The Pacific Northwest Seismograph Network PNSN > Webicorder > School Webicorders [A-M][O-Z]

What is a "Webicorder"?

The Webicorder is a Web display of seismic data. The display looks like paper records made by machines called "helicorders". A plot of the data is called a seismogram.

Each Webicorder picture shows half a day (12 hours) of data. You "read" the seismogram like a book, from left to right starting at the top. The earliest data starts in the upper left and then time increases to the right. Just like a book, when you get to the end of a line on the right side the seismogram continues on the left side of the next line down.
The colors in the seismograms don't really mean anything. We just use the different colors to help us read the seismogram.

There are links to other stations in this set of webicorders across the top of each plot and links back to the main index and other pages across the bottom.

What are all the vertical lines and numbers?

The upper left of the Webicorder shows the date, the station code, and the name of the school. Hour marks in local time (PDT or PST) are shown along the left side of the plot. Corresponding time marks in Greenwich Time (or UTC) are shown along the right side of the plot. The long vertical lines are minute marks.

Example upper left corner from Lawton's Webicorder display.

What does an earthquake look like?

Example Magnitude 3 earthquake in Bremerton recorded on Mt. Rainier.

When an earthquake occurs the seismogram will show ground motions that typically last from several tens of seconds to many minutes depending on the size and distance 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 50,000 times or more depending on the site.

A recording of an earthquake has recognizable characteristics. Typically, one can recognize the arrival of different wave types: P (the fastest traveling waves), S (shear waves), and Surface waves.

Not all the wiggles seen on the seismograms are due to earthquakes. Anything that produces ground vibrations could be recorded. Some of the non-earthquake things are cars and trucks and road construction. Other possibilities are things located in the same building as the seismograph such as fans, refridgerators, air conditioners or people walking around.

Example signal from railroad train (in blue), recorded at Lawton School.

Can you see the differences between the earthquake seismogram and the railroad train? We describe the train signal as a "cigar" shape. It gradually builds up and dies down. The earthquake signal, in contrast, has a very sharp arrival that gradually decays.