how do submarines use gravity gradients to avoid collisions with underwater mountains abstract gravity gradiometers in use today have their origins in naval special warfare because they ensure safe navigation and accurate detection of underwater objects submarines rely on accurate detection of their surroundings and gravity gradiometry is a passive technique that does not compromise the submarine s position because it is a technique that does not emit energy however the way submarines achieve collision avoidance has never been addressed using gravity gradiometry data in real time warns of the existence of an underwater mountain in a submarine s trajectory the method does not require accurate positioning extensive measuring over large areas or a gravity gradient map of the ocean bottom the results of a study demonstrate how gravity gradiometry can be used effectively to detect anomalous mass in a trajectory quickly without involving sophisticated processing or interpretation algorithms for many years geophysicists have known the original use of the modern gravity gradiometry tec

structural setting of the northeastern biga peninsula turkey from tilt derivatives of gravity gradient tensors and magnitude of horizontal gravity components the tilt derivatives or angles are determined using the gravity gradient tensors ggt from two horizontal components gx gy and vertical component gz and the magnitude of the horizontal components mhc we show that the tilt derivatives from ggt and mhc are highly suitable for mapping linear geological structures or edges of target geology the results obtained from theoretical data with and without random noise have been analyzed in this study the tilt derivatives from ggt and mhc allow imaging the horizontal boundaries of gravity sources with a high resolution and show an improvement performance as edge detectors since they are ultra sensitive for detecting source boundaries

gravity gradiometry resurfaces the red october was heading southwest on gorshkov s railroad his speed was thirteen knots installed in the keel was a highly sensitive device called a gradiometer essentially two large lead weights separated by a space of one hundred yards a laser computer system measured the space between the weights down to a fraction of an angstrom distortion of that distance or lateral movement of the weights indicated variations in the local gravitational field with careful use of gravitometers he could plot the vessel s location to within a hundred meters

using fractal crustal magnetization models in magnetic interpretation1 evidence from borehole susceptibility logs and the spectral analysis of aeromagnetic data suggests that the three dimensional distribution of magnetization within the crust can be described as fractal this property can be exploited in magnetic interpretation methods which explicitly require statistical information on the spatial variation of magnetization specifically we address the problem of magnetic source depth estimation through downward continuation and gridding aeromagnetic survey data using the method of kriging when magnetic data are continued downwards the depth at which the power spectrum flattens out the white depth can be taken to be an estimate of the top of the source distribution this procedure assumes that individual sources are uncorrelated with each other taking into account the correlation of the magnetization using a fractal description leads to a reduction in this depth estimate gridding of randomly distributed magnetic measurements using kriging requires an estimate of the covariance of the data compared with the assumption of a white uncorrelated magnetization distribution using fractal covariances for kriging produces gridded estimates which more closely reflect the statistics of the underlying magnetization process and produce maps with a justifiable degree of smoothness

application of satellite magnetic anomaly data to curie isotherm mapping a boundary condition on temperature at depth in the continental crust can in principle be obtained by mapping of the curie isotherm where it forms the base of the magnetic crust an approach to mapping magnetic crustal thickness using satellite magnetic anomaly data is described because magnetic crustal thickness is small with respect to satellite altitude inversion of the anomaly data yields magnetization models expressing regional variations in the vertical integral of magnetization this parameter is inversely correlated with regional heat flow in the western united states suggesting that areas of low apparent magnetization are areas of thin magnetic crust resulting from a shallow curie isotherm for a simple model of a uniformly magnetized magnetic crust or intra crustal layer curie depth is linearly related to apparent magnetization if the relation can be calibrated by two or more curie depth estimates regional apparent curie isotherm configuration can be mapped in an alternative approach a family of curie depth models can be computed using assumed magnetization values in each case the curie depth configuration is used as a boundary condition in a thermal model that model is selected which gives a heat flow distribution best fitting observations conductive heat flow models for a traverse across the rio grande rift using a finite element technique and for a map grid using a one dimensional thermal model approximation are given as examples

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

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

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

curie point depth from spectral analysis of magnetic data in erciyes stratovolcano central turkey curie point depth and heat flow values of the erciyes region are determined to identify the thermal regime of the central anatolia by applying the spectral analysis method to the magnetic anomaly data to compute the spectrum of the data the magnetic anomaly of the region is transformed into 2 d fourier domain to attain the average curie depth this method is useful in determining the top boundary of magnetic anomaly sources and reveals the curie depth as 13 7 km in the study area the obtained results imply a high thermal gradient 42 3 c km 1 and corresponding heat flow values 88 8 mwm 2 in the research area using the temperature value measured at borehole drilled by the general directorate of mineral research and exploration of turkey mta the values for the thermal gradient and heat flow value were computed as 50 7 c km 1 106 5 mwm 2 from the heat flow value the curie point depth was determined as 11 4 km in this region it is concluded from the obtained values that the region has very high geothermal potential caused by partial melting of the lower crust

detection of reservoirs from normalized full gradient of gravity anomalies and its application to shengli oil field east china we present how to detect reservoirs by the 3 d normalized full gradient nfg of gravity anomalies constrained by seismic and drilling data the normalized full gradient represents the full gradient of the gravity anomaly at a point divided by the average of the full gradient at the datum the closed minima on an nfg map indicate the occurrence and horizontal locations of the centers of mass of density anomalies related to oil reservoirs this information can be used to select well locations in an oil field on a cross section the closed minima can be used to estimate the depth to centers of mass of possible hydrocarbon reservoirs some characteristics of the nfg are calculated for a hypothetical case of an anticline saturated with oil and gas the relationship of these characteristics to the geometry and physical parameters of the anticline is studied modeling studies show that the nfg largely depends on the number of terms in the fourier series used to calculate it and it closely related to the length

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

scaling nature of crustal susceptibilities scale invariant or self similar properties have been demonstrated for a wide range of geophysical processes and rock properties evidence from well logs and inferences from aeromagnetic field power spectra suggest that crustal susceptibility also shows this behaviour with a power spectrum proportional to the 4 power of the spatial frequency we examine two large susceptibility measurement data sets and find that they both support the scaling hypothesis

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

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

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

subsurface investigation of the neogene mygdonian basin greece using magnetic data a high resolution ground and marine magnetic survey was executed to determine the structure of the subsurface and the thickness of the sedimentary cover in the mygdonian basin a spacing of approximately 250 m or 500 m between measurement stations was selected to cover an area of 15 km 22 km edge detectors such as total horizontal derivative thdr analytic signal as tilt derivative tdr enhanced total horizontal gradient of tilt derivative ethdr were applied to map the subsurface structure depth was estimated by power spectrum analysis tilt derivative source parameter imaging spi and 2d forward modeling techniques spectral analysis and spi suggest a depth to the basement ranging from near surface to 600 m for some selected locations depth was also calculated using the tdr technique suggesting depths from 160 to 400 m 2d forward magnetic modeling using existing boreholes as constraints was carried out along four selected profiles and confirmed the presence of alternative horsts and grabens formed by parallel normal faults the dominant structural trends inferred from thdr as tdr and ethdr are n s nw se ne sw and e w this corresponds with the known structural trends in the area finally a detailed structural map showing the magnetic blocks and the structural architecture of the mygdonian basin was drawn up by collating all of the results

a gravity gradient method for characterizing the post seismic deformation field for a finite fault summary gravity gradients are an effective method for delineating the extent of subsurface density anomalies the change in subsurface density contrasts due to the seismic deformation gives rise to detectable gravity changes via the dilatational gravity signal or bouguer anomaly solutions for the corresponding gravity gradients of these signals are developed for a vertical strikeslip fault gravity gradient solutions exhibit similar spatial distributions as those calculated for coulomb stress changes reflecting their physical relationship to the stress changes the signals magnitudes of the order of 10 4 e are beyond the resolution of typical exploration instruments improvements to superconducting gravity gradiometers are necessary for gravity gradients to be used as a viable method for the observation of the stress field changes over large spatial scales

feasibility of using full tensor gradient ftg data for detection of local lateral density contrasts during reservoir monitoring summary three dimensional full tensor gradiometry 3 d ftg acquires ultrasensitive measurements of the earth s vector gravity gradient field departures from simple weakening of the field in the vertical direction are due to subsurface variations in density we have undertaken a numerical examination of the feasibility of using this system for detecting time variations in local lateral density contrasts in subsurface layers during reservoir production monitoring our gravity modelling focuses on the value added by taking account of the horizontal components of gravity gradient in imaging local targets we have studied the sensitivity of these components to model and acquisition parameters iterative regularized inversion algorithms that can explain the behaviour of a hydrocarbon reservoir in terms of time lapse density changes have been described these algorithms are based on the homotopy method that utilizes the solution space topology to stabilize the inversion we have introduced the maximum compactness of anomalous sources along one or more directions this allows the use of a priori information natural to time lapse monitoring about the arbitrary shape and spatial locations of the sources the time evolving density contrast within the local target zone is recovered by means of an iterative procedure the treatment of either correlated or random noise fits naturally into this procedure the final scheme has been illustrated by several examples using synthetic ftg data generated from various density distributions of practical interest we have considered the effect of model and data uncertainties on the inversion solution it appears that the iterative process is effective numerically stable and rapidly convergent in the presence of both random and structural noise results show that it is relatively insensitive to the choice of starting model appropriate applications include direct monitoring of gas oil contact and temperature front expansion during steam injection in heavy oil reservoirs at shallow or moderate depths

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

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

deep structure investigations of the geothermal field of the north euboean gulf greece using 3 d local earthquake tomography and curie point depth analysis abstract new findings on the deep origin of the geothermal field and volcanic centres at the north euboean gulf or north evian gulf central greece were obtained by combining a three dimensional traveltime inversion of microseismic data recorded by an on offshore local seismic network with a curie point depth analysis based on aeromagnetic data a magma chamber was detected from low seismic p wave velocity values and high poisson ratios at depths below 8 km also coincident with a curie surface estimated at 7 8 km depth furthermore it was also observed that local geothermal anomalies are generated by hydrothermal flux facilitated by nw se and ne sw oriented faults microseismic activity is also associated with these fault systems

eigenvector analysis of gravity gradient tensor to locate geologic bodies we have developed a new method to locate geologic bodies using the gravity gradient tensor the eigenvectors of the symmetric gravity gradient tensor can be used to estimate the position of the source body as well as its strike direction for a given measurement point the eigenvector corresponding to the maximum eigenvalue points approximately toward the center of mass of the causative body for a collection of measurement points a robust least squares procedure is used to estimate the source point as the point that has the smallest sum of square distances to the lines defined by the eigenvectors and the measurement positions it s assumed that the maximum of the first vertical derivative of the vertical component of gravity vector gzz is approximately located above the center of mass observation points enclosed in a square window centered at the maximum of gzz are used to estimate the source location by increasing the size of the window the number of eigenvectors used in the robust least squares and

consistency investigation vertical gravity estimation and inversion of airborne gravity gradient data a case study from northern sweden for airborne gravity gradient data it is a challenge to distinguish between high frequency intrinsic and dynamically produced noise caused by the aircraft and small scale effects from shallow dens

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

noise reduction through joint processing of gravity and gravity gradient data in mineral and oil exploration gravity gradient data can help to delineate small scale features that cannot be retrieved from gravity measurements removing high frequency noise while preserving the high frequency real signal is one of the most challenging tasks associated with gravity gradiometry data processing we present a method to reduce gravity and gravity gradient data noise when both are measured in the same area based on a least squares simultaneous inversion of observations and physical constraints inferred from the gravity gradient tensor definition and its mathematical properties instead of handling profiles individually our noise reduction method uses simultaneously measured values of the tensor components and of gravity in the whole survey area benefiting from all available information synthetic examples show that more than half of the random noise can be removed from all tensor components and nearly all the noise from the gravity anomaly without altering the high frequency information we apply our method to a set of marine gravity gradiometry data acquired by bell geospace in the faroe shetland basin to demonstrate its power to resolve small scale features

a geophysical study of the granites and the sedimentary basins of the xanthi area n greece intrusive features of varying size can be interpreted from the aeromagnetic map of the xanthi area in n greece

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

curie point depths of macedonia and thrace n greece 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

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

from space to lithosphere inversion of the goce gravity gradients supply to the earth s interior study the emergence of high resolution satellite measurements of the gravitational field goce mission offers promising perspectives for the study of the earth s interior these new data call for the development of innovant analysis and interpretation methods here we combine a forward prism computation with a bayesian resolution approach to invert for these gravity gradient data configuration we apply and test our new method on satellite data configuration i e 225 km height with a global and homogeneous geographic distribution we first quantify the resolution of our method according to both data and parameteriza tion characteristics it appears that for reasonable density contrast values 0 1 g cm 3 crustal structures have to be wider than 28 km to be detectable in the goce signal deeper bodies are distinguishable for greater size 35 km size at 50 km depth 80 km at 300 km depth we invert the six tensor components among which five are independent by carefully testing each of them and their different combinations we enlighten a trade off between the recovery of data and the sensitivity to inversion parameters we particularly discussed this characteristic in terms of geometry of the synthetic model tested 2 plasman et al structures orientation 3 d geometry etc in terms of rms value each component is always better explained if inverted solely but the result is strongly affected by the inversion parameterization smoothing variances etc on the contrary the simultaneous inversion of several components displays a significant improvement for the global ten sor recovery more dependent on data than on density variance or on smoothness control comparing gravity and gradient inversions we highlight the superiority of the gg data to better reproduce the structures especially in terms of vertical location we succesfully test our method on a realistic case of a complex subduction case for both gradient and gravity data while the imaging of small crustal structures requires terrestrial gravity dataset the longest wavelength of the slab is well recovered with both data sets the precision and homogeneous coverage of goce data however counterbalance the heterogeneous and often quite nonexistance coverage of terrestrial gravity data this is particularly true in large areas which requires a coherent assemblage of heterogeneous data sets or in high relief vegetally covered and offshore zones

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

a secondary ionization mass spectrometry calibration of cibicidoides pachyderma mg ca with temperature an evaluation of c pachyderma mg ca using a new suite of warm water multicores from the florida straits shows that the slope of mg ca with temperature is shallower than previously thought using secondary ionization mass spectrometry we have documented that the distribution of magnesium within the polished walls of foraminiferal tests is gaussian suggesting that the mg ca in these samples is not affected by the addition of a secondary high magnesium calcite in the walls the mg ca within a typical c pachyderma test varies by about 20 1 100 and the variability increases slightly in tests with higher mg ca the regression of c pachyderma mg ca with temperature has a slope of 0 13 0 05 mmol mol 1 per c indistinguishable from the slope observed in inductively coupled plasma mass spectrometry measurements from a different subset of the same multicores but about one half the slope of previously published calibrations the largest differences between the calibrations comes at the warm water end of the regression where previously published c pachyderma mg ca values from little bahama bank are at least 3 mmol mol 1 higher than observed in these new cores the reasons for this difference are not fully known but are most likely related to diagenesis at little bahama bank

curie surface of the alkaline provinces of goias gap and alto paranaiba apap central brazil abstract the study area includes the most important carbonatite and kimberlite complexes in brazil located in the brazilian states of goias and minas gerais the central portion of this area involves the azimuth 125 lineament az 125 that consists of an extensive set of faults oriented in the nw se direction that served as a conduit for magma ascent this lineament is the main structural feature associated with these complexes the goias gap and alto paranaiba apap alkaline provinces occur along the az 125 and include highly economically valuable mineralizations in this study we aim to map the depth to the curie isotherm or curie point depths cpd of the study area mainly the gap and apap regions based on spectral analysis of aeromagnetic data the cpd estimations were achieved from a spectral approach known as the centroid method providing the relationship between the spectra of magnetic anomalies and the depths of the magnetic source of a 2 d magnetic data the cpd estimates from approximately 500 overlapping blocks vary from 7 km to 40 km deep the shallower depths are related to the gap and apap regions and the deeper ones are related to the sao franciscana plate the curie depths related to the az 125 are between 30 km and 15 7 km deep according to the results the gap and apap intrusive bodies have shallower roots the major faults of the az 125

curie point depth of the island of crete greece 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

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