Study on the 1906 Colombia‐Ecuador Megathrust Earthquake Based on Tsunami Waveforms Observed at Tide Gauges: Release Variation of Accumulated Slip Deficits in the Source Area

Abstract A tsunami that followed the 1906 Colombia‐Ecuador megathrust earthquake was observed and recorded by several tide gauges. In this study, tide gauge records were first digitized from documents comparing the estimated astronomical tide level changes, and the observed tsunami waveforms were extracted. An inverse analysis was conducted using the observed tsunami waveforms, and we successfully developed a slip distribution model that produced improved tsunami waveforms for tide gauge stations compared with previous studies. Based on a comparison of the developed source model and ruptured areas of other significant earthquakes around Colombia and Ecuador, the 1906 earthquake already ruptured an area affected by the 1979 earthquake, resulting in a substantial release of accumulated slip deficits. In contrast, although the ruptured area of the 1906 earthquake likely covered the source areas of the 1958 and 1942 earthquakes, the release in these areas during the earthquake was moderate and insignificant, and large slip deficits remained after the 1906 earthquake. These results demonstrate that the extent of the release of accumulated slip deficits varied greatly in the source area of the 1906 earthquake.