stress change near the kunlun fault before and after the ms 8 1 kunlun earthquake 1 on 14 november 2001 a great earthquake of ms 8 1 occurred on the kunlun fault in the kusai lake segment of the kunlun mountain qinghai province in northwest china the stresses measured at the sites near the kunlun fault before and after the earthquake show a great drop after the earthquake the values of the horizontal maximum principal stress at two sites are 12 9 mpa and 6 8 mpa before the earthquake measurement of the horizontal maximum principal stress at the same sites after the earthquake showed values of 3 5 mpa and 2 2 mpa respectively this is only about one third of that before the earthquake apparently stress that accumulated near the fault before the earthquake was released along with the rupturing of the surface the direction of the maximum horizontal principal stress also varies before and after the earthquake the direction is found to deviate from that of the regional structure stress field after the earthquake such stress changes offer a basis for predicting large earthquakes in the region

late quaternary sea levels and crustal movements coastal british columbia late quaternary sea level fluctuations on the british columbia coast have been established from studies of terrestrial and marine sediments and landforms these studies indicate that the sea level history of mainland british columbia and eastern vancouver island is very different from that of the queen charlotte islands and western vancouver island specifically in the former areas there was a rapid rise of submerged coastal lowlands between about 13 000 and 10 000 years ago emergence culminated about 6000 9000 years ago depending on the locality when the sea relative to the land was 12 m or more lower than at present in some areas during middle and late holocene time relative sea level rose on the mainland coast and at least locally on eastern vancouver island resulting in inundation of coastal archaeological sites and low lying terrestrial vegetation tidal records and precise levelling suggest ongoing submergence of at least part of this region in contrast shorelines on the queen charlotte i

kinematic model of active deformation in central asia the velocity field of present day deformation in central asia is modelled using a set of four rotating blocks siberia tarim tibet india on a spherical earth a best fit is inverted on the basis of estimated shortening rates across the main thrust zones himalayas tien shan and measured slip rates along the principal strike slip faults altyn tagh and karakorum separating those blocks the fit to the data implies that nearly all the present convergence between india and asia can be accounted for by slip partitioning on these four zones with as much as 50 absorbed by northeastwards extrusion of tibet this suggests that localised deformation governs the present mechanical behaviour of the central asian lithosphere

inversion of strong motion seismograms for the source process of the naganoken seibu earthquake of 1984 abstract the source process of the noganoken seibu earthquake of 1984 m 6 8 has been investigated in detail by using strong motion seismograms recorded at stations within 100 km of the epicenter a new inversion method was applied to analyze the strong motion seismograms we parameterized the problem by using a model in which the fault was composed of a certain number of subfaults which started rupturing with arbitrary magnitude at arbitrary time and we have successfully obtained the dislocation distribution and the characteristics of rupture propagation on the fault the rupture starts at the shallowest point on the central part of the fault and then propagates over the whole source region within about 3 s the total seismic moment estimated from the final solutions is 3 10 25 dyne cm the dislocation is inhomogeneously distributed on the fault plane and reaches a maximum of about 1 5 2 m the largest dislocation occurs in the near surface region on the deeper part of the fault the dislocation seems to be small there were few aftershocks at the center and on the shallow part of the fault most of the large aftershocks m 4 0 were located on the deeper part of the fault these results suggest that the aftershock activity was highest on the unruptured regions of the fault where stresses were concentrated from the distribution of dislocations on the fault the size of the source area is estimated to be approximately 12 km length 6 km depth the main shock ground motions having periods longer than l s were estimated at sites where no recordings exist by using the final source model at the summit of mt ontake the maximum displacement and velocity are 15 and 12 cm s respectively the maximum short period acceleration at the period of 0 1 s is about 300 gal at the summit of mt ontake

correlation of change in magnetotelluric parameters before and after sikkim himalayan earthquakes associated with stress variation abstract mt stations that were recorded before the moderate 5 3 mw 2006 sikkim himalaya earthquake had been reoccupied after 2007 mw 5 0 and 2011 mw 6 9 seismic activities we analyzed the broadband mt data 0 001 1000 s within the 60 km radius from epicenters location and within the focal depth range of 9 30 km the observed change in apparent resistivity in the period range of 0 001 10 s has shown a considerable post seismic decrease of the order 10 30 the 2d geoelectric model constructed with post seismic acquired data also reveals the feature of a decrease in resistivity c1 the relative change decrease of observed apparent resistivity obs after 2006 2007 and 2011 earthquakes find a correlation with combined stress drop 11 18 2 mpa values estimated by arms approach the correlation is further strengthened by a similar change in relative apparent resistivities 2d model derived from 2d model with stress drop integrated stress drop values attribute to the accumulated apparent stresses a 0 23 that reveals the area might be subjugated to 0 6 1 2 mpa stress before 2006 1 1 5 mpa stress before 2007 and 1 7 2 9 mpa before 2011 earthquakes occurrence development of micro cracks and generation of aqueous fluids is possible due to such stressed and slow rate of relentless thrust shear environment within the area of crust therefore resistivity could have been decreased with a fluid transition from compression to dilatancy zones at different depth levels before each earthquake and further decreased upon subsequent stress drops associated with strong ground motions we interpreted that maximum stress might be dropped in dilatational zones oblique to the maximum compression stress directions along n200e n s and nnw sse before 2006 2007 and 2011 earthquakes and resulted in a considerable decrease in apparent resistivity along e w te mode i e yx component

paleoflow directions of a subaqueous lahar deposit around the miocene keserűs hill lava dome complex north hungary as constrained by photo statistics and anisotropy of magnetic susceptibility ams abstract a twofold fabric analysis by using photo statistics on rock surfaces and low field anisotropy of magnetic susceptibility ams is presented making it possible to infer paleoflow directions which in turn helps to constrain the primary volcanic geomorphology of a deeply eroded mid miocene field keser s hill lava dome group visegrad mountains north hungary the analyses were carried out on the ram hill pumiceous sandstone rhps that based on its petrographic features is considered as a subaqueously emplaced laharic deposit the observed anisotropic frequencies of clast a axis azimuths the good agreement of fabric directions obtained for all and most elongated samples elongation 2 5 the good clustering of the declinations of the k1 susceptibilities largely corresponding with the result of image analysis allow to infer reliable flow directions the obtained large scale paleoflow paths show a quasi radial pattern around the central part of the visegrad mountains which quantitatively confirms the previous hypothesis on the volcanic structure namely a central edifice topped syn eruptive topography the rhps is characterized by a clast fabric revealed by photostatistics on cutted rock surfaces considering the lapilli sized fraction as strong as in subaerial pdc deposits but by a significantly weaker magnetic fabric the weak magnetic fabric is supposed to be the result of rock heterogeneity thus the weakening effect of abundant lithic clasts with strong internal magnetic susceptibility anisotropy different from the shape anisotropy of the clasts and the flow related magnetic fabric of the fine grained matrix

uniform postglacial slip rate along the central 600 km of the kunlun fault tibet from 26al 10be and 14c dating of riser offsets and climatic origin of the regional morphology late pleistocene holocene sinistral slip rates on several segments of the kunlun fault in northeastern tibet have been determined these determinations are based on the measured displacement of alluvial surfaces whose surface ages were determined by cosmogenic 2 6 al and 1 0 be dating of quartz pebbles and by 1 4 c dating of charcoal in the west at three sites along the xidatan dongdatan segment of the fault near 94 e terrace riser offsets ranging from 24 to 110 m with cosmogenic ages ranging from 1800 to 8200 yr yield a mean left lateral slip rate of 11 7 1 5 mm yr 1 field observations indicate minimum offsets of 9 12 m this offset when combined with the long term slip rate indicates that great earthquakes m 8 rupture this segment of the fault with a recurrence interval of 800 1000 yr at two sites along the dongxi anyemaqin segment of the fault near 99 e terrace riser offsets ranging from 57 to 400 m with 1 4 c ages ranging from 5400 to 37 000 yr bp yield a minimum slip rate of 10 mm yr 1 at one site the 1937 january 7 m 7 5 and the penultimate earthquakes produced 4 m of left slip and 0 4 m of reverse slip the maximum recurrence interval of earthquakes with such characteristic slip is thus 400 yr farther east near 100 5 e along the maqen segment of the fault the 180 m offset of a lateral moraine emplaced between the last glacial maximum 20 ka and 11 100 yr bp yields a mean slip rate of 12 5 2 5 mm yr 1 the slip rates are constant within uncertainty throughout the 600 km of the kunlun fault that we studied the average slip rate is 11 5 2 0 mm yr 1 extrapolating this rate to the reminder of the fault we conclude that most 80 per cent of the 300 morphological offsets measured in the field or on spot satellite images post date the last glacial maximum most of the terraces we studied were deposited during the humid period of the early holocene optimum 9 5 ka the formation of younger terraces reflects late holocene climate change

neotectonics of the bailongjiang and hanan faults new insights into late cenozoic deformation along the eastern margin of the tibetan plateau

formation and evolution of strike slip faults rifts and basins during the india asia collision an experimental approach the processes which have governed the formation and evolution of large tertiary strike slip faults during the penetration of india into eastern asia are investigated by means of plane strain indentation experiments on layered plasticine models the steady state deformation of plasticine obeys a power creep flow law e c t n the stress exponent n is between 6 and 9 at 25 c uniaxial plane strain tests on cubic specimens show that the growth of faults in layered plasticine results from strain softening a process observed for strain rates ranging from 3 5 10 5 to 3 6 10 3 s 1 fault or shear zones form after only 7 10 bulk strain subsequent deformation is controlled by the geometry of the fault pattern rather than the physical properties of the plasticine a series of nine plane strain indentation experiments shows the influence of boundary conditions as well as that of the internal structure of the plasticine model on the faulting sequence the ubiquity of strain softening in experimental deformation of a variety of rocks as well as the widespread occurrence of shear zones in nature suggest that long term deformation of the continental lithosphere may also be primarily influenced by the geometry of large faults which rapidly develop with increasing strain the deformation and faulting sequence observed in the plasticine indentation experiments may thus be compared to collision induced strikeslip faulting in asia particularly to total offsets and rates of movements on the faults the experiments simulate the evolution of the western ends of the strike slip faults which have probably been analogous to trench fault fault triple junctions the experiments also illustrate mechanisms for the formation of extensional basins such as the south china sea north china basin and andaman sea near active continental margins the basins which appear to absorb terminal offsets along major strike slip faults near such margins may result from mismatch between the sharply angular shape of the deformed continental edge and the more regularly curved trench along which the smoothly flexed oceanic lithosphere subducts the existence of distinct phases of strike slip extrusion corroborates the idea that the discontinuities in time which typify intracontinental tectonics and orogenic cycles may often result from strain localization and the ensuing discontinuous non steady state deformation of the continental lithosphere

experimental study on microwave radiation from deforming and fracturing rock under loading outdoor previous studies have shown that thermal infrared anomalies can be detected in the crust rocks in satellite infrared images before an earthquake however thermal infrared remote sensing is easily affected by weather conditions because of the short wavelength of infrared radiation in this paper instead of infrared radiation we focus on the microwave radiation characteristics of loaded rock first a microwave observation system was built to observe the loading process of rocks in an outdoor environment with a cold sky background then the microwave radiation changes in the loaded granite samples during elastic deformation and fracturing stages were analyzed the experiments yielded the following results first the microwave brightness temperature has a linear positive correlation with the load in the elastic deformation stage of the granite samples and lateral pressure accelerates the changes in the microwave radiation second the microwave brightness temperature usually decreases as the rock develops layered fractures but increases as the rock develops surface fractures which significantly alter the surface morphology and roughness the mechanisms responsible for the changes in microwave radiation during the rock deformation and fracturing processes are discussed this study demonstrates the potential ability to use microwave sensing satellites to observe seismogenic processes and earthquakes

assessing the potential of thermal infrared satellite surveys for monitoring seismically active areas the case of kocaeli izmit earthquake august 17 1999 abstract space time anomalies of earth s emitted radiation in the thermal infrared spectral range tir measured from satellite months to weeks before the occurrence of earthquakes have been interpreted by several authors as pre seismic signals the claimed connection of tir emission with seismic activity has been considered up to now with some caution by the scientific community mainly for the insufficiency of the validation data sets and the scarce importance attached by those authors to other causes e g meteorological that rather than seismic activity could be responsible for the observed tir signal fluctuations in this paper a robust satellite data analysis technique is described which permits us to identify anomalous space time tir signal transients even in very variable observational satellite view angle land topography and coverage etc and natural e g meteorological conditions a statistically well founded definition of tir anomaly is given and proposed as a suitable tool for satellite tir surveys in seismically active regions eight years of meteosat tir observations have been analyzed in order to characterize the tir signal behavior at each specific observation time and location space time tir signal transients have then been analyzed both in the presence validation and in the absence of confutation seismic events looking for possible space time relationships the devastating earthquake which occurred in turkey izmit august 17 m s 7 8 in 1999 has been considered as a test case for validation relatively unperturbed periods no earthquakes with m 5 were taken for confutation purposes quite intense s n 3 5 and rare spatially extensive and time persistent tir signal transients were identified appearing eight days before the izmit main shock in greece moving to turkey on august 13 and disappearing moving back to greece some days after possible implications of such results together with present limitations of the proposed technique will also be discussed in the light of the improved performances expected by its extension to other existing or future satellite packages

magnetic fabrics of the bloodgood canyon and shelley peak tuffs southwestern new mexico implications for emplacement and alteration processes anisotropy of magnetic susceptibility ams of the middle tertiary bloodgood canyon and shelley peak tuffs of the mogollon datil volcanic field has been used to 1 evaluate the ability of ams to constrain flow lineations in low susceptibility ash flow tuffs 2 establish a correlation between magnetic fabric magnetic mineralogy tuff facies and characteristics of the depositional setting and 3 constrain source locations of the tuffs the tuffs are associated with the overlapping bursum caldera and gila cliff dwellings basin the high silica bloodgood canyon tuff fills the gila cliff dwellings basin and occurs as thin outcrops outside of the basin the older shelley peak tuff occurs as thin outcrops both along the boundary between the two structures and outside of the complex ams data were collected from 16 sites of bloodgood canyon tuff basin fill 19 sites of bloodgood canyon tuff outflow and 11 sites of shelley peak tuff sites were classified on the basis of within site clustering of orientations of principal susceptibility axes based on the categories of knight et al 1986 most microscopically visible oxide minerals in the bloodgood canyon tuff outflow and basin fill and in the shelley peak tuff are members of the hematite ilmenite solid solution series however irm acquisition data indicate that bloodgood canyon tuff basin fill and shelley peak tuff have magnetic mineralogy dominated by single or pseudo single domain magnetite and that the magnetic mineralogy of the bloodgood canyon tuff outflow is dominated by hematite hematite in bloodgood canyon tuff outflow is likely to be the result of deuteric and or low temperature alteration of magnetite and iron silicate minerals bulk magnetic susceptibility is higher in magnetite dominated ash flow tuff bloodgood canyon tuff basin fill and shelley peak tuff than it is in hematite dominated ash flow tuff bloodgood canyon tuff outflow bloodgood canyon tuff outflow has the highest total anisotropy h of the three units followed by shelley peak tuff and bloodgood canyon tuff basin fill all three ash flow tuffs are genearlly characterized by oblate susceptibility ellipsoids with those of the bloodgood canyon tuff basin fill nearest to spherical at high values of total anisotropy shelley peak tuff susceptibility ellipsoids attain a prolate shape those of bloodgood canyon tuff outflow attain an increasingly oblate shape three factors may influence differences in total anisotropy and susceptibility ellipsoid shape 1 ash which travelled the greatest distance before deposition may show the best development of magnetic fabric particularly of magnetic lineation 2 deposition of ash in a closed basin may inhibit laminar flow throughout the sheet and the resulting development of flow textures and 3 replacement of magnetite and iron silicates preferentially oriented within the foliation plane by hematite with strong crystalline anisotropy may enhance the magnetic susceptibility within that plane scatter in ams axis orientation within sites may result from 1 greater orientation inaccuracy in block sampled than in fielddrilled samples 2 rheomorphism and 3 low accuracy of ams measurement in low susceptibility ashflow tuffs evaluation of flow lineation based on ams of sites with well clustered k1 axes indicates that 1 bloodgood canyon tuff basin fill flowed along a generally northwest southeast azimuth 2 shelley peak tuff located on the boundary of the bursum caldera and the gila cliff dwellings basin flowed along a nearly east west azimuth and 3 bloodgood canyon tuff outflow sites have k1 susceptibility axes generally radial to the bursum gila cliff dwellings complex but within site scatter of k1 orientations is generally too large to draw conclusions about flow lineation orientation limited petrographic work on pilot thin sections adds flow direction information to ams derived flow lineation information

vashon drift definition of the formation in the georgia depression southwest british columbia vashon drift was deposited during the fraser glaciation late wisconsinan at the time of maximum expansion of the southwestern part of the cordilleran ice sheet when it filled the georgia depression about 14 500 years ago the drift is present throughout the depression and comprises till and glaciofluvial and glaciolacustrine sediments derived from source areas surrounding the coastal trough it is overlain by capilano sediments and underlain by quadra sand also of fraser age drift deposition was diachronous and complex probably caused by alpine glaciers coalescing in the trough with the ice margin repeatedly grounding and floating in seawater studies of bedrock striae till fabrics and clast provenance reveal that vashon ice movement was generally southward although locally controlled by topography a time space diagram is presented that confirms the long held hypothesis that advance and decay of vashon ice were rapid

isolation basin records of late quaternary sea level change central mainland british columbia canada isolation basin records from the seymour belize inlet complex a remote area of central mainland british columbia canada are used to constrain post glacial sea level changes and provide a preliminary basis for testing geophysical model predictions of relative sea level rsl change sedimentological and diatom data from three low lying 4 m elevation basins record falling rsls in late glacial times and isolation from the sea by 11 800 11 200 14c bp a subsequent rsl rise during the early holocene 8000 14c bp breached the 2 13 m sill of the lowest basin woods lake but the two more elevated basins sill elevations of 3 6 m remained isolated at 2400 14c bp rsl stood at 1 49 0 34 m above present mtl falling rsls in the late holocene led to the final emergence of the woods lake basin by 1604 36 14c bp model predictions generated using the ice 5g model partnered with a small number of different earth viscosity models generally show poor agreement with the observational data indicating that the ice model and or earth models considered can be improved upon the best data model fits were achieved with relatively low values of upper mantle viscosity 5 1019 pa s which is consistent with previous modelling results from the region the rsl data align more closely with observational records from the southeast of the region eastern vancouver island central strait of georgia than the immediate north bella bella bella coola and prince rupert kitimat and areas to the north west queen charlotte sound hecate strait underlining the complexity of the regional response to glacio isostatic recovery

organic geochemistry of saanich inlet bc during the holocene as revealed by ocean drilling program leg 169s abstract sites 1033 and 1034 of odp leg 169s in saanich inlet have an unusual diagenetic system that has the appearance of being depth reversed i e a bacterial methane accumulation zone underlain by a sulphate reduction zone during the late pleistocene grey undifferentiated glacio marine clays were deposited with low corg contents

detailed spatial changes in the stress field of the 1984 western nagano earthquake region 1 we estimate the stress field after the 1984 western nagano earthquake from numerous focal mechanisms to precisely determine the focal mechanisms we analyze the earthquakes that occurred around the eastern part of the main shock fault where station coverage is fairly good most of the earthquakes that occurred in this part except the main shock fault are reverse fault types in contrast earthquakes that occurred near the main shock fault have t axes distributed in a belt strike slip oblique slip and reverse fault types occurred equally using the stress inversion method to quantitatively estimate the stress field of these earthquakes revealed that the 2 axis near the main shock fault is close to the vertical direction whereas it is close to the horizontal direction in other regions at the western edge of the study area we observe that the 1 axis rotates toward the ns direction and that the stress ratio 1 2 1 3 is low we estimate that the magnitude of hmin decreases near the main shock fault spatial variation of the stress field around the eastern part of the main shock fault is not generated by static stress changes caused by the main shock local stress anomalies might have occurred around the main shock fault before the main shock

using quantitative textural analysis to understand the emplacement of shallow level rhyolitic laccoliths a case study from the halle volcanic complex germany received february 1 2002 accepted november 8 2002in qualitatively homogeneous magmatic bodies quantitativetextural analysis such as crystal size distribution modalabundance and spatial distribution pattern analyses allowstheir internal heterogeneity to be measured and interpreted inthis study these methods are applied to samples from a 300mdrill core through one of the porphyritic rhyolitic laccoliths petersberg unit of the 300ma halle volcanic complex germany qualitatively thegeochemicallyhomogeneouspetersbergunit does not show much textural variation quantitatively however the crystal size distributions of the three most commonphenocryst phases orthoclase plagioclase and quartz suggestcontinuouscrystalgrowthduringmagmaascentandemplacement but different growth histories of the phenocryst phases throughoutthe genesis of the laccolith in situ cooling did not affect thephenocryst population size distributions of the phenocrysts varyon a centimetre to decimetre scale but are similar on the scale ofthe laccolith the modal abundance of the phenocryst phases isvery similar throughout the drill core quantification of thespatial distribution of phenocrysts however reveals a trend forclusteringtowardstheinteriororupperpartofthelaccolith whichis attributed to flow and shear processes during emplacement anddiscontinuities in the interior relating to the intrusion of differentmagmapulses circularstatisticsoftheorientationoflongaxesofcrystals reveala weakalignment oftheorthoclaseand plagioclasephenocrystsonthesamplescaleasaresultofflowinthemagmainspite of little acicularity in general laccoliths can be fedby several pulses of magma without major cooling betweenbatches

grain orientation and depositional ramps as flow direction indicators of a large scale pyroclastic flow deposit in japan flow lineation was measured using the orientation of the elongated crystals and lithic fragments in the large scale welded ata pyroclastic flow deposit in southwestern japan in order to analyze the effect of preflow topographic relief three different types of lineations were obtained flow lineations radially away from the source were obtained only for samples collected from the surface of the pyroclastic flow plateau samples collected along the floor of narrow valleys have lineations parallel to the axis of valley samples collected from valley walls tend to be parallel to the slope of the valley this evidence suggests the following process earlier flow material moves along the valley axis in the narrow valley bottom when the flow is trapped within a valley it moves toward the bottom of the valley just prior to the final settlement when the basement relief is filled up with the earlier flow units the flow maintains its original radial movement until final settlement asymmetrical depositional ramps on the original surface of the pyroclastic flow provide an independent indicator of the flow direction

late pleistocene bison antiquus from orcas island washington and the biogeographic importance of an early postglacial land mammal dispersal corridor from the mainland to vancouver island abstract a bison antiquus cranium and partial skeleton from ayer pond wetland on orcas island san juan islands washington date to 11 760 70 14 c yr bp they lay in lacustrine sediments below peat unconformably above emergent everson glaciomarine drift 12 000 14 c yr bp several bison finds in similar contexts on orcas and vancouver islands dating between 11 750 and 10 800 14 c yr bp indicate an early postglacial land mammal dispersal corridor with reduced water barriers between mainland and islands new bison dates and published shell dates allow estimation of early postglacial relative sea level trends for the san juans with a drop below modern datum 12 000 14 c yr bp and assist in evaluation of marine reservoir corrections emergence by 60 m is suggested by data from nearby areas a tundra like or meadow community and succeeding open pine parkland before 11 000 14 c yr bp supported bison but horn core reduction suggests suboptimal forage or restricted habitat expanding mixed conifer forests after 11 000 14 c yr bp contributed to bison extirpation dispersing ungulates such as bison must have influenced island vegetation establishment and early succession possible evidence for butchering by early coastal people adds significance to the ayer pond discovery given its pre clovis age

grain size distribution of volcaniclastic rocks 1 a new technique based on functional stereology the power of explosive volcanic eruptions is reflected in the grain size distribution and dispersal of their pyroclastic deposits grain size also forms part of lithofacies characteristics that are necessary to determine transport and depositional mechanisms responsible for producing pyroclastic deposits however the common process of welding and rock lithification prevents quantification of grain size by traditional sieving methods for deposits in the rock record here we show that functional stereology can be used to obtain actual 3d volume fractions of clast populations from 2d cross sectional images tests made on artificially consolidated rocks demonstrate successful correlations with traditional sieving method we show that the true grain size distribution is finer grained than its representation on a random 2d section our method allows the original size of vesicular pumice clasts to be estimated from their compacted shapes we anticipate that the original grain size distribution of welded ignimbrites can also be characterized by this method our method using functional stereology can be universally applied to any type of consolidated weakly to non deformed clastic material regardless of grain size or age and therefore has a wide application in geology

sea level change and paleogeographic reconstructions southern vancouver island british columbia canada abstract forty eight new and previously published radiocarbon ages constrain deglacial and postglacial sea levels on southern vancouver island british columbia sea level fell rapidly from its high stand of about 75 m elevation just before 14 000 cal bp 12 000 radiocarbon yrs bp to below the present shoreline by 13 200 cal bp 11 400 radiocarbon years bp the sea fell below its present level 1000 years later in the central strait of georgia and 2000 years later in the northern strait of georgia reflecting regional differences in ice sheet retreat and downwasting direct observations only constrain the low stand to be below 11 m and above 40 m analysis of the crustal isostatic depression with equations utilizing exponential decay functions appropriate to the cascadia subduction zone however places the low stand at 30 5 m at about 11 200 cal bp 9800 bp the inferred low stand for southern vancouver island when compared to the sea level curve previously derived for the central strait of georgia to the northwest generates differential isostatic depression that is consistent with the expected crustal response between the two regions morphologic and sub bottom features previously interpreted to indicate a low stand of 50 to 65 m are re evaluated and found to be consistent with a low stand of 30 5 m submarine banks in eastern juan de fuca strait were emergent at the time of the low stand but marine passages persisted between southern vancouver island and the mainland the crustal uplift presently occurring in response to the late pleistocene collapse of the southwestern sector of the cordilleran ice sheet amounts to about 0 1 mm yr the small glacial isostatic adjustment rate is a consequence of low viscosity mantle in this tectonically active region

late quaternary stratigraphy and seafloor geology of eastern juan de fuca strait british columbia and washington abstract a combination of shallow sediment cores and high resolution seismic reflection data were used to identify and map four main surficial geologic units in eastern juan de fuca strait these units comprise bedrock unit 1 till diamict unit 2 glacial marine unit 3 and post glacial sediments unit 4 bedrock crops out only in nearshore environments off vancouver island diamicton forms the numerous morainal and drumlin like banks in the region a series of banks including middle and hein banks and the offshore extension of dungeness spit divide the strait into two major areas based on the dominant surficial sedimentary units post glacial sediments are most common to the east and glacial marine sediments to the west glacial marine sediments are represented by several seismo lithologic subunits that suggest progression from ice proximal to ice distal depositional environments radiocarbon dates indicate these sediments are a product of the last phase of glacier retreat there is relatively little modern sediment input to eastern juan de fuca strait so most post glacial sediments are thought to consist of material reworked from glacial outwash or eroded from shallow bank deposits this conclusion is supported by radiocarbon ages from the post glacial sediments most of which are early holocene or younger also there are sandwave fields sediment drifts and barrier spits that appear to be actively maintained the source of sediment to these features is probably the pre existing deposits that occur in banks and extensive coastal exposures

sediment characteristics and sea level history of royal roads anchorage victoria british columbia high resolution and airgun seismic reflection mapping of the approaches to esquimalt harbour juan de fuca strait reveal that offshore sea floor sediments consist of a widespread glaciomarine unit recognizable to the entrance of the strait the upper part of the unit has been dated at approximately 10 000 radiocarbon years bp an early postglacial sea level low of at least 50 m appears to have formed a widespread unconformity nearshore sediments above the unconformity consist of sands muddy fine sands and minor gravel that were deposited in a prograding marine environment sediments have been accumulating off esquimalt harbour at a rate of approximately 1 9 cm per 100 years

glacigenic and associated marine sediments in the weddell sea fjords of spitsbergen and the barents sea a review abstract studies of glacigenic and associated marine sediments in the weddell sea fjords of spitsbergen and barents sea show that during periods of limited glacial coverage interstadials large amounts of material may be brought into the sea mainly by meltwater the major load is deposited relatively close to the icefront 1 at times of maximum glacial extent grounded ice extends onto the shelf with the shelf edge as the outer limit and land and inner shelf areas are eroded main glacial depositional sites are then the outer shelf and shelf edge the sedimentary environment outside an ice shelf is characterized by low clastic supply mainly deposited from icebergs due to low turbidity and a supply of nutrient rich water biogenic matter accumulates leading to a glaciomarine sequence rich in bioclastics sea level lowering results in grounding and seaward expansion of the ice shelf subsequent eustatic rise causes the grounded ice to float deglaciation and sea level rise reduces clastic input to the shelves glacial sediments are reworked and carbonates may accumulate forming tillite carbonate sequence e g late precambrian break up of marine ice sheets such as the barents sea ice sheet seems to have taken place stepwise in response to eustatic rise and climatic changes

magnetic fabric investigations of pyroclastic deposits from phlegrean fields southern italy magnetic fabric investigations of pyroclastic deposits from phlegrean fields southern italy

decoding pyroclastic density current flow direction and shear conditions in the flow boundary zone via particle fabric analysis abstract one of the greatest challenges in volcanology is extracting information from volcanic deposits that inform the conditions at the time of emplacement here we explore particle shape fabric within samples from the column collapse pyroclastic density current pdc deposits generated by the 18 may 1980 eruption of mt saint helens msh particle shape fabric is the mutual alignment of particles within a sample which is dependent on shearing conditions at the time of deposition here particle shape fabric is used to address the following hypotheses 1 particle shape fabric will align with bulk flow direction estimates made by previous studies while resolving fine scale flow direction variations 2 samples extracted from pdc deposits immediately above a basal contact will show higher extents of fabric development i e clast alignment relative to samples extracted well above the contact and 3 samples extracted from cross stratified deposits will have higher extents of fabric development relative to samples extracted from the massive facies we find that fabric orientations approximate previous flow direction interpretations of general flow from south to north and channelization due to paleo topography furthermore shape fabric records flow interaction with the substrate created by debris avalanche deposits leading to fine scale variations in flow paths these variations are recorded in samples extracted near the substrate deposit contact moreover these samples do not show a higher measure of clast alignment relative to samples taken well above flow contacts but do exhibit bimodal clast alignment this suggests some degree of traction transport and thus higher shearing conditions relative to when the currents deposited massive lapilli tuffs samples extracted from the cross stratified deposits do not show higher extents of fabric development relative to the massive deposits supporting previous interpretations that these deposits formed from a rapidly sedimenting concentrated flow boundary zone that was thin enough to be frequently interrupted or influenced by the overriding turbulent portion of the flow finally observations of fine scale variability in measured fabric within a single outcrop indicates unsteady flow conditions and step wise aggradation during deposition this work demonstrates that particle shape fabric analyses can aid in decoding pdc flow conditions future complementary experimental work may allow for the extraction of quantitative information regarding the magnitudes of shear and subsequent particle alignments within the flow boundary zone providing further insight into pdc dynamics

local stress perturbations associated with the 2008 wenchuan m 8 0 earthquake near the longmenshan fault zone in the eastern margin of the tibetan plateau abstract the 2008 wenchuan m 8 0 earthquake induced local stress perturbations near the longmenshan lms fault zone using in situ measurements and stress tensor inversions from focal mechanisms we investigated the post earthquake perturbed stress field at shallow depths 1 2 km in the upper crust above a basal attachment 5 18 km as well as in the middle crust beneath a basal attachment 19 32 km at shallow depths in the beichuan jiangyou section the maximum principal stress 1 orientations changed from a pre earthquake orientation of nww to a post earthquake orientation of nee however near the baoxing an xian and qingchuan mianxian sections the pre earthquake 1 orientation of nw nww was largely unaltered before the mainshock in the upper crust above the basal detachment the entire lms fault zone exhibited a consistent 1 orientation of nw nww however after the earthquake some sections such as the beichuan nanba section achieved 1 orientations of nee that were distinctly different from the pre seismic stress field in the middle crust beneath the basal detachment the stress field was mostly unchanged the crust beneath the basal detachment along the eastern margin of the tibetan plateau is dominated by nww oriented maximum principle stress and strain directions and a thrust faulting stress regime along the entire lms fault zone these observations are representative of the southeastward motion of the bayan har block and its ongoing collision with the south china block along the lms thrust belt the spatially heterogeneous stress field that occurred in the upper crust 18 km after the mainshock was most likely caused by the co seismic static stress changes associated with the wenchuan earthquake prior to the onset of seismic activity the deviatoric stress magnitudes were estimated at less than 22 mpa and 4 mpa at depths of 10 km and 20 km respectively suggesting that the mainshock fault zone has a relatively low fault strength to overcome in order to initiate significant co seismic rupture and aftershocks especially in the crust beneath the basal detachment these smaller deviatoric magnitudes are indicative of the weaker fault materials that resides in the lms region

magnetic fabric flow directions and source area of the lower miocene peach springs tuff in arizona california and nevada we have used anisotropy of magnetic susceptibility ams to define the flow fabric and possible source area of the peach springs tuff a widespread rhyolitic ash flow tuff in the mojave desert and great basin of california arizona and nevada the tuff is an important stratigraphic marker from the colorado plateau to barstow california a distance of 350 km however the location of its source caldera is unknown dated at 18 5 ma by 40ar 39 ar the tuff erupted during the early stages of miocene extension along the lower colorado river the thicker accumulations 100 m occur at kingman arizona and in the piute mountains california on opposite sides of the colorado river extensional corridor our ams studies produced well defined magnetic lineations in 30 of 42 sites distributed throughout the tuff typical ratios of the principal ams axes are 1 01 for the magnetic lineation kmax kint and 1 02 for the foliation kint kmin the bulk magnetic susceptibility of the peach springs tuff averages 2 0 10 3 in the si unit system the subhorizontal lineations which presumably parallel the flow directions form a pattern radiating outward from the approximate center of the outcrop area magnetic foliations define an imbrication that generally dips away from the distal margins and toward the center of the outcrop of the tuff the lineation and imbrication indicate a source region near the southern tip of nevada defining the best intersection of the ams lineations required restoration of major extension strike slip faulting and associated tectonic rotation in the disrupted tuff the optimum intersection of magnetic lineations lies in the southern black mountains of arizona on the eastern side of the colorado river extensional corridor no caldera structures are known from that area but the area contains thick sections of the peach springs tuff above a silicic volcanic center the caldera may be buried under younger deposits in the mohave valley of arizona tertiary granite in the newberry mountains may represent a deeper level of the peach springs tuff vent that has been exhumed by detachment faulting

flow directions in ash flow tuffs a comparison of geological and magnetic susceptibility measurements tshirege member upper bandelier tuff valles caldera new mexico usa this study concludes that the elongation axis k 1 of the ellipsoid of anisotropic magnetic susceptibility ams is a suitable proxy for flow axis in ashflow tuffs 153 oriented samples 176 specimens were studied from 18 sites in the 1 1 ma tshirege member of the bandelier tuff these sites are distributed around the valles caldera at distances of 5 25 km outside of the rim k 1 axes correlate well with postulated radial flow axes at 13 sites k 1 also agrees with measured geological flow indicators mainly imbricated larger clasts at 7 sites at 2 of the 5 sites where significant disagreement is seen between theoretical radial flow directions and measuredk 1 axes thek 1 axes correspond well with geological flow indicators indicating that the divergence of flow from the predicted radial flow pattern is real two major topographic buttresses are suggested as the cause of flow divergence for the tshirege ash flows the san pedro buttress northwest of the caldera and the san miguel buttress in the southeast in situk 1 axes plunge about 7 toward the source at two thirds of the sites therefore the plunge ofk 1 is a plausible in situ indicator for thedirection of flow multiple flow zones in sections of several meters thickness indicate changes of flow direction that are both rapid and large during ash flow emplacement these observations raisre the question of how best to represent mean flow directions in ash flow sheets by eigenvector methods by vector sum methods or by modes a method for measuring imbrication of larger clasts using apparent dips in vertical joints is outlined imbrication determined in this way at one third of the sites dips toward the source i e up flow the minimum k 3 axis of the ams ellipsoid correlates with the flow foliation rather than with the larger clast imbrication the flow axes of ash flows correspond with thek 1 axes not with the declination ofk 3 axes as suggested by some authors initial dip of the sampled ash flows is not large and does not affect the paleomagnetic remanence direction which is reversed with a mean ofd 173 5 i 38 4 95 3 4 n 18 this mean is not different at the 95 confidence level from that of earlier workers the mean pole at 098 0 e 74 8 n a 95 3 3 n 18 is about 15 far sided relative to the expected time averaged geomagnetic pole suggesting a history of emplacement too short to adequately average secular variation

late quaternary sediments and geomorphic history of northern vancouver island british columbia materials from two glacial intervals and one nonglacial interval have been identified on northern vancouver island british columbia the oldest pleistocene unit termed older drift consists of glaciomarine silt and clay 38 000 years bp in age that overlie a till that has only been recorded in well logs older drift is tentatively correlated with dashwood drift of the semiahmoo glaciation early wisconsin or older no sediments of the succeeding olympia nonglacial interval mid wisconsin have been found in the area it is thought that this interval was characterized by a period of degradation in which olympia age sediments were deposited in transient sedimentary environments and subsequently eroded in part during the fraser glaciation late wisconsin the youngest pleistocene unit termed port mcneill drift includes advance deposits till and deglacial sediments all deposited during fraser glaciation ice of this glaciation did not cover most of northern vancouver island until after 20 600

remote sensing rock mechanics rsrm and associated experimental studies abstract the development of remote sensing rock mechanics rsrm was stimulated by meteorological satellite observations using infrared ir thermal images during earthquakes the experimental methods instruments and some typical results concerning the relations between the ir radiation and rock stress are introduced this paper explains that 1 the ir radiation energy including ir radiation temperature and ir spectral radiation intensity increases with loading 2 the ir radiation temperature increases with depth inside the rock specimen surface 3 the ir radiation temperature increases with rock strength and 4 the ir thermal image can anticipate the stress transfer process and rock fracturing location thus the study and application of rsrm includes detection of material behaviour resulting from heterogeneity and or stress application as well as mechanical failure and collapse as a time space forecast the experiment results have been supported by successful earthquake forecasts the key issues and future research directions for rsrm are suggested

detection algorithm of earthquake related rock failures from satellite borne microwave radiometer data it was experimentally confirmed that microwave energy is emitted during the compression of rocks land surface deformations are likely to be accompanied by rock failures from the experimental results we could conclude that the microwave signals generated by rock failures near the land surface are detectable by a satellite borne radiometer therefore we developed an algorithm to evaluate the microwave energy generated by rock failures on the land surface and applied the algorithm to the data of the advanced microwave scanning radiometer for the earth observing system for the earthquake that struck al hoceima morocco on february 24 2004 as a result we detected definitive microwave signals around the epicenter two days before the earthquake only in the entire observation period of six years this paper presents the details of the algorithm and the analysis results

submarine flow tills at victoria british columbia sea cliffs at victoria expose submarine flow tills within an ice contact complex of flow till outwash proglacial cones interbedded with dinoflagellate bearing glaciomarine fine sediments glacial debris flow lobes mainly flow tills were formed by supraglacially englacially and basally transported sediment slumping off an ice margin grounded in the strait of juan de fuca the structures and textures reveal that lobes formed by a conveyor mechanism in some lobes a double sorting phenomenon apparently developed involving an outer winnowed layer of pseudo plastic flow around an inner core of till that was sorted by dewatering and expulsion of fines outward from the centre during flow structures and fabric data indicate lobe travel was gravitationally controlled down cone flanks and independent of ice movement a depositional model for the complex proposes the ice margin produced a proglacial apron of interdigitating cones which accumulated on the sea floor sediment facies variations were probably c

paleoenvironments of the strait of georgia british columbia during the last deglaciation microfaunal and microfloral evidence the strait of georgia is situated between vancouver island and the western canadian mainland it was deglaciated quickly around 12 500 14c yr bp by in situ downwasting the subsequent marine invasion has left glacimarine sediments with foraminifers diatoms and dinocysts characterizing successive paleoenvironments recognizable basinwide the first paleoenvironment represents near ice conditions under the influence of the turbid meltwater plume marked by low algal productivity and few foraminifers mostly elphidium excavatum just off the plume the second environment shows a peak of nonionellina labradorica possibly resulting from an observed sudden increase in diatom numbers mostly ice dwelling forms implying a long annual sea ice cover further away cassidulina reniforme increases n labradorica decreases while other calcareous foraminifer species colonize the area there are fewer ice diatoms more marine planktonic diatoms and dinocysts become more abundant finally after 12 000 14c yr bp calcareous foraminifers are gradually replaced because of dissolution of calcium carbonate by a low diversity arenaceous assemblage at the same time abundant planktonic diatoms and dinocysts indicate warmer surface temperature the succession of fossils and environments compares well with modern horizontal off glacier successions observed in fjords of the european arctic

post glacial evolution of saanich inlet british columbia results of physical property and seismic reflection stratigraphic analysis abstract seismic stratigraphic analysis combined with results from odp leg 169s deep ocean drilling within saanich inlet to depths greater than 100 m below the seafloor provided an opportunity to study the post glacial development of the inlet in a quantitative manner the seismic stratigraphy of saanich inlet is consistent with the general stratigraphy established for southwestern british columbia sediment physical property data collected from odp hydraulic piston cores provide the mechanism with which to correlate the seismic stratigraphy with lithologic descriptions acoustic basement seismic unit 1 is bedrock likely devonian or carboniferous through middle and possibly late cretaceous wrangellian terrane acoustic unit 2 overlies bedrock and is interpreted as till or diamict it is variable in occurrence and thickness and most prominent in the central portion of the inlet with a maximum thickness of 247 m there is no evidence of earlier glacial advances thus it is likely a vashon drift from the latest glaciation the fraser stade acoustic unit 3 correlates with the grey massive silty clay of lithologic unit ii known regionally as the capilano formation and locally as victoria clay it is a glacial marine sediment resulting from outwash of the deteriorating ice sheet largely composed of silty mud with beds and stringers of sand and common ice rafted debris including some boulders sediment of this unit infilled the basin as evidenced by its thickness max 155 m and its flat lying upper surface its density values show a steep normal consolidation profile indicating relatively rapid deposition with no apparent over consolidation hemipelagic and pelagic deposition represented by unit 4 became the dominant sedimentation mechanisms in the holocene as glacial marine outwash declined this transition took place between 14 700 and 12 000 yr bp correlating with a time of rapid glacier recession and major relative sea level lowering relative sea level fell to a low of at least 45 m below present by about 9000 yr bp this low stand resulted in partial isolation of the inlet and the commencement of anoxic conditions in the deeper portions of the inlet unit 4 demonstrates very low bulk density and velocity values as a result of low grain densities high porosities and in situ gas it is a flat lying unit throughout the inlet pinching out on the steep inlet walls the unit thickens significantly to the north and then to the west this thickening results from surface water penetration of the cowichan river sediment plume terrigenous sediment input from the steep terrain on the west side of the inlet and tidal residuals forcing sediment laden waters to the western flank of the inlet incoherence of seismic reflectors within this unit may be the result of differential thickening but may also result from occasional debris flows or other mass wasting processes and fault offsets

pleistocene aminostratigraphy of the georgia depression southwest british columbia amino acid ratios of certain taxa of molluscs and wood were determined for quaternary sediments in the georgia depression southwest british columbia the stratigraphy and proposed ages of established major units are confirmed in all but one case by the amino acid results aspartic acid ratios in clinocardium serripes nuculana mya macoma and hiatella averaged about 0 22 0 23 0 37 0 28 0 28 and 0 27 respectively in late wisconsinan capilano sediments and 0 37 0 35 0 44 0 44 0 56 and 0 44 respectively in early wisconsinan dashwood and semiahmoo sediments d l ratios of aspartic acid in abies averaged about 0 14 in late wisconsinan fraser drift 0 24 in the middle wisconsinan cowichan head formation and 0 37 in the early wisconsinan dashwood and semiahmoo drifts whereas d l ratios of aspartic acid from picea averaged about 0 13 in the cowichan head formation and 0 27 in the sangamonian muir point formation ratios for the muir point formation are judged to be much too low for the age

image analysis and circular statistics for shape fabric analysis applications to lithified ignimbrites computer assisted image analysis can be successfully used to derive quantitative textural data on pyroclastic rock samples this method provides a large number of different measurements such as grain size particle shape and 2d orientation of particle main axes directional or shape fabric automatically and in a relatively short time orientation data reduction requires specific statistical tests mainly devoted to defining the kind of particle distribution pattern the possible occurrence of preferred particle orientation the confidence interval of the mean direction and the degree of randomness with respect to pre assigned theoretical frequency distributions data obtained from image analysis of seven lithified ignimbrite samples from the vulsini volcanic district central italy are used to test different statistics and to provide insight about directional fabrics first the possible occurrence of a significant deviation from a theoretical circular uniform distribution was evaluated by using the rayleigh and tukey 2 tests then the kuiper test was performed to evaluate whether or not the observation fits with a unimodal von mises like theoretical frequency distribution finally the confidence interval of mean direction was calculated with the exception of one sample fpd10 which showed a well developed bimodality all the analysed samples display significant anisotropic and unimodal distributions the minimum number of measurements necessary to obtain reasonable variabilities of the calculated statistics and mean directions was evaluated by repeating random collections of the measured particles at increments of 100 particles for each sample although the observed variabilities depend largely on the pattern of distribution and an absolute minimum number cannot be stated approximately 1500 2000 measurements are required in order to get meaningful mean directions for the analysed samples

a sea level database for the pacific coast of central north america a database of published and new relative sea level rsl data for the past 16 ka constrains the sea level histories of the pacific coast of central north america southern british columbia to central california our reevaluation of the stratigraphic context and radiocarbon age of sea level indicators from geological and archaeological investigations yields 600 sea level index points and 241 sea level limiting points we subdivided the database into 12 regions based on the availability of data tectonic setting and distance from the former cordilleran ice sheet most index 95 and limiting points 54 are 7 ka older data come mainly from british columbia and san francisco bay the stratigraphic position of points was used as a first order assessment of compaction formerly glaciated areas show variable rsl change where data are present highstands of rsl occur immediately post deglaciation and in the mid to late holocene sites at the periphery and distant to formerly glaciated areas demonstrate a continuous rise in rsl with a decreasing rate through time due to the collapse of the peripheral forebulge and the reduction in meltwater input during deglaciation late holocene rsl change varies spatially from falling at 0 7 0 8 mm a 1 in southern british columbia to rising at 1 5 0 3 mm a 1 in california the different sea level histories are an ongoing isostatic response to deglaciation of the cordilleran and laurentide ice sheets

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

late quaternary deglaciation and sea level history of eastern juan de fuca strait cascadia abstract eastern juan de fuca strait of southwestern british columbia northwestern washington state is near the western and southern terminus of late wisconsinan glaciation in north america seismic reflection profiles bathymetric data sediment core data and 41 new radiocarbon dates provide insight into the history of ice retreat and sea level change in the eastern portion of the strait the retreating ice margin appears to have passed through the area between 14 460 200 and 13 595 145 14c yr glacial marine sediments date between 12 889 50 and 11 110 50 14c yr bp wave eroded unconformities drowned prograded deposits and a partially isolated low stand basin are evidence attributed to low stand sea levels following deglaciation and five new control points on the local eustatic sea level curve are assigned based on radiocarbon dating of these features sea level change was rapid from 75 m immediately after deglaciation to possibly 60 4 m at 9920 60 14c yr bp after this time gradual sea level transgression took place relative sea level reached its approximate present position by 5470 115 14c yr bp since then relative sea level has remained constant suggesting eustatic rise is balanced by crustal uplift

precursors for rock fracturing and failure part i irr image abnormalities abstract there are many precursors including the abnormality of infrared radiation irr for rock fracturing and failure as the comprehensive effect of rock thermoelasticity and rock friction the study of the irr abnormality of loaded rock as one of the important issues of remote sensing rock mechanics rsrm is facilitated by the fast development of ir remote sensing imaging technology in view of energy input and consumption by the loading system comprised of loader rock and air the mechanism of surface irr from loaded rock is studied the concepts that surface irr is the comprehensive effect of a series of physical mechanical processes inside loaded rock and that the thermoelastic effect and the frictional thermal effect are two of the main mechanisms are presented here based on retrospective investigation of the fundamental experiments on rsrm during the past decade it is concluded that there are two kinds of irr abnormality as precursors of rock fracturing and failure irr image abnormality and irr temperature curve abnormality the spatial temporal evolution of abnormal surface irr images of loaded rock in a condition of uniaxial stress compressive shear biaxial stress frictional slide and impact is systematically analyzed the fact that large irr can occur in the fracturing center of compressively loaded and shearing fractured strong and brittle rock is also revealed finally the relation between rock stress and irr temperature are studied based on thermomechanical coupling theory for solid materials it is concluded that irr image abnormalities are important precursors for rock fracturing and meaningful for the forecast of rockbursts and tectonic earthquakes

center to center analysis and flow fabric characterization in ash flow tuffs the center to center method of strain analysis can be used to estimate flow lineation in high silica ash flow tuffs it can be used as an alternative or supplement to other techniques for flow lineation identification such as the examination of flow textures in thin sections and the measurement of anisotropy of magnetic susceptibility the center to center method is a modification of a technique described by fry 1979 and by ramsay and huber 1983 for determination of finite strain based on the spacing of particles within a deformed rock in the present study application of the method to an anticlustered array of phenocrysts in the flattening plane of an ash flow tuff produces an ellipse with center to edge distances representative of the minimum distance between centers of phenocrysts in all directions within the flattening plane the long axis of the ellipse corresponds to the maximum axis of finite strain this direction is suggested to correspond to the flow lineation the orientation of the stretching lineation was chosen both by eye and by least squares analysis from center to center plots the calculated orientation of the long ellipse axis can be varied by choice of a maximum distance between digitized objects which are included in the calculation comparison is made between late stage flow lineations identified using the center to center method and the ams anisotropy of magnetic susceptibility method on samples of the high silica oligocene bloodgood canyon tuff from the mogollon datil volcanic field of southwestern new mexico flow lineations based on center to center analyses of flattening plane parallel rock slabs and thin sections agree well with ams derived flow lineations on most samples from which high quality ams lineations were obtained center to center analuses from flattening plane perpendicular lineation parallel planes of ash flow tuff produce ellipses inclined from 15 to 85 to the flattening plane despite compaction of the ash which should cause angles of inclination to be very low the inclined ellipses may result from heterogeneities in grain size and distribution of phenocrysts in vertical sections of tuff or from fragmentation of phenocrysts which occurred during the final stages of emplacement and compression center to center analyses on rock slabs rather than thin sections helps to avoid the effects of either textural heterogeneity and fragmentation of phenocrysts with flow lineation identified by center to center analysis petrographic examination of thin sections cut perpendicular to the flattening plane and parallel to the flow lineation allow for the identification of flow direction

overview of late quaternary stratigraphy in saanich inlet british columbia results of ocean drilling program leg 169s abstract continuous coring in saanich inlet ocean drilling program odp leg 169s british columbia canada yielded a detailed record of late quaternary climate oceanography marine productivity and terrestrial vegetation two sites 1033 and 1034 were drilled to maximum depths of 105 and 118 m recovering sediments ranging in age from 13 300 to less than 300 14 c yr earliest sediments consist of dense largely massive gray glaciomarine muds with dropstones and sand and silt laminae deposited during the waning stages of glaciation deposition of organic rich olive gray sediments began in the fjord about 12 000 14 c yr ago under well oxygenated conditions as reflected by the presence of bioturbation and a diverse infaunal bivalve community at about 10 500 14 c yr a massive gray unit 40 50 cm thick was emplaced in a very short span of time the unit is marked by a sharp lower contact a gradational upper contact and an abundance of reworked tertiary microfossils it has been interpreted as resulting from massive flood events caused by the collapse of glacial dams in the fraser valley of mainland british columbia progressively greater anoxia in bottom waters of saanich inlet began about 7000 14 c yr ago this is reflected in the preservation of varved sediments consisting of diatomaceous spring summer laminae and terrigenous winter laminae correlation of the sediments was based on marked lithologic changes the presence of massive intervals reflecting localized sediment gravity flow events the mazama ash occasional thin gray laminae indicative of abnormal flood events in nearby watersheds varve counts between marker horizons and 71 accelerator mass spectrometry ams radiocarbon dates

co seismic strike slip and rupture length produced by the 2001 ms 8 1 central kunlun earthquake field investigations show that the surface wave magnitude ms 8 1 central kunlun earthquake tibetan plateau of 14 november 2001 produced a nearly 400 kilometer long surface rupture zone with as much as 16 3 meters of left lateral strike slip along the active kunlun fault in northern tibet the rupture length and maximum displacement are the largest among the co seismic surface rupture zones reported on so far the strike slip motion and the large rupture length generated by the earthquake indicate that the kunlun fault partitions its deformation into an eastward extrusion of tibet to accommodate the continuing penetration of the indian plate into the eurasian plate

discrimination of fault planes from auxiliary planes based on simultaneous determination of stress tensor and a large number of fault plane solutions it is well known that there is a large difference in focal mechanism solutions of events even if they occur within a certain small area considering earthquake generating stress to be uniform in a studied area we developed a new method for simultaneously determining the stress tensor and the orientation of fault planes for many events by the use of polarity data of p waves first the number of inconsistent stations is calculated for various values of three parameters in the focal mechanism solution with intervals of 10 this calculation is made for all the events used then four parameters defining the stress tensor are determined by a grid search using the data calculated above with the assumption that the slip direction in the fault plane should be parallel to the direction where the shear stress on the plane becomes maximum a numerical test is made by applying the present method to an artificial data set composed of 25 events with 25 25 readings it is found that a stable solution of the stress tensor is determined by the inversion and about 60 of fault planes are distinguished from auxiliary planes there are no events whose auxiliary planes are incorrectly determined as fault planes this method is used to estimate the earthquake generating stress in the aftershock area of the 1984 western nagano prefecture earthquake central japan the results obtained show that the maximum principal stress is horizontal in the direction of n80 w s80 e there are strike slip events having fault planes almost perpendicular to the fault plane of the main shock

computer assisted image analysis on clast shape fabric from the orvieto bagnoregio ignimbrite vulsini district central italy implications on the emplacement mechanisms abstract computer assisted image analysis can be succesfully used to derive quantitative information about grain size distribution particle shape and fabric on both consolidated and unconsolidated solid aggregates we have developed a new analytical method that provides a series of quantitative textural parameters from whatever particulate deposits by combining commercial image acquisition system with devoted c software after exhaustive tests of the method we applied it to a widespread quaternary ignimbrite formation in central italy the orvieto bagnoregio formation the results suggest some new aspects of emplacement mechanisms of ignimbrites 1 elongated particles shows variable degrees of flow related preferred orientation both on horizontal and vertical planes 2 vertical variations of flow related preferred particle orientations follow a zig zag pattern that we interpret to result from deposition by progressive aggradation during the passage of a particulate flow the filling up of paleovalleys by means of progressive aggradation proceeds flank to flank due to alternating flow directions induced by the already deposited material 3 the occurrence of vertically spaced peaks on the strength of clast orientation suggests the existence of discrete depositional units deposited by aggradation from an unsteady but persisting flow strong fabrics are inferred to result from the high amount of shear stress imparted to particles at the depositional boundary layer which at the same time can be responsible for the development of the basal inversely graded layer image analysis can also provide useful indications of paleoflow directions paleotopographic details and ignimbrite source areas

crustal stress field in southern california and its implications for fault mechanics we present a new high spatial resolution image of stress orientation in southern california based on the inversion of earthquake focal mechanisms we use this image to study the mechanics of faulting in the plate boundary region the stress field contains significant spatial heterogeneity which in some cases appears to be a result of the complexity of faulting and in other cases appears to be a cause temporal changes in the stress field are also observed primarily related to major earthquakes the observed 15 10 rotation of the stress axes due to the 1992 m7 3 landers mainshock implies that the deviatoric stress magnitude in the crust is low of the order of 10 mpa this suggests that active faults in southern california are weak the maximum principal stress axis near the san andreas fault is often at 50 to the fault strike indicating that the shear stress on the fault is comparable to the deviatoric stress the san andreas in southern california may therefore be a weak fault in a low strength crust

anisotropy of magnetic susceptibility in welded tuffs application to a welded tuff dyke in the tertiary trans pecos texas volcanic province usa consideration of published anisotropy of magnetic susceptibility ams studies on welded ignimbrites suggests that ams fabrics are controlled by groundmass microlites distributed within the existing tuff fabric the sum result of directional fabrics imposed by primary flow lineation welding and if relevant rheomorphism ams is a more sensitive indicator of fabric elements within welded tuffs than conventional methods and usually yields primary flow azimuth estimates detailed study of a single densely welded tuff sample demonstrates that the overall ams fabric is insensitive to the relative abundances of fiamme matrix and lithics within individual drilled cores ams determinations on a welded tuff dyke occurring in a choked vent in the trans pecos texas volcanic field reveals a consistent fabric with a prolate element imbricated with respect to one wall of the dyke while total magnetic susceptibility and density exhibit axially symmetric variations across the dyke width the dyke is interpreted to have formed as a result of agglutination of the erupting mixture on a portion of the conduit wall as it failed and slid into the conduit followed by residual squeezing between the failed block and in situ wallrock irrespective of the precise mechanism widespread occurrence of both welded tuff dykes and point welded aggregate pumices in pyroclastic deposits may imply that lining of conduit walls by agglutionation during explosive volcanic eruptions is a common process

holocene depositional evolution of a small active margin estuary of the northwestern united states seismic reflection data uniboom and c14 dated core samples from a small activemargin estuary alsea bay oregon indicate that holocene sediment fills an ancestral river valley which has an axial depth of 55 m below present sea level holocene sediment in the estuarine basin overlies late pleistocene and late pliocene valley fill deposits indicating several sequences of valley down cutting submergence and deposition core samples of holocene fill from six core sites in the estuary were analyzed for age embayment salinity indicators bulk density grain size distribution source mineralogy composition and sedimentary structures deposition of holocene fill has been dominated by lateral channel migration and overbank suspension deposition three stages of deposition during the holocene transgression are indicated on the bases of sedimentary structures grain size distribution and embayment salinity these stages represent periods of transition from 1 a shallow fluvial environment 10 103 7 5 103 yrs b p sedimentation rate between 0 4 and 0 7 cm yr 1 to 2 a deep water estuarine environment 7 5 103 5 103 yrs b p sedimentation rate approximately 1 1 cm yr 1 to 3 a shallow water estuarine environment 5 103 0 yrs b p sedimentation rate approximately 0 21 cm yr 1 a major decline in sedimentation rate at about 5 103 yrs b p follows a decline in the rate of eustatic sea level rise and a corresponding decrease in sediment accumulation rate the holocene fill is comprised of approximately 70 river sand 2 7 103 tonnes 20 river silt and clay 7 5 107 tonnes and 10 beach sand 2 9 107 tonnes comparisons of modern terrestrial sediment supply rates 2 8 105 3 2 105 tonnes yr 1 and long term retention rates of terrestrial sediment 3 45 104 tonnes yr 1 average for the last 1 104 yrs imply that the alsea bay basin has probably trapped 15 of the terrestrial sediment supplied to it

a record of past ocean atmosphere radiocarbon differences from the northeast pacific a record of the 14c age differences between atmosphere and the mixed layer of the northeast pacific ocean was obtained from 58 radiocarbon measurements on shells and associated wood from coastal sediments in british columbia this series of mixed layer reservoir ages spans the holocene and extends into the period of the younger dryas cold event in the north atlantic and surrounding regions the data reflect the extent of upwelling in the northeast pacific and thus constrain models of carbon cycling and ocean circulation most of the reservoir ages are only slightly less than than the present preindustrial value of about 800 years and may be identical when probable sampling errors are taken into account either the north pacific reached a state close to its present mode of circulation at or before the end of the younger dryas or a different circulation fortuitously produced a similar reservoir age our results support the hypothesis that slow changes in atmospheric radiocarbon concentrations over the holocene arose from 14c production rate changes data corresponding to a radiocarbon age of around 6400 years b p give a reservoir age of 1200 years if this result is confirmed it indicates a much greater variability for the holocene ocean circulation than was previously believed possible

numerical modeling of stress and strain associated with the bending of an oil pipeline by a migrating pingo in the permafrost region of the northern tibetan plateau abstract small seasonal pingos formed in quaternary deposits along active fault zones in permafrost of the northern tibetan plateau exert destructive forces to oil pipelines bridges culverts and other engineering facilities along the golmud lhasa railway and highway the pingos are particularly hazardous as they change position or migrate nearly every year three dimensional finite element modeling reveals the enormous force from exerted by a pingo at the 86th station of the highway a good representation of the stress and strain fields resulting from an expansion of a pingo and bending of an oil pipeline at the station are calculated after due consideration of the interaction between permafrost pingo and pipeline this followed establishing an engineering geologic model from the field data and determining the mechanical properties of the media from field and laboratory tests the maximum intermediate and the minimal principal compressive stresses are calculated as well as those for the plastic strain concentrations of principal stress and plastic strain occur beneath the pipeline bend and both the principal compressive stress and resulting plastic strain become very small away from the pingo also the bottom of the pingo is dominated by minimal values of principal stress and strain and the potential bending of a buried pipe caused by an expansion of a pingo is indicated to decrease as depth of burial increases the pingo growth at the 86th station resulted in the bending upward of a 20m section of a buried oil pipeline but it did not break and spill oil analysis of the pipe within the bend found the maximum intermediate and minimal principal compressive stress ranges that leads to plastic strain within the bent pipe compressive stress and plastic strain concentrations form in the inner sides of inflexions in the pipe bend and tensional stress and plastic strain concentrations form in their outer sides where stress exceeds the yield limit of the pipe but many irregularities are present such numerical modeling of stress and strain may offer key parameters for designing oil pipelines and engineered facilities to decrease the hazard from migrating pingos in similar geologic settings in the permafrost of the northern tibetan plateau

post glacial sea level change along the pacific coast of north america abstract sea level history since the last glacial maximum on the pacific margin of north america is complex and heterogeneous owing to regional differences in crustal deformation neotectonics changes in global ocean volumes eustasy and the depression and rebound of the earth s crust in response to ice sheets on land isostasy at the last glacial maximum the cordilleran ice sheet depressed the crust over which it formed and created a raised forebulge along peripheral areas offshore this combined with different tectonic settings along the coast resulted in divergent relative sea level responses during the holocene for example sea level was up to 200 m higher than present in the lower fraser valley region of southwest british columbia due largely to isostatic depression at the same time sea level was 150 m lower than present in haida gwaii on the northern coast of british columbia due to the combined effects of the forebulge raising the land and lower eustatic sea level a forebulge also developed in parts of southeast alaska resulting in post glacial sea levels at least 122 m lower than present and possibly as low as 165 m on the coasts of washington and oregon as well as south central alaska neotectonics and eustasy seem to have played larger roles than isostatic adjustments in controlling relative sea level changes

flow behavior of large scale pyroclastic flows evidence obtained from petrofabric analysis the grain orientations within the matrix of two large scale welded two small scale nonwelded and two nonwelded low aspect ratio pyroclastic flow deposits are measured to analyze flow behavior preferred grain alignments are especially apparent in the middle part of layer 2 of each deposit preferred grain alignments do not vary laterally within a 10 m interval the grain alignments obtained are radial from the source caldera especially in proximal to medial and plateau forming facies of pyroclastic flow deposits grain alignments are controlled by valley channel directions for the valley ponded facies of pyroclastic flow deposits especially at medial to distal locations such local topographic factors strongly affect the data for high aspect ratio and smallscale deposits and weakly affect the data for widespread low aspect ratio pyroclastic flow deposits this work suggests that grain alignment analysis should be used with care when attempting to determine the location of an unknown source

evidence of incremental growth in the vulsinian calderas central italy abstract a comparative work on the vulsini calderas has been carried out fundamentally from volcanological field study drilling and gravity anomalies data on the basis of a detailed stratigraphy four volcanic complexes have been recognized in the vulsini volcanic district from the oldest to the youngest paleo bolsena bolsena montefiascone and latera the latter two complexes having a contemporaneous evolution in their activity each complex gave rise to several little calderas caused by piecemeal collapses due to moderate size explosive eruptions or coherent subsidence of a superficial piston like block nevertheless the extensional volcano tectonic regime affecting this area could have accounted for as much of the total subsidence as the caldera forming eruptions bolsena and latera calderas respectively 16 km and 8 km in average diameter represent the main depressions of the vulsini district and their topographic features are still well preserved several collapses forming the main poligenetic calderas of bolsena and latera are masked at present by the bolsena lake the younger volcanic covering the lacustrine deposits and erosion in a minor amount only the little montefiascone and vepe calderas which represent the youngest collapses of the vulsini area have not been masked bolsena caldera could be considered a depression caused mostly by a subsidence hinged to the southwest by down sagging and by collapses which occurred after the most important explosive eruptions of the paleo bolsena bolsena and montefiascone volcanic complexes meanwhile latera caldera is mostly due to a piecemeal collapse linked to several moderate size ignimbrite units which were emplaced throughout the explosive activity of the latera complex therefore the vulsinian calderas did not form by catastrophic eruptions because several and frequent moderate size eruptions downsagging and tectonic hinged subsidence concur indicating an incremental growth

vent area and depositional mechanisms of the upper member of the neapolitan yellow tuff campi flegrei italy new insights from directional fabric through image analysis in order to provide new information about the source area and depositional mechanisms of the upper member of the neapolitan yellow tuff nyt a prominent pyroclastic deposit of the campi flegrei volcanic district southern italy statistics on directional fabric by means of computer assisted image analysis on 32 rock samples were compiled seventeen samples were collected along vertical direction on two selected exposures and fifteen were taken from outcrops widely distributed all around the campi flegrei volcanic district fabric measurements within the investigated successions reveal a vertically homogeneous direction of the mean particle iso orientation with considerable variability in the strength of particle iso orientation even at cm scale the existence of particle iso orientation can be related to continuous sedimentation from a concentrated bedload region beneath suspension currents producing massive or inversely graded beds by traction carpet sedimentation the considerable vertical variability in the strength of iso orientation is the result of very unstable flow regimes up to the extreme condition of discrete depositional events with a variable combination of traction carpet and or direct suspension sedimentation the vertical homogeneity in the mean orientation values found in the investigated sections may derive from the sequential deposition of laminae to thin beds whose relatively flat upper surfaces were unable to significantly deflect the depositional system of the following currents according to the observed homogeneous mean particle orientation values along the investigated vertical profiles samples collected through areal distribution are considered representative of the local paleo flow directions of the whole deposit the mean directions of the samples collected areally show two different coherent patterns which point to the existence of two different source areas the first which includes all samples from the northern outcrops appears to converge in a narrow area about 2 km ne of the town of pozzuoli largely in coincidence with the inferred area on the basis of the pumice fall distribution the second which includes samples from capo miseno and posillipo areas points to the central part of the pozzuoli bay about 4 km offshore the town of pozzuoli

systematic observations of the slip pulse properties of large earthquake ruptures in earthquake dynamics there are two end member models of rupture propagating cracks and self healing pulses these arise due to different properties of faults and have implications for seismic hazard rupture mode controls near field strong ground motions past studies favor the pulse like mode of rupture however due to a variety of limitations it has proven difficult to systematically establish their kinematic properties here we synthesize observations from a database of 150 rupture models of earthquakes spanning m7 m9 processed in a uniform manner and show the magnitude scaling properties of these slip pulses indicates self similarity further we find that large and very large events are statistically distinguishable relatively early at 15 seconds in the rupture process this suggests that with dense regional geophysical networks strong ground motions from a large rupture can be identified before their onset across the source region

migrating pingos in the permafrost region of the tibetan plateau china and their hazard along the golmud lhasa railway abstract most pingos in the permafrost region of the high northern tibetan plateau form along active fault zones and many change position annually along the zones and thus appear to migrate the fault zones conduct geothermal heat which thins permafrost and control cool to hot springs in the region they maintain ground water circulation through broken rock in an open system to supply water for pingo growth during the winter in overlying fluvial and lacustrian deposits springs remain after the pingos thaw in the summer fault movement earthquakes and man s activities cause the water pathways supplying pingos to shift and consequently the pingos migrate the hazard posed to the new golmud lhasa railway across the plateau by migrating pingos is restricted to active fault zones but is serious as these zones are common and generate large earthquakes pingos have damaged the highway and the oil pipeline adjacent to the railway since 2001 one caused tilting and breaking of a bridge pier and destroyed a highway bridge across the chumaerhe fault another has already caused minor damage to a new railway bridge furthermore the construction of a bridge pier in the north wuli fault zone in july august 2003 created a conduit for a new spring which created a pingo during the following winter measures taken to drain the ground water via a tunnel worked well and prevented damage before the railway tracks were laid however pier vibrations from subsequent train motion disrupted the drain and led to new springs which may induce further pingo growth beneath the bridge the migrating pingos result from active fault movement promoting artesian ground water circulation and changing water pathways under the seasonal temperature variations in the permafrost region they pose a serious hazard to railway construction which in turn can further disturb the ground water conduits and affect pingo migration

directional fabric measurements an investigative approach to transport and depositional mechanisms in pyroclastic flows abstract computer assisted image analysis data of rock fabrics from two quaternary ignimbrites in the vulsini and cimini volcanic districts of central italy are interpreted in terms of transport and depositional mechanisms samples were collected vertically at m spaces up two sections through each deposit the orvieto bagnoregio ignimbrite obi is a non welded ignimbrite that shows both fluctuations in the mean particle orientation values of up to approximately 60 and large variations in the strength of particle iso orientation with height the circular frequency distributions of particle orientations are almost always anisotropic and unimodal in line with a theoretical von mises distribution the circular equivalent of a unimodal log normal distribution in contrast the welded cimina ignimbrite ci shows vertical homogeneities in mean orientation values with height and generally lower degrees of anisotropy such differences are interpreted as being the results of different depositional mechanisms incremental deposition at the base of a density stratified partially turbulent flow for the obi deposition of a laminar mass flow for the ci in the former case during transport particles under solidus temperature are subjected to a frictional regime particles gliding and dispersive pressures which finally produce size inverse grading and variable fabric development depending on the residence time of particles at the basal shear conditions in the latter case elongated particles supported in a laminar flowing viscous matrix undergo periodic motions which tend to develop parallel to flow iso orientation fabric data in the deposit suggest vertical constancy in the rheological properties of the flow absence of rheological decoupling and shearing pervasively during transport a minor importance of plug horizons

surface area and volume measurements of volcanic ash particles by sem stereoscopic imaging abstract surface area of volcanic ash particles is of great importance to research including plume dynamics particle chemical and water reactions in the plume modelling i e plume shape particle interactions dispersion etc remote sensing of transport and so 2 hcl h 2 o co 2 levels forecasting plume location and transportation and deposition of ash particles the implemented method presented in this study offers new insights for surface characterization of volcanic ash particles on macro pore regions surface area and volumes of volcanic ash particles were measured using digital elevation models dem reconstructed from stereoscopic images acquired from different angles by scanning electron microscope sem the method was tested using glycidyl methacrylate gma micro spheres which exhibit low spherical imperfections the differences between measured and geometrically calculated surface areas were introduced for both micro spheres and volcanic ash particles in order to highlight the probable errors in modelling on volcanic ash behaviour the specific surface areas of volcanic ash particles using this method are reduced by half from mean values of 0 045 m 2 g to 0 021 m 2 g for the size increment 63 m to 125 m ash particles mostly have higher specific surface area values than the geometric forms irrespective of particle size the specific surface area trends of spheres and ash particles resemble for finer particles 63 m approximation to sphere and ellipsoid have similar margin of error for coarser particles 125 m but both seem to be inadequate for representation of real ash surfaces