3 d density model of the crust of southern and central finland obtained from joint interpretation of the svekalapko crustal p wave velocity models and gravity data 3 d density model of the crust of southern and central finland obtained from joint interpretation of the svekalapko crustal p wave velocity models and gravity data

deep earthquakes in subducting slabs hosted in highly anisotropic rock fabric analysis of deep subduction zone earthquakes those at depths greater than 60 km reveals the physical and chemical properties of a descending oceanic lithosphere at mantle depths over the past five decades it has been observed that a large fraction of deep earthquakes has non double couple non dc seismic radiation patterns in contrast shallow earthquakes tend to have dc radiation patterns due to mechanisms of shear faulting these observations have been used to argue that deep earthquakes rupture differently from shallow earthquakes here we show that the observed global distribution of non dc deep earthquakes could be caused by shear faulting mechanisms but in a highly anisotropic laminated rock fabric that surrounds the deep earthquakes within subducted slabs for intermediate depth earthquakes 60 300 km we found a large shear wave anisotropy of 25 possibly caused by laminated fabric or aligned melt pockets oriented parallel to the slab interface which provides new supporting evidence for the metamorphic dehydration reactions in slabs however at deep focus depths 300 km the putative metastable phase change mechanism alone cannot explain the seismic anisotropy instead our results and those from recent experiments suggest materials such as magnesite or perhaps carbonatite melt may play a role in generating deep focus earthquakes radiation patterns for deep earthquakes could be a result of shear faulting mechanisms similar to those for shallow earthquakes but in highly anisotropic rock fabric suggest seismic analyses

symplectitic augite evidence for discontinuous precipitation as an exsolution mechanism in ca rich clinopyroxene part of the augite in the artfjallet gabbro consists of symplectitic intergrowths between augite and blebs or lamellae of orthopyroxene mineral compositions are consistent with formation of these symplectites by exsolution of orthopyroxene from magmatic augite at a temperature of ca 900 1000 c the microstructures indicate that the exsolution mechanism is discontinuous precipitation whereby the boundary of an augite grain sweeps through a neighbouring augite leaving the symplectite in its wake the formation of this symplectitic augite is catalysed by the presence of an intergranular water rich fluid phase which promotes grain boundary mobility

joint two dimensional dc resistivity and seismic travel time inversion with cross gradients constraints it is now common practice to perform collocated dc resistivity and seismic refraction surveys that complement each other in the search for more accurate characterization of the subsurface although conventional separate dc resistivity and seismic models can be diagnostic we posit that better results can be derived from jointly estimated models we make the assumption that both methods must be sensing the same underlying geology and have developed an innovative resistivity velocity cross gradients relationship to evaluate the structural features common to both methods the cross gradients function is incorporated as a constraint in a nonlinear least squares problem formulation which is solved using the lagrange multiplier method the resultant iterative two dimensional 2 d joint inversion scheme is successfully applied to synthetic data serving as validation tests here and to field data from collocated dc resistivity and seismic refraction profiling experiments and also compared to conventional separate inversion results the joint inversion results are shown to be superior to those from separate 2 d inversions of the respective data sets since our algorithm leads to resistivity and velocity models with remarkable structural agreement

constraints on seismic anisotropy in the mantle transition zone from long period ss precursors the mantle transition zone mtz of earth is demarcated by solid to solid phase changes of the mineral olivine that produce seismic discontinuities at 410 and 660 km depths mineral physics experiments predict that wadsleyite can have strong single crystal anisotropy at the pressure and temperature conditions of the mtz thus significant seismic anisotropy is possible in the upper mtz where lattice preferred orientation of wadsleyite is produced by mantle flow here we use a body wave method ss precursors to study the topography change and seismic anisotropy near the mtz discontinuities we stack the data to explore the azimuthal dependence of travel times and amplitudes of ss precursors and constrain the azimuthal anisotropy in the mtz beneath the central pacific we find evidence for 4 anisotropy with a se fast direction in the upper mantle and no significant anisotropy in the mtz in subduction zones we observe 4 anisotropy with a trench parallel fast direction in the upper mantle and 3 anisotropy with a trench perpendicular fast direction in the mtz the transition of fast directions indicates that the lattice preferred orientation of wadsleyite induced by mtz flow is organized separately from the flow in the upper mantle global azimuthal stacking reveals 1 azimuthal anisotropy in the upper mantle but negligible anisotropy 1 in the mtz finally we correct for the upper mantle and mtz anisotropy structures to obtain a new mtz topography model the anisotropy correction produces 3 km difference and therefore has minor overall effects on global mtz topography

joint two dimensional cross gradient imaging of magnetotelluric and seismic traveltime data for structural and lithological classification summary collocated magnetotelluric mt and seismic profiling is emerging as a necessary combined approach for deep and near surface imaging but the resulting experimental data are typically interpreted separately since no production programs exist for multidimensional joint inversion of mt and seismic data we present a joint 2 d inversion approach for imaging collocated mt and seismic refraction data with cross gradient structural constraints we describe the main features of the algorithm and first apply it to synthetic data generated for a hypothetical complex geological model for the synthetic data we find that the scheme leads to models with remarkable structural resemblance and improved estimates of electrical resistivity and seismic velocity we apply the scheme to near surface field data to test the consistency of a previously suggested resistivity velocity interrelationship and its potential use for subsurface lithofacies discrimination or structural classification the mt seismic relationship is found to be in excellent accord with that derived previously for dc resistivity and seismic data set at the test site our results suggest that joint mt seismic cross gradient imaging leads to improved characterization of heterogeneous geological targets at near surface to mantle depths

two dimensional joint inversion of radiomagnetotelluric and direct current resistivity data an algorithm for the two dimensional 2d joint inversion of radiomagnetotelluric and direct current resistivity data was developed this algorithm can be used for the 2d inversion of apparent resistivity data sets collected by multi electrode direct current resistivity systems for various classical electrode arrays wenner schlumberger dipole diplole pole dipole and radiomagnetotelluric measurements jointly we use a finite difference technique to solve the helmoltz and poisson equations for radiomagnetotelluric and direct current resistivity methods respectively a regularized inversion with a smoothness constrained stabilizer was employed to invert both data sets the radiomagnetotelluric method is not particularly sensitive when attempting to resolve near surface resistivity blocks because it uses a limited range of frequencies on the other hand the direct current resistivity method can resolve these near surface blocks with relatively greater accuracy initially individual and joint inversions of synthetic radiomagnetotelluric and direct current resistivity data were compared and we demonstrated that the joint inversion result based on this synthetic data simulates the real model more accurately than the inversion results of each individual method the developed 2d joint inversion algorithm was also applied on a field data set observed across an active fault located close to the city of kerpen in germany the location and depth of this fault were successfully determined by the 2d joint inversion of the radiomagnetotelluric and direct current resistivity data this inversion result from the field data further validated the synthetic data inversion results

joint inversion of seismic and magnetotelluric data in the parkfield region of california using the normalized cross gradient constraint we present jointly inverted models of p wave velocity vp and electrical resistivity for a two dimensional profile centered on the san andreas fault observatory at depth safod significant structural similarity between main features of the separately inverted vp and resistivity models is exploited by carrying out a joint inversion of the two datasets using the normalized cross gradient constraint this constraint favors structurally similar vp and resistivity images that adequately fit the seismic and magnetotelluric mt datasets the new inversion code tomoddmt merges the seismic inversion code tomodd and the forward modeling and sensitivity kernel subroutines of the mt inversion code occam2dmt tomoddmt is tested on a synthetic dataset and demonstrates the code s ability to more accurately resolve features of the input synthetic structure relative to the separately inverted resistivity and velocity models using tomoddmt we are able to resolve a number of key issues raised during drilling at safod we are able to infer the distribution of several geologic units including the salinian granitoids the great valley sequence and the franciscan formation the distribution and transport of fluids at both shallow and great depths is also examined low values of velocity resistivity attributed to a feature known as the eastern conductor ec can be explained in two ways the ec is a brine filled high porosity region or this region is composed largely of clay rich shales of the franciscan the eastern wall which lies immediately adjacent to the ec is unlikely to be a fluid pathway into the san andreas fault s seismogenic zone due to its observed higher resistivity and velocity values

direct reservoir parameter estimation using joint inversion of marine seismic ava and csem data a new joint inversion algorithm to directly estimate reservoir parameters is described this algorithm combines seismic amplitude versus angle ava and marine controlled source electromagnetic csem data the rock properties model needed to link the geophysical parameters to the reservoir parameters is described errors in the rock properties model parameters measured in percent introduce errors of comparable size in the joint inversion reservoir parameter estimates tests of the concept on synthetic one dimensional models demonstrate improved fluid saturation and porosity estimates for joint ava csem data inversion compared to ava or csem inversion alone comparing inversions of ava csem and joint ava csem data over the north sea troll field at a location with well control shows that the joint inversion produces estimated gas saturation oil saturation and porosity that is closest as measured by the rms difference l1 norm of the difference and net over the interval to the logged values whereas csem inversion provides the closest estimates of water saturation

sem microprobe study of some symplectic intergrowths replacing cordierite abstract scanning electron microscopy sem involving images produced by back scattered electrons reveals the microstructures of symplectic intergrowths replacing cordierite which generally are too fine grained and or intricately intergrown for investigation using an optical microscope microprobe analysis combined with the sem technique enables accurate identification of the intergrown minerals and permits inference of equations for the local chemical changes involved in the formation of the intergrowths generally the local replacement appears to have involved partial reactions taking place in a larger reactive system intergrowths forming partial pseudomorphs of cordierite in three metamorphic complexes consists of up to three minerals only two of which comprise the intergrowth in any one domain the following intergrown pairs of minerals have been identified quartz al2sio3 quartz biotite biotite oligoclase biotite k feldspar muscovite oligoclase oligoclase andalusite k feldspar andalusite aluminous orthopyroxene al2sio3 and aluminous anthophylite al2sio3

preservation of a magnetization carried by magnetite inclusions during amphibolite grade metamorphic conditions an example from the sarek dykeswarm northern swedish caledonides an outcrop consisting of a 608 myr old sheeted dyke complex and dyke intruded metasediments has been investigated palaeomagnetically it is located in the interior of a nappe the basal and upper parts of which suffered penetrative deformation and amphibolite grade metamorphism during the caledonian orogeny the only trace from the orogeny at the outcrop is a widely spaced network of brittle and ductile shear zones crosscutting dyke contacts foliated amphibolite consisting of hornblende quartz plagioclase garnet and sphene occur locally within them the opaque mineralogy of the dykes differs from that commonly found in continental dykes with ilmenite and pyrrhotite being the major visible opaque phases and there are indications that magnetite inclusions exsolved from silicates carry a primary remanence even though ar 39 40 ar mica ages were reset at ca 430 myr during the orogeny a secondary component carried by pyrrhotite is less prominent but falls on the baltican apw path at 430 myr the inferred primary component has a large directional uncertainty but indicates low palaeolatitudes for the baltscandian margin during rifting less

inversion of seismic refraction and wide angle reflection traveltimes for three dimensional layered crustal structure summary we present a method for the determination of crustal structure by simultaneous inversion of seismic refraction and wide angle reflection traveltimes for 3 d interface geometry and layer velocity crustal structure is represented by layers in which velocity varies linearly with depth separated by smooth interfaces with a cubic b spline parametrization lateral variations in structure are therefore represented by variations in interface depth only the model parametrization we have chosen means that ray paths consist of piecewise circular arc segments for which analytic expressions of trajectory and traveltime are calculated the two point problem of finding the first arrival ray path and traveltime of a specified phase between a given source and receiver is solved using a shooting technique a subspace inversion method is used to solve the inverse problem which is formulated as a non linear optimization problem in which we seek to minimize an objective function that consists of a data residual term and a regularization term before performing the inversion each data pick must be assigned as a refraction or reflection from a particular layer or interface since our method represents structure in terms of interfaces fewer parameters would generally be used in a reconstruction compared to an equivalent 3 d variable velocity inversion the method is well suited to wide angle surveys that consist of many sources and relatively few receivers or vice versa such as marine shot lines used in conjunction with land based receivers data coverage in this kind of survey is often sparse and especially if near offset ray paths are unavailable highly variable a 3 d synthetic test with an array consisting of eight sources lying within a three sided square of 79 receivers is described the test model consists of a three interface structure that includes a layer pinch out and the synthetic data set comprises 987 refraction and 930 reflection travel times contaminated with 75 ms of data noise six iterations of an 18 d subspace method demonstrate that the method can produce an accurate reconstruction that satisfies the data from a 1 d starting model we also find that estimates of a posteriori model covariance and resolution obtained from linear theory are useful in analysing solution reliability despite the non linear nature of the problem application of the method to data collected as part of the 1995 tasgo project in tasmania shows that the method can satisfy 1345 refraction and reflection traveltime picks with a geologically reasonable and robust 254 parameter three interface model the inversion results indicate that the moho beneath nw tasmania varies in depth from 27 km near the coast to 37 km near central tasmania with the major increase in depth occurring across the arthur lineament

seismic signatures of a hydrated mantle wedge from antigorite crystal preferred orientation cpo abstract we report electron backscatter diffraction ebsd measurements of antigorite crystal preferred orientations cpos from 7 samples of antigorite schist from serpentinite melanges adjacent to the motagua fault system in central guatemala the cpos range from diffuse girdle to point distributions of 001 atg girdle distributions of 001 atg are not expected from deformation theory or experiments suggesting that they are a result of growth rather than deformation and may thus be topotactically related to the cpo of the olivine from which the antigorite grew the calculated seismic anisotropy ranges from 6 to 28 in v p and 5 to 33 in v s and is highest for samples with a point maximum of 001 atg for all samples the minimum v p corresponds to the pole to 001 atg and the maximum v p occurs within the foliation for samples with a clearly defined foliation trench parallel shear wave splitting observations for subduction zones can best be explained by a combination of olivine b type cpo and antigorite oriented with 001 parallel to the foliation only a relatively thin 20 km zone of hydrated mantle is required to explain the observed splitting times

constraints on subduction geodynamics from seismic anisotropy 1 much progress has been made over the past several decades in delineating the structure of subducting slabs but several key aspects of their dynamics remain poorly constrained major unsolved problems in subduction geodynamics include those related to mantle wedge viscosity and rheology slab hydration and dehydration mechanical coupling between slabs and the ambient mantle the geometry of mantle flow above and beneath slabs and the interactions between slabs and deep discontinuities such as the core mantle boundary observations of seismic anisotropy can provide relatively direct constraints on mantle dynamics because of the link between deformation and the resulting anisotropy when mantle rocks are deformed a preferred orientation of individual mineral crystals or materials such as partial melt often develops resulting in the directional dependence of seismic wave speeds measurements of seismic anisotropy thus represent a powerful tool for probing mantle dynamics in subduction systems here i review the observational constraints on seismic anisotropy in subduction zones and discuss how seismic data can place constraints on wedge slab and sub slab anisotropy i also discuss constraints from mineral physics investigations and geodynamical modeling studies and how they inform our interpretation of observations i evaluate different models in light of constraints from seismology geodynamics and mineral physics finally i discuss some of the major unsolved problems related to the dynamics of subduction systems and how ongoing and future work on the characterization and interpretation of seismic anisotropy can lead to progress particularly in frontier areas such as understanding slab dynamics in the deep mantle

olivine spinel transitions experimental and thermodynamic constraints and implications for the nature of the 400 km seismic discontinuity the sequence of high pressure phase transitions in olivine is traditionally used as a model for seismic velocity variations in the 200 to 650 km depth interval in a mantle of peridotitic bulk composition it has been proposed that the observed seismic velocity increase at 400 km depth is too sharp and of too small a magnitude to be attributable to the phase change and that the upper mantle must thus be chemically stratified with the 400 km discontinuity being due either to a combination of phase changes in a layer of pyroxene garnet rich piclogite composition or to a chemical boundary between such a piclogite layer and an overlying peridotitic layer using available calorimetric thermoelastic and synthesis data and their associated experimental uncertainties we have derived internally consistent high pressure phase relations for the mg2sio4 fe2sio4 join we find that the divariant transition which is generally regarded as occurring over a broad depth interval for mantle olivine compositions is in fact extremely sharp the seismic discontinuity corresponding to the transition in mg0 9fe0 1 2sio4 should occur over a depth interval isothermal of about 6 km at a depth of approximately 400 km the sharpness of this transition is quite insensitive to uncertainties in the constraining calorimetric thermoelastic and synthesis data in addition we have computed seismic velocity profiles for a model mantle consisting of pure olivine of mg0 9fe0 1 2sio4 composition comparison of these computed profiles to those derived from recent seismic studies indicates that the magnitude of the observed velocity increase at 400 km depth is consistent with a mantle transition zone composed of about 60 70 olivine we conclude that there is no need to infer the existence of pyroxene garnet rich compositions such as eclogite or piclogite in the transition zone since an upper mantle of homogeneous olivine rich peridotitic composition is consistent with the available seismic velocity data

paleointensity determination on the late precambrian tudor gabbro ontario paleointensity determination by the coe modified thellier method was carried out on the 1100 ma tudor gabbro of southern ontario the tudor has a bivectorial natural remanent magnetization nrm the c nrm is a grenvillian uplift thermoviscous remagnetization which overprints the a nrm the surviving primary thermoremanent magnetization trm of the tudor intrusion a sharp junction at 530 c between the a and c vectors in laboratory thermal demagnetization matches the peak metamorphic reheating temperature of 480 500 c in nature when the difference in time scales is taken into account the unblocking temperature distributions of the a nrm and of laboratory trm also match a is carried by single domain or small pseudo single domain grains probably magnetite rods exsolved in plagioclase or pyroxene at temperatures above 580 c arai plots of nrm versus partial trm are linear from 520 c or 530 c to 580 c for 45 specimens of 19 samples from 9 sites the 45 reliable paleointensity values from these specimens give a virtual axial dipole moment vadm of 4 6 0 8 1022 a m2 around 1100 ma this is about one half of the modern field intensity but is similar to the mean cretaceous cenozoic intensity and to most archean and proterozoic vadms keweenawan rocks whose ages are within 20 myr of the tudor gabbro have a vadm of 11 4 1022 a m2 the difference between the tudor and keweenawan vadms is similar to differences recorded over similar time intervals in the cretaceous and seems to represent normal variation in geomagnetic field strength throughout earth s history

sub slab anisotropy beneath the sumatra and circum pacific subduction zones from source side shear wave splitting observations understanding the dynamics of subduction is critical to our overall understanding of plate tectonics and the solid earth system observations of seismic anisotropy can yield constraints on deformation patterns in the mantle surrounding subducting slabs providing a tool for studying subduction dynamics while many observations of seismic anisotropy have been made in subduction systems our understanding of the mantle beneath subducting slabs remains tenuous due to the difficulty of constraining anisotropy in the sub slab region recently the source side shear wave splitting technique has been refined and applied to several subduction systems worldwide making accurate and direct measurements of sub slab anisotropy feasible and offering unprecedented spatial and depth coverage in the sub slab mantle here we present source side shear wave splitting measurements for the central america alaska aleutians sumatra ryukyu and izu bonin japan kurile subduction systems we find that measured fast splitting directions in these regions generally fall into two broad categories aligning either with the strike of the trench or with the motion of the subducting slab relative to the overriding plate trench parallel fast splitting directions dominate beneath the izu bonin japan and southern kurile slabs and part of the sumatra system while fast directions that parallel the motion of the downgoing plate dominate in the ryukyu central america northern kurile western sumatra and alaska aleutian regions we find that plate motion parallel fast splitting directions in the sub slab mantle are more common than previously thought we observe a correlation between fast direction and age of the subducting lithosphere older lithosphere 95 ma is associated with trench parallel splitting while younger lithosphere 95 ma is associated with plate motion parallel fast splitting directions finally we observe source side splitting for deep earthquakes transition zone depths beneath japan and sumatra suggesting the presence of anisotropy at midmantle depths beneath these regions

the significance of u pb zircon dates in lower crustal xenoliths from the southwestern margin of the kaapvaal craton southern africa the combination of high precision id tims u pb geochronology with cathodoluminescence cl imaging and spatially resolved microsampling of zircon provides a high fidelity record of the temporal evolution of samples of the middle and lower crust a suite of xenoliths exhumed in cretaceous kimberlites at the southwestern margin of the kaapvaal craton including eclogite granulite amphibolite and greenschist facies plutonic rocks are the subject of these detailed zircon studies cl imaging demonstrates the complexity of chemical and growth structure in single zircons and highlights the importance of sampling on an intragrain scale to extract end member ages for zircon growth events for these diverse metamorphic rocks linking the zircon chronology to geologic events and processes requires an understanding of the kinetics and thermodynamics of zircon stability during metamorphism using an empirical approach we attempt to relate zircon crystallization dissolution and regrowth to metamorphic conditions through a detailed analysis of zircon chemical zonation patterns mineral inclusions and petrography these lines of evidence indicate the crystallization of zircon under p t conditions ranging from eclogite through greenschist facies we discuss four examples of this approach 1 at the lowest grade of metamorphism examined primary igneous zircon 1900 ma in a syenite xenolith from the klipfontein 08 kimberlite underwent two episodes 1015 and 964 ma of probable fluid mediated resorption and reprecipitation in the greenschist facies 2 an upper amphibolite facies xenolith from the markt kimberlite contains two distinct populations of blocky and fir tree sector zoned zircon which are suggested to date prograde hornblende breakdown reactions 1107 ma and melt infiltration under retrograde metamorphic conditions 1092 ma respectively 3 at granulite facies metamorphic zircon crystallized at 1114 ma during prograde reactions involving hornblende breakdown in a granulite xenolith also from the markt kimberlite later 960 ma zircon resorption followed by minor secondary crystallization occurred in both the amphibolite and granulite xenoliths during retrograde greenschist facies reactions possibly enhanced by fluids 4 in a much older episode of eclogite facies metamorphism recorded in a xenolith from the lovedale kimberlite zircon crystallized with the peak metamorphic mineral assemblage or possibly early on the cooling path in the late archean 2630 ma each of these examples provides unique information regarding the evolution of the kaapvaal craton while the links to metamorphic reactions and p t conditions clarify the interpretation of zircon dates obtained from these samples of the middle to lower crust

a regionalized upper mantle rum seismic model seismic velocity heterogeneity in the earth s mantle is strongly concentrated near its top the shallow heterogeneity of the mantle correlates strongly with surface tectonics we use these observations as constraints of a tomographic experiment aimed at building a regionalized upper mantle rum reference model we use a select set of teleseismic travel times to minimize the mapping of mislocation into structure the data selection emphasizes the robustness of individual picks the form of the rum model is a set of velocity profiles as functions of depth through the upper mantle for each of the different tectonic provinces of earth together the profiles constitute a three dimensional model which incorporates considerable structural detail but is described by only 90 parameters and has only about 22 degrees of freedom this is achieved by irregularly sampling a detailed regionalization of the globe by detailed mapping of subducted lithosphere in the mantle as defined by seismicity and by combining these structures in an irregular grid in which bookkeeping is efficiently handled the resulting rum model includes subducting slabs as sharp fast features in the upper mantle old continents are fast young oceans are slow models have been derived for both compressional and shear velocity the rum model is designed to represent as much of upper mantle heterogeneity as seen by body wave travel times as possible with a simple model it can be useful as a reference model for individual tectonic regions travel times are efficiently generated for the rum model mislocations of explosions of known location are significantly reduced when corrections for the rum model are applied to travel time residuals for a spherically symmetrical earth model

significance of non double couple components of deep and intermediate depth earthquakes implications from moment tensor inversions of long period seismic waves abstract analysis of long period seismic waves suggests that non double couple components in source moment tensors of intermediate depth and deep earthquakes are significant and appear to respond to the state of predominant strain release within slabs the strain regime is partially or fully induced by the sources themselves or by slab structures near the sources we observe consistency in the non double couple components from three different seismic wave inversions among 21 earthquakes studied 17 events have the same sign in the three non double couple components and the signs show a correlation with the state of strain release within the slabs the effects of unmodeled propagation structure and instability of the inversion procedure are unlikely to be responsible for the consistent non double couple components because the suites of seismic waves traverse different paths and the various inversion schemes have the different resolvabilities of the moment tensors

localized polymorphic phase transformations in high pressure faults and applications to the physical mechanism of deep earthquakes earthquake mechanisms based on frictional instabilities are widely accepted for relatively shallow earthquakes such mechanisms in unmodified form are highly unlikely for deep earthquakes because of the expected high frictional shear stresses at depths of 300 700 km several alternative mechanisms have been proposed here i discuss a new type of shear instability observed in experiments on ordinary polycrystalline ice and polycrystalline tremolite by my colleagues and me these shear instabilities lead to rapid stress drops and sound emissions and have the following characteristics 1 a single sharp shear zone forms in the maximum shear stress orientation 2 confining pressure does not suppress the instability and under some conditions raising confining pressure pc lowers the differential stress at which it occurs 3 stress drops can occur repeatedly after reloading at about the same differential stress 4 the mean stress vs temperature conditions at which the instabilities occur in ice and tremolite place them in the fields of thermodynamic stability of ice ii and diopside talc respectively although i have not as yet confirmed the existence of these high pressure phases in the shear zones transformation in the shear zone is implicated because such shear instabilities do not occur in similar materials in which polymorphic phase changes do not occur reconstructive polymorphic phase changes localized along shear zones may be a general phenomenon in crystalline materials stressed non hydrostatically near transition boundaries moreover by analogy the reconstructive phase transformations that are thought to occur in deeply subducted lithosphere may lead to localized shear instabilities manifested by deep earthquakes and produce the observed double couple first motion distribution finally if this is the earthquake source mechanism in deeply subducted lithosphere then earthquakes should shut off when all of the polymorphic phase changes have occurred this may explain the maximum depth of earthquakes at about 680 km

finite difference calculation of travel times the travel times of the first arriving seismic waves through any velocity structure can be rapidly computed on a two or three dimensional numerical grid by finite difference extrapolation from point to point wavefronts rather than the traditional rays are tracked head waves are properly treated and shadow zones are filled by the appropriate diffractions differences of less than 0 03 per cent are found between the results of this technique and raytracing for a complex two dimensional model this scheme is useful for the windowing of finite difference calculations to increase computing speed and promises to aid in earthquake location tomographic inversion and kirchhoff migration in structures that have strong lateral velocity gradients

evidence for deformation induced k feldspar replacement by myrmekite several examples of deformation induced myrmekite have been found in two amphibolite facies mylonites derived from granitic protoliths namely a muscovite poor s c mylonite and a single foliation muscovite poor mylonitic gneiss back scattered sem and conventional optical microscopy show that in both rock types syntectonic myrmekitic intergrowths of oligoclase and quartz formed on the two sides of k feldspar grains that faced the local inferred incremental shortening direction for the mylonite myrmekite does not occur on the two ends of the grain that faced the incremental stretching direction the replacement of k feldspar by plagioclase and quartz results in a volume decrease and is favoured on high normal stress sites around the grains we suggest that the ambient temperature pressure and chemical activities were such that the replacement reaction was favoured but the addition of extra strain energy along the high pressure sides of the grains localized the reaction at these sites this energy could arise from elastic strain or strain associated with tangled dislocations or twin boundaries the relative roles of stress and strain energy concentrations in driving the replacement reaction are not known but both were probably important

anomalously low aftershock productivity of the 2019 mw 8 0 energetic intermediate depth faulting beneath peru abstract the 26 may 2019 peru m w 8 0 earthquake struck within the nearly horizontal underthrust nazca plate at depths from 110 to 150 km below the upper amazon near a steep bend in the plate where it plunges down to a deep earthquake zone little prior seismicity occurred in this region but large intraslab events with similar normal faulting mechanisms have occurred to the west the event is situated in a similar slab position to the 2017 puebla morelos mexico earthquake but the remote location resulted in limited loss of life and damage back projection imaging and finite fault inversion based on teleseismic data suggest a brittle and energetic rupture process with unilateral expansion northward over a 170 km long zone at a rupture speed v r 3 km s with three normal faulting patches of up to 4 5 m slip despite the mainshock size it produced only three m4 0 aftershocks within 300 km one nearby the aftershock productivity of the 2019 peru earthquake is very low even among all large intermediate depth earthquakes but similar to that for other large peruvian intraslab events comparison of aftershock productivity of the peru event with that of global large earthquakes in various tectonic settings suggests that the low aftershock productivity can largely be attributed to regionally homogeneous faulting systems and relatively uniform stress state in the flat peru slab

silicate liquid immiscibility within the crystal mush late stage magmatic microstructures in the skaergaard intrusion east greenland late stage microstructures developed during the last stages of solidification of the skaergaard intrusion comprise a wide array of reactive and non reactive intergrowths reactive microstructures ascribed to open system behaviour include serrated grain boundaries between pyroxene and plagioclase primocrysts fish hook pyroxenes and mafic symplectites they form by the addition of fe and ca and removal of alkalis and silica other microstructures include those formed by internally generated redox reactions between olivine fe ti oxides and pyroxene non reactive microstructures include closely spatially associated granophyric intergrowths and previously undescribed ilmenite rich intergrowths that are interpreted as a consequence of crystallization of separated conjugate immiscible liquids the open system reactive microstructures occur predominantly in the cumulates on the chamber floor appearing in lzb and disappearing to be replaced by a granophyre ilmenite rich intergrowth association in the upper zone they are not common in the marginal border series their distribution mirrors that of efficient expulsion of trapped liquid and can be attributed to the gravitationally driven loss of a si rich immiscible component from the interstitial liquid the loss of the si rich component causes the remaining fe rich liquid to react with the primocrysts bulk rock major element data are consistent with little or no preferential loss of the si rich liquid from the mush but the resolution of the available data is not sufficient to assess the effect of this relative movement on the liquid line of descent of the bulk magma the first appearance of the paired conjugate non reactive intergrowths in mz marginal border series points to the early onset of immiscibility in the bulk liquid

combined analysis of seismic and gravimetric data in the adriatic plate abstract the presence of a structural heterogeneity between the northern part of the adriatic plate central mediterranean and its southernmost sector was hypothesised by different authors and also confirmed recently by 3d velocity models obtained through surface wave tomography and local earthquake tomography however the seismological data leave some uncertainty about the location of the lateral limits of this heterogeneity and about its structural meaning the analysis of the bouguer anomalies observed on a profile running from nw to se along the italian side of the plate has allowed to obtain a laterally improved and better constrained integrated model of the area in particular the gravimetric data have been interpreted through a 2 1 2 d density modelling developed adopting the seismic tomography model as starting point the obtained results support the hypothesis of a 10 km thinning of the crust from nw to se compensated by the presence of a thick transition zone under the crust in the southern part of the adriatic plate the location of the boundary of this lateral heterogeneity was better defined being marked by an increase of the bouguer anomalies the estimated density contrasts of the transition zone with respect to the contiguous layers of lower crust and mantle about 0 5 and 0 1 g cm3 respectively and the comparison with the corresponding velocity contrasts suggest that the material constituting this transition zone might have a composition more similar to that of the mantle

two pyroxene thermometry of precambrian granulites from cape riche albany fraser province western australia coexisting ca poor and ca rich pyroxenes in granulites at cape riche in the precambrian albany fraser province western australia are dominantly chemically homogeneous within individual samples suggesting a major episode of equilibration however occasional grains in a few samples contain exsolved domains interpreted as relics of an earlier higher t assemblage pyroxene pairs in ten presumably isothermal samples from a restricted area are used to i assess the suitability of several versions of the two pyroxene thermometer for application to metamorphic rocks and ii determine the thermal history of the cape riche pyroxenes the various versions of the two pyroxene thermometer applied to the well equilibrated homogeneous pyroxene grains show poor to good precision and yield mean temperatures varying widely from 683 to 893 c in the following order of increasing t lindsley 1983 opx version 683 11 c kretz 1982 kd version 705 19 c ross huebner 1975 709 30 c kretz 1982 solvus version 735 24 c fonarev graphchikov 1982 opx version 750 c lindsley 1983 cpx version 784 40 c fonarev graphchikov 1982 cpx version 820 30 c wood banno 1973 849 16 c powell 1978 854 23 c wells 1977 893 10 c independent t estimates based on mafic assemblages and garnet biotite thermometry suggest that the major episode of metamorphism occurred at 700 800 c p 5 kbar therefore the wells powell wood banno and fonarev graphchikov cpx temperatures are almost certainly too high in the absence of a more precise independent t estimate it is difficult to assess the relative merits of the results obtained from the remaining versions of the two pyroxene thermometer none of which can be unequivocally demonstrated to be seriously in error though the lindsley opx t is probably too low other significant shortcomings evident in the results include the relatively poor precision obtained from the three methods based on purely graphical representation of the augite limb of the solvus i e the ross huebner fonarev graphchikov cpx and lindsley cpx versions and the apparent dependence of derived t on mg fe2 ratio for the powell wood banno and lindsley cpx methods for the bulk compositions of exsolved domains the different versions of the two pyroxene thermometer yield mean temperatures 23 to 82 c overall mean 65 c higher than for homogeneous grains in the same samples these exsolved domains are interpreted as relics of a higher t peak metamorphic assemblage rather than an igneous precursor

the effect of dislocations on bulk diffusion in feldspars during metamorphism there is no significant difference in the diffusion profiles across albite adularia bicrystals that were simultaneously deformed at a strain rate of 10 6s 1 and those from hydrostatic experiments at the same conditions 1500 mpa and 1000 c for 156 h this indicates that the bulk alkali diffusion rate which is the sum of lattice diffusion d 1 and dislocation pipe diffusion dp is not significantly enhanced by dislocations at these conditions and that the maximum value for the ratio of dp d1 is about 105 this is equal to the value previously reported for oxygen diffusion in albite if this ratio is independent of temperature the contribution of either static pre deformed or moving syn deformed dislocations to the bulk diffusion rate of alkalis is probably minor at all metamorphic conditions for al and si diffusion the ratio of dp d1 may be larger if d1 is lower thus a significant contribution from dislocations to bulk diffusion cannot be ruled out especially during simultaneous deformation

data dependent non double couple components of shallow earthquake source mechanisms effects of waveform inversion instability seismic moment tensors are routinely determined for global earthquakes using waveform inversions and the resulting double couple and non double couple characteristics are extensively used in tectonic analyses for shallow events several moment tensor components are intrinsically poorly resolved especially for surface wave inversions which can lead to artificial non double couple components or can obscure actual non double couple components in the source representations the relatively greater instability of surface wave inversions can cause differences between inversions based on only body waves and joint inversions of body and surface waves the harvard cmt catalog exhibits systematic variations in non double couple components with seismic moment which can be attributed to use of only body waves in inversions for small events and combined body and surface waves for large events systematic behavior of non double couple components with regional strain environment is significantly less dependent on seismic moment when solutions influenced by less stable surface waves are omitted

sequential inversion of local earthquake traveltimes and gravity anomaly the example of the western alps summary we present a joint analysis of gravity anomaly and seismic arrival time data recorded in the western alps seismological data were collected by a network of 126 permanent and temporary stations implemented in 1996 a set of 550 local events has been recorded gravity data result from the addition of two new gravity surveys to an existing data base a published velocity model obtained by local earthquake tomography let was used to construct an initial 3 d gravity model using a linear velocity density relationship birch s law while the synthetic bouguer anomaly field calculated for this model has the same shape and wavelength as the observed anomaly its amplitude is strongly underestimated to derive a crustal velocity density model that accounts for both types of observations we performed a sequential inversion of seismological and gravity data the variance reduction of the arrival time data for the final sequential model was comparable to the variance reduction obtained by simple let moreover the sequential model explained 90 per cent of the observed gravity anomaly the main features of our model compared with the let model are 1 an important broadening of the high velocity anomaly associated with the high velocity high density ivrea body 2 a 10 km thick low velocity zone beneath the nappes of digne and castellane and 3 a high velocity zone at more than 25 km depth under the internal zone of the range

geophysical modeling via simultaneous joint inversion of seismic gravity and electromagnetic data application to prestack depth imaging geophysical modeling of multiple geophysical parameters can take place reliably through the simultaneous joint inversion of the different geophysical domains the desired objective is the derivation of a model expressing different geophysical properties of the earth but at the same time showing consistency among the parameters this concept generally referred to as data integration is widespread in geophysics but the way of achieving it is not obvious several authors have proposed different approaches where data interpretation and experience all contributed to the task the result is that no general workflows could be defined that left ample margins for uncertainties and personal judgment

deformation of granitic rocks across the brittle ductile transition abstract a microstructural analysis has been carried out on mylonites and mylonitic gneisses of the eastern peninsular ranges mylonite zone which were formed over a range of metamorphic conditions from lower greenschist to amphibolite facies composite planar fabrics in the form of c and s planes are found at all metamorphic grades fractured feldspars kinked biotites and ductile deformation of quartz characterize the lower greenschist facies mylonites at mid upper greenschist grade orthoclase grains show dynamic recrystallization textures whereas plagioclase exhibits low temperature plasticity with only minor recovery biotite ribbons form by progressive rotation and coalescence of kink band segments to produce chevron fold patterns at epidote amphibolite grade and above recovery processes and annealing recrystallization predominate in all minerals residual orthoclase porphyroclasts show strain related myrmekite formation along those sides of the grains that face the instantaneous shortening direction myrmekite formation due to replacement reactions cannot explain this geometry it is proposed that the myrmekites formed due to a combination of exsolution replacement and strain enhanced diffusion

a review of least squares inversion and its application to geophysical problems geophysical inversion involves the estimation of the parameters of a postulated earth model from a set of observations since the associated model responses can be nonlinear functions of the model parameters nonlinear least squares techniques prove to be useful for performing the inversion a common type of inversion applies iterative damped linear least squares through use of the marquardt levenberg method traditionally this method has been implemented by solving the associated normal equations in conventional ways however singular value decomposition svd produces significant improvements in computational precision when applied to the same system of normal equations iterative least squares modeling finds application in a wide variety of geophysical problems two examples illustrate the approach 1 seismic wavelet deconvolution and 2 the location of a buried wedge from surface gravity data more generally nonlinear least squares inversion can be used to estimate earth models for any set of geophysical observations for which an appropriate mathematical description is available

two dimensional inversion of direct current resistivity data incorporating topography by using finite difference techniques with triangle cells investigation of kera fault zone in western crete in this study we suggest the use of a finite difference fd forward solution with triangular grid to incorporate topography into the inverse solution of direct current resistivity data a new inversion algorithm was developed that takes topography into account with finite difference and finite element forward solution by using triangular grids using the developed algorithm surface topography could also be incorporated by using triangular cells in a finite difference forward solution initially the inversion algorithm was tested for two synthetic data sets inversion of synthetic data with the finite difference forward solution gives accurate results as well as inversion with finite element forward solution and requires less cpu time the algorithm was also tested with a field data set acquired across the kera fault located in western crete greece the fault location and basement depth of sedimentary units were resolved by the developed algorithm these inversion results showed that if underground st

mid mantle anisotropy in subduction zones and deep water transport the earth s transition zone has until recently been assumed to be seismically isotropic increasingly however evidence suggests that ordering of material over seismic wavelengths occurs there but it is unclear what causes this we use the method of source side shear wave splitting to examine the anisotropy surrounding earthquakes deeper than 200 km in slabs around the globe we find significant amounts of splitting 2 4 s confirming that the transition zone is anisotropic here however there is no decrease in the amount of splitting with depth as would be the case for a metastable tongue of olivine which thins with depth suggesting this is not the cause the amount of splitting does not appear to be consistent with processes in the ambient mantle such as lattice preferred orientation development in wadsleyite ringwoodite or mgsio3 perovskite we invert for the orientation of several mechanisms subject to uncertainties in mineralogy and deformation and the best fit is given by updip flattening in a style of anisotropy common to hydrous phases and layered inclusions we suggest that highly anisotropic hydrous phases or hydrated layering is a likely cause of anisotropy within the slab implying significant water transport from the surface down to at least 660 km depth

timescales for the evolution of seismic anisotropy in mantle flow 1 we study systematically the relationship between olivine lattice preferred orientation and the mantle flow field that produces it using the plastic flow recrystallization model of kaminski and ribe 2001 in this model a polycrystal responds to an imposed deformation rate tensor by simultaneous intracrystalline slip and dynamic recrystallization by nucleation and grain boundary migration numerical solutions for the mean orientation of the a axes of an initially isotropic aggregate deformed uniformly with a characteristic strain rate show that the lattice preferred orientation evolves in three stages 1 for small times recrystallization is not yet active and the average a axis follows the long axis of the finite strain ellipsoid 2 for intermediate times the fabric is controlled by grain boundary migration and the average a axis rotates toward the orientation corresponding to the maximum resolved shear stress on the softest slip system 3 for the fabric is controlled by plastic deformation and average a axis rotates toward the orientation of the long axis of the finite strain ellipsoid corresponding to an infinite deformation the infinite strain axis in more realistic nonuniform flows lattice preferred orientation evolution depends on a dimensionless grain orientation lag parameter x defined locally as the ratio of the intrinsic lattice preferred orientation adjustment timescale to the timescale for changes of the infinite strain axis along path lines in the flow explicit numerical calculation of the lattice preferred orientation evolution in simple fluid dynamical models for ridges and for plume ridge interaction shows that the average a axis aligns with the flow direction only in those parts of the flow field where 1 calculation of provides a simple way to evaluate the likely distribution of lattice preferred orientation in a candidate flow field at low numerical cost

chromite symplectites in mg suite troctolite 76535 as evidence for infiltration metasomatism of a lunar layered intrusion abstract despite the very low chromium concentrations in its cumulus olivine 140 ppm lunar troctolite 76535 contains large amounts of cr sporadically but highly concentrated in symplectite assemblages consisting of mg al chromite and two pyroxenes previously proposed symplectite formation mechanisms include crystallization of trapped interstitial melt diffusion of cr from cumulus olivine and or remobilization of cumulus chromite grains these mechanisms would imply that the highly cr depleted nature of mg suite parental magmas and their source materials inferred from cumulus olivine may be illusory we have conducted a detailed petrologic and textural study of symplectites as well as chromite veins intercumulus assemblages olivine hosted melt inclusions and clinopyroxene troilite veins in 76535 with the goals of constraining the origin of the symplectites and the degree of cr depletion in mg suite magmas relative to other lunar basalts orthopyroxene and clinopyroxene in melt inclusions are depleted in cr relative to their symplectite counterparts averaging 900 and 1200 ppm vs 7400 and 8100 ppm cr 2 o 3 respectively olivine in contact with symplectite assemblages may exhibit a diffusion profile of cr going into olivine whereas olivine boundaries away from symplectites show no diffusion profile there is also a distinct lack of primary chromite as inclusions in cumulus phases and melt inclusions multiple textural observations melt inclusion chemistry and modeling of chromite olivine equilibrium rule out previously proposed symplectite formation mechanisms and strongly suggest that chromite was not a primary crystallization product of the 76535 parental magma accordingly the post cumulus addition of cr and fe is required to produce the symplectites after considering multiple models the addition of cr and fe to 76535 via infiltration metasomatism by an exogenous chromite saturated melt is the model most consistent with multiple textural and geochemical observations failure of models that call upon cr diffusion out of olivine grains imply that the observed cr depleted nature of olivine observed in many mg suite lithologies is a primary feature of the cr depleted nature of the mg suite parental magmas and their source materials this substantial depletion of cr in the magma relative to mare basalt magmas still requires a satisfactory explanation in order to be consistent with mg suite petrogenetic models and currently accepted bulk moon compositions additionally if the intimate interaction of migrating melts with early lunar crustal lithologies was a widespread phenomenon after lmo solidification it provides another mechanism by which to reset or delay closure of radiogenic isotopic systems and explain the mg suite ferroan anorthosite age overlap

lamellar pyroxenes and their petrogenetic significance three examples from the czech massif the first event in the crystallization of pyroxenite in nodules from bory was the growth of clinopyroxene at an uncertain 1 190 30 c and 2 5 2 gpa lamellae of garnet and orthopyroxene in cpx nucleated slightly above 1 000 c and equilibrated at 940 20 c and 3 9 6 gpa the growth of lamellae was followed by crystallization of groundmass that corroded lamellar clinopyroxene phenocrysts of clinopyroxene and orthopyroxene in olivine pyroxenite from t i studn crystallized at 1 290 100 c and 2 3 1 4 gpa the lamellae in both phases nucleated between 1 400 and 1 200 c and equilibrated at 860 40 c and 0 2 3 gpa before regional metamorphism the temperatures of nucleation mentioned rest on uncertain assumptions in the phase boundary theory and should be viewed with caution the serpentinized peridotite pyroxenite from destna contains clinopyroxene relics the only primary phase with lamellae of a 1 42 nm sheet silicate topotactically pseudomorphing enstatite possibly a chlorite or vermiculite all phases in lamellae are crystallographically oriented in the hosts the present cases suggest that when applying the theory of phase boundaries a modified procedure of robinson et al should also be considered in which identity of adjacent areas rather than just vectors is the basis of calculation spinel lamellae in cpx are bounded not only by faces parallel to coherent interfaces but also by faces formed by accumulation of incoherent edges of growth ledges

three dimensional seismic refraction tomography a comparison of two methods applied to data from the faeroe basin this paper presents a comparison of two tomographic methods for determining three dimensional 3 d velocity structure from first arrival travel time data the first method is backprojection in which travel time residuals are distributed along their ray paths independently of all other rays the second method is regularized inversion in which a combination of data misfit and model roughness is minimized to provide the smoothest model appropriate for the data errors both methods are nonlinear in that a starting model is required and new ray paths are calculated at each iteration travel times are calculated using an efficient implementation of an existing method for solving the eikonal equation by finite differencing both inverse methods are applied to 3 d ocean bottom seismometer obs data collected in 1993 over the faeroe basin consisting of 53 479 travel times recorded at 29 obss this is one of the most densely spaced large scale 3 d seismic refraction experiments to date different starting models and values for the free parameters of each tomographic method are tested a new form of backprojection that converges more rapidly than similar methods compares favorably with regularized inversion but the latter method provides a simpler model for little additional computational expense when applied to the faeroe basin data bounds on two model features are assessed using regularized inversion with combined smoothness and flatness constraints an inversion of synthetic data corresponding to 100 data recovery from the real experiment shows a marked improvement in lateral resolution at deeper depths and demonstrates the potential of currently feasible 3 d refraction experiments to provide well resolved long wavelength velocity models the similarity of the final models derived from the two tomographic methods suggests that the results from the new form of backprojection can be relied on when limited computational resources rule out regularized inversion

mantle flow in subduction systems the mantle wedge flow field and implications for wedge processes 1 the mantle wedge above subducting slabs is associated with many important processes including the transport of melt and volatiles our understanding of mantle wedge dynamics is incomplete as the mantle flow field above subducting slabs remains poorly understood because seismic anisotropy is a consequence of deformation measurements of shear wave splitting can constrain the geometry of mantle flow in order to identify processes that make first order contributions to the pattern of wedge flow we have compiled a data set of local s splitting measurements from mantle wedges worldwide there is a large amount of variability in splitting parameters with average delay times ranging from 0 1 to 0 3 s up to 1 0 1 5 s and large variations in fast directions we tested for relationships between splitting parameters and a variety of parameters related to subduction processes we also explicitly tested the predictions made by 10 different models that have been proposed to explain splitting patterns in the mantle wedge we find that no simple model can explain all of the trends observed in the global data set mantle wedge flow is likely controlled by a combination of downdip motion of the slab trench migration ambient mantle flow small scale convection proximity to slab edges and slab morphology with the relative contributions of these in any given subduction system controlled by the subduction kinematics and mantle rheology there is also a likely contribution from b type olivine and or serpentinite fabric in many subduction zones governed by the local thermal structure and volatile distribution

mapping of p wave slab anomalies beneath the tonga kermadec and new hebrides arcs abstract p wave velocity anomalies of several per cent fast relative to the jeffreys bullen jb model are seen around subduction zones under the tonga kermadec and new hebrides trenches from inversion of international seismological centre isc travel time residuals from intermediate and deep focus earthquakes mantle heterogeneities outside the model are corrected using previous velocity models ray paths inside the model region are traced allowing two dimensional velocity variations the rays of similar source and receiver locations are combined into summary rays and the hypocenters are relocated as part of the inversion iterations the resulting images are interpreted in conjunction with resolution and error estimations the slab like anomalies are generally continuous in places of high seismicity and decrease in amplitude with depth most coherent slab anomalies are surrounded by large slow patches between the surface and 350 km depth the fast slab beneath the tonga arc appears to end at 550 km depth before the seismicity ends but there is a fast band at 750 1000 km depths below the deepest tongan earthquakes the fast slab like anomaly beneath the kermadec arc tends to flatten to subhorizontal near the bottom of upper mantle and it occurs aseismically near new zealand down to 500 550 km depth interpretations in the lower mantle in many places such as kermadec and new hebrides arcs however are hampered by poor resolution

robust geophysical integration through structure coupled joint inversion and multispectral fusion of seismic reflection magnetotelluric magnetic and gravity images example from santos basin offshore brazil abstractwe have applied a crossgradient joint inversion and geospectral visualization method to marine seismic reflection magnetotelluric gravity and magnetic data sets acquired along a 162 km profile across a segment of santos basin oil province in the continental margin of southeast brazil the main exploration targets are the top of the fractured precambrian crystalline basement and any concealed basement grabens the overlying presalt and salt carbonate deposits and the postsalt cover deposits the results of joint inversion clearly mapped the various units and are a significant improvement over previous models derived from separate 2d seismic reflection processing and 2d magnetotelluric imaging additionally multispectral fusion of these models resulted in a single image that permits highly constrained geologic interpretations enabling a better understanding of basin architecture we suggest that joint inversion and image fusion is the way forward for effective geophysical integration

elastic anisotropy due to aligned cracks in porous rock all theoretical expressions which relate the characteristics of saturated aligned cracks to the associated elastic anisotropy are restricted in some important way for example to the case of stiff pore fluids or of the absence of equant porosity or of a moderately high frequency band because of these restrictions previous theory is not suitable for application to the upper crust where the pore fluid is brine kf k820 the equant porosity is often substantial p 0 1 and the frequency band is sonic to seismic this work removes these particular restrictions recognizing in the process an important mechanism of dispersion a notable feature of these more general expressions is their insensitivity at low frequency to the aspect ratio of the cracks only the crack density is critical an important conclusion of this more general model is that many insights previously achieved concerning the shear wave splitting due to vertical aligned saturated cracks are sustained however conclusions on crack orientation or crack aspect ratio which were derived from p wave data or from shear wave critical angles may need to be reconsidered further the non linear coupling between pores and cracks due to pressure equalization effects means that the linear schoenberg muir calculus may not be applied to such systems the theory receives strong support from recent data by rathore et al on artificial samples with controlled crack geometry

joint inversion for global isotropic and radially anisotropic mantle structure including crustal thickness perturbations we present a new global whole mantle model of isotropic and radially anisotropic s velocity structure sglobe rani based on 43 000 000 surface wave and 420 000 body wave travel time measurements which is expanded in spherical harmonic basis functions up to degree 35 we incorporate crustal thickness perturbations as model parameters in the inversions to properly consider crustal effects and suppress the leakage of crustal structure into mantle structure this is possible since we utilize short period group velocity data with a period range down to 16 s which are strongly sensitive to the crust the isotropic s velocity model shares common features with previous global s velocity models and shows excellent consistency with several high resolution upper mantle models our anisotropic model also agrees well with previous regional studies anomalous features in our anisotropic model are faster sv velocity anomalies along subduction zones at transition zone depths and faster sh velocity beneath slabs in the lower mantle the derived crustal thickness perturbations also bring potentially important information about the crustal thickness beneath oceanic crusts which has been difficult to constrain due to poor access compared with continental crusts

seismic anisotropy changes across upper mantle phase transitions the mantle transition zone is believed to play an important role in the thermochemical evolution of our planet and in its deep water cycle constraining mantle flow at these depths can help elucidate its nature and better understand mantle dynamics and the history of plate tectonics seismic anisotropy i e the directional dependence of seismic wave velocity provides us with the most direct constraints on mantle deformation its detection below 250 km depth is challenging and it is often assumed that the deep upper mantle is seismically isotropic due to a change in mantle deformation mechanism here we present a global model of azimuthal anisotropy for the top 1000 km of the mantle we used a dataset composed of fundamental and higher mode rayleigh wave phase velocity maps which provides resolution of azimuthal anisotropy to much greater depths than in previous studies our model unravels the presence of significant anisotropy in the transition zone challenging common views of mantle deformation mechanisms and reveals a striking correlation between changes in anisotropy amplitudes and in the fast direction of wave propagation where upper mantle phase transitions occur the newly found relation between anisotropy changes and phase transformations gives new insight on the nature of the mtz and suggests that the anisotropy originates from the lattice preferred orientation of anisotropic material while the interpretation of our results in terms of mantle deformation is not straightforward due to many possible scenarios possible explanations for our findings include recrystallization during phase transformations or changes in the slip system across the mtz boundaries which in turn could be explained by changes in the water content of mantle material consistent with the idea that the transition zone acts as a water filter 2013

shearing instabilities accompanying high pressure phase transformations and the mechanics of deep earthquakes deep earthquakes have been a paradox since their discovery in the 1920s the combined increase of pressure and temperature with depth precludes brittle failure or frictional sliding beyond a few tens of kilometers yet earthquakes occur continually in subduction zones to 700 km the expected healing effects of pressure and temperature and growing amounts of seismic and experimental data suggest that earthquakes at depth probably represent self organized failure analogous to but different from brittle failure the only high pressure shearing instabilities identified by experiment require generation in situ of a small fraction of very weak material differing significantly in density from the parent material this fluid spontaneously forms mode i microcracks or microanticracks that self organize via the elastic strain fields at their tips leading to shear failure growing evidence suggests that the great majority of subduction zone earthquakes shallower than 400 km are initiated by breakdown of hydrous phases and that deeper ones probably initiate as a shearing instability associated with breakdown of metastable olivine to its higher pressure polymorphs in either case fault propagation could be enhanced by shear heating just as is sometimes the case with frictional sliding in the crust extensive seismological interrogation of the region of the tonga subduction zone in the southwest pacific ocean provides evidence suggesting significant metastable olivine with implication for its presence in other regions of deep seismicity if metastable olivine is confirmed either current thermal models of subducting slabs are too warm or published kinetics of olivine breakdown reactions are too fast

inversion for anisotropy from non double couple components of moment tensors 1 an inversion method for retrieving seismic anisotropy from non double couple components of seismic moment tensors is presented the method requires a set of highly accurate moment tensors of earthquakes that occurred in a homogeneous anisotropic focal area on differently oriented faults in contrast to standard methods retrieving anisotropy from travel times or from shear wave splitting which yield an overall anisotropy averaged along a whole ray path the presented method yields a local value of anisotropy just in the focal area the method is robust being able to retrieve the orientation as well as strength of anisotropy even for low anisotropy symmetries as for orthorhombic symmetry the method can utilize the moment tensors constrained to have zero trace but using unconstrained moment tensors is advantageous the method is applied to retrieving anisotropy in the tonga subduction zone using moment tensors of deep focus earthquakes reported in the harvard centroid moment tensor catalog the inversion is complemented by tests on synthetic data to assess its stability and the accuracy of the results the inversion indicates that the subduction zone is anisotropic with orthorhombic symmetry the orientation of the intra slab anisotropy is defined by axes azimuth dip a1 320 54 a2 121 38 and a3 223 81 the errors in the azimuth and dip are about 5 the first and second axes lie along the downdip motion of the slab and along the normal to the slab respectively the strength of the p s1 and s2 anisotropy is of 7 3 1 5 13 4 2 5 and 12 6 3 5 respectively the errors of anisotropy strength are only rough estimates which reflect random but not systematic errors in the moment tensors used in the inversion the values for anisotropy strength in the slab are remarkably higher than those observed in the surrounding mantle the symmetry axes of anisotropy coincide with the principal stress directions in the slab this manifests a primary impact of stress on anisotropy formation the retrieved anisotropy in the slab can serve as an additional constraint on its structure and mineralogical composition

ellipticity of teleseismic s particle motion summary in the horizontal components of grf records particle motions of the teleseismic s waves in the period range between 5 and 20s are usually elliptic we correct the particle motions for the effect of azimuthal anisotropy at grf and explain the residual ellipticity by assuming that it is produced at the source side of the wave path by interference of two waves with orthogonal polarizations and differing traveltimes the estimates of polarization direction of the fast wave and time delay between the waves can be found by analysing the residual particle motion for groups of closely spaced seismic events the technique was applied to about 40 grf records of events from the northern and north western pacific in the source regions the s wave pulses propagate in subduction zones it is found that the surface projections of polarization of the fast wave of the shallow events coincide approximately with the strikes of the corresponding island arcs this regularity can be explained by anisotropy in the subduction zones provided that the a axis of olivine is parallel to the plane of subduction the fast direction for the deep events in the sea of japan and the sea of okhotsk is close to the strike of the kurile island arc the time delay between the fast and the slow waves for the deep events is smaller than for the shallow kurile events 0 9s versus 1 4s

constrained resistivity inversion using seismic data summary in this paper we describe and apply a method for constraining structure in anisotropic electrical resistivity inversion structural constraints are routinely used to achieve improved model inversion here a second order curvature based regularization tensor model covariance is used to build structure in the model this structure could be obtained from other imaging methods such as seismic tomography core samples or otherwise known structure in the model our method allows the incorporation of existing geophysical data into the inversion in a general form that does not rely on any one to one correlation between data sets or material properties ambiguities in the resistivity distribution from electrical inversion and in particular anisotropic inversion may be reduced with this approach to demonstrate the approach we invert a synthetic data set showing the regularization tensor explicitly in different locations we then apply the method to field data where we have some knowledge of the subsurface from seismic imaging our results show that it is possible to achieve a high level of convergence while using spatially varying structural constraints common problems associated with resistivity inversion such as source receiver effects and false imaging of strongly resistive or conductive zones may also be reduced as part of the inversion method we show how the magnitude of the constraints in the form of penalty parameters appropriate to an inversion may be estimated reducing the computational expense of resistivity inversion

local earthquake le tomography with joint inversion for p and s wave velocities using structural constraints local earthquake le tomography with joint inversion for p and s wave velocities using structural constraints

characterization of heterogeneous near surface materials by joint 2d inversion of dc resistivity and seismic data 1 we have developed a robust 2d joint inversion scheme incorporating the new concept of cross gradients of electrical resistivity and seismic velocity as constraints so as to investigate more precisely the resistivity velocity relationships in complex near surface environments the results of joint inversion of dc resistivity and seismic traveltime data from collocated experiments suggest that one can distinguish between different types or facies of unconsolidated and consolidated materials refining a previously proposed resistivity velocity interrelationship derived from separate inversions of the respective data sets a consistent interpretive structural model can be obtained from the joint inversion models

seismic anisotropy in the south western pacific region from shear wave splitting 1 we perform shear wave splitting measurements to determine seismic anisotropy in the upper mantle under the remote and still not well understood south western pacific region more precisely the new hebrides subduction zone we obtained 29 good and 35 fair splitting measurements at 8 stations and 93 good and fair null measurements from the data provided by various networks according to the splitting parameters the seismic stations are grouped into eastern and western stations anisotropy of the subducting plate western stations appears to be the result of absolute plate motion apm of the australian plate from fast orientations alone it would be difficult to judge which process is responsible for the anisotropic structure either the absolute plate motion or trench parallel toroidal flow their delay times reveal that these anisotropic parameters can be explained without the presence of the subduction zone and the apm provides a simple explanation for the observed anisotropy on the other hand delay times at eastern stations are higher than that of western stations these stations are located close to the subduction zone and the nearly trench parallel orientation of fast polarization axes and their higher splitting delay times indicate the presence of subduction zone anisotropy at eastern stations is apparently due to the additional effect from toroidal flow near the subduction zone which increases the total anisotropy

improved hydrogeophysical characterization using joint inversion of cross hole electrical resistance and ground penetrating radar traveltime data appropriate regularizations of geophysical inverse problems and joint inversion of different data types improve geophysical models and increase their usefulness in hydrogeological studies we have developed an efficient method to calculate stochastic regularization operators for given geostatistical models the method which combines circulant embedding and the diagonalization theorem of circulant matrices is applicable for stationary geostatistical models when the grid discretization in each spatial direction is uniform in the volume of interest we also used a structural approach to jointly invert cross hole electrical resistance and ground penetrating radar traveltime data in three dimensions the two models are coupled by assuming at all points that the cross product of the gradients of the two models is zero no petrophysical relationship between electrical conductivity and relative permittivity is assumed but is instead obtained as a by product of the inversion the approach has been applied to data collected in a u k sandstone aquifer in order to improve characterization of the vadose zone hydrostratigraphy by analyzing scatterplots of electrical conductivity versus relative permittivity together with petrophysical models a zonation could be obtained with corresponding estimates of the electrical formation factor the water content and the effective grain radius of the sediments the approach provides greater insight into the hydrogeological characteristics of the subsurface than by using conventional geophysical inversion methods

gabbroic rocks from the mathematician ridge failed rift plutonic rocks from the ocean crust provide direct evidence on the petrological processes leading to its formation and evolution the nature of such rocks is important for interpreting the origin of on land ophiolites so far oceanic plutonic rocks have been mainly recovered from slow spreading ridges and their associated fractures1 13 and from trenches14 15 here we report the results of petrological studies of a suite of gabbros and related plutonic and volcanic rocks dredged from the mathematician ridge mr which was a fast spreading ridge 43 mm yr 1 until it was abandoned 3 5 myr ago16 textures and mineral chemistry of the rocks together with structural considerations indicate that before abandonment the mr produced fractionated mid ocean ridge basalt morb and fractionated gabbros the gradual decrease of spreading rate during abandonment resulted in morphological change eruption of more primitive morb and possibly tectonic emplacement of the older ferrogabbros alternatively the latter could have been tectonically emplaced after abandonment

electrical resistivity and seismic refraction tomography to detect buried cavities near surface cavities can pose serious hazards to human safety especially in highly urbanized town centres the location of subsurface voids the estimation of their size and the evaluation of the overburden thickness are necessary to assess the risk of collapse in this study electrical resistivity tomography ert and seismic refraction tomography data are integrated in a joint interpretation process for cavity location in the city of rome ert is a well established and widely employed method for cavity detection however additional information provided by seismic refraction tomography is capable of eliminating some potential pitfalls in resistivity data interpretation we propose that the structure of the cavities defined by ert can be used as a base to optimize seismic refraction tomography investigations within the framework of a joint interpretation process data integration and the insertion of a priori information are key issues for reducing the uncertainties associated with the inversion process and for optimizing both acquisition procedures and computation time herein the two geophysical methods are tested on both synthetic and real data and the integration of the results is found to be successful in detecting isolated cavities and in assessing their geometrical characteristics the cavity location inferred by geophysical non invasive methods has been subsequently confirmed by direct inspection

petrogenesis of orthopyroxene magnetite ilmenite intergrowths from an ultramafic layer a new occurrence of myrmekitic orthopyroxene magnetite ilmenite intergrowth from a thin ultramafic layer within a heterogeneous noritic rock from the frederiksdal area south greenland was investigated chemically and texturally compositionally the intergrown ilmenite and orthopyroxene show the lowest recorded mgo content from pyroxene oxide mineral intergrowths the magnetite ilmenite intergrowth has skeletal morphology consisting of sets of thinly tabular plates parallel to the 111 planes of the spinel structure the orthopyroxene oxide intergrowth is considered to be the result of a simultaneous magmatic crystallization that of the oxide minerals being faster

non double couple earthquakes 1 theory historically most quantitative seismological analyses have been based on the assumption that earth quakes are caused by shear faulting for which the equiv alent force system in an isotropic medium is a pair of force couples with no net torque a double couple or dc observations of increasing quality and coverage however now resolve departures from the dc model for many earthquakes and find some earthquakes especially in volcanic and geothermal areas that have strongly non dc mechanisms understanding non dc earth quakes is important both for studying the process of faulting in detail and for identifying nonshear faulting processes that apparently occur in some earthquakes this paper summarizes the theory of moment tensor expansions of equivalent force systems and analyzes many possible physical non dc earthquake processes contrary to long standing assumption sources within the earth can sometimes have net force and torque components described by first rank and asymmetric sec ond rank moment tensors which must be included in analyses of landslides and some volcanic phenomena non dc processes that lead to conventional symmetric second rank moment tensors include geometrically complex shear faulting tensile faulting shear faulting in an anisotropic medium shear faulting in a heteroge neous region e g near an interface and polymorphic phase transformations undoubtedly many non dc earthquake processes remain to be discovered progress will be facilitated by experimental studies that use wave amplitudes amplitude ratios and complete waveforms in addition to wave polarities and thus avoid arbitrary assumptions such as the absence of volume changes or the temporal similarity of different moment tensor com ponents

upper mantle seismic anisotropy resulting from pressure induced slip transition in olivine seismic anisotropy in the oceanic lithosphere results from flow induced crystallographic preferred orientation of dry olivine during lithosphere creation recent experiments however showed that high water activity changes the flow mechanisms of olivine and hence the crystallographic preferred orientation better explaining the seismic anisotropy in the mantle wedge above subduction zones whether changes in the crystallographic preferred orientation of olivine are unique to the effects of water has become controversial and is critical to resolve here we report low stress high strain experiments on typical dry mantle rock at high pressures and temperatures showing that at 3 gpa pressure induces the same profound transition in olivine crystallographic preferred orientation that is produced by high water activity at lower pressure one important consequence for global tectonics is that alignment of fast seismic waves parallel to trenches beneath subducting slabs probably reflects entrainment of sub lithospheric mantle in the direction of subduction rather than trench parallel flow as interpreted at present from the large variety of crystallographic preferred orientations in olivine in both experiments and natural rocks we infer that in addition to the pressure induced changes in olivine slip systems implied here there are probably further changes in slip systems at higher pressure and temperature seismic anisotropy in earth s oceanic lithosphere and in the mantle wedge above subduction zones is associated with crystallographic preferred orientations of olivine experiments at high pressure and temperature suggest that a pressure of 3 gpa can induce the same changes in the crystal structure of olivine as high water activity at lower pressures

microstructure and geochemistry of plagioclase and microcline in naturally deformed granite abstract naturally deformed feldspars from foliated granites in a shear zone in newfoundland exhibit transitional brittle ductile behaviour brittle failure is subordinate to dynamic recrystallization microcracking strain enhanced diffusion and reaction enhanced ductility during the deformation both plagioclase an 28 and k feldspar are transformed to albite with increasing strain interaction of metamorphic and structural processes at the grain scale is emphasised this is illustrated with examples of quartz filled veins segregation bands in plagioclase and recrystallized polycrystalline aggregates in plagioclase and k feldspar the role of microcracking in plagioclase and of pre existing internal growth structures in the formation of initially coarse grained recrystallized aggregates from large single crystals is suggested

multiple cross gradient joint inversion for geospectral imaging 1 accurate characterization and monitoring of complex subsurface environments require the integration of all the available geophysical geochemical and geological information i developed a generalized cross gradient procedure that seeks multiple geometrically similar images that simplify the integration of cross property subsurface information i jointly invert near surface p wave s wave dc resistivity and magnetic data sets recorded at a field site and compound an integrated subsurface geospectral image based on the multiple property images found it is shown that by analogy to applications in satellite imagery the geospectral image assembles the multiple subsurface parameter values under a common structural framework that facilitates their visualization and analysis

occurrence of low ca clinopyroxene and the role of deformation in the formation of pyroxene fe ti oxide symplectites pyroxene fe ti oxide symplectites in a norite from the leuconoritic phase of the bjerkreim sokndal lopolith sw norway have been studied using empa electron microprobe analysis and tem transmission electron microscopy techniques textural and mineralchemical data indicate that the symplectites formed under subsolidus conditions at t 720 736 c and fo2 10 17 bars solidus temperatures are estimated as 981 1060 c two models of formation are proposed non isochemical replacement of olivine and growth at boundaries between exsolving grains of orthomagmatic high ca pyroxene and fe ti oxide tem reveals the presence of low ca clinopyroxene and this formed in response to strain and or shear stress comparison with published experimental data indicates that strain rates of up to 10 12 s 1 are necessary to explain the occurrence of low ca clinopyroxene the transition from orthopyroxene to low ca clinopyroxene may be related to deformation which accompanied intrusion of the leuconoritic phase of the bjerkreim sokndal lopolith or to local post intrusive faulting and or shearing selected area diffraction shows that the fe ti oxide lamellae are oriented with respect to the pyroxene such that 111 oxide 100 pyroxene the planes of closest oxygen packing in the constituent phases are thus adjacent to one another which leads to minimal misfit between the structures and to low interfacial strain energy the same topotactic relationship exists in both lamellar and vermicular parts of symplectites but is not continuous along the total length of the interface indicating that the form of the intergrowths is a primary growth feature that to some extent can be explained in terms of growth models for duplex cells deformation during growth is probably necessary to account for the lattice distortion observed in the symplectites

an aem study of garnet clinopyroxenite from the sulu ultrahigh pressure terrane formation mechanisms of oriented ilmenite spinel magnetite amphibole and garnet inclusions in clinopyroxene optical microscopy secondary electron microscopy and analytical electron microscopy were used to characterize crystallographic orientation relationships between oriented mineral inclusions and clinopyroxene cpx host from the hujialing garnet clinopyroxenite within the sulu ultrahigh pressure uhp terrane eastern china one garnet clinopyroxenite sample 2hj 2c and one megacrystic garnet bearing garnet clinopyroxenite rz 11d were studied porphyroblastic clinopyroxene from sample 2hj 2c contains oriented inclusions of ilmenite ilm spinel spl magnetite and garnet whereas clinopyroxene inclusions within megacrystic garnet from sample rz 11d contain oriented inclusions of ilmenite and amphibole specific crystallographic relationships were observed between ilmenite spinel plates and host clinopyroxene in sample 2hj 2c and between ilmenite plates and host clinopyroxene in sample rz 11d i e 1 bar 1 00 ilm 0 bar 1 0 cpx 0001 ilm 100 cpx and 110 spl 0 bar 1 0 cpx bar 1 11 spl 100 cpx these inclusions are suggested to be primary precipitates via solid state exsolutions most of the needle like magnetite spinel inclusions generally occur at the rims or along fractures of clinopyroxene within sample 2hj 2c despite the epitaxial relation with host clinopyroxene these magnetite spinel needles would have resulted from fluid melt infiltrations non epitaxial garnet lamellae in clinopyroxene of sample 2hj 2c were formed via fluid infiltration deposition primarily along 010 and subordinately along 100 partings epitaxial amphibole plates with a thickness 1 m and lamellae with a thickness 1 10 m in host clinopyroxene of sample rz 11d were probably results of hydration processes although amphibole plates could otherwise be interpreted as exsolution products temporal relations between mineral inclusions in each sample can be established and a semi quantitative p t path for this garnet clinopyroxenite body was derived accordingly the present results show that the hujialing garnet clinopyroxenite may not have subducted to mantle depths as deep as 250 km during uhp metamorphism as suggested by previous studies this study demonstrates that the crystallographic and temporal spatial relationships between aligned inclusions and host minerals are essential to a correct genetic interpretation of metamorphic rocks

na sws 1 1 a uniform database of teleseismic shear wave splitting measurements for north america 1 this version of shear wave splitting sws database db for north america na contains 6224 pairs of splitting parameters fast polarization directions and splitting times measured using all the available data recorded by digital broadband seismic stations over the period of 1980 2007 and archived at the incorporated research institutions for seismology data management center the measurements were produced using a set of robust procedures that involve automated batch processing and manual screening and were ranked quantitatively on the basis of a uniform criterion the result is a homogeneous database of individual rather than station averaged splitting parameters that can be used by a variety of geoscientists for the understanding of the structure and dynamics of the earth s deep interior beneath na this data brief describes the seismic data and techniques used to generate the sws results the spatial and azimuthal coverage and the limitations of the db the db will be periodically updated and enhanced by adding newly recorded data and by measuring splitting parameters using the pks and skks phases in addition to sks the database can be accessed at http www mst edu liukh sws

petrology of martian meteorite northwest africa 998 nakhlite northwest africa nwa 998 is an augite rich cumulate igneous rock with mineral compositions and oxygen isotopic composition consistent with an origin on mars this 456 gram partially fusion crusted meteorite consists of by volume 75 augite core composition wo39en39fs22 9 olivine fo35 7 plagioclase ab61an35 as anhedra among augite and olivine 3 5 low calcium pyroxenes pigeonite and orthopyroxene replacing or forming overgrowths on olivine and augite 1 titanomagnetite and other phases including potassium feldspar apatite pyrrhotite chalcopyrite ilmenite and fine grained mesostasis material minor secondary alteration materials include iddingsite associated with olivine probably martian calcite crack fillings and iron oxide hydroxide staining both probably terrestrial shock effects are limited to minor cataclasis and twinning in augite in comparison to other nakhlites nwa 998 contains more low calcium pyroxenes and its plagioclase crystals are blockier the large size of the intercumulus feldspars and the chemical homogeneity of the olivine imply relatively slow cooling and chemical equilibration in the late and post igneous history of this specimen and mineral thermometers give subsolidus temperatures near 730 c oxidation state was near that of the qfm buffer from about qfm 2 in earliest crystallization to near qfm in late crystallization and to about qfm 1 5 in some magmatic inclusions the replacement or overgrowth of olivine by pigeonite and orthopyroxene with or without titanomagnetite and the marginal replacement of augite by pigeonite are interpreted to result from late stage reactions with residual melts consistent with experimental phase equilibrium relationships apatite is concentrated in planar zones separating apatite free domains which suggests that residual magma rich in p and ree was concentrated in planar fracture zones and possibly migrated through them loss of late magma through these zones is consistent with the low bulk ree content of nwa 998 compared with the calculated ree content of its parent magma

two dimensional joint inversion of magnetotelluric and local earthquake data discussion on the contribution to the solution of deep subsurface structures abstract joint inversion of data sets collected by using several geophysical exploration methods has gained importance and associated algorithms have been developed to explore the deep subsurface structures magnetotelluric and local earthquake tomography algorithms are generally used individually due to the usage of natural resources in both methods it is not possible to increase data quality and resolution of model parameters for this reason the solution of the deep structures with the individual usage of the methods cannot be fully attained in this paper we firstly focused on the effects of both magnetotelluric and local earthquake data sets on the solution of deep structures and discussed the results on the basis of the resolving power of the methods the presence of deep focus seismic sources increase the resolution of deep structures moreover conductivity distribution of relatively shallow structures can be solved with high resolution by using mt algorithm therefore we developed a new joint inversion algorithm based on the cross gradient function in order to jointly invert magnetotelluric and local earthquake data sets in the study we added a new regularization parameter into the second term of the parameter correction vector of gallardo and meju 2003 the new regularization parameter is enhancing the stability of the algorithm and controls the contribution of the cross gradient term in the solution the results show that even in cases where resistivity and velocity boundaries are different both methods influence each other positively in addition the region of common structural boundaries of the models are clearly mapped compared with original models furthermore deep structures are identified satisfactorily even with using the minimum number of seismic sources in this paper in order to understand the future studies we discussed joint inversion of magnetotelluric and local earthquake data sets only in two dimensional space in the light of these results and by means of the acceleration on the three dimensional modelling and inversion algorithms it is thought that it may be easier to identify underground structures with high resolution

deep structure of the baikal rift zone revealed by joint inversion of gravity and seismology 1 the question of plate boundary forces and deep versus shallow asthenospheric uplift has long been debated in intracontinental rift areas particularly in the baikal rift zone asia which is colder than other continental rifts as previous gravity and teleseismic studies support the dominance of opposing mechanisms in the baikal rift we reconsidered both data sets and jointly inverted them this more effective approach brings insight into location of the perturbing bodies related to the extension in this region our new joint inversion method allows for inverting the velocity density relationship with independent model parametrization we obtain velocity and density models that consistently show 1 crustal heterogeneities that coincide with the main tectonic features at the surface 2 a faster and denser cratonic mantle nw of lake baikal that we relate to the thermal contrast between old and depleted archean siberian platform and paleozoic orogenic belt sayan baikal belt 3 three dimensional topographic variations of the crust mantle boundary with well located upwarpings and 4 the lithosphere asthenosphere boundary uplift up to 70 km depth with a nw dip our resulting velocity and density models support the idea of a combined influence of lithospheric extension and inherited lithospheric heterogeneities for the origin of the baikal rift zone index terms 1234 geodesy and gravity regional and global gravity anomalies and earth structure 7218 seismology lithosphere and upper mantle 8122 citation tiberi c m diament j deverchere c petit mariani v mikhailov s tikhotsky and u achauer deep structure of the baikal rift zone revealed by joint inversion of gravity and seismology