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1.
Cristiano Collettini Massimiliano Barchi Cristina Pauselli Costanzo Federico Giampaolo Pialli 《Journal of Geodynamics》2000,29(3-5)
This paper deals with the geometry and kinematics of the active normal faults in northern Umbria, and their relationship with the seismicity observed in the area. In particular, we illustrate the contribution of seismic reflection data (a network of seismic profiles, NNW–SSE and WSW–ENE trending) in constraining at depth the geometry of the different active fault systems and their reciprocal spatial relationships. The main normal fault in the area is the Alto Tiberina fault, NNW trending and ENE dipping, producing a displacement of about 5 km, and generating a continental basin (Val Tiberina basin), infilled by up to 1500 m with Upper Pliocene–Quaternary deposits. The fault has a staircase trajectory, and can be traced on the seismic profiles to a depth of about 13 km. A set of WSW-dipping, antithetic faults can be recognised on the profiles, the most important of which is the Gubbio fault, bordering an extensional Quaternary basin and interpreted as an active fault based on geological, geomorphologic and seismological evidence. The epicentral distribution of the main historical earthquakes is strictly parallel to the general trend of the normal faults. The focal mechanisms of the major earthquakes show a strong similarity with the attitude of the extensional faults, mapped at the surface and recognised on the seismic profiles. These observations demonstrate the connection between seismicity in the area and the activity of the normal faults. Moreover, the distribution of the instrumental seismicity suggests the activity of the Alto Tiberina fault as the basal detachment for the extensional tectonics of the area. Finally, the action of the Alto Tiberina fault was simulated using two dimensional finite element modelling: a close correspondence between the concentration of shear stresses in the model and the distribution of the present earthquakes was obtained. 相似文献
2.
由地震活动参数分析龙门山-岷山断裂带的现今活动习性与强震危险性 总被引：38，自引：0，他引：38
根据最近28年的区域台网地震资料,利用b值空间分布及断裂带分段的多地震活动参数值的组合方法,结合历史强震背景,分析了沿川北龙门山-岷山断裂带不同断裂段的现今活动习性,并初步判别出了潜在的强震危险段落。研究结果表明:龙门山断裂带中-南段存在6个具有不同现今活动习性的段落,其中,绵竹-茂县段处于相对高应力背景下的频繁中-小震活动状态,被认为是龙门山断裂带上未来最可能发生强震的地段;江油-平武段处于相对高应力背景下的稀疏中-小震活动状态,未来有可能发生中强地震。而岷山断裂带中的岷江断裂段和虎牙断裂段,以及叠溪隐伏逆断层地区均具有相对偏低的应力水平,可能与其不久前分别发生过大地震和强震有关,未来不太长的时期内复发大地震的可能性较小。 相似文献
3.
根据最近34a的区域台网地震资料,利用地震活动性参数b值的空间分布,结合历史强震与现今地震活动背景,分析了川南马边地区主要断裂带的现今活动习性,并初步判别出了潜在的强震危险区域。研究结果表明:1)马边地区的b值空间分布存在明显的空间差异,反映了该区域不同断裂带与断裂段应力积累水平的差异;2)马边-盐津断裂带上存在3个尺度不等的异常低b值区,它们可能是该断裂带上的相对高应力区(或凹凸体),其中位于马边北、沐川西部利店镇附近的凹凸体与位于该断裂带南端盐津附近的凹凸体可能是马边地区未来发生大地震的危险场所,而位于绥江南的小尺度凹凸体有可能是潜在强震的发生地点;3)存在于龙泉山断裂带西南段的凹凸体将是未来发生中强地震的场所;4)金口河-美姑断裂上位于汉源县皇木镇与峨眉山市龙池镇之间的凹凸体存在发生中强地震的可能性 相似文献
4.
Awad Hassoup 《Journal of Seismology》2002,6(4):459-467
The data described here are obtained from the continuous record of earthquakeactivity and lake water-level variation in the Lake Aswan area in Egypt between 1982 and 1997. The seismicity is monitored by a local telemetered seismograph network. The hypocentral parameters of earthquakes have been determined using Hypo71. The earthquake foci are distributed in two seismic zones, shallow and deep in the crust. Shallow events have focal depths of less than 10 km. Deep events extend from 10 to 30 km. The temporal sequence of seismicity iscorrelated with both the water-level variation and the average daily change of the water level in the lake Aswan. The temporal variation of the seismicityindicates that there are only six sequences of increased seismic activity during 1982–1997. The correlation between the seismic activity and the daily variation of the lake water level is poorly observed except with the June 1987 events swarm, which was accompanied by the presence of an anomaly in rate of water level decreasing. It is concluded that the increase in seismic activity in the Aswan reservoir is demonstrating an example of rapid reservoir-triggered seismicity. The deeper seismic sequence in this area, which was associated with the November 14, 1981 mainshock (MD = 5.7), and the earlier seismicity (1981–82), has been correlated with a deeper high velocity anomaly (Awad and Mizoue, 1995-b). 相似文献
5.
Thierry Camelbeeck Pierre Alexandre Kris Vanneste Mustapha Meghraoui 《Soil Dynamics and Earthquake Engineering》2000,20(5-8):405-414
In western Europe, the knowledge of long-term seismicity is based on reliable historical seismicity and covers a time period of less than 700 years. Despite the fact that the seismic activity is considered as low in the region extending from the Lower Rhine Embayment to England, historical information collected recently suggests the occurrence of three earthquakes with magnitude around 6.0 or greater. These events are a source of information for the engineer or the scientist involved in mitigation against large earthquakes. We provide information relevant to this aspect for the Belgian earthquake of September 18, 1692. The severity of the damage described in original sources indicates that its epicentral intensity could be IX (EMS-98 scale) and that the area with intensity VII and greater than VII has at least a mean radius of 45 km. Following relationships between average macroseismic radii and magnitude for earthquakes in stable continental regions, its magnitude Ms is estimated as between 6.0 and 6.5. To extend in time our knowledge of the seismic activity, we conducted paleoseismic investigations in the Roer Graben to address the question of the possible occurrence of large earthquakes with coseismic surface ruptures. Our study along the Feldbiss fault (the western border of the graben) demonstrates its recent activity and provides numerous lines of evidence of Holocene and Late Pleistocene large earthquakes. It suggests that along the 10 km long Bree fault scarp, the return period for earthquakes with magnitude from 6.2 to 6.7 ranges from 10,000 to 20,000 years during the last 50,000 years. Considering as possible the occurrence of similar earthquakes along all the Quaternary faults in the Lower Rhine Embayment, a large earthquake could occur there each 500–1000 years. These results are important in two ways. (i) The evidence that large earthquakes occur in western Europe in the very recent past which is not only attested by historical sources, but also suggested by paleoseismic investigations in the Roer Graben. (ii) The existence of a scientific basis to better evaluate the long-term seismicity in this part of Europe (maximal magnitude and return period) in the framework of seismic hazard assessment. 相似文献
6.
为了分析将地震活动性参数用于判定断裂带现今活动习性、进而评估长期地震危险性的可行性,文中介绍了沿断裂带进行b值扫描与填图的方法,以及进行断裂带分段的多参数值(—b、E、n和—a/—b)组合分析的资料处理、计算及分析步骤;提出了为进行多参数计算的、断裂带分段的参考判据,进而概括了根据计算的参数值、结合强震历史背景、现今地震分布综合分析断裂带现今活动习性空间差异的方法与思路。以5条地震活动水平和监测能力各异的断裂带为试验对象,基于归纳的方法综合分析了各断裂带现今活动习性的空间差异及潜在的地震危险段。文中还就断裂的震后调整运动与低b值的关系以及精定位的地震资料在参数计算中的合理使用等问题进行了讨论。主要认识为:以b值为主的若干地震活动性参数的空间分布可有效地用于断裂带现今活动习性及潜在强震危险段落的判定。沿断裂带b值扫描与填图以及断裂带分段多参数值组合分析两种方法,可分别应用于地震监测能力强和一般的地区;若在监测能力强的地区将两种方法结合起来使用,可获得更可靠的结果。晚期余震活跃或者大震后调整运动的断裂段也可表现出较低b或—b值的特点 相似文献
7.
华北地区近年来小震群活动频繁, 在有数字波形记录的中强地震相对缺乏的背景下, 小震群发震构造精细研究可为华北地区地震危险性分析和地震趋势判断提供重要依据. 本文利用匹配滤波技术对2013年8月22—25日河北蔚县小震群遗漏地震事件进行检测, 并通过地震精定位和震源机制求解分析此次震群的发震构造. 计算结果显示, 通过互相关扫描检测到18次被地震台网常规分析遗漏的地震, 约为地震目录给出的13次地震事件的1.38倍. 该震群发震构造有北东向和北西向两组断裂, 震群活动前期以北东向构造活动为主, 后期地震主要发生在北西向构造, 北西向构造在此次震群活动中地震频度和强度均高于北东向构造. 震源机制计算结果显示北西向构造发震机制以正断拉张为主. 相似文献
8.
Based on seismic data from the regional network for the last 34 years,we analyzed the present fault behavior of major fault zones around the Mabian area,southern Sichuan,and identified the risky fault-segments for potential strong and large earthquakes in the future.The method of analysis is a combination of spatial distribution of b-values with activity background of historical strong earthquakes and current seismicity.Our results mainly show:(1) The spatial distribution of b-values indicates significant heterogeneity in the studied area,which reflects the spatial difference of cumulative stress levels along various fault zones and segments.(2) Three anomalously low b-value areas with different dimensions were identified along the Mabian-Yanjin fault zone.These anomalies can be asperities under relatively high cumulated stress levels.Two asperities are located in the north of Mabian county,in Lidian town in western Muchuan county,and near Yanjin at the south end of the fault zone.These two areas represent potential large earthquake seismogenic sites around the Mabian area in the near future.Besides them,the third relatively smaller asperity is identified at southern Suijiang,as another potential strongearthquake source.(3) An asperity along the southwestern segment of the Longquanshan fault zone indicates the site of potential moderate-to-strong earthquakes.(4) The asperity along the segment between Huangmu town in Hanyuan county and Longchi town in Emeishan city on Jinkouhe-Meigu fault has potential for a moderate-strong earthquake. 相似文献
9.
A seismic gap on the Anninghe fault in western Sichuan,China 总被引：10，自引：0，他引：10
Through integrated analyses of time-varying patterns of regional seismicity, occurrence background of strong and large historical earthquakes along active faults, and temporal-spatial distribution of accu- rately relocated hypocenters of modern small earthquakes, this paper analyzes and discusses the im- plication of a 30-year-lasting seismic quiescence in the region along and surrounding the Anninghe and Zemuhe faults in western Sichuan, China. It suggests that the seismic quiescence for ML≥4.0 events has been lasting in the studied region since January, 1977, along with the formation and evaluation of a seismic gap of the second kind, the Anninghe seismic gap. The Anninghe seismic gap has the background of a seismic gap of the first kind along the Anninghe fault, and has resulted from evident fault-locking and strain-accumulating along the fault during the last 30 years. Now, two fault sections either without or with less small earthquakes exist along the Anninghe fault within the An- ninghe seismic gap. They indicate two linked and locked fault-sections, the northern Mianning section and the Mianning-Xichang section with lengths of 65 km and 75 km and elapsed time from the latest large earthquakes of 527 and 471 years, respectively. Along the Anninghe fault, characteristics of both the background of the first kind seismic gap and the seismicity patterns of the second seismic gap, as well as the hypocenter depth distribution of modern small earthquakes are comparable, respectively, to those appearing before the M=8.1 Hoh Xil earthquake of 2001 and to those emerging in the 20 years before the M=7.1 Loma Prieta, California, earthquake of 1989, suggesting that the Anninghe seismic gap is tending to become mature, and hence its mid- to long-term potential of large earthquakes should be noticeable. The probable maximum magnitudes of the potential earthquakes are estimated to be as large as 7.4 for both the two locked sections of the Anninghe fault. 相似文献
10.
G. F. Karakaisis P. M. Hatzidimitriou E. M. Scordilis D. G. Panagiotopoulos 《Journal of Geodynamics》1998,26(2-4)
The seismicity of western Macedonia is examined in the present paper. On the basis of historical information as well as on instrumental data it is found that this area is characterized by low seismicity. The focal region of the Grevena-Kozani 1995 earthquake exhibits the highest seismicity in terms of probabilities for the generation of strong (Ms ≥ 6.0) earthquakes in a period of fifty years. Two other regions with relatively high seismicity were also distinguished (west of Edessa and around Prespes lakes). Accurate determination of focal parameters of all earthquakes occurred in the area during October 1975-April 1995, by the use of a 3-D crustal model shows that the seismic activity is related to the graben structures of the studied area. Finally, evidence is presented that the triggering of the 1995 earthquake may be related to the impoundment of the Polyfytos artificial lake. 相似文献
11.
Hetty Triastuty Masato Iguchi Takeshi Tameguri 《Journal of Volcanology and Geothermal Research》2009,187(1-2):1-12
Shallow volcano-tectonic (VT) earthquakes recorded at the Kuchinoerabujima island volcano in southwest Japan are analyzed in order to clarify the role of hydrothermal activity in the development of volcanic seismicity. From analysis of shallow VT earthquakes in 2006, two specific episodes of elevated seismicity are observed in April and November 2006. The VT earthquakes have hypocenters at depths of 0–0.4 km beneath the summit crater, and normal fault focal mechanisms with WNW–ESE extension consistent with the tensional stress field indicated by the alignment of craters and fissures. Although the hypocenters and focal mechanisms are found to be largely invariant during these episodes, the corner frequencies of the VT earthquakes underwent a pronounced increase and decrease accompanying the changes in seismicity rates. The corner frequencies increased to 20–25 Hz approximately one month prior to the onset of elevated seismicity, and then decreased to 10–15 Hz in the period of peak seismicity. The rupture length also decreased at the onset of seismicity, thereafter increasing as the seismicity continued. The peak seismicity in terms of the daily number of VT events was accompanied by inflation around the crater, suggestive of a pressure increase in the volcanic system. It is inferred that the increase in shallow VT seismicity and rupture length is related to the development of a fractured zone. The pressure increase in the volcanic system is attributed to the intrusion of hydrothermal fluids, which is supported by an observed increase in fumarolic temperature and activity. The preceding monochromatic events are thus considered to be generated by the effect of fluid-filled cracks. The shortening of rupture length is then inferred to be related to the closing of non-fluid-filled cracks in the fracture zone under the increasing pressure field, leading to a transition from monochromatic events to low-frequency and shallow VT seismicity. 相似文献
12.
中国大陆邻区的地震活动和中国大陆地震的关系 总被引：1，自引：0，他引：1
研究了３个方面的问题，一是中国大陆周边４个地震带地震活跃期与中国大陆地震活跃期的准同步性和它们目前的活动水平；二是欧亚地震带西部与中国大陆的地震活动呈出现明显的超前或滞后性；三是中国大陆邻区６个地震区的强震与中国大陆活跃期的开始或与中国大陆强震的对应关系。 相似文献
13.
Oriented collapse of columns, large-scale destruction debris and temporary abandonment of the area deduced from an archaeological excavation provide evidence for a major (intensity IX) earthquake in Patras, Greece. This, and possibly a cluster of other earthquakes, can be derived from archaeological data. These earthquakes are not included in the historical seismicity catalogues, but can be used to put constraints to the seismic risk of this city. Patras was affected by a cluster of poorly documented earthquakes between 1714 and 1806. The city seems to be exposed to risks of progressive reactivation of a major strike-slip fault. A magnitude 6.4 earthquake in 2008 has been related to it. This fault has also been associated with a total of four events in the last 20 years, a situation reminiscent of the seismic hazard at the western edge of the North Anatolian Fault. 相似文献
14.
— A seismic data file of 3,740 earthquakes from January 1987 to December 1994 has been elaborated for Morocco and the border regions, with 10 main events registering magnitudes from 5 to 5.6. Such seismicity is particularly important for Morocco as the released seismic energy constitutes a considerable part of the total energy radiated during the 20th century. Relative seismicity maps confirm the persistence of the major features of the seismicity of Morocco. An important seismic activity is observed in the Alboran region continental crust, which absorbs the maximum deformation resulting from the convergence of the African and Iberian plates. However, in the longitude window 3.5°– 6° W at depths of 25 to 50 km, a seismic gap zone seems to take place. An explanation of this phenomenon may be provided by the slab breakoff model. Even if the seismicity of Morocco remains moderate, heavy damage is observed when the magnitude of earthquakes exceeds 4.5, especially in the case of traditional buildings. 相似文献
15.
J. Almendros J. M. Ibez G. Alguacil J. Morales E. Del Pezzo M. La Rocca R. Ortiz V. Araa M. J. Blanco 《Journal of Volcanology and Geothermal Research》2000,103(1-4)
Data analyzed in the present work correspond to a 40 days field experiment carried out in Teide Volcano (Canary Islands, Spain) with two short-period small-aperture dense seismic antennas in 1994. The objective of this experiment was to detect, analyze and locate the local seismicity. We analyzed also the background seismic noise to investigate the possible presence of volcanic tremor. From a set of 76 events, we selected 21 of them in base of their good signal-to-noise ratio and their possibility to locate their seismic source by using the seismic antennas. A visual classification based on the S–P time and seismogram shape has permitted to establish three groups of events: local seismicity (S–P time between 3 and 5 s), very local earthquakes (S–P time smaller than 3 s) and artificial explosions. These earthquakes have been located by applying the Zero Lag Cross-Correlation technique and the inverse ray-tracing procedure. Those earthquakes that were recorded simultaneously by both seismic antennas were also located by intersecting both back-azimuths. The analysis of the seismicity has revealed that the amount of seismicity in Teide Volcano is moderate. This seismicity could be distributed in three main areas: inside the Caldera Edifice (below the Teide–Pico Viejo complex), in the eastern border of the Caldera Edifice and offshore of the island. At present, this activity is the only indicator of the volcano dynamics. The analysis of the back-ground seismic noise has revealed that at frequencies lower than 2 Hz, the Oceanic Load signal is predominant over other signals, even over local earthquakes with a magnitude of 2.0. Due to this, although if in the Teide area were present a weak volcanic tremor, or other volcanic signals with predominant peaks below 2 Hz, to observe them would be a very difficult task. 相似文献
16.
信浓川地震带位于日本大地沟北部,地壳运动十分强烈,区内地震主要沿信浓川流域发生,并密集成带,大地构造上处于日本海板块向本州板块俯冲的边界线上。该地震带大多数地震为中强震,且均为浅源地震,地震发生伴随着明显的地下水前兆异常,震中区有强烈的超压热水系的喷溢活动。震中区地下水的温度、电导率以及主要地球化学成分呈线性异常分布,并与地震强弱或地震断裂规模有关,地震断层的规模控制了超压热水系喷溢活动的强度和规模。地震发生与超压热水系喷溢活动有着密切的成生关系,超压热水系喷溢活动使断层发生活动所需应力条件降低,诱发地震发生,同时断层活动为超压热水系向上喷溢提供通道。 相似文献
17.
以川滇活动地块东边界为例,利用最近31年的地震资料,根据精细b值计算结果,研究该边界断裂带的应力空间分布及其强震危险性. 研究结果显示：（1）沿川滇活动地块东边界,b值空间分布显示在不同断裂以及同一断裂不同断裂段存在较大差异,从而反映出应力积累水平的空间差异.（2）小江断裂带主干断裂上的嵩明凹凸体及存在于主干断裂附近巧家与东川间以及嵩明北西的2个凹凸体、存在于安宁河断裂冕宁附近和则木河断裂西昌附近的凹凸体以及位于鲜水河断裂中南段道孚—乾宁间大尺度的凹凸体将是川滇活动地块东边界未来大震或强震的震源区. 相似文献
18.
Western Sichuan is among the most seismically active regions in southwestern China and is characterized by frequent strong (M 6.5) earthquakes, mainly along the Xianshuihe fault zone. Historical and instrumental seismicity show a temporal pattern of active periods separated by inactive ones, while in space a remarkable epicenter migration has been observed. During the last active period starting in 1893, the sinistral strike–slip Xianshuihe fault of 350 km total length, was entirely broken with the epicenters of successive strong earthquakes migrating along its strike. This pattern is investigated by resolving changes of Coulomb failure function (CFF) since 1893 and hence the evolution of the stress field in the area during the last 110 years. Coulomb stress changes were calculated assuming that earthquakes can be modeled as static dislocations in an elastic halfspace, and taking into account both the coseismic slip in strong (M 6.5) earthquakes and the slow tectonic stress buildup associated with major fault segments. The stress change calculations were performed for faults of strike, dip, and rake appropriate to the strong events. We evaluate whether these stress changes brought a given strong earthquake closer to, or sent it farther from, failure. It was found that all strong earthquakes, and moreover, the majority of smaller events for which reliable fault plane solutions are available, have occurred on stress–enhanced fault segments providing a convincing case in which Coulomb stress modeling gives insight into the temporal and spatial manifestation of seismic activity. We extend the stress calculations to the year 2025 and provide an assessment for future seismic hazard by identifying the fault segments that are possible sites of future strong earthquakes. 相似文献
19.
本文通过整理和分析青藏高原西北于田地区强震后,地震迁移的空间分布,迁移特征,同时整理和分析与迁移地震相关的青藏高原主要活动构造的结构和地震活动,分析两者之间的关系。得到以下结论:①迁移地震空间分布具有不均匀性,主要分布在活动地块边界,受大型活动构造带控制;②迁移路径主要有三条,第二条路径更为重要,主要沿着昆仑山脉向唐古拉山、巴颜喀拉山及阿尼玛卿山,在若尔盖盆地东北侧折向东南,向岷山、龙门山迁移;③未来5年内在青藏高原西北于田地区可能发生1~2次6.5级左右地震,在龙门山南段等地震空区内可能发生迁移强地震;④1900年以来发生的地震沿先前存在的地震空区分布。 相似文献
20.
Mircea Radulian Cezar-Ioan Trifu Florin Octavian Cârbunar 《Pure and Applied Geophysics》1991,136(4):499-514
A numerical algorithm is proposed for the simulation of the earthquake process during a seismic cycle. The algorithm is based on a heterogeneous discrete model of the fault plane and assumes there are two kinds of seismicity: background crack-like earthquakes and asperity-like events. An active zone of the fault contains an asperity distribution with a characteristic elementary area. The background seismicity randomly develops shear stress-free surfaces which tend to surround the asperities as in a 2D percolation process. The model parameters are taken from observations on the Vrancea (Romania) intermediate depth seismic region. The results emphasize the significant role of the geometry in the mechanism of the seismic failure. The algorithm predicts the nonlinear behavior in the frequency-magnitude distribution, the decrease of theb-slope associated with the asperity-like events, the magnitude range of major earthquakes, and their recurrence times. 相似文献