scholarly journals Geophysical Characterization of a Sinkhole Region: A Study toward Understanding Geohazards in the Karst Geosites

2021 ◽  
Vol 50 (7) ◽  
pp. 1871-1884
Author(s):  
Sawasdee Yordkayhun
Keyword(s):  
Seismic Tomography ◽  
Surface Defects ◽  
Geophysical Methods ◽  
Soil Layer ◽  
Cohesive Soil ◽  
Near Surface ◽  
Shallow Subsurface ◽  
Limestone Bedrock ◽  
Cavity Development ◽  
Fractured Limestone

The outstanding geosites in Satun UNESCO Global Geopark, Thailand are mainly karst topography. Sinkhole which is originated from the dissolution of karst rocks by groundwater or acidic rainwater is one of the potential natural disasters in these geosites. To gain the confident among geotourism, detecting karst features, cavities and surficial dissolution is crucial in risk assessment and sustainable geopark management. As a part of geohazard assessment, non-invasive geophysical methods were applied for detecting near-surface defects and karst features. In this study, electrical resistivity tomography (ERT), seismic tomography and multichannel analysis of surface waves (MASW) have been integrated to understand the mechanism of an existing sinkhole formation in Satun Geopark region. ERT appeared to be an effective approach to investigate the cavity development at shallow subsurface. MASW and seismic tomography were combined to help constrain the interpretation of lithology and karst features in vicinity of the sinkhole. The results indicated that the sinkhole occurrence in this area was probably developed by forming of cavity due to an increased dissolution of the fractured limestone bedrock. This carbonate layer is in contact with the overlying groundwater and weathering shale or cohesive soil layer. The changing of water table and infiltration of surface water by heavy rainfall allowed for a sudden vertical downward of overlying sediments into the empty voids, leading to the sinkhole hazard.

Phosphorus dynamics in shallow subsurface waters in an uncut and cut subcatchment of a lake on the Boreal Plain

2000 ◽  
Vol 57 (S2) ◽  
pp. 60-72 ◽  
Author(s):  
J E Evans ◽  
E E Prepas ◽  
K J Devito ◽  
B G Kotak
Keyword(s):  
Water Samples ◽  
Soil Layer ◽  
Organic Layer ◽  
Mineral Layer ◽  
Near Surface ◽  
Organic C ◽  
Shallow Subsurface ◽  
Phosphorus Dynamics ◽  
Subsurface Waters ◽  
Composite Samples

Phosphorus dynamics in shallow subsurface waters (<2.5 m depth) were studied in harvested and unharvested subcatchments of a Boreal Plain lake. The organic soil layer was underlain by discontinuous layers of sand and clay glacial till. Total dissolved P (TDP) concentrations (6-798 µg·L-1) of discrete water samples from mineral layers (0.9-2.5 m deep) generally decreased with depth, were negatively related to Ca (rs < -0.7), and were lower in clay. When the groundwater table rose and saturated the organic layer, TDP concentrations increased in the composite (organic mineral layer) but not in the discrete (mineral layer) water samples, indicating that elevated TDP concentrations originate from the near-surface organic layer. TDP concentrations in composite samples were negatively correlated with water table depth (rs = -0.6) and were positively correlated with transmissivity (rs = 0.7) and dissolved organic C concentration (rs > 0.6). In the riparian buffer zone of the harvested subcatchment, TDP concentrations of composite samples decreased during high runoff, but these values remained higher than concentrations in the unharvested subcatchment. However, surface topography and variable depth to confining clay layers resulted in higher groundwater tables in the harvested subcatchment, especially in the cut area. Mean daily TDP export coefficients were similar between the unharvested (14 µg·m-2) and harvested (12 µg·m-2) subcatchments.

Electron Channelling Contrast Imaging of Dislocations

1990 ◽  
Vol 48 (1) ◽  
pp. 600-601
Author(s):  
J.T. Czernuszka ◽  
N.J. Long ◽  
P.B. Hirsch
Keyword(s):  
Field Emission ◽  
Secondary Electron ◽  
Surface Defects ◽  
Spot Size ◽  
Beam Divergence ◽  
Contrast Imaging ◽  
Scattered Electron ◽  
Near Surface ◽  
Filter System ◽  
Electron Channelling

In the 1970s there was considerable interest in the development of the electron channelling contrast imaging (ECCI) technique for imaging near surface defects in bulk (electron opaque) specimens. The predictions of the theories were realised experimentally by Morin et al., who used a field emission gun (FEG) operating at 40-50kV and an energy filter such that only electrons which had lost no more than a few 100V were detected. This paper presents the results of a set of preliminary experiments which show that an energy filter system is unneccessary to image and characterise the Burgers vectors of dislocations in bulk specimens. The examples in the paper indicatethe general versatility of the technique.A VG HB501 STEM with a FEG was operated at 100kV. A single tilt cartridge was used in the reflection position of the microscope. A retractable back-scattered electron detector was fitted into the secondary electron port and positioned to within a few millimetres of the specimen. The image was acquired using a Synoptics Synergy framestore and digital scan generator and subsequently processed using Semper 6. The beam divergence with the specimen in this position was 2.5 mrads with a spot size of approximately 4nm. Electron channelling patterns were used to orientate the sample.

Direct Plan View FIB Liftout for Near-Surface Defect Analysis in TEM

2013 ◽  
Author(s):  
Max L. Lifson ◽  
Carla M. Chapman ◽  
D. Philip Pokrinchak ◽  
Phyllis J. Campbell ◽  
Greg S. Chrisman ◽  
...  
Keyword(s):  
Failure Analysis ◽  
Silicon Germanium ◽  
Focused Ion Beam ◽  
Surface Defects ◽  
Ion Beam ◽  
Misfit Dislocations ◽  
Tem Analysis ◽  
Plan View ◽  
Near Surface ◽  
Straightforward Method

Abstract Plan view TEM imaging is a powerful technique for failure analysis and semiconductor process characterization. Sample preparation for near-surface defects requires additional care, as the surface of the sample needs to be protected to avoid unintentionally induced damage. This paper demonstrates a straightforward method to create plan view samples in a dual beam focused ion beam (FIB) for TEM studies of near-surface defects, such as misfit dislocations in heteroepitaxial growths. Results show that misfit dislocations are easily imaged in bright-field TEM and STEM for silicon-germanium epitaxial growth. Since FIB tools are ubiquitous in semiconductor failure analysis labs today, the plan view method presented provides a quick to implement, fast, consistent, and straightforward method of generating samples for TEM analysis. While this technique has been optimized for near-surface defects, it can be used with any application requiring plan view TEM analysis.

scholarly journals Integrated magnetotelluric and seismic investigation of Cenozoic graben structure near Obrzycko, Poland

2021 ◽  
Author(s):  
Adam Cygal ◽  
Michał Stefaniuk ◽  
Anna Kret
Keyword(s):  
Seismic Data ◽  
Geophysical Methods ◽  
Geological Structure ◽  
Data Sets ◽  
Low Velocity ◽  
Shallow Subsurface ◽  
Geophysical Model ◽  
Novel Approach ◽  
Loose Deposits ◽  
Static Corrections

AbstractThis article presents the results of an integrated interpretation of measurements made using Audio-Magnetotellurics and Seismic Reflection geophysical methods. The obtained results were used to build an integrated geophysical model of shallow subsurface cover consisting of Cenozoic deposits, which then formed the basis for a detailed lithological and tectonic interpretation of deeper Mesozoic sediments. Such shallow covers, consisting mainly of glacial Pleistocene deposits, are typical for central and northern Poland. This investigation concentrated on delineating the accurate geometry of Obrzycko Cenozoic graben structure filled with loose deposits, as it was of great importance to the acquisition, processing and interpretation of seismic data that was to reveal the tectonic structure of the Cretaceous and Jurassic sediments which underly the study area. Previously, some problems with estimation of seismic static corrections over similar grabens filled with more recent, low-velocity deposits were encountered. Therefore, a novel approach to estimating the exact thickness of such shallow cover consisting of low-velocity deposits was applied in the presented investigation. The study shows that some alternative geophysical data sets (such as magnetotellurics) can be used to significantly improve the imaging of geological structure in areas where seismic data are very distorted or too noisy to be used alone

scholarly journals Microanchored borehole fiber optics allows strain profiling of the shallow subsurface

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Cheng-Cheng Zhang ◽  
Bin Shi ◽  
Song Zhang ◽  
Kai Gu ◽  
Su-Ping Liu ◽  
...  
Keyword(s):  
Fiber Optics ◽  
Field Experiments ◽  
Fiber Optic ◽  
Strain Sensing ◽  
Near Surface ◽  
Shallow Subsurface ◽  
Buried Cables ◽  
Capacity Theory ◽  
Confining Pressures ◽  
Strain Determination

AbstractVertical deformation profiles of subterranean geological formations are conventionally measured by borehole extensometry. Distributed strain sensing (DSS) paired with fiber-optic cables installed in the ground opens up possibilities for acquiring high-resolution static and quasistatic strain profiles of deforming strata, but it is currently limited by reduced data quality due to complicated patterns of interaction between the buried cables and their surroundings, especially in upper soil layers under low confining pressures. Extending recent DSS studies, we present an improved approach using microanchored fiber-optic cables—designed to optimize ground-to-cable coupling at the near surface—for strain determination along entire lengths of vertical boreholes. We proposed a novel criterion for soil–cable coupling evaluation based on the geotechnical bearing capacity theory. We applied this enhanced methodology to monitor groundwater-related vertical motions in both laboratory and field experiments. Corroborating extensometer recordings, acquired simultaneously, validated fiber optically determined displacements, suggesting microanchored DSS as an improved means for detecting and monitoring shallow subsurface strain profiles.

Reemitted positron spectroscopy of near-surface defects

1990 ◽  
Vol 42 (4) ◽  
pp. 1910-1916 ◽  
Author(s):  
T. McMullen ◽  
M. J. Stott
Keyword(s):  
Surface Defects ◽  
Near Surface ◽  
Positron Spectroscopy

Seismic tomography for near surface: Uncertainty analysis

2008 ◽  
Author(s):  
Carlos Becerra ◽  
William Agudelo ◽  
Saul Guevara
Keyword(s):  
Uncertainty Analysis ◽  
Seismic Tomography ◽  
Near Surface

scholarly journals Geophysical identification of voids and loosened zones in the shallow subsurface of post-mining areas

2018 ◽  
Vol 66 ◽  
pp. 01001 ◽  
Author(s):  
Zenon Pilecki
Keyword(s):  
Rock Mass ◽  
Geophysical Methods ◽  
Ore Deposits ◽  
Hard Coal ◽  
Shallow Subsurface ◽  
Mining Areas ◽  
Upper Silesian Coal Basin ◽  
Discontinuous Deformation ◽  
Ground Penetrating ◽  
Terrain Surface

The shallow historic exploitation of Zn-Pb/Fe ore deposits as well as hard coal has generated many discontinuous deformations on the terrain surface in the Upper Silesian Coal Basin/Poland. Discontinuous deformations occur in different forms as sinkholes, synclines, cracks, faults or ditches. The basic cause of their occurrence is the presence of void and loosened zones in the shallow subsurface. If the appropriate conditions arise, the sinkhole process begins to move upwards and may cause a discontinuous deformation on the terrain surface. Typically, geophysical methods are used for void and loosened zone identification. The most effective methods are gravimetric, seismic, electric resistivity and ground penetrating radar (GPR). Geophysical testing, requires distinct changes in the physical properties in the rock mass. The identified geophysical anomalies should be verified by control borehole and borehole tests to confirm the presence of the void and loosened zones in the rock mass. The results of control drilling and borehole tests determine the need to apply treatment works. In order to assess the threat of the occurrence of discontinuous deformations in the areas of historical shallow mining in Upper Silesia, a classification system based on geophysical tests has also been developed.

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