scholarly journals Spatial and temporal variation of the ambient noise environment of the Sikkim Himalaya

2022 ◽  
Vol 12 (1) ◽  
Author(s):  
Mita Uthaman ◽  
Chandrani Singh ◽  
Arun Singh ◽  
Niptika Jana ◽  
Arun Kumar Dubey ◽  
...  
Keyword(s):  
Ambient Noise ◽  
Vertical Component ◽  
Foreland Basin ◽  
Spatial And Temporal Variation ◽  
Anthropogenic Activity ◽  
Noise Levels ◽  
Sikkim Himalaya ◽  
Seismic Stations ◽  
Noise Characteristics ◽  
Short Period

AbstractAmbient noise characteristics are perused to assess the station performance of 27 newly constructed broadband seismic stations across Sikkim Himalaya and adjoining Himalayan foreland basin, installed to study the seismogenesis and subsurface structure of the region. Power spectral densities obtained at each station, compared against the global noise limits, reveal that observed vertical component noise levels are within the defined global limits. However, the horizontal components marginally overshoot the limits due to the tilt effect. Ambient noise conditions significantly vary with different installation techniques, analysis revealing that seismic sensors buried directly in the ground have reduced long-period noise in comparison to pier installations. Tectonic settings and anthropogenic activities are also noted to cause a significant rise across short-period and microseism noise spectrum, varying spatially and temporally across the region. Day-time records higher cultural noise than night-time, while the microseism noise dominates during the monsoonal season. An assessment of the effect of the nationwide lockdown imposed due to COVID-19 pandemic revealed a significant decrease in the short-period noise levels at stations installed across the foreland basin marked with higher anthropogenic activity. Our study summarizes the overall ambient noise patterns, validating the stability and performance of the seismic stations across the Sikkim Himalayas.

Seismic noise characteristics in Chinese mainland

2020 ◽  
Author(s):  
Fang Wang ◽  
Weitao Wang ◽  
Jianfeng Long ◽  
Leiyu Mu
Keyword(s):  
Noise Level ◽  
Seismic Noise ◽  
Vertical Component ◽  
Chinese Mainland ◽  
Low Noise ◽  
Noise Characteristics ◽  
Power Spectral ◽  
Short Period ◽  
Power Spectral Densities ◽  
Noise Models

<p>Using the three-component continuous waveform recordings of 880 broadband seismic stations in China Seismic Network from January 2014 to December 2015, we calculated power spectral densities and probability density functions over the entire period for each station，and  investigated the characteristics of seismic noise in Chinese mainland. The deep analysis on the vertical recordings  indicates that the spatial distribution of noise levels is characterized by obvious zoning for different period bands.  Densely populated areas have higher short-period noise level than sparsely populated ones, suggesting that short-period noise is related to the intensity distribution of human activities such as transportation and industry. Meanwhile，the short-period noise level near the basin is higher than the mountainous areas，which is probably caused by the amplification effect of the sedimentary layer. The microseism energy  gradually decreases from the southeastern coastal lines to the inland regions. Furthermore, horizontal-component noise level  showed a striking constrast with the vertical component at microseismic and long-period bands. In consideration of  the zoning chracteristics and the need of seismic observations, high and low noise models were  acquired for each network , which were proved to be a more effective tool to identify locally abnormal signals including earthquake, instrumental error and various distrubance compared with the global new high and low model. </p>

Crustal and lithospheric architecture of the Gulf of Mexico and its continental margins from ambient noise Rayleigh wave tomography

2021 ◽  
Author(s):  
Luan C. Nguyen ◽  
Alan Levander ◽  
Fenglin Niu ◽  
Guoliang Li
Keyword(s):  
Gulf Of Mexico ◽  
Rayleigh Wave ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Ambient Noise ◽  
Vertical Component ◽  
Continental Margins ◽  
Continental Lithosphere ◽  
Short Period

<p>The Gulf of Mexico formed as a result of continental breakup between the North and SouthAmerican plates and a short period of seafloor spreading in the Late Jurassic-Early Cretaceous. This small ocean basin offers an opportunity to further our understanding of continental rifting processes and the geologic evolution of continental margins during and after rifting. However, previous knowledge of lithospheric structure has been limited to crustal investigations. We constructed a 3D shear-wave velocity model for the Gulf of Mexico region using cross-correlations of the ambient noise field and measurement of vertical component Rayleigh wave phase velocities in the period band 15 to 95 s. We employed continuous data recorded by more than 500 stations in seismic networks in the US, Mexico and Cuba. Our model shows distinct variation in lithospheric structures that reliably identify and constrain the properties of extended continental and oceanic domains. We estimate the depth of the lithosphere-asthenosphere boundary to be in the range of 85-100 km with the thinnest lithosphere under the oceanic region. A low velocity zone is observed below the lithosphere centered at ~150 km depth with a minimum shear-wave velocity of ~4.45 km/s. Lithospheric mantle underlying the offshore Texas Gulf Coast between oceanic lithosphere and unextended continental lithosphere is characterized by reduced shear-wave velocity. This might indicate that extension resulted in permanent deformation of the continental lithosphere. The differential thinning between the crystalline crust and mantle lithosphere suggests that the extended continental lithosphere has cooled and thickened by approximately 30 km since breakup.</p>

scholarly journals Local magnitude scale in Slovenia

2013 ◽  
Vol 34 ◽  
pp. 23-28 ◽  
Author(s):  
J. Bajc ◽  
Ž. Zaplotnik ◽  
M. Živčić ◽  
M. Čarman
Keyword(s):  
Vertical Component ◽  
Large Data ◽  
Least Square Method ◽  
Least Square ◽  
Magnitude Scale ◽  
Local Magnitude ◽  
Data Set ◽  
Seismic Stations ◽  
Short Period ◽  
Environment Agency

Abstract. In the paper a calibration study of the local magnitude scale in Slovenia is presented. The Seismology and Geology Office of the Slovenian Environment Agency routinely reports the magnitudes MLV of the earthquakes recorded by the Slovenian seismic stations. The magnitudes are computed from the maximum vertical component of the ground velocity with the magnitude equation that was derived some thirty years ago by regression analysis of the magnitudes recorded by a Wood-Anderson seismograph in Trieste and a short period seismograph in Ljubljana. In the study the present single magnitude MLV equation is replaced by a general form of the Richter local magnitude MWA equation. The attenuation function and station-component corrections that compensate the local effects near seismic stations are determined from the synthetic Wood-Anderson seismograms of a large data set by iterative least-square method. The data set used consists of approximately 18 000 earthquakes during a period of 14 yr, each digitally recorded on up to 29 stations. The derived magnitude equation is used to make the final comparison between the new MWA magnitudes and the routinely calculated MLV magnitudes. The results show good overall accordance between both magnitude equations. The main advantage of the introduction of station-component corrections is the reduced uncertainty of the local magnitude that is assigned to a certain earthquake.

scholarly journals Constraining subglacial geology using ambient noise Rayleigh wave ellipticity

2020 ◽  
Author(s):  
Glenn Jones ◽  
Bernd Kulessa ◽  
Ana Ferreira ◽  
Martin Schimmel ◽  
Andrea Berbellini ◽  
...  
Keyword(s):  
Rayleigh Wave ◽  
Basal Slip ◽  
Ambient Noise ◽  
Time Window ◽  
Sedimentary Rocks ◽  
Vertical Component ◽  
Greenland Ice Sheet ◽  
Degree Of Polarization ◽  
Ice Flow ◽  
Seismic Stations

<p>Basal slip is an important mechanism by which glaciers and ice-sheets flow, and is a major source of uncertainty in simulations of ice-mass loss and sea level rise from the Greenland Ice Sheet (GrIS). Sub-ice geology is a dominant control on ice flow velocity with fast flow often coinciding with the presence of deformable subglacial till eroded from underlying sedimentary rocks. The subglacial geology of Greenland has received relatively little attention thus far and its control on ice flow is poorly understood. Seismic studies of the crust beneath the GrIS have been limited due to a lack of seismic stations and the reliance on earthquake event data. However, in the past decade, there has been a rapid increase in the number of both permanent and temporary seismic stations deployed in Greenland as well developments in ambient noise methods, allowing for improved spatial resolution of crustal geology.</p><p> </p><p>Ellipticity measurements, the ratio of the horizontal to vertical component of a Rayleigh wave, have been shown to be particularly sensitive to the geological structure directly beneath the station. Ambient noise H/V measurements have been used for decades in geotechnical and civil engineering for site characterisation, making them a well-suited technique to determine the subglacial geology of the GrIS. Using all available broadband stations deployed on Greenland from 2012 to 2018 we extract Rayleigh wave ellipticity measurement from ambient noise data using the degree-of-polarization (DOP) method where meaningful signals are defined as a waveform with an arbitrary polarization which remains stable for a given time window. We invert these ellipticity measurements in the period range of 4 – 9 s to generate <em>V</em><sub><em>s </em></sub>profiles of the first 5 km beneath each station. Our inversions indicate that: (1) off-ice stations along the margins of the GrIS produce a good agreement with the litho1.0 model to within error and (2) an additional subglacial layer 1.0 - 2.0km thick with a <em>V</em><sub><em>s</em></sub> < 3.0km is necessary to match the data recorded at several of the on-ice stations. We attribute these observations to the widespread presence of sedimentary rocks beneath the GrIS, potentially capable of sustaining extensive subglacial till layers that can support enhanced basal slip.</p>

A comparative study of island, seafloor, and subseafloor ambient noise levels

1989 ◽  
Vol 79 (1) ◽  
pp. 172-179
Author(s):  
Michael A. H. Hedlin ◽  
John A. Orcutt
Keyword(s):  
New Zealand ◽  
Noise Level ◽  
Ambient Noise ◽  
Drill Hole ◽  
Easter Island ◽  
Single Frequency ◽  
Center Frequency ◽  
Ocean Bottom ◽  
Noise Levels ◽  
Short Period

Abstract A study of seafloor and island stations shows that for the frequency band 0.1 to 10 Hz the seismic noise levels on islands are comparable to the levels on the seafloor. The microseism peak at the seafloor appears to be comparable to the highest levels observed on small islands. For this band, seafloor stations are realistic alternatives when island sites are not available. Seven year averages of the ambient noise levels recorded by Seismic Research Observatory (SRO) stations on three islands (Guam [GUMO], Taiwan [TATO], and New Zealand's north island [SNZO]) are compared with those recorded by the International Deployment of Accelerometers (IDA) station on Easter Island and on and beneath the ocean floor by Ocean Bottom Seismometers (OBSs) and the Marine Seismic System (MSS) deployed in a south Pacific DSDP drill hole at 23.8°S., 165.5°W (Adair et al., 1986). From 0.3 to 2 Hz the SRO displacement power levels fall in the range historically observed by the Scripps' OBSs (decreasing at 70 dB/decade from 1 by 106 nm2/Hz at 0.3 Hz to 1 nm2/Hz at 2 Hz) and are 10 to 15 dB above MSS levels. Above 2 Hz it appears that the same ratios hold (the SRO power levels decrease at 70 dB/decade to 1 by 10−3 nm2/Hz at a frequency of 10 Hz), although this correlation is based on very limited, high gain, short-period data. At frequencies below 0.3 Hz the SRO noise levels peak and decrease to approximately 2 by 103 nm2/Hz at 40 mHz. The noise levels recorded at Easter Island are somewhat higher (decreasing at 70 dB/decade from 1 by 107 nm2/Hz at 0.2 Hz to 1 nm2/Hz at 10 Hz and to 1 by 105 nm2/Hz at 50 mHz). At the microseism peak near 0.2 Hz the MSS levels are from 15 to 20 dB higher than observed by the SRO stations and equivalent to those recorded at Easter Island. There appears to be little dependence of the variance in noise level estimates on frequency. The upper 95 per cent confidence limit generally lies 10 dB above the average noise levels for all island stations. All island noise level curves are dominated by the broad double-frequency microseism peak centered between 0.15 to 0.2 Hz. The single-frequency peak ranges from absent (Easter Island) to discernable (Guam and New Zealand) to obvious (at Taiwan). The center frequency of this peak ranges from 0.07 Hz at Guam and New Zealand to 0.1 Hz at Taiwan. We speculate that the increased amplitude and frequency of the single-frequency microseism peak is due to the interaction between the shallow continental shelf and surface gravity waves and/or the presence of Taiwan in a region of limited fetch.

scholarly journals Exposure to Road, Railway, and Aircraft Noise and Arterial Stiffness in the SAPALDIA Study: Annual Average Noise Levels and Temporal Noise Characteristics

2017 ◽  
Vol 125 (9) ◽  
pp. 097004 ◽  
Author(s):  
Maria Foraster ◽  
Ikenna C. Eze ◽  
Emmanuel Schaffner ◽  
Danielle Vienneau ◽  
Harris Héritier ◽  
...  
Keyword(s):  
Arterial Stiffness ◽  
Aircraft Noise ◽  
Noise Levels ◽  
Annual Average ◽  
Temporal Noise ◽  
Noise Characteristics

scholarly journals Dynamics of Comets

1992 ◽  
Vol 152 ◽  
pp. 255-268 ◽  
Author(s):  
A. Carusi ◽  
G.B. Valsecchi
Keyword(s):  
Molecular Clouds ◽  
Vertical Component ◽  
The Sun ◽  
Giant Molecular Clouds ◽  
Mean Motion Resonances ◽  
Galactic Field ◽  
Mean Motion ◽  
Short Period ◽  
Gravitational Processes

The gravitational processes affecting the dynamics of comets are reviewed. At great distances from the Sun the motion of comets is primarily affected by the vertical component of the galactic field, as well as by encounters with stars and giant molecular clouds. When comets move in the region of the planets, encounters with these can strongly affect their motion. A good fraction of all periodic comets spend some time in temporary libration about mean motion resonances with Jupiter; some comets can be captured by this planet as temporary satellites. Finally, there is a small number of objects with orbital characteristics quite different from those of all other short-period comets.

Influence of Wind-produced Noise on Orientation in the Sole (Solea solea)

1994 ◽  
Vol 51 (6) ◽  
pp. 1258-1264 ◽  
Author(s):  
J. P. Lagardère ◽  
M. L. Bégout ◽  
J. Y. Lafaye ◽  
J. P. Villotte
Keyword(s):  
Spatial Distribution ◽  
Ambient Noise ◽  
Sound Intensity ◽  
Weather Conditions ◽  
Fish Populations ◽  
Positioning System ◽  
Noise Levels ◽  
Orientation Behaviour ◽  
Solea Solea ◽  
Swimming Trajectories

Sole (Solea solea), telemetered in an enclosure using an acoustic positioning system, changed their swimming trajectories and orientation behaviour as a function of wind strength and direction. Monitoring of the spatial variation in both wind-generated currents and noise spectra in the enclosure indicates that these behavioural changes correspond to patterns in the spatial distribution of noise and to sound intensity. Thus, our observations indicate that sole perceives and reacts to horizontal variability in ambient noise levels. Such behaviour may be important in determining movements of fish populations at sea during poor weather conditions.

S254 – Bone Conduction Noise Exposure via Ventilators in the NICU

2008 ◽  
Vol 139 (2_suppl) ◽  
pp. P160-P160
Author(s):  
Angela P Black ◽  
James D Sidman
Keyword(s):  
Ambient Noise ◽  
Noise Exposure ◽  
Bone Conduction ◽  
Sound Level ◽  
Noise Levels ◽  
High Noise ◽  
Endotracheal Tubes ◽  
Level Meter ◽  
Hearing Damage ◽  
Air Conduction

Objectives To demonstrate that neonatal ventilators produce high noise levels through bone conduction (BC) via endotracheal tubes, as well as air conduction (AC) from ambient noise. Methods A sound level meter was used to measure the noise levels 4 feet from the ventilator and in direct contact at the end of a balloon attached to the ETT to simulate the noise presented to the infant. 3 commonly used neonatal ventilators (Sensormedics 3100A, VIP Bird and Bunnell Jet) were examined. Results Noise levels were significantly higher (6 – 14 dB) at the end of the ETT than 4 ft from the ventilator for all ventilators studied. Conclusions Previous studies have shown high ambient noise levels in NICUs, but have failed to address the actual noise presented to the infant. ETT transmission of noise as a direct bone stimulus through the skull has been overlooked. This study has shown that high noise intensities are being presented not only as AC, but as BC to the infants though the ETT. This study demonstrates, therefore, that ear protection alone will not save these at-risk infants from hearing damage. More must be done to decrease noise exposure and develop quieter machines.

Sign in / Sign up

Export Citation Format

Share Document