Figure 9

The vertical and horizontal component OBS data and velocity model for travel time modeling. (a) The vertical component seismograms at OBS JF1 with the travel time reduced with 6 km/s. Green arrows indicate P wave arrivals that propagated through the upper oceanic crust, and green dots are the modeled travel time of this P wave calculated from the velocity structure shown in Figure 9c. (b) Same as Figure 9a but for a horizontal component. Black arrows indicate the S wave arrival with apparent velocity of approximately 6 km/s, which is interpreted as the PPS-converted wave beneath the OBS location. Black dots are the modeled travel time of this PPS phase calculated from the velocity structure shown in Figure 9c. (c) Ray paths and four-layered velocity structure to model the travel time of P wave arrival and converted S wave arrival shown in Figure 9a,b. Black inverted triangle is the OBS location. Blue lines are the structure boundaries. P wave velocity values are indicated to the right of this figure. V p/V s is 1.7 in the crustal layer and 4.2 in the sediment layer. Green and black thin lines are the ray paths for P wave propagating upper oceanic crust and PPS-converted wave which was P-to-S converted beneath the OBS location.