Crustal structure of the peninsular shield beneath Hyderabad (India) from the spectral characteristics of long-period P-waves

1978 ◽  
Vol 51 (3-4) ◽  
pp. 127-137 ◽  
Author(s):  
D.D. Singh ◽  
B.K. Rastogi
Keyword(s):  
Crustal Structure ◽  
Spectral Characteristics ◽  
P Waves ◽  
Long Period ◽  
Peninsular Shield

Observation of gliding tremors from the Gulf of Guinea might help solve over 50 year old mystery

2021 ◽  
Author(s):  
Charlotte Bruland ◽  
Sarah Mader ◽  
Céline Hadziioannou
Keyword(s):  
Spectral Analysis ◽  
Volcanic Activity ◽  
Rayleigh Waves ◽  
Spectral Characteristics ◽  
Gulf Of Guinea ◽  
Seismic Amplitude ◽  
Long Period ◽  
Amplitude Spectra ◽  
Using Data ◽  
Over Time

<p>In the 1960's a peak in the seismic amplitude spectra around 26 s was discovered and detected on stations worldwide. The source was located in the Gulf of Guinea, with approximate coordinates (0,0), and was believed to be generated continuously. A source with similar spectral characteristics was discovered near the Vanuatu Islands, at nearly the antipodal location of the Gulf of Guinea source. Since it was located close to the volcanoes in Vanuatu, this source is commonly attributed to magmatic processes. The physical cause of the 26 s microseism, however, remains unclear.</p><p>We investigate the source location and evolution of the 26 s microseim using data from permanent broadband stations in Germany, France and Algeria and temporary arrays in Morocco, Cameroon and Botswana for spectral analysis and 3-C beamforming to get closer to resolving the source mechanism responsible for this enigmatic signal. We find that the signal modulates over time and is not always detectable, but occasionally it becomes so energetic it can be observed on stations worldwide. Such a burst can last for hours or days. The signal is visible on stations globally approximately 30 percent of the time. Our beamforming analysis confirms that the source is located in the Gulf of Guinea, as shown in previous studies, and that the location is temporally stable. Whenever the signal is detectable, both Love and Rayleigh waves are generated. We discover a spectral glide effect associated with the bursts, that so far has not been reported in the literature. </p><p>The spectral glides last for about two days and are observed on stations globally. Although at higher frequencies, very long period tremors and gliding tremors are also observed on volcanoes as Redoubt in Alaska and Arenal in Costa Rica, suggesting that the origin of the 26 s tremor is also volcanic. However, there is no reported volcanic activity in the area where the source appears to be located.</p><p> </p>

Seismic wave energy inferred from long-period body wave inversion

1988 ◽  
Vol 78 (5) ◽  
pp. 1707-1724
Author(s):  
Masayuki Kikuchi ◽  
Yoshio Fukao
Keyword(s):  
Seismic Wave ◽  
Wave Energy ◽  
Body Wave ◽  
Empirical Relation ◽  
P Waves ◽  
Average Value ◽  
Long Period ◽  
Wave Inversion ◽  
Moment Ratio ◽  
Order Of Magnitude

Abstract The seismic wave energy is evaluated for 35 large earthquakes by inverting far-field long-period P waves into the multiple-shock sequence. The results show that the seismic wave energy thus obtained is systematically less than that inferred from the Gutenberg-Richter's formula with the seismic magnitude. The difference amounts to one order of magnitude. The results also show that the energy-moment ratio is well confined to a narrow range: 10−6 < ES/Mo < 10−5 with the average of ∼5 × 10−6. This average value is exactly one order of magnitude as small as the energy-moment ratio inferred from the Gutenberg-Richter's formula using the moment magnitude. Comparing the energy-moment ratio with Δσo/2μ, where Δσo and μ are the stress drop and the rigidity, we obtain an empirical relation: ES/Mo ∼ 0.1 × Δσ0/2μ. Such a relation can be interpreted in terms of a subsonic rupture where the energy loss due to cohesion is not negligible to the seismic wave energy.

Evidence of tectonic release from underground nuclear explosions in long-period P waves

1983 ◽  
Vol 73 (2) ◽  
pp. 593-613
Author(s):  
Terry C. Wallace ◽  
Donald V. Helmberger ◽  
Gladys R. Engen
Keyword(s):  
Upper Mantle ◽  
High Stress ◽  
Test Site ◽  
Strike Slip ◽  
Body Waves ◽  
Release Time ◽  
P Waves ◽  
Underground Nuclear Explosions ◽  
Nuclear Explosions ◽  
Long Period

abstract In this paper, we study the long-period body waves at regional and upper mantle distances from large underground nuclear explosions at Pahute Mesa, Nevada Test Site. A comparison of the seismic records from neighboring explosions shows that the more recent events have much simpler waveforms than those of the earlier events. In fact, many of the early events produced waveforms which are very similar to those produced by shallow, moderate-size, strike-slip earthquakes; the phase sP is particularly obvious. The waveforms of these explosions can be modeled by assuming that the explosion is accompanied by tectonic release represented by a double couple. A clear example of this phenomenon is provided by a comparison of GREELEY (1966) and KASSERI (1975). These events are of similar yields and were detonated within 2 km of each other. The GREELEY records can be matched by simply adding synthetic waveforms appropriate for a shallow strike-slip earthquake to the KASSERI observations. The tectonic release for GREELEY has a moment of 5 ՠ1024 dyne-cm and is striking approximately 340°. The identification of the sP phase at upper mantle distances indicates that the source depth is 4 km or less. The tectonic release time function has a short duration (less than 1 sec). A comparison of these results with well-studied strike-slip earthquakes on the west coast and eastern Nevada indicate that, if tectonic release is triggered fault motion, then the tectonic release is relatively high stress drop, on the order of several hundred bars. It is possible to reduce these stress drops by a factor of 2 if the tectonic release is a driven fault; i.e., rupturing with the P velocity. The region in which the stress is released for a megaton event has a radius of about 4 km. Pahute Mesa events which are detonated within this radius of a previous explosion have a substantially reduced tectonic release.

Spectral characteristics of a two-section multilayer long-period fiber grating sensor

Optik ◽  
2014 ◽  
Vol 125 (17) ◽  
pp. 4689-4693 ◽  
Author(s):  
Jilong Bao ◽  
Peihong Cheng ◽  
Hongxia Zhao ◽  
Jinxia Wang ◽  
Ligang Wu
Keyword(s):  
Spectral Characteristics ◽  
Fiber Grating ◽  
Long Period Fiber Grating ◽  
Long Period ◽  
Fiber Grating Sensor ◽  
Period Fiber Grating

CO2 laser-induced long-period fibre gratings: spectral characteristics, cladding modes and polarisation independence

1998 ◽  
Vol 34 (14) ◽  
pp. 1416 ◽  
Author(s):  
D.D. Davis ◽  
T.K. Gaylord ◽  
E.N. Glytsis ◽  
S.C. Mettler
Keyword(s):  
Co2 Laser ◽  
Spectral Characteristics ◽  
Long Period

Spectral Characteristics of Mechanically Induced Long-Period Fibre Gratings by New Double-Layer Grating Templates

2005 ◽  
Vol 22 (8) ◽  
pp. 1951-1954 ◽  
Author(s):  
Wang Xin-Wei ◽  
Zhang Zhen-Yu ◽  
Zhuang Huai-Xuan ◽  
Sheng Qiu-Qin
Keyword(s):  
Double Layer ◽  
Spectral Characteristics ◽  
Long Period

scholarly journals The February 9, 1971 San Fernando earthquake: A study of source finiteness in teleseismic body waves

1978 ◽  
Vol 68 (1) ◽  
pp. 1-29 ◽  
Author(s):  
Charles A. Langston
Keyword(s):  
Near Field ◽  
Dislocation Line ◽  
Strong Motion ◽  
Body Waves ◽  
P Waves ◽  
Long Period ◽  
Short Period ◽  
Wave Forms ◽  
San Fernando ◽  
The Time Domain

abstract Teleseismic P, SV, and SH waves recorded by the WWSS and Canadian networks from the 1971 San Fernando, California earthquake (ML = 6.6) are modeled in the time domain to determine detailed features of the source as a prelude to studying the near and local field strong-motion observations. Synthetic seismograms are computed from the model of a propagating finite dislocation line source embedded in layered elastic media. The effects of source geometry and directivity are shown to be important features of the long-period observations. The most dramatic feature of the model is the requirement that the fault, which initially ruptured at a depth of 13 km as determined from pP-P times, continuously propagated toward the free surface, first on a plane dipping 53°NE, then broke over to a 29°NE dipping fault segment. This effect is clearly shown in the azimuthal variation of both long period P- and SH-wave forms. Although attenuation and interference with radiation from the remainder of the fault are possible complications, comparison of long- and short-period P and short-period pP and P waves suggest that rupture was initially bilateral, or, possibly, strongly unilateral downward, propagating to about 15 km depth. The average rupture velocity of 1.8 km/sec is well constrained from the shape of the long-period wave forms. Total seismic moment is 0.86 × 1026 dyne-cm. Implications for near-field modeling are drawn from these results.

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