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The anatomy of a magmatic system, revealed by multi-disciplinary seismological methods in central Costa Rica

Elliot Amir Jiwani-Brown 1, Francisco Munoz 1, Ivan Koulakov 2, Thomas Planès 1, Mauricio Mora 3, Javier Pacheco 4, Matteo Lupi 1

  • Affiliations: 1Département des Sciences de la Terre et de Géophysique, Université de Genève 2Institute of Petroleum, Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences 3Red Sismológica Nacional (RSN), Escuela Centroamericana de Geología, Universidad de Costa Rica 4Observatorio Vulcanológico y Sismológico de Costa Rica (OVSICORI), Universidad Nacional Costa Rica

  • Presentation type: Poster

  • Presentation time: Friday 16:30 - 18:00, Room Poster Hall

  • Poster Board Number: 14

  • Programme No: 1.5.21

  • Theme 1 > Session 5

Abstract

We deployed a temporary network composed of 20 seismic stations, saturated with a further 46-permanent Costa Rica (OVSICORI and RSN) network, from April 2018 to May 2019.  We obtained a database of 967-local-earthquakes, producing an optimised local 1D-velocity-model to more precisely locate events. Clustering and alignments of seismicity obtained with HypoDD were interpreted as diverse interactions between locally-driven fluid-flow in ductile magmatic zones, and brittle deformation within the volcanic system. Intersecting right-and-left-lateral strike-slip regimes dominated local-scale deformation. These two primary motions are linked to the opposing regional-scale tectonic escape of the forearc sliver, and Panama microplate rotation. We observe that Irazú and Turrialba volcanoes are influenced sub-independently, as seismicity associated with each volcano related to geographic proximity to regional-scale tectonic influences.  By focusing on low-frequency seismic noise, we constrained a 3D-shear-velocity model using Ambient Noise Tomography (ANT). This revealed multiple low-velocity anomalies, interpreted as an intermediate depth common magmatic reservoir feeding two shallower magmatic/hydrothermal systems. We also derived a travel-time, local-scale tomography using LOTOS from the relocated earthquake catalogue. The Local Earthquake Tomography (LET) revealed contrasting low and high Vp/Vs ratio anomalies at intermediate crustal depths beneath the volcanoes, suggesting two separately operating magmatic reservoirs, within a larger, shared ductile region. Both intermediate-depth reservoirs showed evidence of feeding from a deeper magmatic source, and also connectivity to the surface through shallow systems of upward-fluid-migration.  The combination of earthquake relocation, ambient-noise and local-earthquake tomography produced comprehensive agreement between three established passive-seismic methods, linking seismicity, neotectonics and volcanism at regional- and local-scales.