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991.
Amr Z. Hamouda 《Acta Geophysica》2006,54(2):165-176
Earthquake hazard parameters such as maximum magnitude, annual mean seismic activity rate, and the Gutenberg-Richter parameter,
have been evaluated for the Hellenic and Cyprean Arc regions of the Eastern Mediterranean. The applied maximum likelihood
procedure permits the combination of both historical and instrumental data. The collected data from different sources cover
earthquakes with magnitude ≥ 3.5 throughout the last two centuries. The historical part of the catalogue only contains the
strongest events, whereas the complete part can be divided into several subcatalogues, each assumed complete above a specific
threshold of magnitude.
The hazard parameters assessment is performed for the two study regions. The Hellenic Arc region was found to be of higher
seismicity level than the Cyprean Arc region. The number of annually expected earthquakes with magnitude ≥ 3.5 is much larger
in the Hellenic Arc (56±2) than in the Cyprean Arc (35±2). The maximum magnitude calculated in the Hellenic Arc zone is 7.8±0.4
for the time period equal to the length of the catalogue, i.e., 210 years. For the Cyprean Arc zone, the maximum possible
magnitude is 6.8±0.4 for the time span of 330 years. 相似文献
992.
The common-ray approximation eliminates problems with ray tracing through S-wave singularities and also considerably simplifies
the numerical algorithm of the coupling ray theory for S waves, but may introduce errors in travel times due to the perturbation
from the common reference ray. These travel-time errors can deteriorate the coupling-ray-theory solution at high frequencies.
It is thus of principal importance for numerical applications to estimate the errors due to the common-ray approximation applied.
The anisotropic-common-ray approximation of the coupling ray theory is more accurate than the isotropic-common-ray approximation.
We derive the equations for estimating the travel-time errors due to the anisotropic-common-ray (and also isotropic-common-ray)
approximation of the coupling ray theory. The errors of the common-ray approximations are calculated along the anisotropic
common rays in smooth velocity models without interfaces. The derivation is based on the general equations for the second-order
perturbations of travel time. 相似文献
993.
Stress Sensitivity of Seismic and Electric Rock Properties of the Upper Continental Crust at the KTB
We test the hypothesis that the general trend of P-wave and S-wave sonic log velocities and resistivity with depth in the pilot hole of the KTB site Germany, can be explained by the progressive
closure of the compliant porosity with increasingly effective pressure. We introduce a quantity θc characterizing the stress sensitivity of the mentioned properties. An analysis of the downhole measurements showed that estimates
of the quantitiy θc for seismic velocities and electrical formation factor of the in situ formation coincide. Moreover, this quantity is 3.5 to 4.5 times larger than the averaged stress sensitivity obtained from
core samples. We conclude that the hypothesis mentioned above is consistent with both data sets. Moreover, since θc corresponds approximately to the inverse of the effective crack aspect ratio, larger in situ estimates of θc might reflect the influence of fractures and faults on the stress sensitivity of the crystalline formation in contrast to
the stress sensitivity of the nearly intact core samples. Finally, because the stress sensitivity is directly related to the
elastic nonlinearity we conclude that the elastic nonlinearity (i.e., deviation from linear stress-strain relationship i.e.,
Hooke's law) of the KTB rocks is significantly larger in situ than in the laboratory. 相似文献
994.
The Harvard CMT catalogue contains 481 shallow earthquakes that occurred between 1 January 1977 and 30 November 2005 within
a broad region defined by the geographical latitude from 3°S to 14°N and by the longitude from 91°E to 102°E. There are 230
events that occurred before the great earthquake of 26 December 2004. Their surface distribution is not uniform and the source
area of the 2004 great event appears as an area of seismic quiescence with a radius of about 100 km. There are 186 events
that occurred between the two great earthquakes of 26 December 2004 and 28 March 2005. Practically all of them are located
to the northwest from the great earthquake of 2005, that in turn was followed by 63 events, mostly located to the southeast.
The cumulative seismic moment from earthquakes before the occurrence of the great event of 2004 increased rather regularly
with time, with sudden increase about twenty years and two years before the occurrence of the great event. The seismic moment
of earthquakes between the two great events increased rapidly during the first ten-fifteen days, then flattened out and increased
slowly with time. After the great event of 2005 the seismic moment shows quiet increase during some 115 days, then sudden
jump, followed by very small activity till the end of our observations. From the spatial distribution of seismic moment of
earthquakes that occurred before the great event of 2004 it follows that its largest release appeared to the southeast from
the great event, around the rupture area of the great earthquake of 2005. The largest release of seismic moment from earthquakes
between the two great events is observed in the vicinity of the 2004 event and further up to the north. The seismic moment
from earthquakes that occurred after the great event of 2005 was mostly released in its vicinity and further down to the south. 相似文献
995.
Seismic Moment Tensor Resolution on a Local Scale: Simulated Rockburst and Mine-induced Seismic Events in the Kopanang Gold Mine, South Africa 总被引:2,自引:0,他引:2
Seismic records contain information about the effect of the source as well as the effect of wave propagation through the rock
mass. The effect of wave propagation is usually not well known as only simplified models of geological structures are available.
Therefore, the information about the source retrieved by inverting seismograms may include errors due to incomplete knowledge
of the rock mass along the propagation path, which in turn cause a distortion in the calculated moment tensor (MT). The distortion
of the MT on a local scale was observed by inverting records of a simulated rockburst conducted at the Kopanang gold mine
in South Africa. A dominant isotropic component of the explosive characteristics was found from the inversion. The deviatoric
components retrieved from the blast are spurious. A test of their stability indicated that they are not significant, assuming
an uncertainty above 5% for velocities and 10% for attenuation within the homogeneous model available for the mine. Thus,
the retrieval of the MT from records of local networks in mines using a homogeneous model of the rock mass seems to be feasible.
However, the homogeneous model of the rock mass can only be applied to close stations, within a few kilometers of the source.
The seismic records from distant stations were too complex to be modelled by a homogeneous rock mass. Records of six mine-induced
seismic events recorded at the Kopanang gold mine were also inverted. A vertical linear dipole along the pressure (P) axis
was found for three of the events, suggesting a pillar burst. The mechanism of two events contains an isotropic implosion
together with a nearly vertical dip-slip, and seems to indicate a combination of a cavity collapse with a down dip-slip along
a nearly vertical fault. One event corresponds to a dipole along the tensional (T) axis. However, it is vertical, thus its
association with tensile faulting of the hangingwall is uncertain. 相似文献
996.
Ezio Faccioli 《Bulletin of Earthquake Engineering》2006,4(4):341-364
The main features of the Risk-UE project approach to assessing the ground-shaking (and related hazards) distribution within urban areas are described, as a basis for developing seismic damage scenarios for European cities. Emphasis was placed in the project on adoption of homogeneous criteria in the quantitative treatment of seismicity and in constructing the ground-shaking scenarios, despite wide differences in amount and quality of data available for the cities involved. The initial steps of the approach include treatment of the regional seismotectonic setting and the geotechnical zonation of the urban area, while the hazard assessment itself takes the form of both a deterministic analysis, and of a probabilistic, constant-hazard spectra analysis. Systematic 1D site response analyses were used, mostly in the softer soil zones, to modify (when needed) the obtained ground motion maps. Earthquake induced hazard effects, such as liquefaction and landsliding, are also briefly dealt with at the end. 相似文献
997.
2006年4月21日03时18分03.7秒,石棉县发生一次ML4.3级地震,仪器测定震中位于北纬29°05′、东经102°12′,即安顺乡麂子坪南西侧。经现场实地考察确定宏观震中位于麂子坪南—紫马之间的山区地带,宏观震中烈度为Ⅳ度强(Ⅳ ),其震中区面积约100平方千米;Ⅳ度区面积约为2 000平方千米;此次地震有感区范围广泛,北至泸定、天全等县,南到冕宁、越西,西达九龙东至汉源县乌斯河镇等地,有感区面积约20 000平方千米。经调查,地震没有造成人员、牲畜等的伤亡,震害地区内个别房屋的屋瓦出现梭动。 相似文献
998.
东亚南北地震带大震活动性研究 总被引:6,自引:0,他引:6
根据中国南北地震带与青藏-印尼“歹”字型构造带在成因上的联系,提出东亚南北地震带的观点,认为该地震带包含蒙古、中国西部、缅甸和印尼苏门答腊地区。研究了该带大地震活动的同步性、主体活动区的有序转移、大地震之间的多次相关迁移与重复等特征,并划分出了该带的5个大震活跃幕:1887-1912年、1913-1937年、1938-1957年、1958-1976年、1977-2005年。苏门答腊2004年12月26日8.7级和2005年3月29日8.5级巨震标志着该地震带最近一次以主体活动区南移到苏门答腊为特征的活跃时段即将结束。尽管未来一、两年内地震带的中部存在发生7级地震的有利时段,但结合强震图像异常指标反映的孕震状况分析,未来7级地震危险区尚不明朗。 相似文献
999.
1000.