Seismographs
By Danielle Stroup
Definition
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Record zigzag trace
Detect earthquakes all over the globe
Time, location, and magnitude
Goal: to accurately record motion
History
• Chinese and Egyptians
• Devices allowed marbles to fall
• 132 AD: Chinese scientist Chang Heng
invented seismoscope
• Invention called a dragon jar
Seismograph Advances
• Modern seismograph invented in the 1800s
• 1855: Luigi Palmeri of Italy
• Recorded time, intensity, and duration for
the first time of small earthquakes
• 1880: JA Ewing invents pendulum
seismograph
• HO Wood and J Anderson: mass suspended
by torsion
Mathematical Theory
• 1841: Earliest mathematical theory by
Forbes
• Considered only simple non-oscillatory
ground displacements
• 1877: Response of a seismograph to
arbitrary, periodic, ground motion written in
Japan; had little influence on the
development of seismographs
Theory
• Tilting was neglected in the early development of
the seismograph.
• Forced damped harmonic-oscillator seismographs
were presented by Perry, Ayrton, and Lippmann
• Had little effect on the construction of
seismographs
• 1890's: the importance of tilt was much debated
• 1900: become convinced that the effect of tilting
could usually be neglected.
Improvements
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Press-Ewing seismograph
Records long period waves
Widely used around the world
Press-Ewing pendulum seismograph uses
the Milne pendulum
Seismographs
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Compact, light weight, battery operated
Performs self-tests
Very detailed computer vibration analysis
Utilized four channels for signals
Blasting seismograph
– Monitor, record, analyze, display, and print
ground vibration and airblast
– Measures seismic wave
– Data from blast events represented
– Displayed on a liquid crystal display (LCD)
Components
• Attached to seismograph to collect data
• Vibration sensor (geophone): three sensors
• Vibration sensor has internal weight that
when moved, creates a voltage
• Measures absolute velocity
• Microphone to measure airblast
Data
• Shows peak particle velocity, displacement,
and the frequency of movement
• Require different standards and limits
depend on the type of structures
• Technology is increasingly utilized
• Sensors are placed very close to the blast
Conclusion
• Instruments have been used for over
eighteen hundred years
• From seismoscopes to seismographs
suitable for detailed studies of earth motion