© Ersoy Emin/AlamySupershear quake hits Izmit in Turkey in 1999.
The convoy was more than 30 kilometres from the Kunlun fault in Tibet when the jeeps suddenly lurched. They had hit a series of parallel cracks, remnants of a magnitude 7.8 earthquake that struck the year before. "It was like driving on steps," recalls Yann Klinger, a geologist from the Paris Institute of Geophysics in France.
The cracks were clear signs that the ground had been squeezed like a sponge then released, violently wrenching it apart. Yet they were much too far from the fault line to be explained by the quake. Mystified, the team took some measurements and moved on.
It transpired that Klinger and his team had stumbled upon the aftermath of a "supershear" earthquake - one that slipped at such blistering speeds that the rip in the Earth overtook its own seismic waves. This created the earthquake equivalent of a sonic boom, capable of striking anything in its path like a hammer blow. While some seismologists had suspected such a quake could happen, physical evidence of their power had been lacking.
Seven years on, and the evidence is mounting that these kinds of earthquakes may be more common than we thought, and not just in remote regions like Tibet. A series of new maps reveals an abundance of so-called "superhighway" faults around the globe where the conditions are just right for earthquakes to zip through the ground at great speed. Worldwide, 60 million people live in these zones - many of them in regions that were not previously considered at risk from earthquakes. And even in places where buildings are designed to cope with the biggest quakes, no one knows if they will be able to withstand a supershear.
