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GeĀ“osciences Azur, Institut de Recherche pour le DeĀ“veloppement, Nice, France.
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- PublicationRestrictedSource analysis of the 2002 Molise, southern Italy, twin earthquakes (10/31 and 11/01)(2005)
; ; ;Vallee, M.; GeĀ“osciences Azur, Institut de Recherche pour le DeĀ“veloppement, Nice, France. ;Di Luccio, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; On October 31, 2002, a moderate size earthquake (Mw = 5.8) occurred in Molise region, southern Italy, causing loss of young human lives in a school collapse and destructions in several villages. The day after, a slightly smaller earthquake happened a few kilometers westward from the first one, without making strong damage. We use a complete set of seismological data (global, regional and local, including both body and surface waves) to better understand the source process of these two events. We show that the two earthquakes are similar, in terms of hypocentral depth, focal mechanism, and source kinematics. Moreover, the imaged slip zones are almost contiguous which makes the time delay between the two shocks (29 hours) an open question. The identified updip rupture propagation has amplified the radiation usually created by such Mw = 5.8 earthquakes at 15ā20 km depth. We model a maximum acceleration zone in agreement with location of damaged villages.204 17 - PublicationOpen AccessThe 2018 unrest phase at La SoufriĆØre of Guadeloupe (French West Indies) andesitic volcano: Scrutiny of a failed but prodromal phreatic eruption(2020-01-11)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; After 25 years of gradual increase, volcanic unrest at La SoufriĆØre of Guadeloupe reached its highest seismic en- ergy level on 27 April 2018, with the largest felt volcano-tectonic (VT) earthquake (ML 4.1 or MW 3.7) recorded since the 1976ā1977 phreatic eruptive crisis. This event marked the onset ofa seismic swarm(180 events, 2 felt) occurring after three previous swarms on 3ā6 January (70 events), 1 st February (30 events, 1 felt) and 16ā17 April (140 events, 1 felt). Many events were hybrid VTs with long-period codas, located 2ā4 km below the vol- cano summit and clustered within 2 km along a regional NW-SE fault cross-cutting La SoufriĆØre. Elastic energy release increased with eachswarmwhereas inter-event time shortened. At the same time, summit fractures con- tinued to open and thermal anomalies to extend. Summit fumarolic activity increased significantly until 20 April, with a maximum temperature of111.4 Ā°C and gas exit velocity of80 m/s, before declining to ~95 Ā°C and ~33 m/s on 25 April. Gas compositions revealed increasing C/S and CO2/CH4 ratios and indicate hydrothermal P-T condi- tions that reached the critical point ofpure water. Repeated MultiGAS analysis of fumarolic plumes showed in- creased CO2/H2S ratios and SO2 contents associated with the reactivation of degassing fractures (T = 93 Ā°C, H2S/SO2 ā 1). While no direct evidence ofupward magma migration was detected, we attribute the above phe- nomena to an increased supply ofdeepmagmatic fluids that heated and pressurized the La SoufriĆØre hydrother- mal system, triggering seismogenic hydro-fracturing, and probable changes in deep hydraulic properties (permeability) and drainage pathways, which ultimately allowed the fumarolic fluxes to lower. Although this magmatic fluid injectionwasmodulated by the hydrothermal system, the unprecedented seismic energy release and the critical point conditions ofhydrothermal fluids suggest that the 2018 sequence ofevents can be regarded as a failed phreatic eruption. Should a similar sequence repeat, we warn that phreatic explosive activity could re- sult fromdisruption ofthe shallowhydrothermal system that is currently responsible for 3ā9mm/y ofnearly ra- dial horizontal displacements within 1 km from the dome. Another potential hazard is partial collapse of the dome's SW flank, already affected by basal spreading above a detachment surface inherited from past collapses. Finally, the increased magmatic fluid supply evidenced by geochemical indicators in 2018 is compatible with magma replenishment of the 6ā7 kmdeep crustal reservoir feeding La SoufriĆØre and, therefore, with a potential evolution of the volcano's activity towards magmatic conditions.163 58