Abstract
Abstract To estimate Moho depth, geoid, gravity anomaly, and other geopotential functionals, gravity data is needed. But, gravity survey was not collected in equal distribution in Ethiopia, as the data forming part of the survey were mainly collected on accessible roads. To determine accurate Moho depth using Global Gravity Models (GGMs) for the study area, evaluation of GGMs is needed based on the available terrestrial gravity data. Moho depth lies between 28 km and 32 km in Afar. Gravity disturbances (GDs) were calculated for the terrestrial gravity data and the recent GGMs for the study area. The model-based GDs were compared with the corresponding GD obtained from the terrestrial gravity data and their differences in terms of statistical comparison parameters for determining the best fit GGM at a local scale in Afar. The largest standard deviation (SD) (36.10 mGal) and root mean square error (RMSE) (39.00 mGal) for residual GD and the lowest correlation with the terrestrial gravity (0.61 mGal) were obtained by the satellite-only model (GO_CONS_GCF_2_DIR_R6). The next largest SD (21.27 mGal) and RMSE (25.65 mGal) for residual GD were obtained by the combined gravity model (XGM2019e_2159), which indicates that it is not the best fit model for the study area as compared with the other two GGMs. In general, the result showed that the combined models are more useful tools for modeling the gravity field in Afar than the satellite-only GGMs. But, the study clearly revealed that for the study area, the best model in comparison with the others is the EGM2008, while the second best model is the EIGEN6C4.
Highlights
Afar depression is found at the junction of the Gulf of Aden (GOA), Red Sea Rift (RSR), and Main Ethiopian Rift (MER) where earthquakes, plate tectonics, and volcanism happen
The Sixth release of the GOCE gravity field model by means of the direct approach (GO_CONS_GCF_2_DIR_R6): is European Space Agency’s (ESA’s) Release 6 GOCE gravity field model using the direct approach based on improved filtering of the reprocessed gradients of the entire mission
The ground measured gravity data were collected in the Geodetic Reference System-1980, which is connected to International Gravity Standardization Network-1971 (IGSN71) system found in Addis Ababa
Summary
Afar depression is found at the junction of the Gulf of Aden (GOA), Red Sea Rift (RSR), and Main Ethiopian Rift (MER) where earthquakes, plate tectonics, and volcanism happen. Advancement of space-based technologies and their launches like Gravity field and steady-state Ocean Circulation Explorer (GOCE) (Floberghagen et al, 2011), Gravity Recovery And Climate Experiment (GRACE) (Tapley et al, 2004), and CHAllenging Minisatellite Payload (CHAMP) (Reigber et al, 2002) plays a remarkable role in determining mathematical model of Earth’s gravitational field, GGM. This study is useful for countries like Ethiopia, where terrestrial gravity data is rare and the region is tectonically, volcanically, and seismically active; earthquakes, plate tectonics, and volcanism all occur in the studied area This indicates that by identifying the best GGMs from this study or using the similar methods mentioned here, the GGMs can be utilized to produce more precise and reliable results of Moho depth, lithospheric thickness, and geoid. Researchers can utilize this technique to evaluate a large number of GGMs across Ethiopia and recommend the best GGM/s for various applications
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