japan sea a pull apart basin abstract recent field work in the hokkaido central belt and marine geology studies along the eastern margin of japan sea in addition to previously published data lead us to propose a new model of opening of the japan sea the synthesis of both on land and offshore structural data gives new constraints about the structural evolution of the system the rhombohedral shape of the japan basin and the particular tectonic behaviour of the margins on both east and west sides can be explained by an early eo oligocene rifting of a pull apart basin accommodated along two large right lateral shear zones east of korea and west of northeast japan and sakhalin it is followed during upper oligocene lower miocene by the main opening of the japan basin as a mega pull apart then a back arc spreading probably related to the subduction process induced the creation of the yamato and tsushima basins at the end of lower miocene and in middle miocene clockwise rotation of southwest japan larger than 20 or major bending of honshu mainland deduced from paleomagnetic studies is unlikely at this time since 1 or 2 my b p to present compression prevails along the eastern margin of the japan sea the generation of marginal basins as pull apart basins along intracontinental strike slip faults is a mechanism which has been proposed by other authors concerning the south china sea the question then is whether the fragmentation of the asiatic continent is an intracontinental deformation related process as proposed here or a subduction related one

constraints on the moho in japan and kamchatka abstract this review collects and systematizes in one place a variety of results which offer constraints on the depth and the nature of the moho beneath the kamchatka peninsula and the islands of japan we also include studies of the izu bonin volcanic arc all results have already been published separately in a variety of venues and the primary goal of the present review is to describe them in the same language and in comparable terms for both regions we include studies using artificial and natural seismic sources such as refraction and reflection profiling detection and interpretation of converted mode body waves receiver functions surface wave dispersion studies in kamchatka and tomographic imaging in japan the amount of work done in japan is significantly larger than in kamchatka and resulting constraints on the properties of the crust and the uppermost mantle are more detailed japan and kamchatka display a number of similarities in their crustal structure most notably the average crustal thickness in excess of 30 km typical of continental regions and the generally gradational nature of the crust mantle transition where volcanic arcs are presently active

crustal characteristic variation in the central yamato basin japan sea back arc basin deduced from seismic survey results abstract the crustal structure of the yamato bank the central yamato basin and the continental shelf in the southern japan sea back arc basin is obtained based on a seismic survey using ocean bottom seismographs and seismic shot to elucidate the back arc basin formation processes the central yamato basin can be divided into three domains based on the crustal structure the deep basin the seamount and the transition domains in the deep basin domain the crust without the sedimentary layer is about 12 13 km thick very few units have p wave velocity of 5 4 6 0 km s which corresponds to the continental upper crust in the seamount and transition domains the crust without the sedimentary layer is about 12 16 km thick the p wave velocities of the upper and lower crusts differs among the deep basin the seamount and the transition domains these results indicate that the central yamato basin displays crustal variability in different domains the crust of the deep basin domain is oceanic in nature and suggests advanced back arc basin development the seamount domain might have been affected by volcanic activity after basin opening in the transition domain the crust comprises mixed characters of continental and oceanic crust this crustal variation might represent the influence of different processes in the central yamato basin suggesting that crustal development was influenced not only by back arc opening processes but also by later volcanic activity in the yamato bank and continental shelf the upper crust has thickness of about 17 18 km and p wave velocities of 3 3 4 1 to 6 6 km s the yamato bank and the continental shelf suggest a continental crustal character

evolution of the canadas edifice and its implications for the origin of the canadas caldera tenerife canary islands the volcano stratigraphic and geochronologic data presented in this work show that the tenerife central zone has been occupied during the last 3 ma by shield or central composite volcanoes which reached more than 3000 m in height the last volcanic system the presently active teide pico viejo complex began to form approximately 150 ka ago the first canadas edifice ce volcanic activity took place between about 3 5 ma and 2 7 ma the ce i is formed mainly by basalts trachybasalts and trachytes the remains of this phase outcrop in the canadas wall cw sectors of la angostura 3 5 3 0 ma and 3 0 2 7 ma boca de tauce 3 0 ma and in the bottom of some external radial ravines 3 5 ma the position of its main emission center was located in the central part of the cc the volcano could have reached 3000 m in height this edifice underwent a partial destruction by failure and flank collapse forming debris avalanches during the 2 6 2 3 ma period the debris avalanche deposits can be seen in the most distal zones in the n flank of the ce i tigaiga breccia a new volcanic phase whose deposits overlie the remains of ce i and the former debris avalanche deposits constituted a new volcanic edifice the ce ii the dyke directions analysis and the morphological reconstruction suggest that the ce ii center was situated somewhat westward of the ce i reaching some 3200 m in height the ce ii formations are well exposed on the cw especially at the el cedro 2 3 2 00 ma sector they are also frequent in the s flank of the edifice 2 25 1 89 ma in tejina 2 5 1 87 ma as well as in the tigaiga massif to the n 2 23 ma during the last periods of activity of ce ii important explosive eruptions took place forming ignimbrites pyroclastic flows and fall deposits of trachytic composition their ages vary between 1 5 and 1 6 ma adeje ignimbrites to the w in the cw the upper ucanca phonolitic unit 1 4 ma could be the last main episode of the ce ii afterwards the can adas iii phase began it is well represented in the cw sectors of tigaiga 1 1 ma 0 27 ma las pilas 1 03 ma 0 78 ma diego hernandez 0 54 ma 0 17 ma and guajara 1 1 ma 0 7 ma the materials of this edifice are also found in the se flank these materials are trachybasaltic lava flows and abundant phonolitic lava and pyroclastic flows 0 6 ma 0 5 ma associated with abundant plinian falls the ce iii was essentially built between 0 9 and 0 2 ma a period when the volcanic activity was also intense in the dorsal edifice situated in the easterly wing of tenerife the so called valleys of la orotava and gu imar transversals to the ridge axis also formed during this period in the central part of tenerife the ce iii completed its evolution with an explosive deposit resting on the top of the ce for which ages from 0 173 to 0 13 ma have been obtained the cc age must be younger due to the fact that the present caldera scarp cuts these deposits on the controversial origin of the cc central vertical collapse vs repeated flank failure and lateral collapse of mature volcanic edifices the data discussed in this paper favor the second hypothesis clearly several debris avalanche type events exist in the history of the volcano but most of the deposits are now under the sea the caldera wall should represent the proximal scarps of the large slides whose intermediate scarps are covered by the more recent teide pico viejo volcanoes

shuttle imaging radar experiment the shuttle imaging radar sir a acquired images of a variety of the earth s geologic areas covering about 10 million square kilometers structural and geomorphic features such as faults folds outcrops and dunes are clearly visible in both tropical and arid regions the combination of sir a and seasat images provides additional information about the surface physical properties topography and roughness ocean features were also observed including large internal waves in the andaman sea

seismological features of island arc crust as inferred from recent seismic expeditions in japan abstract crustal studies within the japanese islands have provided important constraints on the physical properties and deformation styles of the island arc crust the upper crust in the japanese islands has a significant heterogeneity characterized by large velocity variation 5 5 6 1 km s and high seismic attenuation qp 100 400 for 5 15 hz the lateral velocity change sometimes occurs at major tectonic lines in many cases of recent refraction wide angle reflection profiles a middle crust with a velocity of 6 2 6 5 km s is found in a depth range of 5 15 km most shallow microearthquakes are concentrated in the upper middle crust the velocity in the lower crust is estimated to be 6 6 7 0 km s the lower crust often involves a highly reflective zone with less seismicity indicating its ductile rheology the uppermost mantle is characterized by a low pn velocity of 7 5 7 9 km s several observations on pmp phase indicate that the moho is not a sharp boundary with a distinct velocity contrast but forms a transition zone from the upper mantle to the lower crust recent seismic reflection experiments revealed ongoing crustal deformations within the japanese islands a clear image of crustal delamination obtained for an arc arc collision zone in central hokkaido provides an important key for the evolution process from island arc to more felsic continental crust in northern honshu a major fault system with listric geometry which was formed by miocene back arc spreading was successfully mapped down to 12 15 km

formation of the japan sea basin reassessment from ar ar ages and nd sr isotopic data of basement basalts of the japan sea and adjacent regions abstract many studies have examined the japan sea basalts recovered during ocean drilling program odp leg127 128 of these the 40ar 39ar dating undertaken is important in constraining the timing of the formation of the japan sea however the implications of their results do not appear to be fully appreciated by the geological community in this paper i reassess the 40ar 39ar age data of the basalts with reference to nd sr isotopic data the 40ar 39ar dating was performed on basalts somewhat enriched in large ion lithophile elements and recovered from odp sites 794 795 and the lower part of 797 yielding the plateau ages of 21 2 17 7 ma these basalts show the nd sr isotopic signature of a moderately depleted mantle source end 0 6 6 9 in contrast the basalts from the upper part of site 797 have yet to be dated due to their low k content although their nd isotopic compositions are similar to that of morb end 8 4 10 4 by analogy to the secular nd sr isotopic trends reported for sikhote alin and northeast japan the age of the upper basalts at site 797 may be inferred to be younger than the lower basalts probably around 16 ma the nd sr isotopic compositions of the japan sea basalts have been interpreted in terms of eastward asthenospheric flow as have the lavas of the sikhote alin and northeastern japan the timing of volcanic activity in the japan sea region i e from 21 2 to 14 86 ma is consistent with the timing of rotational crustal movements inferred from paleomagnetic studies of the japanese islands i e 14 8 4 2 ma for southwest japan and 16 5 14 4 ma for northeast japan

a seismic study of lithospheric flexure in the vicinity of tenerife canary islands seismic data have been used to determine the crustal and upper mantle structure of tenerife canary islands a volcanic island of tertiary age located on 140 ma oceanic crust reflection data show that oceanic basement dips gently towards the island forming a flexural moat which is infilled by 2 3 km of well stratified material the moat is characterised by a major angular unconformity which we attribute to volcanic loading of pre existing oceanic crust and overlying sediments and the subsequent infilling of the flexure by material that was derived at least in part from the islands refraction data show that the flexed oceanic crust has a mean thickness of 6 41 0 42 km and upper and lower crustal velocities of 4 8 5 4 km s 1 and 6 7 7 3 km s 1 respectively the flexure which has been verified by gravity modelling can be explained by a model in which tenerife and adjacent islands have loaded a lithosphere with a long term 106 yr elastic thickness of approximately 20 km seismic and gravity data suggest that up to 1 5 105 km3 of magmatic material has been added to the surface of the flexed oceanic crust which assuming an age of 6 16 ma for the shield building stage on tenerife implies a magma generation rate of about 0 006 to 0 02 km3 a 1 this rate is similar to estimates from other african oceanic islands e g reunion and cape verdes but is significantly less than that which has been calculated at hawaii there is no evidence in either the seismic or gravity data that any significant amount of magmatic material has underplated the flexed oceanic crust the crustal and upper mantle structure at tenerife therefore differs from other oceanic islands such as hawaii and marquesas where 4 km of underplated material have been reported

groundwater dynamics in fossil fractured carbonate aquifers in eastern arabian peninsula a preliminary investigation abstract eastern arabian peninsula represents the main natural groundwater discharge area of the arabian platform fossil aquifer system in such settings connections between aquifers could strongly affect the flow dynamics water quality and availability as well as karst formation and landscape evolution geological structures such as folds and faults are central to aquifer connectivity yet their role on groundwater flow is poorly understood herein we perform mapping of exposed and buried structural features in the qatar peninsula using landsat sentinel 2 and alos palsar scenes correlated with field gpr and isotopic data to assess their role in aquifer connections and groundwater dynamics our results suggest that ene wsw oriented fold related faults act as vertical conduits along which artesian upward leakages from the deep aruma aquifer take place into the shallower main aquifer unit i e umm er radhuma and rus in southern qatar peninsula on the other hand downward leakage from the freshwater lens in the dammam aquifer take place in northern qatar peninsula the deep brackish and gaseous rich waters ascending along faults in south qatar peninsula in addition to degrading the water quality in the main aquifer unit enhance dissolution of carbonates and evaporites leading to strong karstification that produces abundant collapse features our findings suggest that structure controls can add significant complexity to recharge mechanisms and groundwater dynamics in fossil aquifers future large scale radar subsurface mapping will be essential to resolve the variability of the water heads in such areas and its correlation to structural discontinuities

last stage of the japan sea back arc opening deduced from the seismic velocity structure using wide angle data the japan sea is one of the most well studied back arc basins in the northwestern pacific the seismic crustal model however has been inadequate to elucidate the detailed opening model of the japan sea in 2002 to clarify the late stage of the formation style of the japan sea opening a seismic experiment using 35 ocean bottom seismographs obss an air gun array and a multichannel hydrophone streamer was undertaken in the areas from the southwestern yamato basin the oki ridge and the southwestern oki trough to the coast of the southwestern japan island arc the crusts beneath the southwestern yamato basin and the oki ridge are estimated as having approximately 13 km and 19 5 km respectively the upper and lower crusts of the southwestern yamato basin are approximately 3 2 km and 8 km thick respectively those of the oki ridge are approximately 8 2 km and 10 5 km thick respectively the upper crust of the oki ridge thickens more steeply than that of the southwestern yamato basin however the lower crust thickens more gently the crustal structure of the southwestern yamato basin shows the extended continental crust accompanied with the opening of the japan sea a remarkable structural characteristic the upper crust being thinner than the lower crust caused by listric or complicated normal faults developed in the upper crust of the southwestern yamato basin this deformed upper crust is a common structural characteristic in the southern japan sea which includes the yamato basin the southern yamato basin including the southwestern yamato basin has the thinnest upper and lower crusts in the japan sea for that reason it is suggested that the southern yamato basin had the strongest deformation by a back arc opening and that the period of the opening in the southern yamato basin had been longest in the southern japan sea the formation process of the southern yamato basin is inferred to have two stages rifting and extension of continental crust separating the northeastern and southwestern japan island arcs from the asian continent and further the extension affected by the rotation of the southwestern japan island arc

rapid rotation of southwest japan palaeomagnetism and k ar ages of miocene volcanic rocks of southwest japan summary miocene volcanic rocks have been sampled from the san in district in the central part of southwest japan reliable palaeomagnetic direction and k ar dating data have been obtained from 28 localities a clockwise deflection in declination d 38 5 is observed in the kawai formation having an age of 16 1 1 4 ma whereas a northerly declination is observed in formations younger than 14 2 0 6 ma these data indicate that southwest japan had ceased rotational motion by about 14 ma when compared with the amount of rotation estimated from cretaceous palaeomagnetic data it is apparent that more than 80 per cent of the overall clockwise rotation occurred between about 16 and 14 ma we conclude that the angular velocity of southwest japan about a rotation pole at 129 e 34 n reached 20 myr 1 at about 15 ma the corresponding rate of linear motion of the eastern part of southwest japan was 21 cm yr 1

vertical and lateral collapses on tenerife canary islands and other volcanic ocean islands recent studies demonstrate that tenerife has undergone large lateral collapses this has led to the suggestion that the las canadas caldera one of the best exposed calderas in the world is the result of lateral collapse we have tested this idea using the available structural stratigraphic volcanological and geochronological data we conclude that the las canadas caldera is the result of a complex sequence of vertical collapse events associated with a long history of phonolitic explosive activity in the central part of tenerife our results indicate however that vertical collapses may have played a major role in triggering lateral collapses we propose that the association of vertical and lateral collapse events such as inferred for tenerife can also explain similar sequences of events interpreted to have affected other large volcanic ocean islands

the 0 57 ma plinian eruption of the granadilla member tenerife canary islands an example of complexity in eruption dynamics and evolution the granadilla member is one of the most widely dispersed and largest volume pyroclastic units at tenerife canary islands and represents the culminating eruption to a second cycle of explosive volcanism of the las canadas edifice the member dared at 0 57 ma comprises a plinian fall deposit the granadilla pumice which is overlain by ignimbrite up to 30 m thick the granadilla pumice is up to 9 m thick approximately 10 km from sourer pyle b t value is 5 35 km and is subdivided into four fail units unit 1 is up to 1 2 m thick and is further divisible into another four pumice fall subunits based on bedding and grainsize differences unit 2 is a thin but distinctive ash layer similar to2 cm thick and its wide dispersal 550 km 2 constant thickness planar laminations and ash aggregate textures collectively indicate a phreatoplinian fall origin the lithic rich nature and abundance of unaltered lithic fragments reflect magma interaction with aquifer derived water at depth unit 3 less than or equal to1 8 m thick records a reversal to dry plinian eruptive activity unit 4 the thickest of the fall units up to 6 3 m thick records the maximum dispersal and intensity of the eruption pyle b t and b c values are 5 7 and 6 3 km respectively best illustrated by the presence of large pumice bombs up to 30 cm diameter at distances up to 20 km from vent and reverse grading of lithic and pumice clasts the widespread 500 km 2 nonwelded and pumice rich granadilla ignimbrite unit 5 records the collapse of the plinian eruption column the ignimbrite has a simple sheet like geometry but exhibits a complex internal stratigraphy the base of the ignimbrite locally cuts down through the underlying granadilla pumice removing it entirely indicating up to 9 m of erosion by the pyroclastic flows a coarse vent derived lithic breccia horizon towards the top of the ignimbrite is interpreted to record the onset of caldera collapse late in the eruption minimum volume estimates for the granadilla pumice and ignimbrite are 5 2 and 5 km 3 respectively the dispersal area deposit characteristics and exponential thickness and clast size decay relationships with isopach area 1 2 are consistent with dispersal and fallout from the umbrella region of a moderately high similar to 17 to greater than or equal to 25 km plinian column we propose that the eruption involved two vents probably aligned along a ne sw fissure within the las canadas caldera c 2000 elsevier science b v all rights reserved

on water detection in the martian subsurface using sounding radar several radar experiments are planned to map the martian subsurface down to several kilometers searching for subsurface liquid water reservoirs using different concepts and techniques all based on the penetration property of radio frequency waves in arid soils the penetration depth of low frequency radar is mainly related to the electromagnetic properties of the investigated medium thus a good knowledge of the martian subsurface dielectric profile along the first few kilometers is necessary for future water identification and data interpretation in this work we have investigated the electrical and magnetic properties of the martian surface and subsurface using terrestrial laboratory analogues in the frequency range 1 500 mhz covering the frequency domain of the mars advanced radar for subsurface and ionosphere sounding marsis experiment on board the mars express mission esa 2003 the netlander ground penetrating radar gpr cnes 2007 and future sounding radar that may be updated to the mars exploration program in the follow the water strategy in our approach we constructed experimentally the most common dielectric profile representative of the martian subsurface by measuring the electric permittivity and magnetic permeability of well defined mixtures of basaltic volcanic and sedimentary materials that have been reported for mars we also considered iron oxides hematite and maghemite and evaporites that may be present such as gypsum and their mixtures with representative amounts of the martian geological context under the most common petrophysical and geophysical conditions along the subsurface profile this led to synthetic representative samples of the martian subsurface materials under adequate conditions of porosity and temperature that should exist in the first 2 5 km of the upper crust dielectric measurements show that the first layers of the martian subsurface a few hundred meters which are mainly composed of volcanic iron rich materials could dramatically decrease the radar penetration depth initially foreseen thus limiting deep subsurface exploration we also investigated the constraints on subsurface water detectability in a radar lossy medium and its dielectric identification among surrounding geological materials

lower crustal intrusion on the north atlantic continental margin near the faroe islands in the north atlantic the majority of basalt is intruded into the continent ocean transition rather than extruded onto the surface this melt is intruded into the lower crust as sills which cross cut the continental fabric rather than as an underplate of 100 melt as has often been assumed when continents break apart the rifting is sometimes accompanied by the production of large volumes of molten rock1 2 3 the total melt volume however is uncertain because only part of it has erupted at the surface furthermore the cause of the magmatism is still disputed specifically whether or not it is due to increased mantle temperatures we recorded deep penetration normal incidence and wide angle seismic profiles across the faroe and hatton bank volcanic margins in the northeast atlantic here we show that near the faroe islands for every 1 km along strike 360 400 km3 of basalt is extruded while 540 600 km3 is intruded into the continent ocean transition we find that lower crustal intrusions are focused mainly into a narrow zone 50 km wide on the transition although extruded basalts flow more than 100 km from the rift seismic profiles show that the melt is intruded into the lower crust as sills which cross cut the continental fabric rather than as an underplate of 100 per cent melt as has often been assumed evidence from the measured seismic velocities and from igneous thicknesses are consistent with the dominant control on melt production being increased mantle temperatures with no requirement for either significant active small scale mantle convection under the rift or the presence of fertile mantle at the time of continental break up as has previously been suggested for the north atlantic ocean4 5 6

firn clutter constraints on the design and performance of orbital radar ice sounders radar sounding is a powerful tool for constraining subglacial conditions which influence the mass balance of polar ice sheets and their contributions to global sea level rise a satellite based radar sounder such as those successfully demonstrated at mars would offer unprecedented spatial and temporal coverage of the subsurface however airborne sounding studies suggest that poorly constrained radar scattering in polar firn may produce performance limiting clutter for terrestrial orbital sounders we develop glaciologically constrained electromagnetic models of radar interactions in firn test them against in situ data and multifrequency airborne radar observations and apply the only model we find to be consistent with observation to assess the implications of firn clutter for orbital sounder system design our results show that in the very high frequency vhf and ultrahigh frequency uhf bands radar interactions in the firn are dominated by quasi specular reflections at the interfaces between layers of different densities and that off nadir backscatter is likely the result of small scale roughness in the subsurface density profiles as a result high frequency hf or low vhf center frequencies offer a significant advantage in near surface clutter suppression compared to the uhf band however the noise power is the dominant constraint in all bands so the near surface clutter primarily constrains the extent to which the transmit power pulselength or antenna gain can be engineered to improve the signal to noise ratio our analysis suggests that the deep interior of terrestrial ice sheets is a difficult target for orbital sounding which may require optimizations in azimuth processing and cross track clutter suppression which complement existing requirements for sounding at the margins

radar sounding through the earth s ionosphere at 45 mhz radar sounding from aircraft or ground coupled radars has long provided scientists with a powerful technique to sound through ice layers to retrieve local depth and layering structure more recently it has been used to detect shallow aquifers in warm dry and desert regions at mars a long wavelength radar sounding from low orbit altitudes has produced global maps that reveal the presence of ice layering at all latitudes and glacial deposits on the flanks of volcanoes until now sounding from the earth orbit at wavelengths long enough to penetrate ice sheets and arid sand was thought to be infeasible because of the electromagnetic properties of the ionosphere in this paper we show that a radar sounding at frequencies as low as 45 mhz is in fact theoretically possible under viewing conditions that occur often enough to be practical this conclusion opens up a previously unutilized portion of the electromagnetic spectrum for large scale spaceborne remote sensing of subsurface features on the earth

evolution of the sea of japan back arc and some unsolved issues abstract the sea of japan back arc system provides an exceptional opportunity to study a virtually intact continent ocean back arc system in which recent tectonic inversion has exposed entire sequences of back arc structure on land moreover japan s dense seismic geodetic monitoring networks deployed country wide as well as moveable pools of ocean bottom seismometers provide a rich data set through which to investigate deep back arc structure earlier investigations have produced an initial understanding of back arc opening timing structural evolution temporal spatial patterns of magmatic activity many questions remain among them the mechanism of back arc opening pull apart or trench rollback the dynamics of interacting plates location of the philippine sea plate with time the origin of the anomalously thick japan sea ocean crust and possible influences of far field forces india asia collision given existing high resolution geophysical data sets and extensive on land exposures of back arc sequences and structures the sea of japan back arc is a promising context in which to address both local and more universal questions of how back arc systems evolve here we review the tectonic setting and geological evolution of the sea of japan based our own and others work and briefly discuss outstanding questions that invite further investigation

ground penetrating radar sounding in mafic lava flows assessing attenuation and scattering losses in mars analog volcanic terrains we conducted low frequency 16 to 100 mhz ground penetrating radar surveys on the eroded lava flows at craters of the moon idaho usa volcanic field to evaluate the potential of future radar sounding investigations on mars to map shallow subsurface features radar sounding profiles were obtained from three locations above a lava tube across a volcanic rift and over a scoria cone results were combined with laboratory permittivity and magnetic permeability measurements of field collected samples to deconvolve the electromagnetic attenuation and scattering losses from the total losses and therefore separately quantify both effects on the radar penetration depth our results demonstrate a constrained performance for low frequency sounding radars to characterize mafic arid volcanic terrains that contain a significant amount of ferro oxides 14 mainly in the form of olivine and magnetite penetration depths of 35 m were achieved at a frequency of 100 mhz and depths of 80 m were achieved at 16 mhz with an effective dynamic range of 60 db results indicate that for frequencies below 100 mhz the electromagnetic attenuation dominated the signal losses while above this frequency threshold the volume scattering dominated the losses over our frequency range the observed electromagnetic attenuation and penetration depths were strongly dependent on the magnetic losses ground porosities and degree of heterogeneity rather than the sounding frequency in light of these results we suggest average attenuation and scattering losses measured in terms of db m and discuss the expected penetration depth for the mars orbital radar sounding instruments sharad and marsis in mafic volcanic terrains

40ar 39ar stratigraphy of pyroclastic units from the canadas volcanic edifice tenerife canary islands and their bearing on the structural evolution many felsic pyroclastic units of various types are exposed in different sectors of tenerife new 40ar 39ar determinations allow them to be placed more precisely in the general volcano stratigraphic succession according to geographic distribution stratigraphic position and isotopic ages four main pyroclastic phases may be identified the first san juan de la rambla phase 2 1 ma is only known in the north of tenerife in the tigaiga massif the second adeje phase 1 8 1 5 ma is most completely developed in the southwest of the island but occasionally occurs in the other sectors the third las americas phase 1 ma is only presently known in the southern region the fourth bandas del sur phase 0 7 0 15 ma is essentially exposed in the southeast sector the results of this work emphasise the complexity of the pre 1 ma eruptive history of tenerife and underline the fact that explosive volcanic activity has taken place for at least the last 2 ma vertical collapse structures have developed as a result of pyroclastic flow activity and these may be as old as 1 6 1 8 ma therefore much older than generally considered the precise location of calderas is difficult to ascertain as a result of the repeated lateral flank collapse during the construction of the canadas volcano

stratigraphic review of eocene to oligocene successions along the eastern japan sea implication for early opening of the japan sea abstract stratigraphic review of the on land successions exposed on the back arc side of japan and sakhalin combined with supplemental radiometric dating reveals the existence of late eocene or oligocene marine sediments along the eastern coast of the japan sea this finding implies that the origin of the japan sea dates back to the oligocene or earlier time much older than ever supposed the host eocene to oligocene subaerial to shallow water successions distribute immediate west of the volcanic front of that time and contain volcanic rocks the chemistry of which is characteristic of continental rift or volcanic arc they are associated with parallel dike swarms or normal faults and could be infillings of an incipient back arc rift collective evidence suggests that the rift was rapidly subsided and spread during the following early to middle miocene time however a back arc wide unconformity was produced during a short period from the latest oligocene to the earliest miocene and was succeeded by extensive bimodal volcanism with rapid migration of the volcanic front to the fore arc side these short term events could have been induced by upwelling or inflow of hot asthenosphere beneath the arc rift system followed by rapid subsidence and spreading of the japan sea

microgravimetric model of the las canadas caldera tenerife abstract an approximative method to obtain inner mass distributions starting only from gravimetric data and topographic chart digitalization is described roughly the sensitive subsoil volume is divided into a suitable cell partition of equally determinable regular blocks then the gravimetric effect for unit density for each cell on each surface point is determined a global least squares adjustment for every cell and every regular gravimetric point is carried out in order to derive the anomalous density values for each block and finally by using local polynomial approximation a continuous structural model from the discrete cubist solution is performed a volcanic caldera structure the known caldera of las canadas has been gravimetrically observed in this paper we present the methodology we have developed to analyze the measured gravimetric data and show the results corresponding to the inner mass density distribution for this volcanic structure

volcanic evolution of the island of tenerife canary islands in the light of new k ar data new age determinations from tenerife together with those previously published 93 in all provide a fairly comprehensive picture of the volcanic evolution of the island the oldest volcanic series with ages starting in the late miocene are formed mainly by basalts with some trachytes and phonolites which appear in anaga teno and roque del conde massifs in anaga ne three volcanic cycles occurred one older than 6 5 ma a second one between 6 5 and 4 5 ma with a possible gap between 5 4 and 4 8 ma and a late cycle around 3 6 ma in teno nw after some undated units the activity took place between 6 7 and 4 5 ma with two main series separated by a possible pause between 6 2 and 5 6 ma in the zone of roque del conde s the ages are scattered between 11 6 and 3 5 ma between 3 3 and 1 9 ma the whole island underwent a period of volcanic quiescence and erosion the large canadas volcano made up of basalts trachytes and phonolites was built essentially between 1 9 and 0 2 ma to the ne of this central volcano linking it with anaga is a chain of basaltic emission centers with a peak of activity around 0 8 ma the canadas caldera had several collapse phases associated with large ignimbrite emissions there were at least an older phase more than 1 ma old on the western part of the volcano and a younger one less than 0 6 ma old in the eastern side the two large valleys of guimar and la orotava were formed by large landslides less than 0 8 ma ago and probably before 0 6 ma ago the present canadas caldera was formed by another landslide less than 0 2 ma ago this caldera was later filled by the huge teide volcano which has been active even in historic times during the same period a series of small volcanoes erupted at scattered locations throughout the island the average eruptive rate in tenerife was 0 3 km3 ka with relatively small variations for the different eruptive periods this island and la gomera represent a model of growth by discontinuous pulses of volcanic activity separated by gaps often coinciding with episodes of destruction of the edifices and sometimes extended for several million years the neighbouring gran canaria on the other hand had an initial rapid shield building phase during which more than 90 of the island was built and a series of smaller pulses at a much later period a comparison between these three central islands indicates that the previously postulated westward displacement in time of a gap in the volcanic activity is valid only as a first approximation several gaps are present on each island overlapping in time and not clearly supporting either of the models proposed to explain the evolution of the canaries

deep crustal structure off akita eastern margin of the japan sea deduced from ocean bottom seismographic measurements abstract a seismic exploration was carried out to detect the heterogeneity of the seismic wavespeed structure associated with the plate convergence at the eastern margin of the japan sea two airgun obs ocean bottom seismograph profiles were shot off akita japan where a seismic gap seems to exist but the location of the plate boundary has not been confirmed one of the profiles was 60 km long trending nne ssw named line obs 9 at the northeastern end of the yamato basin and the other was 170 km long trending wnw ese line nt95 1 parallel to the direction of the supposed plate convergence the crustal structure beneath line obs 9 consists of six layers the uppermost layer is sediment three layers are identified beneath the top sedimentary layer and their p wavespeeds are estimated to be 3 3 3 4 km s 5 1 5 4 km s and 5 8 6 3 km s which corresponds to the upper crust underneath these layers a layer with p wavespeed ranges of 6 3 7 2 km s comprises the middle and lower crust the depth of moho is inferred to be 19 km these wavespeed values are comparable with those of the present japanese island arc while the thickness of the crust is one half of that of the japanese arc the crustal model supports the scenario that the yamato basin is formed by extension of the island arc the crustal model for line nt95 1 shows a transition from the extended island arc structure beneath the yamato basin to a thicker crust similar to the japanese arc p wavespeed heterogeneity related to the plate boundary is not detected however a significant change in the structural model along the profile is found around the region where the largest change in the seafloor topography exists in that region the wavespeeds in the middle crust have lower values than those of the neighboring area and the moho begins to deepen towards the japanese island arc from comparison with the relationship between p wavespeed structure and aftershock distribution of the 1993 hokkaido nansei oki earthquake southwest of hokkaido m jma 7 8 the region may correspond to a possible fault position of the pending earthquake

mars north polar deposits stratigraphy age and geodynamical response the shallow radar sharad on the mars reconnaissance orbiter has imaged the internal stratigraphy of the north polar layered deposits of mars radar reflections within the deposits reveal a laterally continuous deposition of layers which typically consist of four packets of finely spaced reflectors separated by homogeneous interpacket regions of nearly pure ice the packet interpacket structure can be explained by approximately million year periodicities in mars obliquity or orbital eccentricity the observed 100 meter maximum deflection of the underlying substrate in response to the ice load implies that the present day thickness of an equilibrium elastic lithosphere is greater than 300 kilometers alternatively the response to the load may be in a transient state controlled by mantle viscosity both scenarios probably require that mars has a subchondritic abundance of heat producing elements

gravity constraints on the structure and volcanic evolution of tenerife canary islands a detailed gravity study of tenerife constrains the internal structure of the island and its active magma system the maximum bouguer anomaly 2636 gu 1 gu 10 6 m s 2 0 1 mgal occurs over the sw part of the postshield las canadas edifice lce while smaller highs occur over the eroded shield volcanoes the main high extends ne and nw over the adjacent dorsal and santiago rift zones a deep low occurs over the northern lce and teide volcano the power spectrum of the anomalies suggests shallow causative structures 3 km inferred to belong to the island s dense core a model computed from the anomalies uses core and carapace densities of 2900 and 2360 kg m 3 respectively except beneath the main high where the core requires a higher density 3210 kg m 3 this part of the body is interpreted as a buried mafic volcano of substantial size the boca tauce volcano containing an old mafic plutonic complex the enigmatic las canadas caldera that truncates the lce shows strong asymmetry dense materials occupy the southern part whereas low density materials occupy the northern part to 2 3 km depth consistent with a vertical collapse origin high density materials in the south are related to the intracaldera extension of the dorsal rift zone the boundary between subcaldera domains is interpreted as the buried head of the giant icod landslide valley the icod landslide appears to have modified the caldera truncating its northern side and to have subsequently controlled the location of the active pico teide pico viejo vent systems voluminous chaotic deposits lying off northern tenerife previously associated with the formation of the caldera and icod valley are better interpreted as being derived from older mass wasting events the southern lce has been buttressed against lateral failure by the buried boca tauce volcano

mechanical relationship between catastrophic volcanic landslides and caldera collapses large scale sector collapses of volcanic edifices and collapse calderas represent some of the most catastrophic geological events taking place at the earth s surface examples of these two processes occurring simultaneously suggest that a mechanical relationship between landslides and collapse calderas may exist we demonstrate that a caldera collapse can trigger large scale landslides in volcanic terrains moderate seismic shocks caused by seismogenic slip on the ring fault on which the caldera subsidence takes place act as the driving force necessary to destabilize the volcano flank this process is favored on steep volcanoes and where flank strength is reduced by agents such as hydrothermal alteration pore fluid pressure increase or the presence of weak soils

oceanic crust in the japan basin of the japan sea by the 1990 japan ussr expedition in september of 1990 a seismic refraction and reflection survey was conducted in the japan basin in the northeastern part of the japan sea as a part of the japan ussr joint expedition twenty six ocean bottom seismometers obss were deployed on two 200 km long lines explosives and an airgun were fired as controlled seismic sources on the two mutually perpendicular lines airguns were also used as the source for the multi channel reflection profiles the crustal structure deduced is that of a typical oceanic basin the crustal thickness is about 8 5 km including 2 km of sediment we obtained a more detailed crustal structure than that obtained previously from the dense airgun shooting data the crustal structure is well resolved to show layer 1a layer 1b layer 2a 2b 2c layer 3 and the mantle the crust basically consists of laterally homogeneous layers but the moho deepens slightly westward

big mantle wedge anisotropy slabs and earthquakes beneath the japan sea abstract the japan sea is a part of the western pacific trench arc backarc system and has a complex bathymetry and intense seismic activities in the crust and upper mantle local seismic tomography revealed strong lateral heterogeneities in the crust and uppermost mantle beneath the eastern margin of the japan sea which was determined using p and s wave arrival times of suboceanic earthquakes relocated precisely with sp depth phases ambient noise tomography revealed a thin crust and a thin lithosphere beneath the japan sea and significant low velocity low v anomalies in the shallow mantle beneath the western and eastern margins of the japan sea observations with ocean bottom seismometers and electromagnetometers revealed low v and high conductivity anomalies at depths of 200 300 km in the big mantle wedge bmw above the subducting pacific slab and the anomalies are connected with the low v zone in the normal mantle wedge beneath ne japan suggesting that both shallow and deep slab dehydrations occur and contribute to the arc and back arc magmatism the pacific slab has a simple geometry beneath the japan sea and earthquakes occur actively in the slab down to a depth of 600 km beneath the ne asian margin teleseismic p and s wave tomography has revealed that the philippine sea plate has subducted aseismically down to the mantle transition zone mtz 410 660 km depths beneath the southern japan sea and the tsushima strait and a slab window is revealed within the aseismic philippine sea slab seismic anisotropy tomography revealed a nw se fast velocity direction in the bmw which reflects corner flows induced by the fast deep subduction of the pacific slab large deep earthquakes m 7 0 depth 500 km occur frequently beneath the japan sea western margin which may be related to the formation of the changbai and ulleung intraplate volcanoes a metastable olivine wedge is revealed within the cold core of the pacific slab at the mtz depth which may be related to the deep seismicity however many of these results are still preliminary due to the lack of seismic stations in the japan sea the key to resolving these critical geoscientific issues is seismic instrumentation in the japan sea for which international cooperation of geoscience communities in the east asian countries is necessary

antarctic surface and subsurface snow and ice melt fluxes abstract this paper presents modeled surface and subsurface melt fluxes across near coastal antarctica simulations were performed using a physical based energy balance model developed in conjunction with detailed field measurements in a mixed snow and blue ice area of dronning maud land antarctica the model was combined with a satellite derived map of antarctic snow and blue ice areas 10 yr 1991 2000 of antarctic meteorological station data and a high resolution meteorological distribution model to provide daily simulated melt values on a 1 km grid covering antarctica model simulations showed that 11 8 and 21 6 of the antarctic continent experienced surface and subsurface melt respectively in addition the simulations produced 10 yr averaged subsurface meltwater production fluxes of 316 5 and 57 4 km3 yr 1 for snow covered and blue ice areas respectively the corresponding figures for surface melt were 46 0 and 2 0 km3 yr 1 respectively thus demonstrating the dominant role of subsurface ov

new sonar evidence for recent catastrophic collapses of the north flank of tenerife canary islands previous sonar surveys show that the north flank of tenerife has been subject to at least four major landslides during the past 1 ma the youngest icod affected the region to the north of the teide pico viejo complex the world s third highest oceanic volcano recently we obtained the first detailed acoustic images of icod using a deep tow side scan sonar the images suggest that tenerife s north flank has experienced at least two types of flow deposit in the recent past the older flow deposit icod i is characterised by a 15 to 20 km wide 65 km long chaotic debris avalanche deposit which includes several very large blocks we believe the deposit to be 170 ka and that it represents the mass wasting products of the canadas edifice remnants of which are now found in the las canadas caldera wall the younger flow deposit icod ii associated with a shute in its proximal part appears to have produced a less chaotic deposit in its distal part which clearly preserves flow structures such as latitudinal boulder ridges and longitudinal shear structures the sonar images cannot determine how much younger icod ii is than icod i although it is likely that they are a consequence of the same lateral collapse event there is evidence from the shute area for erosional scour and sediment deposition since the icod landslide if this is correct then it suggests that mass wasting is an ongoing process that has already started to modify the teide pico viejo complex itself

a giant landslide on the north flank of tenerife canary islands the extent of mass wasting along the north flank of tenerife has been mapped using swath bathymetry gloria side scan sonar and 3 5 khz echo sounder data the marine surveys show that north of tenerife a giant landslide is exposed over an area of 5500 km2 of the seafloor more than twice the surface area of the island the landslide truncates an older ridge and valley topography that is associated with the shield building basalts on tenerife we interpret the ridge and valley topography as the result of subaerial erosion the landslide is estimated to have a length of 100 km a width of up to 80 km and a volume of about 1000 km3 it extends onshore into the orotava and icod valleys which have been interpreted as of landslide origin k ar dating of basaltic flows in the steep headwall of orotava suggests an age of formation for the valley is younger than 0 78 ma and may even be younger than 0 27 ma the icod valley is located immediately to the north of the most recent volcano on tenerife las canadas and has been associated with the collapse of its caldera between 1 2 and 0 2 ma a young age for the landslide is supported by the 3 5 khz echo sounder data which show that the landslide is draped by a thin 10 m layer of younger sediment the landslide did not form however during a single catastrophic event but represents the amalgamation of a number of separate landslides the occurrence of the ridge and valley topography in water depths of up to 2 5 km suggests that the shield building basalts have subsided by at least this amount since they formed 3 3 8 0 ma we speculate that this subsidence is caused by some form of stress relaxation that occurs in the underlying lithosphere the giant landslide imaged in our sonar data is associated with the late stages in the development of the most recent volcano on tenerife las canadas which only began at about 1 8 ma thus landsliding may be a particular feature of the time soon after emplacement when because of incomplete isostatic adjustment oceanic volcanoes have their greatest elevations above sea level and therefore are most susceptible to slope failure

stratigraphy of the bandas del sur formation an extracaldera record of quaternary phonolitic explosive eruptions from the las canadas edifice tenerife canary islands explosive volcanism has dominated the large phonolitic shield volcano of tenerife the las canadas edifice for the last 1 5 m y pyroclastic deposits of the bandas del sur formation are exposed along the southern flanks and record the last two of at least three long term cycles of caldera forming explosive eruptions each cycle began with flank fissure eruptions of alkali basalt lava followed by minor eruptions of basanite to phonotephrite lavas minor phonotephritic to phonolitic lava effusions also occurred on the flanks of the edifice during the latter stages of the second explosive cycle non welded plinian fall deposits and ignimbrites are the dominant explosive products preserved on the southern flanks of these a significant volume has been dispersed offshore many pyroclastic units of the second explosive cycle exhibit compositional zonation banded pumice occurs in most units of the third youngest explosive cycle and ignimbrites typically contain mixed phenocryst assemblages indicating the role of magma mixing mingling prior to eruption at least four major eruptions of the third cycle began with phreatomagmatic activity producing lithic poor accretionary lapilli bearing fallout and or surge deposits the repeated brief phase of phreatomagmatism at the onset of these eruptions is interpreted as reflecting an exhaustive water supply probably a small caldera lake that was periodically established during the third cycle accidental syenite becomes an increasingly important lithic clast type in ignimbrites up sequence and is interpreted as recording the progressive development of a plutonic complex beneath the summit caldera successive eruptions during each explosive cycle increased in volume with the largest eruption occurring at the end of the cycle more than ten major explosive eruptions vented moderately large volumes 1 ges 10 km 3 of phonolitic magma during the last two cycles culminating each explosive cycle was the emplacement of relatively large volume 5 10 km 3 ignimbrites with coarse vent derived lithic breccias interpreted to record a major phase of caldera collapse in the extracaldera record explosive cycles are separated by 0 2 m y periods of non explosive activity repose periods were characterized by erosion remobilization of pyroclastic deposits by discharge events and pedogenesis the current period of non explosive activity is characterized by the construction of the teide pico viejo stratovolcanic complex within the summit caldera this suggests that eruptive hiatuses in the extracaldera record may reflect effusive activity and stratovolcano or shield building phases within the summit caldera alternating effusive and explosive cycles have thus been important in the volcanic evolution of the las canadas edifice

the quaternary pyroclastic succession of southeast tenerife canary islands explosive eruptions related caldera subsidence and sector collapse a much revised quaternary stratigraphy is presented for ignimbrites and pumice fall deposits of the bandas del sur in southern tenerife new ar 41 ar 39 data obtained for the arico granadilla fasnia poris la caleta and abrigo formations are presented allowing correlation with previously dated offshore marine ashfall layers and volcaniclastic sediments we also provide a minimum age of 287 7 ka for a major sector collapse event at the gaimar valley the bandas del sur succession includes more than seven widespread ignimbrite sheets that have similar characteristics including widespread basal plinian layers predominantly phonolite composition ignimbrites with similar extensive geographic distributions thin condensed veneers with abundant diffuse bedding and complex lateral and vertical grading patterns lateral gradations into localized massive facies within palaeo wadis and widespread lithic breccia layers that probably record caldera forming eruptions each ignimbrite sheet records substantial bypassing of pyroclastic material into the ocean the succession indicates that las canadas volcano underwent a series of major explosive eruptions each starting with a plinian phase followed by emplacement of ignimbrites and thin ash layers some of coignimbrite origin several of the ignimbrite sheets are compositionally zoned and contain subordinate mafic pumices and banded pumices indicative of magma mingling immediately prior to eruption because passage of each pyroclastic density current was characterized by phases of non deposition and erosion the entire course of each eruption is incompletely recorded at any one location accounting for some previously perceived differences between the units because each current passed into the ocean estimating eruption volumes is virtually impossible nevertheless the consistent widespread distributions and the presence of lithic breccias within most of the ignimbrite sheets suggest that at least seven caldera collapse eruptions are recorded in the bandas del sur succession and probably formed a complex nested collapse structure detailed field relationships show that extensive ignimbrite sheets e g the arico poris and la caleta formations relate to previously unrecognized caldera collapse events we envisage that the evolution of the nested las cahadas caldera is more complex than previously thought and involved a protracted history of successive ignimbrite related caldera collapse events and large sector collapse events interspersed with edifice building phases

the las canadas caldera tenerife canary islands an overlapping collapse caldera generated by magma chamber migration abstract the las canadas caldera is one of the most important geological structures of tenerife stratigraphic structural volcanological petrological geochronological and geophysical data suggest that the las canadas caldera resulted from multiple vertical collapse episodes that occurred during the construction of the las canadas edifice upper group three long term 200 ka cycles of phonolitic explosive activity each culminating with a caldera collapse have been identified in the upper group during the construction of the upper group the focus of felsic volcanism migrated from west to east using the results of field observations experimental analogue models and numerical studies we propose that the formation of the overlapping las canadas collapse caldera is related to the migration of the associated magma chamber our model implies that each collapse of this overlapping caldera partly or completely destroyed the feeding magma chamber this destruction led to changes in the local stress field that favoured the formation of a new chamber at one side of the previous one resulting in magma chamber migration the proposed model accounts for the formation of the las canadas caldera in particular it explains the geometrical relationships stratigraphy and chronology of the caldera wall deposits comparison with other overlapping collapse calderas suggests that our model may apply to other overlapping calderas

deep slab dehydration and large scale upwelling flow in the upper mantle beneath the japan sea we present a three dimensional p and s wave tomography model beneath the central japan sea using arrival time data obtained by long term ocean bottom seismometer observations the tomographic model is determined down to over 300 km the resulting tomographic image has two features in the mantle wedge first a remarkable low velocity region is spread within the shallow part of the mantle wedge beneath the japan arc with a slight extension beneath the japan sea second an inclined low velocity anomaly exists in the deeper part beneath the japan sea and converges to the slab at 300 km depth moreover its anomaly amplitude is distinctly small compared to the shallow part of the low velocity region these low velocity anomalies are interpreted to represent fluids that were dehydrated from the pacific and philippine sea slabs and melt production affected by the fluid our observations suggest that the deep dehydration from the pacific slab is found at a depth of approximately 300 km and large scale upwelling flow mechanically induced by plate subduction exists beneath the japan sea our results indicate the importance of the deep heterogeneous mantle wedge structure beneath the japan sea with regards to better understanding the magmatism of the subduction dynamics in japan and the evolution of the opening of the japan sea

repeated debris avalanches on tenerife and genesis of las canadas caldera wall canary islands geologic evidence on tenerife canary islands indicates six successive north directed debris avalanche events including the anaga and teno ca 6 ma events that affected the old basaltic series and the tigaiga 2 3 ma roques de garcia possibly 0 6 0 7 ma orotava ca 0 6 ma and icod 0 15 ma avalanche events that affected the canadas and dorsal volcanic edifices the approximate total volume 1000 km3 inferred for these events can account for the volume of previous estimates of offshore volcanic debris these repeated flank failures can also account for the present morphology of las canadas caldera wall which partly bounds a multiepisodic lateral collapse structure 25 km wide

p wave velocity structure of the margin of the southeastern tsushima basin in the japan sea using ocean bottom seismometers and airguns abstract the tsushima basin is located in the southwestern japan sea which is a back arc basin in the northwestern pacific although some geophysical surveys had been conducted to investigate the formation process of the tsushima basin it remains unclear in 2000 to clarify the formation process of the tsushima basin the seismic velocity structure survey with ocean bottom seismometers and airguns was carried out at the southeastern tsushima basin and its margin which are presumed to be the transition zone of the crustal structure of the southwestern japan island arc the crustal thickness under the southeastern tsushima basin is about 17 km including a 5 km thick sedimentary layer and 20 km including a 1 5 km thick sedimentary layer under its margin the whole crustal thickness and thickness of the upper part of the crust increase towards the southwestern japan island arc on the other hand thickness of the lower part of the crust seems more uniform than that of the upper part the crust in the southeastern tsushima basin has about 6 km s layer with the large velocity gradient shallow structures of the continental bank show that the accumulation of the sediments started from lower miocene in the southeastern tsushima basin the crustal structure in southeastern tsushima basin is not the oceanic crust which is formed ocean floor spreading or affected by mantle plume but the rifted extended island arc crust because magnitudes of the whole crustal and the upper part of the crustal thickening are larger than that of the lower part of the crustal thickening towards the southwestern japan island arc in the margin of the southeastern tsushima basin high velocity material does not exist in the lowermost crust for that reason the margin is inferred to be a non volcanic rifted margin the asymmetric structure in the both margins of the southeastern and korean peninsula of the tsushima basin indicates that the formation process of the tsushima basin may be simple shear style rather than pure shear style

seismic structure of the source region of the 2007 chuetsu oki earthquake revealed by offshore onshore seismic survey asperity zone of intraplate earthquake delimited by crustal inhomogeneity abstract the 2007 niigata ken chuetsu oki earthquake occurred on july 16 2007 with a magnitude of 6 8 immediately after the mainshock a dense network of ocean bottom seismometers and temporary land seismic stations were deployed to obtain the accurate aftershock location a seismic survey using ocean bottom seismometers land stations and controlled sources at sea and on land was also conducted along three profiles to estimate the detailed velocity structure of the source region a thick sedimentary layer covers the crust and this layer is thickest near the coast the upper crust has a p wave velocity of 6 km s and a large lateral heterogeneity with respect to thickness and velocity the lower crust with p wave velocity of 7 km s has a thickness of approximately 10 km the thickness of the crust is estimated to be approximately 24 km the precise aftershock distribution was obtained by using the high resolution velocity structure the aftershocks in the upper crust form a plane dipping to the southeast most of the aftershocks are located in the upper crust in addition a small number of aftershocks in the lower crust seem to be positioned on the same plane formed by the aftershocks in the upper crust the mainshock fault estimated from the aftershock distribution is positioned in the high velocity body of the upper crust a large deformation of the sediments above the epicentral region is interpreted to be due to the repeated occurrence of large earthquakes the lower crust immediately below the fault has low velocity the source region of the 2007 event in the upper crust is sandwiched by a weakening structure we suggest that the ductile deformation of both the sediments and the lower crust causes stress accumulation in the source region

seismic evidence for stretched continental crust in the japan sea the japan sea is a major marginal sea in the western pacific comprised of basins and bathymetric highs technically these features were created by multiple rifting and spreading processes as exemplified in the creation of the japan basin and yamato basin however there are smaller scale features for which seismic crustal models have been inadequate to infer or verify their origin and evolution recent advances in marine seismological surveys enable us to obtain heterogeneous seismic crustal structures in sufficient detail to characterize these features in september of 1992 a seismic experiment was conducted to obtain the detailed seismic crustal structure in the southwestern part of the japan sea including the basin and bank areas seventeen ocean bottom seismometers obss were deployed on two lines explosives and airguns were fired as controlled seismic sources the model of the crust obtained in the northern tsushima basin is about 13 km thick including a 1 5 km thick sedimentary layer beneath the bank area the crust is 22 km thick and the upper crust is relatively homogeneous with a p wave velocity of about 6 km s the bank is interpreted to be a stretched continental crust fragment

explosive activity of the reunion island volcanoes through the past 260 000 years as recorded in deep sea sediments the explosive activity of reunion volcanoes since approximately 260 ka is investigated through detailed sedimentologic isotopic and geochemical analyses of three deep sea marine cores twenty four eruptions from piton des neiges and one from piton de la fournaise are identified the marine stratigraphic record of ash layers is undisturbed whereas corresponding tephra deposits on land may have disappeared or have been disturbed through erosion and volcano tectonic processes consequently the new data presented herein may be regarded as a reference sequence of the main explosive events of reunion in addition the chronology based on 18o stratigraphy offers continuous time constraints with respect to other isotopic methods used for dating lavas explosive events were more frequent during the period 180 150 ka the comparison of major element composition and chronologic data between known explosive deposits on land and marine ash layers allows us to propose correlations between marine and land data however most of the marine ash layers do not yet have a recognized subaerial counterpart for the main explosive events known on land we propose the following succession sainte suzanne formations 257 240 ka dalle soudee formation 218 ka salazie formations two groups at 165 168 ka and 80 102 ka saint gilles formations 175 ka saint louis formations 158 161 ka and saint pierre formations 165 166 ka

seismic structure of the crust and uppermost mantle in the incipient stage of back arc rifting northernmost okinawa trough 1 in 1999 a marine seismic structure survey was conducted in the northernmost okinawa trough outcrops of the acoustic basement through the sedimentary layers are seen in the obtained structures velocities of lower layer in upper crust are varying laterally from 5 7 to 6 2 km s and thickness of 6 0 km s layer ranges from 3 to 9 km the lower crust has uniform thickness of about 15 km the pn velocity is 7 7 7 8 km s and the total crustal thickness is about 25 km including sedimentary layers the structure is in a first approximation similar to that of island arcs however the large heterogeneity of upper crust can be interpreted as a result of crustal thinning the low pn velocity and the outcrops of the acoustic basement relate to igneous activity in this area these results suggest that the northernmost part of the okinawa trough is in the incipient stage of a back arc rifting

a crustal structure profile across the northern continental margin of the south china sea an ocean bottom seismometer obs geophysical experiment was carried out across the northern continental margin of the south china sea two dimension kinematic ray tracing was used to construct synthetic records and to define the geological model along the obs profile according to the calculation and interpretation of refracted p wave phases the crustal thickness decreases from 22 km obs 1 in littoral area to 8 km obs 15 in deep sea the lower slope structured by volcanism changes sharply in moho depth from 22 to 9 km the volcanoes over the lower slope were markers of ocean continental transition zone a high velocity layer hvl with an average thickness of 4 km was found in the base of the lower crust over the shelf and slope the south china sea was originated by the passive rifting of south china continent and seafloor spreading however geological and geophysical data collected in the northern margin of the south china sea show a small amount of magma intruded into or erupted onto the crust during pull apart and breakup further analysis shows that the hvz in the base of the thinned continental crust was related to magmatism that occurred after the cessation of seafloor spreading of the south china sea magmatism during the crustal extension and breakup is very weak therefore the northern continental margin of the scs is classified as non volcanic passive margin the southern margin of the south china sea has a crust with a steady thickness of 18 24 km which is different from the nor them margin of the south china sea with a gradually thinned crust they constitute an asymmetrically conjugated pair of passive margins c 2001 elsevier science b v all rights reserved

opening mode of the japan sea inferred from the palaeomagnetism of the japan arc the western edge of the pacific plate is marked by a chain of back arc basins stretching from the aleutians through japan and the philippines to new zealand most of the basins lie behind volcanic island arcs far from continents and are the result of extension of the oceanic lithosphere1 but the japan sea is bounded on one side by continental crust the sikhote alin and korean peninsula of the asian continent and on the other by an active arc with continental fragments it can thus be said to be associated more with continental rifting1 4 than with oceanic processes we report here palaeomagnetic data from the japan arc which indicate that since the early miocene north east japan has rotated counter clockwise through 47 around a vertical axis while south west japan has rotated clockwise through 56 refs 5 8 we attribute this differential rotation which took place concurrently between 21 and 11 myr ago to the back arc opening of the japan sea8 with a double door mode that is there are two fan shaped spreading basins facing each other such a fan shaped opening is probably peculiar to the geological phenomenon of rifting of a continental fragment from thick continental lithosphere

radar based subglacial lake classification in antarctica 1 subglacial lakes in east antarctica can be separated into four categories specified by radar reflection properties definite lakes are brighter than their surroundings by at least 2 db relatively bright and both are consistently reflective specular and have a reflection coefficient greater than 10 db absolutely bright dim lakes are relatively bright and specular but not absolutely bright indicating nonsteady ice dynamics fuzzy lakes are both relatively and absolutely bright but not specular and may indicate saturated sediments or swamps indistinct lakes are absolutely bright and specular but no brighter than their surroundings lakes themselves and the different classes of lakes are not arranged randomly throughout antarctica but are clustered around ice divides ice stream onsets and prominent bedrock troughs with each cluster demonstrating a different characteristic lake classification distribution the lake classification algorithm expands on previous studies and demonstrates a novel way to characterize ice water interactions in east antarctica

lithic breccias in intermediate volume phonolitic ignimbrites tenerife canary islands constraints on pyroclastic flow depositional processes abstract lithic occurrences within quaternary phonolitic ignimbrites on tenerife canary islands fall into three broad groupings 1 massive ignimbrite with large floating lithics 2 basal lithic rich bedforms and 3 matrix to clast supported lithic breccias within ignimbrite massive ignimbrite divisions commonly contain large outsized either solitary or scattered lithics which are mostly monomictic and derived locally from substrate erosion by pyroclastic density currents low and high aspect ratio lithic rich bedforms occur at the base of several ignimbrites most bedforms are asymmetric with steeper lee sides and they are buried by stratified and or massive ignimbrite internally most bedforms are massive some however exhibit an upstream inclined stratification indicating upcurrent migration of the bedform which is interpreted to record antidune like flow regimes locally derived basalt clasts are important constituents of some of these bedforms which have also been sourced through substrate erosion matrix to clast supported pebble to boulder sized lithic breccias occur at various heights within massive ignimbrite lithic breccias at or near the top of most ignimbrites contain vent derived lithics and record a late flux of lithic material from the vent during a sustained pyroclastic flow event extensive boulder sized breccias at the top of two ignimbrites are interpreted to record the onset of caldera collapse late in the pyroclastic flow forming eruptions some breccias contain boulders that are oriented with long axes transverse to flow indicating late stage tractional transport thin bedded matrix supported lithic breccias or lithic trains and stratified ignimbrite are commonly developed adjacent to or immediately above topographic highs these facies laterally merge into massive ignimbrite infilling topographic lows massive ignimbrite is interpreted to be deposited from a high particle concentration hindered settling zone inverse grading and long axis parallel to bedding imbrication of lithics within the thin bedded breccia facies are interpreted to record deposition under modified grain flow conditions a variety of depositional processes are thus recorded and the relationship between lithic breccias ignimbrite facies and topography indicates that there were spatial variations in depositional mechanisms at any one instant the vertical sequence of bedform stratified ignimbrite massive ignimbrite characterises the lower part of several ignimbrites and is interpreted to record increasing rates of deposition from a sustained current multilayered lithic breccias at various heights within massive ignimbrite are a form of clast compositional zonation and reflect temporal changes in supply flow competence and capacity

3d upper mantle structure beneath japan and its surrounding region from inter station dispersion measurements of surface waves abstract three dimensional shear wave speed structure of the upper mantle beneath the japanese islands and the surrounding regions is constructed from the measurements of inter station phase speeds of surface waves we employ the dense broad band seismic network f net deployed throughout japan as well as permanent stations of global seismic network in east asia a temporary broad band seismic network in far east russia which has been constructed as a part of the stagnant slab project since 2004 is also used in combination with the permanent stations using seismic events from 2005 to 2007 with moment magnitude greater than 6 0 and depth shallower than 100 km we measure the phase speeds of the fundamental mode rayleigh and love waves working with the conventional two station technique phase speed maps of the japanese islands and the sea of japan are obtained from the inversions of inter station phase speeds that are measured for a large number of station pairs we have collected over 5300 paths for rayleigh waves and 3800 paths for love waves the phase speed maps of rayleigh waves in the period range from 25 to 140 s are inverted to obtain an isotropic 3d shear wave speed model in the depth range from 40 to 200 km the isotropic s wave model represents prominent fast wave speed anomalies in northeastern japan associated with the subducting pacific plate fast anomalies of the lithosphere beneath the sea of japan are also imaged implying that the average thickness of lithosphere beneath the yamato rise and japan basin is about 60 10 km immediately below this oceanic lithosphere slow anomalies are found in the asthenosphere beneath the entire region of the sea of japan in the depth down to about 200 km in southwestern japan the low angle subduction of the philippine sea plate is mapped clearly indicating that the northern end of the plate extends beyond the northern coast of the chugoku region reaching beneath the oki islands in the sea of japan a strong low velocity anomaly off the west coast of kyushu is found in the depth down to about 130 km which supports the existence of an upwelling flow beneath this area we also invert the phase speed maps of rayleigh and love waves in the period range from 30 to 80 s simultaneously to construct the radially anisotropic shear wave speed model a remarkable anisotropy with sh sv is found in the mantle wedge beneath northeastern japan while only weak anisotropy is seen beneath the sea of japan such anisotropic properties which cannot readily be obtained from body wave studies only will be an important key to understanding the dynamic processes in this tectonically actively region

crustal intrusion beneath the louisville hotspot track we report here the first detailed 2d tomographic image of the crust and upper mantle structure of a cretaceous seamount that formed during the interaction of the pacific plate and the louisville hotspot results show that at 1 5 km beneath the seamount summit the core of the volcanic edifice appears to be dominantly intrusive with velocities faster than 6 5 km s the edifice overlies both high lower crustal 7 2 7 6 km s and upper mantle 8 3 km s velocities suggesting that ultramafic rocks have been intruded as sills rather than underplated beneath the crust the results suggest that the ratio between the volume of intra crustal magmatic intrusion and extrusive volcanism is as high as 4 5 in addition the inversion of moho reflections shows that the pacific oceanic crust has been flexed downward by up to 2 5 km beneath the seamount the flexure can be explained by an elastic plate model in which the seamount emplaced upon oceanic lithosphere that was 10 myr at the time of loading intra crustal magmatic intrusion may be a feature of hotspot volcanism at young hot oceanic lithosphere whereas magmatic underplating below a pre existing moho may be more likely to occur where a hotspot interacts with oceanic lithosphere that is several tens of millions of years old

an anomalously thick layering of the crust of the yamato basin southeastern sea of japan the final stage of back arc spreading abstract the yamato basin is believed to have been formed by back arc spreading of the japanese islands a seismic velocity structure beneath the basin was modeled on the basis of seismic data acquired during the delp 85 wakashio cruise conducted by the japanese research group of the international lithosphere project ilp the dataset consists of multichannel reflection profiles airgun shot refraction profiles recorded by ocean bottom seismometers obss and explosion refraction profiles also recorded by the obss the model indicates that the crustal layering is twice as thick as in a normal oceanic basin but the velocity in each layer and that of the underlying uppermost mantle is very similar to that of oceanic basin crust the crust is 14 km thick at the middle of the oblong basin along its strike and thinner towards the rim of the basin tending toward 11 km stratigraphy of the sedimentary layer and the acoustic basement suggest that volcanism during the late stage of spreading is responsible for the thick layering and the seamount chain located along the spreading axis of the basin

evolution of the north flank of tenerife by recurrent giant landslides geomorphologic analysis of submarine and subaerial surface features using a combined topographic bathymetric digital elevation model coupled with onshore geological and geophysical data constrain the age and geometry of giant landslides affecting the north flank of tenerife shaded relief and contour maps and topographic profiles of the submarine north flank permit the identification of two generations of post shield landslides older landslide materials accumulated near the shore 40 km and comprise 700 km3 of debris thickening towards a prominent axis suggests one major landslide deposit younger landslide materials accumulated 40 70 km offshore and comprise the products of three major landslides the la orotava landslide complex the icod landslide and the east dorsal landslide complex each with an onshore scar a proximal submarine trough and a distal deposit lobe estimated lobe volumes are 80 80 and 100 km3 respectively the old post shield landslide scar is an amphitheatre 20 25 km wide partly submarine now completely filled with younger materials age width relationships for tenerife s coastal platform plus onshore geological constraints suggest an age of ca 3 ma for the old collapse young landslides are all less than 560 ka old the la orotava and icod slides involved failures of slabs of subaerial flank to form the subaerial la orotava and icod valleys offshore they excavated troughs by sudden loading and basal erosion of older slide debris the onshore east dorsal slide also triggered secondary failure of older debris offshore the slab like geometry of young failures was controlled by weak layers deep drainage channels and flank truncation by marine erosion the partly submarine geometry of the older amphitheatre reflects the absence of these features relatively low h l ratios for the young slides are attributed to filling of the slope break at the base of the submarine edifice by old landslide materials low aspect ratios of the failed slabs and channelling within troughs post shield landslides on tenerife correlate with major falls in sea level reflecting increased rates of volcanism and coastal erosion and reduced support for the flank landslide head zones have strongly influenced the pattern of volcanism on tenerife providing sites for major volcanic centres

from unthinned continent to ocean the deep structure of the west iberia passive continental margin at 38 n abstract the crustal and lithospheric mantle structure at the south segment of the west iberian margin was investigated along a 370 km long seismic transect the transect goes from unthinned continental crust onshore to oceanic crust crossing the ocean continent transition oct zone the wide angle data set includes recordings from 6 obss and 2 inland seismic stations kinematic and dynamic modeling provided a 2d velocity model that proved to be consistent with the modeled free air anomaly data the interpretation of coincident multi channel near vertical and wide angle reflection data sets allowed the identification of four main crustal domains i continental east of 9 4 w ii continental thinning 9 4 w 9 7 w iii transitional 9 7 w 10 5 w and iv oceanic west of 10 5 w in the continental domain the complete crustal section of slightly thinned continental crust is present the upper ucc 5 1 6 0 km s and the lower continental crust lcc 6 9 7 2 km s are seismically reflective and have intermediate to low p wave velocity gradients the middle continental crust mcc 6 35 6 45 km s is generally unreflective with low velocity gradient the main thinning of the continental crust occurs in the thinning domain by attenuation of the ucc and the lcc major thinning of the mcc starts to the west of the lcc pinchout point where it rests directly upon the mantle in the thinning domain the moho slope is at least 13 and the continental crust thickness decreases seaward from 22 to 11 km over a 35 km distance stretched by a factor of 1 5 to 3 in the oceanic domain a two layer high gradient igneous crust 5 3 6 0 km s 6 5 7 4 km s was modeled the intra crustal interface correlates with prominent mid basement 10 15 km long reflections in the multi channel seismic profile strong secondary reflected pmp phases require a first order discontinuity at the moho the sedimentary cover can be as thick as 5 km and the igneous crustal thickness varies from 4 to 11 km in the west where the profile reaches the madeira tore rise in the transitional domain the crust has a complex structure that varies both horizontally and vertically beneath the continental slope it includes exhumed continental crust 6 15 6 45 km s strong diffractions were modeled to originate at the lower interface of this layer the western segment of this transitional domain is highly reflective at all levels probably due to dykes and sills according to the high apparent susceptibility and density modeled at this location sub moho mantle velocity is found to be 8 0 km s but velocities smaller than 8 0 km s confined to short segments are not excluded by the data strong p wave wide angle reflections are modeled to originate at depth of 20 km within the lithospheric mantle under the eastern segment of the oceanic domain or even deeper at the transitional domain suggesting a layered structure for the lithospheric mantle both interface depths and velocities of the continental section are in good agreement to the conjugate newfoundland margin a 40 km wide oct having a geophysical signature distinct from the oct to the north favors a two pulse continental breakup

magmatism at rifted continental margins the intense volcanism and uplift observed on many rifted continental margins forming basaltic seaward dipping reflector sequences is accompanied by the emplacement of a thick igneous section at depth partial melting by decompression of passively upwelling asthenosphere that is hotter than normal because it is near a hotspot explains both the thickness of the new igneous crust and the initial elevation of the rifted margins

the construction of chasma boreale on mars the northern polar cap of mars containing enough water to cover the entire planet to a depth of several metres features two major landforms that stand above all others these are the enormous canyon chasma boreale and a series of spiral troughs the processes leading to their formation have remained unclear now two papers in this issue present detailed histories of both systems john holt and colleagues use penetrating radar imagery from mars reconnaissance orbiter s radar sounder to show that depositional processes rather than a catastrophic event formed the chasma boreale isaac smith and john holt use mars reconnaissance orbiter data to rule out erosional cutting of polar ice as the cause of the central troughs and instead conclude that they too are largely depositional having migrated polewards and upwards in elevation in the past two million years the chasma boreale is a large canyon 500 km long up to 100 km wide and nearly 2 km deep that cuts into the north polar layered deposits on mars quite how it formed has been unclear however new penetrating radar imagery has now been used to show that depositional processes rather than catastrophic events were responsible the polar layered deposits of mars contain the planet s largest known reservoir of water ice1 2 and the prospect of revealing a detailed martian palaeoclimate record3 4 but the mechanisms responsible for the formation of the dominant features of the north polar layered deposits npld are unclear despite decades of debate stratigraphic analyses of the exposed portions of chasma boreale a large canyon 500 km long up to 100 km wide and nearly 2 km deep have led most researchers to favour an erosional process for its formation following initial npld accumulation candidate mechanisms include the catastrophic outburst of water5 protracted basal melting6 erosional undercutting7 aeolian downcutting7 8 9 and a combination of these processes10 here we use new data from the mars reconnaissance orbiter to show that chasma boreale is instead a long lived complex feature resulting primarily from non uniform accumulation of the npld the initial valley that later became chasma boreale was matched by a second equally large valley that was completely filled in by subsequent deposition leaving no evidence on the surface to indicate its former presence we further demonstrate that topography existing before the npld began accumulating influenced successive episodes of deposition and erosion resulting in most of the present day topography long term and large scale patterns of mass balance achieved through sedimentary processes rather than catastrophic events ice flow or highly focused erosion have produced the largest geomorphic anomaly in the north polar ice of mars

seismic structure of the extended continental crust in the yamato basin japan sea from ocean bottom seismometer survey abstract we present the result of a seismic experiment conducted using ocean bottom seismometers and an airgun in the yamato basin of the japan sea the japan sea is one of the most well studied back arc basins in the western pacific the japan sea is believed to have been formed by back arc opening however the timing and formation processes of the opening of individual basins in and around the japan sea are not clear to reveal the crustal structure of the yamato basin it is important to consider the formation process of the japan sea therefore we conducted a seismic survey and estimated the p wave seismic velocity structure beneath the 170 km profile using a 2 d ray tracing method a layer with a p wave velocity of 3 4 4 0 km s underlies the sedimentary sections which is thought to consist of a sill and sediment complex the upper crust below the profile varies greatly in thickness the thickness of the upper crust is 3 5 km in the thinnest part and 7 km in the thickest part the thickness of the lower crust is approximately 8 km and is relatively constant over the profile the total thickness of the crust is approximately 15 km including the sedimentary layer the distribution of p wave velocities and the thickness indicate that the crust in the yamato basin is neither a typical continental nor a typical oceanic crust from the point of view of seismic velocity the obtained structure is more similar to a continental crust than to an oceanic crust the large lateral thickness variation in the upper crust and the uniform thickness of the lower crust suggest that the crust in the study area was formed by rifting extension of continental crust during the opening of the japan sea the margins of the continent or of island arcs can be divided into two types volcanic rifted margins and non volcanic rifted margins volcanic rifted margins are normally classified by the presence of a high velocity body in the lower crust at the volcanic rifted margin the high velocity body is formed in the lower crust we did not observe such a high velocity layer at depth on our profile in contrast the acoustic basement consists of a sill and sediment complex therefore we infer that the study area was affected by volcanism during its formation however the magmatism was not significantly massive

echo source discrimination in single pass airborne radar sounding data from the dry valleys antarctica implications for orbital sounding of mars the interpretation of radar sounding data from mars where significant topographic relief occurs will require echo source discrimination to avoid the misinterpretation of surface echoes as arising from the subsurface this can be accomplished through the identification of all radar returns from the surface in order to positively identify subsurface echoes we have developed general techniques for this using airborne radar data from the dry valleys of antarctica these data were collected in a single pass including taylor glacier ice covered lake bonney and an ice free area of taylor valley the pulsed radar 52 5 67 5 mhz was coherently recorded our echo discrimination techniques included a radar simulator using a digital elevation model dem to predict the location and shape of surface echoes in the radar data real and simulated echo strengths were used to calculate a signal to clutter ratio this was complemented by the cross track migration of radar echoes onto the surface these migrated echoes were superimposed on the dem and imagery in order to correlate with surface features using these techniques enabled us to identify a number of echoes in the radar data as arising from the surface and to identify subsurface echoes including a continuous reflector under the main trunk of taylor glacier and multiple reflectors beneath the terminus of taylor glacier surface based radar confirms the thickness of the glacier at three crossing points the results illustrate the importance of using complementary techniques the usefulness of a dem and the limitations of single pass radar sounding data

correcting distortion of polarimetric sar data induced by ionospheric scintillation a correction methodology for distortions induced by ionospheric scintillation on fully polarimetric synthetic aperture radar sar data is proposed the correction is based on deriving the phase distortion induced by the ionosphere from faraday rotation estimates the estimated phase distortion is then used for correction in order to compensate the phase and time doppler history distortions the correction has to be performed at the slant range of the ionospheric layer i e on partially focused single look complex data accordingly the performance of the proposed correction methodology depends among other factors on knowledge of the altitude of the effective ionospheric layer assuming the thin ionospheric layer model its estimation from the sar data itself is therefore also addressed the methodology was applied and validated on simulated p band data for various ionospheric conditions and on real l band data acquired by the advanced land observation satellite phased array l band sar palsar

airborne radar stratigraphy and electrical structure of temperate firn bagley ice field alaska u s a helicopter borne 135 mhz short pulse radar profiles of the bagley ice field southern alaska u s a have been analyzed to determine the nature of radio wave propagation through crevassed stratified wet and draining firn diffractions characterize the firn horizons along the trunk and reflections characterize those of overlying snow fields dynamic stacking was used to form and determine firn depths and unstacked diffraction analysis to determine firn layer properties refractive indices range from 4 1 to 4 5 for the near surface from 1 7 to 2 1 at about 13 17 m depth along the main trunk and to 2 6 to 58 m depth within a snowfield average trunk values correspond with volumetric water contents of about 0 09 which agree with values measured for other glaciers the analysis of the airborne recorded diffractions is confirmed by deriving the approximate refractive index of water from a supraglacial lake bottom diffraction the lack of snowfield diffractions suggests that crevassing and not firn structure caused the trunk diffractions the reasonable values of the indices imply that the diffractions originated from single points or edges orthogonal to the profile transect and they predict low interlayer transmission losses the snowfield penetration suggests that several hundred meters might be penetrated in uncrevassed accumulation zones with improved system design

estimation of the total electron content of the martian ionosphere using radar sounder surface echoes 1 the martian ionosphere s local total electron content tec and the neutral atmosphere scale height can be derived from radar echoes reflected from the surface of the planet we report the global distribution of the tec by analyzing more than 750 000 echoes of the mars advanced radar for subsurface and ionospheric sounding marsis this is the first direct measurement of the tec of the martian ionosphere the technique used in this paper is a novel transmission mode sounding of the ionosphere of mars in contrast to the active ionospheric sounding experiment ais on marsis which generally operates in the reflection mode this technique yields a global map of the tec for the martian ionosphere the radar transmits a wideband chirp signal that travels through the ionosphere before and after being reflected from the surface the received waves are attenuated delayed and dispersed depending on the electron density in the column directly below the spacecraft in the process of correcting the radar signal we are able to estimate the tec and its global distribution with an unprecedented resolution of about 0 1 deg in latitude 5 km footprint the mapping of the relative geographical variations in the estimated nightside tec data reveals an intricate web of high electron density regions that correspond to regions where crustal magnetic field lines are connected to the solar wind our data demonstrates that these regions are generally but not exclusively associated with areas that have magnetic field lines perpendicular to the surface of mars as a result the global tec map provides a high resolution view of where the martian crustal magnetic field is connected to the solar wind we also provide an estimate of the neutral atmospheric scale height near the ionospheric peak and observe temporal fluctuations in peak electron density related to solar activity

polar radar for ice sheet measurements prism abstract we provide an overview of a project to develop and demonstrate radars for imaging the ice bed interface mapping shallow and deep internal layers and measuring ice thickness we developed an ultra wideband very high frequency vhf radar 120 to 300 mhz for simultaneously measuring ice thickness mapping internal layers at depth and imaging the ice bed interface and an ultra high frequency uhf ultra wideband radar 500 to 2000 mhz for fine resolution mapping of near surface internal layers we used these radars to collect data at summit camp greenland during july 2005 and the west antarctic ice sheet wais deep drill core site during january 2006 these results provide us with an unprecedented view of basal characteristics and internal layers we also developed an outreach program a communications system and rovers to facilitate geophysical measurements in the future

stratigraphy structure and geochronology of the las canadas caldera tenerife canary islands after a long period of subaerial fissure fed extrusions of basaltic magmas 12 to 3 ma volcanic activity was then concentrated in the central part of tenerife phonolitic magma chambers formed and a central volcanic complex was constructed the las canadas edifice the formation of a large depression the las canadas caldera truncated the top of the edifice the active twin strato cones teide pico viejo are sited in this depression the history of the las canadas caldera and edifice are established from stratigraphy geochronology k ar dates and volcanological studies two different groups are recognized separated by a major unconformity the lower group is dated at 2 to 3 ma and includes the products of several volcanic centres which together represent several cycles the upper group ranges from 1 56 to 0 17 ma and includes three different formations representing three long term 100 to 300 ka volcanic cycles the periods of dormancy between each formation were of 120 to 250 ka duration the las canadas caldera is a multicyclic caldera which formed over the period 1 18 0 17 ma each cycle of activity represented by a formation culminated in caldera collapse which affected different sectors of the las canadas edifice geological observation and geochronology support an origin by collapse into a magma chamber the minimum volume of pyroclastic ejecta is substantially greater than the present caldera depression volume 45 km3 but approaches the inferred volume of the original caldera depression 140 km3 after the formation of the caldera sector collapses could also occur at the northern flank of the volcano causing the disappearance of the northern side of the caldera wall

reconstruction of subduction and back arc spreading in the nw pacific and aleutian basin clues to causes of cretaceous and eocene plate reorganizations the eocene 50 45 ma major absolute plate motion change of the pacific plate forming the hawaii emperor bend is thought to result from inception of pacific plate subduction along one of its modern western trenches subduction is suggested to have started either spontaneously or result from subduction of the izanagi pacific mid ocean ridge or from subduction polarity reversal after collision of the olyutorsky arc that was built on the pacific plate with ne asia here we provide a detailed plate kinematic reconstruction of back arc basins and accreted terranes in the northwest pacific region from japan to the bering sea since the late cretaceous we present a new tectonic reconstruction of the intraoceanic olyutorsky and kronotsky arcs which formed above two adjacent oppositely dipping subduction zones at 85 ma within the north pacific region during another pacific wide plate reorganization we use our reconstruction to explain the formation of the submarine shirshov and bowers ridges and show that if marine magnetic anomalies reported from the aleutian basin represent magnetic polarity reversals its crust most likely formed in an 85 to 60 ma back arc basin behind the olyutorsky arc the olyutorsky arc was then separated from the pacific plate by a spreading ridge so that the 55 to 50 ma subduction polarity reversal that followed upon olyutorsky ne asia collision initiated subduction of a plate that was not the pacific hence this polarity reversal may not be a straightforward driver of the eocene pacific plate motion change whose causes remain enigmatic

radar sounding evidence for buried glaciers in the southern mid latitudes of mars lobate features abutting massifs and escarpments in the middle latitudes of mars have been recognized in images for decades but their true nature has been controversial with hypotheses of origin such as ice lubricated debris flows or glaciers covered by a layer of surface debris these models imply an ice content ranging from minor and interstitial to massive and relatively pure soundings of these deposits in the eastern hellas region by the shallow radar on the mars reconnaissance orbiter reveal radar properties entirely consistent with massive water ice supporting the debris covered glacier hypothesis the results imply that these glaciers formed in a previous climate conducive to glaciation at middle latitudes such features may collectively represent the most extensive nonpolar ice yet recognized on mars

radar soundings of the subsurface of mars the martian subsurface has been probed to kilometer depths by the mars advanced radar for subsurface and ionospheric sounding instrument aboard the mars express orbiter signals penetrate the polar layered deposits probably imaging the base of the deposits data from the northern lowlands of chryse planitia have revealed a shallowly buried quasi circular structure about 250 kilometers in diameter that is interpreted to be an impact basin in addition a planar reflector associated with the basin structure may indicate the presence of a low loss deposit that is more than 1 kilometer thick