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Lecture 5
Instruments
212
History of instrument development132 AD The first seismoscope was made in
China, a vessel with dragons heads and
frogs.
Early
18th C
Italian seismoscopes.
1784 First a ttempt to record time of shaking.
1851 The speed of seismic waves moving
across the surface was first measured.
1875 The first true seismography was
invented in Italy. The relative motion
between a pendulum and the Earth was
recorded as a function of time.
1887 The oldest known seismogram.
Instrumentation rapidly developed from
there, with mechanical o r optical
amplification of mass motion, with
friction providing damping.
1900 The first global array of 40
photographically recording horizonta l-
component seismographs.
1914 Electromagnetic seismometers were
developed, where the mass is a magnet
moving in an electric coil.
213
The earliest seismometer, 132 AD
3
217
Old inertialpendulum
seismometer,recording on sooted
paper, Azores
218
Inertialpendulum,
Azores
219
Sooting thedrum,Azores
4
220
Recording drumencasement,
Azores
221
Later model inertial penduluminstruments
222
The finalfrontier: Abroadband
seismometer
5
Initial development of field-portable instruments
224
Single-component 1 Hz seismometer
TeledyneGeotech S13
225
Kinemetrics FBA 23 3-componentseismometer
8
Instrument calibration
233
234
Poles & zeroes
More detail: “Of poles and zeros”, Lay, T. & T.C. Wallace, ModernGlobal Seismology, Academic Press, pp 521+xii, 1995, p 175-177
9
235
Instrument response
accelerationlow
displacementhigh
Output proportionalto
Frequency of groundmotion
Long-period instruments–could be very large
Modern seismometers–sensitive to velocity
236
Acceleration, velocity &displacement
Broadband seismometers
10
238
Broadband seismometercharacteristics
• Flat response over broad range, e.g., 50 Hzto 100 s
• High dynamic range because forcedfeedback system prevents mass from makinglarge excursions = enables instrument to besmaller
• Electronic and thus must be powered• Digital output• Examples: Guralp 40T, 3ESP, 3T
239
Comparison with traditionalseismometers
240
Broadband seismometers
STS 2
CMG 3T
11
241
Inside abroadband
seismometer
242
Then & now
digitalAnalogueData type
Cost
Data storage
Datatransmission
Time-keeping
Sensors
expensiveCheap
Central storage, (almost)and free access to (almost)
everyoneAt individual institutes
Recorded digitally at thesite, or transmitted digitallyvia radio transmitters or the
internet
Recorded on paper ortape at the site, or
analogue radiotransmitted
GPSClocks, or radio timesignals
Broadband sensorsInertial sensors
A visit to the WWSSN station atAkureyri, Iceland
13
247
Broadband recording of a teleseism
248
Filtered
249
Broadband, long-period & short-period records
14
Permanent global networkstations
251
Global Network Station, Kyrgyzstan
252
GSN station CASY, AustralianAntarctic
15
253
GSN station, Borg, Iceland
254
Russian network: Irkutsk, Siberia
255
Russiannetwork:
Irkutsk, Siberia
19
265
Data Management Center servers:143 Tbyte
Smaller-scale experiments
267
Coso geothermal area, California
20
268
Coso geothermal area, California
269
Coso geothermal area, California
270
Coso geothermal area, California