Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

SEISMICITY AND ITS RELATION WITH STRUCTURES AT DEPTH Ryan el al. (2016) and Ward et al. (2013) imaged the Moho at a depth of approximately 40 km beneath the range’s front, 50 km beneath the western edge of the Cochabamba Basin. It dips about 5-7° towards the west, indicating westward Nexure of the Brazilian shield. This shield is overthrusted by the subandean fold- and- thrust belt along the Main eastern andean thrust system, dozens of kilometres above. As previously mentioned, the earthquakes recorded during the initial months of the experiment happened at mid-crustal depths, primarily between 10 and 20 km. This places the hypocenters about 25-30 km above the Moho. According to McQuarrie (2002), the sedimentary cover comprises multiple imbricated thrust sheets and numerous folds oriented NNW-SSE (N140-N150) and NE-SW (approximately N050). The Chapare main earthquake (May 18th, 2022), along with its associated cluster, is situated in close proximity to the basal decollement of the thrust system (Fig. 3). These seismic events are related with the activation of either the Main Eastern Andean basal thrust structure or a thrust situated less than 5 km above it in its hanging wall. This observation is consistent with the shallow- dipping fault plane of the focal mechanism associated with the Chapare main shock. Fig. 3. Map and cross section of the seismicity. Upper 6gure indicates high quality earthquakes with red dots, where the black dots stand for low quality earthquakes (less than 4 P and 2 S phases or azimuthal gap upper than 250 degrees). The stars show the May 18th (ML 4.3) and the August 14th 2022 earthquakes (ML 2.5). Green triangles represent the seismic stations, main villages are denoted by squares. The lower 6gure shows the balanced cross section fromMcQuarrie (2002) with seismicity projected within the section A to A’. The main thrust is denoted by red dashed lines, the red stars represent the May 18th and the August 14th 2022 earthquakes. The moment tensor solutions are projected on the cross section.