INVESTIGATION OF MICROSEISM SOURCES WITH OCEAN‐BOTTOM SEISMOMETERS

Geophysics ◽  
1965 ◽  
Vol 30 (4) ◽  
pp. 511-526 ◽  
Author(s):  
H. Bradner ◽  
J. G. Doods ◽  
R. E. Foulks
Keyword(s):  
Noise Spectrum ◽  
Ocean Bottom ◽  
Percent Confidence Level ◽  
The Pacific ◽  
Peak Energy ◽  
Higher Power ◽  
Ocean Bottom Seismometers ◽  
Subsequent Conversion ◽  
The Pacific Ocean ◽  
Incident Waves

Recordings to depths of 5 km have been made on the Pacific Ocean bottom with self‐rising internally recording seismometers. Simultaneous recordings have been made at land stations. The ocean‐bottom noise spectrum is between one and five orders of magnitude higher power than the land spectrum in the region from 0.1 to 9.0 cps. Coherence between two simultaneous instruments separated one‐quarter kilometer is above the 95 percent confidence level from 0.1 cps to 0.6 cps. Attempts to associate narrow‐beam Love and Rayleigh peaks with large storm‐generating areas or with heavy swell striking shore have not produced consistent results. Although some records show the bulk of the microseism peak energy in well‐defined modes, the energy is carried in different modes at different times and locations. Some of our data fit a model of microseism generation in a 100‐mile strip, by a statistical superposition of incident waves and waves reflected from shore; and the subsequent conversion of the energy to Rayleigh and Love modes propagating away from the generation zone. However, the shapes of the mid‐ocean spectra strongly imply additional sources far from shorelines or recognized storms, unless microseisms attenuate far less in the ocean than on land.

scholarly journals Observations of Earth’s Normal Modes on Broadband Ocean Bottom Seismometers

2021 ◽  
Vol 9 ◽  
Author(s):  
Gabi Laske
Keyword(s):  
Normal Modes ◽  
Low Frequency ◽  
Free Fall ◽  
Ocean Bottom ◽  
High Quality ◽  
Broadband Seismometer ◽  
The Pacific ◽  
Ocean Bottom Seismometers ◽  
The Pacific Ocean ◽  
First Time

It is generally thought that high noise levels in the oceans inhibit the observation of long-period earthquake signals such as Earth’s normal modes on ocean bottom seismometers (OBSs). Here, we document the observation of Earth’s gravest modes at periods longer than 500 s (or frequencies below 2 mHz). We start with our own 2005–2007 Plume-Lithosphere-Undersea-Mantle Experiment (PLUME) near Hawaii that deployed a large number of broadband OBSs for the first time. We collected high-quality normal mode spectra for the great November 15, 2006 Kuril Islands earthquake on multiple OBSs. The random deployment of instruments from different OBS groups allows a direct comparison between different broadband seismometers. For this event, mode S06 (1.038 mHz) consistently rises above the background noise at all OBSs that had a Nanometrics Trillium T-240 broadband seismometer. We also report observations of other deployments in the Pacific ocean that involved instruments of the U.S. OBS Instrument Pool (OBSIP) where we observe even mode S04 (0.647 mHz). Earth’s normal modes were never the initial target of any OBS deployment, nor was any other ultra-low-frequency signal. However, given the high costs of an OBS campaign, the fact that data are openly available to future investigators not involved in the campaign, and the fact that seismology is evolving to investigate ever-new signals, this paper makes the case that the investment in a high-quality seismic sensor may be a wise one, even for a free-fall OBS.

scholarly journals PREDICTIVE MODEL FOR DAILY CHANGES OF SHORELINE

1988 ◽  
Vol 1 (21) ◽  
pp. 93
Author(s):  
Kazumasa Kotah ◽  
Shin-ichi Yanagishima
Keyword(s):  
Predictive Model ◽  
Sandy Beach ◽  
Research Facility ◽  
Short Term ◽  
The Pacific ◽  
Line Theory ◽  
The Pacific Ocean ◽  
The One ◽  
Incident Waves ◽  
Daily Changes

Beach profiles have been being measured every day on sandy beach at the Hazaki Oceanographical Research Facility, facing to the Pacific Ocean. Based on the data obtained during the period from March 12, 1986 to September 11, the relation between the daily changes of shoreline position and energy flux of incident waves is analyzed. A tentative predictive model of the short-term shoreline changes is proposed. A combination of this model and the one-line theory is examined.

Geophysical measurements in the region of the Explorer ridge off western Canada

1978 ◽  
Vol 15 (9) ◽  
pp. 1508-1525 ◽  
Author(s):  
R. D. Hyndman ◽  
G. C. Rogers ◽  
M. N. Bone ◽  
C. R. B. Lister ◽  
U. S. Wade ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Seismic Refraction ◽  
Ocean Bottom ◽  
Low Velocity ◽  
Geothermal Heat ◽  
Juan De Fuca Plate ◽  
The North ◽  
The Pacific ◽  
Ocean Bottom Seismometers ◽  
Seismic Reflection Profiles

The region of the Explorer spreading centre off Vancouver Island, British Columbia, has been studied through a marine geophysical survey. Earthquake epicentres located by three ocean bottom seismometers confirm that the boundary between the Pacific plate and the Explorer plate (the northern extension of the Juan de Fuca plate) at present lies along the Sovanco fracture zone, the Explorer ridge, and the Dellwood Knolls. The epicentres of earthquakes in this area as determined by the onshore seismic network are found to be subject to significant errors. The ocean bottom seismometers also have been used for a detailed seismic refraction line just to the north of the Explorer spreading centre employing explosives and a large airgun as sources. A preliminary analysis of the data indicates a fairly typical crustal structure but a shallow and low velocity mantle near the ridge crest, and illustrates the value of ocean bottom seismometers in oceanic refraction studies. A new geothermal heat flux probe was employed in this study that permitted repeated 'pogostick' penetrations without raising the instrument to the surface. Six profiles with a total of 112 penetrations provided valuable data on the nature of hydrothermal circulation in the oceanic crust. Eleven standard heat probe stations provided some restraints on the poorly known age of the oceanic crust along the margin. Seismic reflection profiles using a 3.5 kHz system, a high resolution pulser profiler, and a large airgun were used as aids in the interpretation of the seismic and heat flow data.

scholarly journals Crustal structure in a profile off the pacific coast of Northeastern Japan by the refraction method with ocean bottom seismometers.

1981 ◽  
Vol 29 (4) ◽  
pp. 267-281 ◽  
Author(s):  
Shuzo ASANO ◽  
Toshihiko YAMADA ◽  
Kiyoshi SUYEHIRO ◽  
Toshikatsu YOSHII ◽  
Yoshibumi MISAWA ◽  
...  
Keyword(s):  
Crustal Structure ◽  
Pacific Coast ◽  
Ocean Bottom ◽  
Northeastern Japan ◽  
The Pacific ◽  
Refraction Method ◽  
Ocean Bottom Seismometers

scholarly journals SUSPENSIONS TRANSPORT PREDICTIVE MODELING UNDER VARIOUS SCENARIOS OF FERROMANGANESE NODULES EXTRACTION FROM THE PACIFIC OCEAN BOTTOM

2021 ◽  
pp. 1-9
Author(s):  
A. A. Sukhinov ◽  
A. A. Sukhinov ◽  
S. B. Kirilchik
Keyword(s):  
Pacific Ocean ◽  
Aqueous Medium ◽  
Granulometric Composition ◽  
Water Mass ◽  
Propagation Model ◽  
Ocean Bottom ◽  
Eastern Pacific Ocean ◽  
Ferromanganese Nodules ◽  
The Pacific ◽  
The Pacific Ocean

The article is devoted to the suspensions’ distribution mathematical modeling in the Eastern Pacific Ocean for various scenarios for the ferromanganese nodules extraction. The suspensions propagation model with complex granulometric composition that can interact in an aqueous medium takes into account the suspensions microturbulent diffusion caused by the turbulent aqueous medium movement and the suspensions convection caused by the advective movement of water mass in the ocean; gravitational suspensions deposition under the gravity influence; mutual transitions between different fractions that make up the suspension; interaction of particles with the bottom and with the free surface.

scholarly journals Variability of the Deep-Water Overflow in the Luzon Strait*

2014 ◽  
Vol 44 (11) ◽  
pp. 2972-2986 ◽  
Author(s):  
Chun Zhou ◽  
Wei Zhao ◽  
Jiwei Tian ◽  
Qingxuan Yang ◽  
Tangdong Qu
Keyword(s):  
Deep Water ◽  
Volume Transport ◽  
Luzon Strait ◽  
Stream Velocity ◽  
Ocean Bottom ◽  
Intraseasonal Variation ◽  
The Pacific ◽  
The Pacific Ocean ◽  
Seasonal Time Scale ◽  
Water Overflow

Abstract The Luzon Strait, with its deepest sills at the Bashi Channel and Luzon Trough, is the only deep connection between the Pacific Ocean and the South China Sea (SCS). To investigate the deep-water overflow through the Luzon Strait, 3.5 yr of continuous mooring observations have been conducted in the deep Bashi Channel and Luzon Trough. For the first time these observations enable us to assess the detailed variability of the deep-water overflow from the Pacific to the SCS. On average, the along-stream velocity of the overflow is at its maximum at about 120 m above the ocean bottom, reaching 19.9 ± 6.5 and 23.0 ± 11.8 cm s−1 at the central Bashi Channel and Luzon Trough, respectively. The velocity measurements can be translated to a mean volume transport for the deep-water overflow of 0.83 ± 0.46 Sverdrups (Sv; 1 Sv ≡ 106 m3 s−1) at the Bashi Channel and 0.88 ± 0.77 Sv at the Luzon Trough. Significant intraseasonal and seasonal variations are identified, with their dominant time scales ranging between 20 and 60 days and around 100 days. The intraseasonal variation is season dependent, with its maximum strength taking place in March–May. Deep-water eddies are believed to play a role in this intraseasonal variation. On the seasonal time scale, the deep-water overflow intensifies in late fall (October–December) and weakens in spring (March–May), corresponding well with the seasonal variation of the density difference between the Pacific and SCS, for which enhanced mixing in the deep SCS is possibly responsible.

scholarly journals Madden-Julian oscillation winds excite an intraseasonal see-saw of ocean mass that affects Earth’s polar motion

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
M. Afroosa ◽  
B. Rohith ◽  
Arya Paul ◽  
Fabien Durand ◽  
Romain Bourdallé-Badie ◽  
...  
Keyword(s):  
Large Scale ◽  
Tropical Indian Ocean ◽  
Polar Axis ◽  
Global Scale ◽  
Pacific Basin ◽  
Ocean Bottom ◽  
Madden Julian Oscillation ◽  
Ocean Mass ◽  
The Pacific ◽  
The Pacific Ocean

AbstractStrong large-scale winds can relay their energy to the ocean bottom and elicit an almost immediate intraseasonal barotropic (depth independent) response in the ocean. The intense winds associated with the Madden-Julian Oscillation over the Maritime Continent generate significant intraseasonal basin-wide barotropic sea level variability in the tropical Indian Ocean. Here we show, using a numerical model and a network of in-situ bottom pressure recorders, that the concerted barotropic response of the Indian and the Pacific Ocean to these winds leads to an intraseasonal see-saw of oceanic mass in the Indo-Pacific basin. This global-scale mass shift is unexpectedly fast, as we show that the mass field of the entire Indo-Pacific basin is dynamically adjusted to Madden-Julian Oscillation in a few days. We find this large-scale ocean see-saw, induced by the Madden-Julian Oscillation, has a detectable influence on the Earth’s polar axis motion, in particular during the strong see-saw of early 2013.

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