Production of new surface area by fracturing of rock behind an explosive-initiated high amplitude wave is probably an important mechanism for energy absorption in the region near n explosion in rock. Explosive-initiated high amplitude pulses in cylinders of three different rocks and two concretes were studied to determine the pulse amplitude need to damage the cylinders. An average high amplitude wave velocity of half the elastic wave velocity was observed in a porous limestone. Elastic theory is not expected to apply to a wave fracturing a rock. Rapid decreases in original free surface velocity of the greywacke rock which was most thoroughly tested indicate that this rock sustained tensile stresses about a hundred times greater than its probably tensile strength for times a long as fifty microseconds.