QUAKE FEARS FOR SOUTH CALIFORNIA

[Anonymous]

Quake fears for south California
The
southern part of the San Andreas fault is overdue for a large
earthquake, according to a study in the journal Nature.This end of the
fault has not experienced a major rupture for at least 250 years and is
now primed for a release of the built-up tension.The study by
geophysicist Yuri Fialko provides the most precise measurements yet of
this accumulated stress.But scientists cannot predict when another
quake is likely to strike.
The San Andreas fault runs for roughly
1287km (800 miles) through western and southern California in the US.
It marks the meeting point of the Pacific and North American tectonic
plates.The southern segment begins near the Salton Sea and runs
northward before bending to the west where it meets the San Bernardino
Mountains. Los Angeles is the biggest city located near this part of
the fault.Professor Fialko looked at eight years of radar data from
European Space Agency satellites that measure in detail how the ground
moves and 20 years of global-positioning system (GPS) data.His analysis
suggests the two plates either side of the San Andreas fault are moving
past each other at a rate of about 25mm each year – the fault’s “slip
rate”.The bigger the average slip rate along a fault line, the more
stress might be expected to accumulate on parts of the fault that
remain locked together. In the absence of a sudden rupture to ease the
strain, the fault has built up 5.5-7m of “slip deficit”.
Taking the strainIf
all the strain was released at once, it would have enough energy to
unleash a magnitude-8 earthquake – roughly the size of the devastating
1906 quake in San Francisco.”The southern section of the fault is fully
loaded for the next big event,” Professor Fialko, of the Scripps
Institution of Oceanography in La Jolla, explained.Quakes are predicted
to occur on the southern part of the fault every 200-300 years. And
according to Professor Fialko, the observed movement on the fault is on
a par with the maximum amount of shift the fault has ever experienced
between quakes.Scott Brandenberg, a professor at the University of
California, commented: “This is new evidence that tells us the same
story that we have known for a while.”It’s a reminder that we need to
be ready for it when it happens.”The most recent major earthquakes in
the northern and central zones of the San Andreas fault were in 1857
and 1906 respectively.

[Author]

June 22, 2006 at 12:15 PM