The case for dynamic subsidence of the U.S. east coast since the Eocene

The dynamic subsidence of the United States east coast is addressed using the discrepancy between regional and global estimates of sea level, elevation of paleoshorelines, and adjoint models of mantle convection that assimilate plate motions and seismic tomography. The positions of Eocene and Miocene paleoshorelines are lower than predicted by global sea levels, suggesting at least 50 m, and possibly as much as 200 m of subsidence since the end of the Eocene. Dynamic models predict subsidence of the east coast since the end of Eocene, although the exact magnitude is uncertain. This subsidence has been occurring during an overall global sea-level fall, with the eustatic change being larger than the dynamic subsidence; this results in a regional sea-level fall in the absence of land subsidence. Dynamic subsidence is consistent with the difference between eustasy and regional sea level at the New Jersey coastal plain

The model of surface subsidence process at subsidence through formation

The character of surface subsidence is different and has its peculiarities at different stages of mining operations. The process of surface subsidence is especially different in the initial period of mining lava comparing with other stages of mining development. The simple graphical model of subsidence is created. This model allows determining the value of subsidence at any point of the earth's surface at any given time. The model is implemented on the basis of contour lines. To construct the trough model the data of instrumental measurements on core lines are used. This “chrono-isoline” model of subsidence trough allows predicting the trough profile and subsidence of individual points on the surface. There is no need to perform complex mathematical calculations. The solution of the problem requires a minimum of input data: the depth of the excavation of a long pillar and its size of a specific date

Short-Term Radiographic Evaluation of a Tri-Tapered Femoral Stem in Direct Anterior Total Hip Arthroplasty

Introduction. Direct anterior approach (DAA) total hip arthroplasty (THA) has become increasingly popular, largely due to utilization of a true internervous and intermuscular plane. However, recent literature has demonstrated an increased rate of femoral implant subsidence with this approach. Hence, different femoral implants, such as the tri-tapered femoral stem, have been developed to facilitate proper component insertion and positioning to prevent this femoral subsidence. The purpose of this study was to evaluate the subsidence rate of a tri-tapered femoral stem implanted utilizing a DAA, and to determine if the proximal femoral bone quality affects the rate of subsidence. Methods. A retrospective analysis of 155 consecutive primary THAs performed by a single surgeon was conducted. Age, gender, primary diagnosis, and radiographic measurements of each subject were recorded. Radiological evaluations, such as bone quality, femoral canal fill, and implant subsidence, were measured on standardized anteroposterior (AP) and frog-leg lateral radiographs of the hip at 6-week and 6-month postoperative follow-up evaluations. Results. The average subsidence of femoral stems was 1.18 ± 0.8 mm. There was no statistical difference in the amount of subsidence based on diagnosis or proximal femora quality. The tri-tapered stem design consistently filled the proximal canal with an average of 91.9 ± 4.9% fill. Subsidence was not significantly associated with age, canal flare index (CFI), or experience of the surgeon. Conclusion. THA utilizing the DAA with a tri-tapered femoral stem can achieve consistent and reliable fit regardless of proximal femoral bone quality

Prediction of subsidence due to underground mining by artificial neural networks

Alternatively to empirical prediction methods, methods based on influential functions and on mechanical model, artificial neural networks (ANNs) can be used for the surface subsidence prediction. In our case, the multi-layer feed-forward neural network was used. The training and testing of neural network is based on the available data. Input variables represent extraction parameters and coordinates of the points of interest, while the output variable represents surface subsidence data. After the neural network has been successfully trained, its performance is tested on a separate testing set. Finally, the surface subsidence trough above the projected excavation is predicted by the trained neural network. The applicability of ANN for the prediction of surface subsidence was verified in different subsidence models and proved on actual excavated levels and in levelled data on surface profile points in the Velenje Coal Mine. (C) 2003 Elsevier Science Ltd. All rights reserved

Interseismic deformation above the Sunda Megathrust recorded in coral microatolls of the Mentawai islands, West Sumatra

The geomorphology and internal stratigraphy of modern coral microatolls show that all the outer arc Mentawai islands of West Sumatra have been subsiding over the past several decades. These same islands rose as much as 3 m during the giant megathrust earthquakes of 1797 and 1833, and the current subsidence probably reflects strain accumulation that will lead to future large earthquakes. Average subsidence rates over the past half century vary from 2 to 14 mm yr^(−1) and increase southwestward, toward the subduction trench. The pattern is consistent with rates of subsidence measured by a sparse network of continuously recording Global Positioning System (cGPS) stations and with locking of a 400-km-long section of the underlying subduction megathrust, between about 1°S and 4°S. This record of subsidence and tilting, extending nearly a century into the past, implies that the region is advancing toward the occurrence of another giant earthquake. However, evidence of episodic rather than steady subsidence reflects a behavior that is more complex than simple elastic strain accumulation and relief. Most prominent of these episodes is an extensive emergence/subsidence couplet in about 1962, which may be the result of rapid, aseismic slip on the megathrust, between the islands and the trench. Lower subsidence rates recorded by the corals since about 1985 may reflect failure on many small patches within the locked section of the megathrust

Formation of offshore tidal sandbanks triggered by a gasmined bed subsidence

Offshore gasmining is an example of a human intervention with a morphological impact. On land, it is usually attended with a dish-like bed depression. We show that, if located at sea, such a bed depression can become morphodynamically active by triggering mechanisms related to tidal sand bank formation. To that end, a simple morphological model is considered which describes an erodible bed subject to a tidal wave in a shallow sea. The continuous subsidence is modelled by a sink term in the sediment balance. Then, a linear approximation is carried out to describe the bed evolution after the onset of subsidence. The results, presented in physical space, show that the subsidence triggers the formation of a sand bank pattern that gradually spreads around the centre of subsidence, at a rate that may go up to 160 m year¿1, depending on the tidal transport rate and the tidal eccentricity. The dimension of the depression does not affect the spreading rate nor the orientation of the sand banks, but it does influence their spacing. The main conclusion is that the horizontal extent of the area influenced by the bed depression by far exceeds that of the direct subsidence, thus showing that bed depressions on land and at sea indeed behave in fundamentally different ways. The results suggest that nonlinear effects are worthwhile to be investigated in order to describe finite amplitude development of sand banks as well as the interaction between subsidence and bed forms

Minimizing the residual topography effect on interferograms to improve DInSAR results: estimating land subsidence in Port-Said City, Egypt

The accurate detection of land subsidence rates in urban areas is important to identify damage-prone areas and provide decision-makers with useful information. Meanwhile, no precise measurements of land subsidence have been undertaken within the coastal Port-Said City in Egypt to evaluate its hazard in relationship to sea-level rise. In order to address this shortcoming, this work introduces and evaluates a methodology that substantially improves small subsidence rate estimations in an urban setting. Eight ALOS/PALSAR-1 scenes were used to estimate the land subsidence rates in Port-Said City, using the Small BAse line Subset (SBAS) DInSAR technique. A stereo pair of ALOS/PRISM was used to generate an accurate DEM to minimize the residual topography effect on the generated interferograms. A total of 347 well distributed ground control points (GCP) were collected in Port-Said City using the leveling instrument to calibrate the generated DEM. Moreover, the eight PALSAR scenes were co-registered using 50 well-distributed GCPs and used to generate 22 interferogram pairs. These PALSAR interferograms were subsequently filtered and used together with the coherence data to calculate the phase unwrapping. The phase-unwrapped interferogram-pairs were then evaluated to discard four interferograms that were affected by phase jumps and phase ramps. Results confirmed that using an accurate DEM (ALOS/PRISM) was essential for accurately detecting small deformations. The vertical displacement rate during the investigated period (2007–2010) was estimated to be −28 mm. The results further indicate that the northern area of Port-Said City has been subjected to higher land subsidence rates compared to the southern area. Such land subsidence rates might induce significant environmental changes with respect to sea-level rise

Flooding and subsidence in the Thames Gateway : impact on insurance loss potential

In the UK, household buildings insurance generally covers loss and damage to the insured property from a range of natural and human perils, including windstorm, flood, subsidence, theft, accidental fire and winter freeze. Consequently, insurers require a reasoned view on the likely scale of losses that they may face to assist in strategic planning, reinsurance structuring, regulatory returns and general risk management. The UK summer 2007 flood events not only provided a clear indication of the scale of potential losses that the industry could face from an individual event, with £3 billion in claims, but also identified a need for insurers and reinsurers to better understand how events may correlate in time and space, and how to most effectively use the computational models of extreme events that are commonly applied to reflect these correlations. In addition to the potential for temporal clustering of events such as windstorms and floods, there is a possibility that seemingly uncorrelated natural perils, such as floods and subsidence, may impact an insurer’s portfolio. Where aggregations of large numbers of new properties are planned, such as in the Thames Gateway, consideration of the potential future risk of aggregate losses due to the combination of perils such as subsidence and flood is increasingly important within the insurance company’s strategic risk management process. Whilst perils such as subsidence and flooding are generally considered independent within risk modelling, the potential for one event to influence the magnitude and likelihood of the other should be taken into account when determining risk level. In addition, the impact of correlated, but distinctive, loss causing events on particular property types may be significant, particularly if a specific property is designed to protect against one peril but is potentially susceptible to another. We suggest that flood events can lead to increased subsidence risk due to the weight of additional water and sediment, or rehydration of sediment under flood water. The latter mechanism may be particularly critical on sites where Holocene sediments are currently protected from flooding and are no longer subsiding. Holocene deposits tend to compress, either under their own weight or under a superimposed load such as made ground, built structures or flood water. If protected dry sediments become flooded in the future, subsidence would be expected to resume. This research project aims to investigate the correlation between flood hazards and subsidence hazards and the effect that these two sources of risk will have on insurance losses in the Thames Gateway. In particular, the research will explore the potential hydrological and geophysical drivers and links between flood and subsidence events within the Thames Gateway, assessing the potential for significant event occurrence within the timescales relevant to insurers. In the first part of the project we have identified flood risk areas within the Thames Gateway development zone which have a high risk of flooding and may be affected by renewed or increased subsidence. This has been achieved through the use of national and local-scale 2D and 3D geo-environmental information such as the Geosure dataset (e.g. swell-shrink, collapsible and compressible deposits data layers), PSI data, thickness of superficial and artificial land deposits, and flood potential data etc. In the second stage of the project we will investigate the hydrological and geophysical links between flooding and subsidence events on developed sites; quantify the insurance loss potential in the Thames Gateway from correlated flooding and subsidence events; consider how climate change will affect risk to developments in the Thames Gateway in the context of subsidence and flooding; and develop new ways of communicating and visualise correlated flood and subsidence risk to a range of stakeholders, including the insurance industry, planners, policy makers and the general public

Prospective five-year subsidence analysis of a cementless fully hydroxyapatite-coated femoral hip arthroplasty component

Early subsidence >1.5 mm is considered to be a predictive factor for later aseptic loosening of the femoral component following total hip arthroplasty (THA). The aim of this study was to assess five-year subsidence rates of the cementless hydroxyapatite-coated twinSys (R) stem (Mathys Ltd., Bettlach, Switzerland). This prospective single-surgeon series examined consecutive patients receiving a twinSys (R) stem at Maria Middelares Hospital, Belgium. Patients aged >85 years or unable to come to follow-up were excluded. Subsidence was assessed using Ein Bild Roentgen Analyse - Femoral Component Analysis (EBRA-FCA). Additional clinical and radiographic assessments were performed. Follow-ups were prospectively scheduled at two, five, 12, 24, and 60 months. In total, 218 THA (211 patients) were included. At five years, mean subsidence was 0.66 mm (95% CI: 0.43-0.90). Of the 211 patients, 95.2% had an excellent or good Harris Hip Score. There were few radiological changes. Kaplan-Meier analysis indicated five-year stem survival to be 98.4% (95% CI: 97.6-100%). Subsidence levels of the twinSys (R) femoral stem throughout the five years of follow-up were substantially lower than the 1.5 mm level predictive of aseptic loosening. This was reflected in the high five-year survival rate

Long term time-lapse microgravity and geotechnical monitoring of relict salt-mines, Marston, Cheshire, UK.

The area around the town of Northwich in Cheshire, U. K., has a long history of catastrophic ground subsidence caused by a combination of natural dissolution and collapsing abandoned mine workings within the underlying Triassic halite bedrock geology. In the village of Marston, the Trent and Mersey Canal crosses several abandoned salt mine workings and previously subsiding areas, the canal being breached by a catastrophic subsidence event in 1953. This canal section is the focus of a long-term monitoring study by conventional geotechnical topographic and microgravity surveys. Results of 20 years of topographic time-lapse surveys indicate specific areas of local subsidence that could not be predicted by available site and mine abandonment plan and shaft data. Subsidence has subsequently necessitated four phases of temporary canal bank remediation. Ten years of microgravity time-lapse data have recorded major deepening negative anomalies in specific sections that correlate with topographic data. Gravity 2D modeling using available site data found upwardly propagating voids, and associated collapse material produced a good match with observed microgravity data. Intrusive investigations have confirmed a void at the major anomaly. The advantages of undertaking such long-term studies for near-surface geophysicists, geotechnical engineers, and researchers working in other application areas are discussed