HR: 11:35h
AN: V32A-06 INVITED     [Abstracts]
TI: Seismic Precursors and the Growth of Magmatic Pathways Before Volcanic Eruptions
AU: * Kilburn, C R
EM: c.kilburn@ucl.ac.uk
AF: University College London, UCL Department of Earth Sciences, Gower St, London, WC1E 6BT United Kingdom
AU: Bell, A F
EM: a.bell@ucl.ac.uk
AF: University College London, UCL Department of Earth Sciences, Gower St, London, WC1E 6BT United Kingdom
AU: Smith, R
EM: rosanna.smith@ucl.ac.uk
AF: University College London, UCL Department of Earth Sciences, Gower St, London, WC1E 6BT United Kingdom
AU: Sammonds, P R
EM: p.sammonds@ucl.ac.uk
AF: University College London, UCL Department of Earth Sciences, Gower St, London, WC1E 6BT United Kingdom
AB: Volcanic eruptions are commonly preceded by accelerations in the rate of occurrence of volcano-tectonic (VT) events. Consistent with the Voight Failure Forecasting Model, the accelerations tend to lie between exponential and hyperbolic (faster than exponential) limits. Such behaviour is remarkable, given that the detected VT event rate represents only a small sample of the total amount of fracturing taking place. The most consistent trends are found among short-term precursors to eruptions at subduction-zone volcanoes after long repose intervals (100 y or more). In this case, field data indicate that final accelerations develop hyperbolically over intervals of 15-20 days before eruption. Short-term precursory behaviour is more erratic at frequently erupting basaltic volcanoes and before phases of dome growth during extended andesitic-dacitic activity. For such conditions, stacking of precursory sequences at a particular volcano (to remove random fluctuations) suggests that the underlying acceleration may also follow a hyperbolic trend that emerges at least several days before eruption. The hyperbolic limit can be interpreted in terms of the growth of major fractures that link together to form a pathway for magma ascent. Two limiting cases can be recognised according to how the detected events are related to the major fractures: either the detected events follow the growth of the major fractures directly, or they describe the growth of faults in the damage zones between major fractures. In the second case, linkage of the major fractures is marked by temporary peaks in event rate. Provisional analyses indicate that erratic precursors reflect the first case, but more regular trends the second. In both cases, however, at least a week is likely to be required to identify an accelerating trend. Even under ideal conditions, therefore, seismic forecasts of eruptions are unlikely to be reliable more than days in advance.
UR: http://benfieldhrc.com/VolcAlert/Website/Root/home.htm
DE: 7280 Volcano seismology (8419)
DE: 8400 VOLCANOLOGY
DE: 8419 Volcano monitoring (7280)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005