Seismic imaging: Introduction
Illinois Route 29 (IL 29) is a major north-south transportation route along the western side of the Illinois River Valley (Figure 1 at right). For the most part, the wide river valley provides ample room for an adequate highway corridor. But for several miles north of the town of Chillicothe in northern Peoria and southern Marshall Counties, the river channel swings close to the western margins of the valley, forcing the highway against steep bedrock bluffs. The proximity of the bluffs presents two important geotechnical hazards, potential landslides and potential collapse from abandoned shallow coal mines. The Illinois Department of Transportation (IDOT) has requested assistance from the Illinois State Geological Survey (ISGS) in investigating these and other technical questions concerning a planned improvement of the IL 29 corridor in this area. The identification of underground mines is a critical component of the ISGS's mapping activities along the IL 29 corridor. In this part of the project, geophysical techniques are used to locate old mine workings that may be present beneath the highway corridor. The technique can also estimate the size and depth of the underground mines and indicate areas of potential landslide activity.