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1

Frequency magnitude distribution and spatial correlation dimension of earthquakes in north-east Himalaya and adjacent regions

Tiwari Ram Krishna, Paudyal Harihar

Geologos

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2022

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Vol. 28, No. 2

115--128

EN

The north-east sector of the Himalaya is one of the most active tectonic belts, with complex geological and tectonic features. The b-value and spatial correlation dimension (Dc) of earthquake distribution in the north-east Himalaya and its adjacent regions (20–32°N and 88–98°E) are estimated in the present study. Based on seismicity and faulting pattern, the region is divided into five active regions, namely the (i) South-Tibet, (ii) Eastern-Syntaxis, (iii) Himalayan-Frontal Arc, (iv) Arakan-Yoma belt and (v) Shillong-Plateau. A homogeneous catalogue of 1,416 earthquakes (mb ≥ 4.5) has been prepared from a revised catalogue of the ISC (International Seismological Centre). The b-value has been appraised by the maximum likelihood estimation method, while Dc values have been calculated by the correlation integral meth-od; b-values of 1.08 ± 0.09, 1.13 ± 0.05, 0.92 ± 0.05, 1.00 ± 0.03 and 0.98 ± 0.08 have been computed for the South-Tibet, Eastern-Syntaxis, Himalayan-Frontal Arc, Arakan-Yoma belt and Shillong-Plateau region, respectively. The Dc values computed for the respective regions are 1.36 ± 0.02, 1.74 ± 0.04, 1.57 ± 0.01, 1.8 ± 0.01, and 1.83 ± 0.02. These values are > 1.5, except for the South-Tibet (1.36 ± 0.02). The b-values around the global average value (1.0) reflect the stress level and seismic activity of the regions, while high Dc values refer to the heterogeneity of the seismogenic sources.

2

Spatial analysis of b-value variability in Elazig city and the surrounding area (Eastern Turkey)

Polat Gulten

Acta Geophysica

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2022

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Vol. 70, no 1

15--25

EN

Frequency-magnitude distribution was investigated in Elazig city and the surrounding area (coordinates ranging from 38.1° N to 39° N for latitudes and 39° E to 40° E for longitude) to reveal the present-day crustal stress within the region. For this study, a complete set of 5603 earthquakes of Md≥1 from 1 January 2000 to 31 August 2020 were localized from the Bogazici University, Kandilli Observatory and Earthquake Research Institute, Regional Earthquake-Tsunami Monitoring Center (KOERI) catalogue. For the whole study region, spatial mapping of the frequency-magnitude distribution was thus produced. The frequency-magnitude distribution (b-value) for seismicity within the study area was not homogeneous. Outstanding variations in the b-value were detected with b ranging from b≈slightly more than 0.3–2. In this region, low b-values are mostly dominant in the region except for a few local areas. This study also shows that accumulated stresses are high particularly at the Pütürge segment in contrast to the fault drawn in the south, which represents the main thrust belt that runs through Hani-Lice and stretches to Çüngüş. As expected, stress accumulation in reverse faults is fairly higher. However, the sharing of the tension formed in the compression zone of the Arabian Plate and the Anatolian plate (i.e. stress partitioning in a sense), results in a low share in the reverse fault belt.

3

Earthquake Potential in the Zagros Region, Iran

Madahizadeh R., Mostafazadeh M., Ashkpour-Motlagh S.

Acta Geophysica

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2016

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Vol. 64, no. 5

1462--1494

EN

Seismic strain and b value are used to quantify seismic potential in the Zagros region (Iran). Small b values (0.69 and 0.69) are related to large seismic moment rates (9.96×1017 and 4.12×1017) in southern zones of the Zagros, indicating more frequent large earthquakes. Medium to large b values (0.72 and 0.92) are related to small seismic moment rates (2.94×1016 and 6.80×1016) in middle zones of the Zagros, indicating less frequent large earthquakes. Small b value (0.64) is related to medium seismic moment rate (1.38×1017) in middle to northern zone of the Zagros, indicating frequent large earthquakes. Large b value (0.87) is related to large seismic moment rate (2.29×1017) in northwestern zone, indicating more frequent large earthquakes. Recurrence intervals of large earthquakes (M > 6) are short in southern (10 and 14 years) and northwestern (13 years) zones, while the recurrence intervals are long in the middle (46 and 114 years) and middle to northern (25 years) zones.

4

Analiza zmian parametru b relacji Gutenberga-Richtera w czasie dla ściany 1 w pokładzie 506 w KWK „Bielszowice"

Piecha M., Krzyżanowska A., Kozak M.

Zeszyty Naukowe Instytutu Gospodarki Surowcami Mineralnymi i Energią PAN

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2014

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nr 86

105--113

PL

W kopalniach na bieżąco wykonuje się ocenę stanu zagrożenia tąpaniami opartą na metodzie kompleksowej za pomocą metod szczegółowych (sejsmologicznej, sejsmoakustycznej i wierceń małośrednicowych). W zaktualizowanej metodzie sejsmologii górniczej jednym z parametrów oceny zagrożenia sejsmicznego jest analiza zmian parametru b relacji Gutenberga-Richtera w czasie eksploatacji. W KWK „Bielszowice" eksploatacja prowadzona jest w warunkach zagrożenia tąpaniami. Zagrożenie sejsmiczne przejawia się głównie w poziomie rejestrowanej aktywności sejsmicznej górotworu. W artykule przedstawiono zmiany współczynnika b relacji Gutenberga-Richtera dla ściany 1 w pokładzie 506 w kopalni „Bielszowice". Wartość parametru b wyliczano na bazie ostatnich 20 wstrząsów z krokiem co jedna doba. Próbowano skorelować zmiany współczynnika b ze zmianami obserwowanego zagrożenia sejsmicznego. Małe wartości parametru b świadczyć mogą o wzroście naprężeń w górotworze i mogą prognozować wystąpienie silnych wstrząsów. Wartości współczynnika b większe od wyznaczonej wartości średniej tego współczynnika mogą wskazywać na brak lub słabe naprężenia w górotworze. Analiza trendu współczynnika b z relacji Gutenberga-Richtera ma na celu stworzenie bazy danych dla opracowania średnich wartości współczynnika dla obszaru górniczego Kopalni „Bielszowice".

EN

In hard coal mines, seismic hazard assessment is based on a complex evaluation of a set of geophysical and mining methods (seismology, seismoacoustic, drilling, rock-mass diagnosis). A new version of seismological methodology analyzes the b value of the Gutenberg-Richter relation for an assessment of seismic hazards over time. In the Bielszowice hard coal mine extraction is conducted under a high level of rockburst hazard. This paper presents analysis of the b values of the Gutenberg-Richter relation during exploitation of the 506 coal seam by longwall panel No. 1 in the "Bielszowice" hard coal mine. The b-value was calculated in a sliding time window covering the last 20 seismic events. A low value of b can indicate areas of high stress within the rock mass, meaning the probability of large tremors there. Determination of the average b value for the Bielszowice mine can be used to analyze the seismic hazard for the next longwall panels during future operations.