No description available.

As a preliminary study to the operation of a portable long period seismic system, the effects of environment on the phase response of the Sprengnether 201 and Geotech SL-210 long period vertical seismometers are investigated. It is found that changes in the phase response of the seismometers are related to the zero instability of the moving mass. Pressure changes are not important in this regard; however, temperature variations should be held to less than 1°C. Calculation of the phase response directly from the amplitude response is investigated. It is concluded that it is more practical to carry out a phase calibration directly. The technique may however be useful when only an amplitude calibration is known. Also investigated are the noise properties of two amplifiers: the solid state Geotech AS-330 and the phototube Geotech 12613 amplifiers. The fundamental noise of the seismometer-amplifier combination is negligible. The excess noise of the AS-330 amplifier is of the same order as seismic noise at long periods at a rather noisy site. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

One criterion for distinguishing underground nuclear explosions from earthquakes is that most earthquakes occur at considerably larger depths. Focal depth can he determined with seismograms if both the P and the pP arrival are clearly distinguishable. "REMODE 5A" (REctilinear Motion DEtector), a time-varying polarization filter for the detection of P-type motion, is applied to artificial inputs and earthquakes. It is investigated how variation of the filter parameters affects the output. The length of the time window within which the cross-correlation filter operator is calculated must not be small compared to the signal period, especially if the onset of a quake is to be enhanced. If the window is very short, the filter outputs will be erratic. It makes little difference whether the truncated filter operator is tapered at the ends or not. REMODE 5A removes background noise and much of the signal-generated noise, but its efficiency in picking pP from complicated P coda is not significantly different from more elementary versions of REMODE filters. Through choice of parameters, REMODE 5A can be made arbitrarily selective to the degree of rectilinearity and the incident angle of signal and noise. However, since the sought-for pP and P will often be contaminated by signal-generated noise, too highly selective a filter may easily reject signal. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Different types of sources and receivers used with the seismic cone penetration test were investigated. The sources investigated were mechanical shear and compression wave sources consisting of a hammer-and-weighted-plank source; an on-shore Buffalo gun source utilizing shotgun shells; an off-shore seismic cap source; and an off-shore embedded blade with seismic cap source. The receivers investigated were horizontal and vertical geophones and accelerometers. The hammer shear source used previously with the seismic cone (Rice, 1984), was used as a standard for comparison. The hammer P-wave source was not used successfully with the seismic cone, because the vertical receivers used in the cone do not represent the soil response and thus can not be used with any source, and because the amplitude of the P-waves produced by the source was not large enough to detect on the horizontal receivers. The Buffalo gun source did not give repeatable or accurate shear wave velocities for depths less than 12 meters, but did appear repeatable and accurate below 12 meters. The seismic cap sources including the embedded blade source were found to give reasonable shear wave velocities and reasonable compression wave velocities if the depth at which the seismic cap was fired was kept constant. Both horizontal geophones and accelerometers were found to give similar shear wave velocities for the hammer shear source, but for the Buffalo gun source the accelerometers give differing results from the geophones probably because of a variable phase shift associated with the filtering of the accelerometer. Vertical receivers were not successfully used with the seismic cone because they do not give a response representative of the soil response, because of the vertical stiffness of the cone and rods. The use of compression and shear wave velocities to determine Poisson' ratio gave reasonable results if the strain level and type of compression wave were taken into account. A preliminary determination of the material damping ratio gave results which were higher than expected, probably indicating the seismic wave receivers were responding to the cone-soil system, rather than to the soil alone. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

No description available.

An analysis of waveforms, power spectral density and array responses was performed using geophones and broadband seismometers, co-deployed as part of a geologically motivated study. Broadband seismometers record excellent waveforms but, due to cost and deployment effort, wavefields are usually spatially aliased above ~0.1 Hz. Industry rapidly deploys many thousands of inexpensive, passive geophones to record full, unaliased seismic wavefields; however, waveform quality is limited below the instrument's natural frequency of ≥2 Hz. In 2012, coincident passive and controlled-source seismic surveys were deployed to investigate tectonics in Idaho and Oregon. Broadband stations were deployed at quiet sites every 15 km, taking experienced professionals >1 person-days per station. Fifty 4.5 Hz geophones and "Texan" seismographs at 200-m spacing were deployed per person-day by inexperienced students. Geophone data were continuously recorded for 3 nights and 1 day, while broadband seismometers were deployed for ~2 years. The spectral and array responses of these real deployments were compared. For a M7.7 teleseismic event, the broadband seismometer and geophone recorded nearly identical waveforms down to <0.03 Hz (32 s) and matching power spectral density down to 0.02 Hz (50 s). For quiet ambient noise, the waveforms strongly correlate down to <0.25 Hz (4 s) and the power spectral density match to the low-frequency side of the microseismic peak at ~0.15 Hz (~7 s). By deploying a much larger number of geophones, waveforms can be stacked to reduce instrument self-noise and beamforming can be used to identify wavefield azimuth and apparent velocity. Geophones can be an effective tool in ambient noise seismology down to ~7 seconds and can be used to record large seismic events effectively down to tens of seconds, well below the natural frequency of the instruments. A well-designed deployment of broadbands and geophones can enable full wavefield studies from long period to short period. Scientific and societal applications that could benefit from the improved unaliased wavefield bandwidth include local to regional seismicity, strong ground motion, magma migration, nuclear source discrimination, and crustal studies. / Master of Science / An analysis of seismic responses was performed using common seismology sensors, codeployed as part of a geologically motivated study. Broadband seismometers record seismic activity extremely well, however, due to cost and deployment effort, are less effective above ~0.1 Hz. Industry rapidly deploys many thousands of inexpensive, geophones, to record effectively above ~2 Hz; however, quality of the signal is limited below 2 Hz. In 2012, coincident seismic surveys were deployed to investigate earth structures in Idaho and Oregon. Broadband stations were deployed at every 15 km, taking experienced professionals >1 person-days per station. Fifty geophones and “Texan” seismographs at 200-m spacing were deployed per person-day by inexperienced students. Geophone data were continuously recorded for 3 nights and 1 day, while broadband seismometers were deployed for ~2 years. The seismic responses of these real deployments were compared. For a M7.7 earthquake, the broadband seismometer and geophone recorded nearly identical waveforms down to <0.03 Hz (32 s) and had similar characteristics down to 0.02 Hz (50 s). For low energy seismic signal, the waveforms were comparable down to <0.25 Hz (4 s) and had similar characteristics at ~0.15 Hz (~7 s). By deploying a much larger number of geophones, waveforms can be added together to improve signal quality and determine where the seismic source is located. Geophones can be an effective tool for low energy seismic signal down to ~7 seconds in period and can be used to record large seismic events effectively down to tens of seconds in period. A well-designed deployment of broadbands and geophones can enable full seismic studies from low and high frequencies which would have many scientific and societal benefits.

No description available.

Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Science. / Microfiche copy available in Archives and Science. / Vita. / Bibliography: leaves 313-331. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Science, 1979. / Bibliography: leaves 42-48. / by Janet Catherine Johnston Pruszenski. / M.S.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.