![]()
ABSTRACT Presented are the results of seismic and deformation monitoring of a regional fault performed at the depth of 300 m from the free surface in one of the tunnels of an active mine recovering iron ore. Two different sources were used for seismic illumination of the fault: impacts of a sleeper over the tunnel wall and a delay-fired explosion in the mine. It is demonstrated that in the range of small strains 10–10 the normal stiffness of the dis-continuity exhibits non-linearity—as the amplitude of disturbance increases by an order of magnitude, the normal stiffness of the fault decreases by more than an order of magnitude.
1 Introduction Currently authors test the system of seismic and deformation monitoring of tectonic faults at the I.M.Gubkin Mine of the KMAruda Enterprise, which yields iron ore in the town of Gubkin, Belgorod district, Russia (Adushkin et al., 2017).
The seismic monitoring employs an original method of determining deformation characteristics of a fault developed in IDG RAS in 80s–90s years of the last century, which bases on the analysis of alteration of dynamic parameters of seismic waves when they interact with rock discontinuities (Kabychenko et al., 1996; Kostyuchenko et al., 2002; Kocharyan, 2016). The main parameters taken to "watch over" fault conditions are its stiffnesses, the normal and the shear ones, respectively:
(equation)
where σ and τ are the normal and shear stresses acting in the vicinity of the fault, Wn and Ws are relative normal and shear displacements of its sides.
The transition of a fault to the metastable state is accompanied by a decrease of its shear stiffness (Adushkin et al., 2016). It is this statement that underlie the system of monitoring being developed. The main goal of the work is trying to trace, at an active mine, how does the stiffness of the fault change.
2 RESULTS OF MEASUREMENTS In order to test the system of monitoring, the so called Stretensky Fault was chosen, which, according to geological classification, is a regional one. The fault is steeply-dipping, its thickness reaches 100 m and it is about 10 km long. A more detailed description of the fault one can find in the work by V.V. Adushkin with coauthors (Adushkin et al., 2017).
Site News