Seismic tomography

In engineering geological and geotechnical investigation, seismic tomography is used to assess the quality of rockmass, study about weak zone, highly cracked zone of rock mass in both horizontal and vertical direction and is a means of assessing the effect of grouting operation.

crosshole seismic tomography

   A sketch of seismic tomography S: source, R: receiver

In assessing the concrete quality, it is used to determine void or cracked zone and low quality in concrete mass. These imagers are tools to analyze the characteristic size, extent, and severity of defects and anomalies in the concrete dam, bridges, culverts, etc… In addition, it is used to monitor the quality of constructions in different time, bofore and after applying force or impacted by earthquake, tsunami,…

Seismic tomography utilizes multiple raypaths to achieve 2D or 3D modelling of cross-seismic data. The raypaths provide a wealth of information across the entire volume between boreholes or surfaces.

A seismic tomography survey in a dam.

                      A seismic tomography survey in a dam.

Data production is maintained by utilizing a string of geophones in the receiver borehole or surface creating raypaths for each shot. The information is recorded in the field using a seismic recorder. Geophone separation and interval between source shots is dependent upon the survey objectives and site conditions.

seismic tomography result

A result of seismic tomography in a concrete dam

Seismic tomography is processed by GeoTom CG 3D package which provides graphical displays of velocities, raypath densities, and other parameters for data analysis and modeling. Plot for quality control include traveltime versus distance, residual versus raypath angle, and others.