Hazard and risk assessment procedures of different types of rockfall were analyzed to compare their outcomes when they are applied to the same case study.Although numerous methodologies are available in literature,roc...Hazard and risk assessment procedures of different types of rockfall were analyzed to compare their outcomes when they are applied to the same case study.Although numerous methodologies are available in literature,rockfall hazard and risk analyses are often limited to standard estimations,affected by a margin of uncertainty,especially when relevant engineering projects are about to be realized.Based on the design purpose,different types of approaches can be chosen among the qualitative and quantitative ones available in literature,which allow different levels of analysis.One of the main criticisms related to rockfall events is the risk affecting linear structures,such as road or railways,due both to their strategic relevance for trade and communications and to the great entity of the exposed value(traffic units)traveling along them.In this perspective,a comparison between the qualitative method known as Evolving Rockfall Hazard Assessment(EHRA),the semi-quantitative modified Rockfall Hazard Rating System(RHRS)and the quantitative Rockfall Risk Management(RoMa)approach is herein commented according to a practical application to a case study.It is the case of the rockfall threat along slopes crossed by a strategic road connecting two of the most known spots of eastern Sicily(Italy),at the Taormina tourist complex.Data were retrieved from both recent literature and technical surveys on field.Achieved results highlight how the approaches are affected by a different level of detail and uncertainty,arising also by some necessary assumption that must be taken into account,especially when mitigation measures or territory planning have to be designed.Achieved results can be also taken into account for similar studies worldwide,in order to choose the most suitable procedure based on the design purpose.This is indeed crucial in the perspective of the optimization of time and economic resources in the territorial planning practice.展开更多
Seismic hazard assessment is carried out by utilizing deterministic approach to evaluate the maximum expected earthquake ground motions along the Western Coastal Province of Saudi Arabia. The analysis is accomplished ...Seismic hazard assessment is carried out by utilizing deterministic approach to evaluate the maximum expected earthquake ground motions along the Western Coastal Province of Saudi Arabia. The analysis is accomplished by incorporating seismotectonic source model, determination of earthquake magnitude （Mmax）, set of appropriate ground motion predictive equations （GMPE）, and logic tree sequence. The logic tree sequence is built up to assign weight to ground motion scaling relationships. Contour maps of ground acceleration are generated at different spectral periods. These maps show that the largest ground motion values are emerged in northern and southern regions of the western coastal province in Saudi Arabia in comparison with the central region.展开更多
he logical tree methods are used for evaluate quantitatively relationship between frequency and magnitude, and deduce uncertainties of annual occurrence rate of earthquakes in the periods of lower magnitude earthquake...he logical tree methods are used for evaluate quantitatively relationship between frequency and magnitude, and deduce uncertainties of annual occurrence rate of earthquakes in the periods of lower magnitude earthquake. The uncertainties include deviations from the self-similarity of frequency-magnitude relations, different fitting methods, different methods obtained the annual occurrence rate, magnitude step used in fitting, start magnitude, error of magnitude and so on. Taking Xianshuihe River source zone as an example, we analyze uncertainties of occurrence rate of earthquakes M4, which is needed in risk evaluation extrapolating from frequency-magnitude relations of stronger earthquakes. The annual occurrence rate of M4 is usually required for seismic hazard assessment.The sensitivity analysis and examinations indicate that, in the same frequencymagnitude relations fitting method, the most sensitive factor is annual occurrence rate, the second is magnitude step and the following is start magnitude. Effect of magnitude error is rather small.Procedure of estimating the uncertainties is as follows:①Establishing a logical tree described uncertainties in frequencymagnitude relations by available data and knowledge about studied region.② Calculating frequencymagnitude relations for each end branches. ③ Examining sensitivities of each uncertainty factors, amending structure of logical tree and adjusting original weights. ④ Recalculating frequencymagnitude relations of end branches and complementary cumulative distribution function (CCDF) in each magnitude intervals.⑤ Obtaining an annual occurrence rate of M4 earthquakes under given fractiles.Taking fractiles as 20% and 80%, annual occurrence rate of M 4 events in Xianshuihe seismic zone is 0.643 0. The annual occurrence rate is 0.631 8 under fractiles of 50%, which is very close to that under fractiles 20% and 80%.展开更多
The potential for devastating earthquakes in the Himalayan orogeny has long been recognized. The 2015 MW7.8 Gorkha, Nepal earthquake has heightened the likelihood that major earthquakes will occur along this orogenic ...The potential for devastating earthquakes in the Himalayan orogeny has long been recognized. The 2015 MW7.8 Gorkha, Nepal earthquake has heightened the likelihood that major earthquakes will occur along this orogenic belt in the future. Reliable seismic hazard assessment is a critical element in development of policy for seismic hazard mitigation and risk reduction. In this study, we conduct probabilistic seismic hazard assessment using three different seismogenic source models(smoothed gridded, linear, and areal sources)based on the complicated tectonics of the study area. Two sets of ground motion prediction equations are combined in a standard logic tree by taking into account the epistemic uncertainties in hazard estimation. Long-term slip rates and paleoseismic records are also incorporated in the linear source model. Peak ground acceleration and spectral acceleration at 0.2 s and 1.0 s for 2% and 10%probabilities of exceedance in 50 years are estimated. The resulting maps show significant spatial variation in seismic hazard levels. The region of the Lesser Himalaya is found to have high seismic hazard potential. Along the Main Himalayan Thrust from east to west beneath the Main Central Thrust, large earthquakes have occurred regularly in history; hazard values in this region are found to be higher than those shown on existing hazard maps. In essence, the combination of long span earthquake catalogs and multiple seismogenic source models gives improved seismic hazard constraints in Nepal.展开更多
湘北常澧山地-丘陵地区地理地质环境复杂,滑坡地质灾害点多、面广、零散、频发,是造成人员伤亡和经济损失最主要的地质灾害类型。InSAR、光学遥感、LiDAR、GIS多源遥感综合技术,是目前可行性高、精度良好的滑坡地灾隐患识别和监测技术方...湘北常澧山地-丘陵地区地理地质环境复杂,滑坡地质灾害点多、面广、零散、频发,是造成人员伤亡和经济损失最主要的地质灾害类型。InSAR、光学遥感、LiDAR、GIS多源遥感综合技术,是目前可行性高、精度良好的滑坡地灾隐患识别和监测技术方法,能够满足宏观大范围、时效性等要求。该文基于InSAR形变速率数据、多光谱影像和DEM数据对湖南常澧地区的滑坡地灾隐患进行了识别和提取:首先用2种决策树分类方法对多光谱图像进行了土地利用分类,以便于观察研究区的用地类别及分布情况;然后运用DEM数据提取了高程、坡度、坡向、起伏度和曲率等5项地形地貌因子对研究区进行了滑坡危险性评价;再基于SBAS-InSAR技术对研究区进行地表时序微形变测量;最后在GIS系统内综合危险性评价结果和形变速率对研究区滑坡隐患进行提取和圈定,并基于CART决策树分类结果和研究区水系分布情况,对研究区内除圈定的滑坡隐患点以外的形变速率大于-0.01 m/a的区域进行了危险性推断。本次研究在植被覆盖区和裸露区识别出了数处隐蔽性高、规模小的滑坡隐患,并圈定了滑坡隐患的空间分布范围,面积0.126 km 2,证明了技术方法的有效性,具有一定的实践应用价值。展开更多
文摘Hazard and risk assessment procedures of different types of rockfall were analyzed to compare their outcomes when they are applied to the same case study.Although numerous methodologies are available in literature,rockfall hazard and risk analyses are often limited to standard estimations,affected by a margin of uncertainty,especially when relevant engineering projects are about to be realized.Based on the design purpose,different types of approaches can be chosen among the qualitative and quantitative ones available in literature,which allow different levels of analysis.One of the main criticisms related to rockfall events is the risk affecting linear structures,such as road or railways,due both to their strategic relevance for trade and communications and to the great entity of the exposed value(traffic units)traveling along them.In this perspective,a comparison between the qualitative method known as Evolving Rockfall Hazard Assessment(EHRA),the semi-quantitative modified Rockfall Hazard Rating System(RHRS)and the quantitative Rockfall Risk Management(RoMa)approach is herein commented according to a practical application to a case study.It is the case of the rockfall threat along slopes crossed by a strategic road connecting two of the most known spots of eastern Sicily(Italy),at the Taormina tourist complex.Data were retrieved from both recent literature and technical surveys on field.Achieved results highlight how the approaches are affected by a different level of detail and uncertainty,arising also by some necessary assumption that must be taken into account,especially when mitigation measures or territory planning have to be designed.Achieved results can be also taken into account for similar studies worldwide,in order to choose the most suitable procedure based on the design purpose.This is indeed crucial in the perspective of the optimization of time and economic resources in the territorial planning practice.
基金the support by Deanship of graduate studies and Geophysics Department,at King Abdulaziz University
文摘Seismic hazard assessment is carried out by utilizing deterministic approach to evaluate the maximum expected earthquake ground motions along the Western Coastal Province of Saudi Arabia. The analysis is accomplished by incorporating seismotectonic source model, determination of earthquake magnitude （Mmax）, set of appropriate ground motion predictive equations （GMPE）, and logic tree sequence. The logic tree sequence is built up to assign weight to ground motion scaling relationships. Contour maps of ground acceleration are generated at different spectral periods. These maps show that the largest ground motion values are emerged in northern and southern regions of the western coastal province in Saudi Arabia in comparison with the central region.
文摘he logical tree methods are used for evaluate quantitatively relationship between frequency and magnitude, and deduce uncertainties of annual occurrence rate of earthquakes in the periods of lower magnitude earthquake. The uncertainties include deviations from the self-similarity of frequency-magnitude relations, different fitting methods, different methods obtained the annual occurrence rate, magnitude step used in fitting, start magnitude, error of magnitude and so on. Taking Xianshuihe River source zone as an example, we analyze uncertainties of occurrence rate of earthquakes M4, which is needed in risk evaluation extrapolating from frequency-magnitude relations of stronger earthquakes. The annual occurrence rate of M4 is usually required for seismic hazard assessment.The sensitivity analysis and examinations indicate that, in the same frequencymagnitude relations fitting method, the most sensitive factor is annual occurrence rate, the second is magnitude step and the following is start magnitude. Effect of magnitude error is rather small.Procedure of estimating the uncertainties is as follows:①Establishing a logical tree described uncertainties in frequencymagnitude relations by available data and knowledge about studied region.② Calculating frequencymagnitude relations for each end branches. ③ Examining sensitivities of each uncertainty factors, amending structure of logical tree and adjusting original weights. ④ Recalculating frequencymagnitude relations of end branches and complementary cumulative distribution function (CCDF) in each magnitude intervals.⑤ Obtaining an annual occurrence rate of M4 earthquakes under given fractiles.Taking fractiles as 20% and 80%, annual occurrence rate of M 4 events in Xianshuihe seismic zone is 0.643 0. The annual occurrence rate is 0.631 8 under fractiles of 50%, which is very close to that under fractiles 20% and 80%.
基金supported by the grants of the National Nature Science Foundation of China (No. 41761144076, 41490611)the collaborative research program of the Disaster Prevention Research Institute of Kyoto University (No. 29W-03)+2 种基金the COX visiting professor fellowship of the Stanford University to L.B.the Chinese Academy of Sciences (CAS)The World Academy of Sciences (TWAS) President’s Ph D Fellowship to M.M.R
文摘The potential for devastating earthquakes in the Himalayan orogeny has long been recognized. The 2015 MW7.8 Gorkha, Nepal earthquake has heightened the likelihood that major earthquakes will occur along this orogenic belt in the future. Reliable seismic hazard assessment is a critical element in development of policy for seismic hazard mitigation and risk reduction. In this study, we conduct probabilistic seismic hazard assessment using three different seismogenic source models(smoothed gridded, linear, and areal sources)based on the complicated tectonics of the study area. Two sets of ground motion prediction equations are combined in a standard logic tree by taking into account the epistemic uncertainties in hazard estimation. Long-term slip rates and paleoseismic records are also incorporated in the linear source model. Peak ground acceleration and spectral acceleration at 0.2 s and 1.0 s for 2% and 10%probabilities of exceedance in 50 years are estimated. The resulting maps show significant spatial variation in seismic hazard levels. The region of the Lesser Himalaya is found to have high seismic hazard potential. Along the Main Himalayan Thrust from east to west beneath the Main Central Thrust, large earthquakes have occurred regularly in history; hazard values in this region are found to be higher than those shown on existing hazard maps. In essence, the combination of long span earthquake catalogs and multiple seismogenic source models gives improved seismic hazard constraints in Nepal.
文摘湘北常澧山地-丘陵地区地理地质环境复杂,滑坡地质灾害点多、面广、零散、频发,是造成人员伤亡和经济损失最主要的地质灾害类型。InSAR、光学遥感、LiDAR、GIS多源遥感综合技术,是目前可行性高、精度良好的滑坡地灾隐患识别和监测技术方法,能够满足宏观大范围、时效性等要求。该文基于InSAR形变速率数据、多光谱影像和DEM数据对湖南常澧地区的滑坡地灾隐患进行了识别和提取:首先用2种决策树分类方法对多光谱图像进行了土地利用分类,以便于观察研究区的用地类别及分布情况;然后运用DEM数据提取了高程、坡度、坡向、起伏度和曲率等5项地形地貌因子对研究区进行了滑坡危险性评价;再基于SBAS-InSAR技术对研究区进行地表时序微形变测量;最后在GIS系统内综合危险性评价结果和形变速率对研究区滑坡隐患进行提取和圈定,并基于CART决策树分类结果和研究区水系分布情况,对研究区内除圈定的滑坡隐患点以外的形变速率大于-0.01 m/a的区域进行了危险性推断。本次研究在植被覆盖区和裸露区识别出了数处隐蔽性高、规模小的滑坡隐患,并圈定了滑坡隐患的空间分布范围,面积0.126 km 2,证明了技术方法的有效性,具有一定的实践应用价值。
