Seismic tomography of the Abitagua Batholith using local earthquakes in the Colonso Chalupas Reserve, Napo, Ecuador
Synopsis
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 velocity of the seismic P and S waves. We obtain these velocities through seismic travel time tomography using local earthquakes recorded at five Raspberry Shake stations. We use the INSIGHT software to solve the tomographic inverse problem. We regularized the problem solution by generating L-curves, while the model's resolution level was calculated using the resolution operator. The resulting model is calculated on a 1 km grid. Both velocity values, Vp and Vs, show a gradual decrease from the highest granite elevation to its contact with the sedimentary Amazon 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 1.6 km/s. These changes can be attributed to the transpressive tectonic interaction in the study area, as we are located on the edge of the North Andean Sliver.
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