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The improved calculation method ofb value is presented in this paper. The method can enlarge the role of earthquake occurrence frequency inb value calculation and thus increase theb value variation amplitude. In this case, the combination structure variation between earthquake magnitudes and corresponding
frequencies could be shown clearly. According to the calculation and analysis for limited mainshocks in the complete seismicity
data of selected monitored area with assigned consistent lowest magnitude, the precursor anomaly features, quantitative indexes
and the calculation formula of relative subject function ofb value variation have been preliminarily worked out. The prediction in short period (from 1 to 3 months) for damage earthquakes
in the monitored area mentioned above can be put forward on the basis of the results of quantitative calculation and analysis. 相似文献
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Kiran Kumar Singh Thingbaijam Sankar Kumar Nath Abhimanyu Yadav Abhishek Raj M. Yanger Walling William Kumar Mohanty 《Journal of Seismology》2008,12(1):107-123
Recent seismicity in the northeast India and its adjoining region exhibits different earthquake mechanisms – predominantly
thrust faulting on the eastern boundary, normal faulting in the upper Himalaya, and strike slip in the remaining areas. A
homogenized catalogue in moment magnitude, M
W, covering a period from 1906 to 2006 is derived from International Seismological Center (ISC) catalogue, and Global Centroid
Moment Tensor (GCMT) database. Owing to significant and stable earthquake recordings as seen from 1964 onwards, the seismicity
in the region is analyzed for the period with spatial distribution of magnitude of completeness m
t, b value, a value, and correlation fractal dimension D
C. The estimated value of m
t is found to vary between 4.0 and 4.8. The a value is seen to vary from 4.47 to 8.59 while b value ranges from 0.61 to 1.36. Thrust zones are seen to exhibit predominantly lower b value distribution while strike-slip and normal faulting regimes are associated with moderate to higher b value distribution. D
C is found to vary from 0.70 to 1.66. Although the correlation between spatial distribution of b value and D
C is seen predominantly negative, positive correlations can also be observed in some parts of this territory. A major observation
is the strikingly negative correlation with low b value in the eastern boundary thrust region implying a possible case of extending asperity. Incidentally, application of
box counting method on fault segments of the study region indicates comparatively higher fractal dimension, D, suggesting an inclination towards a planar geometrical coverage in the 2D spatial extent. Finally, four broad seismic source
zones are demarcated based on the estimated spatial seismicity patterns in collaboration with the underlying active fault
networks. The present work appraises the seismicity scenario in fulfillment of a basic groundwork for seismic hazard assessment
in this earthquake province of the country. 相似文献
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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
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The behavior of the Gutenberg-Richter distribution (the frequency-magnitude relation for the earthquakes) in response to advancing the system of seismic observations and applying various methods for estimation of the Gutenberg-Richter b value is studied. The long highly accurate time series of seismological measurements at the Garm geophysical testing site in Tajikistan is an input for the study. We analyzed the data from the detailed catalogue of earthquakes with magnitude M = 0?C5 that occurred within the test site from 1955 through 1992. It is shown that the changes in the design of measurements both as to the number of observation sites and as to the measurement capacities during the development of the seismic network in 1955?C1966 have strongly affected the content of the catalogue. Our study revealed spatiotemporal changes in the minimum magnitude of completeness, which were associated with advancing the design of observations. We have analyzed the accuracy of the calculation of the b value as a function of the reliability of determining the actual minimal magnitude of completeness (the cutoff magnitude) for the catalogue (Mc), the method of calculation of the b value, and the volume of the spatial sample of the earthquakes used. It is established that the pattern of horizontal distribution of the b value is closely correlated to the tectonic structure of the test area, while its vertical distribution distinctly reflects the crustal waveguide at a depth of 9?C17 km, which has been previously revealed approximately in this depth interval according to other seismological data. This suggests that, in the first approximation, the lateral and vertical variations in the b value observed in our study are caused by the changes in the strength properties of the crustal material, namely, by the increased plasticity of the rocks within a thick sedimentary layer and in the waveguide. 相似文献
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A lot of researches onb value have been made in seismology. Since the 1960’s Mogi, Scholz and others have studied AE of rock specimens in laboratory
and discovered that it is related to natural earthquakes. All former researchers used integral specimens to studyb value in the laboratory. However a major earthquake is usually related to a existing seismic-fault in that area. For this
reason, a series of fracture experiments with rock and glass specimens having pre-existing crack or notch is performed in
order to examine the effect of preexisting crack tob value. The experimental results show that theb value begins to decrease as soon as the initiation of the crack and finally drop to a very low value when the specimen breaks
unstably. Based on these, a brief discussion on the possible mechanism ofb value change for natural earthquakes is given.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,9, 393–400, 1987.
Projects sponsored by the Chinese Joint Seismological Science Foundation. 相似文献
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C. Godano 《Pure and Applied Geophysics》1991,137(1-2):85-94
A very simple model of fault fracturing is presented. The fault is envisaged as a series of faultlets whose area is randomly distributed and whose strength have a Gaussian distribution. Faultlet slip occurs when the loading stress reaches its strength. Large earthquakes are generated by coalescence of smaller cracks. Theb value of the Gutenberg-Richter frequency magnitude relation is then calculated. Ab equal to 1 (scale invariance) is obtained only for events with magnitudeM greater than 3. At lower magnitude the number of events decreases with decreasing magnitude. A similar result can be explained by the experimental observation of an anomalous scaling law of real earthquakes. Here the suggestion is advanced that a similar observation could be interpreted by a multifractal approach. 相似文献
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利用模板匹配方法对2015年11月23日青海省祁连县M_S5.2地震进行遗漏地震检测研究,由于主震后短时间内目录中遗漏事件较多,故对主震后1天的连续波形进行检测。主震后1天内青海测震台网记录到的余震个数(包括单台)共62个,选取主震后M_L1.0以上余震30个作为模板事件,通过匹配滤波的方式扫描出遗漏地震31个,约为台网目录给出的0.5倍。基于包络差峰值振幅与震级的线性关系估测检测事件的震级参数,最后将检测后的余震目录与台网余震目录在主震后1天内的最小完备震级进行对比分析,结果发现检测后最小完备震级从M_L1.2降到了M_L0.7,得到青海测震台网在祁连地区最小完整性震级为M_L0.7。 相似文献
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— Analysis of the Koyna-Warna earthquake catalog (1968–1996) shows that on an average there is a positive correlation between the b value (decrease) and fractal dimensions (decrease in both D2s and D2t) of earthquake epicenters 0.5 and 2.5 years prior to 1973 (M5.2) and 1980 (M5.5) events, respectively, except a negative correlation for about five years (1988–1993) prior to the 1993/1994 sequence (M5.4). This positive correlation indicates a weaker clustering, or that the epicenters tend to fill the two-dimensional plane. While the origin of the negative correlation seems to be that during periods of large events (low b value), there is strong clustering around the main shock epicenter (high fractal dimension). Interestingly, during the last year (1995–1996) of the studied period both the b value and correlation dimensions rose significantly, suggesting that stress release occurs through increased levels of low magnitude and increasingly scattered seismicity, suggesting an increased risk of larger magnitude events. Incidentally, during 2000 three earthquakes of magnitude M 5.0, one earthquake of M 4.0, 45 earthquakes of magnitude M 3.0–3.9, and several thousand earthquakes of M < 3 have occurred in the region. Thus it can be inferred that at local scales the relationship yields both positive and negative correlation that appears to be controlled by different modes of failure within the active fault complex.Acknowledgement. The authors are grateful to Dr. B.K. Rastogi of NGRI for providing the catalog of Koyna earthquakes and for useful scientific discussions. The comments of Dr. I. G. Main have improved the quality of paper for which we extend to him our sincere thanks. One of the authors (AOM) thanks the Third World Academy of Science and the Council of Scientific and Industrial Research, India for the Postdoctoral Fellowship award under which this work was carried out. 相似文献
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In this paper, we give a brief introduction to the proposal and development history of the earthquake magnitude concept. Moment magnitude MW is the best physical quantity for measuring earthquakes. Compared with other magnitude scales used traditionally, moment magnitude is not saturated for all earthquakes, regardless of big and small earthquakes, deep and shallow earthquakes, far field and near field seismic data, geodetic and geological data, moment magnitude can be measured, and can be connected with well-known magnitude scales such as surface wave magnitude MS. Moment magnitude is a uniform magnitude scale, which is suitable for statistics with wide magnitude range. Moment magnitude is the preferred magnitude selected by the International Seismological community, and it is preferred by the departments responsible for publishing seismic information to the public.Moment magnitude is a uniform magnitude scale, which is suitable for statistics with wide magnitude range. Moment magnitude is a preferred magnitude for international seismology, it is preferred by the agency responsible for providing information about earthquakes to the public. We provide all formulas used in the calculation of moment magnitude, and the calculation steps in detail. We also analyzed some problems and rules to solve these problems by using different formulas and numerical value calculation steps. 相似文献