THE CASE FOR TEACHING EARTHQUAKE FOCAL MECHANISM SOLUTIONS IN STRUCTURAL GEOLOGY
Several benefits are associated with inclusion of FMS in structural geology courses, including (1) improved motivation, (2) reinforced fundamental concepts and (3) broadened scope. FMS are essential to the study of active tectonics. Related issues of hazard recognition and risk assessment tend to endow structural geology with a sense of urgency and importance for students a significant positive motivator. FMS integrate and reinforce key concepts related to the mechanics of crustal materials. The elastic component of crustal rheology is well illustrated with reference to earthquake data. The cycle of elastic loading, frictional failure, radiation of seismic energy, detection by seismograph stations, and analysis of first-motion records in an inverse process to determine the characteristics of the seismic moment tensor is an excellent example of an important 4D structural/geophysical problem. Resulting FMS provide constraints on present-day crustal kinematics. Use of FMS by structural geologists broadens the scope of our potential influence as scientists working in the public interest, as we seek an improved understanding of hazardous active structures.
FMS are routinely and rapidly computed for earthquakes of magnitude greater than 5.5 worldwide, and are easily obtained at no cost from online databases (e.g., neic.usgs.gov/neis/sopar and www.seismology.harvard.edu/CMTsearch.html). Hence, students can easily acquire FMS for use with corresponding geologic maps and literature to investigate the active tectonics of a given area.