scholarly journals Pre-failure behaviour of an unstable limestone cliff from displacement and seismic data

2010 ◽  
Vol 10 (4) ◽  
pp. 819-829 ◽  
Author(s):  
J.-L. Got ◽  
P. Mourot ◽  
J. Grangeon
Keyword(s):  
Crack Growth ◽  
High Frequency ◽  
Noise Level ◽  
Seismic Noise ◽  
Noise Analysis ◽  
Rapid Change ◽  
Displacement Velocity ◽  
Steady Increase ◽  
Limestone Cliff ◽  
Unstable Rock

Abstract. We monitored the displacement and seismic activity of an unstable vertical rock slice in a natural limestone cliff of the southeast Vercors massif, southeast France, during the months preceding its collapse. Displacement measurements showed an average acceleration of the movement of its top, with clear increases in the displacement velocity and in the discrete seismic event production rate during periods where temperature falls, with more activity when rainfall or frost occurs. Crises of discrete seismic events produce high amplitudes in periodograms, but do not change the high frequency base noise level rate. We infer that these crises express the critical crack growth induced by water weakening (from water vapor condensation or rain) of the rock strength rather than to a rapid change in applied stresses. Seismic noise analysis showed a steady increase in the high frequency base noise level and the emergence of spectral modes in the signal recorded by the sensor installed on the unstable rock slice during the weeks preceding the collapse. High frequency seismic noise base level seems to represent subcritical crack growth. It is a smooth and robust parameter whose variations are related to generalized changes in the rupture process. Drop of the seismic noise amplitude was concomitant with the emergence of spectral modes – that are compatible with high-order eigenmodes of the unstable rock slice – during the later stages of its instability. Seismic noise analysis, especially high frequency base noise level analysis may complement that of inverse displacement velocity in early-warning approaches when strong displacement fluctuations occur.

Correlation between Ambient Seismic Noises and Economic Growth

2020 ◽  
Vol 91 (4) ◽  
pp. 2343-2354 ◽  
Author(s):  
Tae-Kyung Hong ◽  
Jeongin Lee ◽  
Giha Lee ◽  
Junhyung Lee ◽  
Seongjun Park
Keyword(s):  
Economic Growth ◽  
High Frequency ◽  
Noise Level ◽  
Seismic Noise ◽  
Economic Conditions ◽  
Seasonal Effects ◽  
Ambient Seismic Noise ◽  
Frequency Noise ◽  
Noise Levels ◽  
Wide Range

Abstract Human activity is a major source of high-frequency seismic noise. Long-term ambient seismic noise levels and their influencing factors are investigated. The diurnal seismic noise level in 5–15 Hz display high correlation with human activities including traffic and industrial operations that are related to economic conditions. The temporal noise-level variations are consistent among three components. Analysis with seismic noises in three consecutive months of each year enables us to estimate the noise levels without seasonal effects. The daytime seismic noise-level changes in major cities of 11 countries are assessed using the 3 month records for decades. The annual seismic noise levels present strong correlations with gross domestic product (GDP), particularly with manufacturing and industrial GDP. The seismic noise levels increase quickly with GDP in low-GDP regions but slowly in high-GDP regions. This is because high-GDP regions already have large volumes of existing noise-inducing sources and because added sources contribute weakly. The seismic noise levels increased by 14%–111% for 5–23 yr depending on the economic conditions. The correlation between ambient seismic noise level and economy growth is a global feature. The high-frequency noise level may be a proxy to present the economic condition. Economic growth affects the Earth environment in a wide range of aspects.

scholarly journals Seismological assessment of human activity levels during the COVID-19 pandemic

2020 ◽  
Author(s):  
Jeongin Lee ◽  
Tae-Kyung Hong
Keyword(s):  
Human Activities ◽  
High Frequency ◽  
Noise Level ◽  
Seismic Noise ◽  
Activity Levels ◽  
Noise Levels ◽  
Mobility Data ◽  
Community Mobility ◽  
High Infection ◽  
Virus Spreading

Abstract. The COVID-19 virus has a high infection rate, spreading fast in the world. Lockdown and stay-at-home actions have been taken in many countries to reduce the rate of the virus spreading. The daytime ambient seismic noises in 11 major cities of 7 countries are assessed. Daytime seismic noises in 10 am to 6 pm at frequencies ≥ 2 Hz are assessed. The seismic noise levels are compared with the community mobility data that represent the human activities. The high-frequency seismic noise levels present high correlation with the human activities. The human activities decrease with the number of daily confirmed cases. The peak noise-level reductions in lockdown periods were as high as 42–96 %. The noise levels generally started to decrease since the days when the daily confirmed cases reached ~500. The noise level variation presents the lockdown progress. The noise level recovers with time since the end of lockdown. The high correlation between seismic noise level and community mobility suggests possible utilization of seismic noises for anonymous monitoring of human activities.

Seismic noise analysis of broadband stations of the Italian Seismic Network by Power Spectral Density

2020 ◽  
Author(s):  
Maria Catania ◽  
Antonino D'Alessandro ◽  
Luca Greco ◽  
Raffaele Martorana ◽  
Salvatore Scudero
Keyword(s):  
Spectral Density ◽  
Power Spectral Density ◽  
Noise Level ◽  
Seismic Noise ◽  
Noise Analysis ◽  
Seismic Network ◽  
Anthropogenic Source ◽  
Noise Power ◽  
Power Spectral ◽  
Italian Territory

<p>The Italian Seismic Network (IV) consists of more than 500 stations located throughout the Italian territory.</p><p>The detection capability of  network is constrained by its location performance that is affected by the seismic noise levels variations depending on the characteristics of the dominant source. Discriminating the noise level in each stations may allow to improve in its performance, in order to reduce noisy stations to detect even the smaller energetic seismic events sometimes hidden by high noise values. The main goal of this research has been to establish the characteristics (frequency content) and origin of seismic noise background at these sites and secondly to assess the effects of performance of the network.</p><p>For this purpose we have estimated the Power Spectral Density (PSD) of seismic noise selecting only a subset of 233 stations equiped with broadband velocimeters (with minimum period of 40 seconds and with a high sensitivity until to 120s) and operating at least three consecutive years of available data (2015-2017).</p><p>The variations of seismic background noise have been investigated using also the relative Probability Density Funcionts (PDF). The data processing of signals carried out with the robust method proposed by McNamara and Buland, (2004). In this study, the analysis was limited in the frequency band from 0.025 to 30 Hz, in accordance with the seismic sensors bandwidth. Four different frequency bands have been identified: 0.025-0.12, 0.12-1.2, 1.2-10 and 10-30 Hz. Each of these has been associated to a main type of source, in agreement with the literature.</p><p>A preliminary data analysis has been carried out to understand the statistical properties of the noise power, in the four class identified, both in space and frequency domains. Extracting  the PDFs  all stations, it was produced a representative seismic noise model that it could be considered as a new reference noise for Italian territory. Histograms have been computed for each band, both for vertical and horizontal components and its ratio. In addition, a spatial-statistical analysis was performed showing a good correlation of noise level with some weather conditions and anthropogenic source. Several clustering techniques were applied to the data to identified group of stations with similar PSD level, attributable to the same noise source. Furthermore, a correlation between the noise found at the different stations and spatial data (maps of rainfall, winds, coastlines, ect…) was carried out for a better characterization of the type of source.</p>

scholarly journals Crack-Length Estimation for Structural Health Monitoring Using the High-Frequency Resonances Excited by the Energy Release during Fatigue-Crack Growth

Sensors ◽  
2021 ◽  
Vol 21 (12) ◽  
pp. 4221
Author(s):  
Roshan Joseph ◽  
Hanfei Mei ◽  
Asaad Migot ◽  
Victor Giurgiutiu
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Length ◽  
Crack Growth ◽  
Health Monitoring ◽  
Acoustic Waves ◽  
High Frequency ◽  
Fem Analysis ◽  
Signal Frequency ◽  
Propagation Pattern

Acoustic waves are widely used in structural health monitoring (SHM) for detecting fatigue cracking. The strain energy released when a fatigue crack advances has the effect of exciting acoustic waves, which travel through the structures and are picked up by the sensors. Piezoelectric wafer active sensors (PWAS) can effectively sense acoustic waves due to fatigue-crack growth. Conventional acoustic-wave passive SHM, which relies on counting the number of acoustic events, cannot precisely estimate the crack length. In the present research, a novel method for estimating the crack length was proposed based on the high-frequency resonances excited in the crack by the energy released when a crack advances. In this method, a PWAS sensor was used to sense the acoustic wave signal and predict the length of the crack that generated the acoustic event. First, FEM analysis was undertaken of acoustic waves generated due to a fatigue-crack growth event on an aluminum-2024 plate. The FEM analysis was used to predict the wave propagation pattern and the acoustic signal received by the PWAS mounted at a distance of 25 mm from the crack. The analysis was carried out for crack lengths of 4 and 8 mm. The presence of the crack produced scattering of the waves generated at the crack tip; this phenomenon was observable in the wave propagation pattern and in the acoustic signals recorded at the PWAS. A study of the signal frequency spectrum revealed peaks and valleys in the spectrum that changed in frequency and amplitude as the crack length was changed from 4 to 8 mm. The number of peaks and valleys was observed to increase as the crack length increased. We suggest this peak–valley pattern in the signal frequency spectrum can be used to determine the crack length from the acoustic signal alone. An experimental investigation was performed to record the acoustic signals in crack lengths of 4 and 8 mm, and the results were found to match well with the FEM predictions.

High-frequency seismic noise as a function of depth

1991 ◽  
Vol 81 (4) ◽  
pp. 1101-1114
Author(s):  
Jerry A. Carter ◽  
Noel Barstow ◽  
Paul W. Pomeroy ◽  
Eric P. Chael ◽  
Patrick J. Leahy
Keyword(s):  
New York ◽  
High Frequency ◽  
Seismic Noise ◽  
Low Frequency ◽  
Time Variability ◽  
Orthogonal Components ◽  
The Difference ◽  
Frequency Coherence ◽  
Cultural Noise ◽  
Natural Wind

Abstract Evidence is presented supporting the view that high-frequency seismic noise decreases with increased depth. Noise amplitudes are higher near the free surface where surface-wave noise, cultural noise, and natural (wind-induced) noise predominate. Data were gathered at a hard-rock site in the northwestern Adirondack lowlands of northern New York. Between 15- and 40-Hz noise levels at this site are more than 10 dB less at 945-m depth than they are at the surface, and from 40 to 100 Hz the difference is more than 20 dB. In addition, time variability of the spectra is shown to be greater at the surface than at either 335- or 945-m depths. Part of the difference between the surface and subsurface noise variability may be related to wind-induced noise. Coherency measurements between orthogonal components of motion show high-frequency seismic noise is more highly organized at the surface than it is at depth. Coherency measurements between the same component of motion at different vertical offsets show a strong low-frequency coherence at least up to 945-m vertical offsets. As the vertical offset decreases, the frequency band of high coherence increases.

Fatigue Crack Growth Behavior of High Carbon Steel (SM53C) by Using Induction Hardening

2008 ◽  
Author(s):  
Hyun Bae Jeon ◽  
Tae Hoon Song ◽  
Sung Ho Park ◽  
Sun Chul Huh ◽  
Won Jo Park
Keyword(s):  
Fatigue Crack ◽  
Carbon Steel ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
High Frequency ◽  
High Carbon Steel ◽  
Induction Treatment ◽  
Special Focus ◽  
High Carbon ◽  
High Frequency Induction

Recently, with the high performance and efficiency of machine, there have been required the multi-functions in various machine parts, such as the heat resistance, the abrasion resistance and the stress resistance as well as the strength. Fatigue crack growth tests were carried out to investigate the fatigue characteristics of high carbon steel (SM53C) experienced by high-frequency induction treatment. The influence of high-frequency induction treatment on fatigue limit was experimentally examined with the special focus on the variation of surface microstructure and the fatigue crack initiation and propagation through fractography. Also, the shape of hardening depth, hardened structure, hardness, and fatigue-fracture characteristics of SM53C composed by carbon steel are also investigated.

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