HIGH-RESOLUTION SEISMIC TOMOGRAPHY BASED ON COHERENT WAVE TECHNOLOGIES

Abstract eng:
A brand-new high-resolution seismic tomography method is presented. In spite of its great achievements, conventional seismic tomography, which is based on travel time data, has been suffering from low resolution. As an alternative, we have been trying an active seismic tomography based on accurate harmonic wave. Our source is an oscillator that is an eccentric mass driven by a servomotor. Repeating the seismic measurement for a range of different frequencies, we get frequency transfer function. Its Fourier transform yields impulse transfer function that is the key material for the conventional seismological wave analysis. Extremely high precision of frequency of sources enables coherent wave techniques like intensive stacking or phased array of sources. This requires development of a new theory of data analysis based on the indirect measurement strategy. We deployed the instruments in a deep enormous tunnel network of around 600m deep and 5000m wide. This was located in a high seismicity region where moderate size earthquakes of around magnitude six often occur. Detection of change of crustal properties is expected to be a good exercise of the system.

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