Ground Rupture in the Baldwin Hills

Abstract

That the earth-crack ground rupturing of the Baldwin Hills was genetically related to high-pressure injection of fluid into the previously faulted and subsidence-stressed subsurface seems established beyond reasonable doubt (note geological structural maps and cross section line drawings). The fault activation appears to be a near-surface manifestation of stress-relief faulting triggered by fluid injection, a mechanism identified as being responsible for the 1962-1965 Denver earthquakes and for generation of small earthquakes at the Rangely oil field in W. Colorado. These examples of fault activation through response of stressed ground to artificially induced increases in subsurface fluid pressure demonstrate some of the mechanically predictable consequences of injection of fluid into the ground, a practice that is becoming increasingly widespread not only in secondary oil recovery operations, but as a means of industrial waste disposal and ground-water management. Experience in the Baldwin Hills suggests that although fluid injection operations may be conducted for beneficial purposes, the effects of such injection on the geologic fabric can be serious and far-reaching. (20 refs.)