| Summary: | 碩士 === 國立臺灣海洋大學 === 應用地球科學研究所 === 100 === During the Leg 4 of TAIGER experiment (June-July, 2009), a long
MCS/OBS profile of 550 km was shot by R/V Langseth in the West
Philippine Basin. We placed 28 short-period OBSs at a station-to-station
distance of 15 km along this profile. This profile was designed to be 90
degree to the spreading fabric as previously mapped by the multi-beam
echo-sounding data. Because of the Typhoon Molave, R/V Langseth shot
3 times to complete the whole track. The large air-gun sources and
over-lapping shoots allow us to place the shoot geometry into a
single-combined profile. An initial OBS model indicates that the Pn
arrival can be traced up to 80 more km away from the OBS station center.
In this study, P-wave velocity model show that the crust thickness in the
study area is about 6-10 km, and belongs to the typical oceanic crust. The
roughness in the 6.0-7.0 km/sec P-wave velocity may be associated with
the dense volcanic bodies. The multi-beam echo-sounding data show a
big amount of submarine volcanoes, and some over-lapping spreading
ridges. This environment is similar to that of the present-day the Eastern
Pacific Rise with high spreading rate of 9-10 cm/yr. Previous magnetic
lineations indicate that the age of study area is about 40-50 MYBP and
the spreading rate about 8.8 cm/yr. Numerous volcanoes and over-lapping
spreading centers may be related to the motion change of Pacific Plate at
about 45 MYBP. The direction change of the spreading centers between
the West Philippine Basin (NE-SW) and Huatung Basin (N-S) suggest
that the West Philippine Basin was in a counter-clockwise rotation
through its tectonic evolution.
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