Constraining Spatiotemporal Characteristics of Magma Migration at Piton De La Fournaise Volcano From Pre-eruptive Seismicity

Volcano-tectonic seismicity has been recorded for decades on various volcanoes and is linked with the magma transport and reservoir pressurization. Yet earthquakes often appear broadly distributed such that magma movement is difficult to infer from its analysis. We explore the seismicity that occurred before eruptions at Piton de la Fournaise in the last 5years. Using template matching and relocation techniques, we produce a refined image of the summit seismicity, demonstrating that most earthquakes are located on a ring structure. However, only a portion of this structure is activated before each eruption, which provides an indication as to the direction of the future eruptive site. Furthermore, we show that the delay between the pre-eruptive swarm and the eruption onset is proportional to the distance of the eruptive fissures relative to the summit cone. This reveals that the beginning of the intrusion already bears information regarding the future eruption location. Plain Language Summary Earthquakes on volcanoes are usually related to the ascent of magma in the edifice and can therefore provide information concerning an impending eruption. Yet on many occasions, it is not easy to relate the recorded seismicity to the propagation of magma in the volcano. In this study, we detect and locate earthquakes that occurred before 13 eruptions at Piton de la Fournaise, a hawaiian-type volcano located on La Reunion island in the Indian Ocean. We demonstrate that a detailed analysis of the seismicity occurring when the magma starts its ascent can bring important information regarding the future eruption location.