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1991-04-22
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U.S. Geological Survey
National Earthquake Information Center
The National Earthquake Information Center distributes
digital earthquake data on CD-ROM. Currently, six volumes are
available, covering the time period January 1980 through May
1986, with data from the Global Digital Seismograph Network
(GDSN) and other contributing networks. Any event with a
magnitude of 5.5 or greater is included.
The program SONIC1 allows fast and easy access to
the data provided on these discs, along with the capability of
displaying the seismic data. To begin, type SONIC1. The user
will be shown two screens. The second screen prompts you for
the CD-ROM drive letter, including the full path under which
the data resides. From there, the user selects the year,
month, and day of interest. A list of one or more events
is displayed for the given date. Select one. SONIC1 then
determines which stations recorded information for that event,
and then the user may select one station or a range of stations.
After the data is displayed, you have the option of writing this
information to disk.
About the Data
The 1989 event data are from a magnitude 7.1 earthquake that
occurred just south of San francisco on October 17, 1989. This
was the "Loma Prieta" earthquake, named after a small village
near the epicenter. The earthquake caused 62 deaths, 3,757
injuries, and left more than 12,000 people homeless. It caused
of $6 billion dollars of property damage and considerable
disruption of transportation, utility, and communication
facilities. From the geological point of view, the earthquake is
typical of those near plate boundaries throughout the world.
From these data the location of the epicenter and the size and
geometry of the fault break that caused the earthquake can be
determined.
The 1983 data are from 13 seismic events from around the
world occurring in October of that year. Collectively they are
called seismic events because one of them is not an earthquake.
It is a large underground nuclear explosion at the USSR test site
in central Asia. Differences in the characteristics of the
seismic signals from explosions and earthquakes can be used to
monitor the testing activity of foreign countries. Some of these
differences are apparent when the seismic signals from the Loma
Prieta earthquake and the seismic event of October 6, 1983 are
compared.
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