Unusual low-frequency volcanic seismic events with slowly decaying coda waves observed at Galeras and other volcanoes

1997 ◽  
Vol 77 (1-4) ◽  
pp. 173-193 ◽  
Author(s):  
Diego M. Gómez M ◽  
Roberto A. Torres C
Keyword(s):  
Low Frequency ◽  
Coda Waves ◽  
Seismic Events

CHAOTIC ANALYSIS OF A TIME SERIES COMPOSED OF SEISMIC EVENTS RECORDED IN JAPAN

1994 ◽  
Vol 04 (01) ◽  
pp. 87-98 ◽  
Author(s):  
G.P. PAVLOS ◽  
L. KARAKATSANIS ◽  
J.B. LATOUSSAKIS ◽  
D. DIALETIS ◽  
G. PAPAIOANNOU
Keyword(s):  
Time Series ◽  
Lyapunov Exponent ◽  
Initial Conditions ◽  
Low Frequency ◽  
Underlying Mechanism ◽  
Largest Lyapunov Exponent ◽  
Seismic Events ◽  
Earthquake Dynamics ◽  
The Largest Lyapunov Exponent ◽  
Low Dimensional

A chaotic analysis approach was applied to an earthquake time series recorded in the Japanese area in order to test the assumption that the earthquake process could be the manifestation of a chaotic low dimensional process. For the study of the seismicity we have used a time series consisting of time differences between two consecutive seismic events with magnitudes greater than 2.6. The results of our study show that the underlying mechanism, as expressed by the time series, can be described by low dimensional chaotic dynamics. The power spectrum of the time series shows a power law profile with two slopes, α=1.4 in the low frequency and α=0.05 in the high frequency regions, while the slopes of the correlation integrals show an apparent plateau at the scaling region, which saturates at the value D≈3.2. The largest Lyapunov exponent was found to be ≈0.9. The positive value of the largest Lyapunov exponent reveals strong sensitivity to initial conditions of the supposed earthquake dynamics.

scholarly journals Analyzing Low Frequency Seismic Events at Cerberus Fossae as Long Period Volcanic Quakes

2021 ◽  
Author(s):  
Sharon Kedar ◽  
Mark P. Panning ◽  
Suzanne E. Smrekar ◽  
Simon C. Stähler ◽  
Scott D. King ◽  
...  
Keyword(s):  
Low Frequency ◽  
Seismic Events ◽  
Long Period ◽  
Cerberus Fossae

scholarly journals Statistical moments of power spectrum: a fast tool for the classification of seismic events recorded on volcanoes

2020 ◽  
Vol 52 ◽  
pp. 67-74
Author(s):  
Danilo Galluzzo ◽  
Lucia Nardone ◽  
Mario La Rocca ◽  
Antonietta M. Esposito ◽  
Roberto Manzo ◽  
...  
Keyword(s):  
Signal To Noise Ratio ◽  
Low Frequency ◽  
Signal Amplitude ◽  
Low Noise ◽  
Seismic Events ◽  
Spectral Moments ◽  
Spectral Parameters ◽  
Seismic Stations ◽  
Event Classification ◽  
Tectonic Earthquakes

Abstract. Spectral analysis has been applied to almost thousand seismic events recorded at Vesuvius volcano (Naples, southern Italy) in 2018 with the aim to test a new tool for a fast event classification. We computed two spectral parameters, central frequency and shape factor, from the spectral moments of order 0, 1, and 2, for each event at seven seismic stations taking the mean among the three components of ground motion. The analyzed events consist of volcano-tectonic earthquakes, low frequency events and unclassified events (landslides, rockfall, thunders, quarry blasts, etc.). Most of them are of low magnitude, and/or low maximum signal amplitude, therefore the signal to noise ratio is very different between the low noise summit stations and the higher noise stations installed at low elevation around the volcano. The results of our analysis show that volcano-tectonic earthquakes and low frequency events are easily distinguishable through the spectral moments values, particularly at seismic stations closer to the epicenter. On the contrary, unclassified events show the spectral parameters values distributed in a broad range which overlap both the volcano-tectonic earthquakes and the low frequency events. Since the computation of spectral parameters is extremely easy and fast for a detected event, it may become an effective tool for event classification in observatory practice.

scholarly journals Micro-seismic precursory cracks prior to rock-fall on coastal chalk cliffs: a case study at Mesnil-Val, Normandie, NW France

2009 ◽  
Vol 9 (5) ◽  
pp. 1625-1641 ◽  
Author(s):  
G. Senfaute ◽  
A. Duperret ◽  
J. A. Lawrence
Keyword(s):  
Rock Mass ◽  
Frequency Spectrum ◽  
Failure Mechanisms ◽  
Low Frequency ◽  
Rock Fall ◽  
Seismic Events ◽  
Initiation Mechanism ◽  
Frequency Components ◽  
Specific Frequency ◽  
Complete Detachment

Abstract. Erosion of rock cliffs has been considered to be relatively unpredictable. This perceived stochastic nature of the erosional processes often occurs through collapses along fractures in the rock-mass. The prediction of catastrophic cliff failures and collapses remains very difficult. For advancing in this field, it is important to understand the processes through which a crack is initiated, how it develops and propagates until the final failure. This paper examines the micro-seismic signals recorded 15 h prior to a rock-fall located at Mesnil-Val, France. The results lead to the hypothesis that several phases of failure mechanisms contribute to rock-fall occurrence. The most important phases were associated with micro-seismic event families identified by multiplet selection. Each event family contained one specific frequency spectrum showing a progressive decrease of the frequencies as the rock approached failure suggesting the following phases: 1) the micro-seismic events recorded 15 h before the rock-fall were characterised by the highest frequencies in a large spectrum-band, between ~100 and 1000 Hz (family 1), suggesting a crack initiation mechanism or the opening of existing fractures; 2) the micro-seismic events recorded several minutes before the rock-fall were associated with a clear decrease in the highest frequency components (family 2) suggesting that the mechanism was related to the growing and development (or coalesce) of existing micro-cracks into larger fractures; 3) micro-seismic events recorded just before the rock-fall were associated with a lower frequency spectrum than families 1 and 2, the highest frequency components were absent (family 3), the frequency emission source mechanism could be related to the shearing or opening of the existing large fractures permitting the complete detachment of the blocky rock-mass; 4) finally, micro-seismic events with a very low frequency spectrum (lower than 100 Hz) characterized the rock-fall impact on the ground. These encouraging results offer the possibility of using the micro-seismic system to monitor high risk sections of coastline and to advance understanding of cliff failure mechanisms.

Ultra low-frequency electromagnetic disturbances appearing before strong seismic events

2009 ◽  
Vol 429 (2) ◽  
pp. 1549-1552 ◽  
Author(s):  
L. E. Sobisevich ◽  
K. Kh. Kanonidi ◽  
A. L. Sobisevich
Keyword(s):  
Low Frequency ◽  
Seismic Events ◽  
Electromagnetic Disturbances

Man‐induced low‐frequency seismic events in Italy

2014 ◽  
Vol 41 (23) ◽  
pp. 8261-8268 ◽  
Author(s):  
Diana Latorre ◽  
Alessandro Amato ◽  
Marco Cattaneo ◽  
Simona Carannante ◽  
Alberto Michelini
Keyword(s):  
Low Frequency ◽  
Seismic Events

A microearthquake survey in northwest British Columbia and southeast Alaska

1976 ◽  
Vol 66 (5) ◽  
pp. 1643-1655
Author(s):  
Garry C. Rogers
Keyword(s):  
British Columbia ◽  
Low Frequency ◽  
Seismic Events ◽  
Coast Range ◽  
Volcanic Zone ◽  
Southeast Alaska ◽  
Glacier Bay ◽  
Denali Fault

abstract In an 81-day period during the summer of 1969 four portable seismographs were operated in northwest British Columbia and southeast Alaska. One hundred and forty microearthquakes were detected. Epicenters were located near the Queen Charlotte-Fairweather fault and the Denali fault. The Chatham Strait fault showed no activity and only a few events were located in the Quaternary volcanic zone of British Columbia. A scattering of microearthquakes through the archipelago and the Coast Range and a concentration in the Glacier Bay region suggest that the seismicity may be more complex than the pattern indicated by the distribution of larger earthquakes. The most numerous seismic events recorded, numbering in the thousands, were low-frequency events emanating from a number of specific areas where large glaciers are located.

Identification of electromagnetic pre-earthquake perturbations from the DEMETER data by AI technologies

2020 ◽  
Author(s):  
Pan Xiong ◽  
Cheng Long ◽  
Huiyu Zhou ◽  
Roberto Battiston ◽  
Xuemin Zhang ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Area Under The Curve ◽  
Power Spectra ◽  
Low Frequency ◽  
Gradient Boosting ◽  
Seismic Events ◽  
Electric And Magnetic Fields ◽  
Low Frequency Power ◽  
Frequency Power ◽  
Earthquake Data

<p>Many examples of ionospheric perturbations observed in large seismic events were recorded by the low-altitude satellite DEMETER. In this paper, we explore 16 spot-checking classification algorithms, among which, the top classifier with low-frequency power spectra of electric and magnetic fields were used for ionospheric perturbation analysis. Satellite data spanning over about 6 years has been analyzed and about 8,760 earthquakes with magnitudes larger than or equal to 5.0 that occurred all over the world during the analyzed period have been included in the study. We discover that among these methods, gradient boosting based method called LightGBM outperforms the other state-of-the-art methods and achieves AUC (the Area Under the Curve) of 0.9859 and accuracy of 95.01% in a five-fold cross-validation test on the benchmarking datasets. In addition, the LightGBM method shows a strong capability in discriminating electromagnetic pre-earthquake perturbations over different earthquake databases. The results show that electromagnetic pre-earthquake data with the location in its circular region with its center at the epicenter and a radius given by the Dobrovolsky’s formula and the time of a few hours before the shocks is more useful in discriminating electromagnetic pre-earthquake perturbations. Moreover, we observe that during nights, some low-frequency intervals of electric and magnetic fields are the dominant features as rendered by the trained LightGBM model. These observations support the viewpoint that the seismic activities lead to the enhancement of lightning activity and low frequency electromagnetic pre-earthquake data can help us to detect seismic events.</p>

scholarly journals Detection of ULF geomagnetic signals associated with seismic events in Central Mexico using Discrete Wavelet Transform

2010 ◽  
Vol 10 (12) ◽  
pp. 2557-2564 ◽  
Author(s):  
O. Chavez ◽  
J. R. Millan-Almaraz ◽  
R. Pérez-Enríquez ◽  
J. A. Arzate-Flores ◽  
A. Kotsarenko ◽  
...  
Keyword(s):  
Wavelet Transform ◽  
Discrete Wavelet Transform ◽  
Geomagnetic Field ◽  
Seismic Activity ◽  
Seismic Event ◽  
Low Frequency ◽  
Field Measurements ◽  
Seismic Events ◽  
Discrete Wavelet ◽  
Fluxgate Magnetometer

Abstract. The geomagnetic observatory of Juriquilla Mexico, located at longitude –100.45° and latitude 20.70°, and 1946 m a.s.l., has been operational since June 2004 compiling geomagnetic field measurements with a three component fluxgate magnetometer. In this paper, the results of the analysis of these measurements in relation to important seismic activity in the period of 2007 to 2009 are presented. For this purpose, we used superposed epochs of Discrete Wavelet Transform of filtered signals for the three components of the geomagnetic field during relative seismic calm, and it was compared with seismic events of magnitudes greater than Ms > 5.5, which have occurred in Mexico. The analysed epochs consisted of 18 h of observations for a dataset corresponding to 18 different earthquakes (EQs). The time series were processed for a period of 9 h prior to and 9 h after each seismic event. This data processing was compared with the same number of observations during a seismic calm. The proposed methodology proved to be an efficient tool to detect signals associated with seismic activity, especially when the seismic events occur in a distance (D) from the observatory to the EQ, such that the ratio D/ρ < 1.8 where ρ is the earthquake radius preparation zone. The methodology presented herein shows important anomalies in the Ultra Low Frequency Range (ULF; 0.005–1 Hz), primarily for 0.25 to 0.5 Hz. Furthermore, the time variance (σ2) increases prior to, during and after the seismic event in relation to the coefficient D1 obtained, principally in the Bx (N-S) and By (E-W) geomagnetic components. Therefore, this paper proposes and develops a new methodology to extract the abnormal signals of the geomagnetic anomalies related to different stages of the EQs.

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