CA
C. Almagro Vidal
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Time-lapse changes in the subsurface can be analyzed by comparing seismic reflection data from two different states, one serving as the base survey and the second as the monitor survey. Conventionally, reflection data are acquired by placing active seismic sources at the acquisition surface. Alternatively, these data can be acquired from passive sources in the subsurface, using seismic interferometry (SI). Unfortunately, the reflection responses as retrieved by SI inherit an imprint of the passive-source distribution; therefore, monitoring with SI requires high passive-source repeatability, which is very often not achievable in practice.We have developed an alternative by using active seismic data for the base survey and a single passive source (e.g., a seismic tremor produced by induced seismicity) for the monitor survey. By constraining the source-radiation pattern of the (active) base survey according to the characteristics of the (passive) monitor survey, we succeed in extracting the time-lapse response in the image domain. We tested our method with numerically modeled data.
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Time-lapse changes in the subsurface can be analyzed by comparing seismic reflection data from two different states, one serving as the base survey and the second as the monitor survey. Conventionally, reflection data are acquired by placing active seismic sources at the acquisition surface. Alternatively, these data can be acquired from passive sources in the subsurface, using seismic interferometry (SI). Unfortunately, the reflection responses as retrieved by SI inherit an imprint of the passive-source distribution; therefore, monitoring with SI requires high passive-source repeatability, which is very often not achievable in practice.We have developed an alternative by using active seismic data for the base survey and a single passive source (e.g., a seismic tremor produced by induced seismicity) for the monitor survey. By constraining the source-radiation pattern of the (active) base survey according to the characteristics of the (passive) monitor survey, we succeed in extracting the time-lapse response in the image domain. We tested our method with numerically modeled data.
Journal article
(2018)
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Carlos Almagro Vidal, Joost van der Neut, Arie Verdel, Iris Hartstra, Kees Wapenaar
Passive seismic interferometry enables the estimation of the reflection response of the subsurface using passive receiver recordings at the surface from sources located deep in the Earth. Interferometric imaging makes use of this retrieved reflection response in order to study the subsurface. Successful interferometric imaging relies on the availability of passive recordings from sufficient sources in the subsurface. Ideally, these sources should be homogeneously distributed, which is unlikely to happen in practical applications. Incomplete source distributions result in the retrieval of inaccurate reflection responses, containing artefacts which can disturb the interferometric imaging process. We propose an alternative imaging method for passive data based on illumination diagnosis and directionally constrained migration. In this method, passive responses from single transient sources are cross-correlated individually, and the dominant radiation direction from each virtual source is estimated. The correlated responses are imaged individually, thereby limiting the source wavefield to the dominant radiation direction of the virtual source. This constraint enables the construction of accurate images from individual sources with a significantly reduced amount of migrated interferometric artefacts. We also show that the summation of all individual imaging results improves the subsurface image by constructive interference, while migrated crosstalk and artefacts experience cancellation. This process, called Image Interferometry, shows that in case of limited subsurface illumination the interferometric integration can be applied in the image domain rather than in the virtual reflection-response domain, thus eliminating the need for the retrieval of the reflection response as an intermediate step.
...
Passive seismic interferometry enables the estimation of the reflection response of the subsurface using passive receiver recordings at the surface from sources located deep in the Earth. Interferometric imaging makes use of this retrieved reflection response in order to study the subsurface. Successful interferometric imaging relies on the availability of passive recordings from sufficient sources in the subsurface. Ideally, these sources should be homogeneously distributed, which is unlikely to happen in practical applications. Incomplete source distributions result in the retrieval of inaccurate reflection responses, containing artefacts which can disturb the interferometric imaging process. We propose an alternative imaging method for passive data based on illumination diagnosis and directionally constrained migration. In this method, passive responses from single transient sources are cross-correlated individually, and the dominant radiation direction from each virtual source is estimated. The correlated responses are imaged individually, thereby limiting the source wavefield to the dominant radiation direction of the virtual source. This constraint enables the construction of accurate images from individual sources with a significantly reduced amount of migrated interferometric artefacts. We also show that the summation of all individual imaging results improves the subsurface image by constructive interference, while migrated crosstalk and artefacts experience cancellation. This process, called Image Interferometry, shows that in case of limited subsurface illumination the interferometric integration can be applied in the image domain rather than in the virtual reflection-response domain, thus eliminating the need for the retrieval of the reflection response as an intermediate step.
Passive seismics is the set of applications that endeavours the exploration of the
Earth’s mechanical properties using naturally occurring sources in the subsurface.
Conventional imaging of the subsurface is achieved with the aid of reflection
surveys of body waves from the surface. Passive seismics offers the possibility
to retrieve these reflection surveys using recordings of ambient noise and seismic
tremors, without the use of active sources. This thesis explores the use of novel
applications in passive seismics with the purpose to obtain an improved subsurface
image, compared to those obtained using conventional passive seismic imaging.
...
Passive seismics is the set of applications that endeavours the exploration of the
Earth’s mechanical properties using naturally occurring sources in the subsurface.
Conventional imaging of the subsurface is achieved with the aid of reflection
surveys of body waves from the surface. Passive seismics offers the possibility
to retrieve these reflection surveys using recordings of ambient noise and seismic
tremors, without the use of active sources. This thesis explores the use of novel
applications in passive seismics with the purpose to obtain an improved subsurface
image, compared to those obtained using conventional passive seismic imaging.
Our objective is to complement lithospheric seismic tomography with an interferometric method to retrieve high-resolution reflectivity images from local earthquake recordings. The disadvantage of using local earthquakes for the retrieval of reflected body-waves is their usual sparse distribution. We propose an alternative formulation of passive seismic interferometry by multidimensional deconvolution (MDD) which uses the multiples in the full recordings to compensate for missing illumination angles. This method only requires particle-velocity recordings at the surface from passive transient sources and retrieves body-wave reflection responses without free-surface multiples. We conduct an acoustic modelling experiment to compare this formulation to a previous MDD method and Green’s function retrieval by crosscorrelation for different source distributions. We find that in the case of noise-contaminated recordings obtained under severely limited and irregular illumination conditions, the alternative MDD method introduced here still retrieves the complete reflection response without free-surface multiples where the other interferometric methods break down.
...
Our objective is to complement lithospheric seismic tomography with an interferometric method to retrieve high-resolution reflectivity images from local earthquake recordings. The disadvantage of using local earthquakes for the retrieval of reflected body-waves is their usual sparse distribution. We propose an alternative formulation of passive seismic interferometry by multidimensional deconvolution (MDD) which uses the multiples in the full recordings to compensate for missing illumination angles. This method only requires particle-velocity recordings at the surface from passive transient sources and retrieves body-wave reflection responses without free-surface multiples. We conduct an acoustic modelling experiment to compare this formulation to a previous MDD method and Green’s function retrieval by crosscorrelation for different source distributions. We find that in the case of noise-contaminated recordings obtained under severely limited and irregular illumination conditions, the alternative MDD method introduced here still retrieves the complete reflection response without free-surface multiples where the other interferometric methods break down.
Seismic interferometry (SI) presents a set of inexpensive and noninvasive methods that can be applied to any array at the surface to retrieve virtual body-wave reflection responses from earthquake recordings. Conventional SI by cross-correlation requires recordings of wavefields in lossless media generated by a smooth continuous distribution of passive sources with isotropic source radiation patterns and similar power spectra. These conditions are unlikely to be met in the lithosphere: earthquakes are distributed sparsely and generated by complex mechanisms. The resulting anisotropy in the illumination of the receiver array causes the retrieved virtual-source radiation patterns to be irregular, leading to artifacts which can obscure the desired body-wave reflections. SI by multidimensional deconvolution (MDD) can inherently correct for anisotropic illumination of the array and does not rely on the medium being lossless. We propose an alternative formulation of MDD for two-way wavefields: full-field MDD. Different from previous MDD methods for passive two-way wavefield recordings, full-field MDD uses multiples in the passive data to construct the reflection response without free-surface interaction. Therefore, this MDD method profits from additional wavenumbers provided by scattering to compensate for sparse earthquake distributions. Besides, this method does not require wavefield decomposition, which is sensitive to velocity variations at the receiver level. We compare the reflection retrieval by full-field MDD and cross-correlation for a limited passive source distribution in a lithospheric model with a discontinuous Moho at a depth of 50 km. We simulate earthquakes generated by dipole sources along a listric fault-system with power spectra varying within bandwidth 0.2-2.6 Hz. The reflection response retrieved by full-field MDD shows a continuous high-resolution Moho reflection, while cross-correlation yields a very low resolution response obscured by artifacts.
...
Seismic interferometry (SI) presents a set of inexpensive and noninvasive methods that can be applied to any array at the surface to retrieve virtual body-wave reflection responses from earthquake recordings. Conventional SI by cross-correlation requires recordings of wavefields in lossless media generated by a smooth continuous distribution of passive sources with isotropic source radiation patterns and similar power spectra. These conditions are unlikely to be met in the lithosphere: earthquakes are distributed sparsely and generated by complex mechanisms. The resulting anisotropy in the illumination of the receiver array causes the retrieved virtual-source radiation patterns to be irregular, leading to artifacts which can obscure the desired body-wave reflections. SI by multidimensional deconvolution (MDD) can inherently correct for anisotropic illumination of the array and does not rely on the medium being lossless. We propose an alternative formulation of MDD for two-way wavefields: full-field MDD. Different from previous MDD methods for passive two-way wavefield recordings, full-field MDD uses multiples in the passive data to construct the reflection response without free-surface interaction. Therefore, this MDD method profits from additional wavenumbers provided by scattering to compensate for sparse earthquake distributions. Besides, this method does not require wavefield decomposition, which is sensitive to velocity variations at the receiver level. We compare the reflection retrieval by full-field MDD and cross-correlation for a limited passive source distribution in a lithospheric model with a discontinuous Moho at a depth of 50 km. We simulate earthquakes generated by dipole sources along a listric fault-system with power spectra varying within bandwidth 0.2-2.6 Hz. The reflection response retrieved by full-field MDD shows a continuous high-resolution Moho reflection, while cross-correlation yields a very low resolution response obscured by artifacts.