Analysis and quasistatic FE modeling of long period impulsive events associated with explosions at Stromboli volcano (Italy)

Abstract

Broadband seismic measurements performed in 1995 and 1996 in the summit region of Stromboli are analyzed. The experiment in 1995 used an array of four Guralp seismometers and one Wielandt-Streckeisen seismometer. The stations were installed around the craters in a semicircle with a radius of about 500 m. This implies that the seismic signals are dominated by near field motions up to frequencies of about 2 Hz. The observed Strombolian explosions are preceded by long-period ground motions occurring between 20 s and 70 s prior to the ejections. They are obviously generated by a slow pressure increase within the magma conduits. The long-period signals are simple compared to the short period wave forms. Four classes of pulse-shaped seismograms can be distinguished. The radiation pattern is radially symmetric with respect to the crater region. Particle motion analysis indicates that the seismic sources are located between 50 and 200 m below the crater terrace. Hydrostatic model sources were studied by means of finite element calculations with different geometries, i.e. ellipsoids, in a solid cone modeling the topography of Stromboli. The results suggest that the explosive events on Stromboli originate from a shallow vertically elongated volume source.