T017-0008
Water depth dependence of nontidal variations from seafloor pressure in New Zealand
Wednesday, 9 December 2020
Poster
Tomohiro Inoue1, Yoshihiro Ito2, Laura M Wallace3,4, Yutaka Yoshikawa5, Daisuke Inazu6, Emmanuel Garcia2, Tomoya Muramoto7, Kazuaki Ohta8, Syuichi Suzuki9, Ryota Hino10 and Spahr C Webb11, (1)Kyoto University, Kyoto, Japan, (2)Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan, (3)University of Texas at Austin, Institute for Geophysics, Austin, United States, (4)GNS Science, Lower Hutt, New Zealand, (5)Kyoto University Rigakubu, Kyoto, Japan, (6)Tokyo University of Marine Science and Technology, Tokyo, Japan, (7)National Institute of Advanced Industrial Science and Technology, Tsukuba-Shi, Japan, (8)NIED National Research Institute for Earth Science and Disaster Prevention, Tsukuba, Japan, (9)Tohoku University, Sendai, Japan, (10)Tohoku University, Graduate School of Science, Sendai, Japan, (11)Lamont Doherty Earth Observatory, Palisades, NY, United States
Abstract:
Over the last decades, ocean bottom pressure gauges (OBPG) are widely deployed in the world to measure seafloor crustal deformation due to tectonic events, such as slow slip events (SSE). However, any adequate technique to detect SSE from OBPG data has not been established, because some components included in changing of the height of the water column on the OBPG records have not been fully understood and evaluated yet. To remove the oceanographic noise, one major approach is commonly used as a reference-station method using pressure records from a reference station outside of the deforming zone to remove the oceanographic noise under the assumption that the non-tidal components are common-mode over a large region. Fredrickson et al. (2019) recently demonstrated coherence in bottom pressure changes observed between sites in similar water depths offshore Cascadia, leading them to suggest a new method of placing reference sites at common isobaths to achieve large reductions in oceanographic noise in OBP timeseries. Here, we further evaluate the efficiency of considering differences between bottom pressure pairs at a range of water depths using the OBP data acquired during a 2014/2015 experiment offshore New Zealand.
We adopted two statistical quantities to evaluate the similarity between all pairs of OBP data in the HOBITSS experiment to evaluate the differences of OBP; (i) standard deviation (SD) of residual pressure between a pair of sites and (ii) correlation coefficient (CC) between a pair of 2 sites.
Non-tidal components observed on OBPs in the HOBITSS network show strong similarities between site pairs in similar water depths (e.g., within 500 m - 1000 m of each other). The SDs from the shallower pairs with the depths of deeper sites less than 2500 m rapidly increase with increasing depth difference, suggesting for sites in <2500 m water depth, that reference sites within 500-1000 m water depth of other sites are needed for optimal oceanographic noise removal. In contrast, there appears to be very little dependence of the SD on the horizontal distance between site pairs. We discuss about the similarity of OBP from observed and the oceanographic models. Considering the similarity of OBP along isobaths, we further discuss about the slip distribution using the weighted tilt between sites by the error of tilt calculated from SD.
