- On either side of the San Andreas fault, which runs almost
the length of California, cities move apart at the rate of a few centimetres
a year. But at the fault itself, the rocks remain jammed together for years
at a time. When they finally give, say scientists at the US Geological
Survey, the movement accelerates from practically nothing to 3,000mph.
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- Shocks like this over thousands of years build up a pattern
of smaller faults, far below the surface rock, threatening the plains that
lie west of the San Andreas.
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- An earthquake in January 1994 wakened Los Angeles to
the fact that it was 10 miles above a new kind of hazard: a "blind
thrust" fault. Great segments of rock strata had suddenly ridden one
over the other, creating shockwaves but leaving no evidence on the surface
that anything much had happened.
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- The Northridge area of the city felt the full force.
There were 57 deaths.
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- Afterwards, research was intensified into the likelihood
of what Californians have always called "the big one".
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- The most violent earthquake of modern times - one that
sent a tsunami surging towards Japan - may have been in the region of the
American north-west that encompasses Portland, Oregon, and Seattle, but
that was 300 years ago. The most vivid was the 1906 San Francisco quake,
in which the fault moved almost six metres (20ft) in a few seconds, but
most of the damage was done by the fire that followed.
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- With so much business investment and the proliferation
of high-rise buildings up and down the west coast since then, the potential
scale of a Californian catastrophe has soared.
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- The state is still one of the planet's seismology laboratories,
but researchers gave up the tantalising dream of earthquake prediction
a decade ago. Since then, the focus has been on education and preparedness,
as experts tried to calculate how violent the ground movements might be
in future shocks.
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- The Granada Hills around Northridge has risen by 15cm
since January 1994, researchers say: in effect, the earthquake was still
quietly going on.
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- Another blind thrust fault runs almost 30 miles from
downtown Los Angeles to the Coyote Hills in northern Orange county. It
has yet to show what it can do.
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