Source-independent full wavefield converted-phase elastic migration velocity analysis

Abstract

S U M M A R YConverted phase (CP) elastic seismic signals are comparable in amplitude to the primary signals recorded at large offsets and have the potential to be used in seismic imaging and velocity analysis. We present an approach for CP elastic wave equation velocity analysis that does not use source information and is applicable to surface-seismic, microseismic, teleseismic and vertical seismic profile (VSP) studies. Our approach is based on the crosscorrelation between reflected or transmitted PP and CP PS (and/or SS and CP SP) waves propagated backward in time, and is formulated as an optimization problem with a differential semblance criterion objective function for the simultaneous update of both P-and S-wave velocity models. The merit of this approach is that it is fully data-driven, uses full waveform information, and requires only one elastic backward propagation to form an image rather than the two (one forward and one backward) propagations needed for standard reverse-time migration. Moreover, as the method does not require forward propagation, it does not suffer from migration operator source aliasing when a small number of shots are used. We present a derivation of the method and test it with a synthetic model and field micro-seismic data.Key words: Inverse theory; Body waves; Seismic tomography; Computational seismology; Wave propagation. I N T RO D U C T I O NIn recent years, full waveform seismic imaging and velocity analysis methods have become standard and the use of elastic waves is now drawing more attention. Converted phase (CP) waves are an integrated part of the recorded elastic seismic signal and are investigated in numerous studies in the research areas of vertical seismic profile (VSP) data (e.g. Esmersoy 1990; Stewart 1991; Xiao & Leaney 2010), surface reflection (e.g. Purnell 1992;Stewart et al. 2003;Hardage et al. 2011) and transmission seismic data (e.g. Vinnik 1977;Vinnik et al. 1983;Bostock et al. 2001;Rondenay et al. 2001;Brytic et al. 2012;Shang et al. 2012;Shabelansky et al. 2013). In particular, for example Xiao & Leaney (2010) and Shang et al. (2012) showed that the CP seismic images can be calculated using one elastic propagation without using source information (i.e. location, mechanism and time-function). Source information is generally considered mandatory in standard seismic imaging and velocity analysis. However, in * Now at: Earth Sciences Department, Memorial University of Newfound- passive monitoring source information is generally not available and in active source surveys seismic data require special treatment for frequency matching due to coupling differences between soil and vibro-seis or dynamite casing. These factors affect the accuracy of the imaging and velocity estimation and add computational and processing cost. Moreover, CP elastic seismic imaging is shown to have higher resolution in Xiao & Leaney (2010) and fewer artifacts than reflection type imaging in Shabelansky et al. (2012). In this study, we present a source-independent CP (SICP) velocity anal...

Converted-wave seismic imaging: Amplitude-balancing source-independent imaging conditions

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“…For this reason, we have developed a wave speed estimation approach for use with SICW imaging that allows one to find reliable wave speed models and thus obtain improved images (Shabelansky et al, 2015b). To highlight the sensitivity of SICW-ICs to wave speed variations, we present two sets of imaging results; first with severely smoothed wave speed models and second with a smooth elliptical inclusion at the center of the S-wave speed model.…”

“…However, for wave speed optimization analysis, care needs to be taken because this procedure affects to construction of the gradient for the optimization. For more details, see Shabelansky et al (2015b) and Shabelansky (2015, appendix B).…”

Source‐Independent Passive Seismic Reverse‐Time Structure Imaging With Grouping Imaging Condition: Method and Application to Microseismic Events Induced by Hydraulic Fracturing

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“…To map the Moho discontinuity, Shang et al (2012) presented an imaging condition of cross-correlating P and S wavefields after wavefield decomposition during elastic wave propagation of the teleseismic data. Following the same idea, Shabelansky et al (2015) developed a velocity analysis method using reflection/transmission waves and converted waves using both active and passive seismic data. Shabelansky et al (2017) further elaborated the source-independent converted wave imaging condition for better amplitude balancing with the deconvolutional forms.…”