Closing crack earthquakes within the Krafla caldera, North Iceland

Moment tensor analysis with a Bayesian approach was used to analyse a non-double-couple (non-DC) earthquake ($M_w$ ~ 1) with a high isotropic (implosive) component within the Krafla caldera, Iceland. We deduce that the earthquake was generated by a closing crack at depth. The event is well located, with high signal-to-noise ratio and shows dilatational $P$-wave first arrivals at all stations where the first arrival can be picked with confidence. Coverage of the focal sphere is comprehensive and the source mechanism stable across the full range of uncertainties. The non-DC event lies within a cluster of microseismic activity including many DC events. Hence, we conclude that it is a true non-DC closing crack earthquake as a result of geothermal utilization and observed magma chamber deflation in the region at present.Natural Environment Research Council (Grant ID: NE/H025006/1

Shallow geothermal and deep seismicity beneath Peistareykir, NE-Iceland

The seismicity in the central Þeistareykir volcanic system, NE Iceland, between 2009-2012 consists of spatially clustered earthquakes at 2-5 km depth (b.s.l.) southwest of the main geothermal fields. Deep earthquakes are located in a scattered pattern southeast of Þeistareykir at 8-20 km depth (b.s.l.). Although not associated with detectable surface uplift they may be caused by high strain rates within the plastic regime of the crust in the vicinity of the Húsavík-Flatey transform fault system or due to reduced normal friction caused by melt movements at depth

Shallow geothermal and deep seismicity beneath Peistareykir, NE-Iceland

The seismicity in the central Þeistareykir volcanic system, NE Iceland, between 2009-2012 consists of spatially clustered earthquakes at 2-5 km depth (b.s.l.) southwest of the main geothermal fields. Deep earthquakes are located in a scattered pattern southeast of Þeistareykir at 8-20 km depth (b.s.l.). Although not associated with detectable surface uplift they may be caused by high strain rates within the plastic regime of the crust in the vicinity of the Húsavík-Flatey transform fault system or due to reduced normal friction caused by melt movements at depth

Magma paths at Piton de la Fournaise Volcano

International audienceSeveral patterns of magma paths have been proposed since the 1980s for Piton de la Fournaise volcano. Given the significant differences, which are presented here, we propose a reappraisal of the magma intrusion paths using a 17-years-long database of volcano-tectonic seismic events and a detailed mapping of the scoria cones. At the edifice scale, the magma propagates along two N120 trending rift zones. They are wide, linear, spotted by small to large scoria cones and related lava flows and involving magma resulting from high-pressure fractionation of ol ± cpx and presents an eruption periodicity of around 200 years over the last 30 kiloyears. The upper plumbing system originates at the base of the edifice below the Enclos Fouqué caldera. It feeds frequent (1 eruption every 9 months on average), short-lived summit and distal (flank) eruptions along summit and outer rift zones, respectively. Summit rift zones are short and present an orthogonal pattern restricted to the central active cone of Piton de la Fournaise whereas outer rift zones extend from inside the Enclos Fouqué caldera to the NE and SE volcano flanks. To sum up, rift zones of Piton de la Fournaise present strong geometrical and dynamical differences. On the one hand, the lower plumbing system feeds rift zones showing striking similarities to those developed in Hawaii during the alkaline postshield stage. On the other hand, the rift zones connected to upper plumbing system can be compared the rift system of Mount Etna, whose dynamics is know to be linked with the lateral displacement of the east flank