THE GURLAP SEISMOGRAPH: AN EXCELLENT TEACHING AND RESEARCH TOOL

The Gurlap CMG-EDT is an inexpensive seismograph that enables students to study distant and local earthquakes. The instrument is a three component broadband seismometer that is easy to install as a permanent station or as a portable unit for the study of earthquakes in the field. The 3-component instrument provides better S-wave arrival times since the S wave shows up much better on the north and east horizontal components. The broadband instrument doesn’t go offscale to eliminate the clipping problem. The instrument also enables you to determine the “back azimuth” or direction to the quake epicenter. The software SCREAM receives the data from a serial port and displays the waveforms in real time. The monitor of the computer will display north-south and east-west horizontal traces and a vertical component trace. Well-defined P and S waves are used to determine distance to the epicenter and the back azimuth gives the direction.

Many earthquakes are recorded with the Gurlap seismograph each year. These earthquakes usually have a magnitude of 6 or greater however local earthquakes of magnitude less than 6 are also detected. The seismograms of the larger distant events may be used together with the Teachable Moments website www.IRIS.edu/gq/retm to acquire information about the earthquake. The information obtained from the website enables students to learn about plate tectonics theory, damage done by the quake, location of epicenters relative to plate boundaries, intensity of the quake, and the historical earthquake data for the epicentral region.