Repeating Earthquakes along the Colombian Subduction Zone

Colombia is tectonically active, and several large earthquakes have ruptured the Colombia-Ecuador subduction zone (CESZ) during the last century. Among them, the Colombia-Ecuador earthquake in 1906 (Mw8.4) and the Tumaco earthquake in 1979 (Mw8.3) generated destructive tsunamis. Therefore, it is important to characterize the seismic rupture processes and its relation with the interplate coupling along CESZ. We searched for repeating earthquakes by performing waveform similarity analysis. We estimated cross-correlation coefficient values between earthquake pairs within hypocenter differences of 50 km, located within the northern part of CESZ (1°-4° N). We used broadband and short-period seismic waveform data from the seismic network maintained by the Colombian Geological Survey. Our search was performed for the time period between 1993 and 2018. A threshold for the cross-correlation value of 0.9 was used to identify the waveform similarity and to select repeating earthquakes, in which sequences of events occurred in very short time intervals were excluded because they may represent triggered events. We found repeating earthquakes distributed near the trench and beneath the coastal region. This distribution indicates that the repeating earthquakes did not occur within the large slip area of the 1979 Tumaco earthquake where relatively large interplate coupling was estimated by Sagiya and Mora (2019). Our estimated repeating earthquakes located offshore near the trench suggest that the interplate coupling in this region is low. Large slip of the 1906 Colombia-Ecuador earthquake along the trench in the southern part of CESZ was estimated by Yoshimoto et al. (2017), and therefore, the northern and southern parts of CESZ along the trench may have different rupture modes.