Matoza et al St. Helens Infrasound JGR 09

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B04305 MATOZA ET AL.: INFRASOUND FROM LPS AT MOUNT ST. HELENS Figure 17. Same as Figures 15 and 16 but with vertical single-force component (Fz) and long-duration source time function obtained by Waite et al. [2008]. The results are similar to the volumetric crack source (Figure 16), but the predicted P/Vz ratio at CDWR is smaller. Therefore, we conclude that the Fz component is less significant for horizontally propagating infrasound than the volumetric moment tensor component of the source. Figure 18. Pressure wavefield structure from (top) volumetric moment tensor and (bottom) vertical single-force components of the LP source (195 m below ground surface) at t = 40 s. Note how the volumetric source results in more hemispherical wavefronts, whereas the vertical single-force component results in vertically directed energy, and weaker signals at long range. 22 of 38 B04305
B04305 MATOZA ET AL.: INFRASOUND FROM LPS AT MOUNT ST. HELENS Figure 19. Wavefield snapshots and synthetic record sections for (right) the 2.5-D conceptual weathered layer model compared to (left) a homogeneous solid model. For the 495-m-thick surface weathered layer, Vp = 2000 m/s, Vs = 1155 m/s, and r = 2000 kg/m 3 ; for the homogeneous solid beneath the weathered layer, Vp = 3500 m/s, Vs = 2020 m/s, and r = 2650 kg/m 3 ; and for the atmosphere, Vp = 330 m/s, Vs = 0 m/s, and r = 1.2 kg/m 3 . (left) (top) From top to bottom, pressure wavefield snapshots at t = 0.5, 1, 2, and 4 s, synthetic acoustic and (bottom) seismic record sections for the homogeneous solid model. (right) Same as Figure 19 (left) but for the weathered layer model. The source is placed at (0, 0, 60) in each case. 23 of 38 B04305
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