The geodetic and geophysical applications of Earth Gravity Field parameters computed from Global Geopotential Models (GGMs) are quite on the increase despite the inherent commission and omission errors of these models...The geodetic and geophysical applications of Earth Gravity Field parameters computed from Global Geopotential Models (GGMs) are quite on the increase despite the inherent commission and omission errors of these models. In view of this, this study focuses on refining and quantifying terrain-induced effects on Bouguer gravity anomalies computed directly from a total of seven recent GGMs. In the study, the Residual Terrain Model (RTM) technique was used to estimate the residual terrain effects that were added to the GGM-computed Bouguer gravity anomalies at the sixty test points in Enugu State, Nigeria. The computed residual terrain effects range from -24.6 to 37.5 mgal while the percentage of the omission errors of the GGMs based on their Root-Mean-Square (RMS) differences ranges from 7.8% to 44.7%. It can be concluded that GGM-refined Bouguer gravity anomalies are better in accuracy than the unrefined GGM-computed Bouguer gravity anomalies and hence there is need for accurate height information in the development of GGMs. We, therefore, recommend that refined Bouguer gravity anomalies obtained from HUST-Grace2016s, EIGEN-6C4 and GECO that gave best improvement amongst the seven GGMs under consideration should be used to supplement the available terrestrial Bouguer anomalies for geodetic and geophysical applications within the study area.展开更多
A new gravity survey of the Mount Cameroon area has enabled the definition of four major gravimetric do- mains, which coincide with the recognized structural units. In order to determine the nature of superficial and ...A new gravity survey of the Mount Cameroon area has enabled the definition of four major gravimetric do- mains, which coincide with the recognized structural units. In order to determine the nature of superficial and deep structures in this mountainous zone, new gravity data have been processed. These new gravity data was integrated to existing gravity data to propose the new complete Bouguer anomaly map of the region, and then to show major characteristics of the Bouguer gravity of this area. The interpretation of gravity patterns (bouguer maps) in terms of geological data, shows that the Mount Cameroon zone belongs to a wide positive anomaly;these anomalies display complex gravity domains, which seem to be similar to that due to major structural units in the region and volcanic activity of the mountain. In the mountain active zone in particular (between 2000 and 3800 m of altitude), the new anomalies map shows high gravity anomalies (from 11 to 60 mgal), coupled with low gravity at some stations (in the summit, 4060 m) where gravity anomaly is about –30 mgal. The steep WNW-ESE gravity gradients observed on the gravity maps mark the transition between positive in the south and negative anomalies.展开更多
The 1:200,000 middle-large scale Bouguer gravity anomaly data covering the southern segment of the Liaocheng-Lankao fault(SLLF)and its vicinity are analyzed with two methods.First,the Bouguer gravity anomaly data are ...The 1:200,000 middle-large scale Bouguer gravity anomaly data covering the southern segment of the Liaocheng-Lankao fault(SLLF)and its vicinity are analyzed with two methods.First,the Bouguer gravity anomaly data are decomposed by two-dimensional(2 D)wavelet to make the family of multi-scale modes correspond with density structure at different depths.Second,a two and half dimension(2.5 D)human-computer interaction inversion of the Bouguer gravity anomaly data are conducted with the constraints provided by two deep seismic sounding profiles(DSS1 and DSS2)crossing the study area to get the crustal density profiles.Based on the integrated study,we can draw the following conclusions:1)SLLF appears to be a deep fault with almost vertical dipping and rooted into the uppermost mantle;2)In the middle to upper crust SLLF shows an clear turning patterns and segmentation features;3)In the study area the epicentral distributions of the precisely re-located small earthquakes and the historical large earthquakes have a good correspondence with the turning patterns and segmentation features of SLLF;and 4)The results of the horizontal slices from 2 D wavelet decomposition show that there are significant differences in the density structure on the two sides of the fault.A well-defined concave structure with low density exists in the upper crust of the Dongming Depression on the west side of the fault,with the concave center being estimated at a depth of about 8 km.In contrast,the upper crust on the east side presents a relative thinner pattern in depth with a bit higher density.Meanwhile,the low-density structure in the middle crust underneath the fault is presumably caused by the uplift of the upper mantle materials and their intrusion along the deep rupture system.This paper clarified the inconsistency of fault system and epicenters of small earthquakes from upper to lower crust.The results indicated that the fault system plays an important governing role to the seismicity in this area.展开更多
文摘The geodetic and geophysical applications of Earth Gravity Field parameters computed from Global Geopotential Models (GGMs) are quite on the increase despite the inherent commission and omission errors of these models. In view of this, this study focuses on refining and quantifying terrain-induced effects on Bouguer gravity anomalies computed directly from a total of seven recent GGMs. In the study, the Residual Terrain Model (RTM) technique was used to estimate the residual terrain effects that were added to the GGM-computed Bouguer gravity anomalies at the sixty test points in Enugu State, Nigeria. The computed residual terrain effects range from -24.6 to 37.5 mgal while the percentage of the omission errors of the GGMs based on their Root-Mean-Square (RMS) differences ranges from 7.8% to 44.7%. It can be concluded that GGM-refined Bouguer gravity anomalies are better in accuracy than the unrefined GGM-computed Bouguer gravity anomalies and hence there is need for accurate height information in the development of GGMs. We, therefore, recommend that refined Bouguer gravity anomalies obtained from HUST-Grace2016s, EIGEN-6C4 and GECO that gave best improvement amongst the seven GGMs under consideration should be used to supplement the available terrestrial Bouguer anomalies for geodetic and geophysical applications within the study area.
文摘A new gravity survey of the Mount Cameroon area has enabled the definition of four major gravimetric do- mains, which coincide with the recognized structural units. In order to determine the nature of superficial and deep structures in this mountainous zone, new gravity data have been processed. These new gravity data was integrated to existing gravity data to propose the new complete Bouguer anomaly map of the region, and then to show major characteristics of the Bouguer gravity of this area. The interpretation of gravity patterns (bouguer maps) in terms of geological data, shows that the Mount Cameroon zone belongs to a wide positive anomaly;these anomalies display complex gravity domains, which seem to be similar to that due to major structural units in the region and volcanic activity of the mountain. In the mountain active zone in particular (between 2000 and 3800 m of altitude), the new anomalies map shows high gravity anomalies (from 11 to 60 mgal), coupled with low gravity at some stations (in the summit, 4060 m) where gravity anomaly is about –30 mgal. The steep WNW-ESE gravity gradients observed on the gravity maps mark the transition between positive in the south and negative anomalies.
基金financial support from China Scholarship Councilthe support from the Seismic Youth Founding of GEC (Grant No. YFGEC2016008)the National Natural Science Foundation of China(Grant No. 41474077)
文摘The 1:200,000 middle-large scale Bouguer gravity anomaly data covering the southern segment of the Liaocheng-Lankao fault(SLLF)and its vicinity are analyzed with two methods.First,the Bouguer gravity anomaly data are decomposed by two-dimensional(2 D)wavelet to make the family of multi-scale modes correspond with density structure at different depths.Second,a two and half dimension(2.5 D)human-computer interaction inversion of the Bouguer gravity anomaly data are conducted with the constraints provided by two deep seismic sounding profiles(DSS1 and DSS2)crossing the study area to get the crustal density profiles.Based on the integrated study,we can draw the following conclusions:1)SLLF appears to be a deep fault with almost vertical dipping and rooted into the uppermost mantle;2)In the middle to upper crust SLLF shows an clear turning patterns and segmentation features;3)In the study area the epicentral distributions of the precisely re-located small earthquakes and the historical large earthquakes have a good correspondence with the turning patterns and segmentation features of SLLF;and 4)The results of the horizontal slices from 2 D wavelet decomposition show that there are significant differences in the density structure on the two sides of the fault.A well-defined concave structure with low density exists in the upper crust of the Dongming Depression on the west side of the fault,with the concave center being estimated at a depth of about 8 km.In contrast,the upper crust on the east side presents a relative thinner pattern in depth with a bit higher density.Meanwhile,the low-density structure in the middle crust underneath the fault is presumably caused by the uplift of the upper mantle materials and their intrusion along the deep rupture system.This paper clarified the inconsistency of fault system and epicenters of small earthquakes from upper to lower crust.The results indicated that the fault system plays an important governing role to the seismicity in this area.
