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1.
Gravity and magnetotelluric investigations to elicit the origin of Hammam Faraun hot spring,Sinai Peninsula,Egypt 总被引：1，自引：0，他引：1
Mohamed Abdelzaher Jun Nishijima Gad El-Qady Essam Aboud Osama Masoud Mamdoh Soliman Sachio Ehara 《Acta Geophysica》2011,59(3):633-656
There is a clear correlation between the principal areas of current geothermal development and the seismically active boundaries
of the moving segments of lithosphere defined by the plate tectonic models of the Earth. The tectonic position of Egypt in
the northeastern corner of African continent suggests that the most important areas for geothermal exploration are in the
region where a cluster of hot springs with varied temperatures was located around the Gulf of Suez. Gravity and magnetotelluric
surveys were made in the area of Hammam Faraun hot spring, which represents the most promising area for geothermal development
in Egypt. These surveys were carried out for the purpose of eliciting the origin of Hammam Faraun hot spring. The results
of the analyses and interpretations of these data show that the heat source of the hot spring is due to uplift of hot basement
rock. This uplift may cause deep circulation and heating of the undergroundwater. 相似文献
2.
Gravity and magnetic data for the volcanic island of Ischia, Naples, Italy, have been analyzed and interpreted in light of recent geological and volcanological data to define a model of the island's shallow and deep structures. From the interpretation of the gravity data it appears that the shallow structures consist of pyroclastic material (p=2.0 g/cm3). Within these pyroclastics there are domes and lava flows of higher density and eruptive centres filled with lower density material. The basement is a “horst” with the shallowest depth at about 1.0 km, south of the centre of the island, if we assign a density contrast of 0.5 g/cm3 relative to the above pyroclastics.Interpretation of magnetic data measured at 725 stations showed that the basement derived from the gravity interpretation is magnetized. Moreover, this basement is less magnetized on the western side of Ischia which may be caused by the anomalous thermal state of the area, as indicated by surface fumaroles, hot springs etc. and temperature measurements in deep drillings. 相似文献
3.
Donald E. White 《Bulletin of Volcanology》1964,27(1):369-370
A well drilled for geothermal power near Salton Sea in Imperial Valley, Calif., is 5,232 feet deep; it is the deepest well in the world (1962) in a high-temperature hot spring area. In the lower half of the hole temperatures are too high to measure with available equipment, but are at loast 270°C, and may be as much as 370°C. For comparison, maximum temperature heretofore reported at depth (1962) for hot spring areas is 295°C. The well taps a very saline brine of Na-Ca-K-Cl type (about 185,000 ppm Cl) with exceptionally high potassium, and with the highest content of minor alkali elements known for natural waters; Fe, Mn, Zn, Pb, Cu, Ag, and some other metals are also exceptionally high. This brine may be connate, but present evidence favors a source in the magma chamber at depth that supplied late Quaternary rhyolite domes of the area. If the latter is correct, the brine is an undiluted magmatic water that is residual from the separation of a more volatile phase high in CO2, H2S, and with some alkali halides. Elsewhere, the hypothesized volatile phase may account for near-surface hot spring activity of most thermal areas of volcanic association. The residual brine of high salinity may ordinarily remain relatively deep in the volcanic systems because of high specific gravity and low content of volatiles, seldom appearing at the surface except in a greatly diluted form. The hot springs of Arima, Japan, may be a rare example of this type of magmatic water discharging at the surface in moderate concentration (Cl as much as 42,000 ppm). Independent evidence from fluid inclusions in minerals of high-temperature base-metal deposits also favors the existence of magmatic water high in Na, Ca, and Cl, and low in CO2 and other volatile components. During a three-month production test several tons of material precipitated in the horizontal discharge pipe from the well. Amorphous silica with iron and manganese, and bornite are the dominant recognized components. This material contains the astonishingly high contents of about 20 percent copper, 2 percent silver, and notable sulfur, arsenic, bismuth, lead, antimony, and some other minor elements. Total quantities of all elements in the original whole brine are not yet known, but calculated amounts corresponding to 1 to 3 ppm of copper and 0.1 to 0.3 ppm of silver were precipitated from the brine to form the pipe deposits. The brine, therefore, may be man’s first sample of an « active » ore solution. Equally fascinating to many geologists is the possibility that in the lower part of the hole temperatures are so high and pressures are sufficient for young sedimentary rocks to be undergoing transformation into rocks with mineral assemblages of the greenschist facies of metamorphism. Drill cores from 4,400 to 5,000 feet in depth contain chlorite, albite, K-feldspar, epidote, mica, and quartz, with some indication of increase in metamorphic grade downward. Regional geological and geophysical studies favor a depth of about 20,000 feet to pre-Tertiary basement rocks in the general area. A shallow basement or local upfaulting of old metamorphic rocks are not likely possibilities for the thermal area. 相似文献
4.
利用SiO_2地热温标计算了红河断裂带北段14个温泉水的热储温度,并结合当地地温梯度计算了温泉水的循环深度,同时统计分析了886～1987年间的地震频度和震源深度。作者从水对断裂及其围岩的弱化的角度讨论了温泉水深循环对断裂强度、断裂摩擦力和地震活动性的影响。结果表明,各亚段地震活动性差异与水对各亚段的弱化程度有关。认为温泉水循环深度最深的洱源亚段相当于“滑移区”,而温泉水循环深度较浅的剑川亚段和弥渡亚段及温泉稀少的大理亚段则相当于“闭锁区”,强震将孕育于温泉水循环深度较深的地区的两端 相似文献
5.
The Bouguer anomaly map of the Kalabsha and Seiyal areas was analysed on the basis of the available data about the depth to the basement from three boreholes. The density contrast between the basement complex and the Nubia formation was estimated from the gravity values and basement depths. Applying the estimated value of the density contrast, a residual map representing the basement effect and a basement relief map were constructed. The basement depth in Kalabsha and Seiyal areas range from 150 to 500 m below mean sea level. Comparing the general characteristics of the Bouguer anomaly of the Kalabsha and Seiyal areas with the clusters of earthquakes in the area since 1982 till present reveals a gravity low coinciding with a deep focal area. The gravity values increase toward a shallow focal area. 相似文献
6.
2020年6月26日新疆于田县发生MS6.4地震, 地震发生前后对震中80 km内的两个温泉在2019年9月至2020年10月的水文地球化学的变化特征进行了研究, 结果表明: ①温泉水的来源为其周围昆仑山的冰川融水, ②克孜勒沙衣温泉补给高程6 km, 水化学类型为Na-HCO3、 部分平衡水、 温泉循环深度达到1.7 km左右, 其主要气体组分为N2, 幔源氦占10.6%。 ③乌什开布隆温泉补给高程为3.1 km, Ca·Na-HCO3·SO4型, 未成熟水, 可能与浅层冷水发生了混合作用, 循环深度仅达到0.5 km, 该温泉的水化学组分对周围的地震活动有明显的异常响应, 伽师MS6.4地震前, 区域应力的不断加载使断裂带内裂隙发生明显变化, 从而温泉流体行为发生变化, 使乌什开布隆温泉的离子浓度小幅度上升, 且Cl-含量在于田MS6.4地震后16天突增。 因此, 对乌什开布隆温泉及克孜勒沙衣温泉的流体地球化学特征进行连续监测, 可以为未来阿尔金断裂及西昆仑断裂的交会区地震危险性提供有效判断指标。 相似文献
7.
利用水文地球化学数据建立温泉水文循环模型, 探讨温泉水文地球化学变化与地震的关系, 对中强地震短临流体异常判断具有重要的意义。 通过对石棉公益海温泉水常量元素、 微量元素和氢氧同位素以及锶同位素的测量, 探讨了该区域水文地球化学时空变化特征。 因此, 于2008年10月至2019年9月, 共对公益海温泉采集水样206个, 并对温泉水中离子组分和浓度, 温泉逸出气组分、 温泉气体同位素、 碳同位素和氢氧同位素含量进行测量。 分析结果表明: ① 公益海温泉主要为Na-HCO3·Cl型水, δD、 δ18O同位素测值分别为-14.19‰~-14.83‰和-108.67‰~-110.47‰, 分布于大气降水线附近, 说明温泉水主要源于大气降水; ② 据SiO2地温计计算热储温度约94.12℃, 循环深度约4.3 km, 表明大气降水入渗地下, 在热源加热后, 沿着断层和裂隙循环到地表, 形成温泉补给; 并且, 锶同位素和微量元素研究发现, 87Sr和86Sr主要来自硅酸盐类矿物, 微量元素含量较低, 水岩反应程度较弱; ③ 通过对研究区进行长时间连续观测发现, 在公益海周围300 km范围内的3个五级以上的地震使温泉水中常量元素的浓度, 分别出现了震前异常、 同震响应和震后效应。 推测这可能是因为公益海温泉位于公益海断裂和安宁河断裂的交会区, 推测周围的地震会触发公益海温泉水中的离子地球化学特征产生变化。 结合已有地质资料与公益海温泉水文地球化学数据, 建立公益海断裂带温泉水文循环模型, 这些对公益海断裂带周围未来中强地震短临流体异常判断具有重要的意义。 相似文献
8.
T. Vollmayr 《Journal of Geodynamics》1985,4(1-4)
The mean temperature gradient maps from surface down to top basement and down to base Tertiary correspond to the boundaries and internal features of the basin. The Landshut-Neuötting High in Eastern Bavaria is an area of relatively high temperature. The German Eastmolasse part west of this high shows extremely low temperature gradients. In the German Westmolasse area, in addition to a normal Tertiary gradient of about 25°C/km which is assumed to be the Tertiary paleogradient a steep near-surface gradient down to 500–800 m depth is deduced from the present interpretation of the measurements so that due to the southward increasing sediment thickness of the Tertiary in the flat northern margin of the basin there results a higher Tertiary mean gradient than in the south. The intramesozoic gradients are somewhat irregular, but generally tend to increase from north to south. Thus far they compensate to a certain degree the regional trend of the Tertiary gradients so that the mean gradients from surface down to top basement show smaller differences than the mean Tertiary gradients. A slight increase of the Mesozoic temperature gradients as compared with the Tertiary gradients is interpreted by both the lower heat conductivity of the consolidated and carbonate-rich Mesozoic and the northward directed water flow in the Malm karst transporting heat from the deeper southern part of the basin within the Malm karst northward at least since Pliocene time. 相似文献
9.
作为一种新型开发的绿色能源,地热资源被越来越多的人所重视.开采埋藏较深的地热资源风险大,因此开发前的地质和地球物理勘查是十分必要的.采用单一的地球物理方法勘探具有很大的风险,因此采用多种方法进行综合调查可以降低单一方法的风险,取得较好的效果.本文以狮子湖温泉为例,研究了地球物理方法在温泉勘探的应用.本次勘探采用可控源音频大地电磁法(CSAMT-Controlled Source Audio-frequency Magnetotellurics)和微重力测量,CSAMT是针对大地电磁测深法场源的随机性和信号微弱,提出的一种采用可以控制的人工场源改进方案.仪器采用美国Zonge公司生产的GDP-32Ⅱ.该方法由人工向地下供入音频谐变电流建立电磁场,通过仪器在地面接收从地下反馈来的信息,根据不同时代、岩性地层电性特征达到勘查目的.为此我们在测区做了两条剖面,从CSAMT反演图推断,自上而下可分为3个电阻率层,该剖面视电阻率具有很好的层理特征,反映了厚大的中新生代地层（Edn、K）覆盖.剖面西部有明显的泥盆系地层（D）存在.根据视电阻率的变化特点,可以推断这条剖面的5条断层.在剖面中部距地表400～800米深处存在一明显低阻区,推测应为含水破碎带或低阻泥岩.对数据进行二维反演,可以清楚的看到利于储水的盆地构造.CSAMT方法受静态效应影响很大.静态效应位移可能是由地形和电阻率的浅部的横向变化引起的,既是不可避免的,也是不可预测的.因此对数据进行预处理是十分必要的.减少静态效应的影响办法有以下三种：（1）、对效应进行理论计算;（2）、采用空间滤波和相位积分等处理方法;（3）、使用独立的、无静态效应的测量方法.计算静态效应理论值在理论上是简捷的,但在实际的野外条件下,由于无法预测引起静态效应的物体的几何尺寸和电性参数,因此这种方法无法得到可靠的校正值.空间滤波处理是目前广泛采用的一类方法,Bostick（1986）提出了消除MT数据中静态效应的电磁列阵剖面法（EMAP）.EMAP法由于采用连续的剖面测量,可采用窗口可变的自适应空间滤波器-汉宁窗（Hanning window）或叫余弦钟形滤波器消除静态效应.但是这种方法提供了静态效应的要求的数据密度,这就增大了大量的额外测量,提高了获得数据的代价.因此,我们做重力勘探与CSAMT相对比.微重力测量使用美国产LCR-D型重力仪.实测的微重力异常是地下由浅到深各类地质体的物性差异在地面综合叠加的效应,其中包括界面起伏、岩性不均匀、地壳与壳下物质的厚度变化等诸多地质因素在内.实测的重力异常值经过固体潮改正、零点漂移改正、布格改正、正常场改正之后,得到改正后的重力异常值.从微重力反演结果看来,自西往东重力异常逐渐减小,程台阶下降趋势,并趋于平缓,验证了CSAMT的异常结果.从而弥补了CSAMT法的不足.通过这两种方法,我们大致查明了新生代红层盆地的产出形态.该红层盆地西侧边缘位于青山小学一带,自西往东变深;并反演计算出新生代红层与晚古生代泥盆系地层的分界面.深部地球物理勘探的方法有很多,各有各自的优缺点,我们不能从单一的一种方法得到的结论来判断地下地质构造.CSAMT法勘探深度大,但由于本身的物理特性,导致静态效应、近场效应等影响甚大.严重影响我们对地下地质目标体深度的判断,重力和CSAMT法的相互验证,很好的说明了多种地球物理方法综合测定的优势. 相似文献
10.
Gravity data collected by the Geological Survey of Bangladesh are processed and interpreted for imaging of a sediment-basement interface over the northwestern part of Bangladesh. The observed gravity data are processed for discriminating gravitational fields contributed subtly from the shallow basement topographic feature with the twelve nodal piecewise cubic polynomial–based finite–element approach. In spectral analysis, the presence of a widely spread shallow basement feature has been detected and interpretation of gravity data using a two-dimensional gravity inversion technique indicates that its depth ranges from 0.041 km to 0.570 km relative to ground surface. In the northern part of the study area, the inferred basement configuration shows a general depression of the basement in the Takurgaon-Panchagar and Lalmonirhat districts and reaches a maximum depth of about 0.570 km. In the Nilphamari district and its southwestern part, the basement occurs at the most shallow depth due to its upliftment. However, the estimated sediment-basement interface depths are compared with the borehole and other geophysical interpretative information and are found to be consistent. 相似文献
11.
Gravity and magnetic studies have been carried out to map the different depth formations of alluvium, Gondwana, Vindhyan, Mahakoshal, and the crystalline basement in the Narmada–Son lineament (NSL) near the Sahdol–Katni area, India. Higher elevations in the northern part of the study area have lower gravity; the southern part of the study area, however, is moderately elevated and also has a higher gravity anomaly, which justifies the isostatic adjustment. This indicates the presence of high-density material, for example Mahakoshal rocks, in the upper crust which causes the higher anomaly value. The Mahakoshal rocks are widely exposed at Mau, Chanaura, Nadawar, Khamaria, Umria, and near the Tala–Barhi area and also extend from Sidhi to Agoni village further east of the area. The Mahakoshal rocks are thinner between the river Son and Tikwa village which causes a different gravity anomaly pattern changing from the NNE–SSW direction to the N–S direction. However, the trend of magnetic anomaly follows the same pattern toward the NNE–SSW direction, mainly because of the effect of the crystalline basement. Two magnetic highs are prominent in the Tikwa and Amarpur regions, 800 and 400 nTesla, respectively, because of the presence of the crystalline basement. The depth of the crystalline basement obtained by 2½ D gravity–magnetic modelling varies from 2.7 to 2.9 km. From spectral analysis the average depth of the crystalline basement varies from 2.83 to 3.05 km. The different crustal depth sections obtained by 2½ D simultaneous gravity–magnetic modelling correlate well with other constrained data. 相似文献
12.
Fraser E. Goff Charles O. Grigsby Pat E. Trujillo Jr. Dale Counce Andrea Kron 《Journal of Volcanology and Geothermal Research》1981,10(1-3)
Studies of the geology, geochemistry of thermal waters, and of one exploratory geothermal well show that two related hot spring systems discharge in Canõn de San Diego at Soda Dam (48°C) and Jemez Springs (72°C). The hot springs discharge from separate strands of the Jemez fault zone which trends northeastward towards the center of Valles Caldera. Exploration drilling to Precambrian basement beneath Jemez Springs encountered a hot aquifer (68°C) at the top of Paleozoic limestone of appropriate temperature and composition to be the local source of the fluids in the surface hot springs at Jemez Springs. Comparisons of the soluble elements Na, Li, Cl, and B, arguments based on isotopic evidence, and chemical geothermometry indicate that the hot spring fluids are derivatives of the deep geothermal fluid within Valles Caldera. No hot aquifer was discovered in or on top of Precambrian basement. It appears that low- to moderate-temperature geothermal reservoirs (< 100°C) of small volume are localized along the Jemez fault zone between Jemez Springs and the margin of Valles Caldera. 相似文献
13.
Neil C. Sturchio Stanley N. Williams Nestor P. Garcia Adela C. Londono 《Bulletin of Volcanology》1988,50(6):399-412
Hot springs and steam vents on the slopes of Nevado del Ruiz volcano provide evidence regarding the nature of hydrothermal activity within the summit and flanks of the volcano. At elevations below 3000 m, alkali-chloride water is discharged from two groups of boiling springs and several isolated warm springs on the western slope of Nevado del Ruiz. Chemical and isotopic geothermometers suggest that the boiling springs are fed by an aquifer having a subsurface equilibration temperature of at least 175°C, and the sampled warm spring is fed by an aquifer having a subsurface equilibration temperature near 150°C. Similarities in conservative solute ratios (e.g., B/Cl) indicate that the alkali-chloride waters may be related to a single reservoir at depth. Isotopic ratios of hydrogen and oxygen indicate that recharge for the alkali-chloride aquifers comes mostly from higher elevations on the volcano. Steam vents and steam-heated bicarbonate-sulfate springs at higher elevations, along a linear structural trend with the alkali-chloride springs, may be derived partly from the alkali-chloride water at depth by boiling. Steam from the vents (84°C) yields a gas geothermometer temperature of 209°C. Acid-sulfate-chloride and acid-sulfate waters are discharged widely from warm springs above 3000 m on the northern and eastern slopes of Nevado del Ruiz. Similarities in B/Cl and SO4/Cl ratios suggest that the acid waters are mixtures of water from an acid-sulfate-chloride reservoir with various proportions of shallow, dilute groundwater. The major source of sulfate, halogens, and acidity for the acid waters may be high-temperature magmatic gases. Available data on hot spring temperatures and compositions indicate that they have remained fairly stable since 1968. However, the eruption of November 13, 1985 apparently caused an increase in sulfate concentration in some of the acid springs that peaked about a year after the eruption. Long-term monitoring of hot spring compositions over many years will be required to better define the effects of volcanic activity on the Nevado del Ruiz hydrothermal system. 相似文献
14.
裂陷盆地基底的起伏表现为非光滑的几何形态,传统的重力反演结果并不能很好地反映这种特点.此外,大多数情况下,重力观测面并不位于盆地上界面,应为单独的起伏观测面,盆地应为上界面和基底组成的双界面模式.基于此,本文研究了起伏观测面上裂陷盆地基底双界面模式二维重力反演方法.研究中假设沉积盆地的沉积层与基底的密度差随深度按双曲线规律变化.将沉积盆地的沉积层剖分成相邻的垂直柱体,其水平尺寸是已知的,顶面与沉积层上界面重合,底面深度代表基底的深度,即为要反演的参数.反演中引入全变差函数作为盆地模型的约束,使得反演结果呈现非光滑形态,符合裂陷盆地基底特征.为减小反演多解性,引入已知深度点作为约束.建立由重力数据拟合、已知深度约束及全变差函数组成的目标函数,采用非线性共轭梯度算法使目标函数最小化.模型试算结果表明该方法可反演裂陷盆地基底起伏,并通过调整正则化参数的值可反演坳陷盆地基底起伏.将该反演方法用于珠江口盆地惠州凹陷和运城-临汾裂陷盆地实际资料处理,其结果较好地反映了裂陷盆地基底起伏特征,为研究盆地构造、油气勘探等提供重要参考. 相似文献
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16.
Bingqiang Yuan Lijun Song Li Han Shaole An Chunguan Zhang 《Geophysical Prospecting》2018,66(8):1586-1601
The Tobago Basin, which is located offshore northern Venezuela with a southern margin close to Trinidad and Tobago, has an area of approximately 59,600 km2. The Tobago Basin has relatively favourable hydrocarbon prospects, and to date, exploration work has mainly concentrated on small areas of the southwestern portion of the basin. To conduct a comprehensive study of the structural framework of the basin and the characteristics of the basement in order to identify prospective zones for hydrocarbon exploration, shipborne‐measured and satellite‐measured gravity data, shipborne‐measured magnetic data, and aeromagnetic survey data were analysed. A regularisation filtering method was used to separate and obtain regional and residual gravity and magnetic anomalies. Directional gradients of gravity and magnetic anomalies and the total horizontal gradient and vertical second derivative of gravity anomalies were employed to extract information about fault structures. Regression analysis methods were used to determine the basement depth. The geological significance of the gravity and magnetic fields was examined, the structural framework of the basin was assessed, the basement depth was estimated, and favourable hydrocarbon exploration prospects within the basin were identified. The results show that the Tobago Basin contains complex structures consisting mainly of two groups of faults trending in northeasterly and northwesterly directions and that the major northeasterly trending faults control the main structural configuration and depositional system within the basin. The basement of the Tobago Basin has deep rises and falls. It can be divided into the following four secondary tectonic units: the western sub‐basin, the central uplift area, the southern sub‐basin, and the northeastern sub‐basin. The central uplift area and northeastern sub‐basin are most likely to have developed hydrocarbon accumulations and should be targeted for further exploration. 相似文献
17.
A detailed gravity survey was carried out in one of the seismo-active areas at the northwestern region of the High Dam Lake (Kalabsha area) to study its subsurface structure. In order to understand the seismicity of the area, the establishment of a geodynamic model from geological and geodetic data is of great importance. After a series of adjustments and corrections of the measured gravity data, free-air and Bouguer anomaly maps were constructed for the Kalabsha area, and several interpretation techniques were applied to analyse these anomalies. The results of the analysis indicate that the Kalabsha area is affected by several faults trending mainly E-W and N-S. The active area located west of Gebel Marawa is bounded by a set of faults striking NE-SW, N-S and E-W. The throws of these faults range from 160 to 370 m.The minimum depth to the basement complex is about 200 m and its maximum depth is around 600 m. The thickness of the sedimentary column (Nubia sandstone) in the Kalabsha area decreases due west and increases toward the southern and eastern parts of the area. The results explain the tectonic framework of the area well. 相似文献
18.
G.B. Engelen 《Journal of Hydrology》1974,21(2):111-130
The Sasso Lungo group forms an isolated mountain mass in the Italian Dolomites in the SE Alps. The group has an area of ± 9 km2 and its elevation ranges from ± 2000–3000 m. The central part consists of an exhumed, dolomitized reef of Triassic age, which has subsided by gravity tectonics partly into the surrounding and underlying plastic Permian and Triassic formations. The hydrogeological characteristics of the formations are discussed. The central reef mass forms the main aquifer, and it is embedded in impervious formations. The discharge of the snowmelt water and rain takes mainly place through a few large springs around the group at some distance from the reef. The springs are hydraulically connected with low subterranean overflow points in the impervious rim of the reef through natural conduits of permeable moraines and Quaternary valley fills. The central lolomite aquifwe shows no signs of karst drainage. The water moves through a dense network of fractures and joints and it has probably a free, fluctuating water table, subdivided by groundwater divides which coincide in most cases with surface drainage divides. All springs and surface waters were mapped and sampled during the summer and fall periods from 1966 through 1968. The chemical composition of the spring waters was very useful in tracing the origin of the spring waters. 相似文献
19.
1982年9-12月,在漳州温泉区布设了台网进行微震观测。结果表明,在漳州及其以北的沙建温泉区一带均有微震与小震群活动,震级为Ms=-1～1级,震源为3-14km。用震源的分布、震源机制解和微震综合断层面解的结果,研究了地质断裂的现今活动性及其与温泉的关系。认为区内东西向与北东向断裂是控制温泉分布的主要构造,而北西向断裂则是温泉的涌水构造。经探明,在有浅层热储的漳州市以及地质断裂发育的沙建地区,地震波速与介质泊松系数均低于正常值。此外,台网尚观测记录到一些异常的振动现象。根据地震的综合信息,探讨了研究区微震活动与水热活动的关系。 相似文献
20.
A constrained 3D density model of the upper crust along a part of the Deccan Syneclise is carried out based on the complete Bouguer anomaly data. Spectral analysis of the complete Bouguer gravity anomaly map of the study region suggests two major sources: short wavelength anomalies (<100 km) caused primarily due to the density inhomogeneities at shallow crustal level and long wavelength anomalies (>100 km) produced due to the sources deeper than the upper crust. A residual map of the short wavelength anomalies is prepared from the complete Bouguer anomaly using Butterworth high‐pass filter (100 km cut‐off wavelength). Utilizing the constraints from deep resistivity sounding, magnetotellurics and deep seismic sounding studies, 2.5D density models have been generated along 39 profiles of this region. The mismatch between the calculated response of the a priori 2.5D model with the residual (short wavelength) gravity anomalies is minimized by introducing high‐density intrusive bodies (≥2.81 g/cm3) in the basement. With these 2.5D density models, the initial geometry of our 3D density model, which includes alluvium, Deccan trap, Mesozoic sediment and high‐density intrusive bodies in the basement up to a depth of 7 km (upper crust), is generated. In the final 3D model, Deccan trap extends from 200 m to nearly 1700 m below the 90–150 m thick Quaternary sediment. Further down, the sub‐trappean Mesozoic sediment is present at a depth range of 600–3000 m followed by the basement. The derived 3D density model also indicates six intrusive bodies of density 2.83 g/cm3 in the basement at an average depth of about 4–7 km that best fits the residual gravity anomaly of the study area. 相似文献