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1.
The magnitude of shear stress in the lithosphere is bounded from below by the apparent stress and stress drop during intraplate earthquakes. Apparent stresses and stress drops for a number of mid-plate earthquakes are calculated from the earthquake magnitude, SH wave amplitude spectra, and estimates of the length of the fault zone. Apparent stresses vary between 0.1 and 2 bars, ifm b is used as a measure of seismic energy, and stress drops lie between 2 and 70 bars. There is no systematic difference in either apparent stress or stress drop between these intraplate events and typical plate boundary earthquakes. These bounds on intraplate shear stresses are consistent with the inference from current models of plate tectonic driving forces that regional stress differences in the plates are typically on the order of 100 bars. The highest stress drops measured for midplate earthquakes under this model represent nearly total release of local tectonic stress.  相似文献   

2.
《Journal of Geodynamics》2003,35(1-2):173-189
The special type of intraplate microseismicity with swarm-like occurrence of earthquakes within the Vogtland/NW-Bohemian Region is analysed to reveal the nature and the origin of the seismogenic regime. The long-term data set of continuous seismic monitoring since 1962, including more than 26000 events within a range of about 5 units of local magnitude, provides an unique database for statistical investigations. Most earthquakes occur in narrow hypocentral volumes (clusters) within the lower part of the upper crust, but also single event occurrence outside of spatial clusters is observed. Temporal distribution of events is concentrated in clusters (swarms), which last some days until few month in dependence of intensity. Since 1962 three strong swarms occurred (1962, 1985/86, 2000), including two seismic cycles. Spatial clusters are distributed along a fault system of regional extension (Leipzig-Regensburger Störung), which is supposed to act as the joint tectonic fracture zone for the whole seismogenic region. Seismicity is analysed by fractal analysis, suggesting a unifractal behaviour of seismicity and uniform character of seismotectonic regime for the whole region. A tendency of decreasing fractal dimension values is observed for temporal distribution of earthquakes, indicating an increasing degree of temporal clustering from swarm to swarm. Following the idea of earthquake triggering by magma intrusions and related fluid and gas release into the tectonically pre-stressed parts of the crust, a steady increased intensity of intrusion and/or fluid and gas release might account for that observation. Additionally, seismic parameters for Vogtland/NW-Bohemia intraplate seismicity are compared with an adequate data set of mining-induced seismicity in a nearby mine of Lubin/Poland and with synthetic data sets to evaluate parameter estimation. Due to different seismogenic regime of tectonic and induced seismicity, significant differences between b-values and temporal dimension values are observed. Most significant for intraplate seismicity are relatively low fractal dimension values for temporal distribution. That observation reflects the strong degree of temporal earthquake clustering, which might explain the episodic character of earthquake swarms and support the idea of push-like triggering of earthquake avalanches by intruding magma.  相似文献   

3.
川滇地区是我国地震危险性较高的地区之一.本文基于对特大强震的风险性考虑,使用全球地震模型OpenQuake软件,建立了川滇地区地震危险性预测新模型.首先根据构造特征划分多个震源分区,并整理出这些震源分区内断层活动特征与滑动速率;基于震源分区和断层模型,使用GPS应变率转换成的锥形古登堡-里克特关系作为整个区域的地震积累率,并允许超过历史最大震级的特大地震的出现,结合活动断层滑动速率所积累的地震发生率,给出震源分区内断层地震源和背景地震源的地震发生率的比率分配关系;在活动断层分段上,保留了大型断裂或其主要部分,没有根据小的阶区来对断层进行详细分段,以便分配特大地震发生率;并使用地震率平滑方法分配背景地震发生率.最后在OpenQuake中加入地震动预测方程,计算出了川滇地区的PGA分布图,为区域地震危险性提供科学依据.  相似文献   

4.
2022年9月5日四川泸定发生M6.8地震,为研究泸定地震孕震区的应力变化,选取b值、小震调制比和丛集率这3个参数,对泸定地震前的区域地震活动状态进行计算研究。结果显示:泸定及周边区域几次强震发生前,区域地震活动均存在持续时间较长的低b值时段,且在低b值状态下震前短期内出现小震高丛集、高调制比的现象;鲜水河断裂带的地震活动状态分析显示,此次泸定地震前该断裂带存在持续时间近10个月的低b值状态,且短期内出现丛集率升高、调制比高值现象。通过对比分析,认为泸定地震是鲜水河断裂带构造运动的结果。综合分析认为,结合应力场背景和构造条件研究地震活动b值、固体潮调制比和丛集率的时空变化有助于理解大地震的孕育演化过程。  相似文献   

5.
首先讨论龙滩库区水库蓄水与地震活动之间的关系,发现龙滩水库诱发地震特征十分明显,地震共分5丛呈丛集分布.利用库区架设的24个固定和流动台站记录的数字记录资料,在研究得到龙滩库区非弹性衰减和台站场地响应的基础上,精确测定得到了该地区总共1616个ML≥0.1级地震的震源参数,比较了水库诱发地震与构造地震震源参数特征的差异,得到了以下主要结论:1)龙滩水库地震活动与水库蓄水关系密切,不同蓄水阶段5丛的地震活动状态不同,局部断裂构造发育以及岩石透水性能影响着地震活动对蓄水过程的响应.2)龙滩水库诱发地震的地震矩M0随震级ML的增大而增大,两者之间存在较好的线性关系,统计关系为LogM0=1.07 ML+10.17.应力降与地震大小之间的关系和Nuttli的板内地震为增加应力降(ISD)模型的结果比较吻合,统计关系为LogΔσ=0.71 ML-2.89.3)龙滩水库地区地震辐射能量和地震视应力均随震级的增大而增大,后者意味着大地震是比小地震更高效率的地震能量辐射体.4)总体上不同丛地震应力降水平存在差异.地震应力降空间分布上与库水深度有较好的一致性,即库水深的区域应力降水平高.5)与同震级的构造地震相比,水库诱发地震的应力降值比前者明显偏低,大约小10倍.这可能是由于水库蓄水造成地下介质孔隙压力增大或者水的润滑作用,从而导致在一个比较低的构造应力情况下发生水库诱发地震.  相似文献   

6.
A review of the history of earthquake observations in Jamaica is presented; there have been several high-intensity earthquakes in the last 300 years. The observed seismicity of the Jamaica region is discussed in the context of what is known of regional tectonics, and possible source regions of earthquakes are identified but a comparison between instrumentally determined seismicity and macroseismicity shows that the instrumental data are of insufficient quantity or quality to permit direct assessment of earthquake risk by conventional techniques. An alternative approach has been adopted; consideration of the macroseismic record suggests that the peak acceleration in rock with 90 per cent probability of not being exceeded in any 50-year period is of order 0.3 g but that there are very significant local variations caused by near-surface geology. Especially this applies to the capital, Kingston, and envelope response spectra are derived for shallow, intermediate and deep thickness of sediments under the city to demonstate the possibility that localized amplification may occur. A current apparent decline in the seismicity of the Jamaica region is noted but it is shown that the decline in the number of earthquakes of engineering interest is not yet statistically significant.  相似文献   

7.
１９９３年第三季度，全球地震活动水平为中等偏高，明显高于上半年平均水平。日本北海道西南近海发生７．６级浅源地震，但不属于日本海沟地震。埃及西奈半岛发生５．７级地震，为今年亚欧带西段之最大地震。马里亚纳群岛发生８．１级中深震，使西北太平洋地区地震水平达到全球第一。兴都库什地区接连发生三次较大中深震，可能对我国西部地区地震活动有影响。墨西哥恰帕斯州近海发生７．３级地震，美洲带新的地震活动轮回正式开始。印度南部发生６．３级中强震，属于板内地震。  相似文献   

8.
在对构造运动差异较大的柯坪块体和天山中部地区地震活动研究基础上,深入分析了这两个不同构造单元的中强地震活动对整体新疆地震形势的影响。不同构造环境下不同构造单元地震活动差异性很大。柯坪块体内构造运动强烈,它是新疆6级地震主要活动区之一。6级地震发生后的1年内,天山地震带是中强地震的主要响应区,在时间上具有短期预测意义。位于特殊构造环境的中天山地区地震少,地震强度低。4次5级地震后的1~3年,新疆地震活动呈明显增强趋势,中天山地区中强地震活动对周边地区中强地震活动会产生触发作用。  相似文献   

9.
There are two fundamentally different approaches to assessing the probabilistic risk of earthquake occurrence. The first is fault based. The statistical occurrence of earthquakes is determined for mapped faults. The applicable models are renewal models in that a tectonic loading of faults is included. The second approach is seismicity based. The risk of future earthquakes is based on the past seismicity in the region. These are also known as cluster models. An example of a cluster model is the epidemic type aftershock sequence (ETAS) model. In this paper we discuss an alternative branching aftershock sequence (BASS) model. In the BASS model an initial, or seed, earthquake is specified. The subsequent earthquakes are obtained from statistical distributions of magnitude, time, and location. The magnitude scaling is based on a combination of the Gutenberg-Richter scaling relation and the modified Båth’s law for the scaling relation of aftershock magnitudes relative to the magnitude of the main earthquake. Omori’s law specifies the distribution of earthquake times, and a modified form of Omori’s law specifies the distribution of earthquake locations. Unlike the ETAS model, the BASS model is fully self-similar, and is not sensitive to the low magnitude cutoff.  相似文献   

10.
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.  相似文献   

11.
杨欣  聂晓红  夏爱国 《中国地震》2005,21(2):244-253
通过分析昭苏6．1级地震序列特征、震源与介质破裂特性、震源环境与历史地震活动类比及区域地震和前兆资料的异常变化等，对该震前的区域地震活动背景、震后的震情趋势等有了较为细致的了解和判定。主要结果有：①在2003年新疆境内中强地震成组活动的背景下，于现代地震活动很弱的昭苏盆地内发生了6．1级地震；②6．1级地震为主一余型地震序列，震后序列衰减正常；③主震震源机制解结果与现代区域构造应力场特征吻合，表明构造活动具有明显的继承性，并对地震活动有着控制作用；④震源区域构造应力释放充分，区域应力场处于相对稳定的调整状态。综合各类分析结果后认为，震区发生更大地震的可能性很小。  相似文献   

12.
Mechanisms of seismic quiescences   总被引：7，自引：0，他引：7  
In the past decade there have been major advances in understanding the seismic cycle in terms of the recognition of characteristic patterns of seismicity over the entire tectonic loading cycle. The most distinctive types of patterns are seismic quiescences, of which three types can be recognized:post-seismic quiescence, which occurs in the region of the rupture zone of an earthquake and persists for a substantial fraction of the recurrence time following the earthquake,intermediate-term quiescences, which appear over a similar region and persist for several years prior to large plate-rupturing earthquakes, andshort-term quiescences, which are pronounced lulls in premonitory swarms that occur in the hypocentral region hours or days before an earthquake. Although the frequency with which intermediate-term and short-term quiescences precede earthquakes is not known, and the statistical significance of some of the former has been challenged, there is a need, if this phenomena is to be considered a possibly real precursor, to consider physical mechanisms that may be responsible for them.The characteristic features of these quiescences are reviewed, and possible mechanisms for their cause are discussed. Post-seismic quiescence can be readily explained by any simple model of the tectonic loading cycle as due to the regional effect of the stress-drop of the previous principal earthquake. The other types of quiescence require significant modification to any such simple model. Of the possibilities considered, only two seem viable in predicting the observed phenomena, dilatancy hardening and slip weakening. Intermediate-term quiescences typically occur over a region equal to or several times the size of the rupture zone of the later earthquake and exhibit a relationship between the quiescence duration and size of the earthquake: they thus involve regional hardening or stress relaxation and agree with the predictions of the dilatancy-diffusion theory. Short-term quiescences, on the other hand, are more likely explained by fault zone dilatancy hardening and/or slip weakening within a small nucleation zone. Because seismicity is a locally relaxing process, seismicity should follow a behaviour known in rock mechanics as the Kaiser effect, in which only a very slight increase in strength, due to dilatancy hardening or decrease in stress due to slip weakening, is required to cause quiescence. This is in contrast to other precursory phenomena predicted by dilatancy, which require large dilatant strains and complete dilatancy hardening.Lamont-Doherty Geological Observatory  相似文献   

13.
The maximum likelihood estimation method is applied to study the geographical distribution of earthquake hazard parameters and seismicity in 28 seismogenic source zones of NW Himalaya and the adjoining regions. For this purpose, we have prepared a reliable, homogeneous and complete earthquake catalogue during the period 1500–2010. The technique used here allows the data to contain either historical or instrumental era or even a combination of the both. In this study, the earthquake hazard parameters, which include maximum regional magnitude (M max), mean seismic activity rate (λ), the parameter b (or β?=?b/log e) of Gutenberg–Richter (G–R) frequency-magnitude relationship, the return periods of earthquakes with a certain threshold magnitude along with their probabilities of occurrences have been calculated using only instrumental earthquake data during the period 1900–2010. The uncertainties in magnitude have been also taken into consideration during the calculation of hazard parameters. The earthquake hazard in the whole NW Himalaya region has been calculated in 28 seismogenic source zones delineated on the basis of seismicity level, tectonics and focal mechanism. The annual probability of exceedance of earthquake (activity rate) of certain magnitude is also calculated for all seismogenic source zones. The obtained earthquake hazard parameters were geographically distributed in all 28 seismogenic source zones to analyze the spatial variation of localized seismicity parameters. It is observed that seismic hazard level is high in Quetta-Kirthar-Sulaiman region in Pakistan, Hindukush-Pamir Himalaya region and Uttarkashi-Chamoli region in Himalayan Frontal Thrust belt. The source zones that are expected to have maximum regional magnitude (M max) of more than 8.0 are Quetta, southern Pamir, Caucasus and Kashmir-Himanchal Pradesh which have experienced such magnitude of earthquakes in the past. It is observed that seismic hazard level varies spatially from one zone to another which suggests that the examined regions have high crustal heterogeneity and seismotectonic complexity.  相似文献   

14.
亚洲中东部“塑性流动－地震”网络系统及板内构造单元   总被引：1，自引：0，他引：1  
对于地震的网络状分布特征的研究表明，在亚洲的中东部地区存在着两个网络系统，即分布于大部分地区的中东亚网络系统和位于其东南的华东南网络系统。根据多层构造模型，这些地震网络系统实际上是岩石圈下层（含下地壳和岩石圈地幔）塑性流动网络的一种显示。每一“塑性流动－地震”网络系统为不同类型的边界所围限，其中包括一段驱动边界以及若干段约束边界和泄流边界。本地区的两个塑性流动网络系统分别以喜马拉雅弧和台湾弧为驱动边界，对板块内部的构造变形、构造应力场、地震活动性、以及构造单元（亚板块、地体等）的划分起着控制的作用。  相似文献   

15.
I suggest that earthquake precursors can be divided into two major categories, physical and tectonic. I define physical precursor to be a direct or indirect indication of initiation or progression of an irreversible rupture-generating physical process within the preparation zone of a forthcoming earthquake. Tectonic precursor is defined as a manifestation of tectonic movement which takes place outside the preparation zone of an impending earthquake as a link in a chain of particular local tectonism in each individual area preceding the earthquake.Most intermediate-term, short-term and immediate precursors of various disciplines within the source regions of main shocks are considered physical ones. Some precursory crustal deformations around the source regions are, however, possibly tectonic precursors, because they may be caused by episodic plate motions or resultant block movements in the neighboring regions of the fault segments that will break. A possible example of this phenomena is the anomalous crustal uplift in the Izu Peninsula, Japan, before the 1978 Izu-Oshima earthquake ofM s 6.8. Some precursory changes in seismicity patterns in wide areas surrounding source regions also seem to be tectonic precursors, because they were probably caused by the particular tectonic setting of each region. A typical example is a so-called doughnut pattern before the 1923 Kanto, Japan, earthquake ofM s 8.2.Although most studies on earthquake precursors so far seem to regard implicitly all precursory phenomena observed as physical ones, the two categories should be distinguished carefully when statistical analysis or physical modeling is carried out based on reported precursory phenomena. In active plate boundary zones, where a practical strategy for earthquake prediction may well be different from that in intraplate regions, tectonic precursors can be powerful additional tools for intermediate-term earthquake prediction.  相似文献   

16.
Continental intraplate regions are characterized by uniform stresses over thousands of kilometers. Local stresses, with wavelengths of tens to hundreds of kilometers can accumulate at inhomogeneities lying within these regional fields. A variety of geological structures, herein called local stress concentrators (LSCs), act as elastic inhomogeneities. The temporal buildup of stress depends on the particular structure and its geometrical relationship with the regional stress field. The interaction of the local and the regional stress fields can result in the rotation of the latter over wavelengths of tens to hundreds of kilometers. This rotation can be detected by direct measurement or from seismicity data. Intraplate earthquakes (IPEs) result when the local stresses become comparable with their regional counterparts, i.e., hundreds of megapascals. Globally, most of the seismic energy release associated with IPEs occurs within old rifts which contain LSCs most favorable for stress buildup by stress inversion. Of the various LSCs, stepover en echelon faults are associated the largest IPEs. In low tectonic strain rate regions, IPEs are associated with larger stress drops. With the availability of a variety of LSCs, there is generally an absence of repeat earthquakes. Instead, successive earthquakes occur on different structures, leading to the observation of “roaming” earthquakes. These observations suggest a need for a reevaluation of seismic hazard estimation techniques. This study addresses some of these facets of the nature of IPEs with global examples, including a unique, detailed seismicity and geodetic data set collected in a dozen years following the 2001 M 7.7 Bhuj earthquake in western India.  相似文献   

17.
We establish here a comprehensive database of intraplate seismicity in the Pacific Basin. Relocation and analysis of 894 earthquakes yield 403 reliable intraplate earthquakes during 1913–1988. These numbers do not include earthquake swarms, which account for another 838 events. Most of the remainder (304 events) are actually plate boundary earthquakes that have been erroneously located in intraplate regions. A significant number occur in recent years when location capabilities should have guarded against this situation. Relocations involve a careful linear inversion ofP andS arrivals, accompanied by a Monte Carlo statistical analysis. We have also attentively removed the high number of clerical errors and nuclear tests that exist in epicenter bulletins.A geographical examination of the relocated epicenters reveals several striking features. There are three NW-SE lineaments north of the Fiji Plateau and in Micronesia; diffuse seismicity and incompatible focal mechanisms argue against the southernmost, discussed byOkal et al. (1986) andKroenke andWalker (1986), as the simple relocation of the Solomon trench to the North. Besides another striking lineament, along the 130°W meridian, there is also a strong correlation between seismicity and bathymetry in certain parts of the Basin. In the Eastcentral Pacific and Nazca plates there are many epicenters on fracture zones and fossil spreading ridges, and hot spot traces like the Louisville, Nazca and Cocos Ridges also display seismicity.  相似文献   

18.
在研究近期（10年）强震危险性判定和总结四川地区1972--2002年强震预测经验的基础上，清理了中国大陆1920--2002年47次浅源大震事件前地震活动图像特征（M≥4．7），提炼出10个方面12项经验性预测依据：主体活动区、多发时段、关联序列、大陆及地区地震异常图像、地区（带）-地段（震源区）地震增强图像（含信号震、诱发地震、地震条带）、相关地震、窗口地震、复发间隔、大陆及地区缺震、地段缺震与地段强震一缺震转折等。它们在47次震例中的综合出现率≥0．58（即依据比7／12以上）占42例；≥0．66（即8／12以上）占34例。因此，强震（M≥4．7）活动图像经验性预测依据可以作为预测有较大可能发生大地震危险区的依据之一。  相似文献   

19.
— An algorithm recently developed by RUNDLE et al. (2002) to find regions of anomalous seismic activity associated with large earthquakes identified the location of an M w = 5.6 earthquake near Calexico, Mexico. In this paper we analyze the regional seismicity before this event, and a nearby M w = 5.7 event, using time-to-failure algorithms developed by BOWMAN et al. (1998) and BOWMAN and KING (2001a,b). The former finds the radius of a circular region surrounding the epicenter that optimizes the time-to-failure acceleration of seismic release. The latter optimizes acceleration based on the expected stress accumulation pattern for a dislocation source. Both methods found a period of accelerating seismicity in an optimal region, the size of which agrees with previously proposed scaling relations. This positive result suggests that the Rundle algorithm may provide a useful technique to identify regions of accelerating seismicity, which can then be analyzed using signal optimization time-to-failure techniques.  相似文献   

20.
Universality of the Seismic Moment-frequency Relation   总被引：1，自引：0，他引：1  
—We analyze the seismic moment-frequency relation in various depth ranges and for different seismic regions, using Flinn-Engdahl's regionalization of global seismicity. Three earthquake lists of centroid-moment tensor data have been used the Harvard catalog, the USGS catalog, and the Huang et al. (1997) catalog of deep earthquakes. The results confirm the universality of the β-values and the maximum moment for shallow earthquakes in continental regions, as well as at and near continental boundaries. Moreover, we show that although fluctuations in earthquake size distribution increase with depth, the β-values for earthquakes in the depth range of 0–500 km exhibit no statistically significant regional variations. The regional variations are significant only for deep events near the 660 km boundary. For declustered shallow earthquake catalogs and deeper events, we show that the worldwide β-values have the same value of 0.60 ± 0.02. This finding suggests that the β-value is a universal constant. We investigate the statistical correlations between the numbers of seismic events in different depth ranges and the correlation of the tectonic deformation rate and seismic activity (the number of earthquakes above a certain threshold level per year). The high level of these correlations suggests that seismic activity indicates tectonic deformation rate in subduction zones. Combined with the universality of the β-value, this finding implies little if any variation in maximum earthquake seismic moment among various subduction zones. If we assume that earthquakes of maximum size are similar in different depth ranges and the seismic efficiency coefficient, χ, is close to 100% for shallow seismicity, then we can estimate χ for deeper earthquakes for intermediate earthquakes χ≈ 5%, and χ≈ 1% for deep events. These results may lead to new theoretical understanding of the earthquake process and better estimates of seismic hazard.  相似文献   

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