Local and global optimization methods are widely used in geophysical inversion but each has its own advantages and disadvantages. The combination of the two methods will make it possible to overcome their weaknesses. ...Local and global optimization methods are widely used in geophysical inversion but each has its own advantages and disadvantages. The combination of the two methods will make it possible to overcome their weaknesses. Based on the simulated annealing genetic algorithm （SAGA） and the simplex algorithm, an efficient and robust 2-D nonlinear method for seismic travel-time inversion is presented in this paper. First we do a global search over a large range by SAGA and then do a rapid local search using the simplex method. A multi-scale tomography method is adopted in order to reduce non-uniqueness. The velocity field is divided into different spatial scales and velocities at the grid nodes are taken as unknown parameters. The model is parameterized by a bi-cubic spline function. The finite-difference method is used to solve the forward problem while the hybrid method combining multi-scale SAGA and simplex algorithms is applied to the inverse problem. The algorithm has been applied to a numerical test and a travel-time perturbation test using an anomalous low-velocity body. For a practical example, it is used in the study of upper crustal velocity structure of the A＇nyemaqen suture zone at the north-east edge of the Qinghai-Tibet Plateau. The model test and practical application both prove that the method is effective and robust.展开更多
Coastal areas of Bangladesh are especially vulnerable due to their physiographic location and exposure to natural calamities. Around 35 million people living in coastal areas have no access or limited access to safe d...Coastal areas of Bangladesh are especially vulnerable due to their physiographic location and exposure to natural calamities. Around 35 million people living in coastal areas have no access or limited access to safe drinking water. Contamination of water sources by salinity, arsenic or iron are the principal causes of water scarcity. Rising sea levels and unevenness of climatic events due to climate change will exacerbate the situation in coastal areas, especially in the southwestern coastal zone. This study examines one of the vulnerable coastal upazila Tala at Satkhira(an 'upazila' is a medium level administrative unit in Bangladesh) in the southwestern zone of Bangladesh to understand the gravity of the problems. The study develops a GIS based multi-criteria analysis to identify suitable options and locations of fresh water as part of a current and future solution to the problems and further deterioration. To fulfill the objectives, a questionnaire-based GPS guided field survey was conducted to collect details of field level conditions in order to find a suitable solution. Because aquifers are considered the primary source of drinking water, field data have been analyzed for two distinct aquifers, one relatively shallow and one deeper, to understand aquifer quality. Potentiality of different water sources the socioeconomic status of communities, types of water use and corresponding sources and water demand are also evaluated. The analysis finds that alternative water sources that are safe are difficult to find, because both surface and groundwater-based sources are already contaminated, and there are no nearby, easily accessible safe sources. Groundwater-based sources are contaminated by arsenic, iron or salinity, and surface water-based sources are not in use due to maintenance and management issues. In some cases, surface water sources are polluted by flash flooding of high saline water during storm surges or seepage from saline water-based aquacultures. Multiple limitations identified during field observations and field data analysis were considered as an analytical parameter A GIS based multi-criteria analysis incorporated field data, including Geo-spatial and socioeconomic information for road networks, settlement locations, number of households, quality and quantity of existing water sources, water demand and business opportunities. The analysis found some potential options in distributed locations which are consistent with community demand. Suggested options made use of technologies that are already understood and commonly used by communities, like deep tubewells, PSFs(Pond Sand Filter) and WTPs(Water Treatment Plant). In the study area, PSF is the most commonly used method and to make this surface water-based technology sustainable some precautionary measurements are suggested.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos.40334040 and 40974033)the Promoting Foundation for Advanced Persons of Talent of NCWU
文摘Local and global optimization methods are widely used in geophysical inversion but each has its own advantages and disadvantages. The combination of the two methods will make it possible to overcome their weaknesses. Based on the simulated annealing genetic algorithm （SAGA） and the simplex algorithm, an efficient and robust 2-D nonlinear method for seismic travel-time inversion is presented in this paper. First we do a global search over a large range by SAGA and then do a rapid local search using the simplex method. A multi-scale tomography method is adopted in order to reduce non-uniqueness. The velocity field is divided into different spatial scales and velocities at the grid nodes are taken as unknown parameters. The model is parameterized by a bi-cubic spline function. The finite-difference method is used to solve the forward problem while the hybrid method combining multi-scale SAGA and simplex algorithms is applied to the inverse problem. The algorithm has been applied to a numerical test and a travel-time perturbation test using an anomalous low-velocity body. For a practical example, it is used in the study of upper crustal velocity structure of the A＇nyemaqen suture zone at the north-east edge of the Qinghai-Tibet Plateau. The model test and practical application both prove that the method is effective and robust.
基金The Colleges and Universities Humanities and Social Science Fund Project in Jiangxi Province(JC1414).
文摘Coastal areas of Bangladesh are especially vulnerable due to their physiographic location and exposure to natural calamities. Around 35 million people living in coastal areas have no access or limited access to safe drinking water. Contamination of water sources by salinity, arsenic or iron are the principal causes of water scarcity. Rising sea levels and unevenness of climatic events due to climate change will exacerbate the situation in coastal areas, especially in the southwestern coastal zone. This study examines one of the vulnerable coastal upazila Tala at Satkhira(an 'upazila' is a medium level administrative unit in Bangladesh) in the southwestern zone of Bangladesh to understand the gravity of the problems. The study develops a GIS based multi-criteria analysis to identify suitable options and locations of fresh water as part of a current and future solution to the problems and further deterioration. To fulfill the objectives, a questionnaire-based GPS guided field survey was conducted to collect details of field level conditions in order to find a suitable solution. Because aquifers are considered the primary source of drinking water, field data have been analyzed for two distinct aquifers, one relatively shallow and one deeper, to understand aquifer quality. Potentiality of different water sources the socioeconomic status of communities, types of water use and corresponding sources and water demand are also evaluated. The analysis finds that alternative water sources that are safe are difficult to find, because both surface and groundwater-based sources are already contaminated, and there are no nearby, easily accessible safe sources. Groundwater-based sources are contaminated by arsenic, iron or salinity, and surface water-based sources are not in use due to maintenance and management issues. In some cases, surface water sources are polluted by flash flooding of high saline water during storm surges or seepage from saline water-based aquacultures. Multiple limitations identified during field observations and field data analysis were considered as an analytical parameter A GIS based multi-criteria analysis incorporated field data, including Geo-spatial and socioeconomic information for road networks, settlement locations, number of households, quality and quantity of existing water sources, water demand and business opportunities. The analysis found some potential options in distributed locations which are consistent with community demand. Suggested options made use of technologies that are already understood and commonly used by communities, like deep tubewells, PSFs(Pond Sand Filter) and WTPs(Water Treatment Plant). In the study area, PSF is the most commonly used method and to make this surface water-based technology sustainable some precautionary measurements are suggested.
