Tomographic inversion of P-wave velocity and Q structures beneath the Kirishima volcanic complex, southern Japan, based on finite difference calculations of complex traveltimes

We estimate the P-wave velocity and attenuation structures beneath the Kirishima volcanic complex, southern Japan, by inverting the complex traveltimes (arrival times and pulse widths) of waveform data obtained during an active seismic experiment conducted in 1994. In this experiment, six 200–250 kg...

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Bibliographic Details
Published in:	Geophysical journal international Vol. 146; no. 3; pp. 781 - 794
Main Authors:	Tomatsu, Toshitaka, Kumagai, Hiroyuki, Dawson, Phillip B.
Format:	Journal Article
Language:	English
Published:	Oxford, UK Blackwell Publishing Ltd 01-09-2001 Blackwell Science Ltd
Subjects:	active seismic experiment attenuation autoregressive model pipe-like structure pulse width attenuation pulse width pipe-like structure active seismic experiment autoregressive model
Online Access:	Get full text
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Summary:	We estimate the P-wave velocity and attenuation structures beneath the Kirishima volcanic complex, southern Japan, by inverting the complex traveltimes (arrival times and pulse widths) of waveform data obtained during an active seismic experiment conducted in 1994. In this experiment, six 200–250 kg shots were recorded at 163 temporary seismic stations deployed on the volcanic complex. We use first-arrival times for the shots, which were hand-measured interactively. The waveform data are Fourier transformed into the frequency domain and analysed using a new method based on autoregressive modelling of complex decaying oscillations in the frequency domain to determine pulse widths for the first-arrival phases. A non-linear inversion method is used to invert 893 first-arrival times and 325 pulse widths to estimate the velocity and attenuation structures of the volcanic complex. Wavefronts for the inversion are calculated with a finite difference method based on the Eikonal equation, which is well suited to estimating the complex traveltimes for the structures of the Kirishima volcano complex, where large structural heterogeneities are expected. The attenuation structure is derived using ray paths derived from the velocity structure. We obtain 3-D velocity and attenuation structures down to 1.5 and 0.5 km below sea level, respectively. High-velocity pipe-like structures with correspondingly low attenuation are found under the summit craters. These pipe-like structures are interpreted as remnant conduits of solidified magma. No evidence of a shallow magma chamber is visible in the tomographic images.
Bibliography:	istex:CC966D02F475D2425A3494AA0BED8E7DE41470C0 ark:/67375/HXZ-28GJHGVC-P ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23
ISSN:	0956-540X 1365-246X
DOI:	10.1046/j.1365-246X.2001.00491.x