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1.
The residual aeromagnetic total field intensity anomalies in central Anatolia were calculated from the regional aeromagnetic anomalies surveyed by the Mineral Research and Exploration (MTA) of Turkey. The residual aeromagnetic data were analyzed to produce Curie point estimates by the method of OKUBO et al. (1985). The Curie point depth of central Anatolia varies from 7.9 km and 22.6 km. The shallowest Curie point depths were observed around the Cappadocia and Erciyes Volcanic complexes in central Anatolia. A good correlation was deduced between the Curie point depths and the heat-flow data measured previously, which is most certainly important for the geothermal resources of the region. The shallow Curie point depths also correlate well with the hot spring locations in central Anatolia. 相似文献
2.
—?The aeromagnetic data of Macedonia and Thrace were used to produce Curie point estimates. The data were high pass filtered to remove components arising from topography and magnetic core fields which were not adequately modeled by a DGRF. The depth to the centroid, z 0, of the deepest distribution of the magnetic dipoles was obtained by computing a least-squares fit to the lowest-frequency segment of the azimuthally averaged log power spectrum. The average depth to the top of the deepest crustal block was computed as the depth to the top, z t , of the second lowest-frequency segment of the spectrum. The depth to the bottom of the deepest magnetic dipoles, the inferred Curie point depth, was then calculated from z b =2z 0???z t . The Curie depth estimates for Macedonia and Thrace range between 11.2 and 17.3?km. These results are consistent with the depths inferred by extrapolating known geothermal gradient and heat-flow values. 相似文献
3.
—The aeromagnetic data of the island of Crete were inverted to produce Curie point estimates. The data were high-pass filtered to remove components arising from topography and magnetic core fields which were not adequately modeled by IGRF. The depth to the centroid, z 0?, of the deepest distribution of the magnetic dipoles, was obtained by computing a least-squares fit to the lowest-fre quency segment of the azimuthally averaged log power spectrum. The depth to the top of the deepest crustal block was computed as the depth, z t ?, to the centroid of the second deepest distribution, using the second lowest-frequency segment of the spectrum. The depth to the bottom of the deepest dipoles, the inferred Curie point depth, is then z b = 2z 0?z t ?. The Curie depth estimates range between 24 and 28 km. This is in accordance with the depths inferred by extrapolating heat-flow values measured in boreholes. 相似文献
4.
Ground total magnetic field data of Albania were used to produce estimates of the Curie point isotherm. The strategy followed
was to estimate the depth to the bottom of the deepest magnetic sources. Firstly, the average depth to the top of the deepest
crustal block, zt, was computed by linear fitting to the second lowest-frequency segment of the azimuthally averaged power spectrum of the
total magnetic field data. Then, the depth to the centroid of the deepest crustal block, z0, was computed by linear fitting to the lowest-frequency segment of the azimuthally averaged power spectrum of a distribution
of magnetic dipoles. Finally, the depth to the bottom, the inferred Curie point depth, zb, was calculated from zb=2z0−zt. Curie depth estimates for Albania vary from about 17 to 25.5 km (below sea level). These results are consistent with the
depths inferred by extrapolating geothermal gradient and heat-flow values, suggesting that the Curie point depth analysis
is useful to estimate the regional thermal structure. It also suggests that the approach was valid and that ground total magnetic
field data can be used for this purpose. 相似文献
5.
Özcan Bektaş Dhananjay Ravat Aydin Büyüksaraç Funda Bilim Abdullah Ateş 《Pure and Applied Geophysics》2007,164(5):975-998
East Anatolia is a region of high topography made up of a 2-km high plateau and Neogene and Quaternary volcanics overlying
the subduction-accretion complex formed by the process of collision. The aeromagnetic and gravity data surveyed by the Mineral
Research and Exploration (MTA) of Turkey have been used to interpret qualitatively the characteristics of the near-surface
geology of the region. The residual aeromagnetic data were low-pass filtered and analyzed to produce the estimates of magnetic
bottom using the centroid method and by forward modelling of spectra to evaluate the uncertainties in such estimates. The
magnetic bottom estimates can be indicative of temperatures in the crust because magnetic minerals lose their spontaneous
magnetization at the Curie temperature of the dominant magnetic minerals in the rocks and, thus, also are called Curie point
depths (CPDs). The Curie point depths over the region of Eastern Anatolia vary from 12.9 to 22.6 km. Depths computed from
forward modelling of spectra with 200–600 km window sizes suggest that the bottom depths from East Anatolia from the magnetic
data may have errors exceeding 5 km; however, most of the obtained depths appear to lie in the above range and indicate that
the lower crust is either demagnetized or non-magnetic. In the interpretation of the magnetic map, we also used reduction-to-pole
(RTP) and amplitude of total gradient of high-pass filtered anomalies, which reduced dipolar orientation effects of induced
aeromagnetic anomalies. However, the features of the RTP and the total gradient of the high-pass filtered aeromagnetic anomalies
are not highly correlated to the hot spring water locations. On the other hand, many high-amplitude features seen on the total
gradient map can be correlated with the ophiolitic rocks observed on the surface. This interpretation is supported by Bouguer
gravity data. In this paper, we recommend that the sources of the widespread thermal activity seen in East Anatolia must be
investigated individually by means of detailed mapping and modelling of high resolution geophysical data to assess further
the geothermal potential of the region. 相似文献
6.
The magnetic map of Slovakia used in the paper was compiled as part of a project titled Atlas of Geophysical maps and profiles in 2001. The residual magnetic data were analyzed to produce Curie point estimates. To remove distortion of magnetic anomalies
caused by the Earth’s magnetic field, reduction to pole transformation was applied to the magnetic anomalies using the magnetization
angle of the induced magnetization. Anomalies reduced to the pole tend to be better correlated with tectonic structures. We
applied a 3-km upward continuation to the residually compiled magnetic anomalies in order to remove effects of topography.
The depth of magnetic dipoles was calculated by an azimuthally averaged power spectrum method for the entire area. Such estimates
can be indicative of temperatures in the crust, since magnetic minerals lose their spontaneous magnetization according to
Curie temperature of the dominant magnetic minerals in the rocks. The computed Curie point depths in the Slovakia region vary
between 15.2 km and 20.9 km. Heat flow higher than 100 mWm−2 occurs at the central volcanics and eastern part of Slovakia, where the Curie point depths values are shallow. The correlation
between Curie point depths, heat flow and crust depth was investigated for two E-W cross sections. Heat flow and Curie point
depth values are correlated with each other however, these values could not be correlated with crust depth. The Curie point
isotherm, which separates magnetic and non-magnetic parts of the crust, is represented in two cross sections. 相似文献
7.
In this study, we aim to map the Curie point depth surface for the northern Red Sea rift region and its surroundings based on the spectral analysis of aeromagnetic data. Spectral analysis technique was used to estimate the boundaries (top and bottom) of the magnetized crust. The Curie point depth (CPD) estimates of the Red Sea rift from 112 overlapping blocks vary from 5 to 20 km. The depths obtained for the bottom of the magnetized crust are assumed to correspond to Curie point depths where the magnetic layer loses its magnetization. Intermediate to deep Curie point depth anomalies (10–16 km) were observed in southern and central Sinai and the Gulf of Suez (intermediate heat flow) due to the uplifted basement rocks. The shallowest CPD of 5 km (associated with very high heat flow, ~235 mW m?2) is located at/around the axial trough of the Red Sea rift region especially at Brothers Island and Conrad Deep due to its association with both the concentration of rifting to the axial depression and the magmatic activity, whereas, beneath the Gulf of Aqaba, three Curie point depth anomalies belonging to three major basins vary from 10 km in the north to about 14 km in the south (with a mean heat flow of about 85 mW m?2). Moreover, low CPD anomalies (high heat flow) were also observed beneath some localities in the northern part of the Gulf of Suez at Hammam Fraun, at Esna city along River Nile, at west Ras Gharib in the eastern desert and at Safaga along the western shore line of the Red Sea rift. These resulted from deviatoric tensional stresses developing in the lithosphere which contribute to its further extension and may be due to the opening of the Gulf of Suez and/or the Red Sea rift. Furthermore, low CPD (with high heat flow anomaly) was observed in the eastern border of the study area, beneath northern Arabia, due to the quasi-vertical low-velocity anomaly which extends into the lower mantle and may be related to volcanism in northern Arabia. Dense microearthquakes seem to occur in areas where the lateral gradients of the CPD are steep (e.g. entrance of the Gulf of Suez and Brothers Island in the Red Sea). These areas may correspond to the boundaries between high and low thermal regions of the crust. Thus, the variations in the microseismic activity may be closely related to thermal structures of the crust. Indeed, shallow cutoff depths of seismicity can also be found in some geothermal areas (e.g. western area of Safaga city along the Red Sea coastal region and at Esna city along the River Nile). These facts indicate that the changes in the thickness of the seismogenic layer strongly depend on temperature. Generally, the shallow Curie point depth indicates that some regions in our study area are promising regions for further geothermal exploration particularly in some localities along the River Nile, Red Sea and Gulf of Suez coastal regions. 相似文献
8.
Using aeromagnetic data acquired in the area from the Cerro Prieto geothermal field, we estimated the depth to the Curie point isotherm, interpreted as the base of the magnetic sources, following statistical spectral-based techniques. According to our results the Curie point isotherm is located at a depths ranging from 14 to 17 km. Our result is somewhat deeper than that obtained previously based only in 2-D and 3-D forward modeling of previous low-quality data. However, our results are supported by independent information comprising geothermal gradients, seismicity distribution in the crust, and gravity determined crustal thickness. Our results imply a high thermal gradient (ranging between 33 and 38 °C/km) and high heat flow (of about 100 mW/m2) for the study area. The thermal regime for the area is inferred to be similar to that from the Salton trough. 相似文献
10.
基于最新编制的1/100万全国航陆域磁异常图数据,采用功率谱法对中国陆域的居里点深度进行了估算,获得了8004个居里点深度,完成了中国陆域居里面深度图的编制,首次完整的展现了中国陆域的居里面起伏特征.研究表明,居里面在稳定地块表现为坳陷,埋深为28~45km,如塔里木盆地,准噶尔盆地,柴达木盆地,可可西里—巴颜喀拉坳陷区,扬子盆地区,华北盆地区,松辽盆地,二连盆地,巴彦浩特—武威—潮水盆地,珠江口—琼东南盆地等.华北盆地区的居里面深度与塔里木陆块和扬子陆块有较大的差异,相对偏浅,这可能与华北陆块遭受了复杂的后期改造,导致软流圈上隆和岩石圈减薄有关.可可西里—巴颜喀拉地块是青藏高原北部发育的呈NWW向展布的巨型居里面坳陷带,其原因是该地区发育大面积的三叠系沉积地层和较少的岩浆活动,这些稳定的地块都具有莫霍面隆起和居里面坳陷的特征.在活动频繁的造山带居里面以隆起为特征,埋深为18~26km,如东北部山岭区、西北部山岭区、秦岭—大别山地区、西昆仑—西藏—三江—康滇地区、东南沿海地区等.这反映了构造运动及岩浆活动所引起的地壳地温梯度的差异.根据我国816个大地热流数据,对比研究居里面深度与地温梯度和大地热流的关系,结果显示居里面深度与热流值并非线性关系,居里面深度大于30km时,热流值较低,均小于100mW·m~(-2);在居里面深度小于30km的地区,热流值变化范围较大.并且,随着热流值的升高,热流值有向中国东部沿海、藏南—三江地区、秦岭—大别地区、辽东等集中的趋势,这些地区都呈现出居里面隆起的特征,是地热资源勘探开发的重要远景区. 相似文献
11.
Pearlyn C. Manalo Carla B. Dimalanta Noelynna T. Ramos Decibel V. Faustino-Eslava Karlo L. Queaño Graciano P. YumulJr. 《Surveys in Geophysics》2016,37(3):557-578
Ground and aeromagnetic data are combined to characterize the onshore and offshore magnetic properties of the central Philippines, whose tectonic setting is complicated by opposing subduction zones, large-scale strike-slip faulting and arc–continent collision. The striking difference between the magnetic signatures of the islands with established continental affinity and those of the islands belonging to the island arc terrane is observed. Negative magnetic anomalies are registered over the continental terrane, while positive magnetic anomalies are observed over the Philippine Mobile Belt. Several linear features in the magnetic anomaly map coincide with the trace of the Philippine Fault and its splays. Power spectral analysis of the magnetic data reveals that the Curie depth across the central Philippines varies. The deepest point of the magnetic crust is beneath Mindoro Island at 32 km. The Curie surface shallows toward the east: the Curie surface is 21 km deep between the islands of Sibuyan and Masbate, and 18 km deep at the junction of Buruanga Peninsula and Panay Island. The shallowest Curie surface (18 km) coincides with the boundary of the arc–continent collision, signifying the obduction of mantle rocks over the continental basement. Comparison of the calculated Curie depth with recent crustal thickness models reveals the same eastwards thinning trend and range of depths. The coincidence of the magnetic boundary and the density boundary may support the existence of a compositional boundary that reflects the crust–mantle interface. 相似文献
12.
An attempt to define Curie point depths in Greece from aeromagnetic and heat flow data 总被引：1，自引：0，他引：1
G-Akis Tselentis 《Pure and Applied Geophysics》1991,136(1):87-101
The objective of this study is to understand the nature and extent of the regional geothermal system at depth beneath the area of Greece by constructing the Curie isotherms.Spectral analysis of aeromagnetic data in conjunction with heat flow information revealed an almost inverse linear relation between heat flow and Curie depths and was used to construct the Curie isotherms from the existing heat flow data.The results showed that Curie depths in the area range from about 20 km in western Greece, up to 1 km beneath the Hellenic volcanic arc. These results are consistent with the existing geothermal and geotectonic regime in the area. 相似文献
13.
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
14.
Crustal structure and the Moho depth are exceptionally well known beneath Europe. The first digital, high-resolution map of
the Moho depth for the whole European Plate was compiled in 2007 and recently published in Geophysical Journal International. In the past few years, considerable developments have taken place in the receiver function techniques. Different receiver
function techniques provide new, independent information, in particular on the S-wave velocity distribution in the crust and on the Moho depth. This gives an opportunity to compare the Moho depth from the
Moho depth map of the European Plate (H
MM) and the Moho depth from receiver function studies (H
RF). Herein, we also compile and analyze the uncertainty of the crustal thickness determinations data obtained with receiver
function analysis. The uncertainty is found to be ±2 km for 20-km-thick crust and about ±4 km for 60-km-thick crust. Comparison
of the Moho depths shows an approximately linear trend between H
RF and H
MM. For the Moho depth of 30–40 km, the values are approximately equal, while for thin crust, H
RF is about 5 km shallower than H
MM, and for thick crust, it is about 5 km deeper than H
MM. Possible reasons for this, the observed discrepancy between the Moho depths HMM and HRF, are discussed. 相似文献
15.
Investigation into regional thermal structure of the Thrace Region, NW Turkey, from aeromagnetic and borehole data 总被引：1，自引：0，他引：1
Z. Mümtaz Hisarli M. Nuri Dolmaz Mahmut Okyar Ali Etiz Naci Orbay 《Studia Geophysica et Geodaetica》2012,56(1):269-291
The aeromagnetic values over the study region are relatively uniform except for a few anomalies in the northeastern and southwestern
areas. Analyses of aeromagnetic data were performed in NW Turkey, in order to have a look into the subsurface regional thermal
structure of the region. For this purpose, power spectra, reduced to pole (RTP), and band-pass filtered anomalies were produced
using geophysical techniques. Band-pass filtered data were produced from the RTP aeromagnetic anomalies to isolate near surface
and undesired deep effects. Based on the aeromagnetic data interpretation, the thickness of the magnetized crust, named the
Curie Point Depth (CPD), in the study area lies between 9.7 and 20.3 km. The CPD estimates in the Thrace region of Turkey
indicate two shallow CPD (SCPD1 and SCPD2) zones (the Istranca Massif and the Saros Graben area). The deep CPD are located
within the Thrace Basin with sediment thickness of about 9 km. The corresponding heat flow map prepared from the averaged
thermal conductivities and thermal gradients from the CPD reveals the existence of one low heat flow zone (75 mW/m2) over the center of Thrace Basin, and two high heat flow zones over the Istranca Masif (100–125 mW/m2) in the northern side and Saros Graben (125–135 mW/m2) areas in the southern side of the Thrace Basin. 相似文献
16.
Abdullah Ates Funda Bilim Aydin Buyuksarac Attila Aydemir Ozcan Bektas Yasemin Aslan 《Surveys in Geophysics》2012,33(5):869-885
In this paper, aeromagnetic and gravity anomalies obtained from the General Directorate of Mineral Research and Exploration were subjected to upward continuation to 3?km from the ground surface to suppress shallow effects and to expose only regional, deep sources. Then, a reduction to pole (RTP) map of aeromagnetic anomalies was produced from the 3?km upward continued data. A sinuous boundary to the south of Turkey is observed in the RTP map that may indicate the suture zone between the Anatolides and African/Arabian Plates in the closure time of the Tethys Ocean. The sinuous boundary can be correlated with the recent palaeo-tectonic maps. The southern part of the sinuous boundary is quite different and less magnetic in comparison with the northern block. In addition, maxspots maps of the aeromagnetic and gravity anomalies were produced to find out and enhance the boundaries of tectonic units. Crustal thickness, recently calculated and mapped for the western Turkey, is also extended to the whole of Turkey, and the crustal thicknesses are correlated with the previous seismological findings and deep seismic sections. The average crustal thickness calculations using the gravity data are about 28?km along the coastal regions and increase up to 42?km through the Iranian border in the east of Turkey. Density and susceptibility values used as parameters for construction of two-dimensional (2D) gravity and magnetic models were compiled in a table from different localities of Turkey. 2D models indicate that all of the anomalous masses are located in the upper crust, and this could be well correlated with the earthquakes which occurred at shallow depths. 相似文献
17.
The distribution of the focal mechanisms of the shallow and intermediate depth (h>40 km) earthquakes of the Aegean and the surrounding area is discussed. The data consist of all events of the period 1963–1986 for the shallow, and 1961–1985 for the intermediate depth earthquakes, withM
s
5.5. For this purpose, all published fault plane solutions for each event have been collected, reproduced, carefully checked and if possible improved accordingly. The distribution of the focal mechanisms of the earthquakes in the Aegean declares the existence of thrust faulting following the coastline of southern Yugoslavia, Albania and western Greece extending up to the island of Cephalonia. This zone of compression is due to the collision between two continental lithospheres (Apulian-Eurasian). The subduction of the African lithosphere under the Aegean results in the occurrence of thrust faulting along the convex side of the Hellenic arc. These two zones of compression are connected via strike-slip faulting observed at the area of Cephalonia island. TheP axis along the convex side of the arc keeps approximately the same strike throughout the arc (210° NNE-SSW) and plunges with a mean angle of 24° to southwest. The broad mainland of Greece as well as western Turkey are dominated by normal faulting with theT axis striking almost NS (with a trend of 174° for Greece and 180° for western Turkey). The intermediate depth seismicity is distributed into two segments of the Benioff zone. In the shallower part of the Benioff zone, which is found directly beneath the inner slope of the sedimentary arc of the Hellenic arc, earthquakes with depths in the range 40–100 km are distributed. The dip angle of the Benioff zone in this area is found equal to 23°. This part of the Benioff zone is coupled with the seismic zone of shallow earthquakes along the arc and it is here that the greatest earthquakes have been observed (M
s
8.0). The deeper part (inner) of the Benioff zone, where the earthquakes with depths in the range 100–180 km are distributed, dips with a mean angle of 38° below the volcanic arc of southern Aegean. 相似文献
18.
Raj Kumar A.R. Bansal S.P. Anand V.K. Rao Upendra K. Singh 《Geophysical Prospecting》2018,66(1):226-239
The Central Indian region has a complex geology covering the Godavari Graben, the Bastar Craton (including the Chhattisgarh Basin), the Eastern Ghat Mobile Belt, the Mahanadi Graben and some part of the Deccan Trap, the northern Singhbhum Orogen and the eastern Dharwar Craton. The region is well covered by reconnaissance‐scale aeromagnetic data, analysed for the estimation of basement and shallow anomalous magnetic sources depth using scaling spectral method. The shallow magnetic anomalies are found to vary from 1 to 3 km, whereas magnetic basement depth values are found to vary from 2 to 7 km. The shallowest basement depth of 2 km corresponds to the Kanker granites, a part of the Bastar Craton, whereas the deepest basement depth of 7 km is for the Godavari Basin and the southeastern part of the Eastern Ghat Mobile Belt near the Parvatipuram Bobbili fault. The estimated basement depth values correlate well with the values found from earlier geophysical studies. The earlier geophysical studies are limited to few tectonic units, whereas our estimation provides detailed magnetic basement mapping in the region. The magnetic basement and shallow depth values in the region indicate complex tectonic, heterogeneity, and intrusive bodies at different depths, which can be attributed to different thermo‐tectonic processes since Precambrian. 相似文献
19.
20.
S. A. Kovachev I. P. Kuzin L. I. Lobkovskii 《Izvestiya Physics of the Solid Earth》2009,45(9):777-793
The results of detailed seismological observations with bottom seismographs in the Central Kurile segment in August-September,
2006 are discussed. The system of six bottom seismographs was placed on the island slope of the Kurile deep-sea trench southeast
of Urup Island and southwest of the Bussol Strait. Over 230 earthquakes with M
LH = 0.5–5.5 were registered in the area with a radius of 150 km around the center of the observation system at depths up to
300 km during 16 days. Records of 80 earthquakes with hypocenters in the earth crust (h = 0–30 km) beneath the island slope of the Kurile deep-sea trench were first obtained by bottom seismographs. These data
are inconsistent with previous concepts of aseismicity of this zone. The discovery of the unique morphological structure of
the Benioff zone beneath the central Kurile Arc represents the most important result of detailed seismological observations.
The zone consists of an inner seismoactive subzone, which is located beneath the island slope of the arc at depths of 15–210
km, being characterized by an angle of incline of 50° under the latter and crosses the ocean bottom approximately 80 km away
from the trench axis, and outer low-activity subzone. The latter is traceable beyond the trench almost parallel to the inner
zone beginning from a depth of 50 km below the sea bottom up to a depth of approximately 300 km. Due to the slightly lower
incline (∼45°) of the outer subzone, both subzones gradually converge downward. The integral thickness of the Benioff zone
varies from 150 km in its upper part to 125 km at depths of 210–260 km. The medium sandwiched between these subzones is practically
aseismic. The reality of this defined structure is confirmed by the distribution of aftershocks of the earthquake that occurred
on November 15, 2006 (M = 8.3). These seismic events served as foreshocks for the subsequent strong earthquake of January 13, 2007 (M = 8.1) with the hypocenter located beyond the trench under the ocean bottom. Such a structure of this zone within the central
Kurile Arc segment is unique, having no analogues either in the flanks of the Kurile-Kamchatka Arc or other arcs. The results
of detailed seismological observations obtained two months before the first of the catastrophic Central Kurile earthquakes
appeared to be typical for the period of foreshocks (the lower seismic activity of the Simushir block, which hosted the hypocenter
of the earthquake that occurred on November 15, 2006, particularly at depths of 0–50 km, the gentler incline of the recurrence
plot, and other features). 相似文献