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1.
Seismic hazard in mega city Kolkata, India   总被引：2，自引：1，他引：1  
The damages caused by recent earthquakes in India have been a wake up call for people to take proper mitigation measures, especially the major cities that lie in the high seismic hazard zones. Kolkata City, with thick sediment deposit (∼12 km), one of the earliest cities of India, is an area of great concern as it lies over the Bengal Basin and lies at the boundary of the seismic zones III and IV of the zonation map of India. Kolkata has been affected by the 1897 Shillong earthquake, the 1906 Calcutta earthquake, and the 1964 Calcutta earthquake. An analysis on the maximum magnitude and b-value for Kolkata City region is carried out after the preparation of earthquake catalog from various sources. Based on the tectonic set-up and seismicity of the region, five seismic zones are delineated, which can pose a threat to Kolkata in the event of an earthquake. They are broadly classified as Zone 1: Arakan-Yoma Zone (AYZ), Zone 2: Himalayan Zone (HZ), Zone 3: Shillong Plateau Zone (SPZ), Zone 4: Bay of Bengal Zone (BBZ), and Zone 5: Shield Zone (SZ). The maximum magnitude (m max) for Zones 1, 2, 3, 4, and 5 are 8.30 ± 0.51, 9.09 ± 0.58, 9.20 ± 0.51, 6.62 ± 0.43 and 6.61 ± 0.43, respectively. A probability of 10% exceedance value in 50 years is used for each zone. The probabilities of occurrences of earthquakes of different magnitudes for return periods of 50 and 100 years are computed for the five seismic zones. The Peak Ground Acceleration (PGA) obtained for Kolkata City varies from 0.34 to 0.10 g.  相似文献   

2.
In the present paper, the parameters affecting the uncertainties on the estimation of M max have been investigated by exploring different methodologies being used in the analysis of seismicity catalogue and estimation of seismicity parameters. A critical issue to be addressed before any scientific analysis is to assess the quality, consistency, and homogeneity of the data. The empirical relationships between different magnitude scales have been used for conversions for homogenization of seismicity catalogues to be used for further seismic hazard assessment studies. An endeavour has been made to quantify the uncertainties due to magnitude conversions and the seismic hazard parameters are then estimated using different methods to consider the epistemic uncertainty in the process. The study area chosen is around Delhi. The b value and the magnitude of completeness for the four seismogenic sources considered around Delhi varied more than 40% using the three catalogues compiled based on different magnitude conversion relationships. The effect of the uncertainties has been then shown on the estimation of M max and the probabilities of occurrence of different magnitudes. It has been emphasized to consider the uncertainties and their quantification to carry out seismic hazard assessment and in turn the seismic microzonation.  相似文献   

3.
The aim of the present work is to compile and update a catalogue of the instrumentally recorded earthquakes in Egypt, with uniform and homogeneous source parameters as required for the analysis of seismicity and seismic hazard assessment. This in turn requires a detailed analysis and comparison of the properties of different available sources, including the distribution of events with time, the magnitude completeness, and the scaling relations between different kinds of magnitude reported by different agencies. The observational data cover the time interval 1900–2004 and an area between 22°–33.5° N and 25°–36° E. The linear regressions between various magnitude types have been evaluated for different magnitude ranges. Using the best linear relationship determined for each available pair of magnitudes, as well as those identified between the magnitudes and the seismic moment, we convert the different magnitude types into moment magnitudes M W, through a multi-step conversion process. Analysis of the catalogue completeness, based on the M W thus estimated, allows us to identify two different time intervals with homogeneous properties. The first one (1900–1984) appears to be complete for M W ≥ 4.5, while the second one (1985–2004) can be considered complete for magnitudes M W ≥ 3.  相似文献   

4.
The Vienna Basin Transfer Fault (VBTF) is a slow active fault with moderate seismicity (I max~8–9, M max~5.7) passing through the most vulnerable regions of Austria and Slovakia. We use different data to constrain the seismic potential of the VBTF including slip values computed from the seismic energy release during the 20th century, geological data on fault segmentation and a depth-extrapolated 3-D model of a generalized fault surface, which is used to define potential rupture zones. The seismic slip of the VBTF as a whole is in the range of 0.22–0.31 mm/year for a seismogenic fault thickness of 8 km. Seismic slip rates for individual segments vary from 0.00 to 0.77 mm/year. Comparing these data to geologically and GPS-derived slip velocities (>1 mm/year) proofs that the fault yields a significant seismic slip deficit. Segments of the fault with high seismic slip contrast from segments with no slip representing locked segments. Fault surfaces of segments within the seismogenic zone (4–14 km depth) vary from 55 to 400 km2. Empirical scaling relations show that these segments are sufficiently large to explain both, earthquakes observed in the last centuries, and the 4th century Carnuntum earthquake, for which archeo-seismological data suggest a magnitude of M ≥ 6. Based on the combination of all data (incomplete earthquake catalog, seismic slip deficits, locked segments, potential rupture areas, indications of strong pre-catalog earthquakes) we argue, that the maximum credible earthquake for the VBTF is in the range M max = 6.0–6.8, significantly larger than the magnitude of the strongest recorded events (M = 5.7).  相似文献   

5.
Hamdache  M.  Pel&#;ez  J. A.  Kijko  A.  Smit  A. 《Natural Hazards》2016,86(2):273-293

We estimate the energetic and spatial characteristics of seismicity in the Algeria–Morocco region using a variety of seismic and statistical parameters, as a first step in a detailed investigation of regional seismic hazard. We divide the region into five seismotectonic regions, comprising the most important tectonic domains in the studied area: the Moroccan Meseta, the Rif, the Tell, the High Plateau, and the Atlas. Characteristic seismic hazard parameters, including the Gutenberg–Richter b-value, mean seismic activity rate, and maximum possible earthquake magnitude, were computed using an extension of the Aki–Utsu procedure for incomplete earthquake catalogs for each domain, based on recent earthquake catalogs compiled for northern Morocco and northern Algeria. Gutenberg–Richter b-values for each zone were initially estimated using the approach of Weichert (Bull Seismol Soc Am 70:1337–1346, 1980): the estimated b-values are 1.04 ± 0.04, 0.93 ± 0.10, 0.72 ± 0.03, 0.87 ± 0.02, and 0.77 ± 0.02 for the Atlas, Meseta, High Plateau, Rif, and Tell seismogenic zones, respectively. The fractal dimension D 2 was also estimated for each zone. From the ratio D 2/b, it appears that the Tell and Rif zones, with ratios of 2.09 and 2.12, respectively, have the highest potential earthquake hazard in the region. The Gutenberg–Richter relationship analysis allows us to derive that in the Tell and Rif, the number of earthquake with magnitude above Mw 4.0, since 1925 normalized to decade and to square cell with 100-km sides is equal to 2.6 and 1.91, respectively. This study provides the first detailed information about the potential seismicity of these large domains, including maximum regional magnitudes, characteristics of spatial clustering, and distribution of seismic energy release.

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6.
The maximum likelihood estimation of earthquake hazard parameters (maximum regional magnitudem max, activity rate , and theb parameter in the Gutenberg-Richter distribution) is extended to the cases of incomplete and uncertain data. The method accepts mixed data containing only large (extreme) events and a variable quality of complete data with different threshold magnitude values. Uncertainty of earthquake magnitude is specified by two values, the lower and upper magnitude limits. It is assumed that such an interval contains the real unknown magnitude. The proposed approach allows the combination of different quality catalog parts, e.g. those where the assignment of magnitude is questionable and those with magnitudes precisely determined.As an illustration of the method, the seismic hazard analysis for western Norway and adjacent sea area (4–8°E, 58–64°N) is presented on the basis of the strongest earthquakes felt during the period 1831–1889 and three complete catalog parts, covering the period 1890–1987.Paper presented at the 21st General Assembly of the European Seismological Commission held in Sofia, 1988.On leave from Institute of Geophysics, Polish Academy of Sciences, Warsaw, Poland.  相似文献   

7.
Seismic hazard in terms of peak ground acceleration (PGA) has been evaluated in northern Algeria using spatially smoothed seismicity data. We present here a preliminary seismic zoning in northern Algeria as derived from the obtained results.Initially, we have compiled an earthquake catalog of the region taking data from several agencies. Afterwards, we have delimited seismic areas where the b and mmax parameters are different. Finally, by applying the methodology proposed by Frankel [Seismol. Res. Lett. 66 (1995) 8], and using four complete and Poissonian seismicity models, we are able to compute the seismic hazard maps in terms of PGA with 39.3% and 10% probability of exceedance in 50 years.A significant result of this work is the observation of mean PGA values of the order of 0.20 and 0.45 g, for return periods of 100 and 475 years, respectively, in the central area of the Tell Atlas.  相似文献   

8.
Characteristics of the seismicity in depth ranges 0–33 and 34–70 km before ten large and great (M w = 7.0−9.0) earthquakes of 2000–2008 in the Sumatra region are studied, as are those in the seismic gap zones where no large earthquakes have occurred since at least 1935. Ring seismicity structures are revealed in both depth ranges. It is shown that the epicenters of the main seismic events lie, as a rule, close to regions of overlap or in close proximity to “shallow” and “deep” rings. Correlation dependences of ring sizes and threshold earthquakes magnitudes on energy of the main seismic event in the ring seismicity regions are obtained. Identification of ring structures in the seismic gap zones (in the regions of Central and South Sumatra) suggests active processes of large earthquake preparation proceed in the region. The probable magnitudes of imminent seismic events are estimated from the data on the seismicity ring sizes.  相似文献   

9.
A seismic hazard evaluation for three dams in the Rocky Mountains of northern Colorado is based on a study of the historical seismicity. To model earthquake occurrence as a random process utilizing a maximum likelihood method, the catalog must exhibit random space-time characteristics. This was achieved using a declustering procedure and correction for completeness of recording. On the basis of the resulting a- and b-values, probabilistic epicentral distances for a 2 × 10–5 annual probability were calculated. For a random earthquake of magnitude M L 6.0–6.5, this distance is 15 km. Suggested ground motion parameters were estimated using a probabilistic seismic hazard analysis. Critical peak horizontal accelerations at the dams are 0.22g if median values are assumed and 0.39g if variable attenuation and seismicity rates are taken into account. For structural analysis of the dams, synthetic acceleration time series were calculated to match the empirical response spectra. In addition, existing horizontal strong motion records from two Mammoth Lakes, California earthquakes were selected and scaled to fit the target horizontal acceleration response spectra.  相似文献   

10.
Seismic hazard of Egypt   总被引：1，自引：0，他引：1  
Earthquake hazard parameters such as maximum expected magnitude,M max, annual activity rate,, andb value of the Gutenberg-Richter relation have been evaluated for two regions of Egypt. The applied maximum likelihood method permits the combination of both historical and instrumental data. The catalogue used covers earthquakes with magnitude 3 from the time interval 320–1987. The uncertainties in magnitude estimates and threshold of completeness were taken into account. The hazard parameter determination is performed for two study areas. The first area, Gulf of Suez, has higher seismicity level than the second, all other active zones in Egypt.b-values of 1.2 ± 0.1 and 1.0 ± 0.1 are obtained for the two areas, respectively. The number of annually expected earthquakes with magnitude 3 is much larger in the Gulf of Suez, 39 ± 2 than in the other areas, 6.1 ± 0.5. The maximum expected magnitude is calculated to be 6.5 ± 0.4 for a time span of 209 years for the Gulf of Suez and 6.1 ± 0.3 for a time span of 1667 years for the remaining active areas in Egypt. Respective periods of 10 and 20 years were reported for earthquakes of magnitude 5.0 for the two subareas.  相似文献   

11.
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12.
A homogenous earthquake catalog is a basic input for seismic hazard estimation, and other seismicity studies. The preparation of a homogenous earthquake catalog for a seismic region needs regressed relations for conversion of different magnitudes types, e.g. m b , M s , to the unified moment magnitude M w. In case of small data sets for any seismic region, it is not possible to have reliable region specific conversion relations and alternatively appropriate global regression relations for the required magnitude ranges and focal depths can be utilized. In this study, we collected global events magnitude data from ISC, NEIC and GCMT databases for the period 1976 to May, 2007. Data for mb magnitudes for 3,48,423 events for ISC and 2,38,525 events for NEIC, M s magnitudes for 81,974 events from ISC and 16,019 events for NEIC along with 27,229 M w events data from GCMT has been considered. An epicentral plot for M w events considered in this study is also shown. M s determinations by ISC and NEIC, have been verified to be equivalent. Orthogonal Standard Regression (OSR) relations have been obtained between M s and M w for focal depths (h < 70 km) in the magnitude ranges 3.0 ≤ M s  ≤ 6.1 and 6.2 ≤ M s  ≤ 8.4, and for focal depths 70 km ≤ h ≤ 643 km in the magnitude range 3.3 ≤ M s  ≤ 7.2. Standard and Inverted Standard Regression plots are also shown along with OSR to ascertain the validation of orthogonal regression for M s magnitudes. The OSR relations have smaller uncertainty compared to SR and ISR relations for M s conversions. ISR relations between m b and M w have been obtained for magnitude ranges 2.9 ≤ m b  ≤ 6.5, for ISC events and 3.8 ≤ m b  ≤ 6.5 for NEIC events. The regression relations derived in this study based on global data are useful empirical relations to develop homogenous earthquake catalogs in the absence of regional regression relations, as the events catalog for most seismic regions are heterogeneous in magnitude types.  相似文献   

13.
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   

14.
The earthquake hazard parameters and earthquake occurrence probabilities are computed for the different regions of the North Anatolia Fault Zone (NAFZ) using Bayesian method. A homogenous earthquake catalog for M S magnitude which is equal or larger than 4.0 is used for a time period between 1900 and 2015. Only two historical earthquakes (1766, M S = 7. 3 and 1897, M S = 7. 0) are included in Region 2 (Marmara Region) where a large earthquake is expected in the near future since no large earthquake has been observed for the instrumental period. In order to evaluate earthquake hazard parameters for next 5, 10, 20, 50, 100 years, M max (maximum regional magnitude), β value, λ (seismic activity or density) are computed for the different regions of NAFZ. The computed M max values are changed between 7.11 and 7.89. While the highest magnitude value is calculated in the Region 9 related to Tokat-Erzincan, the lowest value in the Region 10 including the eastern of Erzincan. The “quantiles” of “apparent” and “true” magnitudes of future time intervals of 5, 10, 20, 50, and 100 years are calculated for confidence limits of probability levels of 50, 70 and 90 % of the 10 different seismic source regions. The region between Tokat and Erzincan has earthquake hazard level according to the determined parameters. In this region the expected maximum earthquake size is 7.8 with 90 % occurrence probability in next 100 years. While the regional M max value of Marmara Region is computed as 7.61, expected maximum earthquake size is 7.37 with 90 % occurrence probability in next 100 years.  相似文献   

15.
A continuously operated gas monitoring station was emplaced within the epicentral area of the NW Bohemian swarm earthquakes overlying directly the active Mariánské Lázně fault. The recordings of 8-month continuous monitoring period are presented. The variations in radon concentrations are similarly to variations in CO2, i.e. CO2 is considered to be the carrier gas for radon. Very small diurnal variations in gas concentration are caused by the earth tides, as daily variations in meteorological conditions cannot explain a short daily minimum at midday times. Sudden changes in gas concentration, which clearly exceed these diurnal variations occur and are always linked with seismic activities. Decreased gas concentration may indicate compression resulting in reduced fault permeability as is implied by negative peaks following local earthquake swarms. A sudden increase in CO2 and Rn concentration may indicate an increased fault permeability caused by stress redistribution, giving rise to opening of migration pathways. This implies a repeatedly sudden rise in gas concentration before local earthquake swarms. Several variations in gas concentration were monitored linked with remote earthquakes of ground motion amplitudes  >1 μm. These seismic events are accompanied by an interference of the diurnal gas concentration–stress-cycle along the Mariánské Lázně fault. However, if shocks of remote earthquake can alter properties of the migrating fluids or the fault properties it can be suggested that these are able to trigger local seismicity, as indicated in the case of the Slovenia earthquake on 12th July 2004.  相似文献   

16.
Magnitude conversion problem for the Turkish earthquake data   总被引：1，自引：0，他引：1  
Earthquake catalogues which form the main input in seismic hazard analysis generally report earthquake magnitudes in different scales. Magnitudes reported in different scales have to be converted to a common scale while compiling a seismic data base to be utilized in seismic hazard analysis. This study aims at developing empirical relationships to convert earthquake magnitudes reported in different scales, namely, surface wave magnitude, M S, local magnitude, M L, body wave magnitude, m b and duration magnitude, M d, to the moment magnitude (M w). For this purpose, an earthquake data catalogue is compiled from domestic and international data bases for the earthquakes occurred in Turkey. The earthquake reporting differences of various data sources are assessed. Conversion relationships are established between the same earthquake magnitude scale of different data sources and different earthquake magnitude scales. Appropriate statistical methods are employed iteratively, considering the random errors both in the independent and dependent variables. The results are found to be sensitive to the choice of the analysis methods.  相似文献   

17.
The earthquake hazard in Jordan and its vicinity is assessed on the basis of probabilistic methods. For this purpose, an updated earthquake catalog is compiled which covers the period between AD 1–1989. The earthquakes lie between latitudes 27.0°-35.5° N and longitudes 32.0°-39.0° E. Thirteen seismic zones are defined on a regional seismic and tectonic map presented for the area. Point-source and line-source models are used. The seismic hazard parameters, namely, theb-parameter (of the Gutenberg-Richter relation),m 1 (the upper bound magnitude), and 4 (the annual rate of occurrence of earthquakes with local magnitudeM L 4.0) are calculated for each zone. The results of the seismic hazard assessment are displayed as iso-acceleration contours expected to be exceeded during typical economic life times of structures, i.e. 50 and 100 years. For each model, two seismic hazard maps are derived. In order to determine the importance of the South-eastern Mediterranean zone and the north part of the Red Sea zone from a seismic hazard point of view for Jordan, one seismic hazard map which corresponds to 50 years' economic life for every model, excluding the seismicity of these zones, is derived.  相似文献   

18.
Seismicity of Gujarat   总被引：2，自引：2，他引：0  
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.  相似文献   

19.
Hamouda  Amr Z. 《Natural Hazards》2011,59(1):465-479
The entrance of the southern Suez Gulf of the Red Sea is known to be an area of high seismic activity in Egypt. The high rate of seismic activity in this area is mainly related to the adjustment in motion at the triple junction between the African plate, the Arabian plate, and the Sinai microplate. The present study attempts to estimate the Probabilistic Seismic Hazard Analysis (PSHA) for Hurghada site. This was done in two steps; the first one is by estimating specific parameters for the site, such as the mean seismic activity, λ, the Gutenberg-Richter parameter, b, and the maximum regional magnitude, m max. The second step is by selecting a ground motion parameter that is applicable to Hurghada site. The procedure permits the combination of both historical and recent instrumental data. The results of the hazard assessment, expressed as the worst case scenario, detect that Hurghada is exposed to the maximum credible earthquake event of magnitude m max = 7.1 ± 0.31, at hypocentral distance of 31.6 ± 10 km. The possibility of the maximum Peak Ground Acceleration (PGA), which occurred in relation to this event at Hurghada site, is equal to 0.29 g. The mean return periods with the selected accelerations for Hurghada, a horizontal acceleration of 0.1 g, is expected to occur once every 74–106 years, with an average of one every 90 years. This result which obtained from the hazard assessment can be used as an input data for a seismic risk assessment.  相似文献   

20.
The maximum magnitude, the activity rate, and the Gutenberg-Richterb parameter as earthquake hazard parameters, have been evaluated for Sweden. The maximum likelihood method permits the combination of historical and instrumental data. The catalog used consists of 1100 earthquakes in the time interval 1375–1989. The extreme part of the catalog contains only the strongest historical earthquakes, whereas the complete part is divided into several subcatalogs, each assumed complete above a specified threshold magnitude. The uncertainty in magnitude determination was taken into account. For southern Sweden, the calculations giveb-values of 1.04 (0.05) for the whole area south of 60° N and 0.98 (0.06) for a subregion of enhanced seismicity in the Lake Vänern area. For the whole area north of 60° N, theb-value is 1.35 (0.06) and for the seismicity zone along the Gulf of Bothnia 1.26 (0.06). The number of annually expected earthquakes with magnitude equal to or larger than 2.4 [ML(UPP) or MM(UPP)] is 1.8 for the whole southern Sweden, 1.3 for the Lake Vänern region, 3.7 for northern Sweden, and 2.4 for the region along the Gulf of Bothnia. The maximum expected regional magnitude is calculated to 4.9 (0.5) for a time span of 615 years for southern Sweden and the Lake Vänern subregion, and 4.3 (0.5) for a time span of 331 years for northern Sweden and the Gulf of Bothnia subregion. However, several historical earthquakes with magnitude above 5 in nearby areas of Norway indicate that the seismic potential may be higher.  相似文献   

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