Abstract: An improvement in an apparatus for fracturing subterranean formation by explosive fracture wherein opposed end charges are detonated to enhance the explosive capability of a central charge, the improvement comprising intermediate driver charges intermediate the central charge in each of the respective end charges; the driver charges being detonated by the end charges to provide a sustained pressure wave for enhancing the rubblizing and fracturing of the subterranean formation and extend the fracture more deeply into the subterranean formation. Also disclosed are improved apparatus enabling carrying out the split second detonating of the respective explosive charges, containing the explosive charges without entangling cable and the like downhole and preventing misfiring.