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Appraisal of lineaments patterns and crustal architectures around the Owen fracture zone, Arabian Sea, using global gravity model data

Narayan Satya, Kumar Ujjawal, Sahoo Soumyashree Debasis, Pal Sanjit Kumar

Acta Geophysica

2024

Vol. 72, no. 1

29--48

This study evaluates the efficacy of GECO gravity data for geophysical studies, mapping structural and tectonic features and their impact on gravity signatures in the study area. Computed correlation coefficient (96-98%), root-mean-square error (5.1-5.3 mGal), and standard deviation (3.9-4.2 mGal) between the GECO model-derived and ship-borne free-air gravity reveal the efficacy of the GECO gravity data for the geophysical studies in the region. A total horizontal derivative approach was used in order to enhance the residual and regional responses of the Bouguer gravity anomaly. The shorter-wavelength lineaments originated from subsurface mass heterogeneities were found trending in the northwest direction, subsequently east, north-northeast and east-northeast directions. In contrast, the longer-wavelength lineaments originating from deep-seated mass heterogeneities dominated in the east-northeast direction, followed by north-northeast and northwest directions. Lineaments occurring at shallower depths are associated with sedimentary/basement columns and could be utilised in basin demarcation for hydrocarbon exploration. In contrast, deep-seated lineaments originated due to deformities at the crust-mantle boundary or in the mantle and could be used in the region’s seismicity analysis. Spectral analysis and 2D forward modelling results indicate sediment thickness of ~ 2.0-6.0 km, basement thickness of ~ 6-14 km, and Moho depth of ~ 10-18 km. Delineated lineaments and computed basement and Moho depths were further validated with existing data. Anomalously high and low gravity features were interpreted based on Moho depth, basement thickness, and sediment thickness. This study concludes that anomalous gravity anomalies are mainly controlled by Moho topography despite the relatively thicker crust in the northern region. The crustal thickness mainly controls the southern latitude’s gravity signatures.

Evaluation of GGMs based on the terrestrial gravity disturbance and Moho depth in Afar, Ethiopia

Alemu Eyasu

Artificial Satellites : Journal of Planetary Geodesy

2021

Vol. 56, No. 3

78--100

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.