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Submarine Deformation by the Intra-arc Strike-slip System in Southern Chile: Faulting, Sedimentation, and Seismicity Processes on the Liquiñe-Ofqui Fault Zone

Description: 

The Chile subduction margin is strongly shaped by tectonic and climatic processes. The oblique convergence generates strain partitioning, evidenced by large megathrust earthquakes and upper-plate strike-slip fault systems. As a consequence, southern Chile has hosted two of the largest earthquakes recorded in history: the Mw 8.8 Maule 2010 and the Mw 9.5 Valdivia 1960 events. Here, transcurrent deformation is mainly expressed in the Liquiñe-Ofqui Fault Zone (LOFZ).

The LOFZ is a dextral intra-arc strike-slip fault system extending between ~37–48°S. South of ~42°S, it is located in a fjord–archipelago setting, where additional complexity arises from interactions between tectonic, glacial, climatic, and oceanographic processes. In this region, the LOFZ has exhibited seismic swarms related to fluid circulation and larger-magnitude events, such as the M 7.1 event in 1927 and the Mw 6.2 event of April 2007. The latter triggered a landslide and tsunami at latitude 45.5°S, resulting in casualties.

In this work, we study a submarine trace of the LOFZ using multichannel seismic reflection data, collected at 42°S in the Gulf of Ancud, to map the fault system and characterize deformational and depositional processes. We complement our analysis with focal mechanism calculations and relocated seismicity. Our results reveal the submarine continuation of the LOFZ, evidenced by a pull-apart basin and associated transtensional faults. Stratigraphic relationships suggest diachronous fault activity and syn-kinematic sedimentation. Together with ongoing seismicity and a 2008 swarm, this indicates active strike-slip deformation on the continental shelf, with fluids playing a role. The presence of submarine landslides highlights the potential for cascading geohazards. We also observe moraine deposits and changes in sedimentation style within the pull-apart basin, showing interaction between faulting and glacimarine processes. These findings highlight the critical role of fault systems in fjord–archipelago settings in controlling sedimentation, geomorphology, and tsunami hazards.

Session: Subaqueous Evidence for Earthquakes, Coseismic Landslides, Tsunamis and other Cascading Hazards [Poster]

Type: Poster

Date: 4/15/2026

Presentation Time: 08:00 AM (local time)

Presenting Author: Valeria Cortés Rivas

Student Presenter: No

Invited Presentation: 

Poster Number: 157

Authors