Abstract

Research : Solid earth sciences

Lg wave propagation in the area around Japan: observations and simulations

Furumura T, Hong T K, Kennett B LN
Keywords:
Computational seismology, Crustal structure, Finite-difference method simulation, Lg wave, Regional wave, Sn wave, Wave propagation

Figure 2 Record section and snapshot derived by 3-D FDM simulation along profile b-b’ in Figure 1. Record section of vertical-component seismogram along profile from the source in China to central Japan across the Sea of Japan and the snapshots of P (red) and S (green) wavefields at 80, 200, 320, and 440 s from earthquake starts. Theoretical travel time curves for the major phases are shown. Star indicates earthquake source. The snapshots demonstrate the propagation of the Pn, Pg,Sn waves and the development of the Lg wave by multiple wide-angle S-wave reflections in the crust. The Lg wave is severely attenuated after propagation of Sea of Japan as the seismic wave penetrate from the crust into the mantle from through thinner oceanic crust, and due to conversion to P wave at the sea bottom. Severely attenuated Lg wave as propagating in the Sea of Japan is also confirmed in the waveform record section at top.

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Figure 1 Lg wave propagation map in the area around Japan. Summary map of the variation in the Lg wave propagation in the area around Japan derived from the inversion of the Lg/Sn ratio on the 30,000 ray paths. Green marks efficient Lg propagation, and red marks indicate inefficient Lg propagation. Triangles denote major active volcanoes. Dashed lines denote isodepth contours of the crustal thickness at 5-km intervals, and blue lines correspond to the 1,000-m contour of sea depth. Triangles indicate volcano. Efficient propagation of the Lg wave from Asian Continent to western Japan means that the crustal structure is almost continuous across the Korean Peninsula.

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