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

44 PATA Days 2024 S T R AT I G R A P H Y The south-wall of the trench exposed a total of 11 units, differentiated based on color, clast size, clast shape variation, or matrix composition. The current surface is comprised of poorly sorted, cobble-dominant, matrix supported alluvium, which is typical of alluvial fan debris deposits. Unit 1 is a fine-grained, rust-colored, compact clayey deposit. The unit has been identified as the Miocene basement Loma de Las Tapias formation based on its composition and color (Fig. 3). Unit 2 is defined by clast supported, sub-rounded boulder to cobble sized clasts in the hanging-wall, interpreted to indicate a high-energy alluvial fan deposit. Unit 3 is composed of subangular, poorly sorted small pebble to medium cobble sized clasts. Units 1-3 are intensely folded and thrusted in the hanging-wall along F1 (Fig. 3, grid 1-2). Unit 4 is composed of clast-supported gravel to granule sized clasts deposited conformably over Unit 4. Conformably overlying Unit 4 is Unit 5 capping the upthrown side of the trench. Unit 6 is a matrix-supported, poorly sorted, angular pebble to gravel sized clast unit, suggesting high-energy, and a nearby source for the deposition environment (Fig. 3). Unit 7 is composed of poorly sorted, matrix-supported, clayey gravel which display shear fabric between grid 2-3 along F3 (Fig. 3). Unit 8 is characterized by angular pebble that caps the Units 5, 6 and 7 in the hanging-wall. (Fig. 3 grid 3-4). Unit 9 is a clastsupported, poorly sorted, sandy gravel unit capping Unit 6, 7 in the hanging-wall. Unit 10 is a finer clayey gravel unit overlying Unit 9 in the footwall. Unit 11 is clayey angular gravel unit, horizontally deposited in the footwall. Units 12 are clast-supported gravel units preserved in the footwall. EARTHQUAKE EVIDENCE AND EVENT CHRONOLOGY Evidence of past earthquakes at the study site along the Marquesado Fault is indicated by prominent shear fabric observed within fault F1 and F2, between grid 1-3, where the long axes of gravels are oriented in the direction of shear (Fig. 3). Additional evidence of faulting in the trench includes folding and dragging of Units 1-5 along F1, indicative of thrusting and displacement (see Fig. 3, between grid 1-2). The lithological variation between Units 6 and 7, is also suggestive of upliftment, erosion, and deposition of units against the scarp face. It is important to note that the deposition here occurred against the slope fromwest to east (Fig. 2a). The preliminary result from the trench suggests at least four seismic events, E1 (the oldest event) to E4 (themost recent event). Event E1 is interpreted to have displaced and foldedUnits 1-5 together along fault F1 which is evident based on the folding and conformity of Units 1-5 in the hanging-wall. Based on the stratigraphy and geochronology, we suggest E1 occurred after 17-19 ka based on the ages of Unit 4,5 (sample no. MF1,2). E1 is followed by the deposition of Unit 6 at the toe of the scarp, against the slope. E2 is interpreted to have further displaced and folded Units 1-5 along the fault F2, along with aligning pebbles and gravels in the direction of shear within fault zone. Based on the stratigraphy and geochronology, we suggest E2 potentially occurred after the deposition of Unit 6 around 10.2±1 ka (sample no. MF6 Last) (Fig. 53). The event led to the creation of a scarp and the deposition of