BioEd Online

A home to nearly 40 years of some of American football's most exciting games will disappear on 11 April, with the demolition of the Dallas Cowboys' famed Texas Stadium in Dallas, Texas.

But a few seismologists are hoping for one last explosive memory — a geological one to complement the footballing heroics of players such as quarterback Roger Staubach, runner extraordinaire Emmitt Smith, and the late "Bullet" Bob Hayes.

Nicknamed 'Demolicious', a project led by Jay Pulliam of Baylor University in Waco, Texas, will use seismometers around the stadium near Dallas-Fort Worth to get a clearer picture of the Earth's geological features under Texas.

Pulliam and his team hope that seismic waves from the planned explosion can help to image Earth's crust in the region, an area of interest to seismologists because it is where the Ouachita deformation was created when a supercontinent of Africa and South America crashed into North America about 300 million years ago¹. The team also hopes to improve understanding of why small earthquakes occurred in the region in 2008–09 after waste water was pumped deep underground in the process of extracting natural gas from shale.

"It's a terrific opportunity, but like any experiment we don't know what we'll get," says Pulliam.

The biggest limitation is that the 1.5 tonnes of explosives being used will be fired in sequence to trigger a gradual collapse of the 65,000-seat stadium. "We'd prefer a big boom," says Pulliam, adding that a bigger explosion would create better seismic waves.

Prepare for demolition

In January, Baylor geologist Vince Cronin told Pulliam about the planned demolition of the stadium, which was opened in 1971 and mothballed last year when the replacement US$1.3-billion Cowboys Stadium was completed in Arlington, Texas. Pulliam then put together a shoestring project, which largely relies on the USArray seismometer grid that currently has seismic-monitoring stations about 40 kilometres away from the stadium.

The USArray grid includes 400 transportable seismometers that are being placed in temporary sites across the United States, stretching in a line from Canada to Mexico. In 2004, the grid began in the westernmost United States and has since been redeployed in a rolling fashion west to east; currently the grid encompasses Texas. USArray is part of EarthScope, a continental-scale network of instruments funded by the US National Science Foundation.

The system allows seismologists to image parts of the country that have not previously been fully described in detail, says seismologist Brian Stump of the Southern Methodist University in Dallas, who was not involved in the stadium-monitoring project.

On 6 April, Pulliam and Baylor graduate and undergraduate students, together with David Boyd, a geography teacher who uses seismometry in his lessons at Emmett Conrad High School in Dallas, set up instruments such as a seismometer, an accelerometer and a clock linked to the Global Positioning System (GPS), all sited about half a kilometre away from the stadium at the University of Dallas.

These will be used to precisely measure the timing of the explosion, and ground movements near the site, making it possible to interpret the signals picked up by the USArray seismometers 40 kilometres away. The explosion itself is scheduled for early morning on 11 April. An analysis of the timing and speed by which seismic waves triggered by the boom travel through the Earth will be used to infer underground structures.

Seismometer studies

There has been at least one previous attempt to capture seismology data from a stadium demolition — when the Kingdome in Seattle, Washington, was destroyed in 2000.

Arthur Frankel — a US Geological Survey seismologist in Denver, Colorado, who directed the Kingdome study, which involved more than 200 seismometers — explained that the results of that particular experiment were important because they confirmed a companion analysis showing the presence of soft soil in the Seattle basin. This affects the extent to which buildings will shake during an earthquake.

Pulliam and his team may also shed light on a series of earthquakes of magnitude 2.5 to 3.0 that began occurring in the Dallas-Fort Worth metropolitan area in late 2008. Typically, there are few noticeable earthquakes in that region.

Some work has already been done on this: Stump and his colleagues set up five seismometers around the area last year. He and his team reported last month² that the quakes were probably related to the pumping of waste water deep underground, a practice that energy companies were using to extract natural gas from the Barnett Shale, which lies underneath the area. The pumping ceased last summer — along with the earthquakes.

"What Pulliam is doing is a great idea," says Stump, who adds that the experiment could be very valuable in understanding the region's geological structure.

After the stadium is demolished, Pulliam will recover his instruments on 15 April and will match his data with what the USArray instruments pick up. "It's a flier," he says. "We'll see what we get."