Geophysical investigations in the Colorado Delta Region

Abstract

The combined approach of gravity and seismic re-fraction exploration was used to determine depths of the Cenozoic section and to study the fault pattern in the Colorado Delta region. Basement depths measured varied from about 2200 feet to a minimum depth of 15,400 feet along the international border, east of Calexico. A study of the seismicity of the region shows that the greatest seismic activity over the past 60 years has been along the San Jacinto fault system. Continuity of specific major faults is difficult to establish using gravity methods alone because of the lack of indicated vertical throw on the faults. No conclusive evidence is presented for establishing the continuity of the Mission Creek-Banning fault southward into the present area of investigation, although geophysical evidence is presented for a fault present beneath the Sand hills (Algodones Dunes).