Structures and evolution of the plumbing system of Piton de la Fournaise volcano inferred from clustering of 2007 eruptive cycle seismicity

Analysis of seismic activity associated with the eruptions of 2007, which led to the collapse of the Dolomieu crater on April 5th, reveals the link between the seismicity and the magma transfers at Piton de la Fournaise. Three eruptive phases occurred on February 18th, March 30th and April 2nd, 2007, at the summit, 2,000 m, and 600 m high on the South-East flank respectively, illustrating the three types of eruptions defined for the current Piton de la Fournaise activity. We use cross-correlation of seismic waveforms and clustering to improve the earthquake locations and determine the best-constrained focal mechanisms (with an average of 78 P phase polarities). The pre-eruptive seismicity of the February and March eruptions is composed of time extended clusters that also preceded other distal eruptions from 2000 to 2007. Our analysis shows that the seismic swarm prior to the February eruption initiated the intrusion that led to the April 2007 eruption. The seismicity preceding the Dolomieu crater collapse consists of numerous, but time-limited, clusters and specific seismic activity that accompanied the Dolomieu crater collapse. From April 1st to April 5th, earthquakes with CLVD mechanisms combined with normal faulting sources occurred between 0.8 and 0 km asl, until the complete rupture of the shallow magma storage roof. This collapse induced the propagation of a de-pressurization front and triggered a migration of seismicity from 0 to -8 km along a very narrow path. (C) 2011 Elsevier B.V. All rights reserved.