Build. 06.42 - R00m 001 (Seminar Room) / Online

7 July 2026

Caroline Chalumeau (Université Grenoble Alpes)

15:30

Abstract

The South Peru subduction zone is a complex, highly active region, where the flat slab associated with the Nazca Ridge subduction in the North transitions to a much steeper subduction in the South. This transition not only causes the slab to contort, but affects seismicity patterns in the region. Here we use data from 26 seismic stations active from March 2022 to December 2024 as part of the DEEPTrigger project, along with 16 permanent Peruvian stations and 15 permanent Chilean stations, to create a 3-year seismicity catalogue of South Peru. Using PhaseNet for phase picking and PyOcto for phase association, we obtain a total of 166 971 events. These earthquakes are located with NonLinLoc-SSST using a new 3-D P and S-wave velocity model of the region obtained from full-waveform inversion (Kan et al., 2025), then relocated using double difference methods with cross-correlation times to obtain precise locations. We use these precisely-located events to create a new slab model for the region and classify events as upper-plate, interface, intraslab or anthropogenic. 
We thus obtain the first dense and precisely-located earthquake catalog of the region, which helps illuminate known and unknown structures and seismicity patterns. In the flat slab region, we find abundant intraslab microseismicity organized into trench-parallel bands which are likely related to slab bending. We also find numerous shallow seismic swarms where the Nazca Ridge enters subduction, which, in combination with GPS records of nearby stations, hint at the likely presence of slow slip. The edge of the Nazca Ridge is particularly active, down to depths below 80 km. This same edge was activated by the Mw 7.2 Acari earthquake which occurred on June 28th 2024 at the plate interface, and was preceded by a Mw 6.0 intraslab foreshock on June 16th 2024. The Acari mainshock triggered a large aftershock expansion towards the northwest where the Nazca Ridge subducts, and a triggered swarm and possible SSE in that region. It also caused an increase of intraplate seismicity directly downdip along the Nazca Ridge edge, demonstrating the ridge’s ability to concentrate stress. In the south, where the slab transitions to a steeper dip, we image multiple orthogonal intraslab faults suggesting a damaged slab. Further south, in the Arequipa region, intraslab seismicity shuts down while upper plate seismicity forms a large, trenchward-dipping structure seemingly connected to the Incapuquio fault at the surface. Finally, in North Chile, we find a deep band of intraslab seismicity likely linked to metamorphism.