grain size sediment transport regime and channel slope in alluvial rivers the general relationship between channel morphology and the grain size of sediment in the channel bed is an important but poorly known aspect of alluvial rivers an analysis of an equation for total sediment flux in the limits of suspension bedload and mixed modes of transport indicates distinct steady state regimes of channel morphology such regimes are readily seen in published data for modern alluvial rivers by way of a conventional shields plot or a plot of channel slope as a function of relative grain size d h and the ratio ws u where d and ws are respectively mean diameter and fall speed of bed sediments and h and u are respectively mean depth and friction velocity of the flow with slope and mode of transport in an alluvial river constrained by grain size and channel depth alone estimates of discharge and sediment flux follow directly introduction of the sediment flux relationship into conventional diffusion models for the evolution of an alluvial system provides nominal estimates of

mathematical modeling of graded river profiles numerical modeling of the longitudinal profiles of rivers at grade is accomplished using the basic equations of open channel flow sediment transport equations and empirical relations for downstream variation in flow discharge sediment discharge sediment caliber and channel width only in some cases are the computed stream profiles fit exactly by any one of the commonly supported mathematical function analogs to graded profile form exponential logarithmic or power function but in most cases any of these functions can provide a fit with a degree of error smaller than would be noted in treating field data profiles dominated by spatial change in fluid and sediment discharge are distinctly power functions while profiles dominated by sediment size reduction are not necessarily exponential in form other important controls on profile shape are the degree of downstream width change in response to increasing discharge and the general range of sediment size a dynamic model of a river s approach to grade

structure of the 1999 chi chi earthquake rupture and interaction of thrust faults in the active fold belt of western taiwan abstract we summarize the structural characteristics of the surface ruptures of the 1999 mw 7 6 chi chi earthquake in western taiwan and discuss the geological interaction of the chelungpu fault with adjacent faults based on geological investigations seismological analyses and gps measurements of surface co seismic displacements we describe the regional 3 d fault plane and slip distribution of the chi chi earthquake and compare these to the geological features of the chelungpu fault we find that one key feature of the chelungpu fault is the stratigraphy controlled slip surface at the level of the uppermost few kilometers the chelungpu fault slip plane generally follows the bedding plane of the pliocene chinshui shale the second key feature of the chelungpu fault is the difference in structurally geometric configuration between its northern and southern segments the northern fengyuan segment shows a bedding parallel thrust fault within east dipping strata in both footwall and hanging wall in contrast the southern tsaotun segment exhibits east dipping strata are overthrust onto flat lying recent alluvial deposits these two features not only explain a hinterland imbricate thrusting on the hanging wall of the fengyuan segment but also explain the change in strike of the chi chi surface ruptures at the northern end the southern end of the 1999 chi chi rupture is interpreted to be linked to a series of nw trending strike slip faults in particular we propose that the luliao strike slip fault served as the lateral ramp of the chelungpu fault and the gukeng strike slip fault acted as a barrier to end the southern propagation of the 1999 rupture geomorphic features and paleoseismological data indicate that the range front chelungpu fault has generated large earthquakes during the last several thousand years alternatively in the miaoli area to the north and the chiayi area to south historical earthquakes as well as active geomorphic features are not restricted on the range front thrust faults instead more complicated structures including tightly spaced folds duplex structures and strike slip faults are involved in seismogenic processes a more detailed investigation of regional structural characteristics is needed for mitigation against the seismic hazards in the 300 km long active fold belt in western taiwan where several damaging large earthquakes have been documented during the last century

prolonged impact of earthquake induced landslides on sediment yield in a mountain watershed the tanzawa region japan abstract to determine for how long a landslide affects sediment discharge the sediment yields of 15 check dam basins were compared with the time series of landslide distributions in a mountain basin in the tanzawa region central japan the distribution of sediment yield was quantitatively estimated from deposition in the sediment pools of check dams the relationship between the landslide history and sediment discharge in the nakagawa river basin was examined for an approximately 80 year period two major landslide events occurred during this period the 1923 kanto earthquake and the 1972 disaster caused by heavy rainfall the resulting trend in sediment discharge of the whole basin estimated using reservoir sedimentation in the miho dam at its base was nearly constant with high sediment discharge 2897 m 3 km 2 yr 1 in the intervening quarter century despite the recovery of vegetation on landslide areas in this period comparisons of the landslide distributions resulting from the two disasters the sediment yields of check dam basins and the sediment discharge of the whole basin indicate that recent sediment discharge contains landslide debris that was originated by the kanto earthquake that occurred over 80 years ago thus to understand high sediment discharge it is essential to investigate not only the current basin condition and recent events but also the landslide history of the basin for at least the previous 100 years

thrust related river terrace development in relation to the 1999 chi chi earthquake rupture western foothills central taiwan abstract the 21 september 1999 earthquake mw 7 6 produced a surface rupture that extended for 100 km in a general north south direction in front of the western foothills central taiwan the study area located in a segment of the fold thrust belt of central taiwan provides an important natural laboratory to study the relationship between active thrust deformation and fluvial terrace development we recognize from west to east three subparallel thrusts the sanyi houli and shihkang faults in the northern part of the earthquake disaster area the 1999 earthquake rupture occurred only along the shihkang fault whereas the other two faults were inactive along the tachia river in the hanging wall of the shihkang fault eight well developed terrace levels are observed and can be subdivided into lateritic lt5 lt1 and non lateritic terraces ft3 ft1 five levels of lateritic terrace lt5 lt1 are located in the hanging wall of the houli fault and a lateritic terrace lt5 is present in the hanging wall of the sanyi fault stratigraphic and elevation correlations between these well developed fluvial terraces in relationship to nearby geologic structures show that the sanyi fault is the oldest structure lateritic terraces of at least 10 000 yr bp for example overlie the sanyi fault but correlative terraces associated with the houli fault are offset these types of terrace correlations allow us to define the progressive development of the thrust system within the western foothills

structural geology of a classic thrust belt earthquake the 1999 chi chi earthquake taiwan mw 7 6 abstract we document the structural context of the 1999 chi chi earthquake m w 7 6 in western taiwan which is one of the best instrumented thrust belt earthquakes the main surface break and large slip 3 10 m is on two segments of the shallow otherwise aseismic bedding parallel chelungpu sanyi thrust system which shows nearly classic ramp flat geometry with shallow detachments 1 6 km in the pliocene chinshui shale and mio pliocene kueichulin tungkeng formations however rupture is complex involving at least six faults including a previously unknown deeper thrust 8 10 km on which the rupture began we compare the coseismic displacements with a new 3d map of the chelungpu sanyi system the displacements are spatially and temporally heterogeneous and well correlated with discrete geometric segments of the 3d shape of the fault system geodetic displacement vectors are statistically parallel to the nearest adjacent fault segment and are parallel to large scale oblique fault corrugations the displacement magnitudes are heterogeneous at several scales which requires in the long term other non chi chi events or significant aseismic deformation the chelungpu thrust has a total displacement of 14 km but the area of largest chi chi slip 10 m is on a newly propagated north chelungpu chinshui detachment 0 3 km total slip which shows abnormally smooth rupture dynamics

sediment tracing and environmental history for two small catchments karoo uplands south africa abstract as part of an investigation of land degradation in the south african karoo three types of fine sediment signatures radionuclides mineral magnetism and sediment geochemistry were used to trace the origins of fine particulate sediment accumulating in two reservoirs that were constructed around the mid 1930s both reservoirs are fed by gullies that are known to have been in existence before their construction robust chronologies were derived from the 137 cs profiles in the reservoir sediments from aerial photographic records and from an analysis of extreme storm events that have left stratigraphic markers in the reservoir sediments extreme daily rainfalls have become more frequent in the last 30 years but sediment accumulation rates in the two reservoirs differ significantly one reservoir has high sediment accumulation rates between 1958 and 1964 that correlates with an expansion in the area of cereal cultivation the second catchment has no cultivated land but sedimentation rates in the reservoir declined after 1941 when livestock grazing densities decreased by a factor of around three despite the increase in the frequency of high magnitude daily rainfalls after 1970 sediment availability as controlled by land use appears to be the most important limit on changes in sedimentation rates differences in lithology and land use provided an opportunity to evaluate the number of sources that could successfully be discriminated in each catchment at different timescales 137 cs and unsupported 210 pb can be used to trace sources of actively transported or very recently deposited sediment and to discriminate sources of reservoir sediments between topsoils cultivated and uncultivated and subsoils or gully sidewalls lack of current 137 cs inputs means that it will become less useful as a future discriminator of topsoil subsoil sources because it only has a half life of ca 30 years and will eventually be undetectable the potential for unsupported 210 pb to provide an alternative method for discriminating these sources is demonstrated using principal component and discriminant function analysis and the three groups of sediment fingerprint signatures it was possible to discriminate doleritic soils from other potential sources in the catchments including valley fill and soils underlying vegetation that had been recently burned as part of the rangeland management system results suggest that fire was an important contributor to destabilising soil which was subsequently delivered to the reservoir during high magnitude rainfalls it is concluded that 1 changes in the extent of cereal cultivation and livestock grazing density are most closely related to temporal changes in sedimentation rates in each of the two reservoirs 2 temporal changes in the magnitude and frequency of extreme daily rainfalls do not correlate with reconstructed patterns of sediment accumulation through time 3 the gully systems provide connectivity between the dominant hillslope sources and the reservoirs but have not contributed significantly to the sediment deposited in either reservoir and 4 there is no evidence to suggest that sources of sediment accumulating in the reservoirs have changed significantly over the last ca 70 years

taiwan orogeny thin skinned or lithospheric collision abstract the taiwan orogeny is young and presently very active it provides an excellent environment for studying ongoing orogenic processes especially since the region is monitored intensively with dense seismological and geodetic networks and new studies aiming at deciphering shallow and deep structures in and around taiwan have been recently conducted or are being planned the available data can be used continually to test critically hypotheses of the taiwan orogeny hypotheses dealing with the mechanics of mountain building are basic to the understanding of taiwan orogeny and are particularly amenable to testing the widely cited thin skinned tectonics hypothesis was formulated to explain mainly the geologic and relatively shallow

evaluation of factors controlling earthquake induced landslides caused by chi chi earthquake and comparison with the northridge and loma prieta events over 10 000 landslides were triggered by the september 21 1999 chi chi earthquake a large number of these landslides have been mapped from spot images and a smaller number were described in a detailed field investigation geographic information systems gis was used to conduct a spatial characterization of the slope failures including distribution of type size slope angle bedrock geology ground motion and distance from earthquake source the most abundant landslides were shallow disaggregated rock and soil slides landslides occurred primarily in tertiary sedimentary rocks which are well known for their susceptibility to landsliding in many parts of the world landslide concentration values diminish beyond epicentral distances of 40 and 70 km from the epicenter and the surface projection of the fault plane respectively ground motion was found to be the most significant factor in triggering the shallow landslides in the chi chi earthquake overall 74 of all slope failures occurred in regions with vertical ground motions greater than 0 2g and 81 of all slope failures occurred in the region with mean horizontal peak ground accelerations pga greater than 0 15g these factors were used to compare landslides generated by the chi chi earthquake to the landslides triggered by the 1989 loma prieta earthquake and the 1994 northridge earthquake the major difference in distribution of landslides between the chi chi earthquake and the two california earthquakes was the distribution of slope angles in the chi chi earthquake 90 of the failures occurred on slopes steeper than 45 while more than 80 of failures occurred on slopes less than 50 in california apparently reflecting much steeper and tectonically more active geologic setting in taiwan

geomorphological evolution of longitudinal river profiles in the carpathians abstract the main rivers which drain the east and southeast side of the eastern carpathians and those that drain the southern carpathians have been analysed regarding the sediment transit the change of the riverbeds and the type of channel deposits in this paper attention is focused on the concavity of the stream profile on this basis we tried to determine the evolution of some carpathian rivers and thus estimate their long term evolutionary tendencies the concavity index of the east carpathian rivers shows a trend to increase from north to south from the eastern carpathians to the carpathian bend and the bucegi mountains the explanation of this situation required a review of the evolutionary stages of the eastern carpathians in order to establish the age and the evolutionary tendencies of the river network in our study area the rivers suceava moldova and bistri a have followed the same courses since the sarmathian approximately 13 5 million years ago the trotus river between 10 million and 5 4 million years ago the rivers putna buz u prahova and ialomi a suffered the most important changes so the age of their present course is about 2 5 million years the rivers could be grouped according to the mathematical model which fits best the exponential exponential logarithmic and logarithmic model finally we tried to correlate the age of the river with the form of its longitudinal profile the customary theoretical models require that the older a river is the more its concavity should increase in the headwater area and should asymptotically approach a longitudinal equilibrium profile or grade as davis calls it however the carpathian rivers do not follow this general tendency what we have demonstrated is that age had no influence on the form of the longitudinal profiles for the rivers on the exterior side of the carpathians this is because tectonic uplift was important and this phenomenon is still present today with values of over 6 mm year

a new pterodactyloid pterosaur from the kimmeridgian of the cap de la heve normandy france a pterosaur specimen consisting of the associated anterior portions of upper and lower jaws is reported from the upper kimmeridgian argiles d octeville in the cliffs of the cap de la heve near le havre france it is described as a new taxon normannognathus wellnhoferi and referred to the germanodactylidae normannognathus wellnhoferi is distinguished by the association of jaws which bear teeth up to their anterior tip and a tall sagittal crest formed by the premaxillae which begins anterior to the nasopreorbital fenestra has a concave anterior edge and is much higher than the maxilla at that level the dsungaripterus like crest and the slightly upturned upper jaw support the idea of a close relationship between the germanodactylidae and dsungaripteridae

impacts of the chi chi earthquake on subsequent rainfall induced landslides in central taiwan abstract the influence of the chi chi earthquake on subsequent rainfall induced landslides was evaluated by comparing the occurrence of landslides in the choushui river watershed through eight spot images that covered the period from 1996 to 2001 the chi chi earthquake not only triggered serious coseismic landslides itself but also extensively disturbed surface strata around the epicentral area after surface strata have been highly disturbed heavy rainfalls in 2000 and 2001 have triggered more landslides than the earthquake itself compared with the data obtained from images before the earthquake it is obvious that the density of rainfall induced landslides increased significantly after the earthquake and the places where landslides occurred changed as well although typhoon herb in 1996 brought more precipitation than typhoon toraji in 2001 only 9 77 km 2 landslides were induced by herb while 48 8 km 2 landslides almost five times larger than those caused by herb were triggered by toraji besides landslides induced by herb were mainly distributed in mid slope areas with slopes of 20 30 after the chi chi earthquake the rainfall induced landslides occurred mainly in places with slopes between 40 and 50

fluvial response to rapid episodic erosion by earthquake and typhoons tachia river central taiwan abstract analysis of typhoon and earthquake triggered landsliding and fluvial response in the tachia river central taiwan documents highly episodic sediment supply over decade to century timescales landslide data from the chi chi earthquake 1999 and subsequent typhoons 2001 2004 and 2005 quantify the sediment supply from these events fluvial response was investigated by decadal scale and century scale longitudinal river profile data spanning 1904 to 2008 and by sediment delivery recorded in suspended sediment load and reservoir sedimentation data our results show that the different time periods of satellite images and aerial photographs used in previous studies make it difficult to unambiguously identify the causes of landslides previously attributed by some studies to the effects of the chi chi earthquake rather than subsequent high intensity precipitation in response to significant variability in sediment delivery from hillslopes century scale profile variation data indicate substantial bed surface elevation change of 2 6 6 7 m and decade scale bed surface elevation change of 1 1 3 3 m since 1993 the downstream reaches incised in response to bedload sediment trapping by reservoirs while headwater reaches aggraded in response to increased sediment delivery from uplands a tremendous increase in reservoir sedimentation after 2000 likely reflects the effects of the highest decade average daily rainfall since 1900 suspended sediment load data indicate a post chi chi earthquake increase in sediment concentration in low flow events but do not exhibit the clear influence on sediment yields at higher flows as e g typhoons reported by others for fluvial response in the epicentral region

a gis based potential analysis of the landslides induced by the chi chi earthquake the chi chi earthquake struck central taiwan in 1999 triggering many landslides over a broad area a large amount of information was obtained from the field reconnaissance conducted by national center for research on earthquake engineering ncree 2000 investigation report of the geotechnical hazard caused by chi chi earthquake taiwan and other follow up investigations the objective of this research was to analyze the landslide data for assessment of the potential for landslides triggered by the chi chi earthquake and a predictive model was constructed accordingly the analysis was conducted under a geographic information system gis environment and the landslide potential was defined by the information value proposed by jade and sarkar eng geol 36 1993 91 seven factors were selected and the structural equation model was used to describe the relationship among the factors and building of the predictive model verifications of the model were conducted using an independent set of field investigation data and results were satisfactory with the field investigation data displaying higher potential

regional patterns of earthquake triggered landslides and their relation to ground motion 1 we have documented patterns of landsliding associated with large earthquakes on three thrust faults the northridge earthquake in california chi chi earthquake in taiwan and two earthquakes on the ramu markham fault bounding the finisterre mountains of papua new guinea in each case landslide densities are shown to be greatest in the area of strongest ground acceleration and to decay with distance from the epicenter in california and taiwan the density of co seismic landslides is linearly and highly correlated with both the vertical and horizontal components of measured peak ground acceleration based on this observation we derive an expression for the spatial variation of landslide density analogous with regional seismic attenuation laws in its general form this expression applies to our three examples and we determine best fit values for individual cases our findings open a window on the construction of shake maps from geomorphic observations for earthquakes in non instrumented regions

earthquake triggered increase in sediment delivery from an active mountain belt in tectonically active mountain belts earthquake triggered landslides deliver large amounts of sediment to rivers we quantify the geomorphic impact of the 1999 mw 7 6 chi chi earthquake in taiwan which triggered 20 000 landslides coseismic weakening of substrate material caused increased landsliding during subsequent typhoons most coseismic landslides remained confined to hillslopes downslope transport of sediment into the channel network occurred during later storms the sequential processes have led to a factor of four increase in unit sediment concentration in rivers draining the epicentral area and increased the magnitude and frequency of hyperpycnal sediment delivery to the ocean four years after the earthquake rates of hillslope mass wasting remain elevated in the epicentral area

extreme storm events landscape denudation and carbon sequestration typhoon mindulle choshui river taiwan we have performed the first known semicontinuous monitoring of particulate organic carbon poc fluxes and dissolved si concentrations delivered to the ocean during a typhoon sampling of the choshui river in taiwan during typhoon mindulle in 2004 revealed a poc flux of 5 00 105 t associated with a sediment flux of 61 mt during a 96 h period the linkage of high amounts of poc with sediment concentrations capable of generating a hyperpycnal plume upon reaching the ocean provides the first known evidence for the rapid delivery and burial of poc from the terrestrial system these fluxes when combined with storm derived co2 consumption of 1 65 108 mol from silicate weathering elucidate the important role of these tropical cyclone events on small mountainous rivers as a global sink of co2

increase in basin sediment yield from landslides in storms following major seismic disturbance the landslide area along the tachia river catchment of central taiwan was investigated using the remote sensing images of various typhoon and earthquake events taken from 1996 to 2004 and the sediment discharge measured at hydrometric stations our findings indicate that 88 of the coseismic landslides triggered by the 1999 chi chi earthquake were first time occurrences after the chi chi earthquake 59 of the landslide area was reactivated during typhoon toraji and 66 during typhoon mindulle the landslides prone to reactivation were on the formations with closely spaced discontinuities it is suggested that further rock mass defects in the formations were added or opened by the earthquake and that the landslide areas continued to extend until the end of 2004 post 1999 rainstorms delivered large amounts of colluvial sediment into the main channel leading to a 2 fold increase in post seismic sediment discharge while the precipitation was only half that of the pre earthquake rate

remnants of late permian middle triassic ocean islands in northern tibet implications for the late stage evolution of the paleo tethys ocean abstract in this paper we present new data for the tianquan tq and dabure db ocean islands in the western segment of the longmuco shuanghu lancangjiang suture zone northern tibet including the results of major and trace element analyses zircon u pb dating and hf isotope analyses our aim was to assess the genesis of these ocean islands and to consider the implications for the tectonic evolution of the region as a whole both tq and db retain an ocean island type double layered structure comprising a volcanic basement basalt and andesite and an oceanic sedimentary cover sequence conglomerate limestone and chert the basalts and andesites in the tq and db are enriched in light rare earth elements and high field strength elements nb ta zr hf and ti yielding chondrite normalized ree patterns and primitive mantle normalized trace element patterns that are similar to those of ocean island basalts given the small and generally positive ehf t values of the tq andesites 4 25 to 6 22 and db andesites 0 59 to 1 97 mostly 0 we conclude that the basalts were derived from the partial melting of garnet peridotite in the mantle and that the andesites were formed by fractional crystallization of the mafic parent magma derived from the garnet peridotite mantle the ascending magmas underwent varying degrees of fractional crystallization but were not contaminated by crustal material these features indicate that both tq and db are typical ocean islands that formed in an ocean basin geochemical analyses of cherts from tq and db show that they contain terrigenous material indicating the proximity of a continental margin the andesites of tq contain zircons that yield two u pb ages of 251 ma given that ages of 246 247 and 254 ma had been reported previously we conclude that tq formed during the late permian early triassic the andesites of db contain zircons that yield u pb ages of 242 and 246 ma taking into account the youngest age of 244 ma from the db basalt we conclude that db formed during the middle triassic these data combined with the geological history of the region indicate that the development of the longmuco shuanghu lancangjiang paleo tethys ocean continued after the early permian and that the closure of this ocean was diachronous from east to west the eastern segment of the ocean closed during the early triassic however the western segment remained at least partially open until the middle triassic although the ocean was relatively small at this time the ocean finally closed in the late triassic