High-resolution quantitative seismic imaging of a strike-slip fault with small vertical offset in clay rocks from underground galleries: Experimental platform of Tournemire, France

Imaging tectonic faults with small vertical offsets in argillites (clay rock) using geophysical methods is challenging. In the context of deep radioactive waste disposals, the presence of such faults has to be assessed because they can modify the rock-confining properties. In the Tournemire Experimental Platform (TEP, Aveyron, France), fault zones with small vertical offsets and complex shape have been identified from underground works. However, 3D high-resolution surface seismic methods have limitations in this context that led us to consider the detection and characterization of the faults directly from underground works. We investigated the potential of seismic full-waveform inversion (FWI) applied in a transmission configuration to image the clay rock medium in a horizontal plane between galleries and compared it with first-arrival traveltime tomography (FATT). Our objective was to characterize seismic velocities of a block of argillites crossed by a subvertical fault zone with a small vertical offset. The specific measurement configuration allowed us to neglect the influence of the galleries on the wave propagation and to simplify the problem by considering a 2D isotropic horizontal imaging domain. Our FWI scheme relied on a robust adaptation of early arrival waveform tomography. The results obtained with FATT and FWI were in accordance, and both correlated with the geologic observations from the gallery walls and boreholes. We found that even though various simplifications was done in the inversion scheme and only a part of the data was used, FWI allowed us to get higher resolution images than FATT, and it was especially less sensitive to the incomplete illumination because it also used diffracted energy. Our results highlighted the complexity of the fault zone, showing a complex interaction of the main fault system with a secondary system composed of decimetric fractures associated with the presence of water.

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The use of geophysical prospecting for imaging active faults in the Roer Graben, Belgium

Geophysics ◽

10.1190/1.1444925 ◽

2001 ◽

Vol 66 (1) ◽

pp. 78-89 ◽

Cited By ~ 62

Author(s):

Donat Demanet ◽

François Renardy ◽

Kris Vanneste ◽

Denis Jongmans ◽

Thierry Camelbeeck ◽

...

Keyword(s):

High Resolution ◽

Physical Properties ◽

Fault Zone ◽

Geophysical Methods ◽

Depth Range ◽

Electrical Tomography ◽

Reflection Seismic ◽

Refraction Seismic ◽

Geophysical Surveys ◽

Geophysical Techniques

As part of a paleoseismological investigation along the Bree fault scarp (western border of the Roer Graben), various geophysical methods [electrical profiling, electromagnetic (EM) profiling, refraction seismic tests, electrical tomography, ground‐penetrating radar (GPR), and high‐resolution reflection seismic profiles] were used to locate and image an active fault zone in a depth range between a few decimeters to a few tens of meters. These geophysical investigations, in parallel with geomorphological and geological analyses, helped in the decision to locate trench excavations exposing the fault surfaces. The results could then be checked with the observations in four trenches excavated across the scarp. Geophysical methods pointed out anomalies at all sites of the fault position. The contrast of physical properties (electrical resistivity and permittivity, seismic velocity) observed between the two fault blocks is a result of a differences in the lithology of the juxtaposed soil layers and of a change in the water table depth across the fault. Extremely fast techniques like electrical and EM profiling or seismic refraction profiles localized the fault position within an accuracy of a few meters. In a second step, more detailed methods (electrical tomography and GPR) more precisely imaged the fault zone and revealed some structures that were observed in the trenches. Finally, one high‐resolution reflection seismic profile imaged the displacement of the fault at depths as large as 120 m and filled the gap between classical seismic reflection profiles and the shallow geophysical techniques. Like all geophysical surveys, the quality of the data is strongly dependent on the geologic environment and on the contrast of the physical properties between the juxtaposed formations. The combined use of various geophysical techniques is thus recommended for fault mapping, particularly for a preliminary investigation when the geological context is poorly defined.

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High-Resolution Seismic Images and Seismic Velocities of the San Andreas Fault Zone at Burro Flats, Southern California

Bulletin of the Seismological Society of America ◽

10.1785/0120060252 ◽

2008 ◽

Vol 98 (6) ◽

pp. 2948-2961 ◽

Cited By ~ 1

Author(s):

C. C. Tsai ◽

R. D. Catchings ◽

M. R. Goldman ◽

M. J. Rymer ◽

P. Schnurle ◽

...

Keyword(s):

High Resolution ◽

Fault Zone ◽

Southern California ◽

San Andreas Fault ◽

Seismic Velocities ◽

San Andreas ◽

Seismic Images

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Characterization of heterogeneous landfill: seismic waveform inversion and wavefield retrieval to integrated quantitative inversion of high-resolution seismic-electrical datasets

10.5194/egusphere-egu2020-18235 ◽

2020 ◽

Author(s):

Ranajit Ghose

Keyword(s):

High Resolution ◽

Preferential Flow ◽

Waveform Inversion ◽

Geophysical Methods ◽

Matric Suction ◽

Phreatic Surface ◽

Near Surface ◽

Degradation Processes ◽

Seismic Waveform ◽

Seismic Wavefield

<p>A landfill body is typically highly heterogeneous. The scale of these heterogeneities - which are relevant for the purpose of assessment of preferential flow paths, the degradation processes, and the spatio-temporally varying aging and settlements - is quite often small considering the limiting resolution and confidence of the prevalent near-surface geophysical methods. High-density areas act as obstruction to fluid flow and are important for understanding the degradation processes. These areas manifest as scatterers in the recorded seismic wavefield. Strong presence of scattered energy is typical of seismic datasets acquired on landfills. Our research has been concentrated on resolving and monitoring density and porosity variations, as well as distribution of water saturation, phreatic surface, matric suction and stress. Dedicated schemes of early-arrival waveform tomography, full-waveform inversion and interferometric seismic wavefield retrieval complemented by electrical resistivity tomography show promise in high-resolution delineation and monitoring of these properties in a heterogeneous landfill. We will discuss the results of a novel inversion scheme which allows quantitative estimation of spatio-temporally heterogeneous matric suction, stress and porosity.</p>

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Diffuse Tectonic Deformation in the Drum Mountains Fault Zone, Utah, USA: Testing the Utility of Legacy Aerial Photograph-Derived Topography

Frontiers in Earth Science ◽

10.3389/feart.2020.600729 ◽

2021 ◽

Vol 8 ◽

Author(s):

Timothy A. Stahl ◽

Nathan A. Niemi ◽

Jaime E. Delano ◽

Franklin D. Wolfe ◽

Michael P. Bunds ◽

...

Keyword(s):

High Resolution ◽

Fault Zone ◽

Aerial Photograph ◽

Basin And Range ◽

Aerial Photographs ◽

Fault System ◽

Tectonic Deformation ◽

Surface Model ◽

Basin And Range Province ◽

Fault Systems

The Basin and Range province in the western United States hosts numerous low-slip-rate normal faults with diffuse and subtle surface expressions. Legacy aerial photographs, widely available across the region, can be used to generate high-resolution digital elevation models of these previously uncharacterized fault systems. Here, we test the limits and utility of aerial photograph-derived elevation products on the Drum Mountains fault zone—a virtually unstudied and enigmatic fault system in the eastern Basin and Range province of central Utah. We evaluate a new 2-m digital surface model produced from aerial photographs against other remotely sensed and field survey data and assess the various factors that contribute to noise, artifacts, and distortions. Despite some challenges, the new elevation model captures the complex array of cross-cutting fault scarps well. We demonstrate that the fault zone has variable net east- or west-down sense of displacement across a c. 8-km-wide zone of antithetic and synthetic traces. Optically stimulated luminescence ages and scarp profiles are used to constrain net extension rates across two transects and reveal that the Drum Mountains fault zone has average extension rates of c. 0.1–0.4 mm yr−1 over the last c. 35 ka. These rates are both faster than previously estimated and faster than most other faults in the region, and could be an order of magnitude higher if steep faults at the surface sole into a detachment at depth. Several models have been proposed for local and regional faulting at depth, but our data show that the offsets, rates, and geometries of faulting can be generated by the reactivation of pre-existing, cross-cutting faults in a structurally complex zone between other fault systems. This study highlights how legacy aerial-photograph-derived elevation products, in lieu of other high-resolution topographic datasets, can be used to study active faults, especially in remote regions where diffuse deformation would otherwise remain undetected.

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