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

290 PATA Days 2024 Fig. 2: Possible fault scarp market with the red line and green box pointed to the outcrop next to the fault scarp. The black line is trace of Porotoyacu fault that produce this geomorphological indicator. The arrows point to raised and depressed side. R E F E R E N C E S Allen, J. (1982). Sedimentary Structures. Elsevier, 1-633. Audermand, F., & Santis, F. (1991). Survey of Liquefaction Structures Induced by Recent Moderate Earthquakes. Bulletin, 5-16. doi:10.1007/BF02602705 Baby, P., Rivadeneira, M., & Barragán, R. (2004). La cuenca Oriente: Geologia y Petroleo. (I . IFEA, Ed.) Travaux de l' Institut Français d'Etudes Andines. Baize, S., Audin, L., Winter, T., Alvarado, A., Pilatasig, L., Taipe, M., . . . Yepes, H. (2015). Paleoseismology and tectonic geomorphology of the Pallatanga fault (Central Ecuador), a major structure of the South American crust, Elsevier, 237, 14-28. Cornejo, C. (2020). Analisis de sismitas y paleosismologia como indicadores de amgnitudes de la actividad sismica de la falla Santa Rosa, en el piedemonte amazonico, Ecuador. Universidad Amazonica Ikiam, Tena. Costa, C., Alvarado, A., Audermand, F., Audin, L., Benavente, C., Bezerra, H., Perez, I . (2020). Hazardous faults of South America; compilation and overview. Journal of South American Earth Sciences, Volume 104, 102837. Obtenido de https: //doi.org/10.1016/j . jsames.2020.102837. Council, N. R. (1991). The March 5, 1987, Ecuador earthquakes: Mass wasting and socioeconomic effects. Ecuador: National Academic Express. Eguez, A., Alvarado, A., Yepes, H., Machette, M., Costa, C., & Dart, R. (2003). Database and Map of Quaternary faults and folds of Ecuador and its offshore regions. USGS, Volumen 104. doi:10.3133/ ofr03289 The paleoseismological studies in Ecuador have been focused on the Ecuadorian Sierra, as in the case of the Pallatanga Fault (Baize, et al., 2015) study where have been excavated various trenches through of lengths of the trace to extract more information about the behavior of this fault. On the other hand, the Amazonia in Ecuador only has one paleoseismological study realized by (Cornejo, 2022) about the Porotoyacu fault in another outcrop located South of the trace. Approximately 24 seismic events with M 2.5~6.3 detected instrumentally between 1927-2022 have been reported in the study area (IGEPN, 2022) representing mild to moderate seismicity. The objectives of this work are to provide information and understand the geological threat posed by the Porotoyacu fault. It is necessary to relate all the seismic events possibly recorded in the geologic record with their respective magnitude and identification of structures of deformation that could be evidence of recent tectonic activity of the Porotoyacu fault. For this reason, a paleoseismological study was carried out in an outcrop located 0.43 Km from north of the fault trace (Figure. 1). Geomorphology of the site The study site has identified a possible scarp fault (>70 m) with direction SW-NE (Figure 2) that coincides with the SSW- NE regional orientation of the Porotoyacu Fault. In field is observed an unevenness of 7˚ of inclination between two plain surfaces with elevation of 609 m in the initial point (Ip), the scarp fault (Sf) with 611 m and final point (Fp) 615 m, this type of topographic deformation is direct evidence of vertical displacement of Porotoyacu fault by seismicity. this topographic anomaly repeats itself several kilometers beyond the study site, ruling out anthropogenic with the help of orthophotographs a possible trace is established as shown in (Figure 2). Also, to confirm the presence of the fault there is an outcrop that exposes various characteristics of the deformation, such as displacement between layers, fault mirrors or rupture planes with stretch marks, etc. All these characteristics could be related to the presence of the Porotoyacu fault.