Jorge Clavero, Chilean geological and mining survey (Chile)
Manuel Arenas, Chilean Geological and Mining Survey (Chile)
José Naranjo, Chilean Geological and Mining Survey (Chile)
Luis Lara, Chilean Geological and Mining Survey (Chile)
On 21st April 2007 a 6.2 Mw earthquake, associated to an active strike-slip fault (Liquiñe-Ofqui Fault Zone), occurred in Aisén Fjord, southern Chile (45º24'S-73º00'W) causing scores of landslides of different type and volume. The larger ones that impacted the fjord waters generated tsunami waves that killed 3 persons, disappeared other 7 and caused economic losses to the aquaculture industry. The Geological and Mining Survey of Chile (SNGM) started immediately to study the effects of the earthquake, including a cadastre of landslides, tsunami effects and a landslide susceptibility map, in order to give the necessary information to the authorities to manage the emergency, as the sismicity continued. Further works were oriented to generate a tsunami flooding map that was developed under the cooperation of different academic, military and government institutions (SHOA, 2007).
Within this cooperation project the role of SNGM was to determine the input parameters related to possible inducing-tsunami landslides. This task was developed in two stages: initially the determination of parameters of the landslides caused by the 21st April earthquake was done in order to calibrate the selected tsunami simulation model. The second stage consisted in determining parameters of possible landslides that might occur if a similar earthquake affects the area. This study carried out for certain slopes in an area that is located close to populated centres, seems to be the most susceptible to landslides and where new seismic activity was concentrated after the main shock.
The landslides input parameters necessary for the selected tsunami simulation model estimated by SNGM correspond to:
a. Landslide entry point: the geographic location where the mass falls into the water.
b. Volume of the fallen mass.
c. Landslide velocity: speed of the fallen mass when it impacts the water body.
d. Landslide width in the shoreline.
e. Slope: entry angle of the fallen mass.
During the first stage all the parameters, with exception of the two latter, were estimated based on field observation with the aids of field data, aerial photographs, satellite images, topographic maps and GIS tools. The maximum velocities were calculated by transforming the potential to kinetic energy without considering losses by friction or heating. The possible entry velocities were estimated as half of the maximum velocities.
The parameters estimation of actually occurred and also possible landslides was the basis for the tsunami modelling. Finally, a tsunami flooding map was created showing prone areas to be flooded if a worst scenario occurs.
SHOA. 2007. Puerto Aysén Puerto Chacabuco. Cartas de inundación por tsunami generado por remociones en masa. Unpublished. Oceanographic and Hydrographic Survey of Chilean Navy.