Sept. 16, 2002

A Model Earthquake

Steve Roecker, professor of earth and environmental sciences, is helping to build the first accurate subsurface imaging model of how a catastrophic earthquake forms.

The research, a collaboration with the University of Wisconsin-Madison, is part of the San Andreas Fault Observatory at Depth (SAFOD), a national project now under way near California's San Andreas fault, one of the most studied fault zones in the world.

Even with today's technology, researchers still know very little about how earthquakes behave. Scientists have many models of how temblors might form, but most of the models cannot be tested by surface observations.

The biggest problem is that researchers have had limited success recovering relevant data from equipment exposed to intense heat and pressure.

But SAFOD researchers for the first time have lowered durable seismic devices down a two-mile borehole near the earthquake zone. The instruments — several soup-can-sized metal containers — are fastened to a cable connected to a computer. Using wireless technology via satellite, the group can observe — in real time — earthquake emissions very close to where they begin to form.

Roecker's team is now transforming the data into a sophisticated, high-resolution model of the subsurface.

To test how accurate that model is, Roecker in October will set off a series of explosives at the surface to create a "reverse" earthquake that will be recorded by the seismic devices.

These recordings will be used to calibrate the 3-D images previously deduced of the San Andreas Fault. Researchers will then be able to drill into an actual source of a tremor and study it.

Although Roecker's subsurface imaging model will not prevent earthquakes, it will help determine what causes earthquakes to rupture where they do. That information will allow architects to construct buildings better able to withstand bigger trembles.