In 1996, the Education Committee of the Kentucky Geological Survey, in conjunction with the Kentucky Society of Professional Geologists, established the Earth Science Education Network (ESEN). Ordovician) deposition.
at the surface, which has a structural relief of about 400 ft (Withington and Sable, 1969). Soderberg and Keller (1981) suggest that it is underlain by a deep-seated graben of late Precambrian age, The hard dolomite of the Boyle formation was undercut by weathering of the softer shale of the Crab Orchard Formation, which caused the dolomite to fracture and fall. The quakes were so strong the mighty Mississippi River flowed backward for three days. 133 9
Offsets on these fault zones are mostly down to the south. Jeptha Knob, first described by Bucher (1925), has recently been described in detail by Cressman (1981). The Cascadia Subduction Zone, Pacific Northwest By the time Lewis and Clark arrived on the West Coast in 1805, it had been 105 years since the Cascadia Subduction Zone last ruptured, sending a large portion of the Pacific Ocean roaring toward the coast. The fractures are covered by thick layers of rock, which in turn are .