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1

Seismological footprint of an anomalous atmospheric activity registered in March 2021, in Baja California, Mexico

Flores Estrella Hortencia, Ávila Barrientos Lenin, Gonzalez Huizar Hector

Acta Geophysica

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2023

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Vol. 71, no. 1

79--88

EN

On 11 March 2021, a quite short strong signal was recorded by seismic stations of the CICESE Seismic Network, which cannot be associated with any regional or global earthquake. At the CICESE Campus and all along the city of Ensenada, in Baja California, Mexico, people reported vibration of the windows and even a short strong rumbling. Fortunately, houses and buildings did not report any damage. Due to the interaction between the atmosphere and the shallow earth surface, this anomalous atmospheric activity produced a special seismological footprint, with frequencies between 1 and 10 Hz. In this manuscript, we report on the observations of a multiparameter dataset, including seismic data along with wind velocity, wind density, temperature, humidity, atmospheric pressure, and THSW index. The atmospheric perturbation wave was strong enough to be clearly recorded by seismic stations within an area of almost 80 km and to produce some changes in the recorded meteorological parameters. The results from an FK analysis show that the atmospheric activity occurred to the south of Ensenada City and travelled to the north, as shown in the seismic records. We discuss the characteristics of the seismic signals in the frequency domain and the relation to the changes in the atmospheric parameters that could be related to this anomalous atmospheric activity.

2

Microseismic signal denoising using simple bandpass filtering based on normal time–frequency transform

Yao Yanji, Wang Guocheng, Liu Lintao

Acta Geophysica

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2023

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Vol. 71, no. 5

2217--2232

EN

In active underground mining environments, monitoring mine vibrations has important implications for both safety and productivity. Microseismic data processing is crucial for subsurface real-time monitoring during mineral mining processes. Microseismic events are difficult to detect due to their small magnitudes and low signal-to-noise ratios (SNRs). Useful microseismic signals are usually obscured by long-period microseisms, random noise and artificial strong noise. We propose a useful microseismic denoising algorithm based on the normal time–frequency transform (NTFT) to determine the instantaneous frequency, amplitude and phase information from useful microseismic signals. The energy difference in the time–frequency domain between useful microseismic signals and strong noise is small. Therefore, based on the different phase characteristics of microseismic signals and noise in the NTFT phase spectrum, noise can be filtered out by reconstructing the microseismic signals in useful real-time frequency bands. The proposed simple bandpass filtering (SBPF) method is advantageous because the denoising result does not produce phase shifts, energy leakage or artefacts. The only parameter of the proposed method that needs to be defined is the instantaneous cutoff frequency; thus, the denoising operation is simple. We use both synthetic and real data to demonstrate the feasibility of the method for denoising complicated microseismic datasets.

3

Assessment of the subsidence ratio be based on seismic noise measurements in mining terrain

Marcak Henryk, Pilecki Zenon

Archives of Mining Sciences

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2019

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Vol. 64, no. 1

197--212

EN

Subsidence process in the rock mass disturbed by mining can be complicated and can be faster or slower depending on the geological structure and physical and mechanical properties of the rock mass, changes in exploitation geometry, and changes in the rate of exploitation. The most frequently, the sub-sidence process develops over years in a way that is difficult to observe over a short period (days). It has been proven in practice of coal mines in Poland that Knothe’s model describes subsidence process with high accuracy. It is based on treating the rock mass as a stochastic medium and describing subsidence with stochastic equations.It can be assumed that, the complicated stress field as a result of mining activities induce a series of displacements of different sizes in rock mass. The inelastic deformation in rock mass is accompanied by a microseismicity that can be recorded and processed. We assumed that seismic noise with weak seismic events is a low-energy part of the microseismicity. We proposed an analytical solution to examine the distribution of the energy of the seismic noise during subsidence process development based on Knothe’s model. In general a qualitative method of subsidence process assessment by the registration of the seismic noise was described.

PL

Proces osiadania w górotworze naruszonym działalnością górniczą może być skomplikowany. Może przebiegać szybciej lub wolniej w zależności od budowy geologicznej, fizycznych i mechanicznych właściwości górotworu, zmian w geometrii eksploatacji i zmian prędkości eksploatacji. Najczęściej proces osiadania rozwija się przez lata w sposób trudny do zaobserwowania w krótkim okresie (np. dni). W praktyce udowodniono, że w kopalniach węgla w Polsce model Knothego opisuje proces osiadania z dużą dokładnością. Opiera się on na traktowaniu górotworu jako ośrodka stochastycznego i opisuje osiadanie za pomocą równań stochastycznych. Można przypuszczać, że skomplikowane pole naprężeńwytworzone w wyniku działalności górniczej wywołuje w górotworze serię przemieszczeń o różnej wielkości. Niesprężystemu odkształceniu w górotworze towarzyszy mikrosejsmiczność, która może być rejestrowana. W badaniach przyjęliśmy założenie, że szum sejsmiczny wraz ze słabymi zjawiskami sejsmicznymi należy do niskoenergetycznej części sejsmiczności. Zaproponowaliśmy rozwiązanie analityczne, w celu zbadania rozkładu energii szumu sejsmicznego w czasie rozwoju procesu osiadania w oparciu o model Knothego. W efekcie zaproponowano jakościową metodę oceny procesu osiadania poprzez rejestrację szumu sejsmicznego.

4

Micro-seismic monitoring after the shipwreck of the Costa Concordia at Giglio Island (Italy)

Fiaschi A., Matassoni L., Lotti A., Saccorotti G.

Acta Geophysica

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2017

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Vol. 65, no. 5

1019--1027

EN

A microseismic network was used for monitoring the wreck of the Costa Concordia cruise ship, wrecked and run agrounded along the Giglio Island coasts during the night of 13 January 2012, until its removal. The seismic traces were processed by means of real-time and “a posteriori” procedures to detect transients that could be ascribed to wreck movements on the sea bed to integrate this information in an early warning system for assessing the wreck stability. After a first discrimination of the transients using amplitude criteria we proceeded to the localization of the detected signals to focus the attention only on the transients originated in the shipwreck resting area. The results showed that most of the events localized on the wreck were likely related to human work activities or sudden internal brittle failure but not to displacements on the sea-floor. Instead, the displacements are associated to the impact on the vessel of great sea storms which approach were well correlated with the increasing seismic noise at low frequency. The carried out procedures based on this unique dataset represent an opportunity to test seismic monitoring techniques also in not usual engineering context to support emergency management activities.

5

Application of passive seismic to shallow geological structures in urban areas

Mendecki J.M., Glazer M, Mycka M

Studia Quaternaria

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2014

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Vol. 31, Nr 2

115--122

EN

To study the shallow geological structure the Refraction Microtremor (ReMi) method was applied. This technique uses seismic noise analysis where a source of this small vibrations is the human activity e.g.: traffic, production, factories. The surveys were carried out in selected urban areas in the region of the Upper Silesian Industrial District: Sosnowiec–Pogoń , Chorzów–Chorzów Stary and Bytom–Karb. Each area is characterized by the presence of nearby roads with a very high traffic. The results of passive seismic (ReMi) were confronted with data obtained using Multichannel Analysis of Surface Waves (MASW) and resistivity imaging (RI). Seismic surveys were performed by apparatus PASI with 24 channels using geophones of 4.5Hz. The results showed that passive seismic can be satisfactorily used in such urban conditions. The shallow geological structure interpreted by seismic methods have been well-correlated with resistivity studies.

6

Nowoczesny system LOFRES niskoczęstotliwościowej sejsmiki pasywnej

Isakow Z., Pilecki Z., Sierodzki P.

Przegląd Górniczy

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2014

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T. 70, nr 7

92--96

PL

W artykule przedstawiono system LOFRES przeznaczony do badań metodą niskoczęstotliwościowej sejsmiki pasywnej przypowierzchniowych warstw geologicznych z wykorzystaniem szumu sejsmicznego. Scharakteryzowano systemy pomiarowe stosowane w polskich kopalniach przydatne do pomiarów sejsmiki pasywnej. Opisano budowę i działanie systemu LOFRES. Przedstawiono parametry techniczne i testy zastosowanych sejsmometrów Podkreślono pozytywne wyniki testów modelowego systemu. Omówiono przewidywane sposoby wykorzystania systemu.

EN

This paper presents an innovative LOFRES system, designed for research of subsurface geological strata, using the method of low frequency passive seismics based on seismic noise registration. Measurement systems used in Polish mines useful for passive seismic measurements have been characterized. The construction and operation of the LOFRES system have been also described. Specification and tests of the applied seismometers were presented. Positive results of the tests of a model system were highlighted. Potential applications of the system were discussed.

7

Zastosowanie testu Albarello do wykrywania fałszywych maksimów na widmach HVSR uzyskanych z szumu sejsmicznego rejestrowanego w Ojcowie, Raciborzu i Planetarium Śląskim

Mendecki J.M.

Bezpieczeństwo Pracy i Ochrona Środowiska w Górnictwie

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2012

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nr 9

36-40

PL

Krzywa stosunku widm składowej poziomej drgań do składowej pionowej (HVSR, Horizontal to Vertical Spectral Ratio) wyznaczona dla szumu sejsmicznego może zawierać fałszywe maksima, które niepoprawnie zinterpretowane dadzą mylące wyniki parametrów efektów lokalnych, jakimi są współczynnik amplifikacji i częstotliwość rezonansowa warstwy przypowierzchniowej. Niepożądane maksima HVSR są generowane głównie przez instrumentalny lub/i numeryczny szum pojawiający się podczas rejestracji i przetwarzania danych pomiarowych. W celu wykrycia fałszywych pików zaproponowano test statystyczny Albarello, który pozwala na ich wskazanie przy zadanym poziomie istotności. W niniejszej pracy test Albarello zastosowany został do analizy krzywych HVSR obliczonych dla trzech stacji sejsmologicznych, zlokalizowanych w Planetarium Śląskim, Ojcowie i Raciborzu. Dla stacji w Planetarium Śląskim z czterech obserwowanych maksimów test odrzucił dwa, w Ojcowie z sześciu obserwowanych odrzucono trzy, natomiast w Raciborzu zaobserwowano jedno maksimum, które zostało odrzucone, ponieważ hipoteza H0 testu została potwierdzona.

EN

The Horizontal to Vertical Spectral Ratio (HVSR) curve determined for seismic noise may include false maximums which, when misinterpreted, may result in incorrect results of local effects parameters, i.e. the amplification ratio and resonance frequency of the surface layer. Undesirable HVSR maximums are generated by the instrumental and/ or numerical noise appearing during measurement data recording and processing. In order to detect false peaks, the Albarello’s statistical test which detects them by a set level of significance was suggested. In this paper, the Albarello’s test is used to analyse the HVSR curves calculated for three seismologic stations located in the Silesian Planetarium, the towns of Ojców and Racibórz. As regards the station located in the Silesian Planetarium, the test rejected two maximums from four maximums observed. In Ojców, the test rejected three out of six maximums and, in Racibórz, one maximum was observed, however, it was rejected as the test HO hypothesis was confirmed.