Late-semester lecture/activity using seismic focal mechanisms

Jon Lewis

Indiana University of Pennsylvania

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This page first made public: Oct 28, 2005

Summary

This late-semester lecture/activity uses seismic focal mechanisms to build on already-covered concepts of friction, elasticity (rheology), and 3D thinking, and to expand the discussion to include seismic first motions and earthquake locations. This is accomplished, in part, by a hands-on excercise using a toy Slinky.

Geophysics, Rheology/Behavior of Materials, Geophysics and Structural ...(more) | College Lower (13-14), College Upper (15-16)

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Context

Audience

This module seems fitting for a required undergraduate course in structural geology.

Skills and concepts that students must have mastered

A good handle on stereonets and thinking in 3D. Basic understanding of stress versus strain would be helpful.

How the activity is situated in the course

This lecture/activity draws on concepts of friction and elasticity that might typically be covered earlier in the term, and adds seismic first motions using a Slinky (toy) and earthquake locations. As such, it seems fitting for rather late in the term.

Goals

Content/concepts goals for this activity

The goal is a basic-concepts-based understanding of how earthquakes work. Toy Slinkys (Slinkies?) are great tools for students to experience P-wave first motions (ideally with their eyes closed) and to come to appreciate the implications of an elastic rheology. This lecture/activity might serve as a launching point to get into other aspects of geophysics that are of importance to structural geology.

Higher order thinking skills goals for this activity

The basic elements developed in this lecture/activity can be used to get students excited (hopefully) about understanding active tectonic settings. This understanding can then be applied to follow-up exercises using web-based data from NEIC or other earthquake data archives. These exercises might, for example, entail developing hypotheses about strain geometries in different tectonic settings.

Other skills goals for this activity

Working with other students in pairs or small groups. Using tactile senses to "feel" for differences in the response of a Slinky to a sudden deformation.

Description of the activity/assignment

This lecture/activity allows students to "play with" a toy Slinky in order to recognize the implications of an elastic rheology to deformation at shallow crustal levels. Building on already-covered concepts of elasticity and friction, this module adds seismic first motions and earthquake locations to the students conceptual tool bag. As such, this module can be used to segue into other areas of geophyics that are of importance in structural geology (e.g., active tectonics, hazards).