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WITHDRAWN Precursory Seismic Signals Before Two Catastrophic Landslides at Irazú Volcano, Costa Rica

Description: 

W/D At Volcanoes, complex landslide instabilities triggered by nearby earthquakes, rainfall, local deformation, or a combination of all, may induce changes in the lithostatic pressure of the edifice, suddenly affecting their internal dynamics and increasing the risk of catastrophic eruptions. The Irazú volcano in Costa Rica has been recognized to host massive rock landslides in the past. Just in December 2014 and August 2020, a total of 53 million m³ of mass wasting were deposited along the basement of “Rio Sucio”, one of the main tributaries of the Sarapiquí River. Using the near field monitoring network that OVSICORI-UNA operates in the region, we demonstrate that during these events, the nucleation initiated weeks prior to the catastrophic collapse with SSE generating repeating low frequency earthquakes (LFEs) localized along the basement. Our observations show that as the mass accelerates the number of LFEs increases progressively and the inter-event time between them decreases linearly until they merge forming a tremor signal 30 min prior to the collapse. Seismic data exhibit an exponential increase in tremor amplitude, and thus, moment, that suddenly reduces and become quiescent for 20 seconds before the catastrophic failure. We posit that transient embrittlement is the mechanism responsible for such a unique observation. As the slip rate increases, faulting regions with predominantly stable-sliding frictional properties become unstable, as previously observed elsewhere. As a result, the total effective area of contact between the sliding mass and the basement increases dramatically, modulating tremor amplitude with time. The shear strength from the coupled asperities is enough to provide temporal stability to the entire mass, inducing the seismic quiescence. However, the accrued shear stress imposed by the SSE episode on the weak asperities overcomes the frictional strength, inducing the catastrophic failure. Our results provide direct evidence that the mechanics that control landslide nucleation are very similar to those observed in laboratory experiments and at tectonic fault zones during earthquakes

Session: Seismology's Role in Assessing Volcanic Hazard at Multiple Time Scales

Type: Oral

Date: 4/18/2023

Presentation Time: 09:00 AM (local time)

Presenting Author: Esteban J. Chaves

Student Presenter: No

Invited Presentation: 

Authors