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排序方式: 共有393条查询结果,搜索用时 31 毫秒
101.
102.
On May 2, 1993 more than 200 seismic events from an underground mine in Tyrol/Austria were recorded with short-period seismometers of a local seismic network which was introduced in the late 1980s to monitor the tectonic seismicity in Tyrol in greater detail. The cause of this series of mining-associated events has become the subject of intensive investigations — as it was associated with a subsidence affecting an area of 10.000 m2. Underground observations revealed a number of discontinuities along which the rock mass was able to move. Seismic recordings of the close-by seismic stations revealed two types of mechanisms: One mechanism seems to be associated with pure block-sliding along several discontinuities, while other signals indicate additional collapse. The consideration and combination of several seismological principles made possible the construction of a model of the mine collapse. 相似文献
103.
The results obtained in Part I (Soil Dynam. Earth. Engng, 1996, 15, 119-27) of this work for modelling harmonic wave propagation through viscoelastic heterogeneous media that exhibit a small random fluctuation of their material properties about mean values are now used here to investigate SH wave propagation in two naturally occurring media, namely sandstone and topsoil. These results are in the form of depth dependent, deterministic mean values and non-isotropic covariances for both the wave speed profile in the medium and for the fundamental solution in terms of displacement due to a unit point source. The results are also compared against conventional Monte Carlo simulations. 相似文献
104.
Scaling of peak ground motions from digital recordings of small earthquakes at Campi Flegrei,southern Italy 总被引:2,自引:0,他引:2
The dependence of peak ground acceleration and velocity on seismic moment is studied for a set of small earthquakes (0.7<M
L<3.2) recorded digitally at distances of a few km in the Campi Flegrei volcanic area near Naples, Italy, during the ground uplift episode of 1982–1984. Numerical simulations, using the -square spectral model with constant stress drop and ane
–kf high frequency decay, fit well both the velocity and acceleration data for an averagek=0.015. The observed ground motions in the 1–24 Hz frequency band appear to consist of radiation from simple sources modified only slightly by attenuation effects. Moreover, the scaling of peak values agrees closely with those determined in nonvolcanic areas, once the difference in stress drop is taken into account. 相似文献
105.
Jonathan D. Bray Adrian Rodriguez-Marek 《Soil Dynamics and Earthquake Engineering》2004,24(11):815-828
Ground motions close to a ruptured fault resulting from forward-directivity are significantly different than other ground motions. These pulse-type motions can place severe demands on structures in the near-fault region. To aid in the characterization of these special type of ground motions, a simplified parameterization is proposed based on a representative amplitude, pulse period, and number of significant pulses in the velocity–time history. Empirical relationships were developed for estimating the peak ground velocity (PGV) and period of the velocity pulse (Tv) of available forward-directivity motions. PGV in the near-fault region varies significantly with magnitude and distance. Additionally, the PGV for soil sites are systematically larger than those at rocks sites. Tv is a function of moment magnitude and site conditions with most of the energy being concentrated within a narrow-period band centered on the pulse period. Hence, lower magnitude events, which produce lower pulse periods, might produce more damaging ground motions for the stiff structures more common in urban areas. 相似文献
106.
In many parts of the world, the repetition of medium–strong intensity earthquake ground motions at brief intervals of time has been observed. The new design philosophies for buildings in seismic areas are based on multi‐level design approaches, which take into account more than a single damageability limit state. According to these approaches, a sequence of seismic actions may produce important consequences on the structural safety. In this paper, the effects of repeated earthquake ground motions on the response of single‐degree‐of‐freedom systems (SDOF) with non‐linear behaviour are analysed. A comparison is performed with the effect of a single seismic event on the originally non‐damaged system for different hysteretic models in terms of pseudo‐acceleration response spectra, behaviour factor q and damage parameters. The elastic–perfect plastic system is the most vulnerable one under repeated earthquake ground motions and is characterized by a strong reduction of the q‐factor. A moment resisting steel frame is analysed as well, showing a reduction of the q‐factor under repeated earthquake ground motions even larger than that of an equivalent SDOF system. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
107.
近断层地震动作用下钢筋混凝土桥墩的抗震性能 总被引:9,自引:2,他引:9
通过对满足规范延性要求的12根典型钢筋混凝土桥墩试件的线性和非线性地震反应分析,指出在近断层地震动作用下满足延性需求与延性能力比小于1.0的桥墩仍可能发生严重破坏和倒塌,若考虑桥墩的地震损伤性能,允许的延性需求与延性能力比不宜超过0.6-0.8。讨论了桥墩延性抗震设计中强度折减系数Rμ和设计基底剪力系数BSC取值问题。 相似文献
108.
Susan E Hough Stacey Martin Roger Bilham Gail M Atkinson 《Journal of Earth System Science》2003,112(3):353-373
We compiled available news and internet accounts of damage and other effects from the 26th January, 2001, Bhuj earthquake,
and interpreted them to obtain modified Mercalli intensities at over 200 locations throughout the Indian subcontinent. These
values are used to map the intensity distribution using a simple mathematical interpolation method. The maps reveal several
interesting features. Within the Kachchh region, the most heavily damaged villages are concentrated towards the western edge
of the inferred fault, consistent with western directivity. Significant sedimentinduced amplification is also suggested at
a number of locations around the Gulf of Kachchh to the south of the epicenter. Away from the Kachchh region intensities were
clearly amplified significantly in areas that are along rivers, within deltas, or on coastal alluvium such as mud flats and
salt pans. In addition we use fault rupture parameters inferred from teleseismic data to predict shaking intensity at distances
of 0–1000 km. We then convert the predicted hard rock ground motion parameters to MMI using a relationship (derived from internet-based
intensity surveys) that assigns MMI based on the average effects in a region. The predicted MMIs are typically lower by 1–2
units than those estimated from news accounts. This discrepancy is generally consistent with the expected effect of sediment
response, but it could also reflect other factors such as a tendency for media accounts to focus on the most dramatic damage,
rather than the average effects. Our modeling results also suggest, however, that the Bhuj earthquake generated more high-frequency
shaking than is expected for earthquakes of similar magnitude in California, and may therefore have been especially damaging. 相似文献
109.
Introduction The characteristics of ground motions recorded near the fault of an earthquake are quite dif- ferent from the usual far-field ground motions. After the original recognition of their differences in the Port Hueneme earthquake in 1957, a great lot of inhabited structures and lifeline systems were damaged in the major earthquakes happened in the following years. The damages were beyond minds of seismologists and engineers. A quite rational reason is the lack of enough knowledge of t… 相似文献
110.
Marios Apostolou George Gazetas Evangelia Garini 《Soil Dynamics and Earthquake Engineering》2007,27(7):642-654
The rocking of rigid structures uplifting from their support under strong earthquake shaking is investigated. The structure is resting on the surface of either a rigid base or a linearly elastic continuum. A large-displacement approach is adopted to extract the governing equations of motion allowing for a rigorous calculation of the nonlinear response even under near-overturning conditions. Directivity-affected near-fault ground motions, idealized as Ricker wavelets or trigonometric pulses, are used as excitation. The conditions under which uplifting leads to large angles of rotation and eventually to overturning are investigated. A profoundly nonlinear rocking behavior is revealed for both rigid and elastic soil conditions. This geometrically nonlinear response is further amplified by unfavorable sequences of long-duration pulses in the excitation. Moreover, through the overturning response of a toppled tombstone, it is concluded that the practice of estimating ground accelerations from overturning observations is rather misleading and meaningless. 相似文献