scholarly journals Removing Infragravity-Wave-Induced Noise from Ocean-Bottom Seismographs (OBS) Data Deployed Offshore of Taiwan

2014 ◽  
Vol 104 (4) ◽  
pp. 1674-1684 ◽  
Author(s):  
B.-Y. Kuo ◽  
S. C. Webb ◽  
C.-R. Lin ◽  
W.-T. Liang ◽  
N.-C. Hsiao
Keyword(s):  
Ocean Bottom ◽  
Ocean Bottom Seismographs ◽  
Obs Data ◽  
Wave Induced ◽  
Infragravity Wave

Towards upgraded capability in offshore seismic studies with the new National Australian Pool of Ocean Bottom Seismographs

2013 ◽  
Vol 53 (2) ◽  
pp. 482
Author(s):  
Alexey Goncharov ◽  
Nicholas Rawlinson ◽  
Bruce Goleby
Keyword(s):  
Natural Hazard ◽  
Ocean Bottom ◽  
Data Set ◽  
Multi Scale ◽  
Refraction Seismic ◽  
Short And Long Term ◽  
Ocean Bottom Seismographs ◽  
Obs Data ◽  
First Time

In 2013, Australia, for the first time in its history, will obtain a national pool of ocean-bottom seismographs (OBSs) suitable for multi-scale experiments at sea and for onshore-offshore combined observations. Twenty broadband OBS instruments will be purchased for short- and long-term deployment (up to 12 months) to a maximum depth of 6 km. The instruments will be made available to Australian researchers through ANSIR, with only the costs of mobilisation and deployment to be met. It is anticipated that the OBS facility will greatly enhance the research capabilities of Australian scientists in the area of Earth imaging, offshore exploration, and natural hazard assessment. OBS experiments in Australia have been limited so far, with the only data set collected by Geoscience Australia in 1995–96 on a number of coincident reflection/refraction seismic transects across the northwestern Australian Margin. The main findings from that experiment will be reviewed in the context of recent OBS data processing and acquisition advances. The scope of the experiments with the new national Australian pool of OBSs will be presented, as well as practicalities and logistics of the OBS experiments.

Australian national ocean bottom seismograph fleet advances conventional exploration

2017 ◽  
Vol 57 (2) ◽  
pp. 738
Author(s):  
Alexey Goncharov ◽  
Michal Malinowski ◽  
Dejan Sekulic ◽  
Ashby Cooper ◽  
Peter Chia ◽  
...  
Keyword(s):  
Regional Scale ◽  
Seismic Survey ◽  
Ocean Bottom ◽  
P Waves ◽  
Crust And Upper Mantle ◽  
Seismic Surveys ◽  
S Waves ◽  
Industry Standard ◽  
Ocean Bottom Seismographs ◽  
Obs Data

A fleet of new Australian ocean bottom seismographs (OBSs) have broadband frequency range, and similar instruments are available at only five or six institutions globally. These OBSs are multi-purpose devices able to record passive-source seismic data (earthquakes, ambient noise) as well as active-source (airgun generated) data and, at the same time, to monitor seismic survey noise and whale calls for environmentally responsible exploration. OBS data collected during commercial seismic surveys in Australian waters prove that it is possible to image the velocity distribution of the whole crust and upper mantle from analysis of both reflected and refracted phases generated by an industry-standard broadband airgun array. This means that valuable information on a regional scale can be obtained as a by-product of commercial seismic surveys. Three-component recording capability of OBSs allows analysis of S-waves in addition to the P-waves that are conventionally used in marine reflection surveys.

scholarly journals Evaluations of an ocean bottom electro-magnetometer and preliminary results offshore NE Taiwan

2019 ◽  
Vol 8 (2) ◽  
pp. 265-276
Author(s):  
Ching-Ren Lin ◽  
Chih-Wen Chiang ◽  
Kuei-Yi Huang ◽  
Yu-Hung Hsiao ◽  
Po-Chi Chen ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Incomplete Data ◽  
Field Experiments ◽  
Magnetic Data ◽  
Ocean Bottom ◽  
Data Loggers ◽  
Time Drift ◽  
Ocean Bottom Seismographs ◽  
Obs Data ◽  
The Magnetic Field

Abstract. The first stage of field experiments involving the design and construction of a low-power consumption ocean bottom electro-magnetometer (OBEM) has been completed, which can be deployed for more than 180 d on the seafloor with a time drift of less than 0.95 ppm. To improve the performance of the OBEM, we rigorously evaluated each of its units, e.g., the data loggers, acoustic parts, internal wirings, and magnetic and electric sensors, to eliminate unwanted events such as unrecovered or incomplete data. The first offshore deployment of the OBEM together with ocean bottom seismographs (OBSs) was performed in NE Taiwan, where the water depth is approximately 1400 m. The total intensity of the magnetic field (TMF) measured by the OBEM varied in the range of 44 100–44 150 nT, which corresponded to the proton magnetometer measurements. The daily variations in the magnetic field were recorded using the two horizontal components of the OBEM magnetic sensor. We found that the inclinations and magnetic data of the OBEM varied with two observed earthquakes when compared to the OBS data. The potential fields of the OBEM were slightly, but not obviously, affected by the earthquakes.

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

1981 ◽  
Vol 18 (4) ◽  
pp. 776-788 ◽  
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.

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

Sensors ◽  
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.

Acoustic-elastic coupled equation for ocean bottom seismic data elastic reverse time migration

Geophysics ◽  
2016 ◽  
Vol 81 (5) ◽  
pp. S333-S345 ◽  
Author(s):  
Pengfei Yu ◽  
Jianhua Geng ◽  
Xiaobo Li ◽  
Chenlong Wang
Keyword(s):  
Boundary Conditions ◽  
Particle Velocity ◽  
Ocean Bottom ◽  
Receiver Side ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Time Migration ◽  
New Equation ◽  
Obs Data ◽  
Coupled Equation

Conventionally, multicomponent geophones used to record the elastic wavefields in the solid seabed are necessary for ocean bottom seismic (OBS) data elastic reverse time migration (RTM). Particle velocity components are usually injected directly as boundary conditions in the elastic-wave equation in the receiver-side wavefield extrapolation step, which causes artifacts in the resulting elastic images. We have deduced a first-order acoustic-elastic coupled equation (AECE) by substituting pressure fields into the elastic velocity-stress equation (EVSE). AECE has three advantages for OBS data over EVSE when performing elastic RTM. First, the new equation unifies wave propagation in acoustic and elastic media. Second, the new equation separates P-waves directly during wavefield propagation. Third, three approaches are identified when using the receiver-side multicomponent particle velocity records and pressure records in elastic RTM processing: (1) particle velocity components are set as boundary conditions in receiver-side vectorial extrapolation with the AECE, which is equal to the elastic RTM using the conventional EVSE; (2) the pressure component may also be used for receiver-side scalar extrapolation with the AECE, and with which we can accomplish PP and PS images using only the pressure records and suppress most of the artifacts in the PP image with vectorial extrapolation; and (3) ocean-bottom 4C data can be simultaneously used for elastic images with receiver-side tensorial extrapolation using the AECE. Thus, the AECE may be used for conventional elastic RTM, but it also offers the flexibility to obtain PP and PS images using only pressure records.

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

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

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

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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