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Seismic quiescence and accelerating seismic energy release are considered as possible spatio-temporal patterns of the preparation process of the 6 September 2002 Palermo, Italy, earthquake (M 5.8). The detailed properties of the quiescence are analyzed applying the RTL algorithm. The RTL algorithm is based on the analysis of the RTL prognostic parameter, which is designed in such a way that it has a negative value if, in comparison with long-term background, there is a deficiency of events in the time–space vicinity of the tested point. The RTL parameter increases if activation of seismicity takes place. The RTL algorithm identified that a seismic quiescence started from the beginning of November 2001 and reached its minimum at the end of May 2002. The Palermo 2002 earthquake occurred 2 months after the RTL parameter restored its long-term background level. The application of a log-periodic time-to-failure model gives a “predicted” (in retrospect) magnitude M=6.2 main shock on 5 May 2002. 相似文献
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Seismicity pattern in north Sumatra-Great Nicobar region: In search of precursor for the 26 December 2004 earthquake 总被引：1，自引：0，他引：1
Sujit Dasgupta Basab Mukhopadhyay Auditeya Bhattacharya 《Journal of Earth System Science》2007,116(3):215-223
We analyse the seismicity pattern including b-value in the north Sumatra-Great Nicobar region from 1976 to 2004. The analysis suggests that there were a number of significant,
intermediate and short-term precursors before the magnitude 7.6 earthquake of 2 November 2002. However, they were not found
to be so prominent prior to the magnitude 9.0 earthquake of 26 December 2004 though downward migration of activity and a 50-day
short-term quiescence was observed before the event. The various precursors identified include post-seismic and intermediate-term
quiescence of 13 and 10 years respectively, between the 1976 (magnitude 6.3) and 2002 earthquakes with two years (1990–1991)
of increase in background seismicity; renewed seismicity, downward migration of seismic activity and foreshocks in 2002, just
before the mainshock. Spatial variation in b-value with time indicates precursory changes in the form of high b-value zone near the epicenter preceding the mainshocks of 2004 and 2002 and temporal rise in b-value in the epicentral area before the 2002 earthquake. 相似文献
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Variations of seismic mode in the region of the Avachinsky Gulf (Kamchatka, Russia) are considered. Observed anomalies (seismic quiescence, the ring seismicity, reduction of the slope of the earthquake recurrence diagram) provide a basis to consider this region as a place of strong earthquake preparation. The Kamchatka regional catalogues of earthquakes between 1962–1995 were used in the analysis. A reduced seismicity rate is observed during 10 years in an area of 150 km × 60 km in size. During the last five years, in the vicinity of the area considered, earthquakes with M > 5 occurred three times more often than the average over thirty years. It is interpreted as ring seismicity. The block of 220 km × 220~km in size, including the quiescence zone, is characterized by a continuous decrease of the recurrence diagram slope, which has reached a minimum value for the last 33 years in this region. 相似文献
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Anomalous movements were detected simultaneously in both the seismic and the GPS observations in the Tokai area, the central part of the Japanese islands from the late 1990s to 2000. The anomalies are of great concern since the pending risk of a large megathrust earthquake in this area has been predicted for more than 20 years. The GPS data revealed that a slow-slip on the plate interface had commenced beneath Lake Hamana, the center of which is positioned around the edge of the assumed focal zone. On the other hand, the seismic data indicated that a delicate but clear quiescence appeared over a wide area that spreads into the main focal zone. Analyses of the seismicity changes in space and time confirmed that the contrast in the seismicity rate is distinct inside the focal zone. While the integrated seismicity indicated quiescence, some locations were distinguished as activated zones, possibly indicating the appearance of asperities. The rise of the seismicity rate in a quasi-stationary manner suggests an increase in the stress rate at that location. The following hypothesis is proposed based on the simultaneously detected evidences. The slow-slip progressing beneath Lake Hamana will induce a stress shift that invades the interior of the main locked zone, which will increase the contrast of the seismicity rate, possibly reflecting inhomogeneity in the locking strength. Even in this stage, the activated zones still maintain a locked state to prevent overall breakage. Investigations of the b-value changes and of tidal dependence in seismicity that reveal the stress-concentrated state also support the hypothesis. If this is the case, the observed change in seismicity would indicate the process of stress redistribution in the locking state, which represents the preparatory process toward final breakage. Tracking such seismicity changes would yield valid information for predictions of the next Tokai earthquake. 相似文献
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Following the 1999 Mw 7.6 Chi-Chi earthquake, a large amount of seismicity occurred in the Nantou region of central Taiwan. Among the seismic activities, eight Mw ⩾ 5.8 earthquakes took place following the Chi-Chi earthquake, whereas only four earthquakes with comparable magnitudes took place from 1900 to 1998. Since the seismicity rate during the Chi-Chi postseismic period has never returned to the background level, such seismicity activation cannot simply be attributed to modified Omori’s Law decay. In this work, we attempted to associate seismic activities with stress evolution. Based on our work, it appears that the spatial distribution of the consequent seismicity can be associated with increasing coseismic stress. On the contrary, the stress changes imparted by the afterslip; lower crust–upper mantle viscoelastic relaxation; and sequent events resulted in a stress drop in most of the study region. Understanding seismogenic mechanisms in terms of stress evolution would be beneficial to seismic hazard mitigation. 相似文献
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We in this study have calculated the standard normal deviate Z-value to investigate the variations in seismicity patterns in the Taiwan region before and after the Chi-Chi earthquake. We have found that the areas with relatively high seismicity in the eastern Taiwan became abnormally quiet before the Chi-Chi earthquake while the area in the central Taiwan with relatively low seismicity showed unusually active. Such a spatially changing pattern in seismicity strikingly demonstrates the phenomenon of “seismic reversal,” and we here thus present a complete, representative cycle of “seismic reversal” embedding in the changes of seismicity patterns before and after the Chi-Chi earthquake. 相似文献
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采用β统计对汶川地震前后鄂尔多斯块体周缘地区的地震活动率进行了空间扫描分析,并采用JiChen的震源破裂模型计算了汶川地震产生的库仑破裂应力变化,以研究鄂尔多斯块体周缘地区近期地震活动性与汶川地震应力触发作用的关系。结果发现,鄂尔多斯块体西南缘弧形断裂束的南东段与南缘渭河盆地的地震活动率在汶川地震后提高显著,其他区域的地震活动率没有明显提高,库仑破裂应力计算得到两个区域的应力变化范围分别为0.005～0.02 MPa和0.001～0.01 MPa,表明汶川地震有可能触发了这两个区域的地震活动。鄂尔多斯块体东缘的山西断陷带处于库仑破裂应力计算的应力增加区,应力变化范围为0～0.012 MPa,2009年3月以来发生的4次ML4.5～5.2级强有感至微破坏地震有可能被汶川地震所延迟触发。b值、地震能量释放率与空间相关距离SCL等地震活动性参数随时间变化扫描结果显示,该区域可能处于不断趋近高应力累积的状态,其未来大震有可能提前发生。西缘地区为应力减小区,其目前的地震活动处于正常水平状态。 相似文献
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Sujit Dasgupta Basab Mukhopadhyay Manoj Mukhopadhyay 《Journal of the Geological Society of India》2012,80(3):393-402
The Burmese Arc seismic activity is not uniform for its ∼ 1100 km length; only the Northern Burmese Arc (NBA) is intensely active. Six large earthquakes in the magnitude range 6.1–7.4 have originated from the NBA Benioff zone between 1954–2011, within an area of 200 × 300 km2 where the Indian plate subducts eastward to depths beyond 200 km below the Burma plate. An analysis on seismogenesis of this interplate region suggests that while the subducting lithosphere is characterized by profuse seismicity, seismicity in the overriding plate is rather few. Large earthquakes occurring in the overriding plate are associated with the backarc Shan-Sagaing Fault (SSF) further east. The forecasting performance of the Benioff zone earthquakes in NBA as forerunner is analysed here by: (i) spatial earthquake clustering, (ii) seismic cycles and their temporal quiescence and (iii) the characteristic temporal b-value changes. Three such clusters (C1–C3) are identified from NBA Benioff Zones I & II that are capable of generating earthquakes in the magnitude ranges of 7.38 to 7.93. Seismic cycles evidenced for the Zone I displayed distinct quiescence (Q1, Q2 and Q3) prior to the 6th August 1988 (M 6.6) earthquake. Similar cycles were used to forecast an earthquake (Dasgupta et al. 2010) to come from the Zone I (cluster C1); which, actually struck on 4 February 2011 (M 6.3). The preparatory activity for an event has already been set in the Zone II and we speculate its occurrence as a large event (M > 6.0) possibly within the year 2012, somewhere close to cluster C3. Temporal analysis of b-value indicates a rise before an ensuing large earthquake. 相似文献
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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. 相似文献
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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MS8.5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。 相似文献
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The Pattern Informatics (PI) technique [Tiampo, K.F., Rundle, J.B., McGinnis, S., Gross, S., Klein, W., 2002. Mean-field threshold systems and phase dynamics: An application to earthquake fault systems, Europhys. Lett., 60, 481–487] is founded on the premise that changes in the seismicity rate are a proxy for changes in the underlying stress. This new approach to the study of seismicity quantifies its local and regional space–time patterns and identifies regions of local quiescence or activation. Here we use a modification of the PI method to quantify localized changes surrounding the epicenters of large earthquakes in California in an attempt to objectively quantify the rupture zones of these upcoming events. We show that this method can be used to forecast the size and magnitude of future earthquakes. 相似文献
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Konstantinos Leptokaropoulos Eleftheria Papadimitriou Beata Orlecka-Sikora Vasileios Karakostas 《Natural Hazards》2014,73(3):1817-1842
The spatio-temporal variation in seismicity in western Turkey since the late 1970s is investigated through a rate/state model, which considers the stressing history to forecast the reference seismicity rate evolution. The basic catalog was divided according to specific criteria into four subsets, which correspond to areas exhibiting almost identical seismotectonic features. Completeness magnitude and reference seismicity rates are individually calculated for each subset. The forecasting periods are selected to be the inter-seismic time intervals between successive strong (M ≥ 5.8) earthquakes. The Coulomb stress changes associated with their coseismic slip are considered, along with the constant stressing rate to alter the rates of earthquake production. These rates are expressed by a probability density function and smoothed over the study area with different degrees of smoothing. The influence of the rate/state parameters in the model efficiency is explored by evaluating the Pearson linear correlation coefficient between simulated and observed earthquake occurrence rates along with its 95 % confidence limits. Application of different parameter values is attempted for the sensitivity of the calculated seismicity rates and their fit to the real data to be tested. Despite the ambiguities and the difficulties involved in the experimental parameter value determination, the results demonstrate that the present formulation and the available datasets are sufficient enough to contribute to seismic hazard assessment starting from a point such far back in time. 相似文献
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1976年7月28日3点42分在我国河北省唐山地区发生了7.8级强烈地震。地震的发生,是有它的区域构造背景和震区的构造条件的。深入研究这个问题,对认识地震的形成、孕育和发生是十分有意义的。唐山地震震中与深大断裂没有表现直接的联系,而是分布在不引入注目的北东向断裂上。其控制因素我们认为是包围震区的边界断裂起了重要作用。边界断裂的存在使被围限的北东向断裂得到了暂时的平衡,形成相对“闭锁”区段。当区域应力场急剧变化时,“闭锁”就被突破,产生大地震。 相似文献
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Xianfeng Yao Xiao Hu Lixin Yi Xinxiang Zeng Linus Zhang 《Environmental Earth Sciences》2017,76(24):826
In the region of Three Gorges Reservoir (TGR) in China, there has been occurrence of several frequent earthquakes of moderate intensity since reservoir impounding occurred in 2003. These earthquakes are generally believed to be induced by reservoir impoundment and water-level variations. Usually, the geo-stress will change, when natural earthquakes occur. Following this principle, this paper adopted the rate and state theory to simulate and estimate Coulomb stress changes in the TGR region and obtained the pattern of Coulomb stress changes with time and the event sequence as well as the distribution of Coulomb stress changes in space. First, the TGR regional catalogue was analyzed and processed, leading to quantification of the magnitude of completeness and all of the parameters that are used in the stress–seismicity inversion process, including the reference seismicity rates, characteristic relaxation time, fault constitutive parameters, and stress rates. Second, the temporal evolution of the stress changes in different time windows was computed and analyzed, and it was found that there is an association between the Coulomb stress changes and rates of increase in the cumulative number of earthquakes. In addition, the earthquake occurred in November 2008 (M S = 4.1) was analyzed and attempted to simulate the distribution of stress changes in space through the stress–seismicity inversion model. The results proved that the modeled area coincides with the historical area of earthquakes that occurred after 2008. Finally, a prediction was made about the earthquake productivity rates after 2015, which showed a declining earthquake rate over time that ultimately returned to the background seismicity. This result is essentially in agreement with Omori’s law. To conclude, it is rational to use the stress-inversion method to analyze the relationship between induced earthquake seismicity and local stress changes as well as to simulate the area of earthquake occurrence and productivity rates of reservoir-induced earthquakes. 相似文献
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Potential sites of nuclear waste deposits in the Federal Republic of Germany are situated in areas of low seismicity. Nevertheless, seismic hazard assessment has to be performed for a very long time period in order to prove the facilities of the repositories able to withstand seismic induced loads; even though there is a considerable debate whether or not it is possible to quantify the seismic risk in such an area.
A combination of deterministic and probabilistic methods is used to assess the seismic hazard for a site in Northern Germany, fulfilling the standards of the German building code for nuclear power plants. As an example, the site of the former iron ore mine Konrad is investigated. The deterministic method is based on the assumption that the strongest earthquakes inside a tectonic region can happen everywhere there, also near the selected site. For the probabilistic method, several models describing the seismicity in an area of 200 km around the site are used to show the influence of the variability in input parameters, like the maximum intensity of each source region on the exceeding probability of the site intensity. It can be shown that the seismic hazard of a site in an area of low seismicity is mainly caused by the effects of distant but strong source regions and the background seismicity for very low probabilities.
Probabilistic evaluation has the advantage of quantifying the seismic risk. But deterministic and probabilistic methods together seem a practical tool for mutual control of the results and to overcome the weakness of each approach alone. The historical German earthquake catalog with an observation period of about 1200 years is the basis for the input data for a probabilistic model. From a deep knowledge of geological development and structural geology, the time history of the surrounding faults is developed. Indications were found that the nearest and most important fault was active at least 5 Ma ago. The combination of both seismicity and tectonics provides the basis for a long term prognostic with probabilities of exceedance in the order of 10−5 per year.
For the investigated site the following parameters were derived: site intensity as a function of exceeding probability; site acceleration; strong motion duration; site dependent response spectra for the surface and the underground inside the mine. 相似文献
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The first step in a seismicity analysis usually consists of defining the seismogenic units, seismic zones or individual faults. The worldwide delimitation of these zones involves an enormous effort and is often rather subjective. Also, a complete recording of faults will not be available for a long time yet. The seismicity model presented in this paper therefore is not based on individually defined seismic zones but rather on the assumption that each point in a global 1/2° grid of coordinates represents a potential earthquake source. The corresponding seismogenic parameters are allocated to each of these points. The earthquake occurrence frequency, one of the most important parameters, is determined purely statistically by appropriately spreading out the positions of past occurrences. All the other significant seismicity characteristics, such as magnitude-frequency relations, maximum possible magnitude and attenuation laws including the dependence on focal depth are determined in a global 1/2° grid of co-ordinates. This method of interpreting seismicity data allows us to establish a transparent, sufficiently precise representation of seismic hazard which is ideally suited for computer-aided risk analyses. 相似文献
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青藏高原东南缘活动断层相互作用、应力触发与差别响应 总被引：2，自引：0，他引：2
岩石圈、地壳由众多板块、地块及层圈组合而成,是开放性复杂巨系统,活断层在地壳中犹如神经网络也是复杂的开放体系。因此活断层之间存在复杂的相互作用,例如地震断层破裂产生应力扰动,可能触发其他断层破裂,不仅在近处,也会在远处发生。不同的活断层构造产状、活动方式及应变阶段不同,对同一次触发响应不同。触发与差别响应二者的叠加效应在地震活动性上有重要表现。表现之一是区域大震后,余震区外地震活动显著增强处发生继发性大震的概率最大,也即率先出现"远余震、诱发前震、响应震"的地方地震危险性增大,对预测未来地震位置有效。对本区1950—2013年地震统计表明,预测成功率W=1-漏报率-虚报率=80%。同时,对当前地震危险区作了预测。 相似文献
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华北地区距雄安新区300 km范围内包括唐山、邢台和张北三个典型强震区,近50年来,先后发生1966年邢台7.2级、1976年唐山7.8级和1998年张北6.2级强震活动,未来仍具发生破坏性地震的风险。在现今构造应力环境下,3个典型强震区内断裂活动危险性如何、再次发生中强地震对雄安新区地面稳定性有怎样的影响,这些都是要回答的问题。对此,本文首先基于唐山、邢台和张北强震区关键构造部位深孔水压致裂地应力测量数据,依据Byerlee断层滑动失稳摩擦准则,计算各强震区内潜在发震断层的临界失稳状态,探讨断裂活动危险性;之后依据中华人民共和国第五代《中国地震动参数区划图》之《中国大陆及邻区潜在震源区划分图》,厘定雄安新区外围300 km范围内主要潜在震源区和震级上限;最后选取适宜的地震烈度衰减模型,定量计算主要潜在震源区未来发生震级上限地震时对雄安新区地震烈度的影响,进而为雄安新区及重大工程抗震设防提供科学参考。结果表明：(1)唐山、邢台和张北强震区内主要潜在震源区未来发生震级上限地震产生的地震烈度衰减至雄安新区时均位于Ⅳ~Ⅶ度;(2)北京通州及邻区发生8.0级地震、涞水—高碑店沿线发生6.5级地震会在雄安新区产生Ⅶ度地震烈度,震害较轻;(3)其他潜在震源区在雄安新区产生的地震烈度均小于V度,并不会产生显著震害效应。鉴于此,雄安新区抗震设防烈度建议由原Ⅶ度调至Ⅷ度为宜。 相似文献