Geophysics exercise hammers home seismic knowledge

Students use sledgehammers, sensors to image subsurface

By California State University, Bakersfield

April 18^th, 2025

It’s not every day that students get to swing a sledgehammer in class, but 13 geology majors at California State University, Bakersfield recently did just that. Though the exercise might have had the added benefit of relieving a little school year stress, its main purpose was strictly scientific.

In late March, students in Dr. Matt Herman’s geophysics class had the opportunity to use geophones from SensorEra to conduct seismic refraction imaging. Ten state-of-the-art geophones provided by the company were staked into the ground on the Don Hart East Lawn, each one detecting the motion of the ground when seismic waves pass by. That’s where the sledgehammer came in, with students taking turns to strike a metal plate to induce seismic waves.

“We’re trying to produce a force that sends out a seismic wave significant enough to be picked up by these geophones with a sledgehammer and using all our strength,” said geology major Brooklyn Macross.

Students swung the sledgehammer at a metal plate on the ground, first set on the south side of the lawn, then on the north side. The plate was three feet from the first geophone sensor, with nine more sensors set in a line each 30 feet apart. With about five strikes at a time, the students one by one created forces to gather data that would provide an image of the ground’s subsurface.

“One of the main uses for geophysical techniques is to build images of the subsurface, a place humans typically do not have much access to,” Dr. Herman said, explaining that seismic refraction imaging relies on seismic waves traveling faster in deeper rocks. “This allows us to determine the thickness of layers in the Earth, and the speed of seismic waves through those layers.”

The resulting data like that collected by the students tell geologists about the physical properties of the subsurface, allowing them to interpret in context of the actual rocks underground. The recent seismic refraction exercise is one of many approaches Dr. Herman covers in the class, but the partnership with SensorEra brought this particular technique to life in a new practical way.

Although the Geology Department has older seismic imaging equipment, it no longer works, which led Dr. Herman to seek out opportunities to buy new equipment or collaborate with someone who already has it. Through his collaboration with scientists at California Resources Corporation (CRC), Dr. Herman was connected to SensorEra, a company CRC works with to do its own seismic imaging and earthquake monitoring.

Students got to work with high-tech equipment regularly used to perform surveys in the industry. It was “a glimpse into the life of a professional geophysicist, using cutting edge tools of the trade,” Dr. Herman said.

As Nicholas Brooks from SensorEra put it, the geophones are like “a smart watch for the earth.” Equipped with 4G, GPS and WiFi, the sensor data is streamed to the cloud, with results automatically generated to give geologists a better idea of changes in the Earth beneath their feet.

Geophysics exercise hammers home seismic knowledge

Geophone sensors can be used passively, consistently monitoring for earthquake or other movements, or actively for specific projects, like the one the students were undertaking. Knowledge of the subsurface is needed for all kinds of projects, Brooks explained, whether it’s finding the water table to build a well or safely mining rare earth materials in a way that minimizes environmental footprint.

Brooks lives in Houston, where SensorEra is based, but a field experiment with CSUB students while he was in California was worth it to give the young geologists a chance to work with real-world instruments.

“Just getting out to do some proper field geophysics is valuable for students,” Brooks said. “When you’re looking at geophysical data, sometimes it’s difficult to visualize how it’s acquired. They’re also getting some practical hands-on experience and a bit of fun outside. Hopefully at least one out of this group picks it up and becomes a geophysicist in the future because we need new geophysicists coming into the industry.”

Macross agreed that the experience was quite different from working with data she had no part in acquiring.

“It feels real, instead of just looking at data and sitting there all day,” she said. “When I look at data and I compile it and analyze it, I’m like, ‘OK, that’s what this means,’ but really there’s no context for me to go off of. Doing this, I can see how much force I am producing, which is nothing compared to an actual earthquake, but it’s still fun to see what I’m capable of.”

It doesn’t hurt that the experiment was a fun way for students to flex their muscles and test their strength, all in the name of science.

“Honestly, it was stress-relieving — this class is a lot!” said Salvador Osorio-Martinez, a geology major. “No, but jokes aside, it’s actually really fun. To swing something at the ground and then get data from it, I think it’s just really meaningful. Doing work outside of the classroom is really nice.”