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Earth, Planets and Space
Fig. 3 | Earth, Planets and Space

Fig. 3

From: Identification of a nascent tectonic boundary in the San-in area, southwest Japan, using a 3D S-wave velocity structure obtained by ambient noise surface wave tomography

Fig. 3

a Observed vertical cross-spectrum between station A and B (see Fig. 1), which are separated by a distance of 18.986 km. Green dots indicate zero-crossing frequencies. b Phase velocity estimated from the observed cross-spectrum in a by the zero-crossing method. Blue dots show all possible velocities, and red dots show the picked velocities. The black line shows the reference velocity derived by the extended SPAC method, and the green line is the reference dispersion curve obtained from the phase velocity map

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