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Battaglia J.,CNRS Magmas and Volcanoes Laboratory | Metaxian J.-P.,University of Savoy | Garaebiti E.,PMB
Journal of Volcanology and Geothermal Research | Year: 2015

We examined one year of seismic recordings collected in 2008 during a temporary experiment at Yasur volcano (Vanuatu). The volcano has a permanent Strombolian activity that was at a relatively high level during most of our experiment with commonly at least one explosion per minute. Associated with this activity, the network recorded intense seismicicity with hundreds of transients per day. Video recordings indicate that most of the high frequency transients are directly related to the strombolian explosions. They also outline the presence of fewer signals which are not accompanied by any surface activity. The classification of transient events recorded at a station close to the summit indicates that a significant part of the events exhibit waveform similarity. This technique allows the identification of characteristic repeating events among the hundreds of thousands of transients recorded during the experiment. Most of the families of similar events are groups of explosion quakes (EQs) but a few are groups of Long Period events related to deeper processes. By scanning the 9. months of continuous data available at the summit station with master events extracted from these families we reconstruct their temporal evolution. Our results show that several families dominate the activity with a few of them lasting for several months. We show that their temporal evolutions can be used to probe changes in the structure or activity of the volcano. We observe that a major change was induced by a M = 7.3 subduction earthquake which occurred on April 9, 2008 about 80. km from the volcano. While this event did not change significantly the surface morphology of the volcano nor the intensity of the eruptive activity, it interrupted the families as none of them is present both before and after the event. This change in the waveforms can be explained by a drop in the seismic velocity of the volcano caused by the distal event. Numerous other transitions between families are observed, sudden or progressive. These can be interpreted as representative of changes in the eruptive dynamics. The presence of similar EQs, especially for impulsive explosions, indicates that the source mechanism is reproducible and has a stable location for some periods. This favors a source process based on the oscillation of the conduit or oscillation of the edifice in response to the explosive decompression of gas slugs at the free surface of the conduit. Our results suggest that the seismic activity of Yasur is characterized by the presence of dominant modes of resonance of the conduit which may be influenced both by external and internal factors. © 2015 Elsevier B.V. Source

Numerical methods of calculating water flow in soils usually rely on solving Richards' equation, which is obtained by combining the equation of continuity with Darcy's law for water fluxes. In this study, the one-dimensional equation of continuity was solved using tables of precomputed steady-state fluxes read from disk. This results in simpler and faster code for applications such as field water balance models, which may use relatively large depth spacings and many repeated calculations. There is no speed penalty for the use of more complex property descriptions. Steady-state flux tables were computed by integration of Darcy's law, which results in the same solution as Richards' equation, but in principle they could be obtained in some other way. The method is much faster and more stable than conventional iterative methods both because it is noniterative and because good estimates of steady-state fluxes allow accurate solutions with larger vertical grid spacings, which in turn allow larger time steps. It is also both faster and simpler than other noniterative methods that provide good flux estimates because the fluxes are already available without the extra code and the time needed to compute them. © Soil Science Society of America 5585 Guilford Rd., Madison, WI 53711 USA. All rights reserved. Source

Merle O.,CNRS Magmas and Volcanoes Laboratory | Brothelande E.,CNRS Magmas and Volcanoes Laboratory | Lenat J.-F.,CNRS Magmas and Volcanoes Laboratory | Bachelery P.,CNRS Magmas and Volcanoes Laboratory | Garaebiti E.,PMB
Journal of Volcanology and Geothermal Research | Year: 2013

A structural study has been conducted on the resurgent Yenkahe dome (5. km long by 3. km wide) located in the heart of the Siwi caldera of Tanna Island (Vanuatu arc, south Pacific). This spectacular resurgent dome hosts a small caldera and a very active strombolian cinder cone - the Yasur volcano - in the west and exhibits an intriguing graben in its central part. Detailed mapping and structural observations make it possible to unravel the volcano-tectonic history of the dome. It is shown that, following the early formation of a resurgent dome in the west, a complex collapse (caldera plus graben) occurred and this was associated with the recent uplift of the eastern part of the present dome. Eastward migration of the underlying magma related to regional tectonics is proposed to explain this evolution. © 2013 Elsevier B.V. Source

Houk P.,Pacific Marine Resources Institute | Raubani J.,PMB
Journal of Oceanography | Year: 2010

This study identifies linkages between regional ocean productivity and the emergence of large Acanthaster planci starfish populations in Vanuatu. Positive correlations were found between wind stress, chlorophyll-a, and upwelling during January-February 2009, corresponding with coral-eating starfish occurrences. Further, temporal associations have existed between monthly wind stress and upwelling since 2000, and were predictors of past starfish events. Links between starfish emergence and oceanographic features are discussed, drawing upon evidence from other asteroid echinoderms. High regional productivity associated with anomalous oceanographic conditions in Vanuatu, and globally, can be used as early warning indicators of probable, future starfish emergence to aid the foundation and success of local management efforts. © 2010 Springer Science+Business Media B.V. Source

Battaglia J.,CNRS Magmas and Volcanoes Laboratory | Metaxian J.-P.,University of Savoy | Garaebiti E.,PMB
Geophysical Research Letters | Year: 2012

Large earthquakes are often assumed to influence the eruptive activity of volcanoes. A major challenge to better understand the causal relationship between these phenomena is to detect and image, in detail, all induced changes, including subtle, non-eruptive responses. We show that coda wave interferometry can be used to image such earthquake-induced responses, as recorded at Yasur volcano (Vanuatu) following a magnitude 7.3 earthquake which occurred 80km from its summit. We use repeating Long-Period events to show that the earthquake caused a sudden seismic velocity drop, followed by a slow partial recovery process. The spatial distribution of the response amplitude indicates an effect centered on the volcano. Our result demonstrates that, even if no major change in eruptive activity is observed, volcanoes will be affected by the propagation of large amplitude seismic waves through their structure, suggesting that Earthquake-volcano interaction is likely a more common phenomenon than previously believed. © 2012. American Geophysical Union. All Rights Reserved. Source

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