The
southern Illinois region experiences an average of 1-2 small
earthquakes per week. Students in the Basics in Geology
(B.I.G.) group are studying the local geology and geologic
structures of southern Illinois and nearby areas to learn
about the subsurface causes of this earthquake activity.
The B.I.G. group has already gone on several field trips to study the local geology and is planning more trips involving data collection. The photo below (left) reveals possible recent (Quaternary) faulting south of Thebes, Illinois along the Mississippi River. This site was discovered during a recent field trip by the students who participate in Basics in Geology. The approximate location of the study area is shown on the topographic map below.
T
his
structure clearly reveals faulting with vertical offset and
deformation just below the surfacial layer of topsoil. The
schematic below is our preliminary geological interpretation
of this structure, which may turn out to be a slump feature
rather than faulted sediment. The gravel-filled zone in the
middle of the image contains larger light brown colored
clasts probably removed from a lower unit, the McNairy Sand
of the upper Cretaceous (70 million years ago). Our
interpretation of the fault, which is clearly observable on
the photo, is not complete and some 
of
the lithologic units are yet to be identified.
More information about the age of this fault and its possible relationship to southern Illinois earthquake activity will come after we complete our on-site investigations. We plan to investigate this structure and other nearby features with Ground Penetrating Radar (GPR) and other subsurface imaging methods. Our B.I.G. students hope to present the project results at various science symposiums.
