LFEs and Slow Slip Beneath the Aguas Zarcas Landslide: Evidence for Coupled Gravitational and Strike-slip Deformation in Northern Costa Rica
Description:
On 16 July 2023, a ~10 Mm³ high-velocity landslide in Juan Castro Blanco National Park generated woody debris flows that impacted the town of Aguas Zarcas, northern Costa Rica. To quantify ongoing deformation after this catastrophic failure, we deployed a dense near-field array of 15 3-component nodal seismometers in 2024 and detected >1,500 low-frequency earthquakes (LFEs; Mw < 1) organized into repeating families and located using envelope cross-correlation. Building on these detections, expanded template-based searches yield thousands of LFEs that cluster (i) within the landslide basement and (ii) along an intersecting left-lateral strike-slip fault system. LFE recurrence accelerates into tremor-like bursts, implying episodic slow shear at shallow depth rather than isolated brittle failure. Ambient-noise interferometry reveals up to 14% reductions in surface-wave velocity during wet periods, linking hydrologic forcing to transient weakening and strengthening the case for pore-pressure modulation of slip. Photogrammetric analyses further indicate ongoing meter-scale displacements and ~10⁶ m³ of material poised near the crown, underscoring continued hazard. We interpret the observed LFE–tremor sequences as the seismic expression of slow slip events (SSEs) driven by coupled gravitational loading and tectonic shear, demonstrating that this system hosts a spectrum of slip behaviors, from aseismic creep and SSEs to rapid catastrophic collapse. These results motivate real-time LFE/SSE monitoring as a physics-based proxy for evolving instability in hydrothermally altered volcanic terrains.
Session: SSJ-SSOC-SSA Joint Session: From Slow to Fast Earthquakes: Bridging the Spectrum of Fault Slip [Poster]
Type: Poster
Date: 4/16/2026
Presentation Time: 08:00 AM (local time)
Presenting Author: Esteban J. Chaves
Student Presenter: No
Invited Presentation:
Poster Number: 144
Authors
Nahomy Campos nahomy.campos.salas@est.una.ac.cr National University of Costa Rica |
Esteban Chaves Presenting Author Corresponding Author esteban.j.chaves@una.cr National University of Costa Rica |
Sonia Hajaji ssalgado30@gatech.edu Georgia Institute of Technology |
Evelyn Nuñez Alpizar evelyn.nunez.alpizar@una.ac.cr National University of Costa Rica |
Jose Sequeira Arguedas jose.sequeira.arguedas@una.cr National University of Costa Rica |
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LFEs and Slow Slip Beneath the Aguas Zarcas Landslide: Evidence for Coupled Gravitational and Strike-slip Deformation in Northern Costa Rica
Category
SSJ-SSOC-SSA Joint Session: From Slow to Fast Earthquakes: Bridging the Spectrum of Fault Slip