Tsunami source estimate of the 1906 Ecuador-Colombia earthquake

A great earthquake occurred in 1906 along the Ecuador-Colombia subduction zone. The 1906 earthquake has been interpreted as a megathrust earthquake (Mw 8.8) that ruptured the source regions of smaller earthquakes in 1942, 1958, and 1979 [Kanamori and McNally, BSSA, 1982]. However, the slip distribution of the 1906 earthquake has not been estimated. Recent advancement in the tsunami simulation method opened a way to perform quantitative analysis of tsunami waveforms of the 1906 earthquake recorded only at trans-Pacific distances. In this study, we inverted the tsunami source of the 1906 earthquake using far-field tsunami data. We used 3 tide gauge records at Honolulu (Hawaii), San Francisco (California), and Ayukawa (Japan). We assumed 11 × 3 sub-faults along strike and dip direction, respectively, each with dimensions of 50 km × 50 km. We used the phase-corrected tsunami waveforms computed by the method proposed by Watada et al. [JGR, 2014]. Our analysis of tsunami waveforms of the 1906 event indicated Mw 8.4. The large-slip area was estimated in the shallow region, where the resolution was better as shown by our checkerboard test. We compared the observed tsunami waveform at Honolulu station with the simulated tsunami waveforms generated from each sub-fault. This comparison indicated that the arrival times of the simulated tsunami waveforms from this large-slip area were consistent with the observed waveform, supporting our inversion results. Our results show that the source region of the 1906 earthquake did not overlap those of the 1942, 1958, and 1979 earthquakes.