Mark Vardy | NOCS - Academia.edu (original) (raw)

Papers by Mark Vardy

OCEANS 2015 - Genova, 2015

Offshore Technology Conference, 2014

Submarine flows are frequent processes occurring across the seafloor, ranging from dilute turbidi... more Submarine flows are frequent processes occurring across the seafloor, ranging from dilute turbidity currents, debris flows, and slides. However, our understanding of these flows and their erosive behaviour is limited by a paucity of high-resolution field data. Here we present two exceptionally detailed field datasets. The first uses a suite of shallow sediment cores to map out large-volume (>100 km3) individual turbidite beds for hundreds of kilometres across a basin-plain. The second uses high-resolution geophysical imagining coupled with a suite of shallow sediment cores to document a small-scale slide complex, off the coast of Norway. These two datasets document very different types of submarine flow, are situated in different geological settings and occur at different water depths. In both cases, the high-resolution field data enables individual event beds to be documented and the erosion beneath their deposits mapped out. We demonstrate that beneath the turbidite beds, found...

Acquisition of an extensive and multi-disciplinary data set, consisting of high-resolution swath ... more Acquisition of an extensive and multi-disciplinary data set, consisting of high-resolution swath bathymetry, 2D/3D seismic data, multiple short (up to 6 m) and two long (12 m and 14 m, respectively) sediment cores, and in situ FF-CPTu/CPTu (free fall, FF, and traditional cone penetration tests with pore pressure measurements) profiles complemented with geotechnical laboratory data, allows for a detailed analysis of the landslide morphology and stratigraphic controls on the 1996 Finneidfjord landslide. High-resolution geotechnical data from the in situ FF-CPTu/CPTu and boreholes, complemented with geological imaging (CT and X-ray scans) and analyses (e.g., XRF) reveal that the shallow slip plane lies within a thin, seismically-stratified unit, with clay layers sandwiching a sandy layer, identified from the peak in tip resistance (CPTu). This slip plane is currently being analyzed geotechnically (e.g., direct simple shear testing, grain size analyses and plasticity measurements). Of p...

High resolution multibeam bathymetry and airborne LiDAR (light detection and ranging) data, suppl... more High resolution multibeam bathymetry and airborne LiDAR (light detection and ranging) data, supplemented by geomorphological and geological field mapping have been used to investigate the glacial and post-glacial history of Windermere, the largest natural lake in England. In addition, recently acquired piston cores, supplemented with 2D and 3D seismic reflection data from previous surveys have been used to examine the well preserved sequence stratigraphy. The data is used to generate a present-day landscape map, revealing a complex landform record, characterised by nine sub-basins separated by steps, ridges and isolated topographic highs related to the retreat of the British and Irish Ice Sheet (BIIS). Debris flows and anthropogenic features are superimposed on the general bathymetric framework formed since the Last Glacial Maximum. There is also evidence of glacial features preserved onshore, which identify a series of depositional environments that accompanied ice advance, ice ret...

SEG Technical Program Expanded Abstracts 2013, 2013

ABSTRACT Shallow-water submarine landslides are a widely observed landform, seen in fjords, lakes... more ABSTRACT Shallow-water submarine landslides are a widely observed landform, seen in fjords, lakes and rivers at all latitudes. With run outs of several km and the ability to both retrogress inshore as well as generate potentially hazardous tsunamis, they represent a significant hazard to offshore and near-shore infrastructure. However, their complex architecture and sensitivity to subtle changes in the mechanical properties of soils makes them extremely difficult to study, requiring a comprehensive combined assessment of the structural and soil mechanical architecture of the slope and subsurface. Here we present a highly detailed, integrated geophysical, geological and geotechnical study of the parameters controlling submarine slope stability in a fjord in northern Norway.

International Journal of Greenhouse Gas Control, 2015

Seismic Imaging of Depositional and Geomorphic Systems: 30th Annual, 2010

Nature Climate Change, 2014

International Journal of Greenhouse Gas Control, 2014

Submarine Mass Movements and Their Consequences, 2011

Offshore Technology Conference, 2013

We present results from decimetre resolution 3D seismic volumes acquired over Late Quaternary mas... more We present results from decimetre resolution 3D seismic volumes acquired over Late Quaternary mass movement deposits in both Lake Windermere, UK, and the Trondheim Harbour area, central Norway. Both deposits were imaged using the 3D Chirp sub-bottom profiler, which combines the known, highly repeatable source waveform of Chirp profilers with the coherent processing and interpretation afforded by true 3D seismic

In hydrocarbon prospection, the inversion of marine geophysical data for remote reservoir charact... more In hydrocarbon prospection, the inversion of marine geophysical data for remote reservoir characterization has developed enormously over the past 20+ years. While some techniques (e.g., waveform inversion) are computationally expensive to permit widespread application across all targets, other less expensive variants (e.g., impedance and amplitude-versus-angle inversion) have become a standard component of most interpretation workflows. In contrast, there has been very little progress toward the remote classification of near-surface sediments through the inversion of high-resolution geophysical data, with both academia and industry relying on extensive coring and stratigraphic correlations.

However, accurate stratigraphic correlation can be difficult due to inaccuracies in the time-to-depth conversion of the geophysical data, and the potential for loss and/or compression of high porosity and poorly-consolidated seafloor material during the intrusive sampling process. Additionally, when dealing with near-surface sediments (top 10s m below seafloor), the sampling procedure inherently alters the nature of the sampled material, introducing uncertainties on key mechanical parameters (e.g., porosity and undrained shear strength) that are difficult to quantify.

Recently, a new inversion method was presented, which is based on the application of post-stack acoustic impedance inversion to high-resolution marine seismic reflection data using a genetic algorithm and a convolutional forward model. Here, we further test this approach using a synthetic example and a marine, near-surface geophysical case study from a fjordic environment in Norway. We characterize the robustness of the algorithm under a variety of noise conditions and utilize the stochastic optimization approach to derive 95% confidence limits as well as a statistically ‘best’ model. Furthermore, we show how, through the use of global empirical relationships, soil mechanical properties can be derived (including effective stress, over pressure, clay/sand fraction and moisture content), while, through the application of soil mechanical models (e.g., White’s model), it is possible to estimate gas saturation.

In both case studies (synthetic and field), the inversion results demonstrate excellent correlation with direct sampling, even in the presence of modest noise contamination. We can identify metre-scale stratigraphic changes, as well as subtle decimetre-scale structures, such as a 40 cm thick composite landslide glide plane. The high-fidelity remote derivation of such soil properties has significant applications, both within academia and the offshore services/exploration industry.

In contrast to the use of marine seismic reflection techniques for reservoir-scale applications, ... more In contrast to the use of marine seismic reflection techniques for reservoir-scale applications, where seismic inversion for quantitative sediment analysis is common, shallow-water, very-high-resolution seismic reflection data are seldom used for more than qualitative reflection interpretation. Here, a quantitative analysis of very-high-resolution marine seismic reflection profiles from a shallow- water (<50 m water depth) fjord in northern Norway is presented. Acquired using Sparker, Boomer, and Chirp sources, the failure plane of multiple local landslides correlates with a composite reflection that reverses polarity to the south. Using a genetic algorithm, a 1D post-stack acoustic impedance inversion of all three profiles is performed, calibrating against multi-sensor core logger (MSCL) data from cores. Using empirical relationships the resulting impedance profiles are related to remote sediment properties, including: P-wave velocity; density; mean grain size; and porosity. The composite reflector is consistently identified by all three data sources as a finer-grained (by one Phi), lower density (c. 0.2 g/cm3 less than background) thin bed, with an anomalous low velocity zone (at least 100 m/s lower than background) associated with the polarity reversal to the south. Such a velocity contrast is consistent with an accumulation of shallow free gas trapped within the finer- grain, less permeable layer. This study represents the first application of acoustic impedance inversion to very-high-resolution seismic reflection data and demonstrates the potential for directly relating seismic reflection data with sediment properties using a variety of commonly used shallow seismic profiling sources.