small scale heterogeneity at the top of the lower mantle around the mariana slab abstract short period waveform data recorded at the western us seismic array for 14 mariana deep earthquakes near 19 n show two anomalous wave packets within about 30 s after the arrival of the direct p wave simply called p or p wave one at about 13 s called x1 phase and the other around 29 s called x2 phase we perform array analyses to locate the sources of these phases in the first step we measure arrival time slowness back azimuth and amplitude of these phases relative to p the amplitudes of the x1 and x2 phases correlate with each other for the individual events and vary more than an order of magnitude among the events which cluster in a region spanning less than 50 km the amplitude correlation suggests that the two waves have a similar origin and the large amplitude variation eliminates receiver side reverberation as the origin of the phases the x1 phase has a slowness and an arrival azimuth which are not distinguished from those of p waves across the entire array and has nearly constant delay times regardless of the focal depths from 567 to 605 km the x2 phase arrives as a more emergent wave packet with slowness and azimuth different from those of p in the second step we compute composite semblance coefficients for the cases of p to p and s to p single scattering near the foci the x1 and x2 phases are best interpreted as s to p scattered waves generated in the uppermost lower mantle north of the focal region based on three observations 1 highest composite semblance values 2 scatterer locations mutually consistent between the two event groups near the depths of 500 and 600 km and 3 a reasonable amount of elastic property anomalies required the x1 phase scatterer is determined at 19 8 0 3 n 145 7 0 3 e 710 30 km on the other hand the scatterer of the x2 phase appears to split into two objects one at 20 4 0 4 n 145 4 1 0 e 900 80 km and the other at 20 6 0 4 n 147 4 0 5 e 860 40 km although the geometries of the scatterers of x1 and x2 phases are not constrained horizontal or subhorizontal discontinuities are unlikely the changes in elastic properties associated with these heterogeneous objects probably occur within several kilometers according to their high efficiency at converting short period waves they are thus likely to represent sharp chemical variations in major element composition these objects are located within a thickened high velocity anomaly at the top of the lower mantle which has been determined by previous seismic studies a plausible tectonic interpretation of these objects is that they are fragments of former oceanic crust which are entrained in the pacific slab impinging on the more viscous lower mantle

in situ x ray observations of phase assemblages in peridotite and basalt compositions at lower mantle conditions implications for density of subducted oceanic plate 1 phase relationships in klb 1 peridotite normal type mid oceanic ridge basalt nmorb and k rich basalt compositions were investigated experimentally from 28 to 143 gpa and 2050 to 3000 k a laser heated diamond anvil cell with the synchrotron x ray diffraction was developed to perform in situ observations of samples at simultaneous high pressures and temperatures we confirmed that the peridotite composition crystallized into an assemblage of mg perovskite ca perovskite magnesiowustite at pressures below 97 gpa and that nmorb and k rich basalt compositions both crystallized as mg perovskite ca perovskite stishovite an aluminous phase with a cafe2o4 type structure at pressures below 68 gpa the orthorhombic mg perovskite is stable in natural rock compositions at pressures less than 97 gpa corresponding to about 2200 km depth phase transition of silica phase from stishovite to cacl2 type phase was observed at 78 gpa in nmorb composition moreover we observed that nmorb crystallized in to an assemblage of cairo3 type mg fe sio3 ca perovskite pbo2 type silica an aluminous phase with a calcium cati2o4 type structure at 143 gpa corresponding to the core mantle boundary depth we measured the unit cell volumes of minerals in the nmorb composition at high p t and thereby estimated the density of subducted morb to a depth of 1800 km in the lower mantle in this depth regime morb is denser than model mantle densities e g prem and ak135 the estimated density of morb may contribute to an understanding of dynamics of the subducted slab in the deep lower mantle

post stishovite phase boundary in sio2 determined by in situ x ray observations a laser heating diamond anvil cell experiment with an angle dispersive x ray diffraction using synchrotron radiation source at the spring 8 has been developed to observe the phase transition in silica sio2 between the p42 mnm rutile type and pnnm cacl2 type up to pressures of 100 gpa and at temperatures up to 2200 k the transition was observed in the vicinity of 55 gpa at room temperature and showed a positive temperature dependence of the transition pressure the phase boundary was determined to follow the equation p gpa 51 2 0 012 0 005 t k our result gives a transition pressure of near 80 gpa and a depth of 1900 km at an expected lower mantle temperature of 2000 2500 k therefore this sio2 transition is not the cause of recent observations of seismic anomalies between 800 and 1600 km depth in the mid lower mantle

exploration for dimensional stone implications and examples from the precambrian of southern finland dimension stone is a natural rock that must fulfil high qualitative standards defined by both geology based factors and non geological factors the stone itself appearance soundness and the market demand are the two most important aspects in the quality assessment the process of geological dimension stone exploration is a systematic and stepwise procedure including individual steps of desk study field mapping detailed examination geo radar survey and core drilling the location of all economically feasible dimension stone deposits is strictly controlled by geological factors knowledge of these factors is fundamental in identifying new sites with potential for dimension stone in this work the geological constraint on the occurrence of dimension stone in three areas in the precambrian of southern finland has been investigated the deposits are localized to part of an area in which different geological features in combination have produced rock of good dimension stone quality the study shows that for example vertical movements in the crust magmatic evolution of an intrusion and metamorphic grade define the location of rocks suitable for dimension stone

hybrid collapse mechanism at piton de la fournaise volcano reunion island indian ocean 1 recent studies have shown that hydrothermal alteration in the core of volcanoes may weaken the edifice and trigger sector collapse lopez and williams 1993 day 1996 voight and elsworth 1997 van wyk de vries et al 2000 reid et al 2001 alteration of volcanic products must take place over long periods of times before collapse can occur so this process is considered to be less frequent than volcanic failure generated by magmatic intrusion and flank spreading however acceleration of this slow process may occur along one direction as a result of a weak lateral confinement following outward gravitational sliding of a flank of the volcano we present here evidence that the enclos fouque depression of piton de la fournaise volcano results from such a hybrid mechanism seaward sliding of the grand brule trough on top of an ancient hypovolcanic complex led to a lateral unconfined boundary along which collapse of the altered core of the edifice took place the result is a caldera like structure breached on the grand brule slide scaled experiments to simulate this process of pseudocaldera formation reveal tectonic features remarkably similar to those encountered in the field and demonstrate the mechanical consistency of the model similar processes may have played a role in the evolution of other volcanoes

finite element model predictions of static deformation from dislocation sources in a subduction zone sensitivities to homogeneous isotropic poisson solid and half space assumptions 1 dislocation models can simulate static deformation caused by slip along a fault these models usually take the form of a dislocation embedded in a homogeneous isotropic poisson solid half space hipshs however the widely accepted hipshs assumptions poorly approximate subduction zone systems of converging oceanic and continental crust this study uses three dimensional finite element models fems that allow for any combination including none of the hipshs assumptions to compute synthetic green s functions for displacement using the1995 mw 8 0 jalisco colima mexico subduction zone earthquake and associated measurements from a nearby gps array as an example fem generated synthetic green s functions are combined with standard linear inverse methods to estimate dislocation distributions along the subduction interface loading a forward hipshs model with dislocation distributions estimated from fems that sequentially relax the hipshs assumptions yields the sensitivity of predicted displacements to each of the hipshs assumptions for the subduction zone models tested and the specific field situation considered sensitivities to the individual poisson solid isotropy and homogeneity assumptions can be substantially greater than gps measurement uncertainties forward modeling quantifies stress coupling between the mw 8 0 earthquake and a nearby mw 6 3 earthquake that occurred 63 days later coulomb stress changes predicted from static hipshs models cannot account for the 63 day lag time between events alternatively an fem that includes a poroelastic oceanic crust which allows for postseismic pore fluid pressure recovery can account for the lag time the pore fluid pressure recovery rate puts an upper limit of 10 17 m2 on the bulk permeability of the oceanic crust

imaging magma transport during the 1997 seismic swarm off the izu peninsula japan the spatio temporal evolution of a propagating magma filled crack was estimated from inversion of global positioning system gps data tiltmeters and leveling the dike opened at a maximum rate of 50 millimeters per day and had a peak magma flux of 2 x 10 6 cubic meters per day although the spatial resolution was limited slow upward propagation was resolved during the 9 day long intrusion in contrast the earthquakes migrated rapidly upward during the first 12 hours of the swarm and nearly all of the seismic energy was released in the first 2 days comparison of inversion results with accurate hypocenter locations will lead to improved understanding of magma transport through the brittle crust and of the causes of volcanic seismicity

in situ observations of phase transition between perovskite and cairo 3 type phase in mgsio 3 and pyrolitic mantle composition abstract in situ observations of the perovskite cairo3 phase transition in mgsio3 and in pyrolitic compositions were carried out using a laser heated diamond anvil cell interfaced with a synchrotron radiation source for pure mgsio3 the phase boundary between the orthorhombic mg perovskite and cairo3 type phases in the temperature range of 1300 3100 k was determined to be p gpa 130 3 0 0070 0 0030 t 2500 k using platinum as a pressure calibrant we confirmed that the cairo3 type phase remained stable up to pressures of at least 156 gpa and temperatures of 2600 k the consistency of our results with previous theoretical calculations leads us to conclude that the 2700 km seismic discontinuity at the bottom of the lower mantle can be attributed to a phase transition to the cairo3 type phase the phase change from an orthorhombic mg perovskite to a cairo3 type bearing assemblage in a pyrolitic mantle composition was also observed at p 125 gpa which corresponds to the same mantle depth as the seismic discontinuity the phase boundary between the orthorhombic mg perovskite and cairo3 type bearing assemblage was determined to be p gpa 124 4 0 008 0 005 t 2500 k using gold as a pressure calibrant this transition boundary indicates that the temperature at a depth of 2700 km is about 2600 k and the adiabatic temperature gradient in the lower mantle is estimated to be 0 31 k km the partition coefficients and the effect of some elements on the phase equilibrium between the orthorhombic mgsio3 perovskite and cairo3 type mgsio3 were estimated from ab initio calculations our experimental and theoretical results indicate that the d layer consists of a cairo3 type bearing assemblage which is likely to have significant effect on the chemical and thermal evolution of the earth s mantle

the deformation field of the august 2003 eruption at piton de la fournaise reunion island mapped by asar interferometry 1 three independent asar interferograms spanning the august 2003 piton de la fournaise eruption reveal a 3 by 3 km asymmetric pattern of range changes centred on the dolomieu crater northern flank it corresponds to 30 cm of displacement towards the satellite east of the eruptive fissures and 7 cm away from the satellite west of the fissures displacements are caused by dyke emplacement below fissures we model the deformation using a 3d mixed boundary element method for elastic media this consists of a dyke defined by six geometric parameters and an overpressure gradient a neighbourhood algorithm was applied to explore this 7 dimensional parameter space the best fit model is a 57 eastward dipping dyke with a base lying around 1520 m a s l the model provides new evidence of the dyke intrusion related seaward displacements of the volcano eastern flank

estimating source parameters from deformation data with an application to the march 1997 earthquake swarm off the izu peninsula japan we have applied two monte carlo optimization techniques simulated annealing and random cost to the inversion of deformation data for fault and magma chamber geometry these techniques involve an element of randomness that permits them to escape local minima and ultimately converge to the global minimum of misfit space we have tested the monte carlo algorithms on two synthetic data sets we have also compared them to one another in terms of their efficiency and reliability we have applied the bootstrap method to estimate confidence intervals for the source parameters including the correlations inherent in the data additionally we present methods that use the information from the bootstrapping procedure to visualize the correlations between the different model parameters we have applied these techniques to gps tilt and leveling data from the march 1997 earthquake swarm off of the izu peninsula japan using the two monte carlo algorithms we have inferred two sources a dike and a fault that fit the deformation data and the patterns of seismicity and that are consistent with the regional stress field

water partitioning between bridgmanite and postperovskite in the lowermost mantle abstract the lowermost mantle appears to contain geochemically primitive reservoirs of volatile components including water as evidenced by certain ocean island basalts hallis et al 2015 we used ab initio lattice dynamics to calculate the water partition coefficient between bridgmanite and postperovskite using quasi harmonic free energies to determine how water is distributed between nominally anhydrous minerals in the d region in the absence of aluminum hydrogen was incorporated into both phases by a simple substitution of mg 2 2 h and we found that water favors bridgmanite over postperovskite by a factor of about 5 1 at conditions where an average mantle geotherm intersects the phase boundary in the al bearing system hydrogen and aluminum were coupled as si 4 al 3 h defects into both phases and we found that water favors postperovskite over bridgmanite in the al bearing system by a factor of about 3 1 at ambient mantle conditions and by about 8 1 at colder slab conditions our results indicate that aluminum controls the partitioning of water between bridgmanite and postperovskite and that aluminous postperovskite may be a potential host for primordial water in the lowermost region of the mantle the strong partitioning of water into aluminous postperovskite over bridgmanite provides a potential mechanism for dehydration melting in the lowermost mantle that could be a source for ocean island basalts in regions of upwelling

the use of earthquake rate changes as a stress meter at kilauea volcano stress changes in the earth s crust are generally estimated from model calculations that use near surface deformation as an observational constraint but the widespread correlation of changes of earthquake activity with stress has led to suggestions that stress changes might be calculated from earthquake occurrence rates obtained from seismicity catalogues although this possibility has considerable appeal because seismicity data are routinely collected and have good spatial and temporal resolution the method has not yet proven successful owing to the non linearity of earthquake rate changes with respect to both stress and time here however we present two methods for inverting earthquake rate data to infer stress changes using a formulation for the stress and time dependence of earthquake rates application of these methods at kilauea volcano in hawaii yields good agreement with independent estimates indicating that earthquake rates can provide a practical remote sensing stress meter

characterization and quality assessment of granitic building stone deposits a case study of two different portuguese granites abstract several factors determine building stone exploration in order to maximize the extraction processing and application of these natural materials some factors are intrinsic to stones such as their physical mechanical properties while others are related to their exploitability such as quarry reserves or fracturing density during an exploration campaign these factors are not always considered or properly weighed in terms of the negative consequences on quarry activities or rock behaviour under particular conditions in this study two well known portuguese granites are assessed to highlight the main factors these granites have different characteristics weathered and sound and are exploited in quarries with different joint densities the most relevant physical mechanical properties were evaluated and related to the specific petrophysical features of each granite the fracture patterns were identified in the quarries and then modelled in order to compute the quarry yield the weathered granite shows an important microcrack network and a general alteration of the rock forming minerals which has an important impact on its physical mechanical properties and on the resistance to environmental factors moreover the extreme differences in the degree of weathering require careful choices for the possible applications in both quarries the joint sets are similar to the regional faulting but some random joints can be found and consequently diminish the quarry yield the development of horizontal sheet joints during the exploitation process could have a great influence on the quarry productivity if they are not used do delimitate the extracted blocks the modelling of the natural fracture pattern allows us to determine the potential volume of blocks that could be exploited however the quality of the information gathered could lead to an over estimation of the quarry production this example shows the importance of the exhaustive researches during a building stone assessment campaign

source model for the mw 6 7 23 october 2002 nenana mountain earthquake alaska from insar 1 the 23 october 2002 nenana mountain earthquake mw 6 7 occurred on the denali fault alaska to the west of the mw 7 9 denali earthquake that ruptured the same fault 11 days later we used 6 interferograms constructed using radar images from the canadian radarsat 1 and european ers 2 satellites to determine the coseismic surface deformation and a source model data were acquired on ascending and descending satellite passes with incidence angles between 23 and 45 degrees and time intervals of 72 days or less modeling the event as dislocations in an elastic half space suggests that there was nearly 0 9 m of right lateral strike slip motion at depth on a near vertical fault and that the maximum slip in the top 4 km of crust was less than 0 2 m the nenana mountain earthquake increased the coulomb stress at the future hypocenter of the 3 november 2002 denali earthquake by 30 60 kpa

radar interferometry and its application to changes in the earth s surface geophysical applications of radar interferometry to measure changes in the earth s surface have exploded in the early 1990s this new geodetic technique calculates the interference pattern caused by the difference in phase between two images acquired by a spaceborne synthetic aperture radar at two distinct times the resulting interferogram is a contour map of the change in distance between the ground and the radar instrument these maps provide an unsurpassed spatial sampling density 100 pixels km 2 a competitive precision 1 cm and a useful observation cadence 1 pass month 1 they record movements in the crust perturbations in the atmosphere dielectric modifications in the soil and relief in the topography they are also sensitive to technical effects such as relative variations in the radar s trajectory or variations in its frequency standard we describe how all these phenomena contribute to an interferogram then a practical summary explains the techniques for calculating and manipulating interferograms from various radar instruments including the four satellites currently in orbit ers 1 ers 2 jers 1 and radarsat the next chapter suggests some guidelines for interpreting an interferogram as a geophysical measurement respecting the limits of the technique assessing its uncertainty recognizing artifacts and discriminating different types of signal we then review the geophysical applications published to date most of which study deformation related to earthquakes volcanoes and glaciers using ers 1 data we also show examples of monitoring natural hazards and environmental alterations related to landslides subsidence and agriculture in addition we consider subtler geophysical signals such as postseismic relaxation tidal loading of coastal areas and interseismic strain accumulation we conclude with our perspectives on the future of radar interferometry the objective of the review is for the reader to develop the physical understanding necessary to calculate an interferogram and the geophysical intuition necessary to interpret it

granite fracture index to check suitability of granite outcrops for quarrying a correct knowledge of fracture patterns previous to quarrying is important for economical exploitation this work comprises the general characterization of the discontinuities of 10 granite rock masses in ne portugal during the study some discontinuity characteristics such as orientation persistence aperture trace length and spacing were evaluated the differences in the characteristics of the selected granites were described and the most important exploration factors were identified in the granites studied most of the joints are oriented from n10 e to n50 e which is compatible with the regional fracture pattern concerning joint termination the xx type is common while the rr type is rare the persistence index ranges from 3 5 to 25 4 closed joints are predominant in the granites studied n 72 4 and openings of the others are about 1 2 mm as a result of superficial displacement of the granite blocks the percentage of filled joints usually by quartz and pegmatite is different from one granite to another but most are b 20 the average joint length ranges from 11 1 m in post tectonics granites to 4 6 m in syntectonic granites joint spacing varies from 0 98 to 2 8 m with higher values in post tectonic granites joint space distributions of the granites studied are close to log normal and exponential distributions volumetric joint count jv ranges from 0 8 to 2 1 joints m 3 and is used for categorizing the places of each granite the relationships between jv and other joint characteristics such as length spacing and number of joint sets were investigated a granite fracturing index gfi is introduced computed on the basis of volumetric joint count number of joint sets and true joint spacing the gfi classification of studied places allows us evaluate the suitability for profitable exploitation 2007 elsevier b v all rights reserved

compositional change of majoritic garnet in a morb composition from 7 to 17 gpa and 1400 to 1600 c experimental phase relations of an average normal mid ocean ridge basalt n morb composition from 7 gpa to 17 gpa and 1400 to 1600 c reveal the compositional variation of garnet in equilibrium with pyroxene the na2o content of majoritic garnet in equilibrium with pyroxene and stishovite increases up to 2 5 wt with increasing pressure and temperature na enters the garnet structure via the substitution mg fe ca al na si ti the pyroxene garnet partition coefficient dcp ga for na decreases with increasing pressure however clinopyroxene coexisting with garnet becomes more na rich as pressure increases these relationships are independent of the feo content in garnet our experiments confirm that rare majoritic and na rich garnet inclusions in diamonds have formed at transition zone pressure in lithologies of basaltic bulk composition

tectonic significance of mafic volcanic rocks in a mesozoic sequence of the menderes massif west turkey the mesozoic platform sequence of the menderes massif consists of thick succession of detrital and carbonate rocks in this sequence there are mafic metavolcanic rocks at two different levels the first level of mafic metavolcanic intercalations is in the late triassic detrital rich series located in the caltasi formation which is the lowermost unit of the mesozoic platform the second level of the mafic metavolcanic rocks is located in the late cretaceous paleocene selcuk formation laying on top of the platform sequence the caltasi formation which is composed of mica schists thinly bedded cherts calc schist and mafic volcanic intercalations unconformably overlie the bayindir formation which consists of mica schists phyllites and white quartzites of palaeozoic or probably older age the mafic volcanic rocks in the caltasi formation are alkaline basalts with within plate characteristics and are formed during an intraplate extension the caltasi formation is conformably overlain by the kayaalti formation represented by calc schists dolomitic marbles and rudist and emery bearing massive marbles in ascending order the selcuk formation overlies the kayaalti formation and consists of a mica schist matrix with allochthonous blocks of mafic volcanic rocks metaperidotites metagabbros and massive marbles the mafic volcanic rocks in the selcuk formation are tholeiitic basalts and are petrologically similar to mid oceanic basalts the geological and geochemical characteristics of the mafic metavolcanic rocks in the caltasi formation indicate that during the late triassic the menderes platform was segmented probably by the opening of a branch of the neotethyan ocean between the late triassic and the late cretaceous the menderes carbonate platform was built up during the latest cretaceous early paleocene a slab of oceanic crust obducted on this platform and provided slices of mafic metavolcanic rocks into the selcuk formation

phase transition of ca perovskite and stability of al bearing mg perovskite in the lower mantle here using in situ x ray diffraction combined with a laser heated diamond anvil cell at high temperatures and high pressures a phase relationship in klb 1 peridotite composition samples was investigated from 38 to 106 gpa and 300 to 2600 k in order to determine the stability of phases in the lower mantle we observed that al bearing mg perovskite and magnesiowustite remained stable up to 106 gpa which corresponds to a lower mantle depth of 2400 km depth by contrast a phase transition in ca perovskite from a cubic to a tetragonal structure was observed the amount of distortion in this material increases as pressure increases at 300 k the temperature of the tetragonal to cubic structure transition therefore appears to increase with increasing pressure there is a possibility that this ca perovskite phase transition contributes to unidentified seismic anomalies in the lower mantle

rock mass block quality designation for marble production abstract discontinuity spacing measurements are generally carried out along scan lines and or along the rock mass exposures quarry benches and or bore cores for assessing the rock mass quality rock mass block quality designation ratio bqd has been defined for assessment of the block production capacity of rock mass as bqd s 1m l where s 1m cumulative of the discontinuity spacing equal and or greater 1 0 m l scan line length m assessment of the discontinuity spacing measurements made along 2198 m long the scan lines in 6 working and five abandoned limestone quarries in karaburun area in western turkey have shown that while the working quarries had bqd ratios 50 and the abandoned quarries had bqd ratios

dipping low velocity layer in the mid lower mantle evidence for geochemical heterogeneity data from western united states short period seismic networks reveal a conversion from an s to a p wave within a low seismic velocity layer greater than or equal to the 4 percent velocity difference compared to the surrounding mantle in the mid lower mantle 1400 to 1600 kilometers deep east of the mariana and izu bonin subduction zones the low velocity layer about 8 kilometers thick dips 30 to 40 southward and is at least 500 kilometers by 300 kilometers its steep dip large velocity contrast and sharpness imply a chemical rather than a thermal origin ancient oceanic crust subducted into the lower mantle is a plausible candidate for the low velocity layer because of its broad thin extent

internal structure of piton de la fournaise volcano from seismic wave propagation and earthquake distribution abstract arrival times of seismic waves from local earthquakes are inverted for both locating the source and defining the 3 d velocity heterogeneity of piton de la fournaise the lateral heterogeneity of the 2632 m high edifice is resolved as a high velocity plug 1 5 km in diameter surrounded by a low velocity ring which may be interpreted as due to the construction of fournaise on the flank of the older volcano piton des neiges wave mode conversion detected on three component seismograms provides evidence for boundaries of contrasted velocities pre eruptive swarm earthquakes cluster in the high velocity zone under the dolomieu summit crater low strength and cohesion of the surrounding material account for the lack of seismicity for the final 1 3 km radial flow of magma to the vents in enclos fouque beneath the high velocity plug the existence of a body with low velocity for p and even for s waves is well constrained however the walls and base are poorly defined because of the lack of deep earthquakes for sampling the few earthquakes that are located in this depth region usually occur at a depth of around 1 5 km below sea level in the region of the cone this can be considered providing the upper constraint on the lower limit of the aseismic part of the low velocity body the coincidence in time of their occurrence with the swarms above sea level and the eruptions suggests magmatic activation of the low velocity aseismic volume 1 5 km below sea level under the high velocity plug of the cone further down the concentration of seismicity in two swarms between 2 and 4 km under the eastern flank does not allow the structure to be sampled effectively

the grand brule exploration drilling new data on the deep framework of the piton de la fournaise volcano part 1 lithostratigraphic units and volcanostructural implications abstract the sinking of a deep drill hole 3003 5 m for geothermal exploration in the eastern part of the piton de la fournaise volcano on reunion island has revealed the underlying lithostratigraphy six principal sequences have been distinguished a 0 440 m subaerial basaltic flows b 440 556 m a transitional series characterized by an alternation of subaerial basalts and submarine deposits vitric basalt and hyaloclastic breccia c 556 616 m submarine basalts lavas and hyaloclastites d 616 890 m subaerial basalts e 890 1010 m submarine basaltic deposits with abundant argillized hyaloclastites f 1010 3003 5 m a layered intrusive complex comprising 1010 1129 m sheets of gabbro injected into the lavas and hyaloclastites 1129 1920 m a zoned intrusion of olivine gabbro and dolerite 1920 3003 5 m stratified cumulate gabbro wehrlite dunite the occurrence of the first submarine deposits at 440 m 268 m below present sea level and the intercalation with them of subaerial basalts down to 890 m 728 m below present sea level tend to support a hypothesis of sliding into the sea during subsidence of the eastern flank of the fournaise massif the intrusive complex intersected from 1010 m down is regarded as a former shallow magma chamber a large positive gravimetric anomaly 40 50 mgal centered over grand brule and attributed to the intrusive complex indicates that its roof forms an ellipse 3 20 km elongated n s stratigraphic and morphological structural evidence on land and on the sea floor and the results of the mineralogical study of this very large magma chamber suggest that it belongs to an ancient edifice proto fournaise whose activity preceded the construction of the present fournaise and ended at about 0 6 ma on land the evidence for this earlier edifice is to be found in the zeolitised basalts and differentiated lavas hawaiites forming the basement to the phase 1 lava flows certain subsidence structures on the present fournaise are interpreted as resulting from settling of the proto fournaise volcano the destabilization of the east flank grand brule area of the currently active volcano and the location of the ne and se rift zones could be attributed to the same phenomenon

a new model for the evolution of the volcanic island of reunion indian ocean the island of reunion has been studied using data from airborne and shipborne magnetic surveys the subaerial history of reunion spans the last 2 1 million years the brunhes matuyama geomagnetic reversal enables differentiation of volcanic rocks older and younger than 0 78 ma the lower submarine flanks are poorly magnetized and are interpreted as landslide deposits the core of the island is composed of highly magnetized rocks piton des neiges volcano is composed mostly of rocks older than 0 78 ma only its western flank and central area include thick piles of younger rocks piton de la fournaise is a highly and normally magnetized edifice but its northern and eastern flanks are underlain at shallow depth by reversely magnetized formations the latter are regarded as remnants of les alizes volcano associated with the grand brule hypovolcanic complex at the matuyama brunhes transition the island was composed of at least two main volcanoes piton des neiges and les alizes and perhaps also of a third old volcano takamaka at the center north of the island piton de la fournaise grows on the flank of les alizes and is a relatively young focus of volcanism these volcanoes have had successive phases of construction and destruction the analysis of magnetic anomalies over reunion was decisive in defining a new coherent model for the evolution of the island

metastable mantle phase transformations and deep earthquakes in subducting oceanic lithosphere earth s deepest earthquakes occur as a population in subducting or previously subducted lithosphere at depths ranging from about 325 to 690 km this depth interval closely brackets the mantle transition zone characterized by rapid seismic velocity increases resulting from the transformation of upper mantle minerals to higher pressure phases deep earthquakes thus provide the primary direct evidence for subduction of the lithosphere to these depths and allow us to investigate the deep thermal thermodynamic and mechanical ferment inside slabs numerical simulations of reaction rates show that the olivine spinel transformation should be kinetically hindered in old cold slabs descending into the transition zone thus wedge shaped zones of metastable peridotite probably persist to depths of more than 600 km laboratory deformation experiments on some metastable minerals display a shear instability called transformational faulting this instability involves sudden failure by localized superplasticity in thin shear zones where the metastable host mineral transforms to a denser finer grained phase hence in cold slabs such faulting is expected for the polymorphic reactions in which olivine transforms to the spinel structure and clinoenstatite transforms to ilmenite it is thus natural to hypothesize that deep earthquakes result from transformational faulting in metastable peridotite wedges within cold slabs this consideration of the mineralogical states of slabs augments the traditional largely thermal view of slab processes and explains some previously enigmatic slab features it explains why deep seismicity occurs only in the approximate depth range of the mantle transition zone where minerals in downgoing slabs should transform to spinel and ilmenite structures the onset of deep shocks at about 325 km is consistent with the onset of metastability near the equilibrium phase boundary in the slab even if a slab penetrates into the lower mantle earthquakes should cease at depths near 700 km because the seismogenic phase transformations in the slab are completed or can no longer occur substantial metastability is expected only in old cold slabs consistent with the observed restriction of deep earthquakes to those settings earthquakes should be restricted to the cold cores of slabs as in any model in which the seismicity is temperature controlled via the distribution of metastability however the geometries of recent large deep earthquakes pose a challenge for any such models transformational faulting may give insight into why deep shocks lack appreciable aftershocks and why their source characteristics including focal mechanisms indicating localized shear failure rather than implosive deformation are so similar to those of shallow earthquakes finally metastable phase changes in slabs would produce an internal source of stress in addition to those due to the weight of the sinking slab such internal stresses may explain the occurrence of earthquakes in portions of lithosphere which have foundered to the bottom of the transition zone and or are detached from subducting slabs metastability in downgoing slabs could have considerable geodynamic significance metastable wedges would reduce the negative buoyancy of slabs decrease the driving force for subduction and influence the state of stress in slabs heat released by metastable phase changes would raise temperatures within slabs and facilitate the transformation of spinel to the lower mantle mineral assemblage causing slabs to equilibrate more rapidly with the ambient mantle and thus contribute to the cessation of deep seismicity because wedge formation should occur only for fast subducting slabs it may act as a parachute and contribute to regulating plate speeds wedge formation would also have consequences for mantle evolution because the density of a slab stagnated near the bottom of the transition zone would increase as it heats up and the wedge transforms to denser spinel favoring the subsequent sinking of the slab into the lower mantle

phase transition in casio3 perovskite abstract a phase transition in pure casio3 perovskite was investigated at 27 to 72 gpa and 300 to 819 k by in situ x ray diffraction experiments in an externally heated diamond anvil cell the results show that casio3 perovskite takes a tetragonal form at 300 k and undergoes phase transition to a cubic structure above 490 580 k in a pressure range studied here the transition boundary is strongly temperature dependent with a slightly positive dt dp slope of 1 1 1 3 k gpa it is known that the transition temperature depends on al2o3 content dissolved in casio3 perovskite kurashina et al phys earth planet inter 145 2004 67 74 the phase transition in casio3 3 wt al2o3 perovskite therefore could occur in a cold subducted mid oceanic ridge basalt morb crust at about 1200 k in the upper to mid lower mantle this phase transition is possibly ferroelastic type and may cause large seismic anomalies in a wide depth range

compressibility of the calcium aluminosilicate cas phase to 44 gpa abstract in situ x ray diffraction measurements on a calcium aluminosilicate cas phase have been carried out using a laser heated diamond anvil cell up to a pressure of 44 gpa employing a synchrotron radiation source cas is the major mineral formed from sediments subducted into the earth s mantle the sample was heated using a yag laser after each pressure increment to relax the deviatoric stress in the sample x ray diffraction measurements were carried out at t 300 k using an angle dispersive technique the pressure was calculated using an internal platinum metal pressure calibrant the birch murnaghan equation of state for the cas phase obtained from the experimental unit cell parameters showed a density of 0 3 888 g cm 3 and a bulk modulus of k 0 229 9 gpa for k 0 4 7 0 7 when the first pressure derivative of the bulk modulus was fixed at k 0 4 then the value of k 0 239 2 gpa from the experimental compressibility the density of the cas phase was observed to be lower than the density of co existing al bearing stishovite calcium perovskite calcium ferrite type phases and fe al bearing mg perovskite in subducted sediments in the lower mantle therefore the density of subducted sediments in the lower mantle decreases with increasing mineral proportion of the cas phase

discontinuity modelling and rock block geometry identification to optimize production in dimension stone quarries abstract evaluating the reserves of commercial blocks in dimension stone quarries requires determining in situ block geometry furthermore to extract blocks the planes need to be cut and the intersection between the fracture network and the cutting patterns forms smaller blocks the optimization of the cutting patterns can increase quarrying efficiency resulting in less environmental damage in this paper a numerical algorithm was selected from various algorithms and was developed for in situ block identification the optimization approach was adopted to increase quarry productivity and to investigate quarrying direction on a large scale however on a small scale this approach was employed for checking the distance between the cutting planes according to the algorithms developed 3d quarryoptimizer was programmed in the matlab environment to determine the geometry of the blocks and to optimize extraction based on the quality classification of the blocks formed the algorithms developed have such advantages as the optimization approach and taking the geometry of the blocks into consideration this methodology was applied in a marble quarry and a granite quarry research conducted in the granite quarry showed that the program is a practical tool to determine the geometry of in situ blocks and their quality classification the marble quarry was studied for the optimization phase the large scale optimization indicated a maximum difference of 17 in the yield among several quarrying directions on a small scale however a 120 increase in quarry yield was achieved with the optimal interval between the cutting planes

seismic evidence for a 920 km discontinuity in the mantle analysis of hundreds of seismograms from a seismic array in the japanese islands reveals a seismic discontinuity at a depth of about 920 km in the mantle beneath the tonga subduction zone this discontinuity is also evident beneath subduction zones in the japan and flores seas the discontinuity probably represents either a change in mantle chemical composition or the signature of the subducted slab s garnet layer

finding realistic dike models from interferometric synthetic aperture radar data the february 2000 eruption at piton de la fournaise dike intrusions often cause complex ground displacements that are not sufciently explained by simple analytical models we develop a method to nd complex and realistic dike geometries and overpressures from interferometric synthetic aperture radar insar data this method is based on a combination of a boundary element method with realistic topography and a neighbourhood algorithm inversion dike model geometry is roughly a quadrangle with its top reaching the ground the inversion has two stages search and appraisal the appraisal stage involves calculations of model marginal probability density functions using mist val ues calculated during the search stage the mist function takes into account the variance and correlation of data noise synthetic tests show that a model is successfully retrieved within predicted narrow condence intervals we apply the method on insar data of the february 2000 ank eruption at piton de la fournaise and get a trapezoid dike dipping seaward 61 0 n 67 3 with its bottom passing 800n1000 m beneath the summit a model with a basal slip plane does not better explain observed asymmetric displacements and thus this asymmetry is solely attributed to the dipping dike the dike lies above a narrow band of pre eruption seis micity suggesting that lateral magma propagation occurred neglecting topography results in poor modeling at depth and in overestimations of overpressure or opening height both about 30 and volume about 20

equation of state of lower mantle al fe mgsio3 perovskite the compression behavior of various al fe bearing mgsio3 perovskites was investigated by powder x ray diffraction up to 70 gpa on the id30 beamline of esrf grenoble france using diamond anvil cell coupled with co2 laser heating we obtained a reliable equation of state up to typical lower mantle pressures in contrast to fe which essentially increases the room pressure unit cell volume v0 the effect of al is to increase the bulk modulus of silicate perovskite this result contrasts with previous determinations performed at pressures below 10 gpa on samples synthesized in the multi anvil press such a difference can be explained by a change in the substitution mechanism of al in mgsio3 with increasing pressure and temperature in agreement with recent ab initio calculations our results confirm that the earth s lower mantle mg fe si ratio is greater than unity because of the high stiffness of silicate perovskite

block theory and its application block theory is a geometrically based set of analyses that determine where potentially dangerous blocks can exist in a geological material intersected by variously oriented discontinuities in three

magma reservoir subsidence mechanics theoretical summary and application to kilauea volcano hawaii an analytic model has been developed for the prediction of the three dimensional deformation field generated by the withdrawal of magma from a sill like storage compartment during an intrusion or eruption cycle the model is based on the work of berry and sales 1961 1962 and predicts the vertical displacement components over the areal plane model parameters are the depth of burial h the intrusion half width a the intrusion half length b the thickness of the magmatic interior at the moment of melt withdrawal tm and the planform aspect ratio a b the products of the model include areal deformation maps systematic variation in model parameters within the context of kilauea volcano hawaii have revealed that circular and elliptical deformation patterns result from the collapse of draining rectilinear intrusions at depth moreover the geometric parameters of a storage compartment may interact in complex ways to produce similar deformation patterns the model has been applied to kilauea volcano for three periods of pronounced summit subsidence 1 1921 1927 bracketing the steamblast eruptive phases of 1924 2 june 1972 to december 1972 and 3 december 1972 to may 1973 application of the model requires the simultaneous optimization of five predicted deformation features with respect to field measurements and the derivative deformation maps 1 the vertical displacement maxima 2 the vertical displacement gradients over the areal plane 3 the lateral extent of the deformation field 4 the aspect ratio of the subsidence pattern and 5 the strike of the major axis of the deformation field the constrained geometries and volumes of the inferred collapsed storage cavities for each period are 1 1921 1927 depth 3 km a 1500 m b 4500 m tm 20 m v 540 106 m3 2 june 1972 to december 1972 depth 3 3 km a 600 m b 2000 m tm 1 m v 4 8 106 m3 and 3 december 1972 to may 1973 depth 2 2 km a 500 m b 1612 m tm 1 m v 3 2 106 m3 for 2 and 3 calculated magmatic thicknesses tm happen to be in the range 3 48 0 15 m of measurements for sill like bodies in deeply dissected hawaiian shield volcanoes the fits obtained between calculated and observed deformation patterns allow quantification of the location overall dimensions orientation and volume of the discrete still molten interior of sill like compartments from which magma is tapped during eruption or intrusion

widespread uplift and trapdoor faulting on galapagos volcanoes observed with radar interferometry volcanic uplift caused by the accumulation of magma in subsurface reservoirs is a common precursor to eruptions1 2 but for some volcanoes uplift of metres or more has not yet led to an eruption3 here we present displacement maps of volcanoes in the galapagos islands constructed using satellite radar interferometry that might help explain this dichotomy we show that all but one of the seven volcanoes on the islands of isabela and fernandina deformed during 1992 99 cerro azul and fernandina erupted4 5 6 during the observation period and show evidence of inflation co eruptive deflation and shallow dyke intrusion in contrast the largest volcano sierra negra has not erupted yet exhibits spatially and temporally variable deformation with a maximum uplift of 2 7 m between 1992 and 1999 which can be modelled by a shallow inflating sill inflation during 1997 98 however was accompanied by trapdoor faulting on a steeply dipping fracture system within the caldera repeated trapdoor faulting over geological time has formed an arcuate intra caldera ridge within sierra negra and may have acted to relax stresses above the magma chamber inhibiting summit eruptions similar processes may help explain large uplift unaccompanied by eruptive activity at other volcanoes

p p precursors under africa evidence for mid mantle reflectors observations of precursors to p p from a recent exceptionally large deep earthquake in the fiji islands moment magnitude 7 6 at an array of broadband stations in california revealed mid mantle reflectors near depths of 785 kilometers and 1200 kilometers under the southern african rift such observations previously reported primarily in subduction zones suggest that these reflectors may have a global character our analysis which also indicated a sharp uplifted 670 kilometer discontinuity demonstrates the power of sparse regional broadband arrays for the study of weak frequency dependent features in deep earth structure

three dimensional modeling of the 1983 1984 eruption at piton de la fournaise volcano reunion island displacement vectors on 125 points over a 6 km 2 area were calculated zlotnicki et al 1990 for piton de la fournaise volcano reunion island from photogrammetric surveys conducted in september 1981 and again in september 1984 an eruptive crisis with two episodes occurred during the 3 years between the surveys we modeled the displacements from the photogrammetric surveys using a three dimensional mixed boundary element method the model shows that both eruptive episodes were fed by a single dike oriented 165 from north as the dike approached the ground surface it divided into segments that rotated into an en echelon pattern the model that best fits all observations suggests that the stress state within the volcano is quasi isotropic such that horizontal stresses equal the overburden these high horizontal stresses are incompatible with an elastic edifice loaded merely by gravitational forces however they may be attributed to the cumulative effect of repeated dike intrusions

analytical transmission electron microscopy study of a natural morb sample assemblage transformed at high pressure and high temperature natural mid ocean ridge basalt morb samples recovered from diamond anvil cell dac experiments performed between 33 to 89 gpa and 1700 to 2600 k were studied with a transmission electron microscope tem we used the focused ion beam fib lift out technique to prepare the recovered high pressure laser heated samples for tem study observations of tem sections show the presence of five phases for samples transformed at pressures ranging from 33 to 45 gpa al bearing mg perovskite ca silicate perovskite stishovite and two al rich phases the al rich phases were identified by selected area electron diffraction saed patterns and chemical composition analysis and include the new aluminous nal phase with hexagonal structure and the calcium ferrite cf type phase chemical analyses obtained by analytical transmission electron microscopy atem show that mg silicate perovskite is the major host for al with significant amounts also distributed between the cf type and nal phases and less than 1 wt in stishovite beyond pressures of 40 gpa 1100 km depth the al content of mg perovskite and cf type phase increases between 45 and 50 gpa the nal phase disappears this mineralogical change may explain reported seismic anomalies in subduction zones at mid mantle depths

insar observations of the 1995 fogo cape verde eruption implications for the effects of collapse events upon island volcanoes 1 fogo volcano cape verde islands erupted in april 1995 after 43 years of dormancy about 46 106 m3 of lava erupted during 7 5 weeks from vents on the sw flank of pico do fogo into cha das caldeiras interferograms obtained from 1993 1998 ers sar data show ground deformation due to the feeder dike but lack evidence for any volcano wide deformation related to volume changes of a shallow magma reservoir this suggests that fogo is fed from a relatively deep mantle lithospheric source 16 5 km depth consistent with petrological data this supports the concept that cha das caldeiras is the fill of a collapse scar created by a giant landslide and not a collapse caldera overlying a central shallow magma chamber the disturbance of the magmatic system by giant landslides may explain why some oceanic island volcanoes with high magma supply rates currently lack well developed shallow reservoirs

thermodynamic properties and phase relations in mantle minerals investigated by first principles quasiharmonic theory this research has been motivated by geophysics and materials physics the objective of this research has been to advance materials theory and computations for high pressure and high temperature applications to the point that it can make a difference in our understanding of the earth understanding of the mineralogy composition and thermal structure of the earth evolves by close interaction of three fields seismology geodynamics and mineral physics earth s structure is imaged by seismology which obtains body wave velocities and density throughout the earth s interior fig 1 interpretation of this data relies on knowledge of aggregate properties of earth forming materials either measured in laboratory or calculated in many cases by both however the conditions of the earth s interior especially at the core may be challenging for important experiments and materials computations have emerged to contribute decisively to this field earth s evolution is simulated by geodynamics but these simulations need as input information about rheological and thermodynamic properties of minerals including phase transformation properties such as clapeyron slopes our research has concentrated on the phases of the earth s mantle particularly the deep mantle whose conditions are more challenging for experiments the mantle accounts for 83 of the earth s volume in this article we will review the essential first principles approach used to investigate solids at high temperatures and pressures summarize their performance for mantle minerals fig 2 and point to critical results that have stirred us in the current research path the success is remarkable but some limitations point the way to future developments in this field figure 1 a velocities and density profiles kennett et al 1995 b earth s cross section and c composition and mineralogy of earth s layers figure 2 phases proportions versus depth and or pressure ol mg fe 2sio4 olivine also known as phase mg fe

characterizing block geometry in jointed rockmasses the intersection of discontinuities in a jointed rockmass creates in situ blocks of variable three dimensional 3d geometry the size and shape of rock blocks in a rockmass assembly have a dominant influence on the engineering properties of a rockmass and control for example the failure geometry of a rock face and the optimum associated support and surface restraint strategy the distribution of block volumes within a rockmass can be effectively analyzed and communicated using a cumulative volume distribution curve integrated with this analysis a methodology has been developed to characterize the shape and volumetric shape distribution of rock blocks in 3d models of jointed rockmasses the proposed block shape characterization method takes into account two factors the first describes the shortening of the minor principal axis of the block while describes the elongation of the major axis when merged with the block volume distribution the block shape characterization method can effectively describe and classify both the size and shape distributions of any jointed rockmass and is not limited to orthogonal blocks or hexahedra this methodology can classify any polyhedra and has been developed and calibrated based on synthetic joint data and simulated block assemblies a demonstration is given of its effectiveness in characterizing block geometries in the field using mapped fracture data