Patricio Winckler

Reexamination of the magnitudes for the 1906 and 1922 Chilean earthquakes using Japanese tsunami amplitudes: Implications for source depth constraints

Far-field tsunami records from the Japanese tide gauge network allow the reexamination of the moment magnitudes (Mw) for the 1906 and 1922 Chilean earthquakes, which to date rely on limited information mainly from seismological observations alone. Tide gauges along the Japanese coast provide extensive records of tsunamis triggered by six great (Mw >8) Chilean earthquakes with instrumentally determined moment magnitudes. These tsunami records are used to explore the dependence of tsunami amplitudes in Japan on the parent earthquake magnitude of Chilean origin. Using the resulting regression parameters together with tide gauge amplitudes measured in Japan we estimate apparent moment magnitudes of Mw 8.0–8.2 and Mw 8.5–8.6 for the 1906 central and 1922 north-central Chile earthquakes. The large discrepancy of the 1906 magnitude estimated from the tsunami observed in Japan as compared with those previously determined from seismic waves (Ms 8.4) suggests a deeper than average source with reduced tsunami excitation. A deep dislocation along the Chilean megathrust would favor uplift of the coast rather than beneath the sea, giving rise to a smaller tsunami and producing effects consistent with those observed in 1906. The 1922 magnitude inferred from far-field tsunami amplitudes appear to better explain the large extent of damage and the destructive tsunami that were locally observed following the earthquake than the lower seismic magnitudes (Ms 8.3) that were likely affected by the well-known saturation effects. Thus, a repeat of the large 1922 earthquake poses seismic and tsunami hazards in a region identified as a mature seismic gap.

Coastal settlements rehabilitation affected by the 2010 tsunami in Pelluhue County, Chile

The Pelluhue country was one of the most affected during the earthquake and tsunami of February 27, 2010 in central Chile, with 47 deaths, the highest number of per-capita deaths in the country. This study is oriented to analyze the resilience of the urban centers of the commune, from its principal instances: preparation, resistance, recovery and adaptation. The damage generated by the tsunami is studied through an on-site survey, supplemented by surveys conducted in 2013 and 2015, a safety perception consultation and an analysis of the impact of territorial planning instruments in the rehabilitation of urban centers. From these studies it is concluded that the commune experienced a rapid infrastructure recovery between 2010 and 2012. The modifications incorporated in the ordinance of the Community Regulatory Plan at the end of 2012 promoted the use of a new structural typology adapted to the tsunami risk in the Coastal Tourist Zone (ZTBC-1). The use of wood and concrete structural frames on the first floor was adopted in response to the low coefficient of soil occupation suggested in the ordinance of the Community Regulatory Plan for that area, without necessarily complying with structural design criteria. However, in some other areas, within the flooded area, it was rebuilt without adopting adaptation criteria. Even when a consultation was implemented, which does not have adequate representation of the entire population, the survey indicates that the emergency plan implemented by ONEMI, in turn, generated a better perception of safety in the risk areas by residents, but visitors are unaware of the current evacuation measures.

Observations and Modeling of the 27 February 2010 Tsunami in Chile

Chile; Coastal bluffs; Coastal uplift; Loss of life; Pacific islands; Regional scale; Survey data; Tsunami flow; Disasters; Earthquakes; Surveys; Tsunamis