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.

Development of a Compact Broadband Ocean-Bottom Seismometer

2021 ◽  
Author(s):  
Masanao Shinohara ◽  
Tomoaki Yamada ◽  
Hajime Shiobara ◽  
Yusuke Yamashita
Keyword(s):  
Low Frequency ◽  
Plate Boundaries ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Broadband Seismometer ◽  
Seismic Sensors ◽  
Slow Earthquakes ◽  
Short Period ◽  
Ocean Bottom Seismometers

Abstract Studies of very-low-frequency earthquakes and low-frequency tremors (slow earthquakes) in the shallow region of plate boundaries need seafloor broadband seismic observations. Because it is expected that seafloor spatially high-density monitoring requires numerous broadband sensors for slow earthquakes near trenches, we have developed a long-term compact broadband ocean-bottom seismometer (CBBOBS) by upgrading the long-term short-period ocean-bottom seismometer that has seismic sensors with a natural frequency of 1 Hz and is being mainly used for observation of microearthquakes. Because many long-term ocean-bottom seismometers with short-period sensors are available, we can increase the number of broadband seafloor sensors at a low cost. A short-period seismometer is exchanged for a compact broadband seismometer with a period of 20 or 120 s. Because the ocean-bottom seismometers are installed by free fall, we have no attitude control during an installation. Therefore, we have developed a new leveling system for compact broadband seismic sensors. This new leveling system keeps the same dimensions as the conventional leveling system for 1 Hz seismometers so that the broadband seismic sensor can be installed conveniently. Tolerance for leveling is less than 1°. A tilt of up to 20° is allowed for the leveling operation. A microprocessor controls the leveling procedure. Some of the newly developed ocean-bottom seismometers were deployed in the western Nankai trough, where slow earthquakes frequently occur. The data from the ocean-bottom seismometers on the seafloor were evaluated, and we confirmed that the long-term CBBOBS is suitable for observation of slow earthquakes. The developed ocean-bottom seismometer is also available for submarine volcanic observation and broadband seafloor observation to estimate deep seismic structures.

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.

Comparison of the S/N ratios of low-frequency hydrophones and geophones as a function of ocean depth

1981 ◽  
Vol 71 (5) ◽  
pp. 1649-1659
Author(s):  
Thomas M. Brocher ◽  
Brian T. Iwatake ◽  
Joseph F. Gettrust ◽  
George H. Sutton ◽  
L. Neil Frazer
Keyword(s):  
Nova Scotia ◽  
Continental Margin ◽  
Low Frequency ◽  
Weather Conditions ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Scotian Shelf ◽  
Ocean Bottom Seismometers ◽  
Particle Velocities ◽  
Refraction Data

abstract The pressures and particle velocities of sediment-borne signals were recorded over a 9-day period by an array of telemetered ocean-bottom seismometers positioned on the continental margin off Nova Scotia. The telemetered ocean-bottom seismometer packages, which appear to have been very well coupled to the sediments, contained three orthogonal geophones and a hydrophone. The bandwidth of all sensors was 1 to 30 Hz. Analysis of the refraction data shows that the vertical geophones have the best S/N ratio for the sediment-borne signals at all recording depths (67, 140, and 1301 m) and nearly all ranges. The S/N ratio increases with increasing sensor depth for equivalent weather conditions. Stoneley and Love waves detected on the Scotian shelf (67-m depth) are efficient modes for the propagation of noise.

Low‐frequency attenuation in the Pacific Ocean

1976 ◽  
Vol 59 (3) ◽  
pp. 700-702 ◽  
Author(s):  
R. H. Mellen ◽  
D. G. Browning
Keyword(s):  
Pacific Ocean ◽  
Low Frequency ◽  
The Pacific ◽  
The Pacific Ocean

scholarly journals Species Composition and New Records of Diatom Taxa on Phyllodictyon pulcherrimum (Chlorophyceae) from the Gulf of California

Diversity ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 339
Author(s):  
Francisco Omar López-Fuerte ◽  
David Alfaro Siqueiros Beltrones ◽  
María del Carmen Altamirano-Cerecedo
Keyword(s):  
Gulf Of California ◽  
New Records ◽  
American Continent ◽  
Epiphytic Diatoms ◽  
Taxonomic Analysis ◽  
The North ◽  
The Pacific ◽  
The Pacific Ocean ◽  
First Time ◽  
The North Pacific

A taxonomic analysis of diatoms found on Phyllodictyon pulcherrimum yielded a total of 244 diatom taxa (all illustrated) within 27 orders, 45 families, and 86 genera. The Taxa were briefly documented in a list including identification references and morphometric data. Thirty-eight of the taxa identified at the species and infraspecific levels represent new records for the coasts of Mexico. Seven were recorded for the first time on the American continent: Auricula flabelliformis, A. pulchra, Campylodiscus scalaris, Coscinodiscus mesoleius, Dimeregramma fulvum, Navicula palpebralis var. angulosa, and Seminavis barbarae, and one, Nitzschia fusiformis, for the Pacific Ocean. This is the second record of the chlorophyte P. pulcherrimum in the north Pacific and the third for Mexican waters. The results confirm that surveying rare macroalgae species as hosts for epiphytic diatoms provides opportunities to seek new records of diatom taxa, or even new taxa, in regions around the world.

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.

A new species ofTriptolemma(Porifera: Pachastrellidae) from the Pacific Ocean with a revision of the genus

2010 ◽  
Vol 91 (2) ◽  
pp. 329-338 ◽  
Author(s):  
Marco Bertolino ◽  
D. Pica ◽  
G. Bavestrello ◽  
N. Iwasaki ◽  
B. Calcinai
Keyword(s):  
New Species ◽  
Pacific Ocean ◽  
Chemical Dissolution ◽  
Typical Pattern ◽  
Etching Mechanism ◽  
The Pacific ◽  
The Pacific Ocean ◽  
First Time ◽  
A New Species ◽  
Thick Crust

A new species,T. strongylatasp. nov. is described on the basis of material collected from the Pacific Ocean. The new species is characterized by the presence of sinuous strongyles. Moreover the incomplete description ofT. simplex(Sarà, 1959) is implemented on the basis of new abundant material allowing, for the first time, the complete description of the skeleton of aTriptolemmaspecies and the detecting of the presence of monaxonic spicules in the spicular complement of the genus. The skeleton is composed of a thick crust of disorderly arranged mesotriaenes and scattered microscleres, supported by diverging spicule tracts formed by oxeas towards the surface. Both species were recorded associated to boring sponges(SpiroxyaandCliona)in excavations of the calcareous scleraxis of precious corals or in organogenic concretions. In the cavities where the tissue ofTriptolemmawas recorded the wall of the excavation partially lost its typical pattern characterized by ovoid scars and became irregularly eroded. Our hypothesis is thatTriptolemmainsinuates inside the erosions produced by other sponges and it is able to enlarge them by an etching mechanism based on chemical dissolution only.

RECORDS OF CYAMUS BALAENOPTERAE BARNARD AND NEOCYAMUS PHYSETERIS (POUCHET), TWO SPECIES OF WHALE-LICE (AMPHIPODA), FROM THE NORTHEAST PACIFIC

1959 ◽  
Vol 37 (6) ◽  
pp. 895-897 ◽  
Author(s):  
L. Margolis
Keyword(s):  
Pacific Ocean ◽  
First Record ◽  
Physeter Macrocephalus ◽  
Balaenoptera Acutorostrata ◽  
Northeast Pacific ◽  
The Pacific ◽  
The Pacific Ocean ◽  
First Time

Cyamus balaenopterae Barnard from Balaenoptera acutorostrata and Neocyamus physeteris (Pouchet) from Physeter macrocephalus are reported for the first time from the Pacific Ocean. This is the first record of a cyamid from B. acutorostrata.

Explorers' and Travelers' Narratives: A Peregrination Through Different Editions

2003 ◽  
Vol 30 ◽  
pp. 213-222 ◽  
Author(s):  
I.S. MacLaren
Keyword(s):  
Native People ◽  
James Cook ◽  
The Third ◽  
The Pacific ◽  
The Press ◽  
Field Notes ◽  
The Pacific Ocean ◽  
First Editions ◽  
First Time ◽  
George Iii

Researchers keen to examine the representation of native people in European accounts of exploration and travel need bring under review the mechanism by which field notes became books, and, once they were books, the multiplicity and diffusion of editions, often themselves quite different from one another. An example that illustrates well this need is British Royal Naval Captain James Cook's posthumously published account of his third voyage to the Pacific Ocean in the years 1776-80. The standard scholarly source is J.C. Beaglehole's monumental edition, The Journals of Captain James Cook on His Voyages of Discovery (1955-74), a twenty-year editing project for the Hakluyt Society, which made available for the first time Cook's own writings until his death at Kealakekua Bay, Sandwich Islands (Hawaii), on 14 February 1779, during the third voyage. However, the need for Beaglehole's project arose, according to the president of the Hakluyt Society, because the original publications differed very widely from Cook's own writings. They were “official” accounts, published by order of George III, and they performed that always interesting exercise—they “improved” on Cook's own writings. It is well known that Cook did not prepare his journals for the press: in the case of the first two voyages to the Pacific, this was his choice. In the case of the third, the choice was not his to make, he being five years deceased. How wide are those differences?In the case of Cook's description of a month-long mooring in Nootka Sound, on the west coast of Vancouver Island, do substantive differences occur between Cook's logs and journal and Bishop John Douglas' edition? Answering that question necessarily involves consulting first editions of the various published accounts.

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