A comparison of horizontal and vertical peak accelerations and velocities recorded by S-net ocean-bottom seismographs in the Japan Trench area with the values recorded by stations on the ground in and around the Kanto Basin

ABSTRACT A large-scale permanent ocean-bottom seismograph network, named S-net, has been established in the Japan Trench area and consists of 150 observatories equipped with seismometers and tsunamimeters. Most stations at water depths <1500 m were buried to a depth of about 1 m while they were sited freely on the seafloors at greater water depths. To understand the characteristics of strong ground motions on the offshore area, we compared the horizontal vector peak ground accelerations (PGA), peak ground velocities (PGVs), and acceleration response spectra (ARS) between the land and S-net sites for nine earthquakes (5.3≤Mw≤7.1) using ground-motion prediction equations developed for Japan. We found that the observed values of PGAs and short-period (<0.5 s) ARS were generally similar between the land and S-net sites, whereas the PGVs and ARS for the periods longer than 0.5 s were apparently larger at the S-net sites. These results based on data covering a wide area on the seafloors were generally similar to the previous results based on limited ocean-bottom stations. However, analysis of the residuals, within the source-to-site distance of 200 km, revealed that the residual values were smaller in the shallow water region compared to those toward the Japan Trench, which is characterized by proximity to high Qs in the Pacific plate, the presence of thick unconsolidated sediments on the upper crust, and increasing heights of water columns. The difference of station settings in the shallow and deep water regions may also have contributed to the biased distribution of residuals at the short periods. Quantifications of these results are expected to contribute to the predictions of ground motions for earthquake early warning and seismic demand analysis of offshore facilities and await further analysis of a larger data set.

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Queen Charlotte fault zone: microearthquakes from a temporary array of land stations and ocean bottom seismographs

Canadian Journal of Earth Sciences ◽

10.1139/e81-071 ◽

1981 ◽

Vol 18 (4) ◽

pp. 776-788 ◽

Cited By ~ 23

Author(s):

R. D. Hyndman ◽

R. M. Ellis

Keyword(s):

Fault Zone ◽

Strike Slip ◽

Ocean Bottom ◽

Small Component ◽

Queen Charlotte Islands ◽

The North ◽

Vertical Fault ◽

Linear Sections ◽

Ocean Bottom Seismographs ◽

Steep Slopes

A temporary array of land and ocean bottom seismograph stations was used to accurately locate microearthquakes on the Queen Charlotte fault zone, which occurs along the continental margin of western Canada. The continental slope has two steep linear sections separated by a 25 km wide irregular terrace at a depth of 2 km. Eleven events were located with magnitudes from 0.5 to 2.0, 10 of them beneath the landward one of the two steep slopes, some 5 km off the coast of the southern Queen Charlotte Islands. No events were located beneath the seaward and deeper steep slope. The depths of seven of these events were constrained by the data to between 9 and 21 km with most near 20 km. The earthquake and other geophysical data are consistent with a near vertical fault zone having mainly strike-slip motion. A model including a small component of underthrusting in addition to strike-slip faulting is suggested to account for the some 15° difference between the relative motion of the North America and Pacific plates from plate tectonic models and the strike of the margin. One event was located about 50 km inland of the main active zone and probably occurred on the Sandspit fault. The rate of seismicity on the Queen Charlotte fault zone during the period of the survey was similar to that predicted by the recurrence relation for the region from the long-term earthquake record.

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Ocean-Bottom Seismographs Based on Broadband MET Sensors: Architecture and Deployment Case Study in the Arctic

Sensors ◽

10.3390/s21123979 ◽

2021 ◽

Vol 21 (12) ◽

pp. 3979

Author(s):

Artem A. Krylov ◽

Ivan V. Egorov ◽

Sergey A. Kovachev ◽

Dmitry A. Ilinskiy ◽

Oleg Yu. Ganzha ◽

...

Keyword(s):

Site Response ◽

The Arctic ◽

Laptev Sea ◽

Ocean Bottom ◽

Arctic Seas ◽

Shirshov Institute ◽

Study Results ◽

Ocean Bottom Seismographs ◽

The Laptev Sea

The Arctic seas are now of particular interest due to their prospects in terms of hydrocarbon extraction, development of marine transport routes, etc. Thus, various geohazards, including those related to seismicity, require detailed studies, especially by instrumental methods. This paper is devoted to the ocean-bottom seismographs (OBS) based on broadband molecular–electronic transfer (MET) sensors and a deployment case study in the Laptev Sea. The purpose of the study is to introduce the architecture of several modifications of OBS and to demonstrate their applicability in solving different tasks in the framework of seismic hazard assessment for the Arctic seas. To do this, we used the first results of several pilot deployments of the OBS developed by Shirshov Institute of Oceanology of the Russian Academy of Sciences (IO RAS) and IP Ilyinskiy A.D. in the Laptev Sea that took place in 2018–2020. We highlighted various seismological applications of OBS based on broadband MET sensors CME-4311 (60 s) and CME-4111 (120 s), including the analysis of ambient seismic noise, registering the signals of large remote earthquakes and weak local microearthquakes, and the instrumental approach of the site response assessment. The main characteristics of the broadband MET sensors and OBS architectures turned out to be suitable for obtaining high-quality OBS records under the Arctic conditions to solve seismological problems. In addition, the obtained case study results showed the prospects in a broader context, such as the possible influence of the seismotectonic factor on the bottom-up thawing of subsea permafrost and massive methane release, probably from decaying hydrates and deep geological sources. The described OBS will be actively used in further Arctic expeditions.

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Ocean-Bottom Seismographs

Structure and Development of the Greenland-Scotland Ridge ◽

10.1007/978-1-4613-3485-9_14 ◽

1983 ◽

pp. 257-286 ◽

Cited By ~ 3

Author(s):

R. B. Whitmarsh ◽

R. C. Lilwall

Keyword(s):

Ocean Bottom ◽

Ocean Bottom Seismographs

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Turbidity Current in the Northern Suruga Bay Recorded by Ocean Bottom Seismographs after Passing Typhoon No. 24 in 2018

Zisin (Journal of the Seismological Society of Japan 2nd ser ) ◽

10.4294/zisin.2020-7 ◽

2021 ◽

Vol 73 (0) ◽

pp. 197-207

Author(s):

Hisatoshi BABA ◽

Nagisa NAKAO ◽

Takahito NISHIMIYA ◽

Masanao SHINOHARA ◽

Shintaro ABE ◽

...

Keyword(s):

Turbidity Current ◽

Ocean Bottom ◽

Suruga Bay ◽

Ocean Bottom Seismographs

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Characteristics of Low-Frequency Horizontal Noise of Ocean-Bottom Seismic Data

Seismological Research Letters ◽

10.1785/0220200349 ◽

2021 ◽

Author(s):

Chao An ◽

Chen Cai ◽

Lei Zhou ◽

Ting Yang

Keyword(s):

Water Waves ◽

Noise Source ◽

Random Noise ◽

Low Frequency ◽

Ocean Bottom ◽

Coherent Noise ◽

Infragravity Waves ◽

Low Frequencies ◽

Bottom Currents ◽

Ocean Bottom Seismographs

Abstract Horizontal records of ocean-bottom seismographs are usually noisy at low frequencies (< 0.1 Hz). The noise source is believed to be associated with ocean-bottom currents that may tilt the instrument. Currently horizontal records are mainly used to remove the coherent noise in vertical records, and there has been little literature that quantitatively discusses the mechanism and characteristics of low-frequency horizontal noise. In this article, we analyze in situ ocean-bottom measurements by rotating the data horizontally and evaluating the coherency between different channels. Results suggest that the horizontal noise consists of two components, random noise and principle noise whose direction barely changes in time. The amplitude and the direction of the latter are possibly related to the intensity and direction of ocean-bottom currents. Rotating the horizontal records to the direction of the principle noise can largely suppress the principle noise in the orthogonal horizontal channel. In addition, the horizontal noise is incoherent with pressure, indicating that the noise source is not ocean surface water waves (infragravity waves). At some stations in shallow waters (<300 m), horizontal noise around 0.07 Hz is found to be linearly proportional to the temporal derivative of pressure, which is explained by forces of added mass due to infragravity waves.

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