Ma. Garces et Ra. Hansen, WAVE-FORM ANALYSIS OF SEISMOACOUSTIC SIGNALS RADIATED DURING THE FALL1996 ERUPTION OF PAVLOF VOLCANO, ALASKA, Geophysical research letters, 25(7), 1998, pp. 1051-1054
Theoretical modeling of acoustic and seismic signals associated with t
he 1996 strombolian eruption of Pavlof volcano suggests that volcanic
tremor at Pavlof originates in the deeper part of the magma conduit, a
nd is generated by random fluid oscillations in the magma flow. Explos
ions are believed to occur in the shallower part of the magma conduit,
and to be caused by the rapid and violent expansion of metastable mag
ma-gas mixtures. The effect of increasing the exsolved quantities of H
2O and CO2 gas with reduced pressure in the melt is to decrease the so
und speed and density of the magma-gas mixture. This causes an acousti
c decoupling of the upper and lower parts of the magma conduit. The re
duced sound speed and density of the melt at shallow depths present a
sharp impedance contrast, which strongly reflects acoustic energy orig
inating at depth and traps it in the lower part of the magma conduit.
Alternatively, acoustic energy originating from the upper part of the
conduit remains trapped in the low-velocity region formed by the exsol
ved gas in the melt, and hence shallow explosions may preferentially c
ouple into the atmosphere. Explosion signals may be triggered by an in
creased flow of melt at depth, and may be preceded and accompanied by
vigorous mass flux transients.