Publication Date:
1994
Description:
A prototype early warning system to provide San Francisco and Oakland,
California a few tens-of-seconds warning of incoming strong ground shaking from
already-occurred M = or 〉 3.7 aftershocks of the magnitude 7.1 17 October 1989
Loma Prieta earthquake was operational on 28 October 1989. The prototype system
consisted of ground motion sensors in the epicentral area, a central receiver, a radio
repeater, and radio receivers. One of the radio receivers provided about 20 sec of
warning before shaking from the M 4.5 Loma Prieta aftershock that occurred on 2 November
1989 at 0550 UTC. In its first 6 months of operation, the system generated triggers for
all 12 M 〉 3.7 aftershocks for which trigger documentation is preserved. Because
the prototype system demonstrated that potentially useful warnings of strong shaking
from aftershocks are feasible, the USGS has completed a portable early warning system
for aftershocks that can be deployed anywhere. One of the radio receivers was deployed
at the California Department of Transportation (CALTransformations) headquarters at the
damaged Cypress Street section of the I-880 freeway in Oakland, California on 28 October
1989 and provided about 20 sec ..., did not trigger on any M〈or=3.6 aftershocks,
and produced one false trigger as a result of a now-corrected single point of failure
design flaw.
Keywords:
Seismology
;
Early warning systems (earthquakes, volcanic eruptions, tsunamis etc.)
;
Aftershocks
;
Detectors
;
Location
;
Magnitude
;
Instruments
;
Source parameters
;
Strong motions
;
Seismometer
;
BSSA
;
San
;
Francisco
;
Oakland
;
California
;
Loma
;
Prieta
;
ground
;
motion
;
sensors
;
epicentral
;
area
;
central
;
receiver
;
radio
;
repeater
;
radio
;
receivers
;
California
;
Department
;
of
;
Transportation
;
headquarters
;
CALTransformations
;
I-880
;
freeway
;
triggers
;
prototype
;
system
;
USA
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