geological evidence for past large earthquakes and tsunamis along the hikurangi subduction margin new zealand abstract the hikurangi subduction margin new zealand has not produced large subduction earthquakes within the short written historic period 180 years and the potential of the plate interface to host large m 7 to great m 8 earthquakes and tsunamis is poorly constrained the geological record of past subduction earthquakes offers a method for assessing the location frequency and approximate magnitude of subduction earthquakes to underpin seismic and tsunami hazard assessments we review evidence of holocene coseismic coastal deformation and tsunamis at 22 locations along the margin a consistent approach to radiocarbon age modelling is used and earthquake and tsunami evidence is ranked using a systematic assessment of the quality of age control and the certainty that the event in question is an earthquake to identify possible subduction earthquakes we use temporal correlation of earthquakes combined with the type of earthquake evidence likely primary fault source and the earthquake certainty ranking we identify 10 past possible subduction earthquakes over the past 7000 years along the hikurangi margin the last subduction earthquake occurred at 520 470 years bp in the southern hikurangi margin and the strongest evidence for a full margin rupture is at 870 815 years bp there are no apparent persistent rupture patches suggesting segmentation of the margin is not strong in the southern margin the type of geological deformation preserved generally matches that expected due to rupture of the interseismically locked portion of the subduction interface but the southern termination of past subduction ruptures remains unresolved the pattern of geological deformation on the central margin suggests that the region of the interface that currently hosts slow slip events also undergoes rupture in large earthquakes demonstrating different modes of slip behaviour occur on the central hikurangi margin evidence for subduction earthquakes on the northern margin has not been identified because deformation signals from upper plate faults dominate the geological record large uncertainties remain in regard to evidence of past subduction earthquakes on the hikurangi margin with the greatest challenges presented by temporal correlation of earthquake evidence when working within the uncertainties of radiocarbon ages and the presence of upper plate faults capable of producing deformation and tsunamis similar to that expected for subduction earthquakes however areas of priority research such as improving the paleotsunami record and integration of submarine turbidite records should produce significant advances in the future

diatom evidence for earthquake induced subsidence and tsunami 300 yr ago in southern coastal washington fossil diatoms from four stratigraphic sections along the tidal niawiakum river southwestern washington provide an independent paleoecological test of a relative sea level rise that has been attributed to subsidence during an inferred earthquake in the cascadia subduction zone about 300 yr ago diatom assemblages in a buried soil and overlying mud indicate a sudden and lasting shift from marshes and forests near or above highest tides to mud flats and incipient tidal marshes with a progressive return to high level tidal marshes by sediment aggradation and perhaps gradual tectonic uplift the amount of coseismic submergence required to generate the paleoecological changes observed at these sites could have ranged from a minimum of 0 8 1 0 m to a maximum of 3 0 m fossil diatoms also provide an independent test of previous inferences that the subsidence was shortly followed by a tsunami the inferred tsunami deposit is a distinct sandy interval that widely overlies the buried marsh and forest soil diatoms from this interval consist of species observed on modern sand flats of the open bay identifying a bayward source for the sand occurrences of the same sand flat species above the buried soil in the farthest up valley outcrop where a sandy interval is not recognizable suggest that the tsunami extended farther landward than was previously inferred from the stratigraphy these data rule out proposed alternatives to the coseismic subsidence model that is climatically induced sea level rise temporary submergence caused by storms and support the hypothesis that a great earthquake struck southwestern washington 300 yr ago

proterozoic metamorphism and cooling in the southern lake superior region north america and its bearing on crustal evolution abstract metamorphism along the southern margin of the archean superior province has been historically attributed to the penokean orogeny a narrow corridor of amphibolite facies rocks north of the main suture does record 1 83 1 80 ga metamorphic monazite u th pb ages that mark the culmination of arc accretion however subsequent widespread amphibolite facies metamorphism and associated magmatism is recorded along the regions of greatest penokean crustal thickening the tectonically buried archean proterozoic continental margin in minnesota new monazite geochronology reveals a profound midcrustal metamorphic imprint caused by emplacement of the 1 775 ga east central minnesota batholith at moderate depths in northern wisconsin and upper peninsula michigan metamorphic monazite growth at 1 78 1 745 ga and far from geon 17 intrusions reflect a previously little recognized regional amphibolite facies metamorphic event associated with ca 1 76 ga yavapai interval accretion not solely penokean induced crustal collapse south of the penokean suture penokean terrane rocks were twice metamorphosed to upper greenschist facies first during yavapai accretion and again during geon 16 mazatzal accretion geon 16 overprinting also affected a small part of the continental margin in the northeast orogen the peavy metamorphic node south directed basement thrusts there likely accommodated substantial mazatzal foreland shortening suggesting thick skinned deformation mazatzal amphibolite facies metamorphism occurred throughout iowa and southernmost wisconsin south of the baraboo quartzite 40 ar 39 ar mineral cooling ages from eastern wisconsin reveal a limited metamorphic aureole associated with the intrusion of the 1 47 ga wolf river batholith in part reflecting its rapid emplacement at shallow crustal levels a local area of anomalously young 40 ar 39 ar mica ages away from known midcontinent rift exposures probably reflect shallow crustal level reheating during rifting not exhumation the pattern and degree of proterozoic metamorphism preserved across the northern interior of the north american midcontinent is highly variable and is a reflection of multiple accretionary and intrusive events between 1 87 and 1 47 ga collectively the geo and thermochronologic data reveal a progressive tectonic younging toward the south and overall waning of proterozoic metamorphism in this region these results demonstrate a changing tectonic environment from active margin to continental interior as laurentia grew southward and stabilized over a few hundred million years

laboratory observation of boundary layer flow under spilling breakers in surf zone using particle image velocimetry abstract a boundary layer flow under spilling breakers in a laboratory surf zone with a smooth bottom is investigated using a high resolution particle image velocimetry piv technique by cross correlating the images oscillatory velocity profiles within a viscous boundary layer of o 1 mm in thickness are resolved over ten points using piv measurements taken for an earlier study and the present study flow properties in the wave bottom boundary layer wbbl over the laboratory surf zone are obtained including the mean velocities turbulence intensity reynolds stresses and intermittency of coherent events the data are then used to estimate the boundary layer thickness phase variation and bottom shear stress it is found that while the time averaged mass transport inside the wbbl is onshore in the outer surf zone it changes to offshore in the inner surf zone the zero eulerian mass transport occurs at h hb 0 92 in the outer surf zone the maximum overshoot of the streamwise velocity and boundary layer thickness are not constant across the surf zone the bottom shear stress is mainly contributed by the viscous stress through mean velocity gradient while the reynolds stress is small and negligible the turbulence level is higher in the inner surf zone than that in the outer surf zone although only a slight increase of turbulent intensity is observed inside the wbbl from the outer surf zone to the inner surf zone the variation of phase inside and outside the wbbl was examined through the spatial velocity distribution it is found the phase lead is not constant and its value is significantly smaller than previous thought by analyzing instantaneous velocity and vorticity fields a remarkable number of intermittent turbulent eddies are observed to penetrate into the wbbl in the inner surf zone the size of the observed large eddies is about 0 11 to 0 16 times the local water depth its energy spectra follow the 5 3 slope in the inertial subrange and decay exponentially in the dissipation subrange

large scale laboratory study of breaking wave hydrodynamics over a fixed bar a large scale wave flume experiment has been carried out involving a t 4 s regular wave with h 0 85 m wave height plunging over a fixed barred beach profile velocity profiles were measured at 12 locations along the breaker bar using lda and adv a strong undertow is generated reaching magnitudes of 0 8 m s on the shoreward side of the breaker bar a circulation pattern occurs between the breaking area and the inner surf zone time averaged turbulent kinetic energy tke is largest in the breaking area on the shoreward side of the bar where the plunging jet penetrates the water column at this location and on the bar crest tke generated at the water surface in the breaking process reaches the bottom boundary layer in the breaking area tke does not reduce to zero within a wave cycle which leads to a high level of residual turbulence and therefore lower temporal variation in tke compared to previous studies of breaking waves on plane beach slopes it is argued that this residual turbulence results from the breaker bar trough geometry which enables larger length scales and time scales of breaking generated vortices and which enhances turbulence production within the water column compared to plane beaches transport of tke is dominated by the undertow related flux whereas the wave related and turbulent fluxes are approximately an order of magnitude smaller turbulence production and dissipation are largest in the breaker zone and of similar magnitude but in the shoaling zone and inner surf zone production is negligible and dissipation dominates

potassium distribution and metasomatism in pelites and schists how and when relation to postdepositional events a large global database for over 9000 archean to holocene pelites in numerous basins has been developed to evaluate diagenetically unaltered and altered compositions the mineralogy and geochemistry of quaternary muds and ancient mudstones provide first order controls on diagenetic potassium metasomatism in pelites clay mineralogy of quaternary muds is dominated by smectite and kaolinite with minor detrital mica and illite thus k2o is 4 k al is 0 25 and k rb is 220 in most quaternary muds with diagenetic alteration of clays to illite smectite and illite k2o content increases to 4 8 and k al rises to 0 2 0 5 or more in extreme potassium metasomatism authigenic k feldspar develops sources of potassium are internal to shale sandstone units wherein detrital k feldspar is dissolved during diagenesis providing k for clay illitization in closed system isochemical alteration as in some gulf coast and north sea basin cases potassium in amounts greater than that available from closed system alteration is provided from extraformational circulating brines in open system diagenesis k rb with diagenesis varies according to whether the metasomatizing fluid was relatively poor in rb seawater derived brines or richer in rb as in many hydrothermal waters diagenetic fluids may originate from seawater or meteoric water enriched in cations by water rock interactions along their subsurface migration paths and or by dissolution of evaporites potassium metasomatizing fluids penetrate low permeability pelites through faults fractures and microfractures and by diffusion in the mineral matrix typically k metasomatism possibly with pb zn cu ba and f mineralization occurs long after sediment deposition and burial at temperatures of 50 to 150 c related to tectonic activity and fluid movement different modes of metasomatism are recognized and correlated with geological setting in the passive margin gulf coast tertiary basin open system k metasomatism where present is limited to areas adjacent to steeply dipping growth faults which act as conduits for episodic pulses of altering fluids migrated upward from deeper basin sources in contrast widespread pervasive open system k metasomatism produced by continuous long term gravity advective and diffusive flow of brine from the late paleozoic appalachian ouachita wichita mountains highland to altered earlier paleozoic shales plus sandstones bentonites and carbonates in the illinois and anadarko ardmore foreland basins this mode of k alteration following major mountain building events is characteristic of many precambrian and paleozoic collision orogens and associated foreland basins another mode is in rift basins with no external drainage in which indigenous waters are evaporated to brines these brines cause albitization of k feldspar to yield potassium for illitization of detrital clays

revising estimates of spatially variable subsidence during the a d 1700 cascadia earthquake using a bayesian foraminiferal transfer function

remote sensing of breaking wave phase speeds with application to non linear depth inversions abstract a number of existing models for surface wave phase speeds linear and non linear breaking and non breaking waves are reviewed and tested against phase speed data from a large scale laboratory experiment the results of these tests are utilized in the context of assessing the potential improvement gained by incorporating wave non linearity in phase speed based depth inversions the analysis is focused on the surf zone where depth inversion accuracies are known to degrade significantly the collected data includes very high resolution remote sensing video and surface elevation records from fixed in situ wave gages wave phase speeds are extracted from the remote sensing data using a feature tracking technique and local wave amplitudes are determined from the wave gage records and used for comparisons to non linear phase speed models and for non linear depth inversions a series of five different regular wave conditions with a range of non linearity and dispersion characteristics are analyzed and results show that a composite dispersion relation which includes both non linearity and dispersion effects best matches the observed phase speeds across the domain and hence improves surf zone depth estimation via depth inversions incorporating non linearity into the phase speed model reduces errors to o 10 which is a level previously found for depth inversions with small amplitude waves in intermediate water depths using linear dispersion considering the controlled conditions and extensive ground truth this appears to be a practical limit for phase speed based depth inversions finally a phase speed sensitivity analysis is performed that indicates that typical nearshore sand bars should be resolvable using phase speed depth inversions however increasing wave steepness degrades the sensitivity of this inversion method

metasaprolite in the mcgrath gneiss minnesota usa viewing paleoproterozoic weathering through a veil of metamorphism and metasomatism abstract a 2100 ma 420 cm thick metasaprolite which is devoid of plagioclase but contains abundant microcline occurs in the archean mcgrath gneiss beneath the overlying paleoproterozoic denham formation despite being recrystallized under amphibolite facies conditions and chemically modified by potassium metasomatism mass fluxes related to weathering and metasomatism of the mcgrath metasaprolite can be estimated by judicious application of several geochemical parameters and the a c n k plot fedo et al 1995 the metasaprolite yields values of 67 94 for the plagioclase index of alteration 62 72 for the chemical index of alteration and 47 for the feldspar index of weathering and the total mass flux removed by weathering is a minimum of 2 4 moles cm 2 such values correspond to an intermediate degree or intensity of weathering compared to other more intensely weathered paleosols in the region such as those beneath the baraboo and sioux quartzites potassium metasomatism occurred at 1742 ma during the geon 17 yavapai tectonothermal event when a minimum of 0 33 moles cm 2 k 2 o was added to the metasaprolite although the absence of pedogenic textures precludes interpretation of climatic conditions during weathering of the mcgrath gneiss the level of atmospheric p co 2 can be estimated by application of sheldon s 2006 method which yields a minimum of 3 7 pal for a weathering duration of 100 000 years

quantifying offshore fore arc deformation and splay fault slip using drowned pleistocene shorelines arauco bay chile most of the deformation associated with the seismic cycle in subduction zones occurs offshore and has been therefore difficult to quantify with direct observations at millennial time scales here we study millennial deformation associated with an active splay fault system in the arauco bay area off south central chile we describe hitherto unrecognized drowned shorelines using high resolution multibeam bathymetry geomorphic sedimentologic and paleontologic observations and quantify uplift rates using a landscape evolution model along a margin normal profile uplift rates are 1 3 m ka near the edge of the continental shelf 1 5 m ka at the emerged santa maria island 0 1 m ka at the center of the arauco bay and 0 3 m ka in the mainland the bathymetry images a complex pattern of folds and faults representing the surface expression of the crustal scale santa maria splay fault system we modeled surface deformation using two different structural scenarios deep reaching normal faults and deep reaching reverse faults with shallow extensional structures our preferred model comprises a blind reverse fault extending from 3 km depth down to the plate interface at 16 km that slips at a rate between 3 0 and 3 7 m ka if all the splay fault slip occurs during every great megathrust earthquake with a recurrence of 150 200 years the fault would slip 0 5 m per event equivalent to a magnitude 6 4 earthquake however if the splay fault slips only with a megathrust earthquake every 1000 years the fault would slip 3 7 m per event equivalent to a magnitude 7 5 earthquake

transition from locked to creeping subduction in the shumagin region alaska 1 gps velocities from the alaska peninsula are modeled to determine the extent of locking on the alaska aleutian subduction interface the observations which span from the semidi islands to sanak island encompass the 1938 mw 8 3 rupture zone and the transition into the shumagin gap model parameters are optimized using a simulated annealing method coupling variation along strike of the plate interface show a nearly fully locked 90 subduction zone at the semidi islands decreasing to about 30 locked at the shumagin islands and freely slipping to the west of the shumagins independent rupture of the shumagin segment could produce repeated mw 7 6 earthquakes unless a significant fraction of the slip on the interface occurs as afterslip following large earthquakes southwest directed velocities at most of the sites may be attributed to clockwise rotation of a bering block

evidence for biological and hydrological controls on the development of a paleoproterozoic paleoweathering profile in the baraboo range wisconsin u s a abstract we examined a complete late paleoproterozoic paleoweathering profile beneath the baraboo quartzite from south central wisconsin usa in order to interpret biological and hydrological controls on ancient terrestrial weathering processes detailed thin section investigations were used to identify characteristic pedogenic features associated with saprolitization and formation of an overlying regolith and the isocon method a geochemical mass balance technique was employed to characterize elemental gains and losses the age of the sub baraboo profile is well constrained by the youngest detrital zircon ages previously reported from the basal baraboo quartzite 1712 ma and the 1749 ma crystallization age of the underlying baxter hollow granite and rhyolite parent materials micromorphologic evidence of paleoweathering comprises clay illuviation features indicative of clay movement sepic plasmic fabrics formed by repeated wetting and drying cycles redoximorphic features redox related depletions and concentrations of fe indicative of variable drainage and redox conditions and dissolution and alteration of feldspars and mafic minerals now sericite and fe oxides geochemical evidence for weathering includes depth dependent whole rock losses of na ca mg si ba sr fe and mn and relative enrichment of several immobile elements there is also evidence for post weathering k metasomatism previously dated as 1456 ma that includes 30 net additions of k and rb geochemical patterns for the baraboo profile resemble those of the previously studied and older pronto 2 475 2 44 ga and ville marie 2 38 2 215 ga paleoweathering profiles but with important differences related to baraboo profile development beneath a regolith cover and under conditions of variable hydrology during weathering in spite of its age and greenschist facies metamorphism the baraboo paleoweathering profile is remarkably similar to some modern weathering profiles formed on granite

coastal evidence for holocene subduction zone earthquakes and tsunamis in central chile abstract the 500 year historical record of seismicity along the central chile coast 30 34 s is characterized by a series of m 8 0 8 5 earthquakes followed by low tsunamis 10 m but the frequency of such large events is unknown we extend the seismic history of central chile through a study of a lowland stratigraphic sequence along the metropolitan coast north of valparaiso 33 s at this site higher relative sea level during the mid holocene created a tidal marsh and the accommodation space necessary for sediment that preserves earthquake and tsunami evidence within this 2600 yr long sequence we traced six laterally continuous sand beds probably deposited by high tsunamis plant remains that underlie the sand beds were radiocarbon dated to 6200 5600 5000 4400 3800 and 3700 cal yr bp sediment properties and diatom assemblages of the sand beds for example anomalous marine planktonic diatoms and upward fining of silt sized diatom valves point to a marine sediment source and high energy deposition grain size analysis shows a strong similarity between inferred tsunami deposits and modern coastal sediment upward fining sequences characteristic of suspension deposition are present in five of the six sand beds despite the lack of significant lithologic changes between the sedimentary units under and overlying tsunami deposits we infer that the increase in freshwater siliceous microfossils in overlying units records coseismic uplift concurrent with the deposition of five of the sand beds during our mid holocene window of evidence preservation the mean recurrence interval of earthquakes and tsunamis is 500 years our findings imply that the frequency of historical earthquakes in central chile is not representative of the greatest earthquakes and tsunamis that the central chilean subduction zone has produced

rupture across arc segment and plate boundaries in the 1 april 2007 solomons earthquake the largest earthquakes are generated in subduction zones and the earthquake rupture typically extends for hundreds of kilometres along a single subducting plate these ruptures often begin or end at structural boundaries on the overriding plate that are associated with the subduction of prominent bathymetric features of the downgoing plate here we determine uplift and subsidence along shorelines for the 1 april 2007 moment magnitude m w 8 1 earthquake in the western solomon islands using coral microatolls which provide precise measurements of vertical motions in locations where instrumental data are unavailable we demonstrate that the 2007 earthquake ruptured across the subducting simbo ridge transform and thus broke through a triple junction where the australian and woodlark plates subduct beneath the overriding pacific plate previously no known major megathrust rupture has involved two subducting plates we conclude that this event illustrates the uncertainties of predicting the segmentation of subduction zone rupture on the basis of structural discontinuities

co2 drawdown and cooling at the onset of the great oxidation event recorded in 2 45 ga paleoweathering crust abstract the archean atmosphere is thought to have been devoid of oxygen but instead containing high concentrations of greenhouse gases such as co2 and possibly ch4 that were required to keep the earth surface environments warm enough for maintenance of liquid water under faint young sun conditions earlier studies have suggested that the co2 concentrations must have been as high as over 1000 times present atmospheric levels pal to overcome the effects of weaker solar luminosity however more recent studies of precambrian paleosols imply existence of at least tenfold lower but still high pco2 levels the appearance of minute amounts of atmospheric o2 at the transition of archean and proterozoic is well documented however the bulk composition of the atmosphere and its dynamics at this crucial time is still widely debated different paleoclimate proxies of the 2 45 ga kuksha paleoweathering crust suggest its formation in a cool temperate climate paleoatmospheric pco2 estimates by geochemical and isotopic mass balance models suggest remarkably low paleoatmospheric co2 levels with the best guess estimates of atmospheric co2 between 1 and 10 pal we speculate that the kuksha paleoweathering crust either predates or partly overlaps with the onset of huronian glaciation and corresponds to a time interval of low co2 level during the first recorded large glaciation in earth history

linkage between turbulent kinetic energy waves and suspended sediment concentrations in the nearshore zone abstract knowledge about the tradeoffs among turbulent kinetic energy tke waves and suspended sediment concentrations sscs in the nearshore zone is relevant for understanding beach morphodynamics at different temporal and spatial scales a field measurement lasting for nearly three tidal cycles was conducted to holistically discern couplings between tke waves and sscs with further evaluation of the relative significance of tke and waves on sscs under various wave conditions over a meso macro tidal beach yintan to the north of beibu gulf china the results showed a dramatic increase in wave groupiness intensity from the shoaling wave condition to the breaking wave condition and a clear decrease further into the surf bore condition the near bed tkes under the surf bore condition were an order of magnitude larger than those under the breaking and shoaling wave conditions at the measurement position the averaged sscs in the near bed approximately 10 cm under the surf bore condition were 1 5 and 4 5 times larger than those under breaking and shoaling wave conditions respectively the variations in relative wave height were a decisive indicator for the differences in tke intensities among different wave conditions while the occurrence of peak tkes at the wave front within the intrawave cycle was associated with flow acceleration regardless of wave conditions mean sscs were well correlated with waves in terms of both incident wave scale and wave group scale which was limited to the shoaling wave condition and the occurrence of near bed intrawave peak sscs was always related to the offshore wave phase further tke contributed more effectively to sediment suspension at the wave group scale than at the incident wave scale especially under broken wave condition among the hydrodynamic factors tke played the most important role in the variations in sscs for all wave conditions flow acceleration served as the second most important factor under the broken wave condition while wave group single wave and advection were equivalent and less important factors for sscs

the geodetic signature of the earthquake cycle at subduction zones model constraints on the deep processes recent megathrust events in tohoku japan maule chile and sumatra indonesia were well recorded much has been learned about the dominant physical processes in megathrust zones partial locking of the plate interface detailed coseismic slip relocking afterslip viscoelastic mantle relaxation and interseismic loading these and older observations show complex spatial and temporal patterns in crustal deformation and displacement and significant differences among different margins a key question is whether these differences reflect variations in the underlying processes like differences in locking or the margin geometry or whether they are a consequence of the stage in the earthquake cycle of the margin quantitative models can connect these plate boundary processes to surficial and far field observations we use relatively simple cyclic geodynamic models to isolate the first order geodetic signature of the megathrust cycle coseismic and subsequent slip on the subduction interface is dynamically and consistently driven a review of global preseismic coseismic and postseismic geodetic observations and of their fit to the model predictions indicates that similar physical processes are active at different margins most of the observed variability between the individual margins appears to be controlled by their different stages in the earthquake cycle the modeling results also provide a possible explanation for observations of tensile faulting aftershocks and tensile cracking of the overriding plate which are puzzling in the context of convergence compression from the inversion of our synthetic gnss velocities we find that geodetic observations may incorrectly suggest weak locking of some margins for example the west aleutian margin

an alternative segmentation model for the alaskan aleutian megathrust subduction zones are the regions on earth capable of generating the largest earthquakes our current earthquake catalogs are limited in time and only a handful of magnitude 9 events have been recorded or documented therefore it is crucial to develop methods to infer which subduction zones are capable of producing very large magnitude earthquakes for this purpose subduction zones are typically broken into segments sources during the modeling process this allows modelers to assign different rates and maximum magnitudes to certain sections of the subduction zone the aleutian megathrust is one example of a subduction zone that is modeled using this approach in previous u s geological survey usgs hazard maps the alaskan megathrust was segmented using coupled or locked zones geologic data and historic earthquakes wesson et al 1999 2007 in this study we adapt a bayesian approach developed to examine seismotectonic zoning to determine the location of segment boundaries le goff and fitzenz 2012 to the particular geometry of the alaskan megathrust this approach examines a predefined geographic area for contrasts in seismic activity rates and finds the marginal probability density function for the location of the limit between zones the advantages of this approach are 1 that it is reproducible and results can be expanded to include additional earthquake catalog data over time and 2 other data types can be used to build prior distributions for the location of segment boundaries using this approach we find evidence for two robust segment boundaries along the aleutian megathrust these are in different locations than the segment boundaries used in the 2007 usgs hazards maps and are supported by recent interpretations of historical events

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

evolution of the turbulence structure in the surf and swash zones the velocity field and turbulence structure within the surf and swash zones forced by a laboratory generated plunging breaking wave were investigated using a particle image velocimetry measurement technique two dimensional velocity fields in the vertical plane from 200 consecutive monochromatic waves were measured at four cross shore locations shoreward of the breaker line the phase averaged mean flow fields indicate that a shear layer occurs when the uprush of the bore front interacts with the downwash flow the turbulence characteristics were examined via spectral analysis the larger scale turbulence structure is closely associated with the breaking wave and the bore generated turbulence in the surf zone then the large scale turbulence energy cascades to smaller scales as the turbulent kinetic energy tke evolves from the outer surf zone to the swash zone smaller scale energy injection during the latter stage of the downwash phase is associated with the bed generated turbulence yielding a 1 slope in the upper inertial range in the spatial spectra depth integrated tke budget components indicate that a local tke equilibrium exists during the bore front phases and the latter stage of the downwash phases in the outer surf zone the tke decay resembles the decay of grid turbulence during the latter stage of the uprush and the early stage of the downwash as the production rate is small because of the absence of strong mean shear during this stage of the wave cycle as well as the relatively short time available for the growth of the bed boundary layer

the plinian eruptions of 1912 at novarupta katmai national park alaska the three day eruption at novarupta in 1912 consisted of three discrete episodes episode i began with plinian dispersal of rhyolitic fallout layer a and contemporaneous emplacement of rhyolitic ignimbrites and associated proximal veneers the plinian column was sustained throughout most of the interval of ash flow generation in spite of progressive increases in the proportions of dacitic and andesitic ejecta at the expense of rhyolite accordingly plinian layer b which fell in unbroken continuity with purely rhyolitic layer a is zoned from 99 to 15 rhyolite and accumulated synchronously with emplacement of the correspondingly zoned ash flow sequence in mageik creek and the valley of ten thousand smokes vtts only the andesiterichest flow units that cap the flow sequence lack a widespread fallout equivalent indicating that ignimbrite emplacement barely outlasted the plinian phase on near vent ridges the passing ash flows left proximal ignimbrite veneers that share the compositional zonation of their valley filling equivalents but exhibit evidence for turbulent deposition and recurrent scour episode ii began after a break of a few hours and was dominated by plinian dispersal of dacitic layers c and d punctuated by minor proximal intraplinian flows and surges after another break dacitic layers f and g resulted from a third plinian episode iii intercalated with these proximally are thin intraplinian ignimbrites and several andesite rich fall flow layers both cd and fg were ejected from an inner vent 400 m wide nested within that of episode i into which the rhyolitic lava dome novarupta was still later extruded two finer grained ash layers settled from composite regional dust clouds layer e which accumulated during the d f hiatus includes a contribution from small contemporaneous ash flows and layer h settled after the main eruption was over both are distinct layers in and near the vtts but distally they merge with cd and fg respectively they are largely dacitic but include rhyolitic shards that erupted during episode i and were kept aloft by atmospheric turbulence published models yield column heights of 23 26 km for a 22 25 km for cd and 17 23 km for fg and peak mass eruption rates of 0 7 1x108 0 6 2x108 and 0 2 0 4x108 kg s 1 respectively fallout volumes adjusted to reflect calculated redistribution of rhyolitic glass shards are 8 8 km3 4 8 km3 and 3 4 km3 for episodes i ii and iii microprobe analyses of glass show that as much as 0 4 km3 of rhyolitic glass shards from eruptive episode i fell with cde and 1 1 km3 with fgh most of the rhyolitic ash in the dacitic fallout layers fell far downwind se of the vent near the rhyolite dominated ignimbrite however nearly all of layers e and h are dacitic showing that the downwind rhyolitic ash is of co plinian rather than co ignimbrite origin

video derived near bed and sheet flow sediment particle velocities in dam break driven swash abstract this short communication considers a video based approach to quantify near bed and sheet flow swash zone sediment particle velocities over a mobile bed in a laboratory setting and relate the profile shape to sheet thickness and a velocity that can be measured outside the sheet layer by for instance a current meter near bed high speed imagery was recorded during a dam break driven swash event in a flume with optically clear walls repeated swash events for two different median sediment sizes were tested optical current meter ocm analysis was applied to bed parallel image time stacks extracted at elevations from below the at rest bed to within the lower water column ocm results were compared to in situ velocity measurements where possible obtained with an acoustic doppler profiling velocimeter adpv ocm results compared well with adpv measurements for moderate suspended sediment concentrations based on visual observation sediment concentrations were not measured too high of a sediment concentration over saturated the image and did not provide distinct sediment particle trajectories in a consistent direction for ocm analysis this saturation occurred during uprush for both sediment sizes too little of a sediment concentration provided an inadequate number of sediment particle trajectories to track such as during flow reversal for the coarser sediment for coarser sediment backwash velocities were well resolved in ocm analysis with velocities comparing well correlation coefficient 0 8 to adpv estimates the dimensionless backwash sheet flow sediment particle velocity profile normalized by the velocity at the top of the sheet scaled with the dimensionless elevation normalized by the sheet layer thickness to the 0 62 power with 95 confidence intervals for the exponent ranging from 0 47 to 0 76

near bed turbulent kinetic energy budget under a large scale plunging breaking wave over a fixed bar hydrodynamics under regular plunging breaking waves over a fixed breaker bar were studied in a large scale wave flume a previous paper reported on the outer flow hydrodynamics the present paper focuses on the turbulence dynamics near the bed up to 0 10 m from the bed velocities were measured with high spatial and temporal resolution using a two component laser doppler anemometer the results show that even at close distance from the bed 1 mm the turbulent kinetic energy tke increases by a factor five between the shoaling and breaking regions because of invasion of wave breaking turbulence the sign and phase behavior of the time dependent reynolds shear stresses at elevations up to approximately 0 02 m from the bed roughly twice the elevation of the boundary layer overshoot are mainly controlled by local bed shear generated turbulence but at higher elevations reynolds stresses are controlled by wave breaking turbulence the measurements are subsequently analyzed to investigate the tke budget at wave averaged and intrawave time scales horizontal and vertical turbulence advection production and dissipation are the major terms a two dimensional wave averaged circulation drives advection of wave breaking turbulence through the near bed layer resulting in a net downward influx in the bar trough region followed by seaward advection along the bar s shoreward slope and an upward outflux above the bar crest the strongly nonuniform flow across the bar combined with the presence of anisotropic turbulence enhances turbulent production rates near the bed

random wave runup and overtopping a steep sea wall shallow water and boussinesq modelling with generalised breaking and wall impact algorithms validated against laboratory and field measurements abstract a semi implicit shallow water and boussinesq model has been developed to account for random wave breaking impact and overtopping of steep sea walls including recurves at a given time breaking is said to occur if the wave height to water depth ratio for each individual wave exceeds a critical value of 0 6 and the boussinesq terms are simply switched off the example is presented of waves breaking over an offshore reef and then ceasing to break as they propagate inshore into deeper water and finally break as they run up a slope this is not possible with the conventional criterion of a single onset of breaking based on rate of change of surface elevation which was also found to be less effective generally the runup distribution on the slope inshore of the reef was well predicted the model is tested against field data for overtopping available for anchorsholme blackpool and corresponding 1 15 scale wave flume tests reflection of breaking waves impacting a steep sea wall is represented as a partial reversal of momentum flux with an empirically defined coefficient offshore to nearshore significant wave height variation was reasonably predicted although nearshore model spectra showed distinct differences from the experiments the breaking wave shape described by a shape parameter was also not well represented as might be expected for such a simple model overtopping agreement between model field and flume was generally good although repeatability of two nominally identical flume experiments was only within 25 different distributions of random phase between spectral components can cause overall overtopping rates to differ by up to a factor of two predictions of mean discharge by eurotop methods were within a factor of two of experimental measurements

a particle image velocimetry investigation on laboratory surf zone breaking waves over a sloping beach particle image velocimetry piv measurements were performed in a wave tank under water waves propagating and breaking on a 1 15 sloping beach the wave transformation occurred in the surf zone over a large domain covering several wavelengths from incipient breaking to swash zone beyond the shoreline piv spatial interrogation windows must be small enough to obtain accurate velocities and one window covers only a small part of the domain to overcome this problem and to measure the instantaneous velocity field over the whole surf zone area we have split the full field into 14 overlapping smaller windows of the same size local measurements were synchronized with each other using pulsed ttl triggers and wave gauge data the full velocity field was then reconstructed at every time step by gathering the 14 piv fields we then measured the complete space time evolution of the velocity field over the whole surf zone we determined also the ensemble period average and phase average components of the flow with their associated fluctuating parts we used the piv images and velocity measurements to estimate the void fraction in each point of the surf zone special attention was given to the calculation of the spatial derivatives in order to obtain relevant information on vorticity and on the physical terms that appear in the fluctuating kinetic energy transport equation

precambrian paleosols and atmospheric co2 levels abstract precambrian atmospheric pco2 levels were previously estimated using a simple thermodynamic model based on the mineral assemblage in paleosols in addition to theoretical flaws with that model recalculation of pco2 levels using more recent thermodynamic data gives significantly lower values a new model based on the mass balance of weathering in paleosols gives consistent results from three separate 2 2 ga old paleosols the calculated pco2 value of 23 3 3 times present atmospheric levels is insufficient to overcome the faint young sun paradox suggesting that another greenhouse gas such as ch4 was present at elevated levels relative to the present atmosphere to account for the discrepancy applying this new approach to other precambrian paleosols a proterozoic pco2 curve is generated which indicates consistently high pco2 from 2 5 to 1 8 ga ago and a substantial drop in atmospheric pco2 at some time between 1 8 and 1 1 ga ago

a possible source mechanism of the 1946 unimak alaska far field tsunami uplift of the mid slope terrace above a splay fault zone in 1946 megathrust seismicity along the unimak segment of the alaska subduction zone generated the largest ever recorded alaska aleutian tsunami the tsunami severely damaged pacific islands and coastal areas from alaska to antarctica it is the charter member of tsunami earthquakes that produce outsized far field tsunamis for the recorded magnitude its source mechanisms were unconstrained by observations because geophysical data for the unimak segment were sparse and of low resolution reprocessing of legacy geophysical data reveals a deep water high angle reverse or splay thrust fault zone that leads megathrust slip upward to the mid slope terrace seafloor rather than along the plate boundary toward the trench axis splay fault uplift elevates the outer mid slope terrace and its inner area subsides multibeam bathymetry along the splay fault zone shows recent but undated seafloor disruption the structural configuration of the nearby semidi segment is similar to that of the unimak segment portending generation of a future large tsunami directed toward the us west coast

laboratory observations of flow and sediment transport induced by plunging regular waves 1 two parallel experiments involving the evolution and runup induced by plunging regular waves near the shoreline of a sloping bed are considered 1 a rigid bed experiment allowing direct hot film measurements of bed shear stresses and 2 a sediment bed experiment allowing for the measurement of pore water pressures as well as observation of sediment suspension and bed morphological changes both experiments utilize the same initial bed profile and wave forcing the experiments show that the mean bed shear stresses experienced onshore of incipient breaking are amplified by nearly a factor of 2 relative to prebreaking conditions whereas their corresponding turbulent fluctuations are amplified even more strongly by a factor of 5 6 the plunging processes lead to a series of vortices whose formation may be explained as the result of shear layer instability measurements show that these vortices can significantly enhance peaks in the offshore directed bed shear stresses moreover near bed pore pressure measurements indicate that these vortices cause large upward directed pressure gradients which in turn produce a corresponding series of suspended sediment plumes shoreward of the initial breaking event these findings are related to the induced morphological changes over both short and long time scales the present results are also compared and contrasted with previous experiments utilizing a similar methodology but involving plunging solitary waves

uplift and subsidence reveal a nonpersistent megathrust rupture boundary sitkinak island alaska we report stratigraphic evidence of land level change and tsunami inundation along the alaska aleutian megathrust during prehistoric and historical earthquakes west of kodiak island on sitkinak island cores and tidal outcrops fringing a lagoon reveal five sharp lithologic contacts that record coseismic land level change radiocarbon dates 137cs profiles computerized tomography scans and microfossil assemblages are consistent with rapid uplift circa 290 0 520 300 and 1050 790 cal yr b p and subsidence in a d 1964 and circa 640 510 cal yr b p radiocarbon 137cs and 210pb ages bracketing a sand bed traced 1 5 km inland and evidence for sudden uplift are consistent with russian accounts of an earthquake and tsunami in a d 1788 the mixed uplift and subsidence record suggests that sitkinak island sits above a nonpersistent boundary near the southwestern limit of the a d 1964 mw 9 2 megathrust rupture

stable creeping fault segments can become destructive as a result of dynamic weakening faults in earth s crust accommodate slow relative motion between tectonic plates through either similarly slow slip or fast seismic wave producing rupture events perceived as earthquakes these types of behaviour are often assumed to be separated in space and to occur on two different types of fault segment one with stable rate strengthening friction and the other with rate weakening friction that leads to stick slip the 2011 tohoku oki earthquake with moment magnitude m w 9 0 challenged such assumptions by accumulating its largest seismic slip in the area that had been assumed to be creeping here we propose a model in which stable rate strengthening behaviour at low slip rates is combined with coseismic weakening due to rapid shear heating of pore fluids allowing unstable slip to occur in segments that can creep between events the model parameters are based on laboratory measurements on samples from the fault of the m w 7 6 1999 chi chi earthquake the long term slip behaviour of the model which we examine using a unique numerical approach that includes all wave effects reproduces and explains a number of both long term and coseismic observations some of them seemingly contradictory about the faults at which the tohoku oki and chi chi earthquakes occurred including there being more high frequency radiation from areas of lower slip the largest seismic slip in the tohoku oki earthquake having occurred in a potentially creeping segment the overall pattern of previous events in the area and the complexity of the tohoku oki rupture the implication that earthquake rupture may break through large portions of creeping segments which are at present considered to be barriers requires a re evaluation of seismic hazard in many areas

intercalibration of radioisotopic and astrochronologic time scales for the cenomanian turonian boundary interval western interior basin usa we develop an intercalibrated astrochronologic and radioisotopic time scale for the cenomanian turonian boundary ctb interval near the global stratotype section and point in colorado usa where orbitally influenced rhythmic strata host bentonites that contain sanidine and zircon suitable for 40ar 39ar and u pb dating paired 40ar 39ar and u pb ages are determined from four bentonites that span the vascoceras diartianum to pseudaspidoceras flexuosum ammonite biozones utilizing both newly collected material and legacy sanidine samples of j obradovich comparison of the 40ar 39ar and u pb results underscores the strengths and limitations of each system and supports an astronomically calibrated fish canyon sanidine standard age of 28 201 ma the radioisotopic data and published astrochronology are employed to develop a new ctb time scale using two statistical approaches 1 a simple integration that yields a ctb age of 93 89 0 14 ma 2 total radioisotopic uncertainty and 2 a bayesian intercalibration that explicitly accounts for orbital time scale uncertainty and yields a ctb age of 93 90 0 15 ma 95 credible interval total radioisotopic and orbital time scale uncertainty both approaches firmly anchor the floating orbital time scale and the bayesian technique yields astronomically recalibrated radioisotopic ages for individual bentonites with analytical uncertainties at the permil level of resolution and total uncertainties below 2 using our new results the duration between the cenomanian turonian and the cretaceous paleogene boundaries is 27 94 0 16 ma with an uncertainty of less than one half of a long eccentricity cycle

formation and diagenesis of a sub huronian saprolith comparison with a modern weathering profile an early proterozoic paleosol that preserves archean granite protolith textures occurs beneath the lorrain formation in the early proterozoic huronian supergroup near ville marie quebec textural mineralogical and geochemical comparisons between this saprolith and a modern weathering profile developed on the devonian toorongo granodiorite in eastern australia indicate similarities that can be attributed to the effects of primary weathering reactions the comparison also reveals anomalous features at ville marie that are caused by diagenetic reactions between the weathered granite and meteoric waters k metasomatism in the form of sericite replacement of kandites is ubiquitous in the ville marie saprolith zone and is ascribed to reaction of low na k meteoric waters with the weathered profile as they moved along a relatively permeable unconformity surface earlier diagenetic reactions may have produced calcite alteration occurring in a thin zone at the base of the profile thought to represent the po

flow kinematics of focused wave groups on a plane beach in the u k coastal research facility measurements are presented of the water particle kinematics of focused wave groups generated in the u k coastal research facility single and repeated wave groups are considered at normal and 20 incidence to a 1 20 plane beach the single focused wave groups model extreme transient events without the complication of reflections during the data acquisition process a symmetry based separation of harmonics method is used to interpret the water particle kinematics at the point of focus although the largest component is linear there are also considerable second order kinematics terms both low frequency and high frequency away from the free surface the 2nd order difference contribution to the kinematics is a return current opposed to the direction of wave advance for repeated wave groups the measured kinematics confirms the presence of a low frequency free wave followed by higher frequency waves of the main group and trailing higher order harmonic waves in the breaker and surf zones there is also evidence of the saw tooth behaviour of broken waves followed by scatter due to breaker induced turbulence pulsatile wave breaking of repeated wave groups at oblique incidence is found to drive a longshore current

are rupture zone limits of great subduction earthquakes controlled by upper plate structures evidence from multichannel seismic reflection data acquired across the northern ecuador southwest colombia margin 1 subduction of the nazca plate beneath the ecuador colombia margin has produced four megathrust earthquakes during the last century the 500 km long rupture zone of the 1906 mw 8 8 event was partially reactivated by three thrust events in 1942 mw 7 8 1958 mw 7 7 and 1979 mw 8 2 whose rupture zones abut one another multichannel seismic reflection and bathymetric data acquired during the sisteur cruise show evidence that the margin wedge is segmented by transverse crustal faults that potentially correlate with the limits of the earthquake coseismic slip zones the paleogene neogene jama quininde and esmeraldas crustal faults define a 200 km long margin crustal block that coincides with the 1942 earthquake rupture zone subduction of the buoyant carnegie ridge is inferred to partially lock the plate interface along central ecuador however coseismic slip during the 1942 and 1906 earthquakes may have terminated against the subducted northern flank of the ridge we report on a newly identified manglares crustal fault that cuts transversally through the margin wedge and correlates with the limit between the 1958 and 1979 rupture zones during the earthquake cycle the fault is associated with high stress concentration on the plate interface an outer basement high which bounds the margin seaward of the 1958 rupture zone may act as a deformable buttress to seaward propagation of coseismic slip along a megathrust splay fault coseismic uplift of the basement high is interpreted as the cause for the 1958 tsunami we propose a model of weak transverse faults which reduce coupling between adjacent margin segments together with a splay fault and an asperity along the plate interface as controlling the seismogenic rupture of the 1958 earthquake

the tectonic fabric of the ocean basins 1 we present a global community data set of fracture zones fzs discordant zones propagating ridges v shaped structures and extinct ridges digitized from vertical gravity gradient vgg maps we use a new semi automatic fz tracking program to test the precision of our hand digitized traces and find a mean absolute deviation of less than 3 4 km from the raw vgg minima that most clearly delineate each feature and less than 5 4 km from the fz location predicted by fitting model profiles to the vgg data that represent the morphology of the individual fzs these offsets are small considering gravity data only provide an approximation for the underlying basement morphology we further investigate the origin of non fz seafloor fabric by combining published abyssal hill heights computed from gravity anomalies with global half spreading rates a residual abyssal hill height grid with spreading rate effects removed combined with our interpreted tectonic fabric reveals several types of seafloor fabric distinct from typical abyssal hills where discordant zones do not overprint abyssal hill signals residual abyssal hill height anomalies correspond to seafloor that accreted near mantle thermal anomalies or zones of melt depletion our analysis reveals several areas where residual abyssal hill height anomalies reflect pseudo faults and extinct ridges associated with ridge propagation and or microplate formation in the southern pacific ocean

identifying coseismic subsidence in tidal wetland stratigraphic sequences at the cascadia subduction zone of western north america tidal wetland stratigraphy reveals that great plate boundary earthquakes have caused hundreds of kilometers of coast to subside at the cascadia subduction zone however determining earthquake recurrence intervals and mapping the coastal extent of past great earthquake ruptures in this region are complicated by the effects of many sedimentologic hydrographic and oceanographic processes that occur on the coasts of tectonically passive as well as active continental margins tidal wetland stratigraphy at many cascadia estuaries differs little from that at similar sites on passive margin coasts where stratigraphic sequences form through nonseismic processes unrelated to coseismic land level changes methods developed through study of similar stratigraphic sequences in europe provide a framework for investigating the cascadia estuarine record five kinds of criteria must be evaluated when inferring regional coastal subsidence due to great plate boundary earthquakes the suddenness and amount of submergence the lateral extent of submerged tidal wetland soils the coincidence of submergence with tsunami deposits and the degree of synchroneity of submergence events at widely spaced sites evaluation of such criteria at the cascadia subduction zone indicates regional coastal subsidence during at least two great earthquakes evidence for a coseismic origin remains equivocal however for the many peat mud contacts in cascadia stratigraphic sequences that lack 1 contrasts in lithology or fossils indicative of more than half a meter of submergence 2 well studied tsunami deposits or 3 precise ages needed for regional correlation paleoecologic studies of fossil assemblages are particularly important in estimating the size of sudden sea level changes recorded by abrupt peat mud contacts and in helping to distinguish erosional and gradually formed contacts from coseismic contacts reconstruction of a history of great earthquakes for the cascadia subduction zone will require rigorous application of the above criteria and many detailed investigations

late holocene paleoseismology of shuyak island alaska we report stratigraphic evidence of land level changes along the eastern portion of the alaska aleutian megathrust four marshes on shuyak island record variable amounts of coseismic deformation during four pre 20th century earthquakes we combine these data with paleoseismic evidence from across the kodiak kenai and prince william sound segments of the megathrust these indicate that in the last 2000 years ad 1964 was the only one to rupture all three segments simultaneously and generate a mw 9 2 earthquake the kodiak segment ruptured independently on four further occasions with magnitudes mw 8 0 in ad 1788 and c 400 440 320 bp and independently but around the times of great earthquakes in the prince william sound segment c 850 and c 1500 bp

observations of turbulence within a natural surf zone abstract here the reynolds stresses u w and w where u and w are the cross shore alongshore and vertical turbulence velocities respectively and the angle brackets represent time averaging are used to diagnose turbulence dynamics beneath natural breaking surf zone waves the data were collected at truc vert beach france during a 12 day period in 1 3 m water depth with strong cross shore and alongshore currents under high energy wave conditions offshore significant wave heights ranged between 2 and 8 m the u w term is predominantly negative increases with the ratio of wave height hs to water depth h degree of wave breaking and decreases in magnitude toward the bed this supports the view that the cross shore shear stress is due to breaking induced vortices that transport high speed cross shore flow downward and disintegrate close to the bed the occasional positive sign of u w within the lower 15 20 of the water column indicates that sometimes surface generated turbule

detection limits of tidal wetland sequences to identify variable rupture modes of megathrust earthquakes abstract recent paleoseismological studies question whether segment boundaries identified for 20th and 21st century great m8 earthquakes persist through multiple earthquake cycles or whether smaller segments with different boundaries rupture and cause significant hazards the smaller segments may include some currently slipping rather than locked in this review we outline general principles regarding indicators of relative sea level change in tidal wetlands and the conditions in which paleoseismic indicators must be distinct from those resulting from non seismic processes we present new evidence from sites across southcentral alaska to illustrate different detection limits of paleoseismic indicators and consider alternative interpretations for marsh submergence and emergence we compare predictions of coseismic uplift and subsidence derived from geophysical models of earthquakes with different rupture modes the spatial patterns of agreement and misfits between model predictions and quantitative reconstructions of coseismic submergence and emergence suggest that no earthquake within the last 4000 years had a pattern of rupture the same as the mw 9 2 alaska earthquake in 1964 from the alaska examples and research from other subduction zones we suggest that if we want to understand whether a megathrust ruptures in segments of variable length in different earthquakes we need to be site specific as to what sort of geological based criteria eliminate the possibility of a particular rupture mode in different earthquakes we conclude that coastal paleoseismological studies benefit from a methodological framework that employs rigorous evaluation of five essential criteria and a sixth which may be very robust but only occur at some sites 1 lateral extent of peat mud or mud peat couplets with sharp contacts 2 suddenness of submergence or emergence and replicated within each site 3 amount of vertical motion quantified with 95 error terms and replicated within each site 4 syncroneity of submergence and emergence based on statistical age modelling 5 spatial pattern of submergence and emergence 6 possible additional evidence such as evidence of a tsunami or liquefaction concurrent with submergence or emergence we suggest that it is possible to consider detection limits as low as 0 1 0 2 m coseismic vertical change

deformation and slip along the sunda megathrust in the great 2005 nias simeulue earthquake seismic rupture produced spectacular tectonic deformation above a 400 kilometer strip of the sunda megathrust offshore northern sumatra in march 2005 measurements from coral microatolls and global positioning system stations reveal trench parallel belts of uplift up to 3 meters high on the outer arc islands above the rupture and a 1 meter deep subsidence trough farther from the trench surface deformation reflects more than 11 meters of fault slip under the islands and a pronounced lessening of slip trenchward a saddle in megathrust slip separates the northwestern edge of the 2005 rupture from the great 2004 sumatra andaman rupture the southeastern edge abuts a predominantly aseismic section of the megathrust near the equator

rupture extent of the 1938 alaskan earthquake as inferred from tsunami waveforms using tsunami waveforms we estimate the source parameters of the 10 november 1938 alaskan earthquake the earthquake ruptured a 300 kin long segment of the alaskan arc which corresponds to the aftershock area the seismic moment is approximately 20x102o nm or mw 8 2 and the moment release was concentrated in the eastern end of the aftershock zone the tsunami and seismic evidence strongly suggest that the 1938 earthquake did not rupture into the shumagin islands gap

great tsunamigenic earthquakes during the past 1000 yr on the alaska megathrust large to great earthquakes and related tsunamis generated on the alaska megathrust produce major hazards for both the area of rupture and heavily populated coastlines around much of the pacific ocean recent modeling studies suggest that single segment ruptures as well as multi segment 1964 type ruptures can produce great earthquakes m8 and significant hazards both in the near field and to distant locations through the generation of tsunamis we present new paleoseismological data from kodiak island and a new analysis of radiocarbon data based on bayesian age modeling to combine our observations with previous geological historical and archaeological investigations we suggest that in addition to multi segment ruptures in a d 1964 and 1020 1150 95 age estimate a single segment rupture occurred in 1788 with coseismic land surface deformation across kodiak island and a tsunami that is recorded in historical documents and in sediment sequences and another similar rupture of the same kodiak segment at a d 1440 1620 these indicate shorter intervals between ruptures of the kodiak segment than previously assumed and more frequent ruptures than for the prince william sound segment

the paleoproterozoic baraboo paleosol revisited quantifying mass fluxes of weathering and metasomatism chemical climofunctions and atmospheric pco2 in a chemically heterogeneous protolith abstract the paleoproterozoic baraboo paleosol is the most chemically mature precambrian paleosol in the lake superior region having formed under the influence of a warm humid climate in a region of subdued topography we have determined the chemical variability among six samples of granitic protolith and found that such variability is inherited in the weathering profile to minimize the effect of sample heterogeneity on various geochemical calculations transformed compositions of saprolite and regolith were generated by obtaining linear least squares fits to the concentrations of sio2 tio2 al2o3 and zr through the weathering profile and summing the totals to 100 fortunately use of measured or transformed compositions makes little difference in calculation of mass fluxes however transformed compositions allow for clearer comparisons among paleosols and are essential for determining certain paleosol parameters such as chemical depletion fraction calculations of total and reduced mass fluxes chemical index of alteration feldspar index of weathering and chemical depletion fraction demonstrate that the baraboo paleosol is chemically more mature than the paleoproterozoic pronto and cambrian timna paleosols but less mature than modern subtropical and tropical soils estimates of mean annual temperature matppm and mean annual precipitation mapppm for baraboo are 14 3 19 2 9 4 c and 1177 1695 658 mm yr 1 confirming the previous interpretation of a warm humid climate although the level of atmospheric pco2 is poorly constrained due to the uncertainty in duration of weathering and possibility of regolith removal by erosion pco2 is calculated to be 4 8 pre industrial atmospheric level 280 ppm for 100 000 years of weathering which is consistent with the pco2 level at 1 7 ga predicted by the weak sun model

source of high tsunamis along the southernmost ryukyu trench inferred from tsunami stratigraphy abstract four paleotsunamis deposits are exposed in a trench on the coastal lowland north of the southern ryukyu subduction zone trench radiocarbon ages on coral and bivalve shells show that the four deposits record tsunamis date from the last 2000 yrs including a historical tsunami with a maximum run up of 30 m in 1771 for an average recurrence interval of approximately 600 yrs ground fissures in a soil beneath the 1771 tsunami deposit may have been generated by stronger shaking than recorded by historical documents the repeated occurrence of the paleotsunami deposits supports a tectonic source model on the plate boundary rather than a nontectonic source model such as submarine landslides assuming a thrust model at the subduction zone the seismic coupling ratio may be as low as 20

from a black to a gray box a mass balance interpretation of pedogenesis we utilize chemical elements as tracers in a mass balance analysis that provides functional relationships among soil chemical composition bulk density and volume change in relation to parent material these analytical functions are based on the principle of conservation of mass and include a term quantifying mass flux into out of the soil and between horizons we apply the technique to the oldest member of a chronosequence developed on marine terraces in northern california it is an alfisol that evolved from beach sand to its present state nearly one third of its weight is composed of secondary clay minerals in about 240 ky aside from large increases in organic carbon desilication is the dominant factor in soil evolution 29 50 83 g cm 2 si was leached from the beach sand during pedogenesis the rate of desilication is roughly 2 1 t km 2 yr 1 0 21 g cm 2 ky 1 an order of magnitude slower than that implied by the si denudation rate calculated for the mattole river watershed weathering of primary minerals and synthesis of secondary minerals is relatively well advanced suggesting that the rate of desilication may be declining the local beach is composed of quartz and sodic plagioclase with smaller amounts of chlorite mica and kaolinite the soil has substantially different mineralogy sand is dominated by quartz and clay is dominated by kaolinite halloysite chloritic intergrades and gibbsite bases are also leached though the total mass was much less 57 2 55 g cm 2 of na in the beach sand was lost as plagioclase weathered by focusing on elemental and mineralogical gains and losses we emphasize the essential connection between the pedologic environment and the external hydrochemical environment

the angular velocities of the plates and the velocity of earth s centre from space geodesy summary using space geodetic observations from four techniques gps vlbi slr and doris we simultaneously estimate the angular velocities of 11 major plates and the velocity of earth s centre we call this set of relative plate angular velocities geodvel for geodesy velocity plate angular velocities depend on the estimate of the velocity of earth s centre and on the assignment of sites to plates most geodetic estimates of the angular velocities of the plates are determined assuming that earth s centre is fixed in an international terrestrial reference frame itrf and are therefore subject to errors in the estimate of the velocity of earth s centre in itrf2005 and itrf2000 earth s centre is the centre of mass of earth oceans and atmosphere cm the velocity of cm is estimated by slr observation of lageos s orbit herein we define earth s centre to be the centre of mass of solid earth ce we determine the velocity of ce by assuming that the portions of plate interiors not near the late pleistocene ice sheets move laterally as if they were part of a rigid spherical cap the geodvel estimate of the velocity of ce is likely nearer the true velocity of cm than are the itrf2005 and itrf2000 estimates because 1 no phenomena can sustain a significant velocity between cm and ce 2 the plates are indeed nearly rigid aside from vertical motion and 3 the velocity of cm differs between itrf2005 and itrf2000 by an unacceptably large speed of 1 8 mm yr 1 the velocity of earth s centre in geodvel lies between that of itrf2000 and that of itrf2005 with the distance from itrf2005 being about twice that from itrf2000 because the geodvel estimates of uncertainties in plate angular velocities account for uncertainty in the velocity of earth s centre they are more realistic than prior estimates of uncertainties geodvel differs significantly from all prior global sets of relative plate angular velocities determined from space geodesy for example the 95 per cent confidence limits for the angular velocities of geodvel exclude those of revel sella et al for 34 of the 36 plate pairs that can be formed between any two of the nine plates with the best constrained motion the median angular velocity vector difference between geodvel and revel is 0 028 myr 1 which is up to 3 1 mm yr 1 on earth s surface geodvel differs the least from the geodetic angular velocities that altamimi et al determine from itrf2005 geodvel s 95 per cent confidence limits exclude 11 of 36 angular velocities of altamimi et al and the median difference is 0 015 myr 1 geodvel differs significantly from nearly all relative plate angular velocities averaged over the past few million years including those of nuvel 1a the difference of geodvel from updated 3 2 myr angular velocities is statistically significant for all but two of 36 angular velocities with a median difference of 0 063 myr 1 across spreading centres eight have slowed down while only two have sped up we conclude that plate angular velocities over the past few decades differ significantly from the corresponding angular velocity averaged over the past 3 2 myr

a possible transoceanic tsunami directed toward the u s west coast from the semidi segment alaska convergent margin the semidi segment of the alaska convergent margin appears capable of generating a giant tsunami like the one produced along the nearby unimak segment in 1946 reprocessed legacy seismic reflection data and a compilation of multibeam bathymetric surveys reveal structures that could generate such a tsunami a 200 km long ridge or escarpment with crests 1 km high is the surface expression of an active out of sequence fault zone recently referred to as a splay fault such faults are potentially tsunamigenic this type of fault zone separates the relatively rigid rock of the margin framework from the anelastic accreted sediment prism seafloor relief of the ridge exceeds that of similar age accretionary prism ridges indicating preferential slip along the splay fault zone the greater slip may derive from quaternary subduction of the patton murray hot spot ridge that extends 200 km toward the east across the north pacific estimates of tsunami repeat times from paleotsunami studies indicate that the semidi segment could be near the end of its current inter seismic cycle gps records from chirikof island at the shelf edge indicate 90 locking of plate interface faults an earthquake in the shallow semidi subduction zone could generate a tsunami that will inundate the us west coast more than the 1946 and 1964 earthquakes because the semidi continental slope azimuth directs a tsunami southeastward this article is protected by copyright all rights reserved

beach ridges as paleoseismic indicators of abrupt coastal subsidence during subduction zone earthquakes and implications for alaska aleutian subduction zone paleoseismology southeast coast of the kenai peninsula alaska abstract the kenai section of the eastern alaska aleutian subduction zone straddles two areas of high slip in the 1964 great alaska earthquake and is the least studied of the three megathrust segments kodiak kenai prince william sound that ruptured in 1964 investigation of two coastal sites in the eastern part of the kenai segment on the southeast coast of the kenai peninsula identified evidence for two subduction zone earthquakes that predate the 1964 earthquake both coastal sites provide paleoseismic data through inferred coseismic subsidence of wetlands and associated subsidence induced erosion of beach ridges at verdant cove paleo beach ridges record the paleoseismic history whereas at quicksand cove buried soils in drowned coastal wetlands are the primary indicators of paleoearthquake occurrence and age the timing of submergence and death of trees mark the oldest earthquake at verdant cove that is consistent with the age of a well documented 900 year ago subduction zone earthquake that ruptured the prince william sound segment of the megathrust to the east and the kodiak segment to the west soils buried within the last 400 450 years mark the penultimate earthquake on the southeast coast of the kenai peninsula the penultimate earthquake probably occurred before ad 1840 from its absence in russian historical accounts the penultimate subduction zone earthquake on the kenai segment did not rupture in conjunction with the prince william sound to the northeast therefore the kenai segment which is presently creeping can rupture independently of the adjacent prince william sound segment that is presently locked

multi segment earthquakes and tsunami potential of the aleutian megathrust abstract large to great earthquakes and related tsunamis generated on the aleutian megathrust produce major hazards for both the area of rupture and heavily populated coastlines around much of the pacific ocean here we use paleoseismic records preserved in coastal sediments to investigate whether segment boundaries control the largest ruptures or whether in some seismic cycles segments combine to produce earthquakes greater than any observed since instrumented records began virtually the entire megathrust has ruptured since ad1900 with four different segments generating earthquakes m8 0 the largest was the m9 2 great alaska earthquake of march 1964 that ruptured 800 km of the eastern segment of the megathrust the tsunami generated caused fatalities in alaska and along the coast as far south as california east of the 1964 zone of deformation the yakutat microplate experienced two m8 0 earthquakes separated by a week in september 1899 for the first time we present evidence that earthquakes 900 and 1500 years ago simultaneously ruptured adjacent segments of the aleutian megathrust and the yakutat microplate with a combined area 15 greater than 1964 giving an earthquake of greater magnitude and increased tsunamigenic potential

segmentation of megathrust rupture zones from fore arc deformation patterns over hundreds to millions of years arauco peninsula chile 1 this work explores the control of fore arc structure on segmentation of megathrust earthquake ruptures using coastal geomorphic markers the arauco nahuelbuta region at the south central chile margin constitutes an anomalous fore arc sector in terms of topography geology and exhumation located within the overlap between the concepcion and valdivia megathrust segments this boundary however is only based on 500 years of historical records we integrate deformed marine terraces dated by cosmogenic nuclides syntectonic sediments published fission track data seismic reflection profiles and microseismicity to analyze this earthquake boundary over 10 2 10 6 years rapid exhumation of nahuelbuta s dome like core started at 4 1 2 ma coeval with inversion of the adjacent arauco basin resulting in emergence of the arauco peninsula here similarities between topography spatiotemporal trends in fission track ages pliocene pleistocene growth strata and folded marine terraces suggest that margin parallel shortening has dominated since pliocene time this shortening likely results from translation of a fore arc sliver or microplate decoupled from south america by an intra arc strike slip fault microplate collision against a buttress leads to localized uplift at arauco accrued by deep seated reverse faults as well as incipient oroclinal bending the extent of the valdivia segment which ruptured last in 1960 with an mw 9 5 event equals the inferred microplate we propose that mechanical homogeneity of the fore arc microplate delimits the valdivia segment and that a marked discontinuity in the continental basement at arauco acts as an inhomogeneous barrier controlling nucleation and propagation of 1960 type ruptures as microplate related deformation occurs since the pliocene we propose that this earthquake boundary and the extent of the valdivia segment are spatially stable seismotectonic features at million year scale

microfossils from coastal environments as indicators of paleo earthquakes tsunamis and storms abstract coastal risk assessment and hazard mitigation require datasets on centennial and millennial temporal scales to capture natural variability and multiple occurrences of the largest but least frequent events coastal sediments from low energy depositional environments archive geologic evidence of paleo earthquakes tsunamis and storms many of the best reconstructions of these events are derived from changes in microfossil diatoms foraminifera and pollen assemblages in this review we explain how microfossils are used to reconstruct records of paleoearthquakes by quantifying the amount of coseismic and interseismic vertical land movements along tectonically active coastlines examples from the united states alaska and the pacific northwest japan and chile show that microfossil based transfer functions may provide continuous records of vertical land movement during earthquake deformation cycles we discuss how microfossil habitat preferences and taphonomic character are used to constrain sediment provenance e g beach nearshore or offshore sources and identify overwash deposits and how this information can be used to reconstruct the recurrence of tsunamis and storms analysis of overwash deposits from thailand and malaysia indicates the ability of microfossils to resolve individual waves within tsunami sediments and an example from the sendai coastal plain in japan uses foraminifera to ascribe a beach to nearshore provenance for the 2011 tohoku tsunami deposit finally we present recent examples from the gulf of mexico on the use of foraminifera to estimate the volume and distance of transport of storm overwash from hurricanes

paleomagnetism structure and longitudinal correlation of middle precambrian dykes from northwestern ontario and minnesota a primary magnetization about 2 1 ga old is well preserved in the kenora kabetogama dyke swarm in minnesota and ontario its direction the mean for 12 dykes incorporating results from 30 paleomagnetic sites is 115 9 55 6 yielding a paleomagnetic pole position of latitude 42 7 s longitude 4 2 e dm 7 3 dp 5 2 the primary nature of the magnetization can be demonstrated using geochemistry to correlate individual dykes over distances that can exceed 300 km whereas the remanence direction varies between dykes it remains constant along a dyke sufficient proof that it was formed during initial cooling of the intrusion a weak longitudinal increase in hydrous alteration mgo content and degree of magnetic overprinting is observed as the swarm is followed to the south and may reflect increasing proximity to a precambrian continental margin that underwent rifting sedimentation and deformation during the time interval 2 2 1 6 ga bp although the cause of the longitudinal changes in terms of ma

downdip variations in seismic reflection character implications for fault structure and seismogenic behavior in the alaska subduction zone seismic reflection data collected offshore of alaska peninsula across the western edge of the semidi segment show distinctive variations in reflection characteristics of the megathrust fault with depth suggesting changes in structure that may relate to seismic behavior from the trench to 40 km landward two parallel reflections are observed which we interpret as the top and bottom of the subducted sediment section from 50 95 km from the trench the plate interface appears as a thin 400 ms reflection band deeper and farther landward the plate interface transitions to a thicker 1 1 5 s package of reflections where it appears to intersect the forearc mantle wedge based on our preferred interpretation of the continental moho synthetic waveform modeling suggests that the thin reflection band is best explained by a single 100 to 250 m thick low velocity zone whereas the thick reflection band requires a 3 to 5 km thick zone of thin layers the thin reflection band is located at the center of the 1938 mw 8 2 semidi earthquake rupture zone that now experiences little interplate seismicity the thick reflection band starts at the downdip edge of the rupture zone and correlates with a dipping band of seismicity and projects to the location of tremor at greater depth we interpret the thin reflection band as a compacted sediment layer and or localized shear zone the thick reflection band could be caused by a wide deformation zone with branching faults and or fluid rich layers representing a broad transition from stick slip sliding to slow slip and tremor

precambrian time units and nomenclature the geon concept a geologic calendar using the concept of geon a time unit of 108 a is suggested as an alternative to the recently proposed complex nomenclature for proterozoic periods

kinematics and depth integrated terms in surf zone waves from laboratory measurement kinematics of nominally periodic surf zone waves have been measured in the laboratory using lda laser doppler anemometry above trough level as well as below for weakly plunging breakers transforming into bores in shallower water the aim was to determine through phase or ensemble averaging periodic flow structures in a two dimensional vertical plane from large scale down to small scale vortical structures coherent multiple vortical structures were evident at the initiation of breaking becoming elongated along the surface during bore propagation the initial region is likely to become more extensive as waves become more strongly plunging and could explain the difference in turbulence characteristics between plunging and spilling breakers observed elsewhere

persistent termini of 2004 and 2005 like ruptures of the sunda megathrust to gain insight into the longevity of subduction zone segmentation we use coral microatolls to examine an 1100 year record of large earthquakes across the boundary of the great 2004 and 2005 sunda megathrust ruptures simeulue a 100 km long island off the west coast of northern sumatra indonesia straddles this boundary northern simeulue was uplifted in the 2004 earthquake whereas southern simeulue rose in 2005 northern simeulue corals reveal that predecessors of the 2004 earthquake occurred in the 10th century ad in ad 1394 2 and in ad 1450 3 corals from southern simeulue indicate that none of the major uplifts inferred on northern simeulue in the past 1100 years extended to southern simeulue the two largest uplifts recognized at a south central simeulue site around ad 1422 and in 2005 involved little or no uplift of northern simeulue the distribution of uplift and strong shaking during a historical earthquake in 1861 suggests the 1861 rupture area was also restricted to south of central simeulue as in 2005 the strikingly different histories of the two adjacent patches demonstrate that this boundary has persisted as an impediment to rupture through at least seven earthquakes in the past 1100 years this implies that the rupture lengths and hence sizes of at least some future great earthquakes and tsunamis can be forecast these microatolls also provide insight into megathrust behavior between earthquakes revealing sudden and substantial changes in interseismic strain accumulation rates

late holocene great earthquakes in the eastern part of the aleutian megathrust abstract the great earthquake mw 9 2 of ad 1964 may not be typical of other megathrust earthquakes in the region during the last 4000 years we present new field data from three sites copper river delta the lower katalla river valley and puffy slough to enhance the temporal and spatial resolutions of the paleoseismic records of multiple great earthquakes differences in the spatial patterns of coseismic uplift and subsidence suggest different rupture combinations of the kodiak prince william sound and western yakutat segments of the plate boundary the longest and most comprehensive records all come from the prince william sound segment most sites here reveal net subsidence over multiple earthquake cycles except where probable upper plate faulting contributes locally to net uplift with measurable differences between sites only a few kilometres apart we identify the katalla area as a source of local seismic hazard similar to other locations in the western part of the yakutat microplate including the two mw8 ruptures in ad 1899 we use a bayesian radiocarbon modelling approach to estimate the age and recurrence intervals of multiple great earthquakes for the prince william sound segment of the megathrust the long interval 883 34 2 years between the penultimate earthquake and ad 1964 contrasts with the older earthquakes that have intervals ranging from 420 to 610 years with a mean of 535 years