Module Overview for Instructors

Measuring Depth to Bedrock Using Seismic Refraction

This module is designed to introduce students to geophysical concepts and related earth science principles to illustrate how geophysics can be used to inform engineering projects in an urban environment.

Module Goals

  1. Students will explore the relationship between seismic refraction survey design and subsurface imaging
  2. Students will analyze and interpret seismic refraction data to infer depth to bedrock
  3. Students will estimate the difficulty of completing an urban renewal project, based on their interpretations of seismic refraction data

Assessment: Assessment of student learning can be approached flexibly. Each unit of the module includes student handouts and exercises that can be used for formative assessments. In addition, each unit includes a set of multiple choice and short answer questions that can be given to students as homework, on quizzes, or on exams.

Outline

The module covers material sequentially, but the units can also be taught as stand-alone lessons.

Unit 1: Introduction to shallow seismology to explore our subsurface environment

This unit is designed to provide an introduction to geophysical imaging of the shallow subsurface, motivate students to become invested in the uses of seismic refraction, provide career context, and build enthusiasm for the following units. In this unit, students use seismic data to calculate wavelength, frequency, and travel time, laying the groundwork for understanding how seismic refraction can be used to infer physical properties of sub-surface materials.

Unit 2: How seismic waves travel through the ground

This unit presents a basic introduction to seismic refraction. In the first exercise, students explore Snell's Law, discovering the relationship between layer velocities and the incident angle for critical refraction. In the second exercise, students pick arrival times off of a travel-time/offset plot of data collected on the University of Wyoming campus, use their interpretations to calculate soil thickness and layer velocities, and sketch a cross-section of the subsurface soil and bedrock layers.

Unit 3: Codorus Creek case study: Measuring and interpreting seismic refraction data

This exercise is focused on using field data (either provided datasets or collected on your own) to retrieve information about the shallow subsurface. In part 1, students design a seismic refraction survey to measure the depth to bedrock along Codorus Creek, where an urban renewal project needs this information to determine what kinds of machinery they will need to use for the work. In part 2, students analyze seismic refraction data from Codorus Creek to determine the depth to bedrock and to evaluate how difficult it will be to excavate the overburden for the urban renewal project. Finally, there is also an optional exercise that entails collecting your own dataset using instrumentation resources available at the IRIS PASSCAL Instrument Center, defining a research question, doing background research and interpreting your results.

Making the Module Work

To adapt all or part of the module on Measuring Depth to Bedrock Using Seismic Refraction for your classroom you may also want to read through Using IGUaNA Modules for Your Course, which includes sample pathways through portions of IGUaNA modules. Theà la carte option is recommended where content and exercises are distributed throughout a semester-long course.