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Impact of Rough Topography and Seamount Subduction on Near-trench Deformation in the Taltal Seismic Gap, Northern Chile

Description: 

North Chile has hosted numerous great earthquakes (Mw > 8.0); however, the Taltal segment (23.5°S–26°S) shows no historical record of major events since at least 1600 CE. This prolonged quiescence, alongside high interseismic coupling and geo-archaeological evidence of tsunamis larger than those recorded historically, characterizes the region as a mature seismic gap. This segment is characterized by the subduction of the Taltal Ridge and rough seafloor topography, which deforms the frontal wedge and influences frictional properties along the plate interface. Thus, it remains unclear whether the resulting structural complexity limits rupture propagation, or if the apparent quiescence is a consequence of the short historical record.

We characterize the offshore structure and plate boundary deformation by integrating reprocessed legacy seismic reflection data (1995 CINCA project), high-resolution bathymetry, local microseismicity, and seafloor geodetic measurements. We identify a highly deformed upper plate featuring extensive subduction erosion and possible collapse structures associated with seamount subduction. At the trench, we find grabens ~1 km of vertical offset and ~10 km wide. This geometry persists in the shallowest section of the plate boundary, but the contact flattens landward, with a broad zone of reflectivity that we interpret as grabens filled with eroded material. Furthermore, recent offshore geodesy data suggest that locking extends to the trench despite these complex features. If, as proposed, tsunami-earthquakes are favored by complex plate contact geometries that might decrease rupture velocity, then this area may be capable of generating such events. Therefore, the lack of historical great earthquakes, despite clear evidence of coupling, suggests either a recurrence interval >400 yr or that the region may be limited in its ability to generate great earthquakes, with the tsunami geo-archaeological record reflecting ≤8.0 M events that included a tsunami-earthquake component. These results offer key structural constraints for modeling the interplay of splay faulting and shallow locking.

Session: Linking Subduction Zone Processes and Cascading Hazards in Alaska, Cascadia, Chile and Beyond - II

Type: Oral

Date: 4/16/2026

Presentation Time: 02:30 PM (local time)

Presenting Author: Valeria Cortés Rivas

Student Presenter: No

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