Surge Zone Research Articles

Research on the Optimal Spacing of Multiple Roof Smoke Blocking Structures in a Long Corridor

In a long and narrow corridor, the installation of roof smoke blocking structures is a measure to slow down the spread of fire smoke. When employing multiple smoke blocking structures, the spacing between these structures is a critical parameter that needs to be considered for optimal effectiveness. This paper analyzes the smoke blocking performance of double structures at different spacing and measures the smoke flow velocity both upstream and downstream of the double structures. According to the analysis of the smoke velocity vector obtained from numerical simulation, the smoke can be divided into three zones based on the flow state of the smoke after passing through the front smoke screen structure, namely the vortex zone, surge wave zone, and steady flow zone. When the rear smoke screen is located in the surge zone, the smoke blocking effect is optimal. Analysis of the morphology of the smoke layer indicates that the length of the vortex region is directly proportional to the upstream smoke flow velocity. The numerical and experimental results both indicate that an excessively large or small spacing between the structures fails to achieve optimal smoke control effectiveness. When the spacing is within an optimal range, the smoke velocity is the lowest. Finally, using a real architectural corridor as a case background, this paper presents a design example of roof smoke blocking structures. In order to arrange as many smoke blocking structures as possible, an appropriate spacing between the structures should be slightly larger than the vortex region. The smoke control effectiveness of multiple roof structures was validated through numerical simulation. As a result, the time required for smoke to pass through the corridor increases by 110 s.

Modeling Gas Compressor Station Operation to Minimize Fuel Costs for Surge Zone Protection

Gas transportation through the pipeline network requires high pressure; otherwise, movement will be impossible. Due to friction with the walls of the pipes, the gas loses both speed and pressure. Therefore, it is necessary to increase the pressure in the main pipeline, which can extend for thousands of kilometers. For this purpose, compressor stations are located along the main network, facilitating the gas transport process by raising it to the required pressure. Compressor stations mainly consume the transported gas, with approximately 5% expended on gas compression. This article presents a study on the fuel cost for compressor stations, using mathematical models to optimize the operation of gas compressor units. The objective is to minimize gas consumption as a fuel and provide an optimization method with control over blower revolutions and valve installations to ensure safe transportation. Mathematical modeling of the described process detected the technically unjustified fuel gas consumption during the operation of gas compressor units at a specific compressor station under consideration. The paper proposes a method for minimizing costs, which can serve as the basis for providing recommendations to engineers-dispatchers. Compressor stations of the type under study lack measuring instruments for mass flow; therefore, the methods such as PID controllers, MPC, or neural networks are not applicable here.

Division and Effect Evaluation of Fracking Outburst Elimination Zones in Surface Extraction Wells of Coalbed Methane

Surface hydraulic fracturing is an important measure for increasing reservoir permeability, which has advantages such as engineering safety and a large impact range and can be implemented ahead of the mine’s underground engineering. However, its underground outburst reduction range and effect are rarely reported, and there is a lack of connection with underground fracturing wells. Taking coalbed methane wells in the Lu’an Mining Area as an example, underground observation, microseismic monitoring, and numerical simulation methods were used to study the fracturing range and outburst control effect of surface wells. The fracturing zone of coalbed methane wells is approximately elliptical in shape, with the main fractures extending along the direction of the maximum horizontal principal stress. It can be divided into five zones: sand laying zone (radius of 140~150 m), fracture propagation zone (radius of about 180 m), fracturing fluid permeability zone (width of about 1 m), gas surge zone (width of 2~3 m), and final desorption zone (width of about 2 m). The stress around the fracturing zone increases along the direction of maximum and minimum principal stresses, while the stress value within the zone decreases, with a range of approximately 5~20% of the original geostress. The outburst reduction index Δh2 in the fracturing zone significantly decreased after fracturing. The percent of Δh2 (< 150 Pa) increased from 38.3% to 100% after fracturing. A model for evaluating the effectiveness of surface fracturing and outburst prevention was proposed, and the model was used in Tunliu Mine. The results showed that the standard‐reaching rate of extraction was high, and the danger of outburst could be completely eliminated. The research results can provide a reference for the arrangement of the coalbed methane wells and can also provide effective guidance for outburst prevention and control work during mining and excavation on a more macro scale. It provides a new idea and method for making up for the shortcomings such as the small impact range and safety hazards of underground fracturing.

Turbocharger surge behavior for sudden valve closing downstream the compressor and effect of actuating variable nozzle turbine

Surge is an unstable phenomenon appearing when a valve closing reduces the compressor flow rate. This phenomenon is avoided for automotive turbochargers by defining a surge margin during powertrain system design. This surge margin established with measurements in steady state testing regime limits the maximal engine torque at low levels of output. An active control of the compressor could reduce the surge margin and facilitate a transient compressor operation for a short time in surge zone. In this paper, an experimental study of the transient operation of a turbocharger compressor entering the surge zone is performed. Control of the turbocharger speed is sought to avoid unsteady operation using the variable geometry turbine (VGT) nozzle actuator. From a given stable operating point, surge is induced by reducing the opening of a valve located downstream of the compressor air circuit. The effect of reducing the speed of rotation by controlling the VGT valve is investigated, as this should lead to more stable compressor operation. The rotation speed of the turbocharger is controlled to avoid an unstable operating point using servo-actuator of variable geometry turbine. From a stable operating point, the surge appearance is caused by closing a butterfly valve downstream the air circuit of the compressor. The effect on the compressor rotation speed when the opening of variable geometry turbocharger valve is modified is studied. Measurements have been conducted for different control profiles of the VGT valve placed downstream the compressor. This article presents the means used to carry out these tests as well as the results of the measurements of the instantaneous signals of pressure, temperature, flow rate and rotation speed, allowing the analysis of the surge phenomenon.

Characterization and impact assessment of super cyclonic storm AMPHAN in the Indian subcontinent through space borne observations

Tropical cyclones can cause extensive damage in coastal regions as a result of high winds, storm tide, and intense rainfall. The West Bengal state in India was severely affected by a recent cyclonic storm 'Amphan' a 'super cyclone'with a high wind speed of above 220 km/h. The present study aimed to assess the impact of the cyclone Amphan in the potential impact zone covering the two states of India (Odisha and West Bengal) and the west coast of Bangladesh. The present study analyzed the land use land cover, rainfall variability, and potential storm surge along the cyclone track to assess the possible impact on the coastal landscape as well as community. The cyclone Amphan was formed in the Northern Indian Ocean near Equatorial Easterly wave over south Andaman Sea and adjoiningsoutheast Bay of Bengal (BoB) at 10° N 87° E on 16 May 2020 as deep depression and moved toward the north direction and had land fall at the coast of West Bengal on 20 May 2020 as an extremely severe cyclonic storm with the wind speed 155 km/h and central pressure of 960hpa.The cyclone devastated the coastal districts of West Bengal due to the high intensity of precipitation along with the extreme storm surge. About 100 people lost their lives and ~20 million people severely affected in West Bengal alone. Within the West Bengal state, around 7877 sq km area was observed under the potential storm surge zone. Cropland was observed as the most surge affected land cover with 5191 sq km area (65.9%), followed by wetlands (1635.2 sq km (20.75%) along with 38.34 sq km (0.48%)) of built up land under the potential surge impact zone The cyclone more severely affected the west Medinapur and South 24 Parganas, which were also the most affected by COVID-19 which resulted in slow evacuation, delay in medical support and concomitant increase in loss of life. The present study provided near real time cyclone hazard and risk assessment to help in prioritization of coastal mitigation and planning.

Impacts of climate change on the tourism sector of a Small Island Developing State: A case study for the Bahamas

This study examines the direct and indirect impacts of climate change to the tourism sector on the islands of New Providence and adjacent Paradise Island in the Bahamas. The assessment was carried out by conducting a geospatial analysis of tourism establishments at risk using Geographic Information Systems (GIS). We combined the geospatial analysis with publicly available databases to assess the integrated climate-related impacts pertaining to a Small Island Developing State (SIDS) economy. Our study estimated that many tourism properties currently lie in a storm surge zone and the extent of properties at risk increases with a future scenario of a 1 m rise in sea level. While sea level rise (SLR) by itself only threatens a small number of properties, when combined with weak (Category 1), moderate (Category 3) and strong (Category 5) storms the resulting coastal flooding impacts 34%, 69%, and 83% of the tourism infrastructure (hotels and resorts), respectively. In addition to flooding, properties are also susceptible to coastal erosion with 28% of the total hotels and resorts on the two islands being situated within 0–50 m and 60% of the tourism infrastructure within 0–100 m of the coastline. Considering the economic importance of the sector, the potential impacts on the tourism infrastructure will cause significant losses in revenue and employment for the two islands. Furthermore, the majority of the tourism on these islands is beach-based and visitor expenditures will decline due to their vulnerability. These losses will have far-reaching social-economic consequences for the Bahamas. Our findings reveal a need for integrated coastal zone management that incorporates tourism management strategies with adaptation measures to deal with climate change.

Empirical findings on the transmission of draft tube instabilities along the penstocks of hydraulic plants

On EDF hydraulic production plants equipped with Francis turbines, there have been related some cases of significant pressure fluctuations detected in the upper parts of the penstock when units were operating in the high load pressure surge zone. There was no decrease of the Peak-to-Peak pressure fluctuations along the penstock in the upstream part as it could be expected. To understand the phenomenon, on site tests have been carried out using innovative non-intrusive dynamic pressure sensors in many points along the penstock allowing the analysis of upward and downward waves and their “interferences”. These interferences cause in some cases standing waves for which the envelope of pressure oscillations along the penstock exhibits nodes and anti-nodes whose positions are relatively fixed along the penstock for a given operating point of the turbine. It appears that the ratio [Frequency of surge]/[Natural frequency of the penstock] conditions directly the number of nodes. This point is important because upper zones of the penstock close to the surge tank have generally not been designed to withstand high values of pressure fluctuations. For high number of ratio (3, 5, 7…), long term operation may induce mechanical fatigue of the penstock. A statistical approach was performed based on the dynamic signal databases of EDF and GE comprising data analysis of 21 occurrences of strong axial pressure surges of high load. It seems that certain values of the frequency ratio favour this resonance. This emphasizes the role of water exchanges between the rope and the penstock (complementarily with the draft tube) in establishing the conditions of resonance.

Additions to the Cone Shell Faunas of Australia and Aruba (Conidae, Conilithidae)

Two new cone shells, one in the family Conidae and one in the family Conilithidae, are described from eastern Australia and Aruba. The new conid, Tesselliconus devorsinei n. sp., was dredged from 30 m depth off southern Queensland, Australia, and represents the newest member of a poorly-known deeper Neritic Zone Tesselliconus species complex that includes T. sandwichensis and T. athenae from Hawaii, T. kashiwajimensis from southern Japan, and T. edaphus from the Panamic Province. The new conilithid, Jaspidiconus vantwoudti n. sp., was found to be endemic to the Dutch Antilles island of Aruba, where it occurs in shallow subtidal rocky areas in the surf and surge zone.

Safety Analysis of a Solid Oxide Fuel Cell/Gas Turbine Hybrid System Fueled With Gasified Biomass

The effect of biomass gas on the safety performance of a solid oxide fuel cell (SOFC)/micro gas turbine (GT) hybrid system was studied with consideration of the fuel cell working temperature, fuel cell temperature gradient requirement, compressor surge zone, and turbine inlet temperature (TIT). The safety performance of the hybrid system on the design condition and off-design condition was also analyzed. Results show that the hybrid system is good adaptability to low concentrations of biomass gas. The electrical efficiency could reach 50% with different biomass gases and is higher than the other combined power systems that used biomass gas. The wood chip gas (WCG) would make the fuel cell or GT easier overheat than the other three gases. The cotton wood gas (CWG) and corn stalk gas (CSG) are easy to cause the TIT too low or the compressor surge. In the safety zone, considering the hybrid system load adjustment range, the effecting order (from large to small, following is same) is WCG, grape seed gas (GSG), CSG, and CWG. Considering the hybrid system electric efficiency, the effecting order is WCG, GSG, CWG, and CSG.

Climatic and geometric controls on the global distribution of surge-type glaciers: implications for a unifying model of surging

AbstractControls on the global distribution of surge-type glaciers hold the keys to a better understanding of surge mechanisms. We investigate correlations between the distribution of surge-type glaciers and climatic and glacier geometry variables, using a new global geodatabase of 2317 surge-type glaciers. The highest densities of surge-type glaciers occur within an optimal climatic envelope bounded by temperature and precipitation thresholds. Across all regions with both surge-type and normal glaciers, the former are larger, especially at the cold, dry end of the climatic spectrum. A species distribution model, Maxent, accurately predicts the major clusters of surge-type glaciers using a series of climatic and glacier geometry variables, but under-predicts clusters found outside the climatically optimal surge zone. We interpret the results in terms of a new enthalpy cycle model. Steady states require a balance between enthalpy gains generated by the balance flux and losses via heat conduction and meltwater discharge. This condition can be most easily satisfied in cold, dry environments (thin, low-flux glaciers, efficient conductive heat losses) and warm, humid environments (high meltwater discharges). Intermediate conditions correspond to the optimal surge zone, where neither heat conduction nor runoff can effectively discharge enthalpy gains, and dynamic cycling can result.

Simulation of the behaviour of a centrifugal chiller during quick start-up

During quick start-ups (0–80,000 rpm in a few seconds) of centrifugal chillers, there is substantial risk for lack of superheating out of the evaporator. Moreover, the compressor passes through the surge zone which can lead to damaging flow reversal. These problems cannot be addressed with experiments and need computing help. The work presented here takes into account the mechanical inertia of the fluid, which can no longer be neglected in the momentum equation written in local form in each component of the chiller. All properties are derived from the internal specific energy and density, which are determined locally by the integration of mass and energy equations applied to finite volumes of the components: evaporator, condenser and pipes. The simulations show that without proper control strategies of the electronic expansion valve, liquid can enter the compressor. New strategies are therefore designed which also help to avoid compressor stall.

Numerical Analysis of Wave and Hydrodynamic Models for Energy Balance and Primitive Equations

A numerical analysis of wave and hydrodynamic models is used to investigate the influence of WAve and Storm Surge (WASS) in the regional and coastal zones. The numerical analyzed system consists of the WAve Model Cycle 4 (WAMC4) and the Princeton Ocean Model (POM) which used to solve the energy balance and primitive equations respectively. The results of both models presented the incorporated surface wave in the regional zone affected the coastal storm surge zone. Specifically, the results indicated that the WASS generally under the approximation is not only the peak surge but also the coastal water level drop which can also cause substantial impact on the coastal environment. The wave–induced surface stress affected the storm surge can significantly improve storm surge prediction. Finally, the calibration of wave module according to the minimum error of the significant wave height (Hs) is not necessarily result in the optimum wave module in the WASS analyzed system for the WASS prediction. Keywords—energy balance equation, numerical analysis, primitive equation, storm surge, wave.

Identifying shark mating behaviour using three-dimensional acceleration loggers

Little is known about the reproductive strategies and mating behaviour of most sharks. Understanding mating behaviour is important as it can determine reproductive success and possibly rates of multiple paternity and fecundity. Additionally, some sharks appear to have specific habitat requirements for mating activities. We tested the utility of a 3-dimensional acceleration logger to identify mating events in free-living nurse sharks Ginglymostoma cirratum in an area where behav- iours can be observed directly, thus allowing corroboration of acceleration data. Loggers were attached to 4 adult females and were recovered after recording periods of 23.2 to 99.8 h (mean ± SD = 50.0 ± 35.1 h). We used acceleration data to classify several behaviours, including swimming, rest- ing, resting in a surge zone, and mating, with examples of each behaviour confirmed via direct obser- vation. Twenty-six mating events were inferred from acceleration data, ranging from 21 s to 20.1 min in duration (median = 2.22 min), with no events taking place during the nighttime hours between 23:00 and 07:00 h. Four events lasted longer than 9 min and took place during periods when logger- equipped sharks were not acoustically detected within the shallow study site. The similarity in mat- ing behaviours between this and some other species raises the possibility that accelerometry could be used to quantify mating in a variety of shark species. This is the first study to classify mating and other behaviours in free-living sharks from acceleration data.

The goldrim surgeonfish (Acanthurus nigricans; Acanthuridae) from Diego Garcia, Chagos Archipelago: first record for the central Indian Ocean

The goldrim surgeonfish (also known as the whitecheek surgeonfish in the aquarium trade), Acanthurus nigricans (Linnaeus), is a common and widespread member of tropical reef fish communities throughout the Pacific Ocean. It has been reported at low densities at Cocos (Keeling) and Christmas Islands in the eastern Indian Ocean. Named nigricans for its characteristically dark body color, the species usually inhabits shallow depths on the outer reef crest just below the surge zone, but has been observed as deep as 67 m (Chave and Mundy, 1994). The species feeds on filamentous algae (Randall, 2001). In this paper I report the first occurrence of Acanthurus nigricans in the central Indian Ocean (Chagos Archipelago) and provide information on its biogeography and hybridization with A. leucosternon Bennett.

Experiments and modelling of surge in small centrifugal compressor for automotive engines

In this paper the surge phenomenon in small centrifugal compressors used for turbocharging internal combustion engines is analyzed. The experimental work was focused on the measurement of compressor behaviour within the surge zone by means of a specifically designed facility. The presented model is based on the introduction of a fluid inertia term that accounts for the non quasi steady effects and the use of a compressor map extended to the surge and negative flows zone obtained from experimental tests. The compressor model was implemented in a one-dimensional gas-dynamic model. The comparison of the modelled and measured evolution of instantaneous pressure during deep surge operation shows good agreement. Furthermore, the model is also able to predict the amplitude and frequency of pressure pulses when the compressor operates in surge with different outlet duct lengths.

On Evacuation and Deaths from Hurricane Katrina

| 754 the next hurricane. More knowledge about a hazard is usually associated with the person taking more protective actions or adjustments, but knowledge can be inconsistent, thus reducing its impact. Some individuals with more knowledge become overconfi dent and consider themselves less vulnerable due to their knowledge. Women perceive risk diff erently from men and are more likely to be risk averse and to perceive hazards as risky. Racial and ethnic minorities and individuals with low income and little education tend to have higher perceptions of risk from natural hazards, perhaps due to their lack of resources and their vulnerable positions in society. However, studies also show that African-Americans are less likely to evacuate than whites. Households with children are more likely to evacuate from a hurricane, while households with elderly are less likely to evacuate. Baker reports that the three most important factors in determining whether people evacuate are 1) the vulnerability of their locations; 2) whether they believe they have been told by authorities that they must evacuate; and 3) the severity of the hurricane. People who live on beaches or barrier islands or who live in the surge zone or in mobile homes realize their vulnerability and are more likely to evacuate than those who live inland in nonsurge zones. People who evacuate usually perceive a personal risk to themselves or to their family. Th e perceived risk is aff ected by whether the evacuation is “recommended (voluntary)” or “ordered (mandated),” and by the forecast severity of the storm. An “evacuation order” is most effi cient for convincing people to evacuate, but dissemination by the media may not be suffi cient. Baker reports that the public is most eff ectively informed when authorities go door-to-door notifying residents of the need to evacuate or drive through neighborhoods announcing the evacuation over loudspeakers. For some, such as those in health care facilities, evacuation may not be off ered as an individual option. Others who do not evacuate do not perceive a large risk, or stay at home to look aft er their property and pets or for work-related reasons. Th us, residents of New Orleans might have chosen to stay at home because they did not perceive a high risk. Th ey had been warned to evacuate for Category-4 hurricanes ON EVACUATION AND DEATHS FROM HURRICANE KATRINA

Eyewitness accounts of the 25 June 1997 pyroclastic flows and surges at Soufrière Hills Volcano, Montserrat, and implications for disaster mitigation

Abstract Eyewitness and survivor accounts allow reconstruction of the sequence of events on 25 June 1997, when a sustained partial collapse of the lava dome occurred leading to the death of 19 people. An unsteady pyroclastic flow was generated with three distinct pulses. The third flow pulse caused most of the damage to infrastructure and most, if not all, of the casualties. Pyroclastic surges detached along most of the path of the third flow pulse, and one travelled 70 m up an adjacent hillside. Observations were made that will be important for the development of mitigation measures at future events involving high-temperature flows and surges. Temperatures remained high (300-400°C) at the periphery of the most voluminous and extensive surge, even though dynamic pressure and velocity were low, causing the death of seven victims. Some people survived at the margins of the surge zone but suffered serious burns when they were forced to walk across the hot surge deposits to safety. Deflagration of buildings and vegetation was immediate within the pyroclastic surge and intense fires burned long after the volcanic activity had ceased. Fires could be a serious secondary hazard in an urban area. Search-and-rescue efforts were hampered in the immediate aftermath of the pyroclastic flows and surges by smoke and ash in the atmosphere. The hot, locally gas-rich surge deposits posed a major hazard to search-and-rescue workers and volcanologists for days afterwards. Despite the efforts of officials, scientists and concerned members of the public, about 80 people were in Zones A and B of the Exclusion Zone on 25 June 1997. Our findings suggest that many had become accustomed to the pyroclastic flows and had become overconfident in their own ability to judge the threat by observing repeated flows that had gradually increased runout but remained restricted to valleys. Many people had contingency plans and believed that there would be observable or audible warning signs from the volcano if the activity were to escalate significantly. However, there were no such discernible warnings and individual contingency plans proved inadequate. Public education should concentrate on correcting such public misapprehension of hazardous phenomena and attendant risks in future volcanic crises.

Partitioning of space and food resources by three fish of the genus Diplodus (Sparidae) in a Mediterranean rocky infralittoral ecosystem

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 152:273-283 (1997) - doi:10.3354/meps152273 Partitioning of space and food resources by three fish of the genus Diplodus (Sparidae) in a Mediterranean rocky infralittoral ecosystem Sala E, Ballesteros E White sea bream Diplodus sargus, two-banded sea bream D. vulgaris and sharpsnout sea bream D. puntazzo coexist in Mediterranean infralittoral rocky habitats. Diets of the 3 species were quantitatively analysed, and the relative abundance of algae found in stomach contents was compared with the abundance of algae in the different habitats. These results were compared with observational studies on distribution and feeding use of the habitats. The results suggest that there was marked resource partitioning between the 3 species of Diplodus in the rocky infralittoral. D. sargus mainly exploited the surge zone, while D. puntazzo and D. vulgaris preferentially exploited deeper waters. Diet analysis suggested a strong feeding niche overlap between D. sargus and D. vulgaris, although they fed in different habitats, except small individuals (total length <13 cm) of both species, which shared the same resources. D. vulgaris and D. puntazzo showed strong habitat overlap, although they exploited different food resources. D. sargus and D. puntazzo showed low spatial and feeding-niche overlap. Habitat partitioning appeared to be as important as food partitioning in structuring Diplodus assemblages. Resource partitioning · Littoral fish · Infralittoral habitats · Diplodus · Mediterranean Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 152. Publication date: June 26, 1997 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1997 Inter-Research.

Photosynthesis in air and in water of Acanthophora najadiformis growing within a narrow zone of the intertidal

In this work, we investigated photosynthetic gas exchange responses of the red alga Acanthophora najadiformis (collected in 1991 from a shore near Netanya, Israel) to heating, light, inorganic carbon and desiccation of the thalli. This was done to elucidate some of the contributing causes for its particular restricted vertical distribution within the lower intertidal zone of the Israeli Mediterranean rocky shore. In contrast to other common intertidal species, the photosynthetic performance of A. najadiformis was very sensitive to desiccation and to high temperature, and these factors may thus prevent the alga from growing above the surge zone. On the other hand, this species photosynthesized five times faster in air than in water (provided it was kept highly hydrated), and this may be the reason why it does not succeed in competing with other algae in the subtidal which use HCO3-more efficiently.

The Irish Variscides: a fold belt developed within a major surge zone

An arcuate fold belt characterizes the Irish Variscides south of the Dingle-Dungarvan line. The folds are cross-cut by numerous faults which tend to be sinistral in the west and dextral in the east. Clockwise transection of major fold axes by minor folds and by cleavage has been recorded in the east, while anticlockwise transections are common in the west. These and other features suggest that north-south dextral and sinistral shearing occurred in the east and west respectively. This is considered to be a consequence of the morphology of the Munster Basin which allowed the development of a surge zone. In the centre of the fold belt the Variscan sole thrust is believed to lie at the base of, or within, the Old Red Sandstone. However to the east, thinning of the Upper Palaeozoic cover sequence forces the sole thrust to cut down laterally stratigraphic section into Lower Palaeozoic basement. In the depocentre the sole thrust surged ahead by propagating along bedding surfaces or possibly a Devonian-Carboniferous extensional detachment beneath the basin, while to the east and offshore to the west its propagation was inhibited by the absence of easy decollement horizons within the basement. Consequently the tip-line became strongly arcuate and the thrust developed into a surge zone. The sole thrust propagated northwards by stick-slip processes. Much of the deformation within the cover sequence occurred during sticking events, particularly fold tightening and accommodation faulting.