Calibration of seismographic systems : USGS stations in the central California network

Healy, J. H.; O’Neill, M. E.

doi:10.3133/ofr77736

Cited by 8 publications

(11 citation statements)

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“…The response curves of the different instruments (seismometers, amplifiers, modulators) are carefully matched before installation in the field and should not vary by more than a few percent between any given pair of instruments [Healy and O'Neill, 1977]. Such variations should not change the results significantly, but they are the most difficult source of uncertainty to eliminate.…”

Section: Errors Without Driftmentioning

confidence: 99%

Monitoring velocity variations in the crust using earthquake doublets: An application to the Calaveras Fault, California

Poupinet¹,

Ellsworth²,

Fréchet³

1984

J. Geophys. Res.

924

781

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We present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet, or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates. We compute differences in arrival times between seismograms recorded at the same station in the freqency domain by cross correlation of short windows of signal. A moving-window analysis of the entire seismograms, including the coda, gives g(t), the difference in arrival times versus running time along the seismogram. The time resolution of the method is an order of magnitude better than the digitization interval. The g(t) technique is illustrated with a pair of microearthquakes, M = 1.7 and 2.0, that occurred before and after the Coyote Lake, California, earthquake (M = 5.9) of August 6, 1979, and on the same segment of the Calaveras fault that ruptured during the earthquake. The coda wave arrivals for some stations are progressively delayed for the second earthquake in the doublet, so that its seismogram appears as a stretched version of the earlier event. We interpret this systematic variation in 6(t) along the coda as a change in the average S velocity in the upper crust in the time interval between the two doublets. S wave velocities appear to have decreased by 0.2% in an oblong region 5-10 km in radius at the south end of the aftershock zone.

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Section: Errors Without Driftmentioning

confidence: 99%

Monitoring velocity variations in the crust using earthquake doublets: An application to the Calaveras Fault, California

Poupinet¹,

Ellsworth²,

Fréchet³

1984

J. Geophys. Res.

924

781

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“…Healy and O'Neill (1977) This function (with G L g omitted) is shown in Figure 6. Note that below the free period (f 0 = 1 Hz) the amplitude falls off to the third power of frequency (f~*).…”

Section: Seismometer and L-padmentioning

confidence: 99%

“…The resistances T and S associated with the L-pad ( Figure 1) are chosen separately for each seismometer so that GLE will be the standard 1.0 V/(cm/sec) (Eaton, 1975). Healy and O'Neill (1977) give the following relationship between the parameters of the seismometer and L-pad: RR= amplifier input impedance, fixed at 10,000 ohms.…”

Section: Seismometer and L-padmentioning

confidence: 99%

“…The method is described in Healy and O'Neill (1977). In this report we seek to clarify some aspects of their presentation, to introduce a simple computer program for routine calculation of amplitude-response curves, and to show how the effects of additional system components may be included.…”

Section: Introductionmentioning

confidence: 99%

“…Several reports exist that describe various methods to calculate the amplitude response either of the complete short-period telemetry system, from seismometer to recording medium, or of individual components of the system (Eaton, 1975(Eaton, , 1977Dratler, 1980;Bakun and Dratler, 1976;Healy and O'Neill, 1977). With the exception of Eaton.…”

Section: Introductionmentioning

confidence: 99%

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Calculation of the frequency response of the USGS telemetered short-period seismic system

Stewart¹,

O’Neill²

1980

Open-File Report

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A procedure for calibrating short-period telemetered seismograph systems

Chapman

Snoke

Bollinger

1988

Bulletin of the Seismological Society of America

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Efficient low-frequency calibration of the entire seismograph system can be accomplished by Fourier analysis of the system response to automatically generated transient test functions applied to the seismometer calibration coil. Typically, such calibrations are restricted to frequencies less than 10 Hz by the ambient ground motion, system noise, and limited dynamic range. To extend the calibration to a broader frequency range, we disconnect the seismometer and take advantage of the fact that the relative amplitude response of the electronic components in most systems can be measured with high accuracy at frequencies from as low as 0.02 Hz to the Nyquist frequency (e.g., 50 Hz) using standard electronics test equipment. The low-frequency amplitude response of the seismometer can then be isolated by dividing the total system response by that obtained for the electronic components. An iterative least-squares procedure is used to estimate the natural frequency and damping coefficient of the seismometer, along with a scaling parameter that specifies the absolute gain of the system. The phase response of the system is calculated directly from the amplitude response using the Hilbert transform. The procedure assumes that the seismometer is an ideal damped harmonic oscillator and that the system as a whole acts as a minimum phase filter. The only instrumental constants that must be known from independent measurement are the seismometer calibration coil force constant and the inertial mass.

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Calibration of seismographic systems : USGS stations in the central California network

Cited by 8 publications

References 0 publications

Monitoring velocity variations in the crust using earthquake doublets: An application to the Calaveras Fault, California

Monitoring velocity variations in the crust using earthquake doublets: An application to the Calaveras Fault, California

Calculation of the frequency response of the USGS telemetered short-period seismic system

A procedure for calibrating short-period telemetered seismograph systems

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