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Volcán Tabor, Ibagué, Tolima

 Volume 4 Chapter 15

Chapter 15

Interplate Coupling along the Nazca Subduction Zone on the Pacific Coast of Colombia Deduced from GeoRED GPS Observation Data

By Takeshi SAGIYA and Héctor MORA–PÁEZ

Pages 305–321

Manuscript accepted March 5, 2019


The Nazca Plate subducts beneath Colombia and Ecuador along the Pacific coast where large megathrust events repeatedly occur. Distribution of interplate coupling on the subducting plate interface based on precise geodetic data is important to evaluate future seismic potential of the megathrust. We analyze recent continuous GPS data in Colombia and Ecuador to estimate interplate coupling in the Nazca subduction zone. To calculate the interplate coupling ratio, in addition to the MORVEL plate velocities, three different Euler poles for the North Andean Block are tested but just two of them yielded similar results and are considered appropriate for discussing the Pacific coastal area. The estimated coupling distribution shows four main locked patches. The middle two locked patches correspond to recent large earthquakes in this area in 1942, 1958, and 2016. The southernmost locked patch may be related to slow slip events. The northern locked patch has a smaller coupling ratio of less than 0.5, which may be related to the large earthquake in 1979. However, because of the sparsity of the GPS network, detailed interpretation is not possible. If we assume that the seismic moment accumulation rate is correctly estimated, the recurrence interval for a 1979–type earthquake is estimated to be ca. 124 years. More GPS data, including seafloor GPS/acoustic sensors, will greatly improve the current estimates of interplate coupling. 

Keywords:    interplate coupling, Nazca, GPS, North Andean Block.