Elastic wave travel time anomaly detection  in areas of subsidence

One of the signs of decompaction in the thickness of the soil massif and  possible settling of its surface is a sharp increase in the time of elastic waves  propagation on this site.

Methods for detecting such anomalies may be different. One of the most effective is the inverted VSP with the location of receiving lines on the surface and by excitation of elastic waves  pulses at different depths in the well. Anomaly at the location of the potential collapse of the soil in the mining field is illustrated. Field data of this section are obtained  by the field team of the department of active seismic of Mining Institute UB RAS (Perm).

Manifestation of  low-velocity anomalous zones on the not longitudinal VSP profiles 

On  longitudinal wave velocity vertical section along the inverted VSP profile at the place of  manifestation of  increased travel time anomaly the distinct  wide zone of  low velocities of longitudinal waves  propagation Vp can be traced with a sharp, almost vertical Eastern border.

Wide anomalous zone is traced to the depths of about 20-25 m. Deeper a narrowing is observed, probably representing the channel of surface water filtering in the thickness of soil and bedrock above the salt workings.

Spatial distribution of anomalous zones displaying on horizontal sections

Areal distribution of anomalous low-velocity zones displayed on horizontal cross sections obtained from reversed VSP velocities Vp spatial sampling.

The complex elongated shape of the velocity anomalies of Vp indicates their possible adherence to the orthogonal system of faults and to the ancient buried channels and valleys developed in the thickness of the bedrocks and filled with weak soils and materials of the weathering crust.