Tracking of velocity variations at depth in the presence of surface velocity fluctuations

Cacqueray, Benoit de; Roux, Philippe; Campillo, Míchel; Catheline, Stéfan

doi:10.1190/geo2012-0071.1

Cited by 5 publications

(3 citation statements)

References 17 publications

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“…Constraints on the deeper parts of the fault, i.e., estimates of its dip [Yang et al, 2011], are limited due to the analysis of high-frequency surface waves. The application of double-beamforming techniques offers a potential tool to focus on noise wavefield components that are sensitive to properties at deeper parts of the fault [de Cacqueray et al, 2013]. The identification of a critical frequency f c , above which the wavefield within the FZ has significantly different properties compared to the surrounding region, is also compatible with observations based on ballistic waves.…”

Section: Discussionmentioning

confidence: 69%

Seismic fault zone trapped noise

et al. 2014

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Systematic velocity contrasts across and within fault zones can lead to head and trapped waves that provide direct information on structural units that are important for many aspects of earthquake and fault mechanics. Here we construct trapped waves from the scattered seismic wavefield recorded by a fault zone array. The frequency-dependent interaction between the ambient wavefield and the fault zone environment is studied using properties of the noise correlation field. A critical frequency f c ≈ 0.5 Hz defines a threshold above which the in-fault scattered wavefield has increased isotropy and coherency compared to the ambient noise. The increased randomization of in-fault propagation directions produces a wavefield that is trapped in a waveguide/cavity-like structure associated with the low-velocity damage zone. Dense spatial sampling allows the resolution of a near-field focal spot, which emerges from the superposition of a collapsing, time reversed wavefront. The shape of the focal spot depends on local medium properties, and a focal spot-based fault normal distribution of wave speeds indicates a ∼50% velocity reduction consistent with estimates from a far-field travel time inversion. The arrival time pattern of a synthetic correlation field can be tuned to match properties of an observed pattern, providing a noise-based imaging tool that can complement analyses of trapped ballistic waves. The results can have wide applicability for investigating the internal properties of fault damage zones, because mechanisms controlling the emergence of trapped noise have less limitations compared to trapped ballistic waves.

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Section: Discussionmentioning

confidence: 69%

Seismic fault zone trapped noise

et al. 2014

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“…Laboratory physical modeling is frequently proposed with non‐contact ultrasonic techniques to study seismic wave propagation at various scales, with a wide range of applications in civil engineering (Ruiz and Nagy, 2004; Lu et al, 2011; Abraham et al, 2012), near‐surface geophysics (Bodet et al, 2005, 2009; Bretaudeau et al, 2011; Bergamo et al, 2014), exploration seismic (Campman et al, 2004, 2005; de Cacqueray et al, 2011, 2013), or seismology (Nishizawa et al, 1997; van Wijk and Levshin, 2004). The non‐contact character of ultrasonic techniques and their high‐density sampling abilities provide flexibility that gives the opportunity to reproduce typical seismic records in the laboratory.…”

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confidence: 99%

Small‐Scale Seismic Monitoring of Varying Water Levels in Granular Media

Pasquet

Bodet

Bergamo

et al. 2016

Vadose Zone Journal

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Core Ideas We tested the sensitivity of seismic measurements to water saturation variations. We used ultrasonic techniques to reproduce a small‐scale seismic acquisition setup. Measurements were performed on glass bead layers with varying water levels. Results of 3D numerical modelling were used to validate data at the dry state. Data difference trends between the dry and wet models match with the water level. Physical properties of soils in the vadose zone, and especially their water content, are characterized by strong spatial and temporal variations mostly driven by weather and anthropogenic activities. To understand this variability and help water resource management, seismic methods have been recently suggested as a complement to electrical and electromagnetic techniques. The simultaneous in situ estimation of pressure (P) and shear (S) wave velocities (VP and VS, respectively) and their ratio (VP/VS) offers novel perspectives for the monitoring of space and time variations of vadose zone mechanical properties. However, the seismic response in partially saturated and unconsolidated soils remains complex and deserves to be studied both theoretically and experimentally. In this study, we tested the sensitivity of seismic measurements (i.e., P‐wave travel times and surface‐wave phase velocities) to water saturation variations using controlled physical models at the laboratory scale. Ultrasonic techniques were used to reproduce a small‐scale seismic acquisition setup at the surface of glass bead layers with varying water levels. Travel times and phase velocity measurements obtained at the dry state were validated with both theoretical models and numerical simulations and serve as reference datasets. The increasing water level clearly affected the recorded wave field in both its phase and amplitude. In these cases, the collected data cannot yet be inverted in the absence of a comprehensive theoretical model for such partially saturated granular media. The differences in travel time and phase velocity observed between the dry and wet models show patterns that interestingly match the observed water level and depth of the capillary fringe, thus offering attractive perspectives for studying soil water content variations.

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“…This can be addressed by cross‐equalization techniques for surface acquisition (Ross, Cunningham, and Weber ; Rickett and Lumley ), time‐lapse wave separation with buried systems in the field (Cotton, Michou, and Forgues ), or array‐processing techniques on physical models (de Cacqueray et al . ).…”

Section: Introductionmentioning

confidence: 97%

Using slowness and azimuth fluctuations as new observables for four‐dimensional reservoir seismic monitoring

Cacqueray

Roux

Campillo

2015

Geophysical Prospecting

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Four‐dimensional imaging using geophysical data is of increasing interest in the oil and gas industries. While travel‐time and amplitude variations are commonly used to monitor reservoir properties at depth, their interpretation can suffer from a lack of information to decipher the parts played by different parameters. In this context, this study focuses on the slowness and azimuth angle measured at the surface using source and receiver arrays as complementary observables. In the first step, array processing techniques are used to extract both azimuth and incidence angles at the source side (departure angles) and at the receiver side (arrival angles). In the second step, the slowness and angle variations are monitored in a laboratory environment. These new observables are compared with traditional arrival‐time variations when the propagation medium is subject to temperature fluctuations. Finally, field data from a heavy‐oil permanent reservoir monitoring system installed onshore and facing steam injection and temperature variations are investigated. The slowness variations are computed over a period of 152 days. In agreement with Fermat's principle, strong correlations between the slowness and arrival‐time variations are highlighted, as well as good consistency with other techniques and field pressure measurements. Although the temporal variations of slowness and arrival time show the same features, there are still differences that can be considered for further characterization of the physical changes at depth.

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Tracking of velocity variations at depth in the presence of surface velocity fluctuations

Cited by 5 publications

References 17 publications

Seismic fault zone trapped noise

Seismic fault zone trapped noise

Small‐Scale Seismic Monitoring of Varying Water Levels in Granular Media

Using slowness and azimuth fluctuations as new observables for four‐dimensional reservoir seismic monitoring

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