Evidencia morfo-estratigráfica de los predecesores del terremoto del Maule del 2010, Isla Santa María, centro-sur de Chile.
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Date
2024
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Universidad de Concepción
Abstract
Comprender el comportamiento sísmico de márgenes de subducción es indispensable para desarrollar modelos probabilísticos que permitan estimar la ocurrencia de futuros eventos. Para esto es necesario contar con registros multi-milenarios que indiquen la recurrencia sísmica en el largo término. En esta tesis se reconstruyó la historia paleosísmica del segmento del Maule a través del análisis de la planicie de cordones litorales arenosos en la Isla Santa María, localizada en el extremo sur del área de ruptura del terremoto del Chile de 2010 (Mw 8.8). Para esto, se analizó la respuesta de la costa de la isla al ciclo sísmico; que produce levantamiento cosísmico y hundimiento intersísmico, monitoreando la principal playa de la isla durante las últimas ocho décadas (entre 1941 a 2021). Las observaciones muestran que la progradación costera y posterior construcción de cordones litorales, fue continua y no respondió sólo al levantamiento cosísmico asociado a terremotos previos, sino también al lento hundimiento intersísmico. De este modo, se interpreta que los 24 cordones litorales estudiados han registrado cambios en el nivel de la costa asociados a ciclos sísmicos completos, lo que permite reconstruir la recurrencia sísmica de los últimos 4500 años. Durante este periodo, los intervalos de recurrencia han sido variables, sugiriendo un comportamiento débilmente periódico con al menos tres etapas con comportamiento característico: La Etapa I, entre 4400 y 3000 años antes del presente, exhibe una recurrencia de 214 ± 75 años; la Etapa II, entre 2900 y 1800 años antes del presente, muestra una recurrencia de 65 ± 22 años; y la Etapa III, entre 1700 y 600 años antes del presente, una de 243 ± 55 años. Comparando estos resultados con la recurrencia cuasi periódica del segmento tectónico adyacente de Valdivia, se propone que, a pesar de que ambos segmentos comparten características tectónicas similares, la dinámica de acreción frontal de sedimentos, las “splay faults” y la deformación de la placa superior del segmento del Maule podrían controlar el tamaño y la periodicidad de sus terremotos.
Understanding the seismic behavior of subduction margins is essential to develop probabilistic models to estimate the occurrence of future earthquakes. This requires multi millennial records that provide long-term seismic recurrence. In this thesis, the paleoseismic history of the Maule segment was reconstructed through the analysis of the sandy coastal ridge plain on Santa María Island, located at the southern end of the rupture area of the 2010 Chile earthquake (Mw 8.8). The response of the island's coastline to the seismic cycle, which produces seismic uplift and interseismic subsidence, was analyzed by monitoring the main beach of the island during the last eight decades (between 1941 and 2021). The observations show that coastal progradation and construction of beach ridges was continuous and did not respond only to seismic uplift associated with previous earthquakes, but also to slow interseismic subsidence. Thus, it is interpreted that the 24 beach ridges studied have registered changes in coastal level associated with complete seismic cycles, which allows reconstructing the seismic recurrence of the last 4500 years. Over this period, recurrence intervals have been variable, suggesting a weakly periodic behavior with at least three stages with distinctive behavior: Stage I, between 4400 and 3000 years before present, exhibits a recurrence of 214 ± 75 years; Stage II, between 2900 and 1800 years before present, shows a recurrence of 65 ± 22 years; and Stage III, between 1700 and 600 years before present, one of 243 ± 55 years. Comparing these results with the quasi-periodic recurrence of the adjacent Valdivia tectonic segment, it is proposed that, although both segments have similar tectonic characteristics, the dynamics of frontal sediment accretion, splay faults and upper plate deformation of the Maule segment would control the size and periodicity of their earthquakes.
Understanding the seismic behavior of subduction margins is essential to develop probabilistic models to estimate the occurrence of future earthquakes. This requires multi millennial records that provide long-term seismic recurrence. In this thesis, the paleoseismic history of the Maule segment was reconstructed through the analysis of the sandy coastal ridge plain on Santa María Island, located at the southern end of the rupture area of the 2010 Chile earthquake (Mw 8.8). The response of the island's coastline to the seismic cycle, which produces seismic uplift and interseismic subsidence, was analyzed by monitoring the main beach of the island during the last eight decades (between 1941 and 2021). The observations show that coastal progradation and construction of beach ridges was continuous and did not respond only to seismic uplift associated with previous earthquakes, but also to slow interseismic subsidence. Thus, it is interpreted that the 24 beach ridges studied have registered changes in coastal level associated with complete seismic cycles, which allows reconstructing the seismic recurrence of the last 4500 years. Over this period, recurrence intervals have been variable, suggesting a weakly periodic behavior with at least three stages with distinctive behavior: Stage I, between 4400 and 3000 years before present, exhibits a recurrence of 214 ± 75 years; Stage II, between 2900 and 1800 years before present, shows a recurrence of 65 ± 22 years; and Stage III, between 1700 and 600 years before present, one of 243 ± 55 years. Comparing these results with the quasi-periodic recurrence of the adjacent Valdivia tectonic segment, it is proposed that, although both segments have similar tectonic characteristics, the dynamics of frontal sediment accretion, splay faults and upper plate deformation of the Maule segment would control the size and periodicity of their earthquakes.
Description
Tesis presentada para optar al grado de Doctor en Ciencias Geológicas
Keywords
Estratigrafía, Sismología Chile, Terremotos Chile 2010