The Analysis of Gas Emissions at the Seabed offshore SW Taiwan from the Records of Ocean Bottom Seismometers
Abstract
The offshore area of southwestern Taiwan is in an incipient of orogeny, where the principal tectonic feature transfers from passive margin (west) to active accretionary complex (east). Due to the thick and rapid sediment accumulation and lateral compressive stress, a series of mud diapirs and mud volcanos take place on the SW Taiwan and its offshore area. Mud volcano is a major passage for gas emissions. For understanding characteristic of gas activities, we deployed five 4-componet ocean bottom seismometers (OBS) on the southeast of submarine mud volcano, MV1, which is about 100 m high and lies at about 450 m deep near SW Taiwan. The 5 OBSs were located in a 400 x 400 m2 area and operated from April 14 to April 29 in 2015. The signals which could be associated with gas activities are characterized by: (1) clear and sharp first arrival, (2) short durations, only 0.3 0.6 secs, (3) a horizontal harmonic oscillation following, (4) high frequency content above 5 Hz. At present, 745 events were picked from the whole record of OBS01 by STA/LTA ratio method and were verified manually. Those events are only recognized at one station and do not be recorded by other OBSs simultaneously, even if the nearest station is only 286 m apart. This observation suggests that the source of those signals should be near the seabed and around the station. We performed the cross-correlation analysis for all events and only 64 events can be classified into three groups with high correlation. The events in each group could be generated by the same source and the gas might emit or migrate along the same channels repeatedly. However, we do not observe any regular pattern on their occurrence in time. Further investigation will be proceed to get more information on gas activities in shallow sediments of the marine area.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.S43A2795C
- Keywords:
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- 3384 Acoustic-gravity waves;
- ATMOSPHERIC PROCESSESDE: 0728 Ice shelves;
- CRYOSPHEREDE: 4560 Surface waves and tides;
- OCEANOGRAPHY: PHYSICALDE: 7255 Surface waves and free oscillations;
- SEISMOLOGY