The 2007 caldera collapse of Piton de la Fournaise volcano: Source process from very-long-period seismic signals

Zacharie Duputel,Luis Rivera

doi:10.1016/j.epsl.2019.115786

Abstract

In April 2007, Piton de la Fournaise volcano experienced its largest caldera collapse in at least 300 yr. This event consisted of a series of 48 subsidence increments characterized by very-long-period (VLP) seismic signals equivalent to Mw 4.4 to 5.4. Source analysis of VLP events suggests a piston-like mechanism with a collapsing crack source corresponding to the contraction of the magma reservoir and a single force representing the collapse of the above rock column. We show that the collapse dynamics is primarily controlled by magma withdrawal from the reservoir, which was likely in a bubbly state at the time of the event. Similar to the 2018 Kilauea collapse, we observe a reduction of the time-interval between successive subsidence increments, which results from the acceleration of magma withdrawal and a progressive weakening of the edifice at the beginning of the sequence.

Highlights

Caldera collapses are frequent in the evolution of basaltic systems, they have been monitored at only a few volcanoes worldwide (e.g., Kumagai et al, 2001; Michon et al, 2007; Neal et al, 2019)
We investigate the caldera collapse that affected the summit of Piton de la Fournaise in 2007
The surface collapse activity started on April 5 with a M w ∼ 5.4 VLP event visible at teleseismic distances

Summary

Introduction

Caldera collapses are frequent in the evolution of basaltic systems, they have been monitored at only a few volcanoes worldwide (e.g., Kumagai et al, 2001; Michon et al, 2007; Neal et al, 2019). Geodetic co-eruptive measurements show a significant deflation of the volcano before the collapse (Peltier et al, 2009; Fontaine et al, 2014; Froger et al, 2015), suggesting that the low-altitude eruption induced a sudden depressurization of the magma reservoir that resulted in the collapse of the rock column below the summit (Michon et al, 2007) This major failure within the edifice was accompanied by a sudden decrease of seismic velocities in the summit area (Duputel et al, 2009) and an exponentially decaying post-eruptive deflation of the central cone (Froger et al, 2015). To mitigate any bias due to the effect of lateral heterogeneities on teleseismic surface waves, our analysis accounts for

Seismological observations and waveform simulations

Moment tensor inversion

Single force inversion

Joint inversion of moment tensor and force

VLP precursors and smaller collapse events

Discussion and conclusion