scholarly journals Quantifying sediment mass redistribution from joint time-lapse gravimetry and photogrammetry surveys

2020 ◽  
Vol 8 (2) ◽  
pp. 555-577
Author(s):  
Maxime Mouyen ◽  
Philippe Steer ◽  
Kuo-Jen Chang ◽  
Nicolas Le Moigne ◽  
Cheinway Hwang ◽  
...  
Keyword(s):  
Gravity Data ◽  
River Sediments ◽  
Time Lapse ◽  
New Combination ◽  
Gravity Changes ◽  
Surface Displacements ◽  
Sediment Mass ◽  
Mass Redistribution ◽  
Average Loss ◽  
Slow Landslide

Abstract. The accurate quantification of sediment mass redistribution is central to the study of surface processes, yet it remains a challenging task. Here we test a new combination of terrestrial gravity and drone photogrammetry methods to quantify sediment mass redistribution over a 1 km2 area. Gravity and photogrammetry are complementary methods. Indeed, gravity changes are sensitive to mass changes and to their location. Thus, by using photogrammetry data to constrain this location, the sediment mass can be properly estimated from the gravity data. We carried out three joint gravimetry–photogrammetry surveys, once a year in 2015, 2016 and 2017, over a 1 km2 area in southern Taiwan, featuring both a wide meander of the Laonong River and a slow landslide. We first removed the gravity changes from non-sediment effects, such as tides, groundwater, surface displacements and air pressure variations. Then, we inverted the density of the sediment with an attempt to distinguish the density of the landslide from the density of the river sediments. We eventually estimate an average loss of 3.7 ± 0.4 × 109 kg of sediment from 2015 to 2017 mostly due to the slow landslide. Although the gravity devices used in this study are expensive and need week-long surveys, new instrumentation currently being developed will enable dense and continuous measurements at lower cost, making the method that has been developed and tested in this study well-suited for the estimation of erosion, sediment transfer and deposition in landscapes.

scholarly journals Quantifying sediment mass redistribution from joint time-lapse gravimetry and photogrammetry surveys

2019 ◽  
Author(s):  
Maxime Mouyen ◽  
Philippe Steer ◽  
Kuo-Jen Chang ◽  
Nicolas Le Moigne ◽  
Cheinway Hwang ◽  
...  
Keyword(s):  
Gravity Data ◽  
River Sediments ◽  
Time Lapse ◽  
New Combination ◽  
Gravity Changes ◽  
Sediment Mass ◽  
Mass Redistribution ◽  
Sediment Redistribution ◽  
Average Loss ◽  
Slow Landslide

Abstract. The accurate quantification of sediment mass redistribution is central to the study of surface processes, yet it remains a challenging task. Here we test a new combination of terrestrial gravity and drone photogrammetry methods to quantify sediment redistribution over a 1-km2 area. Gravity and photogrammetry are complementary methods. Indeed, gravity changes are sensitive to mass changes and to their location. Thus, by using photogrammetry data to constrain this location, the sediment mass can be properly estimated from the gravity data. We carried out 3 joint gravity-photogrammetry surveys, once a year in 2015, 2016 and 2017 over a 1-km2 area in southern Taiwan featuring both a wide meander of the Laonong River and a slow landslide. We first removed the gravity changes from non-sediment effects, such as tides, groundwater, surface displacements and air pressure variations. Then, we inverted the density of the sediment, with an attempt to distinguish the density of the landslide from the density of the river sediments. We eventually estimate an average loss of 4.7 ± 0.4 × 109 kg of sediment from 2015 to 2017, mostly due to the slow landslide. Although the gravity devices used in this study are expensive and need week-long surveys, new instrumentation progresses shall enable dense and continuous measurements at lower cost, making this method relevant to improve the estimation of erosion, sediment transfer and deposition in landscapes.

Estimating saturation and density changes caused by CO2 injection at Sleipner — Using time-lapse seismic amplitude-variation-with-offset and time-lapse gravity

2017 ◽  
Vol 5 (2) ◽  
pp. T243-T257 ◽  
Author(s):  
Martin Landrø ◽  
Mark Zumberge
Keyword(s):  
Gravity Data ◽  
Time Lapse ◽  
Co2 Injection ◽  
Injection Point ◽  
Amplitude Variation With Offset ◽  
Seismic Method ◽  
Seismic Amplitude ◽  
Gravity Measurements ◽  
Measured Time ◽  
Best Fit

We have developed a calibrated, simple time-lapse seismic method for estimating saturation changes from the [Formula: see text]-storage project at Sleipner offshore Norway. This seismic method works well to map changes when [Formula: see text] is migrating laterally away from the injection point. However, it is challenging to detect changes occurring below [Formula: see text] layers that have already been charged by some [Formula: see text]. Not only is this partly caused by the seismic shadow effects, but also by the fact that the velocity sensitivity for [Formula: see text] change in saturation from 0.3 to 1.0 is significantly less than saturation changes from zero to 0.3. To circumvent the seismic shadow zone problem, we combine the time-lapse seismic method with time-lapse gravity measurements. This is done by a simple forward modeling of gravity changes based on the seismically derived saturation changes, letting these saturation changes be scaled by an arbitrary constant and then by minimizing the least-squares error to obtain the best fit between the scaled saturation changes and the measured time-lapse gravity data. In this way, we are able to exploit the complementary properties of time-lapse seismic and gravity data.

scholarly journals Numerical models for ground deformation and gravity changes during volcanic unrest: simulating the hydrothermal system dynamics of a restless caldera

Solid Earth ◽  
2016 ◽  
Vol 7 (2) ◽  
pp. 557-577 ◽  
Author(s):  
A. Coco ◽  
J. Gottsmann ◽  
F. Whitaker ◽  
A. Rust ◽  
G. Currenti ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Pore Pressure ◽  
Hydrothermal System ◽  
Ground Deformation ◽  
Numerical Models ◽  
Gravity Data ◽  
Ground Surface ◽  
Campi Flegrei ◽  
Hazard Evaluation ◽  
Gravity Changes

Abstract. Ground deformation and gravity changes in restless calderas during periods of unrest can signal an impending eruption and thus must be correctly interpreted for hazard evaluation. It is critical to differentiate variation of geophysical observables related to volume and pressure changes induced by magma migration from shallow hydrothermal activity associated with hot fluids of magmatic origin rising from depth. In this paper we present a numerical model to evaluate the thermo-poroelastic response of the hydrothermal system in a caldera setting by simulating pore pressure and thermal expansion associated with deep injection of hot fluids (water and carbon dioxide). Hydrothermal fluid circulation is simulated using TOUGH2, a multicomponent multiphase simulator of fluid flows in porous media. Changes in pore pressure and temperature are then evaluated and fed into a thermo-poroelastic model (one-way coupling), which is based on a finite-difference numerical method designed for axi-symmetric problems in unbounded domains.Informed by constraints available for the Campi Flegrei caldera (Italy), a series of simulations assess the influence of fluid injection rates and mechanical properties on the hydrothermal system, uplift and gravity. Heterogeneities in hydrological and mechanical properties associated with the presence of ring faults are a key determinant of the fluid flow pattern and consequently the geophysical observables. Peaks (in absolute value) of uplift and gravity change profiles computed at the ground surface are located close to injection points (namely at the centre of the model and fault areas). Temporal evolution of the ground deformation indicates that the contribution of thermal effects to the total uplift is almost negligible with respect to the pore pressure contribution during the first years of the unrest, but increases in time and becomes dominant after a long period of the simulation. After a transient increase over the first years of unrest, gravity changes become negative and decrease monotonically towards a steady-state value.Since the physics of the investigated hydrothermal system is similar to any fluid-filled reservoir, such as oil fields or CO2 reservoirs produced by sequestration, the generic formulation of the model will allow it to be employed in monitoring and interpretation of deformation and gravity data associated with other geophysical hazards that pose a risk to human activity.

Co-seismic gravity changes in the Koyna-Warna region: Implications of mass redistribution

2017 ◽  
Vol 90 (6) ◽  
pp. 704-710 ◽  
Author(s):  
K. N. D. Prasad ◽  
N. Srinivas ◽  
A. E. Meshram ◽  
A. P. Singh ◽  
V. M. Tiwari
Keyword(s):  
Gravity Changes ◽  
Mass Redistribution

History Matching Time-Lapse Surface-Gravity and Well-Pressure Data With Ensemble Smoother for Estimating Gas Field Aquifer Support—A 3D Numerical Study

SPE Journal ◽  
2012 ◽  
Vol 17 (04) ◽  
pp. 966-980 ◽  
Author(s):  
M.. Glegola ◽  
P.. Ditmar ◽  
R.G.. G. Hanea ◽  
O.. Eiken ◽  
F.C.. C. Vossepoel ◽  
...  
Keyword(s):  
History Matching ◽  
Numerical Study ◽  
Gravity Data ◽  
Time Lapse ◽  
Added Value ◽  
Pressure Data ◽  
Production Forecast ◽  
Gas Field ◽  
Ensemble Smoother ◽  
Reservoir State

Summary Water influx is an important factor influencing production of gas reservoirs with an active aquifer. However, aquifer properties such as size, porosity, and permeability are typically uncertain and make predictions of field performance challenging. The observed pressure decline is inherently nonunique with respect to water influx, and large uncertainties in the actual reservoir state are common. Time-lapse (4D) gravimetry, which is a direct measure of a subsurface mass redistribution, has the potential to provide valuable information in this context. Recent improvements in instrumentation and data-acquisition and -processing procedures have made time-lapse gravimetry a mature monitoring technique, both for land and offshore applications. However, despite an increasing number of gas fields in which gravimetric monitoring has been applied, little has been published on the added value of gravity data in a broader context of modern reservoir management on the basis of the closed-loop concept. The way in which gravity data can contribute to improved reservoir characterization, production-forecast accuracy, and hydrocarbon-reserves estimation is still to be addressed in many respects. In this paper, we investigate the added value of gravimetric observations for gas-field-production monitoring and aquifer-support estimation. We perform a numerical study with a realistic 3D gas field model that contains a large and complex aquifer system. The aquifer support and other reservoir parameters (i.e., porosity, permeability, reservoir top and bottom horizons) are estimated simultaneously using the ensemble smoother (ES). We consider three cases in which gravity only is assimilated, pressure only is assimilated, and gravity and pressure data are assimilated jointly. We show that a combined estimation of the aquifer support with the permeability field, porosity field, and reservoir structure is a very challenging and nonunique history-matching problem, in which gravity certainly has an added value. Pressure data alone may not discriminate between different reservoir scenarios. Combining pressure and gravity data may help to reduce the nonuniqueness problem and provide not only an improved gas- and water-production forecast and gas-in-place evaluation, but also a more-accurate reservoir-state description.

Analytical modelling and joint inversion of surface displacements and gravity changes at volcanoes

2021 ◽  
Author(s):  
Mehdi Nikkhoo ◽  
Eleonora Rivalta
Keyword(s):  
Source Parameters ◽  
Surface Displacement ◽  
Point Sources ◽  
Gravity Change ◽  
Density Estimate ◽  
Mass Change ◽  
Long Valley Caldera ◽  
Gravity Changes ◽  
Surface Displacements ◽  
Volcanic Reservoirs

<p>Gravity change observations at volcanoes provide information on the location and mass change of intruded magma bodies. Gravity change and surface displacement observations are often combined in order to infer the density of the intruded materials. Previous studies have highlighted that it is crucial to account for magma compressibility and the shape of the gravity change and deformation source to avoid large biases in the density estimate. Currently, an analytical model for the deformation field and gravity change due to a source of arbitrary shape is lacking, affecting our ability to perform rapid inversions and assess the nature of volcanic unrest.  </p><p>Here, we propose an efficient approach for rapid joint-inversions of surface displacement and gravity change observations associated with underground pressurized reservoirs. We derive analytical solutions for deformations and gravity changes due to the volume changes of triaxial point-sources in an isotropic elastic half-space. The method can be applied to  volcanic reservoirs that are deep compared to their size (far field approximation). We show that the gravity changes not only allow inferring mass changes within the reservoirs, but also help better constrain location, shape and the volume change of the source. We discuss how the inherent uncertainties in the realistic shape of volcanic reservoirs are reflected in large uncertainties on the density estimates. We apply our approach to the surface displacements and gravity changes at Long Valley caldera over the 1985-1999 time period. We show that gravity changes together with only vertical displacements are sufficient to constrain the mass change and all the other source parameters. We also show that while mass change is well constrained by gravity change observations the density estimate is more uncertain even if the magma compressibility is accounted for in the model.</p>

scholarly journals Dependency of hydration and growth conditions on the mechanical properties of oral biofilms

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
J. Pattem ◽  
M. Davrandi ◽  
S. Aguayo ◽  
B. Slak ◽  
R. Maev ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Bacterial Diversity ◽  
Time Lapse ◽  
Growth Conditions ◽  
New Combination ◽  
Growth Media ◽  
Phenotypic Properties ◽  
Growth Environment ◽  
Oral Biofilms ◽  
The Impact

AbstractWithin the oral cavity, dental biofilms experience dynamic environments, in part due to changes in dietary content, frequency of intake and health conditions. This can impact bacterial diversity and morpho-mechanical properties. While phenotypic properties of oral biofilms are closely related to their composition, these can readily change according to dynamic variations in the growth environment and nutrient availability. Understanding the interlink between phenotypic properties, variable growth conditions, and community characterization is an essential requirement to develop structure–property relationships in oral-biofilms. In this study, the impact of two distinct growth media types with increasing richness on the properties of oral biofilms was assessed through a new combination of in-vitro time-lapse biophysical methods with microbiological assays. Oral biofilms grown in the enriched media composition presented a decrease in their pH, an increase in soluble EPS production, and a severe reduction in bacterial diversity. Additionally, enriched media conditions presented an increase in biofilm volumetric changes (upon hydration) as well as a reduction in elastic modulus upon indentation. With hydration time considered a major factor contributing to changes in biofilm mechanical properties, we have shown that it is less associated than media richness. Future investigations can now use this time-lapse approach, with a clearer focus on the extracellular matrix of oral biofilms dictating their morpho-mechanical properties.

A geophysical investigation of the active Hockley Fault System near Houston, Texas

Geophysics ◽  
2013 ◽  
Vol 78 (4) ◽  
pp. B177-B185 ◽  
Author(s):  
Shuhab D. Khan ◽  
Robert R. Stewart ◽  
Maisam Otoum ◽  
Li Chang
Keyword(s):  
Ground Penetrating Radar ◽  
Fault Location ◽  
Gravity Data ◽  
Time Lapse ◽  
Radar Data ◽  
Airborne Lidar ◽  
Fault System ◽  
Geophysical Investigation ◽  
Geophysical Surveys ◽  
Ground Penetrating

Sedimentation and deformation toward the Gulf of Mexico Basin cause faulting in the coastal regions. In particular, many active (but non-seismic) faults underlie the Houston metropolitan area. Using geophysical data, we have examined the Hockley Fault System in northwest Harris County. Airborne LiDAR is an effective tool to identify fault scarps and we have used it to identify several new faults and assemble an updated map for the faults in Houston and surrounding areas. Two different LiDAR data sets (from 2001 to 2008) provide time-lapse images and suggest elevation changes across the Hockley Fault System at the rate of 10.9 mm/yr. This rate is further supported by GPS data from a station located on the downthrown side of the Hockley Fault System indicating movement at 13.8 mm/yr. To help illuminate the subsurface character of the faults, we undertook geophysical surveys (ground-penetrating radar, seismic reflection, and gravity) across two strands of the Hockley Fault System. Ground-penetrating radar data show discontinuous events to a depth of 10 m at the main fault location. Seismic data, from a vibroseis survey along a 1-km line perpendicular to the fault strike, indicate faulting to at least 300-m depth. The faults have a dip of about 70°. Gravity data show distinct changes across the fault. However, there are two contrasting Bouguer anomalies depending on the location of the transects and their underlying geology. Our geophysical surveys were challenged by urban features (especially traffic and access). However, the survey results consistently locate the fault and hold significant potential to understand its deformational features as well as assist in associated building zoning.

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