Study On The Upper-crust Electrical Structure And Its Geological Meaning In Tangshan-Qinghuagndao Coastal Region Of Hebei Province

Tangshan-Qinhuangdao coastal region is located in the northeast of the North China Plain and belongs to the coastal plain of eastern Hebei province.This region adjoins to the west of Bohai Sea,the east of Tianjin new coastal area,the south of Liaoning coastal economic belt and the north of the Yellow-River-Delta high-efficiency ecological economic zone.Therefore it plays a very important role in promoting the regional coordinated development of Beijing,Tianjin,Hebei and even the whole nation.On the tectonic location,this region is in the east of the border of Sino-Korean-paraplatform Yanshan fold belt and North China down-faulted basin,in which faults and folds are very developed.Thus it has very favorable occurrence conditions for geothermal water resources.Exploiting and utilizing the geothermal water resources in this region is very significant to relief the pressure imposed on the region for the shortage of water and energy resources as well as environmental problems,and further to promote the regional coordinated development of economy and society.In order to get scientific evaluation on the geothermal water resources in Tangshan-Qinhuangdao coastal region,it is necessary to have a detailed research for its stratum,lithology and geological structure distribution in the upper crust.On the electrical property,underground hot water reservoirs usually show the characteristics of low resistivity anomalies,this provides an important physical basis for using magnetotelluric sounding for geothermal exploration.In 2007 and 2012,we totally completed ten magnetotelluric sounding profiles in Tangshan-Qinhuangdao coastal region.These profiles can basically control all the main geological blocks in the region.According to the inversion results of these profiles,we can roughly divide the stratum and geological structure distribution in the upper crust of the region and preliminarily predict the geothermal prospects areas in the region.We processed the magnetotelluric sounding data collected from all the ten profiles using standard data processing procedure and inversed the processed data using two dimensional nonlinear conjugate gradient inverse method to obtain their resistivity structure models.Finally,we selected nine fairly consistent resistivity structure models for data interpretation.According to the resistivity structure models and combining with the regional geological structure and stratum data as well as geophysical exploration and drilling data,we firstly had a division for the geological structure distribution of each profile and determined ten geological structure blocks in the research region,such as Xihe high,Jianhe sag,Laowangzhuang-Luochaowan high,Nanpu sag,Xinanzhuang-Baigezhuang high,Shijiutuo sag,Matouying high,Laoting sag,Jianggezhuang high and Changli sag.Based on the results from the division of the geological structure blocks,We then divided stratigraphic units in each geological structure block on the profiles and classified seven different strata,including Quaternary,Neogene Minghuazhen,Neogene Guantao,Paleogene,Mesozoic,Carboniferous-Permian and pre-Cambrian-Ordovician formations.Finally,we conducted a comprehensive analysis of the resistivity structure characteristics as well as geological structure and stratum distribution on each profile and delineated sixteen geothermal water prospects on the nine profiles.