a scaling law for slow earthquakes with the availability of the global positioning system and other technical advances a growing number of unusual earthquake phenomena occurring at relatively long periods have been recognized they include deep episodic tremor low frequency earthquakes slow slip events and silent earthquakes based on data chiefly from western japan ide et al report that these slow seismic events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes a diverse array of unusual earthquake phenomena occurring at relatively long periods slow events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes indicating that they comprise a new earthquake category recently a series of unusual earthquake phenomena have been discovered including deep episodic tremor1 low frequency earthquakes2 very low frequency earthquakes3 slow slip events4 and silent earthquakes5 6 7 8 9 each of these has been demonstrated to arise from shear slip just as do regular earthquakes but with longer characteristic durations and radiating much less seismic energy here we show that these slow events follow a simple unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes we find that their seismic moment is proportional to the characteristic duration and their moment rate function is constant with a spectral high frequency decay of f 1 this scaling and spectral behaviour demonstrates that they can be thought of as different manifestations of the same phenomena and that they comprise a new earthquake category the observed scale dependence of rupture velocity for these events can be explained by either a constant low stress drop model or a diffusional constant slip model this new scaling law unifies a diverse class of slow seismic events and may lead to a better understanding of the plate subduction process and large earthquake generation

paleotsunami research along the nankai trough and ryukyu trench subduction zones current achievements and future challenges abstract located near japan s most densely populated and industrially active region the nankai trough subduction zone has long been highlighted as a high risk area for damaging earthquakes and tsunamis in contrast less attention has been paid the adjacent ryukyu trench because historical and geological records are scarce in order to develop better quantitative estimates of the timing and size of the earthquakes and tsunamis generated along these subduction zones comprehensive studies using geological seismological and historical methods have been conducted since the 1990s studies of tsunami deposits in this region have contributed to our current understanding of the history of tsunamis over the last 6000 years following the 2011 t hoku earthquake and tsunami paleotsunami research has especially focused on guiding and enhancing tsunami disaster management and mitigation measures the last nine years have seen a rapid increase in paleotsunami data from the nankai trough and ryukyu trench coasts these recent studies reveal that there are significant differences in the size and recurrence pattern of earthquakes and tsunamis along these subduction zones for instance large earthquakes have repeatedly occurred along the nankai trough every 100 200 years on the other hand large earthquakes and tsunamis may not have occurred over the last few thousand years at the junction between these subduction zones there is also no evidence for the occurrence of large earthquakes along the northern and central ryukyu trench over this time period large earthquakes and tsunamis may have occurred every few hundred years at the southern end of the ryukyu trench nevertheless data on the occurrence of these earthquakes are still insufficient both in quantity and quality to estimate the maximum size or recurrence pattern

deep marine arc apron deposits and syndepositional magmatism in the alisitos group at punta cono baja california mexico rocks exposed at punta cono include very fine grained to coarse grained tuffs lapilli tuffs and tuff breccias deposited in a deep marine environment syndepositional basaltic intrusive activity was common in one locality a hyaloclastite peperite complex formed slumped sections with fluidal basalt clasts derived from intrusions that entered the sediment pile from below are present elsewhere abundant soft sediment folds in fine grained laminated subaqueous fall out tuff suggest steep gradients these are cut by shallow channels filled with coarse grained tuff lapilli tuff and rare tuff breccia the combination of marine fossils extreme textural immaturity abundant slump features and syndepositional magmatism indicates deposition upon the submarine flanks of an active volcano recognition of magma wet sediment interaction is hampered in volcaniclastic rocks because of the similarity between host and intrusive fragments products of magma water sediment interactions at punta maria include 1 jigsaw puzzle hyaloclastite formed by non explosive hydroclastic fragmentation of magma upon contact with water and water bearing sediment 2 peperites produced by mixing of magma with sediment and 3 an unusual tuff breccia unit the result of non explosive mixing of wisps of lava with sediment during remobilization of an unconsolidated section low explosivity magma water sediment interactions are favoured by relatively high hydrostatic pressures in sub wave base settings

tsunami recurrence revealed by porites coral boulders in the southern ryukyu islands japan information about past tsunami hazards such as their recurrence interval and magnitude is needed for future disaster prediction and mitigation we examined radiocarbon ages of the surfaces of massive coral boulders cast ashore by past tsunamis in the southern ryukyu islands japan where few historical and geological records of past tsunamis are available we selected only non eroded porites coral boulders along the shoreline because their characteristics make it possible to determine the probable timing of their deposition by tsunamis and we applied a dating method that uses the cumulative probability distributions of large numbers of radiocarbon measurements of those boulders to determine the timing of past tsunamis the results demonstrate that the southern ryukyu islands have repeatedly experienced tsunami events since at least 2400 yr ago with a recurrence interval of 150 400 yr the largest porites tsunami boulder that we studied long axis 9 m which is probably the largest single colony tsunami boulder in the world was displaced by the a d 1771 meiwa tsunami although the 1771 meiwa tsunami was likely the largest event in at least the past 700 yr calculations of current velocity show that all identified tsunamis occurring before 1771 were probably large enough to cause considerable damage to human built structures and loss of life this study demonstrates that by reliably dating large numbers of selected coastal boulders it is possible to ascertain the timing recurrence interval and magnitude of past tsunamis in a location where few adequate survey sites of sandy tsunami deposits exist

glauconitic sediments on the continental shelf off vancouver island british columbia canada abstract the tectonically active vancouver island continental margin is characterized by a very narrow 80 km continental shelf and an extremely steep continental slope the shelf is marked by high wave and current energies on the inner nondepositional shelf and very slow rates of sediment accumulation on the outer shelf within the muddy sands of the outer shelf and slope glauconitic grains are frequently an important constituent of the sand fraction occurring in four principal forms a locally abundant pale green infillings of benthic foraminifera b very abundant pale to moderately dark green dull grains displaying varying degrees of fracturing of the external surfaces c scarce moderately dark green altered and expanded mica grains and d scarce very dark green small 200 m grains with polished highly fractured surfaces mineralogically the grains mainly reflect their origins as detrital sediments they consist most commonly of quartz plagioclase minerals chlorite smectite and illite also a mixed layer mineral smectite illite occurs in significant amounts in glauconitic grams but is absent in unaltered mud fragments and in the clay fraction of sediments from the outer shelf the appearance of this mineral reflects the first stages of glauconite authigenesis bulk analyses of glauconitic grains yielded k2o values of less than 2 reflecting their very early stage of evolution but 19 28 fe2o3 several times the level in the surrounding matrix sediments microprobe analyses and scanning electron microscopy show that glauconitic smectite forms in the pores and along fractures in the host grains commonly as a boxwork arrangement or rosette clusters of blades fe2o3 and k2o values at these sites can reach 32 5 and 7 5 respectively several lines of evidence including radiocarbon age determinations on glauconitized foraminifera tests indicate a recent age for the vancouver island shelf glauconitic grains

tidal sensitivity of shallow very low frequency earthquakes in the ryukyu trench we show that the activity between 2002 and 2014 of shallow very low frequency earthquakes vlfes which occur in shallow subduction zones of the ryukyu trench responds to ocean and earth tides tidal sensitivity is highest in the central portion of the ryukyu trench and lowest in the southwest the lag of peak vlfe activation behind the peaks of shear stress or normal stress is laterally heterogeneous along the ryukyu trench the lateral variation of the lag between the peaks of sensitivity and stresses can be explained by the dependence of vlfe activation on thrust encouraging shear stress on the plate the effective normal stress which is calculated through rock experiments and from the sensitivity of vlfe for shear stress is 0 25 mpa in the central ryukyu trench which implies that high pore pressure on the plate interface would induce the vlfes the lateral variation of the sensitivity can be explained by differences in pore pressure within the plate interface although tidal sensitivity is lowest in the southwestern ryukyu trench it increased temporarily during the middle of the decay of vlfe swarm activity this is interpreted as reflecting a temporary increase in pore pressure on the fault frictional heterogeneity or fault weakening during the slip of slow slip events

shallow water eruption fed mafic pyroclastic deposits along a paleoproterozoic coastline kangerluluk volcano sedimentary sequence southeast greenland abstract the 200 300 m thick volcano sedimentary sequence at kangerluluk is part of the psammite zone one of four major zones which constitute the 1 8 ga ketilidian orogen in south greenland three lithofacies are emphasized in the study 1 the conglomerate sandstone 2 the volcanic and 3 the pyroclastic lithofacies the 2 40 m thick conglomerate sandstone lithofacies represents a subaerial to subaqueous fan delta deposit matrix and clast supported conglomerates are interpreted as debris flow and longitudinal gravel bar deposits erosive based conglomerate channel fills attest to stream incision trough crossbedded sandstone interpreted as lunate megaripples planar bedded sandstone indicative of upper flow regime bar top sands and small scale trough crossbeds reflecting ripples follow up section form collectively with the conglomerate 0 40 2 50 m thick fining upward sequences the sandstone dominated unit up section from the conglomerates and composed of planar and low angle crossbeds minor ripples and graded beds as well as mudstone is indicative of a lower shoreface deposit below normal wave base the clastic sedimentary rocks are suggestive of a fan delta setting the 100 200 m thick volcanic lithofacies composed of pillowed and pillow brecciated lava flows is consistent with shallow water deposition interstratification of lava flows with both conglomerate sandstone and pyroclastic lithofacies intrusion of dykes into volcaniclastic rocks and peperite formation accentuate contemporaneity between volcanism and sedimentation and is a common feature of island arcs the 1 50 m thick pyroclastic lithofacies with sharp depositional contacts to the overlying volcanic and underlying conglomerate sandstone lithofacies was emplaced in a subaqueous setting the lithofacies is divided into a planar to crossbedded tuff lapilli tuff and a bedded lapilli tuff breccia whereby both deposits are inferred to result from shallow water surtseyan type eruptions the 5 15 m thick bedded lapilli tuff breccia with abundant bomb sag structures and graded beds is considered a result of subaqueous eruptions strong enough to form an insulating steam cupola characterized by ballistically emplaced bombs that rapidly collapsed allowing for transport via mass flow processes the deposits are considered proximal to the vent the 2 50 cm thick planar to crossbedded tuff lapilli tuff featuring abundant euhedral and broken crystals of feldspar 2cm and minor pyroxene 1 cm are massive graded crossbedded and stratified the planar but laterally discontinuous beds characterized by abundant low angle scours are interpreted as low to high concentration sediment gravity flows produced directly from subaqueous tephra jets that collapsed due to massive water ingestion local breccia size pyroclasts disrupting beds are interpreted as bomb sags the mafic eruption fed surtseyan type deposits postulated to be a subaqueous counterpart of cold subaerial base surges originate from subaqueous tuff cones formed along a rugged volcanic dominated shoreline featuring high energy fan deltas

very low frequency earthquakes along the ryukyu subduction zone 1 a total of 1314 very low frequency earthquakes vlfes were identified along the ryukyu trench from seismograms recorded at broadband networks in japan f net and taiwan bats in 2007 the spectra of typical vlfes have peak frequencies between 0 02 to 0 1 hz among those waveforms from 120 vlfes were inverted to obtain their centoroid moment tensor cmt solutions and locations using an examination grid to minimize a residual between the observed and synthetic waveforms within an area of 11 14 in latitude and longitude and at depths of 0 to 60 km most of the vlfes occur on shallow thrust faults that are distributed along the ryukyu trench which are similar to those earthquakes found in honshu and hokkaido japan the locations and mechanisms of vlfes may be indicative of coupled regions within the accretionary prism or at the plate interface this study highlights the need for further investigation of the ryukyu trench to identify coupled regions within it

very low frequency earthquakes off the pacific coast of tohoku japan we found very low frequency earthquakes vlfes at a shallow subduction zone close to the japan trench off the pacific coast of tohoku japan centroid moment tensor solutions of vlfes showed reverse fault mechanisms with a compression axis in the east west direction a cross correlation analysis of seismograms with template events between 2005 and 2013 revealed three major vlfe clusters and their temporal evolution a vlfe cluster in the central off tohoku region located in the large slip area of the 2011 tohoku earthquake was detectable only before the tohoku earthquake however vlfes in the northern and southern off tohoku regions at the rim of the large slip area were activated after the tohoku earthquake the change in the activity may reflect the stress redistribution by the coseismic and or afterslip processes of the tohoku earthquake

proterozoic sedimentation and volcanism in the singhbhum crustal province india and their implications abstract the proterozoic volcano sedimentary succession comprising successively younger dhanjori chaibasa dhalbhum dalma and chandil formations of the singhbhum crustal province india records sedimentation and volcanism in a rapidly changing tectonic scenario cooling of the vast volume of archaean singhbhum granite possibly induced an isostatic readjustment the associated tensional regime and deep seated fractures controlled the formation of the proterozoic singhbhum basin the dhanjori formation unconformably overlies the singhbhum granite and is entirely terrestrial dominantly fluvial at the base the conglomerate deposits coarse grained sandstone and shale represent the distal fringe of an alluvial fan complex the rest of the formation including the volcaniclastic rocks consists almost entirely of fining upward fluvial cycles the base of the dhanjori formation is a sequence boundary and the formation itself represents a lowstand systems tract the dhanjori volcano sedimentary succession displays evidence of having passed through passive as well as active phases of continental rifting with an increasingly important influence of volcanism on the sedimentation through time the chaibasa formation sharply overlies the dhanjori formation and a transgressive lag demarcates their contact the basal part of the chaibasa formation immediately overlying the transgressive lag deposit represents a transgressive systems tract while offshore shales that sharply overlie the shallow marine sandstones up section represent marine flooding surfaces the shallow marine subtidal sandstones bear an excellent record of sandwave migration and provide a rare opportunity to unlock the late palaeoproterozoic lunar orbital periodicities unlike the chaibasa the overlying dhalbhum formation is entirely terrestrial fluvial aeolian indicating that the chaibasa dhalbhum contact is a sequence boundary the dalmas overlying the dhalbhum formation represents concordant lava outpourings without any break in sedimentation these lavas are genetically related to mantle plume upwelling in an intracontinental rift setting the volcano sedimentary package lying north of the dalma volcanic belt chandil formation is of mesoproterozoic age the entire late palaeoproterozoic volcano sedimentary package displays post depositional compressional deformation and greenschist to amphibolite facies metamorphism dated at ca 1600 ma forming the so called north singhbhum fold belt the volcano sedimentary package lying south of the dalma volcanic belt was pushed further south towards the singhbhum granite batholith complex as a result of uplift related to the dalma plume the singhbhum granite batholith acted as a rigid body this gave rise to a compressional stress regime that induced shearing thrusting at ca 1600 ma along the singhbhum shear zone the dalma plume magmatism was possibly part of a 1600 ma global tectono thermal event

k bentonites volcanic ash preservation and implications for early to middle devonian volcanism in the acadian orogen eastern north america lower to middle devonian marine strata in the appalachian foreland basin feature up to 80 or more thin k bentonites that represent ancient volcanic ashes the time vs space distribution of k bentonites through the lochkovian to eifelian stages representing 30 m y shows a distinct pattern of clustered multiple beds several scattered beds and thick intervals with no k bentonites four clusters of 7 to 15 individual closely spaced layers occur in the middle lochkovian bald hill k bentonites kalkberg new scotland formations late pragian or early emsian sprout brook k bentonites esopus formation and early eifelian two clusters the tioga middle coarse zone and tioga a g k bentonites onondaga formation detailed examination of these devonian k bentonites shows that in many cases they do not represent a single eruption multilayered beds fossil layers within beds authigenic minerals e g glauconite and phosphate nodules subjacent hardgrounds and an irregular distribution of beds through space and time raise questions about the depositional history and preservation potential of volcanic ash in marine environments and the degree to which the beds represent a primary record of volcanism these and other lines of evidence indicate that postdepositional physical biological and geochemical processes e g sedimentation rate event and background physical processes burrowing have modified the primary record of these water laid ash fall events these factors may lead to preservation of primary ash deposits or to their resedimentation and or partial to complete mixing with background sediments the preservation potential and resulting distribution of the devonian k bentonites can be analyzed across a spectrum of preservational magnafacies in this paper i present a model of ash preservation the model incorporates environmentally related physical biological and chemical processes active in epicontinental seas and marine foreland basins conclusions based on the model indicate that the middle lochkovian early emsian and early eifelian were times of peak volcanic activity in eastern north america related to times of increased tectonism in the acadian orogen

very low frequency earthquakes within accretionary prisms are very low stress drop earthquakes 1 we report characteristic p wave spectra and stress drops of very low frequency vlf earthquakes that occurred within the accretionary prism along the nankai trough southwestern japan although many vlf earthquakes showed no distinct phases on a raw seismogram a few showed slightly distinct phases the arrival times of some phases were consistent with the calculated p wave arrival times the corner frequencies of the vlf earthquakes were calculated using the stacked p wave spectra assuming an omega square spectrum stress drops were very low i e in the range of 0 1 10 kpa which corresponds to 0 1 1 of those of ordinary earthquakes such extremely low stress drops of the vlf earthquakes suggest that the fault strength within the accretionary prism may have weakened due to the existence of a fluid within the thrust fault system of the accretionary prism

theoretical wave modeling of large wave ripples in volcaniclastic sediments ordovician llewelyn volcanic group north wales abstract volcaniclastic sedimentary rocks of ordovician age underlying the garth tuff member of the capel curig volcanic formation north wales were deposited on a shallow marine shelf deposition at the capel curig anticline 2 km southwest of capel curig was on a high energy proximal offshore to foreshore analysis of large wave ripples and associated sedimentary structures suggests a shallow marine depositional environment above storm wave base and in water depths of 10 30 m this estimate of water depth from wave calculations is similar to that estimated by facies analysis

interplate coupling in the kanto district central japan and the boso peninsula silent earthquake in may 1996 i studied crustal deformation in the kanto district central japan based on continuous gps data horizontal as well as vertical displacement rate demonstrate significant interaction between the landward kanto block and the philippine sea plate although the subduction effect of the pacific plate is not apparent it is reasonable to consider the entire kanto district is displaced westward due to the interaction with the pacific plate the gps velocity data were inverted to estimate the slip deficit distribution on the sagami trough subduction zone the result delineates a strongly coupled region on the plate interface part of which corresponds to the 1923 kanto earthquake the strongly coupled region is located shallower than 20 km in addition the plate interaction is laterally heterogeneous even in the same depth range implying thermal structure is not the only factor controlling interplate coupling the gps data also detected a silent earthquake event on the interface of the philippine sea slab east of the boso peninsula in the middle of may 1996 the silent rupture propagated over a 50 km 50 km wide area during about a week the maximum slip was approximately 50 mm and the released seismic moment was 4 7 1018nm mw 6 4 there was a small seismicity triggered by this silent event the silent slip was located in the peripheral of the strongly coupled area suggesting that frictional properties and or stress conditions are inhomogeneous on the plate boundary interface

very low frequency earthquakes spatiotemporally asynchronous with strong tremor during the 2014 episodic tremor and slip event in cascadia we find very low frequency earthquakes vlfes in cascadia during the 2014 episodic tremor and slip event under washington and vancouver island using a grid search centroid moment tensor inversion method the very low frequency earthquakes occur when and where there is no strong tremor detected contrasting with previous findings where tremor and very low frequency earthquakes have a clear spatiotemporal relationship this challenges our current understanding of the dynamic relationship between the different types of slow earthquakes and their relationship to slow slip we interpret these findings to suggest that vlfes and tremor may have their own seismic cycles resulting from asperities of different sizes or characteristics that respond pseudo independently to stress loading we propose that very low frequency earthquakes and tremor are subject to asynchronous seismic cycles

depositional facies of high energy beach to offshore sequence comparison with low energy sequence a study of the nearshore zone and continental shelf of a high energy coast was made in the ventura port hueneme area of california during the summer of 1974 to investigate depositional facies characteristics and compare them with similar facies from a low energy coastal setting analysis of box cores can cores and vibracores permits recognition of three principal zones 1 nearshore facies backshore to 9 m water depth made up primarily of parallel ripple and cross bedded clean sand bioturbation is only locally significant 2 transition facies 9 to 18 m water depth a zone of fine sand and silty sand characterized by an increase in biogenic over physical sedimentary structures that are commonly preserved as laminated to burrowed beds wave ripple bedding and parallel lamination are important structures in this facies 3 offshore facies 18 m water depth sandy silt is the primary texture and bioturbation is the dominant sedimentary structure remnant parallel lamination is the only physical sedimentary structure present comparison of the results of this study with a previous description of a low energy beach to offshore sequence at sapelo island georgia indicates that the two areas do not differ greatly in their facies or overall vertical sequence of sedimentary structures the principal difference is in the thickness of the three facies the california facies are significantly thicker than their georgia counterparts this difference is in direct response to the role of higher wave energy on the california coast

localized tsunamigenic earthquakes inferred from preferential distribution of coastal boulders on the ryukyu islands japan the occurrence of large earthquakes and tsunamis along the ryukyu trench is a subject of continuing interest the key to which is the long term geological record here we describe the clast size and spatial distributions of 2900 boulders on the reefs of the ryukyu islands japan as markers of paleotsunamis and causative tsunamigenic earthquakes boulders of tsunami origin were observed only at a specific island group at the southern end suggesting the local occurrence of tsunamigenic earthquakes there in contrast in the central to northern ryukyu islands no evidence exists of tsunamis larger than those at the southern end of the ryukyu islands during the past 2000 3000 yr these islands have numerous boulders deposited by storm waves during the past 2300 yr or earlier their spatial distribution has not been disturbed by large tsunamis this suggests that large tsunamis did not strike this area during that period nevertheless these regions are seismically active our study shows that coastal boulder deposits present great potential to not only ascertain the histories and effects of paleotsunamis but also to constrain fault models of the causative earthquakes

from soft sediment deformation to fluid assisted faulting in the shallow part of a subduction megathrust analogue the sestola vidiciatico tectonic unit northern apennines italy

eruption processes and facies architecture of the orion central kimberlite volcanic complex fort a la corne saskatchewan kimberlite mass flow deposits in a sedimentary basin abstract the fort a la corne diamondiferous kimberlite field consists of at least 70 bodies of volcaniclastic kimberlite hosted within a contemporaneous non volcanic sedimentary succession this study of the three dimensional stratigraphy and facies architecture across the orion central kimberlite volcanic complex highlights the variations in upper and extra vent processes the sedimentary succession consists of continental to marginal marine quartz sandstones and mudstones overlain by marginal to deep marine dark mudstone and muddy sandstones and siltstones relatively thin conformable volcaniclastic kimberlite packages are interbedded throughout the host rock stratigraphy extremely thick up to at least 211 m thick discordant to concordant volcaniclastic packages series infill at least three elongate northwest trending craters 145a 145b and 219 craters and contain laterally equivalent conformable extra crater deposits bound by marine mudstones indicative of a prevailing dominantly marine environment the volcaniclastic deposits within the 145a and 145b craters respectively are separated by a considerable hiatus whereas the deposit infilling the 219 crater was formed around the same time as 145b crater deposit multiple depositional units of massive to stratified olivine rich sand to pebble sized volcaniclastic facies infill craters and were emplaced by megaturbidite pulses fed by crystal rich eruption fountains which interacted with the crater relief stacked normally graded thick to very thick bedded matrix supported olivine rich facies characterized by brief depositional breaks between some beds represent syn to post eruptive turbidite pulses associated with the early eruptive event in the 145a crater thin layers of light grey kimberlitic mudstone underlie or occur near the base of and above the main volcaniclastic packages associated with the 145b and 219 eruptions crater infilling volcaniclastic deposits were later reworked by storm induced currents into thin to medium graded moderately sorted fine to coarse olivine rich sandstone with intercalated discontinuous muddy laminae laminated to cross laminated olivine rich silt to sand sized volcaniclastic facies constitutes a small volume volcaniclastic turbidite which marks the last preserved kimberlite emplacement event at orion central

downstream changes in sand composition roundness and gravel size in a short headed high gradient stream northwestern italy abstract we assessed changes in grain composition and roundness of the 1 2 and 2 3 size fractions of sand along a 16 km length of the graveglia river liguria italy to its mouth at the tyrrhenian sea and then for 1 km along the beach rocks exposed in the drainage area include ophiolites ribbon chert limestone shale sandstone and quaternary sands the erosion of shale and limestone bedrock yields large amounts of sand but sand grains of these rock types decrease rapidly in abundance downstream chiefly through dilution rather than abrasion carbonate rock fragments that reach the beach survive wave abrasion but most shale grains do not predictably monocrystalline and polycry talline quartz and chert are the most durable grain types but serpentine basalt and unidentified rock fragments also show significant resistance to both stream and wave abrasion polycrystalline quartz feldspar basalt serpentine sandstone and shale grains are more abundant in the coarser sand size fraction monocrystalline quartz carbonate rock fragments and unidentified rock fragments are more abundant in the finer sand size fraction and chert and plutonic rock fragments have no size preference a comparison of the outcrop areas of the different rock types with the corresponding percentages of different grain types present in each of three drainage areas indicates that shale which breaks down readily to silt and clay size particles and chert which does not readily break down into sand size fragments are underrepresented in the sands limestone and serpentine however are overrepresented in comparison to outcrop area in certain drainage areas the overrepresentation of limestone reflects in part a sampling bias sand was sampled adjacent to limestone outcrops but the overrepresentation of serpentine reflects its resistance to weathering compared to other aluminosilicates and its durability shale limestone and serpentine increase in roundness downstream and along the beach to a maximum limiting value of 5 rho units medium grained shale clasts attain high rounding in only a few kilometers of transport downstream decrease in gravel size follows an exponential formula that can be expressed in linear form using phi size size 0 1167 distance km 10 29

stability of bedforms in a tidal environment abstract large scale bedforms developed in a tide dominated salt estuary near sapelo island georgia are morphologically separated into two distinct groups megaripples include bedforms 4 to 15 m in wavelength and 10 to 75 cm in height sand waves are 15 to 45 m in wavelength and 85 to 130 cm in height and can be further subdivided into megarippled forms and smooth crested forms ebb oriented geometry of large scale bedforms is maintained through both ebb and flood portions of the tidal cycle bedforms are in equilibrium with peak tidal flow and ebb orientation is the direct result of large pressure gradients and related bed shear values that develop during the ebb bedform heights can be statistically related to flow power shear velocity water depth and sediment grain size mean flow velocity values used in many previous studies of bedform stability did not produce significant f statistic values in a multiple linear regression procedure used to discern relationships among variables stability fields of bedform types can be empirically defined using parameters statistically significant in the regression analysis flow power shear velocity water depth and sediment grain size were used in various combinations to construct bivariate plots showing separate stability fields of sand waves and megaripples

slow earthquakes and nonvolcanic tremor nonvolcanic tremor is observed in close association with geodetically observed slow slip events in subduction zones accumulating evidence points to these events as members of a family of slow earthquakes that occur as shear slip on the downdip extensions of fault zones in a regime that is transitional between a frictionally locked region above and a freely slipping region below by virtue of their locations and their properties slow earthquakes are certain to provide new insights into the behavior of earthquakes and faulting and into the hazard they embody

abundant and diverse early paleozoic infauna indicated by the stratigraphic record marine benthic animals have lived within the sediment since the late precambrian an abundant early paleozoic infauna is indicated by bioturbated zones and diversity of deposit feeder and suspension feeder trace fossil genera burrow depths extended tens of centimetres below the sediment water interface trace fossil evidence of an abundant early paleozoic infauna conflicts with evidence from the shelled fauna which lacks infauna this requires reinterpretation of early paleozoic community structure and raises new questions about interactions between early paleozoic soft bodied and skeletonized animals

shallow marine event sedimentation in a volcanic arc related setting the ordovician suri formation famatina range northwest argentina abstract the loma del kilometro member of the lower ordovician suri formation records arc related shelf sedimentation in the famatina basin of northwest argentina nine facies grouped into three facies assemblages are recognized facies assemblage 1 massive and parallel laminated mudstones facies a locally punctuated by normally graded or parallel laminated silty sandstones facies b records deposition from suspension fall out and episodic storm induced turbidity currents in an outer shelf setting facies assemblage 2 massive and parallel laminated mudstones facies a interbedded with rippled top very fine grained sandstones facies d is interpreted as the product of background sedimentation alternating with distal storm events in a middle shelf environment facies assemblage 3 normally graded coarse to fine grained sandstones facies c parallel laminated to low angle cross stratified sandstones facies e hummocky cross stratified sandstones and siltstones facies f interstratified fine grained sandstones and mudstones facies g massive muddy siltstones and sandstones facies h tuffaceous sandstones facies 1 and interbedded thin units of massive and parallel laminated mudstones facies a is thought to represent volcaniclastic mass flow and storm deposition coupled with subordinated suspension fall out in an inner shelf to lower shoreface setting the loma del kilometro member records regress ive transgressive sedimentation in a storm and mass flow dominated high gradient shelf volcano tectonic activity was the important control on shelf morphology while relative sea level change influenced sedimentation the lower part of the succession is attributed to mud blanketing during high stand and volcanic quiescence progradation of the inner shelf to lower shoreface facies assemblage in the middle part represents an abrupt basinward shoreline migration an erosive based non volcaniclastic turbidite unit at the base of this package suggests a sea level fall pyroclastic detritus andesites and a non volcanic terrain were eroded and their detritus was transported basinward and redeposited by sediment gravity flows during the low stand the local coexistence of juvenile pyroclastic detritus and fossils suggests reworking of rare ash falls the upper part of the loma del kilometro member records a transgression with no evidence of contemporaneous volcanism biostratinomic paleoecologic and ichnologic analyses support this paleoenvironmental interpretations and provide independent evidence for the dominance of episodic sedimentation in an arc related shallow marine setting fossil concentrations were mainly formed by event processes such as storms and volcaniclastic mass flows high depositional rates inhibited formation of sediment starved biogenic concentrations collectively trace fossils belong to the cruziana ichnofacies low diversity scarcity and presence of relatively simple forms indicate benthic activity under stressful conditions most probably linked to high sedimentation rates contrasting sedimentary dynamics between normal shelves and their volcaniclastic counterparts produce distinct and particular signatures in the stratigraphic record arc related shelves are typified by event deposition with significant participation of sediment gravity flows relatively high sedimentation rates textural and mineralogical immaturity of sediments scarcity and low diversity of trace fossils and dominance of transported and reworked faunal assemblages genetically related to episodic processes

volcanism and related slope to shallow marine volcaniclastic sedimentation an archean example near chibougamau quebec canada abstract volcaniclastic sedimentary rocks and k rich lava flows of the archean hauy formation are discontinuously exposed in a 850 m thick sequence in the waconichi synclinorium northwest of chibougamau quebec the interstratified sedimentary rocks comprise two major sedimentary facies associations the graded bedded facies association wbfa indicative of deposition by sediment gravity flows and the wavy bedded facies association wbfa defined by wave induced structures the gbfa is near the base of the stratigraphic section and is interstratified up section with the wbfa in the gbfa the abundance of synsedimentary folding truncated slump folds load casts and low angle erosional surfaces as well as sediments deposited by turbidity currents and debris flows support designation as a volcanic slope deposit in the wbfa trough crossbeds wavy bedded gravels and plane bedded volcaniclastic sandstones are indicative of a nearshore setting the abundance of angular to subangular lithic volcanic fragments and broken and euhedral pyroxene crystals in the sediments is suggestive of a pyroclastic origin some beds may represent primary pyroclastic material but unequivocal petrographic recognition of pumice or glass shards is not possible because of metamorphic overprint composition suggests an initial magmatic or phreatomagmatic eruption subsequently reworked along the shoreline and transported downslope lava flows comprising massive to lobate andesites and massive to blocky basalts constitute most of the stratigraphic sequence pillowed flows are strikingly absent from the section both compositional types have an increase in vesicularity and change in flow form up section from massive to lobate or blocky suggesting progressively shallower water depths the composite character represented by hauy lava flows and associated volcaniclastic sediments in characteristic of stratovolcanoes the studied section is an integral part of an evolved arc with an adjacent backarc basin the volcano sedimentary facies indicate the development of a volcanic island in one of these basins

cyclic deposits and hummocky cross stratification of probable storm origin in upper cretaceous rocks of the cape sebastian area southwestern oregon abstract cyclic deposits containing hummocky cross stratification occur in the upper part of the cape sebastian sandstone of bourgeois 1980 a shallow marine transgressive sandstone of late cetaceous age on the southern oregon coast the cycles average 1 6 m in thickness and consist where complete of a lower hummocky cross stratified sandstone a middle planar and ripple bedded sandstone with a shale bed in its middle part and an upper bioturbated sandstone noteworthy features of the hummocky cross stratification include the presence of depositional domes in addition to scoured depressions the absence of significant bedform migration and the presence of a small proportion of dip angles greater than the angle of repose 34 in addition to the large proportion of low 15 deg dip angles the lower stratified fining upward part of the cycle up to the top of the shale bed is interpreted as having accumulated under conditions of initially great but gradually decreasing current velocity and deposition rate the currents probably had a strong oscillatory component and the depositional event is inferred to have been a storm the part of the planar and ripple bedded sandstone above the shale bed was probably deposited during relatively fair weather after the storm but before re establishment of a normal benthic fauna the bioturbated sandstone is interpreted to have been deposited during fair weather or during minor storms separated by long intervals of fair weather

aseismic crustal movement in southern ryukyu trench southwest japan 1 anomalous crustal deformation following the mw 7 1 march 31 2002 hualien earthquake was observed over 5 years using the global positioning system gps network in the south ryukyu islands the analysis showed an afterslip event at a depth of 30 km on the subducting philippine sea plate the magnitude of the cumulative moment reached 7 4 the released moment of the afterslip exceeded the mainshock itself the afterslip promoted coulomb failure stress on the fault of the repeating slow slip events sses in the vicinity of the afterslip the increase in the slip rate of the sses predicted through the change in the coulomb failure stress is 13 this is close to the observed increase in slip rate 19 after the earthquake this suggests that the afterslip had accelerated the slip rate of the sses after the earthquake

factors affecting seismic moment release rates in subduction zones the amount of shallow seismic activity in subduction zones varies greatly from region to region we quantify this seismicity by calculating seismic moment release rates and seismic slip rates for 24 subduction zones to calculate the moment release we sum the seismic moment for all interplate thrust type events with surface wave magnitude ms 7 0 occurring from 1904 to 1980 we present a time history plot of the seismic moment release for each subduction zone these exhibit the differences in the seismic release patterns for subduction zones where the time window of our study is not representative the total moment release is corrected using information on repeat times the moment release rates are compared with various subduction parameters in order to determine which factors influence the degree of coupling these parameters include the age of the subducting lithosphere absolute velocities of the upper and subducting plates convergence velocity and length maximum depth and dip of the wadati benioff zone the moment release rate decreases as the age of the subducting lithosphere increases when the zones belonging to a single subducting plate are considered this age versus moment release relation is consistent for the zones in which the pacific cocos philippine sea and indian plates are subducting the moment release rates for the subduction zones in which the pacific plate is subducting are much higher than for zones of other plates with similar age the age versus moment release relation holds among the zones which belong to one subducting plate however zones with similar ages but belonging to different plates do not have the same moment release rates this suggests that within a single plate the age is the dominating factor affecting the strength of seismic coupling but that each plate as a whole has a characteristic moment release budget zones with retreating upper plates tend to have lower moment release rates the moment release rate does not increase with convergence velocity no simple relationship was found between these two parameters the moment release rate depends most clearly on the age of the subducting lithosphere and the absolute velocity of the upper plate these are the two independent subduction zone parameters among the variables considered the other variables depend on these two parameters

volcaniclastic processes on modern submarine arc stratovolcanoes sidescan and photographic evidence from the rumble iv and v volcanoes southern kermadec arc sw pacific abstract studies of volcaniclastic processes on modern submarine arc stratovolcanoes are rare facies models of submarine volcanism and associated volcaniclastic deposits have to date emphasized general and or regional processes two andesite alkali basaltic volcanoes rumble iv and v volcanoes from the southern kermadec arc are mapped with swath bathymetry and sidescan imagery and photographic data to characterise volcaniclastic processes on these modern submarine arc stratovolcanoes and their interaction with ambient marine processes the principal observation from the rumble iv and v data is the fine scale spatial variability in the distribution of effusive lavas various volcaniclastic deposits and hemipelagic pelagic sediments mass movement of volcaniclastic deposits is common and includes 1 epiclastic debris flows 2 pillow breccia talus deposition penecontemporaneous with lava eruption 3 traction particulate gravity flows and possibly 4 sector collapse epiclastic redeposition is inferred to be mobilised by episodic but frequent localised small volume flows which largely redeposit debris on the edifice winnowed and rippled volcaniclastic sediment indicates bottom current activity is common but localised over the entire height of both volcanoes down to a water depth of 2200 m these currents also possibly entrain detritus for subsequent mobilisation by particulate gravity flows irregular and ragged spatter agglutinates on rumble iv interpreted as evidence of lava fountaining and wellsorted fines poor scoriaceous material on rumble v interpreted as evidence of explosive eruption indicate the transition between effusive and explosive volcanism is between 650 and 700 m water depth other southern kermadec volcanoes e g tangaroa have scoriaceous detritus at 960 970 m water depth positions of these effusive explosive transition zones are likely to oscillate up and down the volcano during glacioeustatic fluctuations

plate geometry model and seismicity in the northern ryukyu subduction zone japan deduced from amphibious seismic observations abstract in this study the geometry of the subducted philippine sea plate interface beneath the northern ryukyu trench subduction zone was estimated based on seismic tomography and focal mechanism estimations using passive data obtained from a temporary amphibious seismic network and permanent land stations using relocated low angle thrust type earthquakes and information obtained from previous studies we constrained the plate geometry from the trench axis to a depth of 60 km with uncertainties of

the significance of grain scale stresses in the kinetics of metamorphism during metamorphism phases grow and dissolve dominantly along grain boundaries bulk diffusion models for the development of metamorphic textures often assume that diffusion is homogeneous in regions of each phase rather than being localised along phase boundaries under isotropic stress chemical potentials of components involved in reactions are likely to be buffered along grain boundaries between phases thus inhibiting diffusion and growth motive forces must exist which overcome this and it is proposed here that local heterogeneous stresses will be important a mathematical theory for stress controlled growth is derived this theory predicts that the growth rates of two phases along their mutual interface will be linked in a quantifiable way it forms a basis for considering the important effects of stresses induced by local volumetric changes during metamorphism and it provides a link between these effects and those related to pressure solution in deforming rocks

spatial relationship between shallow very low frequency earthquakes and the subducted kyushu palau ridge in the hyuga nada region of the nankai subduction zone

constraints on backstop geometry of the southwest ryukyu subduction based on reflection seismic data abstract based on the analysis of 45 seismic reflection profiles the top of the ryukyu arc basement is mapped in the forearc region east of taiwan the ryukyu arc slope dips 10 trenchward while beneath the forearc basins the arc basement shows a series of morphologic along arc highs and lows one of the basement highs the nanao basement rise has been described as an area uplifted by the subduction of the gagua ridge the other one the hoping basement rise is suggested in this study to be an uplifted feature caused by the subduction or the underplating of some local asperity the nature of this asperity could either be a detached block of the luzon arc an isolated seamount or some material removed from the frontal part southernmost extremity of the ryukyu margin from seismic reflection profiles we infer that the right lateral transcurrent fault system located at the rear of the accretionary wedge defines the surface projection of the southern termination of the ryukyu arc basement two crustal sections across the ryukyu subduction system demonstrate that the backstop terminates in the form of a near vertical wall with its height over 5 km such an unusual geometry could be produced by crustal truncation at the toe of the backstop

distinguishing primary and resedimented vitric volcaniclastic layers in the burdigalian carbonate shelf deposits in monferrato nw italy abstract a multidisciplinary study including stratigraphic sedimentological biostratigraphic petrographic magnetic fabric and sem analyses has been performed on six volcaniclastic layers vls interbedded in the burdigalian shelf succession of the monferrato nw italy the aim was to distinguish between the volcanic and sedimentary processes that produced these deposits to suggest a depositional model for volcaniclastic sedimentation in a shelf environment and to discuss the use of vls for stratigraphic correlations two kinds of vls have been distinguished single volcaniclastic layers svls and multiple volcaniclastic layers mvls svls are single beds of well sorted vitric siltites mainly consisting of volcanic components and minor terrigenous and intrabasinal grains the vitric fraction mainly consists of blocky fragments they show a very low magnetic anisotropy degree and a prominent magnetic lineation these vls are interbedded in outer shelf marls and are interpreted as primary pyroclastic fall deposits mvls which can be up to 10 m thick show limited lateral continuity and are made up of several decimetre thick graded beds separated by erosional surfaces and consisting of vitric arenites and siltites with about 15 non volcanic components two kinds of mvls have been distinguished 1 type 1 mvls interbedded in storm dominated glaucony rich calcarenites and showing rough low angle cross stratification hummocky cross stratification water escape and load structures these deposits are characterized by a slightly foliated magnetic fabric and are interpreted as storm layers deposited between fairweather and storm wave base 2 type 2 mvls are interbedded in outer shelf marls and are characterized by parallel lamination and by a well developed magnetic foliation they are interpreted as storm induced distal shelf turbidites triggered by storm activity acting in the more internal part of the shelf the monferrato vls resulted from explosive eruptions of volcanic edifices located outside of the basin that produced an extensive tuff blanket that was uniformly distributed on a carbonate dominated shelf above storm wave base the vls were immediately reworked by storm activity and the resulting deposits are type 1 mvls below storm wave base primary pyroclastic fall deposits were preserved corresponding to svls storm induced turbidity currents gave rise to type 2 mvls that were deposited below storm wave base preservation of vls in a shelf environment is hampered by the high energy conditions of the shelf consequently these deposits are characterized by a restricted lateral continuity and their use as correlation tools may be misleading

slow earthquakes linked along dip in the nankai subduction zone we identified a strong temporal correlation between three distinct types of slow earthquakes distributed over 100 kilometers along the dip of the subducting oceanic plate at the western margin of the nankai megathrust rupture zone southwest japan in 2003 and 2010 shallow very low frequency earthquakes near the nankai trough as well as nonvolcanic tremor at depths of 30 to 40 kilometers were triggered by the acceleration of a long term slow slip event in between this correlation suggests that the slow slip might extend along dip between the source areas of deeper and shallower slow earthquakes and thus could modulate the stress buildup on the adjacent megathrust rupture zone

a shallow marine volcaniclastic facies model an example from sedimentary rocks bounding the subaqueously welded ordovician garth tuff north wales u k abstract volcaniclastic sedimentary rocks bounding the ordovician garth tuff in north wales were deposited in a shallow marine setting adjacent to a magmatic arc the volcaniclastic sedimentary rocks are primarily of angular to euhedral quartz angular euhedral feldspar and volcanic rock fragments these grains are of a pyroclastic origin but have been reworked to various degrees sedimentary rock fragments rounded quartz muscovite biotite iron rich chlorite and various clay minerals occur in lesser amounts the sedimentary rocks can be divided into a proximal offshore to foreshore facies association poffa and an offshore to lower shoreface facies association olsfa the sand dominated poffa exposed near capel curig is characterized by large wave ripples hummocky cross stratification co sets of trough cross beds reactivation surfaces plane beds and graded turbidite layers in suspension deposited mudstone water depths calculated from bedding plane exposure of large wave ripples and determined by the presence of hummocky cross stratification and by facies association vary from a few meters to around 30 m 45 50 m theoretical maximum in a 45 m thick stratigraphic section beneath the tuff eight kilometers to the southeast the garth tuff is bounded by a thick sequence of suspension deposited laminated mudstone with thin graded beds of siltstone and fine grained sandstone this facies association olsfa represents the introduction of material by distal turbidites and by pelagic sedimentation the olsfa was deposited in water depths well below storm wave base possibly in excess of 200 m no evidence of storm waves or surface generated currents occur until over 40 m above the tuff this study documents marine sedimentary rocks deposited in water depths ranging from foreshore to offshore as the bounding facies of the garth tuff it is thus reasonable to conclude that the garth tuff was emplaced and welded in water depths greater than the thickness of the tuff in the area of this study

the potential for a great earthquake along the southernmost ryukyu subduction zone interseismic gps data along the hualien suao coast ne taiwan shows a pattern of strain accumulation that is consistent with a potential future large shallow earthquake along the southernmost ryukyu subduction zone the measured shortening rate parallel to the ryukyu trench is 80 mm yr about twice of the shortening rate perpendicular to the ryukyu trench we invert for slip deficit rates and the geometric configuration of the plate interface our preferred fault model dips 10 northward and extends about 70 km from the ryukyu trench to a depth of 13 km the slip deficit rate exhibits a left lateral motion of 78 mm yr and a normal motion of 36 mm yr on a 290 trending fault the slip rate budget of the southernmost ryukyu subduction zone is close to the plate convergence rate suggesting the plate interface is fully locked assessments of seismic hazard in this region need to consider the potential threat from m w 7 5 8 7 tsunami earthquakes generated by shallow ruptures

combined flow model for vertical stratification sequences in shallow marine storm deposited beds abstract we develop a model to help explain the wide variety of vertical stratification sequences in shallow marine sandstones this model embodied in a set of vertical sequence cartoons predicts or accounts for vertical stratification sequences in beds of free sandstone deposited from a full range of decelerating combined flows as well as from purely unidirectional and oscillatory flows according to the model vertical stratification sequences in storm deposited sandstone beds are the outcome of the time history of the bed configuration as deposition proceeds the idealized sequences are based on the initial velocities and subsequent deceleration histories of the unidirectional and oscillatory flow components twenty qualitatively different sequences starting with plane bed are generated and an additional 26 sequences result from omitting one or more of the lowermost intervals in succession the model thus accounts for 46 distinct kinds of sequences five major simplifying assumptions are built into the model bidirectional flows linear deceleration of both unidirectional and oscillatory flow components time independent deposition rate time independent sediment size and equilibrium bed configurations owing to these assumptions the model is likely to be applicable to only a small subset of vertical stratification sequences observed in shallow marine sandstones as more information on combined flow bed configurations becomes available these assumptions could be relaxed to provide a more refined and complete representation of vertical stratification sequences since the model generates vertical sequences formed from any kind of decelerating flow the bouma sequence for deposits from purely unidirectional turbidity currents and also sequences resulting from decelerating purely oscillatory flows similar in appearance to many proposed generalized tempestite sequences are end member cases in the model the model is also extended slightly to explain the geometry of the uppermost bedding surfaces of storm generated sandstones by consideration of disequilibrium effects

submarine volcaniclastic rocks in this chapter we are concerned with underwater volcaniclastic eruptions and products as well as pyroclastic flows and debris generated on land and transported by mass flowage into the sea submarine fallout deposits derived from land based eruptions are treated in chapter 7 clastic materials redistributed as mass flows or turbidity currents originating from the rapid build up of tephra and epiclastic volcanic debris along coastal parts of volcanoes are also discussed in various places throughout the text e g chap 13

the submarine eruption and emplacement of the lower rhyolitic tuff formation ordovician n wales the lower rhyolitic tuff formation up to 600 m thick represents an eruptive cycle of acidic ash flow tuff which is stratigraphically associated with marine sediments and subaqueously emplaced basalt lavas the formation comprises volcaniclastic and pyroclastic megabreccias and breccias massive welded and non welded acidic ash flow tuffs reworked tuffs and tuffities siltstones rhyolite intrusions and extrusions its basal contacts vary from conformable to disconformable and unconformable the inter relationships of these variations to pre syn and post emplacement structures define a submarine asymmetric downsag caldera the main eruptive centre coincident with the thickest accumulation of intracaldera tuffs lies close to its north margin on the north side of the snowdon massif to the sw the intracaldera tuffs thin progressively and much of the formation comprises tuffs reworked in the vicinity of a caradocian shoreline to the ne and e outflow tuffs escaped into a deeper marine basin many of the features of the caldera are similar to those of subaerial calderas and it is concluded that the enveloping sediments and lavas and the character of the reworked tuffs hold the key to the recognition of its submarine development subsequent resurgence resulted in only local and short lived emergence of the intracaldera tuffs

on the biannually repeating slow slip events at the ryukyu trench southwestern japan 1 global positioning system data show that about 20 slow slip events occurred during 1997 2007 in the southwestern part of the ryukyu arc japan where large interplate thrust earthquakes are not known to have occurred in spite of relatively fast plate convergence they recur fairly regularly on one patch of the subduction fault which is as deep as 20 40 km and mechanically isolated in an uncoupled subduction zone they have time constants of a month or so and release seismic moment equivalent of mw 6 6 on average this is one of the best recorded sequences of repeating fault slips with enough events for statistical analyses they have fairly constant recurrence interval of 0 5 year but do not show preferred months of occurrence in a year suggesting that they are not controlled by seasonal forcing the correlation between intervals and amounts of fault slip show statistically significant time predictable recurrences there is one significant disruption in the rhythm but the stress perturbations due to nearby earthquakes do not appear to play a significant role this part of the fault might be an altered asperity that used to rupture fast but now slips only slowly because of the increased ambient temperature

beaches and beach related facies holocene barrier islands of georgia the mesotidal coast of georgia encompasses diverse sedimentary features and depositional environments most of which typify major facies of the entire georgia bight a broad embayment on the southeastern u s shelf barrier island strandline environments especially include tidal inlets and shoals the beach shoreface foreshore and backshore and dunes and washover fans low energy beach segments may grade directly into small seaside tidal flats relict salt marsh deposits crop out on erosional beaches all deposits are in dynamic equilibrium with fluctuating coastal conditions and a gradual rise in sea level most of these facies are important in interpreting ancient epeiric transgressive regressive coastal sequences pronounced local variations in the overall sequence result from complex latero vertical relationships between 1 the shoreface foreshore and shoals and 2 the shoals low energy beaches and beach related tidal flats washover fans and relict deposits on erosional beaches cause perturbations within present day lateral relationships but are normal in transgressive facies tracts along such coasts close stratigraphic control of outcrops or cores would be necessary for detailed reconstructions of or correlations among ancient analogs

slow earthquakes coincident with episodic tremors and slow slip events we report on the very low frequency earthquakes occurring in the transition zone of the subducting plate interface along the nankai subduction zone in southwest japan seismic waves generated by very low frequency earthquakes with seismic moment magnitudes of 3 1 to 3 5 predominantly show a long period of about 20 seconds the seismicity of very low frequency earthquakes accompanies and migrates with the activity of deep low frequency tremors and slow slip events the coincidence of these three phenomena improves the detection and characterization of slow earthquakes which are thought to increase the stress on updip megathrust earthquake rupture zones

distribution and significance of crystalline perlitic and vesicular textures in the ordovician garth tuff wales diverse spherulitic and granular crystalline fabrics perlitic textures and fabrics related to the growth and migration of vesicles occur in the garth tuff a largely welded ordovician ignimbrite defining the distribution of such textures helps to constrain the ignimbrite s cooling and degassing history suites of spherulitic and perlitic textures closely reflect variation in cooling rates seven facies are defined based on the style and intensity of crystallisation 1 a medium to coarsely crystalline equigranular facies 2 an intensely spherulitic facies 3 a sparsely spherulitic facies 4 a pectinate facies 5 a microcrystalline to cryptocrystalline equigranular facies 6 a lithophysal facies and 7 a transitional perlite pectinate facies textural changes from facies 1 to 5 reflect progressively higher cooling rates facies 1 occurs in proximal settings in the ignimbrite s core facies 2 to 5 successively envelop facies 1 with facies 2 becoming the dominant fabric in the ignimbrite s core in medial settings facies 5 is typically developed in the originally glassy perlitic zones at the ignimbrite s welded margins crystallisation under hydrous conditions is reflected by second boiling textures in the sporadically developed lithophysal facies the seventh facies reflects a subtle interplay between cooling hydration and crystallisation which locally prevented perlitic fracturing the distribution of amygdales reflects patterns of volatile migration and entrapment in the lower levels of the ignimbrite amygdales occur in irregular concentrations or rare subvertical pipe like structures pipe like structures attest to fumarolic activity while the ignimbrite was in a rheomorphic state amygdales are widespread and evenly distributed in the upper levels of the ignimbrite however the top of the welding profile is characterised by a thin poorly vesiculated originally vitrophyric horizon that abruptly caps an intense concentration of amygdales ductile and brittle fabrics developed during the upward migration of gas microscopic drag folds occur around some amygdales jigsaw fit to clast rotated breccias originated through both late stage pneumatic fracturing and autobrecciation vaporisation of water at the flow base provided a significant source of volatiles in addition to gas released during cooling and crystallisation secondary alteration has enhanced or modified some fabrics perlitic zones were susceptible to patchy chlorite sericite carbonate diagenetic alteration diagenesis and metamorphism have contributed to the infilling of vesicles

characteristic silent earthquakes in the eastern part of the boso peninsula central japan 1 analysis of global positioning system gps data shows transient crustal deformation in the boso peninsula central japan for about fifty days from october 2002 the southeastward horizontal displacements detected suggest the occurrence of interplate aseismic slip between the philippine sea plate and the north american plate six years after a similar event in 1996 we estimate an area of aseismic slip with moment magnitude mw 6 6 centered off the boso peninsula adjacent to associated seismic activity slip evolution of the 2002 aeismic slip started on october 4 and migrated from north to south for about ten days followed by gradual subsidence and restarting of slip which lasted until december 2 propagating more southward similarities in focal area and slip process between the 1996 and the 2002 events suggest the boso aseismic slips as characteristic silent earthquakes together with the repetitive occurrence of seismic swarm in a similar region every six to seven years a more tightly coupled southern area that did not release enough energy in the 1996 event may have caused the differences in magnitude central slip area and duration between the 1996 and the 2002 events if the hypothesized recurrence interval for strain accumulation is true based on swarm seismicity

sedimentation history of the palaeoproterozoic dhanjori formation singhbhum eastern india abstract the palaeoproterozoic dhanjori formation eastern india is a terrestrial dominantly fluvial volcano sedimentary succession basal conglomerate coarse grained sandstone and shale rests directly on the granite basement and represents the distal fringe of an alluvial fan complex sieve sheet flood mass flow and alluvial channel and overbank deposits comprise the fan segment the rest of the formation is entirely constituted by fining upward fluvial cycles an event of basin tilting and volcanic eruption intervened and resulted a second phase of dhanjori sedimentation although the general fluvial depositional framework remained unaltered the two members of the dhanjori formation display different paleocurrent trends related to fluvial response to basin tilting in the lower member spatial variability in paleocurrent directions occurs as a consequence of fan development unlike the first phase the second phase of fluvial deposition incorporates profuse volcanics and accompanying volcaniclastic deposits these volcanic and volcaniclastic rocks might have locally blocked the river courses resulting in short lived lacustrine deposition composition of the volcanics varies upward from ultramafic to mafic the dhanjori volcanism took place in an intracontinental rift setting as is evident from the interbedded terrestrial deposits interbedded volcanic and volcaniclastic rocks in different stratigraphic levels suggest episodic volcanic eruption a semiarid paleoclimate is proposed and is consistent with development of an alluvial fan comprised of coarse clastic deposits

slow slip events and seismic tremor at circum pacific subduction zones 1 it has been known for a long time that slip accompanying earthquakes accounts for only a fraction of plate tectonic displacements however only recently has a fuller spectrum of strain release processes including normal slow and silent earthquakes or slow slip events and continuous and episodic slip been observed and generated by numerical simulations of the earthquake cycle despite a profusion of observations and modeling studies the physical mechanism of slow slip events remains elusive the concurrence of seismic tremor with slow slip episodes in cascadia and southwestern japan provides insight into the process of slow slip a perceived similarity between subduction zone and volcanic tremor has led to suggestions that slow slip involves fluid migration on or near the plate interface alternatively evidence is accumulating to support the notion that tremor results from shear failure during slow slip global observations of the location spatial extent magnitude duration slip rate and periodicity of these aseismic slip transients indicate significant variation that may be exploited to better understand their generation most slow slip events occur just downdip of the seismogenic zone consistent with rate and state dependent frictional modeling that requires unstable to stable transitional properties for slow slip generation at a few convergent margins the occurrence of slow slip events within the seismogenic zone makes it highly likely that transitions in frictional properties exist there and are the loci of slow slip nucleation slow slip events perturb the surrounding stress field and may either increase or relieve stress on a fault bringing it closer to or farther from earthquake failure respectively this paper presents a review of slow slip events and related seismic tremor observed at plate boundaries worldwide with a focus on circum pacific subduction zones trends in global observations of slow slip events suggest that 1 slow slip is a common phenomena observed at almost all subduction zones with instrumentation capable of recording it 2 different frictional properties likely control fast versus slow slip 3 the depth range of slow slip may be related to the thermal properties of the plate interface and 4 the equivalent seismic moment of slow slip events is proportional to their duration mo different from the mo 3 scaling observed for earthquakes

fluidization of wet sediments during the emplacement and cooling of various igneous bodies during the emplacement and cooling of igneous bodies fluidization of wet sediment by water vapour may occur by heating or by pressure relief during the opening of fractures momentary fluidization causes sediment reconstitution and local transport continuous fluidization can result in substantial sediment displacement theoretical considerations show that fluidization due to heating is not likely to occur at depths where pressure is much greater than 312 bars studies of the emplacement of sills of andesite ayrshire fluid rhyolite ramsey island and viscous rhyolite moelwyn hills recognize a wide range of phenomena attributable to wet sediment fluidization and in places modify existing interpretations the transgressive bases of the subaqueously welded ash flow tuffs of the capel curig volcanic formation are consistent with emplacement attended by fluidization of the subjacent sediment evidently fluidization is a means by which large volumes of wet sediment can be replaced by igneous material with minimal disturbance of the remaining host also fluidization can result in exceptionally complex contact relationships between sedimentary host and intrusive rocks and can cause fractures formed during cooling to be thoroughly pervaded by sediment fluidization is commonly associated with the formation of peperites

submarine silicic volcanism and associated sedimentary and tectonic processes ramsey island sw wales lower ordovician marine strata formed in an ensialic marginal basin environment record early episodes of distant explosive silicic volcanism and a later volcanotectonic episode which was a precursor to the development of a wide variety of near to source submarine silicic volcanic phenomena the early episodes are represented by well bedded turbiditic tuffs these and older strata at least 770 m thick in normal stratigraphical succession are allochthonous and large scale wet sediment sliding with reworking of strata in cohesive debris flows reflects major disturbance of the sea floor during the emplacement of silicic magmas volcanotectonic uplift along a n s fault exceeded 1 km and led to the emergence and erosion of a rhyolitic volcanic island this was followed closely by submergence and in water depths perhaps of about 500 m there accumulated welded and non welded rhyolitic ash flow tuffs rhyolitic turbiditic tuffs rhyolite lavas and a wide variety of debris flow deposits shallow intrusions of 9low9 viscosity rhyolite were emplaced contemporaneously the more or less simultaneous emplacement of rhyolitic tuff with both 9low9 viscosity and high viscosity rhyolites is attributed to variable water content related perhaps to volatile fluxing in a magma body the location of the near to source extrusive rocks and consanguineous intrusions along the contemporary n s fault is considered to reflect channelling of magma initially along a deep crustal fracture

fiamme formed by diagenesis and burial compaction in soils and subaqeuous sediments pumice clasts can be diagenetically altered at low temperature and flattened by compaction to form fiamme examples are described from trachytic pumice fall layers alternating with palaeosoils on sao miguel in the azores and from ordovician lacustrine volcaniclastic sedimentary rocks from the english lake district

activation of very low frequency earthquakes by slow slip events in the ryukyu trench long term activity of shallow very low frequency earthquakes vlfes in the ryukyu trench unassociated with recent large thrust earthquakes was analyzed using a broadband seismometer network the distribution of shallow vlfes was divided into three large clusters the activity of the vlfes is modulated by repetitive slow slip events and the activity of these vlfes increases to 2 3 times its ordinary rate at 10 20 days after the onset of the slow slip events the activation of vlfes could be generated by small increases on the order of approximately 0 1 0 5 kpa in coulomb failure stress suggesting that stress in the plate interface where the vlfes occur is frequently released in small amounts moreover the distribution of vlfes is complementary to the historical tsunami source area and locked area the distribution of the vlfes indicates heterogeneity in interplate coupling along the trench

isolated pods of subaqueous welded ash flow tuff a distal facies of the capel curig volcanic formation ordovician north wales acidic welded tuffs of the capel curig volcanic formation were deposited from ash flows that transgressed from a proximal subaerial to a distal submarine environment isolated pods of welded tuff enveloped by marine sediments represent a distal facies of the formation deposited beyond the limits of the continuous ash flow tuff sheets various mechanisms for the separation of the tuff pods from a parent flow are discussed and it is concluded that it is most likely that the formation of the pods was due to disruption of a subaqueous ash flow during transport rather than by downslope collapse at the front of a previously deposited ash flow tuff sheet

occurrence of megaripples in a ridge and runnel system sapelo island georgia morphology and processes abstract during 20 31 october 1982 we observed the formation of megaripples in en echelon runnel systems 0 2 2 km long and 8 15 m wide on nanny goat and cabretta island beaches sapelo island georgia the runnels contained a complex assemblage of lower flow regime bedforms which were dominated by large sinuous to lunate megaripples with heights of 15 to 50 cm and wave lengths of 4 to 14 m at times smaller megaripples 80 to 100 cm long and 5 to 10 cm high formed on the backs of the large megaripples small linguoid lunate ripples were superimposed on the megaripples the magaripples form in the fine sand 0 125 0 25 mm during rising high tide associated with higher than normal wave energies and northeasterly waves and wind as the tide rises wave generated surges override the ridge and are translated into unidirectional pulsating flow along the runnel to the south on sapelo island thus producing the megaripples as the tide lowers waves no longer override the ridge and small linguoid lunate ripples form on top of the megaripples as water drains from the runnel because our measured velocity values are lower than those required by experimental work to produce megaripples in fine sand they may represent minimum velocities due to averaging pulses over time and distance these large lower flow regime bedforms produce sets of high angle cross laminae oriented along shore within upper flow regime plane beds and should be allowed for during environmental interpretation of nearshore deposits in the rock record

a subaqueous welded tuff from the ordovician of county waterford ireland abstract the metal man tuff mmt from the ordovician of county waterford ireland was emplaced and welded in water depths greater than the thickness of the pyroclastic flow the mmt is the basal member of the middle tramore volcanic formation mtvf of the 5 km thick tramore group the mmt consists of a 10 m thick basal graded zone that represents a pyroclastic flow consisting of angular clasts of black mudstone pumice gray flow banded rhyolite and pink massive rhyolite set in a matrix of non deformed ash shards and pumice maximum grain size grades from large cobbles and small boulders to pebbles the basal 10 30 cm is depleted with respect to the largest boulders resulting in an inversely graded basal layer the basal graded zone passes upward into a transition zone with a strong eutaxitic foliation defined by elongated fiamme of mudstone and flattened pumice overlying this is an upper welded zone with a pronounced eutaxitic foliation columnar jointing flattened ash shards and shards deformed around phenocrysts and spheroids the presence of these features indicate that the deposit is welded was hot and was in motion as the shards deformed the mmt represents a pyroclastic flow that was a hot primary product of an eruption rather than re mobilized cold pyroclastic debris the mmt is bounded by suspension deposited fine grained tuff tuffaceous mudstone and terrigenous mudstone deposited below storm wave base many of the mudstone horizons contain brachipod faunas from shelf depth water nowhere in the 5 km thick tramore group is there terrigenous sandstone evidence of unidirectional flowing water nor any indication of shoreline alluvial environments or subaerial exposure it thus seems reasonable to conclude that the mmt was emplaced and welded subaqueously the geochemistry of the mmt is typical of other high silica 70 78 wt sio2 rhyolite from the ordovician of ireland the chemistry of the mmt is consistent from top to bottom allowing it to be distinguished from associated syndepositional intrusive rock and fine grained tuffs

fault model of the 1771 yaeyama earthquake along the ryukyu trench estimated from the devastating tsunami 1 the 24 april 1771 yaeyama earthquake generated a large tsunami with a maximum runup of 30 m causing significant damage in south ryukyu japan despite the weak ground shaking previously proposed mechanisms of the tsunami include intraplate faulting or submarine landslide in the forearc slope in this study i estimate the fault parameters of the 1771 earthquake by numerically computing the tsunami heights and comparing them with the recorded heights the result indicates that the source fault of the tsunami is very close to the ryukyu trench the results are consistent with a thrust faulting earthquake that had a fault width of less than 50 km the 1771 yaeyama tsunami was caused by a tsunami earthquake mw 8 0 that occurred in the subducted sediments beneath the accretionary wedge

a mega splay fault system and tsunami hazard in the southern ryukyu subduction zone abstract in april 1771 a subduction earthquake generated a great tsunami that struck the south ryukyu islands and killed 12 000 people whereas its mechanism is still enigmatic nakata and kawana 1995 nakamura 2006 matsumoto et al 2009 in this paper we show its probable source on a mega splay fault system existing along the southern ryukyu forearc analyses of deep multi channel seismic reflection profiles indicate that the mega splay fault system is rising from the summit of a 1 km high ridge situated at a 5 landward dipping plate interface an outer ridge marks the seafloor outcrop of the splay fault system and separates the landward inner wedge and the oceanward outer wedge the inner wedge is uplifting and exhibits widespread normal faulting while the outer wedge shows folded structures the mega splay fault system is parallel to the ryukyu trench east of 125 5 e and is estimated to be 450 km long the origin of this south ryukyu mega splay fault system is ascribed to a resistant subduction of the elevated transverse ridges associated with the subducting portion of the trench parallel luzon okinawa fracture zone in contrast no similar splay fault is found west of 125 5 e where the oblique subduction has produced large shear zones along the south ryukyu forearc we infer that a thrust earthquake linked to the mega splay fault system is responsible for the south ryukyu tsunami however another possible scenario of generating a large tsunami affecting the south ryukyu islands is that the subducted ridge in the western end of the mega splay fault system nucleated a large earthquake and simultaneously triggered the 100 km long e w trending strike slip fault west of 125 5 e and induced a southward dipping tsunami genic subsidence in any case after a quiescence of 241 yr a large earthquake and tsunami is anticipated in the south ryukyu forearc in the near future

volcaniclastic sedimentation in and around an ordovician subaqueous caldera lower rhyolitic tuff formation north wales the lower rhyolitic tuff formation of ordovician age in north wales records the collapse infilling and subsequent resurgence of a volcanic caldera with an original diameter of about 15 km this volcanic center controlled patterns of volcaniclastic sedimentation providing enough topographic relief for both a shallow lagoon depositional basin within the caldera and a source of sediment derived from the rim within the caldera sediment consists of tuffaceous laminated siltstone and immature coarse grained volcaniclastic sandstone containing plane beds ripple cross laminations symmetrical wave ripples and hummocky cross stratification coarse grained matrix supported conglomerate layers and layers of ash flow tuffs are also present these sediments accumulated in shallow water above fair weather wave base conglomerate units represent debris flows from the caldera rim a nearby shoreline and elevated areas associated with resurgent domes sedimentation outside of the caldera consisted of deposition of background suspension and volcanic ash suspension and turbidite deposition on a pyroclastic apron the outer margin of the apron was dominated by fine grained suspension and turbidite deposition whereas the inner margin of the apron contains hummocky cross stratification and other evidence of reworking by episodic storm waves local highs with associated shallow water sedimentation existed outside the caldera even though deposited in high energy marine environments all sedimentary rocks are both texturally and mineralogically very immature this textural immaturity differs from the typical very mature marine sediments and was caused by rapid depositional rates and a local volcanic sediment source

subduction of thick oceanic plateau and high angle normal fault earthquakes intersecting the slab the role of seamounts on interplate earthquakes has been debated however its impact on intraslab deformation is poorly understood here we present unexpected evidence for large normal fault earthquakes intersecting the slab just ahead of a subducting seamount in 1995 a series of earthquakes with maximum magnitude of 7 1 occurred in northern ryukyu where oceanic plateaus are subducting the aftershock distribution shows that conjugate faults with an unusually high dip angle of 70 80 ruptured the entire subducting crust seismic reflection images reveal that the plate interface is displaced over 1 km along one of the fault planes of the 1995 events these results suggest that a lateral variation in slab buoyancy can produce sufficient differential stress leading to near vertical normal fault earthquakes within the slab on the contrary the upper surface of the seamount plate interface may correspond to a weakly coupled region reflecting the dual effects of seamounts plateaus on subduction earthquakes

the pitts head tuff formation a subaerial to submarine welded ash flow tuff of ordovician age north wales the pitts head tuff formation of ordovician caradoc age was emplaced as a thick c 700 m intracaldera sequence and two outflow units comprising welded acidic ash flow tuff the pitts head pyroclastic flows were erupted subaerially but the lower and most extensive of the outflows crossed a shoreface and continued for several kilometres offshore the flow entered the sea without disruption and following deflation and tuff emplacement displaced the shoreface several kilometres to the east and northeast post eruption subsidence in the northeast resulted here in the rapid establishment of environments deeper than had previously existed the lower outflow tuff is parataxitically to eutaxitically welded in both the subaerial and marine environments the extremely regular plane parallel welding foliation of the subaerial tuffs however contrasts with the locally highly deformed foliation of the tuff deposited beyond the shoreface the deformed foliation associated with irregular zones of intense siliceous nodule development is ascribed to the upward streaming of water vapour generated at the tuff sediment boundary elsewhere rheomorphism within the tuff was caused by instability resulting from emplacement on slopes related to faulting continued movement initiated extensive brecciation detachment and local gravity sliding of large rafts of tuff

transient fault slip in guerrero southern mexico the guerrero region of southern mexico has ac cumulated more than 5 m of relative plate motion since the last major earthquake in early 1998 a continuous gps site in guerrero recorded a transient displacement modeling indicates that anomalous fault slip propagated from east to west along strike of the subduction megathrust campaign gps and leveling data corroborate the model the moment release was equivalent to an mw 6 5 earthquake no m 5 earthquakes accompanied the event indicating the frictional regime is velocity strengthening at the location of slip

the early palaeozoic break up of northern gondwana sedimentology physical volcanology and geochemistry of a submarine volcanic complex in the bavarian facies association saxothuringian basin germany abstract ordovician volcano sedimentary successions of the bavarian facies association in the saxothuringian basin record the continental rift phase of the separation of the saxothuringian terrane from gondwana an 80 m succession from the vogtendorf beds and randschiefer series arenig middle ordovician exposed along the northern margin of the munchberg gneiss massif in northeast bavaria were subjected to a study of their sedimentology physical volcanology and geochemistry the randschiefer series previously has been interpreted as lavas tuffs sandstones and turbidites but the studied ordovician units include four main lithological associations mature sandstones and slates pillowed alkali basalts and derivative mass flow deposits trachyandesitic lavas and submarine pyroclastic flow deposits interbedded with turbidites eight lithofacies have been distinguished based on relict sedimentary structures and textures which indicate deposition on a continental shelf below wave base the explosive phase that generated the pyroclastic succession was associated with the intrusion of dykes and sills and was succeeded by the eruption of pillowed basalts debris flow deposits overlie the basalts ordovician volcanism in this region therefore alternated between effusive and explosive phases of submarine intermediate to mafic volcanism based on geochemical data the volcanic and pyroclastic rocks are classified as basalts and trachyandesites according to their geochemical characteristics especially to their variable concentrations of incompatible elements such as the high field strength elements hfse they can be divided into three groups group i which is formed by massive lavas at the base of the succession has extraordinarily high contents of hfse the magmas of this group were probably derived from a mantle source in the garnet stability field by low ca 1 degrees of partial melting and subsequent fractionation group ii which comprises the pillow lavas at the top of the sequence displays moderate enrichment of hfse this can be explained by a slightly higher degree of melting ca 1 6 for the primary magma group i and ii melts fractionated from their parental magmas in different magma chambers the eruption centres of groups i and ii therefore cannot be the same and the volcanic rocks must have originated from different vents the sills and pyroclastic flow deposits of group iii stem at least partly from the same source as group i rocks of group i most likely mixed together with group ii components during the formation of the group iii flows which became hybridised during eruption transportation and emplacement the sedimentological and geochemical data best support a rift as the tectonic setting of this volcanism analogous to modern continental rift zones hence the rift associated volcanic activity preserved in the vogtendorf beds and randschiefer series represents an early ordovician stage of rift volcanism when the separation of the saxothuringian terrane from gondwana had just commenced

on the emplacement of ignimbrite in shallow marine environments abstract the emplacement of primary pyroclastic flow deposits on the sea floor can occur 1 by nonturbulent dense flows that conserve their heat under water or 2 because the flow either turbulent or nonturbulent temporarily pushes back the shoreline the feasibility of the second mechanism has been investigated theoretically and experimentally using a simple analogue system the experiments involved sustained turbulent saline currents of different densities flowing into a sectorial tank of ambient fluid that was either lighter or denser than the current the currents in all cases displaced the entire layer of ambient fluid up to a distance r irrespective of whether they were denser or lighter r is analogous to the shoreline displacement distance up to which hot ignimbrite can be emplaced by a pyroclastic flow entering the sea by varying flow rate density contrast and depth of the ambient fluid layer a simple equation for r is found that is in good agreement with the experimental data the effect of seawater boiling on shoreline displacement was also investigated by experiments using currents of carbonate solution that produced gas when flowing into a layer of ambient acid the distance r was not reduced in these experiments the equations show that pyroclastic flows of about 10 km 3 or more are capable of pushing back the sea at least a couple of kilometres and possibly more in areas of extensive shallow water enabling hot ignimbrite to be laid down on the seabed at depths corresponding to a few tens of metres shoreline displacement is thus a feasible mechanism for the emplacement of welded ignimbrite in shallow marine settings emplacement of subaerially erupted ignimbrite below storm wave base is not ruled out by the calculations but requires a combination of high discharge rate sustained eruption low density contrast between flow and water steep bathymetric gradient and small island volcano application of the model to the 1883 krakatau eruption suggests that seawater displacement may explain the occurrence of primary ignimbrite on the seabed 10 km northwest of the volcano

discussion on the submarine eruption and emplacement of the lower rhyolitic tuf formation ordovician north wales journal vol 143 1986 pp 411 424 and reply

genesis of crystal rich epiclastic rocks from subaqueous silicic lava domes role of thermal shock on quartz phenocrysts abstract deposits in the palaeozoic marine basin of the sarrabus region se sardinia western mediterranean italy show the presence of rhyolitic micropillow lithofacies in the uppermost sector of extrusive subaqueous acid domes these particular volcanic rocks contain quartz phenocrysts affected by curved fractures attributed to thermal shock produced in the magma water interface the flanks of subaqueous domes contain proximal epiclastic sandstones and greywackes characterized by the presence of non mature angular quartz clasts very similar to the occurrences detected in the rhyolitic micropillows therefore a syngenetic referred to acid domes and proximal unreworked character is inferred for these epiclastic deposits a genetic model is proposed to explain the association of lithofacies volcanic and epiclastic in direct relationship with the subaqueous growth and erosion of the domes this process of genesis of texturally unmature epiclastic rocks not related to explosive acid volcanism seems rather new and the conclusions of the paper may be in sharp contrast with some of the criteria previously described for distinguishing between pyroclastic and epiclastic crystal rich rocks

a silent slip event on the deeper cascadia subduction interface continuous global positioning system sites in southwestern british columbia canada and northwestern washington state usa have been moving landward as a result of the locked state of the cascadia subduction fault offshore in the summer of 1999 a cluster of seven sites briefly reversed their direction of motion no seismicity was associated with this event the sudden displacements are best explained by 2 centimeters of aseismic slip over a 50 kilometer by 300 kilometer area on the subduction interface downdip from the seismogenic zone a rupture equivalent to an earthquake of moment magnitude 6 7 this provides evidence that slip of the hotter plastic part of the subduction interface and hence stress loading of the megathrust earthquake zone can occur in discrete pulses