scholarly journals Audible acoustics from low-magnitude fluid-induced earthquakes in Finland

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Oliver D. Lamb ◽  
Jonathan M. Lees ◽  
Peter E. Malin ◽  
Tero Saarno
Keyword(s):  
Low Frequency ◽  
Acoustic Signals ◽  
Body Waves ◽  
Microphone Arrays ◽  
Geothermal System ◽  
Induced Earthquakes ◽  
Acoustic Coupling ◽  
Helsinki Metropolitan Area ◽  
System Project ◽  
Engineered Geothermal System

AbstractEarthquakes are frequently accompanied by public reports of audible low-frequency noises. In 2018, public reports of booms or thunder-like noises were linked to induced earthquakes during an Engineered Geothermal System project in the Helsinki Metropolitan area. In response, two microphone arrays were deployed to record and study these acoustic signals while stimulation at the drill site continued. During the 11 day deployment, we find 39 earthquakes accompanied by possible atmospheric acoustic signals. Moment magnitudes of these events ranged from $$-0.07$$ - 0.07 to 1.87 with located depths of 4.8–6.5 km. Analysis of the largest event revealed a broadband frequency content, including in the audible range, and high apparent velocities across the arrays. We conclude that the audible noises were generated by local ground reverberation during the arrival of seismic body waves. The inclusion of acoustic monitoring at future geothermal development projects will be beneficial for studying seismic-to-acoustic coupling during sequences of induced earthquakes.

scholarly journals Slithering CSF: Cerebrospinal Fluid Dynamics in the Stationary and Moving Viper Boa, Candoia aspera

Biology ◽  
2021 ◽  
Vol 10 (7) ◽  
pp. 672
Author(s):  
Bruce A. Young ◽  
Skye Greer ◽  
Michael Cramberg
Keyword(s):  
Cerebrospinal Fluid ◽  
Cardiac Cycle ◽  
Low Frequency ◽  
Mean Amplitude ◽  
The Body ◽  
Body Waves ◽  
Lower Amplitude ◽  
Lateral Undulation ◽  
Recovery From Anesthesia ◽  
The Relationship

In the viper boa (Candoia aspera), the cerebrospinal fluid (CSF) shows two stable overlapping patterns of pulsations: low-frequency (0.08 Hz) pulses with a mean amplitude of 4.1 mmHg that correspond to the ventilatory cycle, and higher-frequency (0.66 Hz) pulses with a mean amplitude of 1.2 mmHg that correspond to the cardiac cycle. Manual oscillations of anesthetized C. aspera induced propagating sinusoidal body waves. These waves resulted in a different pattern of CSF pulsations with frequencies corresponding to the displacement frequency of the body and with amplitudes greater than those of the cardiac or ventilatory cycles. After recovery from anesthesia, the snakes moved independently using lateral undulation and concertina locomotion. The episodes of lateral undulation produced similar influences on the CSF pressure as were observed during the manual oscillations, though the induced CSF pulsations were of lower amplitude during lateral undulation. No impact on the CSF was found while C. aspera was performing concertina locomotion. The relationship between the propagation of the body and the CSF pulsations suggests that the body movements produce an impulse on the spinal CSF.

scholarly journals Acoustic source localization using the open spherical microphone array in the low-frequency range

2019 ◽  
Vol 283 ◽  
pp. 04001
Author(s):  
Boquan Yang ◽  
Shengguo Shi ◽  
Desen Yang
Keyword(s):  
Source Localization ◽  
Generalized Inverse ◽  
Microphone Array ◽  
Low Frequency ◽  
Poor Performance ◽  
Microphone Arrays ◽  
Three Dimension ◽  
Frequency Range ◽  
Array Aperture ◽  
Regularization Matrix

Recently, spherical microphone arrays (SMA) have become increasingly significant for source localization and identification in three dimension due to its spherical symmetry. However, conventional Spherical Harmonic Beamforming (SHB) based on SMA has limitations, such as poor resolution and high side-lobe levels in image maps. To overcome these limitations, this paper employs the iterative generalized inverse beamforming algorithm with a virtual extrapolated open spherical microphone array. The sidelobes can be suppressed and the main-lobe can be narrowed by introducing the two iteration processes into the generalized inverse beamforming (GIB) algorithm. The instability caused by uncertainties in actual measurements, such as measurement noise and configuration problems in the process of GIB, can be minimized by iteratively redefining the form of regularization matrix and the corresponding GIB localization results. In addition, the poor performance of microphone arrays in the low-frequency range due to the array aperture can be improved by using a virtual extrapolated open spherical array (EA), which has a larger array aperture. The virtual array is obtained by a kind of data preprocessing method through the regularization matrix algorithm. Both results from simulations and experiments show the feasibility and accuracy of the method.

Fish Attraction with Pulsed Low-Frequency Sound

1968 ◽  
Vol 25 (7) ◽  
pp. 1441-1452 ◽  
Author(s):  
Joseph D. Richard
Keyword(s):  
Acoustic Stimulus ◽  
Low Frequency ◽  
Reef Fishes ◽  
Test Site ◽  
Acoustic Signals ◽  
Commercial Fisheries ◽  
Test Results ◽  
Potential Applications ◽  
Predatory Fishes ◽  
Underwater Television

A series of tests were conducted to determine the effectiveness of pulsed low-frequency acoustic signals for attracting fishes. The acoustic signals were contrived to simulate the hydrodynamically generated disturbances normally associated with active predation. Underwater television was used to observe fish arrivals during both control and test periods. Demersal predatory fishes were successfully attracted although they habituated rapidly to the acoustic stimulus. Members of the families Serranidae, Lutjanidae, and Pomadasyidae were particularly well represented among the fishes attracted. Sharks were also attracted in considerable numbers. Herbivorous reef fishes, although common around the test site, were not attracted. Possible relationships between the test results and the hearing capabilities of fishes are discussed. It is concluded that acoustic attraction techniques have potential applications in certain existing commercial fisheries.

Coherence of low‐frequency acoustic signals in the deep ocean

1974 ◽  
Vol 56 (4) ◽  
pp. 1122-1125 ◽  
Author(s):  
J. D. Shaffer ◽  
R. M. Fitzgerald ◽  
A. N. Guthrie
Keyword(s):  
Low Frequency ◽  
Deep Ocean ◽  
Acoustic Signals

Rain parameter estimation using impact generated low‐frequency acoustic signals

2003 ◽  
Vol 113 (4) ◽  
pp. 2278-2278
Author(s):  
T. K. Mani ◽  
P. R. Saseendran Pillai ◽  
James Kurian ◽  
Supriya M. Hariharan
Keyword(s):  
Parameter Estimation ◽  
Low Frequency ◽  
Acoustic Signals

scholarly journals A numerical analysis of the thermohydraulics of an EGS project in Turkey

2018 ◽  
Vol 240 ◽  
pp. 05001
Author(s):  
Ali Cemal Benim ◽  
Aydin Cicek ◽  
Arif Mert Eker
Keyword(s):  
Porous Media ◽  
Numerical Model ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Domain Size ◽  
Geothermal System ◽  
Enhanced Geothermal System ◽  
Discretization Scheme ◽  
Modelling Assumptions ◽  
System Project

A numerical study of the thermohydraulics of an enhanced geothermal system project in Turkey is presented. The solid structures are modelled as porous media, using the numerically determined hydraulic fracturing data of other authors. The influence of several numerical modelling aspects such as the domain size, grid resolution, temporal resolution as well as the discretization scheme are investigated and assessed to obtain highly accurate numerical solutions under the applied modelling assumptions. Using the suggested mathematical and numerical model, different production scenarios are investigated.

"Smooth" Rhythms as Probes of Entrainment

1993 ◽  
Vol 10 (4) ◽  
pp. 503-508 ◽  
Author(s):  
Robert O. Gjerdingen
Keyword(s):  
Frequency Domain ◽  
Amplitude Modulation ◽  
Acoustic Signal ◽  
Low Frequency ◽  
Digital Filtering ◽  
Acoustic Signals ◽  
Frequency Range ◽  
Carrier Wave ◽  
The Brain

If one hypothesizes rhythmic perception as a process employing oscillatory circuits in the brain that entrain to low-frequency periodicities in the neural firings evoked by an acoustic signal, then among the conceptually purest probes of those oscillatory circuits would be acoustic signals with only simple sinusoidal periodicities in the appropriate frequency range (perhaps from 0.3 Hz to 20 Hz). Such signals can be produced by the low- frequency amplitude modulation of an audible carrier wave by one or more sinusoids. The resulting rhythms are "smooth" in that their amplitude envelopes are smoothly varying with no obvious points of onset or offset. Because preliminary experiments with smooth rhythms have produced some unexpected results, and because smooth rhythms can be precisely controlled and varied (including, for example, the digital filtering of their Fourier components in the frequency domain), they are proposed as versatile stimuli for studies in rhythmic perception.

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