holocene alluvial sediment storage in a small river catchment in the loess area of central belgium abstract soil erosion and sediment deposition widely affect landscape development particularly in erosion prone areas with loess derived soils nevertheless until now few attempts were made to quantify soil losses and sediment storage over long centennial or millennial timescales in this study the holocene alluvial sediment storage in a small river catchment 52 km2 of the belgian loess belt is estimated and a preliminary sediment budget for the catchment is presented in the valley of the nethen river c 13 km long a detailed survey of the alluvial sediment archive was conducted hand augerings and percussion drillings were made along cross valley transects at 12 locations in the catchment ams 14c dating of peat samples provided a temporal framework for the interpretation of the cores results show that the thickness of holocene sediment deposits in the nethen valley is 4 to 6 m which corresponds to a total clastic sediment mass of 14 106 t stored in the valley bottom three alluvial units could be distinguished and associated with deposition phases from 9600 to 2900 b c 2900 b c to a d 1000 and a d 1000 to present in contrast to the older sediments units 1 and 2 deposits from the last 1000 year unit 3 contain little organic matter they are seldom intercalated with peat layers and devoid of tufa unit 3 reaches a thickness of c 2 m thereby representing 50 of the holocene sediment mass stored in the alluvial plain the mean sedimentation rate in the alluvial plain for this last phase is 26 t ha 1 a 1 which is about tenfold larger than the sedimentation rates calculated for the older holocene sediment units sediment supply towards the alluvial plain has therefore increased tremendously since medieval times these results are in contrast to dating results obtained for colluvial sediments in a nearby dry valley within the catchment of the nethen where soil erosion and sediment deposition started in the early iron age and was already substantial during the roman age this means that there is a time lag of about one millennium between the onset of high sedimentation rates in the upstream area and high deposition rates in the alluvial plain this is probably caused by a change in coupling sediment connectivity between the plateau slopes and rivers as soil erosion proceeds first the dry zero order valleys in the catchment act as sediment traps and only after these are filled sediment reaches the floodplains the preliminary sediment budget for the nethen catchment illustrates that 50 of the sediment that was eroded during the holocene was stored in colluvial deposits which are mainly located on footslopes and in dry valley bottoms another 29 of the sediment mass is stored in the alluvial plain

viscosity in transition zone and lower mantle implications for slab penetration 1 the evolution of a subducting slab is strongly influenced by the viscosity of the mantle which it overlies however there is still no consensus about the viscosity in the transition zone and shallower lower mantle we use a numerical self consistent subduction model and run a set of experiments in order to find critical patterns of viscosity that would allow the evolution of the different subduction styles that can actually be found in nature our results show that a jump in viscosity of 5 times from transition zone to lower mantle gives the most reasonable results optimal values of viscosity in the transition zone are in the range of 3 1020 1021 pa s higher values would produce piling up of the slab and later sinking or even slab flattening lower viscosities result in velocities 30 cm yr that are too high while the new slab subducts through the upper mantle and transition zone a phenomenon that is rarely seen in nature reduction of the clapeyron slope related to the spinel perovskite transition variations in oceanic crustal thickness and in the age of the slab do not influence much the style of subduction when overriding velocity is applied to the upper plate the previously penetrating slab tends to lay at the 660 km boundary but does not substantially change the subduction velocity

bed waves at the basin scale implications for river management and restoration an extensive literature about fluvial sediment waves slugs or pulses has emerged in the past 20 years the concept has been useful in many respects but has been applied to diverse phenomena using a variety of definitions moreover inferred linkages between channel bed changes and sediment loads are often not justifiable this paper reviews concepts of large fluvial sediment waves at scales extending to several tens of kilometres it points out constraints on the inferences that can be made about sediment loads based on changes in channel bed elevation at this scale where channel sediment interacts with storage in floodplain and terrace deposits the type area of g k gilbert s initial sediment wave concept is re examined to show that neither wave translation nor dispersion occurred in the simple manner commonly assumed channel aggradation and return to graded conditions provide an alternative theory explaining gilbert s observed bed elevation changes recognizing the evidence and implications of the former passage of a large scale bed wave is essential to the accurate diagnosis of catchment conditions and the adoption of appropriate river restoration goals or methods sediment loads water quality channel morphologic stability and aquatic ecosystems often reflect changes in sediment storage long after the channel bed has returned to grade copyright 2006 john wiley sons ltd

buffers barriers and blankets the dis connectivity of catchment scale sediment cascades abstract catchment configuration and the nature of connectivity within and between landscape compartments affect the operation of sediment cascades and geomorphic responses to disturbance events of differing magnitude and frequency this paper introduces the concept of landform impediments termed buffers barriers and blankets that impede sediment conveyance by limiting the connectivity between landscape compartments buffers restrict sediment delivery to channels barriers inhibit sediment movement along channels and blankets drape channel or floodplain surfaces affecting the accessibility of sediment to entrainment these features operate as a series of switches which turn on off processes of sediment delivery determining the effective catchment area at any given time using previously documented examples the role of these features in affecting the operation of sediment cascades in a low relief passive landscape setting such as the australian landmass is contrasted to examples from high relief uplifting settings in new zealand the australian examples are further explored by examining how changes to landscape connectivity brought about by human disturbance since european settlement have impacted upon landscape sensitivity and prospects for river recovery this approach to analysis of impediments to sediment conveyance is generic and can be applied in any environmental setting

a microseismicity survey of axial seamount juan de fuca ridge an array of ocean bottom seismometers and hydrophones were deployed within the caldera of axial seamount located at the intersection of the cobb eickelberg seamount chain and the juan de fuca ridge recent manned submersible dives have discovered the presence of two distinct hydrothermal vent fields the objective of the microseismicity survey was to determine baseline information necessary for designing an optimal experiment to monitor seismicity associated with submarine volcanic and hydrothermal systems with an instrument deployment period of eight days over 1500 events were recorded and examined most events occurred within three periods of swarm activity the location of the swarm events is believed to be within the low temperature vent field in the northwest portion of axial s caldera these impulsive high frequency events are interpreted to be tectonic in origin no harmonic tremor like events were observed on any of the instruments indicating a lack of magmatic movement only nine local events were recorded on more than one instrument and none of these could be located unambiguously monochromatic 20 hz signals were also recorded and are interpreted to originate from whales observed in the immediate vicinity

microearthquakes at the puhagan geothermal field philippines a case of induced seismicity abstract the puhagan area in southern negros is the only known philippine geothermal field where there is a clear correlation between increased levels of local seismicity and the development and early production phases of a geothermal power project during commissioning of the palinpinon i power plant in may 1983 a large increase in the microseismic event rate occasionally exceeding 100 events per day was noted this seismic activity is characterized by swarms of events lasting from several hours to a month separated by long periods of reduced activity the largest events have local magnitudes of 2 4 because the swarms appear to be triggered by both reinjection and production of fluids it is difficult to relate them to a single triggering mechanism an epicenter study was conducted during july to october 1983 using a simplified joint determination algorithm modified for a uniform velocity structure the vast majority of the hypocenters occur in a narrow zone with a wnw lineation in the production sector of the field correlating with a known fault trace with very little activity in the reinjection sector 1 km to the north first motions suggest activity has been induced on several non parallel faults in the area however a majority of the events are consistent with normal faulting or oblique slip on steeply dipping nw se trending planes

fluvial sediment budgets in the north carolina piedmont phillips j d 1991 fluvial sediment budgets in the north carolina piedmont geomorphology 4 231 241 sediment budgets for four large 1000 km 2 drainage basins in the piedmont physiographic province of north carolina were estimated from data compiled during erosion and sedimentation surveys budgets for the upper tar upper neuse haw and deep river basins showed broadly similar trends in allocation of eroded sediment among yield and storage sediment yield as a percentage of mean annual gross erosion within the basins averaged 10 this was less than the rate of alluvial storage which averaged 14 of annual gross erosion about 76 of the mean annual erosion was stored as colluvium on hillslopes there are relatively small differences in sediment delivery and storage ratios among the study basins this suggests that the relative order of magnitude of the allocation of eroded sediment for southern piedmont rivers is colluvial storage alluvial storage and yield of the sediment that does reach the streams more than half is stored as alluvium on an average annual basis aggrading channels and floodplains siltation of benthic habitats and sediment pollution problems are thus likely to persist unless dramatic reductions in upland erosion or in sediment delivery to streams are realized with respect to longer term basin evolution results point to the need for an improved understanding of the temporal scales of colluvial and alluvial sediment storage

comparative geomorphic analysis of surficial deposits at three central appalachian watersheds implications for controls on sediment transport efficiency abstract factors that control the routing and storage of sediments in the appalachian region are poorly understood this study involves a comparative geomorphic analysis of three watersheds underlain by sandstones and shales of the acadian clastic wedge these areas include the fernow experimental forest tucker county west virginia the north fork basin pocahontas county west virginia and the little river basin augusta county virginia gis based analyses of surficial map units allow first order approximation of sediment storage volumes in valley bottoms estimates of volumes are examined in tandem with morphometric analyses and the distribution of bedrock channels to make inferences regarding controls on sediment transport efficiency in the central appalachians the fernow and north fork areas are characterized by v shaped valleys with mixed reaches of alluvial bedrock channels distributed throughout the drainage network in contrast the little river valley is notably wider and gravelly alluvial fill is abundant comparator watershed parameters for the fernow north fork and little river areas include respectively 1 basin area 15 2 km 2 49 3 km 2 41 5 km 2 2 basin relief 0 586 km 0 533 km 0 828 km 3 drainage density 4 2 km 1 3 3 km 1 4 7 km 1 4 ruggedness 2 5 1 7 3 9 5 shreve magnitude 139 287 380 6 total valley bottom area km 2 0 76 km 2 1 86 km 2 3 09 km 2 7 average hillslope gradients 17 2 18 4 22 1 8 total debris fan surface area 0 113 km 2 0 165 km 2 0 486 km 2 and 9 debris fan frequency 2 0 km 2 1 0 km 2 2 8 km 2 the storage volumes in valley bottoms were estimated using map polygon areas and surface heights above channel grade the little river contains significantly higher sediment volumes in floodplain terrace and fan storage compartments total volumes of the valley bottoms are approximately twice that of the fernow and north fork areas combined unit storage volumes for the fernow north fork and little river are 5 2 10 4 m 3 km 2 5 5 10 4 m 3 km 2 and 1 6 10 5 m 3 km 2 respectively a conceptual model postulates that valley width morphometry and style of delivery from hillslopes are the primary factors controlling the efficiency of sediment transport steep debris flow prone hillslopes at the little river deliver high volumes of gravelly sediment at magnitudes greater than transport capacity of the channel patterns of stream power are complex as low order tributaries are under capacity and high order tributaries over capacity with respect to sediment load aggraded alluvial fill insulates valley floor bedrock from vertical erosion and valley widening dominates expansion of the valley width creates a positive response via increased storage capacity and lower unit stream power conversely the fernow and north fork are characterized by diffusive mass movement on hillslopes with incremental bedload transport to higher order tributaries rates of hillslope delivery are balanced by the rate of channel export mixed alluvial bedrock reaches provide the optimal channel configuration for active incision of the valley floor low expansion of valley width promotes high unit stream power and processes of vertical erosion the model implies that the fernow and north fork have been more effective at sediment transport during the late quaternary given similar climatic and tectonic settings variation in bedrock lithofacies is likely the primary factor modulating the efficiency of sediment transport

evidence for a metastable olivine wedge inside the subducted mariana slab abstract an anomalous seismic velocity structure is revealed inside the subducted pacific plate at northern mariana near the deepest earthquake foci we observe anomalous later phases in the p wave coda for a small cluster of deep earthquakes and an anomalous differential p wave slowness between a few pairs of the earthquakes belonging to the cluster we interpret these observations with a 5 low velocity wedge which is nearly 25 km wide at the depth of 590 km and is truncated at 630 km the wedge is bounded by two steeply dipping 60 70 transition layers with the thickness of about 4 km the highly localized seismic anomaly inside the slab represents a wedge of metastable olivine embedded in dry ringwoodite deep earthquakes occur across only one of the boundaries of the metastable wedge with some of them outside the wedge the mechanism of deep earthquakes is discussed based on the spatial pattern of seismicity relative to the wedge

two dimensional compressional wave velocity structure under san francisco volcanic field arizona from teleseismic p residual measurements a low compressional wave velocity region in the midcrust below the san francisco mountain stratovolcano arizona has been detected by the teleseismic p residual technique this region is approximately 6 km wide lies between elevations of 9 km and 34 km below sea level and has a compressional velocity reduction of more than 6 with respect to the surrounding rocks several mechanisms are found to be quantitatively sufficient to produce such a feature these include 1 a cool silicic pluton enclosed in a more mafic crust 2 high temperature near but below the solidus in a quartz bearing rock in the low velocity region 3 high density of water filled cracks having pore pressures nearly equal to lithostatic pressure and 4 the presence of melt either in intergranular pores or in crystal poor dikes

operation of a digital seismic network on mount st helens volcano and observations of long period seismic events that originate under the volcano during 1981 we operated with the cooperation of the u s geological survey a 9 station digital seismic array on mount st helens volcano in washington state one of our stations was placed inside the crater of the volcano six were located on the flanks of the volcano within two km of the crater and two were approximately ten km from the crater four of the instruments recorded three components of motion and the remaining five recorded only the vertical component in addition to the monitoring and recording performed by the digital instruments we carried out a one day experiment during which we complimented our crater monitoring seismometer by the addition of two ink recording instruments during the one day experiment we had six observers including 4 usgs scientists who had significant experience working and making observations in the crater recording times of rockfall felt earthquake occurrences and changes in steam emissions from the dome in the crater using information obtained during the one day experiment we are able to classify seismic events recorded by our digital instruments as earthquakes rockfalls helicopter noise and a type of event that is unique to volcanoes which we call long period waveforms of these long period events have a duration of up to 30 seconds and a spectrum that is peaked at approximately 2 hz the frequency at which the peak in the spectrum occurs is nearly the same at all stations which means that the unique waveform of long period events is due to a source effect not a path effect the peak frequency is fairly insensitive to the amplitude of the signal which means that the size of the source region is constant independent of the signal amplitude long period events were not felt and were accompanied by no visible changes inside the crater which lead us to conclude that they are some sort of seismic disturbance generated inside the volcano

holocene erosion sedimentation and stratigraphy at raven fork southern blue ridge mountains usa holocene colluvial and alluvial stratigraphy and a radiocarbon chronology are presented for the valley of the lower three kilometers of raven fork a mountain stream draining 194 km 2 of high relief 1 3 km terrain of the southern blue ridge mountains in western north carolina usa which is in a region that lacks good chronological data lower hillslopes alluvial colluvial fans alluvial bottomlands first terrace and floodplain and the modern stream channel are landforms described with respect to soils stratigraphy and sedimentary structures standard methods for subsurface investigations core holes excavation units exposures are used in conjunction with extensive archeological excavations and cultural chronologies radiocarbon ages from each landform are used to calculate long term average rates of sedimentation results indicate that the first half of the holocene experienced somewhat more rapid rates of hillslope sedimentation 0 3 to 1 1 mm yr than the last half of the holocene 0 1 0 2 mm yr on footslopes toeslopes and alluvial colluvial fans prior to historic time we suggest that these subtle differences in the rates of sedimentation were driven by changes in global paleoclimate that favored a high frequency of heavy rainfall including tropical storms and or severe thunderstorms and more and possibly larger floods during the first half of the holocene prehistoric rates of vertical accretion on the first terrace t1 ranged from 0 1 to 0 8 mm yr between about 10 000 and 3000 calendar years ago and incision below t1 formed the late holocene floodplain beginning at about 6000 years ago we suggest that this incision is linked to a reduction in the supply of sediment and a reduction in the magnitude of floods historical rates of sedimentation on all parts of the depositional landscape 2 0 2 7 mm yr on hillslopes and fans and 5 8 6 5 mm yr on floodplains were about an order of magnitude greater than prehistoric rates we attribute these rates to human impacts such as timber harvest and land clearing which caused accelerated erosion we attribute the abundance of fine grained sediment in streams of the southern blue ridge province which is atypical in many mountain streams around the world to the regionally widespread mantle of saprolite as a source of sediment to the fluvial system holocene sedimentation on all depositional landforms in the valley led to sedimentary burial of archeological materials which highlights the need to consider site burial on lower hillslopes and terraces for evaluation of the cultural resources in the southern blue ridge mountains these findings show that the entrenched condition of the raven fork channel was inherited from the middle holocene and can be considered a natural state for this mountain stream casting doubt on the negative connotation that is often assigned to entrenched channels

the magma system of mount st helens non linear high resolution p wave tomography abstract high resolution three dimensional images of p wave velocity anomalies below mt st helens washington were derived using tomographic inversion the model is a 27 5 21 20 km target volume parameterized by blocks 0 5 km per side the area included 39 stations and 5454 local events leading to 35 475 rays used in the inversion to diminish the effects of noisy data the laplacian was constrained to be small within horizontal layers providing smoothing of the model non linear effects were compensated for by iterating three dimensional ray tracing using pseudo bending between inversions and relocating earthquakes relative to the updated three dimensional model the structural differences between the linear and non linear inversions appear to be insignificant although the amplitudes of the anomalies are larger in the non linear models results indicate a low velocity anomaly 7 approximately 1 km in lateral extent from 1 5 to 3 km depths between 3 and 6 km depth the anomaly appears to spread out below 6 km depth the low velocity feature changes to a higher velocity perturbation with lower velocity perturbations flanking around the perimeter of the volcano the higher velocity material which correlates with the higher seismicity at that depth is interpreted as being a plug capping the low velocity magma chamber which begins below 9 km depth

a temporal change in coda wave attenuation observed during an eruption of mount st helens during the past few years there have been numerous reports of changes in coda wave attenuation occurring before major earthquakes these observations are important because they may provide insight into stress related structural changes taking place in the focal region prior to the occurrence of large earthquakes the results of these studies led us to suspect that temporal changes in coda wave attenuation might also accompany volcanic eruptions by measuring power decay envelopes for earthquakes at mount st helens recorded before during and after an eruption that took place during september 3 6 1981 we found that coda q sup 1 for frequencies between 6 and 30 hz was 20 30 higher before the eruption than after the change is attributed to an increase in the density of open microcracks in the rock associated with inflation of the volcano prior to the eruption q sup 1 was found to be only weakly dependent on frequency and displayed a slight peak near 10 hz the weak frequency dependence is attributed to the dominance of intrinsic attenuation over scattering attenuation since it is generally accepted that intrinsic attenuation is constant with frequency whereas scattering attenuation decreases strongly at higher frequencies the weak frequency dependence of q sup 1 more at mount st helens contrasts with results reported for studies in nonvolcanic regions the peak in q sup 1 near 10 hz at mount st helens is attributed to the scale length of heterogeneity responsible for generating backscattered waves results for nonvolcanic regions have shown this peak to occur near 0 5 hz thus a smaller scale length of heterogeneity is required to explain the 10 hz peak at mount st helens copyright american geophysical union 1988 less

quantifying human impacts on rates of erosion and sediment transport at a landscape scale establishing background geologic rates of erosion is prerequisite to quantifying the impact of human activities on earth s surface here we present 10 be estimates of background erosion rates for ten large 10 000 100 000 km 2 river basins in the southeastern united states an area that was cleared of native forest and used intensively for agriculture these 10 be based rates are indicative of the pace at which the north american passive margin landscape eroded before european settlement 8 m m y comparing these background rates to both rates of post settlement hillslope erosion and to river sediment yields for the same basins we find that following peak disturbance late 1800s and early 1900s rates of hillslope erosion 950 m m y exceeded 10 be determined background rates more than one hundred fold although large basin sediment yields during peak disturbance increased 5 10 above pre settlement norms rivers at the time were transporting only 6 of the eroded material work by others suggests that the bulk of historically eroded material remained and still remains as legacy sediment stored at the base of hillslopes and along valley bottoms because background erosion rates such as we present here reflect the rate at which soil is generated over millennial time scales they can inform and enhance landscape management strategies

the sediment delivery problem abstract the linking of on site rates of erosion and soil loss within a drainage basin to the sediment yield at the basin outlet and improved knowledge and representation of the associated processes of sediment delivery represent a major research need within the field of erosion and sedimentation and also an important scale problem in drainage basin studies this paper reviews the limitations of the sediment delivery ratio concept by considering the problems of temporal and spatial lumping and its blackbox nature some recent advances in our understanding of the sediment delivery system and its modelling are described and the lack of detailed empirical investigations is highlighted the significance of recent concern for the role of sediments in the transport of nutrients and contaminants to sediment delivery studies is introduced and the need for further work in this field is emphasised

impacts of pre vs postcolonial land use on floodplain sedimentation in temperate north america abstract this paper evaluates the relative importance of anthropogeomorphic sedimentation on floodplains in the mid latitudes of north america before and after the arrival of euroamericans geohistorical and geoarchaeological theories have emerged that have conflicts concerning the relative effectiveness of pre and postcolonial anthropogeomorphic change in north america many geoarchaeologists paleoecologists historians and cultural geographers have concluded that intensive precolonial land use resulted in substantially humanized landscapes prior to the arrival of colonists this presents a geomorphic paradox to fluvial geomorphologists and river restorationists who interpret buried floodplain soils as evidence of landscape stability evidence for these theories is reviewed from a geomorphic perspective while making distinctions between ecological and geomorphic change and recognizing spatial and temporal variability in some locations mid millennial land use generated erosion and floodplain sedimentation subsequent indigenous population declines and reductions in land use intensity may have been followed by precolonial geomorphic stability and pedogenesis an abandoned landscape hypothesis that floodplain soils developed on precolonial anthropogenic alluvium and were subsequently buried should be considered where indigenous populations and land use activities were high variability is also noted in postcolonial floodplain sedimentation many stratigraphic studies show that rates of sedimentation increased greatly after colonization in response to land clearance for agriculture timbering and mining an inventory of studies that document postcolonial floodplain sediment shows strong spatial patterns most studies of postcolonial sedimentation cluster in the eastern usa from the mid atlantic southward and in the mississippi valley from wisconsin to mississippi but many occurrences of mining sediment are scattered throughout the west few of the studies reviewed in the west document anthropogenic floodplain sediment from agriculture or logging although more thorough regional inventories could change that vast areas of temperate north america do not have historical deposits that are well represented in the scientific literature so assumptions that legacy sediment on floodplains is ubiquitous are ill founded spatial and temporal variations in pre and postcolonial floodplain sedimentation are complex and more research is needed to fill in the knowledge gaps

tomographic inversion for three dimensional velocity structure at mount st helens using earthquake data tomographic inversion is applied to 17 659 p phase observations at 21 stations from 2023 earthquakes in the vicinity of mount st helens to study the three dimensional velocity structure block size for the inversion is 2 km horizontally and 2 km or more vertically locations of hypocenters are assumed known and are based on a reference one dimensional layered velocity structure a conjugate gradient technique lsqr is used to invert the large sparse system of equations augmented by regularization with a laplacian roughening matrix resolution is estimated by computing the impulse response of the inversion for various critical locations and uncertainties of the estimates are determined by a jackknife approach the results of the inversion show a remarkable correlation with known geological and geophysical features the spirit lake and spud mt plutons are characterized by high velocity regions extending to approximately 9 km depth the st helens seismic zone a band of diffuse seismicity extending nnw from the volcano is evident as a prominent low velocity lineation the change in character of the velocity anomalies south of st helens corresponds well with the near cessation of seismic activity there a low velocity anomaly beneath the crater from 6 to 16 km depths may represent modern magma accumulations

waveform effects of a metastable olivine tongue in subducting slabs we constructed velocity models of subducting slabs with a kinetically depressed olivine and spinel transition and examined the effect that such structures would have on teleseismic p waveforms using a full wave finite difference method these two dimensional calculations yielded waveforms at a range of distances in the downdip direction the slab models included a wedge shaped low velocity metastable olivine tongue moto to a depth of 670 km as well as a plausible thermal anomaly one model further included a 10 km thick fast layer on the surface of the slab the principal effect of moto is to produce grazing reflections at wide angles off the phase boundary generating a secondary arrival 0 to 4 seconds after the initial arrival depending on the take off angle the amplitude and timing of this feature vary with the lateral location of the seismic source within the slab cross section careful analysis of waveforms from earthquakes with depths near 400 km simple sources and adequate station coverage in appropriate geometries will be required to resolve whether moto is present

constraining kinetics of metastable olivine in the marianas slab from seismic observations and dynamic models abstract transformation kinetics associated with the presence of a metastable olivine wedge in old and fast subducting slabs has been the subject of many studies in the last years even with improvements in kinetics models many of the parameters are still not well constrained in particular there is no consensus on the blocking temperature that could inhibit the transformation from olivine to spinel recently based on anomalous later phases in the p wave coda and differential p wave slowness a wedge of metastable olivine was detected in the marianas subduction zone that is approximately 25 km wide at a depth of 590 km and is truncated at 630 km in this work a thermomechanical model was used to mimic the subduction in the marianas and try different blocking temperatures for the olivine spinel transformation the model includes among other features non linear elasto visco plastic rheology based on laboratory data phase transformations latent heat proper coupling between stress and thermal state of the slab and force balance of the system the results show a positive correlation between the blocking temperature depth of the wedge and its distance from the trench or subduction angle we compare these results to the situation in the marianas and suggest that a blocking temperature for the olivine spinel transformation of approximately 725 c would be the most likely the volume of the wedge presents some oscillations that we relate to a runaway effect of the transformation kinetics in the mantle transition zone namely the interaction between latent heat release and the advection of the isotherms due to the subduction velocity the inclusion of shear heating in the model was fundamental to modeling such a subduction zone without shear heating the slab shows a higher level of internal stress and the necessary bending to mimic the marianas subduction zone cannot be reached

the influence of olivine metastability on deep subduction of oceanic lithosphere abstract the dynamics of subduction of oceanic lithosphere is mainly controlled by thermal buoyancy forces and mineralogy in self consistent models the influence of metastable olivine mo on the dynamics and evolution of subducting oceanic lithosphere is investigated we consider both phase boundaries olivine ol to spinel sp 410 km and sp to perovskite pv magnesiowustite mw 660 km treating the kinetics of the phase transition in a simplified way while models do not allow the formation of mo penetrate straight into the lower mantle slabs with a sufficient amount of mo flatten out at the 660 km boundary before penetrating at a later stage furthermore our models show that the effect of mo to slow down subduction velocities within the transition zone is rather moderate

experimental constraints on the depth of olivine metastability in subducting lithosphere the hypothesis that metastable olivine persists in some subducting slabs into the transition zone has wide implications for mantle dynamics and rheology in order to evaluate this possibility we derive new thermo kinetic subduction zone models to predict the extent of olivine metastability within the stability fields of its high pressure polymorphs wadsleyite and ringwoodite our updated models improve on previous work by incorporating experimental kinetic data on realistic mantle compositions mg fe 2sio4 rather than analogue systems furthermore latent heat due to the transformation is fed back into both the kinetics and the thermal model we also consider the effects of transformation stress on growth kinetics and the possibility of an intracrystalline transformation mechanism previously thought to be important only at high shear stresses our models predict significantly smaller wedges of metastable olivine than previous work in the case of tonga for example where high values of lithospheric age 100 140 million years and convergence rate 14 cm per year are most favorable for metastability models considering only grain boundary nucleation and interface controlled growth predict olivine metastability to 600 km depth in contrast to 660 km predicted previously by kirby et al rev geophys 34 1996 261 when intracrystalline transformation is considered the depth of metastability is further reduced by as much as 100 km due to the large increase in the density of nucleation sites inhibition of growth by transformation stress can increase the depth interval over which the transformation takes place but is unlikely to be a dominant factor especially if the intracrystalline mechanism operates these results indicate that the existence of metastable olivine at depths corresponding to those of the deepest earthquakes 680 km requires subduction of old lithosphere 100 million years and a high vertical subduction velocity 15 cm per year such conditions currently may only be achieved in the very northern part of the tonga subduction zone yet earthquakes occur at depths down to 680 km in other subduction zones in which lithospheric age and or subduction velocity are relatively low e g indonesia and the marianas therefore mechanisms other than transformational faulting in metastable olivine must operate to cause the deepest earthquakes

slab dynamics in the transition zone abstract seismic images of horizontal slab segments in across or below the transition zone invoke scenarios in which slabs are laid down in the mantle through progressive trench retreat however observations of subduction characteristics do not exhibit a clear correlation between trench retreat and slab dip in the transition zone instead analysis of a range of subduction characteristics demonstrates that while transition zone slabs include slabs of many ages and subduction velocities with both retreating and advancing trench motion they also have several enigmatic characteristics such as faster sinking rates and a larger range in slab dip than slabs that extend to either shallower or deeper depths comparison of subduction characteristics with several analytical and numerical models of subduction dynamics suggests that many of the possible mechanisms for trapping slabs in the transition zone e g positive buoyancy sources viscous resistance slab weakening are only viable if the slab is already shallow dipping two scenarios for the formation of stagnant slabs are proposed 1 trench retreat prior to slabs entering the transition zone or caused by the negative buoyancy forces associated with the wadsleyite and ringwoodite phase transitions and 2 slow lateral migration of slabs in stable subduction zones

observations of volcanic tremor at mount st helens volcano digital recordings of ground motion during tremor episodes accompanying eruptions at mount st helens volcano in the state of washington on august 7 and october 16 18 1980 are studied the spectra of the vertical component waveforms contain at least two dominant peaks at 1 0 and 1 3 hz for all events recorded during both eruptions that were studied spectra of horizontal ground motion show peaks at 0 9 and 1 1 hz the relative amplitude of the two peaks changes between tremor episodes and during single tremor episodes and shows no consistent relation to amplitude of ground motion spectra of long period earthquakes are very similar to those of tremor events suggesting that tremor is composed of many long period earthquakes that occur over a period of time the unique waveform of tremor events observed at mount st helens must be due to a source effect since the relative amplitude of the two dominant peaks changes during tremor episodes the path effect on tremor waveforms is small since there are no peaks in the spectra of waveforms recorded during tectonic earthquakes occurring in the vicinity of mount st helens the consistency of the location of the spectral peaks for the wide range of tremor amplitudes means that there must be a physical length at the source that is constant independent of the amplitude of motion at the source variations in amplitude of motion generated during tremor events must be due to variations in the force driving the tremor amplitudes of ground motion varies between 0 11 and 4 7 m seismic moment rates during the two eruptions are calculated using the model of aki et al 1977 and found to vary between 6 1018 and 1 1020 dynes cm s 1 which are larger than values found by aki et al 1977 who studied amplitudes of shallow tremor events recorded during the october 1963 eruption of kilauea volcano in hawaii study of tremor amplitudes recorded at corvallis oregon leads to the conclusion that tremor accompanying the cataclysmic may 18 1980 eruption was at least one order of magnitude larger in amplitude than tremor during august and october

earthquake source parameters and the frequency dependence of attenuation at coalinga mammoth lakes and the santa cruz mountains california least squares best fits were calculated to the fourier amplitude spectra of p and s waves of locally recorded earthquakes attenuation amplification and earthquake source parameters were calculated from parameters of the fits approximately 8200 spectra were fit at 39 sites at coalinga mammoth lakes and the santa cruz mountains california typically the spectra were fit from 2 to 45 hz for p waves and 2 to 20 hz for s waves the source spectral falloff of p waves was limited to be no greater than f 2 5 f is frequency by low attenuation sites in the sierra nevada attenuation was measured through t the travel time divided by q attenuation was considered to be frequency dependent according to t to f which is equivalent to q qof negative values of were found to minimize the sum of squared residuals at most of the sites studied attenuation and amplification varied from site to site systematically with site geology source parameters were determined for individual earthquakes by averaging fit parameters from between four and 18 spectra depending on the earthquake seismic moments ranged from roughly 5 1012 to 1015 nm at coalinga and mammoth lakes moments ranged from 2 1011 to 3 1014 nm in the santa cruz mountains when the fits were determined using negative values of a the seismic moments trended approximately as fc 3 fc is the corner frequency for 0 5 stress drops varied from roughly 0 2 to 50 mpa at coalinga and mammoth lakes stress drops were lower in the santa cruz mountains ranging from approximately 0 05 to 8 mpa

wet subduction versus cold subduction 1 in situ x ray diffraction study of post spinel transformation in hydrous peridotite 2 wt h2o indicates that the phase boundary is shifted to higher pressures by 0 6 gpa relative to anhydrous peridotite at 1473 k whereas it shows no obvious shift at high temperature around 1873 k a linear equation for the boundary is p gpa 0 002 t k 26 3 which is applicable for temperatures below 1800 k the present data shows that a significant part of the depressions seen in the 660 km seismic discontinuity may be affected by existence of water it is also well resolved that the olivine wadsleyite phase transformation corresponding to the 410 km seismic discontinuity is shifted to lower pressures by 1 2 gpa by the addition of water thus the topography of seismic discontinuities in the transition zone associated with slabs can be attributed not only to cold subduction but also wet subduction

digital processing of regional network data abstract much more than hypocenter location can be done with digital time histories obtained from regional seismic networks examples are given of how these data can be routinely processed to provide readily accessible intermediate results for subsequent studies among which are velocity inversion using teleseismic p residuals composite focal mechanism studies and spectral analysis the processing must be designed to be as routine and as complete as possible only with these two objectives achieved can the seismic networks be as productive as they should be

source parameters of the 1980 mammoth lakes california earthquake sequence from the more than 1500 mammoth lakes earthquakes recorded on three component digital seismographs spudich et al 1981 150 were used in an analysis of the locations mechanism and source parameters a composite fault plane solution of nine earthquakes 3 9 m 5 1 defines a right lateral strike slip mechanism on a steeply dipping nearly east west plane striking s75 e or left lateral strike slip on a nearly north south plane striking n10 e vertical cross sections of well located aftershocks indicate possibly three east west planes that coincide with the locations of the four largest earthquakes with ml 6 0 using the spectral analysis of s waves brune 1970 source parameters for 67 earthquakes were determined forty eight had magnitudes greater than or equal to 3 0 seismic moments ranged from 9 20 1018 dyn cm to 2 33 1024 dyn cm earthquakes with seismic moment greater than about 1 0 1021 dyn cm had nearly constant stress drops 50 bars earthquakes with seismic moment less than about 1 0 1021 dyn cm had stress drops that apparently decrease as seismic moment decreases

modeling the sensitivity of sediment and water runoff dynamics to holocene climate and land use changes at the catchment scale abstract an increasing number of studies have indicated that soil erosion sediment redistribution and water discharge during the holocene have varied greatly under influence of environmental changes in this paper we have used a modeling approach to study the driving forces for soil erosion and sediment redistribution on the one hand and water discharge on the other hand during the holocene for the belgian dijle catchment soil erosion and sediment redistribution was modeled using the spatially distributed watem sedem model several scenarios of past land use and climate were used to model soil erosion colluvial sedimentation and sediment export to the fluvial system and those scenarios were combined with a sensitivity analysis modeling results are validated based on an available time differentiated field based sediment budget water discharge was modeled using the spatially distributed stream model with a daily time step the model was calibrated based on contemporary discharge data the results indicate that soil erosion has increased between the early holocene and the current situation by ca 9 due to climatic variations and by ca 6000 due to changes in land use the average discharge has increased by ca 7 mainly due to land use changes and the discharge also shows more peaks the decrease in cropland area and increase in built up area since 1775 ce has resulted in a decrease in soil erosion and in a further increase in discharge showing the difference in sensitivity of both processes to land use changes

upper crustal structure of the mount hood oregon region as revealed by time term analysis seismic refraction data with a dense areal distribution were collected to study the seismic structure of mount hood and the surrounding region this area is typical of cascade volcanoes and is geologically quite complex the prime goals of this project were to search for velocity variations in the upper crustal rocks and to determine if the velocity of these rocks is anisotropic a new system including 100 remote recording units was developed to facilitate the collection of data in this type of survey the data collected in this study reveal a large variation in velocity and thickness of the uppermost crustal rocks that is probably typical of the high cascade province a regional structural pattern surrounding mount hood where there is a marked thinning of low velocity near surface rocks suggests that the present edifice of mount hood lies on top of a much larger structure possibly the roof of a large batholith that was emplaced prior to the eruption of the volcanic rocks that form the modern mountain a straightforward time term analysis of the data reveals this structure when the time terms are used to correct the travel time observations for the variation in structure under each station the remaining set of residuals indicates a variation of travel time with azimuth while a systematic error in the time term reduction cannot be ruled out this variation is probably the result of anisotropic velocity structure in the underlying refractor the alignment of the direction of maximum velocity with the direction of maximum principal stress and the decrease in anisotropy with depth suggest that the anisotropic velocity structure is related to the opening and closing of fractures in the present stress field the direction of maximum velocity is about n25 w and the degree of anisotropy appears to vary with depth from about 3 near the surface to zero at depths below 8 km

crustal structure of mauna loa volcano hawaii from seismic refraction and gravity data abstract in october 1978 the u s geological survey established a 100 km long seismic refraction profile normal to the kona coast of hawaii island analysis of these data along with available gravity data suggest that the oceanic crust dips about 3 landward under the submerged flank of the island increasing to 8 5 under the kona coast maximum vertical deflection of the base of crust from beneath the deep ocean to a point beneath the summit of mauna loa is about 9 km high velocity high density rocks vp about 7 1 km sec density about 2 9 gm cm 3 comprise the bulk of the volcanic edifice and reach to within a few kilometers of the surface beneath the north flank of mauna loa the data also suggest that an elongate high velocity high density body lies parallel to the kona coast just below the surface this body probably represents an extinct buried rift zone

long wavelength character of subducted slabs in the lower mantle abstract the high resolution seismic tomography provides the detailed information about the fate of the subducted plates in the mantle while the slab deformation in the transition zone is quite complex and differs among the individual subduction zones it could be generally concluded that most slabs seem to penetrate into the lower mantle the character of the fast seismic velocity anomalies however changes when the slabs cross the 670 km discontinuity while in the upper mantle tomography resolves relatively narrow plate like structures in the lower mantle it rather indicates thick blobs of seismically fast material such thickening of the downgoing slabs is traditionally attributed to the effect of the viscosity increase in the lower mantle here we study the deformation of the slabs in the lower mantle in a viscous model with a non linear composite rheology including the diffusion creep the dislocation creep and a power law stress limiter we perform numerical simulations of the subduction process in a 2d cartesian domain and concentrate especially on the effect of the change of the rheological parameters across the 670 km boundary on the slab deformation in the upper part of the lower mantle the thickening or the buckling of the plate is indeed observed in the models with relatively low yield stress 0 1 gpa of the stress limiting mechanism and with a viscosity increase at the 670 km discontinuity further we show that both the major mantle phase transitions and the strength of the crust layer have significant consequences for the creation of the buckling instabilities in the lower mantle

locations and spectral properties of earthquakes accompanying an eruption of mount st helens a joint hypocenter determination routine has been developed to accurately determine the locations of earthquakes occurring under mount st helens the method has a special application to mount st helens where most of the earthquakes are suspected to occur at shallow depth in a rather limited volume under the volcano differences in elevation among stations are allowed for in this routine the location procedure determines a best half space velocity and one station correction for each station simultaneously with earthquake hypocenters arrival time data from an array of portable digital seismic event recorders are supplemented with data from stations of the permanent university of washington seismic network operating at the volcano earthquakes are found to occur along a line trending south east of the dome inside the crater the shallowest events occur near the dome with hypocentral depth increasing with increasing distance from the dome station corrections can be interpreted to imply the existence of a high velocity body beneath the crater which extends at least between depths of 5 and 2 1 km beneath the crater floor spectra are calculated from earthquake waveforms recorded at three stations the spectra show very little evidence for local site or path effects on frequency content of waveforms stress drops of earthquakes are calculated from measurements of corner frequency and low frequency spectral amplitude stress drops of earthquakes vary between 5 and 5 bars there is no evidence for a limiting corner frequency for small earthquakes as has been found for earthquakes occurring in mammoth lakes california data fit well a linear trend between log seismic moment and log source radius fit to data for earthquakes ranging in size from 1014 to 1027 dyn cm suggesting that there is no limiting source radius observed for earthquakes in this range of size

the temporal and spatial quantification of holocene sediment dynamics in a meso scale catchment in northern bavaria germany the aufsess river catchment 97 km2 in northern bavaria germany is studied to establish a holocene sediment budget and to investigate the sediment dynamics since the early times of farming in the third millennium bce the temporal characterization of the sediment dynamics is based on an intensive dating program with 73 osl and 14 14c ages to estimate soil erosion and deposition colluvial and alluvial archives are investigated in the field by piling and trenching supported by laboratory analyses the sediment budget shows that 58 of these sediments are stored as colluvium in on and foot slope positions 9 are stored as alluvium in the floodplains and 33 are exported from the aufsess river catchment colluviation starts in the end neolithic c 3100 bce while first indicators of soil erosion derived alluviation is recorded c 2 3 ka later the pattern of sedimentation rates also displays differences between the colluvial and alluvial system with a distinct increase in the middle ages c 1000 c

volcanic earthquakes and their relationship to eruptions at ruapehu and ngauruhoe volcanoes abstract crustal earthquakes near ruapehu and ngauruhoe fall into two classes each of which can be subdivided on the one hand there are high frequency events 3 hz with sharp well defined phases mainly concentrated beneath ruapehu crater lake low frequency events the low frequency events resemble minakami s b type and explosion earthquakes but sometimes occur where no vent exists and rather deeper than his formal definition difficulty in applying minakami s classification rigorously and the fact that low frequencies may be due to abnormal attenuation of higher frequencies along the path rather than to their suppression or absence at the source has led to reclassification of earthquakes near the volcanoes into two broad groups tectonic and volcanic the former includes all high frequency earthquakes and those discrete events in which dominant low frequencies are due to path effects the latter includes multiple and emergent events which show evidence of prolonged or repetitive source mechanism dominant low frequencies are ascribed to occurrence in heat weakened material and high frequencies to instantaneous source mechanisms operating in competent rock the term volcano tectonic describes tectonic earthquakes within some arbitrary distance of a volcano at ngauruhoe and ruapehu volcanic earthquakes accompany explosive vent clearing eruptions subsequent open vent degassing and ash emission however although often powerful and prolonged usually occurs without earthquakes such activity is however frequently accompanied by volcanic tremor at ruapehu under closed vent conditions when lake temperature is low low frequency earthquakes up to magnitude ml 3 4 have occurred without any eruption five types of phreatic eruptions are identified at ruapehu each having a distinctive seismic pattern the three most explosive types appear to be generated by a chain reaction process and all involve flashing of water to steam the first by failure of the roof with little precursory seismicity after a closed vent period during which lake temperature decreases the second after prolonged heating of the lake and much preliminary volcanic tremor interpreted as due to rising magma and the third under open vent conditions in the wake of one of the two preceding types a fourth probably occurs in wet sediments near the base of the lake as a result of upward migration of hot gas and a fifth aseismic or accompanied by very weak volcanic tremor is associated with convective overturn within crater lake

what drives orogeny in the andes the andes the world9s second highest orogenic belt were generated by the cenozoic tectonic shortening of the south american plate margin overriding the subducting nazca plate we use a coupled thermomechanical numerical modeling technique to identify factors controlling the intensity of the tectonic shortening from the modeling we infer that the most important factor was accelerated westward drift of the south american plate changes in the subduction rate were less important other important factors are crustal structure of the overriding plate and shear coupling at the plates9 interface the model with a thick 40 45 km at 30 ma south american crust and relatively high friction coefficient 0 05 at the nazca south american interface generates 300 km of tectonic shortening during 30 35 m y and replicates the crustal structure and evolution of the high central andes the model with an initially thinner

ten conceptual models of large scale legacy sedimentation a review abstract considerable interest has been directed toward the recognition and documentation of legacy sediment i e anthropogenic sediment in fluvial systems little has been written however to identify implicit or explicit theories about how these deposits form and evolve over decennial to centennial time scales this review attempts to redress this void by examining conceptual models of the physical behavior and characteristics of catchment scale anthropic fluvial sedimentation events these concepts which are not unique to anthropogenic sediment include cascades sediment delivery ratios waves aggradation degradation episodes residence times budgets connectivity stream power nonlinear dynamical systems and geohistorical geoarchaeological and chronostratigraphic principles a broad definition of legacy sediment as episodically produced anthropogenic sediment is adopted that includes early episodes of large scale human induced sedimentation throughout the world the models apply to a variety of environments so the examples from north america following the introduction of european settlement can be related to other post settlement sedimentation episodes elsewhere during aggradation episodes rates of erosion and sedimentation often increased an order of magnitude in response to land clearance for agriculture timbering or mining these sediments may remain as a lasting geomorphic legacy that provides evidence of anthropogenic change and governs modern rates of sediment production and nonpoint source pollution

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

land use and climatic impacts on the rhine system rheinlucifs quantifying sediment fluxes and human impact with available data abstract the rheinlucif project investigates the effects of land use and climatic impacts on sediment fluxes in the river rhine catchment among the world s large rivers the rhine system has been particularly affected by land use changes for 7500 years resulting in its transformation to an entirely man controlled environment geomorphologically this transformation is performed by largely man induced sediment fluxes since the mid holocene as the large scale of the rhine catchment inhibits a renewed recording of stratigraphic records the main goal is to synthesize quantitative data on sediment flux climatic and human impacts from already available data from various fields of earth surface and social sciences particularly history and archaeology this paper presents the first steps and results of methodological groundwork exploring how to derive sediment budgets from available spatially distributed data soil maps geological maps dems furthermore a new basically statistical approach utilising archaeological data is outlined this approach provides time series of quantified human impact i e information on population densities and open land woodland ratios the first results derived from four different sediment budget approaches are helpful in order to assess the quality of available data for budget calculation purposes although some estimates on erosion and alluvial deposition seem to broadly agree a considerable disparity of holocene erosion and colluviation values occurs when these values are compared to the outcome of an independently recorded soil mapping campaign in a pilot area however in general the results suggest that all applied approaches chiefly require an improved estimation of sediment storage on the one hand this accounts for the need of more precise information on holocene floodplain deposits on the other hand as the larger portion of man induced sediments still resides in the sloping parts of catchments realistic estimates on man induced colluvial deposition on slopes are essential apart from budgeting issues all data on holocene erosion and sedimentation in the rhine catchment lacked a sufficient dating control therefore further investigations on fluxes between budget components necessitate additional datings quantified data on human impact is indispensable to the modelling of sediment fluxes because human impact is deemed to be the major driving force of sediment production and re distribution although the archaeological approach was developed and tested by utilising well documented data about the neolithic era the promising statistical evaluation suggests that this method can be applied to even less well documented proto prehistoric and historic periods

seismicity and source parameters of earthquakes in the region of the large tolbachik fissure eruption this study discusses the focal mechanisms of 61 earthquakes and dynamic parameters of 97 earthquakes mi 2 0 and focal depths 0 20 km occurring in the region of the large tolbachik fissure eruption in 1975 1978 variations of these parameters during the different eruptive stages are examined three stages can be distinguished 1 june 27 july 2 1975 from the beginning of the seismic preparation to the large earthquakes of july 2nd withm 5 0 2 july 2nd july 6th 1975 before the onset of eruption 3 from july 6th 1975 to the end of 1976 during the eruption

natural streams and the legacy of water powered mills gravel bedded streams are thought to have a characteristic meandering form bordered by a self formed fine grained floodplain this ideal guides a multibillion dollar stream restoration industry we have mapped and dated many of the deposits along mid atlantic streams that formed the basis for this widely accepted model these data as well as historical maps and records show instead that before european settlement the streams were small anabranching channels within extensive vegetated wetlands that accumulated little sediment but stored substantial organic carbon subsequently 1 to 5 meters of slackwater sedimentation behind tens of thousands of 17th to 19th century milldams buried the presettlement wetlands with fine sediment these findings show that most floodplains along mid atlantic streams are actually fill terraces and historically incised channels are not natural archetypes for meandering streams

use of reservoir deposits to reconstruct the recent changes in sediment yields from a small granite catchment in the yimeng mountain region china information on recent changes in sediment yields from small catchments provides a better understanding of temporal trends in soil loss from certain physical and human influenced landscapes that have been subjected to recent environmental changes and will help bridge the current knowledge gap that exists between hillslope erosion and sediment transport in rivers the yimeng mountain region characterized by alternating granite and limestone is one of the most susceptible regions to soil erosion in northern china and has been subjected to intensive anthropogenic activity in recent years soil loss from areas underlain by granite is particularly obvious and is the main sediment source for the yihe river in this study we used reservoir deposits to estimate the changes in sediment yields over the past 50 years from a small catchment underlain by granite namely the jiangzhuang catchment in the yimeng mountain region three cores were collected from the jiangzhuang reservoir in the catchment the activities of 137cs and 210pbex at different depths clay grain size 5 m contents and sedimentary organic carbon soc contents in the cores were analysed with reference to human activity and environmental change in the catchment the chronologies of the cores were established by 137cs and 210pbex dating the area specific sediment yield ssy for different time periods since dam construction was estimated from each core by referring to the original capacity curve of the reservoir the results indicate that the depth profiles of 137cs 210pbex clay and soc contents in cores from the jiangzhuang reservoir reflect the general history of human disturbances on the catchment over the past 50 years the estimated ssy value from each core for each period ranged from 7 2 2 7 to 23 7 8 3 t ha 1 y 1 with a mean of 12 5 4 6 t ha 1 y 1 ssy decreased during 1954 1972 and then showed a general tendency to increase the temporal pattern of the sediment yield largely reflects the history of environmental change influenced by human activity in the catchment

simultaneous inversion for q and source parameters of microearthquakes accompanying hydraulic fracturing in granitic rock an inversion that fits spectra of earthquake waveforms and gives robust estimates of corner frequency and low frequency spectral amplitude has been used to determine source parameters of 223 microearthquakes induced by hydraulic fracturing in granodiorite assuming a 2 source model the inversion fits the p wave spectra of microearthquake waveforms to determine individual values of corner frequency and low frequency spectral amplitude for each event and one average frequency independent q for all source receiver paths we also implemented a constraint that stress drops of all microearthquakes be similar but not equal and found that this constraint did not significantly degrade the quality of the fits to the spectra the waveforms analyzed were recorded by a borehole seismometer the p wave q was found to be 1070 for q values as low as 600 and as high as 3000 the misfit between model and spectra increased by less than 5 per cent and the average corner frequency changed by less than 15 per cent from those obtained with a q of 1070 average stress drop was 3 7 bars seismic moments obtained from spectra ranged from 1013 to 1018 dyne cm the low stress drops are interpreted to result from underestimation of the actual stress drops because of a nonuniform distribution of stress drop and slip along the fault planes spatially varying stress drops and slips result from the strong rock heterogeneity due to the injection of fluid into the rock stress drops were found to be larger near the edges of the seismic zone in regions that had not been seismically active during previous injections the seismic moments determined from spectra were used to obtain a coda length to moment relation then moments were estimated for 1149 events from measurements of coda lengths from events whose moments could not be measured from spectra because of saturation or a low signal to noise ratio the constant of proportionality between cumulative number of events and seismic moment is higher than that found for tectonic regions the slope is so high that the seismic energy release is dominated by the large number of small events in the absence of information about the number of events smaller than we studied we cannot estimate the total seismic energy released by the hydraulic injection

seismic precursors to the mount st helens eruptions in 1981 and 1982 six categories of seismic events are recognized on the seismograms from stations in the vicinity of mount st helens two types of high frequency earthquakes occur near the volcano and under the volcano at depths of more than 4 kilometers medium and low frequency earthquakes occur at shallow depths less than 3 kilometers within the volcano and increase in number and size before eruptions temporal changes in the energy release of the low frequency earthquakes have been used in predicting all the eruptions since october 1980 during and after eruptions two types of low frequency emergent surface events occur including rockfalls and steam or gas bursts from the lava dome

catena linking of landscape geochemical processes and reconstruction of pedosedimentogenesis a case study of defensive constructions of the mid 17th century south russia abstract the catena concept along with previously proposed meanings of this term has recently acquired a soil evolutionary content the prospects of wider special and chronological study of dated pedotopocatenas include the possibility of a more detailed analysis of the mutual dependence of soil geomorphological relationships through distinguishing relatively homogeneous climatic stages of pedogenesis and denudation with this purpose the present study comprised earthen defensive constructions which within the rampart ditch system combine erosive trans accumulative catenas and accumulators of pedolithosediments the goal was to develop a system of the most information rich pedogenetic indicators to reconstruct the dynamics of erosion accumulative processes on the basis of dated earthen defensive constructions of a historical period using the example of a frontier rampart within a ditch from the mid 17th century soil samples were collected within the limits of the erosion and trans accumulative catenas as well as in the closing alignment of the ditch over the vertical profile in eight strata of pedosediments of up to 1 m high the granulometric composition concentration of macroelements and trace elements 25 metals and oxides in soils and in particles with sizes 0 01 mm in size the content of organic carbon and its qualitative composition the sum of the elements accumulated in the soil p ca k mg mn cu as well as the geochemical ratios which reflect the processes of leaching can serve as palaeogeographic tracers of the climatic variability at the level of intra secular changes under forest steppe conditions the history of the formation of pedosediments over 3 5 centuries in the forest steppe zone of eastern europe comprises two wet periods 1890 1935 1976 2013 when the average annual rates of pedosedimentogenesis were similar 2 80 2 85 mm yr 1 and two periods of geomorphological lull and a xeromorphic climatic condition span 1821 1890 and 1666 1741 these periods correspond to diminution of the average rate of accumulation of sediments down to 2 47 mm yr 1 the results of the present study suggest the need for purposeful research and wide inclusion of dated sites of the anthropogenic relief formation with flow geochemical series over the topographic gradient into studies of soil geomorphologic interrelations and calibration of mathematic models of natural processes using on site data

volcanic tremors at etna a model for hydraulic origin spectral analysis of volcanic tremors at etna reveals 2 characteristic features 1 the escaping vapor and gas streams drive the magma in random turbulent motion generating a seismic wave emission according toa f n exp m f k wherea amplitude f frequency n m k parameters 2 sudden transients in the boundary conditions of the piping system generate hydraulic pressure pulses which in the seismogram appear as wave packages their monochromatic frequency content suggests that their origin is associated with strong resonance phenomena it is conclusive that volcanic eruptions may be distinguished and classified according to different eigenfrequencies of the fissure and pipe network involved in the volcanic activity furthermore positions of active dykes may be traced following the amplitude distributions associated with pronounced spectral lines in the tremor spectra

geometry of magma bodies beneath long valley california determined from anomalous earthquake signals one hundred and ninety two small earthquakes which occurred recently near the southern edge of long valley caldera at depths from 1 to 13 km are used to map the subsurface geometry of magma bodies in the caldera seismograms of these events recorded northwest north northeast and east of long valley with ray paths through the caldera are often anomalous in that s wave arrivals are absent and high frequency p wave energy is missing these anomalous ray paths intersect in an area of the south central caldera which we interpret to be a region of molten or partially molten rock this magma body lies between about 4 1 2 and at least 13 km depth and is 10 km long by 5 km wide beneath 7 km the magma appears to be relatively contiguous below 7 km and more dispersed above another magma body may be present in the northwest caldera coincident with an interpreted 7 8 km deep reflection from the top of a magma chamber

historical erosion and sedimentation in two small watersheds of the southern blue ridge mountains north carolina usa sediment bodies produced during historical periods of human land use sometimes referred to as legacy sediment may be found in various locations within drainage basins and potentially remobilized by hydrogeomorphic processes accompanying land use change the amounts and locations of stored legacy sediment can be significant factors in modern drainage basin function and should be accounted for when possible in this study late nineteenth century erosion and sediment storage were investigated and used to construct approximate sediment budgets for two small blue ridge mountain drainage basins in north carolina usa erosion was quantified using a distributed implementation of the universal soil loss equation usle and calibrated on the separate bases of soil profile truncation data and recent published rates for long term erosion in the region sediment yield information was reconstructed from pond sediments trapped behind a mill dam alluvial sediment storage was quantified using field studies of streambank and floodplain sediment profiles and digital elevation data colluvial storage was calculated as a residual in the sediment budget and further evaluated using soil profile studies of footslope deposits and soil survey maps the proportions of erosion accounted for by the different budget terms in the most reliable budget are 28 sediment yield i e a sediment delivery ratio of 0 28 69 colluvial storage and 3 alluvial storage blue ridge basins with low levels of ground disturbance erode like piedmont basins at high levels of ground disturbance primarily due to higher slope angles sediment delivery ratio is high relative to those given for much larger basins in the adjacent and more frequently studied piedmont province and generally in accordance with published sediment delivery curves that reflect higher hydrogeomorphic connectivities within smaller basins low values for alluvial storage in blue ridge basins may be explained by high sediment transport within steep channels colluvial storage values have high uncertainties because of the well known problem of error accumulation in residual budget terms field data on colluvial deposits reported here are not sufficient to correct for this problem and in general the acquisition of accurate field data on historical colluviation remains an important methodological issue in historical sediment budgeting

parameters and a magnitude moment relationship from small earthquakes observed during hydraulic fracturing experiments in crystalline rocks using source parameters estimated from seismic spectra and magnitudes estimated from coda lengths we demonstrate that the log linear relationship between moment and magnitude holds for events with magnitudes as low as 6 using as a data set events induced by hydraulic fracturing experiments at the fenton hill new mexico hot dry rock hdr geothermal site we find that the relationship between magnitude m and seismic moment mo is log mo 17 27 0 77m moreover the linear relationship between seismic moment and source radius r holds for the fenton hill microearthquakes analyses of the fenton hill data yield the following relationship log r 2 28 0 19log mo

ground motion in the near field of a fluid driven crack and its interpretation in the study of shallow volcanic tremor we present a study of the motion of the ground in the near field of a fluid driven tensile crack embedded in a layered half space the source that we consider is the jerky opening of a channel connecting two fluid filled cracks and the cause of this opening is the excess pressure of fluid in one of the cracks we make a complete representation of the three components of ground motion in the space time and frequency domains and analyze the effects of fluid compressibility source depth and medium structure on the ground response the calculations show the presence of a dominant frequency of motion which depends not only on the source geometry and bulk modulus of the fluid but also on medium characteristics receiver position and the component of motion being considered using this source model we view an episode of volcanic tremor as a continuous sequence produced by numerous jerky openings of channels occurring randomly in time along a chain of cracks our results are applied to the october 5 6 1963 east rift eruption of kilauea volcano hawaii and found to be compatible with available seismic data suggesting that magma is transported through an ensemble of cracks with the area of 1 1 km each pair of cracks constituting an individual dike segment which opens in discrete increments at a rate of 1 s we obtain the following parameters for each dike segment opening increase in cavity volume 40 m3 stress drop 0 004 bar seismic moment 1019 dyn cm and force applied by the fluid to open the dike 1014 dyn the total moment integrated over the entire duration of tremor for the eruption is 0 5 1024 dyn cm roughly equivalent to a single magnitude m 5 earthquake the seismic source parameters and other field observations offer constraints on the process of mass transport and are compatible with the excess pressure and viscosity of magma of about 40 bars and 102 p respectively

the waveguide effect of metastable olivine in slabs we use a finite difference algorithm to compute p sv synthetic seismograms for deep earthquakes recorded at regional seismic stations located above a subducting slab we calculate synthetics for 2 d slab models in which the 410 km discontinuity is uplifted owing to the exothermic nature of the transition the equilibrium model and models in which the 410 km discontinuity is depressed owing to inhibited kinetics of the olivine transition the metastable model in the latter case the existence of the low velocity wedge of metastable olivine has a profound influence on the waveforms of deep focus earthquakes the wedge acts as a geometrical waveguide with the energy focusing effect apparent even after the wavefront has traveled the several hundred kilometers from the wedge boundary to the earth s surface the guided energy is most pronounced for receivers located near the surface projection of the deep slab but is observable over a range of 300 km and so may provide a valuable diagnostic for discriminating between equilibrium and metastable models of subduction a recent search for such guided energy using regionally recorded p and s waves from deep events in tonga yielded negative results

variability in fluvial geomorphic response to anthropogenic disturbance abstract humans have greatly impacted the processes and intensities of erosion sediment transport and storage since the introduction of agriculture in many regions around the world accelerated floodplain sedimentation can be related to increases in human pressure on the environment however the relation between the intensity of anthropogenic disturbance and the magnitude of change in fluvial sediment dynamics is not straightforward and often non linear here we review a number of case studies from contrasting environmental settings in the european loess belt the eastern mediterranean mountain ranges and the eastern usa detailed field based sediment archive studies and sediment budgets covering time periods ranging from 200 to over 5000 year as well as the use of pollen and sediment provenance techniques show that no overarching concept of changes in floodplain sedimentation following anthropogenic disturbance can be established slope channel dis connectivity controls the existence of thresholds or tipping points that need to be crossed before significant changes in downstream sediment dynamics are recorded following human impact this coupling can be related to characteristics of human pressure such as its duration intensity and spatial patterns but also to the geomorphic and tectonic setting furthermore internal feedback mechanisms such as those between erosion and soil thickness further complicate the story all these factors controlling the propagation of sediment from eroding hillslopes to river channels vary between regions hence only unique patterns of fluvial geomorphic response can be identified as a result unravelling the human impact from current day sediment archives and predicting the impact of future human disturbances on fluvial sediment dynamics remain a major challenge this has important implications for interpreting contemporary sediment yields as well as downstream sediment records in large floodplains deltas and the marine environment in terms of changes in the drivers of environmental change