seismic tomography a window into deep earth abstract the goal of this paper is to provide an overview of the current state of the art in seismic tomography and trace its origins from pioneering work in the early 1970s to its present status as the pre eminent tool for imaging the earth s interior at a variety of scales due to length limitations we cannot hope to cover every aspect of this diverse topic or include mathematical derivations of the underlying principles rather we will provide a largely descriptive coverage of the methodology that is targeted at readers not intimately familiar with the topic the relative merits of local versus global parameterization ray tracing versus wavefront tracking backprojection versus gradient based inversion and synthetic testing versus model covariance are explored a variety of key application areas are also discussed including body wave traveltime tomography surface wave tomography attenuation tomography and ambient noise tomography established and emerging trends many of which are driven by the ongoing rapid increases in available computing power will also be examined including finite frequency tomography full waveform tomography and joint tomography using multiple datasets several practical applications of seismic tomography including body wave traveltime attenuation and surface waveform are presented in order to reinforce prior discussion of theory

a high resolution p wave model for the top 1200 km of the mantle this work attempts to map aspherical velocities in the top 1200 km of the mantle that are illuminated by the international seismological centre p wave data the processing includes summary ray sorting and hypocentral redetermination to cope with the extreme variation of ray coverage a multicell inversion is used to simultaneously constrain anomalies in overlapping cells the multicell solutions are summed after inversion to form the final model named p1200 at cell size of 1 1 and about 50 km in thickness the lateral resolution of the model is about 1 2 in major subduction zones and about 5 15 in most places major features in the model withstood tests on signal coherency and different reference models the long wavelength parts of the p1200 model correlate well with previous global models especially the s12 model of shear wave among the large features in the transition zone and below there are two fast bands one from canada to south america and another from siberia through east asia and the philippine sea to western australia there are also slow patches under the central pacific and from india to eastern africa though most subduction zones have slab like high velocity anomalies they are sandwiched by broad slow velocities at shallow depths some of the slabs appear to penetrate the 660 km discontinuity and stagnant slabs are also seen in the transition zone plume like slow anomalies exist below some prominent hot spots like hawaii iceland yellowstone and french polynesia

megafauna associated with hydrothermal vents in the manus back arc basin bismarck sea abstract the vent fauna of manus back arc basin were investigated during the 21st cruise of the akademik mstislav keldysh in may june 1990 communities associated with three active hydrothermal fields were explored during a series of dives by the dsrv mir at least sixteen vent species were collected some of them are new material for physiological and biochemical analyses was collected as well special attention was paid to the exploration of spatial distribution of animals distributional information is combined with our knowledge on the biology of animals to construct a food web of the community species composition of the communities investigated is similar but relative abundance varies these differences seem to be a result of temporal changes in the communities early stages of the cycle of the manus basin vents are hypothetically dominated by vestimentiferans but mesogastropods will replace them with time faunal composition and community structure of the manus basin reinforce the likelihood that the hydrothermal vents of western pacific spreading centres have been in communication with each other the manus basin vent fauna displays close affinity with the communities of the north fiji and lau basins as compared with the mariana trough vent region

is a pyrolitic adiabatic mantle compatible with seismic data in this paper the simplest average physical model of a mantle convecting as a whole i e following an adiabatic temperature gradient with a single composition pyrolite with phase transitions is tested directly against global seismic data instead of against spherically symmetric seismic models constraints from seismic data on average velocities and lower mantle velocity gradients are hard to reconcile with an adiabatic pyrolitic mantle given the current state of knowledge of elastic and anelastic mineral parameters at high pressure and temperature this physical model generally gives a a stronger baseline offset between upper and lower mantle average travel time residuals than allowed by the data and b an insufficient decrease in velocity with depth in the lower mantle above 2500 km we tested 105 upper and 105 lower mantle models that were selected randomly within the mineral parameter uncertainties only 2 lower mantle models and 24 upper mantle models yield whole mantle seismic structures that are compatible with global isc p and s travel times and central frequencies of toroidal and spheroidal fundamental modes with angular order higher than 18 to improve the fit to the seismic data the physical model would require a a lower velocity transition zone composition than dry pyrolite at least around continents and subduction zones as well as b a gradual change in physical state of the lower mantle that decreases the velocity depth gradient e g a superadiabatic temperature gradient

seeping hydrocarbons and related carbonate mineralisations in sediments south of lihir island new ireland fore arc basin papua new guinea hydrocarbon gases have been sampled from both cold seeping and heat venting areas in the new ireland fore arc basin in the vicinity of lihir island highest concentrations of up to 10 l l ch4 with a 13cch4 value of 54 9 pdb have been measured in the deep ocean water within a long and narrow deep sea basin located between edison seamount and an uplifted structure named mussel cliff surface sediments of the seep area were covered with chemoautotrophic deep sea fauna such as calyptogena species and tube worms large authigenic calcite concretions occur in the sediments between 50 and 200 cm sediment depth the carbon isotopes of the carbonates in the concretions range from 15 to 40 pdb indicating a mixture of two co2 sources normal marine inorganic carbon fixed in biogenic shells and co2 from anaerobe bacterial oxidation processes of methane accordingly 14c ams dating suggests that authigenic calcite mineralisation incorporated relatively young carbon from methane oxidation in contrast the c1 c2 ratio of 234 and the 13cch4 value of 24 1 pdb in the hot hydrothermal vent of lihir harbour indicates a mixture of a major abiogenic carbon source for methane formation related to magmatism associated with lihir volcano the observed variable fluid characteristics within only 20 km distance between hot hydrothermal venting and the methane seeping deep sea area indicates highly variable heat flow situations and or sediment distributions which control the gas geochemical characteristics in the new ireland fore arc basin

a review on natural and human induced geohazards and impacts in karst karst environments are characterized by distinctive landforms related to dissolution and a dominant subsurface drainage the direct connection between the surface and the underlying high permeability aquifers makes karst aquifers extremely vulnerable to pollution a high percentage of the world population depends on these water resources moreover karst terrains frequently underlain by cavernous carbonate and or evaporite rocks may be affected by severe ground instability problems impacts and hazards associated with karst are rapidly increasing as development expands upon these areas without proper planning taking into account the peculiarities of these environments this has led to an escalation of karst related environmental and engineering problems such as sinkholes floods involving highly transmissive aquifers and landslides developed on rocks weakened by karstification the environmental fragility of karst settings together with their endemic hazardous processes have received an increasing attention from the scientific community in the last decades concurrently the interest of planners and decision makers on a safe and sustainable management of karst lands is also growing this work reviews the main natural and human induced hazards characteristic of karst environments with specific focus on sinkholes floods and slope movements and summarizes the main outcomes reached by karst scientists regarding the assessment of environmental impacts and their mitigation

taking the earth s temperature temperature has a direct effect on the dynamics of the earth s interior but it is not easy to measure temperatures at great depths an indirect way to study the earth s temperature is through seismology as shown by this study of seismic tomography

strength stiffness and microstructure characteristics of biocemented calcareous sand calcareous sands are known as problematic soils in nature and challenge geotechnical engineers in many practical projects microbially induced calcite precipitation micp is an innovative soil imp

imaging of subducted lithosphere beneath south america tomographic images are produced for the deep structure of the andean subduction zone beneath western south america the data used in the imaging are the delay times of p pp and pwp phases from relocated teleseismic earthquakes in the region regionally structural features larger than about 150 km are resolved by the data presentations of layer anomaly maps and cross sections reveal 1 the nazca slab is probably continuous laterally and at depth over most regions 2 the offset between the north and south deep earthquake zones containing the 1994 deep bolivia main shock and its aftershocks can be modelled by a northwest striking and steeply northeast dipping slab structure and 3 the nazca slab clearly penetrates the lower mantle beneath central south america but is partly deflected in the southern deep zone

trench migration and subduction zone geometry seismic tomography results show a large variety in upper mantle structure along convergent plate boundaries we numerically investigate the effect of trench migration on the evolution of a slab with temperature dependent viscosity encountering a viscosity interface we find that subduction zone geometry is sensitive to even small rates 1 cm yr of retrograde motion increase in trench migration rate decreases the dip angle of the slab and its ability to penetrate the lower mantle upon including a background mantle flow it turns out that trench migration relative to the upper mantle flow is more decisive than the absolute plate velocities subduction zone geometry appears to be strongly time dependent we conclude that individual tectonic setting and time dependent slab behaviour can account for many different types of observable subduction zone anomalies our model temperature can adequately account for magnitudes and patterns of seismic anomalies as obtained from seismic tomography

long wavelength s wave velocity structure throughout the mantle summary long wavelength s wave velocity anomalies are obtained for the entire mantle by inverting 6ooo long period 40 100s sh body waves and lo00 long period 100 500 s love waves in the shallow mantle the patterns of fast and slow velocity anomalies correlate well with age and tectonics in the depth range of 400 1000 km we find two antipodal fast velocity anomalies one in the western pacific and the other in south america they form a fairly strong i 2 anomaly moreover the 1 2 anomaly is the largest spherical harmonic component throughout the entire mantle except for in the layer of 1000 1300 km depth a fast velocity anomaly near the caribbean previously reported by several other investigators is found between the depths of 1000 and 1300km with diminishing amplitudes it can be traced to canada and the aleutians and may be related to old subducted slabs in the same depth interval similar size anomalies can be found in the middle of the pacific and in the indian ocean these could be checked by more detailed studies to judge the reliability of this study heterogeneity power has a peak at the surface and a secondary peak at the bottom of the mantle d consistent with the existence of chemical and or thermal boundary layers at the base of the mantle we also find a fast velocity anomaly which surrounds the pacific ocean this feature has been found by other researchers previously but its interpretation is difficult due to the trade off between velocity anomaly and core mantle boundary deformation

an empirical relationship between seismic attenuation and velocity anomalies in the upper mantle we use recent p wave attenuation q 1 and velocity vp tomographic models of the tonga fiji region to obtain an empirical relation between attenuation and velocity for the upper mantle the attenuation and velocity anomalies show a strong inverse correlation allowing the determination of an empirical relationship the relationship is similar to a predicted relation derived from laboratory experiments on peridotite and dunite assuming the observed anomalies result from temperature variations the results here suggest that the observed anomalies are generally consistent with the effect of temperature and demonstrate that the combination of velocity and attenuation data provides powerful constraints on the physical state of upper mantle materials we find that the chosen geotherm and activation energy has a strong effect on the position of the solidus within the seismic data

three dimensional p wave velocity structure beneath the indonesian region abstract we present the p wave seismic tomography image of the mantle to a depth of 1200 km beneath the indonesian region the artb inversion method is applied to a dataset of 118 203 p wave travel times of local and teleseismic events taken from isc bulletins although the resolution is sufficient for detailed discussion in only a limited part of the study region the results clarify the general tectonic framework in this region and indicate a possible remnant seismic slab in the lower mantle structures beneath the philippine islands and the molucca sea region are well resolved and high velocity zones corresponding to the slabs of the molucca sea and philippine sea plates are well delineated seismic zones beneath the manila negros and cotabato trenches are characterized by high velocity anomalies although shallow structures were not resolved the molucca sea collision zone and volcanic zones of the sangihe and philippine arcs are dominated by low velocity anomalies the philippine sea slab subducts beneath the philippine islands at least to a depth of 200 km and may reach depths of 450 km the southern end of the slab extends at least to about 6 n near southern mindanao in the south the two opposing subducting slabs of the molucca sea plate are clearly defined by the two opposing high velocity zones the eastward dipping slab can be traced about 400 km beneath the halmahera arc and may extend as far north as about 5 n unfortunately resolution is not sufficient to reveal detailed structures at the boundary region between the halmahera and philippine sea slabs the westward dipping slab may subduct to the lower mantle although its extent at depth is not well resolved this slab trends n s from about 10 n in the philippine islands to northern sulawesi a ne sw trending high velocity zone is found in the lower mantle beneath the molucca sea region this high velocity zone may represent a remnant of the former subduction zone which formed the sulawesi arc during the miocene the blocks along the sunda and banda arcs are less well resolved than those in the philippine islands and the molucca sea region nevertheless overall structures can be inferred the bowl shaped distribution of the seismicity of the banda arc is clearly defined by a horseshoe shaped high velocity zone the tomographic image shows that the indian oceanic slab subducts to a depth deeper than 300 km i e deeper than its seismicity beneath andaman islands and sumatra and may be discontinuous in northern sumatra along southern sumatra java and the islands to the east the slab appears to be continuous and can be traced down to at least a depth of the deepest seismicity where it appears to penetrate into the lower mantle

engineering characteristics of the calcareous sand in nansha islands south china sea calcareous sand is widespread on the coral reefs of nansha islands south china sea it represents a special soil type due to its compressibility which results from high void ratio sediments and crushable particles in oceanic engineering calcareous sand is commonly used as building foundations and backfill material for road embankments or airport runways site investigations of coral reef geology geomorphology and sedimentation on yongshu reef nansha islands south china sea indicate that calcareous sand is the main composition of the upper reef flat the only available site for constructions therefore it is very important to estimate the engineering characteristics of calcareous sand this paper presents the site geology of calcareous sand on yongshu reef and results of corresponding laboratory plate load tests the bearing capacity and deformational behavior of calcareous sand are studied results of this study show that 1 the bearing capacity of dry sand exceeds 500 kpa when the relative density is 68 so calcareous sand can be compacted to achieve greater bearing capacity and reduce settlement 2 plastic deformation is the main part of the ground settlement 3 the bearing capacity of saturated calcareous sand is 50 less than that of the dry sand 4 square foundation can provide greater bearing capacity than circular one with the same area 5 calcareous sand ground is obviously stiffer than quartz sand ground 6 the effective depth of load transmission is about 1 0 to 2 0 times of the load plate width and increases with the imposed load

shear wave velocity structure beneath europe the northeastern atlantic and western asia from waveform inversions including surface wave mode coupling summary waveforms of 449 seismograms have been inverted for s wave velocity structures beneath europe the northeastern atlantic and western asia down to a depth of 670 km recorded waveforms were used in the time window starting at the s wave arrival and ending after the fundamental mode rayleigh wave arrival the inversion method is based on the partitioned waveform inversion nolet 1990 with the difference that synthetic seismograms are calculated taking surface wave mode coupling into account in order to model body waves in laterally heterogeneous media more accurately the partitioning of the inversion procedure makes non linear optimization feasible even for inversions including surface wave mode coupling the non linear inversion of the waveforms resulted in linear constraints on the 3 d velocity structure in a second step these constraints were used in a linear inversion for the 3 d shear wave velocity model beneath europe the northeastern atlantic and western asia the eur sc 95 model is presented which is characterized by a wide range of length scales of the velocity structures in central europe where the ray density is highest small scale structures are recovered such as the presence of high velocities associated with the hellenic subduction zone on the edges of the inversion model where the ray density and therefore also the resolution is poorer we find larger scale features such as the relatively laterally homogeneous high velocity structure beneath the russian platform to a depth of 300 km in this paper we discuss the inversion method data processing parametrization difficulties due to the introduction of surface wave mode coupling spatial resolution of the model and structures in the eur sc 95 model

toward quantifying uncertainty in travel time tomography using the null space shuttle 1 the solution of large linear tomographic inverse problems is fundamentally non unique we suggest to explore the non uniqueness explicitly by examining the null space of the forward operator we show that with the null space shuttle it is possible to assess robustness in tomographic models and we illustrate the concept for the global p wave model mit p08 we found a broad range of acceptable solutions compatible with the travel time data the root mean square rms velocity perturbations vary from 0 2 to 0 6 in the lowermost mantle and from 0 3 to 1 3 in the upper mantle such large variations in average amplitudes prohibit meaningful inferences on temperature or chemical variations in the earth from tomographic models alone on a global scale much short wavelength structure resides in the null space of the forward operator suggesting that the data do not everywhere resolve structure on the smallest length scale 200 km allowed by the block parameterization used in mit p08 and similar models this indicates that great care should be taken when interpreting such structure as a practical measure we suggest that only those structures for which the wave speed perturbations do not change sign within the range of models permitted by the data should be considered robust with this criterion the model null space analysis shows that the high velocity anomalies in the lower mantle which are often interpreted as remnants of slabs of subducted lithosphere are required by the seismic data low velocity anomalies underneath for instance hawaii iceland and africa show varying degrees of robustness

signature of slab fragmentation beneath anatolia from full waveform tomography when oceanic basins close after a long period of convergence and subduction continental collision and mountain building is a common consequence slab segmentation is expected to have been relatively common just prior to closure of other oceans in the geological past and may explain some of the complexity that geologists have documented in the tibetan plateau also we focus on the eastern mediterranean basin which is the last remainder of a once hemispherical neo tethys ocean that has nearly disappeared due to convergence of the india and africa arabia plates with the eurasia plate we present new results of full waveform tomography that allow us to image both the crust and upper mantle in great detail we show that a major discontinuity exists between western anatolia lithosphere and the region to the east of it also the correlation of geological features and the crustal velocities is substantially stronger in the west than in the east we interpret these observations as the imprint in the overriding plate of fragmentation of the neo tethys slab below it this north dipping slab may have fragmented following the eocene about 35 million years ago arrival of a continental promontory central anatolian core complex at the subduction contact from the eocene through the miocene slab roll back ensued in the aegean and west anatolia while the cyprus bitlis slab subducted horizontally beneath central and east anatolia following collision of arabia about 16 million years ago the cyprus bitlis slab steepened exposing the crust of central and east anatolia to high temperature and resulting in the velocity structure that we image today slab fragmentation thus was a major driver of the evolution of the overriding plate as collision unfolded

massif central france new constraints on the geodynamical evolution from teleseismic tomography the massif central the most significant geomorphological unit of the hercynian belt in france is characterized by graben structures which are part of the european cenozoic rift system ecris and also by distinct volcanic episodes the most recent dated at 20 ma to 4000 years bp in order to study the lithosphere asthenosphere system beneath this volcanic area we performed a teleseismic field experiment during a six month period a joint french german team operated a network of 79 mobile short period seismic stations in addition to the 14 permanent stations inversion of p wave traveltime residuals of teleseismic events recorded by this dense array yielded a detailed image of the 3 d velocity structure beneath the massif central down to 180 km depth the upper 60 km of the lithosphere displays strong lateral heterogeneities and shows a remarkable correlation between the volcanic provinces and the negative velocity perturbations the 3 d model reveals two channels of low velocities interpreted as the remaining thermal signature of magma ascent following large lithospheric fractures inherited from hercynian time and reactivated during oligocene times the teleseismic inversion model yields no indication of a low velocity zone in the mantle associated with the graben structures proper the observation of smaller velocity perturbations and a change in the shape of the velocity pattern in the 60 100 km depth range indicates a smooth transition from the lithosphere to the asthenosphere thus giving an idea of the lithosphere thickness a broad volume of low velocities having a diameter of about 200 km from 100 km depth to the bottom of the model is present beneath the massif central this body is likely to be the source responsible for the volcanism it could be interpreted as the top of a plume type structure which is now in its cooling phase

deep structure of an arc continent collision earthquake relocation and inversion for upper mantle p and s wave velocities beneath papua new guinea we examine mechanisms of lithospheric growth and modes accommodating subcrustal convergence following the cessation of subduction by analyzing the seismicity and upper mantle velocities in the new guinea arc continent collision earthquakes in the papua new guinea png region from 1967 to 1984 have been relocated in a joint inversion with seismic velocities using p and s wave arrival times recorded by seismographs in png a total of 957 well recorded earthquakes were chosen for use in three dimensional velocity inversions from an initial catalog of 12 960 events based on the stability of initial hypocenter relocations constant velocity blocks were defined as irregular polyhedra to give fine detail in heavily sampled areas without introducing a large number of poorly controlled parameters and to exploit a priori knowledge of the geometry of velocity anomalies spherical geometry was used to accurately calculate long ray paths up to 1500 km in length most of the 700 best located hypocenters from the png data set are in the upper mantle beneath the finisterre huon fh ranges the newly accreted island arc terrane beneath the papuan peninsula and in the new britain seismic zone an oceanic subduction system these hypocenters show a well defined seismic zone dipping vertically or steeply to the north beneath the northern fh ranges from 125 to 250 km depth continuous along strike with the new britain seismic zone to the east which shows earthquakes to 600 km depth the steeply dipping intermediate depth seismicity flattens near 100 km depth beneath the fh ranges and forms a subhorizontal seismic zone beneath the fh ranges by contrast seismicity continues upward to the surface beneath new britain where the arc has not yet collided with new guinea the 100 km deep flat zone does not continue south of the fh ranges but appears to be truncated below the eastern and southern boundaries of the island arc terrane and no clear evidence for a south dipping seismic zone could be found the relationship of the flat part of the slab 100 km beneath the fh ranges and surface faulting is difficult to discern the apparent surface suture bounding the south side of the fh ranges is 100 km directly above the southern termination of intermediate depth seismicity nowhere in png could clear evidence for arc polarity reversal be found from seismicity all of the well located subcrustal earthquakes beneath the papuan peninsula lie in a narrow horizontal line between 125 and 175 km depth that follows the center of the peninsula and are distinctly separated from the fh seismic zone to the north these events do not require a southward subducting plate beneath the papuan peninsula an alternate and reasonable explanation for these events is that they are a result of unstable thickening of the lithosphere information on lateral heterogeneity in the mantle is limited because large variations in crustal velocities dominate the observed pattern of travel time residuals allowing for only crustal heterogeneity reduces travel time residual variances by 40 from a simple one dimensional structure while allowing for additional mantle heterogeneity results in 10 further reduction for the various parameterization s attempted here inversions with several different block geometries show low velocities at 35 to 171 km km depth beneath the bismarck sea back arc basin and high velocities just south of the intermediate depth fh seismic zone the pattern of lateral heterogeneity supports the inference from seismicity of north dipping slabs beneath both northeast new guinea and new britain

macrobenthos community structure and trophic relationships within active and inactive pacific hydrothermal sediments hydrothermal fluids passing through sediments create a habitat hypothesized to influence the community structure of infaunal macrobenthos here we characterize the density biomass species composition diversity distributions lifestyle and nutritional sources of macroinfauna in hydrothermal sediments in ne and sw pacific settings and draw comparisons in search of faunal attributes characteristic of this habitat there is increasing likelihood that seafloor massive sulfide deposits associated with active and inactive hydrothermal venting will be mined commercially this creates a growing imperative for a more thorough understanding of the structure dynamics and resilience of the associated sediment faunas and has stimulated the research presented here macrobenthic assemblages were studied at manus basin 1430 1634 m papua new guinea png as a function of location south su vs solwara 1 and hydrothermal activity active vs inactive and at middle valley 2406 2411 m near juan de fuca ridge as a function of habitat active clam bed microbial mat hot mud inactive background sediment the studies conducted in png formed part of the environmental impact assessment work for the solwara 1 project of nautilus minerals niugini limited we hypothesized that hydrothermally active sites should support a higher densities and biomass b greater dominance and lower diversity c a higher fraction of deposit feeders and d greater isotopic evidence for chemosynthetic food sources than inactive sites manus basin macrofauna generally had low density o1000 ind m

a rapid method to map the crustal and lithospheric thickness using elevation geoid anomaly and thermal analysis application to the gibraltar arc system atlas mountains and adjacent zones we present a method based on the combination of elevation and geoid anomaly data together with thermal field to map crustal and lithospheric thickness the main assumptions are local isostasy and a four layered model composed of crust lithospheric mantle sea water and the asthenosphere we consider a linear density gradient for the crust and a temperature dependent density for the lithospheric mantle we perform sensitivity tests to evaluate the effect of the variation of the model parameters and the influence of rms error of elevation and geoid anomaly databases the application of this method to the gibraltar arc system atlas mountains and adjacent zones reveals the presence of a lithospheric thinning zone sw ne oriented this zone affects the high and middle atlas and extends from the canary islands to the eastern alboran basin and is probably linked with a similarly trending zone of thick lithosphere constituting the western betics eastern rif rharb basin and gulf of cadiz a number of different even mutually opposite geodynamic models have been proposed to explain the origin and evolution of the study area our results suggest that a plausible slab retreating model should incorporate tear and asymmetric roll back of the subducting slab to fit the present day observed lithosphere geometry in this context the lithospheric thinning would be caused by lateral asthenospheric flow an alternative mechanism responsible for lithospheric thinning is the presence of a hot magmatic reservoir derived from a deep ancient plume centred in the canary island and extending as far as central europe

shear modulus and q of forsterite and dunite near partial melting from forced oscillation experiments an apparatus designed to determine the complex shear modulus of rock samples by forced torsion oscillations at high temperature and in the seismic frequency band 0 003 30 hz is briefly described measurements were performed on natural dunite from aheim norway up to 1400 c and on polycrystalline forsterite up to 1500 c at 1 atm pressure the two materials were chosen to study by comparison the effect of melt on the elasticity and anelasticity of mantle rocks between 1000 and 1200 c the absolute values of the shear modulus g are almost equal for both materials above 1200 c g for natural dunite decreases progressively with temperature and at 1400 c and 1 hz reaches 13 of its value at 1100 c in contrast g of pure forsterite depends little on temperature for petrological reasons supported by simultaneous measurements of the electric resistivity there is strong evidence that the decrease of g in dunite above 1200 c is due to melt from the lower melting components of the dunite based on different models estimates of the melt fraction are made at high temperature in both materials q 1 is characterized by a monotonic decrease with frequency according to with 0 25 an apparent activation energy of 38 5 kcal mol 1 for forsterite and 48 8 kcal mol 1 for dunite was found with no significant change in the regime of partial melting from this it is concluded that q 1 even at partial melting is dominated by solid state high temperature background absorption there is no indication from these experiments for a constant q band at low seismic frequencies or an increase of q proportional to frequency as suggested by some seismologists the present results are in good qualitative agreement with those for young s modulus obtained previously by strain retardation experiments

how well can we resolve the deep seismic slab with seismic tomography the three dimensional p and s velocity tomographic images around the wadati benioff zone under the island arcs of the northwest pacific are analyzed estimations of resolution and error show that the fast seismic anomalies associated with the subduction zones are generally real and resolvable the anomalies are slab like in most parts of the upper mantle and become folded and broadened with depth near the bottom of the upper mantle fingering of the slabs including segmenting and shallow angle spreading is indicated the fingering under japan and the izu bonin trench has a tendency to flatten to sub horizontal while possible downward spreading is seen under parts of the kuril trench

bias in reported seismic arrival times deduced from the isc bulletin summary the accurate timing of seismological data is crucial for most quantitative examinations in seismology we present evidence that traveltime data from many stations contain systematic variations in timing which can be identified by checking the median of station delay times as a function of time this function is expected to be constant but many deviations are found several hundred stations that report arrival times to the isc have been examined the median station delay times of almost 8 per cent of these stations show changes of more than 1 s and thus exceed the structural signal in the data temporal variations of 0 5 1 s are common changes in the distribution of observed earthquakes and other possible explanations of such variations have been tested and fail to explain most of the observations therefore the bulk of the observed changes must be caused by flaws in the timing of the data or by biased picking of arrival times for instance at one station with a strong annual variation of noise level the arrival times are on average picked several tenths of a second later during months with a high noise level because of their systematic nature these errors will not necessarily cancel out by using the large number of traveltimes in the isc bulletin and may therefore introduce a bias in many investigations if the observed timing variations are due to the recording equipment at the stations the errors will be present in the digital waveform data as well tomographic studies could potentially be affected but in particular studies of temporal variations of earth structure based on traveltime data e g inner core rotation need to be looked at with caution as results might be influenced by station effects the exact nature of the bias is study dependent and needs thorough investigation in each individual case

storm cycles in the last millennium recorded in yongshu reef southern south china sea large storm relocated porites coral blocks are widespread on the reef flats of nansha area southern south china sea detailed investigations of coral reef ecology geomorphology and sedimentation on yongshu reef indicate that such storm relocated blocks originated from large porites lutea corals growing on the spurs within the reef front living coral zone because the coral reef has experienced sustained subsidence and reef development during the holocene dead corals were continuously covered by newly growing coral colonies for this reason the coral blocks must have been relocated by storms from the living sites and therefore the ages of these storm relocated corals should approximate the times when the storms occurred rapid emplacement of these blocks is also evidenced by the lack of coral overgrowth encrustation or subtidal alteration u series dating of the storm relocated blocks as well as of in situ reef flat corals suggests that during the last 1000 years at least six strong storms occurred in 1064 30 1210 5 1201 4 1336 9 1443 9 1685 8 1680 6 1872 15 ad respectively with an average 160 year cycle 110 240 years the last storm which occurred in 1872 15 ad also led to mortality of the reef flat corals dated at similar to 130 years ago thus the storm had significant impacts on coral reef ecology and morphology c 2004 elsevier b v all rights reserved

effective parameters for the particle breakage of calcareous sands an experimental study abstract calcareous sediments have different behavior under monotonic and cyclic loadings compared to that of terrigenous soils particle breakage is considered the most important feature of calcareous soils and has been used in many experimental investigations recently this phenomenon affects some characteristics of carbonate sediments such as compressibility shearing strength and permeability in this study experiments were conducted to evaluate the parameters that affect the particle breakage of calcareous sands including confining pressure relative density axial strain drainage conditions and grain size distribution the input energy per unit volume of the soil was also calculated to analyze the effect of this parameter on the particle breakage in the testing program two calcareous sands from different locations in the persian gulf namely bushehr port bp and hormuz island hi sands were used for the triaxial compression tests the experimental results showed that the input energy played an important role in the particle breakage behavior of used soils in comparison to other parameters considered in this study axial strain as a representation of the effect of deviatoric loading had major influences on the amount of crushing the results also indicated that hi sand particles yielded at a higher stress than bp sand

p and s wave travel time inversions for subducting slab under the island arcs of the northwest pacific we have observed slablike high p and s velocity anomalies around the wadati benioff zone under island arcs of the northwest pacific through travel time tomographic inversions nineteen years of international seismological centre travel time residuals for events and stations in this large region are used analyses of resolution and noise show that the images are generally well resolved the images illustrate that slab anomalies are continuous along strike in most parts of the upper mantle of the region and become contorted and generally broadened with depth near the bottom of the upper mantle fingering of the slabs including segmenting and spreading is indicated the fast anomalies associated with the japan izu bonin and mariana subduction zones tend to flatten to subhorizontal at depth while downward spreading may occur under parts of the mariana and kurile arcs the fast anomalies below 700 km are not in the shape of a single coherent sheet the principal compressional axes of focal mechanisms in the region consistently follow the downdip direction of the high velocity slab even when it bends to subhorizontal at depth the depth at which compression begins to dominate the downdip stress regime in the slab apparently depends on bending of the slab and its dip slab fingering and intense deep seismicity probably are the consequence of the slab encountering a barrier of some form around the 670 km discontinuity

geotechnical implications of subsurface water rise in kuwait abstract there is evidence that groundwater is rising under kuwait city this paper discusses the causes and geotechnical implications of such a rise an explanatory model for the problem of rising groundwater including the contributing parameters is introduced downward percolation from subsurface pipe networks and from excess irrigation together with the local geologic conditions form the main source of the problem potential geotechnical problems are presented based on reviewed and conducted laboratory and field tests reduction in shear strength of the cemented soil type due to saturation is evident

on ach or how reliable is regional teleseismic delay time tomography abstract ach named after aki et al 1976 bull seismol soc am 66 501 524 aki et al 1977 j geophys res 82 277 296 is a standard widely used method for three dimensional seismic imaging of the earth the fundamental hypothesis which underlies the method is that the time residuals generated outside the given target volume from the seismic source to the bottom of the modelled zone are approximately constant across the seismic array the main purpose of this study is to check this assumption we computed travel times for a given station and event distribution using a three dimensional global earth model taken from seismic tomography we found that the relative residuals generated outside the target volume are not negligible and that the fundamental hypothesis underlying ach is thus not verified these deviations are generated in the lower and or upper mantle and the corresponding proportions are entirely dependent on the raypaths the bias in the inverted model is statistically similar to the input model outside the target volume we thus recommend caution in any interpretations involving ach generated models a secondary somewhat independent outcome of this study is that fermat s principle used to linearise the inverse problem in ray theory based tomography seems to be valid without any restrictions given our input model is representative for the true earth for rays with turning points in the lower mantle for rays with turning points in the upper mantle the constant raypath approximation is probably not true this applies to global tomography as well

whole mantle p wave travel time tomography abstract a method of tomographic inversion to obtain three dimensional velocity perturbations in the earth s whole mantle has been developed and applied to more than two million p wave arrival time data reported by international seismology center isc the model is parameterized with 32 768 blocks the divisions in latitude longitude and radius are 32 64 and 16 respectively horizontal cell size is 5 6 5 6 the layer thicknesses vary with depth 29 km just below the surface and 334 km just above the core mantle boundary starting from a spherically symmetric earth model we obtained a three dimensional model using the following iterative procedures first we relocated all the events second we backprojected the residual into the whole mantle third we refined the spherically symmetric earth model the solutions have been converged in five iterations we adopted the following techniques in the backprojection procedure the first order smoothness was introduced as a damping which makes the solution independent of the starting model and its apparent fluctuation minimal the basic equations for delay times and smoothness are solved using the conjugate gradient method an iterative method which guarantees the convergence of solution into the exact least squares solution the weight on the smoothness i e the damping factor was objectively determined by a simplified cross validation technique the final solution was obtained as an average of the ten solutions each of which was derived from one tenth of the total data set the reliability of the solution is examined in two ways 1 mapping the resolution given by the reconstruction of checkerboard patterns and 2 mapping the variance given from the gaussian noise input this is the first result which delineates the whole mantle structure with its reliability mapping the longest wavelength anomalies of the lower mantle are similar to those of previous studies by dziewonski 1984 and hager and clayton 1989 however the shorter wavelength patterns have many discrepancies the fast anomalies of the uppermost mantle beneath the shield and the slow anomalies beneath the active tectonic regions are clearly seen we also revealed the l 2 pattern at the transition zone reported by the previous surface wave and free oscillation studies the most striking feature is that of the fast anomalies lying along the extension of the large subducting plate up to depths of about 1000 km or more the resolving powers in these regions are generally good

seismic attenuation in the eastern australian and antarctic plates from multiple scs waves the attenuation of seismic shear waves in the mantle beneath the eastern australian and antarctic plates is analyzed using a large data set of multiple scsn waves reflected n times at the core mantle boundary and n 1 times at the surface the data are the transverse components of deep earthquakes from the subduction zones north and east of australia recorded at stations in antarctica australia indonesia new caledonia and new zealand the data are filtered with narrow band pass filters at 5 frequencies in the range 0 013 0 040 hz the scsn 1 scsn amplitude ratios of successive scs phases are compared to the ratios computed for synthetic seismograms for the same paths and same focal mechanisms in order to eliminate the effects of source radiation and geometric attenuation the synthetic seismograms are computed from a summation of toroidal modes for the 1 d reference model prem dziewonski anderson 1981 the observed to computed spectral ratios appear consistent for similar paths they reveal that the attenuation is not frequency dependent that the contribution of scattering to attenuation is low and that the prem model is a valuable reference model for the study region at the considered frequencies an inversion of the data at 0 026 hz is performed to retrieve the quality factor q in the upper mantle in regions defined using a priori constraints inferred from seismic shear velocities q values close to those of prem are found beneath the australian and antarctic cratons lower values beneath the eastern australian phanerozoic margin and very low values beneath the oceanic region between australia and antarctica where ridges and a triple junction are present the australian antarctic discordance along the south indian ridge appears as an exception with a q value close to those of stable continents the highest q values are found beneath the subduction zones a feature which is not apparent in global attenuation models possibly because of its narrow lateral extension and because it extends at depths larger than those sampled by surface waves despite limitations due to the uneven distribution of the scsn bounce points at the surface and to the difficulty of collecting a large number of high quality data our approach appears very promising it is complementary to the more widely used determination of seismic attenuation using surface waves because it provides increased depth coverage and a broader spectral coverage it therefore has a considerable potential in future investigations of mantle structure and dynamics

delay time tomography of the upper mantle below europe the mediterranean and asia minor summary the method of linearized delay time tomography is applied to retrieve the p velocity heterogeneity of the upper mantle in central europe the mediterranean and asia minor the upper mantle is parametrized in slowness cell functions with lateral dimensions of 1 the model parametrization includes event mislocation vectors and station delay time corrections in all 20 000 parameters describe the model delay time data selected from the isc data base 1964 1982 from regional events and from stations up to 90 of epicentral distance are used about 18 000 events and 937 stations contributed nearly 500 000 delay times we discuss the tomographic method the data processing the cell model employed the computation of the ray geometry the use of composite rays in tomography and the cell hit count the inversions are performed with two different iterative row action methods lsqr and sirt results obtained with the lsqr method will be shown only the spatial resolution is investigated with sensitivity analyses using two different synthetic velocity models a spike model and a model with harmonically varying velocity anomalies the spatial resolution is estimated to be high on the order of the cell size in the mantle below central and southeastern europe the mapped velocity heterogeneity exhibits primarily low velocities around a depth of 200 km and just above the transition from upper to lower mantle this indicates a systematic deviation of the reference model jeffreys bullen from the radially averaged earth structure which may violate the basic assumptions underlying the linearized approach a posteriori investigation of the data also indicates the presence of a low velocity zone and the existence of strong velocity depth gradients

evidence for active subduction at the new guinea trench 1 recent seismic tomography imaging shows clear evidence for southwestward subduction along the entire length of the new guinea trench ngt in indonesia and papua new guinea viewed in conjunction with the occurrence of large mw 7 thrust earthquakes that are known to have occurred on the trench this confirms conclusions of earlier studies that the ngt is an active inter plate boundary the 650 km long slab is visible to a depth of about 300 km and subducts with a dip angle that varies from 30 at 136 e to 10 at 143 e the improved clarity of the seismic tomography in this region stems from the use of a more accurate data set of p and s wave arrival times and hypocentral locations

a laboratory investigation of effects of trench migration on the descent of subducted slabs a laboratory investigation of viscous slabs subducted from a migrating trench reveals a range of possible behaviours the slab dip in a uniform mantle is found to be steady or oscillatory depending on the rates of descent and trench migration in addition density and viscosity interfaces are used to model the increased resistance to sinking of stiff slabs through the seismic discontinuity at a depth of about 660 km in earth s mantle if the slab is denser than the lower layer and its dip in the upper layer is steady it can continue to descend through the lower layer in a tabular form and in either a steady or oscillatory manner or it can be laid horizontally on the interface for a distance before descending in a chain of diapirs resulting from gravitational instability at the interface if the slab dip in the upper layer is unstable the slab sinks into the lower layer in a chain of large diapirs at a spacing determined by the frequency of oscillations set by instability of the slab within the upper layer the style of penetration depends on the trench migration speed and the ratio of sinking velocities in the two layers estimates for mantle slabs indicate that they may range across the major regime transitions the experimental system provides a gross simplification of mantle conditions but the results are a testimony to the possibility of a range of complex behaviour of subducted lithosphere they also indicate that the relationship between the structural features in the lower mantle revealed by seismic imaging and present day tectonic processes at the surface may not be obvious tomographic images of western pacific subduction zones and data for the migration rates of associated trenches suggest a dependence of slab behaviour on migration rate similar to that seen in the experiments

resolution experiments for nw pacific subduction zone tomography we investigate the resolving power of isc neic p travel time data in tomographic inversions for the geometry of the subduction zones in the nw pacific from thermal models for the kurile japan izu bonin mariana and ryukyu slabs we generate three dimensional synthetic velocity anomalies for subducting slabs which are then projected onto a cell model for the uppermost 1400 km of the mantle using these synthetic models we compute synthetic delay times for ray paths corresponding to the source and receiver locations used for the actual data add gaussian noise invert the synthetic data and compare the resulting velocity structure to the initial synthetic models this comparison is illustrated for sections through the kuriles and the mariana arcs a variety of resolution artifacts are observed which in many cases resemble features visible in the tomographic results obtained from inverting the actual isc neic data

particle obstruction and crushing of dredged calcareous soil in the nansha islands south china sea abstract the bearing capacity of the dredged calcareous soil in the nansha islands south china sea typically exceeds that of terrigenous dredger fill furthermore the shear strength of calcareous soil exceeds that of siliceous sand under identical conditions it is mainly caused by the interparticle obstruction between calcareous soil particles to explore the obstruction mechanism of calcareous soil particles a series of triaxial tests were performed on calcareous soils under both consolidated undrained cu and consolidated drained cd conditions respectively particle shape characteristics and particle crushing were also investigated to study the formation mechanism of obstruction force test results indicate that irregular particle shape is the prerequisite for the emergence of particle obstruction in calcareous soils a simple obstruction dilatation model was developed to describe the relationship among particle obstruction dilation and particle crushing the obstruction force varies greatly during the shearing process which is mainly influenced by particle size and stress level under low confining pressure particle obstruction results in dilatation and increases internal friction angle in contrast obstruction causes particle breakage increases the apparent cohesion and ultimately decreases the effective internal friction angle under high confining pressures the particle obstruction of calcareous soil noticeably improves shear strength therefore the effect of particle obstruction on strength should be considered in coral reef engineering design work

crust and upper mantle p and s wave delay times at eurasian seismic stations median crust and upper mantle p and s wave delay times based on residuals for teleseismic p and s wave arrival times included in the groomed isc neic database of engdahl et al bull seism soc am 88 1998 722 are estimated as functions of time and azimuth for eurasian seismic stations the effects of source and lower mantle 3 d structure on the station residuals are corrected by ray tracing all phase data to a depth of 400 km below the station through the 3 d p and s wave models of bijwaard et al j geophys res 103 1998 30055 and bijwaard seismic travel time tomography for detailed global mantle structure university of utrecht utrecht the netherlands 1999 179 pp respectively in general crust and upper mantle p and s station delays based on medians of azimuthally binned residuals are spatially coherent and can be qualitatively associated with eurasian tectonic features such as orogens and cratons as well as with structural elements such as sediment and crustal thickness and average uppermost mantle velocities paired p and s station delays are correlated with a rather poorly determined slope s p delay time ratio of about 1 9 2001 elsevier science b v all rights reserved

control of seafloor aging on the migration of the izu bonin mariana trench article i nfo recent global kinematic studies reveal that most of the trenches roll back but a significant number of them advance toward the upper plate those advancing trenches are mostly located in the western pacific and correspond to the subduction of very old mesozoic oceanic lithosphere while retreating trenches are commonly explained by the slab pull action of the descending lithosphere the origin of advancing trenches is still debated since this relationship is dependent upon the adopted reference frame we select region where geological studies show the variability of trench migration style with time the izu bonin mariana ibm region represents a key example the detailed reconstruction of the trench migration of the ibm subducting system reveals that after a long episode of asymmetric rollback the ibm trench recently started advancing we propose that this change from retreating to advancing trench mode results from the subduction of progressively older and stiffer lithospheric material we test this hypothesis by means of two dimensional 2 d numerical models reproducing the effects of the lithospheric aging during subduction the result of our numerical tests shows that the entrance of old and stiff lithosphere forces the trench to advance because the increasing stiffness of the slab prevents the slab to unbend once it has subducted we adapt this physical result to the ibm evolution showing that the switch from trench retreat to trench advance can reconcile the shape of ibm slab as previously suggested finally we discuss the possibility that the subduction of the cretaceous lithosphere might have triggered the change of the motion of the pacific plate around 5 ma

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

tomographic inversion of p and pp data for aspherical mantle structure below the northwest pacific region summary to investigate the morphology of subducted slab in the mantle below northwest pacific island arcs we inverted traveltime residuals for aspherical variations in p wave propagation velocity relative to the radially symmetric iasp91 reference model the tomographic method used is based on a step wise linearization of the inversion problem first we relocated isc international seismological centre hypocentres with re identified p and pp phase data using the iasp91 traveltime tables the variance of p residuals relative to iasp91 traveltimes was 17 per cent less than the variance of p data reported by the isc relative to the jeffreys bullen j b traveltime tables second we performed a linearized lsqr inversion for earth structure and source relocation with the p and pp residuals obtained from the first step using iasp91 as the reference model for seismic velocities the incorporation of the depth phase pp in the tomographic inversions has two major advantages 1 the pp data provide constraints on focal depth and thus reduce the trade off between source relocation and structure and 2 the pp ray paths improve the sampling of earth structure in the shallow mantle and transition zone we used more than 2 times 106 and about 1 times 105p and pp wave traveltime residuals respectively from about 40 000 earthquakes with epicentres in the study region that were recorded at one or more of the 2300 globally distributed seismological stations considered in this study we assessed the spatial resolution in the tomographic images with checker board type sensitivity tests these tests reveal high resolution of upper mantle and transition zone structure particularly below the central part of our study region structure with wavelengths of the order of 100 km is resolved below japan whereas structure with wavelengths of the order of 300 km is well resolved below the kuril izu bonin and ryukyu arcs small scale structure is poorly resolved in depth below the northern part of the kuril kamchatka arc and below the izu bonin and mariana arcs this limits the interpretation of slab structure and mantle flow from tomographic images alone with this limitation in mind we conclude from the tomographic images that subducted slab deflects in the mantle transition zone below the geographical area encompassed by the kuril basin the japan sea and the northern part of the philippine sea this is in good agreement with the results of other recently published tomographic studies the occurrence of earthquakes several hundred kilometres off the inclined wadati benioff seismic zones and inferences about 660 km discontinuity topography in contrast slab like structures of high p wave velocity are imaged in the lower mantle below the deepest earthquakes of the northern kuril kamchatka and mariana seismic zones this is indicative of local slab penetration of the lower mantle from tomographic images we cannot discern between compositionally or thermally induced variations in seismic velocity however with regard to the nature of the boundary between upper and lower mantle our observations argue against either compositional mantle layering with large contrasts in intrinsic density or phase changes with steep clapeyron slopes

structure and evolution of lithospheric slab beneath the sunda arc indonesia tomographic imaging reveals seismic anomalies beneath the sunda island arc indonesia that suggest that the lithospheric slab penetrates to a depth of at least 1500 kilometers the sunda slab forms the eastern end of a deep anomaly associated with the past subduction of the plate underlying the mesozoic tethys ocean in accord with previous studies the lithospheric slab was imaged as a continuous feature from the surface to the lower mantle below java with a local deflection where the slab continues into the lower mantle the deep slab seems to be detached from the upper mantle slab beneath sumatra this complex slab structure is related to the tertiary evolution of southeastern asia and the indian ocean region

signature of remnant slabs in the north pacific from p wave tomography summary a 3 d ray tracing technique was used in a global tomographic inversion in order to obtaintomographicimagesofthenorthpacific thedatareportedbythegeophysical surveyofrussia 1955 1997 wereusedtogetherwiththecataloguesoftheinternational seismologicalcenter 1964 1991 andtheusgeologicalsurveynationalearthquake information center 1991 1998 and the recompiled catalogue was reprocessed the final data set used for following the inversion contained 523430 summary ray paths the whole of the earth s mantle was parametrized by cells of 2 2 and 19 layers the large and sparse system of observation equations was solved using an iterative lsqr algorithm asubhorizontalhigh velocityanomalyisrevealedjustabovethe660kmdiscontinuity beneaththealeutiansubductionzone thishigh velocityfeatureisobservedatlatitudes of up to 70 n and is interpreted as a remnant of the subducted kula plate which disappeared through ridge subduction at about 48ma a further positive velocity perturbation feature can be identified beneath the chukotka peninsula and okhotsk sea extending from 300 to 660km depth and then either extending further down to 800km chukotka or deflecting along the 660km discontinuity okhotsk sea this high velocity anomaly is interpreted as a remnant slab of the okhotsk plate accreted to siberia at 55ma

importance of the reference model in linearized tomography and images of subduction below the caribbean plate in linearized delay time tomography the choice of a one dimensional reference model is very important for correct mapping of seismic anomalies we demonstrate that the use of an inadequate background model results in artifacts in tomographic images which may give rise to erroneous interpretations particularly the absence or presence of upper mantle discontinuities in the reference model influences the mapping of structures e g subducting slabs at the transition between upper and lower mantle new tomographic images of the mantle below the caribbean region are presented these show the extent of the lesser antilles subduction zone down to 600 km which is well below the seismic zone a high velocity anomaly is imaged from the mid american trench to lower mantle depths 1400 km

geomorphological analysis of the drainage system on the growing makran accretionary wedge abstract the morphology of six adjacent major catchments draining the onshore makran accretionary wedge in southeast iran and southwest pakistan was studied to examine how the channel pattern and the length profiles may reflect the recent and active growth of the wedge qualitative field surveys were combined with the quantitative analysis of channel steepness and concavity measured from digital elevation models these profiles were compared with modelled profiles using a stream power approach assuming homogeneously uplifting uniform rock substratum results show a distinct difference between the studied western and eastern catchments the three western rivers are in morphological equilibrium whereas the two eastern rivers exhibit profiles with prominent convexities and knickpoints thus notably diverging from equilibrium concave up shapes all the studied catchments share the same base level flow on similar lithologies and developed under uniform climate conditions therefore we interpret the morphometric differences in terms of differential rock uplift rate as a response to local tectonic activity this interpretation is consistent with both uplift rates of marine terraces along the coast of makran and the recorded seismicity the geomorphological analysis presented here extends coastal information to wide inland areas and documents longer term tectonic behaviour than the seismotectonic record hence the steeper surface slope and faster surface uplift rates recorded by the eastern catchments compared to equilibrium of the western catchments are regional long term signals relevant for a wide part of the makran accretionary wedge we attribute the regional geomorphic difference to quaternary variations in tectonic regimes that forced differential uplift rates of the wedge surface we hypothesize that the different tectonic regimes are related to different subduction rates

active hydrothermal mounds in the okinawa trough backarc basin japan abstract dive studies by the shinkai 2000 were made in september 1984 and july 1986 in the central axial rift of the middle okinawa trough a possible active backarc basin in a nascent stage hydrothermally active mounds were discovered on a small knoll 27 34 4 n 127 08 6 e directly south of the area where a high heat flow higher than 1 w m2 had been observed previously the largest mound 5 6 m high and 15 25 m wide has several peaks and ridges along which yellow materials are exposed shimmering water was noted at several places on the yellow materials the rest of the mound is thinly covered by brown materials the temperature of the ejecting water was higher than that of the ambient seawater by 2 3 c and a 40 cm long thermometer inserted into the mound recorded a temperature of 20 50 c analysis of the ejected water showed a methane content of about 200 nl kg it is possible that further dive studies will reveal larger scale hydrothermal activity in the area

the role of hydrogeology in solution subsidence development and its environmental impacts a case study for sazlica nigde turkey solution subsidence and other types of collapse failures developed in the vicinity of sazlica have been a major source of environmental problems such as groundwater pollution soil erosion and foundation failures extensive pumping of water from the lake dipsiz during irrigation seasons creates landslide developments at the shores of the lake five stages of landslide development were observed in the unconsolidated soils around lake dipsiz bowl shaped solution subsidence features with depths from 1 to 3 m and diameters between 1 and 60 m were formed due to excess pumping and recharge and discharge features of unconfined aquifer the pumping activities must be controlled to prevent further environmental problems lake dipsiz and other subsidence developments are the groundwater exposure areas highly vulnerable to contamination the proposed remedies for overcoming the environmental problems are the establishment of conservation areas around such natural features ceasing the removal of top soil controlling the urbanization and keeping the livestock farming away from the areas susceptible to pollution

simultaneous travel time inversion for earthquake location and subduction zone structure in the central aleutian islands a combined location and velocity inversion technique is applied to travel time data from 151 well recorded central aleutian earthquakes the data include p and s wave arrivals at stations of a local network and p pp and sp wave arrivals at teleseismic stations after correction for crustal structure at the reflection points the depth phases pp and sp provide important constraints on subduction zone structure not ordinarily resolved by other types of data the structure is assumed to vary only across the arc and in depth it is parameterized with cubic splines by specifying the velocity at each point of a gridded arc cross section to avoid ray tracing it is assumed that the velocity part of the problem is linear preliminary results show that deep earthquakes apparently occur within a narrow downdip zone near the upper surface of the descending slab in contrast with previous studies which have located them within the presumably stronger and colder inner core of the slab a slab thickness of 80 100 km and a downdip length of about 400 km well below the deepest seismic activity are indicated the slab is characterized by seismic velocities as much as 11 higher than the surrounding mantle in its upper portions and 4 6 higher at depth a sharp velocity gradient and lower velocities occur directly beneath the volcanic arc near the top of the slab the slab anomaly appears to spread out and fall off very slowly with depth these are probably not real effects but consequences of the omission of three dimensional ray tracing

superplumes plates and mantle magmatism in two dimensional numerical models 1 two dimensional numerical models are systematically presented for magmatism in a convecting mantle internally heated by incompatible radioactive elements plate tectonics is self consistently modeled as a part of convection of newtonian fluid with temperature and stress history dependent viscosity driven by thermal and compositional buoyancy while magmatism is modeled as an upward migration of basaltic magma generated by decompression melting ridge magmatism actively takes place to chemically differentiate the mantle and a superplume is well developed in the lowermost mantle as a broad hot region enriched in basaltic component provided that the lithosphere is mechanically strong enough to inhibit spontaneous initiation of subduction by its own weight and that the internal heating rate is sufficiently high hot narrow plumes frequently rise up from the superplume to induce deep magma generation and hot spot magmatism which in turn frequently induces new plate margins the frequent plate margin formation keeps the activity of plate tectonics rather steady the thermal and chemical state of the mantle remains rather steady too as the internal heating rate becomes lower however the narrow plumes from superplume become sporadic and significantly colder deep magma generation becomes rare and new plate margin formation becomes less frequent as a consequence the activity of plate tectonics and the thermal and chemical state of the mantle become fluctuating much with time the mantle structure and plume behavior modeled here match with many observations for those of the earth from the archean to the present

tomographic imaging of the alaska subduction zone the alaska subduction zone is characterized by the pacific plate descending beneath the north american plate causing abundant seismic activity in the crust and along the wadati benioff zone down to a depth of approximately 200 km we have used 142 908 p wave arrival times from 12 237 shallow and intermediate depth earthquakes recorded by the alaska earthquake information center jointly run by the geophysical institute university of alaska fairbanks and u s geological survey in the period from january 1977 to november 1991 to investigate the three dimensional 3 d p wave velocity structure beneath central and southern alaska travel times and ray paths are accurately calculated by using an efficient 3 d ray tracing technique the nonlinear tomographic problem is solved by iteratively conducting linear inversions and the velocity structure and hypocentral locations are simultaneously determined we conducted two types of inversions one is an inversion with a laterally homogeneous starting model the others are what we call slab inversions in which we introduce into the initial model the high velocity subducting pacific plate as a priori information we found that the slab inversions gave a seismologically more plausible result and a final root mean square travel time residual significantly smaller than that of the inversion with the homogeneous starting model detailed p wave tomographic images are obtained for the crust and upper mantle down to a depth of 200 km with spatial resolutions of 30 60 km the tomographic image of the upper crust correlates well with the major surface geological features such as slow sedimentary basins and fast ultramafic bodies prominent low velocity anomalies exist in the crust and upper mantle beneath active volcanoes in the mantle wedge the low velocity anomalies dip toward the continental side and extend to a depth of about 150 km which are considered to be associated with the active volcanism in the alaska subduction zone the results suggest that the subducting pacific plate has a thickness of 45 55 km and a p wave velocity 3 6 higher than that of the surrounding mantle

lithospheric structure of the aegean obtained from p and s receiver functions combined p and s receiver functions from seismograms of teleseismic events recorded at 65 temporary and permanent stations in the aegean region are used to map the geometry of the subducted african and the overriding aegean plates we image the moho of the subducting african plate at depths ranging from 40 km beneath southern crete and the western peloponnesus to 160 km beneath the volcanic arc and 220 km beneath northern greece however the dip of the moho of the subducting african plate is shallower beneath the peloponnesus than beneath crete and rhodes and flattens out beneath the northern aegean observed p to s conversions at stations located in the forearc indicate a reversed velocity contrast at the moho boundary of the aegean plate whereas this boundary is observed as a normal velocity contrast by the s to p conversions our modeling suggests that the presence of a large amount of serpentinite more than 30 in the forearc mantle wedge which generally occurs in the subduction zones may be the reason for the reverse sign of the p to s conversion coefficient moho depths for the aegean plate show that the southern part of the aegean crustal thickness of 20 22 km has been strongly influenced by extension while the northern aegean sea which at present undergoes the highest crustal deformation shows a relatively thicker crust 25 28 km this may imply a recent initiation of the present kinematics in the aegean western greece crustal thickness of 32 40 km is unaffected by the recent extension but underwent crustal thickening during the hellenides mountains building event the depths of the aegean moho beneath the margin of the peloponnesus and crete 25 28 and 25 33 km respectively show that these areas are also likely to be affected by the aegean extension even though the cyclades crustal thickness of 26 30 km were not significantly involved in this episode the aegean lithosphere asthenosphere boundary lab mapped with s receiver functions is about 150 km deep beneath mainland greece whereas the lab of the subducted african plate dips from 100 km beneath crete and the southern aegean sea to about 225 km under the volcanic arc this implies a thickness of 60 65 km for the subducted african lithosphere suggesting that the aegean lithosphere was not significantly affected by the extensional process associated with the exhumation of metamorphic core complexes in the cyclades

worldwide distribution of group velocity of mantle rayleigh waves as determined by spherical harmonic inversion we have determined the worldwide distribution of group velocity of mantle rayleigh waves for periods between 100 and 300 sec without assuming any regionalization group slowness 1 u is expressed by spherical harmonics and the coefficients up to angular order 7 have been determined from travel times of rayleigh waves by a least squares method from these u has been synthesized since we cannot obtain information about the odd terms of the expansion from one circuit measurements around the world we have used group velocities of mainly r 2 and r 3 the overall pattern of u for periods between 100 and 200 sec is consistent with results of previous pure path and regional studies group velocities for tectonically active regions are low and those of the shields and the northwestern pacific are high

closing the gap between regional and global travel time tomography recent global travel time tomography studies by zhou 1996 and van der hilst et al 1997 have been performed with cell parameterizations of the order of those frequently used in regional tomography studies i e with cell sizes of 1 2 these new global models constitute a considerable improvement over previous results that were obtained with rather coarse parameterizations 5 cells the inferred structures are however of larger scale than is usually obtained in regional models and it is not clear where and if individual cells are actually resolved this study aims at resolving lateral heterogeneity on scales as small as 0 6 in the upper mantle and 1 2 3 in the lower mantle this allows for the adequate mapping of expected small scale structures induced by for example lithosphere subduction deep mantle upwellings and mid ocean ridges there are three major contributions that allow for this advancement first we employ an irregular grid of nonoverlapping cells adapted to the heterogeneous sampling of the earth s mantle by seismic waves spakman and bijwaard 1998 second we exploit the global data set of engdahl et al 1998 which is a reprocessed version of the global data set of the international seismological centre their reprocessing included hypocenter redetermination and phase reidentification finally we combine all data used p pp and pwp phases into nearly 5 million ray bundles with a limited spatial extent such that averaging over large mantle volumes is prevented while the signal to noise ratio is improved in the approximate solution of the huge inverse problem we obtain a variance reduction of 57 1 synthetic sensitivity tests indicate horizontal resolution on the scale of the smallest cells 0 6 or 1 2 in the shallow parts of subduction zones decreasing to approximately 2 3 resolution in well sampled regions in the lower mantle vertical resolution can be worse up to several hundreds of kilometers in subduction zones with rays predominantly pointing along dip important features of the solution are as follows 100 200 km thick high velocity slabs beneath all major subduction zones sometimes flattening in the transition zone and sometimes directly penetrating into the lower mantle large high velocity anomalies in the lower mantle that have been attributed to subduction of the tethys ocean and the farallon plate and low velocity anomalies continuing across the 660 km discontinuity to hotspots at the surface under iceland east africa the canary islands yellowstone and the society islands our findings corroborate that the 660 km boundary may resist but not prevent present day large scale mass transfer from upper to lower mantle or vice versa this observation confirms the results of previous global mantle studies that employed coarser parameterizations

directional variations in travel time residuals of teleseismic p waves in the crust and mantle beneath northern tien shan we study the directional variation in travel time residuals using 13 820 p wave arrivals from 1 998 teleseismic events 15 d 98 4 1 mb 7 3 recorded in 1991 1997 by the kyrgyz digital seismic network knet based on a modified version of the iasp91 model that accounts for the kyrgyz crustal thickness beneath knet we convert p wave travel times to travel time residuals dt the de pendence of dt on backazimuth is modeled as one two and four lobed variations in a horizontal plane backus 1965 a least squares fit of the azimuthal variation of dt indicates that the crust in the northern tien shan is about 11 15 km thicker than it is in the kazakh shield and the chu depression from nine knet stations the one lobe model estimates that the slowest p wave travel time direction is 5 0 4 8 almost directly north and the magnitude of variation is 1 71 0 13 sec this result is consistent with an upwelling lower mantle plume for the two lobe model the slowest p wave travel time directions anisotropy term are 89 7 and 269 7 4 7 i e trending east west we find p wave velocity anisotropy of 2 0 2 9 associated with a layer with a thickness of 440 km at the top of the lower mantle the fast direction of the p wave travel time north south azimuthal anisotropy at the top of the lower mantle is 1 parallel to the absolute motion of the india plate and 2 close to the direction of the upwelling hot mantle flow the last result suggests that the azimuthal aniso tropy of the travel time residuals is due to the shape preferred orientation of middle mantle material that results from plume intrusion shear wave splitting studies mak eyeva et al 1992 wolfe and vernon 1998 estimated the fast polarization direction to be parallel to the strike of the geological structures of the northern tien shan 71 29 thus the fast polarization direction determined from these shear wave splitting studies using knet data contradicts differs by 90 the fast travel time direction 0 3 and 179 7 4 7 we determine here using p wave travel time residuals using knet data this suggests that the azimuthal anisotropy determined from p wave travel time variations and from shear wave splitting in sks and skks have different sources

the influence of trench migration on slab penetration into the lower mantle abstract a two dimensional numerical convection model in cartesian geometry is used to study the influence of trench migration on the ability of subducted slabs to penetrate an endothermic phase boundary at 660 km depth the transient subduction history of an oceanic plate is modelled by imposing plate and trench motion at the surface the viscosity depends on temperature and depth a variety of styles of slab behaviour is found depending predominantly on the trench velocity when trench retreat is faster than 2 4 cm a the descending slab flattens above the phase boundary at slower rates it penetrates straight into the lower mantle although flattening in the transition zone may occur later leading to a complex slab morphology the slab can buckle independent of whether it penetrates or not especially when there is a localised increase in viscosity at the phase boundary flattened slabs are only temporarily arrested in the transition zone and sink ultimately into the lower mantle the results offer a framework for understanding the variety in slab geometry revealed by seismic tomography

the effect of small scale structure on normal mode frequencies and global inversions presently very little is known about the characteristic length scales of the structures in the upper mantle in generating synthetic seismograms and in large scale inversions one usually assumes that the upper mantle is smooth so that ray theory can be used however it is known that structures in the mantle exist on a scale of a few hundred kilometers notably near subduction zones and other tectonic features in this paper a model of all the subduction zones and spreading ridges is used to investigate the effect of small scale structures on normal mode frequency shifts and on global inversions the normal mode frequency shifts for this model have the same characteristics as observed normal mode frequency shifts furthermore the global models obtained from inversions of synthetic data for the model of subduction zones and spreading ridges are similar in character to the models obtained from global inversions of real data for a realistic set of wave paths the model obtained from the synthetic inversions differs appreciably from a smoothed version of the true model this is due to an uneven path coverage and to a lesser extent due to neglecting scattering effects this means that the models obtained from global inversions of seismological data may contain appreciable artifacts

lateral variations in mantle velocity structure and discontinuities determined from p pp s ss and ss sds travel time residuals on the basis of p pp s ss arrival times and ss s410s ss s660s differential times we construct models of mantle p and s velocity structure and boundary topography of the 410 km and 660 km discontinuities events from the catalog of the international seismological centre isc are relocated relative to the international association of seismology and physics of the earth s interior 1991 iasp91 velocity model using both p and s arrival times the arrival times are corrected for ellipticity and the pp and ss residuals are corrected for the topography at the bounce point the cap averaged pp p and ss s differential time residuals plotted at the pp and ss surface reflection points form broad coherent patterns the geographic distribution of the cap averaged residuals agrees quite well with pp p and ss s differential time residuals derived from long period global digital seismograph network gdsn data a robust lp inversion scheme is used to infer global mantle structure synthetic tests indicate that for regions well sampled by ss s410s and ss s660s differential times the velocity estimates are not seriously contaminated by the topography of the 410 and 660 km discontinuities however estimates of boundary deflections may be influenced by extensive p and s velocity variations of 3 or greater we find the 410 km discontinuity to be depressed by as much as 24 km beneath north america conversely the discontinuity is deflected upward underneath eurasia in some regions the topography of the 660 km discontinuity is quite distinct from that of the 410 km discontinuity but the two appear to be positively correlated a series of depressions are found at several intersections of the 660 km discontinuity with known subduction zones the elevated topography in the 410 km discontinuity beneath europe is underlain by a trough in the 660 km discontinuity a number of subduction zones are characterized by a thinning of the transition zone negative p and s velocity anomalies underlying back arc basins and tectonically active continental regions encircle the pacific where they are resolved the stable continental cratons are systematically positive velocity features that extend below 200 km with the inclusion of pp and ss travel time residuals we are better able to constrain midmantle structure most notably in the depth range 35 660 km beneath the northwest pacific we observe high p velocity where they are resolved mid ocean ridges are most clearly imaged as low velocity features in the s model the northern portion of the mid atlantic ridge is underlain by negative s velocity anomalies in the pacific the east pacific rise is an extensive low s velocity anomaly

subducting slabs stagnant in the mantle transition zone the p wave velocity structure beneath the western pacific is found from the international seismological center first arrival data special attention was paid to the deep structure beneath the wadati benioff zone we discretized the whole mantle into blocks with finer blocks in the region of interest to obtain the velocities of all the blocks this way of discretization minimizes a problem with tomographic studies of regional scale difficulty in making corrections for the effects outside the region of interest our solution is iterative with the alternate step of the relocation of earthquakes using the whole mantle model of inoue et al 1990 as a starting model a first order smoothness constraint was imposed to suppress the possible fluctuation of the solution around the initial model the essential result depends little on whether the reference spherical model is smooth or discontinuous near 400 and 670 km depths we examined the resolution by calculating the resolving kernels for selected blocks and by reconstructing the checkerboard test patterns of velocity perturbation and the test structures of subducting lithosphere the resolution is depth dependent but in general good enough to see the slab configuration beneath the southern kurile japan izu bonin arcs and the java arc it is relatively poor beneath the northern kurile and mariana arcs the seismic image of subducting slab beneath the southern kurile to bonin arcs bends to subhorizontal near the leading edge of the wadati benioff zone and extends continentward over a distance of more than 1000 km the subhorizontal portion of the slab connects a high velocity blob to the bottom that reaches a depth of at least 800 km across the 670 km discontinuity under the japan arc although the image of the java slab directly penetrates the 670 km discontinuity it then bends to a shallow dip with a considerable spread reaching a depth of about 1200 km these results suggest that descending slabs of lithosphere in the western pacific tend to be stagnant in the transition zone under a subtle control of the 670 km discontinuity although stagnant slab materials eventually descend into the lower mantle they no longer maintain their original configuration below the 670 km discontinuity

large scale three dimensional seismic tomography of the zagros and pamir hindukush regions abstract the nature of the deep seismic structure of the zagros and pamir hindukush regions is inferred from the three dimensional p wave velocity images obtained using the aki christofferson and husebye ach inversion technique we use teleseismic 25 90 p wave arrival times recorded at 24 seismic stations during the period 1977 1986 a study of the azimuthal variation of residuals reveals that despite the crustal doubling the pamir hindukush region is characterized by faster arrivals 1 0 s of teleseismic p waves the iranian plateau on the other hand exhibits delayed arrivals 0 4 1 0 s from teleseisms the results of the ach inversion reveal contrasting p wave velocity characteristics in the upper mantle of these deformed zones in the depth interval 0 200 km the pamir hindukush region is characterized by 1 4 faster velocities relative to the iranian plateau accounting for the anomalous crustal thickening in the hindukush results in the subcrustal mantle up to 200 km exhibiting a significant higher velocity 2 comparable to that of the indian plate however in the depth interval 200 450 km the pamir hindukush region has 1 3 lower velocities relative to the indian plate while the upper mantle beneath the central iranian plateau is 2 4 slower relative to the surrounding region the high velocity upper mantle till a depth of 200 km beneath the hindukush region reflects the possible presence of both the oceanic lithosphere and the crust and uppermost mantle of the indian plate which subducted beneath eurasia the low velocity observed beneath central iran could be a reflection of the upper mantle thermal anomalies related to the pliocene quaternary volcanism in this region

thermal structure of the continental lithosphere constraints from seismic tomography our ability to determine constrained estimates of the temperature structure of the continental lithosphere is hindered by the lack of independent observations of temperature within the crust presently used techniques for the estimation of crustal temperatures rely primarily on near surface temperature and heat flow observations coupled to estimates of crustal structure and associated distribution of thermal parameters within the crust the achievements of seismic tomography in providing an image of the heterogeneous nature of the earth s interior may provide an additional tool to help both constrain estimates of thermal structure within the crust and provide a means to evaluate assumptions of the spatial distribution of thermal parameters thermal conductivity heat production within the crust we have developed preliminary tools which help to exploit the information content of the seismic results as contained in the observed velocity anomalies these techniques allow thermal compositional t x tomography of the lithosphere providing a means to separate the temperature from compositional effects in producing velocity anomalies the resulting thermally dominated seismic structure can then be used in conjunction with surface heat flow observations as an additional constraint on estimates of the temperature structure of the crust

geology of the onshore makran accretionary wedge synthesis and tectonic interpretation abstract this contribution is a synthesis of studies carried out since 2004 in the makran accretionary wedge exposed in se iran these studies were intended to improve our understanding of the behaviour of accretionary wedges and of the significance of the makran wedge in the frame of tethys tectonics reassessing the stratigraphy and structure of the iranian makran has allowed distinguishing four main litho tectonic units the lithological content of these four units is briefly described to discuss the sedimentary environments which record the general filling of an oceanic basin with clastic sediments derived from the north the petrology of ophiolites exposed in the backstop region to the north of the accretionary wedge itself demonstrates the existence of an oceanic basin formed in the jurassic late cretaceous to the north of continental slivers which had separated from central iran there is petrological evidence for a subduction related magmatic arc during the late cretaceous which sourced much of the clastic material in the cretaceous lower miocene turbidites present throughout the wedge the literature survey shows that the late cretaceous to present evolution of the pakistan part of the makran fold and trust belt is in its major attributes similar to that of the iranian makran these observations and results are discussed in a tectonic model that integrates knowledge on the oman mountains on the other side of the current oman subduction

mantle structure beneath indonesia inferred from high resolution tomographic imaging we investigated mantle structure beneath the indonesian region by means of tomographic inversions of traveltime residuals of direct p and the surface reflected depth phases pp and pwp the hypocentres and phase data used in the inversions were derived from the reprocessing of data reported to international data centres which include data from the australian skippy project we used more than 6 0 10 data from more than 50 000 globally distributed earthquakes recorded at a subset of nearly 3000 seismological stations worldwide the use of depth phases improved the sampling of the upper mantle structure in particular beneath the back arc regions the mapping of distant aspherical mantle structure into the study region was minimized by combining a high resolution regional with a low resolution global inversion the inversion was linearized around the ak135 reference velocity model and a combination of minimum norm and gradient damping was applied to constrain the solution inversion of different subsets of the data and test inversions of synthetic data indicate that resolution is sufficient to substantiate the conclusions pertinent to the complex large scale structure of the subducted slab beneath the indonesian archipelago the tomographic images confirm previous evidence for regional slab penetration into the upper part of the lower mantle but suggest a more complex trajectory of mantle flow beneath indonesia the implied lateral variation in the shape of the upper mantle slab is generally in good agreement with inferences from seismicity the data reveal a seismic anomaly beneath the sunda arc which is detected to at least 1500 km in depth and forms the eastern end of a deep anomaly associated with the past subduction of lithosphere of the mesozoic tethys ocean below java the lithospheric slab is probably continuous from the earth s surface to the lower mantle but beneath sumatra the deep slab seems to be detached from the seismogenic slab the high resolution images suggest that the subducted slab is deflected in the transition zone beneath the banda arc and that the descending slabs form a spoon shaped structure north of the banda sea we detect the two opposing subducted slabs of the molucca sea plate this is consistent with previous studies but our images suggest that the westward subduction has a significantly steeper dip than the eastward subduction slab structure beneath the banda and molucca seas is explained in the context of the continent arc collision between australia and the southeast indonesian island arc and the arc arc collision between sangihe and halmahera inversion of traveltime residuals of direct s phases a novelty for this region largely confirms the inferences from the p wave data even though less detail is resolved

on the kinematics of shelly carbonate sand using x ray micro tomography abstract shelly carbonate sands are highly compressible soils due to the susceptibility of their loose and intricate fabric to collapse under loading an accurate assessment of the physical phenomena taking place at the grain scale is critical for a better understanding and modelling the mechanical behaviour of this material this paper presents a study on the grain kinematics of shelly carbonate sand through analysis of in situ 4d x ray tomography images acquired during oedometer compression two sands from the persian gulf with coarse and fine grading were investigated an adaptive watershed segmentation technique is used here to identify the grains in the image s prior to loading and a digital volume correlation dvc technique is employed to obtain the displacement field of each grain under loading the displacement fields are used to reconstruct the grains in their new positions and compute the associated translation and rotation an extensive statistical analysis was carried out to demonstrate the effect of grain morphology and local fabric coordination number on grain kinematics the new findings presented here shed light on the mechanisms of grain rearrangement leading to the compressible fabric of shelly carbonate sands and are also critical to better understand other weak grained sands and or silica sands with an open fabric

three dimensional modeling of plume lithosphere interaction in order to understand better the dynamics of hot spots such as hawaii we present a three dimensional numerical model for the interaction of a thermal plume with a moving lithosphere the model domain is a rectangular box filled with fluid whose viscosity depends upon temperature and pressure the lithosphere is represented by a layer of cold highly viscous fluid moving with an imposed horizontal velocity u in the x direction and a thermal plume is generated by a circular temperature anomaly on the bottom of the box the steady flow is determined numerically using a hybrid spectral finite difference technique the flow is characterized by a stagnation streamline of width y x1 5 that represents the edge of the spreading plume material we illustrate the detailed behavior of the model using the example of the hawaiian plume our best fitting hawaiian model is obtained by adjusting the plume buoyancy flux b until the predicted topography anomaly matches the observed hawaiian swell topography we find b 4100 kg s 1 which implies a plume radius of 90 km for an assumed plume mantle temperature contrast of 300 c the predicted topography is supported primarily by density anomalies beneath the lithosphere and cannot be explained by lithospheric erosion we therefore conclude that the classical lithospheric reheating model is unable to account for hotspot swells the horizontal flux of buoyancy associated with the swell exceeds b by up to 80 suggesting that current estimates of b for mantle plumes are too high empirically derived scaling laws for the width of the stagnation streamline and for the topography anomaly exhibit power law dependencies on b and u that agree well with those predicted by the refracted plume model of olson 1990 the principal weakness of the model is that the predicted geoid topography ratio of 0 010 for the hawaiian swell is about twice the observed value of 0 004 0 006

travel time tomography of the european mediterranean mantle down to 1400 km abstract the 3 d p wave velocity structure of the mantle below europe the mediterranean region and a part of asia minor is investigated this study is a considerable extension of an earlier tomographic experiment that was limited to imaging upper mantle structure only here the earth s volume under study encompasses the mantle to a depth of 1400 km and we increase the number of international seismological centre isc data for inversion by a factor of four by taking more years of observation and by including data from teleseismic events the most important departure from the earlier study is that we do not use the jeffreys bullen model as a reference model but an improved radially symmetric velocity model the pm2 model which is appropriate for the european mediterranean mantle our inversion procedure consists of two steps first the radial model pm2 is determined from the isc delay times by a nonlinear trial and error inversion of the data as opposed to the jeffreys bullen model the new reference model has a high velocity lithosphere a low velocity zone and seismic discontinuities at depths of 400 and 670 km next the isc data are corrected for effects related to the change in reference model and inverted for 3 d heterogeneity relative to the pm2 model we follow this two step approach to attain a better linearizable tomographic problem in which ray paths computed in the pm2 model provide a better approximation of the actual ray paths than those computed from the jeffreys bullen model hence the two step scheme leads to a more credible application of fermat s principle in linearizing the tomographic equations inversion results for the 3 d heterogeneity are computed for both the uncorrected isc data and for the pm2 data the data fit obtained in the two step approach is slightly better than in the inversion of isc data using the jeffreys bullen reference model a comparison of the tomographic results demonstrates that the pm2 data inversion is to be preferred to assess the spatial resolution an analysis is given of hit count patterns sampling of the mantle by ray paths and results of sensitivity tests with 3 d synthetic velocity models the spatial resolution obtained varies with position in the mantle and is studied both in map view and in cross section in the well sampled regions of the mantle the spatial resolution for larger scale structure can qualitatively be denoted as reasonable to good and at least sufficient to allow interpretation of larger scale anomalies a comparison is made of the results of this study with independent models of s velocity heterogeneity obtained in a number of investigations and with a prediction of the seismic velocity structure of the mantle computed from tectonic reconstructions of the mediterranean region in the context of this comparison interpretations of large scale positive anomalies found in the mediterranean upper mantle in terms of subducted lithosphere are given specifically addressed are subduction below southern spain below the western mediterranean and italy and below the aegean in the last region a slab anomaly is mapped down to depths of 800 km

hydrogeologic role in sinkhole development in the desert of kuwait sinkhole development is unlikely in desert areas with very low precipitation however a few cases of land subsidence and sinkhole development took place within the suburbs of kuwait city a few sinkholes developed in a sudden and rapid way leading to great economic losses in this paper the mechanism and causes of such a land subsidence are described decline in groundwater level and downward infiltration of excess irrigation are suggested to be the main factors in the development of the land subsidence in kuwait urbanization and excessive garden irrigation are most probably the triggers of the sudden and rapid land subsidence