Seismic characterization of fracturing at the Aspo Hard Rock Laboratory, Sweden, from the kilometer scale to the meter scale

In 1986, the Swedish Nuclear Fuel and Waste Management Co. (SKB) decided to build an underground research laboratory, the Aspo Hard Rock Laboratory (HRL). The Aspo HRL offers the possibility to test and demonstrate a full site investigation sequence. As part of this work, various seismic techniques were tested and demonstrated, from the kilometer to the meter scale. The preliminary investigation stage comprised surface reflection profiling and VSP. The VSP measurements, though limited to one borehole, played an important role in defining the site model. Shallow reflection surveys in crystalline rock have been judged as basically feasible, but further development is required to reduce costs. During the construction of the laboratory, the objective of the seismic investigations was to check and refine the site model. Within the zone of excavation disturbance experiment project, seismic tomographic analyses were made for P- and S- wave velocity and attenuation, at 5-15 m scale. Crosshole reflection imaging was also performed. The tracer retention understanding experiments project also included transmission and reflection tomography but on a 100-300 m scale. For the experiments where both transmission and reflection measurements were processed, the seismic surveys also produced information regarding the intrinsic mechanical properties of the rock besides inferring a geometrical model of the rock structures. (C) 2001 Elsevier Science Ltd. All rights reserved.