灰色系统理论在东北地震活跃期预测研究中的应用

运用灰色系统理论,对东北地区下一个地震活跃期开始时间以及活跃期内可能发生的最大地震的震级进行预测。分别取两个地震活跃期之间的时间间隔和每一活跃期内的最大地震的震级为原始数据列,用五步建模法建立灰色GM(1,1)模型。 用所建模型进行预测,得到东北地区下一个地震活跃期约于1997年开始,活跃期内可能发生的最大地震为7.2级。文中对预测结果的多解性进行了探讨。     

Influence of slow active faults in probabilistic seismic hazard assessment: the northwestern margin of the València trough

Areas of low strain rate are typically characterized by low to moderate seismicity. The earthquake catalogs for these regions do not usually include large earthquakes because of their long recurrence periods. In cases where the recurrence period of large earthquakes is much longer than the catalog time span, probabilistic seismic hazard is underestimated. The information provided by geological and paleo-seismological studies can potentially improve seismic hazard estimation through renewal models, which assume characteristic earthquakes. In this work, we compare the differences produced when active faults in the northwestern margin of the València trough are introduced in hazard analysis. The differences between the models demonstrate that the introduction of faults in zones characterized by low seismic activity can give rise to significant changes in the hazard values and location. The earthquake and fault seismic parameters (recurrence interval, segmentation or fault length that controls the maximum magnitude earthquake and time elapsed since the last event or T_e) were studied to ascertain their effect on the final hazard results. The most critical parameter is the recurrence interval, where shorter recurrences produce higher hazard values. The next most important parameter is the fault segmentation. Higher hazard values are obtained when the fault has segments capable of producing big earthquakes. Finally, the least critical parameter is the time elapsed since the last event (T_e), when longer T_e produces higher hazard values.     

Space-time distribution patterns of destructive earthquakes in the inner belt of central Japan: Activity intervals and locations of earthquakes

Based on a block structure model of the inner belt of central Japan, an examination was conducted of the space-time distribution patterns of destructiv magnitudes M 6.4 or greater (M =Japan Meteorological Agency Scale). The distribution patterns revealed a periodicity in earthquake activit seismic gaps. Major NW—SE trending left-lateral active faults divide the inner belt of central Japan into four blocks, 20–80 km wide. The occurrenc A.D. with M ≥ 6.4, which have caused significant damage, were documented in the inner belt of central Japan. The epicenters of these earthquakes close to the block boundaries.

Using the relationship between the magnitude of earthquakes which occurred in the Japanese Islands and the active length of faults that generated them, movement is calculated for each historical earthquake. Space—time distributions of earthquakes were obtained from the calculated lengths, the latitud of generation. When an active period begins, a portion or segment of the block boundary creates an earthquake, which in turn appears on the ground surf active period ends when the block boundary generates earthquakes over the entire length of the block boundary without overlapping.

Five seismic gaps with fault lengths of 20 km or longer can be found in the inner belt of central Japan. It is predicted that the gaps will generate ea magnitudes of 7.0. These data are of significance for estimating a regional earthquake risk over central Japan in the design of large earthquake resist

The time sequences of earthquakes on the block boundaries reveal a similar tendency, with alternating active periods with seismic activity and quiet pe activity. The inner belt of central Japan is now in the last stage of an active period. The next active period is predicted to occur around 2500 A.D.     

Continued seismic activity at the Koyna reservoir site, India

Following the impounding of the Shivaji Sager Lake in 1962, tremors became prevalent in the Koyna region, considered previously to be aseismic. During ensuing years the tremor frequency appears to have been dependent on the rate of increase of water level, maximum water level reached, and the period for which high levels were retained. This culminated in a burst of seismic activity from September 1967 to January 1968 following the record water levels in the reservoir and included the earthquake of September 13, 1967 with magnitude 5.5 and the damaging December 10, 1967 earthquake of magnitude 6.0. During the next five years water levels were kept low and no significant earthquakes occurred subsequent to the October 29, 1968 earthquake of magnitude 5.

The reservoir was filled to maximum capacity during September 1973 and this was followed by a conspicuous increase in seismic activity which included an earthquake of magnitude 5.1 on October 17, 1973. However, seismic activity during 1973 was much less severe than that of 1967. This relative decrease in seismicity may indicate that (a) the “threshhold level” for relatively large magnitude earthquakes had increased; (b) a major portion of the accumulated strains had been released; and/or (c) the importance of the longer period of high loading in 1967. Similar observations have been made at other seismically active reservoir sites.     

我国核电站选址的区域稳定性研究

核能是重要的能源之一。利用核能发电在世界能源构成中占有愈来愈重要的地位。 修建核电站,要求严格的安全和环境条件,必须绝对保证核电站在各种可能遭遇的自然和人为事件情况下,均不致发生造成放射性物质外泄的事故。因此,除了要求核电站建筑物和各种装置本身安全可靠并拥有周密而充分的安全措施外,特别要求在选择厂址时,必须充分查明和预测各种可能遭受的自然灾害。在各种能危及核电站安全的自然灾害中,与工程地质直接有关的问题有许多方面,本文仅就核电站选址中,厂址地区的区域稳定问题作一简要探讨。     

Probabilities of earthquake occurrences in Mainland Southeast Asia

The frequency–magnitude distributions of earthquakes are used in this study to estimate the earthquake hazard parameters for individual earthquake source zones within the Mainland Southeast Asia. For this purpose, 13 earthquake source zones are newly defined based on the most recent geological, tectonic, and seismicity data. A homogeneous and complete seismicity database covering the period from 1964 to 2010 is prepared for this region and then used for the estimation of the constants, a and b, of the frequency–magnitude distributions. These constants are then applied to evaluate the most probable largest magnitude, the mean return period, and the probability of earthquake of different magnitudes in different time spans. The results clearly show that zones A, B, and E have the high probability for the earthquake occurrence comparing with the other seismic zones. All seismic source zones have 100 % probability that the earthquake with magnitude ≤6.0 generates in the next 25 years. For the Sagaing Fault Zone (zones C), the next Mw 7.2–7.5 earthquake may generate in this zone within the next two decades and should be aware of the prospective Mw 8.0 earthquake. Meanwhile, in Sumatra-Andaman Interplate (zone A), an earthquake with a magnitude of Mw 9.0 can possibly occur in every 50 years. Since an earthquake of magnitude Mw 9.0 was recorded in this region in 2004, there is a possibility of another Mw 9.0 earthquake within the next 50 years.     

青藏高原东北缘推覆体构造稳定性定量化评价——以龙门山推覆体为例

2008年5月12日汶川特大地震震害调查及分析表明,目前以活动断裂和历史地震调查为重点的工程区域构造稳定性评价方法存在漏判与误判特大地震问题,从而为工程安全埋下重大安全隐患。以龙门山活动推覆体为例,在已有研究成果基础上,利用岩体结构控制论、拜尔利定律等普适性原理对龙门山地壳岩体结构力学特征、控震结构面的抗剪强度与地震震级的线性相关性、地震震级与抗震设防烈度的关系进行了定量研究,对评价区域构造稳定性的关键问题进行了探讨。结果表明,推覆体型活动地块边界带中的滑脱层是对推覆体区域构造稳定性起主要控制作用的构造结构面--控震结构面,地震震级与滑脱层的埋深、抗剪切强度存在显著相关性：8级地震的震源深度接近20 km、7级地震的震源深度接近14 km、6级地震的震源深度接近10 km,据此对研究区及邻近的古地震进行了深度核定,圈定了龙门山活动推覆体-岷山地块的6级以上强震可能发生的范围、对应Ⅶ－Ⅺ度的抗震设防烈度范围。此研究成果弥补了以往根据活动断裂-发震断裂-历史最大震级与对应地震烈度评价工程区域构造稳定性,因历史地震资料疏漏不全、活动断裂带研究平面与深度范围局限以及忽视区域构造稳定性的岩体力学实质而导致评价结果常常出现误判与漏判的诸多缺陷。     

Precursory accelerating seismic crustal deformation in the Northwestern Anatolia Fault Zone

We present the results of a systematic search for the identification of accelerating seismic crustal deformation in the broader northern Aegean area and in northwestern Turkey. We found that accelerating seismic deformation release, expressed by the generation of intermediate magnitude earthquakes, is currently observed in NW Turkey. On the basis of the critical earthquake model and by applying certain constraints which hold between the basic quantities involved in this phenomenon, it can be expected that this accelerating seismic activity may culminate in the generation of two strong earthquakes in this area during the next few years.The estimated epicenter coordinates of the larger of these probably impending earthquakes are 39.7°N–28.8°E, its magnitude is 7.0 and its occurrence time t_c=2003.5. The second strong event is expected to occur at t_c=2002.5 with a magnitude equal to 6.4 and epicenter coordinates 40.0°N–27.4°E. The uncertainties in the calculated focal parameters for these expected events are of the order of 100 km for the epicenter, ±0.5 for their magnitude and ±1.5 years for their occurrence time.     

Seismicity of Gujarat

Paper describes tectonics, earthquake monitoring, past and present seismicity, catalogue of earthquakes and estimated return periods of large earthquakes in Gujarat state, western India. The Gujarat region has three failed Mesozoic rifts of Kachchh, Cambay, and Narmada, with several active faults. Kachchh district of Gujarat is the only region outside Himalaya-Andaman belt that has high seismic hazard of magnitude 8 corresponding to zone V in the seismic zoning map of India. The other parts of Gujarat have seismic hazard of magnitude 6 or less. Kachchh region is considered seismically one of the most active intraplate regions of the World. It is known to have low seismicity but high hazard in view of occurrence of fewer smaller earthquakes of M????6 in a region having three devastating earthquakes that occurred during 1819 (M _w7.8), 1956 (M _w6.0) and 2001 (M _w7.7). The second in order of seismic status is Narmada rift zone that experienced a severely damaging 1970 Bharuch earthquake of M5.4 at its western end and M????6 earthquakes further east in 1927 (Son earthquake), 1938 (Satpura earthquake) and 1997 (Jabalpur earthquake). The Saurashtra Peninsula south of Kachchh has experienced seismicity of magnitude less than 6.     

Precursory activity in seismic belts containing the focal region of forthcoming large intraplate earthquake

Seismic activity in the region surrounding the foci is investigated for three severe earthquakes (two with a magnitude of 6.1 and one with a magnitude of 5.3) which have occurred in Japan in recent years. The most conspicuous feature commonly noticed is precursory activation of seismic belts which include the focal regions of main shocks. The repetition of the same pattern in the space-time distribution of earthquake occurrence along the seismic belt is also observed for each case. The precursory activity of seismic belts terminates in rather a short period and, after that, the area around the focus of the forthcoming large earthquake becomes quiescent, which demonstrates the appearance of the seismic gap of the second kind (Mogi, 1979). The periods of seismic quiescence for the cases investigated in this paper are longer than those which are given by the regression relationship between earthquake magnitude and precursor time proposed for example, by Sekiya (1977). However, our definition of anomalous seismic activity is clear, and it is possible to give a physical meaning to it as an increase in the local stress field in the seismic belt. We propose that a kind of coupling between intraplate tectonic blocks, analogous to interplate coupling in the subduction region, is responsible for the formation of the stress field relevant to these earthquakes. Although this is at present only one of the possible viewpoints on the formation of the focal region of large intraplate earthquakes, it may be worthwhile to study various precursory phenomena in-connection with this hypothesis.     

Fuzzy probabilistic seismic hazard analysis with applications to Kunming city,China

China is prone to highly frequent earthquakes due to specific geographical location, which could cause significant losses to society and economy. The task of seismic hazard analysis is to estimate the potential level of ground motion parameters that would be produced by future earthquakes. In this paper, a novel method based on fuzzy logic techniques and probabilistic approach is proposed for seismic hazard analysis (FPSHA). In FPSHA, we employ fuzzy sets for quantification of earthquake magnitude and source-to-site distance, and fuzzy inference rules for ground motion attenuation relationships. The membership functions for earthquake magnitude and source-to-site distance are provided based on expert judgments, and the construction of fuzzy rules for peak ground acceleration relationships is also based on expert judgment. This methodology enables to include aleatory and epistemic uncertainty in the process of seismic hazard analysis. The advantage of the proposed method is in its efficiency, reliability, practicability, and precision. A case study is investigated for seismic hazard analysis of Kunming city in Yunnan Province, People’s Republic of China. The results of the proposed fuzzy logic-based model are compared to other models, which confirms the accuracy in predicting the probability of exceeding a certain level of the peak ground acceleration. Further, the results can provide a sound basis for decision making of disaster reduction and prevention in Yunnan province.     

Seismic hazard map of Coimbatore using subsurface fault rupture

This study presents the future seismic hazard map of Coimbatore city, India, by considering rupture phenomenon. Seismotectonic map for Coimbatore has been generated using past earthquakes and seismic sources within 300 km radius around the city. The region experienced a largest earthquake of moment magnitude 6.3 in 1900. Available earthquakes are divided into two categories: one includes events having moment magnitude of 5.0 and above, i.e., damaging earthquakes in the region and the other includes the remaining, i.e., minor earthquakes. Subsurface rupture character of the region has been established by considering the damaging earthquakes and total length of seismic source. Magnitudes of each source are estimated by assuming the subsurface rupture length in terms of percentage of total length of sources and matched with reported earthquake. Estimated magnitudes match well with the reported earthquakes for a RLD of 5.2% of the total length of source. Zone of influence circles is also marked in the seismotectonic map by considering subsurface rupture length of fault associated with these earthquakes. As earthquakes relive strain energy that builds up on faults, it is assumed that all the earthquakes close to damaging earthquake have released the entire strain energy and it would take some time for the rebuilding of strain energy to cause a similar earthquake in the same location/fault. Area free from influence circles has potential for future earthquake, if there is seismogenic source and minor earthquake in the last 20 years. Based on this rupture phenomenon, eight probable locations have been identified and these locations might have the potential for the future earthquakes. Characteristic earthquake moment magnitude (M _w ) of 6.4 is estimated for the seismic study area considering seismic sources close to probable zones and 15% increased regional rupture character. The city is divided into several grid points at spacing of 0.01° and the peak ground acceleration (PGA) due to each probable earthquake is calculated at every grid point in city by using the regional attenuation model. The maximum of all these eight PGAs is taken for each grid point and the final PGA map is arrived. This map is compared to the PGA map developed based on the conventional deterministic seismic hazard analysis (DSHA) approach. The probable future rupture earthquakes gave less PGA than that of DSHA approach. The occurrence of any earthquake may be expected in near future in these eight zones, as these eight places have been experiencing minor earthquakes and are located in well-defined seismogenic sources.     

The Earthquake Threat in Southwestern British Columbia: A Geologic Perspective

Ten moderate to large (magnitude 6–7) earthquakes have occurred in southwestern British Columbia and northwestern Washington in the last 130 years. A future large earthquake close to Vancouver, Victoria, or Seattle would cause tens of billions of dollars damage and would seriously impact the economies of Canada and the United States. An improved understanding of seismic hazards and risk in the region has been gained in recent years by using geologic data to extend the short period of instrumented seismicity. Geologic studies have demonstrated that historically unprecedented, magnitude 8 to 9 earthquakes have struck the coastal Pacific Northwest on average once every 500 years over the last several thousand years; another earthquake of this size can be expected in the future. Geologic data also provide insights into the likely damaging effects of future large earthquakes in the region. Much of the earthquake damage will result directly from ground shaking, but damage can also be expected from secondary phenomena, including liquefaction, landslides, and tsunamis. Vancouver is at great risk from earthquakes because important infrastructure, including energy and transportation lifelines, probably would be damaged or destroyed by landslides and liquefaction-induced ground failure.     

Occurrences of major earthquakes by groups in North China

The earthquakes with magnitude M 6 which occurred in North China (30°–42°N, 105°–124°E) from 780 B.C. to 1978 A.D. have been analysed. Most of them appear in groups, each of which is confined to a definite region and period of time, called respectively the active region and active period. From 780 B.C. to 1000 A.D., groupings of earthquakes were not apparent, due to scanty data. Since 1000 A.D., 16 groups of earthquakes can be recognized. Statistics show that about 73% of the earthquakes occurred in groups. This implies that grouping of earthquakes of M 6 is a characteristic feature of seismic activity in North China. On this basis, a concept of a unified seismogenic process of major earthquakes has been proposed with the support of the geodetic data. Finally, the significance of this concept with regards to earthquake prediction has been discussed.     

白龙江引水工程代古寺水库及其周围地区地震危险性评估

白龙江引水工程是我国拟建的一项重大战略工程,而代古寺水库是该工程的水源枢纽。代古寺水库及其周围地区(本文研究区)活动断层发育、大地震频发,故亟需开展可靠的地震危险性评估,为该研究区内的工程建设和运营保驾护航。由于传统评估方法物理依据不足,难以正确评估研究区的地震危险性,故本文采用了基于地震物理预测的地震危险性评估新方法。研究结果表明,该研究区位于海原地震区,未来100年内该研究区的地震危险性主要源于海原地震区的下一次M_S8.5标志性地震。根据断层地震活动、发震潜力与展布特征,我们预判了该标志性地震的可能发震断层和震中位置;应用地震烈度衰减关系,考虑不同震中位置,分别计算了其产生的地震烈度。为确保“百年大计”的白龙江引水工程代古寺水库水资源枢纽安全,我们建议该研究区的抗震设防烈度不宜低于8度。     

Global strain rates in western to central Himalayas and their implications in seismic hazard assessment

The Himalayas has experienced varying rates of earthquake occurrence in the past in its seismo-tectonically distinguished segments which may be attributed to different physical processes of accumulation of stress and its release, and due diligence is required for its inclusion for working out the seismic hazard. The present paper intends to revisit the various earthquake occurrence models applied to Himalayas and examines it in the light of recent damaging earthquakes in Himalayan belt. Due to discordant seismicity of Himalayas, three types of regions have been considered to estimate larger return period events. The regions selected are (1) the North-West Himalayan Fold and Thrust Belt which is seismically very active, (2) the Garhwal Himalaya which has never experienced large earthquake although sufficient stress exists and (3) the Nepal region which is very seismically active region due to unlocked rupture and frequently experienced large earthquake events. The seismicity parameters have been revisited using two earthquake recurrence models namely constant seismicity and constant moment release. For constant moment release model, the strain rates have been derived from global strain rate model and are converted into seismic moment of earthquake events considering the geometry of the finite source and the rates being consumed fully by the contemporary seismicity. Probability of earthquake occurrence with time has been estimated for each region using both models and compared assuming Poissonian distribution. The results show that seismicity for North-West region is observed to be relatively less when estimated using constant seismicity model which implies that either the occupied accumulated stress is not being unconfined in the form of earthquakes or the compiled earthquake catalogue is insufficient. Similar trend has been observed for seismic gap area but with lesser difference reported from both methods. However, for the Nepal region, the estimated seismicity by the two methods has been found to be relatively less when estimated using constant moment release model which implies that in the Nepal region, accumulated strain is releasing in the form of large earthquake occurrence event. The partial release in second event of May 2015 of similar size shows that the physical process is trying to release the energy with large earthquake event. If it would have been in other regions like that of seismic gap region, the fault may not have released the energy and may be inviting even bigger event in future. It is, therefore, necessary to look into the seismicity from strain rates also for its due interpretation in terms of predicting the seismic hazard in various segments of Himalayas.     

Universal precursor seismicity pattern before locked-segment rupture and evolutionary rule for landmark earthquakes

Despite extensive investigations, no precursor patterns for reliably predicting major earthquakes have thus far been identified. Seismogenic locked segments that can accumulate adequate strain energy to cause major earthquakes are highly heterogeneous and low brittle. The progressive cracking of the locked segments with these properties can produce an interesting seismic phenomenon: a landmark earthquake and a sequence of smaller subsequent earthquakes (pre-shocks) always arise prior to another landmark earthquake within a well-defined seismic zone and its current seismic period. Applying a mechanical model, magnitude constraint conditions, and case study data of 62 worldwide seismic zones, we show that two adjacent landmark earthquakes reliably occur at the volume-expansion point and peak-stress point (rupture) of a locked segment; thus, the former is an identified precursor for the latter. Such a precursor seismicity pattern before the locked-segment rupture has definite physical meanings, and it is universal regardless of the focal depth. Because the evolution of landmark earthquakes follows a deterministic rule described by the model, they are predictable. The results of this study lay a firm physical foundation for reliably predicting the occurrence of future landmark earthquakes in a seismic zone and can greatly improve our understanding of earthquake generation mechanism.     

中国西部及邻区大地震时空特征、地质背景及发展趋势分析

在中国西部及邻区有一个以中国南北地震带—蒙古东部地震带、喜马拉雅地震带和帕米尔—天山—阿尔泰山—蒙古西部地震带为3条边而组成的巨型中亚三角形地震带,其大地震发生的强度之大、频度之高以及重复率之高、重复周期之短,在世界大陆上绝无仅有。这些大地震在空间上受到大地构造位置、构造应力场-滑移线场、介质力学条件、壳内低阻流变层和先存力学脆弱带等五位一体的复合控制,震中主要分布于3条边与活动断裂带交叉处的中—上地壳中;在时间上存在以21.5 a±为最小单元的多种周期。印度板块的持续顶撞和推挤,是该带大地震孕育的能源,而太阳黑子活动和地球自转速率变化可能是该带地震的触发因素。以2001年昆仑山大地震和2008年汶川大地震为标志,中亚三角形地震带可能进入了一个新的107.5 a活动中周期。果真如此,则未来数十年内在该三角形的3条边及其周缘,可能分别发生若干个M≥8.0级大地震和多个M≥7.0级强地震。     

Assessment of the statistical earthquake hazard parameters for NW Turkey

We performed a probabilistic analysis of earthquake hazard input parameters, NW Turkey covers Gelibolu and Biga Peninsulas, and its vicinity based on four seismic sub-zones. The number of earthquakes with magnitude M ≥ 3.0 occurred in this region for the period between 1912 and 2007 is around 5130. Four seismic source sub-zones were defined with respect to seismotectonic framework, seismicity and fault geometry. The hazard perceptibility characterization was examined for each seismic source zone and for the whole region. The probabilities of earthquake recurrences were obtained by using Poisson statistical distribution models. In order to determine the source zones where strong and destructive earthquakes may occur, distribution maps for a, b and a/b values were calculated. The hazard scaling parameters (generally known as a and b values) in the computed magnitude–frequency relations vary in the intervals 4.28–6.58 and 0.59–1.13, respectively, with a RMS error percentage below 10 %. The lowest b value is computed for sub-zone three indicating the predominance of large earthquakes mostly at Gelibolu (Gallipoli) and north of Biga Peninsula (southern Marmara region), and the highest b value is computed for sub-zone two Edremit Bay (SW Marmara region). According to the analysis of each seismic sub-zone, the greatest risk of earthquake occurrence is determined for the triangle of Gelibolu–Tekirda? western part of Marmara Sea. Earthquake occurrence of the largest magnitude with 7.3 within a 100-year period was determined to be 46 % according to the Poisson distribution, and the estimated recurrence period of years for this region is 50 ± 12. The seismic hazard is pronounced high in the region extending in a NW–SE direction, north of Edremit Bay, west of Saros Bay and Yenice Gönen (southern Marmara region) in the south. High b values are generally calculated at depths of 5–20 km that can be expressed as low seismic energy release and evaluated as the seismogenic zone.     

藏南安岗地堑的史前大地震遗迹、年龄及其地质意义

地表调查发现, 沿近南北向亚东-谷露裂谷中段的安岗地堑存在地震大滑坡、多世代断层崖和断层崩积楔等多种类型的史前大地震遗迹.进一步的观测和年代分析表明: 该区的古地震滑坡体至少存在新、老两期, 其中规模最大的"尼续大滑坡体"应该是最新一次大地震所形成.该区T₁到T₆各阶地的形成时代从新到老分别为7.7~2.1 ka、11.0~10.5 ka、17.6~12.1 ka、25.7~22.9 ka、58.4~70.6 ka和130~150 ka, 它们沿主边界正断层的平均垂直断距依次为2.8 m、6.1~7.9 m、10.3~12.5 m、16.6~19.0 m、28.0 m和76.0 m.其中T₁和T₂阶地上的断崖剖面揭示, 最近两次大地震发生在距今约5.8±1.0 ka和2.4±0.2 ka.综合分析认为: 安岗地堑的大地震活动具有较明显的丛集性特征, 并且在距今约23~26 ka以来一直处于大地震活跃期, 期间的断层垂直活动速率为0.8~1.3 mm/a, 大地震的原地复发间隔大致为3.3~3.6 ka, 特征地震的矩震级为7.0~7.2, 推算整个尼木地堑群的大震复发间隔最短可能只有约1.0~1.2 ka.研究结果指示, 藏南裂谷的大地震活动性明显比藏北的近南北向正断层更显著.