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1.
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
2.
V.V. Adushkin 《Russian Geology and Geophysics》2018,59(5):571-583
This paper presents an analysis of the development of the current seismic state of the Kuznetsk coal basin, which is characterized by an increase in technogenic seismicity of different types under the influence of prolonged intensive mining operations. The development of technogenesis led to a significant increase in technogenic seismicity in the Kuznetsk Basin in the 1970-1980s, when the number of technogenic earthquakes began to exceed the number of natural earthquakes. Among the various types of induced seismicity, special attention is paid to strong technogenic tectonic earthquakes with a regional magnitude Mb ≥ 3 and, accordingly, a seismic energy release of more than 109 J, i.e., earthquakes of energy class K > 9. These small-focus earthquakes are often accompanied by destruction of underground mines, collapse of quarries and pits, damage to surface facilities and equipment, and other adverse effects. In this paper, such earthquakes are defined as technogenic tectonic to emphasize their dual origin: technogenic impacts and the subsequent relaxation of tectonic stresses. It is also noted that the Earth’s interior in Kuzbass initially had its own natural seismicity and a developed system of tectonic faults. Natural seismotectonic activity combined with constantly increasing scales of mining and explosive consumption has led to an increase in the number of technogenic seismic events and their intensity. A striking example of such an event was the 18 June, 2013 Bachat earthquake with a regional magnitude Mb= 5.8 and a seismic intensity of 7 in the epicentral zone. It was the world’s largest man-made earthquake induced by the mining of solid minerals. We consider the possible causes of this catastrophic earthquake and discuss the conditions favoring the formation of foci of such technogenic tectonic earthquakes resulting from changes in the geodynamic and hydrogeological conditions in the Earth’s crust under man-caused impacts. These induced changes in natural processes are accompanied by a change in the stress-strain state, resulting in the concentration of tectonic stresses at heterogeneities and in fault zones, which become sources of induced technogenic seismicity.The paper discusses the current period of the occurrence and increase in such anthropogenic seismicity in the Kuzbass region with increasing scales of coal mining and blasting. Over the last 20 years, the consumption of explosives at Kuzbass enterprises increased from 100-200 to 500-600 thousand tons per year, and, accordingly, the amounts of broken and transported rock increased from several million tons per year to a billion tons per year, which disturbed the dynamic equilibrium in the Earth’s crust and changed the existing field of tectonic stresses. Moreover, the continuously increasing consumption of explosives has also increased the technogenic impact on the crust structures. The location of the epicenters of large-scale blasts inducing seismic events with regional magnitudes Mb= 3.0-4.5 has made it possible to identify regions with the greatest technogenic impact in Kuzbass. Using the data of the ISC seismological catalog, we separated seismic events with the above magnitudes into day and night ones. Since blasting work is forbidden at night, night seismic events are referred to as technogenic tectonic earthquakes (night event criterion). The maximum magnitude of seismic events induced by blasting operations in the Kuznetsk Basin was estimated at Mb ≤ 4.4. The annual number of technogenic tectonic earthquakes with 3.0 ≤ Mb ≤ 3.4, 3.5 ≤ Mb ≤ 3.9, 4.0 ≤ Mb ≤ 4.4, and Mb ≥ 4.5 was determined based on the night event criterion. The regions of their occurrence were identified from the location of the epicenters of technogenic tectonic earthquakes. 相似文献
3.
An attempt has been made to quantify the variability in the seismic activity rate across the whole of India and adjoining
areas (0–45°N and 60–105°E) using earthquake database compiled from various sources. Both historical and instrumental data
were compiled and the complete catalog of Indian earthquakes till 2010 has been prepared. Region-specific earthquake magnitude
scaling relations correlating different magnitude scales were achieved to develop a homogenous earthquake catalog for the
region in unified moment magnitude scale. The dependent events (75.3%) in the raw catalog have been removed and the effect
of aftershocks on the variation of b value has been quantified. The study area was divided into 2,025 grid points (1°×1°) and the spatial variation of the seismicity
across the region have been analyzed considering all the events within 300 km radius from each grid point. A significant decrease
in seismic b value was seen when declustered catalog was used which illustrates that a larger proportion of dependent events in the earthquake
catalog are related to lower magnitude events. A list of 203,448 earthquakes (including aftershocks and foreshocks) occurred
in the region covering the period from 250 B.C. to 2010 A.D. with all available details is uploaded in the website . 相似文献
4.
We discuss historical evidence for seismicity on the southern margin of the Siberian craton collected from old local newspapers. The reported earthquakes vary in magnitude from M = 2.5 to 4.5, and their macroseismic locations agree well with the regional tectonic framework. The new data prove seismic activity in the area and can be used in seismic risk assessment. 相似文献
5.
On February 13, 1981 a relatively strong earthquake occurred in the Lake Vänern region in south-central Sweden. The shock had a magnitude ofML = 3.3 and was followed within three weeks by three aftershocks, with magnitudes 0.5 ≤ ML ≤ 1.0. The focal mechanism solution of the main shock indicates reverse faulting with a strike in the N-S or NE-SW direction and a nearly horizontal compressional stress. The aftershocks were too small to yield data for a full mechanism solution, but first motions of P-waves, recorded at two stations, are consistent for the aftershocks. Dynamic source parameters, derived from Pg- and Sg-wave spectra, show similar stress drops for the main shock (2 bar) and the aftershocks (1 bar), while the differences in seismic moment (1.5·1020 resp. 4·1018dyne cm), fault length (0.7 resp. 0.2 km) and relative displacement (0.15 resp. 0.03 cm) are significant. 相似文献
6.
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
7.
A review of the seismicity and seismic history of Egypt indicates areas of high activity concentrated along Oligocene-Miocene faults. This supports the idea of recent activation of the Oligocene-Miocene stress cycle. There are similarities in the spatial distribution of recent and historical epicenters. Destructive earthquakes in Egypt are mostly concentrated in the highly populated areas of the Nile Valley and Nile Delta. Some big earthquakes located near the plate boundary as far away as Turkey and Crete were strongly felt in Egypt. The distribution of the energy release shows a possible tectonic connection between active zones in Egypt and the complicated tectonic zones in Turkey and Crete through geologically verified fault systems. The distribution of intensity shows a strong directivity along the Nile Valley. This is due to the presence of a thick layer of loose sediments on top of the hard rock in the Nile Valley graben. The distribution of b-values indicates two different zones, comparable with stable and unstable shelf areas. Stress loads in the northern Red Sea and northern Egypt are similar. Geologically, northern Egypt is a part of the Unstable Shelf area. The probability to have an earthquake with intensity V or larger within 94 years is more than 80% in the Nile Valley and Nile Delta areas, Egypt-Mediterranean coastal area, Aswan High Dam area, Gulf of Aqaba-Levant Fault zone and in the oil fields of the Gulf of Suez. The maximum expected intensity in these areas and within the same period is V–VI for a 80% probability and VII–VIII+ for a 10% probability. Intensity VIII–IX has been reported for several earthquakes in both historical and recent time. 相似文献
8.
Space–time seismic clusters, localized bursts of seismic activity, are a feature of background seismicity before the occurrence of large earthquakes, a feature that agrees with observations of diminishing Gutenberg–Richter b-value, fractal dimension, and entropy, and is therefore suggestive of high stress. However, identification and quantification of these space–time clusters, particularly when they are small, is not an easy task and requires a priori assumptions. A novel method for space–time cluster identification, based on an extension of the concept of apparent velocities, is proposed because space–time clusters in the background seismicity have a particular signature in the apparent velocity domain. The contents of histogram peaks due to clusters in the apparent velocity histogram can be used to quantify the cluster activity compared with null hypothesis levels. Identification of the earthquakes corresponding to the apparent velocities in the peaks allows identification of cluster activity in time and space. Apparent velocity peaks do appear in real catalog data for southern California and northern Baja California before the Landers 1992 M = 7.3, Hector Mine 1999 M = 7.1, El Mayor-Cucapah 2010 M = 7.2, and Ridgecrest 2019 M = 7.1 earthquakes, and they appear only within 15 to 25 years before the occurrence of large earthquakes. They are not observed either long before the large earthquakes or after them, and hence could be related to high local states of stress and be of value as a possible precursory observable.
相似文献9.
The problem of assessing seismic hazard in low-seismicity areas becomes obvious in many practical applications. A typical low-seismicity area, which experienced damaging earthquakes in historical times, is the North German Plain, for which a case study is presented. It is shown how seismic hazard assessments are influenced by different interpretations of historical key earthquakes, changes in b-value as well as variations of the upper bound magnitude assumed for the seismic source regions. The latter strongly influences the hazard results in the case of very low b-values for long return periods. 相似文献
10.
Turkey has been divided into eight different seismic regions taking into consideration the tectonic environments and epicenters
of the earthquakes to examine relationships of the modal values (a/b), the expected maximum magnitudes (Mmax) and the maximum intensities (Imax). For this purpose, the earthquakes for the time period 1900–1992 from the Global Hypocenter Data Base CD-ROM prepared by
USGS, and for the time period 1993–2001 from the PDE data and IRIS data are used. Concerning the relationships developed between
different magnitude scales and between surface wave magnitudes (MS) and intensity for different source regions in Turkey, we have constructed a uniform catalog of MS. We have estimated the values of Mmax and Imax using the Gumbel III asymptotic distribution. Highest a-values are observed in the Aegean region and the lowest b-values are estimated for the North Anatolian Fault. Maximum values of a/b, Mmax and Imax are related to the eastern and western part of the North Anatolian Fault and the Aegean Arc. The lowest values of all parameters
are observed near the Mid Anatolian Fault system. Linear relationships have been calculated between a/b, Mmax and Imax using orthogonal regression. If one of the three parameters is computed, two other parameters can be calculated empirically
using these linear relationships. Hazard maps of Mmax and Imax values are produced using these relationships for a grid of equally spaced points at 1°. It is observed that the maps produced
empirically may be used as a measure of seismic hazard in Turkey. 相似文献
11.
In the paper we report the state-of-the-art of seismicity study in the Baikal rift system and the general results obtained. At present, the regional earthquake catalog for fifty years of the permanent instrumental observations consists of over 185,000 events. The spatial distribution of the epicenters, which either gather along well-delineated belts or in discrete swarms is considered in detail for different areas of the rift system. At the same time, the hypocenters are poorly constrained making it difficult to identify the fault geometry. Clustered events like aftershock sequences or earthquake swarms are typical patterns in the region; moreover, aftershocks of M ⩾ 4.7 earthquakes make up a quarter of the whole catalog. The maximum magnitude of earthquakes recorded instrumentally is MLH7.6 for a strike-slip event in the NE part of the Baikal rift system and MLH6.8 for a normal fault earthquake in the central part of the rift system (Lake Baikal basin). Predominant movement type is normal faulting on NE striking faults with a left lateral strike-slip component on W–E planes. In conclusion, some shortcomings of the seismic network and data processing are pointed out. 相似文献
12.
Valry Ferber Jean-Claude Auriol Yu-Jun Cui Jean-Pierre Magnan 《Engineering Geology》2009,104(3-4):200-210
We conducted a study of the spatial distributions of seismicity and earthquake hazard parameters for Turkey and the adjacent areas, applying the maximum likelihood method. The procedure allows for the use of either historical or instrumental data, or even a combination of the two. By using this method, we can estimate the earthquake hazard parameters, which include the maximum regional magnitude Mˆmax, the activity rate of seismic events and the well-known bˆ value, which is the slope of the frequency-magnitude Gutenberg-Richter relationship. These three parameters are determined simultaneously using an iterative scheme. The uncertainty in the determination of the magnitudes was also taken into consideration. The return periods (RP) of earthquakes with a magnitude M ≥ m are also evaluated. The whole examined area is divided into 24 seismic regions based on their seismotectonic regime. The homogeneity of the magnitudes is an essential factor in such studies. In order to achieve homogeneity of the magnitudes, formulas that convert any magnitude to an MS-surface scale are developed. New completeness cutoffs and their corresponding time intervals are also assessed for each of the 24 seismic regions. Each of the obtained parameters is distributed into its respective seismic region, allowing for an analysis of the localized seismicity parameters and a representation of their regional variation on a map. The earthquake hazard level is also calculated as a function of the form Θ = (Mˆmax,RP6.0), and a relative hazard scale (defined as the index K) is defined for each seismic region. The investigated regions are then classified into five groups using these parameters. This classification is useful for theoretical and practical reasons and provides a picture of quantitative seismicity. An attempt is then made to relate these values to the local tectonics. 相似文献
13.
Ntungwa Maasha 《Tectonophysics》1975,27(4):381-393
The seismicity of Uganda has been studied using new data and all other available, previously determined locations of earthquakes (mb 4.0) up to December 1973. A magnitude—frequency graph suggests that since 1963 there is nearly complete coverage of all events with body magnitudes mb 4.2 in Uganda. The distribution of the earthquakes affirms that the Lake Amin—Lake Mobutu region experienced the greatest number of earthquakes, while the area around the Ruwenzori Mountain is probably the most seismically active area in Uganda if not in East Africa. The occurrence of earthquakes and the presence of faults of Cenozoic age in the Ruwenzori fold belt indicate that this area is a tectonically active zone (zone of weakness) probably connecting the eastern and western rifts across the Lake Victoria basin. 相似文献
14.
Short term spatial and temporal variations in seismicity prior to the three sequences of earthquakes of mb 5.8 of the Burma—Szechwan region are studied. Six years (1971–1976) of ISC seismicity data, as reported in the Regional Catalogue of Earthquakes, are considered. During the period, six earthquakes of body wave magnitude mb 5.8 occurred in four sequences. Of these, three sequences are preceded by swarm activity in the epicentral regions. Evison (1977b) suggested that the swarm before the sequences of large shocks is a possible long-term precursor. He derived the conclusion by analyzing earthquakes in New Zealand and California. The analysis of the seismicity data for the region under investigation supports Evison's view and suggests that a relation between swarms and sequences of large events exists. The precursory time period (i.e. the time from beginning of the swarm to the main shock) for the Szechwan earthquakes of mb = 5.9 (Feb. 6, 1973) and mb = 5.8 (May 10, 1974) and the Burma earthquake of mb = 6.2 (Aug. 12, 1976) are 305, 317 and 440 days, respectively. 相似文献
15.
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
16.
Seismicity of Sinai Peninsula, Egypt 总被引：1，自引：1，他引：0
Kamal Abdel-Rahman Abdullah M. S. Al-Amri Enayat Abdel-Moneim 《Arabian Journal of Geosciences》2009,2(2):103-118
The Sinai Peninsula has a triangular shape between the African and Arabian Plates and is bounded from the western and eastern borders by the Gulf of Suez and Gulf of Aqaba–Dead Sea rift systems, respectively. It is affected by strong and destructive earthquakes (e.g., March 31, 1969 and November 22, 1995) and moderate earthquakes (m b?>?5) throughout its history. After the installation of the Egyptian National Seismic Network (ENSN), a great number of earthquakes has been recorded within and around Sinai. Consequently, the seismogenic source zones and seismotectonic behavior can be clearly identified. Available data, including both historical and instrumental (1900–1997), have been collected from national and international data centers. While the data from 1998 till December 2007 are gathered from ENSN bulletins. The seismogenic source zones that might affect Sinai Peninsula are defined more precisely in this work depending on the distribution of earthquakes, seismicity rate (a value), b value, and fault plane solution of the major earthquakes. In addition, the type of faults prevailed and characterized these zones. It is concluded that the Gulf of Aqaba zone–Dead Sea transform zone, Gulf of Suez rift zone, Cairo–Suez District zone, and Eastern Mediterranean dislocation zone represent the major effective zones for Sinai. Furthermore, there are two local seismic zones passing through Sinai contributing to the earthquake activities of Sinai, these are the Negev shear zone and Central Sinai fault (Themed fault) zone. The source parameters, a and b values, and the maximum expected moment magnitude have been determined for each of these zones. These results will contribute to a great extent in the seismic hazard assessment and risk mitigation studies for Sinai Peninsula to protect the developmental projects. 相似文献
17.
The traditional interpretation of the Gillberga synform north of Lake Vänern in SW Sweden pictures it as a tectonically undisturbed rock sequence decreasing in age upwards. Our investigations suggest that a number of major sub-horizontal thrust planes are present in the sequence. Low-angle thrusting seems to be a major feature in the Precambrian basement of SW Sweden and adjacent parts of SE Norway. It is suggested that this may be indicative of a major global suture, be it interplate or intraplate. 相似文献
18.
An instrumental earthquake catalog covering the time span between 1903 and 2007 and for the area bounded by 32°N–38°N and 35°E–43°E has been compiled in this research. The catalog has a magnitude of completeness (M c ) with 3.5. Least squares and statistical probability Gumbel’s techniques with different approaches have been applied on the instrumental events in order to assess the average recurrence time periods for different earthquake magnitudes. The constants a and b of Gutenberg-Richter and the average recurrence times have been computed firstly for the study area and secondly for the central and northern parts of Dead Sea fault system. The different statistical computations using Knopoff and Kagan formalism are generally in agreement and suggest an average recurrence time of 203 years for an earthquake of magnitude 7 for the region. The occurrence of large well-documented historical earthquakes in Lebanon and western Syria, the existence of active fault segments, the absence of large earthquakes during the study period, the increasing number of the low-magnitude earthquakes, and the continued accumulation of the strain since 1900 indicate therefore the probability of an earthquake occurrence of a large magnitude. This should be permanently taken into consideration in seismic hazard assessment on the local and regional scales. 相似文献
19.
Global regression relations for conversion of surface wave and body wave magnitudes to moment magnitude 总被引：1，自引：0，他引：1
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
20.
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