Application of wave-theoretical seismoacoustic models to the interpretation of explosion and eruption tremor signals radiated by Pavlof volcano, Alaska

Tremor and explosion signals recorded on September 29 during the Fall 1996 Pavlof eruption are interpreted using video images, field observations, and seismic data. Waveform analysis of tremor and explosions provided estimate s of the melt's volcano-acoustic parameters and the magma conduit dimension s. Initial mass fractions of 0.25% water and 0.025% carbon dioxide in the m elt can explain the resonance characteristics of the tremor and explosion p ulses inferred from seismic data. The magma conduit is modeled as a three-s ection rectangular crack. We infer that the tremor-radiating region consist s of the lowermost two sections, both with cross-sectional areas of similar to 10 m(2). The deeper section is 43 m long, with magma sound speed of 230 m/s, density of 2600 kg/m(3), and viscosity of 1.0x10(6) Pa s. The section above it, defined by the water nucleation depth, is 64 m long with magma s ound speed of 91 m/s, density of 2000 kg/m(3), and viscosity of 1.4x10(6) P a s. An average magma flow velocity of 1.2 m/s, with superposed random osci llations, acts as:the tremor source, Explosions are postulated to occur in the uppermost part of the magma conduit after water comes out of solution. The explosion source region consists of a 15 m long,section, with cross-sec tional area of 20 m(2), sound speed of 51 m/s, density of 1000 kg/m(3), and viscosity of 1.5x10(3) Pa s. A burst pressure of 220 MPa at 14 m depth wou ld generate an acoustic pulse whose amplitude and character match the obser ved signal. Waveform analysis of the explosion pulses shows that the explos ive event may be preceded by a long-period fluid transient: which may trigg er the metastable magma-gas mixture. The modeling procedure illustrates the synergy of fluid dynamic, seismic, and acoustic models and data with geolo gical and visual observations.