Islands are valuable land resources in the ocean,and their detailed subsurface seismic velocity structures are highly important for underground space utilization,engineering construction,and geological disaster preven...Islands are valuable land resources in the ocean,and their detailed subsurface seismic velocity structures are highly important for underground space utilization,engineering construction,and geological disaster prevention.Ambient noise tomography and the horizontal–vertical spectral ratio(HVSR)method use ambient noise recordings instead of earthquake signals to study the underground velocity structure,making them easy to implement on islands and consequently becoming potential optimization schemes for the investigation of detailed island structures.However,the application of these technologies to small granite islands along coasts is relatively insufficient,and the applicability needs to be further verified.This study ambient noise tomography and HVSR analysis were carried out by using a dense array of seismic data on Wuzhizhou Island,Hainan.It was found that natural activities mainly cause the ambient noise below 8 Hz on Wuzhizhou Island.Moreover,high-quality noise cross-correlation functions of 3–8 Hz can be extracted.The results of ambient noise tomography and HVSR analysis show that the underground S-wave velocity structure and sedimentary characteristics of Wuzhizhou Island are coupled with its topography.The high-terrain area of Wuzhizhou Island exhibits low-velocity anomalies,where a sedimentary layer did not develop.On the other hand,the low-terrain area of Wuzhizhou Island exhibits high-velocity anomalies,where a thin Quaternary sedimentary layer developed.These results imply that subsurface magmatic activity controls the island topography and affects the distribution of the island sedimentary layer.This study successfully verifies the feasibility of detection methods based on ambient noise in small granite islands along the coast.It also provides key basic information for studying the geological evolutionary history,island spatial planning,and geological disaster prevention of Wuzhizhou Island.展开更多
Carbon-bearing stratum normally features low resistance and high polarization.If the lithostratigraphy of the exploration area contains large amounts of carbon,the induced polarization anomaly caused by metal sulfide ...Carbon-bearing stratum normally features low resistance and high polarization.If the lithostratigraphy of the exploration area contains large amounts of carbon,the induced polarization anomaly caused by metal sulfide ore bodies will be inundated by the high polarization of carbon-containing wall rock.In this work,we adopted time-domain induced polarization(TDIP)and controlled-source audio-frequency magnetotellurics(CSAMT)on deep prospecting of the carbon-bearing stratum of the Ar Horqin Banner,Inner Mongolia.The underground medium is divided into target geologic bodies according to the geological information within the known exploration line borehole,and the physical properties of various target geologic bodies are calculated using weighted averages to build a geologic-geophysical model that can fit the observation data.Consequently,we can determine the range and morphological characteristics of the electrical properties of the ore-bearing geologic bodies in the inversion results in the study area.Then we can use the characteristics summarized from the known exploration line to interpret unknown exploration line.Results indicated that,when the diff erence in physical properties between the ore body and interference wall rock is not clear,the geologic body can be classifi ed via the paragenetic(associated)assemblage relations of the underground medium.Geological interpretation is guided by the comprehensive physical properties of ore-bearing geologic bodies to avoid interferences.展开更多
基金supported by the geological survey project(Grant No.DD20220992,Grant No.DD20242841,Grant No.DD20230592 and Grant No.DD20220993)Innovation Foundation of Science and Technology for“Nanhai New Star”Projects(Grant No.NHXXRCXM202353)of Hainan province。
文摘Islands are valuable land resources in the ocean,and their detailed subsurface seismic velocity structures are highly important for underground space utilization,engineering construction,and geological disaster prevention.Ambient noise tomography and the horizontal–vertical spectral ratio(HVSR)method use ambient noise recordings instead of earthquake signals to study the underground velocity structure,making them easy to implement on islands and consequently becoming potential optimization schemes for the investigation of detailed island structures.However,the application of these technologies to small granite islands along coasts is relatively insufficient,and the applicability needs to be further verified.This study ambient noise tomography and HVSR analysis were carried out by using a dense array of seismic data on Wuzhizhou Island,Hainan.It was found that natural activities mainly cause the ambient noise below 8 Hz on Wuzhizhou Island.Moreover,high-quality noise cross-correlation functions of 3–8 Hz can be extracted.The results of ambient noise tomography and HVSR analysis show that the underground S-wave velocity structure and sedimentary characteristics of Wuzhizhou Island are coupled with its topography.The high-terrain area of Wuzhizhou Island exhibits low-velocity anomalies,where a sedimentary layer did not develop.On the other hand,the low-terrain area of Wuzhizhou Island exhibits high-velocity anomalies,where a thin Quaternary sedimentary layer developed.These results imply that subsurface magmatic activity controls the island topography and affects the distribution of the island sedimentary layer.This study successfully verifies the feasibility of detection methods based on ambient noise in small granite islands along the coast.It also provides key basic information for studying the geological evolutionary history,island spatial planning,and geological disaster prevention of Wuzhizhou Island.
基金The Research is funded by Comprehensive Intelligent Mapping System and Application of Geological Survey(DD20190415)Exploration and Development Tracking and Result Integration of Energy and Important Mineral Resources(DD20190457)Resource Assessment and Prediction for Main Tectonic Metallogenetic Domains in the World(DD20190459).
文摘Carbon-bearing stratum normally features low resistance and high polarization.If the lithostratigraphy of the exploration area contains large amounts of carbon,the induced polarization anomaly caused by metal sulfide ore bodies will be inundated by the high polarization of carbon-containing wall rock.In this work,we adopted time-domain induced polarization(TDIP)and controlled-source audio-frequency magnetotellurics(CSAMT)on deep prospecting of the carbon-bearing stratum of the Ar Horqin Banner,Inner Mongolia.The underground medium is divided into target geologic bodies according to the geological information within the known exploration line borehole,and the physical properties of various target geologic bodies are calculated using weighted averages to build a geologic-geophysical model that can fit the observation data.Consequently,we can determine the range and morphological characteristics of the electrical properties of the ore-bearing geologic bodies in the inversion results in the study area.Then we can use the characteristics summarized from the known exploration line to interpret unknown exploration line.Results indicated that,when the diff erence in physical properties between the ore body and interference wall rock is not clear,the geologic body can be classifi ed via the paragenetic(associated)assemblage relations of the underground medium.Geological interpretation is guided by the comprehensive physical properties of ore-bearing geologic bodies to avoid interferences.
