震兆平静的再认识--海城地震30周年有感于经验性地震预报的议论

从对海城地震时期所关注的平静震兆的再认识中,阐明了经验性地震预报在探索地震预报从无到有的历程中所能发挥的作用。     

Effect of Aftershocks on Assessment of Seismic Hazard for Hebei Seismic Zone,China

In this paper,the earthquake hazard parameters(λm,b and Mmax) from the maximum likelihood method for the raw catalogue and declustered catalogues have been used to discuss the effect of the aftershocks on the earthquake hazard estimation.The declusterd catalogues have been compoiled from the raw catalogues by deleting the aftershocks in different time interval after main shock according to the criteria for the aftershock activity period.As an example,Hebei seismic zone is taken to show the effect of the aftershock on the earthquake hazard assessment because three strong earthquakes with the aftershocks occurred from 1966,to 1976,The results have been shown that the effect of the aftershocks on the parameters λm,b is significant.The difference between the clustered and declustered catalogues has reached in seismic activity rate and recurrence period,at most,45% and 90%,respectively,But the diffeence in Mmax is smaller,Based on this,the suggestion that the aftershocks should be omitted in the estimation of the earthquake hazard could be made,but how long the aftershocks activity duration is still left to the future research.     

Locating Small Aftershocks Using a Small-Aperture Temporary Seismic Array

In this paper, we developed a specialized method to locate small aftershocks using a small-aperture temporary seismic array. The array location technique uses the first P arrival times to determine the horizontal slowness vector of the incoming P wave, then combines it with S–P times to determine the event location. In order to reduce the influence of lateral velocity variation on the location determinations, we generated slowness corrections using events well-located by the permanent broadband network as calibration events, then we applied the corrections to the estimated slownesses. Applications of slowness corrections significantly improved event locations. This method can be a useful tool to locate events recorded by temporary fault-zone arrays in the near field but unlocated by the regional permanent seismic network. As a test, we first applied this method to 64 well-located aftershocks of the 1992 Landers, California, earthquake, recorded by both the Caltech/USGS Southern California Seismic Network and a small-aperture, temporary seismic array. The average horizontal and vertical separations between our locations and the well-determined catalogue locations are 1.35 and 1.75 km, respectively. We then applied this method to 132 unlocated aftershocks recorded only by the temporary seismic array. The locations show a clear tendency to follow the surface traces of the mainshock rupture.     

Statistical Research on the Seismic Quiescence Before the 1988 Lancang-Gengma Earthquakes with M=7.6 and 7.2 in Yunnan Province,China

In this paper,the temporal and spatial variation process of seismicity in areas from Lancang to Tengchong before the 1988 Lancang-Gengma earthquakes(M=7.6,7.2),January 1980 to October 1988,is studied in detail according to the theory that the whole process of earthquake sequence in the time stage of anomalous seismicity before a strong event may be considered as the non-homogeneous Poisson process.The results demonstrate that(1)from April 1985 to April 1988,there existed an obvious difference of seismicity in spatial distribution in the whole region; to the north of Lancang,there occurred two seismic quiescent belts:one is 210 km long for M≥3.5 events and anotheris 160 km long for M≥3.0 events; therefore,this may be classified into four sub-regions from south to north,that is,the south region,the mid-region,the mid'-region,and the north region.(2)Before the mainshocks,there existed anomalous seismic quiescence for as Song as 42 months in the mid-region(M≥3.5)and 32.5 months in the mid'-region(M≥3.0)     

考虑主余震作用的近海桥墩时变地震易损性分析

基于OpenSEES平台,以某近海刚构桥桥墩为例,选取符合场地类型的地震波,并根据地震记录构造主余震序列。运用"能力需求比"分析方法建立不同服役时间节点桥墩控制截面在不同损伤状态条件下的地震易损性曲线,研究氯离子侵蚀和主余震序列对桥墩抗震性能的影响。结果表明:同一损伤状态的超越概率随着服役时间延长和PGA增大而不断变大,且随着损伤状态等级提高,超越概率逐渐降低。轻微损伤状态下,主余震序列对桥墩易损性影响较小;中等损伤、严重破坏和完全倒塌状态下,同一服役期,考虑主余震序列作用下桥墩的超越概率相比于仅考虑主震作用明显增大。     

1988年云南澜沧－耿马大地震前地震活动平静的统计研究

本文根据大地震前包含异常活动时段的地震序列全过程可以看作是非齐次油松过程的理论，详细研究了１９８８年１１月澜沧－耿马大地震前（１９８０．１－１９８８．１０）澜沧到腾冲地区地震活动在时间和空间上的变化过程。结果表明：①１９８５年４月－１９８８年４月全区地震活动在空间上存在着明显的差异，其中澜沧向北延伸分别出现２１０ｋｍ的Ｍ≥３．５和１６０ｋｍ的Ｍ≥３．０的地震活动平静地段。因此，由南向北将全带划分为南区、中区、中′区、北区四个研究小区；②在包含主震和余震区的中区，主震前分别出现了持续时间长达４２个月（Ｍ≥３．５）和３２．５个月（中′区，Ｍ≥３．０）的异常地震活动平静，并在０．９９和０．９７的置信度水平上通过统计显著性检验；③与此同时，在南区却出现了长达４２个月（Ｍ≥３．５）的异常地震活动增强时段，其置信度可达０．９５。然而在北区，于１９８５年９月结束了长达５２个月的地震活动增强，置信度仅０．８５，显然它是受１９７６年龙陵地震余震活动的影响，因为该区正好包含龙陵地震的余震区。     

安宁河断裂的地震平静图像及其含义

区域地震活动图像,尤其是平静图像及其动态变化,一直是中长期地震预测研究的一个重要方面.我们曾注意到自1977年开始环绕川滇活动地块东边界的安宁河断裂出现了区域性的地震平静.     

南天山地震带地震平静与中强震关系再研究

地震活动的平静现象可分为4种:无震平静和震后平静可归于非前兆性平静;震前平静和场兆平静则可归于前兆性平静。本文分类统计了南天山地震带东、西段的地震平静现象,分析了平静特征及其与主震的关系。平静的层次性特点有助于判定未来震级和地点。     

Precursory Seismic Quiescence before the 1994 Kurile Earthquake (Mw = 8.3) Revealed by Three Independent Seismic Catalogs

—We have found that the M _w = 8.3 Kurile earthquake on October 4, 1994 followed an outstanding seismic quiescence starting 5–6 years before the mainshock near the ruptured area. We have analyzed three independent seismic catalogs Institute of Seismology and Volcanology, Hokkaido University (ISV), Japan Meteorological Agency (JMA) and International Seismology Center (ISC). In spite of selecting different magnitude bands and time windows all three catalogs presented the common feature of the seismic quiescence. This fact strongly suggests that the seismic quiescence should not be a man-made change but actually occurred. Moreover we have confirmed that the seismic quiescence was the most significant and the earthquake was the largest in the past twenty-five years in this region. Therefore we confidently interpret this seismic quiescence as an indication of a preparation process for the M _w = 8.3 Kurile earthquake.     

Possible Mechanism of Precursory Seismic Quiescence: Regional Stress Relaxation due to Preseismic Sliding

—We propose a new model to physically explain the seismic quiescence precursory to a large interplate earthquake. A numerical simulation is performed to quantitatively examine possible stress changes prior to a great interplate earthquake in a subduction zone. In the present study, the frictional force following a laboratory-derived friction law, in which the friction coefficient is dependent on slip rate and slip history, is assumed to act on a dip-slip fault plane of infinite width in a uniform elastic half-space. The values of friction parameters are determined so that the result of numerical simulation may explain some properties of great interplate earthquakes in subduction zones, such as the recurrence interval and the seismic coupling coefficient. The result of simulation reveals that significant quasi-stable sliding occurs prior to a great earthquake and, accordingly, stresses are changed on and around the plate boundary. In a relatively wide area of the overriding continental plate, the compres sional horizontal-stress perpendicular to the trench axis is decreased for a few years before the occurrence of a great earthquake. This decrease in regional compressional stress may account for the appearance of seismic quiescence prior to a great interplate earthquake.     

中强地震平静是汶川8.0级地震前最显著的地震活动异常

本文对四川地区1923年以来5.0级以上地震资料进行了分析研究。 结果表明, 研究区中强地震经历了4个较为完整的周期活动, 中强地震具有16年的准周期活动特征, 平静期持续5年左右, 从2008年汶川8.0级地震开始, 研究区将进入第5个活动周期, 其可能的持续时间为2024年前后。 2008年汶川8.0级地震前, 5.0～5.9级、 6.0～6.9级、 7.0～8.0级三个档次的地震事件的平静间隔均达到统计时段的历史之最, 三个档次地震的平静均被汶川8.0级地震直接打破, 中强地震超长平静是汶川8.0级地震前最为显著的异常现象。     

基于损伤性能并考虑主余震作用的消能减震结构抗震设计

综合考虑余震影响和结构损伤,提出一种基于损伤性能的消能减震结构抗震设计方法。为满足结构抵抗余震的性能要求,提出结合主余震的损伤性能目标。以Park-Ang双参数损伤模型为基础建立了结构层间损伤计算公式,通过损伤程度评估结构抗震性能,给出消能减震结构基于损伤性能的抗震设计流程。     

大震前地震活动平静现象一种可能的机制:断层的蠕滑-匀阻化

许多大地震前地震活动存在明显的平静现象,由于其普遍性,地震平静现象被认为是具有物理意义的地震前兆并被作为地震预报的重要依据.关于大震前地震平静现象的物理机制,国内外学者从不同角度进行了研究,其中包括用破裂强度的双峰式分布、扩容硬化、震前滑动造成的应力松弛、震源体内外介质性质的差异和相互作用等机制解释强震孕育过程中短期地震活动的平静现象.尽管在一些模型中把岩石力学实验结果作为证据之一,但来自与地震活动最相似的岩石变形声发射的实验证据并不多.因为以往大量的实验结果表明,在恒定的加载条件下(等位移速率、等应力速率等),岩石破坏失稳前声发射活动多表现为加速特征,尽管一些岩石破坏前声发射活动加速现象不明显,但也难以观测到平静现象.然而,在我们开展的一系列断层结构和介质不同的中尺度标本的声发射实验中,一些标本破坏失稳前声发射活动表现出明显的相对平静现象,据此我们对大地震前地震活动平静现象的物理机制进行了讨论.     

纬度圈上的大地震带

根据Ms≥6.0大地震活动的空间分布,有地震带和地震区之分.中国境内既有纵贯南北缘经度分布并把我国地震活动分隔成东西两部分的南北地震带,也有横穿北纬40左右呈东西向分布的阴山、燕山地震带,以及呈片状展布的东北深震区等.     

强余震的灾害评估

极震区的烈度分布是由主震和大余震产生的。最重的地震灾区为余震区，其范围可由震级与地震区烈度的统计关系求得。在震级与震中烈度关系中，初期余震的烈度略高于主震，晚期强余震的烈度比主震的低。不同烈度对建筑物的损害程度可通过烈度与损失率曲线进行评估。强余震和后续强震的人口伤亡比主震轻。     

强大地震前地震活动增强区及其力学研究

通过对85次6级以上地震前地震活动增强区的深入研究表明:① 强大地震前出现的地震活动增强区具有一定的普遍性;② 增强区的规模和形成时间都随震级而增大;③ 增强区尺度与震源区尺度之比随震级增大而减小;④ 增强区形成的时间因地区各异,中国东部地区较西部地区长．运用坚固体孕震模式和硬包体理论,对以上特征进行了定性和半定量的初步解释,从而应用地震活动增强区进行了2次地震的长期预测尝试．可见,强震前的地震活动增强区是具有一定力学基础的现象．      

Increment of Macroseismic Intensity at Seismic Stations of the Kamchatka Region Relative to the Petropavlovsk Seismic Station

The paper presents the method and results of calculating the increment of macroseismic intensity at seismic stations of Kamchatka. Calculation is based on measurement of the relative level of maximum accelerations of intense earth vibrations in the phase of S-waves of comparatively strong regional earthquakes and the root-mean-square deviation of acceleration in the phase of P-waves of a strong distant earthquake. In the latter case, records of an earthquake with a magnitude of 9.1, which occurred in Japan on March 11, 2011, were used. The Petropavlovsk seismic station was used as the reference station. At the foundation of this station rests on rocky soil composed of siliceous shales. An estimate of the increment for the majority of digital stations is presented. Anomalously high intensity values were noted at a number of stations. The data obtained are used to assess the properties of soils in the investigated area. At several stations, the intensity of the horizontal component of soil vibrations above the intensity of the vertical component is much greater than the corresponding design value, which is probably due to the presence of resonant soil layers under these stations. The discrepancy in the incremental intensity estimates from records of intense oscillations from regional earthquakes and from records of a very strong remote earthquake obtained from sensors located in basements of heavy-frame concrete structures is revealed. To avoid distortion in recording ground vibrations, it is desirable to place seismic instruments far from such structures. The results obtained in the study can be used for seismic microzoning of construction sites in the investigated territory.     

东南亚及印度等国家地震活动及相关背景材料

本文文介绍了东南亚、印度等12个国家的地震活动性、负责地震监测和研究的组织机构、台站建设及分布、仪器设备情况、历史地震及损失情况等。     

Measuring Seismic Waves Induced by Large Earthquakes with GPS

Independent GPS position solutions at 1-sec interval, derived from the International GPS Service (IGS) data and orbit÷clock products, clearly show seismic waves generated by the magnitude 7.9 Denali Fault, Alaska earthquake of November 3, 2002. Surface seismic waves with periods of about 20 sec and amplitudes of up to 20 cm were detected up to 4,000 km from the epicenter. This confirms the previous findings reported by Larson et al. (2003); we use additional station data along with different processing software and strategies. The seismic waves from the May 26, 2003 magnitude 7.0 Japanese earthquake were also observed in the 1-sec position solution series at station MIZU, about 80 km from the epicenter. This earthquake, however, could not be detected by GPS at station USUD, about 410 km away. Similarly, the Algerian May 21, 2003 earthquake of magnitude 6.8 could not be detected by GPS at the nearest IGS station located approximately 800 km from the epicenter.     

A Damage Mechanics Model for Aftershocks

— All earthquakes are followed by an aftershock sequence. A universal feature of aftershock sequences is that they decay in time according to the modified Omori’s law, a power-law decay. In this paper we consider the applicability of damage mechanics to earthquake aftershocks. The damage variable introduced in damage mechanics quantifies the deviation of a brittle solid from linear elasticity. We draw an analogy between the metastable behavior of a stressed brittle solid and the metastable behavior of a superheated liquid. The nucleation of microcracks is analogous to the nucleation of bubbles in the superheated liquid. In this paper we obtain a solution for the evolution of damage after the instantaneous application of a constant strain to a rod. We show that the subsequent stress relaxation can reproduce the modified Omori’s law. It is argued that the aftershocks themselves cause random fluctuations similar to the thermal fluctuations associated with phase transitions.