3D SEISMIC DATA REVEALS CROSS-BASIN FAULTING IN THE SACRAMENTO VALLEY

It has been our observation that most geologists have mapped faults in the Sacramento Valley in a northwest to southeast trend and sub-parallel to several known major fault systems such as the Midland Fault System. Few sizable faults have been described in the literature which have a "cross-basin" or "counter regional" southwest to northeast trend, such as the Stockton Arch, Dry Slough, and Willow Slough Faults. This paper will describe several additional "cross-basin" faults in the natural gas province of the Sacramento Valley of California.

Interpretation of several regional 3D seismic surveys has resulted in the identification of several additional cross-basin faults that were not known to the authors. These faults are usually part of a series or system of faults, primarily in the Yolo and Solano County area, and can be mapped for several ten's of miles. We have taken the liberty of naming these faults the "Crossroads System", the "West Bunker System", and the "Denverton System" of faults, in addition to the "Winters - Dry Slough System" of faults. Many of these cross-basin faults are located on the westerly flank of the Sacramento Valley Syncline and appear to be related to the subsidence of the basin in an extensional environment. Cross-basin faults are important in their effect on deposition and formation of traps for natural gas. The "Crossroads System" for example, acted as a growth fault during deposition of the Cretaceous Winters Formation and acted as a barrier to gas migration in the Crossroads Gas Field.

It is suggested that additional "cross-basin" faults will be identified as geophysical interpretation of 3D seismic continues to drive the exploration for natural gas in the Sacramento Valley.