A shock absorber, adapted to be disposed above a perforating gun in a tool string and adapted to be disposed in a wellbore, includes a crushable element disposed between an inner and outer housing, a frangible breakup element, and a detonating cord disposed within the frangible breakup element and connected to the perforating gun. In operation, a detonation wave propagates within the detonating cord on its way toward the perforating gun. However, before the detonation wave reaches the perforating gun, the detonation wave propagates through the frangible breakup element. In response to the passage of the detonation wave through the frangible breakup element, the frangible element shatters into a multitude of pieces. Before the frangible element shatters, the frangible element absolutely prevents any shock from being absorbed by the shock absorber of the present invention. As a result, preloading effects are avoided. However, after the frangible element shatters, the shock absorber of the present invention is ready to absorb the shock resultant from the detonation of the perforating gun. After the frangible element shatters, in response to the detonation wave passing therethrough, the inner and outer housings move in opposite directions relative to one another in response to a received shock and the crushable element begins to permanently deform. An upward or a downward shock may be absorbed by the shock absorber, but only after the frangible breakup element shatters in response to the detonation wave in a detonating cord passing therethrough.