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To illustrate
this we compare in the left panel a shakemap computed with the numbers of
stations that may have been expected in very near-real-time following the
Northridge earthquake. The contours in all maps are in g and the numbers are
given in tenths of a g. This map defines a region of 0.4 g PGA and an area of
the northern San Fernando Valley where PGA exceeded 1 g. The center illustrates a case with 40
km station spacing as may be
anticipated in many areas of California. With a station located to the north
of the fault plane an area of high ground motion is defined, but note that
the region with greater than 0.4 g is no longer well defined. The right panel illustrates a case with 40
km station spacing without a fortuitously located station. In this case the region of strong shaking
is not defined.
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