Normal Fault Geometry and Associated Structure From Surface Exposure in S. Oregon as an Analogue to Subsurface Structure Maps

R. K. Davies, M. F. Crawford, W. F. Dula, M. J. Cole, and G. A. Dorn

Digital topographical data are used to construct structure maps on well-exposed basalt flows that cap conspicuous fault-bounded tilt blocks in south central Oregon. These topographic/structure maps serve as analogues to similar structures mapped from 3-D seismic data in the subsurface. The areal coverage of the surface data, however, is much larger than the average 3-D seismic survey and allows a more extensive picture of the structural geometry. The 80 m horizontal data spacing of the digital surface data is at an equivalent to the average 3-D seismic line spacing, and we expect similar mapped resolution. Fault resolution is improved in selected areas mapped at a 3m horizontal spacing or "below seismic resolution".

Narrow bands of closely-spaced contours define the hanging wall and footwall contacts of the faults. Dip magnitude and azimuth maps clearly demonstrate the fault polygons and their distinct geometry: long faults composed of short gently curved, overlapping segments. Topographical highs on the exposed surface occur predominantly in the footwall of the faulted blocks and appear to favor regions of fault overlap. The area of uplift is analogous in areal extent to subsurface hydrocarbon traps. The topographical expression of the surface is dramatically enhanced using 3-D visualization tools that allow simulated flight above the computer generate relief maps.

These digital surface data provide the explorationists with reservoir scale analogues to sub-surface structure, and provide structural detail often poorly imaged in the sub-surface.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California