ISSN:
1365-246X
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Geosciences
Notes:
We demonstrate the effects that the subducting plate, 3-D velocity and Q structures of the upper mantle beneath Japan can have on the amplitudes of seismic waves observed above the inhomogeneous structure, and we explore the possibility of finding the fine velocity and Q structures by means of the amplitude distribution. The methods used for the computation of the seismograms are the ray tracing and also Gaussian beams, which give more accurate amplitudes at caustics and shadow zones. First, we construct a slab velocity model by calculating the temperature distribution within and around the subducting slab, and investigate the effects of relative source location within the slab, possible detachment of shallow and deep parts of the slab, and elevation and depression of the 400 km discontinuity within the slab. The possibility of detecting the location of the leading edge of the subducted slab is also examined by calculating the amplitude distribution of incident plane waves. The distribution of the ray amplitudes is also calculated for a velocity model including the Pacific plate subducting beneath Japan. We finally adopt a 3-D velocity and Q structure model including the subducting Pacific plate and Philippine Sea plate in the uppermost mantle beneath Japan, obtained from previous studies. The calculations for incident plane waves reveal that there may be large variations of the amplitudes on the surface. It is found that the maximum amplitude distribution of waveforms calculated by the Gaussian-beam method for most of the above cases gives a smoothed pattern of the corresponding ray amplitudes, and that the amplitudes for low-frequency waves are smoother than those of high frequencies. From all these calculations, we find that the amplitude distributions are very sensitive to the velocity heterogeneities, suggesting that the amplitude distribution may be used to obtain the source location within the slab, and fine velocity and Q structures of the upper mantle near the subduction zone.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1365-246X.1992.tb02103.x
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