build your own seismograph
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DESCRIPTIONBuild your own seismograph. Alan Kafka, Boston College Michael Hubenthal, IRIS. We didn’t feel it so how do we know?. Your Task. design and construct a seismograph using common household and craft materials provided. An excellent design will be…. - PowerPoint PPT Presentation
Build your own seismographAlan Kafka, Boston CollegeMichael Hubenthal, IRIS
We didnt feel it so how do we know?
Your Taskdesign and construct a seismograph using common household and craft materials provided
An excellent design will bemade of the common inexpensive materials provided for this exercise;capable of determining the relative size of each disturbance it measures;capable of measuring vibrations continuously for at least one minute;capable of capturing the time when these disturbances occurred;capable of measuring vibrations from three different sources: a bang on or shaking of the table holding the seismograph; a person jumping up and down on the floor next to the table on which your seismograph is located; and a ball bounced off of a wall or floor nearby.
Seismoscopes - indicate that motion has occurred, azimuth, perhaps some simple measure of size.
Seismograph records ground motion as a continuous function of time.
First SeismoscopeAD 132, Zhang Heng of China's Han dynasty2 meters in diameterEight points around the top were dragon's heads holding bronze ballsPendulum inside
European Seismoscopes (function)1703 - Proposed by J. de la Haute Feuille - bowl of mercury.1731 Nicholas Cirillo - simple pendulums1783 - Domemico Salsano, a clock-maker and mechanic of Naples, invented a "geo-sismometrocommon pendulum, eight and a half "parisian" feet long. equipped with a brush to record motion with slow-drying ink on an ivory slab.
Seismoscope (time)1784 - A. Cavalli bowl of mercury with moving pots beneath to catch every minute (timing never built)1796 - Duca della Torre Pendulum A record, written by a pencil attached pressed gently against paper. Hair on the pendulum mass was a hair which would start the clock
Seismoscope (period)1844 James Ford Inverted pendulum designRecognized value of long period instrumentcommon pendulum, 10-20ft = period of 4-5s
Seismograph1875 Cecchi (Italy) seismoscopestart a clock start into motion the recording surface at the time of an earthquake.
Seismograph1889- von Rebeur's horizontal pendulum
How does a seismograph work?
To measure horizontal ground motion:A heavy mass is decoupled from the Earth by means of a pendulum.
When the ground moves, the mass tends to remain stationary because of its inertia, but the support (frame) moves with the Earth.
The movement of the Earth relative to the stationary mass is recorded on a rotating drum.
To measure vertical motion:
The principle is the same, but the mass is suspended on a spring.
With a modern seismograph, the ground motion is also recorded on a computer.
Three Sumatra Earthquakes Recorded atWeston ObservatoryBoston CollegeSame Distance, Different Magnitudes=133Seismograms are shown on the same scale.AS1 Seismograms
Phoenix Country Day School, Paradise Valley, AZ=7Weston High School,Weston, MA=38Parkfield, CA EarthquakeMagnitude 6.0, 09/28/04Same Earthquake, Different DistancesSeismograms are shown on the same scale.Time (sec/102)AS1 Seismograms
El Salvador and India Earthquakes Recorded at Devlin Hall Boston CollegeSame Magnitude, Different Distances
IndiaMagnitude 7.7, January 26, 2001El SalvadorMagnitude 7.7, January 13, 2001Seismograms are shown on the same scale.=33=106AS1 Seismograms
The Great Sumatra Earthquake of 2004Seismograms Recorded at Boston CollegeMagnitude 9.0December 26, 2004Magnitude 8.7March 28, 2005
Magnitude 6.7Gulf of CaliforniaJanuary 4, 2006
Seismology = The study of seismic waves.
Seismograph = Instrument that records seismic waves as a function of time.
Seismogram = The record of ground motion that is produced by a seismograph.
****http://earthquake.usgs.gov/learn/topics/seismology/history/history_seis.php*On at least one occasion, probably at the time of a large earthquake in Gansu in AD 143, the seismoscope indicated an earthquake even though one was not felt. The available text says that inside the vessel was a central column that could move along eight tracks; this is thought to refer to a pendulum, though it is not known exactly how this was linked to a mechanism that would open only one dragon's mouth. The first ever earthquake recorded by this seismograph was supposedly somewhere in the east. Days later, a rider from the east reported this earthquake.
*In 1703, J. de la Haute Feuille proposed filling a bowl to the brim with mercury, so that an earthquake would cause some of the mercury to spill out (de la Haute Feuille, 1703; Favaro, 1884). In order to determine the direction of the shock, the mercury spilling out in each of the eight principal directions of the compass was to be collected in cavities or other containers.
The honor of being the first European to record the use of a mechanical device as an aid to the study of earthquakes goes to Nicholas Cirillo (1747). Cirillo employed simple pendulums in an investigation of a series of earthquakes in Naples in 1731. He observed the amplitude of pendulum oscillations at the locations where the shaking was most severe, and also at locations somewhat removed from the zone of severest shaking. He found the amplitude to decrease with the inverse square of the distance, a result he anticipated from "the common laws in other sorts of motions" (Cirillo, 1747, p. 682).*Much of the next phase of the development (to the present) was focused on using electronics to both extend the dynamic range of the instrument while also minaturizing them. *******************