Abstract Ground failures, ranging from long tension cracks or fissures to surface faults, are caused by man-induced water-level declines in more than 14 areas in the contiguous United States. These failures are associated with land subsidence caused by compaction of underlying unconsolidated sediment. Fissures, which range in length from dekameters to kilometers, typically open only a few centimeters by displacement but are eroded by surface runoff into gullies 1 to 2 m wide and 2 to 3 m deep. Surface faults commonly attain scarp heights of 0.5 m and lengths of 1 km; the highest and longest scarps are 1 m and 16.7 km, respectively. Scarps grow by aseismic creep at rates approximately ranging from 4 to 60 mm/yr; modern fault movement is high angle and normal. Fault movement commonly correlates with seasonal water-level fluctuations, and examples of seasonal water-level recoveries halting fault movement have been reported. The greatest economic impact from ground failure is in the Houston-Galveston, Texas, metropolitan region where more than 86 surface faults have caused millions of dollars of damage and losses of property value. Most ground failures probably are caused by localized differential compaction, although this mechanism has not been demonstrated everywhere. Earth fissures formed by this mechanism are caused by stretching related to bending of the overburden that overlies the differentially compacting zone. Surface faults form when differential compaction is discrete across preexisting faults. Fissures that form complex polygonal patterns probably are caused by tension induced by capillary stresses in the zone above a declining water table. Ground failures can be predicted either by determining potential areas of differential compaction or by monitoring surface deformation in areas of ongoing water-level decline. Potential ground-failure sites can be resolved by either technique to within a few dekameters.

Abstract This volume represents some of the papers presented at the SEPM Research Symposium GeologicHistory of the Oceans at the Annual Meeting, March 1971, in Houston, Texas. Knowledge of oceanic sediments has been acquired in two ways: 1) directly by sampling and observation, and 2) indirectly through seismic investigations. Until the past decade, direct sampling and observation techniques could only provide information on the surficial materials of the ocean floor. The development of the piston corer has permitted oceanographic vessels to sample the upper 20 meters, and more recently the upper 30 meters, of the ocean floor, but such cores rarely penetrate the Pleistocene and enter older sediments. Until recently, most knowledge of the deeper sedimentary materials in the ocean basins was obtained through seismic reflection studies. The purpose of this volume is to present a number of observations, ideas, interpretations, and speculations which will be of value in considering the meaning of the increasing volume of data from older deep sea deposits.