Comparison of AS-1 and USGS Magnitudes
[click
image to view at full size] |
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 |
