ABSTRACT:

Interrelation between large volumes of mined and moved rock mass and geo-dynamics of the area and mine-induced seismicity has been shown for the Khibini and Lovozero massifs of the Kola peninsula. Conditions of mine-induced seismicity formation have been studied as well as their experimental verification given.

RESUMÉ:

Sur l'example des massifs de Khibini et de Lovozero de la peninsule de Kola est montree la correlation des volumes grandes de la masse minerale extrace et traunsportee avec la geodynamique de la region et la seismicite technogenique sout examinees et la confirmation experimentale est donnee.

ZUSSAMMENFASSUNG:

Am Beispiel der Massive Chibiny und Lowozero der Haibinsel Kola ist die Wechelbezichund der grossen Volumina der zu gavinnenden und zu fordernden Masse zu due geodynamischen Verhaltnissen des Regions und der technogenen Seismizitat gezeigt. Es wurden die Bedingungen der Formierung der technogenen Seismizitat untersucht und ist die experimentelle Bestatigung gegeben.

The effect of the modern mining operations on the environment has gained qualitatively new character. It is not a direct effect of open-pit mining, waste dumps and beneficiation tailings on the day surface. Large-scale open-pit and underground mining operations might be the reason of great geo-mechanic catastrophes. Strong mine-teconic bursts testify to that in coal mines of Utah, USA, salt mines of Verra in Germany, in Tashtagolskoye deposit, Rudny Altay, in Northern and Southern Ural bauxite mines, in apatite mines of the Khibiny and in rare-metal ones of the Lovozero massif. According to their energy released and effect on the environment these rock bursts could be classified as mine-induced earthquakes, with their probability increasing with deepening of output and depth of mining. This principle is illustrated in Fig.1, which shows the correlation between volumes of mined rock mass and parameters of dynamic behaviour in the Khibiny massif. It is explained by the fact, that significant volumes of mined and moved rock mass strongly affect the geodynamic behaviour of the area of large-scale mining operations, causing abnormal deformation of adjacent rock masses and, as a result, an increasement of mine-induced seismicity. Similar events have been registered during hydrotechnical engineering while filling water reservoirs and during oil and gas pumping down from deep wells. Under the influence of mining character variable deformations in rock mass are ten times larger than the background values and, thus, an increasement of seismicity has been registered in the Khibiny apatite and Lovozero rare-metal mines with experiments (Markov et. al.,1980; Panasenko,1983; Kozyrev et. al.,1988). According to existing ideas mine-induced earthquakes differ from native ones only by seismic energy release behaviour under the influence of anthropogenic factors. A great number of foreshocks is characteristic for them-preceding shocks or mine-tectonic bursts and slow decrease of aftershocks as well as increased magnitude due to shallow site occurrence. The main conditions for mine-induced earthquake formation are the presence of large enough working, technological blasts as trigger mechanism of avalanche fracturing (Sobolev, 1982), highstrength brittle rocks with tectonic faults in the area of mining, high level of horizontal tectonic stresses and "favourable" geomorphological factors (mountaneous relief). Under the influence of mining (Fig. 2, b) the stresses in the area of stopping space reach their limit values much more earlier and could be realized as mine-tectonic burst or mine-induced earthquake. It should be noted, that the boundary between mine- tectonic burst and mine-induced earthquake is purely an assumption and is usually determined as the value of energy released.

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