Where was that earthquake?

Sara Harris, Brett Gilley, and Ido Roll

University of British Columbia

Undergraduate introductory-level geosciences lab for majors and non-majors.

No prior experience needed.

This is part of a sequence of lab activities related to earthquakes.

By the end of this activity, students will be able to:

1. Explain how differences in travel times can be used to estimate distance traveled
2. Locate a starting point on a map using paired arrival time data.

In small groups, students "invent" a way to figure out the location of a house, based on the walking times of two housemates to various locations near their house. This cover story is an analogy for using the arrival time differences between P and S waves to locate an earthquake epicenter. Students then create and compare graphs analogous to a Jeffreys-Bullen diagram and come up with a generalized way to use this type of graph to find distances. The activity prepares students for learning how to locate an epicenter and makes the relationship between distance and arrival times meaningful, since they have to figure out how to use arrival time differences to estimate distance.

1. Give students another location in the same scenario, a different distance away.
2. Change Polly and/or Sam's speeds and apply to the same scenario.
3. Give students some data for another of the pairs of friends and ask them to locate this different house on the same map.