Dynamic fracturing: field and experimental observations

We analyzed a system of complex joints in thick dolomite layers that are ex posed within the western margins of the Dead Sea basin. These joints displa y two dominant features: 'tree-like' branching and a gradual increase of de nsity that leads to local fragmentation. The development of this joint syst em is investigated in laboratory experiments with samples of brittle/ductil e layered composites. The samples were subjected to layer-parallel extensio n and displayed three styles of fracturing: planar fractures, known from pr evious tests; branching fractures and clustering fractures, observed here f or the first time in layered composites. Based on fracture morphology, we d educed that the branching and clustering fractures in the experiments, and the tree-like, closely spaced joints in the field, propagated at dynamic. h igh-velocity growth rates. It is proposed that the morphological features d escribed here could be used as field criteria to recognize dynamic rates of rock fracturing. (C) 2001 Elsevier Science Ltd. All rights reserved.