a cellular model of river meandering river meandering has been successfully modelled using vector based methods but these can not simulate multiple or braided channels conversely cellular braided river models fail to replicate meandering this paper describes a new method to simulate river meandering within a cellular model caesar a novel technique for determining bend radius of curvature on a cell by cell basis is described that importantly allows regional information on bend curvature to be transferred to local points this local curvature is then used to drive meandering and lateral erosion through two methods key difficulties are identified including the deposition of material on point bars and cut off development but the method illustrates how meandering can be integrated within a cellular framework this demonstrates the potential to produce a single model that can incorporate both meandering and braiding copyright 2006 john wiley sons ltd

alpine and pacific styles of phanerozoic mountain building subduction zone petrogenesis of continental crust a broad continuum exists between two distinct end member types of mountain building alpine type orogenic belts develop during subduction of an ocean basin between two continental blocks resulting in collision they are characterized by an imbricate sequence of oceanward verging nappes some alpine belts exhibit superimposed late stage backthrusting sediments are chiefly platform carbonates and siliciclastics in some cases associated with minor amounts of bimodal volcanics pre existing granitic gneisses and related continental rocks constitute an autochthonous parautochthonous basement metamorphism of deeply subducted portions of the orogen ranges from relatively high pressure hp to ultrahigh pressure uhp calcalkaline volcanic plutonic rocks are rare and have peraluminous s type bulk compositions in contrast pacific type orogens develop within and landward from long sustained oceanic subduction zones they consist of an outboard oceanic trench accretionary prism and an inboard continental margin island arc the oceanic assemblage consists of first cycle in part melanged volcaniclastics and minor but widespread cherts deep water carbonates intimately mixed with disaggregated ophiolites the section recrystallized under hp conditions recumbent fold vergence is oceanward a massive slightly older to coeval calcalkaline arc is sited landward from the trench complex on the stable non subducted plate it consists of abundant dominantly intermediate metaluminous i type volcanics resting on old crust both assemblages are thrown into open folds intruded by comagmatic i type granitoids and metamorphosed locally to regionally under high t low p conditions in the subduction channel of collisional and outboard circumpacific terranes combined extension above and subduction below allows buoyancy driven ascent of ductile thin aspect ratio slices of hp uhp complexes to midcrustal levels where most closely approached neutral buoyancy exposure of rising sheets caused by erosion and gravitational collapse results in moderate amounts of sedimentary debris because exhumed sialic slivers are of modest volume at massive sialic buildups associated with convergent plate cusps syntaxes tectonic aneurysms may help transport hp uhp complexes from mid to upper crustal levels the closure of relatively small ocean basins that typify many intracratonic suture zones provides only limited production of intermediate and silicic melts so volcanic plutonic belts are poorly developed in alpine orogens compared with circumpacific convergent plate junctions generation of a calcalkaline arc mainly depends on volatile evolution at the depth of magma generation phase equilibrium studies show that under typical subduction zone p t trajectories clinoamphibole ca al hydrous silicates constitute the major hydroxyl bearing phases in deep seated metamorphic rocks of morb composition other hydrous minerals are of minor abundance ca and na clinoamphiboles dehydrate at pressures of above approximately 2 gpa but low temperature devolatilization may be delayed by pressure overstepping thus metabasaltic blueschists and amphibolites expel h2o at melt generation depths and commonly achieve stable eclogitic assemblages partly serpentinized mantle beneath the oceanic crust dehydrates at roughly comparable conditions for reasonable subduction zone geothermal gradients however white micas biotites remain stable to pressures 3 gpa accordingly attending descent to depths of 100 km mica rich quartzofeldspathic lithologies that constitute much of the continental crust fail to evolve substantial amounts of h2o and transform incompletely to stable eclogite facies assemblages underflow of amphibolitized oceanic lithosphere thus generates most of the deep seated volatile flux and the consequent partial melting to produce the calcalkaline suite along and above a subduction zone where large volumes of micaceous intermediate and felsic crustal materials are carried down to great depths volatile flux severely diminishes thus continental collision in general does not produce a volcanic plutonic arc whereas in contrast the long continued contemporaneous underflow of oceanic lithosphere does

modeling the evolution of incised streams ii streambank erosion incision and ensuing widening of alluvial stream channels is widespread in the midsouth and midwestern united states and represents an important form of channel adjustment streambanks have been found to contribute as much as 80 of the total suspended load the location timing and magnitude of streambank erosion are difficult to predict results from field studies to characterize the resistance of fine grained materials to hydraulic and geotechnical erosion the impact of pore water pressures on failure dimensions and shearing resistance and the role of riparian vegetation on matric suction streambank permeability and shearing resistance are used to enhance the channel evolution model concepts conservational channel evolution and pollutant transport system this paper discusses the conceptualization of the above mentioned physical processes and demonstrates the ability of the derived model to simulate streambank failure processes the model is tested against observed streambank erosion of a bendway on goodwin creek miss between march 1996 and march 2001 where it accurately predicts the rate of retreat of the outside bank of the bendway the observed change in average channel width within the central section of the bendway is 2 96 m over the simulation period whereas a retreat of 3 18 m 7 4 larger is simulated the observed top bank retreat within the central section of the bendway is 3 54 m over the simulation period whereas a retreat of 3 01 m 15 smaller is simulated doi 10 1061 asce0733 94292008134 7905 ce database subject headings bank erosion limit equilibrium mathematical models sensitivity analysis numerical analysis

channel evolution of the pre channelized danube river in bratislava slovakia 1712 1886 channel adjustments of the danube river near bratislava slovakia are reconstructed from historical river maps for 1712 1886 the period preceding mid course channelization the study reach comprised an anastomosing meandering planform characteristic of the upper area of a large alluvial fan the key mechanisms of channel change were avulsions through channel switching into chute channels meander development through progression and cutoffs and abandonment of secondary channels the gravel bed danube river was characterized by rapid rates of lateral erosion maxima from 7 5 to 37 m a 1 and extensive areas of point bars and gravel bars within three to seven years new bars were stabilized by salici populetum woodlands which subsequently developed into more stable vegetated islands human interventions were relatively common and frequent in the past though increasing fluvial activity during the 18th century was responsible for their limited effectiveness uncontrollable lateral erosion at petr alka village terminated only by a switch in position of the danube river upstream from bratislava 1766 1774 appears to be closely related to increasing ice floods and other high magnitude flood events in the latter half of the 18th century these events were coincident with the peak of the little ice age the effect of floods was probably amplified by human works which resulted in stabilization of secondary channels simplification of the river pattern and concentration and widening of the main channel a further sign of channel readjustment to new conditions was the evolution of new large meanders a tendency for channel switching and production of new anastomosing meandering parallel channels copyright 2002 john wiley sons ltd

large intermediate depth earthquakes and the subduction process this study provides an overview of intermediate depth earthquake phenomena placing emphasis on the larger tectonically significant events and exploring the relation of intermediate depth earthquakes to shallower seismicity especially we examine whether intermediate depth events reflect the state of interplate coupling at subduction zones and whether this activity exhibits temporal changes associated with the occurrence of large underthrusting earthquakes historic record of large intraplate earthquakes m b 7 0 in this century shows that the new hebrides and tonga subduction zones have the largest number of large intraplate events regions associated with bends in the subducted lithosphere also have many large events e g altiplano and new ireland we compiled a catalog of focal mechanisms for events that occurred between 1960 and 1984 with m 6 and depth between 40 and 200 km the final catalog includes 335 events with 47 new focal mechanisms and is probably complete for earthquakes with m b 6 5 for events with m 6 5 nearly 48 of the events had no aftershocks and only 15 of the events had more than five aftershocks within one week of the mainshock events with more than ten aftershocks are located in regions associated with bends in the subducted slab focal mechanism solutions for intermediate depth earthquakes with m 6 8 can be grouped into four categories 1 normal fault events 44 and 2 reverse fault events 33 both with a strike nearly parallel to the trench axis 3 normal or reverse fault events with a strike significantly oblique to the trench axis 10 and 4 tear faulting events 13 the focal mechanisms of type 1 events occur mainly along strongly or moderately coupled subduction zones where a down dip extensional stress prevails in a gently dipping plate in contrast along decoupled subduction zones great normal fault earthquakes occur at shallow depths e g the 1977 sumbawa earthquake in indonesia type 2 events with strike subparallel to the subduction zone and most of them with a near vertical tension axis occur mainly in regions that have partially coupled or uncoupled subduction zones and the observed continuous seismicity is deeper than 300 km the increased dip of the downgoing slab associated with weakly coupled subduction zones and the weight of the slab may be responsible for the near vertical tensional stress at intermediate depth and consequently the change in focal mechanism from type 1 to type 2 events events of type 3 occur where the trench axis bends sharply causing horizontal parallel to the trench strike extensional or compressional intraplate stress type 4 are hinge faulting events for strongly coupled zones we observed temporal changes of intermediate depth earthquake activity associated with the occurrence of a large underthrusting event after the occurrence of a large underthrusting event the stress axis orientation of intermediate depth earthquakes changes from down dip tensional to down dip compressional e g 1960 chile 1974 peru 1982 tonga and 1952 kamchatka earthquakes or the number of large intermediate events decreases for a few years e g 1964 alaska and 1985 valparaiso earthquakes we conclude that even though the stress changes induced by slab pull and slab distortion control the general pattern of intermediate depth seismicity spatial and temporal variations of the intraplate stress associated with interplate coupling are important in controlling the global occurrence of large intermediate depth events

ordovician ocean plate stratigraphy and thrust duplexes of the ballantrae complex sw scotland implications for the pelagic deposition rate and forearc accretion in the closing iapetus ocean abstract the ballantrae complex at bennane lea in sw scotland contains important ocean plate stratigraphy basalt chert mudstone sandstone in an accretionary prism that is associated with a classic ordovician ophiolite we used the ocean plate stratigraphy to sub divide the prism into 11 tectonic units to determine the depositional age of bedded cherts zircons were separated from 9 tuff beds from 6 different units all the tuffs have early to middle ordovician ages even though their present positions are mutually distant these ages are consistent with microfossil records of radiolaria and graptolites the stratigraphic structural relationships demonstrate that the ocean plate stratigraphy has been repeated by bedding parallel thrusts this is typical of a modern accretionary duplex we calculated the sedimentation rate of early to middle ordovician bedded cherts at bennane lea on the basis of u pb zircon ages obtained from several tuff beds the data indicate that the depositional rate 0 6 3 m myr was as slow as that of mesozoic cenozoic equivalents defined by radiolaria the age spectra of detrital zircons from ballantrae sandstones show prominent single peaks at ca 467 and 478 ma and a lack of precambrian zircons integration of our new zircon ages with published isotopic data and palaeo geographic maps indicates that the sandstones were deposited near an intra oceanic arc and far from any continent containing precambrian rocks the pelagic to clastic sediments at bennane lea were deposited in the closing iapetus ocean from ca 477 ma to ca 464 ma when they were accreted with the intra oceanic arc of ballantrae

stability of an upland gravel bed stream swinhope burn northern england some upland gravel bed streams often undergo frequent channel change in response to floods and changes in sediment supply however in others where local conditions permit long term channel planform stability can be observed this paper uses evidence from swinhope burn in upper weardale northern england to demonstrate relative channel stability over a 180 year period channel planform change is identified using seven historical maps and air photographs dating from 1815 to 1991 the 1 4 km study reach has retained a stable meandering pattern over a period of 180 years with a temporary but dramatic change to a straight low sinuosity partly divided channel at some point between 1815 and 1856 identifiable on the 1844 tithe map channel planform stability observed over the historic period is related in part to the low channel gradient upstream of a cross valley moraine situated at the lower end of the study reach this moraine has led to partial closure of the valley system and the development of a small upstream floodplain or sedimentation zone average width of 150 m the resulting low channel gradient 0 012 inhibits coarse bedload transport and encourages overbank sedimentation cohesive banks promote lateral channel stability and the wide floodplain reduces potential coupling between the channel and valley side slope sediment sources the probable cause of the observed channel planform change is the combination of a succession of four major floods in the river wear catchment during the 1820s and episodic inputs of sediment generated by upstream metal mining between 1823 and 1846 large floods in the past 40 years have produced very little evidence of lasting channel change however locally a channel avulsion has been documented following a flood in february 1997 this represents a useful modern analogue for previous mechanisms of channel change

slab pull and the seismotectonics of subducting lithosphere this synthesis links many seismic and tectonic processes at subduction zones including great subduction earthquakes to the sinking of subducted plate earthquake data and tectonic modeling for subduction zones indicate that the slab pull force is much larger than the ridge push force interactions between the forces that drive and resist plate motions cause spatially and temporally localized stresses that lead to characteristic earthquake activity providing details on how subduction occurs compression is localized across a locked interface thrust zone because both the ridge push and the slab pull forces are resisted there the slab pull force increases with increasing plate age thus because the slab pull force tends to bend subducted plate downward and decrease the force acting normal to the interface thrust zone the characteristic maximum earthquake at a given interface thrust zone is inversely related to the age of the subducted plate the 1960 chile earthquake mw 9 5 the largest earthquake to occur in historic times began its rupture at an interface bounding oceanic plate 30 m y old however this rupture initiation was associated with the locally oldest subducting lithosphere weakest coupling the rupture propagated southward along an interface bounding progressively younger oceanic lithosphere terminating near the subducting chile rise prior to a great subduction earthquake the sinking subducted slab will cause increased tension at depths of 50 200 km with greatest tension near the shallow zone resisting plate subduction plate sinking not only leads to compressional stresses at a locked interface thrust zone but may load compressional stresses at plate depths of 260 350 km provided that the shallow sinking occurs faster than the relaxation time of the deeper mantle this explains k mogi s observations of m 7 thrust earthquakes at depths of 260 350 km immediately downdip and within 3 years prior to five great shallow earthquakes of northern japan the slab pull model explains the lower layer of double seismic zones as due to tension from the deeper sinking plate and the upper layer as due to localized in plate compression as plate motion is resisted by the bounding mantle just downdip of the interface thrust zone there occurs an aseismic 20 50 dip increase of subducted plate this slab bend reflects the summed slab pull force of deeper plate and probably is at the crustal basalt to eclogite phase change resistance to subduction provided by a continually developing slab bend may be an important factor in the size of slab pull force delivered to an interface thrust zone

modeling a 200 yr interruption of the holocene sapropel s1 an oceanic general circulation model previously used to simulate the conditions associated with the holocene sapropel s1 is used to simulate the effects of a climate deterioration represented as a cooling event on the sapropelic circulation mode the enhanced cooling 2 3 c induces deep convection in the adriatic and the gulf of lions and intermediate water formation in the aegean where in all cases there had previously been only stagnant unventilated waters the depths of ventilation to 1250 m are in agreement with core data from this period the short decadal timescales involved in modifying the sapropelic circulation suggest that such a climatic deterioration may be associated with the interruption of s1 between 7100 and 6900 14c yr b p which divided the sapropel into two subunits

modeling the evolution of incised streams i model formulation and validation of flow and streambed evolution components a robust computational model for simulating the long term evolution of incised and restored or rehabilitated stream corridors is presented the physically based model simulates the three main processes that shape incised streams hydraulics sediment transport and streambed and bank adjustments a generalized implicit preissmann scheme is used for the spatial and temporal discretization of the flow governing equations to accommodate large time steps and cross sections spaced at irregular intervals the solution method introduces several enhancements that increase its robustness specifically to simulate flashy flows transport of cohesive or cohesionless graded bed material is based on a total load concept and suspended and bed load transport modes are accounted for through nonequilibrium effects the model simulates channel width adjustment by hydraulic erosion and gravitational mass failure of heterogeneous bank material the present paper focuses mainly on the treatment of streamflow hydraulics and evolution of graded streambeds and reports simulations of published experiments on degrading and aggrading channels with graded bed material description and validation of the model s stream bank erosion component and the application of the model to incised stream systems are presented elsewhere

the mechanism of great banda sea earthquake of 1 february 1938 applying the method of preliminary determination of focal mechanism to a historical event abstract a moment tensor solution is derived for the great 1938 banda sea earthquake one of the largest events for which no definitive focal geometry has been published we apply the method of preliminary determination of focal mechanism which consists of inverting for a moment tensor using exclusively the spectral amplitudes of mantle rayleigh and love waves while discarding the phase information which can be affected by uncertainties in relative timing between historical records from a dataset of 17 records at seven stations we obtain a robust solution featuring a very large moment of 8 37 10 28 dyn cm the centroid depth being constrained around 60 km by minimizing the rms residual of the inversion the method involves an inherent two fold 180 indeterminacy on the orientations of strike and slip which is lifted by the examination of the polarization of long period body waves read individually on original records resulting in a mostly thrust faulting mechanism strike 276 dip 63 slip 70 this approach coupled with more traditional relocation efforts allows a rare glimpse of this exceptional event confirmed here to rank among the 10 largest moments ever published within the extremely complex regional plate tectonics pattern the 1938 event took place in a region of sparse seismicity and away from the presumed locations of block boundaries the deeper than normal focus of the event agrees well with the generally minor level of reported damage and with the generation of a relatively benign tsunami available modern focal mechanisms in its vicinity are too few and too scattered to allow any meaningful comparison but the 1938 event shares its compressional axis with that of the smaller and deeper 1963 shock to the southwest which probably expresses coherence in the regional contortion of the subducting australian plate lithosphere

form and growth of bars in a wandering gravel bed river the changing form of developing alluvial river bars has rarely been studied in the field especially in the context of the fixed compound mainly alternate gravel bars that are the major morphological feature of the wandering style century scale patterns of three dimensional growth and development and the consequent scaling relations of such bars are examined along the gravel bed reach of lower fraser river british columbia canada a retrospective view based on maps and aerial photographs obtained through the twentieth century shows that individual bars have a life history of about 100 years except in certain protected positions a newly formed gravel bar quickly assumes its ultimate thickness and relatively quickly approaches its equilibrium length growth continues mainly by lateral accretion of unit bars consistent with the lateral style of instability of the river bar growth is therefore allometric mature bars approach equilibrium dimensions and volume that scale with the overall size of the channel accordingly the bars conform with several published criteria for the ultimate dimensions of alternate barforms sand bars observed farther downstream have notably different morphology fraser river presents a typical wandering channel planform exhibiting elements of both meandered and low order braided channels hydraulic criteria to which the fraser bars conform illustrate why this planform develops and persists the modest rate of bed material transfer along the channel typical of the wandering type determines a century length time scale for bar development this time scale is consistent with estimates that have been made for change of the macroform elements that determine the overall geometry of alluvial channels copyright 2009 john wiley sons ltd

modeling high sinuosity meanders in a small flume meandering channels with exposed point bars and sinuosities near 2 0 can spontaneously develop in a mix of diatomaceous earth and kaolinite clay the experimental streams that were studied were as small as 4 cm wide they showed many of the characteristics found in large meandering streams such as migration of channels formation of point bars clay plugs chutes and bar scrolls most of the meander series began as a first sharp bend that induced subsequent bends down stream sediment transport specifically bed load together with the slope of the floodplain were the dominant influences if not the cause of the channel instabilities that led to channel migration and bend formation bank cohesion allowed migrating channels to assume sinuous shapes and to maintain fairly uniform widths the experiments were conducted in a small flume and used simple equipment the use of light fine grained materials in flume experiments may prove to be valuable in learning more about the conditions of soil slope and flow which produce various meandering planforms

measuring streambank erosion due to ground water seepage correlation to bank pore water pressure precipitation and stream stage limited information exists on one of the mechanisms governing sediment input to streams streambank erosion by ground water seepage the objective of this research was to demonstrate the importance of streambank composition and stratigraphy in controlling seepage flow and to quantify correlation of seepage flow erosion with precipitation stream stage and soil pore water pressure the streambank site was located in northern mississippi in the goodwin creek watershed soil samples from layers on the streambank face suggested less than an order of magnitude difference in vertical hydraulic conductivity ks with depth but differences between lateral ks of a concretion layer and the vertical ks of the underlying layers contributed to the propensity for lateral flow goodwin creek seeps were not similar to other seeps reported in the literature in that eroded sediment originated from layers underneath the primary seepage layer subsurface flow and sediment load quantified using 50 cm wide collection pans were dependent on the type of seep intermittent low flow lf seeps flow rates typically less than 0 05 l min 1 persistent high flow hf seeps average flow rate of 0 39 l min 1 and buried seeps which eroded unconsolidated bank material from previous bank failures the timing of lf seeps correlated to river stage and precipitation the hf seeps at goodwin creek began after rainfall events resulted in the adjacent streambank reaching near saturation i e soil pore water pressures greater than 5 kpa seep discharge from hf seeps reached a maximum of 1 0 l min 1 and sediment concentrations commonly approached 100 g l 1 buried seeps were intermittent but exhibited the most significant erosion rates 738 g min 1 and sediment concentrations 989 g l 1 in cases where perched water table conditions exist and persistent hf seeps occur seepage erosion and bank collapse of streambank sediment may be significant copyright 2007 john wiley sons ltd

coccolithophore assemblages during the holocene climatic optimum in the ne mediterranean aegean and northern levantine seas greece paleoceanographic and paleoclimatic implications recent paleoceanographic findings suggest that during the holocene ne mediterranean climate was less stable than previously thought several recently generated aegean paleoceanographic records of sapropel s1 suggest that during the holocene short term potentially global cooling episodes reflecting the n atlantic climatic fluctuations and possibly related to solar variability are superimposed on the underlying regional subtropical tropical control on the hydrography and ecosystems detailed quantitative analyses of coccolithophores have been performed on the deep sea deposits of the ne mediterranean sea four gravity core records from north aegean sea sl 152 se aegean ns 14 ns 18 and south cretan continental margin northern levantine sea hcmr 2 22 respectively with a focus on the regional expression of sapropel s1 deposition in all sites higher values of florisphaera profunda helicosphaera carteri braarudosphaera bigelowii and the increase of stratification s index within sapropel intervals can be interpreted as the result of elevated marine production in the deep photic zone and enhanced inflow of fresh water input during the s1 period the stratification s index is significantly higher in the north aegean in respect to se aegean and the south cretan margin scm reflecting increased coccolithophore productivity at the lower photic zone being associated with a remarkably stratified water column the concomitant increased presence of b bigelowii indicates the prominent riverine input in the north aegean basins and possible influx of black sea waters after 9 0 ka bp consequently the increased stratification of the water column is linked to the significant freshening of the north aegean surface waters particularly during the early stages of the holocene climatic optimum s1a depositional interval a series of cooling events detected towards the end of sapropelic conditions 7 2 ka bp mostly in the north aegean site may be linked to outbursts of cold northerly air masses and relevant pulses in the deep intermediate water ventilation that caused the enhancement of surface marine productivity and the temporary cessation of s1 at 8 0 ka bp in contrast in the se aegean and the northern levantine sea the water column remains still warm and stratified influenced by moderate fresh water input for at least 1 more ky

seepage erosion in layered stream bank material current stream restoration practices often require anthropogenic manipulation of natural field soils to reconstruct stream banks in the absence of stabilizing vegetation for this study researchers conducted laboratory experiments on reconstructed non vegetated stream banks with layered soils experiencing seepage the objective of the study was to determine the effect of seepage pore water pressure and bank geometry on erosion and bank stability of layered streambanks the experimental design consisted of an intermediate size soil lysimeter packed with a sandy clay loam top soil and an underlying fine sand layer at three bank slopes 90 45 and 26 shallow groundwater flow and seepage resulted in bank failure of geometrically stable banks pop out failures liquid deformation and piping were all observed failure mechanisms in the underlying sand material dependent on the bank angle groundwater seepage processes created small scale failures of the underlying sand leading to larger scale failures of the overlying sandy clay loam the underlying sand layer eroded according to the initial bank angle and change in overburden loading the overlying loam layer failed along linear failure planes the gradually sloped bank i e 26 slope failed faster hypothesized to be due to less confining pressure and greater vertical seepage forces researchers analyzed the laboratory experiments using the bank stability and toe erosion model version 4 1 the model calculated an accurate shear surface angle similar to the failure angle observed in the lysimeter tests the model predicted failure only for the undercut 90 bank slope and indicated stable conditions for the other geometries steeper initial bank slopes and undercut banks decreased the bank factor of safety the observed failure mechanisms and measured saturation data indicated an interaction between overburden pressure seepage forces and bank slope on bank stability future bank stability modeling would benefit by incorporating lateral seepage erosion and soil liquefaction prediction calculations copyright 2009 john wiley sons ltd

a simplified 2d model for meander migration with physically based bank evolution abstract the rate of migration calculated by numerical models of river meandering is commonly based on a method that relates the rate of migration to near bank excess velocity multiplied by a dimensionless coefficient notwithstanding its simplicity since the early 1980s this method has provided important insight into the long term evolution of meander planforms through theoretical exercises its use in practice has not been as successful because the complexity of the physical processes responsible for bank retreat the heterogeneity in floodplain soils and the presence of vegetation make the calibration of the dimensionless coefficient rather challenging this paper presents a new approach that calculates rates of meander migration using physically based streambank erosion formulations the university of illinois rvr meander model which simulates meandering river flow and bed morphodynamics is integrated with algorithms for streambank erosion of the us department of agriculture channel evolution computer model concepts the performance of the proposed approach is compared to that of the more simple classic method through the application to several test cases for idealized and natural planform geometry the advantages and limitations of the approach are discussed focusing on simulated planform pattern the impact of soil spatial heterogeneity the relative importance of the different processes controlling bank erosion hydraulic erosion cantilever and planar failure the requirements for obtaining stable migration patterns centerline filtering and interpolation of bank physical properties and the capability of predicting the planform evolution of natural rivers over engineering time scales i e 50 to 100 years the applications show that the improved physically based method of bank retreat is required to capture the complex long term migration patterns of natural channels which cannot be merely predicted from hydrodynamics only

slab decoupling in the tonga arc the june 22 1977 earthquake the june 22 1977 earthquake in the southern tonga arc is a large normal faulting event with downdip rupture propagation on a steeply dipping fault plane we use a standard least squares inversion of p and sh waves for the source time function to determine a source consisting of two subevents located at depths of 40 55 and 105 125 km and a total time duration of 50 s the ratios of the spectral amplitudes of the radial modes 0s0 1s0 and 2s0 independently require a centroid depth of at least 100 km at their lower frequencies the body wave analysis suggests a moment of 1 04 1028 and the 0s0 spectral amplitude suggests a value of 1 8 2 0 1028 dyn cm the emerging picture is that of a complete rupture of the sinking lithospheric slab starting from 40 km depth and propagating down to 125 km this indicates that the decoupling of the overriding lithosphere from the slab in this area of the tonga arc takes place by gravitational pull

the source rupture process of the great banda sea earthquake of november 4 1963 abstract the banda sea earthquake of november 4 1963 is one of the largest m w 8 3 intraplate events it involved oblique thrusting at an intermediate depth within the subducted lithosphere near the abrupt bend in the southeastern banda arc 6 86 s 129 58 e to better understand the tectonic significance of this earthquake the detailed source process of the banda sea event was determined by body wave analysis the rupture history was established by deconvolving source time functions from long period p wave seismograms using both individual station and multi station time domain deconvolution methods the seismic moment release occurred within the first 50 s of rupture initiating at a depth near 120 km and expanding laterally and downdip over a vertical extent of about 50 km slip and moment release were concentrated in one main region near the hypocenter at depths between 110 and 130 km the along strike rupture length was only about 100 km so it is difficult to resolve any horizontal directivity the compressional stress orientation inferred from the focal mechanism parallels the strike of the slab and reflects the importance of contortion of the lithosphere in this region the banda sea event may be part of a major detachment at the leading edge of the subducted australian continental shelf

historical analysis indicates seepage control on initiation of meandering in analytical and numerical models of river meandering initiation of meandering typically occurs uniformly along the streamwise coordinate in the channel based on a historical analysis of the nierskanaal here we show how and under which circumstances meandering has initiated in isolated sections of a channel the nierskanaal was constructed by the end of the 18th century as a straight channel between the river niers and the river meuse the purpose of this measure was to reduce flood risk in the downstream reaches of the river niers the banks on the dutch part of the channel were left unprotected and developed into a morphodynamically active channel featuring a meandering planform and valley incision the planform development and incision process is analysed using topographic maps and airborne lidar data meandering initiated in three sections of the channel where the channel sinuosity developed asynchronously sedimentary successions in the study area show layers of iron oxide indicating groundwater seepage from aeolian river dunes and river deposits located nearby only at the spots where meandering has initiated iron oxide is found close to the surface level this provides a clue that seepage triggered bank erosion by increasing moisture content of the banks the isolated meandering sections expanded in the longitudinal direction valley incision has developed in the first decades after the construction of the channel and diminished after a gravel layer was reached gravel was deposited in the downstream half of the channel bed acting as an armouring layer the spatial variation in meandering behaviour as observed in the nierskanaal justifies efforts to implement the influence of floodplain heterogeneity and the effect of seepage on bank erosion in meander models

chute cutoff as a morphological response to stream reconstruction the possible role of backwater stream restoration efforts often aim at creating new unconstrained meandering channels without weirs and bank revetments in reconstructed streams the initial morphological response of the new streams is often rapid until a dynamic equilibrium is reached here we report on a chute cutoff that occurred within 3 months after realization of a stream restoration project caused by a plug bar that formed in response to a backwater effect the temporal evolution of the morphology of both the new and the old channels was monitored over a period of nearly 8 months including precutoff conditions the observations can be separated into three stages stage 1 is the initial period leading to cutoff vulnerability stage 2 is the actual cutoff and stage 3 is the morphological adjustment in response to the cutoff in stage 1 a plug bar was deposited in one of the channel bends hydrodynamic model results show the location of the plug bar coincides with a region where bed shear stress decreased in downstream direction due to backwater longitudinal channel bed profiles show that the channel slope decreased soon after channel reconstruction hence sediment from upstream was available to form the plug bar after the plug bar was deposited an embayment formed in the floodplain at a location where the former channel was located stage 2 the former channel was filled with sediment prior to channel construction it is likely that the sediment at this location was less consolidated and therefore prone to erosion the chute channel continued to incise and widen into the floodplain and after 6 months acted as the main channel conveying the discharge during the majority of time stage 3 the cutoff channel gradually continued to fill with sediment from the moment the plug bar formed until the chute channel incised into the floodplain sedimentary successions of the deposited material show upward fining which is in agreement with observations of chute cutoffs in rivers although the artificial setting limits the degree in which the observed processes can be projected on natural rivers the observations prompt to investigate the role of backwater effects in natural chute cutoff initiation

seismic moment release during slab rupture beneath the banda sea summary the highest intermediate depth moment release rates in indonesia occur in the slab beneath the largely submerged segment of the banda arc in the banda sea to the east of roma termed the damar zone the most active western part of this zone is characterized by downdip extension with moment release rates 10 18 nm yr 1 per 50 km strike length implying the slab is stretching at 10 14 s 1 consistent with near complete slab decoupling across the 100 200 km depth range differential vertical stretching along the length of the damar zone is consistent with a slab rupture front at 100 200 km depth beneath roma propagating eastwards at 100 km myr 1 complexities in the slab deformation field are revealed by a narrow zone of anomalous in plane p axis trends beneath damar where subhorizontal constriction suggests extreme stress concentrations 100 km ahead of the slab rupture front such stress concentrations may explain the anomalously deep ocean gateways in this region in which case ongoing slab rupture may have played a key role in modulating the indonesian throughflow in the banda sea over the last few million years

cenozoic evolution of the savu basin indonesia forearc basin response to arc continent collision abstract a seismo stratigraphic analysis of the savu basin relates the evolution of a complexly evolved forearc basin to the late miocene recent collision with australia initial early miocene subsidence of the outer forearc basin and the subsequent development of a middle late miocene volcanic proto arc located in the south of the basin both resulted from the late oligocene early miocene eastward propagation of the java timor trench block faulting of the relatively thick continental forearc basement probably determined the rather irregular and scattered pattern of middle late miocene volcanic centres just north of the accretionary prism the forearc basement is flexed down and reshaped into a trenchward dipping backstop that facilitates backthrusting of the accretionary prism the southern forearc basement probably acted as a barrier against compression the thickness of this continental basement is suggested to be a critical factor in the response of the forearc to continent collision owing to its strength the savu basin did not react to collision by the development of northward verging inter arc thrusts in contrast it responded to the underthrusting of continental crust by reactivation of the basement ridges this resulted in the differentiation of the forearc basin into a presently extinct and uplifted miocene south savu basin and a pliocene recent active north savu basin the simultaneous late miocene recent uplift of large segments of the outer forearc and subsidence of the north savu basin is interpreted to result from tectonic underplating of continental material and uplift caused by the buoyancy of the subducted continental crust the relatively recent decoupling of this crust from the oceanic slab and the subsequent isostatic rebound may superimpose the initial effects of post collision extension on arc continent collision

role of shallow phase changes in the subduction of oceanic crust detailed studies of the seismicity of several subduction zones demonstrate that shallow dipping thrust zones turn to steeper angles at depths of about 40 kilometers an increased downward body force resulting from shallow phase changes in subducted oceanic crust may be the cause of this increased dip angle in addition the volume reduction associated with phase changes may produce sufficiently large stresses in neighboring rocks to cause the seismicity of the upper benioff zone

late quaternary nannofossil indicators of climate change in two deep sea cores associated with the leeuwin current off western australia the stratigraphic variations in nannoflora observed in the two deep sea cores recovered from the offshore western australia revealed a sequence of paleoceanographic changes for the last 250 kyr the dominance of small placolith taxa in the upper photic flora indicates continuous mild upwelling for the isotope stages 7 5 in this region the most important controlling factor for the abundance variation of florisphaera profunda in this region is considered to be the lower photic temperature rather than the stability of water column or the water turbidity the significant reduction in the abundance of f profunda combined with the stable in the northern core rs96gc21 and reduced in the southern core rs9 150 abundance of the small taxa suggest an intensified upwelling for the penultimate glaciation the sharp increase in f profunda abundance indicates a weakening of upwelling at the last interglacial climax lic offshore western australia after isotope stage 5 the existence of upwelling is not clear except in stage 2 when it was not strong enough to produce blooms of emiliania huxleyi among the subordinate taxa calcidiscus leptoporus calciosolenia murrayi neosphaera coccolithomorpha and oolithotus fragilis provide meaningful paleoceanographic signals supporting the conclusions of previous studies a weakening or cessation of leeuwin current for the glacial periods the shift of dominance from small gephyrocapsa mostly g ericsonii to small reticulofenestra mostly r parvula can be an useful datum event offshore western australia the reduced diversity of nannoflora during the interglacial periods can be explained by a lessened competition within nannoplankton community caused by particularly favorable conditions for the opportunists such as e huxleyi f profunda and small placoliths the variations in nannofossil abundance suggests an increased aeolian flux at the stages 6 and 2 offshore north west cape as well as at stage 6 offshore southwestern australia

organic geochemical evidence of late glacial holocene climate instability in the north aegean sea sedimentary molecular biomarker compositions organic carbon and caco3 concentrations and bulk organic 13c and total 15n values document a series of paleoclimatic changes that have affected organic matter production and sedimentation in the north aegean sea from the termination of the latest glacial maximum through the middle holocene continental environmental conditions have been inferred from land plant biomarkers paleoproductivity patterns of diatoms prymnesiophytes dinoflagellates and nannoplankton were discerned from marine derived biomarkers although organic matter is predominantly marine variations in the proportion of marine and land contributions and in its general preservation are evident rapid changes in the eastern mediterranean thermohaline circulation evidently occurred in parallel to sea surface temperature oscillations enhanced deep water ventilation accompanied cold intervals in the late last glacial the younger dryas and during an interruption of deposition of the s1 sapropel probably in response to strengthening of north winds over the region in contrast decreased thermohaline circulation occurred during the warm interval associated with the s1 sapropel during this period increased freshwater inputs diminished ventilation of deep water masses and enhanced organic matter production and preservation intriguing fluctuations in sea surface temperatures and the concentrations of marine and terrestrial biomarkers within the sapropelic layer most prominently in the interruption from 8 2 to 7 8 calibrated radiocarbon conventional kyr bp support the hypothesis that several distinct events of deep water reoxygenation occurred in the north aegean sea during deposition of the s1 sapropel these events reflect centennial excursions to the more common low productivity and well ventilated conditions of the mediterranean that may possibly be related to north atlantic oscillation cycles

late glacial fluvial response of the niers rhine western germany to climate and vegetation change the niers valley was part of the rhine system that came into existence during the maximum saalian glaciation and was abandoned at the end of the weichselian the aim of the study was to explain the late pleniglacial and late glacial fluvial dynamics and to explore the external forcing factors climate change tectonics and sea level the sedimentary units have been investigated by large scale coring transects and detailed cross sections over abandoned channels the temporal fluvial development has been reconstructed by means of geomorphological relationships pollen analysis and 14c dating the niers rhine experienced a channel pattern change from braided via a transformational phase to meandering in the early late glacial this change in fluvial style is explained by climate amelioration at the late pleniglacial to late glacial transition at ca 12 5 k 14c yr bp and climate related hydrological lithological and vegetation changes a delayed fluvial response of ca 400 14c yr transitional phase was established the channel transformations are not related to tectonic effects and sea level changes successive river systems have similar gradients of ca 35 40 cm km 1 a meandering river system dominated the allerod and younger dryas periods the threshold towards braiding was not crossed during the younger dryas but increased aeolian activity has been observed on the younger dryas point bars the final abandonment of the niers rhine was dated shortly after the younger dryas to holocene transition traces of laacher see pumice have been found in the niers valley indicating that the niers rhine was still in use during the younger dryas copyright 2005 john wiley sons ltd

re evaluation of the large deep earthquake of january 21 1906 abstract the large deep earthquake of january 21 1906 is re evaluated using old seismogram data and updated analysis techniques from the p and pp p time data the hypocentre parameters are determined as follows origin time 13h 49min 35s latitude 33 8 n longitude 137 5 e depth 340 km the body wave magnitude m b is re evaluated from the amplitude and periods of p pp and s waves the average value of 7 4 is obtained this value is the smallest among any values assigned previously to this shock and it is denied that the earthquake is the world s largest deep shock in this century the focal mechanism is estimated from the p wave first motions and amplitude distribution of p and s waves synthetic body waves are used to constrain the mechanism and to determine the seismic moment the mechanism solution suggests the down dip compression typical of this region a seismic moment of 1 5 10 27 dyn cm is obtained this value and the re evaluated value of m b are consistent with the moment b relation obtained for other deep earthquakes

alluvial and colluvial sediment storage in the geul river catchment the netherlands combining field and modelling data to construct a late holocene sediment budget abstract we used a combined approach of a two dimensional erosion and hillslope sediment delivery model watem sedem and detailed geomorphological reconstructions to quantify the different components in a sediment budget for the geul river catchment southern netherlands since the high middle ages hillslope erosion and colluvium deposition were calculated using the model while floodplain storage was estimated using field data our results show that more than 80 of the total sediment production in the catchment has been stored as colluvium mostly generated by hillslope erosion while almost 13 is stored in the floodplain since the high middle ages this situation resembles a capacity limited system model results for the period prior to the high middle ages with a nearly completely forested catchment show that far less sediment was generated and that most of the sediments were directly transported to the main river valleys or out of the catchment a supply limited system geomorphological analysis of a large alluvial fan shows the sensitivity of the study area to changes in the percentage of arable land our combined field data modeling study presents an elegant method to calculate a catchment sediment budget for a longer period and is able to identify and quantify the most important sediment storage elements furthermore it provides a valuable tool to calculate a sediment budget while only limited dated fluvial sediment sequences are available

buoyancy driven rapid exhumation of ultrahigh pressure metamorphosed continental crust abstract preservation of ultrahigh pressure uhp minerals formed at depths of 90 125 km require unusual conditions our subduction model involves underflow of a salient 250 150 km wide 90 125 km long of continental crust embedded in cold largely oceanic crust capped lithosphere loss of leading portions of the high density oceanic lithosphere by slab break off as increasing volumes of microcontinental material enter the subduction zone buoyancy driven return toward midcrustal levels of a thin 2 15 km thick low density slice finally uplift backfolding normal faulting and exposure of the uhp terrane sustained over 20 million years rapid 5 mm year exhumation of the thin aspect ratio uhp sialic sheet caught between cooler hanging wall plate and refrigerating downgoing lithosphere allows withdrawal of heat along both its upper and lower surfaces the intracratonal position of most uhp complexes reflects consumption of an intervening ocean basin and introduction of a sialic promontory into the subduction zone uhp metamorphic terranes consist chiefly of transformed yet relatively low density continental crust compared with displaced mantle material otherwise such complexes could not return to shallow depths relatively rare metabasaltic metagabbroic and metacherty lithologies retain traces of phases characteristic of uhp conditions because they are massive virtually impervious to fluids and nearly anhydrous in contrast h2o rich quartzofeldspathic gneissose schistose more permeable metasedimentary and metagranitic units have backreacted thoroughly so coesite and other uhp silicates are exceedingly rare because of the initial presence of biogenic carbon and its especially sluggish transformation rate uhp paragneisses contain the most abundantly preserved crustal diamonds

channel changes in the jarama and tagus rivers central spain over the past 500 years abstract long term channel changes of the tagus and the jarama rivers in central spain were studied in relation to variations in hydroclimatic factors such as rainfall and flooding and also with respect to human activities undertaken in their valleys data were taken from historical 1580 1823 and topographical 1877 1988 maps as well as aerial photographs 1945 1999 the available hydroclimatic data consists of a series of monthly rainfall totals 1859 1994 and mean river flow values recorded at gauging stations 1911 1985 in addition a historical flood record 1550 1947 was produced from documentary sources some of the data was incorporated into a geographical information system gis to quantify the changes in the course of the rivers the results show there have been two distinct periods before and after human intervention in the river system which took place around 1950 during the earlier period 1550 1950 a correlation exists between climate frequency and magnitude of flooding and changes in fluvial geomorphology between 1860 and 1892 an increase in flood frequency and magnitude occurred which produced half of the cut offs recorded in the study area between 1823 and 1877 the meanders length l width w and radius of curvature rc of the tagus river have decreased since 1750 however those of the jarama reached their maximum values during flood periods both rivers have different geomorphological responses during flood events which can explain these different trends floods in the jarama not only led to the cut offs but also enlarged the channel size l w and rc in the second period 1956 present flow regulation via dams and gravel mining modified the system completely and impeded the natural development of these rivers

source retrieval for mantle earthquakes by iterative deconvolution of long period p waves abstract long period p waves of eighteen deep and intermediate depth earthquakes in a moment range 1 10 26 3 10 28 dyn cm are analysed by the method of kikuchi and fukao this issue to iteratively derive point dislocations on a plane the fault plane is defined as the plane of point dislocations that gives the best fit between the synthetic and observed waveforms for dip slip type earthquakes the fault plane is found to dip more steeply than the auxiliary plane in general point dislocations tend to cluster into one or a few subevents we characterize the largest subevent by its maximum moment rate m 0 m and its half duration from which the associated stress drop can be roughly estimated for earthquakes shallower than 400 km half duration is approximately constant 5 s so that stress drop increases from 1000 bar as m 0 m increases the value of for the great banda sea earthquake of 1963 h 100 km is exceptionally large 10 s for which 700 bar for earthquakes deeper than 400 km increases from 3 s to 9 s as m 0 m increases so that is approximately constant 700 bar stress drop so obtained approximates to an overall stress drop with a possible exception of the several largest earthquakes the distribution of point dislocations and the moment rate function indicate that rupture most often expands in a fan shaped fault area and that a large part of the rupture front ceases propagation in a coherent manner a sharp contrast in stress drop behavior across a depth of 400 km may be related to the olivine spinel transition within the downgoing slab of lithosphere

the 1977 sumba earthquake series evidence for slab pull force acting at a subduction zone the great 1977 sumba earthquake occurred at the eastern sunda trench just west of the collision of australian continental lithosphere with the island arc the length of the aftershock zone of this normal faulting earthquake is about 200 km aftershocks are concentrated 65 115 km east of the main shock epicenter with very few aftershocks in a 50 km long segment that spans the main shock epicenter relocated hypocenters and focal mechanism data are consistent with normal faulting throughout the upper 28 km of the oceanic lithosphere there is no evidence for thrust faulting of the deeper aftershocks these data imply that the neutral bending surface must be at least 35 40 km deep a second aftershock zone about 180 km northwest of the main shock became active immediately following the main shock but events were concentrated during days 50 52 this zone is a 70 km long lineation that trends toward the main shock epicenter and reflects right lateral strike slip faulting within the subducted oceanic plate seismicity exists to a depth of about 650 km in the very old plate beneath the sunda banda arc and that plate s negative buoyancy causes very large slab pull forces great interface thrust earthquakes are absent at the sumba region and slab pull forces are inferred to have partially decoupled the subducted plate from the overriding plate this decoupling permits slab pull stresses to be guided updip to the region of the sumba main shock such shallow acting slab pull provides a bending moment at the trench and explains the deformation and timing observed for the entire sumba earthquake series in this model slab pull forces stretch the subducted plate until the increasing stresses at the shallow subduction zone lead to a subduction zone earthquake postseismically the released oceanic plate undergoes a pulse of downdip strain returning the plate to a less extended state the moment of this downdip plate motion could exceed the seismic moment of the main shock

oblique aggradation a novel explanation for sinuosity of low energy streams in peat filled valley systems low energy streams in peatlands often have a high sinuosity however it is unknown how this sinuous planform formed since lateral migration of the channel is hindered by relatively erosion resistant banks we present a conceptual model of holocene morphodynamic evolution of a stream in a peat filled valley based on a palaeohydrological reconstruction coring ground penetrating radar gpr data and 14c and osl dating were used for the reconstruction we found that the stream planform is partly inherited from the late glacial topography reflecting stream morphology prior to peat growth in the valley most importantly we show that aggrading streams in a peat filled valley combine vertical aggradation with lateral displacement caused by attraction to the sandy valley sides which are more erodible than the co evally aggrading valley fill due to this oblique aggradation in combination with floodplain widening the stream becomes stretched out as channel reaches may alternately aggrade along opposed valley sides resulting in increased sinuosity over time hence highly sinuous planforms can form in peat filled valleys without the traditional morphodynamics of alluvial bed lateral migration improved understanding of the evolution of streams provides inspiration for stream restoration this article is protected by copyright all rights reserved

soil properties controlling seepage erosion contributions to streambank failure the majority of sediment leaving catchments may be from streambank failure seepage erosion of unconsolidated sand above a restrictive layer is an important erosion process in incised streams that leads to streambank failure by undercutting banks the objective of this study was to determine the impact of soil properties on seepage erosion and the resulting streambank failure seepage flow and sediment concentrations were measured in situ at eight locations along the banks of a deeply incised stream in northern mississippi using field observations as a guide the soil profile conditions of a shallow 45 cm streambank consisting of 30 cm of topsoil a 10 cm conductive layer and a 5 cm restrictive layer were mimicked in laboratory lysimeter experiments to quantify the hydrologic properties controlling seepage erosion and bank failure under a 40 cm head the time to flow initiation and the flow rate were linearly related to the slope of the restrictive layer seepage erosion began within minutes of flow initiation and resulted in substantial 3 to 34 cm undercutting of the bank sediment concentrations of seeps were as high as 660 g l 1in situ and 4500 g l 1 in the lysimeters sediment concentrations were related to the layer slope thereby indicating the importance of detailed site characterization the usda ars streambank stability model demonstrated the increase in instability of banks due to undercutting by seepage erosion but failed to account for the sediment loss due to sapping for stable banks and overestimated the sediment loads for failed banks published in 2006 by john wiley sons ltd

active tectonics of the eastern sunda and banda arcs the tectonics of the eastern sunda and banda arcs of eastern indonesia are inferred from the centroid depths seismic moments and fault plane solutions of 63 large earthquakes that occurred between 1962 and 1984 source parameters are estimated by inverting long period teleseismic p and sh waves earthquakes show that the collision of the australian continent with the banda arc shortens the upper plate beneath the forearc and back arc basin over the broad area between the timor and seram troughs along the eastern end of the sunda arc and along the southern banda arc earthquakes reveal that the arc and forearc respond to collision by shortening in the direction of convergence by elongating in the direction perpendicular to convergence and by thrusting over the back arc basin shallow thrust and strike slip earthquakes beneath the banda basin the back arc basin demonstrate that deformation within the back arc accommodates some of the northward motion of the australian continent the rate of north south shortening of the entire upper plate at the longitude of timor calculated from the seismic moments of the earthquakes over the 22 year period is roughly 20 of the predicted convergence rate between australia and southeast asia strike slip faulting within the banda basin results also in eastward motion of the banda arc with respect to western indonesia and australia eastward extrusion of the banda arc results in thrusting at the aru trough earthquakes due to thrusting of the back arc basin beneath the volcanic arc are too shallow to corroborate that the arc s polarity has reversed although the wetar back arc thrust zone at present has a high seismic slip rate earthquakes and their mechanisms provide evidence that the lithosphere of the weber basin a 7500 m deep forearc basin rests on the subducting lithosphere without intervening asthenosphere so that the weber basin subsides in response to sinking of the subducting lithosphere closure of the banda basin is geometrically incompatible with the australian plate subducting simultaneously beneath both the timor and seram troughs instead the bird s head which subducts beneath seram is decoupled from the australian plate in western new guinea and probably moves west or southwest with respect to australia in the eastern indonesian example strike slip faulting plays a major role in the evolution of the collision zone and clearly demonstrates the complexity in three dimensions of continental accretion and mountain building by arc continent collision

microearthquake seismicity and fault plane solutions related to arc continent collision in the eastern sunda arc indonesia the collision of australia with the eastern sunda and banda arcs of indonesia represents a modern example of the early stages of arc continent collision in order to obtain a more detailed view of the tectonics of the collision zone a microearthquake survey was conducted around the savu sea the region that encompasses the transition from subduction of indian ocean lithosphere on the west to collision or subduction of australian continental litho sphere on the east intermediate depth earth quakes were concentrated near pantar island the easternmost active volcano of the sunda arc and outline a northwest dipping zone that strikes n65oe from 70 to 150 km depth the seismic zone probably marks the western edge of the collision zone and its more northerly strike and the orientations of nodal planes from fault plane solutions indicate a 25 o bend in the subducted slab to a depth of at least 150 km because the convergence rate and the timing of collision from geologic observations on timor suggest that the oart of the slab now at 150 km depth was at the trench when australia first collided with timor we infer that continental crust or at least rifted continental margin crust caused the bend in the convergent margin and has been subducted to 150 km depth fault plane solutions of several events show nearly vertical nodal planes that trend parallel to the strike of the seismic zone along which a northwest side down sense of dis placement is indicated these events are concentrated at the southern top side of the seismic zone and suggest that the subducted lithosphere is presently detaching in the 50 100 km depth range beneath the eastern savu sea fault plane solutions for earthquakes within the upper part of the detaching slab 70 100 km depth have p and t axes whose trends lie parallel to the strike of the seismic zone and horizontal southeast trending b axes these earthquakes are interpreted as due to stresses caused by the bend in the subducting plate

use of the mantle magnitude m m for the reassessment of the moment of historical earthquakes the mantle magnitudemm is used on a dataset of more than 180 wavetrains from 44 large shallow historical earthquakes to reassess their moments which in many cases had been previously estimated only on the basis of the earthquake s rupture area we provide 27 new or revised values ofmo based on the spectral amplitudes of surface waves recorded at a number of stations principally uppsala and pasadena among them and most significantly we document a large low frequency component to the source of the 1923 kanto earthquake the low frequency seismic moment is 2 9 1028 dyn cm in accord with geodetic observations on the other hand we revise downwards the seismic moment of the 1906 ecuador event which did not exceed 6 1028 dyn cm

holocene millennial scale productivity variations in the sicily channel mediterranean sea 1 the calcareous nannofossil assemblages of ocean drilling program hole 963d from the central mediterranean sea have been investigated to document oceanographic changes in surface waters the studied site is located in an area sensitive to large scale atmospheric and climatic systems and to high and low latitude climate connection it is characterized by a high sedimentation rate the achieved mean sampling resolution is 70 years that allowed the sicily channel environmental changes to be examined in great detail over the last 12 ka bp we focused on the species florisphaera profunda that lives in the lower photic zone its distribution pattern shows repeated abundance fluctuations of about 10 15 such variations could be related to different primary production levels given that the study of the distribution of this species on the sicily channel seafloor demonstrates the significant correlation to productivity changes as provided by satellite imagery productivity variations were quantitatively estimated and were interpreted on the basis of the relocation of the nutricline within the photic zone led by the dynamics of the summer thermocline productivity changes were compared with oceanographic atmospheric and cosmogenic nuclide proxies the good match with holocene master records as with ice rafted detritus in the subpolar north atlantic and the near 1500 year periodicity suggest that the sicily channel environment responded to worldwide climate anomalies enhanced northern hemisphere atmospheric circulation which has been reported as one of the most important forcing mechanisms for holocene coolings in previous mediterranean studies had a remarkable impact on the water column dynamics of the sicily channel

qualitative and quantitative applications of lidar imagery in fluvial geomorphology the potential for geomorphological mapping and quantitative calculations of light detection and ranging lidar data within fluvial geomorphology was studied for two river catchments within belgium dijle and ambleve which differ in physical settings and floodplain morphology two commercial of the shelf lidar datasets with different specifications horizontal resolution and vertical accuracy were available for parts of the floodplains of both catchments real time kinematic rtk global positioning system gps data were used as ground truth for error calculations qualitative analysis of lidar data allowed the identification of former channel patterns levees colluvial hillslope and fan deposits these results were confirmed by field data topographic surveys and historical maps the pixel resolution proved to be an important factor in the identification of small landforms only features with a width equal to or larger than lidar resolution can be detected this poses limits on the usability of regionally available lidar data which often have a horizontal resolution of several metres the lidar data were also used in a quantitative analysis of channel dynamics in the study area the width of the dijle river channel increased 3 m on average between 1969 and 2003 a sediment budget of channel processes for the period 1969 2003 indicated a total river bank erosion of 16 1 103 m3 and a total within channel deposition of 7 1 103 m3 resulting in a net river erosion of 9 0 103 m3 or c 0 4 mg year 1 per metre river length sequential lidar data can in theory be used to calculate vertical sedimentation rates as long as there is control on the error of the reference levels used copyright 2008 john wiley and sons ltd

on going orogeny in the outer arc of the timor tanimbar region eastern indonesia abstract the timor tanimbar islands of eastern indonesia form a non volcanic arc in front of a 7 km deep fore arc basin that separates it from a volcanic inner arc the timor tanimbar islands expose one of the youngest high p t metamorphic belts in the world providing us with an excellent opportunity to study the inception of orogenic processes undisturbed by later tectonic events structural and petrological studies of the high p t metamorphic belt show that both deformation and metamorphic grade increase towards the centre of the 1 km thick crystalline belt kinematic indicators exhibit top to the north sense of shear along the subhorizontal upper boundaries and top to the south sense in the bottom boundaries of the high p t metamorphic belt overall configuration suggests that the high p t metamorphic rocks extruded as a thin sheet into a space between overlying ophiolites and underlying continental shelf sediments petrological study further illustrates that the central crystalline unit underwent a barrovian type overprint of the original high p t metamorphic assemblages during wedge extrusion and the metamorphic grade ranged from pumpellyite actinolite to upper amphibolite facies quaternary uplift marked by elevation of recent reefs was estimated to be about 1260 m in timor in the west and decreases toward tanimbar in the east in contrast radiometric ages for the high p t metamorphic rocks suggest that the exhumation of the high p t metamorphic belt started in western timor in late miocene time and migrated toward the east thus the tectonic evolution of this region is diachronous and youngs to the east we conclude that the deep seated high p t metamorphic belt extrudes into shallow crustal levels as a first step followed by doming at a later stage the so called mountain building process is restricted to the second stage we attribute this quaternary rapid uplift to rebound of the subducting australian continental crust beneath timor after it achieved positive buoyancy due to break off of the oceanic slab fringing the continental crust in contrast tanimbar in the east has not yet been affected by later doming a wide spectrum of processes starting from extrusion of the high p t metamorphic rocks and ending with the later doming due to slab break off can be observed in the timor tanimbar region

mechanism and tectonic implications of the great banda sea earthquake of november 4 1963 abstract the banda sea earthquake of november 4 1963 h 100 km mb 7 8 is probably one of the largest intermediate depth shocks to have occurred worldwide this century the mechanism of this earthquake is studied in detail on the basis of p wave first motion surface wave and aftershock data from the analysis of long period multiple surface waves a seismic moment of 3 1 1028 dyn cm is obtained which is the largest reported so far for any intermediate or deep focus shock this value together with the estimated fault area of 90 70 km2 gives an average dislocation of 7 0 m and a stress drop of 120 bar this event represents an oblique thrust movement on a plane with dip direction n170 e dip 48 and rake 52 a geometrical consideration for the fault plane and the configuration of the inclined seismic zone beneath the banda arc suggests almost definitely that the large scale faulting took place within the subducted plate and offset it further repetition of such large scale faulting might eventually break the subducted plate the 1963 banda sea earthquake thus represents a seismological manifestation of the large scale deformation of the subducted plate in the mantle

source times and scaling relations of large earthquakes source time is a kinematic fault parameter corresponding to the duration of seismic source time functions and is accurately determined from phase spectra of long period surface waves source times are determined for 36 large earthquakes during the last three decades scaling relations among source times seismic moments and fault dimensions are derived seismic moment is proportional to the cube of source time and fault dimension is proportional to source time source times for low angle thrust earthquakes along deep sea trenches are found to be longer than those of other types such as intraplate shocks and deep shocks they are also significantly longer than the rupture times expected from a haskell model suggesting that generally there exists an introductory stage of faulting that precedes the main stage of the rupture propagation