This work studies the effects of long human habitation on site geotechnical conditions. It is focused on the city of Zefat that is located on the borders of the Dead Sea Transform in northern Israel. The city of Zefat, suffered severe damage and loss of life in historical earthquakes, as a consequence of earthquake induced landslides (EILS). In this work we evaluate the current EILS hazard for the city of Zefat using a GIS-based regional Newmark analysis, with calibration of the calculated Newmark displacement (representing EILS hazard) using maps of field evidence and historical documents testifying to slope instability that occurred in historical earthquakes.
We found that the core city of Zefat is built on a layered anthropogenic material, few meters deep which, was deposited as a result of more than 2000 years of human habitation. The anthropogenic material is mechanically weak, susceptible to slope failure and to amplification of seismic-shaking. It is responsible for the city's devastation in historical earthquakes and it is the source for the current high seismic hazard as well.
Our model shows that earthquakes of magnitudes (Mw) 5, 6 and 7 at distances of up to 10 km, 50 km and more than 100 km, respectively, are likely to induce landslides in the core city of Zefat. The current engineering status of the city is poor, and as a consequence severe damage and loss of life are expected in future earthquakes due to EILS, unless major engineering efforts are made. Cities in the Eastern Mediterranean with comparable long habitation histories (e.g., Jerusalem, Tiberias, Nablus, Amman) are expected to have similar geotechnical problems in their old sections and are advised to take appropriate engineering steps to reduce damage and loss of life in future earthquakes.
Evaluation of historical earthquake magnitudes based on reported local-damage may, however, lead to overestimated magnitudes where the damaged sites are built on anthropogenic talus (a common setting in the vicinity of the Dead Sea Transform). 相似文献
结合物理模型试验,分析斜坡坡度、波陡、相对水深、护面类型和破波参数等因素对堆石防波堤不规则波浪反射系数的影响规律。将常用的Van der Meer公式,Seelig公式,Postma公式和Davison公式计算值和实测值进行比较,并结合试验数据,基于有效波高和平均周期定义的Iribarren数,得出堆石防波堤不规则波浪反射系数经验公式。结果表明,该公式能较好地计算不规则波作用下块石和扭王块体护面堆石防波堤波浪反射系数。 相似文献
Controlled laboratory experiments reveal that the lower part of turbidity currents has the ability to enter fluid mud substrates, if the bed shear stress is higher than the yield stress of the fluid mud and the density of the turbidity current is higher than the density of the substrate. Upon entering the substrate, the turbidity current either induces mixing between flow‐derived sediment and substrate sediment, or it forms a stable horizontal flow front inside the fluid mud. Such ‘intrabed’ flow is surrounded by plastically deformed mud; otherwise it resembles the front of a ‘bottom‐hugging’ turbidity current. The ‘suprabed’ portion of the turbidity current, i.e. the upper part of the flow that does not enter the substrate, is typically separated from the intrabed flow by a long horizontal layer of mud which originates from the mud that is swept over the top of the intrabed flow and then incorporated into the flow. The intrabed flow and the mixing mechanism are specific types of interaction between turbidity currents and muddy substrates that are part of a larger group of interactions, which also include bypass, deposition, erosion and soft sediment deformation. A classification scheme for these types of interactions is proposed, based on an excess bed shear stress parameter, which includes the difference in the bed shear stress imposed by the flow and the yield stress of the substrate and an excess density parameter, which relies on the density difference between the flow and the substrate. Based on this classification scheme, as well as on the sedimentological properties of the laboratory deposits, an existing facies model for intrabed turbidites is extended to the other types of interaction involving soft muddy substrates. The physical threshold of flow‐substrate mixing versus stable intrabed flow is defined using the gradient Richardson number, and this method is validated successfully with the laboratory data. The gradient Richardson number is also used to verify that stable intrabed flow is possible in natural turbidity currents, and to determine under which conditions intrabed flow is likely to be unstable. It appears that intrabed flow is likely only in natural turbidity currents with flow velocities well below ca 3·5 m s?1, although a wider range of flows is capable of entering fluid muds. Below this threshold velocity, intrabed flow is stable only at high‐density gradients and low‐velocity gradients across the upper boundary of the turbidity current. Finally, the gradient Richardson number is used as a scaling parameter to set the flow velocity limits of a natural turbidity current that formed an inferred intrabed turbidite in the deep‐marine Aberystwyth Grits Group, West Wales, United Kingdom. 相似文献
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