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Damage caused by the earthquake of 7 December 1986 (M = 5.7) and its aftershocks in low-storey residential buildings in the town of Strazhitza, Bulgaria, situated in the epicentral zone are systematized. A scale of damages is compiled for two types of buildings which is coordinated with the MSK-64 scale. The territorial distribution of the seismic intensity is compared with the results of the detailed engineering-geological study. A correlation between the Quarternary deposit thickness and the observed seismic intensity is obtained.Paper presented at the 21st general assembly of the European Seismological Commission held in Sofia, 1988. 相似文献
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The mechanical model for plane strain, time-harmonic seismic wave propagation problems in cracked, multi-layered geological regions with surface topography and non-parallel interfaces was described in the first part of this work. Here, this model is used to investigate the response of such a region to the presence of traveling elastic waves generated by a seismic source. The computational methodology that was developed in the first part is based on a combination of both the regular (displacement-based) and the hypersingular (traction-based) Boundary Integral Equation Method (BIEM). First, the accuracy and convergence characteristics of this hybrid BIEM are studied. Then, a series of problems involving four different configurations of a reference geological deposit with both interface and internal cracks are solved, for a loading that is due to a seismically-induced pressure wave propagating upwards from the underlying rigid half-plane. The purpose of the numerical study is to investigate the influence of various key parameters of the problem, such as frequency and incidence angle of the incoming wave, size of the surface relief, location and size of the buried cracks, interaction effects between cracks and finally the presence of layers, on both the scattered displacement field and the stress concentration field. 相似文献
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Forty-six mining-induced seismic events with moment magnitude between ?1.2 and 2.1 that possibly caused damage were studied. The events occurred between 2008 and 2013 at mining level 850–1350 m in the Kiirunavaara Mine (Sweden). Hypocenter locations were refined using from 6 to 130 sensors at distances of up to 1400 m. The source parameters of the events were re-estimated using spectral analysis with a standard Brune model (slope ?2). The radiated energy for the studied events varied from 4.7 × 10?1 to 3.8 × 107 J, the source radii from 4 to 110 m, the apparent stress from 6.2 × 102 to 1.1 × 106 Pa, energy ratio (E s/E p) from 1.2 to 126, and apparent volume from 1.8 × 103 to 1.1 × 107 m3. 90% of the events were located in the footwall, close to the ore contact. The events were classified as shear/fault slip (FS) or non-shear (NS) based on the E s/E p ratio (>10 or <10). Out of 46 events 15 events were classified as NS located almost in the whole range between 840 and 1360 m, including many events below the production. The rest 31 FS events were concentrated mostly around the production levels and slightly below them. The relationships between some source parameters and seismic moment/moment magnitude showed dependence on the type of the source mechanism. The energy and the apparent stress were found to be three times larger for FS events than for NS events. 相似文献
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J. Van k N.V. Kondorskaya I.V. Fedorova L. Christoskov A.I. Zakharova S. Dineva O.V. Nosova I.A. Kireev L.S. Chepkunas 《Tectonophysics》1985,118(3-4)
Routine determination of network magnitudes by means of the Eurasian homogeneous magnitude system (HMS) is described and tested on a selection of recent shallow earthquakes. The HMS earthquake magnitudes appear to be more accurate and more reliable than the conventional earthquake magnitudes used in the present seismological practice. A preliminary investigation of correlations between magnitudes determined from different wave types shows a possible dependence of the correlation on the type of focal mechanism of earthquakes. 相似文献
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Gospodinov Dragomir Dineva Savka Dahnér-Lindkvist Christina 《Journal of Seismology》2022,26(5):1023-1037
Aftershock series of even comparatively small seismic events can pose a risk to the mining operation or the personnel in deep underground mines as the main shocks and some of the aftershocks can cause damage in the rock mass. Stochastic modeling was applied in this study for the analysis of the temporal evolution of aftershock occurrence probability during a M1.85 aftershock sequence in Kiirunavaara Mine, Sweden. The Restricted Epidemic-Type Aftershock Sequence (RETAS) model was chosen for estimation of the aftershock occurrence probability. This model considers all events with magnitude above the magnitude of completeness M0 and has the advantage of including the Modified Omori Formula (MOF) model and Epidemic-Type Aftershock Sequence (ETAS) model as its end versions, considering also all intermediate models. The model was applied sequentially to data samples covering cumulative periods of time, starting from the first 2 h after the main event and increasing them by 2 h until the period covered the entire 72-h sequence. For each sample, the best-fit RETAS version was identified and the probability of a M?≥?0.5 aftershock for every next 2 h was determined through Monte Carlo simulation. The feasibility of the resulting probability evolution for suspension and re-starting of the mining operations was discussed together with possible prospects for future development of the methodology.
相似文献8.
We have developed a simple semblance-weighted stacking technique to estimate crustal thickness and average VP/VS ratio using teleseismic receiver functions. We have applied our method to data from 32 broadband seismograph stations that cover a 700 × 400 km2 region of the Grenville orogen, a 1.2–0.98 Ga Himalayan-scale collisional belt in eastern North America. Our seismograph network partly overlaps with Lithoprobe and other crustal refraction surveys. In 8 out of 9 cases where a crustal-refraction profile passes within 30 km of a seismograph station, the two independent crustal thickness estimates agree to within 7%. Our regional crustal-thickness model, constructed using both teleseismic and refraction observations, ranges between 34.0 and 52.4 km. Crustal-thickness trends show a strong correlation with geological belts, but do not correlate with surface topography and are far in excess of relief required to maintain local isostatic equilibrium. The thickest crust (52.4 ± 1.7 km) was found at a station located within the 1.1 Ga mid-continent (failed) rift. The Central Gneiss Belt, which contains rocks exhumed from deep levels of the crust, is characterized by VP/VS ranging from 1.78 to 1.85. In other parts of the Grenville orogen, VP/VS is found to be generally less than 1.80. The thinnest crust (34.5–37.0 km) occurs northeast of the 0.7 Ga Ottawa–Bonnechere graben and correlates with areas of high intraplate seismicity. 相似文献
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This work addresses in‐plane pressure P and vertically polarized shear SV seismic wave propagation in a finite, laterally inhomogeneous, multilayered poroelastic geological region resting on the homogeneous elastic half‐space. The particular approach followed here is based on a combination of the (i) viscoelastic approximation (isomorphism) to Biot's equations of dynamic poroelasticity and on the (ii) boundary integral equation method (BIEM) using frequency‐dependent fundamental solutions of the governing wave equations. The problem is formulated under plane strain conditions and time‐harmonic motions are assumed. Validation of the viscoelastic isomorphism and verification of the BIEM is done by solution of benchmark examples. These simulation studies reveal that the proposed methodology is able to depict a sensitivity of the seismic signals recovered to the following parameters: (i) poroelastic properties of fluid saturated layers; (ii) lateral geological inhomogeneity; (iii) surface topography and (iv) frequency content and direction of the incident wave. It is concluded that the combination of viscoelastic isomorphism with BIEM software provides an effective numerical tool for evaluating site‐effect phenomena in multilayered, fluid saturated geological regions with complex geometry. The numerical results obtained demonstrate that dynamic poroelasticity interacting with other physical peculiarities of the Earth's surface layers, such as lateral heterogeneity, material properties along the wave path, local geological profile and type of elastic wave, gives rise to complex seismic signals on the free surface at the site of interest. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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In this work, a hybrid boundary integral equation method (BIEM) is developed, based on both displacement and hypersingular traction formulations, for the analysis of time-harmonic seismic waves propagating through cracked, multi-layered geological regions with surface topography and under plane strain conditions. Specifically, the displacement-based BIEM is used for a multi-layered deposit with interface cracks, while the regularized, traction-based BIEM is used when internal cracks are present within the layers. The standard uni-dimensional boundary element with parabolic shape functions is employed for discretizing the free surface and the layer interfaces, while special discontinuous boundary elements are placed near the crack tips to model the asymptotic behaviour of both displacements and tractions. This formulation yields displacement amplitudes and phase angles on the free surface of a geological deposit, as well as stress intensity factors near the tips of the cracks. Finally, in the companion paper, numerical results are presented which show that both scattered wave and stress concentration fields are sensitive to the incidence seismic wave parameters and to specific site conditions such as surface topography, layering, the presence of cracks and crack interaction. 相似文献