IN A typical year our planet suffers 18 major earthquakes and one great quake measuring 8 or higher on the Richter scale. Predicting when or where the next one will happen remains impossible, but by now you鈥檇 think we would at least have a clear-cut system for identifying the faults that cause them. Not so. A blistering row over whether a convention centre in Salt Lake City, built for this year鈥檚 winter Olympics, is or isn鈥檛 straddling an active fault reveals just how uncertain is our knowledge of the ground beneath our feet (see 鈥淥lympic palace on shaky ground?鈥�).
Faults and cracks buried under the roads and parking lots of cities are the most difficult to map, yet the most important to know about. Measuring tiny variations in gravitational and magnetic fields can help. And in Los Angeles in recent years, scientists have made progress by placing scores of seismographs in homes and buildings, and analysing the way they detect waves from controlled underground explosions. None of these options is exactly cheap, however, so the world beneath many cities in earthquake zones remains woefully underexplored.
Where it isn鈥檛, the sparse knowledge we have has all too often been won the hard way. Breakthroughs in seismology have a nasty habit of coming after the event. In the 19th century, scientists suspected earthquakes were caused by local phenomena. It took the terrible San Francisco quake of 1906 to give rise to the famous 鈥渆lastic-rebound鈥� theory. Years later, the dogma took hold that quakes only occur where the ground is visibly fractured 鈥� till an earthquake in fracture-free central California in 1983 revealed this to be untrue. Now we know that 鈥渂lind鈥� thrust faults buried deep underground can also wreak havoc. And in 1994, it took 69 deaths and $13 billion worth of toppled buildings and bridges in Northridge to confirm that these thrust faults can shake the ground more vigorously than the more common 鈥渟trike-slip鈥� faults
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Can we break this painful pattern of after-the-event discovery? In the US, many researchers are backing an ambitious project called EarthScope to do for the geo-sciences what the human genome project has done for biology. One of its aims is to move 400 hi-tech seismographs across the US over a ten-year period. Another is to set up hundreds of sophisticated global positioning receivers and strain meters to chart the tiniest ground movements. The result will be an inverted telescope designed to image with unprecedented detail the Earth鈥檚 鈥渋nner space鈥�. The funding remains precarious. It shouldn鈥檛 be.
In the meantime, the row in Utah looks set to run and run with no resolution in sight. Let鈥檚 hope it doesn鈥檛 take an earthquake to provide one.