Dynamic fracturing: field and experimental observations

We analyzed a system of complex joints in thick dolomite layers that are exposed within the western margins of the Dead Sea basin. These joints display two dominant features: ‘tree-like’ branching and a gradual increase of density that leads to local fragmentation. The development of this joint system is investigated in laboratory experiments with samples of brittle/ductile layered composites. The samples were subjected to layer-parallel extension and displayed three styles of fracturing: planar fractures, known from previous tests; branching fractures and clustering fractures, observed here for the first time in layered composites. Based on fracture morphology, we deduced that the branching and clustering fractures in the experiments, and the tree-like, closely spaced joints in the field, propagated at dynamic, high-velocity growth rates. It is proposed that the morphological features described here could be used as field criteria to recognize dynamic rates of rock fracturing.