The Abitagua Batholith is a Jurassic intrusive and is considered the source of the alluvial gold deposits currently exploited in the Jatunyaku and Napo rivers. The northern part of this granite formation is located within the Colonso Chalupas Reserve, and our objective is to characterize the seismic P and S waves of this batholith. We obtain these velocity values through seismic travel time tomography using local earthquakes recorded at five Raspberry Shake stations. We use the local earthquakes recorded between 2023 and 2024, with the arrival times of P and S waves manually picked. A total of 465 earthquakes were used to perform the tomography. The Ecuador a priori seismic velocity model was interpolated onto a 1-km grid in all three spatial directions, and we use the INSIGHT software to solve the tomographic inverse problem. The inverse problem was regularized by generating L-curves, while the model's resolution level was calculated using the resolution operator. The resulting model extends from the Inchillaqui River in the north to the Jatunyaku River in the south. Both velocity values, Vp and Vs, show a gradual decrease from the highest granite elevation to its contact with the Arajuno, Chambira, Tiyuyacu, and Tena formations. The P-wave velocity decreases from 3.9 km/s to 2.5 km/s, while the S-wave velocity decreases from 2.6 km/s to 2.1 km/s. These changes in velocity indicate that the granite is not homogeneous, with its eastern portion being less dense than its central portion. These changes can be explained by the transpressive tectonic interaction in the study area, as we are on the edge of the North Andean Sliver. Compression and shear stresses may have weakened the batholith on its flanks, with more faults and fractures.
Keywords: Abitagua Batholith, seismic tomography, P-wave velocity, S-wave velocity, fracture.