Seismic Reflection and Drill Hole Study of the Herald-Phillipstown Fault in the Wabash Valley
S. Chatterjee1 and J. L. Sexton2
1Department of Geological Sciences, Indiana University, Bloomington, IN-47405-1403
2Department of Geology, Southern Illinois University, Carbondale, IL-62901
Five seismic reflection profiles from the Wabash Valley area of southeastern
Illinois successfully imaged the Herald-Phillipstown fault. From the reflection
profiles and geophysical
well logs, it was interpreted that the Herald-Phillipstown
fault is an inverted flower structure. The main fault of the group is a steeply
dipping normal fault with associated splay faults that are reverse in character. All
the faults of this inverted flower structure are basement penetrating. Structural
contour maps as well as maps of various reflector surfaces are prepared using
two way travel time as well as depth. These maps show that the reflectors are
undulating in character. Also distinct east-west rotational movements of the
reflectors are observed along these faults and the main fault shows a curved
geometry from south to north. The combination of the rotational movement, the
curved nature of the fault plane and the undulating reflectors resulted in variation
of offsets along these faults. The nature of faults of the inverted flower structure
as observed on the seismic reflection profiles also indicates that there has been
a change in the stress regime from extensional to compressional. Structural
cross sections were generated using
geophysical
well logs from drill holes
located along these seismic lines to analyze the nature of these faults at
shallower depths. From these cross sections numerous shallow faults were
observed and many of them can be correlated with those observed on seismic
records indicating upward migration of basement penetrating faults into shallow
younger sediments.
AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas