On the prediction of low‐frequency geomagnetic pulsations for geophysical prospecting

Geophysics ◽  
1989 ◽  
Vol 54 (5) ◽  
pp. 635-642 ◽  
Author(s):  
Hing‐Lan Lam
Keyword(s):  
Background Noise ◽  
Low Frequency ◽  
Field Work ◽  
Magnetic Activity ◽  
Time Of Day ◽  
Virtual Absence ◽  
Long Period ◽  
The Earth ◽  
Short Period ◽  
Geomagnetic Soundings

Pulsations of the earth’s magnetic field due to solar‐terrestrial interaction are used for geomagnetic soundings to study conductive structures in the earth. However, the pulsations are also the unwanted background noise for magnetic exploration surveys. It is, therefore, desirable to conduct the sounding or survey work during geomagnetic conditions optimum for that particular undertaking. This paper relates the pulsational activity to a parameter (the DRX index) which characterizes the magnetic activity for each individual day and which is routinely forecast in Canada. By using the relations established in this study, it is possible to infer the future levels of pulsations from the forecast DRX, and a period of desired pulsational activity can thus be selected for the field work. In the course of a day, the afternoon is appropriate for conducting magnetic surveys because of a generally lower level of pulsational activity and a virtual absence of intense short‐period pulsations, while morning is optimal for carrying out induction soundings because of more intense pulsational activity and a tendency of enhanced long‐period pulsations to recur during that time of day.

Prediction of pressure-generated earth motion using optimum filters

1975 ◽  
Vol 65 (3) ◽  
pp. 637-650
Author(s):  
E. J. Douze ◽  
G. G. Sorrells
Keyword(s):  
Atmospheric Pressure ◽  
Acoustic Waves ◽  
Background Noise ◽  
Single Channel ◽  
Pressure Variation ◽  
Long Period ◽  
System A ◽  
The Earth ◽  
Multichannel Filtering ◽  
Time Trace

abstract The performance of long-period seismographs is often seriously degraded by atmospheric pressure variation; the problem is particularly severe at periods greater than 20 sec. The pressure variations associated with wind-generated turbulence and acoustic waves are sufficient to deform the surface of the Earth, thus adding to the background noise level recorded by the seismometer. If microbarographs are operated together with the seismograph system, a large percentage of the atmospherically generated noise can be eliminated by the use of optimum filters. The filters are designed based on the least-mean-squares criterion, with the seismograph time trace as the desired output and the microbarographs as the inputs. Single-channel filters, using only one microbarograph, located at the seismometer vault are used to attenuate wind-generated noise. In order to attenuate the noise on windless days from other pressure sources, multichannel filtering is usually necessary and therefore an array of microbarographs is required. The filters used to predict the wind-generated noise are shown to be stable despite the complicated source. The performance of the multichannel varies widely depending on the structure of pressure variations predominating in the atmosphere.

Definition and identification of seismic events in the USSR in 1971

1974 ◽  
Vol 64 (3-1) ◽  
pp. 607-636
Author(s):  
Ola Dahlman ◽  
Hans Israelson ◽  
Atle Austegard ◽  
Gunnel Hörnström
Keyword(s):  
Focal Depth ◽  
Seismic Monitoring ◽  
Seismic Events ◽  
Long Period ◽  
The Earth ◽  
Short Period ◽  
Complete Test ◽  
Period Data ◽  
Test Ban ◽  
Test Ban Treaty

abstract Seismic events reported to have occurred in the USSR in 1971 are studied to assess the seismic monitoring problem as it may occur in the context of a complete test-ban treaty. Available epicenter data of a total of 199 events, 180 earthquakes and 19 explosions, are presented. Focal depth estimates reported by the National Oceanic and Atmospheric Administration, U.S., and the Institute of Physics of the Earth, Moscow, are compared. Identification parameters determined using short- and long-period data from Hagfors Observatory and supplementary short-period data from the Yellowknife array station in Canada are presented. To study the combined operative efficiency and applicability of available identification parameters, the reported depth estimates and the identification data are assessed in a defined way.

scholarly journals Resonant absorption of Alfven Waves and the Associated Phenomenon of Magnetic Reconnection

1990 ◽  
Vol 142 ◽  
pp. 245-249
Author(s):  
C. Uberoi
Keyword(s):  
Surface Waves ◽  
Magnetic Reconnection ◽  
Low Frequency ◽  
Resonant Absorption ◽  
Magnetic Activity ◽  
Alfven Wave ◽  
Flux Transfer Events ◽  
Long Period ◽  
Magnetospheric Cusp ◽  
Zero Frequency

The mathematical analysis of the Alfven Wave equation in inhomogeneous magnetic fields which explain the resonance absorption of Alfven surface waves near a resonant layer can also be used to show that magnetic reconnection process can arise near the zero frequency resonant layer driven by very low frequency Alfven surface waves. The associated phenomena of resonant absorption and magnetic reconnection in inhomogeneous plasmas can explain the recent obsrevations of intense magnetic activity in the long period geomagnetic micropulsations range, at magnetospheric cusp latitudes, during the time of occurence of flux transfer events.

GEOMAGNETIC MICROPULSATION RESULTS FROM BYRD STATION AND GREAT WHALE RIVER

1965 ◽  
Vol 43 (12) ◽  
pp. 2099-2122 ◽  
Author(s):  
J. A. Jacobs ◽  
C. S. Wright
Keyword(s):  
High Frequency ◽  
Preliminary Report ◽  
Magnetic Activity ◽  
Reasonable Accuracy ◽  
Long Period ◽  
Ground Station ◽  
The Earth ◽  
Abrupt Changes ◽  
The Magnetic Field ◽  
Phase Differences

Early reports from the near-conjugate stations at Great Whale River and Byrd Station were based on the scanty data available in early 1961 (Lokken et al., Martin et al. 1961). The increased volume of data seems now to justify another preliminary report, in which the chief emphasis is on the time-agreement of the abrupt commencements of the numerous examples of Birkeland's "Polar Elementary Storms". Passing reference only is made to the associations at Byrd between VLF hiss and other ionospheric phenomena that are being reported by Stanford University. In the auroral zones, the magnetic activity is usually so great, even during the IQSY, that magnetograms can be employed usefully to supplement the micropulsation records. Using selected nighttime occasions, when the change in H is so sudden that a reasonable accuracy in the timing of the micropulsations can be achieved, it is found that the time differences between the two conjugate stations average ± 1 minute, although there is clear evidence that the two stations are not conjugate at all times, as evidenced by the lack of similarity of records. It is confirmed that the more abrupt changes in the magnetic field are associated with high-frequency "riders" of the order of 1 c.p.s., and that these events are often seen with the same riders at the same time at our mid-latitude stations. The return currents that show up in these lower latitudes must be taken into consideration when the areas of conjugate station agreement are considered. The daytime regime of regular (Pc) variations did not lend itself to accurate time comparison, except for very long-period oscillations at the two stations, when the maximum excursions were so far apart in time that one could reasonably assume that the indicated phase differences on the records at the two stations were correct. On this assumption, the long-period oscillations are nearly coincident at the two stations. This may usually be true for the shorter-period oscillations also, but, in many cases, considerable phase differences do exist. These, however, may be due partly to differences in the electronic equipment.The general course of the geomagnetic diurnal variation at Byrd is shown, but these data may apply only to the two auroral conjugate stations and to periods of low solar activity.Up to the present time, only two cases of coincident satellite and ground station abrupt commencements have been observed. These were detected readily only by our mid-latitude stations, possibly because the two events occurred when these stations were on the side of the earth facing the solar wind. It is possible that nighttime coincidences will appear chiefly at the two auroral stations.

scholarly journals Elastic and Viscoelastic Models of Crust Deformation in Strike-slip Fault

2021 ◽  
Vol 873 (1) ◽  
pp. 012097
Author(s):  
Maulidia Ain Bening ◽  
David P. Sahara ◽  
Dian Kusumawati ◽  
Wahyu Triyoso ◽  
Sri Widiyantoro ◽  
...  
Keyword(s):  
Strike Slip ◽  
Strike Slip Fault ◽  
Earth’S Crust ◽  
Actual State ◽  
Elastic Materials ◽  
Crust And Upper Mantle ◽  
Long Period ◽  
The Earth ◽  
Short Period ◽  
Earth's Crust

Abstract The crust, when viewed over a long period, moves towards one another. Crusts might experience sudden slip on a fault plane and caused fractures or cracks. There are three different types of faults, normal, reverse, and strike-slip faults. Induced stress due to sudden rupture on fault planes capable of creating stress and need to be measured quantitatively to comprehend the earthquake process. To understand the stress that occurs in strike-slip faults in the earth’s crust, the previous researchers study the use of elastic materials as the material of the earth’s crust, so that the earth crust’s deformation is elastic. However, elastic material has linear stress and strain relationship that results in reversible deformations or returns to their original shape. This material is not suitable for modeling the earth’s crust’s long-term deformation, where the deformation of the earth’s crust can be permanent, so a model is needed to solve this problem. In this study, we will compare the stress in the strike-slip fault in the upper crust with elastic materials, while the lower crust and upper mantle have viscoelastic materials compared to purely elastic materials through numerical simulations. This comparison is made to see the comparison between the two approaches with the earth’s layers’ actual state. The two models is chosen to represent the different failure processes of the earth crust, i.e. the elastic deformation part describes the response to stress in a short period, and the viscous deformation can explain the response over a more extended period. The study of both materials above is based on plate tectonic theory, in which the lithosphere plates will relatively move to each other because the layer material underneath is solid but can flow like a liquid for a long period.

Characterization of global seismograms using an automatic-picking algorithm

1994 ◽  
Vol 84 (2) ◽  
pp. 366-376
Author(s):  
Paul S. Earle ◽  
Peter M. Shearer
Keyword(s):  
Travel Time ◽  
Upper Mantle ◽  
Low Frequency ◽  
Travel Times ◽  
Comparable Amount ◽  
Arrival Times ◽  
Long Period ◽  
Automatic Phase ◽  
Short Period ◽  
Sample Rate

Abstract An automatic phase picker is useful for quickly identifying and timing phase arrivals in large seismic data bases. We have developed an automatic phase picker that is sensitive to small changes in amplitude and applied it to over 7 yr of global data distributed by the National Earthquake Information Center (NEIC). Our phase-picking algorithm is based on a short-term-average to long-term-average ratio (STA/LTA) taken along an envelope function generated from the seismogram. The algorithm returns arrival times and corresponding pick qualities. The procedure requires few input parameters and is easily adapted to various types of data. We produce global travel-time plots from both high-frequency (20- or 40-Hz sample rate) and low-frequency (1-Hz sample rate) data. These plots clearly image the predominant high- and low-frequency phases in the NEIC data base. Picks made from the long-period seismograms are less precise, but they reveal far more phase arrivals than the short-period picks. A number of phases resulting from reflections and phase conversions at upper mantle discontinuities can be identified in the low-frequency picks; however, a search of the short-period picks for upper mantle discontinuity phases, between P and PP and prior to P′P′, has so far been unsuccessful. In the long-period S and SS picks, we observe a discrepancy in SV and SH travel times, a possible result of upper mantle anisotropy. To check the accuracy and consistency of our algorithm, we present comparisons between hand-picked times and automatic-picked times for identical seismograms. Travel-time residuals from the short-period automatic picks and data reported to the International Seismological Centre (ISC) picks exhibit a comparable amount of scatter. Histograms of the ISC residuals and automatic-pick residuals are similar in shape and width for P and PcP. These observations suggest that human picking errors are not a major contributor to the scatter observed in ISC travel times, although direct comparisons between ISC reported picks and automatic picks on particular seismograms occasionally identify operator mispicks.

The Origin of the Moon and its Relationship to the Origin of the Solar System

1962 ◽  
Vol 14 ◽  
pp. 133-148 ◽  
Author(s):  
Harold C. Urey
Keyword(s):  
Solar System ◽  
The Moon ◽  
The Past ◽  
The Earth ◽  
Short Period ◽  
Origin Of The Moon

During the last 10 years, the writer has presented evidence indicating that the Moon was captured by the Earth and that the large collisions with its surface occurred within a surprisingly short period of time. These observations have been a continuous preoccupation during the past years and some explanation that seemed physically possible and reasonably probable has been sought.

Discussion following the presentation by F. Deubner

1977 ◽  
Vol 36 ◽  
pp. 69-74
Keyword(s):  
List Type ◽  
The Sun ◽  
Type Number ◽  
Harmonic Motion ◽  
Locally Excited ◽  
Long Period ◽  
Coherent Wave ◽  
Short Period ◽  
Global Modes

The discussion was separated into 3 different topics according to the separation made by the reviewer between the different periods of waves observed in the sun :1) global modes (long period oscillations) with predominantly radial harmonic motion.2) modes with large coherent - wave systems but not necessarily global excitation (300 s oscillation).3) locally excited - short period waves.

scholarly journals Isolation and Analysis of Six timeless Alleles That Cause Short- or Long-Period Circadian Rhythms in Drosophila

Genetics ◽  
2000 ◽  
Vol 156 (2) ◽  
pp. 665-675
Author(s):  
Adrian Rothenfluh ◽  
Marla Abodeely ◽  
Jeffrey L Price ◽  
Michael W Young
Keyword(s):  
Nuclear Translocation ◽  
Phase Response Curve ◽  
Fixed Number ◽  
Constant Darkness ◽  
Genetic Screens ◽  
Protein Levels ◽  
Long Period ◽  
Short Period ◽  
Molecular Oscillation ◽  
New Alleles

Abstract In genetic screens for Drosophila mutations affecting circadian locomotion rhythms, we have isolated six new alleles of the timeless (tim) gene. Two of these mutations cause short-period rhythms of 21–22 hr in constant darkness, and four result in long-period cycles of 26–28 hr. All alleles are semidominant. Studies of the genetic interactions of some of the tim alleles with period-altering period (per) mutations indicate that these interactions are close to multiplicative; a given allele changes the period length of the genetic background by a fixed percentage, rather than by a fixed number of hours. The timL1 allele was studied in molecular detail. The long behavioral period of timL1 is reflected in a lengthened molecular oscillation of per and tim RNA and protein levels. The lengthened period is partly caused by delayed nuclear translocation of TIML1 protein, shown directly by immunocytochemistry and indirectly by an analysis of the phase response curve of timL1 flies.

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