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Overview of seismic instruments presented at the WORKSHOP

Overview of seismic instruments presented at the WORKSHOP High Quality Seismic Stations and Networks for Small Budgets  Volcan, Panama 8-13. March 2004 by Jens Havskov, Department of Geoscience University of Bergen Norway. Before: Seismographs were specially made

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Overview of seismic instruments presented at the WORKSHOP

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  1. Overview of seismic instruments presented at the WORKSHOP High Quality Seismic Stations and Networks for Small Budgets  Volcan, Panama 8-13. March 2004 by Jens Havskov, Department of Geoscience University of Bergen Norway

  2. Before: • Seismographs were specially made • Few standard components were used • Very specialized software • Now: • Stations and networks are mainly made with standard industrial components • Digital technology used throughout • More standardized software • Sensors currently the most specialized element • Now possible to build a seismic station with mainly off the shelf products

  3. SENSORS • Trend is to use more broad band sensors (BB), even when overkill, however BB sensors now have a similar price as 1 Hz sensors • 1 Hz sensors will go out except when used with feedback technique • 4.5 Hz geophones the cheapest sensor, now used by several, either directly or with a feedback technique • FBA based sensors will probably dominate the market in the future Typical geophone

  4. Spring Volt out ~ Acceleration Mass R Force coil Displacement transducer C Simplified principle behind Force Balanced Accelerometer. The displacement transducer normally uses a capacitor C, whose capacitance varies with the displacement of the mass. A current, proportional to the displacement transducer output, will force the mass to remain stationary relative to the frame. The FBA can have the digitizer integrated in feedback loop

  5. 13 cm The Kinemetrics 3-component Episensor, an FBA accelerometer

  6. Kinemetrics Episensor internals

  7. Left: The internals of the Güralp CMG-3T BB sensor. Right: Sensor with digitizer. Photo’s supplied by Nathan Pearce, Güralp.

  8. ---------------- 2 mm ------------ Principal elements of a MEMS (micro electro mechanical systems) accelerometer with capacitive transducer. The mass is the upper mobile capacitor plate which can rotate around the torsion bars. The displacement, proportional to acceleration, is sensed with the variance in the capacitance. For high sensitive applications, a feedback circuit is added which controls a restoring electrostatic force, thus we have a FBA. The size of the sensor above is about 2 mm. Figure from www.silicondesigns.com/tech.html.

  9. Signals band pass filtered with different filter widths. The signals have been corrected for instrument response to show displacement. The maximum amplitude in nm is shown to the right on top of the traces.

  10. Noise curves in a rural environment. The 3 dotted lines correspond to the maximum, mean and minimum levels published by Brune and Oliver (1959), the dashed lines give two extreme examples observed in the US and the full line curves give the limits of fluctuation of seismic noise at a European station on bedrock in a populated area 15 km away from heavy traffic (figure from Wilmore, 1979).

  11. Different sensors at Univeristy of Bergen vault

  12. Raw traces for different sensors A small window of the common traces for Z-channels. The numbers above the traces to the right are max amplitude in counts and the numbers to the left, the DC offset in counts.

  13. Displacement 1-20 Hz A small window of the common traces for the Z-channels. The traces have been corrected for instrument response and show displacement in the frequency band 1-20 Hz. The numbers above the traces to the right are max amplitude in nm and the numbers to the left, the DC offset in nm. Notice that the last 3 traces are not from the same time window.

  14. Displacement 0.2-1.0 Hz A small window of the common traces for the Z-channels. The traces have been corrected for instrument response and show displacement in the frequency band 0.2-1.0 Hz. The numbers above the traces to the right are max amplitude in nm and the the numbers to the left, the DC offset in nm

  15. Acceleration and displacement. The seismograms in the figure show the first few seconds of a P-wave of a small earthquake. On the site there is also an accelerometer installed (A) next to the seismometer (S). The top traces show the original records in counts. The signal from the seismometer is similar to the accelerometer signal, but with higher frequency contents for this later, and the amplitudes are different. The middle traces show the two signals converted to accelerations and the bottom traces, converted to displacement (frequency band 1-20 Hz). The signals are now very similar and of the same amplitude.

  16. Instrument sensitivity of several Geotech seismometers ranging from the short period S-13 to very broad band 54000 seismometer. The curves show input acceleration equivalent to sensor internal noise in dB relative to 1(ms-2)2/Hz . NLNM is the Peterson New Low Noise Model (Peterson, 1993). Slightly modified from Geotech home page, www.geoinst.com.

  17. Predicted total noise equivalent acceleration of a standard electronic circuit with a 4.5 Hz geophone. The contribution from each element is shown and the Peterson noise curves are shown for reference. Thermal noise is the noise due to Brownian thermal motion of the mass, Johnson noise is caused by thermal fluctuation of the electrons within any dissipative element in the electronic circuit, voltage and current noises are generated within the amplifier. Figure from Barzilai et al (1998).

  18. The equivalent ground acceleration noise spectrum for a digitizer with its input shorted, using a low-sensitivity virtual sensor of 4.5 Hz and G=30 V/(m/s). The record of the digitizer noise has been reduced to the equivalent ground motion using its response combined with an imaginary low-sensitivity sensor. The spectrum then shows the worst-case sensitivity for ground motion that can be achieved with this digitizer and sensor. Of course, a more sensitive sensor would give a lower equivalent ground noise. The smooth curves on top and bottom are the Peterson New Low-Noise and New High-Noise models, for reference.

  19. Sensor name C f0 Dam Mas Rg CDR Rc G K Dyn Mov Geodevice JC-V103 1 1.0 0.01 1000 100 5.0mm Geodevice JC-V104 3 1.0 0.7 350 70 Geodevice JC-45-3 3 4.5 0.02 300 yes 2.0mm Geo Space GS1 1 1.0 0.54 0.70 4550 280 Geo Space GS-11D (1) 1 4.5 0.34 0.023 380 32 1.8mm Geo Space HS1 1 4.5 0.28 0.028 1295 45 Geotech S-13 1 1.0 ~0.02 5.0 3600 6300 23 629 0.198 164 3.0mm Geotech S-13J 1 1.0 0.9 6400 20 344 140 1.5mm Input/Output SM-6 1 4.5 0.26 0.016 375 --- 28 --- 4.0mm Kinemetrics Ranger SS1 1 1.0 0.07 1.45 5000 6530 100 345 0.40 Mark products L4C 1 1.0 0.28 1.0 5500 8905 yes 276 6.2mm Mark products L4A 1 2.0 0.28 0.5 5500 8905 276 Mark products L22 1 2.0 88 Mark products L28B 1 4.5 0.48 0.02 395 35 2.0mm Sprengnether S6000 3 2.0 0.5 280 45 0.44

  20. Name C f-range Out In W G Wt Dyn. Resolution NEGATIVE FEED BACK Geodevice FSS-3B 3 1.0-40 8 12 0.6 800 12 120 GeoSIG VE53 3 1.0-50 10 12 0.5 1000 2.5 120 Geotech KS-10 1 0.05-20 500 3 140 Kinemetrics WR –1 1 0.05-20 2.5 ±12 0.3 160 5 125 Lennartz LE-3Dlite 3 1.0-80 5.0 12 0.1 400 2 120 3nm/s, 1Hz Lennartz LE-3D/5s 3 0.2-40 12 0.1 400 7 120 1nm/s, 1Hz Lennartz LE-3D/20s 3 0.05-40 10 12 0.6 1000 7 120 2nm/s, 1Hz ACCELEROMETERS Akashi V450 1 DC-6 Hz 6.6 ±12 50.2 8.6 0.005 μg Eentec EA-140 3 DC-100 5.0 12 0.4 5.0 140 2 μg Geodevice BBAS-2 3 DC- 5.0 12 0.4 2.5 2 135 GeoSIG AC63 3 DC-100 10 12 0.8 5.0 3 120 GeoSIG AC23 3 0.1-50 10 ±12 0.5 10.0 2.5 102 Geotech PA-22 3 DC-50 4.5 ±15 0.5 2.25 5 114 10 μg Güralp CMG-5 3 DC-100 5.0 12 1.2 5.0 5 155 Input/Output SF3000 3 DC-100 3.6 ±12 0.4 1.2 0.5 120 0.3 μg Kinemetrics FBA-23 3 DC-50 2.5 ±12 0.2 2.5 2 135 Kinemetrics EpiSensor 3 DC-200 10 12 0.4 2.5 155 Sprengnether FBX23 3 DC-50 10 ±12 0.4 10 1 90 11 μg Sprengnether FBX26 3 DC-50 10 ±12 0.2 10 1 135 0.4 μg VELOCITY BB Eentec P-123 3 0.1-50 10 12 0.2 2000 5 130 Eentec R1 rotational (1) 3 0.05-20 5 12 0.2 50 1 106 Eentec EP-105 3 0.03-50 10 12 0.2 2000 5 135 Eentec EP-300 3 0.017-50 7.5 12 0.4 2000 9.5 150 Eentec PMD223 3 0.017-32 7.5 12 0.3 2000 11 146 Eentec PMD103 3 0.033-50 10 12 0.5 2000 5.3 132 Geodevice FBS-3 3 0.05-40 10 12 0.6 1000 12 120 Geodevice MBS-1 3 0.017-50 10 12 2.0 1000 12 140 Geodevice BBS-1 3 0.008-50 10 12 2.0 1000 14 140 Geotech KS-2000 3 0.01-50 10 12 2000 7 160 Geotech KS-54000IRIS 3 0.003-5 20 24 1.2 2400 66 (4) Güralp CMG-1T 3 0.003-50 10 12 0.7 1500 14 Güralp CMG-3T (2) 3 0.003-100 10 12 2.9 1500 12 180 Güralp CMG3-ESP 3 0.1-50 10 12 0.9 2000 9 170 Güralp CMG-6T 3 0.03-100 10 12 0.8 1500 3 Güralp CMG-40T 3 0.03-50 10 12 0.6 3200 7 145 Nanometrics Trillium 3 0.033-30 8 12 0.4 1500 11 Sprengnether S-3000Q, 3 1.0-250 ±12 0.1 278 2 Sprengnether WB 2023 3 0.03-20 36 12 0.2 1000 5 Sprengnether WB2123 3 0.016-50 36 23 1000 5 Streckeisen STS-2 3 0.033- 20 12 1.8 1500 145 Streckeisen STS-1 (3) 1 0.003-10

  21. Main units of a seismic recorder. There are no flow arrows between the units since all can have 2 way communication. The GPS can be connected to the digitizer or the recorder. The power supply may be common for all elements or each may have its own regulator, but usually the power source is unique (e.g. a battery).

  22. 12 bit: ± 2048 counts 16 bit: ± 32768 counts 24 bit: ± 8388608 counts The analog to digital conversion process. The arrows show the location and values (amplitudes) of the samples and the signal is thus approximated with a sequence of numbers available at time intervals Δt.

  23. AD7710 Crystal Rate Hz ADC number of Bits Dynamic range (dB) ADC number of bits Dynamic range (dB) 25 20.0 120 31 22.1 133 50 19.5 117 62 21.9 132 100 18.5 111 125 21.6 130 250 15.5 93 21.1 127 500 13.0 78 20.8 125 1000 10.5 63 20.1 121 Effective resolution of 2 different analog to digiial convers as a function of sample rate. F is the output data rate (samples per second), AD7710 is a chip from Analog Devices and Crystal is the Crystal chip set.

  24. Unfiltered and filtered record of seismic background noise in a residential area in Western Norway on a hard rock site. The recording is made with a 4.5 Hz geophone and a 16-bit ADC at a sample rate of 50 Hz (GeoSIG GBV116). The filter is an 8-pole Butterworth filter with zero phase shift.

  25. A 5 Hz signal is digitized at a rate of 2 Hz. The digitization points are indicated with black dots. Depending on where the samples are taken in time, the output signal can either be interpreted as a straight line (points in middle) or a 1 Hz sine wave.

  26. A FIR filter compared to Butterworth filters. The FIR filter has a gain of -150 dB at the 50 Hz Nyquist frequency, while the 10 and 25 Hz Butterworth filters have gains of –42 and -112 dB respectively.

  27. Seismic spectrum as a function of magnitude

  28. Manufacturer and/or name N C H Sen-siti- vity, μV Dyn dB In-put V G fac-tor Cross talk, dB Alias DB R M ohm Sample rate, Hz Power W Out- put Drift ppm GPS Buf Tri Earth Data PS6-24 3-6 1.0 140 8 1-10 120 120 1.0 1- 1000 1.5 232 485 GPS N N Geodevice EDAS-24L 3-6 0.5 130 10 110 135 1-500 1.0 232 GPS N N Geotech DR24 1-6 4.8 129 20 1-256 80 130 10-1000 4.0 232 0.5 GPS Geotech 49.65 16 bit 1-3 140 90 4.5 (84) 10.0 50, 100 1.4 232 N N Güralp DM24 3-6 3.3 129 10 1 140 1.0 1-200 1.5 232 422 1 GPS Y Y Güralp DM-16-R8, 16 bit 8 305 90 10 1 140 1.0 1-200 3.0 232 422 1 GPS Y Hakusan LS-7000Xt 6 2.0 135 10 1-10 ~ 130 1-200 1.2 232 T GPS Y Y Kinemetrics Q330 3-6 4.7 135 20 1-30 ~ 130 1-200 < 1 232 T GPS Y N Kinemetrics Q730BL 1-3 1.9 142 20 1 145 ~ 130 1-250 10 232 T GPS Y N Lennartz M24 3 10 1-500 < 2 232 422 pps N N Nanometrics HDR 24 3-6 7.2 130 14 1 80 140 1.0 20- 500 4.4 232 422 GPS Y Y Nanometrics RD (1) 3-6 0.5 130 1 25-500 232 422 pps N N Nanometrics Trident 3 0.7 142 10 0.4-8 130 100 20-200 1.5 (2) GPS RefTek 72A 3-6 2.2 130 100 1-32 80 140 2.0 1-1000 0.5 GPS Y Y SARA SADC10 4 305 90 10 1 120 0.06 0.01-200 0.4 232 1.6 GPS N N SARA SADC20 3 0.8 130 2.5 1 140 14 (3) 1.0 10-200 0.5 232 1.6 GPS N N Public domain SEISAD18 (4) 3 9.5 108 2.5 1-16 120 14 (3) 2.5 25-200 0.4 232 422 10 pps N N Symmetric Res PAR8CH 8 10 120 10 1-16 140 0.02 1e-5 5000 1.1 lpt GPS Y N TAIDE enterp. TDE-324F 3 0.7 142 10 1-2 140 130 1.0 20-200 3.0 232 GPS N N

  29. The current trend in the development of the different elements of the portable recorders is: • Computer: Based on a standard computer and operating system: • Linux seems to be the favorite operating system, but Windows NT/2000 is also used. • Single board PC’s with low power consumption. • Communication and data transfer: • -RS232 • Ethernet/TCP/IP • USB + others • Sample rate, dynamic range and sensitivity: • Sample rates from 1-1000 Hz, • Dynamic range of at least 22 bit • LSB (least significant bit) resolution of 0.1 μV. • Standard Data acquisition software • Power consumption: Below 2 W.

  30. PC104 computer 8 cm

  31. Field equipment made by UiB

  32. 13cm x 18cm x 34cm

  33. Nanometrics Taurus, the next generation handheld recorder (25 x 15 x 6 cm). Power consumption 0.8 W. From Nanomtrics home page, www.nanometrics.ca.

  34. Name C H Bit Rate T C O Storage Com Trig P o Env Wt Strong motion recorders with built in accelerometers, most can also be used with seismometers Geodev. GSMA2400 3 22 5 100-500 0.5 M S SLT 1.3 P 10.0 Geotech DS-2400 3-6 22 3.8 10-1000 0.5 P SD ST 6.3 P 16.0 Geotech LLC 3 16 14.0 200 0.5 M S L 3.3 P 24.0 Kinemetrics QDR (1) 3 11 100 57 M S L 1.0 0.1 Kinemetrics Etna 3 18 8.0 100-250 P S L 2.2 P 9.0 KinemetricsMtWhit. 18 19 3.5 100-200 P S L 18 P 68 GeoSIG IA-1 (2) 3 16 50-300 M T 5.7 3.3 GeoSIG GSR18 3 18 5.0 100-250 20 M SD SL 1.6 P 7.2

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