Recent Helicorder Displays

from the University of South Carolina

South Carolina Seismic Network



Here are the Days/Stations available for viewing

| 05/18/2009 | 05/17/2009 | 05/16/2009 | 05/15/2009 | 05/14/2009 | 05/13/2009 | 05/12/2009 | JSC EHZ CO | Jenkinsville

| 05/18/2009 | 05/17/2009 | 05/16/2009 | 05/15/2009 | 05/14/2009 | 05/13/2009 | 05/12/2009 | LHS EHZ CO | Liberty Hill

| 05/18/2009 | 05/17/2009 | 05/16/2009 | 05/15/2009 | 05/14/2009 | 05/13/2009 | 05/12/2009 | COW EHZ CO | Cow Castle Creek


These displays digitally simulate actual seismograms that are routinely recorded at USC. The seismograms show a record of how the ground moved at a particular seismograph station in South Carolina during a 24-hour period. The seismogram is "read" like a book, from left to right and top to bottom (this is the direction that time increases). As with a book, the right end of any horizontal line "connects" with the left end of the line below it. The colors of the horizontal lines have no particular significance. The colors alternate to aid in distinguishing different consecutive traces. Time is indicated at the left end of the lines in Universal Time Coordinate (UTC or Greenwich) time and at the right end of the lines in local Eastern time.

When an earthquake occurs the seismogram will show ground motion fluctuations that typically last from several tens of seconds to many minutes depending on the size of the earthquake. The height of the recorded waves on the seismogram (wave amplitude) is a greatly magnified representation of the actual ground motion. The magnification is roughly 100,000 times or more. A recording of an earthquake has recognizable characteristics. Typically, one can recognize the arrival of different wave types: P (the fastest traveling waves), S, and Surface waves. On these seismograms you may see local earthquakes in the Southeastern U.S. or even earthquakes elsewhere in the world. Almost any earthquake in the World having a magnitude greater than 6.5 will be seen on these seismograms.

Not all the wiggles seen on the seismograms are due to earthquakes. Anything that produces ground vibrations could be recorded, for example a car that passes by the seismometer (this is why we try to locate most of our seismometers well away from roads). Since the electrical signals from the seismometers are typically transmitted to the University of South Carolina over FM radio, electromagnetic interference may also show up on the seismogram. Such noise is usually easy to distinguish from earthquake generated signals because the the noise is often "spiky" in appearance. Telemetry dropouts may cause sustained periods of high amplitude noise.

Other interesting signals are also recorded. Sonic booms, trains, and man-made blasts are the most common. The quarry and mining activities in northern and central South Carolina are regularly seen on these stations.

To see more digitized displays like these from around the world, go to:

"http://earthquake.usgs.gov/eqcenter/helicorders.php"

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