Spatial distribution of low-frequency earthquakes suggestive of geofluid among the aftershocks of the 2008 Iwate-Miyagi Nairiku Earthquake in northeastern Japan

2020 ◽  
Author(s):  
Masahiro Kosuga
Keyword(s):  
Stress Field ◽  
Pore Pressure ◽  
High Frequency ◽  
Low Frequency ◽  
Local Stress ◽  
Ductile Deformation ◽  
Stress Axis ◽  
Upper Crust ◽  
The West ◽  
Northeastern Japan

<p>In northeastern Japan, low-frequency earthquakes (LFEQs) occur preferentially at depths from the lower crust to the uppermost mantle near the active volcanoes. Many researchers have suggested the contribution of geofluid to the occurrence of these unusually deep LFEQs. Recent observations show that relatively low-frequency earthquakes occur even in the upper crust as well. Investigation of the generation mechanism of shallow LFEQs is quite important because it is directly related to the mechanism of closely located high-frequency earthquakes in the brittle upper crust. One of the areas of enhanced shallow LFEQ seismicity is the aftershock zone of the 2008 Iwate-Miyagi Nairiku Earthquake (Mw 6.8) located to the west of the 2011 great Tohoku earthquake. We detected LFEQs by using the frequency index (FI) defined by the logarithm of a ratio of high- and low-frequency spectral amplitudes. We used 2–4 Hz and 10–20 Hz bands for low- and high-frequency ranges. We analyzed more than 4000 events observed by a dense temporary seismic network deployed just after the occurrence of the mainshock. Our detection revealed that there are five LFEQs dominant clusters in the aftershock zone trending NNE-SSW with a length of about 40 km: the northern and the southern edge of the aftershock zone, to the north of the mainshock epicenter, the eastern and western edge of the central aftershock zone. In the area near the mainshock epicenter, hypocenter distribution shows two planes: mainshock fault dipping to the west and a conjugate fault dipping to the east. The previous study has shown that the events with N-S trending largest principle stress axis are distributed along the conjugate plane. In contrast, the events along the mainshock fault have E-W trending largest principle axis that is consistent with the relative motion of the subducting Pacific plate beneath the Tohoku region. The former anomalous groups are interpreted to be caused by local stress change by the mainshock applied to a neutral stress field with high pore pressure suggested by high Vp/Vs ratio. An interesting feature is the preferential distribution of LFEQs along the conjugate plane. Also, the hypocenter of LFEQs migrated with time from deeper to the shallower part of the plane. These observations strongly suggest that the existence and movement of geofluid are responsible for both the unusual stress field and the occurrence and migration of LFEQs. The location of LFEQs at the northern and eastern edge of the aftershock zone is close to the areas of postseismic slip detected by GNSS observation, which is suggestive of the increased pore pressure in the area. The LFEQs at the southern and western edge of the aftershock zone occur in calderas, suggesting that these LFEQs occur in hotter and/or fluid-rich areas where the ductile deformation occurs. Thus, though the interpretation of the cause of LFEQs is not unique, the distribution of LFEQs plays a crucial role in understanding the contribution of geofluids not only to the seismogenic processes of aftershocks but to the faulting mechanism in the upper crust.</p>

Seismic effects of the MILROW and CANNIKIN nuclear explosions

1972 ◽  
Vol 62 (6) ◽  
pp. 1411-1423 ◽  
Author(s):  
E. R. Engdahl
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Test Site ◽  
High Gain ◽  
High Yield ◽  
Upper Crust ◽  
Seismic Effects ◽  
Underground Nuclear Explosions ◽  
Low Level ◽  
Nuclear Explosions

abstract Seismic effects of the underground nuclear explosions MILROW (October 1969, about 1 megaton) and CANNIKIN (November 1971, under 5 megatons) were monitored by a network of continuously recording, high-frequency, high-gain seismographs located on Amchitka and nearby islands. Each explosion was immediately followed by hundreds of small, discrete events (mB < 4), of similar focal mechanism and with a characteristic low-frequency signature, which were apparently related to the deterioration of the explosion cavity. This activity intensified, then terminated within minutes of a large, complex multiple event and concurrent formation of a surface subsided area that signaled complete collapse of the explosion cavity (MILROW, 37 hr; CANNIKIN, 38 hr). A number of small explosion-stimulated tectonic events, apparently unrelated to the collapse phenomenon, occurred intermittently for several weeks following each explosion—near the explosion cavity and up to 13 km southeast of CANNIKIN ground zero along the Island. These events were confined to the upper crust of the Island, had characteristic high-frequency signatures, and, near the Rifle Range Fault, had focal mechanisms which could be correlated with pre-existing faulting. The evidence points to a short-term interaction of the explosions with local ambient tectonic stresses. Because these stresses are of relatively low level on Amchitka, the observed seismic effects were significantly less extensive and smaller than similar effects reported from high-yield explosions at the Nevada Test Site. Continuous monitoring of the natural seismicity of the Amchitka region since 1969 has not revealed other evidence for an interaction between either MILROW or CANNIKIN and natural tectonic processes. The structural stability and apparent low level of stress in the upper crust of Amchitka suggest that the Island effectively is seismically decoupled from the active subduction zone below.

Determination of Site Response in Anchorage, Alaska, on the Basis of Spectral Ratio Methods

2002 ◽  
Vol 18 (1) ◽  
pp. 85-104 ◽  
Author(s):  
A. Martirosyan ◽  
U. Dutta ◽  
N. Biswas ◽  
A. Papageorgiou ◽  
R. Combellick
Keyword(s):  
Shear Wave ◽  
Shear Wave Velocity ◽  
High Frequency ◽  
Site Response ◽  
Low Frequency ◽  
Spectral Ratio ◽  
Frequency Range ◽  
The West ◽  
Site Coefficients ◽  
Average Shear

This paper deals with the site response (SR) in the Anchorage basin in south-central Alaska. The investigation is based on the analysis of seismograms of 114 earthquakes recorded by 22 weak-motion stations and 46 earthquakes recorded by 19 strong-motion stations in the study area. We have computed SR for 41 sites, using standard spectral ratio and horizontal-to-vertical spectral ratio methods in the frequency range from 0.5 to 11 Hz. Based on these results, we have calculated band-average site response values in two frequency ranges: low frequency (from 0.5 to 2.5 Hz) and high frequency (from 3 to 7 Hz). There is a good correlation between SR values and surficial geology of the Anchorage area in the low-frequency range. SR values increase by a factor of three from the foothills of the Chugach Mountains in the east to the west towards the deeper part of the basin. The highest site response values (SR>2.5) in the same frequency range are observed in the west-central part of the city, which is underlain by cohesive facies of the Bootlegger Cove formation. The SR has a good correlation with the uppermost 30-m time-average shear-wave velocity with a correlation coefficient of 0.82. Moreover, the low-frequency SR values are close to the NEHRP site coefficients for 1 sec. However, high-frequency SR values lack correlation with 30-m average shear-wave velocity and short-period NEHRP site coefficients.

scholarly journals Thermal Monitoring of the Lithosphere by the Interaction of Deep Low-Frequency and Ordinary High-Frequency Earthquakes in Northeastern Japan

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1546
Author(s):  
Yota Suzuki ◽  
Hirofumi Muraoka ◽  
Hiroshi Asanuma
Keyword(s):  
Upper Mantle ◽  
High Frequency ◽  
Thermal Evolution ◽  
Basaltic Magma ◽  
Low Frequency ◽  
Thermal Monitoring ◽  
Geothermal Resources ◽  
Northeastern Japan ◽  
Spatial And Temporal Characteristics ◽  
Magma Replenishment

Deep low-frequency earthquakes (LFEs) are known to occur in dehydration phenomena from the subducting hydrous slab and in magmatic phenomena beneath Quaternary volcanoes in Japan. To realize the spatial and temporal characteristics of the magmatic deep low-frequency earthquakes, their hypocenters along with those of ordinary overhead high-frequency earthquakes are analyzed beneath six volcanic fields in northeastern Japan. This trial clarifies the rising basaltic magma conduits and rheological profiles of the lithosphere. Deep low-frequency earthquakes tend to form three vertical clusters corresponding to the rheological strength peak of the peridotite upper mantle, gabbroic lower crust, and granitic upper crust. Interactive aseismic gaps between low- and high-frequency earthquakes reveal the brittle–plastic transition as an isothermal indicator in the lithosphere. This relationship provides a tool to monitor the thermal evolution of the lithosphere and to explore sustainable geothermal resources with basaltic magma replenishment systems.

scholarly journals ANALYSIS OF HIGH FREQUENCY BREAKING WAVES AND LOW FREQUENCY SURGES GENERATED IN HARBORS DUE TO PASSAGE OF DEEP-DRAFT TANKERS

2018 ◽  
pp. 27
Author(s):  
Arpit Agarwal ◽  
Scott Fenical ◽  
Kirsten McElhinney ◽  
Paul Carangelo ◽  
David Krams
Keyword(s):  
High Frequency ◽  
Pressure Field ◽  
Low Frequency ◽  
Breaking Waves ◽  
Wave Activity ◽  
The West ◽  
Ship Traffic ◽  
Corpus Christi ◽  
Navigation Channel ◽  
Over Time

Cline’s Point Marina, located in Port Aransas, TX, has been experiencing detrimental conditions near the marina’s entrance and within the marina itself during the passage of deep-draft ship traffic. The wave activity is primarily generated by pressure field effects from large, laden outbound vessels in Corpus Christi Ship Channel (CCSC). The basin was originally protected by an approximately 180 ft. long breakwater constructed in 1976 on the west side of the entrance which by 1980 has deteriorated and partially failed to 120 ft. long breakwater and continued deteriorating over time, reaching its approximate 60 ft. long current condition by 2003. The deterioration of this breakwater has reportedly resulted in enhanced penetration of deep-draft vessel wave activity into the marina (Figure 1). Mott MacDonald (MM) evaluated the mechanisms by which waves are generated in the navigation channel, transform, and enter the harbor, quantified the level of protection afforded by past and present entrance breakwater configuration(s), and developed conceptual alternatives for improving conditions inside the marina.

Observation of secondary slip systems in tungsten bicrystals

1984 ◽  
Vol 42 ◽  
pp. 478-479
Author(s):  
J. R. Fekete ◽  
R. Gibala
Keyword(s):  
Stress Field ◽  
Grain Boundaries ◽  
Deformation Behavior ◽  
Stress Axis ◽  
Polycrystalline Materials ◽  
Slip Systems ◽  
Metallic Materials ◽  
Twist Boundary ◽  
Secondary Slip ◽  
Plane Normal

The deformation behavior of metallic materials is modified by the presence of grain boundaries. When polycrystalline materials are deformed, additional stresses over and above those externally imposed on the material are induced. These stresses result from the constraint of the grain boundaries on the deformation of incompatible grains. This incompatibility can be elastic or plastic in nature. One of the mechanisms by which these stresses can be relieved is the activation of secondary slip systems. Secondary slip systems have been shown to relieve elastic and plastic compatibility stresses. The deformation of tungsten bicrystals is interesting, due to the elastic isotropy of the material, which implies that the entire compatibility stress field will exist due to plastic incompatibility. The work described here shows TEM observations of the activation of secondary slip in tungsten bicrystals with a [110] twist boundary oriented with the plane normal parallel to the stress axis.

Simulations of high-resolution images of amorphous silicon films

1986 ◽  
Vol 44 ◽  
pp. 544-545
Author(s):  
G. Y. Fan ◽  
J. M. Cowley
Keyword(s):  
Electron Microscope ◽  
High Frequency ◽  
Fourier Transformation ◽  
Amorphous Materials ◽  
Low Frequency ◽  
Chromatic Aberration ◽  
Structure Information ◽  
Frequency Components ◽  
High Resolution Images ◽  
Spatial Frequency Spectrum

It is well known that the structure information on the specimen is not always faithfully transferred through the electron microscope. Firstly, the spatial frequency spectrum is modulated by the transfer function (TF) at the focal plane. Secondly, the spectrum suffers high frequency cut-off by the aperture (or effectively damping terms such as chromatic aberration). While these do not have essential effect on imaging crystal periodicity as long as the low order Bragg spots are inside the aperture, although the contrast may be reversed, they may change the appearance of images of amorphous materials completely. Because the spectrum of amorphous materials is continuous, modulation of it emphasizes some components while weakening others. Especially the cut-off of high frequency components, which contribute to amorphous image just as strongly as low frequency components can have a fundamental effect. This can be illustrated through computer simulation. Imaging of a whitenoise object with an electron microscope without TF limitation gives Fig. 1a, which is obtained by Fourier transformation of a constant amplitude combined with random phases generated by computer.

SEM image sharpness analysis

1996 ◽  
Vol 54 ◽  
pp. 142-143
Author(s):  
M. T. Postek ◽  
A. E. Vladar
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Quantitative Information ◽  
Primary Electron ◽  
Image Sharpness ◽  
Critical Dimensions ◽  
Sem Image ◽  
Frequency Changes ◽  
Electron Microscopes ◽  
Scanning Electron

Fully automated or semi-automated scanning electron microscopes (SEM) are now commonly used in semiconductor production and other forms of manufacturing. The industry requires that an automated instrument must be routinely capable of 5 nm resolution (or better) at 1.0 kV accelerating voltage for the measurement of nominal 0.25-0.35 micrometer semiconductor critical dimensions. Testing and proving that the instrument is performing at this level on a day-by-day basis is an industry need and concern which has been the object of a study at NIST and the fundamentals and results are discussed in this paper.In scanning electron microscopy, two of the most important instrument parameters are the size and shape of the primary electron beam and any image taken in a scanning electron microscope is the result of the sample and electron probe interaction. The low frequency changes in the video signal, collected from the sample, contains information about the larger features and the high frequency changes carry information of finer details. The sharper the image, the larger the number of high frequency components making up that image. Fast Fourier Transform (FFT) analysis of an SEM image can be employed to provide qualitiative and ultimately quantitative information regarding the SEM image quality.

Real Ear Sound Pressure Levels Developed by Three Portable Stereo System Earphones

1992 ◽  
Vol 1 (4) ◽  
pp. 52-55 ◽  
Author(s):  
Gail L. MacLean ◽  
Andrew Stuart ◽  
Robert Stenstrom
Keyword(s):  
High Frequency ◽  
Sound Pressure ◽  
Low Frequency ◽  
Test System ◽  
Output Frequency ◽  
Frequency Effects ◽  
Adult Men ◽  
Frequency Responses ◽  
Significant Difference ◽  
Sound Pressure Levels

Differences in real ear sound pressure levels (SPLs) with three portable stereo system (PSS) earphones (supraaural [Sony Model MDR-44], semiaural [Sony Model MDR-A15L], and insert [Sony Model MDR-E225]) were investigated. Twelve adult men served as subjects. Frequency response, high frequency average (HFA) output, peak output, peak output frequency, and overall RMS output for each PSS earphone were obtained with a probe tube microphone system (Fonix 6500 Hearing Aid Test System). Results indicated a significant difference in mean RMS outputs with nonsignificant differences in mean HFA outputs, peak outputs, and peak output frequencies among PSS earphones. Differences in mean overall RMS outputs were attributed to differences in low-frequency effects that were observed among the frequency responses of the three PSS earphones. It is suggested that one cannot assume equivalent real ear SPLs, with equivalent inputs, among different styles of PSS earphones.

Evaluation of Special Hearing Aids for Deaf Children

1971 ◽  
Vol 36 (4) ◽  
pp. 527-537 ◽  
Author(s):  
Norman P. Erber
Keyword(s):  
Hearing Aids ◽  
High Frequency ◽  
Hearing Aid ◽  
Low Frequency ◽  
Acoustic Stimulation ◽  
Deaf Children ◽  
Frequency Range ◽  
Frequency Limit ◽  
Unpublished Studies ◽  
Published Research

Two types of special hearing aid have been developed recently to improve the reception of speech by profoundly deaf children. In a different way, each special system provides greater low-frequency acoustic stimulation to deaf ears than does a conventional hearing aid. One of the devices extends the low-frequency limit of amplification; the other shifts high-frequency energy to a lower frequency range. In general, previous evaluations of these special hearing aids have obtained inconsistent or inconclusive results. This paper reviews most of the published research on the use of special hearing aids by deaf children, summarizes several unpublished studies, and suggests a set of guidelines for future evaluations of special and conventional amplification systems.

Efeitos do Método Pilates sobre a variabilidade da frequência cardíaca, flexibilidade e variáveis antropométricas em indivíduos sedentários

2016 ◽  
Vol 17 (1) ◽  
pp. 66
Author(s):  
Maria Lina Silva Leite
Keyword(s):  
High Frequency ◽  
Low Frequency

O objetivo deste estudo foi avaliar os efeitos do Método Pilates sobre a variabilidade da frequência cardíaca, na flexibilidade e nas variáveis antropométricas em indivíduos sedentários. O presente estudo contou com 14 voluntárias do sexo feminino, na faixa etária entre 40 e 55 anos, que realizaram 20 sessões de exercícios do Método Pilates, duas vezes por semana, com duração de 45 minutos cada sessão, dividida em três fases: repouso, exercício e recuperação. As variáveis estudadas foram: os dados antropométricos, flexibilidade avaliada utilizando o teste de sentar-e-alcançar com o Banco de Wells, e intervalos R-R usando um cardiotacômetro. O processamento dos sinais da frequência cardíaca foi efetuado em ambiente MatLab 6.1®, utilizando a TWC. Os dados coletados foram submetidos ao teste de normalidade de Shapiro Wilk e foi utilizado o teste de Wilcoxon e Anova One Way (α = 0,05). Nos resultados, observou-se que não houve diferenças significativas entre os valores antropométricos e de frequência cardíaca, porém houve aumento da flexibilidade com o treinamento. Comparando a primeira e a vigésima sessão com relação aos parâmetros low frequency (LF), high frequency (HF), e relação LF/HF, não houve diferença na fase de repouso e foram constatadas diferenças significativas de LF (p = 0,04) e HF (p = 0,04) na fase de exercício e diferença significativa de LF/HF (p = 0,05) na fase de recuperação. Comparando os parâmetros nos períodos de repouso, exercícios e recuperação durante a primeira sessão e durante a vigésima sessão, não houve diferença significativa nos parâmetros LF, HF e LF/HF. Pode-se concluir que, em relação à flexibilidade, foi observada uma melhora significativa, enquanto a análise da frequência cardíaca caracterizou a intensidade do exercício de 50% da capacidade funcional das voluntárias. Em relação aos parâmetros LF, HF e LF/HF foram observados um aumento da variabilidade da frequência cardíaca, provavelmente produto da atividade do Método Pilates. A Transformada Wavelet (TWC) mostrou-se um Método adequado para as análises da variabilidade da frequência cardíaca.Palavras-chave: frequência cardíaca, Transformada Wavelet, Pilates.

Sign in / Sign up

Export Citation Format

Share Document