deep seismic structure of the seismogenic plate boundary in the off sanriku region northeastern japan we determined the deep seismic structure of the seismogenic plate boundary zone of off sanriku the northern part of the japan trench inner slope area travel time data from aftershocks of the 1994 far off sanriku earthquake m 7 5 recorded both by ocean bottom seismographs and the local land seismic network enable us to image the three dimensional seismic velocity structure of the region along the plate boundary there exists a p wave low velocity layer of ca 7 km s 1 and with thickness 10 km as the topmost layer of the subducting pacific plate the present analysis indicates that this layer interpreted as the subducting oceanic crust continues without any velocity variations at least down to ca 40 km depth in the overriding plate we found a zone of considerable high p wave velocity ca 8 km s 1 between the pacific coastal line of the northeastern japan arc at the longitude of 142 5 e this manifests that the trenchward toe of the mantle wedge has significantly higher velocity than that beneath the land area of the arc the landward limit of the high p wave velocity toe corresponds to the down dip limit of the seismogenic plate boundary further to the east the p wave velocity is ca 6 km s 1 the structure image obtained indicates that the nature of the overriding plate is significantly different along the plate boundary in the eastern half of the seismogenic zone the island arc crust and subducting oceanic crust are in contact with each other whereas the high velocity mantle wedge makes up the hanging wall of the deeper part of the seismogenic zone

precise p and s wave velocity structures in the kitakami massif northern honshu japan from a seismic refraction experiment the kitakami massif which is located in the eastern part of northern honshu japan is composed of two geological units the northern kitakami terrane is characterized as a jurassic accretionary complex while the southern kitakami terrane consists of pre silurian basement and silurian lower cretaceous marine sediments the boundary region of these two units called the hayachine tectonic belt htb is composed of mafic to ultramafic rocks the kitakami massif experienced intense granitic intrusions in the cretaceous we present a detailed crustal structure model for the eastern part of the massif derived from an extensive seismic refraction experiment conducted on a 194 km n s line the uppermost crust is covered with a very thin 0 5 1 km surface layer with a velocity of 3 1 5 4 km s the velocity structure below this layer shows remarkable lateral variation in the northern kitakami terrane the p wave velocity and vp vs at the top of the basement are 5 85 5 95 km s and 1 68 1 70 respectively the seismic attenuation in this region is high qp 150 200 and qs 70 100 in contrast the uppermost crust in the southern kitakami terrane is characterized by a high p wave velocity 6 05 6 15 km s and vp vs 1 74 1 77 the qp and qs also show high values of 300 400 and 150 200 respectively such a structural difference persists to 14 to 16 km depth at which the p wave velocity increases to 6 45 km s the low velocity and high attenuation in the northern kitakami terrane represent a highly deformed structure of the accretionary complex the high p wave velocity and vp vs in the southern kitakami terrane indicate the relatively mafic crustal composition which may result from the fragment of the oceanic crust incorporated by the accretion process or the uplifting in the latest jurassic early cretaceous a midcrustal interface determined from wide angle reflections shows an abrupt southward depth decrease from 25 to 20 km under the htb the p wave velocity and vp vs between 14 and 16 km depth and the midcrustal interface are 6 45 6 55 km s and 1 74 1 78 respectively the moho depth under the northern kitakami terrane decreases southward from 34 to 32 km in the southern kitakami terrane the moho dips slightly southward the p wave velocity and the vp vs ratio in the lower crust are 6 9 7 0 km s and 1 75 1 76 respectively the p wave velocity in the uppermost mantle is not well resolved but is probably less than 7 7 km s the s wave velocity derived from relatively clear sn is 4 35 4 40 km s our results show that the htb is a prominent structural boundary extending to the moho the crust of kitakami massif was not homogenized by the cretaceous granitic intrusions and the original structural difference remains in the upper crust

tomographic imaging outside a seismic network application to the northeast japan arc the conventional local tomography can determine the 3d seismic velocity structure right beneath a seismic network but it cannot determine the 3d structure outside a seismic network in this study we show that such a limitation of tomography can be overcome if many earthquakes occur outside a seismic network in the northeast japan arc earthquakes occur actively from the japan trench to the pacific coast we detected and used sp depth phase to relocate the suboceanic earthquakes accurately and then used p and s wave arrival times from the relocated suboceanic events and the earthquakes under the northeast japan land area to determine the 3d p and s wave velocity and poisson s ratio structures of the entire northeast japan arc from the japan trench to the japan sea coast our results exhibit strong lateral heterogeneities under the forearc region the mainshock hypocenters of large interplate earthquakes m 7 0 8 2 mainly cluster near the boundaries of high and low velocity and poisson s ratio above the subducting pacific slab a few large earthquakes are located in areas with high velocity and low poisson s ratio these results suggest that lateral heterogeneities on the slab boundary can affect the rupture nucleation of large thrust earthquakes and the degree of interplate seismic coupling

spatial distribution of focal mechanisms for interplate and intraplate earthquakes associated with the subducting pacific plate beneath the northeastern japan arc a triple planed deep seismic zone the northeastern japan arc is located in one of the most seismically active subduction zones in the world in this study we relocated hypocenters and determined focal mechanisms of small earthquakes m 5 beneath the arc in order to investigate in detail the stress distribution in and around the descending oceanic plate in the hypocenter relocation we adopted a source region station correction method in which station corrections vary with hypocenter locations we have developed a new focal mechanism determination technique named master solution method which is analogous to the master event method in hypocenter determination we applied the method to p and sh wave amplitude data to obtain 1106 focal mechanism solutions from the new mechanism solutions and relocated hypocenters we found that there occur both low angle thrust fault lt type and downdip compression dc type earthquakes at depths from 40 to 70 km near the aseismic front the dc type events are underlying the lt type events almost all the earthquake clusters are composed of lt type events the western limit of the region where lt type events have occurred is subparallel to the trench axis although it undulates considerably it delineates the westernend of the active region of interplate seismicity furthermore we found that normal fault nf type events also occur at depths from 70 km in the upper plane of the double planed deep seismic zone which is characterized mainly by dc type event these nf type events are distributed only in a thin uppermost portion of the slab close to the plate boundary below these in the lower plane are downdip extension de type events this result indicates that the deep seismic zone in the northeastern japan arc is not double planed but triple planed even beneath the land area which cannot be explained by any simple models

salt weathering simulation using a single immersion technique samples of concrete were subjected in an environmental cabinet to six different diurnal cycles of temperature and humidity change representative of desert surface conditions in the presence of a range of saturated salt solutions the samples were not subjected to repeated immersion or continuous partial immersion as has been the case in most previous experiments breakdown did occur nonetheless the two most effective cycles were one from egypt with a very high daytime maximum and one from the negev with high nocturnal humidity conditions cycles with relatively modest temperature and humidity cycles were ineffective in causing debris liberation

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

seismic imaging of arc magma and fluids under the central part of northeastern japan abstract a dense seismic network was temporarily deployed during 1997 1999 in the central part of northeastern japan by japanese university research groups using the local earthquake arrival time data recorded by the network we have determined high resolution three dimensional images of p wave velocity vp s wave velocity vs and vp vs ratio in this area our results show that low vp low vs and high vp vs areas are extensively distributed in the uppermost mantle along the volcanic front in the lower crust low vp low vs and high vp vs areas are visible but they are confined to the individual volcanic areas in contrast the upper crust of volcanic areas shows low vp low vs and low vp vs rather than high vp vs these observations suggest that partial melting materials exist in the uppermost mantle along the volcanic front and they spread up to the midcrust of the volcanic areas low vp low vs and low vp vs in the upper crust of the volcanic areas suggest the presence of h2o rather than melt there deep low frequency microearthquakes perhaps caused by the rapid movement of fluids are located mostly at the edge of partial melting zones particularly at their upper surface distinct s wave reflectors bright spots with large reflection coefficients are distributed in the midcrust with slightly low vp vs suggesting that most of them are filled with h2o

p wave tomographic imaging of the crust and upper mantle beneath the japan islands more than 50 000 high accuracy arrival times from 1200 shallow and deep earthquakes selected from the japan university network earthquake catalog are used to investigate the three dimensional 3 d seismic velocity structure beneath japan travel times and ray paths are accurately calculated by using an efficient 3 d ray tracing technique p wave tomographic images of the crust and upper mantle to a depth of 500 km beneath the japan islands are determined with spatial resolutions of 25 50 km the obtained p wave velocity in the crust and uppermost mantle is slightly higher and relatively homogeneous in western japan in contrast with an average lower velocity and a large heterogeneity in eastern japan where many active volcanoes exist this feature correlates well with the distributions of heat flow and gravity anomalies low velocity low v zones are imaged in the crust and uppermost mantle beneath active volcanoes the low v zones in the mantle wedge dip toward the west and extend continuously to a depth of about 200 km a high velocity high v zone corresponding to the subducted pacific plate is delineated the thickness of the high v zone is estimated to be 80 90 km in southwestern japan the descending philippine sea plate is also delineated its thickness is estimated to be 30 km

rock warming and drying under simulated intertidal conditions part ii weathering and biological influences on evaporative cooling and near surface micro climatic conditions as an example of biogeomorphic ecosystem engineering the way in which rocks and engineering materials heat up and dry out in the intertidal zone is of relevance to both weathering and ecology these behaviours can be measured in the laboratory under controlled conditions designed to replicate those occurring in the field previous studies have demonstrated differences in thermal behaviours between rock types and through time as a result of soiling in terrestrial environments but the influence of weathering and colonization on rock behaviours in the intertidal zone has not been previously assessed we measured the warming and drying of blocks of rock limestone and granite and marine concrete during low tide events simulated in the laboratory before and after a period of exposure eight months on rock platforms in cornwall uk as well as differences between the material types temperatures of control unexposed and field exposed blocks differed in the order of 1 to 2 c drying behaviours were also different after field exposure differences during the first few hours of exposure to air and heat were attributed to discolouration and albedo effects over longer periods of time changes in the availability of near surface pore water as a result of micro scale bioerosion of limestone and the development of bio chemical crusts on marine concrete observed using scanning electron microscopy sem are suggested as mechanisms enhancing and reducing respectively the efficiency of evaporative cooling the retention of moisture by epilithic biofilms may also influence thermal and drying behaviours of granite these observations represent one of the first examples of cross scalar biogeomorphic linkages in the intertidal zone the significance of the results for the subsequent efficiency of weathering and near surface micro climatic conditions experienced by colonizing organisms is discussed the involvement of microorganisms in the creation of more or less ecologically stressful conditions through the alteration of substratum geomorphic properties and behaviours is suggested as an example of biogeomorphic ecosystem engineering copyright 2011 john wiley sons ltd

seismic anisotropy in the uppermost mantle back arc region of the northeast japan arc petrophysical analyses of ichinomegata peridotite xenoliths 1 a dense network of seismic stations has been deployed across the northeast japan arc to investigate mantle wedge structures to attain independent petrophysical constraints we determined the seismic properties of ichinomegata mantle xenoliths from the back arc region that were brought to the surface from the mantle lithosphere by volcanic eruptions we calculated the seismic properties of the xenoliths from olivine and pyroxene crystal preferred orientations and single crystal elastic constants the small magnitude of measured s wave splitting delay time of 0 22 s in the area where the xenoliths were entrained can be explained by the average seismic properties of mantle xenoliths for an approximately 20 km thick horizontal anisotropic layer indicating that the mantle lithosphere could be one of the dominant sources of seismic anisotropy this layer is possibly related to deformation in the uppermost mantle lithosphere due to back arc spreading along the northeast japan arc

morphology of the subducting slab boundary in the northeastern japan arc abstract the detection and location of the subducting slab boundary is crucial for a better understanding of the mechanical coupling between the subducting oceanic plate and the overlying continental plate and of the occurrence of large and destructive earthquakes on the main thrust zone in the forearc region of subduction zones it is also important for the understanding of the dehydration of the subducting slab and the genesis of island arc magmatism and volcanism in this study we have estimated the morphology of the upper surface of the subducting pacific plate under northeastern ne japan by using 1372 sp converted waves at the slab boundary and 666 earthquakes beneath the pacific ocean that are well located with sp depth phases we found that the pacific slab beneath ne japan subducts at a small dip angle of less than 10 for the first descent to about 20 km depth and has a steeper dip angle of 15 25 at 30 50 km depth and about 30 at deeper areas the slab depth is approximately 50 km under the pacific coast 150 km under the japan sea coast and nearly 100 km beneath the volcanic front at 60 150 km depths earthquakes in the lower plane of the double seismic zone occur in the central part of the slab while the upper plane events occur within 10 15 km beneath the slab boundary there is a change in the slab surface geometry around 38 n which corresponds to the landward extension of an oceanic fracture zone the strike of the slab is nne in the north and becomes ne in the south the southern part of the slab has a steeper dip angle than the northern part we believe that these features are related to the different patterns of interplate seismicity and mechanical coupling between the northern and southern parts of ne japan many great m8 0 8 5 interplate earthquakes have occured in northern ne japan during recorded history 830 1995 and microearthquakes show a wide distribution in the forearc region from the japan trench to the pacific coast suggesting strong interplate seismic coupling in that region in contrast only a few m7 0 7 5 class earthquakes have occurred in southern ne japan in the same period and microearthquakes tend to cluster in many small areas suggesting weaker interplate coupling there the subducted slab may be segmented by the oceanic fracture zones and the degree of seismic coupling changes from segment to segment the behavior of the segment in southern ne japan might be affected by the subducted seamounts so that the slab subducts at a steeper dip angle this interpretation is supported by geomagnetic topographic and geological studies which show that many small sized seamounts were subducted in the past from the southern part of the japan trench but almost no seamounts were subducted beneath the northern part

seismic structure of the northeastern japan convergent margin a synthesis many studies recently made on the basis of seismic observations have revealed a detailed structure of the crust and the upper mantle beneath the northeastern japan arc and its relationship to seismic and volcanic activity spatial distributions of the depths to the conrad and the moho discontinuities estimated from shallow earthquake data and seismic explosion data show that both discontinuities are deep in the middle of the land area and shallow toward the coastlines of the japan sea and the pacific ocean the pn velocity has a lateral variation it is as low as 7 5 km s beneath the land area while that beneath the japan sea and the pacific ocean is 8 0 8 2 km s it changes abruptly at the transition zones which are located along the coastlines precise structure and location of the subducted pacific plate beneath the land area is inferred from converted or reflected seismic waves at the top or bottom of the plate the pacific plate is composed of a thin 5 km low velocity upper layer and a thick high velocity lower layer its total thickness being 80 90 km the upper plane seismicity of the double seismic zone is confined to the thin low velocity upper layer which probably corresponds to the subducted former oceanic crust the lower plane seismicity lies at the middle of the high velocity lower layer and the lower half of the plate below it is incapable of generating earthquakes the shallower portion of the upper surface of the plate beneath the pacific ocean along which major seismicity with low angle thrust faultings is actually occurring is also located by seismic observations on land and in the sea the pacific plate subducts at an extremely low angle of 5 for the first 25 km depth and then the dip steepens rather abruptly to 30 normal fault type events at the top of the plate have not been detected in the portion where the downward bending is the largest but have been ditected near the trench axis where it is rather small tomographic inversions for seismic velocity structure clearly delineate the inclined high velocity pacific plate with a thickness of 80 90 km and low velocity zones in the crust and the mantle wedge beneath active volcanoes seismic attenuation tomography also shows similar zones of low q value beneath active volcanoes although its spatial resolution is much lower the low velocity zones with 2 6 velocity lows are continuously distributed from the upper crust just beneath active volcanoes to a depth of 100 150 km in the mantle wedge and are approximately parallel to the dip of the underlying pacific plate these low velocity zones probably reflect the pathway of magma ascent from a depth in the mantle wedge to the earth s surface corresponding to a portion of the subduction induced secondary mantle wedge flow

gypsum formation in non calcareous building sandstone a case study of scrabo sandstone this paper addresses one central issue of building stone research an origin for calcium in gypsum formation in non calcareous sandstones a comparative study of scrabo sandstone from outcrops and a 120 year old building in central belfast shows how weathering has significantly altered the mineralogy preliminary results suggest that the occurrence of gypsum throughout the stone blocks is related to chemical reactions between a pore filling mineral constituent actinolite ca mg amphibole and sulphur oxides from urban pollution these findings advocate an internal source of calcium for gypsum formation and provide new evidence to explain the enhanced decay displayed in some scrabo sandstone copyright 2001 john wiley sons ltd

the nature and pattern of debris liberation by salt weathering a laboratory study a laboratory simulation of salt weathering was used to ascertain the effects of sodium sulphate and sodium carbonate under negev conditions using a single immersion technique three main points were addressed what are the grain size and textural characteristics of the debris liberated from limestones and a sandstone what do scanning electron microscope observations of the weathered samples tell us about the decay processes involved and how does the rate of debris liberation change during the course of 100 cycles the grain size characteristics of the liberated debris tended to be multimodal and were related to the original petrological characteristics of the rock large amounts of fines were produced which are believed to be analogous to the rock flour of arid areas blistering was also observed scanning electron microscope analysis revealed differences in the style of attack for different rock types and salt treatments and revealed the pattern of salt crystallization in pores and the nature of cracking the rate of debris liberation tended to decline or remain constant through time the reasons for this remain obscure but it is evident that diurnal cycles of temperature and humidity change can cause continuing rock weathering long after the initial input of salt to the rock has taken place

deep low frequency microearthquakes in or around seismic low velocity zones beneath active volcanoes in northeastern japan abstract precise hypocenter relocations have been made for shallow intraplate microearthquakes beneath northeastern japan by applying source region station corrections the relocated hypocenter distribution shows that most of the events are confined to the upper 15 km of the crust which forms the brittle seismogenic zone in this volcanic arc it also shows that exceptionally deep microearthquakes well below the base of the seismic aseismic boundary occur at twelve locations of northeastern japan they occur in the lowermost crust or in the uppermost mantle where rheological properties of rocks are presumed to be in the ductile regime all the 153 events presently detected in the lowermost crust or in the uppermost mantle have anomalously low predominant frequencies 1 5 5 hz both for p and s waves in contrast to those 8 20 hz of normal shallow events in the brittle seismogenic zone the magnitudes of these events are small m 2 2 moreover all of these events are located beneath active volcanoes and or near p wave low velocity zones in the uppermost mantle the proximity of these events to the active volcanoes and other anomalous features suggest that these deep low frequency events are generated by magmatic activity of mantle diapirs in the uppermost mantle

end permian to mid triassic termination of the accretionary processes of the southern altaids implications for the geodynamic evolution phanerozoic continental growth and metallogeny of central asia the altaids is one of the largest accretionary orogenic collages in the world with the highest rate of phanerozoic continental growth and significant metallogenic importance it is widely accepted that subduction related orogenesis of the altaids started in the late precambrian and gradually migrated southward present coordinates however it is uncertain when and how the building of the altaids was finally completed based on structural geology geochemical geochronological and paleomagnetic data this paper presents late paleozoic to early mesozoic accretionary tectonics of two key areas north xinjiang in the west and inner mongolia in the east together with neighboring mongolia the late paleozoic tectonics of north xinjiang and adjacent areas were characterized by continuous southward accretion along the wide southern active margin of siberia and its final amalgamation with the passive margin of tarim which may have lasted to the end permian to early mid triassic in contrast in inner mongolia and adjacent areas two wide accretionary wedges developed along the southern active margin of siberia and the northern active margin of the north china craton which may have lasted to the mid triassic the final products of the long lived accretionary processes in the southern altaids include late paleozoic to permian arcs late paleozoic to mid triassic accretionary wedges composed of radiolarian cherts pillow lavas and ophiolitic fragments and high pressure ultrahigh pressure metamorphic rocks permian alaskan type zoned mafic ultramafic complexes intruded along some major faults of the tien shan we define a new tarim suture zone immediately north of the tarim craton that is probably now buried below the tien shan as a result of northward subduction of the tarim block in the cenozoic the docking of the tarim and north china cratons against the southern active margin of siberia in the end permian to mid triassic resulted in the final closure of the paleoasian ocean and terminated the accretionary orogenesis of the southern altaids in this part of central asia this complex geodynamic evolution led to formation of giant metal deposits in central asia and to substantial continental growth

lithium boron and lead isotope and trace element systematics of quaternary basaltic volcanic rocks in northeastern japan mineralogical controls on slab derived fluid composition abstract across arc li b pb isotope systematics together with trace element geochemistry and phase relationships in subducting slabs are used to understand the petrogenesis of lavas from the northeastern japan arc pb nb ratios and pb isotope compositions of the arc lavas decrease with depth to slab whereas li y u nb th nb and la sm show an upward profile across the arc with peaks at 180 km depth to the wadati benioff zone wbz the peaks in these profiles may reflect the influence of lawsonite breakdown in the slab at 180 km depth b nb ratios of the arc lavas do not show clear across arc variation and the 11b values show a concave upward across arc profile with minimum values at around 180 km in depth of the wbz these results possibly reflect the decomposition of tourmaline at 180 km our results suggest that accessory minerals and minor phases in the subducting slab play important roles in determining the chemical compositions of fluid released by dehydration and the resulting trace element and isotope composition of arc lavas li isotope compositions of the lavas are morb like and do not show systematic across arc variation contrasting with izu arc lavas which show maximum 7li values at the volcanic front and a systematic decrease towards the back arc the strikingly different results for the northeastern japan arc and the izu arc are likely to be caused by differing extents of li isotope fractionation due to differing subduction zone physical characteristics such as thermal structure of the subducting slab and subduction angle thus not only chemical characteristics of the subducting slab but also the physical as well as chemical characteristics of the subduction zone could affect the li isotope compositions of subducting slabs producing heterogeneity in the li isotope composition of the mantle

three dimensional structure of vp vs and vp vs beneath northeastern japan implications for arc magmatism and fluids we estimated both p v p and s wave velocity v s structures beneath northeastern japan by applying a tomographic method to 169 712 p and 103 993 s wave arrival time data from 4338 local events the average value of v p v s ratio is 1 69 in the upper crust 1 75 in the lower crust and 1 77 in the uppermost mantle these differences in v p v s ratio may mainly reflect the lithological variations with depth low v p low v s and high v p v s zones are extensively distributed along the volcanic front in the uppermost mantle and are downward to the back arc side in the mantle wedge here the low v p low v s and high v p v s values are interpreted because of partial melting materials which imply the presence of a vast amount of melt in the uppermost mantle in the lower crust low v p low v s and high v p v s zones are not continuously visible along the volcanic front but are confined to individual volcanic areas which suggests that melting of lower crustal materials occurs just beneath each active volcano in contrast the upper crust beneath active volcanoes exhibits low v p low v s and low v p v s these results suggest that the partial melting zones under northeastern japan spread out from the uppermost mantle along the volcanic front up to the midcrust right beneath active volcanoes the low v p low v s and low v p v s features in the upper crust suggest the existence of h 2 o rather than melt right beneath active volcanoes

in situ weathering rind erosion abstract the use of cosmogenic nuclide dating methods place in doubt the long term future of weathering rinds wrs as a chronometric tool why estimate ages when radiometric control is possible this paper presents evidence that wrs can provide invaluable clues about what particular sample would provide the most accurate cosmogenic age by avoiding inheritance of cosmogenic nuclides and by avoiding boulders undergoing spalling the key to this new use requires testing the occurrence and nature of wr erosion back scattered electron microscopy reveals that ignimbrite andesite basalt and granitic clasts experience wr erosion in all subsurface and surface contexts thus far studied in arizona california hawaii oregon and washington to understand the magnitude of wr erosion we measured wr thicknesses all while controlling the cosmogenic and surface stability ages of clasts by chlorine 36 and rock varnish microlamination dating methods our data reveal that traditional methodologies of sampling cobbles remove two thirds of the true thickness of weathering rinds calling into question many beliefs including the notion that clay minerals are not produced during weathering rind formation comparisons of optical and electron microscope measurements support concerns that measurement of wrs by color changes while useful as a pedagogical tool creates serious biases in underestimating the true dynamics of wrs in the end we found that concordance of wr and rock coating age trends indicates the ideal boulder for cosmogenic nuclide dating offsets reveal either ongoing boulder erosion invalidating zero erosion model ages or a potential problem with inheritance of cosmogenic nuclides

an automatic processing system for broadcasting earthquake alarms in japan most of the damage caused by large earthquakes is concentrated within areas less than about 100 km from the focal regions we have developed an earthquake alarm system that determines earthquake parameters within a few seconds of the p wave s arrival at the closest station and then transmits the earthquake information before the s wave arrival in areas of possible serious earthquake damage since an earthquake alarm system requires the determination of reliable earthquake parameters as quickly as possible it is unreasonable to wait until waveform data from numerous stations have been collected for analysis for this reason we have developed a novel method of determining the hypocentral location by using the arrival times for only a few stations as well as the lack of p wave arrivals at other stations at a given time the use of not yet arrived data makes it possible not only to determine reliable hypocenter parameters within a few seconds but also to detect erroneous arrival time readings and remove them automatically since the available waveform data increases with time the system was designed to redetermine earthquake parameters every second our method was deployed in a real time system starting in july 2002 the real time system locates 10 20 events per day which includes a few felt earthquakes occurring in and around japan it was shown from the waveform data for about 100 felt earthquakes that almost all the events except those far from the network could be located within a few seconds when most of seismic energy has not even arrived at some stations close by we recently started widespread broadcasting of earthquake information in real time by using a satellite transmission system

pn travel time tomography of the paleo continental collision and rifting zone around korea and japan abstract a recent dense deployment of seismic stations in south korea and japan allows regional seismic imaging of the far east asian region that experienced continental collisions and riftings we perform seismic imaging based on a mantle lid p wave pn travel time tomography to exploit the tectonic imprints in the lithosphere the average pn velocity in the region is estimated to be 7 95 0 03 km sec the inverted pn velocities illuminate the tectonic structures high velocities of 8 15 km sec are observed in the precambrian massif regions while low velocities of 7 8 km sec are associated with the fold belt and sedimentary basin regions in the southern korean peninsula the pn velocity is estimated to be low in the backarc basins including the ulleung and the yamato basins while it is estimated to be higher on the continental fragments including the south korea plateau and the oki bank the high velocity structures along the japanese islands support the separation of the japanese province from the eurasia plate the high velocity anomaly along the east coast of the korean peninsula around the hupo bank suggests intrusion and solidification of high density material in the lower crust and mantle lid

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

hot fingers in the mantle wedge new insights into magma genesis in subduction zones abstract quaternary volcanoes in the northeast japan arc can be grouped into 10 volcanic clusters striking transverse to the arc these have an average width of 50 km and are separated by parallel gaps 30 75 km wide this clustering of volcanic centres topographic profiles low velocity regions in the mantle wedge and local negative bouguer gravity anomalies along the japan sea side of the volcanic arc are closely correlated all these observations may be related to locally developed hot regions within the mantle wedge that have the form of inclined 50 km wide fingers each of the 10 fingers recognised extends from deep mantle 150 km below the back arc region towards the shallower mantle 50 km beneath the volcanic front quaternary volcanoes are built immediately above the hot mantle fingers the volcanic basement along the fingers has been uplifted by repeated injection of magmas into the crust accompanied by quaternary volcanic activity at the surface although volcanic activity is rare along the japan sea coast tomographic results show that hot low velocity mantle fingers exist within the mantle wedge the negative bouguer anomalies at the rear of the volcanic arc could be caused by magmas supplied from the hot mantle fingers these have not yet been erupted but have accumulated at the moho discontinuity

salt weathering and experimental desalination treatment of building sandstone sydney australia local sandstone used in nineteenth century buildings in sydney has been affected by salt weathering and surface crust formation this study trialled two approaches namely washing and vacuuming and poulticing to salt removal treatment of weathered sandstone blocks from the sydney hospital and australian museum both treatments removed solutes from the stones in laboratory tests icp titration of sampled scrapings at depths of 0 2 2 5 and 50 mm showed substantial between sample variation with no significant difference being recorded in solute levels after treatment mann whitney u test except for sulfur and sodium sulfur levels increased at the surface 0 2 mm following washing and vacuuming but not poulticing for the hospital and museum samples sodium levels increased at the surface 0 2 mm following poulticing but not washing and vacuuming for the hospital samples the presence of surface crusts may have contributed to some of the variation in desalination responses

above the weathering front contrasting approaches to the study and classification of weathered mantle abstract weathered mantle comprises the materials above bedrock and below the soil it can vary in thickness from millimeters to hundreds of meters depending primarily on climate and parent material study of the weathered mantle comes within the realms of four disciplines geology geomorphology soil science and civil engineering each of which uses a different approach to describe and classify the material the approaches of engineers geomorphologists and geologists are contrasted and compared using example papers from the published literature soil scientists rarely study the weathering profile as such and instead concentrate upon soil forming processes and spatial distribution primarily in the solum engineers including engineering geologists study the stability and durability of the weathered mantle and the strength of the materials using sophisticated procedures to classify weathered materials but their approach tends to be one dimensional furthermore they believe that the study of mineralogy and chemistry is not useful geomorphologists deal with weathering in terms of process how the weathered mantle is formed and with respect to landform evolution using a spatial approach geologists tend to ignore the weathered mantle because it is not bedrock or to study its mineralogy and or chemistry in the laboratory i recommend that the approaches of the various disciplines be integrated geomorphologists and geologists should consider using engineering weathering classifications and geologists should adopt a spatial perspective to weathering as should engineers and engineering geologists

mapping the crustal thickness in shillong mikir hills plateau and its adjoining region of northeastern india using moho reflected waves abstract in this study we have tried to detect and collect later phases associated with moho discontinuity and used them to study the lateral variations of the crustal thickness in shillong mikir hills plateau and its adjoining region of northeastern india we use the inversion algorithm by nakajima et al nakajima j matsuzawa t hasegawa a 2002 moho depth variation in the central part of northeastern japan estimated from reflected and converted waves physics of the earth and planetary interiors 130 31 47 having epicentral distance ranging from 60 km to 150 km taking the advantage of high quality broadband data now available in northeast india we have detected 1607 moho reflected phases pmp and sms from 300 numbers of shallow earthquake events depth 25 km in shillong mikir hills plateau and its adjoining region notably for pmp phase this could be identified within 0 5 2 3 s after the first p arrival in case of sms phase the arrival times are observed within 1 0 4 2 s after the first s arrival we estimated the crustal thickness in the study area using travel time difference between the later phases pmp and sms and the first p and s arrivals the results shows that the moho is thinner beneath the shillong plateau about 35 38 km and is the deepest beneath the brahmaputra valley to the north about 39 41 km deeper by 4 5 km compared to the shillong plateau with simultaneous observation of thinnest crust 33 km in the western part of the shillong plateau in the garo hills region

tomographic imaging of seismic velocity structure in and around the onikobe volcanic area northeastern japan implications for fluid distribution abstract we estimated three dimensional p vp and s wave velocity vs and vp vs structures in and around the onikobe volcanic area northeastern japan by local travel time tomography we used travel time data from source and receiver pairs located within and outside the study area which plays an important role in obtaining the optimum ray coverage and in elucidating the deeper structure more accurately detailed information on deeper structures is essential for imaging the complete volcanic system from the magmatic source zone through areas of shallow hydrothermal circulation more than 50 000 travel time data for the p waves and 35 000 for the s waves were used to image the velocity structure our results show the following dominant features 1 two conduits in the upper crust with low vp and low vs indicative of h2o rich fluid pathways one lying beneath naruko volcano the other beneath the focal area of the 1962 northern miyagi earthquake m6 5 2 an underlying broad region in the lower crust with low vp low vs and high vp vs suggestive of a zone of partial melt from which the fluids in 1 are derived and 3 low vp vs areas near the surface of the sanzugawa and onikobe calderas suggesting a diffuse vapor saturated cap

slab temperature and thickness from seismic tomography 2 izu bonin japan and kuril subduction zones delay times from teleseismic and local p wave arrivals are used to invert for a high resolution three dimensional velocity model beneath the northwest pacific the model shows high velocity slabs with average velocity anomalies of the order of 3 4 assuming the positive velocity deviations in the subducting lithosphere are to first order due to a temperature anomaly the results of a theoretical slab temperature profile based on the diffusion equation are converted to a synthetic slab velocity model temperature variations between the ambient mantle and the interior of the slab are converted to p wave velocity perturbations using dvp dt 4 8 10 4 km s 1 c 1 a nonlinear optimization scheme compares the tomograms obtained via tomography to the theoretically predicted models in order to determine the optimal values for slab thickness and mantle potential temperature using 1180 100 c as the potential temperature thickness estimates of 88 8 km 85 8 km and 84 8 km are obtained for the izu bonin japan and kuril slabs respectively a correlation exists between slab thickness and age which is strong if mantle temperature variations along the slab strike can be ruled out in the process of estimating slab thickness the predicted slab velocity model is used as a filter to enhance the initial minimum norm tomographic result the initial tomogram is modified to closely resemble the synthetic slab tomogram by using only null space components the use of the null space components guarantees that the enhanced solution will satisfy the original seismic delay times the enhanced slab images show very continuous and narrow slabs compared to the initial tomographic results

tomographic inversion for p wave velocity structure beneath the northeastern japan arc using local and teleseismic data we have determined three dimensional p wave velocity structure up to a depth of 296 km beneath northern tohoku honshu japan by inverting arrival times of local and teleseismic events simultaneously velocities in the upper crustal layers correlate well with the surface geology and bouguer gravity anomalies low velocity zones are ubiquitous in the crust and the uppermost mantle beneath the quarternary volcanic areas a well known feature of a pronounced low velocity mantle wedge underlain by the dipping high velocity high v pacific plate is generally recovered over the study area strong heterogeneity within the high velocity pacific plate is suggested by the presence of a pronounced low velocity anomaly confined to the depths of 130 200 km the decreased seismicity of intermediate focus events may be correlated with the low velocity zone a two dimensional inversion scheme was invoked to determine stably the average mantle structure perpendicular to the island arc in the depths of 50 150 km the inclined high v zone has a thickness of 80 100 km with its top coinciding with the upper plane of the double planed deep seismic zone below the depth of 200 km the high v zone is shifted toward the bottom of the 80 km thick reference slab in the intermediate depth layer 150 200 km the high v zone is not clearly visible within the 80 km thick reference slab

contour scaling of a sandstone by salt weathering under simulated hot desert conditions a laboratory study has been used to investigate relationships between salts and contour scaling a weathering feature commonly observed on rock surfaces in salt rich environments surface disaggregation and essentially surface parallel cracks were produced in sandstone blocks using 10 per cent solutions of sodium sulphate and magnesium sulphate applied daily to single exposed surfaces for sixty days a control block soaked once in saturated magnesium sulphate and subsequently wetted daily with distilled water showed extensive surface disaggregation but no cracking both surface disaggregation and subsurface cracking were associated with relative concentrations of microcrystalline salt a tentative model of contour scaling is proposed which involves linking together potential cracks by salt induced fracturing of intervening crack stopping grains further control blocks treated respectively with 10 per cent and saturated sodium chloride showed no evidence of subsurface cracking and only limited surface disaggregation of the saturated block

silica mobility and fluid movement during metamorphism of the connemara schists ireland quartz veins are developed in a wide range of metasediment types in the upper amphibolite facies rocks of connemara and attest to considerable migration of silica contrary to common assumptions there is clear evidence that these veins do not primarily result from movement of fluid to regions of lower p t down the regional geothermal gradient under amphibolite facies conditions a dilute chloride fluid moving down temperature has the potential to alter 60g of plagioclase to muscovite for each gram of vein quartz precipitated while cooling over the temperature interval from 650 to 500 c the absence of significant metasomatic effects in the vein walls effectively precludes a simple origin from such through flowing externally derived fluids the oxygen isotopic composition of matrix quartz shows considerable differences between different rock types quartzite pelite and marble with a range of 18osmow from c 11 5 quartzite to 18 5 marble in each rock type vein quartz compositions closely match those of the matrix quartz these results demonstrate the importance of local segregation processes in the formation of veins and suggest that fluid convection cells were not developed during metamorphism on a scale larger than the individual sedimentary formations if at all both oxygen isotope data and the absence of metasomatism indicate that veins form primarily by segregation of quartz from the host lithologies with only a relatively minor component of through flow of externally derived fluid veins are clearly not the major pathways of metamorphic dewatering it is proposed that abundant veins in the predominantly pelitic ballynakill formation formed during peak metamorphic d3 folding because the formation was embrittled by high fluid pressures but was capped by impermeable marble hence the pelitic formation fractured repeatedly and the pore fluid drained through the fractures to form veins while irreversible loss through the rest of the succession was a much less important process in the central mountains of connemara rather pure unreactive quartzites are cut by widely spaced laterally extensive quartz veins that are axial planar to d3 folds these veins may mark pathways whereby metamorphic fluid made its way through the massive impermeable quartzite from lower parts of the nappe pile but here too oxygen isotope data indicate considerable segregation of locally derived quartz reflecting the importance of pumping of fluid between wail rocks and fractures relative to the component of through flow

laboratory simulation of rock weathering by salt crystallization and hydration processes in hot arid environments the results of a series of experiments are reported in this paper which were designed to differentiate between the forces of crystal growth and hydration in salt weathering using a single salt hydrate system sodium sulphate five contrasting rock types and several diurnal temperature relative humidity cycles which permitted or inhibited these processes and simulated ground surface climates in hot arid environments it was shown that hydration of sodium sulphate is an effective mechanism of rock disintegration but that it is significantly less destructive than crystal growth pressure crystallization of thenardite na2so4 is in turn more effective in rock weathering than the crystal growth of mirabilite na2so4 10h2o in general rates of disintegration were most rapid where the diurnal temperature range was extreme and relative humidity lowest

modification of garnet by fluid infiltration during regional metamorphism in garnet through sillimanite zone rocks dutchess county new york metapelitic rocks from a progressive metamorphic sequence in dutchess county new york record evidence for reaction between garnet and fluids associated with quartz plagioclase veins and for net transfer among garnet interiors mineral inclusions and fluid garnet fluid reaction resulted in modification of preexisting garnet textures compositions and growth zoning patterns the textural and compositional record of garnet fluid interaction varies with grade and with proximity of garnet to quartz veins garnet zone rocks do not contain evidence for extensive reaction with vein forming fluids in upper stauroliteand kyanite zone rocks garnet that is crosscut by quartz veins contains a fluid inclusion filled region near the garnet vein interface this region truncates growth zoning patterns and quartz inclusions fluid inclusions in garnet decrease in abundance away from quartz veins in some rocks lacking quartz veins fluid inclusions are concentrated in garnet interiors and in particular near fractures and are notably lacking around mineral inclusions in garnet inferences from textural and compositional features combined with thermobarometric results indicate that preexisting garnet grains were modified at t 525 550 c and 4 kbar by one or more reactions involving fluids the fluid pathways included foliationparallel channels in the rock as well as microcracks in mineral grains

deep structure of arc volcanoes as inferred from seismic observations possible evidence for deep seated magmatic activity beneath the northeastern japan arc has been obtained from micro earthquake observations tomographic inversions for p wave velocity clearly delineate low velocity zones which are inclined to the west and continuously distributed from the uppermost mantle to the upper crust beneath active volcanoes exceptionally deep 22 40 km micro earthquakes are found at 10 locations around the low velocity zones beneath active volcanoes all these events have extremely low predominant frequencies suggesting a close relation to the magmatic activity in this depth range at shallower depths 8 15 km distinct reflectors of s waves from shallow events are found at five locations in or around the low velocity zones their locations and reflection coefficients suggest that the reflectors are very thin magma bodies existing in the mid crust these observations shed some light on the state of magma at depths beneath volcanic arcs

seismic activity and deformation process of the overriding plate in the northeastern japan subduction zone abstract we estimated the temperature distribution within the crust of the northeastern japan arc from p wave velocity perturbations obtained by travel time tomography by comparing the estimated temperature distribution with the focal depth distribution of shallow precisely relocated microearthquakes we found that the brittle to ductile or stick slip to stable sliding transition occurs at the 400 c isotherm and that the transition depth has considerable lateral variations the brittle seismogenic zone the upper portion of the crust becomes locally thin in the p wave low velocity areas where the temperature is estimated to be relatively high concentration of shallow microearthquakes high topography and relatively large contractile deformation of the crust are also observed in these low velocity areas active faults are not distributed in the low velocity areas but lie just along the edge of those areas or outside them all these observations suggest that earthquake occurrence and deformation within the crust is governed to a considerable degree by the thermal regime of this volcanic arc which is characterized by a horizontally inhomogeneous distribution of temperature

postseismic crustal deformation following the 1993 hokkaido nansei oki earthquake northern japan evidence for a low viscosity zone in the uppermost mantle 1 postseismic crustal deformation following the 1993 hokkaido nansei oki earthquake m 7 8 northern japan was observed by gps tide gauge and leveling measurements in southwestern hokkaido as a result of comprehensively analyzing these three kinds of geodetic data we found the chief cause of the postseismic deformation to be viscoelastic relaxation of the coseismic stress change in the uppermost mantle afterslip on the main shock fault and its extension by contrast cannot explain the deformation without unrealistic assumptions the viscoelastic structure which we estimated from the postseismic deformation consists of three layers an elastic first layer with thickness of 40 km a viscoelastic second layer with thickness of 50 km and viscosity of 4 1018 pa s and an elastic half space this model suggests the presence of an anomalously low viscosity zone in the uppermost mantle the depth of the viscoelastic layer roughly agrees with that of the high temperature portion and the low vp zones of the mantle wedge beneath the coast of the japan sea in northern honshu these correlations suggest that the low viscosity primarily results from high temperature of the mantle material combined with partial melt and the presence of h2o these correlations also suggest that the low viscosity zone in the uppermost mantle is widely distributed in the back arc side of the volcanic front and that postseismic deformation induced by viscoelastic relaxation may be frequently observed after large earthquakes in this area

experimental frost and salt weathering of chalk i experiments are described in which chalk cubes were soaked in solutions of either sodium chloride sodium sulphate or magnesium sulphate at concentrations of 5 5 per cent and 12 5 per cent or in a mixed solution of sodium chloride and sodium sulphate or in distilled water after removal of excess liquid the cubes were subjected to six freeze thaw cycles with temperatures ranging from either 15 to 10 c or 15 to 30 c the results confirm that frost weathering can be enhanced by the presence of certain salts but the extent of weathering was much less than that previously reported for samples frozen totally immersed in the same liquids evidence is presented which suggests that salt crystallization is the major weathering process operative when non immersed samples are frozen but a combination of frost and salt weathering operates when fully immersed samples are frozen

observations of three dimensional salt distribution in building sandstone observations of three dimensional salt distributions within three sandstone blocks after 120 years of exposure in an aggressive urban environment are presented based on measurements of soluble ion concentrations results indicate a complex distribution of sulphur and chloride where distributions are not consistent between salt types dictated by conditions at the six surfaces of the blocks this highlights the dangers of extrapolating the results of salt weathering simulations with regard to salt accumulation patterns or the results of fieldwork which rely on single surface samples from individual stones the widely held perception that urban environments are dry with shallow surface wetting of building stone does not appear to hold true for certain building stone copyright 2000 john wiley sons ltd

evolution of the mongol okhotsk ocean as constrained by new palaeomagnetic data from the mongol okhotsk suture zone siberia summary this paper presents new data from palaeomagnetic investigations on the upper palaeozoic and mesozoic geological units from the siberian platform and the mongol okhotsk suture zone within the southern portion of the mongol okhotsk suture we collected palaeomagnetic samples from the late permian belektuy formation borzya region 50 7un 116 9ue and the middle late jurassic shadaron formation unda daya 51 5un 117 5ue we sampled the late permian alentuy formation khilok region 50 8un 107 2ue the early to middle jurassic irkutsk sedimentary basin isb 52 0un 104 0ue the late jurassic badin formation mogzon region 51 8un 112 0ue and the early cretaceous gusinoozesk formation gusinoe lake region 51 2un 106 5ue additionally in the northern region of the mongol okhotsk suture apart from the results of the isb and gusinoozersk formations which show very large ellipses of confidence and might be the present day geomagnetic field overprint our results allow us to constrain the evolution of the mongol okhotsk ocean palaeomagnetically from the late permian to the middle late jurassic they confirm that this large permian ocean closed during the jurassic ending up in the late jurassic or the beginning of the cretaceous in the eastern end of the suture zone as suspected on geological grounds however although geological data suggest a middle jurassic closure of the mongol okhotsk ocean in the west trans baikal region our data show evidence of a still large palaeolatitude difference between the amuria and siberia blocks this is interpreted as a result of the quite fast closure of the ocean after the middle jurassic finally our new palaeomagnetic results exhibit very large tectonic rotations around local vertical axes which we interpret as probably arising both from collision processes and from a left lateral shear movement along the suture zone due to the eastward extrusion of mongolia under the effect of the collision of india into asia

calcium loading of quartz sandstones during construction implications for future decay damage to quartz sandstones in polluted urban environments is frequently associated with the presence of calcium salts especially gypsum for this association to occur it is necessary to identify external sources of calcium this paper describes an experiment in which the demolition of two sandstone test walls dumfries and dunhouse sandstones built with a lime mortar demonstrates the loading of the outer 1 2 cm of blocks with calcium although this calcium may eventually be mobilized into the interior of blocks a significant initial effect is a marked reduction in permeability identified by before and after measurement using a gas permeameter it is suggested that this sealing effect helps to constrain moisture and possibly salt cycling through the outer exposed surface of blocks eventually this may contribute to the rapid catastrophic decay of individual blocks and is a factor that must be built into any future modelling of this decay process copyright 2001 john wiley sons ltd

late quaternary uplift rate inferred from marine terraces shimokita peninsula northeastern japan a preliminary investigation of the buried shoreline angle after estimating tectonic uplift rates along the northern part of the northeast japan forearc the overriding plate in the northeast japan subduction zone by mapping the elevation of the inner edges of marine terrace surfaces we refined this estimate through elevation measurements of the buried shoreline angle beneath well dated marine terrace surfaces from which we could derive more accurate paleo sea levels the uplift rate initially inferred from the inner edge of marine terrace t4 correlated with marine isotope stage mis 5e by tephrochronology increases eastward from 0 11 0 22 m ky 1 around the backarc volcanic front to 0 17 0 32 m ky 1 in the forearc on the peninsula of shiriyazaki we refined the uplift rates for t4 on the basis of the shoreline angle elevation from the reconstructed profile of the paleo sea cliff and wave cut platform on a rocky coast and the reconstructed profile of the swash zone sediments and terrace deposits on a sandy coast the refined uplift rates were 0 14 0 25 m ky 1 on the rocky coast and 0 14 0 23 m ky 1 on the sandy coast slightly slower than the rates we inferred from the height of t4 and about one half to three fourths of previously reported rates by extrapolation from the example of the sandy coast the refined uplift rate around the volcanic front was 0 09 0 18 m ky 1 the vertical deformation across the forearc of the shimokita peninsula since mis 5e is possibly associated with regional isostatic uplift of 0 09 0 18 m ky 1 and anticlinal deformation by an offshore fault interpreted from acoustic profiles of 0 05 0 07 m ky 1

three dimensional attenuation structure beneath the northeastern japan arc estimated from spectra of small earthquakes abstract a fine scale three dimensional attenuation structure beneath the northeastern japan arc has been obtained using a joint inversion for source parameters site response and q values data used for this study are p wave spectra of microearthquakes occurring in the subducting pacific plate the subducting plate is found to have higher q values than the overlying mantle there is an along arc variation in the distribution of low q zones in the crust and the mantle wedge within the study area for the southern part of the study area low q zones are distributed in the crust beneath the volcanic front they extend into the mantle wedge and become deep toward the west that is toward the backarc region on the other hand the northern part of the study area has low q zones at two depth ranges at shallower depths just beneath the volcanic front and at the deeper part of the mantle wedge beneath the backarc region the region without active volcanoes along the volcanic front has relatively high mantle q values seismic activity in the lower plane of the double planed deep seismic zone is high beneath this relatively high q region of the mantle wedge spatial distribution of low q zones found in the present study is nearly consistent with that of the low velocity zones estimated from studies of travel times tomography partial melting zones in the mantle wedge whose existence has been suggested from the study of seismic velocity structure and laboratory experiments are located in the low q zones obtained in the present study these results suggest that spatial distribution of q values is closely related to heterogeneous distribution of temperature in the mantle wedge

moho depth variation in the central part of northeastern japan estimated from reflected and converted waves abstract we detected reflected p and s waves at the moho in seismograms of shallow crustal earthquakes in the central part of northeastern ne japan p to s and s to p mode converted waves at the moho are also detected in seismograms of intermediate depth earthquakes in the subducted pacific slab the depth distribution of the moho in the central part of ne japan is estimated by using travel time differences between these later phases and the first p and s arrivals we collected travel time data of 496 reflected waves from 67 shallow earthquakes and 200 converted waves from 65 intermediate depth earthquakes the depth to the moho estimated is deep beneath the land and becomes shallower toward the eastern and western coastlines the moho depth is about 34 km in the middle of the land area about 30 km under the coastline of the japan sea and 27 29 km under the coastline of the pacific ocean

3 d seismic velocity structure of the crust and the uppermost mantle in the northeastern japan arc 3 d seismic velocity structure of the crust and the uppermost mantle beneath the northeastern japan arc is investigated by using arrival time data from local earthquakes we use a velocity model composed of three layers corresponding to the upper crust the lower crust and the uppermost mantle respectively taking into account the observed regional variation of pn velocity the uppermost mantle is further divided into three parts by two pn velocity boundaries near the coasts of the japan sea and the pacific ocean the velocities within the upper crust the lower crust and the three parts of the uppermost mantle are assumed to be constant locations of two pn velocity boundaries and depth distributions of the conrad and the moho discontinuities are expressed by continuous functions of unknown parameters station corrections and hypocenters are also introduced to be unknowns these unknown parameters are determined by inverting arrival time data of p and s wave first arrivals and clear later arrivals of pg and p waves the pn velocity boundary between the land and the pacific ocean is located approximately along the pacific coastline and that between the land and the japan sea is nearly along the japan sea coastline the conrad and the moho discontinuities are at depths ranging from 14 to 20 km and from 27 to 36 km respectively the conrad and the moho depths have similar spatial distributions they are deep beneath the land and become shallower toward the western and the eastern coastlines beneath the land they are shallow in the central part of the tohoku district and become deeper toward both the north and the south directions in the north they become shallow again

mantle wedge structure in the miyagi prefecture forearc region central northeastern japan arc and its relation to corner flow pattern and interplate coupling 1 we applied three dimensional 3 d seismic tomography to both active source data and local earthquake data recorded at onshore and offshore seismic stations in the miyagi prefecture forearc region of central northeastern japan to obtain a detailed seismic velocity model of the mantle wedge the velocity model showed a clear boundary that divides the mantle wedge into an oceanward high velocity toe and a landward low velocity region that extends trenchward from beneath currently active arc volcanoes the top of the seaward dipping boundary is about 20 30 km landward from the coastline and its bottom is approximately beneath the coastline we consider that this velocity boundary represents the trenchward limit of corner flow and the high velocity toe represents a stagnant mantle wedge the high spatial resolution of the tomographic image we produced allowed us to identify a spatial correlation between velocity variations in the mantle wedge immediately above the plate boundary and the spatial extent of the rupture areas of the large interplate earthquakes that occur repeatedly in the region our results suggest that variations of the volume fraction of serpentinization in the mantle wedge cause the irregularity of rupture patterns of megathrust earthquake sequences we also identified a swarm of active microseismicity in the mantle wedge well above the seismogenic plate boundary this activity may be related to dehydration of a detached seamount

teleseismic evidence for lateral heterogeneities in the northeastern japan arc we have measured and analyzed 4211 p wave first arrival times from 100 teleseismic events recorded by 67 high sensitivity seismic stations in the northeastern japan arc the relative travel time residuals show regional variations of about 1 6 s the mean relative residuals averaged for all 100 events produce a spatial pattern of early arrivals at stations near the pacific coast and delayed arrivals in the central part of the island arc and along the japan sea coast large delayed arrivals are observed at stations in volcanic areas this pattern is generally consistent with the heat flow distribution and the major structural features that have been determined by local and regional earthquake studies large early arrivals appear in northern kanto and southern tohoku for the rays from the teleseismic events in the southwestern direction using a simple and plausible model of plate subduction we have shown that this anomalous pattern can be explained by the change of the geometry of the subducting pacific plate beneath kanto the observed teleseismic residual distributions can be explained with a 3 d velocity model which includes the high velocity subducting pacific plate and low velocity anomalies in the crust and mantle wedge beneath active volcanoes suggesting that the 3 d model represents well the velocity structure in this region these teleseismic observations provide a new piece of information on the significant lateral heterogeneities of seismic velocity structure in the northeastern japan arc

subduction of a wedge shaped philippine sea plate beneath kanto central japan estimated from converted waves and small repeating earthquakes 1 we estimate the configuration of the philippine sea plate phs subducted beneath kanto to understand the seismotectonics in the tokyo metropolitan area in addition to small repeating earthquakes that delineate both the upper and lower boundaries of the phs previously unrecognized converted waves at its upper boundary from lower boundary repeater sources provide a new constraint on the position of the boundary the results from 794 s to p and 212 p to s converted waves together with 200 repeater locations show that 1 the phs has a wedge like shape decreasing in thickness from 50 km beneath tokyo to zero at its northeastern limit and 2 the phs is relatively flat in the eastern part of kanto and bends upward near its northeastern limit from the fact that the phs in the izu bonin forearc also has a similar wedge like shape we infer that its shape was formed before its subduction on the other hand the relatively flat phs at its northeastern limit and its upward bend are probably a consequence of ongoing deformation from an interaction with the underlying thick pacific plate pac the history of the phs as a forearc before subduction and its contact with the pac after subduction suggests that the temperature of this part of the phs is colder than other regions which probably causes anomalously deep seismicity on the phs in kanto colder phs temperatures imply that the source regions of large earthquakes may extend deeper than expected an important fact when assessing the locations of disastrous earthquakes for tokyo

seismic velocity structure of the crust beneath the japan islands abstract more than 13 000 arrival times of 562 local shallow earthquakes selected from the japan university network earthquake catalog are used to investigate the seismic velocity structure of the crust beneath the japan islands we simultaneously determined the hypocenter parameters p and s wave station corrections and depth distributions of the conrad and moho discontinuities beneath the whole of the japan islands by applying an inversion method the p and s wave station corrections show similar distribution patterns they are negative relatively late arrivals of seismic waves in hokkaido and positive relatively early arrivals of seismic waves in western japan in eastern honshu they are positive along the coast of the pacific ocean and negative in the land area and along the coast of the japan sea the conrad discontinuity is located at a depth range from 12 to 22 km in hokkaido the conrad is shallow in the eastern pan and becomes deep toward the west in ne honshu the conrad is deep beneath the land area and becomes shallow toward the surrounding seas in western japan the conrad is shallow in the northern part and becomes deep toward the south the moho is located in a depth range from 25 to 40 km in hokkaido the moho has the shape of a circular cone with a maximum depth of 36 km in most parts of the japan islands the moho is deep beneath the land area and becomes shallow toward the surrounding seas the moho is deepest up to 40 km beneath the central part of the chubu district

mapping the crustal thickness in southwest japan using moho reflected waves in this work we have tried to detect and collect later phases associated with the moho discontinuity and use them to study the lateral variations of the crustal thickness in southwest sw japan we first compute synthetic seismograms for local earthquakes taking into account the focal mechanism solutions estimated from first motion polarity data then we compare the synthetics with the observed waveforms to detect the major later phases in seismograms of shallow crustal earthquakes in sw japan taking the advantage of the high quality and great quantity of hi net waveform data now available throughout the entire japan islands we have detected 1659 moho reflected phases pmp and sms from shallow events in sw japan we estimated the crustal thickness in the study area using travel time differences between these later phases and the first p and s arrivals our results show that the moho is deep in chubu district and becomes shallower along the coastlines of the japan sea and the pacific ocean a thinner crust appears in osaka bay and awajii island where the 1995 kobe earthquake m7 2 occurred

the method for consecutive subtraction of selected anomalies the estimated crustal velocity structure in the 1996 onikobe m 5 9 earthquake area northeastern japan summary the consecutive subtraction of selected anomalies cssa method has been presented to provide a new opportunity to improve the quality of inversion results in seismic tomography the basic idea of the iterative method is to determine in each step a parameter that subtracts the total largest square residuals the criteria proposed control the selection of the best solution from all candidates by inspecting their convergence to the accurate solution in the lsq sense resolution measures were defined by estimating the convergence degree the matching of the lanczos lsqr and cssa methods has been demonstrated from the perspective of the projection technique the storage and work requirements for both algorithms were compared revealing that cssa is also efficient for large and sparse systems synthetic models were reconstructed comparing cssa and lsqr and indicating that cssa gives us more reliable results when large sized structures are considered at the same time the simultaneous subtraction of the selected anomalies algorithm was examined numeral tests revealed that this algorithm is able to produce results that are similar to those obtained by lsqr complicated velocity structure can lead to ambiguous results a problem that can be solved by setting the appropriate starting vector for the cssa inversion the difference between the starting vector and the starting or reference model is discussed the cssa method was applied to p wave arrival times from shallow earthquakes to determine deep structure in the focal area of the onikobe m 5 9 earthquake 1996 in the northern part of honshu japan a specific feature of the traveltime residuals is a set of positive values corresponding to late p wave arrivals tomography revealed a low velocity body in the focal area from the surface down to the hypocentres local anomalies with the lowest perturbations were found in the surface layer of 0 2 km around the onikobe epicentre to the north of the focal area and to the northeast of naruko volcano

prograde reactions and garnet zoning reversals in staurolite schist british columbia significance for thermobarometric interpretations an outcrop of staurolite bearing pelitic schist from the solitude range in the south western rocky mountains british columbia was examined in order to determine the nature of prograde garnet and staurolite producing reactions using information from garnet zoning and inclusion mineralogy although not present as a matrix phase chloritoid is present as inclusions in garnet and is interpreted to have participated in the simultaneous growth of garnet and staurolite by a reaction such as chloritoid quartz garnet staurolite h2o a garnet zoning trend reversal which is most pronounced with respect to almandine and grossular components is present in the outer core of garnets the location of the zoning reversal corresponds to the outer limit of chloritoid inclusions in garnet as there is no evidence for polymetamorphism the zoning reversal is interpreted to indicate continued garnet growth by prograde reaction s during a single metamorphic event after the exhaustion of chloritoid as a matrix phase metamorphic conditions recorded by mineral rim compositions are 550 600 c at 6 7 kbar because there is no evidence for partial resorption of garnet during production of staurolite we interpret these results to represent peak conditions

autocorrelation analysis of ambient noise in northeastern japan subduction zone abstract we obtained ambient seismic noise interferograms as seismic reflection images using autocorrelation functions acfs in the northeastern japan subduction zone the acfs with a time window length of 120 s were calculated from the continuous seismic records obtained at each seismic station over an analysis period of 300 days these acfs show some distinct signals with relatively large amplitude without any significant temporal variations during the analysis period the signals which are stable appear at both small lag times of less than 10 s and large lag times of 20 50 s during the analysis period the lag time of 10 s corresponds to the travel time of the pp reflection arrival from the continental mohorovicic discontinuity the signals with the large lag times between 30 and 50 s correspond to the back scattered signals from the mantle wedge or the plate boundary these signals are identified clearly at the stations located on the back arc side in the acfs calculated from the records obtained from the fore arc side stations weak signals interpreted as the reflection from the plate boundary with a lag time range of 20 to 30 s are observed we constructed depth migrated images using the acfs to obtain the reflectivity profile by assuming that the acfs represent green s functions composed of a random wavefield excited by stochastic sources or scatterers distributed in the vertical or near vertical direction from the stations further we assumed that the acfs can be treated as zero offset seismic traces recorded at each of the stations the depth migrated images show a relatively seismically transparent structure within the subducting pacific slab and a reflective structure within the mantle wedge this reflective structure is characterized by low velocity zones corresponding to the wedge flow imaged by 3 d seismic velocity tomography

the impact of landslides and salt weathering on roman structures at high latitudes conway castle great britain a case study conway castle is an immense historical structure dating back to 1289 ac it was built on highly dipping thickbeds of indurated shale argillite and sandstone it is surrounded by conway bay railway lines and tall dense forests indicating high relative humidity and rainfall in this coastal area the castle suffers from weathering noted as honeycomb black crust exfoliation and discoloration with white salt efflorescence at some parts these are diagnostic features for salt weathering as confirmed by the laboratory investigations using scanning electron microscopy x ray diffraction xrd point xrd and hydrochemical analysis the salt is found to be from three sources namely water spray from conway bay that is part of the irish sea chemical alteration of the mortar s carbonate content into sulfate salts by acid rain and wet deposition of air pollutants on the surface of the stone the cracks noted in the southwestern tower of this castle are a result of landslides in this area that resulted from three factors a high dip angle of the indurated sandstone and shale thickbeds about 60 65 to the south under this castle b undercutting of these beds in the dip direction by the surface water of conway bay and c seismic waves generated by the trains passing close to this castle all these factors result in land sliding even at a low rate however the net result is cracks in the tower close to these factors

supraslab earthquake clusters above the subduction plate boundary offshore sanriku northeastern japan seismogenesis in a graveyard of detached seamounts 1 thousands of offshore repeating earthquakes with low angle thrust focal mechanisms occur along the subduction plate boundary of ne japan double difference relocation methods using p and s wave arrivals reveal clusters of events above these repeating events to assure good depth control we restrict our study to events that are close to seismic stations these supraslab earthquake clusters are regional features at depths of 25 to 50 km and most of these clusters are below the depth of the forearc moho which we determined from converted waves seismicity over this depth range does not occur under the inland area of ne japan except just below the vicinity of the arc volcanoes re entrants in the inner trench slope indicate that repeated collisions of seamounts have occurred in the past our preliminary interpretation of supraslab clusters is that they represent seismicity in seamounts detached from the pacific plate during slab descent driven by the resistance of seamounts to subduction detachment during slab descent probably occurs on the sedimented and hydrothermally altered seafloor on which seamounts were originally constructed since these are known as zones of weakness during active island growth high fluid pressure produced during dehydration of clay minerals and other low temperature hydrous minerals could enable detachment at depths seamount crust is thus accreted to forearcs possibly leading to a long term component of near coastal uplift supraslab earthquake clusters may be our most direct evidence of the fates of seamounts and suggest that tectonic underplating is actively occurring in this subduction system

deep structure of japan subduction zone as derived from local regional and teleseismic events we have determined a detailed three dimensional p wave velocity structure of the japan subduction zone to 500 km depth by inverting local regional and teleseismic data simultaneously we used 45 318 p wave arrivals from 1241 shallow and deep earthquakes which occurred in and around the japan islands the arrival times are recorded by the japan university seismic network which covers the entire japan islands densely and uniformly we also used 4211 travel time residuals from 100 teleseismic events which are read from seismograms recorded by seismic stations in northeastern japan in comparison with the previous results obtained from only local and regional events the present result for the area around the lower plate boundary and the mantle below the plate is determined more reliably because of the addition of 7035 data from 100 teleseismic events and 41 very deep earthquakes in the crust and uppermost mantle low velocity zones are clearly visible beneath active volcanoes in the mantle wedge the low velocity zones generally parallel with the slab and exist continuously to a depth of about 200 km which is consistent with the petrological geochemical and geodynamic studies we consider that the existence of volcanism related low velocity anomalies in the mantle wedge is a general seismological characteristic of subduction zones in light of all the available tomographic results for many subduction zones in the world the pacific slab beneath japan is imaged more clearly than in previous studies as a high velocity zone with a thickness of 80 90 km and a p wave velocity 4 6 higher than the normal mantle lower velocity anomalies are found in the mantle below the slab

biogenic origin of coastal honeycomb weathering honeycomb weathering occurs in two environments in late cretaceous and eocene sandstone outcrops along the coastlines of south west oregon and north west washington usa and south west british columbia canada at these sites honeycomb weathering is found on subhorizontal rock surfaces in the intertidal zone and on steep faces in the salt spray zone above the mean high tide level in both environments cavity development is initiated by salt weathering in the intertidal zone cavity shapes and sizes are primarily controlled by wetting drying cycles and the rate of development greatly diminishes when cavities reach a critical size where the amount of seawater left by receding tides is so great that evaporation no longer produces saturated solutions encrustations of algae or barnacles may also inhibit cavity enlargement in the supratidal spray zone honeycomb weathering results from a dynamic balance between the corrosive action of salt and the protective effects of endolithic microbes subtle environmental shifts may cause honeycomb cavity patterns to continue to develop to become stable or to coalesce to produce a barren surface cavity patterns produced by complex interactions between inorganic processes and biologic activity provide a geological model of self organization surface hardening is not a factor in honeycomb formation at these study sites salt weathering in coastal environments is an intermittently active process that requires particular wind and tidal conditions to provide a supply of salt water and temperature and humidity conditions that cause evaporation under these conditions salt residues may be detectable in honeycomb weathered rock but absent at other times honeycomb weathering can form in only a few decades but erosion rates are retarded in areas of the rock that contain cavity patterns relative to adjacent non honeycombed surfaces copyright 2010 john wiley sons ltd

variable weathering response in sandstone factors controlling decay sequences differences in weathering response characteristics of fine and coarse grained stanton moor sandstone samples were assessed in a laboratory weathering simulation experiment using a variable combination of salt weathering and freeze thaw cycles preliminary analysis of permeability characteristics identified similar mean values for each type of stanton sandstone but significant differences in the range of values between the two sample sets with coarse grained samples of stanton moor sandstone displaying a restricted range of values in comparison to fine grained samples which showed much greater within block variation data indicated that the greater the range in initial permeability values the greater the potential for salt and moisture ingress and retention and hence eventual disruption of the fabric of the stone experimental data also identified different stages in decay sequences with significant structural change occurring during the initial preparatory stage before material breakdown and loss became apparent evidence suggests that relatively minor structural and mineralogical differences between samples of the same stone type can have a significant influence on weathering behaviour resulting in distinct rates and patterns of breakdown copyright 2005 john wiley sons ltd

spatial and temporal evolution of the subducting pacific plate structure along the western pacific margin 1 tomographic images of the subducting pacific plate beneath the izu bonin mariana arc illustrate a progression of geometries from shallow dipping to vertical from north to south along the arc recent advances in technology and inversion techniques have improved resolution of slab structure beneath the western pacific island arcs but reasons for the variation in geometry and morphology are still poorly understood by comparing high resolution tomographic images of the western pacific and updated paleogeographic reconstructions we are able to link the spatiotemporal evolution of the subducting pacific plate back to the mid miocene we have reconstructed tectonic motions along the kurile japan izu bonin mariana arc system and the ryukyu arc to provide an independent additional interpretation of the subducting pacific plate using the most current plate motion data we then investigate the plausibility of our model and three other proposed models based on the interpreted slab structure from tomographic images the new reconstruction agrees with the basic characteristics of former trench retreat models but illustrates the importance of the collision of the ogasawara plateau with the trench in the mid miocene and its subsequent effect on the slab structure at depth and the impact of other aseismic ridge collisions along the plate boundary the combination of evidence in changed physical properties imaged with tomography and the current interpreted slab morphology can be analyzed with the past plate motions to understand subduction zone processes

estimation of crustal discontinuities from reflected seismic waves recorded at shillong and mikir hills plateau northeast india in this study an attempt is made to determine seismic velocity structure of the crust and upper mantle beneath the shillong mikir hills plateau in northeast india region the principle of the technique is to relate seismic travel times with crustal thickness above the conrad and moho discontinuities broadband digital waveforms of the local earthquakes make a precise detection of the seismic phases possible that are reflected at these discontinuities the results show that the conrad discontinuity is at 18 20 0 5 km beneath the shillong mikir hills plateau and the moho discontinuity is at 30 1 0 km beneath the shillong plateau and at 35 1 0 km beneath the mikir hills

three dimensional inversion of regional p and s arrival times in the east aleutians and sources of subduction zone gravity highs free air gravity highs over forearcs represent a large fraction of the power in the earth s anomalous field yet their origin remains uncertain seismic velocities as indicators of density are estimated here as a means to compare the relative importance of upper plate sources for the gravity high with sources in the downgoing plate p and s arrival times for local earthquakes recorded by a seismic network in the eastern aleutians are inverted for three dimensional velocity structure between the volcanic arc and the downgoing plate a three dimensional ray tracing scheme is used to invert the 7974 p and 6764 s arrivals for seismic velocities and hypocenters of 635 events one dimensional inversions show that station p residuals are systematically 0 25 0 5 s positive at stations 0 30 km north of the aleutian volcanic arc indicating slow material while residuals at stations 10 30 km south of the arc are 0 1 0 25 s negative both features are explained in three dimensional inversions by velocity variations at depths less than 25 35 km tests using a one dimensional or a two dimensional slab starting model show that below 100 km depth velocities are poorly determined and trade off almost completely with hypocenters for earthquakes at these depths the locations of forearc velocity highs in the crust of the upper plate correspond to the location of the gravity high between the trench and volcanic arc free air anomalies calculated from the three dimensional velocity inversion result match observed gravity for a linear density velocity relationship between 0 1 and 0 3 mg m 3 km s 1 when a 50 km thick slab is included with a density of 0 055 0 005 mg m 3 values outside these ranges do not match the observed gravity the slab alone contributes one third to one half of the total 75 150 mgal amplitude of the gravity high but predicts a high that is much broader than is observed the inclusion of upper plate velocity anomalies predicts the correct width of the anomaly 100 150 km where the anomaly is most positive because the forearc gravity high is continuous along the entire aleutian arc and is found in most arcs globally high upper plate forearc velocities are suspected to be a common feature of the upper plate of most subduction zones the forearc mass excesses appear to be sustained by upward regional flexure of the upper plate that partly balances the depression of the lower plate at the trench thus elevating high density and high velocity material thus a part of the downward flexure of the subducting plate is regionally compensated by shallow positive mass anomalies in the upper plate and the strength of the upper plate helps generate the forearc gravity highs

sandstone weathering a century of research and innovation abstract a review of sandstone weathering research particularly in the past 100 years reveals a trajectory of enquiry from early description and classification of features to development of process based explanations to decreasing scales of investigation and a disparity between understanding of process es and explanations of the genesis of sandstone weathering features developments in expositions on mesoscale weathering features on sandstone surfaces are discussed demonstrating a range of approaches to weathering phenomena field based and laboratory based that must be linked to provide an explanation of observed features on a landform scale throughout the twentieth century a thematic chronology highlights certain trends in research description of forms often in arid and semi arid environments single process form models an emphasis on experimentation difficulties in measuring weathering rates and a persistent emphasis on physical causes of breakdown a new research agenda is promoted in which biodeterioration and chemical processes gain parity a holistic approach based on conceptual modeling of weathering systems gains prominence and scale issues are addressed more rigorously

structural and petrological constraints on the tectonic evolution of the garnet lherzolite facies higashi akaishi peridotite body sanbagawa belt sw japan 1 the higashi akaishi peridotite body in the sanbagawa metamorphic belt is a unique example of a kilometer scale body including garnet lherzolite facies rocks from an oceanic subduction type orogen in this body four distinct deformational phases d1 d2 d3 and d4 can be defined the tectonic significance of d1 is unclear microstructural observations and application of garnet orthopyroxene geothermobarometry suggest that d2 took place during high temperature subduction up to depths of 100 km from 2 3 gpa to above 2 8 gpa at temperature of 700 800 c or more d3 represents a major phase of exhumation after exhumation the higashi akaishi body became juxtaposed with the adjacent besshi and eclogite units at a depth of around 35 km 1 gpa the common history of the two units after d3 is shown by the intertectonic growth of tremolite between d3 and d4 that corresponds to a stage of intertectonic growth of plagioclase in the besshi and eclogite units both the spatial distribution and the estimated pressure temperature p t conditions of this intertectonic phase of mineral growth in the different units are in excellent agreement the development of an antigorite schistosity during the late stage of d2 indicates an anticlockwise p t path with cooling at depths of around 100 km the association of the antigorite bearing fabric and the onset of exhumation after the d2 stage suggest that the density decrease due to antigorite formation may have been sufficient to trigger the exhumation of dense ultramafic body from uhp conditions in subduction zones syn d2 water introduction and the anticlockwise p t path are expected when convection in the mantle wedge brings peridotite toward a subduction boundary through mantle wedge or when peridotite is dragged down along a subduction boundary that is progressively cooling immediately after initiation of subduction

deep structure of the northeastern japan arc and its relationship to seismic and volcanic activity evidence for possible deep seated magmatic activity beneath northeastern japan can be obtained from seismic observations tomographic inversions of p wave velocity data show low velocity zones distributed in the crust and upper mantle beneath active volcanoes in or around these zones anomalously low frequency micro earthquakes perhaps caused by magmatic activity are found at depths of 25 40 km distinct s wave reflectors corresponding to the upper surfaces of magma bodies are found at depths of 10 18 km large crustal earthquakes also occur around the low velocity zones these observations reveal the distribution of magma reservoirs at depths and elucidate its relation with shallow seismicity beneath volcanic arcs

simultaneous estimation of attenuation structure source parameters and site response spectra application to the northeastern part of honshu japan abstract we have developed an inversion method for estimating q structure by the use of a large number of waveform data from earthquakes we divide an area to be analyzed into small blocks and simultaneously estimate the q value in each block source parameters for each event and site response spectrum for each station the source spectrum is assumed to be expressed by the 2 model and values of corner frequencies and low frequency levels of source spectra are estimated amplitudes are calculated by taking the orientation of focal mechanism solutions into account a trade off among estimated parameters is tested by numerical experiments using three sets of artificial data in a case when artificial data include error of 15 in the orientation of the p axis of focal mechanism solutions the inverted result shows that the original checkerboard pattern of q structure is well reconstructed although estimated q 1 values are about 10 higher than those of the original one the result without the corrections for radiation effect shows that the checkerboard pattern is only reconstructed in the blocks having a sufficient number of ray paths we applied this inversion method to a real data set in the northeastern part of honshu japan estimated q p structure shows that low q p regions are distributed beneath the volcanic front and they move towards the west with increasing depth previous studies of three dimensional seismic velocity structure in this area show that p wave low velocity regions exist in the crust beneath the volcanic front and they are inclined towards the west in the mantle wedge the low q p regions estimated in this study coincide in general with the p wave low velocity regions

p wave anisotropic tomography beneath northeast japan we determined a 3 d p wave anisotropic tomography beneath northeast japan by using first p arrival times the travel time inversion is parameterized with an isotropic component and two anisotropic parameters for each grid node by assuming p wave azimuthal anisotropy with hexagonal symmetry axis distributed horizontally the geometries of the conrad and moho discontinuities and the upper boundary of the subducting pacific plate are taken into account in the model our extensive synthetic tests show that the anisotropic velocity inversion method is reliable our results show that low velocity zones exist below active volcanoes in the crust in the fore arc mantle wedge and in the central portion of the mantle wedge above the high velocity pacific slab which are similar to the previous tomographic images anisotropic velocity variations are revealed in the crust mantle wedge and the subducting pacific slab the anisotropic patterns are complex and different in the upper and lower crust in the mantle wedge the fast direction of p velocity is generally trench parallel in the fore arc area while it becomes trench normal in the back arc area which agree well with the shear wave splitting results the trench parallel fast direction is revealed beneath the volcanic front which may suggest the existence of complex 3 d mantle flows in the mantle wedge the fast velocity direction in the subducting pacific slab is mostly n s which is likely due to the original fossil anisotropy of the pacific plate formed at the mid ocean ridge our result also suggests that the anisotropy is weak in the upper crust and the average amplitude of the velocity anisotropy in the mantle is no larger than 4

palaeomagnetism of east siberian traps and kimberlites two new poles and palaeogeographic reconstructions at about 360 and 250 ma summary we studied basalt sills and dykes and kimberlite pipes from the eastern part of the siberian platform these are spread out over a few hundred kilometres and are divided into two age groups late permian early triassic mir aikhal and olenyek regions and late devonian early carboniferous viluy and markha basins aikhal region the palaeomagnetic poles determined for each sill or dyke are statistically different from each other but averaging all corresponding directions from these sills and dykes with those from kimberlites of different generations yields results with acceptable statistics this is probably due to the averaging out of secular variation and or changes in magnetic polarity the resulting palaeomagnetic poles allow one to reconstruct the palaeopositions of siberia during the two large flood basalt events at about 360 and 250 ma a significant rotation of the siberian platform during the devonian and carboniferous is suggested the new data are in general agreement with some earlier palaeomagnetic poles for the late permian early triassic traps of the tungusska basin and significantly reduce uncertainties for previous late devonian early carboniferous siberian poles which were very scattered together with geological and absolute age data the palaeomagnetic data support the hypothesis that kimberlite magmatism and trap intrusions were both rapid and relatively close in time the 360 ma event is emerging as a magmatic event with considerable extent over the russian and siberian platforms related to incipient continental break up and triple junction formation possibly at or near the time of the frasnian famennian mass extinction

the role of the east asian active margin in widespread extensional and strike slip deformation in east asia east asia is a region of widespread deformation dominated by normal and strike slip faults deformation has been interpreted to result from extrusion tectonics related to the india eurasia collision which started in the early eocene in east and se china however deformation started earlier than the collision latest cretaceous to palaeocene suggesting that extrusion tectonics is not the only driving mechanism for east asia deformation it is suggested that the east asian active margin has influenced deformation in east asia significantly along the margin cenozoic back arc extension took place behind several adjoining arcs implying eastward rollback of the subducting slab and collapse of the overriding plate towards the retreating hinge line we show that extension took place along a c 7400 km long stretch of the east asian margin during most of the cenozoic physical models are presented simulating overriding plate collapse and back arc extension the models reproduce important aspects of the strain field in east asia for geometrical and rheological conditions scaled to represent east asia modelling shows that the active margin can be held responsible for deformation in east asia as far west as the baikal rift zone located c 3300 km from the margin

a holistic approach to the assessment of the groundwater destructive effects on stone decay in edfu temple using aas sem edx and xrd the objective of this study is to investigate the groundwater influences on sandstone in horus temple in addition to studying the deterioration processes affecting the temple building materials specific investigations were carried out to measure the groundwater features and quality both inside and outside the temple to evaluate the resulted deterioration processes our results argue that the temple was built on a hill of silt and clay belonging to the cretaceous era it rises on the south part of the nile valley far from the nile for about 1200 m groundwater quality is strongly influenced by the dominating minerals and stone aquifer affected by three major water sources the temple faces many deterioration processes due to the effect of groundwater characterized by high salinity index these processes led finally to two main mechanisms the first related to micro deterioration and the second resulting from structural defects these mechanisms affirmed that the stone building materials were highly characterized by weakness fracture disintegration cracks and crevices collapsing of their components furthermore the dominating major salt species are halite gypsum sylvite and thenardite and minor quantities of carbonates and bi carbonates in addition to phosphate as or trace constituents

tectonic stress state in ne japan as part of the okhotsk plate abstract an existing geodetic flow velocity model obtained by using an internal free network adjustment technique is used to derive estimates for various strain rates parameters in ne japan the greatest shortening rates of the principal strains trending e w are located in regions where much steady internal frame invariant plastic flow deformation is observed to be taking place the internal geodetic adjustment technique yielded the internal deformation in the tohoku arc most of the intraplate deformations including the much folding deformations observed in the inner zone are produced from within an interseismic transient elastic loading at a strongly coupled locked japan trench would not be needed the observed ongoing extensive ductile folding deformation in the inner zone of tohoku may mean that the geodetic strain rates causing shortening at 2 3 cm yr probably reflect the more correct level of the deformation which is steady permanent in ne japan as compared with seismic faulting data which indicate 0 5 cm yr shortening the calculated principal strain rates are used to make an interpretation for the origin of the deviatoric principal stresses within the greater regional plate tectonic framework the tectonic stress state in ne japan as part of the okhotsk plate could mostly be influenced by the okhotsk plate which is extruding southward to lessen the significant accumulated contractional deformation in ne asia in the verkhoyansk cherskii mountains the principal strain rates are n s extensional essentially everywhere in ne japan as a result of the southerly extrusion except in its southernmost leading edge in the uetsu fossa magna province where the japan alps rampart rises in front of the extrusion here an e w compressional stress state prevails a second e w contractional zone is found in north central tohoku extending from the sanriku province in the outer zone to the inner zone in the japan sea side being more prevalent in the latter zone the calculated rotation rates from the geodetic flow model are clockwise cw in both of the e w contractional regions ne japan extruding southward faces buttresses in 1 the oga ojika line ool and or a crustal weakness zone between the northern and the southern halves of tohoku approx at 38 5 n latitude and especially 2 the japanese alps rampart these obstacles cause the northern and southernmost tohoku to veer to its right and rotate cw thereby setting up the e w trending compressional deformation in their respective inner zones between the ool or the 38 5 n boundary and the kanto tectonic line ktl the sense of the differential rotations is counterclockwise ccw towards the ocean to the se the northern tohoku north of the ool and the southernmost tohoku south of the ktl cannot rotate ccw towards the ocean because of the izu block s collision in the south and the relatively strong coupling along the subduction interface beneath the japan trench in the north off sanriku the relatively stronger long term coupling between the northern tohoku and the pacific plate at the sanriku coast with respect to that in off fukushima is due to a flatter subduction of the pacific slab there increasing the plates interface contact area the flattening of the subduction dip angle was caused by ccw rotation and shifting of the northern tohoku along the dextral honjo matsushima line roughly corresponding to the ool towards the pacific and overriding of the subduction zone during the formation of the japan sea

seismogenic structure in the source zone of the 1918 m7 5 nanao earthquake in the northern south china sea abstract as a typical rifted margin the coastal region of the northern south china sea has experienced many large crustal earthquakes in the past 400 years for example two destructive earthquakes with m7 0 in 1600 and m7 5 in 1918 occurred close to the nanao island however the mechanism of these earthquakes and seismotectonics of the region are still unclear in this work we make the first study of the detailed three dimensional crustal structure in the source zone of the 1918 nanao earthquake m7 5 using newly acquired wide angle seismic reflection data our results show that current seismicity mostly occurred in a midcrustal low velocity zone or its nearby high to low velocity transitional areas we ascertain locations of the ene strike littoral fault zone and the nw strike huanggangshui fault based on the seismic reflection profiles these faults have caused a large scale vertical dislocation of the sedimentary basement the structure of the upper crust is very heterogeneous containing many high or low velocity anomalies however the lower crustal structure is less heterogeneous mainly characterized by low velocity mostly in the northern part of the study area and high velocity mainly in the southern part the crust in the seismicity zone shows strong heterogeneity reflecting highly cracked structural features possibly caused by destructive earthquakes we infer that the midcrustal low velocity zone and the intersection between the littoral fault zone and the huanggangshui fault could reflect weak structures in the crust and form a local stress buildup which strongly affected or controlled the generation of intraplate seismicity the 1918 nanao earthquake very likely occurred within the current seismicity zone with a depth range of 15 25 km estimated from our tomographic images and previous geological and geophysical results

seismic scatterers within subducting slab revealed from ambient noise autocorrelation 1 we reconstructed new migrated images from autocorrelation functions of ambient noise at seismic stations in northeastern japan during the analysis period the autocorrelation functions having a frequency range of 0 5 2 hz showed some coherent signals at large lapse times of 10 50 s as well as at small lapse times of less than 10 s these signals were also coherent in space along cross sections across the japan subduction zone the migrated images show seismic scatterers within the subducting pacific slab at the depth range of 50 150 km the distribution of the scatterers within the subducting slab is comparable to the double seismic zone in the subduction zone in particular the thickness of the distribution of the seismic scatterers is consistent with that of two planes of the double seismic zone this indicates inhomogeneities in the seismic velocity structure around the upper and lower planes of the seismicity the new migrated images suggest that seismic scatterers such as fluid from dehydration reactions of the hydrated metamorphosed mantle exist in the lower as well as upper plane of the seismicity in the double seismic zone this fluid may act as a scatterer within the subducting slab

crystal growth during a single stage opening event and its implications for syntectonic veins abstract the crystallization of a fluid filled vein or cavity and interpretation of the microstructure in a deformed rock is an important problem for geologists dynamic crystallization experiments using ice and an aqueous solution have been used as an analogue system for single stage opening events and have shown that the presence or absence of a deviatoric stress is an important factor in the development of texture as a result of crystallization from a fluid the textures can vary from 1 coarse crystal aggregates involving static growth where there is no significant macroscopic deviatoric stress at the time of crystallization the free face growth model to 2 polycrystalline aggregates involving static growth which develop from a mixture of skeletal crystals and fluid in a stressed environment in the latter situation the crystals and fluid coexist until the macroscopic stress can be transmitted between impinging crystals and at this stage fast dynamic recrystallization and grain boundary migration occurs this recrystallization has been termed the contact growth model and the resulting metamorphic texture is compared with examples in natural quartz veins during a single stage vein opening uncomplicated by intragranular deformation either free face and or contact growth textures can develop from the fluid filled void depending upon the kinematic environment