Summary. A first-order form of the Euler's equations for rays in an ellipsoidal model of the Earth is obtained. The conditions affecting the velocity law for a monotonic increase, with respect to the arc length, in the angular distance to the epicentre, and in the angle of incidence, are the same in the ellipsoidal and spherical models. It is therefore possible to trace rays and to compute travel times directly in an ellipsoidal earth as in the spherical model. Thus comparison with the rays of the same coordinates in a spherical earth provides an estimate of the various deviations of these rays due to the Earth's flattening, and the corresponding travel-time differences, for mantle P -waves and for shallow earthquakes. All these deviations are functions both of the latitude and of the epicentral distance. The difference in the distance to the Earth's centre at points with the same geocentric latitude on rays in the ellipsoidal and in the spherical model may reach several kilometres. Directly related to the deformation of the isovelocity surfaces, this difference is the only cause of significant perturbation in travel times. Other differences, such as that corresponding to the ray torsion, are of the first order in ellipticity, and may exceed 1 km. They induce only small differences in travel time, less than 0.01s. Thus, we show that the ellipticity correction obtained by Jeffreys (1935) and Bullen (1937) by a perturbational method can be recovered by a direct evaluation of the travel times in an ellipsoidal model of the Earth. Moreover, as stated by Dziewonski & Gilbert (1976), we verify the non-dependence of this correction on the choice of the velocity law. 相似文献
This study examines the local geological conditions and soil structure as possible causes of the collapse of the Zümrüt Building
2 February 2004. This catastrophe resulted in 92 fatalities and 35 injuries. This study also examines other views which claim
weak soil structure, elastic and consolidation settlement of soil and excessive groundwater extraction as well as subsidence
resulting from the underground silt erosion as possible factors. Zümrüt Building was constructed on normally consolidated,
low plasticity clay. The underground water table was 30 m in depth. The internal friction angle of soil was 8°–30°, its cohesion
was between 34 and 127 kN/m2 and standard penetration test numbers varied between 11 and 50. The underground water level beneath Zümrüt Building had risen
4.5 m since its construction. Therefore the claim that subsidence resulting from the decrease of underground water level contributed
to the collapse is incorrect. Secondly the settlement, resulting from the filling up of the pores created by the silt receding
with the underground water, was 4.4 mm in total, and attributing this as the primary cause of the collapse is also incorrect.
Soil properties, in situ and laboratory test results showed that the existing and/or expected settlement and the differential
ground settlement in the Zümrüt building vicinity had the potential to cause structural damage. The tensile stresses caused
by differential settlements recorded here are thought to be an indicator, but not the main cause contributing to the collapse
of the building. The Zümrüt Building collapse was due to several compounding mistakes during the construction phase. These
were geotechnical and other project faults and the use of low quality construction materials. The resulting catastrophe caused
92 fatalities, 35 injuries and a material loss of approximately US$7 million. 相似文献
The paper is dedicated to the review of methods of seismic hazard analysis currently in use, analyzing the strengths and weaknesses of different approaches. The review is performed from the perspective of a user of the results of seismic hazard analysis for different applications such as the design of critical and general (non-critical) civil infrastructures, technical and financial risk analysis. A set of criteria is developed for and applied to an objective assessment of the capabilities of different analysis methods. It is demonstrated that traditional probabilistic seismic hazard analysis (PSHA) methods have significant deficiencies, thus limiting their practical applications. These deficiencies have their roots in the use of inadequate probabilistic models and insufficient understanding of modern concepts of risk analysis, as have been revealed in some recent large scale studies. These deficiencies result in the lack of ability of a correct treatment of dependencies between physical parameters and finally, in an incorrect treatment of uncertainties. As a consequence, results of PSHA studies have been found to be unrealistic in comparison with empirical information from the real world. The attempt to compensate these problems by a systematic use of expert elicitation has, so far, not resulted in any improvement of the situation. It is also shown that scenario-earthquakes developed by disaggregation from the results of a traditional PSHA may not be conservative with respect to energy conservation and should not be used for the design of critical infrastructures without validation. Because the assessment of technical as well as of financial risks associated with potential damages of earthquakes need a risk analysis, current method is based on a probabilistic approach with its unsolved deficiencies.
Traditional deterministic or scenario-based seismic hazard analysis methods provide a reliable and in general robust design basis for applications such as the design of critical infrastructures, especially with systematic sensitivity analyses based on validated phenomenological models. Deterministic seismic hazard analysis incorporates uncertainties in the safety factors. These factors are derived from experience as well as from expert judgment. Deterministic methods associated with high safety factors may lead to too conservative results, especially if applied for generally short-lived civil structures. Scenarios used in deterministic seismic hazard analysis have a clear physical basis. They are related to seismic sources discovered by geological, geomorphologic, geodetic and seismological investigations or derived from historical references. Scenario-based methods can be expanded for risk analysis applications with an extended data analysis providing the frequency of seismic events. Such an extension provides a better informed risk model that is suitable for risk-informed decision making. 相似文献
The concept of a natural hazard is a human construct. It is the interaction with human communities and settlements that defines
a natural phenomenon as a natural hazard. Thus the end point of hazard mitigation and hazard vulnerability assessment must
involve an attempt to reduce, or mitigate, the impact of the natural hazard on human communities. The responsibility to mitigate
hazard impact falls primarily upon governments and closely connected non-government and private institutional agencies. In
particular, it is most often local government that takes the responsibility for safeguarding its own communities, infrastructure
and people. Hazard vulnerability of specific local communities is best assessed by the local government or council, which
then faces the responsibility to translate that assessment into community education and infrastructural safeguards for hazard
mitigation. This paper illustrates the process of local government engagement in hazard mitigation in Australia, through the
Natural Disaster Risk Management Studies, as a first step towards natural disaster reduction. 相似文献