博士 / 國立中央大學 / 地球物理研究所 / 98 / Broadband records from ocean-bottom seismometers(OBSs) deployed in the Okinawa trough and the Huatung basin were analyzed to provide seafloor noise characteristics and the detection thresholds for teleseismic body and surface waves. Ambient noise levels on the horizontal components are 10-40 dB higher than on the vertical component, with the sensor seated on the surface of the sediment. On the vertical components, infragravity waves are 10-30 dB more energetic at the shallower Okinawa trough sites ( 2000 m depth) than at the deeper Huatung basin site (~4700 m). From 0.03 Hz to 0.2 Hz, the Huatung basin noise levels are comparable to that of the broadband stations in Taiwan on a quiet day. The microseism peaks (~0.2-0.5 Hz) of OBSs reach or exceed the high noise model of continental stations. At regional distances Mw 6.5 is required for recording prominent Rayleigh waves if the source radiation is unfavorable, but 6.2 is sufficient for a favorable focal mechanism. Several tens to over one hundred high-fidelity P, Pdiff and PKP waveforms have been recorded per year by OBSs at high corner frequency 0.1 Hz with a minimum Mw 5.3-6.0. The number of recording drops to less than 5 per year at 1 Hz with Mw 6.4 and distances less than 90o.
The OBS deployed ~180 km east of Taiwan provides a first glimpse into the upper mantle beneath the westernmost section of the Philippine Sea or the Huatung basin. We measured inter-station phase velocities of Rayleigh waves between the OBS and stations on the eastern coast of Taiwan. The phase velocities show smooth variations from 3.8 to 3.9 km/s for periods of 25-40 s. In this short period range, phase velocities are comparable to those characterizing the 15-30 Ma Parece-Vela basin of the Philippine Sea. The seismological evidence, together with the correlation in seafloor depth, suggests that the Huatung basin and the Parece-Vela basin may have a similar age. This is at odds with the previous geochronological study suggesting an early-Cretaceous age for the Huatung basin.
We have joint-forced with the National Sun Yat-Sen university and the Taiwan Ocean Research Institute in designing and building a wide-band OBS that is aimed for 3 month deployment in shallow waters around Taiwan. An array of 10 of this low-coast, low power budget instrument is scheduled for deployment in the northeast corner of Taiwan in summer of 2010. The experimental test is reported in this thesis.
| Identifer | oai:union.ndltd.org:TW/098NCU05134001 |
| Creators | Ching-ren Lin, 林慶仁 |
| Contributors | Ban-Yuan Kuo, Chien-Ying Wang, 郭本垣, 王乾盈 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 110 |
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