Velocity dispersion in fractured rocks in a wide frequency range

0392585 - GLÚ 2014 RIV NL eng J - Journal Article
Vilhelm, J. - Rudajev, Vladimír - Lokajíček, Tomáš - Živor, Roman
Velocity dispersion in fractured rocks in a wide frequency range.
Journal of Applied Geophysics. Roč. 90, March (2013), s. 138-146. ISSN 0926-9851. E-ISSN 1879-1859
R&D Projects: GA AV ČR IAA300130906
Institutional research plan: CEZ:AV0Z30130516
Keywords : fracture stiffness * fractured rocks * seismic velocity measurement * velocity anisotropy * velocity dispersion
Subject RIV: DC - Siesmology, Volcanology, Earth Structure
Impact factor: 1.301, year: 2013

Experimental measurements of fracture-induced seismic waves velocity variations at frequencies ~ 1 kHz, ~ 40. kHz and ~ 1 MHz were performed directly in the field at the rocky outcrop and in the laboratory on specific rock samples collected from the outcrops. The peridotite-lherzolite outcrop appeared macroscopically uniform and contained three systems of visible parallel sub-vertical fractures. This rock has substantial bulk density and higher than average value of seismic wave velocity. The presence of fracture systems gives rise to its velocity anisotropy. The seismic waves passing through the rock fractures are subject to velocity dispersion and frequency dependent attenuation. Our data, obtained from field and laboratory measurements, were compared with theoretical model predictions. In this model we successfully used displacement discontinuity approach. For the velocity dispersion evaluation we used multi-frequency measurements. The a priori observation of orientations and densities of fracture sets allowed evaluation of their stiffness. Our approach revealed that the first arrivals of seismic waves can be used for evaluation of P-wave group velocities, the specific case, in which we expect anomalous velocity dispersion. Our observations contribute to the issue of up-scaling of well-log derived velocities in fractured rock to the scale of standard seismic exploration frequencies.
Permanent Link: http://hdl.handle.net/11104/0221399