Real-time passive monitoring with a fibre-optic ocean bottom array

AbstractThe deployment of real-time permanent ocean-bottom seismic and tsunami observatories is significant for disaster mitigation and prevention during the occurrence of large subduction earthquakes near trough areas. On April 1, 2016, a moderate-sized suboceanic earthquake occurred beneath Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) stations that were recently deployed in deep ocean-bottom areas near the Nankai Trough in southwest Japan. P-waves arrived at the ocean-bottom station within 4 s of the origin time, which was 6 and 13 s earlier than the arrival of P- and S-waves at a land station in the coastal area, respectively; this implies earlier detection of strong motion than at land stations. However, the waveforms are amplified by sediment layers and even contaminated with acceleration offsets at some stations, which would lead to overestimations during source investigations. Such amplification and offset did not occur at a borehole station connected to DONET. The amplifications caused by the sediment layers and the offset were found to have a considerable spatial variation, not only between the DONET stations and land and borehole stations but also among the DONET stations, implying that the amplitude evaluation could be unstable. Therefore, procedures for correcting or suppressing the amplification and offset problem are required for conducting waveform analyses, such as magnitude estimations and source modeling, during large subduction earthquakes.

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Application of Cabled Offshore Ocean Bottom Tsunami Gauge Data for Real-Time Tsunami Forecasting

2007 Symposium on Underwater Technology and Workshop on Scientific Use of Submarine Cables and Related Technologies ◽

10.1109/ut.2007.370824 ◽

2007 ◽

Cited By ~ 2

Author(s):

Hiroaki Tsushima ◽

Ryota Hino ◽

Hiromi Fujimoto ◽

Yuichiro Tanioka

Keyword(s):

Real Time ◽

Ocean Bottom ◽

Tsunami Forecasting ◽

Gauge Data

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Dual-Purpose Fibre Optic System Providing Simultaneous, Real-Time Communications and Distributed Vibration Sensing for Pipeline Applications

Volume 1: Risk Assessment and Management; Emerging Issues and Innovative Projects; Operations and Maintenance; Corrosion and Integrity Management ◽

10.1115/ipc1998-2013 ◽

1998 ◽

Cited By ~ 1

Author(s):

E. Tapanes

Keyword(s):

Real Time ◽

Vibration Monitoring ◽

Fibre Optic ◽

Dual Purpose ◽

Integrity Testing ◽

Sensing Technology ◽

Channel Bandwidth ◽

Vibration Sensing ◽

Fibre Optic System ◽

Optic Communication

A proprietary fibre optic sensing technology has been developed and is capable of simultaneously utilising an existing fibre optic communication cable as an integrity-testing sensing cable, thus providing continuous, real-time monitoring of the fibre cable and any structure near the cable (ie., ground, tunnels, ducts, pipes, buildings, equipment, vessels, etc.). With this system, simultaneous fibre optic communications and real-time vibration monitoring was demonstrated using a wavelength multiplexed fibre system for a channel bandwidth of 500 MHz over 18 km of standard singlemode fibre. Real-time vibration monitoring was also demonstrated using standard singlemode and multimode fibre over lengths of 28 km and 53 km, respectively. Trials of the system are currently underway in Australia and the first commercial field installation with this capability is to be completed in mid-1998 in Indonesia. This paper highlights the benefits and potential of this dual-capacity system and details results obtained to-date.

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Method for Near-Real Time Estimation of Tsunami Sources Using Ocean Bottom Pressure Sensor Network (S-Net)

Geosciences ◽

10.3390/geosciences9070310 ◽

2019 ◽

Vol 9 (7) ◽

pp. 310 ◽

Cited By ~ 3

Author(s):

Mayu Inoue ◽

Yuichiro Tanioka ◽

Yusuke Yamanaka

Keyword(s):

Real Time ◽

Time Window ◽

Tsunami Source ◽

Ocean Bottom ◽

Bottom Pressure ◽

Source Estimation ◽

Observation Network ◽

Tsunami Source Estimation

A dense cabled observation network, called the seafloor observation network for earthquakes and tsunami along the Japan Trench (S-net), was installed in Japan. This study aimed to develop a near-real time tsunami source estimation technique using the ocean bottom pressure data observed at those sensors in S-net. Synthetic pressure waveforms at those sensors were computed for 64 earthquake tsunami scenarios with magnitude ranging between M8.0 and M8.8. The pressure waveforms within a time window of 500 s after an earthquake were classified into three types. Type 1 has the following pressure waveform characteristic: the pressure decreases and remains low; sensors exhibiting waveforms associated with Type 1 are located inside a co-seismic uplift area. The pressure waveform characteristic of Type 2 is that one up-pulse of a wave is within the time window; sensors exhibiting waveforms associated with Type 2 are located at the edge of the co-seismic uplift area. The other pressure waveforms are classified as Type 3. Subsequently, we developed a method to estimate the uplift area using those three classifications of pressure waveforms at sensors in S-net and a method to estimate earthquake magnitude from the estimated uplift area using a regression line. We systematically applied those methods for two cases of previous large earthquakes: the 1952 Tokachi-oki earthquake (Mw8.2) and the 1968 Tokachi-oki earthquake (Mw8.1). The locations of the large computed uplift areas of the earthquakes were well defined by the estimated ones. The estimated magnitudes of the 1952 and 1968 Tokachi-oki earthquakes from the estimated uplift area were 8.2 and 7.9, respectively; they are almost consistent with the moment magnitudes derived from the source models. Those results indicate that the tsunami source estimation method developed in this study can be used for near-real time tsunami forecasts.

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