Determination of Shallow Shear-Wave Attenuation in the Mississippi Embayment Using Vertical Seismic Profiling Data

Ge, Jiandang; Pujol, José; Pezeshk, Shahram; Stovall, Scott

doi:10.1785/0120080027

Cited by 9 publications

(5 citation statements)

References 20 publications

(37 reference statements)

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“…These values are similar to those calculated by Wang et al (1994) from the distance decay of direct arrivals of critically refracted waves. Ge et al (2009) used a synthetic wave-propagation algorithm that included reverberations within layers, dispersion effects, and anelastic (intrinsic) attenuation to confirm that the estimates of attenuation that they obtained from the spectral-ratio method using VSP measurements were consistent with intrinsic attenuation. They found that they could match the amplitudes of the synthetics using their measured quality factors as estimates of Q in , suggesting that scattering effects are not a significant contributor to their estimates of attenuation and, by analogy, to those of Pujol et al (2002).…”

Section: Seismic Survey Datamentioning

confidence: 95%

“…These surveys were conducted using three methods: vertical seismic profiling (VSP), spectral analysis of surface waves (SASW), and seismic refraction. Pujol et al (2002) and Ge et al (2009) used VSP measurements from a compressed-air-driven hammer to estimate S-wave attenuation in seven shallow (approximately 60 m deep) boreholes located in the region around Memphis. Quality factors were estimated for the 10-50 Hz frequency band from the slopes of the uphole-downhole Fourier spectral ratios.…”

Section: Seismic Survey Datamentioning

confidence: 99%

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Estimates of Shear-Wave Q and 0 for Unconsolidated and Semiconsolidated Sediments in Eastern North America

Campbell¹

2009

Bulletin of the Seismological Society of America

127

117

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Measured and calculated values of the effective quality factor Q ef and the site attenuation parameter κ 0 for unconsolidated and semiconsolidated sediments in eastern North America (ENA) indicate that the latter is strongly dependent on sediment thickness. Estimates of κ 0 for National Earthquake Hazard Reduction Program (NEHRP) BC site profiles (sediment plus hard rock) in the Mississippi Embayment and the Atlantic Coastal Plain were found to increase from about 9 to 31 msec for sediment thicknesses ranging from 116 to 600 m. Stochastic simulations using the 175 m thick hypothetical NEHRP BC site profile used to estimate ENA ground motions in the national seismic hazard maps by the U.S. Geological Survey (USGS) indicate that κ 0 20 msec provides a smaller estimate of amplification that agrees more closely with the low-strain short-period site coefficients in the NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures (NEHRP Provisions) than the 10 msec value used by the USGS. A linear regression of the κ 0 estimates compiled in this study indicates that κ 0 20 msec corresponds to a relatively thick BC sediment thickness of 460 116 m. These same stochastic simulations indicate that the relatively shallow USGS site profile provides estimates of amplification that are smaller than the low-strain long-period site coefficients in the NEHRP Provisions. The dependence of both site attenuation and site amplification on sediment thickness suggests that the use of a single reference site condition for hazard mapping might not be appropriate. Instead, these results imply that either a regional set of reference site profiles should be developed or that a more uniform site condition such as hard rock should be used to define a more stable reference site condition in ENA. * Note: Values in italics represent the BC section of the sedimentary column. The values for Q ef were taken from data provided by Cramer et al. (2004) and Boore and Joyner (1991); all other data were taken from Gomberg et al. (2003) and Cramer et al. (2004). Intermediate Q ef values are intermediate to those of Cramer and Boore and Joyner. The values of κ 0 for each layer were calculated from equation (10).

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Section: Seismic Survey Datamentioning

confidence: 95%

Section: Seismic Survey Datamentioning

confidence: 99%

Estimates of Shear-Wave Q and 0 for Unconsolidated and Semiconsolidated Sediments in Eastern North America

Campbell¹

2009

Bulletin of the Seismological Society of America

127

117

View full text Add to dashboard Cite

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“…The methods applied on the recorded data are generally based on spectral‐ratio analysis (e.g. Gibbs et al 1994; Parolai et al 2007; Ge et al 2009), matching techniques (e.g. Raikes & White 1984), spectral modelling, measurements of the amplitude decay in the time domain, synthetic modelling, rise time analysis, pulse amplitude method analysis (e.g.…”

Section: Introductionmentioning

confidence: 99%

Determination of shallowS-wave attenuation by down-hole waveform deconvolution: a case study in Istanbul (Turkey)

Parolai

Bindi

Ansal

et al. 2010

Geophysical Journal International

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S U M M A R YThe estimation of shear wave velocity and attenuation in near-surface geology is of primary importance in engineering seismology. In fact, their knowledge is essential for site response studies when preparing improved seismic hazard scenarios. In this study, we propose two approaches for estimating the average shear wave quality factor Qs by using recordings of a vertical array of accelerometers. The methods are mainly based on the deconvolution of the wavefield recorded in a borehole with that recorded at the surface.The first method requires the Fourier transform of the deconvolved wavefield to be fitted with a theoretical transfer function valid for the vertical or nearly vertical (in the case at hand up to 30 • incidence angle) propagation of S waves. The second method is based on the spectral fitting of the Fourier transform of only the acausal part of the deconvolved wavefield with a theoretical transfer function.Both methods can be applied without any prior knowledge of the subsoil structure (since they are based on empirical data analysis) and do not require a precise knowledge of the azimuthal orientation of the sensors in the boreholes (which is seldom available). First, we describe the theoretical framework of the proposed methodologies for Qs estimation, which are based on the assumption that the structure in the borehole is weakly heterogeneous in the vertical direction (i.e. no large impedance contrast exists between the borehole sensor and the surface). Second, by using synthetic accelerograms, we verify that in a realistic subsoil structure, the assumption of vertical homogeneity can hold and we investigate the robustness and the suitability of the proposed methods. Finally, only the method that was shown to provide the more stable results, based on fitting the borehole-to-surface spectral ratio with a theoretical function, is applied to earthquakes signals recorded by a vertical array of accelerometers installed in Ataköy (western Istanbul). Results show that using borehole data provides a fair and robust estimate of an average Qs (of about 30, 46 and 99 for the 0-50, 0-70, 0-140 m depth ranges, respectively) that can be used for numerical simulations of ground motion.

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“…A common method used to find the quality factor Q is the spectral ratio technique (e.g., Gibbs et al, 1994;Parolai et al, 2007;Ge et al, 2009). It typically begins by computing the ratio of the Fourier spectra of isolated P and S waves between the surface and downhole seismograms, after taking into account instrument responses and other gain factors not related to attenuation.…”

Section: Methodsmentioning

confidence: 99%

Seismic‐Wave Propagation in Shallow Layers at the GONAF‐Tuzla Site, Istanbul, Turkey

Raub

Bohnhoff

Petrović

et al. 2016

Bulletin of the Seismological Society of America

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Using the first dataset available from the downhole Geophysical Observatory of the North Anatolian Fault, we investigated near-surface seismic-wave propagation on the Tuzla Peninsula, Istanbul, Turkey. We selected a dataset of 26 seismograms recorded at Tuzla at sensor depths of 0, 71, 144, 215, and 288 m. To determine near-surface velocities and attenuation structures, the waveforms from all sensors were pairwise deconvolved and stacked. This produced low-noise empirical Green's functions for each borehole depth interval. From the Green's functions, we identified reflections from the free surface and a low-velocity layer between ∼90 and ∼140 m depth. The presence of a low-velocity zone was also confirmed by a sonic log run in the borehole. This structure, plus high near-surface P-and S-wave velocities of ∼3600-4100 and ∼1800 m=s, lead to complex interference effects between upgoing and downgoing waves. As a result, the determination of quality factors (Q) with standard spectral ratio techniques was not possible. Instead, we forward modeled the Green's functions in the time domain to determine effective Q values and to refine our velocity estimates. The effective Q P values for the depth intervals of 0-71, 0-144, 0-215, and 0-288 m were found to be 19, 35, 39, and 42, respectively. For the S waves, we obtained an effective Q S of 20 in the depth interval of 0-288 m. Considering the assumptions made in our modeling approach, it is evident that these effective quality factors are biased by impedance contrasts between our observation points. Our results show that, even after correcting for a free-surface factor of 2, the motion at the surface was found to be 1.7 times greater than that at 71 m depth. Our efforts also illustrate some of the difficulties of dealing with site effects in a strongly heterogeneous subsurface.Online Material: Plots of resistivity and caliper logs and the spectra of all 26 events.

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Determination of Shallow Shear-Wave Attenuation in the Mississippi Embayment Using Vertical Seismic Profiling Data

Cited by 9 publications

References 20 publications

Estimates of Shear-Wave Q and 0 for Unconsolidated and Semiconsolidated Sediments in Eastern North America

Estimates of Shear-Wave Q and 0 for Unconsolidated and Semiconsolidated Sediments in Eastern North America

Determination of shallowS-wave attenuation by down-hole waveform deconvolution: a case study in Istanbul (Turkey)

Seismic‐Wave Propagation in Shallow Layers at the GONAF‐Tuzla Site, Istanbul, Turkey

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