Weak Induced Seismicity in the Korobkov Iron Ore Field of the Kursk Magnetic Anomaly
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Weak Induced Seismicity in the Korobkov Iron Ore Field of the Kursk Magnetic Anomaly A. N. Besedinaa*, S. B. Kishkinaa, G. G. Kocharyana, V. I. Kulikova, and D. V. Pavlova a
Academician Sadovsky Institute of Geosphere Dynamics, Russian Academy of Sciences, Moscow, 119334 Russia *e-mail: [email protected] Received March 26, 2020 Revised May 22, 2020 Accepted May 29, 2020
Abstract—The article presents the analysis of seismic observations in mine roadways. The recorded seismic signals are connected with dynamic deformation of rock mass under massive blasting. The source of induced seismicity are dynamic movements deformation of rocks with an amplitude of 3–30 μm along fractures 1–15 m long. These events feature low values of reduced energy, probably, due to shallow depth of mining. Distribution of induced seismicity events in time and space agreed with patterns of larger seismic events due to remote earthquakes, which implies weak probability of nasty geodynamic phenomena in the course of mining in the Korobkov Field. Keywords: Induced seismicity, seismic monitoring, underground mining, geodynamic activity, focal source parameters, magnitude. DOI: 10.1134/S1062739120036818
INTRODUCTION
With the development of digital technologies, the sensitivity of seismological observations allowed registering and analyzing very weak events with small magnitudes. Studying such sources made it possible to distinguish two main types of mining-induced earthquakes [1–7]. The first one is microevents (M (1 ÷ 3) ⋅10−6 . Dynamic strains caused by the blast in room 1.1 did not exceed the value of 5·10–7, and after blasts in rooms nos. 2 and 3 they were one or two orders of magnitude less. The values ε ≥ 10 −6 are typical for the initiation of deformation events by seismic waves [23].
JOURNAL OF MINING SCIENCE Vol. 56 No. 3 2020
WEAK INDUCED SEISMICITY IN THE KOROBKOV IRON ORE FIELD
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Fig. 6. Dependence of the magnitudes of registered events on the distance to station T3. Straight line shows an approximate sensitivity threshold of a seismic observation system.
Emitted seismic energy was calculated by integrating the velocity spectrum [1]: Es = 4πρ CJR 2 , where J is the energy flux; R is the distance between the source and station. The energy flux is determined as: 2
f2
J = 3 ⋅ 2 ∫ V ( f ) df , f1
f1 =10 Hz; f 2 =1 kHz; V ( f ) is the modulus of velocity spectrum [1]. The source radius r0 was estimated from circular break model [24]: KCβ
r0 =
2π f 0
(4)
with the value of released stress: Δσ =
7 M0 , 16 r03
(5)
K = 1.66 is the constant which gives good agreement with the results of mine observations [1]. The calculated seismic energy varies from 10–3 to 1 J with a change in the seismic moment
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