OKLAHOMA GEOLOGICAL SURVREY, UNIV. OKLAHOMA COLLEGE OF EARTH AND ENERGY
24 HR SEISMOGRAM OF EAST-WEST EARTH VELOCITY AT STATION OKCFA IN SOUTHERN OKLAHOMA CITY
Updated each hour. Note that all times are GMT.
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This is a 24 hour seismogram of East-West earth velocity in Southern
Oklahoma City, seismograph station OKCFA. The East-West component of the
seismometer is digitized 200 times per second, and the digits are
transmitted by internet to the Oklahoma Geological Survey Observatory
near Leonard Oklahoma.
At Leonard, the 200 samples per second are read into computer memory (RAM)
and written on disk. Each five minutes the seismogram is printed on
a monitor at Leonard. Each hour a copy of the seismogram is transmitted
to the webserver.
The times on the seismogram are all Greenwich Mean Time, abbreviated GMT.
Subtract five hours from GMT to obtain Central Daylight Time (CDT).
Subtract six hours from GMT to obtain Central Standard Time (CST).
The short red line shows where 24 hour old data is being written over
by data which was current at the time the plot was captured.
Seemingly random slow undulations are caused by wind slowly rocking
the ground. Organized vibrations, lasting minutes, are waves from distant
earthquakes (called "teleseisms"). Short spikes (a fraction of a minute)
are very small earthquakes in or near Oklahoma County. Their magnitude is
usually in the range of -0.2 to 1.5. The Richter scale and other
earthquake magnitude scales do have negative magnitudes for very small
earthquakes. See example seismogram below.
This plot was made by Jim Lawson and Amie Gibson using the free Linux
operating system, rnning on a PII 350 MHz computer. Murray McGowan, Mike Smart and
others at the Guralp factory in Reading UK wrote the plotting software
(Murray) and digitizer software (Mike).
The seismometer is a Guralp CMG-3ESPC three component force feedback with corners at 120 sec ( 0.00833 Hz), and 0.02 sec ( 50 Hz). The digitizer is a
Guralp DM24NET. Timing is by GPS. The seismometer is in a one meter deep
pit in alluvium.