curie surface of borborema province brazil abstract the curie surface interpreted from magnetic data through spatial frequency domain techniques is used to provide information on the thermal structure of borborema province the borborema province is part of the neoproterozoic collision of an orogenic system situated between the sao francisco congo and sao luis west africa cratons which formed the gondwana supercontinent the curie surface of borborema province varies from 18 to 59 km which reveals the complexity in the crustal composition of the study area the thermal structure shows different crustal blocks separated by the main shear zones which corroborates the evolution model of allochthonous terranes the curie surface signature for the west portion of pernambuco shear zone may indicate processes of mantle serpentinization once the curie isotherm is deeper than mohorovic discontinuity in this region the amplitude of bouguer anomaly decreases which corroborates long wavelength anomaly observed in the magnetic anomaly we interpreted this pattern as evidence of the brasiliano pan africano s subduction collision event earthquakes in the region are concentrated mainly in shallow curie surface regions less resistant crust and in transition zones between warm and cold blocks we calculated the horizontal gradient of the curie depth to emphasize the signature of contact between the thermal blocks these regions mark possible crustal discontinuities and have high correlation with orogenic gold occurrence in the study area

curie point depth beneath the barramiya red sea coast area estimated from spectral analysis of aeromagnetic data abstract the geothermal regime beneath the barramiya red sea coast area of the central eastern desert of egypt has been determined by using the curie point depth which is temperature dependent this study is based on the analysis of aeromagnetic data the depth to the tops and centroid of the magnetic anomalies are calculated by power spectrum method for the whole area the result of this investigation indicates two new maps of the curie point depth cpd and the surface heat flow q maps of the study area the coastal regions are characterized by high heat flow 83 6 mw m2 due to the geothermic nature of the region and shallow curie depth 22 5 km where cpd depends on the tectonic regime and morphology in the eastern part of the area the western portion of the studied area has a lower heat flow

curie isotherm depth from aeromagnetic data constraining shallow heat source depths in the central aeolian ridge southern tyrrhenian sea italy the salina lipari and vulcano volcanic ridge and the surrounding sea sectors aeolian archipelago southern tyrrhenian sea italy are characterized by vents responsible for a recent 40 ka 1889 1890 ad effusive and explosive subareal activity and repeated 56 to 7 ka in age submarine explosive eruptions from source areas located between lipari and vulcano a spectral depth estimation of the magnetic bottom using a fractal method on aeromagnetic data from vulcano lipari and salina volcanic ridge allows us to constrain the curie isotherm depth the elevated portion of the isotherm is between 2 and 3 km below salina and vulcano and about 1 km below lipari the curie depth results in the context of other geological and geophysical evidence suggest that the rise of the curie isotherm is mainly due to the occurrence of shallow heat sources such as magma ponds and associated hydrothermal systems the short wavelength magnetic anomaly field reflects magnetic contrasts from highly magnetized volcanic bodies low magnetization sediments and hydrothermally altered rocks borehole temperature data verify the curie temperature derived from the magnetic methods on the island of vulcano we conclude that the whole vulcano lipari and salina volcanic ridge is active and should be monitored

thermal structure beneath kuju volcano central kyushu japan abstract thermal conditions beneath kuju volcano central kyushu japan are simulated in two manners simulation of the regional high heat flow around kuju volcano shows that the underlying magma reservoir is not molten but maintains high temperatures of 400 700 c simulation of the thermal processes beneath the solfatara field in the central part of kuju volcano suggests that the geothermal reservoir is a two phase reservoir heated by magmatic steam

thermal structure of the crust in inner east anatolia from aeromagnetic and gravity data abstract inner east anatolia has many hot spring outcomes in this study the relationship between the thermal structure and hot spring outcomes is investigated the residual aeromagnetic and gravity anomalies of the inner east anatolia surveyed by the mineral research and exploration mta of turkey show complexities the magnetic data were analyzed to produce curie point depth estimates the depth of magnetic dipole was calculated by azimuthally averaged power spectrum method for the whole area the curie point depth cpd map covering the inner east anatolia has been produced the curie point depths of the region between sivas and malatya vary from 16 5 to 18 7 km values of heat flow were calculated according to continental geotherm from the model the heat flow values vary between 89 and 99 mw m 2 heat flow values are incorporated with surface heat flow values gravity anomalies were modeled by means of a three dimensional method the deepest part of the basin 12 14 km determined from the 3d model are located below the settlement of hafik and to the south of zara towns two dimensional cross sections produced from the basin depths curie values and moho depths based on the analysis of magnetic gravity anomalies thermal structures and geology it seems likely that the hot springs are not related to rising asthenosphere in the regions of shallow cpds 16 5 km and mostly hot springs are related to faulting systems in inner east anatolia

estimation of curie point temperature and geothermal structure of island arcs of japan abstract curie depth analysis from aeromagnetic data was performed in a nationwide project to assess the geothermal resources of japan creation of a curie depth map of japan was completed in 1984 and it agrees well with thermal structures such as the high temperature gradient regions of volcanic chains low temperature regions of the forearc basins and the intermediate temperature regions of the backarc basins measured temperature gradient t data were gathered in order to estimate the curie temperature from the t and the curie depths when t is assumed to be constant with respect to depth a remarkable difference is found in the estimated curie temperature t e c of the backarc and forearc side of the basins in the backarc side an average t e c of 450 c is reasonable for both the curie depth estimated from aeromagnetic data average depth of about 10 km in the backarc side and the temperature gradients average gradient of 4 5 c 100 m the average t e c on the forearc side was found to be low at about 300 c the difference in the curie temperatures between the two areas may be due to a regional difference in rock type e g granite as opposed to basalt in the case of the northeast japan arc as suggested by some authors the isotherms may suddenly fall between the volcanic front and the trench based on model studies we recognized that a curie depth map obtained by the algorithm we developed should include an averaging effect this suggests that the inferred curie depth curve across the line marking the sudden fall in the curie isotherm should gradually increase towards the trench therefore the low curie temperature that we estimated may indicate an apparent shallow curie depth caused by the averaging effect against an area bearing deep curie depths hence the reasons for the inconsistency of the estimated curie temperature between the forearc side and backarc side may be as follows 1 the averaging effect of the curie depth estimate which makes the curie depth apparently shallower in the forearc side and 2 the lower curie temperature of basaltic rocks which are assumed to be distributed along the east side of the aseismic front

curie point depths in northeast china and their geothermal implications for the songliao basin abstract this work integrates processing and interpretation of the combined geomagnetic anomaly model of ngdc 720 v3 1 to better constrain thermal structures of the northeast china lithosphere which shows intensive extension and active volcanism during the mesozoic and cenozoic numerical tests demonstrate that magnetic anomalies calculated at 20 km altitude can be used for accurate curie depth estimation averaged curie depths using a 3d fractal exponent of 3 0 vary from 13 2 0 to 33 4 1 km with a mean of 22 2 4 km in northeast china with temperature dependent thermal conductivity models constrained by incorporated surface heat flow and curie depths in different geological blocks the thermal lithospheric thicknesses are estimated mostly between 45 and 90 km based on 1d steady state thermal conduction equation beneath the songliao basin the moho temperatures are abnormally high ranging from ca 700 to 1000 c and the mantle contributes about 65 of the total surface heat flow the shallow curie points and thermal lithosphere asthenosphere boundary together with high moho temperatures and mantle heat flow support abnormally high geotherms in the songliao basin originated from hot upper mantle upwelling triggered likely by lithospheric delamination

melting features along the ryukyu slab tear beneath the southwestern okinawa trough 1 the present day active volcanic front associated with the ryukyu subduction zone extends from japan to the ilan plain northern taiwan and is located within the okinawa trough 80 100 km above the ryukyu slab an abnormal amount of arc volcanism which consists of basalt andesite and rhyolite occurs within the southwestern okinawa trough above a slab tear of the ryukyu subduction zone cbvt the power spectrum analysis of magnetic data shows the occurrence of a thin crust above the slab tear and a thick crust beneath this volcanic area we suggest that an excess of h2o rich fluid might occur at the slab tear and might increase the melt flux both are conveyed obliquely to the uppermost mantle and lower crust cbvt magmas after interactions basaltic magmas would rise up accounting for the contrast of magnetization between this volcanic body and the adjacent ot crust

lateral variation of crustal properties from aerogeophysical data in northern brazil abstracta new method is proposed for the study of crustal azimuthal anisotropy and the lateral variation of other crustal aerogeophysical parameters using a quantitative approach the processing of a large newly acquired high resolution set of aerogeophysical data is considered using the existing radon transform and the geostatistical analysis approaches the data set includes an area of the guyana shield in northern brazil which was not included in previous surveys the area is covered by dense rain forest vegetation and thick soil layers parameterization was performed considering the possible anisotropic character of the geophysical 2d data application of the newly proposed geostatistical data processing yielded high resolution images of the lateral variation of quantitative geophysical parameters which indicate good correlation with previously determined seismic anisotropy in the area average anisotropy as measured by the radon transform and variogram analysis is scale dependent at scales gr

curie point depths of bulgarian territory inferred from geomagnetic observations and its correlation with regional thermal structure and seismicity abstract the basal depth of the magnetic layer curie point depths of bulgarian territory was calculated using geomagnetic field observation and the variations of this border were mapped for the first time the adopted computational method transforms the spatial data into the frequency domain and provides a relationship between radially averaged power spectrum of the magnetic anomalies and the depths to the magnetic sources the magnetic layer bottom thus obtained has normal 28 32 km values in the moesian platform and central part of bulgaria which are the relatively most stable regions of the investigated territory in the moesian platform cpd and moho are very close but the magnetic layer s bottom is still marked as a thermal boundary in the southern part calculated depths gradually reach the minimal values of the derived curie isotherm up to 14 16 km with relatively high gradient according to the results from geothermal modeling and paleomagnetic investigations magnetic layer s bottom of the bulgarian territory corresponds to different curie temperatures they vary from 400 425 c in the regions of rila rhodope unit up to 550 600 c in the moesian platform west and east balkan unit the obtained results comprise useful information concerning regional estimates of the correlation between different geophysical and geological characteristics of the earth s crust of the bulgarian territory

a new contribution to the geology of the egyptian red sea shelf using geophysical data abstract the study examines the egyptian red sea shelf and throws more light on the structural set up and tectonics controlling the general framework of the area and nature of the crust herein an integrated study using gravity and magnetic data with the available seismic reflection lines and wells information was carried out along the offshore area the bouguer and reduced to pole aeromagnetic maps were processed and reinterpreted in terms of rifting and plate tectonics the qualitative interpretation shows that the offshore area is characterized by positive gravity everywhere that extremely increases towards the centre of the graben supporting the presence of an intrusive zone below the axial main trough the gravity data were confirmed by the presence of high magnetic amplitudes magnetic linearity and several dipoles concentrated along the rift axis for at least 250 km the lineament analysis indicates widespread of the erythrean red sea trend that was offset cut by transform faults in the ne direction aqaba the tectonic model suggests the presence of one tensional n65 e and two compressional n15 w n30 w phases of tectonism resulted in six cycles of deformations classified into three left lateral n35 e n15 e and n s and three right lateral n85 w n45 w and n60 w the basement relief map reveals a rough basement surface that varies in depth between 1 and 5 6 km it outlines several offshore basins separated from each other by ridges the models show that the basement consists of tilted fault blocks which vary greatly in depth and composition and slopes generally to the west they indicate that the coastal plain is underlain by acidic basement blocks continental crust with no igneous activity while suggesting elevated basic materials oceanic crust below the rift axis the study suggests that northern red sea forms an early stage of seafloor spreading or at least moved past the late stage of continental rifting

thermal investigation in the cappadocia region central anatolia turkey analyzing curie point depth geothermal gradient and heat flow maps from the aeromagnetic data in this study curie point depth cpd heat flow geothermal gradient and radiogenic heat production maps of the cappadocian region in central anatolia are presented to reveal the thermal structure from the aeromagnetic data the large circular pattern in these maps matches with previously determined shallow 2 km in average depression estimated cpds in this depression filled with loose volcano clastics and ignimbrite sheets of continental neogene units vary from 7 to 12 km while the geothermal gradient increases from 50 to 68 c km heat flows were calculated using two different conductivity coefficients of 2 3 and 2 7 wm 1 k 1 the radiogenic heat production was also obtained between 0 45 and 0 70 w m 3 in this area heat flow maps were compared with the previous regional heat flow map of turkey and significant differences were observed in contrast to linear heat flow increment through the northeast in the previous map in the literature produced maps in this study include a large caldera like circular depression between nevsehir aksaray nigde and yesilhisar cities indicating high geothermal gradient and higher heat flow values in addition active deformation is evident with young magmatism in the neogene and quaternary times and a large volcanic cover on the surface boundaries of volcanic eruption centers and buried large intrusions are surrounded with the maxspots of the horizontal gradients of magnetic anomalies analytic signal as map pointing out exact locations of causative bodies is also presented in this study circular region in the combined map of as and maxspots apparently indicates a possible caldera

an attenuating structure beneath the aso caldera determined from the propagation of seismic waves the attenuation of amplitude is seen in seismic waves which pass through the central region of the aso caldera in kyushu japan it is also recognized from spectral analysis of seismic waves that the higher frequencies of the p wave are reduced in the waves which pass through the central region of the caldera it is shown that the relative attenuation increases remarkably for the frequency range of 5 to 10 hz the specific attenuation factor q of the p wave train is about 100 from the surface projection of the ray paths with low q values through the aso caldera to each station the attenuating region is located beneath the center of the caldera extending to the north of the central cones in conjunction with the low q value of the p wave and the decreases of s wave amplitudes the relative p wave residual times have comparatively large values for seismic waves passing through the central region beneath the caldera in order to attempt to provide additional information on the depth configuration of the attenuating material the ray paths of p wave s first arrivals are located in three dimensional space it indicates that the low velocity material is located beneath the center of the caldera at depths of about 6 to 9 km however lowvelocity anomalies above the depth of 6 km and below the depth of 15 km were not able to be detected because most of the available seismic ray paths had crossed the caldera at depths of about 6 to 15 km furthermore the relative residual times have numerous errors resulting from incorrect hypocenter locations origin times inhomogeneities in the structure and uncertainty of the velocity structure at shallow depths in the aso caldera refraction or reflection studies are required for an accurate estimate of the structure and more detailed properties of the attenuating material

curie depth map for sinai peninsula egypt deduced from the analysis of magnetic data abstract sinai peninsula is considered as a unique region in the world due to its geographical location tectonic and thermal activities it is located geographically at the crossroads of europe asia and africa constituting a triple junction point between the three continents it is also characterized by thermal manifestations represented by several hot springs with varied temperatures 30 70 c most of these hot springs are located along the shoreline of the gulf of suez in this study we aim to map the curie depth isotherm surface for sinai peninsula based on the analysis of ground magnetic data spectral analysis technique will be used to estimate the boundaries top and bottom of the magnetized crust the depths obtained for the bottom of magnetized crust are assumed to correspond to curie point depths where the magnetic layer loss its magnetization results of this study indicate that the shallow curie depths 15 18 km are located at the southern part of sinai peninsula and along the shoreline of the gulf of suez and depths increase 22 25 km towards the central and north western portions of sinai peninsula the whole average curie depth point of sinai peninsula is about 20 km generally the shallow depths to curie isotherm indicate that sinai peninsula is a promising area for further geothermal exploration particularly near the eastern side of the gulf of suez

normal mode sensitivity to earth s d layer and topography on the core mantle boundary what we can and cannot see the core mantle boundary cmb is earth s most profound internal boundary separating the liquid iron outer core and the solid silicate mantle the detailed structure near the cmb has a major influence on mantle convection and the evolution of the core seismic observations such as topography on the cmb thin ultra low velocity zones ulvzs seismic anisotropy and the anticorrelation between shear wave and bulk sound velocity heterogeneities have mainly been made using body waves and are still poorly constrained we investigate the sensitivity of earth s free oscillations to these features and specifically show how large individual anomalies must be for them to be observable in addition we discuss the possible trade offs between these different lowermost mantle structures although modes have strong sensitivity to all the structures inserted the results illustrate the limits of what normal modes can resolve our tests show that i even small scale features such as ulvzs with a thickness larger than 19 km can be observed as long as their distribution contains a long wavelength component ii the peak to peak amplitude of cmb topography has a larger influence than its pattern and has to be smaller than 5 km to fit the data iii the effect of scaling between shear wave velocity and density anomalies is less constrained but a laterally varying pattern is implied by a simple test suggesting the presence of chemical variations iv a strong trade off exists between anisotropy in compressional wave velocity and incidence angle whereas shear wave anisotropy is less observable these findings provide valuable information for future normal mode studies on structures in earth s lowermost mantle and their trade offs

interpretation of magnetic anomalies and estimation of depth of magnetic crust in slovakia 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

three dimensional p wave velocity structure in the upper crust beneath kuju volcano central kyushu japan kuju volcano lies near aso caldera at the center of kyushu island western japan after a few hundred years of dormancy a phreatic explosion accompanied by a small ash eruption occurred on 11 october 1995 this study was undertaken to determine the subsurface seismic velocity structure associated with the active magmatic regime in the kuju volcanic region the three dimensional upper crustal p wave velocity structure beneath kuju volcano was determined using methods for the simultaneous inversion of p wave arrival times from local earthquakes in and around the kuju volcanic region for velocities and hypocentral parameters results reveal two shallower low velocity anomalies located in the northern and southern parts of kuju volcano consistent with the presence of significant negative bouguer gravity anomalies in addition a high velocity anomaly is located approximately 5 km northwest of mt kuju one of the domes in kuju volcano beneath this high velocity anomaly a low velocity anomaly is present this velocity structure suggests a magmatic regime that has a lid consisting of cooled solid material overlying a chamber of partially molten material

time scales of tectonic landscapes and their sediment routing systems abstract in regions undergoing active tectonics the coupling between the tectonic displacement field the overlying landscape and the redistribution of mass at the earth9s surface in the form of sediment routing systems is particularly marked and variable coupling between deformation and surface processes takes place at a range of scales from the whole orogen to individual extensional fault blocks or contractional anticlines at the large scale the attainment of a steady state between the overlying topography and the prevailing tectonic conditions in active contractional orogens requires an efficient erosional system with a time scale dependent on the vigour of the erosional system generally in the range 10 6 10 7 years the catchment fan systems associated with extensional fault blocks and basins of the western usa are valuable natural examples to study the coupling between tectonic deformation landscape and sediment routing systems even relatively simple coupled systems such as an extensional fault block and its associated basin margin fans have a range of time scales in response to a tectonic perturbation these response times originate from the development of uniform steady state relief during the accumulation of displacement on a normal fault c 10 6 years the upstream propagation of a bedrock knickpoint in transverse catchments following a change in tectonic uplift rate c 10 6 years or the relaxation times of the integrated catchment fan system in response to changes in climatic and tectonic boundary conditions 10 5 10 6 years the presence of extensive bedrock or alluvial piedmonts increases response times significantly the sediment efflux of a mountain catchment is a boundary condition for far field fluvial transport but the fluvial system is much more than a simple transmitter of the sediment supply signal to a neighbouring depocentre fluvial systems appear to act as buffers to incoming sediment supply signals with a diffusive time scale c 10 5 10 6 years dependent on the length of the system and the extent of its floodplains stream channels and proximal gravel fans the vocabulary for explaining landscapes would benefit from a greater recognition of the importance of the repeat time and magnitude of perturbations in relation to the response and relaxation times of the landscape and its sediment routing systems landscapes are best differentiated as buffered or reactive depending on the ratio of the response time to the repeat time of the perturbation furthermore landscapes may be regarded as steady or transient depending on the ratio of the response time to the time elapsed since the most recent change in boundary conditions the response of tectonically and climatically perturbed landscapes has profound implications for the interpretation of stratigraphic architecture

apparent magnetization intensity map on sakurajima volcano kyushu japan inferred from low altitude high density helicopter borne aeromagnetic surveys abstract in november 2005 we conducted the first low altitude high density helicopter borne aeromagnetic survey over sakurajima volcano kyushu japan to provide a baseline for subsequent measurement of changes in magnetic anomalies related to volcanic processes because previously acquired aeromagnetic data cannot resolve small scale geological feature although the observation error was considered to be 5 0 a m were located on the lava around an ei craters and on the northeastern flank of kita dake 2 the lowermost values of apparent magnetization

depth to curie temperature across the central red sea from magnetic data using the de fractal method abstract the central red sea rift is considered to be an embryonic ocean it is characterised by high heat flow with more than 90 of the heat flow measurements exceeding the world mean and high values extending to the coasts providing good prospects for geothermal energy resources in this study we aim to map the depth to the curie isotherm 580 c in the central red sea based on magnetic data a modified spectral analysis technique the de fractal spectral depth method is developed and used to estimate the top and bottom boundaries of the magnetised layer we use a mathematical relationship between the observed power spectrum due to fractal magnetisation and an equivalent random magnetisation power spectrum the de fractal approach removes the effect of fractal magnetisation from the observed power spectrum and estimates the parameters of depth to top and depth to bottom of the magnetised layer using iterative forward modelling of the power spectrum we applied the de fractal approach to 12 windows of magnetic data along a profile across the central red sea from onshore sudan to onshore saudi arabia the results indicate variable magnetic bottom depths ranging from 8 4 km in the rift axis to about 18 9 km in the marginal areas comparison of these depths with published moho depths based on seismic refraction constrained 3d inversion of gravity data showed that the magnetic bottom in the rift area corresponds closely to the moho whereas in the margins it is considerably shallower than the moho forward modelling of heat flow data suggests that depth to the curie isotherm in the centre of the rift is also close to the moho depth thus curie isotherm depths estimated from magnetic data may well be imaging the depth to the curie temperature along the whole profile geotherms constrained by the interpreted curie isotherm depths have subsequently been calculated at three points across the rift indicating the variation in the likely temperature profile with depth

probing magnetic bottom and crustal temperature variations along the red sea margin of egypt abstract over 50 magnetic bottom depths derived from spectra of magnetic anomalies in eastern egypt along the red sea margin show variable magnetic bottoms ranging from 10 to 34 km the deep magnetic bottoms correspond more closely to the moho depth in the region and not the depth of 580 c which lies significantly deeper on the steady state geotherms these results support the idea of wasilewski and coworkers that the moho is a magnetic boundary in continental regions reduced to pole magnetic highs correspond to areas of younger granites that were emplaced toward the end of the precambrian other crystalline precambrian units formed earlier during the closure of ocean basins are not strongly magnetic in the north magnetic bottoms are shallow 10 15 km in regions with a high proportion of these younger granites in the south the shoaling of the magnetic bottom associated with the younger granites appears to be restricted to the aswan and ras banas regions complexity in the variation of magnetic bottom depths may arise due to a combination of factors i regions of younger precambrian granites with high magnetite content in the upper crust leaving behind low curie temperature titanomagnetite components in the middle and lower crust ii rise in the depth of 580 c isotherm where the crust may have been heated due to initiation of intense magmatism at the time of the red sea rifting 20 ma and iii the contrast of the above two factors with respect to the neighboring regions where the moho and or curie temperature truncates lithospheric ferromagnetism estimates of fractal and centroid magnetic bottoms in the oceanic regions of the red sea are significantly below the moho in places suggesting that oceanic uppermost mantle may be serpentinized to the depth of 15 30 km in those regions

geophysical investigation of the geothermal potential under the largest volcanic cover in anatolia kars plateau ne turkey in this study curie point depth cpd geothermal gradient radiogenic heat production and heat flow maps were constructed based on different thermal conductivity coefficients using magnetic anomaly data for the kars plateau which has the largest volcanic cover in turkey the bottom depths of the magnetic crust in the research area were revealed by the cpd map for the first time in this investigation there are two apparent magnetic anomaly trends in the study area the first is the horasan senkaya sarikamis selim arpacay trend in the ne sw direction and the other is the hanak ardahan arpacay trend in the nw se direction two other prominent elongations extend into the ardahan gole senkaya and kars digor axes all these trends represent mountain chains and or stratovolcanoes in the region and no anomalies are observed around the non volcanic outcrops curie depths are shallow up to 14 km between horasan and kagizman towns and 12 km in the northwestern part of the study area gradient values can reach 50 c km 1 in the northwestern sector together with the high heat flows represented by the 150 wm 1 k 1 contours the deepest cpd region lies between gole and susuz towns where the geothermal gradient decreases to 27 c km 1 heat flows decrease 60 wm 1 k 1 in the same area an apparent gap around the kars plateau was observed in previous regional heat flow maps of turkey by other authors who used the bottom hole temperatures of boreholes and hot springs temperatures this gap has been accurately filled from the results of this study and geothermal exploration areas and the geothermal potential of the kars plateau have thus been determined for future exploration activity on the basis of the tectonic elements and earthquake data

crustal magmatism and lithospheric geothermal state of western north america and their implications for a magnetic mantle abstract the western north american lithosphere experienced extensive magmatism and large scale crustal deformation due to the interactions between the farallon and north american plates to further understand such subduction related dynamic processes we characterize crustal structure magmatism and lithospheric thermal state of western north america based on various data processing and interpretation of gravimetric magnetic and surface heat flow data a fractal exponent of 2 5 for the 3d magnetization model is used in the curie point depth inversion curie depths are mostly small to the north of the yellowstone snake river plain hotspot track including the steens mountain and mcdermitt caldera that are the incipient eruption locations of the columbia river basalts and yellowstone hotspot track to the south of the yellowstone hotspot track larger curie depths are found in the great basin the distinct curie depths across the yellowstone snake river plain hotspot track can be attributed to subduction related magmatism induced by edge flow around fractured slabs curie depths confirm that the great valley ophiolite is underlain by the sierra nevada batholith which can extend further west to the california coast range the curie depths thermal lithospheric thickness and surface heat flow together define the western edge of the north american craton near the roberts mountains thrust rmt to the east of the rmt large curie depths large thermal lithospheric thickness and low thermal gradient are found from the differences between curie point and moho depth we argue that the uppermost mantle in the oceanic region is serpentinized the low temperature gradients beneath the eastern great basin montana and wyoming permit magnetic uppermost mantle either by serpentinization metasomatism or in situ magnetization which can contribute to long wavelength and low amplitude magnetic anomalies and thereby large curie point depths

high density crustal intrusive bodies beneath shillong plateau and indo burmese range of northeast india revealed by gravity modeling and earthquake data abstract modeling and analysis of gravity and earthquake data of a critically dynamic northeastern region of india assumes a special significance for understanding the seismicity and geodynamics in this paper the relation between lateral heterogeneity of gravity interfaces with subsurface structures and seismic characteristics of northeast india are studied in detail to understand the seismicity and dynamics of the region using bouguer gravity earthquake and magnetotelluric data the modern scaled power spectral analysis of gravity data has brought out crustal lateral heterogeneity at a depth of 8 33 km 19 73 km and 37 14 km that correlate well with 10 km upper crust 20 km lower crust and a moho at 28 42 km revealed by 1d seismic crustal velocity and tomography studies the inferred crustal depths support thinner crust over uplifted shillong plateau and gradual increase of depths over subduction interface of indo burmese range 2d gravity modeling constrained by seismic velocity model and 3d euler deconvolution technique along two specific e w and three n s regional gravity transects delineated three significant high density anomalous heterogeneous intrusive bodies presumably due to underplating beneath shillong plateau mikir massif and indo burmese range based on the seismicity and stress pattern analysis through seismic b value variation we infer that the study region exhibits compressive stress concentrations in the form of brittle deformation at shallow depths and weakening of lower crust by high density intrusive mafic ultramafic bodies of ductile nature which may cause intense seismicity besides the ongoing collision of north drifting indian plate with eurasia to the north and the eastern subduction interface of indo burmese range we also infer that the ne to nw trending v shaped areas outlined north of shillong plateau south of mikir massif and ne sw trending thrust belt of schuppen exhibit aseismic nature and may be the future impounding seismic sources in this region

effects of the karacadag volcanic complex on the thermal structure and geothermal potential of southeast anatolia the karacadag volcanic complex kvc is the largest volcanic unit in se turkey it is also defined as a shield volcano on the northernmost part of the arabian plate the main goal of this study is to investigate the geothermal potential of this region associated with the magnetic signature of this volcanic complex and surrounding area besides this primary objective the possibility of there being volcanic intrusion into the buried fault zones under the volcanic cover are also investigated to determine the interrelations between the active tectonics and heat flow in the area a spectral analysis method is applied to the magnetic anomalies of the volcanic rocks to identify the curie point depth cpd and geothermal gradient as well as to estimate heat flow and radiogenic heat production of radioactive minerals in the complex a tilt angle map is also presented in correlation with instrumentally recorded earthquake magnitudes to indicate tectonic trends that are consistent with the maps of the thermal parameters in this study in contrast with expectations for the kvc area the region around akcakale and suruc grabens is the most prolific zone for geothermal potential despite them not showing strong magnetic anomalies curie point depths are shallow down to 18 km around the akcakale graben and deeper down to 22 km around the bitlis zagros suture zone where the geothermal gradients increase from 26 to 32 c km 1 through the graben area heat flows in this zone are in the range from 75 to 90 mw m 2 depending on the thermal conductivity coefficient 2 3 2 5 2 7 and 3 0 w m 1 k 1 used radiogenic heat production values also indicate slightly changing spectra in the range 0 19 to 0 25 w m 3 none of these parameters are focused around mt karacadag however the earthquake epicenters generally m 4 are aligned with the boundary faults of the akcakale graben where the cpd geothermal gradient and heat flow maps indicate relatively high potential we thus suggest that this graben area would be good for future geothermal exploration on the contrary considering the low geothermal gradient and heat flow values mt karacadag can be accepted as being an extinct volcano despite its apparent high magnetic anomalies

curie point depth geothermal gradient and heat flow estimation and geothermal anomaly exploration from integrated analysis of aeromagnetic and gravity data on the sabalan area nw iran prospecting the geothermal resources in northwest of iran conducted in 1975 revealed several promising areas and introduced the sabalan geothermal field as a priority for further studies the sabalan mt representing the sabalan geothermal field is a large stratovolcano which consists of an extensive central edifice built on a probable tectonic horst of underlying intrusive and effusive volcanic rocks in this study curie point depth cpd geothermal gradient and heat flow map were constituted from spectral analysis of the aeromagnetic data for the nw of iran the top of the geothermal resource i e the thickness of the overburden was evaluated by applying the euler deconvolution method on the residual gravity data the thickness of the geothermal resource was calculated by subtracting the euler depths obtained from the cpds in the geothermal anomalous region the geothermal anomalous region was defined by the heat flow value greater than 150 mw m2 cpds in the investigated area are found between 8 8 km in the sabalan geothermal field and 14 1 in the northeast the results showed that the geothermal gradient is higher than 62 c km and the heat flow is higher than 152 mw m2 for the geothermal manifestation region the thickness of the geothermal resource was also estimated to vary between 5 4 and 9 1 km these results are consistent with the drilling and other geological information findings indicate that the cdps agree with earthquake distribution and the type of thermal spring is related to the depth of the top of the geothermal resource

curie point depth investigation of central anatolia turkey 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

mantle flow induced crustal thinning in the area between the easternmost part of the anatolian plate and the arabian foreland e turkey deduced from the geological and geophysical data abstract eastern anatolia consisting of an amalgamation of fragments of oceanic and continental lithosphere is a current active intercontinental contractional zone that is still being squeezed and shortened between the arabian and eurasian plates this collisional and contractional zone is being accompanied by the tectonic escape of most of the anatolian plate to the west by major strike slip faulting on the right lateral north anatolian transform fault zone natfz and left lateral east anatolian transform fault zone eatfz which meet at karliova forming an east pointing cusp the present day crust in the area between the easternmost part of the anatolian plate and the arabian foreland gets thinner from north ca 44 km to south ca 36 km relative to its eastern eahp and western sides central anatolian region this thinner crustal area is characterized by shallow cpd 12 16 km very low pn velocities

curie point depths of the island of kyushu and surrounding areas japan as part of a comprehensive nationwide evaluation of geothermal resources for japan the first of the curie point depth maps covering the island of kyushu has been prepared the map was created by inverting gridded regional aeromagnetic data two satisfactory algorithms were developed to invert the gridded data based upon a distribution of point dipoles the first algorithm estimates x0 y0 and z0 the coordinates of the centroid of the distribution by computing a least squares fit to the radial frequency of the fourier transform the second algorithm estimates centroid depth only by computing a least squares fit to the squared amplitude of the frequency estimates the average depth to the top zt of the collection of point dipoles was estimated by a variation of the second algorithm the depth to the bottom of the dipoles inferred curie point depth is zb 2z0 zt the depth estimates are hand contoured to produce the final map the curie point depth map is then compared to regional geology and heat

thermal structure of the panama basin by analysis of seismic attenuation abstract using recordings of earthquakes on oceanic bottom seismographs and onshore stations on the coastal margins of colombia panama and ecuador we estimate attenuation parameters in the upper lithosphere of the panama basin the tomographic images of the derived coda q values are correlated with estimates of curie point depth and measured and theoretical heat flow our study reveals three tectonic domains where magmatic hydrothermal activity or lateral variations of the lithologic composition in the upper lithosphere can account for the modeled thermal structure and the anelasticity we find that the costa rica ridge and the panama fracture zone are significant tectonic features probably related to thermal anomalies detected in the study area we interpret a large and deep intrinsic attenuation anomaly as related to the heat source at the costa rica ridge and show how interactions with regional fault systems cause contrasting attenuation anomalies

geothermal resources in egypt integrated with gis based analysis abstract the energy of egypt is generally derived from petroleum products however advancements in the development of the generation capacity using sustainable and renewable resources for example solar wind and geothermal resources and investment in nuclear power plants are planned the geology and structure setting of egypt affirms that reasonable geothermal resources are available particularly along the gulf of suez the red sea the western desert and parts of the nile valley the main objective of this research is to develop a geothermal favourability map of egypt which may be considered as a screening tool for the assessment of optimal areas for geothermal development digital data layers and maps were employed in a gis model to select the most promising areas for geothermal potentiality the arcgis model includes six thematic layers distance to faults bouguer anomaly distance to seismic activity curie depth heat flow and temperatures at different depths the validation of the generated geothermal favourability map was performed by a comparison with thermal water wells and hot springs generally the most encouraging zones for geothermal probability in egypt are located near the shorelines of the gulf of suez and the red sea

subsurface structural features of the basement complex and geothermal resources using aeromagnetic data in the bahariya oasis western desert egypt egypt gives priority to western desert in land reclamation and sustainable development projects the bahariya oasis a northernmost oasis of egypt is closer to the capital compared to other remote oases and represents the most interesting potential candidates for the sustainable development many researches provide insight into the hydrogeology and structural geology of the bahariya oasis however very few attempts have been done to investigate its geothermal potentiality the aim of present study is to reflect the geothermal resources of the bahariya oasis encountered with the predominant structures utilizing aeromagnetic and borehole data the main subsurface structures and the depth to basement map were retrieved from the 2d modelling of the aeromagnetic data the results of the 2d models were verified by well stratigraphic data spectral analysis of the aeromagnetic data was applied to estimate the curie point depth cpd and to produce geothermal gradient and heat flow maps for the bahariya oasis the results of the study indicated that the depth to the basement rocks in the area ranges from 0 6 to 4 0 km the cpd is 15 km in the central parts and increases to 24 km eastward the geothermal gradient varies from 20 to 35 c km with an average 30 c km however the heat flow changes from 60 to 100 m w m2 with an average of 90 m w m2 these results in addition to basement structures imply a high temperature gradient and heat flow correlating with shallow curie depths the results are in agreement with previous work in the same region

curie point depth estimates from aeromagnetic data from death valley and surrounding regions california aeromagnetic data were analyzed to determine the curie point depth cpd by power density spectral and three dimensional inversion methods within and surrounding death valley in southern california we calculated the cpd for 0 5 regions using 2d power density spectral methods and found that the cpds varied between 8 and 17 km however the 0 5 region may average areas that include shallow and deep cpds and because of this limitation we used the 3d inversion method to determine if this method may provide better resolution of the cpds the final 3d model indicates that the depth to the bottom of the magnetic susceptible bodies varies between 5 and 23 km even though both methods produced roughly similar results the 3d inversion method produced a higher lateral resolution of the cpds the shallowest cpds occur within the central and southern death valley panamint valley coso geothermal field and the tecopa hot springs region deeper 15 km cpds occur over outcropping granitic and precambrian lithologies in the panamint range grapevine mountains black mountains and the argus range the shallowest cpd occurs within the central death valley over a possible seismically imaged magma body and slightly deeper values occur within the panamint valley southern death valley and tecopa hot springs the shallow cpd values suggest that partially molten material may also be found in these latter regions the cpd computed heat flow values for the region suggest that the entire area has high heat flow values 100 mw m 2 on the other hand locally extremely high values 200 mw m 2 occur within the panamint valley the southern and central death valley and tecopa hot springs region these locally high heat flow values may be related to midcrustal magma bodies but additional geophysical experiments are needed to determine if the magma bodies exist

a study of spectral methods of estimating the depth to the bottom of magnetic sources from near surface magnetic anomaly data summary based on a critical evaluation of several different spectral magnetic depth determination techniques on areally large synthetic layered and random magnetization models we recommend the following considerations in the usage of the methods as necessary prerequisites to successful bottom depth determinations 1 using windows with sufficient width to ascertain that the response of the deepest magnetic layer is captured and by verifying the spectra and computing the depth estimates with the largest possible windows 300 500 km 2 avoiding filtering to remove arbitrary regional fields accomplished by compiling magnetic anomalies derived from modern spherical harmonic degree 13 earth s main field models e g recent international geomagnetic reference field models igrf or comprehensive models cm 3 ascertaining the near circularity of the autocorrelation function to avoid analysing biased spectra containing strong anomaly trends and 4 avoid determining the slopes from the exponential low wavenumber part of the spectra in the cases of layered magnetization we also describe the details of the new spectral peak forward modelling method and discuss the conditions under which the method can lead to useful results we found that despite all these precautions in some cases the results can still be erroneous and therefore we recommend a critical evaluation of the results by modelling heat flow and taking into account seismic information on the crustal and lithospheric thicknesses and seismic velocities wherever possible in the southcentral us east of the rockies where the surface heat flow ranges between 40 and 65 mw m 2 w e obtained the magnetic bottom depth of 40 10 km using the approach of the forward modelling of the spectral peak this range is similar to the seismically derived crustal thickness of 45 50 km suggesting therefore that the entire crust may be magnetic in this region because of the uncertainties in the various heat flow contributing parameters such as the variations in thermal conductivity radiogenic heat and hydraulic regime we could not constrain the lithospheric thickness beyond an estimate ranging approximately from 100 to 200 km

subduction control on the curie isotherm around the pacific north america plate boundary in northwestern mexico gulf of california preliminary results abstract spectral analysis of namag magnetic data enabled us to estimate depths to the curie isotherm along the pacific north america plate boundary the estimated depths for the gulf of california and southern baja california peninsula correlate quite well with the depths to the moho available from previous studies based on receiver function and seismic refraction in northernmost baja california and southwestern usa no correlation is observed between depths to the curie isotherm and depths to the mantle obtained from receiver function analysis depths to the curie isotherm are shallower along the coastal plains of sonora and sinaloa differences between receiver function based mantle depths and curie depths are equally large however there is more consistency with depths established by seismic refraction studies four zones with shallow curie isotherm are identified in southern gulf of california gs1 gs2 gs3 and gs4 gs1 is located at the gulf of california mouth the alarcon rise is located between gs1 and gs2 pescaderos basin is located northwest of gs2 gs3 stretches from the carmen basin to the farallon basin gs4 extends from tiburon island up to northern guaymas basin northernmost shallow curie depth zone gn1 comprises upper and lower delfin basins as well as the consag and wagner basins a northern prolongation also covers pinacate volcanic center the southern shallow curie isotherm zones are associated with lithospheric asthenospheric material upwelling zones gn1 also includes a convective component related to the younger magmatism of the pinacate volcanic field deeper curie depths are found at southern baja california peninsula interpreted as associated with thicker continental or stretched crust it is possible that the crust is underlain or underplated by magnetic oceanic crust as suggested by satellite magnetic anomalies centered at the magdalena shelf a contrasting pattern features northern baja california deep curie zones to the west contrasting with relative shallower curie isotherm areas to the east the prolongation towards the peninsula of the extinct shirley transform fracture zone roughly separates the two domains observed along the peninsula and suggests that the curie isotherm along the peninsula is controlled by differences subduction of the guadalupe and magdalena microplates major differences pointed out between northern and southern gulf of california might indicate that subduction also played a key role at the beginning of the opening of the gulf of california however currently the curie pattern is controlled by the rifting processes shallow curie zones correlating quite well with the rift basins and the lithosphere asthenosphere upwelling material

an attempt to define curie point depths in greece from aeromagnetic and heat flow data 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

investigations into the tectonic lineaments and thermal structure of kutahya denizli region western anatolia from using aeromagnetic gravity and seismological data abstract residual aeromagnetic map of western anatolia displays intense anomalies especially in the nw of the region curie point depth cpd map obtained from the residual aeromagnetic anomalies is indicative of larger area of shallow curie levels than previously defined two important shallow depth regions located at between kutahya and denizli are determined from cpd and thermal gradient tg map the intense aeromagnetic anomalies are located in the west of kutahya along the e w direction these anomalies are resulted from the metamorphic units of menderes massif the analytic signal as map produced from residual aeromagnetic data shows the e w trending geological bodies causing magnetic anomalies which become intense in the west and south of kutahya it is also observed from the as map that thermal structures or bodies are buried under the non magnetic surface geology the maxspot map derived from the location of the horizontal gradient of aeromagnetic anomalies can be well correlated with not only tectonic lineaments but also the distribution of earthquake data bouguer anomalies of the region can also be well correlated with the graben system and thus provide supportive information about the geothermal energy potential of the study area

analysis of the relation between bottom hole temperature data and curie temperature depth to calculate geothermal gradient and heat flow in coahuila mexico abstract estimations of the curie temperature depth using aeromagnetic data are commonly employed to study the thermal structure of the crust in this research we estimated the curie temperature depth with the de fractal method and calculated the geothermal gradient and the heat flow of 24 blocks uniformly distributed in the mexican state of coahuila the reliability of the de fractal method was evaluated by comparing the geothermal gradient results with the bottom hole temperature data available from petroleum boreholes the maps show that the regional faulting is associated with recent volcanism characterized by shallow curie temperature depth 17 km furthermore changes of the fractal parameter have a relationship to the tectonic history of this region and the geology of each analyzed block the results of our statistical analyses showed that the geothermal gradient estimated with the de fractal method is more closely related to the bottom hole temperature data than the estimations obtained with the centroid method additionally the similarity between bottom hole temperature and curie temperature depth calculated geothermal gradient indicated that conduction is the predominant heat transfer mechanism

determination of tectonic and crustal structure of the eastern pontide orogenic belt ne turkey using gravity and magnetic data the eastern pontide orogenic belt is one of the most complex geodynamic settings within the alpine belt subduction polarity which is responsible for the formation of the eastern pontide magmatic arc is still under debate because of limited geological geophysical and geochemical data this orogenic belt is mainly divided into three subzones depending on lithological characteristics and facies changes as in northern southern and axial zones from north to south these zones are separated from each other by near vertical faults that display the block faulting tectonic style of this belt in this study the tectonic and crustal structure of the eastern pontides which as yet have not been prospected by using geophysical data has been investigated with potential field data the horizontal gradient map obtained from gravity data shows a number of steep and gentle lineaments it seems that these lineaments e w ne and nw trending correspond to major structural zones of continental crust additionally the moho depth and curie point depth variation maps of the eastern pontide orogenic belt have been computed with the power spectral method of the radial wavenumber carried out by using the fast fourier transform method as a result of this method we estimated that the depths of the moho and curie point varied between 29 0 1 2 47 2 1 9 km and 14 3 0 7 27 9 1 4 km respectively our findings indicate that the moho depth generally increases from north to south in the region however the curie point depth level within the crust has an undulating surface not a horizontal one

a discussion of structural and thermal control of magnetic anomalies on the mid norwegian margin we discuss the correlation between the depth extent of magnetic sources the curie temperature depth and crustal structures on the mid norwegian margin spectral methods can be used to estimate the depth extent of magnetic sources even if the bottom is located in the lower crust however only with limited resolution the bottom of the magnetic surfaces is often regarded to represent the depth to the curie isotherm however comparison with a 3d model based on the interpretation of potential field and seismic reflection data and thermal modelling shows that the depth extent of the magnetic sources is merely controlled by the overall geometry of the crystalline crust and not the temperature distribution the observed changes in the magnetic field between the inner and outer part of the mid norwegian margin appears not to reflect as previously assumed the depth to the curie temperature but the geometry of the basement and lower crust our 3d model of the mid norwegian margin reveals a basement configuration that involves a basement with different petrophysical properties which can be connected with lithological basement units of onshore norway

curie point depth in the sw caribbean using the radially averaged spectra of magnetic anomalies abstract we have estimated the curie point depth cpd using the average radial power spectrum in a tectonically complex area located in the sw caribbean basin data analyzed came from the world digital magnetic anomaly map and three methods have been used to compare results and evaluate uncertainties centroid spectral peak and forward modeling results show a match along the three methods suggesting that the cpd values in the area ranging between 6 km and 50 km the results share the following characteristics a high values 30 km are in continental regions b there is a trend of maximum cpd values along the sw ne direction starting from the central cordillera in colombia to the maracaibo lake in venezuela c there is a maximum cpd at the sierra nevada de santa marta colombia as well as between costa rica nicaragua and nicaragua honduras borders the lowest cpd values

geothermal energy reconnaissance of southeastern nigeria from analysis of aeromagnetic and gravity data given the daunting energy challenges currently bedeviling nigeria with demand for electrical power exceeding availability alternative energy sources preferentially renewable are vigorously considered this is the first study to examine geothermal energy prospects in southeastern nigeria with the ultimate aim of locating and mapping regions of shallow curie point depths cpds crustal thickness and geologic structures supportive of a geothermal system we estimated cpd using the spectral analysis technique on magnetic field anomalies gravity anomalies were subjected to a series of procedures to assess geological structures result reveals deeper cpds within central and southern regions of okposi afikpo and biase towns in an approximate range of 18 4 to 19 3 km shallow cpds 9 8 17 4 km have also been obtained within obubra and abakaliki regions estimated crustal thickness moho ranges between 26 5 and 35 8 km part of the region with shallow cpd correlates with regions of shallow moho depths particularly in abakaliki and deeper moho depths coincide with deeper cpd estimates at the afikpo location the estimated geothermal gradient and heat flow values range between 29 0 and 45 0 oc and 52 2 101 5 mw m2 respectively and fall within values evaluated from deep wells drilled for oil exploration within the adjoining anambra basin region this study recommends the regions with shallow depths for possible geothermal power plant location gravity data evaluations also reveal significant subsurface intrusions within ugbodo obubra and abakaliki locations overall this study is a step forward toward a better evaluation of the geothermal energy resources potential of southeastern nigeria

depths to the magnetic layer bottom in the south china sea area and their tectonic implications p the depths to the magnetic layer bottom z b in the south china sea scs area are estimated by computing radially averaged amplitude spectra of total field magnetic anomalies we test different sizes of moving windows in which the spectra are calculated to better understand how window sizes affect the depth estimations apart from lowering the resolutions of estimated z b larger windows do not necessarily incur presumable increases in z b in the scs area although the centroid method is taken as our primary technique for estimating z b for cross check the spectral peak and the non linear inversion methods are also applied to those windows where spectral peaks do appear in a single window we may find discrepancy in z b estimated from different techniques but for all windows showing spectral peaks the estimated z b from one technique are grossly correlated with those from another our results show that most parts of the central scs ocean basin and the northern continent ocean transition cot zone have significantly smaller z b than the surrounding continental blocks in the surrounding continental regions z b are averaged at about 34 km a depth close to the moho depth the average z b is about 22 km in the central basin but this value is much larger than the moho depth signifying that the uppermost 10 km or so of the mantle beneath the central basin is also magnetized the strong faulting and recent magmatism within the cot zone can account for the small z b near the northern continental margin the estimated z b are also found very correlative to surface heat flow this observation verifies dominant contributions to surface heat flow from incoming mantle heat flow due to thermal conduction the positive correlations observed among z b from different techniques as well as the good correlation between surface heat flow and z b support the reasoning that our estimated z b are within an acceptable range of accuracy

curie point depth map of turkey summary a curie point isotherm map of the whole of turkey has been prepared from aeromagnetic data by means of a spectral analysis technique the most characteristic signature of this map is that the shallow depths generally correlated with the young volcanic rocks and the thinned crustal thicknesses in the west reveal geothermal fields and several hot springs the orogenic pontide belt of the black sea region in the north the western taurus belt in the south and some high plateaus in eastern turkey show that the deepest curie isotherm depths range between 20 and 29 km depth contour lines elongating in an almost e w direction are due to the overlapping percentage of adjacent data blocks of 50 per cent in the e w direction and to magnetic anomalies trending in the e w direction curie isotherm depths are in the range 6 to 10 km in the aegean region and are characterized by e w and ne sw trending graben structures as expected since the region has crustal thinning and many hot springs and geothermal fields these imply the existence of shallow heat sources that could be utilized for electricity heating of towns and cities greenhouse and health purposes

magsat data and curie depth below deccan flood basalts india ground and airborne magnetic data are severely disturbed due to random susceptibility variations in deccan flood basalts however magnetic satellite magsat data over the deccan flood basaltic region of the indian subcontinent exhibit filtering of surficial noise three passes over deccan traps show a low at about 20 n latitude and a high at about 23 n latitude spectral analysis of these passes and an available 2 d magsat vertical intensity map indicate a deep 40 4 km magnetic interface it is interesting to note that the determination of curie depth from magsat matches and confirms the geothermal data model the estimates correspond to the moho depth derived from gravity and deep seismic sounding studies the study suggests a continental shield like geothermal gradient of about 14 c km below the area

evaluation of curie point depths geothermal gradients and near surface heat flow from high resolution aeromagnetic hram data of the entire sokoto basin nigeria abstract an evaluation of curie point depths geothermal gradients and near surface heat flow has been carried out from the spectral analysis of the recently acquired high resolution aeromagnetic hram data of the entire sokoto basin in northwestern nigeria the hram data was divided into twenty two 22 overlapping blocks and each block analyzed using the spectral centroid method to obtain depth to the top centroid and bottom of magnetic sources the depth values were subsequently used to evaluate the curie point depth cpd geothermal gradient and near surface heat flow in the study area the result shows that the cpd varies between 11 13 and 27 83 km with an average of 18 57 km the geothermal gradient varies between 20 84 and 52 11 c km with an average of 33 99 c km and the resulting heat flow varies between 52 11 and 130 28 mw m 2 with an average of 84 97 mw m 2 such heat flow values are suggestive of anomalous geothermal conditions and are recommended for detailed geothermal exploration in the basin

aeromagnetic study of the island of hawaii an aeromagnetic study of the island of hawaii provides new insight on magnetic properties of subsurface rock and geologic structure on a regional scale spectral depth analysis delineates two shallow magnetic zones each roughly 1 5 km thick lying at a depth of 1 km one zone of unknown origin lies in the center of the island and correlates with a regional magnetic high the other zone coincides with pronounced magnetic lows paralleling kilauea s active east rift zone these magnetic lows probably depict rocks chemically altered by hydrothermal fluids in which titanomagnetite has been destroyed analysis of magnetic terrain effects indicates that magnetization also decreases with depth within mauna kea and mauna loa we estimate that magnetization is reduced by about half at a depth of 1 km the magnetic method is particularly useful in delineating the lateral extent of local shield structures such as rifts summit calderas pit craters and vent fissures rifts possess characteristic magnetic patterns primarily long wavelength linear magnetic low zones we propose alteration processes reduce magnetizations along the flanks of rifts on the other hand along young rifts e g kilauea s east rift zone short wavelength magnetic anomalies probably reflect slowly cooled unaltered intrusions altered rock may also produce magnetic lows that help define buried summit calderas

curie point depth from spectral analysis of magnetic data in central southern europe abstract the basal depth of the outer layer with internal magnetic sources was calculated from magnetic data available within a roughly 500 km wide and 1200 km long area running from central germany to southern italy the dataset deriving from different aeromagnetic surveys is reduced to the reference altitude of 3000 m a s l and a reference year of 1980 0 the adopted method which transforms the spatial data into the frequency domain provides a relationship between the two dimensional spectrum of the magnetic anomalies and the top and centroid depths of the magnetic sources the magnetic layer bottom depth mlbd thus obtained is 29 33 km deep in the stable areas central europe variscan units corsica sardinia variscan block and corresponds to the moho having an average temperature of 560 c from the alps to the apennines mlbd ranges between 22 and 28 km and is clearly shallower than the moho in these units the wide variation of mlbd appears to be compatible with the presence of shallow magnetised bodies consisting of lower crustal rocks ivrea verbano zone ophiolitic units penninic zone and voltri massif and intrasedimentary basic volcanic bodies po basin an average value of 25 km can be attributed to mlbd which corresponds to a temperature of 550 c in the peri tyrrhenian zone and the ligurian sea mlbd is below the moho which ranges from 17 to 20 km depth and it has a temperature matching approximately to the curie temperature of magnetite 580 c

thermal and crustal structure of the aso volcano and surrounding regions constrained by gravity and magnetic data japan abstract the aso volcano forms a large caldera that is one of the most active volcanoes in japan much evidence suggests the existence of a high temperature zone beneath the active central cones of the aso volcano and a recent study using seismic observations revealed an attenuation in amplitude of seismic waves that pass through the central region of the aso caldera the sww nee trending futagawa active fault a part of the oita kumamoto tectonic line which dips north lies to the west of the caldera and joins the caldera rim but there are no scars within the caldera an elongate magnetic positive anomaly from the central cones to the west exists close to the futagawa fault this anomaly connects the central cones and the two lateral volcanoes west to the caldera magnetic analyses through spectral method and forward modeling delineate a highly magnetized two dimensional buried prism source dipping north beneath the fault the lower bounds are about 10 km depth outside the caldera and quite shallow depths of about 3 km inside the caldera the area to the north of the oita kumamoto tectonic line forms a gravity depression whereas the area to the south is a regional gravity high a two layered two dimensional gravity model yields a normal fault dipping north with a throw of 1 3 km whereas a multi layered two dimensional gravity model gives a depression of high density basement within the caldera the greatest depth is about 2 km below the surface available temperature depth data suggest the possibility of a sudden change between the inside high temperature zone and the outside low temperature zone of the caldera therefore the difference in the lower boundary of magnetic sources between the area inside and outside the caldera is possibly attributed to the difference of depth of the curie point magnetic sources along the futagawa fault are likely to be related to materials produced by the volcanic activity if so the passage for magma for aso volcanism could be along the futagawa fault

curie temperature depth estimation using a self similar magnetization model summary the earth s crust is magnetized down to the curie temperature depth at about 10 to 50 km this limited depth extent of the crustal magnetization is discernible in the power spectra of magnetic maps of south africa and central asia at short wavelengths the power increases as rapidly towards longer wavelengths as expected for a self similar magnetized crust with unlimited depth extent above wavelengths of about 100 km the power starts increasing less rapidly indicating the absence of deep seated sources to quantify this effect we derive the theoretical power spectrum due to a slab carved out of a self similar magnetization distribution this model power spectrum matches the power spectra of south africa and central asia for a self similarity parameter of 4 and curie temperature depths of 15 to 20 km

curie point depths based on spectrum analysis of aeromagnetic data west anatolian extensional province turkey the curie point depth map of western anatolia was constituted from spectral analysis of the aeromagnetic data the curie point depth values from 53 overlapping blocks 90 90 km in size have been estimated from the band pass filtered data the slope of the longest wavelength part of the radially averaged log power spectrum divided by the radial frequency produced the depth to the centroid z0 for the deepest crustal block the depth to the top zt was obtained by the slope of the second longest wavelength part of the spectrum from these depths the curie point depth was then calculated by using zb 2z0 zt the curie point depth estimates for western anatolia range between 8 2 and 19 9 km

coeval extension and compression in late mesozoic recent thin skinned extensional tectonics in central anatolia turkey abstract the central anatolian crust is composed of high grade metamorphic rocks covered by tertiary shallow marine to continental sedimentary rocks with a middle miocene recent volcanic activity in cappadocia after the late cretaceous closure of the tethyan ocean and following plate collision core complexes formed in nigde and kirsehir regions of central anatolia recent geophysical studies indicate the presence of low seismic velocity zones beneath central anatolia interpreted as regionally thinned and or hot mantle lithosphere or asthenospheric upwelling we present new structural data covering a 300 km wsw nne trending transect between konya and yozgat cities to suggest that central anatolian cenozoic tectonic regime is extensional and the narrow fold thrust zones once taken as evidence of crustal convergence resulted from gravitational movements curie point depths map of central anatolia shows a large scale diameter 140 km upwarping c 15 km of the regional crust we interpret as due to asthenospheric upwelling these considerations suggest that 1 the central anatolian crust deforms by extension transcurrent faults like the central anatolian fault zone accommodate the crustal stretching by transfer faulting 2 post late cretaceous crustal extension favored the placement of hot and low density asthenospheric material in cappadocia by processes that may be explained by rayleigh taylor instability phenomenon 3 in central anatolia large post eocene horizontal crustal displacements we estimate a minimum of 50 km are not achieved by crustal contraction as previously proposed but thin skin extensional tectonics and 4 tethyan suture lines need to be reviewed since their traces may be modified by later extensional displacements

interpretation of low seismicity in the eastern anatolian collisional zone using geophysical seismicity and aeromagnetic and geological data the eastern anatolia is a continental collisional zone between the arabia eurasia plates and is currently being accompanied by the westward escape of the anatolian crustal block to the west southwest along two major strike slip fault zones the natf and the eatf although these major fault zones have experienced historical earthquakes with moderate to high magnitude notably there is a low seismicity zone on the active eatf between the bitlis and poturge massifs the low seismicity zone is characterized by thinner crustal structure relative to its environs the shallow curie point depth scpd ca 12 14 km in between 39 40 e and 38 5 39 n in the easternmost part of the anatolian plate and moderate to high b values more than 0 7 we consider that the shallow cpd and moderate to high b values in the low seismicity zone characterized by thinner crustal area are closely related with the higher thermal structure of the crust which most probably resulted from crust hot asthenospheric mantle interactions