Using Seismic Tomography for Quality Characterisation of Quarry Rock Mass in Akure, Ondo State, South West Nigeria

Granite quarrying in the Akure area of Ondo State provides essential aggregate for construction in South West Nigeria, and the rock mass quality within quarry faces directly determines blast design, fragmentation efficiency, and the quality of produced aggregates. This professional study applies seismic tomography to characterise spatial variations in rock mass quality across two active quarry faces in Akure South Local Government Area. Cross-hole seismic tomographic surveys were conducted between boreholes and shot-receiver configurations on two quarry faces, generating a total of 420 ray paths for travel-time tomographic inversion. The resulting two-dimensional compressional wave velocity models resolve metre-scale variations in rock mass quality, with velocities ranging from 2,200 metres per second in heavily jointed and clay-filled fracture zones to 5,600 metres per second in competent, massive granite. Rock mass quality designation values estimated from the velocity field using published empirical correlations range from poor (RQD of 30 to 50 percent) in fracture-concentrated zones to excellent (RQD over 90 percent) in intact rock regions. The velocity tomograms directly guided the redesign of blast pattern geometry, concentrating decked charges in fracture zones to improve fragmentation while reducing overbreak in competent zones. Blast performance assessment using post-blast fragmentation analysis confirmed a 22 percent improvement in mean fragment size distribution. The study demonstrates that seismic tomography provides actionable, cost-effective rock mass characterisation data for quarry management. Keywords: seismic tomography, rock mass quality, quarry, Akure, granite