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

Fig. 3: Dip of the stratified layers as a function of distance from the fault core. to 45° at 20 meters from it. Based on the information from Armijo et al. (2010), the stratification of the Abanico Formation in this sector should have an approximate dip of 33°, so the presence of this tilting near the fault core is consistent with a local-scale fault- bend folding. Themain fault exhibits an approximate orientation of strike/dip = N32O/43NE (Figure 4a,b), while the rest of the measurements represent the major joints (>50 cm continuity) found in the hanging wall. In the outcrop, the joints observed decrease from the fault core (Figure 4c), and are represented every two to three meters in the stereographic nets in (Figure 4d,e). Groups of joints are defined according to the mean azimuth/dip, with strike/dip around N65E/76NW for set 1, strike/dip N85W/42N for set 2, strike/dip N67W/46SW for set 3, and strike/dip N17W/49E (set 4) for set 4. Note that sets 1 and 2 have orientations almost perpendicular to the main fault, while set 4 are nearly parallel. The damage zone observed in the outcrop, on a metric scale, is characterized by the mentioned joints, where the number of joints per cubic meter shows a tendency to decrease with the distance from the fault core (Figure 5c), exhibiting an abrupt decay beyond 10 meters from the fault core, which is consistent with other damage zones studied in other faults (e.g. Muschelkalk, Germany; Meier et. al., 2015). The bedding-parallel joints are also present throughout the outcrop, with spacings ranging from 1 to 5 centimeters in the shale strata and from 5 to 10 centimeters in the tuffs. On a centimeter scale, within the first two meters from the fault core, minor discontinuities are observed like parallel to the set, parallel to the stratification, with spacings of 1 centimeter, and with a strike/ dip of N63E/51NW with spacings of 10 to 15 centimeters. Thus, blocks of approximately 1x3x3 cubic centimeters are observed near the fault core, which gradually increase in size to approximately 6x3x3 cubic centimeters at 6 meters distance.