Abstract

Robust and accurate lithological parameters are essential in engineering, geology, geophysics, geodesy, and resource exploration. Among these parameters, rock density plays a fundamental role in gravimetric geodesy and geophysics. However, the systematic collection, analysis, and categorization of rock density data remain insufficient in many countries around the world, including Ethiopia. Ethiopia is characterized by extreme topographic variations (exceeding 4500 m) and complex geology, dominated by Cenozoic volcanic formations associated with the East African Rift System. Consequently, the commonly adopted upper continental crustal density of 2670 kg/m3 is inadequate for precise geodetic applications (e.g., the definition and realization of the geodetic vertical datum) as well as for gravimetric modeling and interpretation (e.g., the compilation of Bouguer, isostatic, and mantle gravity maps) in the country. To address these limitations, we prepared the first comprehensive digital rock density model of Ethiopia, with a particular focus on its applications in gravimetric geodesy and geophysics. The rock density model has been prepared by integrating the Ethiopian geological database, comprising 88 lithological units, with established global rock-density databases to assign representative density values and their uncertainties to each geological unit. The height-weighted average densities, accounting for the mass contribution of elevated terrain, were computed from a 90-m-resolution digital elevation model. The rock density map shows significant density variations across Ethiopia, ranging from 1528 to 2892 kg/m3. The average height-weighted density of Ethiopia is 2430 ± 352 kg/m3, which is 9% lower than the standard density of 2670 kg/m3. We expect that the use of the rock density model instead of assuming only a constant density value for the whole country will improve the accuracy of gravimetric geoid modeling and orthometric height determination, both essential for the modernization of the geodetic vertical datum. This demonstrates the necessity of region-specific density models for countries in tectonically active and/or geologically complex settings. The study also provides a transferable methodological framework for developing similar products in other data-sparse regions.

IPC Classification

Keywords