Broadband wavelength slip model of the 1906 Ecuador-Colombia megathrust-earthquake based on seismic intensity and tsunami data

摘要

The 1906/01/31 Ecuador-Colombia earthquake (Mw8.4-8.6), is one of the largest megathrust earthquakes that have occurred at the interface of the Nazca and South-American plates. Recently the source process of the earthquake has been re-examined using historical tsunami waveforms, yielding a slip distribution mainly near to the trench, and a smaller moment magnitude than previous estimations. Previous studies have shown that tsunami data can sufficiently constrain the long wavelength characteristics of slip during an earthquake. However to fully understand strong ground motion generation process during earthquakes in a broadband frequency range, the study of shorter wavelength slip, responsible for high frequency ground motion generation, is also necessary. In this study we use the tsunami-slip model of the 1906 earthquake, as well as comprehensive macro-seismic intensity estimations of the earthquake, to elaborate a broadband-wavelength (BB) source model appropriate for the generation of broadband frequency strong ground motions as well as tsunami modeling. Our results show that a BB slip model of the earthquake is able to satisfactorily reproduce observed intensity values as well as tsunami waveforms. Our BB slip model implies an increase in total moment magnitude to a value up to 8.6 respect to the estimation from tsunami data, which represent the contribution of short wavelength slips to seismic radiation. The methodology developed in this study is suitable to study the generation process of high frequency ground motions during large earthquakes.