Lecture 5
Instruments
History of instrument development
132 AD
The first seismosc ope w a s m a d e i n
China, a vessel w ith dragons h e ads a n d
frogs.
Early
1 8th C
Ita l i a n seismoscope s .
1 784
Fi r st a tte mpt to re c o r d ti m e o f shaking.
1 851
The spe e d o f seismic waves m o vin g
a c ross th e sur f a c e w a s f i r st m e a sur e d .
1 875
The first true seismograph y was
i n v e nte d i n Italy. T h e r e l ati ve m oti o n
b etw e e n a pendulum and th e E art h w a s
recorded as a fun cti o n o f time.
1 887
The oldest known seismo gram.
I n strum e ntati o n r api d l y developed f r o m
th e r e , w ith mechanical o r o pti c a l
a mplificati o n o f m a s s m oti o n , w it h
f r i cti o n providing d a mping.
1 900
The first global array of 40
ph oto g r aphically r e c ord i n g horizonta lc o mpo n e nt seismograph s .
1 914
E l e ctromagneti c seismomete r s were
develope d , w h e re th e mass is a ma g n et
moving in an electr i c coil.
212
The earliest seismometer, 132 AD
213
1
Inertial pendulum systems
Schematic inertial pendulum
seismometer
215
Milne
seismograph,
1902
216
2
Old inertial
pendulum
seismometer,
recording on sooted
paper, Azores
217
Inertial
pendulum,
Azores
218
Sooting the
drum,
Azores
219
3
Recording drum
encasement,
Azores
220
Later model inertial pendulum
instruments
221
The final
frontier: A
broadband
seismometer
222
4
Initial development of fieldportable instruments
Single-component 1 Hz seismometer
Teledyne
Geotech S13
224
Kinemetrics FBA 23 3-component
seismometer
225
5
Ocean-bottom seismometers
226
Strong motion seismometer
227
Wilmore Mk II
seismometer
228
6
Paper drum recorder
229
Geophone
230
Frequency
responses of
long-period
seismometers
231
7
Instrument calibration
233
Poles & zeroes
More detail: “Of poles and zeros”, Lay, T. & T.C. Wallace, Modern
Global Seismology, Academic Press, pp 521+xii, 1995, p 175-177
234
8
Instrument response
Frequency of ground Output proportional
motion
to
high
displacement
low
acceleration
Long-period instruments–could be very large
Modern seismometers–sensitive to velocity
235
Acceleration, velocity &
displacement
236
Broadband seismometers
9
Broadband seismometer
characteristics
• Flat response over broad range, e.g., 50 Hz
to 100 s
• High dynamic range because forced
feedback system prevents mass from making
large excursions = enables instrument to be
smaller
• Electronic and thus must be powered
• Digital output
• Examples: Guralp 40T, 3ESP, 3T
238
Comparison with traditional
seismometers
239
Broadband seismometers
STS 2
CMG 3T
240
10
Inside a
broadband
seismometer
241
Then & now
Sensors
Inertial sensors
Broadband sensors
Data type
Analogue
digital
Time-keeping
Clocks, or radio time
signals
GPS
Data
transmission
Recorded on paper or
tape at the site, or
analogue radio
transmitted
Recorded digitally at the
site, or transmitted digitally
via radio transmitters or the
internet
Data storage
At individual institutes
Cost
Cheap
Central storage, (almost)
and free access to (almost)
everyone
expensive
242
A visit to the WWSSN station at
Akureyri, Iceland
11
Why two sets of instruments?
244
Broadband records
245
Broadband records expanded
246
12
Broadband recording of a teleseism
247
Filtered
248
Broadband, long-period & shortperiod records
249
13
Permanent global network
stations
Global Network Station, Kyrgyzstan
251
GSN station CASY, Australian
Antarctic
252
14
GSN station, Borg, Iceland
253
Russian network: Irkutsk, Siberia
254
Russian
network:
Irkutsk, Siberia
255
15
Irkutsk recording station
256
Irkutsk recording station
257
A modern mega-experiment:
US Array
16
USArray Stations, 26 Oct 2009
259
Installing a sensor
260
Instrument installation
261
17
The
completed
vault
262
Solar panels
263
Hmmm, wonder why my station
isn’t working…
264
18
Data Management Center servers:
143 Tbyte
265
Smaller-scale experiments
Coso geothermal area, California
267
19
Coso geothermal area, California
268
Coso geothermal area, California
269
Coso geothermal area, California
270
20
Coso geothermal area, California
271
Coso geothermal area, California
272
GPS clock at Desert Peak, NV
273
21