Thickness Of Subsurface Layer Research Articles

Geoelectrical investigation to delineate potential aquifers in Shahroud, Iran

One of the world's most pressing needs today is access to groundwater. Although hydrological parameters can generally be estimated using underground studies, these methods are time-consuming and expensive. By taking the direct relationship of these parameters with electrical resistivity and measuring it with a cheaper and faster geoelectric method, a qualitative estimate of these parameters will be obtained. The electrical resistivity method is one of the most widely used methods to probe aquifers. The main objective of this paper is to show how, by interpreting and modeling the data of this exploratory method along with other geological information, the hydrogeological modeling of groundwater reservoirs can be done, and then, with an informed vision, the wells can be drilled for exploitation. For this purpose, the electrical resistivity data at 189 points and 9 profiles in the Shahroud region with Schlumberger array, after reviewing and making some modifications, were subjected to one-dimensional inverse modeling. According to the peripheral vision, the electrode distance was considered to be 50 meters and the length of the profiles is different. The longest profile was 1000 meter and related to profile 3. Then, using the results of modeling along with other available information, the hydrogeological models of the area were prepared in the form of iso-resistivity contour map and interpreted in terms of resistivity and thickness of subsurface layer using computer software Geographic Information System (GIS). Similarly, the thickness map of the aquifer unit (s) was also prepared to classify the good and poor zones. Using the prepared models and also considering the direction and piezometric of the groundwater flow inside the aquifer, suitable places were identified and suggested for future exploitation.

CHARACTERIZATION OF ROCK LAYERS BASED ON REFRACTION SEISMIC METHOD: A CASE STUDY OF MENTARANG’S HYDRO-POWER PLANT, MALINAU REGENCY, NORTH KALIMANTAN

North Kalimantan Province is a new province that is dynamic in development in order to prosper the inhabitants. The research and exploration to make a plan to develop new renewable energy are one of their main programs. The hydro-power plant of Mentarang, Malinau Regency, Kalimantan Utara is a plan program in 2020. The research study of hydro-power plants is essential as a reference in the development plan and avoids the hazard, miss calculation due to human error, etc. Seismic refraction is used in the feasibility study and detailed engineering study (FS DED) of Mentarang's Hydro-power plant. Analysis from the Seismic refraction method can be used as an input parameter for deciding the feasibility of Mentarang's hydro-power plant. This study aims to characterize the sub-surface layers, structure, and sub-surface layer thickness within this area. The seismic refraction method uses the intercept time or travel-time versus distance and processed using the reciprocal method, then it is modelled using inversion and resulted in a 2D profile. This research study was used the seismic refraction method with geometry acquisition of 14 sources with two spread and 5 meters of geophone interval. The analysis result of the 2D inversion profile model, in general, is classified as four strata layers. These strata are categorized as weathered layers with 5-15 meters of thickness, clay, and Sandstone about 5-20 meter of layer thickness, Sandstone with the layer thickness of about 20-50 meters, and lastly, granite, lava rocks, or limestone with depth more than 70 meters below the subsurface. There is a possibility of a structure at an offset of 70 meters, but this method's limitation will overestimate the conclusion. Therefore, it is necessary to bring another method that more sensitive to work further in research study evaluation of hydro-power plant Mentarang, Malinau Regency, North Kalimantan.

Geo-electric assessment for groundwater potential at permanent site of Waziri Umaru Federal Polytechnic, Birnin Kebbi, Kebbi State North Western, Nigeria

Vertical Electrical Soundings (VES) afford fast and economical measurements used in geophysical exploration. VES was used for groundwater exploration at the permanent site of Waziri Umaru Federal Polytechnic, Birnin Kebbi. Eighteen (18) Vertical Electrical Sounding (Schlumberger array, maximum AB/2 distance 100 m) were performed, data were acquired using ABEM terrameter (SAS 300c), to determine the geoelectric units in the subsurface stratigraphy as well as to delineate groundwater potential in the area via electrical resistivity soundings. Field data collected was analyzed using computer software (IPI2win) which gives an automatic interpretation of the apparent resistivity in ohm-meter. Data was interpreted in terms of the resistivity and thickness of subsurface layers. Results indicates that three to five (3-5) distinct layers in the study area namely; top soil which is mainly sand, clayey sand/loose sand, sandy clay/fine sand and clay unit were delineated. The result also revealed that water bearing formation exists in the third layer in some identified VES locations i.e VES 3, VES5, VES13 and VES14 with very good aquifers, with thickness and corresponding resistivity values of 40.5, 37.5, 45.8, 60 m and 173, 148, 222 and 432 Ωm respectively. The electrical resistivity data, therefore gives reasonable accurate results that can be used to understand stratigraphy and sedimentary configuration in ground water exploration.

Application of WRF-Hydro modeling system in Chenhe Basin and comparison with Xin'anjiang model

本文利用全球陆面数据同化系统与降雨观测数据，以陕西半湿润区陈河流域为研究对象，驱动WRF-Hydro模型，研究该模型的表现和适用性，并在结构、参数、输入输出和模拟结果方面与新安江模型对比.考虑到次表面层与实际包气带的区别，引入土层厚度乘子ZSOILFAC对前者进行等比缩放，发现其与新安江模型反推包气带的厚度有较好的一致性.研究表明：在陈河流域中WRF-Hydro计算步长须在建议值的基础上缩小；WRF-Hydro模型善于模拟洪水细节，新安江模型表现好且稳定；前者的径流深和洪峰合格率平于或略低于后者；在两个指标均合格的洪水中，前者平均均方根误差比后者小21.5%，但对于其他洪水，前者平均均方根误差比后者大56.2%；WRF-Hydro在洪水起涨时刻模拟较好，表现出其在中小流域应用的潜力.;The WRF-Hydro modeling system (WRF-Hydro model) was used for flood forecast in semi-humid small and medium catchment in China, proposed by the National Center for Atmospheric Research Center (NCAR) in 2013. The Global Land Data Assimilated System (GLDAS) and observed rainfall data are adopted to drive WRF-Hydro model in Chenhe Basin located in the south-central Shanxi Province. This study examine the practical features and applicability of the model, and also compare with Xin'anjiang (XAJ) model in structure, parameters, inputs & outputs and simulation results. Given the excessive time consume in model running, the stepwise approach for calibration is used for five main parameters in this study. The multiplier for subsurface layer thickness (ZSOILFAC) is introduced to modify this thickness to establish contact between subsurface layer and aeration zone to meet the actual situation of the basin, and the good agreement between subsurface layer modified by ZSOILFAC and the aeration thickness evaluated by XAJ model is achieved. The results show that the time step is supposed to be reduced from 6 s recommended by User's Guidance to 1 s when spatial resolution of routing grid is 100 m in Chenhe Basin. WRF-Hydro model is good at simulating the details of flood, while XAJ model performs well and stably. The qualified rates of runoff depth and flood peak for the former are equal or slightly inferior to those for the latter. The mean root mean square Error (RMSE) of the former is 21.5% less than that of the latter for the flood events with qualified runoff depth and flood peak; while mean RMSE of the former is 56.2% greater than that of the latter for others. WRF-Hydro model has good skills in simulating the start time of observed hydrograph and has promising potential for hydrological simulation, flood forecasting and water resources evaluation for small- and medium-sized catchments.

Shear-wave velocity estimation using a combination of ambient noise from small aperture array and small-scale active seismic measurements: a case study in the area of the natural gas fields of Northern Germany

In recent years, numerous induced seismic events have occurred in the proximity of the natural gas field in Northern Germany. To monitor the seismicity and to asses the seismic hazard potential, a local monitoring network was installed in the area. Focusing on the seismicity hazard assessment, a major challenge is the characterisation of potential site effects due to local soil characteristics. This is quantitatively performed by estimating the shear-wave velocity (V s) variation with subsurface layer thickness. Such local effects can only be covered with a coarse spatial resolution due to the limited number of monitoring stations. Profiles were determined at three test sites (Langwedel, Walle and Bomlitz) by using a combined approach of small aperture 2D array ambient noise and small-scale active 1D measurements. The high-resolution frequency-wavenumber (HRFK), spatial autocorrelation (SPAC) and multichannel analysis of surface waves (MASW) methods were applied to the recorded ambient noise and active seismic data using various array sizes supplemented by the active measurements. This jointly allowed obtaining phase velocity dispersion curves covering a wide frequency range from 2 up to 32 Hz. The inversion of the obtained dispersion curves results in average S-wave velocity profiles down to depths of 70 m, identifying thin near-surface layers of a few meters as well as thicker layers of tens of meters in greater depth. A comparison with available borehole data shows a good correlation with the layering. Additionally, to asses the impact of a seismic event at the test sites, PGV estimations for various seismic events were performed. The final results of the test surveys demonstrate that the combined approach represents a suitable tool for near-surface characterisation, which can be used to improve the seismic hazard assessment in the area of the natural gas fields in Northern Germany.

Термическая структура вод в северо-западной части Тихого океана и роль ветра и адвекции в ее формировании

Two basic types of vertical thermal structure are defined in the North-West Pacific on the data obtained in CTD survey conducted from May 29 to July 9, 2013 . One of them prevailed in the coastal areas of the Bering Sea and at East Kamchatka where the depth of winter convection was 160-200 m and even more. The other extended over the open ocean with lesser depth of convection as 90-130 m. Their difference in the cold subsurface layer thickness is analyzed in relation with temporal variations of the sea surface temperature and wind stress during preceding winter. The wind forcing contributes to deepening of winter convection in the coastal areas because of the shoreward Ekman transport but induces mostly horizontal advection in the open ocean. The wind-driven flows promote additional cooling in the subsurface layer in the western Bering Sea and major part of the NW Pacific, except the Alaska Stream area where they cause a warming in this layer. The warm intermediate layer in the whole region is supported mainly by westward advection of relatively warm water in the Alaska Stream and partially by the compensatory flow from the south that balances the Ekman transport in the upper layers.

Modelling deuterium release from tungsten after high flux high temperature deuterium plasma exposure

Tungsten is a primary candidate for plasma facing materials for future fusion devices. An important safety concern in the design of plasma facing components is the retention of hydrogen isotopes. Available experimental data is vast and scattered, and a consistent physical model of retention of hydrogen isotopes in tungsten is still missing. In this work we propose a model of non-equilibrium hydrogen isotopes trapping under fusion relevant plasma exposure conditions. The model is coupled to a diffusion-trapping simulation tool and is used to interpret recent experiments involving high plasma flux exposures. From the computational analysis performed, it is concluded that high flux high temperature exposures (T = 1000 K, flux = 1024 D/m2/s and fluence of 1026 D/m2) result in generation of sub-surface damage and bulk diffusion, so that the retention is driven by both sub-surface plasma-induced defects (bubbles) and trapping at natural defects. On the basis of the non-equilibrium trapping model we have estimated the amount of H stored in the sub-surface region to be ∼10−5 at−1, while the bulk retention is about 4 × 10−7 at−1, calculated by assuming the sub-surface layer thickness of about 10 μm and adjusting the trap concentration to comply with the experimental results for the integral retention.

Multichannel analysis of surface waves (MASW) for seismic site characterization using 2D genetic algorithm at Bahrah area, Wadi Fatima, Saudi Arabia

The present study deals with the seismic site classification of Bahrah area, Wadi Fatima, to characterize the local site conditions. The dynamic behavior of sediments was studied by the application of surface wave inversion. The multichannel analysis of surface waves (MASW) shallow geophysical technique was utilized for site classification. MASW survey was carried out at 66 sites along with 13 seismic refraction profiles at suitable localities. MASW and seismic refraction profiles were processed and compared with the available borehole data. The integration of MASW techniques with seismic refraction and borehole data progressively enhanced the subsurface visualization and reliability of the shear wave velocity estimation in the subsurface in the study area. The subsurface shear-wave velocity model was achieved by the solution of an inverse problem-based dispersion of surface waves and propagation in a vertically heterogeneous medium. The 2D genetic algorithm was employed for the inversion of dispersion curves to obtain velocity and thickness of subsurface layers. The depth to engineering bedrock and velocity of shear waves in the first 30 m was deciphered and mapped. The depth of bedrock in study area varies from 4 to 30 m, and VS 30 ranges from 320 to 800 m/s. The most of study area falls in B and C class categories in addition to few sites of D class according to the NEHRP guidelines.

Forecasting groundwater vulnerability in the coastal region of southern Tamil Nadu, India—a fuzzy-based approach

This paper presents applied research on fuzzy logic modeling to forecast the distribution of salinity in the coastal region of southern Tamil Nadu, India. Geoelectrical resistivity data has been used in this research, apart from nominal approach of salinity forecasting using geochemical data analysis. The data collected using vertical electrical sounding (VES) method was fed as an input for fuzzy inverting algorithm to evaluate true resistivity and thickness of subsurface layers. Inverted resistivity values have been subjected to fuzzy rule-based approach for salinity forecasting. Classifications have been made on the basis of linguistic variables with five linguistic terms of resistivity range using a triangular membership function of fuzzy logic. The purpose is to find the saltwater intrusion in the coastal region of Tuticorin district, Tamil Nadu, India. This research work reveals that fuzzy logic would be the effective tool for solving complex problems as well as enhancement in integrating multiple features necessary for the study. The results overlain in the surrounding regions which were mapped the threatening zones; hence, to mark pre-awareness in the regions, more rainwater harvesting system and avoidance of human anthropogenic activities need to be implemented.

Mini-RF and LROC observations of mare crater layering relationships

The lunar maria cover approximately 17% of the Moon's surface.Discerning discrete subsurface layers in the mare provides some constraints on thickness and volume estimates of mare volcanism. Multiple types of data and measurement techniques allow probing the subsurface and provide insights into these layers, including detailed examination of impact craters, mare pits and sinuous rilles, and radar sounders. Unfortunately, radar sounding includes many uncertainties about the material properties of the lunar surface that may influence estimates of layer depth and thickness. Because they distribute material from depth onto the surface, detailed examination of impact ejecta blankets provides a reliable way to examine deeper material using orbital instruments such as cameras, spectrometers, or imaging radars. Here, we utilize Miniature Radio Frequency (Mini-RF) data to investigate the scattering characteristics of ejecta blankets of young lunar craters. We use Circular Polarization Ratio (CPR) information from twenty-two young, fresh lunar craters to examine how the scattering behavior changes as a function of radius from the crater rim. Observations across a range of crater size and relative ages exhibit significant diversity within mare regions. Five of the examined craters exhibit profiles with no shelf of constant CPR near the crater rim. Comparing these CPR profiles with LROC imagery shows that the magnitude of the CPR may be an indication of crater degradation state; this may manifest differently at radar compared to optical wavelengths. Comparisons of radar and optical data also suggest relationships between subsurface stratigraphy and structure in the mare and the block size of the material found within the ejecta blanket. Of the examined craters, twelve have shelves of approximately constant CPR as well as discrete layers outcropping in the subsurface, and nine fall along a trend line when comparing shelf-width with thickness of subsurface layers. These observations suggest that surface CPR measurements may be used to identify near-surface layering. Here, we use ejected material to probe the subsurface, allowing observations of near-surface stratigraphy that may be otherwise hidden by layers higher from remote observations.

A novel and generalized approach in the inversion of geoelectrical resistivity data using Artificial Neural Networks (ANN)

The non-linear apparent resistivity problem in the subsurface study of the earth takes into account the model parameters in terms of resistivity and thickness of individual subsurface layers using the trained synthetic data by means of Artificial Neural Networks (ANN). Here we used a single layer feed-forward neural network with fast back propagation learning algorithm. So on proper training of back propagation networks it tends to give the resistivity and thickness of the subsurface layer model of the field resistivity data with reference to the synthetic data trained in the appropriate network. During training, the weights and biases of the network are iteratively adjusted to make network performance function level more efficient. On adequate training, errors are minimized and the best result is obtained using the artificial neural networks. The network is trained with more number of VES data and this trained network is demonstrated by the field data. The accuracy of inversion depends upon the number of data trained. In this novel and specially designed algorithm, the interpretation of the vertical electrical sounding has been done successfully with the more accurate layer model.

Simulation for ground penetrating radar (GPR) study of the subsurface structure of the Moon

Abstract Ground penetrating radar (GPR) is currently within the scope of China's Chang-E 3 lunar mission, to study the shallow subsurface of the Moon. In this study, key factors that could affect a lunar GPR performance, such as frequency, range resolution, and antenna directivity, are discussed firstly. Geometrical optics and ray tracing techniques are used to model GPR echoes, considering the transmission, attenuation, reflection, geometrical spreading of radar waves, and the antenna directivity. The influence on A-scope GPR echoes and on the simulated radargrams for the Sinus Iridum region by surface and subsurface roughness, dielectric loss of the lunar regolith, radar frequency and bandwidth, and the distance between the transmit and receive antennas are discussed. Finally, potential scientific return about lunar subsurface properties from GPR echoes is also discussed. Simulation results suggest that subsurface structure from several to hundreds of meters can be studied from GPR echoes at P and VHF bands, and information about dielectric permittivity and thickness of subsurface layers can be estimated from GPR echoes in combination with regolith composition data.

SEISMIC REFRACTION METHOD: A TECHNIQUE FOR DETERMINING THE THICKNESS OF STRATIFIED SUBSTRATUM

The seismic refraction survey is a very important geophysical technique used in the investigation of subsurface characteristics. This is why this study was carried out to emphasize the ability of the seismic refraction method in determining the thickness of stratified layers of soil and rock. The results obtained are generalized expressions that relate travel time, offset distance, velocity and thickness of subsurface layers.

Vertical electrical sounding (VES) methods to delineate potential groundwater aquifers in Akobo area, Ibadan, South-western, Nigeria

Vertical electrical resistivity soundings were conducted in order to delineate groundwater potential aquifers in Akobo area, Ibadan, South western, Nigeria. Twenty-one vertical electrical soundings were conducted using the Schlumberger configuration, covering the area. The data were interpreted with the help of Abaque (master) curve. The geoelectrical sections for the study area were: the topsoil, the clayey sand, sandy clayey, shale/clay basement and the fresh basement. The dominant rocks comprise suites of quartz schist and pegmatite. Interpretations of vertical electrical sounding (VES) were used to generate longitudinal conductance map. Isoresistivity contour map was prepared and interpreted in terms of resistivity and thickness of sub-surface layer at 56 m spacing using computer software (SURFER), and resistivity results were correlated with the existing lithology. Similarly, aquifer unit(s) thickness map was also prepared, in which good, moderate and poor zones are classified. The study reveals that the weathered and fractured horizons that occur in the easternmost part of the area constitute the productive water-bearing zones referred to as good groundwater potential aquifers with a thickness value greater than 20 m. Key words: Electrical resistivity, fractured horizon, groundwater potential aquifers, vertical electrical soundings, weathered horizon.

Determination of groundwater potential in Asaba, Nigeria using surface geoelectric sounding

Providing potable water has been a major concern to the people of Asaba the capital city of Delta State, Nigeria. This study which is aimed at identifying formations that present fresh and healthy aquifer water for the people employed the use of the geoelectric sounding to probe the subsurface. Data collected were interpreted in terms of the true resistivity and thickness of subsurface layers and result correlated with record from existing borehole. Results indicate that there are four to five distinct formations in the study area. Analyses of the data suggest that water bearing formation exist in the third formation having resistivity range of 318 to 567 Ωm. The thickness of the aquifer ranges from 20.4 to 33.9 m, while the depth range is from 43.5 to 52.8 m. The study therefore indicates the presence of thick and highly prolific aquifer zone which is an indication of adequate water resource in the area. It is recommended that boreholes for good drinking water and water scheme be drilled to the third layer of the various locations investigated. Key words: Schlumberger array, groundwater, geoelectric sounding, electrical resistivity, aquifer, electrode separation.

Effect of the Surface Oxidation on the Hot-Dip Zinc Galvanizing of Cast Iron

Effect of the Surface Oxidation on the Hot-Dip Zinc Galvanizing of Cast Iron In presented work authors analyzed the high-temperature oxidation process from the point of view of its influence on effects obtained during cast iron hot-dip zinc coating. Research concerned the influence of the high-temperature oxidation, as a preliminary stage previous to coating with zinc on the change of surface layer structure as well as subsurface layer of cast iron with flake, vermicular and nodular graphite. To obtain proper results of Zn coating the special chemical etching of cast iron after oxidation is necessary. The effects were compared to these obtained during cast iron coating without preliminary thermal processing. To comparative analysis both optical and scanning microscope, RTG measurement and profile measurement gauge results were applied. As a consequence of conducted high-temperature oxidation in subsurface layer of cast iron pores have been created, that in result of coating in liquid zinc were filled with new phase and in this way the new zone with different properties was obtained. It was additionally stated that the cast iron layer enriched in zinc is considerably thicker than layers got with application of other methods. Thickness of sub-surface layer where "after-graphite" pores are filled with zinc depends directly on the kind of graphite. When the flake and vermicular/compacted graphite is observed depth of penetration reaches 120 μm, whereas in nodular cast iron it reaches only 15μm, although sometimes single voids filled with zinc are observed at 75μm depth.

Investigation of Shallow Sedimentary Structure of the Anchorage Basin, Alaska, Using Simulated Annealing Inversion of Site Response

Abstract This study deals with shallow sedimentary structure of the Anchorage basin in Alaska. For this purpose, inversion of site response [SR( f )] data in the frequency range 0.5–11.0 Hz from various sites of the basin has been performed using the simulated annealing method to compute subsurface layer thickness, shear-wave velocity ( β ), density, and shear-wave quality factor. The one-dimensional (1D) models for the aforementioned parameters were obtained with preset bounds on the basis of available geological information such that the L -2 norm error between the observed and computed site response attained a global minimum. Next, the spatial distribution of the important parameter β was obtained by interpolating values yielded by the 1D models. The results indicate the presence of three distinct velocity zones as the source of spatial variation of SR( f ) in the Anchorage basin. In the uppermost part of the basin, the β values of fine-grain Quaternary sediments mainly lie in the range of 180–500 m/sec with thickness varying from 15 to 50 m. This formation overlies relatively thick (80–200 m) coarse-grain Quaternary sediments with β values in the range of 600–900 m/sec. These two Quaternary units are, in turn, overlain on Tertiary sediments with β >1000 m/sec located at depths of 100 and 250 m, respectively, in the central and western side along the Knik Arm parts of the basin. The important implication of the result is that the sources of spatial variation of SR( f ) in the Anchorage basin for the frequency band 0.5–11 Hz, besides in the uppermost 30 m, are found to be deeper than this depth. Thus, use of commonly considered geological formations in the depth intervals from 0 to 30 m for the ground-motion interpretation will likely yield erroneous results in the Anchorage basin.

A Hydrogeophysical Model of the Relationship between Geoelectric and Hydraulic Parameters, Central Jordan

Geoelectrical soundings using the Schlumberger array were carried out in the vicinity of 23 pumping test sites to determine aquifer parameters, central Jordan. On the basis of aquifer geometry, the area has been di-vided into two hydraulic units: the northern flood plain and the flood plain to its south. Field resistivity data are interpreted in terms of the true resistivity and thickness of subsurface layers. These parameters are then correlated with the available pumping test data. Significant correlations between the transmissivity and modified transverse resistance as well as between the hydraulic conductivity and formation factor were ob-tained for the two hydraulic units, in central Jordan are presented here.

A comprehensive seismic velocity model for the Netherlands based on lithostratigraphic layers

AbstractA seismic velocity model is necessary to map depth and thickness of subsurface layers interpreted from seismic reflection images. We have built a seismic velocity model (VELMOD-1) for the entire Netherlands area, both onshore and offshore, using non-confidential data (sonic logs, time-depth pairs, lithostratigraphic marker depths and downhole position data) of 720 boreholes in DINO - National Geoscientific Portal, and a preliminary isochore map (in seismic traveltime representation) of the layer of the Zechstein Group. The model is based on the Vint-zmidmethod applied to the following lithostratigraphic layers: Lower, Middle and Upper North Sea groups; Chalk Group; Rijnland Group; Schieland, Scruff and Niedersachsen groups; Altena Group; Lower and Upper Germanic Trias groups; Upper Rotliegend Group; and Limburg Group. Per layer, the linear least squares approximation, applied to Vintas a function of zmid, provides parameters V0and K for a linear velocity function V(z) = V0+ K · z. In VELMOD-1, K is constant, at least at the scale of structural elements, whereas V0varies with location. At borehole locations, V0is calibrated such that traveltime through the layer according to the linear velocity model equals the traveltime according to the borehole data. A kriging procedure is applied to the calibrated V0(x, y)-values resulting in an estimated V0-value at any other location. The model V0-values were determined on an areal grid with cells of 1 km × 1 km. On the same grid, kriged interval velocities constitute the model for the Zechstein Group. These interval velocities stem directly from interval velocities at borehole locations; at other positions they are also dependent on the thickness (in terms of seismic traveltime isochores) of the layer of the Zechstein Group. Maps are presented of the distributions of both V0and its standard deviation for two layers: that of the Chalk Group and that of the Lower and Upper Germanic Trias groups.

A thin subsurface layer of a polymer film studied by atomic force microscopy

A thin subsurface layer of a PMMA based resist film was studied in an atomic force microscope (AFM). An analysis of the AFM image allowed a modified subsurface layer thickness to be estimated, in which the polymer density is greater than that in the bulk of the film.