An improved neighborhood algorithm: Parameter conditions and dynamic scaling

Wathelet, Marc

doi:10.1029/2008gl033256

Cited by 436 publications

(283 citation statements)

References 11 publications

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“…The inversions were performed with the inversion tool of the Geopsy software package, which uses a global search approach with a neighborhood algorithm (Wathelet 2008). The broad-band dispersion curves previously derived were inverted, which in most cases involved joint inversion of both the Rayleigh and Love dispersion curves, with sometimes several various modes.…”

Section: Inversion and Derivation Of Velocity Profilesmentioning

confidence: 99%

“…In the present study, when possible, we also use multi-mode inversion, and Rayleigh-wave and Love-wave joint inversion. The data processing was performed using the Geopsy software (Wathelet et al 2004Wathelet 2005Wathelet , 2008. The first step of the analysis consisted of examining the Fourier amplitude spectra to estimate the energy content of the seismic ambient noise wavefield, as well as to identify stations that produced spurious estimates, which were then removed from the analysis (e.g., Fig.…”

Section: Acquisition Layoutmentioning

confidence: 99%

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Characterization of site conditions (soil class, VS30, velocity profiles) for 33 stations from the French permanent accelerometric network (RAP) using surface-wave methods

Hollender

Cornou

Dechamp

et al. 2017

Bull Earthquake Eng

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Data provided by accelerometric networks are important for seismic hazard assessment. The correct use of accelerometric signals is conditioned by the station site metadata quality (i.e., soil class, V S30 , velocity profiles, and other relevant information that can help to quantify site effects). In France, the permanent accelerometric network consists of about 150 stations. Thirty-three of these stations in the southern half of France have been characterized, using surface-wave-based methods that allow derivation of velocity profiles from dispersion curves of surface waves. The computation of dispersion curves and their subsequent inversion in terms of shear-wave velocity profiles has allowed estimation of V S30 values and designation of soil classes, which include the corresponding uncertainties. From a methodological point of view, this survey leads to the following recommendations: (1)

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Section: Inversion and Derivation Of Velocity Profilesmentioning

confidence: 99%

Section: Acquisition Layoutmentioning

confidence: 99%

Characterization of site conditions (soil class, VS30, velocity profiles) for 33 stations from the French permanent accelerometric network (RAP) using surface-wave methods

Hollender

Cornou

Dechamp

et al. 2017

Bull Earthquake Eng

View full text Add to dashboard Cite

show abstract

“…The Geopsy forward modelling code (Wathelet et al 2004) solves the associated eigenvalue problem for Love and Rayleigh waves (Dunkin 1965). The inversion is based on a neighbourhood algorithm (Wathelet 2008), using a direct search of the parameter space across a specified range for S-wave velocities, P-wave velocities and densities. The starting model is picked randomly from this parameter space.…”

Section: Velocity-depth Profile From Surface Wave Inversionmentioning

confidence: 99%

“…S-wave velocity-depth profiles were obtained from inversion of the dispersion curves in Figs 5(a)-(c) using Geopsy (Wathelet et al 2004;Wathelet 2008). The Geopsy forward modelling code (Wathelet et al 2004) solves the associated eigenvalue problem for Love and Rayleigh waves (Dunkin 1965).…”

Section: Velocity-depth Profile From Surface Wave Inversionmentioning

confidence: 99%

Ice shelf structure derived from dispersion curve analysis of ambient seismic noise, Ross Ice Shelf, Antarctica

et al. 2016

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S U M M A R YAn L-configured, three-component short period seismic array was deployed on the Ross Ice Shelf, Antarctica during November 2014. Polarization analysis of ambient noise data from these stations shows linearly polarized waves for frequency bands between 0.2 and 2 Hz. A spectral peak at about 1.6 Hz is interpreted as the resonance frequency of the water column and is used to estimate the water layer thickness below the ice shelf. The frequency band from 4 to 18 Hz is dominated by Rayleigh and Love waves propagating from the north that, based on daily temporal variations, we conclude were generated by field camp activity. Frequency-slowness plots were calculated using beamforming. Resulting Love and Rayleigh wave dispersion curves were inverted for the shear wave velocity profile within the firn and ice to ∼150 m depth. The derived density profile allows estimation of the pore close-off depth and the firn-air content thickness. Separate inversions of Rayleigh and Love wave dispersion curves give different shear wave velocity profiles within the firn. We attribute this difference to an effective anisotropy due to fine layering. The layered structure of firn, ice, water and the seafloor results in a characteristic dispersion curve below 7 Hz. Forward modelling the observed Rayleigh wave dispersion curves using representative firn, ice, water and sediment structures indicates that Rayleigh waves are observed when wavelengths are long enough to span the distance from the ice shelf surface to the seafloor. The forward modelling shows that analysis of seismic data from an ice shelf provides the possibility of resolving ice shelf thickness, water column thickness and the physical properties of the ice shelf and underlying seafloor using passive-source seismic data.

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“…The direct search algorithm is based on a neighborhood algorithm and the forward method uses matrix solutions for a stack of homogeneous elastic layers. The method is described in detail by Wathelet et al (2004) and Wathelet (2008) (see program Dinver from Geopsy package).…”

Section: Inversion For Shear Wave Velocitymentioning

confidence: 99%

Inversion of Scholte wave dispersion and waveform modeling for shallow structure of the Ninetyeast Ridge

2008

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The construction of S-wave velocity models of marine sediments down to hundreds of meters below the seafloor is important in a number of disciplines. One of the most significant trends in marine geophysics is to use interface waves to estimate shallow shear velocities which play an important role in determining the shallow crustal structure. In marine settings, the waves trapped near the fluid-solid interface are called Scholte waves, and this is the subject of the study. In 1998, there were experiments on the Ninetyeast Ridge (Central Indian Ocean) to study the shallow seismic structure at the drilled site. The data were acquired by both ocean bottom seismometer and ocean bottom hydrophone. A new type of seafloor implosion sources has been used in this experiment, which successfully excited fast and high frequency (>500 Hz) body waves and slow, intermediate frequency (<20 Hz) Scholte waves. The fundamental and first higher mode Scholte waves have both been excited by the implosion source. Here, the Scholte waves are investigated with a full waveform modeling and a group velocity inversion approach. Shear wave velocities for the uppermost layers of the region are inferred and results from the different methods are compared. We find that the full waveform modeling is important to understand the intrinsic attenuation of the Scholte waves between 1 and 20 Hz. The modeling shows that the S-wave velocity varies from 195 to 350 m/s in the first 16 m of the uppermost layer. Depths levels of high S-wave impedance contrasts compare well to the layer depth derived from a P-wave analysis as well as from drilling data. As expected, the P-to S-wave velocity ratio is very high in the uppermost 16 m of the seafloor and the Poisson ratio is nearly 0.5. Depth levels of high S-wave impedance contrasts are comparable to the layer depth derived from drilling data.

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An improved neighborhood algorithm: Parameter conditions and dynamic scaling

Cited by 436 publications

References 11 publications

Characterization of site conditions (soil class, VS30, velocity profiles) for 33 stations from the French permanent accelerometric network (RAP) using surface-wave methods

Characterization of site conditions (soil class, VS30, velocity profiles) for 33 stations from the French permanent accelerometric network (RAP) using surface-wave methods

Ice shelf structure derived from dispersion curve analysis of ambient seismic noise, Ross Ice Shelf, Antarctica

Inversion of Scholte wave dispersion and waveform modeling for shallow structure of the Ninetyeast Ridge

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