USU researcher studying quakes

Several years ago, scientists discovered shifts in the earth’s surface occurring so gradually they didn’t register on a seismograph. It is believed these movements, which occur for months or years at a time, can predict or cause future earthquakes.

These so-called silent earthquakes have become the focus of a study conducted by Tony Lowry, an assistant professor in geology at USU.

“This is something very new. It is very much a topic of research, seeing what they do to the earthquake cycle,” Lowry said. “They probably change stress in such a way that favors another earthquake. Beyond that, we are still trying to figure it out.”

Lowry said silent quakes tend to occur where larger earthquakes are predicted. Even though the movement is slow enough people cannot feel them, it is believed these quakes increase the seriousness and danger of earthquakes by shifting the stress of fault lines.

“It happens very slowly and doesn’t produce shaking. Silent earthquakes are basically just slip events on faults. They are essentially the same things that cause earthquakes we feel,” Lowry said. “Slips on faults evolve through time, but it is relevant to when and where an earthquake happens.”

By studying the shape of the ground surface with Global Positioning Satellite systems, scientists are able to record silent earthquakes.

The majority of Lowry’s work has been conducted in southern Mexico. Using a GPS system, Lowry recorded a movement of 10 centimeters in the course of three months. He said the shifts occurring there are contrary to what would be expected considering the normal movements of plate tectonics.

“What you would have expected to see is just having a steady movement, moving steadily in a straight line along the fault lines, but then it is superimposed by something,” he said.

Lowry has said weather patterns could play a role in causing silent quakes. The weight of precipitation can create enough pressure to move the earth’s surface. In previously published information, he said the smallest amount of pressure could cause significant movement of faults leading to silent quakes and, possibly, earthquakes of greater magnitude.

Mexico experiences one silent quake a year, Lowry said.

Silent quakes have also been recorded in California, Washington, Oregon, Hawaii, New Zealand and Japan. In the northeastern area of the United States, there is one silent quake about every 14 months.

Silent quakes have not occurred in Utah, he said. However, there is a GPS measuring system located near Sardine Canyon that has been set up by the University of Utah and EarthScope.

“You never really know. We are very close to a fault here. The East Cache Fault has certainly produced greater than magnitude 7 earthquakes and it will do so in the future,” Lowry said.

Lowry is currently in the process of installing GPS systems in Colorado and New Mexico. He said these instruments often sit in one specific location for more than 10 years.

When silent quakes are recorded in high-risk areas, the seismic hazard level is raised for safety reasons.

“Because we are recognizing that stress is being placed on areas where we expect large earthquakes, they raise the seismic hazard level,” Lowry said.

Lowry began studying silent earthquakes while in New Zealand during the mid 1990s. During his stay there, he said he happened upon different kinds of data supporting the idea of silent quakes. At the time, however, Lowry said few people in the field were recognizing such movements. Soon after, he started seriously researching these subtle movements in an effort to determine their exact role in high magnitude earthquakes.

He said, “These are going on all the time, and they are probably related somehow.”

-ariek@cc.usu.edu