Precursory seismic quiescence

Seventeen cases of precursory seismic quiescence to mainshocks with magnitudes fromM _L=4.7 toM _S=8.0 are summarized. The amount of rate decrease ranges from 45% to 90%. The significance of these changes varies between 90% and 99.99%. The assumption that the background rate is approximately constant is fulfilled in most crustal volumes studied. All quiescence anomalies seem to have abrupt beginnings, and the rate during the anomalous period is fairly constant. The duration of the precursors ranges from 15 to 75 months, and it is not clear what factors determine that time. At least three successful predictions have been based on seismic quiescence. These cases have shown that mainshocks can be predicted based on quiescence, but they have also shown that the interpretation of the data in real time is difficult and nonunique. If a false alarm is defined as a period of quiescence with a significance level larger than a precursory quiescence in the same tectonic area, then we estimate, based on searches in four areas, that the false alarm rate may be on the order of 50%. Failure to predict may be expected in perhaps 50% of mainshocks, even in carefully monitored areas. Quiescence cannot be used as a precursor in tectonic environments with low seismic activity. Most characteristics of the phenomenon are still poorly defined, but data exist which probably permit at least a doubling of the presently available data on case histories.     

大震前地震活动图像演变及中期向短期过渡的地震活动性标志

通过多震例分析，表明大震前地震活动图像具有类似的演变形式，即空段－背景空区－增强活动－条带－平静，地震平静可以看作是中期短期过渡的地震活动性标志，从图像演变角有助于识别异常平静，并有可能把震前平静的时间尺度缩短至几个月量级。     

华东地区M_L≥4.0地震平静预测意义分析

用统计学上的χ~2检验方法对华东地区M_L≥4.0地震平静进行了统计检验,得出在较高的置信概率下可以将平静时间T≥140天作为平静异常的判别标准。总结了华东地区自1970年以来出现的平静异常,并分析了其对应中强地震的情况。研究表明,M_L≥4.0地震平静异常是华东地区中强震前的一种普遍现象。62.5%的平静异常后发生了M_S≥4.5地震;绝大多数平静异常前存在着地震活动的增强过程,多次活动增强后连续发生了平静异常且之后发生了M_S≥5.0地震。     

Precursory seismic quiescence: A preliminary assessment of the hypothesis

Numerous cases of precursory seismic quiescence have been reported in recent years. Some investigators have interpreted these observations as evidence that seismic quiescence is a somewhat reliable precursor to moderate or large earthquakes. However, because failures of the pattern to predict earthquakes may not, in general, be reported, and because numerous earthquakes are not preceded by quiescence, the validity and reliability of the quiescence precursor have not been established.We have analyzed the seismicity rate prior to, and in the source region of, 37 shallow earthquakes (M 5.3–7.0) in central California and Japan for patterns of rate fluctuation, especially precursory quiescence. Nonuniformity in rate for these pre-mainshock sequences is relatively high, and numerous intervals with significant (p<0.10) extrema in rate are observed in some of the sequences. In other sequences, however, the rate remains within normal limits up to the time of the mainshock. Overall, in terms of an observational basis for intermediate-term earthquake prediction, no evidence is found in the cases studied for a systematic, widespread or reliable pattern of quiescence prior to the mainshocks.In earthquake sequences comprising full seismic cycles for 5 sets of (M 3.7–5.1) repeat earthquakes on the San Andreas fault near Bear Valley, California, the seismicity rates are found to be uniform. A composite of the estimated rate fluctuations for the sequences, normalized to the length of the seismic cycle, reveals a weak pattern of a low rate in the first third of the cycle, and a high rate in the last few months. While these observations are qualitative, they may represent weak expressions of physical processes occurring in the source region over the seismic cycle.Re-examination of seismicity rate fluctuations in volumes along the creeping section of the San Andreas fault specified by Wyss and Burford (1985) qualitatively confirms the existence of low-rate intervals in volumes 361, 386, 382, 372 and 401. However, only the quiescence in volume 386 is found by the present study to be statistically significant.     

华北块体中等地震活动平静特征

采用累计频度方法,对华北活动地块Ms≥5．5地震前中等地震聚集活动区的地震做了时空扫描,并对平静现象进行了定量分析,结果表明：对各Ⅱ级活动地块采用不同的扫描方法．在强震前都表现出明显的增强、平静过程,平静的时间长短与所给定的构造区域有关。本文给出了华北3个Ⅱ级活动地块的发震模式。对各活动地块分别进行了R值检验,表明3个活动地块采用不同的发震模式均具有较高的预报效能。     

Relative Seismic Quiescence Before Large Aftershocks

--In terms of the modified Omori's formula and Akaike's Information Criterion, thirteen aftershock sequences have been analysed quantitatively, to check if any anomalous change of seismic activity took place before the occurrence of the largest aftershock. The analysis follows the method proposed by . The epicentre distribution of the main shocks covers the Aegean Sea (Greece) area and the surrounding regions. The earthquakes occurred from 1988 to 1998.¶Although difficulties existed for a quantitative treatment of seismic quiescence, the results of the temporal analysis of the aftershock activities seem to be promising. In eight of thirteen cases the observed temporal pattern is similar. The aftershock activity decreases significantly before the occurrence of the largest aftershock, with respect to the level expected according to the modified Omori's formula. Thereafter, the activity recovers to its previous level just before or immediately after the occurrence of the main aftershock. Moreover, an estimation of the reliability of the method is made, based on the results of this study as well as of previous similar investigations. From a total of 41 aftershock sequences which have been analysed following Matsu'ura's method, 29 of them (71%) show a remarkable relative quiescence before the occurrence of the main shock.¶Although it is difficult to construct a model which explains the precursory pattern, the real time monitoring and check for seismic quiescence could at least contribute to a 'qualitative' prediction of the largest aftershock which could at times be as large and disastrous as the main shock.     

Precursory seismic quiescence: Past,present, and future

Precursory seismic quiescence has played a major role in most of the succesful earthquake predictions made to date. In addition to these successes, the number of detailed post-mainshock documentations of precursory quiescence is steadily growing. These facts suggest that precursory quiescence will play an important role in earthquake prediction programs of the future. For this reason it is important to critically evaluate the present state of knowledge concerning this phenomenon. The history of observations of precursory seismic quiescence includes work on seismic gaps and seismic preconditions as well as actual studies of temporal quiescence. These papers demonstrated the importance of quantitative evaluation of seismicity rates and the benefits of systematic analysis. During the early 1980's the impact of man-made effects on seismicity rates was demonstrated for the first time. Despite progress in catalog understanding, the identification and correction of man-made seismicity changes remains as the major barrier to earthquake prediction using these data. Effects of man-made changes are apparent in many past studies of seismicity patterns, making the results difficult to evaluate. Recent experience with real-time anomalies has demonstrated the necessity of determining the false alarm rates associated with quiescence precursors. Determination of false alarm rates depends on quantitative definitions of anomalies and statistical evaluations of their significance. A number of successful predictions, which have been made on the basis of seismic quiescence, provide important lessons for present and future work. There are many presently unanswered questions regarding seismic quiescence which must be answered before we can determine the reliability of this phenomena as a precursor.     

Investigations at Sites Contaminated with Dense, Non-Aqueous Phase Liquids (NAPLs)

Increasingly, ground water supplies are being found to be contaminated with organic substances. Depending on the nature of these substances and the method by which they were introduced into the environment, they may form a second, dense liquid phase. Several such cases have been reported in the recent literature. In other cases, such a second phase might have actually been present but was not found because the principles governing its distribution were not understood and no effort was made to look for it. In this case, the undetected material could continue to migrate and act as a source of dissolved organics.
This article reviews the general principles governing the behavior of dense, immiscible second-phase organic liquids in both the unsaturated and saturated zones, based primarily on the petroleum industry literature for primary hydrocarbon migration and on the oil spill literature. This specialized knowledge can be used to conduct a meaningful and efficient investigation of such contamination sites and can also be used to select and implement successful remedial measures. Several actual case studies applying the principles of multi-phase flow are also presented.     

Statistical assessment of seismicity patterns in Italy: Are they precursors of subsequent events?

The variations of seismicity rate in Central Apenninesprior to the sequence started in September, 1997 (at00:33 UTC, M _L5.6) has been analysedby statistical methods, with the purpose of pointingup eventual periods of quiescence. The analysis wascarried out on the instrumental catalogue of theIstituto Nazionale di Geofisica (ING), covering theperiod from January 1975 to March 1998. In apreliminary phase, the catalogue was declustered usingthe Reasenberg algorithm. After that, eventualmagnitude shifts due to variations in the modalitiesof observation have been individuated and corrected.The subsequent analysis, carried out making use of theZmap software package, has put in evidence thatthe sequence of September 1997 was preceded bya 2.5 year period characterised by absence of eventsof magnitude larger than 3.2, in an area approximately20 × 40 km wide, including the epicentre of themain shock. The statistical methodology shows thatonly 1/10³ of the space-time volumes analysed inthis study, exhibited quiescence of the same level.The study of seismicity rate change correlated toprevious main shocks in a larger area of CentralApennines shows that none of them were preceded by aseismic quiescence, specially close to the epicentreof the main shock, and lasting until the time ofoccurrence of the main shock as in the 1997 case.Actually, we found other patterns of precursoryquiescence with different time or space distribution.We conclude that precursory quiescence is a realfeature of Central Apennines seismicity, but it isdifficult to define a simple hypothesis, which appliesto the generality of cases and can be tested beforeimplementation in a system of earthquake riskmitigation.     

试用累积求和方法研究地震活动平静现象及大震概率预报

以表征区域地震活动强度背景的震级期望值作为单个地震事件的目标值,利用震级累积和C值随时间的变化分析地震活动相对平静现象,并给出其显著性检验. 文中还定量分析了平静异常与大震的关系,提出了利用核函数对大震发生时间进行概率外推的方法. 用上述方法对华北区的山西、张家口-渤海地震带的部分地区及新疆区域进行计算,显示该方法能够描述地震活动平静现象,并可合理地对未来大震发生时间进行概率外推估计.     

Distribution of Seismicity Before the Larger Earthquakes in Italy in the Time Interval 1994–2004

The Region–Time–Length (RTL) algorithm has been applied to different instrumental catalogues to detect seismic quiescence before medium-to-large earthquakes in Italy in the last two decades. RTL performances are sensitive to the choice of spatial and temporal parameters. The method for automatic parameters selection developed by Chen and Wu has been applied to twelve Italian earthquakes with magnitude greater than 5. The limits of the method in constructing maps of seismic quiescence before the earthquake are demonstrated, and a simple improvement is proposed. Then a new technique, namely RTL_surv, is proposed for routine surveys of the Italian seismicity. RTL_surv has been applied to all the earthquakes with magnitude greater than 4 in the Italian area in the time interval 1994–2004; four different sub-areas have been identified, with different characteristics in the level of recorded seismicity. One subarea—Tyrrhenian Sea—was characterized by a too low level of recorded seismicity for the application of the method. In the other three subareas a seismic quiescence was detected before at least the 66% of the earthquakes with magnitude greater or equal to 4 and all the earthquakes with magnitude greater than 5.     

Conditional Probabilities for Large Events Estimated by Small Earthquake Rate

We examined forecasting quiescence and activation models to obtain the conditional probability that a large earthquake will occur in a specific time period on different scales in Taiwan. The basic idea of the quiescence and activation models is to use earthquakes that have magnitudes larger than the completeness magnitude to compute the expected properties of large earthquakes. We calculated the probability time series for the whole Taiwan region and for three subareas of Taiwan—the western, eastern, and northeastern Taiwan regions—using 40 years of data from the Central Weather Bureau catalog. In the probability time series for the eastern and northeastern Taiwan regions, a high probability value is usually yielded in cluster events such as events with foreshocks and events that all occur in a short time period. In addition to the time series, we produced probability maps by calculating the conditional probability for every grid point at the time just before a large earthquake. The probability maps show that high probability values are yielded around the epicenter before a large earthquake. The receiver operating characteristic (ROC) curves of the probability maps demonstrate that the probability maps are not random forecasts, but also suggest that lowering the magnitude of a forecasted large earthquake may not improve the forecast method itself. From both the probability time series and probability maps, it can be observed that the probability obtained from the quiescence model increases before a large earthquake and the probability obtained from the activation model increases as the large earthquakes occur. The results lead us to conclude that the quiescence model has better forecast potential than the activation model.     

四川九寨沟7.0级地震中长期预测的回顾认识

回顾了2013年郭增建提出的基于地震活动性的"静中动"和后期与作者共同发展的"准静中动"方法,以1987年1月8日在甘肃南部迭部县发生的5.9级地震作为标志性的"准静中动"地震,结合国家地震局在1989年综合划定的1990—2000年南北地震带10年地震危险区,用中长期预测的时间尺度,指出了南北地震带北段三个未来可能发生6~7级地震的地区,其中一个就是四川省九寨沟地区。回顾分析中对"静中动"方法预测效能、存在的问题及一些中长期预测的问题进行讨论,得到两点认识:一是通过这次地震的再次验证,证明"静中动"方法是一种可行的预测地震的独立指标方法,在验证的基础上对该方法进行了优化认识;二是基于"静中动"方法与南北地震带北段10年地震危险区对应地震较为准确的启发,初步认为前兆可以划分为平静期的前兆与活跃期的前兆,而前者可能对于地震的预测意义更大,未来可以沿这一思路开展进一步的论证和研究。     

华东地区大震前的地震平静及发震模式研究

Wyss 等人的地震平静理论是一种较系统的、目前较为广泛认同的平静理论。根据该平静理论, 以累计频度定量计算方法对华东地区( 苏、鲁、沪、皖, 黄海) 1970 年以来大震前的平静现象进行了研究, 并对该地区MS ≥5.5 地震的发震模式进行了探讨。结果表明, 多数震例在震前出现了平静异常, 平静异常大多出现在震前半年至一年内, 发震模式形式多样, 说明了震源区及其邻近断层结构的不均匀和复杂程度的差异。     

Precursory seismicity of the 1994 eruption of Popocatépetl Volcano,Central Mexico

Popocatépetl Volcano is located in the central Mexican Volcanic Belt, within a densely populated region inhabited by over 20 million people. The eruptive history of this volcano indicates that it is capable of producing a wide range of eruptions, including Plinian events. After nearly 70 years of quiescence, Popocatépetl reawakened in December 21, 1994. The eruptive activity has continued up until the date of this submission and has been characterized by a succession of lava dome growth-and-destruction episodes, similar to events that have apparently been typical for Popocatépetl since the fourteenth century. In this regime, the episodes of effusive and moderately explosive activity alternate with long periods of almost total quiescence. In this paper we analyze five years of volcano-tectonic seismicity preceding the initial eruption of the current episode. The evolution of the V-T seismicity shows four distinct stages, which we interpret in terms of the internal processes which precede an eruption after a long period of quiescence. The thermal effects of a magma intrusion at depth, the fracturing related to the slow development of magma-related fluid pathways, the concentration of stress causing a protracted acceleration of this process, and a final relaxation or redistribution of the stress shortly before the initial eruption are reflected in the rates of V-T seismic energy release. A hindsight analysis of this activity shows that the acceleration of the seismicity in the third stage asymptotically forecast the time of the eruption. The total seismic energy release needed to produce an eruption after a long period of quiescence is related to the volume of rock that must be fractured so imposing a characteristic threshold limit for polygenetic volcanoes, limit that was reached by Popocatépetl before the eruption.     

On low period sub-oceanic Rayleigh waves and their attenuation

Summary In most cases it is found that Rayleigh waves in the period range I to 12 secs fail to cross appreciable oceanic paths. Several explanations have been given, but none seem very much satisfactory. Here an attempt has been made to show that the attenuation of the Rayleigh waves in the low period range is due to their passage through a non-uniform earth's crust, the non-uniformity arising due to the ocean. The ocean has been taken to be an indentation in a flat earth's crust, with horizontal bottom and slant sides. Approximate numerical calculations hint that the vertical component of displacement is attenuated more than the horizontal component.     

A sequence of seismic activity in the Kanto area precursory to the 1923 Kanto earthquake

The Kanto earthquake (M=7.9) that occurred along the Sagami Trough in the Sagami Bay on 1 September 1923 was one of the most disastrous earthquakes in Japanese history. The Kanto area includes Metropolitan Tokyo and Yokohama which are densely populated, and hence it has been a matter of great concern, from the viewpoints of earthquake prediction and disaster prevention, whether or not the 1923 Kanto earthquake was preceded by precursory seismicity. A study using the most complete lists of earthquakes catalogued recently by Utsu and the Japan Meteorological Agency reveals that seismic activity in the Kanto area was appreciably higher before and after the Kanto earthquake, and that the Kanto earthquake was preceded by a sequence of anomalous seismic activity, quiescence, and foreshocks. Such higher activity before and after the Kanto earthquake is contrasted with low seismicity during the recent 30-year period. A model is proposed to explain the precursory seismic activity, subsequent quiescence, and foreshocks for the Kanto earthquake. In the model, the transition from precursory seismic activity to quiescence is ascribed to time-dependent fracture due to stress-aided corrosion. Foreshocks are related to an acceleration of premonitory slip shortly before the mainshock slip.     

Second round of evaluations of proposed earthquake precursors

This review summarizes the result of the second round of nominations for the IASPEI Preliminary List of Significant Precursors. Currently this List contains five cases of precursors: (1) foreshocks, (2) preshocks, (3) seismic quiescence before major aftershocks, (4) radon decrease in ground water, and (5) ground water level increase. A list of four cases that could not be accepted nor rejected by the panels reviewing them contains three on crustal deformations and one on seismic quiescence. In the second round 10 nominations were evaluated, nine new ones and one which had been considered previously. Two were accepted for the List, two were placed in the category of undecided cases. To date, a total of 40 nominations have been evaluated by IASPEI. For 37 of these the nominations, the mail reviews, the panel opinions, and, where supplied, the author's reply were published. This evaluation process remains active throughout the International Decade for Natural Hazards Reduction. Additional nominations are invited.The IASPEI Sub-commission on Earthquake Prediction does not guarantee that precursors accepted for the List can be used for earthquake prediction, nor does rejection of a nomination mean that the particular method could never become useful for prediction. However, the List, as well as the interchanges between authors and reviewers, allow us to gauge the state-of-the-art in earthquake prediction research. It is clear that we do not have an earthquake prediction capability, because the manner in which to use the few precursors on the List for predictions is not known. It also appears that many of the results thought to be conclusive by the authors, may not command the respect of the seismological research community at large. A more quantitative approach to data analysis, the use of rigorous statistical techniques, and high quality, long-term data sets are needed to make progress in earthquake prediction research.     

Estimation of periodicities in hydrologic data

Periodicites in hydrologic data are frequently estimated and studied. In some cases the periodic components are subtracted from the data to obtain the stochastic components. In other cases the physical reasons for the occurrence of these periodicities are investigated. Apart from the annual cycle in the hydrologic data, periods corresponding to the 11 year sunspot cycle, the Hale cycle and others have been detected.The conclusions from most of these studies depend on the reliability and robustness of the methods used to detect these periodicities. Several spectral analysis methods have been proposed to investigate periodicities in time series data. Several of these have been compared to each other. The methods by Siddiqui and Wang and by Damsleth and Spjotvoll, which are stepwise procedures of spectrum estimation, have not been evaluated.Two of the methods of spectral analysis proposed by Siddiqui and Wang and by Damsleth and Spjotvoll are investigated in this study by using generated and observed data. Siddiqui and Wang's method is found to be superior to the Damsleth and Spjotvoll's method.     

Mechanisms of seismic quiescences

In the past decade there have been major advances in understanding the seismic cycle in terms of the recognition of characteristic patterns of seismicity over the entire tectonic loading cycle. The most distinctive types of patterns are seismic quiescences, of which three types can be recognized:post-seismic quiescence, which occurs in the region of the rupture zone of an earthquake and persists for a substantial fraction of the recurrence time following the earthquake,intermediate-term quiescences, which appear over a similar region and persist for several years prior to large plate-rupturing earthquakes, andshort-term quiescences, which are pronounced lulls in premonitory swarms that occur in the hypocentral region hours or days before an earthquake. Although the frequency with which intermediate-term and short-term quiescences precede earthquakes is not known, and the statistical significance of some of the former has been challenged, there is a need, if this phenomena is to be considered a possibly real precursor, to consider physical mechanisms that may be responsible for them.The characteristic features of these quiescences are reviewed, and possible mechanisms for their cause are discussed. Post-seismic quiescence can be readily explained by any simple model of the tectonic loading cycle as due to the regional effect of the stress-drop of the previous principal earthquake. The other types of quiescence require significant modification to any such simple model. Of the possibilities considered, only two seem viable in predicting the observed phenomena, dilatancy hardening and slip weakening. Intermediate-term quiescences typically occur over a region equal to or several times the size of the rupture zone of the later earthquake and exhibit a relationship between the quiescence duration and size of the earthquake: they thus involve regional hardening or stress relaxation and agree with the predictions of the dilatancy-diffusion theory. Short-term quiescences, on the other hand, are more likely explained by fault zone dilatancy hardening and/or slip weakening within a small nucleation zone. Because seismicity is a locally relaxing process, seismicity should follow a behaviour known in rock mechanics as the Kaiser effect, in which only a very slight increase in strength, due to dilatancy hardening or decrease in stress due to slip weakening, is required to cause quiescence. This is in contrast to other precursory phenomena predicted by dilatancy, which require large dilatant strains and complete dilatancy hardening.Lamont-Doherty Geological Observatory