Volcanic Vent Geometry and Infrasonic Radiation via FDTD Modeling

Volcanic infrasound is a direct measure of the atmospheric pressure disturbance excited by eruptions and explosions. The infrasonic waves propagate efficiently into the atmosphere and are less distorted by attenuation than associated seismic waves. Atmospheric conditions (wind and stratification) and surface geometry near volcanoes do affect infrasonic radiation, however, and these can be accounted for using numerical modeling, e.g. finite difference-time domain methods (FDTD). We modeled volcanic explosions using a vertically vibrating piston source buried in an infinite rigid halfspace. Different cylinders of varying radius and depth were investigated to determine controlling factors of vent geometry on wave propagation. The results show that the transient waveform and the sound intensity level radiated from the vent was significantly affected by the vent geometry. We found that diffraction which infrasound propagating into the atmosphere suffers depends critically on the radius of vent and the wavelength of the acoustic disturbance. Observations at Karymsky volcano, Russia, showed good correlation of waveform distortions and predicted synthetic models. The method allows us to determine an effective vent radius for volcanic explosions via infrasonic inverse modeling.