scholarly journals Low-Frequency Seismic Noise Properties in the Japanese Islands

Entropy ◽  
2021 ◽  
Vol 23 (4) ◽  
pp. 474
Author(s):  
Alexey Lyubushin
Keyword(s):  
Seismic Noise ◽  
Extreme Values ◽  
Time Window ◽  
Low Frequency ◽  
Seismic Energy ◽  
Day Length ◽  
Time Interval ◽  
Probability Densities ◽  
Seismic Vibrations ◽  
Japanese Islands

The records of seismic noise in Japan for the period of 1997–2020, which includes the Tohoku seismic catastrophe on March 11, 2011, are considered. The following properties of noise are analyzed: The wavelet-based Donoho–Johnston index, the singularity spectrum support width, and the entropy of the wavelet coefficients. The question of whether precursors of strong earthquakes can be formulated on their basis is investigated. Attention is paid to the time interval after the Tohoku mega-earthquake to the trends in the mean properties of low-frequency seismic noise, which reflect the constant simplification of the statistical structure of seismic vibrations. Estimates of two-dimensional probability densities of extreme values are presented, which highlight the places in which extreme values of seismic noise properties are most often realized. The estimates of the probability densities of extreme values coincide with each other and have a maximum in the region: 30°N ≤ Lat ≤ 34°N, 136°E ≤ Lon ≤ 140°E. The main conclusions of the conducted studies are that the preparation of a strong earthquake is accompanied by a simplification of the structure of seismic noise. It is shown that bursts of coherence between the time series of the day length and the noise properties within annual time window precede bursts of released seismic energy. The value of the lag in the release of seismic energy relative to bursts of coherence is about 1.5 years, which can be used to declare a time interval of high seismic hazard after reaching the peak of coherence.

scholarly journals Global Seismic Noise Entropy

2020 ◽  
Vol 8 ◽  
Author(s):  
Alexey Lyubushin
Keyword(s):  
Seismic Noise ◽  
Time Window ◽  
Low Frequency ◽  
Seismic Energy ◽  
Reference Points ◽  
Global Network ◽  
Time Interval ◽  
Time Step ◽  
The World ◽  
Rotation Of The Earth

Data of continuous records of low-frequency (periods from 2 to 1,000 min) seismic noise on a global network of 229 broadband stations located around the world for 23 years, 1997–2019, are analyzed. The daily values of the entropy of the distribution of the squares of the orthogonal wavelet coefficients are considered as an informative characteristic of noise. An auxiliary network of 50 reference points is introduced, the positions of which are determined from the clustering of station positions. For each reference point, a time series is calculated, consisting of 8,400 samples with a time step of 1 day, the values of which are determined as the medians of the entropy values at the five nearest stations that are operable during the given day. The introduction of a system of reference points makes it possible to estimate temporal and spatial changes in the correlation of noise entropy values around the world. Estimation in an annual sliding time window revealed a time interval from mid-2002 to mid-2003, when there was an abrupt change in the properties of global noise and an intensive increase in both average entropy correlations and spatial correlation scales began. This trend continues until the end of 2019, and it is interpreted as a feature of seismic noise which is connected with an increase in the intensity of the strongest earthquakes, which began with the Sumatran mega-earthquake of December 26, 2004 (M = 9.3). The values of the correlation function between the logarithm of the released seismic energy and the bursts of coherence between length of day and the entropy of seismic noise in the annual time window indicate the delay in the release of seismic energy relative to the coherence maxima. This lag is interpreted as a manifestation of the triggering effect of the irregular rotation of the Earth on the increase in global seismic hazard.

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.

scholarly journals Noise matters: elephants show risk-avoidance behaviour in response to human-generated seismic cues

2021 ◽  
Vol 288 (1953) ◽  
pp. 20210774
Author(s):  
Beth Mortimer ◽  
James A. Walker ◽  
David S. Lolchuragi ◽  
Michael Reinwald ◽  
David Daballen
Keyword(s):  
Seismic Noise ◽  
Information Transfer ◽  
Conservation Management ◽  
Sensory Ecology ◽  
Loxodonta Africana ◽  
Relevant Information ◽  
African Elephants ◽  
Risk Avoidance ◽  
Biologically Relevant ◽  
Seismic Vibrations

African elephants ( Loxodonta africana ) use many sensory modes to gather information about their environment, including the detection of seismic, or ground-based, vibrations. Seismic information is known to include elephant-generated signals, but also potentially encompasses biotic cues that are commonly referred to as ‘noise’. To investigate seismic information transfer in elephants beyond communication, here we tested the hypothesis that wild elephants detect and discriminate between seismic vibrations that differ in their noise types, whether elephant- or human-generated. We played three types of seismic vibrations to elephants: seismic recordings of elephants (elephant-generated), white noise (human-generated) and a combined track (elephant- and human-generated). We found evidence of both detection of seismic noise and discrimination between the two treatments containing human-generated noise. In particular, we found evidence of retreat behaviour, where seismic tracks with human-generated noise caused elephants to move further away from the trial location. We conclude that seismic noise are cues that contain biologically relevant information for elephants that they can associate with risk. This expands our understanding of how elephants use seismic information, with implications for elephant sensory ecology and conservation management.

scholarly journals Early Event-related Potential Effects of Syllabic Processing during Visual Word Recognition

2005 ◽  
Vol 17 (11) ◽  
pp. 1803-1817 ◽  
Author(s):  
Manuel Carreiras ◽  
Marta Vergara ◽  
Horacio Barber
Keyword(s):  
Word Recognition ◽  
Visual Word Recognition ◽  
Time Window ◽  
Low Frequency ◽  
Event Related Potential ◽  
Visual Word ◽  
Early Event ◽  
New Paradigm ◽  
Behavioral Studies ◽  
N400 Component

A number of behavioral studies have suggested that syllables might play an important role in visual word recognition in some languages. We report two event-related potential (ERP) experiments using a new paradigm showing that syllabic units modulate early ERP components. In Experiment 1, words and pseudowords were presented visually and colored so that there was a match or a mismatch between the syllable boundaries and the color boundaries. The results showed color-syllable congruency effects in the time window of the P200. Lexicality modulated the N400 amplitude, but no effects of this variable were obtained at the P200 window. In Experiment 2, high-and low-frequency words and pseudowords were presented in the congruent and incongruent conditions. The results again showed congruency effects at the P200 for low-frequency words and pseudowords, but not for high-frequency words. Lexicality and lexical frequency effects showed up at the N400 component. The results suggest a dissociation between syllabic and lexical effects with important consequences for models of visual word recognition.

scholarly journals Pharmacological Interventions and Rehabilitation Approach for Enhancing Brain Self-repair and Stroke Recovery

2019 ◽  
Vol 18 (1) ◽  
pp. 51-64 ◽  
Author(s):  
Rafał Szelenberger ◽  
Joanna Kostka ◽  
Joanna Saluk-Bijak ◽  
Elżbieta Miller
Keyword(s):  
Functional Organization ◽  
Time Window ◽  
Early Stage ◽  
Low Frequency ◽  
Stroke Recovery ◽  
Therapeutic Window ◽  
Cell Therapies ◽  
Brain Functions ◽  
Neuroprotective Strategies

Neuroplasticity is a natural process occurring in the brain for the entire life. Stroke is the leading cause of long term disability and a huge medical and financial problem throughout the world. Research conducted over the past decade focused mainly on neuroprotection in the acute phase of stroke while very little studies target the chronic stage. Recovery after stroke depends on the ability of our brain to reestablish the structural and functional organization of neurovascular networks. Combining adjuvant therapies and drugs may enhance the repair processes and restore impaired brain functions. Currently, there are some drugs and rehabilitative strategies that can facilitate brain repair and improve clinical effect even years after stroke onset. Moreover, some of the compounds such as citicoline, fluoxetine, niacin, levodopa, etc. are already in clinical use or are being trialed in clinical issues. Many studies are also testing cell therapies; in our review, we focused on studies where cells have been implemented at the early stage of stroke. Next, we discuss pharmaceutical interventions. In this section, we selected methods of cognitive, behavioral, and physical rehabilitation as well as adjuvant interventions for neuroprotection including noninvasive brain stimulation and extremely low-frequency electromagnetic field. The modern rehabilitation represents a new model of physical interventions with the limited therapeutic window up to six months after stroke. However, previous studies suggest that the time window for stroke recovery is much longer than previously thought. This review attempts to present the progress in neuroprotective strategies, both pharmacological and non-pharmacological that can stimulate the endogenous neuroplasticity in post-stroke patients.

First results from the pisa seismic noise super-attenuator for low frequency gravitational wave detection

1988 ◽  
Vol 132 (5) ◽  
pp. 237-240 ◽  
Author(s):  
R. Del Fabbro ◽  
A. Di Virgilio ◽  
A. Giazotto ◽  
H. Kautzky ◽  
V. Montelatici ◽  
...  
Keyword(s):  
Gravitational Wave ◽  
Seismic Noise ◽  
Low Frequency ◽  
Gravitational Wave Detection ◽  
Wave Detection ◽  
First Results

scholarly journals A new estimator of heat periods for decadal climate predictions – a complex network approach

2016 ◽  
Vol 23 (4) ◽  
pp. 307-317 ◽  
Author(s):  
Michael Weimer ◽  
Sebastian Mieruch ◽  
Gerd Schädler ◽  
Christoph Kottmeier
Keyword(s):  
Climate Model ◽  
Extreme Values ◽  
Regional Climate ◽  
Low Frequency ◽  
Research Field ◽  
Temperature Threshold ◽  
Fixed Temperature ◽  
Correlation Threshold ◽  
Decadal Climate ◽  
Decadal Predictions

Abstract. Regional decadal predictions have emerged in the past few years as a research field with high application potential, especially for extremes like heat and drought periods. However, up to now the prediction skill of decadal hindcasts, as evaluated with standard methods, is moderate and for extreme values even rarely investigated. In this study, we use hindcast data from a regional climate model (CCLM) for eight regions in Europe and quantify the skill of the model alternatively by constructing time-evolving climate networks and use the network correlation threshold (link strength) as a predictor for heat periods. We show that the skill of the network measure to estimate the low-frequency dynamics of heat periods is superior for decadal predictions with respect to the typical approach of using a fixed temperature threshold for estimating the number of heat periods in Europe.

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