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

350 1 2 T H I N T E R N AT I O N A L I N Q U A M E E T I N G O N PA L E O S E I S M O L O G Y , A C T I V E T E C T O N I C S A N D A R C H A E O S E I S M O L O G Y ( PATA ) , O C T O B E R 6 T H - 1 1 T H , 2 0 2 4 , L O S A N D E S , C H I L E PATA Days 2024 (1) Servicio Nacional de Geología y Minería, Chile, Santa María 104, Providencia, Chile. (2) Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile. (3) Department of Anthropology, College of Liberal Arts and Sciences, Turlington Hall, University of Florida, Gainesville, USA. (4) Departamento de Geografía, Facultad de Arquitectura y Urbanismo, Universidad de Chile, Portugal 84, Santiago, Chile. (5) Departamento de Antropología, Facultad de Ciencias Sociales, Universidad de Chile, Ignacio Carrera Pinto 1045, Santiago, Chile. (6) Escuela de Geología, Facultad de Ciencias, Ingeniería y Tecnología, Universidad Mayor, Manuel Montt 367, Santiago, Chile. *Email: ismael.murillo@sernageomin.cl / geaston@uchile.cl K E Y W O R D S Paleotsunami, sedimentary record, coastal uplift, La Ligua river, Central Chile Ismael Murillo (1,2) Gabriel Easton (2) Daniel Hernández (3) Daniela Villela (1) Max Forch (2) Luciano Duhalde (4) José Gonzalez-Alfaro (2) Silvana Valls (5) Cristina Ortega (6) UPPER HOLOCENE TSUNAMI DEPOSITS AT THE MOUTH OF LA LIGUA AND PETORCA RIVERS , CENTRAL CHILE (32°24 ' 50 '' S) A B S T R A C T This study presents an analysis of sedimentary record in the estuaries of La Ligua and Petorca rivers, revealing evidence of past tsunamis in Central Chile. The best preserved paleotsunami deposit (event B), dated between 1401 and 1540 AD, is recognized by a distinctive sandy layer with erosional base, rip-ups and high concentrations of heavyminerals, CaO, Fe2O3 andMn. This deposit indicates a significant stratigraphic change, probably associated with coastal uplift caused by a near-field earthquake. These findings suggest that this event may precede the 1730 earthquake and tsunami. Furthermore, a historical tsunami (event A) associatedwith the 1730 event is evidenced by a distinctive lenticular sandy layer, with benthic foraminifera (Ammonia beccarii), within the present- day floodplain deposits of the La Ligua River. These results improve the historical record of tsunamis and highlight the importance of integrated sedimentary studies to understand tsunami recurrence and impact in Central Chile. I N T R O D U C T I O N Chile's historical susceptibility to tsunamigenic mega- earthquakes linked to the Nazca-South America subduction zone, underscores the importance of studying paleotsunami records for disaster risk evaluation. The central zone of Chile, between 31°S and 34°S, experienced a major earthquake (Mw > 9) in 1730,