Institute Seminars

The shallow megathrust offshore central Chile (~32°–34°S) has not ruptured coseismically since 1730, despite repeated earthquakes on deeper segments beneath the coast. This behavior indicates strong downdip segmentation and defines a mature tsunami gap along Chile's most densely populated coast. The margin has been influenced by the quasi-stationary collision of the Juan Fernández Ridge (JFR) since ~12–13 Ma. Here, we study whether this long-lived ridge–margin interaction explains the observed segmentation using controlled-source seismic data across the ridge–trench collision zone. P-wave velocity models image a broad low-velocity zone (2.0–5.0 km/s) extending from the trench to ~40–60 km landward, sharply bounded by higher velocities (>6.0 km/s) associated with the Coastal Cordillera basement. This reduced-velocity zone reflects dominant accretion in the syn-collision sector and subduction erosion in the post-collision sector. Near the southern edge of the active collision zone, an additional low-velocity zone is imaged near the San Antonio Canyon, coincident with the Teniente–San Antonio fault system, forming a mechanically weak domain between the upper plate and the subducting slab beneath the forearc basin. South of the JFR collision zone, this weak domain thins markedly, indicating re-established upper-plate rigidity. Depth-migrated reflection images reveal splay faults rooted in the decollement and reaching the seafloor, indicating potential pathways for shallow coseismic slip and tsunami generation. Despite these indicators, geodetic models show strong shallow locking. We propose that the rigid Coastal Cordillera backstop mechanically decouples shallow weak domains from deeper locked segments, explaining both high coupling and long recurrence of shallow tsunamigenic rupture.
 

Experience with the startup procedure of geothermal plants for the generation of heat and electricity

* Bestec, Bismarckstraße 19, 76870 Kandel, Germany (https://www.bestec-for-nature.com/)