KMAH index and separation of PSP-waves from streamer data

Brazilian Journal of Geophysics

ABSTRACT. Performing the velocity analysis, during the seismic processing, is very complex for converted waves. The problem becomes even more challenging when there is more than one wave conversion. The use of PSP-wave reflection events allows obtaining a more detailed set of information, which is interesting to other steps of seismic processing and other kinds of processing routines, which enhance the structural characterization of a model. Using PSP reflection events presents much more difficulty to recover velocity information, since it involves the nonhyperbolicity generated by the difference of datum between source and receivers, layered media with large offsets, and wave conversion. It is much more complicated to characterize the wave conversion in a PSP reflection than in PS reflection events because the wave conversion happens twice during the wave propagation. Since there is no specific mathematical description for this kind of traveltime event, we propose to treat the velo...

Geophysical Journal …, 2002

We present a scheme to separate P-and SV-wavefields from multi-component OBC data in the ¢ ¡ ¤ £ domain. Based on the plane-wave components with known horizontal slowness, the whole P-and SV-wavefields are separated into the direction of observed P-and SV-wave oscillation, respectively, by rotation of horizontal and vertical components. The incident P-and SV-waves are extracted from the separated wavefields by plane wave partitions at seabed. Parameters used in the separation are the local seismic wave velocities and density at the receiver location. Numerical tests on synthetic data for plane-layered model show good performance and accuracy of the scheme. Amundsen, L. & Reitan, A., 1995. Decomposition of multicomponent sea-floor data into upgoing and downgoing P-and S-waves, Geophysics, 60, 563-572. Dankbaar, J.W.M., 1988. Separation of P-and S-waves, Geophys. Prosp., 33, 970-986. Greenhalgh, S.A., Mason, I.M., Lucas, E., Pant, D. & Eames, R.T., 1990. Controlled direction reception filtering of P-and S-waves in © space, Geophys. J. Int., 100, 221-234.

Geophysical Prospecting, 2020

Recently, the interest in PS-converted waves has increased for several applications, such as sub-basalt layer imaging, impedance estimates and amplitude-versus-offset analysis. In this study, we consider the problem of separation of PP-and PS-waves from pre-stacked multicomponent seismic data in two-dimensional isotropic medium. We aim to demonstrate that the finite-offset common-reflection-surface traveltime approximation is a good alternative for separating PP-and PS-converted waves in common-offset and common shot configurations by considering a two-dimensional isotropic medium. The five parameters of the finite-offset common-reflection-surface are firstly estimated through the inversion methodology called very fast simulated annealing, which estimates all parameters simultaneously. Next, the emergence angle , one of the inverted parameters, is used to build an analytical separation function of PP and PS reflection separation based on the wave polarization equations. Once the PP-and PS-converted waves were separated, the sections are stacked to increase the signal-to-noise ratio using the special curves derived from finite-offset common-reflection-surface approximation. We applied this methodology to a synthetic dataset from simple-layered to complex-structured media. The numerical results showed that the inverted parameters of the finite offset common-reflection-surface and the separation function yield good results for separating PP-and PS-converted waves in noisy common-offset and common shot gathers.

Geophysical Research Letters, 2005

Geophysical Research Letters, 2005

Studia Geophysica et Geodaetica, 2007

A series of kinematic inversions based on robust non-linear optimization approach were performed using travel time data from a series of seismic refraction experiments: . These experiments were performed in Central Europe from 2000 were processed in this study. The goal of this work was to find seismic velocity models yielding travel times consistent with observed data.

Arabian Journal of Geosciences, 2013

On 19 May 2009, an earthquake sequence of M w =4.8 occurred at 25.20°N 37.76°E about 60 km onshore of the Red Sea coastline, Saudi Arabia. In the present study, the digital waveform data from the largest four events were used to estimate the source parameters and attenuation characteristics along the source-to-station path in the Arabian Shield. A grid search technique, combined with an assumption of circular source model, was applied to find the best-fit spectral amplitude over the space parameters: long period spectral level (Ω 0 ), corner frequency (f 0 ) and asymptotic high-frequency fall-off (γ). Consequently, the spectral parameters were used to estimate source parameters: seismic moment, fault radius (assumed circular rupture model) and stress drop. Seismic moments are founded to be within the range of 2.34E+14 to 2.83E+16 Nm and their corresponding moment magnitudes range from 3.5 to 4.8; the fault radius ranges from 369 to 1,498 m, and stress drops are observed in the range of 8.7 to 32.0 b. The spectral slopes beyond the corner frequency displayed ω −2.4 to ω −2.6 behaviours in contrast with Brune's source model of ω −2 . This finding requires more detailed investigations on large data sets to distinguish the behaviour mechanism of the spectral slopes at high frequencies. By taking the ratio between observed and calculated spectra, the attenuation curves for P and S waves were derived along the source-to-station paths. The preliminarily results exhibited high quality factors of Q α =3,883 and Q β =3,530 for P and S waves, respectively. To this end, the ratio Q β /Q α is founded to be slightly less than unity indicating that the body waves from source-to-station paths crossed a crustal volume that is partially saturated with fluids causing lower attenuation effect on P waves than on S waves in the Arabian Shield.

2013

Conventional and adaptive plane-wave beamforming with simultaneous recordings by large-aperture horizontal and vertical line arrays during the 2009 Philippine Sea Engineering Test (PhilSea09) reveal the rate of occurrence and the two-dimensional arrival structure of seismic phases that couple into the deep ocean. A ship-deployed, controlled acoustic source was used to evaluate performance of the horizontal array for a range of beamformer adaptiveness levels. Ninety T-phases from unique azimuths were recorded between Yeardays 107 to 119. T-phase azimuth and S-minus-P-phase timeof-arrival range estimates were validated using United States Geological Survey seismic monitoring network data. Analysis of phases from a seismic event that occurred on Yearday 112 near the east coast of Taiwan approximately 450 km from the arrays revealed a 22 clockwise evolution of T-phase azimuth over 90 s. Two hypotheses to explain such evolution-body wave excitation of multiple sources or in-water scattering-are presented based on T-phase origin sites at the intersection of azimuthal great circle paths and ridge/coastal bathymetry. Propagation timing between the source, scattering region, and array position suggests the mechanism behind the evolution involved scattering of the T-phase from the Ryukyu Ridge and a T-phase formation/scattering location estimation error of approximately 3.2 km.

Keywords: Body waves Interferometry Ambient noise Microseism Lithosphere Mots cle´s : Ondes de volume Interfé romé trie Bruit ambiant Microsé isme Lithosphè re A B S T R A C T

JOURNAL OF GEOPHYSICAL …, 1994

Four data sets characterizing gross crustal waveguide configuration and attenuation properties in Eurasia (surface topography, Moho depth, sediment thickness, and Lg coda Q value) are used to examine path influences on short-period regional P/Lg ratios. Linear regressions show considerable correlations between log P/Lg and waveguide properties for both earthquake and explosion data. This is of interest because P/Lg ratios are considered to be promising regional discriminants for which it is desi•'able to reduce scatter caused by propagation effects. To develop a comprehensive and stable model describing the path effects, multivariate regression is applied to the data set. The waveguide properties considered are highly correlated with each other, causing collinearity in the regression process. After backward elimination, we obtain a final model with statistically significant regression coefficients, which involves two independent variables: the path attenuation term TA and maximum sediment thickness on each path. These two factors are associated with (1) the overall intrinsic and scattering attenuation in the waveguide and (2) the localized blockage effects caused by waveguide geometry, respectively. Using the final model to correct the observed P/Lg measurements reduces the variances for separate earthquake data and explosion data by 40% and 27%, respectively. This correction slightly enhances the performance of the discriminant for periods near 1 s. appears surprisingly robust when crossing a zone where its waveguide is strongly deformed. Regan and Harkrider [1989] simulated the extreme cases of transitions from continent to ocean crust and vice versa, for Copyright 1994 by the American Geophysical Union. Paper nu•nber 94JB02123. 0148-0227/94/94J B-02123505.00 transverse-component L s propagation. In this case, the L s amplitude did decrease, but the attenuation is not sufficient to explain observed values. The strongest attenuation predicted involves a reduction of a factor of 2-3 in amplitude. However, it is well known that L s is totally eliminated when traversing oceanic crust [Press and Ewing, 1952]. Thus other factors and/or more complex structures must be considered to explain the observed attenuation of L;,. Recently, Cao and Muirhead [1993] successfully modeled Ls blockage with a P-SV finite difference method after introducing a water layer above the free surface. The water layer strongly attenuates R s , the short-period fundamental mode Rayleigh wave, but has less effect on Lg. However, interpretation of the influence of variable waveguide structure without water-covered segments is still open. The most important factor with predictable effect on Lg other than the waveguide structure is the quality factor Q, accounting for both intrinsic attenuation and scattering losses. Many investigations of Q using the decay of Lg amplitude with epicentral distance have been conducted in western Europe [e.g.,