Abstract of paper presented to the combined Northeastern and Southeastern sections of the Geological Society of America meeting, March 14 - 16, 1991, in Baltimore, MD.
Joseph J. Gerencher, Jr., "Classroom Applications of a Multi-Axis Lehman Seismograph System"
A three-axis seismograph system, composed of two home-made Lehman
horizontal seismometers and a borrowed vertical seismometer, has recently been installed
within and beneath the Earth Science classroom/laboratory at Moravian College. The
Lehman seismometers, constructed from common materials at a cost of approximately $120
each, are adjusted to have a free period of 18 seconds. One Lehman seismometer is
mounted E-W on a table in the classroom and the other is mounted N-S in the basement,
along with the vertical seismometer. All three seismometers are monitored by an
Apple IIe computer via user-generated software, and a television/monitor in the front of
the room continuously displays all output in real time. Movements of students in the
room greatly disturb the seismometer there, but have no apparent influence on the basement
units. The system triggers the data saving routines on the output of either basement
unit, but saves digitized data from all three seismometers.
Students attending class in the room are surprised that earthquakes from throughout the world are routinely recorded and that, although the classroom seismometer responds sensitively to their weight, this unit does not respond to their footsteps or their jumping up and down. Since the system was made operational in 1988, several earthquakes have been received while classes were meeting in the room. On those occasions, formal instruction was halted and all efforts to directly sense the seismic motions were unsuccessful.
The software, capable of managing four simultaneous seismometer inputs on either the Apple IIe or the IIgs, is now available from the author.