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Description of microseismic and sonic tomography systems

The method of sonic 2-D tomography is a small-scale variant of the cross-hole time-travel tomography used in geophysical high-resolution investigations. Both sides of the masonry structure must be accessible. A series of receivers (small geophones) is positioned on one side of the wall and connected to a multi-channel seismograph. On the other side of the wall a series of pulses are generated by hitting the surface along a profile in correspondence to the receivers line. For every shot the arrivals to all the receivers are recorded. The source-receiver rays cover a section across the wall.

The interpretation consists of a tomographic reconstruction of the distribution of the sonic velocities across the section (which is divided in pixels). This velocity distribution is expressed, via graphical routines, in a grey-scale or in a colour scale.

Another kind of seismic tomography is the so-called Tomographic Seismic Sounding (TSS). In this case the transducers are in a hole drilled in the wall, while the energising points are along straight profiles at different distances from the hole. A triangular section is covered by the seismic rays. The data treatment uses algorithms similar to the 2-D tomography.

The result is a velocity profile along the axis of the hole. This method gives the variations of velocities with the highest resolution.

A "prototype" for seismic tomography is not included in target of the Project as seismic tomography is a procedure, not an instrument. The research program foresees the technological development of several equipment items at different stages of the process: prototypes of new P-waves and S-waves transducers will be proposed. Also suitable positioning tools will be built. The software for the tomographic reconstruction has been improved.

Instead of a "prototype", a "package" for the application of micro-seismic tomographies on masonry structures can be proposed. This can include a high-dynamic, high frequency seismograph; a set of specific tools (energy systems, receiving transducers, positioning tools, etc); one software package for data processing and imaging.

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Università degli Studi di Pisa
Via Diotisalvi 2
56126 Pisa
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