Ambient Seismic Noise Tomography: Some of Sisprobe Work
The records for the Marathon passive seismic project are of good quality and show usable ambient seismic noise especially in the period band [0.15, 1.5]s (∼0.7-7 Hz) used for the tomography. The microseismic noise at high frequency is mostly coming the Great Lakes. At lower frequency, the noise comes from East-North-East direction (North Atlantic ocean).
The noise cross-correlations show essentially the fundamental mode of the Rayleigh waves travelling at an average velocity of ∼3 km/s. Due to the high velocity and the long wavelengths, we only used data from station pairs more than 900 m apart. It resulted in ∼1300 dispersion curves used for the inversion.
The 3D S-wave velocity model is presented together with its uncertainties. The top of the gabbro intrusive slab is clearly imaged.
As the demand for minerals are increasing, old mining areas are being revisited with the hope of further extracting resources. Some of these areas have been abandoned more than a century ago and as a result the exact location and the extent of the old mined out regions are unknown. Accurate knowledge of the mined out areas are important in order to plan infrastructure and future development.
In other circurmstances, mine operators are intersted to detect remnant areas amongst older workings that have been hydrofilled so that these remnant areas can be mined. Seismic imaging methods have the potential to delineate these mined out areas from intact rock, but have traditionally been too expensive to be used routinetly.
In this paper, we attempt to use a new passive method (called ambient noise surface wave tomography) to image old workings of an old Australian gold mine. Since the method does not require the use of a costly active source, it can be implemented at a fraction of the cost of a conventional active survey. The goal of the project was to see if the ambient seismic noise method could be used to identify old mine workings, mineral deposits, faults or shears and determine the thickness of the slag-heap.
In this paper, we first describe two applications of the passive seismic method (called ambient noise surface wave tomography) in mineral exploration and mining.
In the first, we imaged old workings of an old Australian gold mine and showed that the method could be used to identify old mine workings, mineral deposits, faults or shears and determine the thickness of the slag-heap.
In the second we demonstrated how the method can be used to define the geological setting of a magmatic Cu-PGE deposit.