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

Based on our results, the most well-preserved paleotsunami deposit (event B), dated between 1401 deformation. It potentially correlates with a 1520 ± 50 C.E. paleotsunami identified in Tirúa, further south, by Dura et al. (2017). We propose that this event could be a predecessor to the 1730 earthquake. The most recent event (event A) is associated with a thin, lenticular sand layer (Figure 2) containing benthic foraminifera (Amonia beccarii), indicating marine sediment transport inland. Its age, constrained by historical horse remains and archaeological evidence, suggests a potential correlation with the 1730 tsunami. C O N C L U S I O N S This study provides the first geological evidence of paleotsunamis in the mouths of the La Ligua and Petorca rivers, contributing to the understanding of the recurrence and magnitude of tsunamis in central Chile. The paleotsunami deposits identified in this work, once differentiated from other coastal processes, highlight the extent of past tsunami inundations. The paleoenvironmental evolution, based on sedimentary facies associations, reveals dynamic changes depositional environments in the estuary throughout the Upper Holocene, influenced by changes in base level, sediment supply, and tsunami events. The proposed prehistoric paleotsunami deposit (event B) dated between 1401 and 1540 C.E., potentially linked to a near-field mega-earthquake, enriches the historical record and suggests that it could be a predecessor of the 1730 event. Furthermore, geological evidence suggests that the 1730 tsunami can also be recognized in the geological record in the study area. These findings have significant implications for tsunami risk assessment in central Chile and emphasize the need for integrated sedimentary and geomorphological studies to improve our understanding of the recurrence and impact of paleotsunamis, which will ultimately lead to more accurate risk models, resilient infrastructure design, and effective evacuation plans. The methodology and results presented here offer a valuable framework for future research in similar estuarine systems and coastal regions around the world. A C K N O W L E D G E M E N T S The present study has beenmade possible by the generous support of the National Geology and Mining Service (SERNAGEOMIN) and FONDECYT project #1201387. R E F E R E N C E S Costa, P. J. M., Andrade, C., y Dawson, S., (2015). Geological Recognition of Onshore Tsunami Deposits. Coastal Research Library, 8, 3–32. https: //doi. org/10.1007/978-3- 319-06305-8_1 Easton, G., González-Alfaro, J., Villalobos, A., Álvarez, G., Melgar, D., Ruiz, S., Sepúlveda, B., Escobar, M., León, T., Báez, J. C., Izquierdo, T., Forch, M., y Abad, M., (2022). Complex Rupture of the 2015 Mw 8.3 I llapel Earthquake and Prehistoric Events in the Central Chile Tsunami Gap. Seismological Research Letters. https: //doi. org/10.1785/0220210283 Goldfinger, C., Ikeda, Y., Yeats, R. S., y Ren, J., (2013). Superquakes and supercycles. Seismological Research Letters, 84(1), 24–32. https: //doi.org/10.1785/0220110135 Dura, T., Cisternas, M., Horton, B. P., Ely, L. L., Nelson, A. R., Wesson, R. L., y Pilarczyk, J. E., (2015). Coastal evidence for Holocene subduction-zone earthquakes and tsunamis in central Chile. Quaternary Science Reviews, 113, 93–111. https: //doi.org/10.1016/j . quascirev.2014.10.015 Dura, T., Horton, B. P., Cisternas, M., Ely, L. L., Hong, I ., Nelson, A. R., Wesson, R. L., Pilarczyk, J. E., Parnell, A. C., y Nikitina, D., (2017). Subduction zone slip variability during the last millennium, south-central Chile. Quaternary Science Reviews, 175, 112– 137 .https: //doi.org/10.1016/j . quascirev.2017.08.023