Comparison of AS-1 and USGS Magnitudes

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Comparing actual and AS-1/AmaSeis magnitudes (September, 2003). The AS-1 magnitude calculations result in accurate magnitude determinations. Standard deviations of the differences between AS-1 (single station) and USGS (average of many stations) magnitudes are similar to other (standard seismograph) single station uncertainties. MS Magnitudes: N = 64; Standard Deviation = 0.26 magnitude units. mb Magnitudes: N = 111; Standard Deviation = 0.25 magnitude units. mbLg Magnitudes: N = 16; Standard Deviation = 0.26 magnitude units

Continuous or short duration (several weeks or months) recording of earthquakes with an educational seismograph is an excellent component of an in depth science experience that includes record keeping, mathematical calculations and opportunities for significant learning about earthquakes, seismology, plate tectonics and related Earth science. Using the seismograph and recorded seismograms, students can "do science" using their own real data rather than just reading about or listening to descriptions of science. Monitoring earthquakes requires the useful exercises of maintaining an instrument, good record keeping, retrieving additional information on the earthquake from the Internet, and making consistent observations of data. Over 3 1/2 years of experience with monitoring earthquakes with the AS-1 seismograph ( www.amateurseismologist.com ) demonstrates that even in the relatively low seismicity Midwest or eastern North America, frequent (mostly teleseismic) earthquakes are recorded at relatively quiet sites. Visible earthquake seismograms are present every few days and an event that produces a seismogram that can be used for magnitude or distance calculations occurs, on the average, about once per week. The AmaSeis software (developed by Alan Jones for the AS-1 seismograph with support from IRIS) is easy to use and provides several useful features and tools for archiving, viewing and analyzing data. Exercises that use the recorded earthquake data include determining magnitude and epicenter to station distance. Although the AS-1 is a relatively simple and inexpensive seismograph, the results of these analyses are reasonably accurate thus validating the students' efforts and increasing the interest in learning. Additional information about the AS-1 seismograph, AS-1 magnitude calculations and using the AS-1/AmaSeis seismograph in educational seismology is contained at www.eas.purdue.edu/~braile .

Contributed by: Larry Braile, Purdue University