scholarly journals The nature of Earth's correlation wavefield: late coda of large earthquakes

2018 ◽  
Vol 474 (2214) ◽  
pp. 20180082 ◽  
Author(s):  
B. L. N. Kennett ◽  
Thanh-Son Pham
Keyword(s):  
Travelling Waves ◽  
Synthetic Seismograms ◽  
Time Behaviour ◽  
Similar Time ◽  
Period Range ◽  
Correlation Field ◽  
The Earth ◽  
Time Distance ◽  
Seismic Wavefield ◽  
Large Earthquakes

The seismic correlation wavefield constructed from the stacked cross-correlograms of the late coda of earthquake signals at stations across the globe provides a wealth of observed pulses as a function of inter-station distance. The interval from 3 to 10 h after the onset of major earthquakes is employed for the period range from 15 to 50 s. The observations can be well matched by synthetic seismograms for a radially stratified Earth. Many of the correlation phases have similar time behaviour to those in the regular wavefield, but others have no correspondence. All such correlation phases can be explained by the interaction of arrivals with a common slowness at the each of the stations being correlated. Using a generalized ray description of the seismic wavefield, the time-distance behaviour of these correlation phases arises from differences in accumulated phase on different propagation paths through the Earth. Distinct arrivals emerge from the correlation field when there are many ways in which combinations of seismic phases can arise with the same difference in propagation legs. The constituents of the late coda are dominated by steeply travelling waves, and in consequence features associated with multiple passages through the whole Earth emerge distinctly, such as high-order multiples of PKIKP .

scholarly journals Observation evidences of atmospheric Gravity Waves induced by seismic activity from analysis of subionospheric LF signal spectra

2007 ◽  
Vol 7 (5) ◽  
pp. 625-628 ◽  
Author(s):  
A. Rozhnoi ◽  
M. Solovieva ◽  
O. Molchanov ◽  
P.-F. Biagi ◽  
M. Hayakawa
Keyword(s):  
Gravity Waves ◽  
Fresnel Zone ◽  
Signal Amplitude ◽  
Magnetic Storms ◽  
Frequency Range ◽  
Atmospheric Gravity Waves ◽  
Period Range ◽  
Before And After ◽  
Atmospheric Gravity ◽  
Large Earthquakes

Abstract. We analyze variations of the LF subionospheric signal amplitude and phase from JJY transmitter in Japan (F=40 kHz) received in Petropavlovsk-Kamchatsky station during seismically quiet and active periods including also periods of magnetic storms. After 20 s averaging, the frequency range of the analysis is 0.28–15 mHz that corresponds to the period range from 1 to 60 min. Changes in spectra of the LF signal perturbations are found several days before and after three large earthquakes, which happened in November 2004 (M=7.1), August 2005 (M=7.2) and November 2006 (M=8.2) inside the Fresnel zone of the Japan-Kamchatka wavepath. Comparing the perturbed and background spectra we have found the evident increase in spectral range 10–25 min that is in the compliance with theoretical estimations on lithosphere-ionosphere coupling by the Atmospheric Gravity Waves (T>6 min). Similar changes are not found for the periods of magnetic storms.

scholarly journals The effect of earthquakes on the ERP during 1977–1985

1988 ◽  
Vol 128 ◽  
pp. 399-404 ◽  
Author(s):  
Richard S. Gross
Keyword(s):  
Earth Rotation ◽  
The Earth ◽  
Time Period ◽  
Earth Rotation Parameters ◽  
Rotation Parameters ◽  
Large Earthquakes

The effect on the Earth Rotation Parameters (ERP) of all the large earthquakes that occurred during 1977–1985 is evaluated. It is found that they cannot have caused the variations observed in the ERP during this time period.

scholarly journals Connection of large earthquakes occurring moment with the movement of the Sun and the Moon and with the Earth crust tectonic stress character

2010 ◽  
Vol 10 (7) ◽  
pp. 1629-1633 ◽  
Author(s):  
M. K. Kachakhidze ◽  
R. Kiladze ◽  
N. Kachakhidze ◽  
V. Kukhianidze ◽  
G. Ramishvili
Keyword(s):  
Tectonic Stress ◽  
Point Of View ◽  
The Sun ◽  
Compression Stress ◽  
The Moon ◽  
Caucasus Region ◽  
The Earth ◽  
Triggering Factor ◽  
Exogenous Factors ◽  
Large Earthquakes

Abstract. It is acceptable that earthquakes certain exogenous (cosmic) triggering factors may exist in every seismoactive (s/a) region and in Caucasus among them. They have to correct earthquake occurring moment or play the triggering role in case when the region is at the limit of the critical value of the geological medium of course. Our aim is to reveal some exogenous factors possible to initiate earthquakes, on example of Caucasus s/a region, taking into account that the region is very complex by the point of view of the tectonic stress distribution. The compression stress directed from North to South (and vice versa) and the spread stress directed from East to West (and vice versa) are the main stresses acted in Caucasus region. No doubt that action of the smallest external stress may "work" as earthquakes triggering factor. In the presented work the Moon and the Sun perturbations are revealed as initiative agents of earthquakes when the directions of corresponding exogenous forces coincide with the directions of the compression stress or the spreading tectonic stress in the region.

scholarly journals Note on the electrical waves occurring in nature

1911 ◽  
Vol 85 (576) ◽  
pp. 145-150 ◽  
Keyword(s):  
Solitary Wave ◽  
Travelling Waves ◽  
Lightning Discharge ◽  
Considerable Proportion ◽  
Transient Currents ◽  
Electrical Field ◽  
Natural Period ◽  
Electric Wave ◽  
General Properties ◽  
The Earth

It has often been pointed out that whenever a lightning discharge occurs between a cloud and the earth, or between two charged clouds, it must give rise to a violent disturbance of the local electrical field, which will spread outwards as an electric wave from the region of the discharge. A lightning discharge may be aperiodic or oscillatory; accordingly a solitary wave or a train of waves, as the case may be, travels in all directions from the centre of discharge till its energy is dissipated by divergence into space or by the absorption of the atmosphere, and thus the disturbance may reach great distances. In wireless telegraphy these vagrant waves are a source of great trouble to the telegraph operator. Being often very intense pulses or trains they frequently set the receiving autenna, whatever its natural period may be, into more violent vibration than do the signals being listened for, and not infrequently they compel the complete suspension of traffic. By those engaged in wireless telegraphy, all these and similar disturbances are called, variously, “atmospherics,” “strays,” “statics,” or “X’s.” When the usual telephonic method of receiving the Morse dots and dashes is employed, the strays are heard in the telephone as sharp clicks, as rattling noises, or as prolonged grinding or fizzing sounds. There is no doubt that some of these noises are due to other causes than vagrant waves. For example, it is well known that wind-driven hail, snow, or rain, produce in an earthed antenna transient currents that can affect the resonant circuits and the telephone of the receiving apparatus, and other very local causes are conceivable. But the travelling waves mentioned above, it has sometimes been surmised, form a considerable proportion of the strays heard on any occasion. It is the purpose of the observations described below to settle whether the proportion of strays due to vagrant waves of distant origin is indeed of importance. If it is, then the general properties of these waves, the limits of distance through which they can travel, and their meteorological significance (if any), all seem worthy of investigation. The particular point we are here enquiring into does not seem to have been investigated before. The sum total of the work published on the whole subject is very small, and no investigations specially directed towards the discrimination of the various causes are known to us.

scholarly journals Spheroidal free periods of the earth observed at eight stations around the world

1964 ◽  
Vol 54 (2) ◽  
pp. 755-776
Author(s):  
L. E. Alsop
Keyword(s):  
Phase Velocity ◽  
Rayleigh Waves ◽  
Vertical Motion ◽  
Present Theory ◽  
Period Range ◽  
Moving Source ◽  
The Earth ◽  
Spectral Peaks ◽  
The World ◽  
Different Parts

ABSTRACT Spectral peaks corresponding to the spheroidal free periods of oscillation of the earth exist in the spectra of eight seismograms written at stations in different parts of the world shortly after the great Chilean earthquake of 22 May 1960. These data have been combined with those previously reported by various authors to obtain a very precise phase velocity vs period curve for Rayleigh waves in the period range of 200 to 3200 seconds. The observed spectral amplitudes lend some support to the assumption of a moving source, but they also indicate that the present theory is not adequate. The vertical motion is found to be symmetric with respect to reflections through the pole.

scholarly journals A Review on the Mechanism of Reservoir-Induced Seismicity for Nepalese Context

2020 ◽  
Vol 19 (1) ◽  
pp. 215-221
Author(s):  
Umesh Raj Joshi ◽  
Ramesh Kumar Maskey ◽  
Kumud Raj Kafle
Keyword(s):  
Active Zone ◽  
Induced Seismicity ◽  
Seismic Events ◽  
Reservoir Induced Seismicity ◽  
The Earth ◽  
Richter Scale ◽  
Active Zones ◽  
Large Earthquakes ◽  
Storage Type ◽  
Tectonic Movements

 Over 90 cases of Reservoir Induced Seismicity have been recorded around the earth. The magnitude was varying from 3.0 to 6.3 on the Richter scale. A Reservoir Induced Seismicity (RIS) can increase the frequency of earthquakes in seismically active zones and cause a shock in seismically inactive zones. Nepal is situated in a seismically active zone with six large earthquakes of magnitude equal to or greater than 7.6. It increases the risk of RIS, while several storage-type hydropower projects are being proposed in Nepal. Seismic activities recorded around the Kulekhani-I reservoir could be a reservoir induced seismicity. However, consistent data of seismic events and reservoir levels during all phases of filling or drawing of water level is missing. This paper reviews the researches on seismic activities caused by reservoirs or tectonic movements, and the need for the study on the mechanism of RIS for the Nepalese context is identified.

Microseisms in the 11- to 18-second period range

1957 ◽  
Vol 47 (2) ◽  
pp. 111-127
Author(s):  
Jack Oliver ◽  
Maurice Ewing
Keyword(s):  
Deep Water ◽  
Littoral Zone ◽  
Vertical Component ◽  
Time Correlation ◽  
Period Range ◽  
The Earth ◽  
Seismograph Station ◽  
The Waves ◽  
Second Period ◽  
Wave Recorder

Abstract Storm microseisms in the 11- to 18-second period range recorded at Palisades and Bermuda are attributed to ocean swell of identical periods in the vicinity of the seacoast near the seismograph station. Evidence is based on travel time, correlation with wave-recorder data, and dispersion of the waves from hurricane Dolly, which remained in deep water when near the Palisades station and passed at a speed greater than the group velocity of ocean swell. Ground-particle motion is longitudinal, with little or no vertical component. With some qualifications, the results agree with the classical surf theory of microseism generation. Certainly, the energy is transferred to the earth within the littoral zone.

scholarly journals Identifying Optimal Intensity Measures for Predicting Damage Potential of Mainshock–Aftershock Sequences

2020 ◽  
Vol 10 (19) ◽  
pp. 6795
Author(s):  
Zhou Zhou ◽  
Xiaohui Yu ◽  
Dagang Lu
Keyword(s):  
Structural Damage ◽  
Damage Index ◽  
Damage Potential ◽  
Earthquake Intensity ◽  
Period Range ◽  
Intensity Measures ◽  
Aftershock Sequences ◽  
Optimal Intensity ◽  
Reasonable Prediction ◽  
Large Earthquakes

Large earthquakes are followed by a sequence of aftershocks. Therefore, a reasonable prediction of damage potential caused by mainshock (MS)–aftershock (AS) sequences is important in seismic risk assessment. This paper comprehensively examines the interdependence between earthquake intensity measures (IMs) and structural damage under MS–AS sequences to identify optimal IMs for predicting the MS–AS damage potential. To do this, four categories of IMs are considered to represent the characteristics of a specific MS–AS sequence, including mainshock IMs, aftershock IMs (i.e., IMMS and IMAS, respectively), and two newly proposed IMs through taking an entire MS–AS sequence as one nominal ground motion (i.e., IM1MS–AS), or determining the ratio of IMAS to IMMS (i.e., IM2MS–AS), respectively. The single-degree-of-freedom systems with varying hysteretic behaviors are subjected to 662 real MS–AS sequences to estimate structural damage in terms the Park–Ang damage index. The intensities in terms of IMMS, IMAS, and IM1MS–AS are correlated with the accumulative damage of structures (i.e., DI1MS–AS). Moreover, the ratio (i.e., DI2MS–AS) of the AS-induced damage increment to the MS-induced damage is related to IM2MS–AS. The results show that IM2MS–AS exhibits significantly better performance than IMMS, IMAS, and IM1MS–AS for predicting the MS–AS damage potential, due to its high interdependence with DI2MS–AS. Among the considered 22 classic IMs, Arias intensity, root-square velocity, and peak ground displacement are respectively the optimal acceleration-, velocity-, and displacement-related IMs to formulate IM2MS–AS. Finally, two empirical equations are proposed to predict the correlations between IM2MS–AS and DI2MS–AS in the entire structural period range.

A Discussion on the measurement and interpretation of changes of strain in the Earth - A discussion on the measurement and interpretation of changes of strain in the Earth

1973 ◽  
Vol 274 (1239) ◽  
pp. 183-184 ◽  
Keyword(s):  
Elastic Properties ◽  
Elastic Moduli ◽  
Free Oscillations ◽  
Precise Information ◽  
Tidal Forces ◽  
The Earth ◽  
Large Earthquakes ◽  
New Instruments

It was at the beginning of the century that A. A. Michelson first used interferometric methods to measure the tilting of the ground due to tidal forces but for many years few more observations were made, and those few added little to Michelson’s results. Subsequently new instruments were devised to measure tilting of the ground, the variation of gravity due to tides and horizontal components of strain, but until some twelve years ago attention was concentrated on the effects of tides and few observations were made. It is indeed now clear that observations of the response of the Earth to the tide-raising potential are unlikely to tell us anything significant about the bulk elastic properties of the Earth, although at one time it seemed that they could contribute to that end. The change in emphasis may be traced to the first observations of the free oscillations of the Earth excited by the shocks of large earthquakes and detected by tilt meters, gravity meters and strain guages. The periods of the free oscillations are much higher than the tidal periods; a large number can be estimated and they now provide rather precise information about the density and elastic moduli within the Earth. The first instruments were not sensitive enough to detect oscillations excited by any but the quite rare very large earthquakes, but recently more sensitive horizontal and vertical accelerometers have been constructed and observations have been obtained of oscillations excited by smaller and more numerous shocks, so that a broad flow of data may be expected in future.

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