Test of the EEPAS Forecasting Model on the Japan Earthquake Catalogue

The EEPAS (Every Earthquake a Precursor According to Scale) model is a method of forecasting earthquakes based on the notion that the precursory scale increase () phenomenon occurs at all scales in the seismogenic process. The rate density of future earthquake occurrence is computed directly from past earthquakes in the catalogue. The EEPAS model has previously been fitted to the New Zealand earthquake catalogue and successfully tested on the California catalogue.Here we describe a further test of the EEPAS model in the Japan region spanning 1965–2001, initially on earthquakes with magnitudes exceeding the threshold value 6.75. A baseline model and the Gutenberg-Richter b-value were fitted to the JMA catalogue over the learning period 1926–1964. The performance of EEPAS, with the key parameters unchanged from the New Zealand values, was compared with that of the baseline model over the testing period, using a likelihood ratio criterion. The EEPAS model proved superior. A sensitivity analysis shows that this result is not sensitive to the choice of the learning period or b-value, but that the advantage of EEPAS over the baseline model diminishes as the magnitude threshold is lowered. When key model parameters are optimised for the Japan catalogue, the advantage of EEPAS over the baseline model is consistent for all magnitudes above 6.25, although less than in the New Zealand and California regions.These results add strength to the proposition that the EEPAS model is effective at a variety of scales and in a variety of seismically active regions.     

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.     

西南地区前兆震群以及显著地震与区域强震的时空特征

本文系统清理并分析了西南划分的五个预报区[1]中的强震发生前的前兆震群和显著性地震特征。在西南划分的五个预报区中,各区域的前兆震群和显著地震存在共性特征,但又具有明显的区域个性。从共性特征上看,西南划分的五个预报区的前兆震群和显著性地震发生后1-2年可能发生强震,强震一般发生在前兆震群或显著性地震附近地区或相关联构造带上;川滇往往是块体内部构造较复杂的区域,发生的强震会有前兆震群或显著性地震发生。从个性特征上看,西南划分的五个预报区的前兆震群和显著性地震发生与西南地区的地震地质构造具有一定关系,也就是说特殊的构造使得各区域的前兆震群和显著性地震具有明显的个性特征。     

1997年青海省震群活动的某些特征

对青海省１９９６年１２月～１９９７年７月发生的４起震群活动的特征进行了研究,对其空间分布图象进行了分析．结果表明,锡铁山震群和大武震群为前兆性震群,龙羊峡震群和茫崖震群为非前兆震群．４起震群在总体上形成ＮＷ向条带．根据震群的总体特点及地震空区等,讨论了青海省近期地震活动趋势     

震群活动的一种可能的触发机制

分析了1975年2月4目辽宁海城地震后的熊岳、1976年4月6日内蒙和林格尔地震后的凉城、以及1976年7月28日唐山大震后的宝坻等震群活动的时空分布特点.由位错模式计算了大地震在相应地区产生的附加应力(张应力)的大小(3——6巴),它和由这些震群中的小地震计算的应力降的大小相当.附加的张性应力相当于减小围压.根据不同应力途径的三轴压缩实验以及原地庄水诱发地震的试验结果指出,上述量级的应力变化可以在地壳浅处应力水平已经很高的地区触发地震活动.考虑到地下流体的扩散特性及其作用,初步解释了震群活动的高潮滞后大地震的观测事实,从而引出了大地震对其附近的震群活动的一种可能的触发机制.      

前兆震群和S波偏振

海城地震前的小震群活动构成了显著的前兆震群, 并在预报这次地震中起到了一定的作用.其他许多中国的大地震象海城地震一样, 也有类似的前兆震群.我们利用 S 波资料研究这些前兆震群的初步结果表明, 它们的 S 波偏振性质是相当稳定的.      

震群活动和地震预报综述

研究震群和大地震的关系、用前兆震群预报未来地震的发生,是世界范围内比较活跃的课题之一。文章例举了震群的一些指标以说明前兆性震群的预报意义,并从大范围的众多震群活动阐述大震前震群活动的一些特征。根据震群的分布可确定未来大震的发生地点,并解释不同类型震群的力学成因。     

Earthquake swarms and volcanism in New Zealand

The term « swarm » is used to describe a group of related earthquakes, concentrated in space and time, without an obvious principal event. Large shallow earthquakes are often followed by aftershocks, but the pattern in which aftershocks occur differs in detail from that of a swarm. Sequences of New Zealand earthquakes that have been called swarms differ markedly from one another. The most vigorous of them, near Taupo in 1922, appears to have been an ordinary tectonic earthquake accompanied by foreshocks and aftershocks, and by surface faulting. No fault movements accompanied the 1964 swarm in the same area. Other localities that have experienced swarms include Great Barrier Island, Matamata, Kawerau, and Opunake. Swarms are considered by some writers to be characteristic of volcanic regions. Although all New Zealand swarms have occurred in areas of Quaternary volcanism, there are still no observations showing what part, if any, volcanism plays in the generation of earthquake swarms.     

浙江珊溪水库地震：震源参数测定及断层结构和应力状态描述

利用遗传算法,搜索符合Brune ω^2模型的拐角频率（fc）及零频幅值（Ωc）的最佳值,测定浙江珊溪水库震区88条小震（1．5≤ML≤4．6）的地震矩（M0）、震源尺度（r）及静态应力降（△σ）。地震矩M0在10^10～10^14N·m范围内,与拐角频率fc遵循Mo∝fc^-3的规律;震源尺度和地震矩、应力降之间呈现多重标度特征,地震矩大于临界值2．3×10^12N·m（相应的震源尺度特征值约160m）时,震源尺度与地震矩的关系较强;而应力降（△σ）在震源尺度大于160m后基本趋向恒定,不随震源尺度的增大而增大。浙江珊溪水库震区自2002年7月以来,经历2次大规模的震群活动。震群释放的应力降大小与该震群的规模成正比关系,大的应力降集中在发震断层中段5～6km深度的区域,其发生时间既可以在主震之前,也可以在主震之后。     

由震群信息熵分析山东及沿海地区的地震危险性

本文利用震群信息熵概念,通过对山东及沿海地区16次震群的分析、研究,初步探讨了震群信息熵在该区地震中期预报中的应用及未来地震的危险性。同时,应用震群综合指标对1976年春在长岛发生的两次震群进行了分析研究。结果表明:1976年春在长岛附近发生的黑山、砣矶震群均为前兆震群。两个前兆震群所对应的大震是相隔4、5个月之后的1976年7月28日河北唐山7.8级地震。     

三种震群活动

震群是一种地震序列,在地震活动性问题研究中占有重要地位,具有特殊意义。文章讨论了三种震群：小震群、中强震群和强烈震群的地区分布特征及其前兆意义,并提供三种震群的世界分布图。     

2008年汶川8.0级地震对地震预测研究的启示思考

2008年汶川8.0级地震已经过去10年, 在此期间关于地震预测相关的基础研究和实践工作从未停止, 本文作者从地震预测业务人员角度, 分析了2008年汶川8.0级地震相关的地震地质、 大地测量、 地震学、 前兆观测异常等方面的现象。 针对不同研究方向, 从震情跟踪角度提出了预测意义的讨论、 可能问题的分析、 不成熟的一些建议, 并就综合预测给出了一些粗浅的思考和认识, 期望对地震预测预报工作起到抛砖引玉的作用。     

The precursory earthquake swarm

Prior swarms near the sites of eleven moderate to large earthquakes from diverse tectonic settings in the New Zealand and California regions yield regressions for the estimation of magnitude and time of occurrence, and thus offer a possible basis for long-range forecasting.     

江苏及邻区震群活动特征分析

系统地整理研究了江苏及其邻近地区36次小震群活动,总结了震群活动的参数特征,探讨了震群活动与大震的关系,分析检验了前兆震群类型的判定指标.江苏地区震群活动分布集中,强度以ML2.0～3.9地震为主,震群序列总频次在30次以下居多,持续时间在15天以内的震群占总数的55％;震群序列中地震总频次和震群持续时间与震群的最大震级之间不成正比;研究区78％震群发生后对应M4.6以上中强地震,其中500km范围内时间间隔在1年内的占对应地震总数的57％,具有一定的中短期地震预测指示意义;震群与未来中强地震的距离较为离散,但尚无在原地发生大地震的震例.震群强度大小与未来中强地震的对应率高低和对应的地震强度大小没有明显的相关关系,震群频次的多少与其后发生地震的对应率高低也没有明显的相关关系.采用U-p组合或者全组合判定震群类型的效果相对较好,检验正确率约占总数的50％,但总体而言效果并不十分有效,需要参考其它方法和手段综合判定.     

Structural Preconditions of West Bohemia Earthquake Swarms

The West Bohemia and adjacent Vogtland are well known for quasi-periodical earthquake swarms persisting for centuries. The seismogenic area near Nový Kostel involved about 90 % of overall earthquake activity clustered here in space and time. The latest major earthquake swarm took place in August–September 2011. In 1994 and 1997, two minor earthquake swarms appeared in another location, near Lazy. Recently, the depth-recursive tomography yielded a velocity image with an improved resolution along the CEL09 refraction profile passing between these swarm areas. The resolution, achieved in the velocity image and its agreement with the inverse gravity modeling along the collateral 9HR reflection profile, enabled us to reveal the key structural background of these West Bohemia earthquake swarms. The CEL09 velocity image detected two deeply rooted high-velocity bodies adjacent to the Nový Kostel and Lazy focal zones. They correspond to two Variscan mafic intrusions influenced by the SE inclined slab of Saxothuringian crust that subducted beneath the Teplá-Barrandian terrane in the Devonian era. In their uppermost SE inclined parts, they roof both focal zones. The high P-wave velocities of 6,100–6,200 m/s, detected in both roofing caps, indicate their relative compactness and impermeability. The focal domains themselves are located in the almost gradient-free zones with the swarm foci spread near the axial planes of profound velocity depressions. The lower velocities of 5,950–6,050 m/s, observed in the upper parts of focal zones, are indicative of less compact rock complexes corrugated and tectonically disturbed by the SE bordering magma ascents. The high-velocity/high-density caps obviously seal the swarm focal domains because almost no magmatic fluids of mantle origin occur in the Nový Kostel and Lazy seismogenic areas of the West Bohemia/Vogtland territory, otherwise rich in the mantle-derived fluids. This supports the hypothesis of the fluid triggering of earthquake swarms. The sealed focal domains retain ascending magmatic fluids until their critical pressure and volumes accumulated cause rock micro-fractures perceived as single earthquake bursts. During a swarm period, the focal depths of these sequential events become shallower while their magnitudes grow. We assume that coalescence of the induced micro-fractures forms temporary permeability zones in the final swarm phase and the accumulated fluids release into the overburden via the adjacent fault systems. The fluid release usually occurs after the shallowest events with the strongest magnitudes M_L > 3. The seasonal summer declines of hydrostatic pressure in the Cheb Basin aquifer system seem to facilitate and trigger the fluid escape as happened for the 2000, 2008, and 2011 earthquake swarms. The temporary fluid release, known as the valve-fault action, influences the surface aquifer systems in various manners. In particular, we found three quantities, the strain, mantle-derived ³He content in CO₂ surface sources and ground water levels, which display a 3–5 months decline before and then a similar restoration after each peak earthquake during the swarm activities. The revealed structure features are particularly important since the main Nový Kostel earthquake swarm area is proposed as a site for the ICDP project, ‘Eger Rift Drilling’.     

Demarcation and Scaling of Long-term Seismogenesis

A space-time envelope of minor seismicity related to major shallow earthquakes is identified from observations of the long-term Precursory Scale Increase () phenomenon, which quantifies the three-stage faulting model of seismogenesis. The envelope, which includes the source area of the major earthquake, is here demarcated for 47 earthquakes from four regions, with tectonic regimes ranging from subduction to continental collision and continental transform. The earthquakes range in magnitude from 5.8 to 8.2, and include the 24 most recent mainshocks of magnitude 6.4 and larger in the San Andreas system of California, the Hellenic Arc region of Greece, and the New Zealand region, together with the six most recent mainshocks of magnitude 7.4 and larger in the Pacific Arc region of Japan. Also included are the destructive earthquakes that occurred at Kobe, Japan (1995, magnitude 7.2), Izmit, Turkey (1999, magnitude 7.4), and W.Tottori, Japan (2000, magnitude 7.3). The space (A _P ) in the space-time envelope is optimised with respect to the scale increase, while the time (T _P ) is the interval between the onset of the scale increase and the occurrence of the earthquake. A strong correlation is found between the envelope A _P T _P and the magnitude of the earthquake; hence the conclusion that the set of precursory earthquakes contained in the envelope is intrinsic to the seismogenic process. Yet A _P and T _P are correlated only weakly with each other, suggesting that A _P is affected by differences in statical conditions, such as geological structure and lithology, and T _P by differences in dynamical conditions, such as plate velocity. Among other scaling relations, predictive regressions are found between, on the one hand, the magnitude level of the precursory seismicity, and on the other hand, both T _P and the major earthquake magnitude. Hence the method, as here applied to retrospective analysis, is potentially adaptable to long-range forecasting of the place, time and magnitude of major earthquakes.     

辽宁地区震群序列特征及其性质判定方法的研究

本文在以往研究震群性质及其预测方法的基础上，从统计的角度出发，结合“八五”和“九五”地震预报攻关成果中有关震群序列参数的分析方法，对1974年以来，在辽宁及其邻近地区发生的23个震群作了详细研究。根据这些震群时序分布的表象特征，将其分为四种类型：Ⅰ增强型；Ⅱ衰减型；Ⅲ增减型；Ⅳ双丛（峰）型。又根据这些震群参数及有关特征量的统计特征，经认真分析，给出了识别震群性质的标志和定量指标（其中有些是对老指标的修正），进而总结出了较适合辽宁地区的震群性质综合判定方法。同时，与以往判定震群性质的方法还作了比较研究，结果表明，本文方法较以往方法判定结果的质量、信度和科学性等方面都有所提高，因此，可作为辽宁地区中强震短临预报的参考依据。     

Tomographic determination of the upper crustal structure in the Jiashi strong earthquake swarm region

IntroductionBetween January and April of 1997, 7 earthquakes with M(6.0 occurred successively in Jiashi, Xinjiang. The continual occurrence of strong earthquakes within such a small area and in such a short period of time is exceptional for intraplate earthquakes. The Jiashi earthquake swarm took place on the northeast side of the Pamirs, where the Tarim basin, South Tianshan and West Karakoram meet (HU, et al, 1989). This is also a place where a number of active faults develop, so it is…     

Study on medium-short term earthquake forecast in Yunnan Province by precursory events

Introduction Yunnan is a very active region of earthquake in China. Since Yunnan Regional Seismological Network established in 1965, 37 years have past and thousands of seismic events have been recorded. Among them, 9 are great earthquakes of M7.0, more than 150 are moderately strong earthquakes of M =5.0~6.9 and about 6 000 are earthquakes of M3.0. Figure 1 shows the epicenter distribution of M3.5 earthquakes occurred in 1965~2002 in Yunnan region and Figure 2 the magnitude-frequency dis…