HR: 08:00h
AN: V31B-01    [PDF]
TI: A Trigger Mechanism for Volcanic Low-Frequency Seismic Events on Montserrat
AU: * Neuberg, J W
EM: locko@earth.leeds.ac.uk
AF: School of Earth Sciences, The University of Leeds, Leeds, LS2 9JT United Kingdom
AU: Tuffen, H
EM: tuffen@min.uni-muenchen.de
AF: Department of Earth and Environmental Sciences, University of Munich Theresienstrasse 41, Munich, 80333 Germany
AU: Jolly, A
EM: a.jolly@earth.leeds.ac.uk
AF: School of Earth Sciences, The University of Leeds, Leeds, LS2 9JT United Kingdom
AU: Green, D
EM: d.green@earth.leeds.ac.uk
AF: School of Earth Sciences, The University of Leeds, Leeds, LS2 9JT United Kingdom
AB: Seismic observations of low-frequency earthquake swarms on Montserrat point to a non-destructive, repeatable source mechanism in a confined area inside or near the conduit. While the seismic wave propagation pattern of the subsequent resonance in and around the conduit is well studied, the trigger mechanism has remained elusive. In this contribution we suggest a trigger mechanism based on new field evidence for fracture and healing of magma in volcanic conduits, together with seismic observations from Montserrat and finite element modelling of magma deformation during conduit flow. As a seismic trigger we suggest a stick-slip motion of highly-viscous magma in the glass transition, that periodically generates networks of seismogenic shear fractures a few metres in length. These fractures are rapidly filled by fine-grained material [cataclasite] that is generated by friction processes on the fracture surfaces, such as corner abrasion, and is locally redeposited by gas flowing within the fracture system. Filled fractures are then swiftly healed as reloading leads to annealing and a return to cohesive viscous deformation. Such a fast healing process, probably on the order of tens of seconds, leads to a repeatable trigger mechanism. Due to a strong lateral viscosity gradient in the conduit, highly-viscous magma near the conduit walls, which can exhibit brittle behaviour, co-exists with low-viscosity, fluid magma in the conduit centre; such that brittle failure provides the seismic trigger mechanism while the fluid part can still act as a seismic resonator.
DE: 8414 Eruption mechanisms
DE: 8419 Eruption monitoring (7280)
DE: 8434 Magma migration
DE: 8439 Physics and chemistry of magma bodies
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting