Coal fire mapping of East Basuria Colliery,Jharia coalfield using vertical derivative technique of magnetic data

The present study deals with the coal fire mapping of East Basuria Colliery, Jharia coalfield, India, using the magnetic method. It is based on the fact that rise in temperature would result significant changes in magnetic susceptibility and thermo-remanent magnetization (TRM) of the overlying rocks. Magnetism increases slowly with the rise of temperature until the Curie temperature. Generally, rock/ overburden loses magnetization and becomes paramagnetic due to heating to Curie temperature, which results with significant reduction in magnetic susceptibility. However, magnetism increases significantly after cooling below the Curie temperature. Several data processing methods such as diurnal correction, reduction to pole (RTP), first and second vertical derivatives have been used for analysis of magnetic data and their interpretation. It is observed that the total magnetic field intensity anomaly of the area varies approximately from 44850 to 47460 nT and the residual magnetic anomaly varies approximately from ?1323 to 1253 nT. The range of the magnetic anomaly after RTP is approximately 1050–1450 nT. About 20 low magnetic anomaly zones have been identified associated with active coal fire regions and 11 high magnetic anomaly zones have been identified associated with non-coal fire regions using vertical derivative techniques.     

Detection and delineation of coal mine fire in Jharia coal field,India using geophysical approach: A case study

Coal mine fire is a serious problem in Jharia coal field, India. The coal mine fire can be detected with different techniques such as borehole temperature measurement, thermo-compositional analysis, remote sensing techniques, thermo-graphic measurement and geophysical methods. In this study, various geophysical methods were used to detect the surface and subsurface coal mine fires. Geophysical techniques used in the present study are apparent resistivity, self-potential (SP), magnetic method and thermography. Geophysical anomalies such as low SP value of \(-60\hbox { mV}\), high negative magnetic response and low apparent resistivity value helped us to detect and delineate the fire and non-fire areas laterally as well as depthwise. Furthermore, the thermography survey was carried out in the coal field using thermal imaging camera in order to substantiate the geophysical methods. This integrated approach was found to be more advantageous for the detection and delineation of surface and subsurface fire with respect to use of any specific techniques. Moreover, the level of threat towards the locality, national railway line was also assessed unambiguously using the above techniques. Hence, proper planning and implementation towards the mitigation of hazard can be achieved on the basis of the reported results.     

Subsurface tectonic pattern and basement topography as interpreted from aeromagnetic data to the south of El-Dakhla Oasis,western desert,Egypt

The study area lies to the south of El-Dakhla Oasis in the central part of the western desert, Egypt. It is limited by the latitudes 24–25°?N and the longitudes 28–30°?E. The main purpose of this work is the investigation of the subsurface structure and the delineation of the main structural elements at different subsurface levels. This study aims also to estimate the basement depth, the basement relief, and consequently, the thickness of the sedimentary cover. The study is based on acquired aeromagnetic data prepared by "La Compagnie General De Géophysique" for the Egyptian General Petroleum Company and Conoco (1977), geological information and results of previous studies in the region. The study involves the analysis for the aeromagnetic data and generating of reduced to pole magnetic map from which different magnetic maps are calculated. The calculated maps are first vertical derivative map and downward continuation map at depth level 400 m. Trend analysis technique is used to define the fault pattern affecting the studied area at different subsurface levels. It is applied to the reduced to pole magnetic map, the first vertical derivative map, and the downward continuation map at depth level 400 m of the study area. All results obtained from the interpretation process were combined together to draw the general view of the subsurface structures of the area. The NE–SW, E–W, and N–S trends are important surface and subsurface (basement) structural trends. This is attributed to the rejuvenation of movements on these old (basement) tectonic trends after the deposition of the sedimentary cover. Basement depth calculation from the aeromagnetic data is achieved using different techniques. The applied techniques included natural spectral analysis and Euler deconvolution. The depth values obtained vary from 400 to 1,700 m.     

Subsurface structural features of the basement complex and mineralization zone investigation in the Barramiya area,Eastern Desert of Egypt,using magnetic and gravity data analysis

In the Barramiya area, the majority of gold deposits are generally related with the quartz veins that associated with shear zones cutting the crystalline basement rocks. The quartz vein system is controlled by shear zone and general faults. The present study is to delineate the general faults, shear zones, geological limits, and basement rock relief, using airborne magnetic and gravity data analysis at the Barramiya gold mine and surrounding area, Eastern Desert of Egypt. To achieve our goal, we have applied on magnetic and gravity data the following techniques: reduction to pole (RTP), analytical signal, tilt derivative, total horizontal derivative, 3D Euler deconvolution, downward continuation, and source parameter imagining power spectrum techniques. The analytical signal used to map the types of rock boundaries. Tilt derivative and total horizontal derivative filters helped to delineate fractures and the contact zones of the formations that host the main Barramiya shear zone. 3D Euler deconvolution techniques helped to delineate the fault trends which represented at the following direction: NNE–SSW and NNW–SSE. The average depths of both regional and residual causes have been estimated by applying downward continuation, source parameter imagining, and power spectrum techniques. According to the results of the present study, the depth of the basement rocks is relatively high (~?80-m depth) in the western part of the study area and the basement rocks cropped out in the surface at the rest of the area. Our results are coinciding with the previous geological studies.     

向上延拓对斜导数方法处理航磁异常的影响

分析了中国南部某地利用斜导数方法处理航磁数据时遇到的问题,由于受到浅源磁干扰场的影响,用斜导数方法处理后的航磁数据异常形态复杂,从而影响地质解释效果。为此提出了向上延拓与斜导数方法联合使用的改进办法,通过实例阐述了应用斜导数方法处理航磁数据应注意的问题。改进后的方法,能充分体现航磁资料在地质解释方面的优势。     

重力勘探新技术在寻找古潜山中的应用

以渤海湾盆地某凹陷为例,介绍下延一定深度的垂直二次导数、三维视密度反演、在LCT平台上的重、磁、地震正反演等新技术在寻找一些小规模、低幅度、大埋深的古潜山构造的应用效果。下延一定深度的垂直二次导数异常比常规的重力处理技术,即常规的垂直二次导数异常,从平面上能更好、更直观地反映小规模、低幅度、大埋深的古潜山构造;三维视密度反演技术反映地质体的横向密度变化情况,从纵向上为潜山研究提供证据;利用LCT平台上的重、磁、地震联合正反演技术可以定量地确定潜山埋深、幅度等。     

Estimating the depth of underground coal fires using data integration techniques

Underground coal fires in China cause serious environmental problems, in addition to the loss of valuable coal resources. The present study aims at developing a quick and practical method to estimate the depth of coal fires using data integration techniques.
  In coal fields which have underground coal fires, the subsurface fires are associated with surface thermal anomalies. Airborne thermal infrared scanner data and colour infrared photographs were used in this study to depict the coal fire front and the outcrop of coal seams, respectively. A Digital Elevation Model (DEM) of the study area was produced from topographic maps at 1:25 000 scale. Finally, taking into account the spreading direction of the coal fires and the relationships between thermal anomalies, relief factors and the occurrence of coal seams, the depths of the coal fires were obtained automatically by means of integration of remote sensing data and GIS techniques. This helped to target the fire fighting operations and made them more cost effective.     

磁法和瞬变电磁法探测煤层火烧区边界及富水性

新疆天山某煤炭勘查区,需查明一水平内火烧煤层的下边界及其富水性。在综合分析该区地质资料及物性参数的基础上,采用了以磁法和瞬变电磁法为主的物探方法。磁法勘探测网设计为20m×80m,并在后期对西部测线进行了加长。根据测区实测磁异常分布图、低通滤波后磁异常分布图、向上延拓30m磁异常分布图及垂向二阶导数磁异常分布图,圈定火烧区主要分布在测区的北部。瞬变电磁法勘探测网设计为40m×80m,依据下1、下5及下10煤层底板富水异常分布图,解释下1、下5煤底板的富水性主要集中在测区的北部,与火烧区范围高度一致,而下10煤层底板富水性极不均匀,仅在测区北部煤层露头附近,受砂岩裂隙的影响,接受降水补给形成零星砂岩裂隙富水区。该解释成果经矿方钻孔验证,结论基本可靠。     

Quality Evaluation of Offshore Data in the Earth Magnetic Anomaly Grid（2-arc-Minute Resolution）：Taking the Southern Section of the Kolbeinsey Ridge in the Arctic Region as an Example

In order to evaluate the quality of the offshore magnetic data in the Earth Magnetic Anomaly Grid (2-arc-minute resolution)(EMAG2), the authors chose the aeromagnetic data at 1∶500 000 and 1∶1 000 000 scales of the southern section of the Kolbeinsey Ridge with a total area of 193 500 km² to compare and analyze. Based on the EMAG2 data, the authors obtained the EMAG2 (downward continuation 4 km) and the aeromagnetic anomaly (upward continuation 4 km) using the analytical continuation method. Then, the correlation coefficients between the aeromagnetic anomaly (upward continuation 4 km) and the EMAG2, and the aeromagnetic anomaly and the EMAG2 (downward continuation 4 km) were calculated by the correlation analysis method. Finally, through comprehensive analysis of the features of these correlation coefficients and differences, the quality of the magnetic data of the southern section of the Kolbeinsey Ridge was evaluated in the database EMAG2. The results showed that the EMAG2 integrated a large number of the airborne or offshore magnetic data. The quality of the offshore magnetic data is relatively high in the offshore areas with dense lines. However, the quality of the offshore magnetic data is relatively low if the EMAG2 data at 4 km altitude is converted to the anomaly data at sea level.     

Temporal transition analysis of coal mine fire of Jharia coalfield,India, using Landsat satellite imageries

Coal is dominant energy source of world at large and India in particular for several decades and expected to being continued for foreseeable future. However, fire in this fossils fuel is still a global catastrophe for the major coal-producing countries. There are several direct and cascading distress of coal mine fire has been encountered by environment, economy, safety and society. Without knowledge of actual status and extent of coal mine fire, any scope for its better managements may be futile. In India, the coal mine fire of well-known Jharia coalfield (JCF) has been continued since last ten decades and still spreading towards newer areas. The aim of this paper is to highlight the chronological net lateral spatial changes in coal mine fire areas of JCF using Landsat satellite thermal imageries. The mapping of coal mine fire area of JCF during 1988–2013 has been carried out with consecutive 5-year intervals. The lateral changes in surface and subsurface fire areas along with propagation towards new area have been studied. The study also included to evaluate changes of status and extent fire during this time span and effect of its management efforts. On the basis of aforementioned analysis, the study concludes a slow reducing trend in coal mine fire area during last 25 years.     

Aeromagnetic signature analysis of Gasus area and its surrounding,central eastern desert,Egypt

This study presents analysis and interpretation of aeromagnetic data to construct subsurface structure maps and determine the depths to magnetic basement. Subsequent analysis steps are applied to the total magnetic intensity (TMI) data. These steps include Reduction to the Pole (RTP) map that was derived from the TMI map then subjected to spectral frequency analysis to isolate RTP map into high and low frequencies and determine pseudo-depth for each map from power spectrum in which there were two main average levels (interfaces) at depth 1.3 and 0.7 km for the deep-seated and near-surface magnetic structures, respectively. 3D Euler deconvolution technique is applied to calculate the depth to the magnetic contacts; the results show clustering of solutions, the shallow solutions are related to the outcrops less than 80 m from flight level, and the solutions which are related to sedimentary cover locations (Um al-Huweitat, Wasif, and Mohamed Rabah basins) are ranged between 200 and to more than 1100 m. Moreover, anomaly enhancement techniques such as tilt derivative (TD), horizontal tilt derivative (TDX), and source edge detect (SED) are applied to enhance shallow features, and determining structure element boundary for both shallow- and deep-seated anomalies and revealing possible faults such as 2D forward modeling are applied to selected profiles to adjust the interpreted structures and map the boundaries and basement relief of the three basins (Mohammed Rabah, Wasif, and Um al-Huweitat). The analysis shows that the study area is affected with network of dip–slip faults due to high shearing and compression stress which formed grabens and horsts at different depth levels in the study area. The trends of predominant faults related to deep-seated structures are NW–SE with depths ranged between 1 and 1.4 km and in regard to the shallow-seated structure, the predominant fault trends are NW–SE, NNW–SSE, and NNE–SSW with depths ranged between 0.3 and 0.8 km.     

Crustal Magnetic Studies over Krishna-Godavari Basin in Eastern Continental Margin of India

Total field magnetic data were collected over the Krishna-Godavari basin covering 20, 000 sq.km with an average spacing of 8.5 km. This was mainly to study the long wavelength features related with the deep structures. Aeromagnetic map of the region compared well with the ground maps. The anomaly maps show a combination of NE-SW, NS/NNE-SSW and NW-SE trends. The anomalies of ground data are transformed to isolate the sources at different depths. The second vertical derivative and downward continuation maps bring out clearly the NE-SW and NS/NNE-SSW trends related to the coastal basin and Eastern Ghats implying that they are shallow. These are probably superposed on much deeper NW-SE trending structural features of Pre-Gondwana breakup as evidenced in the Horizontal Gradient of Pseudogravity and upward continuation maps. From the offshore magnetic data it appears that these trends extend up to the Ocean Continent Boundary. It is inferred that the deeper features are associated with rifting of Dharwar and Bastar cratons within the Indian plate, prior to the rifting of India from Gondwanaland. The superposed horst and graben structures are related to the formation of the pull-apart Krishna-Godavari basin as a result of rifting and drifting of India from Gondwanaland. These two structural features are associated with two different tectonic events.     

重磁数据稳定向下延拓的水平导数迭代法

向下延拓是重磁数据处理的常用手段,能有效地区分叠加异常、增强浅部异常,但现有向下延拓算法的计算大多是不稳定的,且易受噪声的干扰,往往造成异常形态的畸变.提出一种基于水平导数和向上延拓联合迭代的向下延拓算法,由于向上延拓和水平导数的计算是稳定的,因此该向下延拓方法可有效地增强结果的准确性和稳定性.理论模型试验表明该方法的向下延拓结果比Fourier变换计算结果更加稳定、准确,且受噪音干扰小.将该方法应用于实际数据的处理,结果显示该方法能稳定和准确地完成异常的向下延拓任务,且有效地增强了浅部局部异常.      

东北地区火成岩的航磁异常特征分析

为了解不同时代火成岩的航磁异常特征,对东北地区1∶20万的航磁资料进行了化极、向上延拓及垂向导数的处理。通过与地质图进行对比分析,总结出研究区火成岩的航磁特征:区内广泛分布的各时代花岗岩表现出了不同的磁异常特征,寒武纪、石炭纪、三叠纪等时代的花岗岩表现为高磁异常,而二叠纪及侏罗纪花岗岩表现为低磁异常,其中磁异常最高的岩性为石炭纪花岗岩,磁异常最低的是二叠纪花岗岩。测区内存在的喷出岩-古近纪玄武岩磁异常较高,而更新统玄武岩并未见明显的异常特征。     

Numerical modeling for analyzing thermal surface anomalies induced by underground coal fires

Coal seams burning underneath the surface are recognized all over the world and have drawn increasing public attention in the past years. Frequently, such fires are analyzed by detecting anomalies like increased exhaust gas concentrations and soil temperatures at the surface. A proper analysis presumes the understanding of involved processes, which determine the spatial distribution and dynamic behavior of the anomalies.In this paper, we explain the relevance of mechanical and energy transport processes with respect to the occurrence of temperature anomalies at the surface. Two approaches are presented, aiming to obtain insight into the underground coal fire situation: In-situ temperature mapping and numerical simulation. In 2000 to 2005, annual temperature mapping in the Wuda (Inner Mongolia, PR China) coal fire area showed that most thermal anomalies on the surface are closely related to fractures, where hot exhaust gases from the coal fire are released. Those fractures develop due to rock mechanical failure after volume reduction in the seams. The measured signals at the surface are therefore strongly affected by mechanical processes.More insight into causes and effects of involved energy transport processes is obtained by numerical simulation of the dynamic behavior of coal fires. Simulations show the inter-relation between release and transport of thermal energy in and around underground coal fires. Our simulation results show a time delay between the coal fire propagation and the observed appearance of the surface temperature signal. Additionally, the overall energy flux away from the burning coal seam into the surrounding bedrock is about 30-times higher than the flux through the surface. This is of particular importance for an estimation of the energy released based on surface temperature measurements. Finally, the simulation results also prove that a fire propagation rate estimated from the interpretation of surface anomalies can differ from the actual rate in the seam.     

Relationship in metastasis of coal fire and land use/cover using thermal imagery and support vector machine classifier

The objective of the present study was to delineate temporal and spatial changes in the coal fire and land use/cover within Bastacolla area of Jharia coal field. Studying this variation helped to decipher interconnection among the dynamics of the coal fire and concomitant changes in land use/cover. The detection of coal fires during a span of 14 years along with transitioning land use/cover was cost-effective and enabled planning for management of coal resources and environment. Landsat series of satellite data of 2002, 2009, 2013, and 2016 were processed for generating land surface temperature profiles vis-a-vis classified land use/cover of the study area. A single cut-off temperature was derived for mapping of coal fires using land surface temperature profile from 2002 to 2016. The satellite images were classified using support vector machines, and for depicting land use/cover change, post-classification change detection was done. Classification accuracy obtained was excellent with kappa coefficient ranging from 0.897 for classified image of 2002 to 0.799 for classified image of 2016. Results revealed that coal fires had shifted to the central west part of the area. Furthermore, pockets of coal fire from northern and eastern part of the study area have diminished. OB dumps and coal quarry/coal dump may be attributed towards the spatial change in coal fire while; OB dumps showed connotation with the highest temperature zones. Ground verifications for temperature profiles and coal fires were carried out using thermal camera which enunciated good agreement with results.     

Geological interpretation of Bouguer gravity and aeromagnetic data from the Gobi-desert covered area,Eastern Tianshan,China: Implications for porphyry Cu-Mo polymetallic deposits exploration

In this study, Bouguer gravity and aeromagnetic data have been used to better understand the geology and mineral resources near the late Carboniferous-late Permian porphyry Cu-Mo polymetallic mineralization in the Chinese Eastern Tianshan belt, which is extensively covered by Gobi-desert. The reduced-to-pole (RTP) transformation of regional-scale aeromagnetic data shows that the porphyry Cu-Mo deposit is within a cluster of magnetic anomaly highs that overprint on a northeast trending magnetic gradient belt generally along the crustal-scale Kanguertag-Huangshan fault. The 10 km upward continuation transformation of both Bouguer gravity and aeromagnetic data indicates that the known porphyry Cu-Mo polymetallic deposits are located on the flanks of prominent gravity and magnetic anomaly highs. These anomalies are spatially correlated with the late Carboniferous-late Permian igneous rocks and in the Tuwu-Yandong mineralization district are centered over the granodiorite rocks genetically related to porphyry copper systems. In order to minimize interpretational ambiguities, a useful approach that is correlation analysis (CA) based on correlation coefficient (CC) given by gravity and magnetic data was employed to separate positively and negatively correlated anomalies features. The CA procedure is applied to 10 km upward continuation transformation of both Bouguer gravity and RTP transformed aeromagnetic data for mapping correlative magnetization and density contrast anomalies from deep sources, which may be associated with the porphyry Cu-Mo polymetallic mineralization. Five prominent CC positive anomalies have been found in the southern margin of Dananhu-Tousuquan arc. Those anomalies zones could be interpreted to reflect a late Carboniferous-late Permian magmatic belt that is favorable for additional discoveries of late Carboniferous to late Permian porphyry copper systems in north region of Eastern Tianshan.     

航磁异常深部弱信号提取技术研究

磁异常通常是地下不同深度磁性地质体产生磁场的叠加,在规范高度的航磁测量结果中,深部磁性体所产生的异常通常表现为弱而平缓,其水平与垂向分辨率均较低,在航磁资料处理解释中难以有效捕获。因此,应用适当方法提取由深部地质体引起的弱磁信息是十分必要的。本文采用精度高且稳定的位场延拓技术将航磁异常向下延拓,可以稳定增强磁异常幅度,随着延拓面与场源之间距离的减小,浅成磁信号与深成磁信号的视深度差异将增大,在对数功率谱上可以将其区分,而后可利用匹配滤波方法将浅部信号剥离,从而得到深部弱信号,同时可计算深部弱信号的视深度。     

内蒙古阿巴嘎旗白音图嘎地区航磁在断裂构造解译中的应用

内蒙古阿巴嘎旗白音图嘎地区为浅覆盖区,地表构造形迹难以识别。笔者以最新的高精度航磁资料为依据,论述了区内深大断裂的磁场特征,并对航磁在断裂构造解疑中的应用进行了探讨。根据区内构造磁异常特征,在航磁△T化极垂向一次导数基础上,全区共解译断裂构造15条。构造方向主要为北东、北西方向,其中F1、F2、F3、F4、F7、F8、F9位于白音图嘎幅,岩性主要为宝力高庙组,为基岩出露区,脉岩比较发育,为花岗斑岩脉、正长斑岩脉,地表出露岩脉主要呈北西向,与航磁解译构造较为吻合,经向上延拓后构造不明显,显示底部为同一岩性基底;F5、F14、F15经向上延拓构造变得更加清晰,推断该构造由深部大的构造引起。     

综合物探方法在内蒙火区探测中的应用

煤层在自燃过程中,煤层上覆岩石受到高温烘烤,在磁性、导电性和温度等方面将发生显著的变化。为此,采用以磁法为主的综合物探方法,能从不同的角度提取火区特征信息,各种方法互相验证,可提高圈定火区范围的准确性和勘探效率。大量勘探实例表明,磁法是目前圈定火区范围的有效方法之一,用正磁异常划分火区有效可靠;火区范围存在高氡值异常;测温受火区深度的影响较大,明火和近地表火区反映明显。