Content area
Full text
ABSTRACT
This paper presents results about the effectiveness of different student-centered instructional methods on undergraduate student perceptions of a spatial phenomenon, earthquake P and S wave shadow zones, in introductory geology classes. Textbooks commonly illustrate earthquake P and S wave shadow zones using ray tracing techniques with an epicenter at the North Pole and the shadow zone south of the equator. Shadow zones differ for earthquake locations elsewhere. Shadow zones for earthquakes at locations around the world can be hand plotted using a globe and a map of the Earth. The plotter gains experience in using latitude and longitude for plotting, understanding global geography, translating spherical geographic data to a two-dimensional map, and gains a better understanding of seismic waves and the Earth's interior. The concept also explains how satellite orbits appear on flat maps and the concept of great circle paths. The shadow zone can also be mapped digitally using a Geographic Information System (GIS), such as ArcView(TM) GIS with the similar results. Overall, 81.5% of the student participants considered both instructional methods an enhancement to their understanding of the earth's interior, globes, maps and shadow zones. The results suggest that student alternate conceptions of the representation of geospatial data in 2D and 3D can be influenced by both traditional paper exercises and activities that teach with GIS technology.
INTRODUCTION
Most introductory geology courses cover seismology and earthquakes and many institutions have local seismographs for research or demonstration purposes that are used to explain the generation of seismograms. For example, a home-made Lehman seismograph is running at the authors' institution (see Kroll, 1987, and Gerencner and Jackson, 1991, for instructions and further references). The concept of the compression and shear wave seismic shadow zone is often discussed. The shadow zone results from the properties of P and S waves as they encounter the earth's low velocity liquid core. Shear waves cannot be transmitted through a liquid and so are converted to P waves or reflected at the surface of the liquid outer core. Compression waves refract at the mantle-core boundary and are bent from their original path (Murphy and Nance 1999, p. 185).
The shadow zone phenomenon is illustrated in virtually all introductory geology/earth science texts that deal with seismology, earthquakes, and...