Lecture 5 Powerpoint slides

1

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

2

Inertial pendulum systems

215

Schematic inertial pendulumseismometer

216

Milneseismograph,

1902

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

6

226

Ocean-bottom seismometers

227

Strong motion seismometer

228

Wilmore Mk IIseismometer

7

229

Paper drum recorder

230

Geophone

231

Frequencyresponses oflong-period

seismometers

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

12

244

Why two sets of instruments?

245

Broadband records

246

Broadband records expanded

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

16

256

Irkutsk recording station

257

Irkutsk recording station

A modern mega-experiment:US Array

17

259

USArray Stations, 26 Oct 2009

260

Installing a sensor

261

Instrument installation

18

262

Thecompleted

vault

263

Solar panels

264

Hmmm, wonder why my stationisn’t working…

19

265

Data Management Center servers:143 Tbyte

Smaller-scale experiments

267

Coso geothermal area, California

20

268


269


270


21

271


272


273

GPS clock at Desert Peak, NV

Documents

Lecture 5 Powerpoint slides