. This moderate-magnitude earthquake, the first to occur in the region immediately west of the 1945 rupture zone since the advent of instrumental recording, may be analogous to the activity of stage one associated with the 1945 earthquake. While by no means providing conclusive evidence of an impending earthquake, the characteristic patterns identified in the recent seismicity indicate that this region should be closely monitored in the future.Lamont-Doherty Geological Observatory Contribution Number 2853.     

Prediction of central California earthquakes from soil-gas helium fluctuations

The observations of short-term decreases in helium soil-gas concentrations along the San Andreas Fault in central California have been correlated with subsequent earthquake activity. The area of study is elliptical in shape with radii approximately 160×80 km, centered near San Benito, and with the major axis parallel to the Fault. For 83 percent of theM>4 earthquakes in this area a helium decrease preceded seismic activity by 1.5 to 6.5 weeks. There were several earthquakes without a decrease and several decreases without a corresponding earthquake. Owing to complex and unresolved interaction of many geophysical and geochemical parameters, no suitable model is yet developed to explain the observations.     

Short-term and intermediate-term geochemical precursors

Detection of precursory phenomena in observation data is essential to earthquake prediction studies. Continuous monitoring of radon concentration in groundwater in Japan in one case showed a short-term anomaly related to a nearby earthquake. With the exception of the 1978 Izu-Oshimakinkai earthquake (M7.0), however, no abnormal change has been noted. This may be due partially to difficulty in detecting insignificant precursory signals from observation data, which ordinarily contains a noise-induced fluctuations, and partially to lack of understanding of the mechanism controlling the appearance of precursory phenomena. In order to increase our knowledge of the variation pattern of precursory changes in radon concentration of groundwater, hydrologic precursors with significant features are examined in this paper. Complexity of appearance of precursory phenomena and problems in assignment of the specific earthquake are discussed.     

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.     

华北地下水位强震短期异常演化及前兆判别标志研究

对地下水位地震前兆异常开展了参数提取方法的研究, 并以其提取的结果为输入, 对1984～2002年华北地区地下水位异常参数分布做了全时空扫描, 继而将全部图像与华北地区构造活动性量化评估的数字化图像进行了叠加, 实现了地下水位异常动态扫描与区域构造活动性背景的结合。 在此基础上, 对1985年以来华北地区5级以上地震前的地下水位短期图像演化情况做了全面分析, 提取出了判别异常区的指标以及地震短期异常区的演化特征, 并最终建立了华北地区强震前地下水位短期前兆的判别标志。     

新形势下中国地震预报的发展战略

简述了各国科学家近年来对地震预报可能性的争论,结合中国20多年的经验讨论了新形势下中国地震预报的发展战略问题.     

Long-range Earthquake Forecasting with Every Earthquake a Precursor According to Scale

Scaling relations previously derived from examples of the precursory scale increase before major earthquakes show that the precursor is a long-term predictor of the time, magnitude, and location of the major earthquake. These relations are here taken as the basis of a stochastic forecasting model in which every earthquake is regarded as a precursor. The problem of identifying those earthquakes that are actually precursory is thus set aside, at the cost of limiting the strength of the resulting forecast. The contribution of an individual earthquake to the future distribution of hazard in time, magnitude and location is on a scale determined, through the scaling relations, by its magnitude. Provision is made for a contribution to be affected by other earthquakes close in time and location, e.g., an aftershock may be given low weight. Using the New Zealand catalogue, the model has been fitted to the forecasting of shallow earthquakes exceeding magnitude 5.75 over the period 1965–2000. It fits the data much better than a baseline Poisson model with a location distribution based on proximity to the epicenters of past earthquakes. Further, the model has been applied, with unchanged parameters, to the California region over the period 1975–2001. There also, it performs much better than the baseline model fitted to the same region over the period 1951–1974; the likelihood ratio is 10¹⁵ in favor of the present model. These results lend credence to the precursory scale increase phenomenon, and show that the scaling relations are pervasive in earthquake catalogues. The forecasting model provides a new baseline model against which future refinements, and other proposed models, can be tested. It may also prove to be useful in practice. Its applicability to other regions has still to be established.     

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。     

Prediction of strong earthquakes in Vrancea,Romania, using the CN algorithm

The application of the CN algorithm to a new earthquake catalogue, for the period from 1932 to 1993, obtained by merging Romanian and U.S.S.R. data, allows us to monitor, on the intermediate time scale. the preparation of strong, intermediate-depth earthquakes in the Vrancea region. Four of the five strong earthquakes with magnitudes above 6.4 are predicted. The total duration of the Time of Increased Probability (TIP) of the occurrence of an earthquake (TIP) occupies 21.7% of the time interval under consideration, i.e., about 2.5 years for each strong earthquake.     

加卸载响应比理论在华南地区中强震的应用

用加卸载响应比理论对华南地区12例中强以上地震进行研究, 结果表明有8例在震前响应比值有明显的高值( Y≥ 2. 0)异常显示, 通过对响应比值随时间变化特征的分析表明, 响应比对5级左右地震有较好的中短期预测效果, 因此响应比理论可作为华南地区地震预测方法。