Initial Publication Date: June 23, 2023 | Revision: July 15, 2026

Module Overview for Instructors

Locating Subsurface Features using Gravity and Magnetics

Module Goals

Students willexplain how density variations in the subsurface allow the imaging of buried structures by referencing the equation for gravitational acceleration.
Students will explore Earth's ambient magnetic field and interpret magnetic data to detect objects in the subsurface.
Students will apply gravity and magnetics principles to interpret real-world data sets for hazards and infrastructure.

Assessment: Assessment of student learning can be approached flexibly. Each unit of the module includes student handouts and exercises that can be used as summative assessments. Formative assessments can be conducted as check-ins and conversations with students throughout the module. Learn more about assessing student learning in this module.

Taught in its entirety, parts of this module are more appropriate for majors-level students. However, aspects work well in introductory courses.

Show more about teaching the module in introductory courses

If you are interested in decreasing the time and technical level of the module, while still introducing students to the applications of gravity and magnetism for locating features underground, we suggest:

Unit 1 - As is
Unit 2 - As is, although the smartphone magnetics survey could be bypassed if short on time
Unit 3 - Have students:
- Skip the GeoPark gravity lab (Part 1)
- Complete the Weyandt Farm magnetics lab (Part 2)
- Complete the stairwell gravity lab using the provided dataset (Part 3)

Show more about teaching the module in advanced courses

If you are interested in increasing the technical level of the module for students who are already familiar with some geophysics concepts, we suggest:

For students with some familiarity with geophysics: Have students complete all components of the module, including all "optional extension" questions.
For students who are very familiar with geophysics: Skip Unit 1 and Unit 2 and complete Unit 3 materials only.
If a gravimeter is available, have students collect their own data to complete Unit 3 Part 3's stairwell gravity lab.
Note that raw data is provided in tabs at the end of Unit 3 Part 1 (GeoPark gravity) and Unit 3 Part 2 (Weyandt Farm magnetism) data spreadsheets. Instructors may choose to modify activities or develop their own and provide students with only the raw datasets for analysis. For example, instructors could provide students only the raw data from Unit 3 Part 1's GeoPark gravity survey, and ask them to attempt to correct for drift using the technique introduced in Unit 3 Part 3's stairwell gravity lab.

Outline

The module covers material sequentially, but the units can also often be taught as standalone lessons.

Unit 1: Locating Buried Objects Using Gravity

This in-class/lab/homework activity introduces students to the idea that the gravitational acceleration g varies across Earth's surface and is sensitive to buried features. Students are asked to "read" and run interactive animations of the equation for gravitational acceleration to understand how measured gravity profiles are sensitive to the mass and depth of buried objects.

Unit 2: Environmental Magnetism

This module introduces students to the underlying principles of magnetism. Students are introduced to major magnetism concepts through a narrated video, and concepts are reinforced through a worksheet that allows students to simulate changes in the magnetic fields around two magnets and to explore properties of the Earth's magnetic field as a function of position. Students then explore the significance of a magnetic dataset acquired as part of an archaeological survey.

Unit 3: Gravity and Magnetics Field Data Exercises

This activity focuses on practical application of concepts discussed in Units 1 and 2 through the analysis of measured or provided field datasets. Students will follow experimental procedures to measure gravity changes inside a building and/or analyze magnetic prospecting data. Students will gain the ability to interpret real datasets, justify their findings, describe limitations of the measurements, and produce graphics to communicate their data.