Shear-wave splitting and anisotropy in the Charlevoix seismic zone, Quebec, in 1985

1989 ◽  
Vol 26 (12) ◽  
pp. 2691-2696 ◽  
Author(s):  
Goetz G. R. Buchbinder
Keyword(s):  
Active Region ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Crack Density ◽  
Shear Wave Splitting ◽  
Velocity Variation ◽  
Seismic Zone ◽  
Wave Polarization ◽  
Wave Splitting

During the month of October 1985 a second experiment was undertaken in the Charlevoix seismic zone to further test the hypothesis that shear-wave splitting could be observed in a seismically active region. The first experiment had been undertaken in 1984 and yielded only a very limited amount of data. Seismograms recorded by digital three-component seismographs located very close to the epicentres of seven earthquakes showed shear-wave splitting over 15 different paths. The amount of [Formula: see text] wave variation varied from about 24 to 160 ms or from 0.4 to 8.7% of the [Formula: see text] wave velocity. The largest value occurred over the shortest path of about 7 km, for which essentially the whole path may be anisotropic, leading to a crack density (ε) of less than 0.09. For the rest of the data, all with less than 3% shear-wave-velocity variation, ε varies from 0.005 to 0.03, if whole-path anisotropy is assumed. These values of ε are not significantly different from those obtained in 1984. The average azimuth of the initial shear-wave polarization is 37°, also similar to that observed in 1984. All the data in the zone can be explained by the presence of saturated vertical cracks striking 37 °east of north.

Field Measurements of Shear Wave Velocity Profiles in the New Madrid Seismic Zone Using the NEES Field Shaker

2011 ◽  
Author(s):  
Brent Rosenblad ◽  
Jianhua Li ◽  
Jonathan Bailey ◽  
Ryan Goetz
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Field Measurements ◽  
Velocity Profiles ◽  
New Madrid Seismic Zone ◽  
Seismic Zone ◽  
New Madrid

Shear-wave velocity measurement of soils using Rayleigh waves

1992 ◽  
Vol 29 (4) ◽  
pp. 558-568 ◽  
Author(s):  
K. O. Addo ◽  
P. K. Robertson
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Rayleigh Waves ◽  
Ground Surface ◽  
Wave Dispersion ◽  
Velocity Variation ◽  
Surface Wave Dispersion ◽  
Waveform Data ◽  
Cone Penetration Tests

A modified version of the spectral analysis of surface waves (SASW) equipment and analysis procedure has been developed to determine in situ shear-wave velocity variation with depth from the ground surface. A microcomputer has been programmed to acquire waveform data and perform the relevant spectral analyses that were previously done by signal analyzers. Experimental dispersion for Rayleigh waves is now obtainable at a site and inverted with a fast algorithm for dispersion computation. Matching experimental and theoretical dispersion curves has been automated in an optimization routine that does not require intermittent operator intervention or experience in dispersion computation. Shear-wave velocity profiles measured by this procedure are compared with results from independent seismic cone penetration tests for selected sites in western Canada. Key words : surface wave, dispersion, inversion, optimization, shear-wave velocity.

Transportation Routes in Soils Susceptible to Ground Failure: New Madrid Seismic Zone

2000 ◽  
Vol 1736 (1) ◽  
pp. 127-133
Author(s):  
Salome Romero ◽  
Glenn J. Rix ◽  
Steven P. French
Keyword(s):  
Remote Sensing ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Data Sources ◽  
New Madrid Seismic Zone ◽  
Seismic Zone ◽  
Remote Sensing Imagery ◽  
Geologic Maps ◽  
Transportation Routes

Geologic deposits susceptible to ground motion amplification under seismic loading in the New Madrid Seismic Zone are delineated using multiple data sources including in situ measurements, geologic maps, and remote-sensing imagery. Soils are classified on the basis of the recommendations from the National Earthquake Hazards Reduction Program, which recommends a classification based on the average shear wave velocity of the geologic material in the upper 30 m. Measurements of shear wave velocity were obtained from Central United States Earthquake Consortium state geologists, the U.S. Geological Survey, and several researchers. However, since this is a predominantly rural area, limited field test data are available. Therefore, several other data sources are introduced including geologic maps and remote-sensing imagery to extrapolate dynamic properties in areas lacking extensive field measurements. Each data source was incorporated into a geographic information system for subsequent analysis. Bridges susceptible to failure from amplification of seismic waves and located on key transportation routes are identified for subsequent risk assessment or seismic retrofitting since the performance of these structures affects disaster planning and rescue efforts and may have severe consequences for the national economy.

Shear-wave velocity of the sedimentary basin in the upper Mississippi embayment using S-to-P converted waves

1996 ◽  
Vol 86 (3) ◽  
pp. 848-856
Author(s):  
Kou-Cheng Chen ◽  
Jer-Ming Chiu ◽  
Yung-Tun Yang
Keyword(s):  
Travel Time ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Sedimentary Basin ◽  
Vertical Component ◽  
Seismic Zone ◽  
Mississippi Embayment ◽  
Upper Mississippi Embayment ◽  
Converted Waves

Abstract From mid-October 1989 to August 1992, 40 three-component PANDA (Portable Array for Numerical Data Acquisition) stations were deployed in the central New Madrid seismic zone. Three-component digital seismograms recorded by the PANDA stations in the region are characterized by (1) the very weak direct S arrivals on the vertical component, which can be identified unambiguously from the two horizontal components, and (2) at least two prominent secondary arrivals between the direct P and S arrivals, one (Sp) dominant on the vertical component and another (Ps) with smaller amplitude on the two horizontal components. Travel-time differences between the Sp and S and between the P and Ps are the same for different earthquakes recorded at the same station but are different at different stations even for the same event. Polarization analyses of three-component seismograms and travel-time measurements confirm the interpretation that these two secondary arrivals are the P-to-S (Ps) and S-to-P (Sp) converted waves that occur at the bottom of the sedimentary basin beneath each station. Since abundant well-log data are available in the upper Mississippi embayment, the thickness of the sediments beneath each seismic station can be estimated. Travel-time differences between the direct and the converted waves can be used to calculate average shear-wave velocity for the sediments beneath each station. The estimated shear-wave velocities of the sediments beneath PANDA stations vary from 0.45 to 0.67 km/sec. The higher shear-wave velocity associated with thicker sediments can be interpreted as a consequence of increasing compaction of unconsolidated sediments due to increasing overburden.

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