scholarly journals Earthquake seismology in Greenland – improved data with multiple applications

2006 ◽  
Vol 10 ◽  
pp. 57-60 ◽  
Author(s):  
Tine B. Larsen ◽  
Trine Dahl-Jensen ◽  
Peter Voss ◽  
Thomas Møller Jørgensen ◽  
Søren Gregersen ◽  
...  
Keyword(s):  
Continental Shelf ◽  
High Frequency ◽  
Regional Scale ◽  
Broad Band ◽  
Low Frequency ◽  
Low Frequency Oscillations ◽  
The Earth ◽  
New Information ◽  
Seismological Observatory ◽  
Earthquake Seismology

Earthquake seismology is a rapidly evolving field that has provided a wealth of new information about deep geological structures on a regional scale over the last decade as well as information about dynamic processes in the Earth. A major leap forward was the development of portable digital broad band (BB) seismographs around 1990. Without any changes in configuration, these are able to record the signals from large distant earthquakes, as well as the signals from weak local events. BB seismographs typically cover a frequency range from 0.0083 Hz to 50 Hz, making them useful for studies ranging from the high frequency signals from explosions to the very low frequency oscillations following major earthquakes. The first seismological observatory in Greenland was established in 1907 in Qeqertarsuaq (GDH) and was in service for about five years (Hjelme 1996). Later, seismographs were established in Ivittut (1927) and Illoqqortoormiut (1928; SCO), and the network has been regularly upgraded and expanded ever since (Fig. 1). Prior to the development of BB seismographs, each station was equipped with a set of seismographs with different frequency sensitivities in an attempt to cover both distant and local earthquakes. Now just one small instrument is needed at each location. The Geological Survey of Denmark and Greenland (GEUS) operates four permanent BB seismographs in Greenland (Fig. 1), two of them in collaboration with foreign institutions. In addition to the permanent network, there are currently 13 temporary BB seismographs active in Greenland, of which eight are operated by GEUS. Three of the temporary seismograph stations were established as part of the Danish Continental Shelf Project (Marcussen et al. 2004), and the remainder in connection with research projects. Three temporary seismographs were deployed during 2005 as part of a research project aiming to resolve very deep regional structures in North Greenland: the Citronen Fjord station (CFJ, Continental Shelf Project), and the stations in Kullorsuaq (KUL) and Daneborg (DBG).

Nonrandom variability in respiratory cycle parameters of humans during stage 2 sleep

1990 ◽  
Vol 69 (2) ◽  
pp. 630-639 ◽  
Author(s):  
M. Modarreszadeh ◽  
E. N. Bruce ◽  
B. Gothe
Keyword(s):  
High Frequency ◽  
Minute Ventilation ◽  
Power Spectra ◽  
Low Frequency ◽  
Neural Mechanism ◽  
Normal Subjects ◽  
Feedback Loops ◽  
Low Frequency Oscillations ◽  
Stage 2 Sleep ◽  
Correlated Components

We analyzed breath-to-breath inspiratory time (TI), expiratory time (TE), inspiratory volume (VI), and minute ventilation (Vm) from 11 normal subjects during stage 2 sleep. The analysis consisted of 1) fitting first- and second-order autoregressive models (AR1 and AR2) and 2) obtaining the power spectra of the data by fast-Fourier transform. For the AR2 model, the only coefficients that were statistically different from zero were the average alpha 1 (a1) for TI, VI, and Vm (a1 = 0.19, 0.29, and 0.15, respectively). However, the power spectra of all parameters often exhibited peaks at low frequency (less than 0.2 cycles/breath) and/or at high frequency (greater than 0.2 cycles/breath), indicative of periodic oscillations. After accounting for the corrupting effects of added oscillations on the a1 estimates, we conclude that 1) breath-to-breath fluctuations of VI, and to a lesser extent TI and Vm, exhibit a first-order autoregressive structure such that fluctuations of each breath are positively correlated with those of immediately preceding breaths and 2) the correlated components of variability in TE are mostly due to discrete high- and/or low-frequency oscillations with no underlying autoregressive structure. We propose that the autoregressive structure of VI, TI, and Vm during spontaneous breathing in stage 2 sleep may reflect either a central neural mechanism or the effects of noise in respiratory chemical feedback loops; the presence of low-frequency oscillations, seen more often in Vm, suggests possible instability in the chemical feedback loops. Mechanisms of high-frequency periodicities, seen more often in TE, are unknown.

Oscillations in a Collapsed-Tube Analog of the Brachial Artery Under a Sphygmomanometer Cuff

1989 ◽  
Vol 111 (3) ◽  
pp. 185-191 ◽  
Author(s):  
C. D. Bertram ◽  
C. J. Raymond ◽  
K. S. A. Butcher
Keyword(s):  
High Frequency ◽  
Flow Characteristics ◽  
Low Frequency ◽  
Collapsible Tube ◽  
Tube Size ◽  
Low Frequency Oscillations ◽  
Central Segment ◽  
Experimental Parameters ◽  
Aqueous Flow ◽  
Low Frequency Mode

To determine whether self-excited oscillations in a Starling resistor are relevant to physiological situations, a collapsible tube conveying an aqueous flow was externally pressurized along only a central segment of its unsupported length. This was achieved by passing the tube through a shorter and wider collapsible sleeve which was mounted in Starling resistor fashion in a pressure chamber. The tube size and material, and all other experimental parameters, were as used in our previous Starling resistor studies. Both low- and high-frequency self-excited oscillations were observed, but the low-frequency oscillations were sensitive to the sleeve type and length relative to unsupported distance. Pressure-flow characteristics showed multiple oscillatory modes, which differed quantitatively from those observed in comparable Starling resistors. Slow variation of driving pressure gave differing behavior according to whether the pressure was rising or falling, in accord with the hysteresis noted on the characteristics and in the tube law. The results are discussed in terms of the various possible mechanisms of collapsible tube instability, and reasons are presented for the absence of the low-frequency mode under most physiological circumstances.

Interaction between High Frequency Oscillations and Low Frequency Oscillations in Beam-Plasma System

1967 ◽  
Vol 23 (6) ◽  
pp. 1430-1431 ◽  
Author(s):  
Takaya Kawabe ◽  
Yoshinobu Kawai ◽  
Kazuo Takayama ◽  
Shoji Kojima
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Plasma System ◽  
High Frequency Oscillations ◽  
Low Frequency Oscillations ◽  
Beam Plasma

scholarly journals Influence of the Solid Inner Core and Compressibility of the Fluid Core on the Earth Nutation

1991 ◽  
Vol 127 ◽  
pp. 250-253
Author(s):  
Sergei Diakonov
Keyword(s):  
Infinite System ◽  
Inner Core ◽  
Equations Of Motion ◽  
Liquid Core ◽  
Low Frequency ◽  
Approximate Solutions ◽  
Low Frequency Oscillations ◽  
The Earth ◽  
Fluid Core ◽  
Harmonic Representation

While calculating low frequency oscillations of the Earth liquid core spherical harmonic representation of the deformation field is usually used [1-3]:Substitution of (1) into the equations of motion gives an infinite system of differential equations for scalar functions Sɭm and Tɭm . Approximate solutions of such a system are obtained by truncating of the system. But results of [4] show that sometimes such method divergences.

Observation of Turbulent Waves in a Helium Plasma by Optical Spectroscopy

1975 ◽  
Vol 30 (10) ◽  
pp. 1271-1278
Author(s):  
W. R. Rutgers
Keyword(s):  
Energy Density ◽  
Field Strength ◽  
High Frequency ◽  
Low Frequency ◽  
Turbulent Plasma ◽  
Helium Plasma ◽  
High Frequency Oscillations ◽  
Low Frequency Oscillations ◽  
Frequency Domains ◽  
Turbulent Heating

Abstract From the combined Stark-Zeeman pattern of helium allowed and forbidden optical lines the frequency spectrum, the field strength and the dominant polarization of microfields were determined in a turbulent plasma. Two frequency domains of oscillations were found in a turbulent heating experiment: low-frequency oscillations with dominant polarization perpendicular to the current direction and high-frequency oscillations (f~fpe) with random polarization. The r.m.s. field strength of the oscillations is between 2 kV/cm and 10 kV/cm. The energy density of turbulent microfields amounts to 1‰ of the thermal energy density.

High-Frequency and Low-Frequency Oscillations in a Plasma in a Magnetic Field

1966 ◽  
Vol 21 (11) ◽  
pp. 2421-2421
Author(s):  
Kiyoe Kato ◽  
Takaya Kawabe ◽  
Mikiko Koganei ◽  
Eiich Kawasaki
Keyword(s):  
Magnetic Field ◽  
High Frequency ◽  
Low Frequency ◽  
Low Frequency Oscillations

Monitoring Seismicity on Mars - the Marsquake Service for InSight

2020 ◽  
Author(s):  
John Clinton ◽  
Domenico Giardini ◽  
Savas Ceylan ◽  
Martin van Driel ◽  
Simon Stähler ◽  
...  
Keyword(s):  
High Frequency ◽  
Body Wave ◽  
A Priori ◽  
Broad Band ◽  
Low Frequency ◽  
Ambient Vibration ◽  
Crustal Layer ◽  
Seismic Waveforms ◽  
Seismic Vibrations ◽  
Back Azimuth

<p>InSight landed on Mars in late November 2018, and the SEIS seismometer package was fully deployed by February 2019. By January 2020, SEIS continues to exceed performance expectations in terms of observed minimum noise. The Marsquake Service (MQS) has been setup to create and curate a seismicity catalogue for Mars over the lifetime of the InSight mission. Seismic waveforms are downloaded daily from the station and are analysed and processed by the MarsQuake Service, with the goal of detecting seismic vibrations not due to local ambient sources. To this end, every precaution is applied to eliminate possible non-seismic sources, such as noise induced by atmospheric phenomena, lander vibrations and orbiter activity. At the date of submission, we have detected 365 events, of different quality and SNR levels. Signal amplitudes remain small and signal can generally only be detected at night. Some events show only low-frequency waves in the 1-10 sec band, others have a high-frequency content up to several Hz, and others have a more broad-band character. A special class of events involves the excitation of a very prominent ambient vibration at 2.4Hz. Despite the scattered nature of the energy, in many cases, distinct phases can be inferred in the waveforms. Body wave character, and back-azimuth, can only be confirmed for 3 broadband events so far.  The MQS approach for determining distances from broadband events identifies phases as mantle P and S-phases and uses an a priori set of several thousand martian models, derived from geophysical, mineralogical and orbital constraints. High frequency events are currently located assuming phases are trapped crustal Pg and Sg and using a simple crustal layer. The MQS works in conjunction with the Mars Structural Service (MSS) on building and adopting updated models. The MQS consists of an international team of seismologists that screen incoming data to identify and characterise any seismicity. In this presentation, we present the MQS, demonstrate how we detect and characterise marsquakes, and describe the challenges we face dealing with the Martian dataset.</p>

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