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by CSMIP
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Introduction
On October 2, 1985 an earthquake occurred approximately 8
kilometers (5 miles) southeast of San Bernardino near the community of
Redlands, which is located about 110 km east of Los Angeles. According
to the Associated Press, telephone service was disrupted for a few
minutes and some plate glass windows were cracked in Redlands.
High-rise buildings in Los Angeles and chandeliers in Palm Springs
swayed during the earthquake. The earthquake may be associated with
the San Jacinto fault zone. No known surface rupture was associated
with the earthquake.
Strong-motion records were obtained at six stations instrumented
by the California Strong Motion Instrumentation Program (CSMIP). This
report presents copies of the analog records recovered as of October 5,
1985 and the instrumentation layout for each of the structures.
Perhaps the most noteworthy of the records obtained from this
earthquake are those from the San Bernardino County Law and Justice
Center in Rancho Cucamonga. This building incorporates a system of
seismic isolators at the foundation level. Seismic sensors are
attached both to the foundation slab and to the building above the
isolators. Building instrumentation was completed by CSMIP only
last
month. Construction of the building itself is still underway.
Although the records are of low amplitude (4% g), their uniqueness
makes them important.
Preliminary hypocentral parameters determined at the California
Institute of Technology (Hutton, personal communication) are:
Origin time: 2 October 1985, 23:44:15 GMT (16:44:15 PDT)
Epicenter: 34.03 N, 117.25 W
Depth: 15 km, approximate.
Magnitude: 4.9 ML
The approximate epicenter and station locations are shown on the map in
Figure 1. The stations are also listed in Table 1.
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