Temperature correction and usefulness of ocean bottom pressure data from cabled seafloor observatories around Japan for analyses of tsunamis, ocean tides, and low-frequency geophysical phenomena

Abstract

Ocean bottom pressure (OBP) data obtained by cabled seafloor observatories deployed around Japan, are known to be significantly affected by temperature changes. This paper examines the relationship between the OBP and temperature records of six OBP gauges in terms of a regression coefficient and lag at a wide range of frequencies. No significant temperature dependency is recognized in secular variations, while substantial increases, at rates of the order of 1 hPa/year, are commonly evident in the OBP records. Strong temperature dependencies are apparent for periods of hours to days, and we correct the OBP data based on the estimated OBP-temperature relationship. At periods longer than days, the temperature corrections work well for extracting geophysical signals for OBP data at a station off Hokkaido (KPG2), while other corrected data show insufficient signal-to-noise ratios. At a tsunami frequency, the correction can reduce OBP fluctuations, due to rapid temperature changes, by as much as millimeters, and is especially effective for data at a station off Shikoku (MPG2) at which rapid temperature changes most frequently occur. A tidal analysis shows that OBP data at a station off Honshu (TM1), and at KPG2, are useful for studies on the long-term variations of tidal constituents.

Interplate Slip Following the 2003 Tokachi‐oki Earthquake From Ocean Bottom Pressure Gauge and Land GNSS Data

“…In this study, we assumed that the instrumental drift was linear, based on the conclusion of Inazu and Hino (). This assumption is reasonable at PG2 for the following two reasons.…”

“…For the seafloor pressure instruments, instrumental drift must be included in the estimated linear term and the pressure change due to tectonic movement. Because Inazu and Hino () showed that the annual mean pressure values of these two stations from 2000 to 2002 are almost linear within their standard deviations, we assumed that the instrumental drift could be modeled as a linear term. The estimated preseismic vertical velocity was −30 and −8.4 mm/yr for PG1 and PG2, respectively.…”

Geodetic constraints on afterslip characteristics following the March 9, 2011, Sanriku‐oki earthquake, Japan

“…There seems no apparent coseismic offset for the foreshock in the corrected OBP records. Even in the corrected records, it was difficult to detect the postseismic displacement, as indicated by Inazu and Hino [2012]. Thus we assume the zero displacement at TM1 and TM2 for the co‐ and postseismic displacement in this study.…”

“…See Text S1 in the for more detailed description of the above analysis of the OBP data. The OBP data from the seafloor cabled system needs an additional temperature compensation [ Inazu and Hino , 2012] to detect vertical seafloor displacements (). There seems no apparent coseismic offset for the foreshock in the corrected OBP records.…”

The detectability of shallow slow earthquakes by the Dense Oceanfloor Network system for Earthquakes and Tsunamis (DONET) in Tonankai district, Japan

“…7, in the future we have to enhance the sampling of the differential data from daily to higher than 1 Hz to detect the temporal and local leveling change due to shallower VLF swarms. In the hydraulic pressure gauges of DONET, water temperature gauges are also installed, which helps us to reduce the noise component in both the stack and differential data by temperature correction (Inazu and Hino 2011).…”