Testing time-predictable earthquake recurrence by direct measurement of strain accumulation and release

Probabilistic estimates of earthquake hazard use various models for the temporal distribution of earthquakes, including the 'time-predictable' recurrence model formulated by Shimazaki and Nakata (which incorporates the concept of elastic rebound described as early as 1910 by H. F. Reid). This model states that an earthquake occurs when the fault recovers the stress relieved in the most recent earthquake. Unlike time-independent models (for example, Poisson probability), the time-predictable model is thought to encompass some of the physics behind the earthquake cycle, in that earthquake probability increases with time. The time-predictable model is therefore often preferred when adequate data are available, and it is incorporated in hazard predictions for many earthquake-prone regions, including northern California, southern California, New Zealand and Japan. Here we show that the model fails in what should be an ideal locale for its application -- Parkfield, California. We estimate rigorous bounds on the predicted recurrence time of the magnitude approximately 6 1966 Parkfield earthquake through inversion of geodetic measurements and we show that, according to the time-predictable model, another earthquake should have occurred by 1987. The model's poor performance in a relatively simple tectonic setting does not bode well for its successful application to the many areas of the world characterized by complex fault interactions.     

Progress of research on anomalies of astronomical time and latitude observations before earthquake

This paper introduces the discovery of the phenomenon that short-term anomalous fluctuations appeared in residuals of astronomical time and latitude observations before earthquakes and the progress of related researches carried out for many years.The relations between the anomalous variations of time and latitude residuals of astronomical time and latitude instruments in different regions and the earthquakes around these instruments as well as the characteristics of residuals’ anomalous variations are analyzed.The significance of the anomalous fluctuations in residuals of astronomical time and latitude caused by the anomalous variations of the local plumb line before earthquake and detecting the vertical variation with astronomical time and latitude observations as well as the importance of carrying out further researches are discoursed.The possibility that the phenomenon will become an effective short-term earthquakes precursor,the current situations and the problems to be solved,are discussed.Also we offer the proposals to develop new roboticized astrometric instruments with high-precision and set up test observation networks in earthquake-prone areas in order to do research in-depth,optimize methods of observing and extracting anomalous information for short-term earthquake prediction,and so on.     

Earth science: microseismicity data forecast rupture area

On 28 September 2004 there was an earthquake of magnitude 6.0 at Parkfield, California. Here we show that the size distribution of the micro-earthquakes recorded in the decades before the main shock occurred allowed an accurate forecast of its eventual rupture area. Applying this approach to other well monitored faults should improve earthquake hazard assessment in future.     

Migration of seismic scatterers associated with the 1993 Parkfield aseismic transient event

The time-varying deformation field within a fault zone, particularly at depths where earthquakes occur, is important for understanding fault behaviour and its relation to earthquake occurrence. But detection of this temporal variation has been extremely difficult, although laboratory studies have long suggested that certain structural changes, such as the properties of crustal fractures, should be seismically detectable. Here we present evidence that such structural changes are indeed observable. In particular, we find a systematic temporal variation in the seismograms of repeat microearthquakes that occurred on the Parkfield segment of the San Andreas fault over the decade 1987-97. Our analysis reveals a change of the order of 10 m in the location of scatterers which plausibly lie within the fault zone at a depth of approximately 3 km. The motion of the scatterers is coincident, in space and time, with the onset of a well documented aseismic transient (deformation event). We speculate that this structural change is the result of a stress-induced redistribution of fluids in fluid-filled fractures caused by the transient event.     

云南省姚安县地震前天体引潮力和NCEP的异常现象

本文采用天体引潮力对地震诱发作用计算模型和NCEP数据提取异常增温信息,分析2009.7.9发生在我国云南省楚雄彝族自治州姚安县Ms6.0级地震。分析表明：NCEP异常增温图像可以较好的反映地震构造活动时空演变过程,并且天体引潮力对地应力处于临界状态的活动断层具有明显的诱发作用。两者的相互结合分析对于地震的预报具有指导作用。     

气象奇点与云南最大震级预报研究

根据地震活动与气象要素之间的密切关系,采用大量气象资料选取预报因子,将气象统计理论应用于地震预报,开创了地震预报的数值预报新方法,并对中国云南5个地震分区,分上下半年做出了最大震级预报,其置信度达到特别显著水平。这对提高地震预报水平将具有深远意义。     

Abnormally large short term and impending earthquake geomagnetic anomaly implies a possibility of earthquake pre warning

The study found that strong magnetic anomalies repeatedly took place before big earthquakes. Based on geomagnetic record analysis results,we discussed a possible pattern of the magnetic anomalies prior to earthquake. In meizoseismal area or epicenter,in a time period of 36 h to about 10 min before earthquake,the exceptional big geomagnetic change increases with the magnitude of earthquake. We calculated that,in a place of 1 km from the epicenter,the magnetic anomaly before destructive earthquakes of Ms 6～9 can reach to 102～104 nT(the magnitude of earth magnetic field is 104 nT) ,rather than the magnitude of 10 nT from seismomagnetic effect theories since 1960s. From this we speculated the abnormal magnetic ULF near epicenter before earthquake seems to be an "intermittent magnetic eruption". Accordingly,we proposed that geomagnetic induction earthquake alarm can be a new pre-warning method to surmount hardship in solving the puzzledom of earthquake imminent prediction.     

地震预报现状与水平—由澜沧耿马地震谈起

云南是个多地震地区,70年代以来,继通海、昭通、龙陵大震后,又发生了澜沧耿马大震。历次大震给云南各族人民的生命和财产带来了重大损失。因此,人们越来越关心地震预报工作。本文通过到灾区实地考察所得到的资料,并就目前地震预报概况,对澜沧耿马地震为什么没能作出准确的临短预报作一较祥细的介绍。     

Study on seismogenesis of the 1997 Jiashi earthquake swarm, western China

The 1997 Jiashi swarm earthquakes are relocated using the master event method improved by the authors. From the relocated hypocenters and focal mechanisms of the earthquakes, it is inferred that a pair of echelon faults, striking in northern north-west direction, right-step allocated and right-laterally moved, may exist in the earthquake swarm region. The composite focal mechanism obtained by analyzing the data of 2177 P-wave first motion polarities indicates that both mean P- and T-axis are horizontal, orienting in N19°E and N110°E respectively, and the mean B-axis is nearly vertical. The co-seismic deformation caused by this earthquake swarm is compressive nearly in North-South and extensional nearly in East-West. Obviously low earthquake stress drops are found via analyzing the source spectra of the swarm earthquakes, which may be one of the main reasons why the Jiashi earthquake swarm has lasted for a long period of time. The interaction between discontinuous segments of the echelon fault has been discussed. The result indicates that the stress drop is usually low for the earthquakes occurring on the right step echelon faults.     

人工神经网络在地震分析预报中的应用

为了探索人工神经网络应用于地震分析预报的可能性,以福建及其周边地区地震活动为例,采用ｂ值、地震频次、地震能量释放、空间集中度４项地震活动性指标作为神经网络的输入,用具有Ｓ－型特性函数的ＢＰ网络对由每年地震的活动指标组成的标准样本进行训练,由训练结束后的权值和阈值及待预报样本的因子测值计算出网络输出值,作为地震活动性的预测．结果表明,用神经网络可以在一定精度范围内使震级预报的内检符合率达１００％,在例子中,外推预报准确率达８８％以上．     

Earthquake slip on oceanic transform faults

Oceanic transform faults are one of the main types of plate boundary, but the manner in which they slip remains poorly understood. Early studies suggested that relatively slow earthquake rupture might be common; moreover, it has been reported that very slow slip precedes some oceanic transform earthquakes, including the 1994 Romanche earthquake. The presence of such detectable precursors would have obvious implications for earthquake prediction. Here we model broadband seismograms of body waves to obtain well-resolved depths and rupture mechanisms for 14 earthquakes on the Romanche and Chain transform faults in the equatorial Atlantic Ocean. We found that earthquakes on the longer Romanche transform are systematically deeper than those on the neighbouring Chain transform. These depths indicate that the maximum depth of brittle failure is at a temperature of approximately 600 degrees C in oceanic lithosphere. We find that the body waves from the Romanche 1994 earthquake can be well modelled with relatively deep slip on a single fault, and we use the mechanism and depth of this earthquake to recalculate its source spectrum. The previously reported slow precursor can be explained as an artefact of uncertainties in the assumed model parameters.     

The potential for giant tsunamigenic earthquakes in the northern Bay of Bengal

The great Sumatra-Andaman earthquake and Indian Ocean tsunami of 2004 came as a surprise to most of the earth science community. Although it is now widely recognized that the risk of another giant earthquake is high off central Sumatra, just east of the 2004 earthquake, there seems to be relatively little concern about the subduction zone to the north, in the northern Bay of Bengal along the coast of Myanmar. Here I show that similar indicators suggest a high potential for giant earthquakes along the coast of Myanmar. These indicators include the tectonic environment, which is similar to other subduction zones that experience giant megathrust earthquakes, stress and crustal strain observations, which indicate that the seismogenic zone is locked, and historical earthquake activity, which indicates that giant tsunamigenic earthquakes have occurred there in the past. These are all consistent with active subduction in the Myanmar subduction zone and I suggest that the seismogenic zone extends beneath the Bengal Fan. I conclude therefore that giant earthquakes probably occur off the coast of Myanmar, and that a large and vulnerable population is thereby exposed to a significant earthquake and tsunami hazard.     

Real-time forecasts of tomorrow's earthquakes in California

Despite a lack of reliable deterministic earthquake precursors, seismologists have significant predictive information about earthquake activity from an increasingly accurate understanding of the clustering properties of earthquakes. In the past 15 years, time-dependent earthquake probabilities based on a generic short-term clustering model have been made publicly available in near-real time during major earthquake sequences. These forecasts describe the probability and number of events that are, on average, likely to occur following a mainshock of a given magnitude, but are not tailored to the particular sequence at hand and contain no information about the likely locations of the aftershocks. Our model builds upon the basic principles of this generic forecast model in two ways: it recasts the forecast in terms of the probability of strong ground shaking, and it combines an existing time-independent earthquake occurrence model based on fault data and historical earthquakes with increasingly complex models describing the local time-dependent earthquake clustering. The result is a time-dependent map showing the probability of strong shaking anywhere in California within the next 24 hours. The seismic hazard modelling approach we describe provides a better understanding of time-dependent earthquake hazard, and increases its usefulness for the public, emergency planners and the media.     

卫星红外异常预测短临地震的系统研究Ⅱ——异常基本特征与预测基本思路

肯定了用卫星红外异常预测作短临地震新方法的可行性基础上,提出了地震主震前卫星红外异常与地面增温异常对应的规律,并发现有时震前出现线状云和“热通道”。总结了震兆红外异常的定性和半定量判据;红外异常预测地震的基本思路,并用它进行过多次较成功的预测。同时评述了10多年来该方法取得的试用效果。指出了尚存的问题和努力的方向。认为：该方法有广阔的开发应用前景,可望成为短临地震预报的新武器。     

基于经验公式的湖北省历史地震目录修订研究

本文通过对不同版本的历史地震目录的收集和整理,利用已掌握的历史地震资料,结合地震学、地震地质学等相关学科的研究成果,对湖北省历史地震进行了全面、系统地整理和修订。我们收集了湖北省区域内地震地质资料和1990年以来发生地震的现场考察资料,结合当地经济、地质和建筑特点对有感区域的地震烈度进行了重新判定,通过选取多个地区的地震烈度衰减关系,对烈度-震级的对应关系进行重新标定,并利用经验公式对地震目录中部分历史地震的震级、时间等参数进行了修订。本文最终提取并重新确定了15个遗漏的历史地震,另对3个历史地震做出地震参数的校改建议,研究结果对新的地震区划工作和历史地震研究有重要意义。     

《地震战线》与地震预报知识的普及

"文革"十年,中国大陆经历了新中国成立以后的第一个地震活跃期。为了减少地震造成的破坏,全国范围内开展了以"群测群防、专群结合"为特点的大规模地震预报工作。但是在科技水平还无法准确预报地震的情况下,如何开展地震预报,如何在大众中普及预报方法,成为这项工作面临的首要问题。在此背景下,《地震战线》应运而生。文章在分析了《地震战线》的创刊背景、出版经过和该刊的主要内容及其特点的基础上,探讨了"文革"期间《地震战线》在地震预报知识普及中的作用和特点。     

2018年四川兴文5.7级地震及西昌5.1级地震震前红外前兆异常追踪

本文回顾和分析了2018年12月16日四川兴文5.7级地震及10月31日西昌5.1级地震前热红外异常的发现和追踪过程,详细叙述了两次地震的亮温资料在震前表现出的同一区域性热异常,以及各个时段的不同表现特征;并根据表现特征对热异常的追踪过程划分出4个阶段,分别为识别阶段、预判定阶段、追踪和逼近阶段及验证阶段,各阶段所关注的异常形态及转折信号可为地震预判提供较为明确的指示信息。另外,本文还对该手段的预测效能和技术问题进行了简单的说明和讨论。     

Extent, duration and speed of the 2004 Sumatra-Andaman earthquake imaged by the Hi-Net array

The disastrous Sumatra-Andaman earthquake of 26 December 2004 was one of the largest ever recorded. The damage potential of such earthquakes depends on the extent and magnitude of fault slip. The first reliable moment magnitude estimate of 9.0 was obtained several hours after the Sumatra-Andaman earthquake, but more recent, longer-period, normal-mode analyses have indicated that it had a moment magnitude of 9.3, about 2.5 times larger. Here we introduce a method for directly imaging earthquake rupture that uses the first-arriving compressional wave and is potentially able to produce detailed images within 30 min of rupture initiation. We used the Hi-Net seismic array in Japan as an antenna to map the progression of slip by monitoring the direction of high-frequency radiation. We find that the rupture spread over the entire 1,300-km-long aftershock zone by propagating northward at roughly 2.8 km s(-1) for approximately 8 minutes. Comparisons with the aftershock areas of other great earthquakes indicate that the Sumatra-Andaman earthquake did indeed have a moment magnitude of approximately 9.3. Its rupture, in both duration and extent, is the longest ever recorded.     

历史时期宝鸡地区地震灾害的时空分布特征*

目的探讨分析历史时期宝鸡地震灾害的时空分布特征。方法通过对历史文献资料的搜集和整理,对101-2000年间宝鸡地区地震灾害的记录数据做了统计和分析。结果历史时期宝鸡地区地震灾害在时空分布上呈现出不甚均匀的特性。在时间方面,百年际变化呈现周期性的起伏变化,显示相对平静和显著活跃相互交替的特点;在空间方面,震灾的高发区主要集中在岐山、凤翔、陇县。统计显示宝鸡较大的震害大部分来自于邻近地区的波及震,震源在宝鸡地区的较大震害较少。结论近年来,随着南北地震带地震活动的增强,宝鸡地区受到邻区中强地震活动的波及影响也更加明显。因而该地区的地震区位分析和地震预测成为未来防震抗震的关键问题。     

Characters of variation of LURR during the earthquake sequence of Xinjiang

The theory of the loading/unloading response ratio (LURR) was applied to the Jiashi earthquake sequence which occurred at the beginning of 1997 in Xinjiang, and found that, before the earthquakes with relatively high magnitudes in the sequence, the ratio showed anomalies of high values. That is to say, the LURR theory can be applied to the short-term earthquake prediction in some cases, especially in the early period after a strong earthquake, such as the forecasts for some strong earthquakes in the Jiashi sequence.