Mass movement-induced tsunamis: main effects during the Patagonian Fjordland seismic crisis in Aisén (45°25'S), Chile

Abstract

The epicentre of the long-lasting seismic crisis started on the evening of January 22, 2007 and it was located 20 km to the west of Puerto Chacabuco in the Patagonian fjordland, Chile (45º25'S). Approximately 7,000 events were recorded up to early May, four of which reached magnitudes greater than 5 (Richter), with local intensities up to VII in Puerto Chacabuco and Puerto Aisén and VI in Coihaique. The seismic swarm was located within the Liquiñe-Ofqui Fault Zone (LOFZ), which controls the emplacement of several monogenetic volcanic cones and larger stratovolcanoes. The January 23 (Ms 5,2) and April 1 (Ms 5,4) events caused minor damages in salmon industry installations near the epicentral zone, however the earthquake that occurred at 13:54 hours (local time) on April 21 (Mw 6,2) triggered various mass movements on the Fiordo Aisén slopes and generated tsunamis. Debris fl ows and tsunami waves caused the death of three people and the disappearance of seven, in addition to severe damages to the salmon industry installations. A similar phenomenon had occurred in 1927, but then fewer people inhabited the area. Initially, confusion dominated the scientifi c coordination of the emergency management due to seismic data misinterpretation. RESUMEN. Tsunamis inducidos por movimientos en masa: principales efectos durante la crisis sísmica de laPatagonia Archipelágica en Aisén (45º25'S), Chile. En la noche del 22 de enero de 2007 comenzó una crisis sísmica, cuyos epicentros se localizaron principalmente en el fiordo Aisén, a unos 20 km al noroeste de Puerto Chacabuco, en la zona archipelágica de Patagonia, en Chile (45º25'S). Hasta comienzos de mayo, los sismógrafos habían registrado cerca de 7.000 sismos, de los cuales cuatro habían sobrepasado la magnitud 5 (Richter), con intensidades locales de hasta VII en Puerto Chacabuco y Puerto Aisén y VI en Coihaique. El enjambre sísmico está asociado a estructuras geológicas de la Zona de Falla Liquiñe-Ofqui (ZFLO) la cual, además, controla el emplazamiento de numerosos conos volcánicos, así como estratovolcanes mayores. Aunque los sismos del 23 de enero (Ms 5,2) y 1 de abril (Ms 5,4) de 2007 produjeron algunos daños menores en instalaciones de salmoneras cercanas a la zona epicentral, el sismo ocurrido a las 13:54 hora local del 21 de abril (Mw 6,2) fue el que produjo los mayores efectos, generándose diversos tipos de remociones en masa en laderas de las riberas del fi ordo Aisén, tres de las cuales, con los mayores volúmenes, generaron veloces tsunamis. Flujos de detritos y tsunamis causaron la muerte de tres personas y la desaparición de siete, y severos daños en las instalaciones de las salmoneras. En una primera instancia, las características del proceso probablemente similar a uno ocurrido en 1927, cuando en la zona había escasa población, fueron novedosas y produjeron confusión y errores en la coordinación del manejo de la emergencia.

Landslides Cause Tsunami Waves: Insights From Aysén Fjord, Chile

“…Shortly after the 2007 earthquake and landslide crisis, which occurred in a seismically active region with modern faulting and volcanism [Legrand et al, 2011], the first scientific efforts by Servicio Nacional de Geología y Minería and the University of Chile focused on its subaerial consequences [Naranjo et al, 2009;Sepúlveda and Serey, 2009]. Field reconnaissance carried out a few days after the main shock and analyses of aerial photographs taken before and after the event led to the identification of a total of 538 landslides.…”

“…The earthquake triggered hundreds of subaerial landslides along the fjord flanks. Some of the landslides eventually involved a subaqueous component that, in turn, generated a series of displacement wavestsunami-like waves produced by the fast entry of a subaerial landmass into a water bodywithin the fjord [Naranjo et al, 2009;Sepúlveda and Serey, 2009;Hermanns et al, 2013]. These waves, with run-ups several meters high along the shoreline, caused 10 fatalities.…”

Eos, Transactions, American Geophysical Union Volume 94, Number 34, 20 August 2013

“…The earthquake triggered hundreds of subaerial landslides along the fjord flanks. Some of the landslides eventually involved a subaqueous component that, in turn, generated a series of displacement wavestsunami-like waves produced by the fast entry of a subaerial landmass into a water body-within the fjord [Naranjo et al, 2009;Sepúlveda and Serey, 2009;Hermanns et al, 2013]. These waves, with run-ups several meters high along the shoreline, caused 10 fatalities.…”

“…Shortly after the 2007 earthquake and landslide crisis, which occurred in a seismically active region with modern faulting and volcanism [Legrand et al, 2011], the first scientific efforts by Servicio Nacional de Geología y Minería and the University of Chile focused on its subaerial consequences [Naranjo et al, 2009;Sepúlveda and Serey, 2009]. Field reconnaissance carried out a few days after the main shock and analyses of aerial photographs taken before and after the event led to the identification of a total of 538 landslides.…”

“…Field reconnaissance carried out a few days after the main shock and analyses of aerial photographs taken before and after the event led to the identification of a total of 538 landslides. These were mapped in greater detail during new field surveys in 2008and 2009[Sepúlveda et al, 2010.…”