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This image shows the crown of a large lateral spread, which
moved downhill to the left. The failure occurred in a cultivated
field. The lateral spread acted like a carpet sliding on a
slippery floor; the failure surface is only about 1 to 2 feet
deep, and the slope only moved laterally a few feet. Nevertheless,
a structure resting on shallow foundations could have been
seriously damaged by this event.
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The earthquake that struck on January 26 was of the “blind
thrust” type, one of the largest such quakes ever recorded.
It occurred on a fault plane that did not break the surface
of the earth, like the Northridge earthquake that hit Los
Angeles in 1994. However, some small faults were found along
the edge of the epicentral area, which separated the area
that lurched northward in the earthquake from areas to the
east that did not move. These so-called “tear faults”
showed a lateral offset of about 10-25 centimeters and could
be traced over 2 kilometers across the desert.
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