Interaction of seismic and air waves recorded at Stromboli Volcano

Abstract

Explosion‐quake seismograms recorded at Stromboli show that seismic phases with a high‐amplitude and high‐frequency content propagate with a velocity of approximately 330 m/s ‐ the sound speed. The analysis of seismograms, recorded at a distance of 500 m from one of the three active vents, shows for the first onset a low‐frequency and particle motion characteristic of a p‐wave, which loses its longitudinal polarization with the onset of the air‐wave. Recording the explosion‐quakes simultaneously with a microphone we could ascertain that the high‐frequency onset coincided with the air‐wave's. In order to better understand the seismic wavefield generated by the atmospheric pressure, we performed a controlled source experiment at Stromboli using a seismic gun. Seismograms with the same two phases and particle motions comparable with the volcano‐seismic data were obtained. A second experiment demonstrated, that the air‐wave propagates at least in the uppermost 1 m of the ground. We suggest that the seismic source of the corresponding seismograms is an explosion at the top of the magma column and conclude that the p‐ and air‐waves are both generated in the same point and at the same time.

An overview of volcano infrasound: From hawaiian to plinian, local to global

“…Iguchi and Ishihara (1990) and Yamasato (1997) installed infrasonic microphones at distances of 2-5 km from Sakurajima, Suwanosejima, and Unzen Volcanoes in Japan, recording numerous explosions, pyroclastic flows (Yamasato, 1997), harmonic infrasonic tremor (Sakai et al, 1996), and impulsive signals associated with long period (LP) events (Iguchi and Ishihara, 1990;Yamasato, 1998). Acoustic studies began at Stromboli Volcano in the early 1990s (Braun and Ripepe, 1993;Vergniolle and Brandeis, 1994;Buckingham and Garces, 1996). Kamo et al (1994) proposed to integrate infrasound into volcanic eruption early warning systems, similar to more recent work by Garces et al (2008).…”

Strombolian explosions: 1. A large bubble breaking at the surface of a lava column as a source of sound

“…Measurements suggest that seismic waves are much less energetic than acoustic waves produced in air [Braun and Ripepe, 1993] and hence have been neglected in our model. In summary, among the different damping coefficients, the largest is the viscous damping.…”

Seismo-acoustic signals associated with degassing explosions recorded at Shishaldin Volcano, Alaska, 2003–2004

“…When the foam layer reaches a critical thickness it is forced to collapse and creates a gas slug that rises to the liquid-air interface where it causes a Strombolian explosion (Jaupart and Vergniolle 1989). A seismic signal may be induced by the coalescence into a large gas bubble (Braun and Ripepe 1993;Ripepe and Braun 1994;Ripepe and Gordeev 1999;Ripepe et al 2001b) and/or by the oscillation of the rising bubble before it reaches the fluid-air interface, whereas the bubble burst itself, i.e. the connection of volcanic gas to the atmosphere, does not appear on the seismogram due to the lack of coupling between source (oscillation in air) and conduit walls .…”