BOSEMENA: Borehole- and Sediment physical properties Measurements in the Nankai Accretionary complex, Japan
Final Report Abstract
IODP expedition 365 was one of the most successful Nankai expeditions up to now. A ~5.3 years long record of borehole pressure and temperature data was recovered. In addition, a long-term borehole monitoring system (LTBMs) at site C0010 was deployed. Thanks to smooth deployment operation, extra time could be used for coring operations. Based on four boreholes the strata and physical properties above and below the megasplay fault at site C0010 is characterized. The overthrust hangingwall mudstone is more deformed than the younger footwall sediments. Hanging- and footwall differ in physical properties e.g. porosity and p-wave velocity. The underthrust mudstones show higher porosities and lower velocities than the hanging wall sediments. Borehole pressure and temperature were processed to distinguish between seismological, deformation, meteorological and tidal effects/events. The tides are dominant in frequency and amplitude in the pressure record that is why the tides were removed for event characterization. Several seismological events caused pressure transients e.g. the Tohoku-Oki earthquake. After tide removal, meteorological phenomena such as typhoons in the north east pacific were visible in the dataset. All in all the results of the project are documented in detail in the IODP Exp365 proceedings volume.
Publications
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Proceedings of the International Ocean Discovery Program. Volume 365. NanTroSEIZE Stage 3: Shallow Megasplay Long-Term Borehole Monitoring System. Expedition 365 of the riser drilling platform from and to Shimizu, Japan. Site C0010, 26 March–27 April 2016.
Saffer, D., Kopf, A., Toczko, S., and the Expedition 365 Scientists
