ARCHIVED REPORTS_1990 - Laserfiche WebLink

Home Browse Search

KLEBNFELDER The Stockton Fault passes from near Tracy to directly beneath (and beyond) Stockton in a northeasterly direction to approximately one mile south of Foothill Landfill. Its position is known only from oil well-log data; no surface expression of this fault has been mapped. Based on a review of the "San Joaquin County Council of Governments' Seismic Safety Element, May 1973"4, subsurface data indicate that no appreciable movement has occurred on the Stockton Fault since Mid-Pliocene time, perhaps five million years ago or more. Ordinarily such evidence would lead to the conclusion that this fault is inactive and therefore does not pose an earthquake threat. However, the existence of three earthquake epicenters located near the easternmost subsurface positions of the Stockton Fault raises questions regarding the inactivity of this fault. On April 10, 1881, an earthquake occurred in the eastern area of the fault at an unspecific location, having an estimated Modified Mercalli Intensity of VII. Although direct correlations between earthquake effects (damage, personal reaction, etc.) and Richter Magnitude are not precise, it seems likely that this earthquake was of approximate Magnitude 5+. Two other earthquakes of smaller size (Magnitude —4), occurred approximately 5 miles southeast of Linden on September 19 and 20, 1940. e latter of these epicenters was instrumentally located, but only in a"rough" manner. It is not certain, _ therefore,whether or not these epicenters lie along the northeast extension of the Stockton Fault. Linden is approximately 8 miles west of Foothill Landfill. Because the data is limited it is difficult to assess the potential for earthquake activity on the Stockton fault. Surface Soils There are many different soil series mapped around Foothill Landfill. Each soil series represents a different set of characteristics: slope, presence of a hardpan, drainage, permeability, runoff capability, chance of flooding and hazard of erosion, to name a few. Soil profiles in the vicinity of the landfill vary from 4 to 60 inches deep. Soils in San Joaquin County had been mapped at the time of this reports, while soil in Stanislaus County had not been mapped. There are fourteen different map units within one mile of Foothill landfill. Soils and map units with similar properties named above have been grouped together, and are presented on Plate 1-5. FOOTHILL 6