regional moment tensor inversion for strong aftershocks of the august 17 1999 izmit earthquake mw 7 4 we analyzed the source mechanisms of the thirty largest aftershocks 4 0 ml 6 2 of the august 17 1999 izmit earthquake mw 7 4 by applying the regional moment tensor inversion method using data from near regional broadband stations the inversion solutions were compared to 17 well constrained first motion solutions and were seen to be in good agreement we found that the dominance of strike slip motion is the main characteristic of the izmit earthquake sequence significant aftershock activity was recorded to the west and east of the un ruptured extremities in the east the aftershocks located near the town of duzce represent an early replica of the november 12 1999 duzce earthquake mw 7 2 in terms of locations and source mechanisms in the marmara sea where the fault geometry is still very poorly resolved most aftershocks have right lateral strike slip solutions with strike direction parallel to the submerged branches of the north anatolian fault

strong ground motion and damage in the taipei basin from the moho reflected seismic waves during the march 31 2002 hualien taiwan earthquake 1 the march 31 2002 hualien offshore earthquake ml6 8 mw7 0 caused minor damage near its epicenter but significant damage in taipei about 110 km from the epicenter the recorded pga values around the taipei basin vary in a factor of 5 the high pga values in the southeastern part of the basin correspond to the most significant damage area during the earthquake strong ground motion recordings from this event recorded at stations around the taipei basin exhibit several distinct large amplitude seismic arrivals that can be interpreted as the pmp smp and sms phases the largest amplitude of the critically reflected s wave from the moho sms and the amplification of soft shallow sediments unique for each site are responsible for the maximum peak ground motion and the significant damage in the taipei basin during the hualien offshore earthquake

more than ten years of lusi a review of facts coincidences and past and future studies abstract the lusi mud eruption in east java indonesia has continued unabated for more than ten years with no end in sight this review summarizes what has been learned about this intriguing system from its inception to the current 2017 well established metastable geysering system that continuously erupts mud breccia gas steam and water we discuss the initiation of lusi highlighting discrepancies and evidence through the published data to build a comprehensive database that emphasizes how the results converge towards a natural scenario of this system we argue that attempts to understand constrain or predict the behaviour of this system that rely on a drilling trigger can not explain subsequent observations on the other hand we show that a well constrained conceptual model recognizing lusi as a volcanically linked hydrothermal system has provided important insights for the documented observations over the last eleven years the response of lusi to the yogykarta earthquake falls directly within the range of earthquake triggering phenomena globally of similar hydrothermal geothermal systems suggesting a natural trigger as the more likely culprit for the lusi phenomenon we also offer some future directions of additional scrutiny for understanding this newborn tectonic scale volcanic hydrothermal complex

incised channels and gully erosion in northern iberian peninsula controls and geomorphic setting abstract gully erosion has scarcely been reported in the cantabrian cordillera northern iberian peninsula even though this phenomenon is relatively frequent in this mountain range a total of 133 permanent channels with evidences of gully erosion have been mapped in a 71 8 km2 study area on the northern slope of this mountain range the underlying ordovician unit comprises quartzite sandstone and slate which are partially mantled by different surficial deposits the relief is fairly steep with average slopes of 27 and hillsides with level drops of the order of 700 m and generally vegetated by atlantic heaths a result of the degradation suffered by the natural vegetation following forest fires the mapped channels present different morphological features shallow and deep channels some of them with associated ravines and are usually related to headcut in first and second order pre existing channels although some of them are located on unchanneled hillsides with no evidence of pre existing channels moreover lower reaches of first and second order channels are often incised into bedrock a field description and morphometric study has been carried out on channels affected by gully erosion based on their cartography digital terrain models and several layers of thematic mapping this study describes some of the relations between relief factors the type of substratum and the development of gully erosion i there are robust correlations between morphometry relief and erosion intensity and ii gullying is strongly influenced by the presence of a deep regolith the erosion forms observed and the described relations suggest that gully development is associated to landsliding processes which are ultimately controlled by ground water movement through a porous regolith regional uplift and deforestation are argued to be the most likely causes of channel incision and gullying

a study of crustal and upper mantle structure of northwestern turkey the crustal thickness and uppermost mantle p wave velocity at several seismic stations in northwestern turkey were estimated using the established travel time distance relation method the data suggest a flat layered crust of average thickness 28 4 3 45 km with an average uppermost mantle p wave velocity of 8 05 0 17 km s this is similar to results obtained for the north aegean sea and suggests a close structural link between the two areas

s wave attenuation in the sea of marmara turkey abstract this paper presents the estimates of frequency dependent attenuation of s waves for five different regions of the crust in the sea of marmara the estimation method for the s wave attenuation is based on the rate of decay of the s wave to coda wave amplitude ratio with distance qs 1 the epicentral distances of the selected earthquakes are between 15 and 70 km and the duration magnitudes are between 2 4 and 3 9 the quality factors qs are calculated at frequencies 1 5 3 6 and 12 hz and a lapse time 50 s the frequency dependency of average qs values calculated at these frequencies for five regions is 40 5f1 03 0 06 the estimated qs values for five regions ranging from 13 1f1 22 0 05 to 94 3f0 83 0 04 indicate the regional differences in the rheology and tectonic activity of the crust

geomorphic threshold conditions for ephemeral gully incision abstract ephemeral gully erosion in cultivated land is an important source of sediment that is frequently being overlooked and not accounted for in soil erosion studies furthermore little is known about the factors controlling ephemeral gully erosion in this paper the available information on the initiation and location of ephemeral gullies is summarised focusing on the relationship between the upslope drainage area a and the critical slope gradient s cr for ephemeral gully initiation by plotting the non linear relationship between critical slope gradient measured immediately upstream of the incision head and drainage area at the incision head for gullied sites it was possible to draw a straight line on log log paper through the lower most points for each of the available datasets representing a critical slope area relationship for incision consequently below this line no incision occurs this line or critical relation can also be written as a power function between critical slope and area although many factors vary between the different datasets the exponent of the drainage area relationship 0 4 showed very little variation the observed critical slope area relationship can be related to a simple model of channel initiation by overland flow furthermore this relationship can be used to identify potentially unstable sites where control measures should be undertaken

topographic controls on glacier sediment landform associations around the temperate north patagonian icefield topographic controls on glacier sediment landform associations around the temperate north patagonian icefield

catchment scale analysis of the effect of topography tillage direction and unpaved roads on ephemeral gully incision high resolution airphotographs and digital elevation models dems were used to study areas prone to gully incision in a small agricultural catchment in northern israel data are analyzed to understand better the integrated effect of environmental and human factors on gully incision the effect of flow accumulation slope unpaved roads density and tillage direction on gully width and length is found discontinuous and topography in the form of the topographic threshold was found to be the most dominant factor on gully incision in the catchment scale the topographic threshold coefficients observed in yehezkel catchment were lower than those found in previous studies due to the effect of large rainfall events during the early winter season when the soil in fields is still unprotected by crops in addition a survey of previous studies shows that in cultivated areas there is relationship between the topographic threshold coefficients a multiplier and b exponent the influence of unpaved roads and tillage direction on gully incision was also found significant and consistent during the two seasons observed while the non parametric test showed that it added to the prediction in 15 of the gullies incision points density plot show that of the two parameters the unpaved roads were found to have greater influence on gully head location than tillage direction studying the phenomenon on the catchment scale allows better understanding of the effect of spatial variation on gully head location copyright 2009 john wiley sons ltd

the effect of the subglacial water pressure on the sliding velocity of a glacier in an idealized numerical model in order to interpret observed short term variations of the sliding velocity of a glacier the effect of a variable subglacial water pressure on the sliding velocity has been studied using an idealized numerical model in particular the transient stages of growing or shrinking water filled cavities at the ice bedrock interface were analysed it was found that the sliding velocity was larger when cavities were growing than when they had reached the steady state size for a given water pressure the smallest sliding velocities occurred while cavities were shrinking when cavitation is substantial a small drop of water pressure below the steady state value e g by 0 5 bar can temporarily cause backward sliding a limiting water pressure at which sliding becomes unstable is derived the consequences of more realistic assumptions than those of the model are discussed

crustal attenuation characteristics in northwestern turkey in the range from 1 to 10 hz we have analyzed the aftershocks m l 4 5 following the 1999 izmit earthquake m w 7 4 to infer the frequency dependent attenuation characteristics of both p and s waves in the frequency range from 1 to 10 hz and in the distance range from 10 to 140 km a linear predictive model is assumed to describe the spectral amplitudes in terms of attenuation and source contributions the results show that both p and s waves undergo a strong attenuation along ray paths shorter than 40 km while the secondary arrivals significantly contribute to the spectral amplitudes over the distance range from 40 to 60 km as also confirmed by the computation of synthetic seismograms for longer ray paths the decrease in attenuation suggests an increase in the propagation efficiency with depth finally the spectral attenuation curves are flattened or sloped upward at low frequencies in the range from 100 to 140 km due to the contemporary arrivals of direct waves and postcritical reflections from the moho in terms of geometrical spreading and anelastic attenuation the attenuation in the range from 10 to 40 km is well described by a spreading coefficient n 1 for both p and s waves and the quality factors can be approximated by qs f 17 f 0 80 for 1 f 10 hz and qp f 56 f 0 25 for 2 5 f 10 hz for ray paths in the range from 60 to 80 km the attenuation weakens but the interaction between seismic waves and propagation medium is more complex the multilapse time window analysis mltwa is applied to quantify the amount of scattering loss and intrinsic absorption for s waves the seismic albedo b decreases from 0 5 at 1 hz to 0 3 at 10 hz while the total quality factor qt increases from about 56 to 408 the multiple lapse time window analysis mltwa results provide only an average estimate of the attenuation properties in the range from 10 to 80 km in fact by neglecting the variation of attenuation with depth the mltwa results underestimate attenuation for distances less than 40 km and do not capture the significant features caused by the integrated energy of the secondary arrivals observed in the range from 40 to 60 km

two dimensional modelling of the within field variation in rill and gully geometry and location related to topography abstract the topography rill pattern and geometry were surveyed within a small agricultural field the rill network and dimensions were converted to a grid based system and used to calculate the slope gradient and contributing area for each grid cell a strong correlation was found between the rill cross sections and a power function of slope gradient and contributing area the slope and area exponents were 1 28 and 0 89 respectively for all rill points and 1 02 and 0 87 respectively for the rill points not lying in the depositional area these exponents are within the range reported for field studies in a one dimensional context our data confirmed the potential of an inverse slope area relationship with an area exponent of 0 5 to predict areas prone to rilling and the location of ephemeral gullies however the prediction of individual rill starting points was not possible because of the major influence of small local variations in topography on overland flow discharge both the prediction of the rill cross sections and the prediction of the location of the two ephemeral gullies in the field were significantly improved when the tillage direction was taken into account in calculating the contributing area therefore tillage patterns should be given more attention when developing routing procedures for hydrological and erosion models

enhanced ground motions due to large amplitude critical moho reflections sms in the sea of marmara turkey 1 aftershocks of the 17 august 1999 mw 7 4 kocaeli earthquake were used to investigate the large amplitude sms arrivals in the sea of marmara we produced the event record sections from the transverse components of s and sms arrivals at a distance of 10 to 200 km for the data recorded towards the east and west in the sea of marmara for the data recorded towards the west we observed that the amplitude of sms phases enhances the ground motion by a factor of 2 to 3 the dipping moho and or anisotropy in the upper mantle or deep convex structure or deep lens are possible sources for the large amplitude sms phases since the study area has a potential of creating damaging earthquakes in the future the effect of large amplitude sms phases on the ground motion should be considered in the studies of the seismic hazard of the region

eco geomorphic implications of hillslope aspect inferences from analysis of landscape morphology in central new mexico 1 we investigate the influence of hillslope aspect on landscape morphology in central new mexico where differences in soils vegetation and landforms are observed between mesic north facing and xeric south facing slopes slope area and curvature area relations derived from a digital elevation model dem are used to characterize the opposing hillslope morphologies in all geologies and elevation ranges studied topographic data reveal significantly steeper slopes in north facing aspects and shallower slopes in south facing aspects north facing slope curvatures are also greater than south facing curvatures using a conceptual slope area model we suggest that for a given drainage area steeper north facing slopes imply lower soil erodibility we argue that this interpretation consistent with recent views of ecosystem control on semiarid erosion rates shows the influence hillslope aspect on topography and its associated vegetation communities observed valley asymmetry in the region reinforces this concept and suggests a long term legacy of aspect modulated ecogeomorphic processes

reflected seismic waves and their effect on strong shaking during the 1989 loma prieta california earthquake our data indicate that critical and postcritical reflections from crustal layers and the moho produced increased shaking at discrete distances along the san francisco peninsula during the 1989 loma prieta earthquake these reflections may have produced an increase in amplitude that is as much as 10 times greater than that of the direct arrival peak amplitude distance patterns measured from explosive sources synthetic seismograms aftershocks and the mainshock of the 1989 loma prieta earthquake indicate that 1 point sources such as explosions produce similar peak amplitude distance relations as distributed double couple sources when the crustal structure is approximately a poisson solid 2 peak amplitudes from smaller point sources explosions may be scaled to those of larger sources earthquakes and 3 reflections caused a pattern of high amplitudes at specific distances along the san francisco peninsula that geographically correlates with areas of reported damage following from the loma prieta mainshock our study indicates that critical and postcritical reflections were stronger influences on the locations of strong shaking than local geology because a number of sites around the san francisco bay that are underlain by unconsolidated sediments experienced much less shaking than sites that were underlain by hard rock furthermore some severely shaken hard rock sites were farther from the epicenter than many of the less severely shaken soft sediment sites models of the regional crustal structure and seismic wave propagation paths may be useful in identifying sites around the san francisco bay region that are at risk due to reflected seismic energy and this type of analysis may be useful in other seismically active regions

regional wave propagation in turkey and surrounding regions this paper was published by the american geophysical union agu copyright 2000 agu see also http www agu org journals gl gl0003 1999gl008375 pdf 1999gl008375 pdf http atlas geo cornell edu turkey publications gok et al 2000 htm

s wave attenuation in the marmara region northwestern turkey the frequency dependent attenuation of shear waves in the crust is estimated by using two different methods based on the rate of time decay of coda wave amplitude qc 1 and the rate of decay of the s wave to coda wave amplitude ratio with distance qs 1 the epicentral distances of selected earthquakes range between 20 and 110 km and magnitudes are around 3 the quality factors qc are calculated at frequencies of 1 5 3 6 12 and 24 hz and lapse times of 40 50 60 and 70 s estimated qc values show a dependence on frequency and lapse time we observed the similarity in the frequency dependency of qc 41 1 07 f1 08 0 03 and qs 50 1 7 f1 09 0 05 for a lapse time of 50 s indicating that the attenuation mechanism for coda waves is similar to that of the direct s waves

ground motion scaling in the marmara region turkey summary predictive relationships for the ground motion in the marmara region northwestern turkey are parametrized after regressing three component waveforms from regional earthquakes in the frequency range 0 4 15 0 hz and in the distance range 10 200 km the data set consists of 2400 three component recordings from 462 earthquakes recorded at 53 stations moment magnitudes m w range between 2 5 and 7 2 the largest event for which we have waveforms available m w 7 2 occurred in duzce on 1999 november 12 the aftershocks of that earthquake together with the aftershocks of the 1999 august 17 izmit event m w 7 4 are included in the dataset regressions are performed independently on fourier velocity spectra and on peak ground velocities for a large number of sampling frequencies a simple model is used to relate the logarithm of the measured ground motion to excitation site and propagation terms results obtained for peak velocities are used to define a piecewise continuous geometrical spreading function g r a frequency dependent q f and a distance dependent duration function the latter is used through random vibration theory rvt in order to predict time domain characteristics i e peak values of the ground motion the complete model obtained for the peak ground motion was used to match the results of the regressions on the fourier amplitudes fourier velocity spectra for the combined horizontal motion are best fit by a hinged quadrilinear geometrical spreading function for observations in the 10 200 km hypocentral distance ranges as a function of frequency f 100 f 1 0 hz r 1 0 for r 30 km r 0 6 for 30 100 km the frequency dependent crustal shearwave quality factor q f coefficient q f 180 f 0 45 the t 5 75 per cent duration window provides good agreement between observed and predicted peak values by modelling the behaviour of the small earthquakes at high frequency we also quantified a regional parameter 0 055 s spectral models with one single corner frequency brune and with two corner frequencies atkinson and silva fit the observed high frequency excitation levels equally well whereas the model by atkinson and silva fits the low frequency observations slightly better than brune s rvt is used to predict the absolute levels of ground shaking following boore s implementation of the stochastic ground motion model boore s smsim codes our regional empirical predictive relationships are compared to the ones adopted in several regions of the world from california to western united states

scale effects on the estimation of erosion thresholds through a distributed and physically based hydrological model abstract slope incision and subsequent development of rills gullies and channels are responsible for significant soil losses and are often irreversible with very high restoration costs particularly in semiarid environments the location of potential areas of erosion where these processes occur is vital to land management and conservation the study of the relationship between the local slope s and the drainage area a through the geomorphological relationship s a b combined with hydrologic simulation models has proved to be appropriate for the identification and characterisation of potential areas of incision especially when it takes into account the spatial distribution of soil properties and the evolution of hydrological processes however physical properties of soil digital elevation models dems and flow algorithms used may affect the results this study employs a distributed physically based hydrological model to evaluate the infiltration runoff relationships and their influence on selecting critical area from three dems with different resolutions the results show a significant scale effect on flow distribution and the location of threshold points on slopes the results obtained from a 30 m dem significantly differ from those obtained from 10 and 5 m dems because the former was unable to capture the spatial variability of geomorphic processes the selected set of critical points shows high s a correlations for different values of critical shear stress the physical model confirmed the dominance of surface runoff in the study site and was validated from field identification of erosion risk areas although for incision areas

dem based modelling of surface runoff using diffusion wave equation a digital elevation model dem based overland flow routing model was developed for computation of surface runoff for isolated storm events the model operates on a grid or cell basis and routes the rainfall excess generated over the cells following the dem derived drainage paths to the catchment outlet the rainfall excess for each cell of the catchment was computed using the philip two term infiltration model utilizing the physical properties of the cell the overland flow was described by a finite volume based numerical solution of the diffusion wave approximation of the st venant equations the cell physical properties such as topographic characteristics land use soil etc were extracted from published maps for discretized cells of the catchment using a geographic information system the results of model application indicate that the model satisfactorily predicted the runoff hydrograph the cell based structure of the model allowed for generation of spatially distributed catchment information in terms of the model computed variables such as the depth of flow and discharge

the effect of crustal structure on strong ground motion attenuation relations in eastern north america strong ground motion attenuation relations are usually described by smoothly decreasing functions of distance however consideration of wave propagation in the crust suggests that attenuation relations should be more complex such complexity may be present in strong ground motion data for eastern north american earthquakes which show amplitudes in the distance range of 60 to 150 km that lie above the trends at smaller and greater distances using a wavenumber integration method to compute green s functions and close in recordings of several earthquakes as empirical source functions we have generated synthetic seismograms that are in good agreement with regional and strong motion recordings of eastern north american earthquakes from these synthetic seismograms we have shown that the observed interval of relatively high amplitudes may be attributable to postcritically reflected s waves from the moho the presence and location of the interval of relatively high amplitudes is highly dependent on the crustal velocity structure and may therefore be expected to show regional variation however for any realistic structure model there will be a transition in the attenuation relation from an interval at shorter distances less than about 100 km that is dominated by direct waves to an interval at greater distances that is dominated by postcritically reflected waves the synthetic seismograms have response spectral velocities that match those of the recorded data and their m blg values are in good agreement with observed values

the contribution of postcritical moho reflections sms to ground motions of the 2008 mw 7 9 wenchuan earthquakethe contribution of postcritical moho reflections sms to ground motions

first surface velocity maps for glaciers of monte tronador north patagonian andes derived from sequential pleiades satellite images we apply cross correlation to pleiades satellite images to generate accurate high resolution monthly surface velocity maps of monte tronador glaciers between march and june 2012 measured surface displacements cover periods as short as 19 days with a precision of 0 58 m 11 m a 1 these glaciers follow a radial flow pattern with maximum surface speeds of 390 m a 1 associated with steep icefalls the lower reaches of the debris covered tongues of verde and casa pangue glaciers are almost stagnant whereas ventisquero negro another debris covered glacier shows acceleration at the front due to calving into a proglacial lake low elevation debris covered glacier tongues show increasing velocities at the beginning of the accumulation season whereas higher elevation clean ice tongues reduce their speed during this period this contrasting behavior is probably in response to an increase in water input to the subglacial system from winter rainfall events at low elevations and a decrease in meltwater production at higher elevations these sequential velocity maps can help to identify the controls on glacier surface velocity aid in the delimitation of ice divides and could also contribute to more realistic calibration of ice flux mass balance models in this glacierized area

ice motion of the patagonian icefields of south america 1984 2014 2015 american geophysical union all rights reserved we present the first comprehensive high resolution mosaic of ice velocity of the northern npi and southern patagonian icefields spi from multiple synthetic aperture radar and optical data collected between 1984 and 2014 the results reveal that many of the outlet glaciers extend far into the central ice plateaus which implies that changes in ice dynamics propagate far inside the accumulation area we report pronounced seasonal to interannual variability of ice motion on pio xi and jorge montt a doubling in speed of jorge montt a major slow down of o higgins significant fluctuations of upsala and a deceleration of san rafael which illustrate the need for sustained continuous time series of ice motion to understand the long term evolution of the rapidly thinning icefields the velocity product also resolves major ambiguities in glacier drainage in areas of relatively flat topography illustrating the need to combine topography and flow direction to map drainage basins

flow resistance and sediment transport by concentrated overland flow in a grassland valley abstract flow resistance and sediment transport data are needed from well vegetated humid environments to evaluate surface wash erosion and channel incision by overland flow in humid environments runoff in valley floors can reach depths of several centimetres but erosion is often limited by dense grass cover intense grazing reduces grass cover but the impacts of this on sediment transport processes are poorly understood we conducted flume experiments in a grassed valley of coastal california to investigate flow resistance and sediment yield under natural conditions and with progressive clipping of grass cover flow resistance has a laminar like relationship with reynolds number but we attribute this to very low velocity beneath submerged stems and not to the state of flow the sediment transport relations provide support for the concept of a threshold shear stress below which erosion is effectively prevented by surface resistance shear stress partitioning suggests that on a densely grassed surface over 90 of flow resistance is exerted on plant stems this effectively prevents sediment transport at boundary shear stresses as high as 1000 1800 dyn cm2 complete clipping of the grass cover reduces the critical shear stress for sediment transport to 11 38 of that under natural conditions continued surface wash erosion and channel initiation are prevented however by strong soil cohesion provided by a dense root mat even with reduction of root density boundary shear stresses of at least 250 430 dyn cm2 are required for channel incision

short term variations in glacier flow controlled by subglacial water pressure at lauteraargletscher bernese alps switzerland short term variations in horizontal and vertical surface motion were studied with high temporal resolution during the ablation season in lauteraargletscher bernese alps switzerland horizontal surface flow speed oscillated diurnally showing a correlation with the water level in a borehole flow speed increased as a function of the water level with an asymptote at the ice overburden level this observation implied that the flow variations were principally controlled by the local water pressure which enhanced basal motions detailed examination of the diurnal variations however showed that the speed was larger when the pressure was increasing than when it was decreasing greater speed with increasing pressure was interpreted by subglacial watercavity opening and or longitudinal stress coupling with the upper reaches of the glacier upward surface movements were observed when the glacier flow speed increased simultaneous measurement of internal vertical strain in a borehole showed that the uplift had two different sources vertical straining of ice and volume increase of subglacial water cavities the vertical surface movement was largely affected by the vertical strain and the uplift events could not be simply attributed to cavity opening

an advance of soler glacier north patagonian icefield at c ad 1222 1342 soler glacier is a temperate outlet glacier on the eastern side of the north patagonian icee eld in chile the glacier is currently receding from its little ice age maximum position attained sometime between ad 1600 and 1900 across the snout and foree eld of the glacier is an arcuate belt of well sorted granule gravel and coarse sand containing tree remains these sediments are interpreted as reworked glaciolacustrine material elevated to the glacier surface by thrusting and folding radiocarbon dating of samples of tree remains in these reworked glaciolacustrine sediments demonstrates that the glacier overrode this lake bed sometime between ad 904 and ad 1334 in situ tree remains plastered onto a large boulder in front of the glacier constrain this advance to the period between ad 1222 and ad 1342 this advance precedes by several hundred years the maximum little ice age extent of other north patagonian icee eld outlet glaciers suggesting either an early age for the onset of little ice age conditions or a previously unrecognized period of glacier advance prior to the advance at c ad 1222 to ad 1342 soler glacier was more recessed than at present cone rming the dynamic response of patagonian glaciers to holocene climatic e uctuations

hillslope to valley transition morphology new opportunities from high resolution dtms abstract the search for the optimal spatial scale for observing landforms to understand physical processes is a fundamental issue in geomorphology topographic attributes derived from digital terrain models dtms such as slope curvature and drainage area provide a basis for topographic analyses the slope area relationship has been used to distinguish diffusive hillslope from linear valley processes and to infer dominant sediment transport processes in addition curvature is also useful in distinguishing the dominant landform process recent topographic survey techniques such as lidar have permitted detailed topographic analysis by providing high quality dtms this study uses lidar derived dtms with a spatial scale between 1 and 30 m in order to find the optimal scale for observation of dominant landform processes in a headwater basin in the eastern italian alps where shallow landsliding and debris flows are dominant the analysis considered the scaling regimes of local slope versus drainage area the spatial distribution of curvature and field observations of channel head locations the results indicate that i hillslope to valley transitions in slope area diagrams become clearer as the dtm grid size decreases due to the better representation of hillslope morphology and the topographic signature of valley incision by debris flows and landslides is also best displayed with finer dtms ii regarding the channel head distribution in the slope area diagrams the scaling regimes of local slope versus drainage area obtained with grid sizes of 1 3 and 5 m are more consistent with field data and iii the use of thresholds of standard deviation of curvature particularly at the finest grid size were proven as a useful and objective methodology for recognizing hollows and related channel heads

the 20th century advance of glaciar pio xi chilean patagonia glaciar pio xi the largest glacier in south america has experienced an advance during the 20th century unlike virtually all other glaciers in patagonia which are retreating rapidly climatological records of the last 80 years are analyzed together with ice velocity and meteorological measurements collected during november 1995 near the tidewater front of glaciar pio xi ice speeds of up to 50 m d 1 were measured the maximum occurring during a period when air temperatures were high

critical shear stress for erosion of cohesive soils subjected to temperatures typical of wildfires received 26 february 2004 revised 15 september 2004 accepted 5 november 2004 published 22 january 2005 1 increased erosion is a well known response after wildfire to predict and to model erosion on a landscape scale requires knowledge of the critical shear stress for the initiation of motion of soil particles as this soil property is temperature dependent a quantitative relation between critical shear stress and the temperatures to which the soils have been subjected during a wildfire is required in this study the critical shear stress was measured in a recirculating flume using samples of forest soil exposed to different temperatures 40 550 c for 1 hour results were obtained for four replicates of soils derived from three different types of parent material granitic bedrock sandstone and volcanic tuffs in general the relation between critical shear stress and temperature can be separated into three different temperature ranges 275 c which are similar to those for water repellency and temperature the critical shear stress was most variable 1 0 2 0 n m 2 for temperatures 2 0 n m 2 between 175 and 275 c and was essentially constant 0 5 0 8 n m 2 f or temperatures 275 c the changes in critical shear stress with temperature were found to be essentially independent of soil type and suggest that erosion processes in burned watersheds can be modeled more simply than erosion processes in unburned watersheds wildfire reduces the spatial variability of soil erodibility associated with unburned watersheds by eliminating the complex effects of vegetation in protecting soils and by reducing the range of cohesion associated with different types of unburned soils our results indicate that modeling the erosional response after a wildfire depends primarily on determining the spatial distribution of the maximum soil temperatures that were reached during the wildfire

waves of accelerated motion in a glacier approaching surge the mini surges of variegated glacier alaska u s a periods of dramatically accelerated motion in which the flow velocity increases suddenly from about 55 cm d to a peak of 100 300 cm d and then decreases gradually over the course of a day occurred repeatedly during june and july 1978 81 in variegated glacier alaska a surging type glacier that surged in 1982 83 these mini surges appear to be related mechanistically to the main surge the flow velocity peak propagates down glacier as a wave at a speed of about 0 3 km h over a reach of about 6 km in length it is accompanied by a propagating pressure wave in the basal water system of the glacier in which after a preliminary drop the pressure rises rapidly to a level greater than the ice overburden pressure at the glacier bed and then drops gradually over a period of 1 2 d usually reaching a new low for the summer the peak velocity is accompanied by a peak of high seismic activity due to widespread fresh crevassing it is also accompanied by a rapid uplift of the glacier surface amounting to 6 11 cm which then relaxes over a period of 1 2 d maximum uplift rate coincides with the peak in flow velocity the peak in accumulated uplift lags behind the velocity peak by 2 h the uplift is mainly due to basal cavitation driven by the high basal water pressure although the strain wave associated with the mini surge motion can also contribute basal cavitation is probably responsible for the pulse of high turbidity that appears in the terminal outflow stream in association with each mini surge in the down glacier reach where the mini surge waves are attenuating the observed strain wave corresponds to what is expected for the propagating pulse in flow velocity but in the reach of maximum mini surge motion the strain wave has a form quite different possibly related to special features in the mini surge initiation process from that point up stream the flow acceleration in the mini surges is due to enhanced basal sliding caused by the high basal water pressure and the consequent reduction of bed friction a preliminary velocity increase shortly before the pressure wave arrives is caused by the forward shove that the main accelerated mass exerts on the ice ahead of it and the resulting preliminary basal cavitation causes the drop in water pressure shortly before the pressure wave arrives the mini surge wave propagation is controlled by the propagation of the water pressure wave in the basal water conduit system the propagation characteristics result from a longitudinal gradient up glacier increase in hydraulic conductivity of the basal water system in response to the up glacier increase of the basal water pressure in the mini surge wave the mini surge waves are initiated in a succession of areas situated generally progressively up glacier during the course of the summer season in these areas presumably melt water that has accumulated in subglacial reservoirs is released suddenly into the basal water system immediately below generating a pressure rise that propagates down stream from there relationships of the mini surges to the main surge are seen in the role of high basal water pressure in causing the rapid glacier motion in both phenomena in the pulse propagation features of both and in the high outflow turbidity associated with both the mini surges of variegated glacier have a strong resemblance to movement and uplift events observed in unteraargletscher and findelengletscher switzerland this bears on the question whether the mini surges are a particular characteristic of surge type glaciers prior to surge

the north anatolian fault within the sea of marmara a new interpretation based on multi channel seismic and multi beam bathymetry data abstract we analyze 2200 km of multi channel seismic reflection profiles that have become recently available in the sea of marmara this analysis benefits from the recent acquisition of multi beam bathymetric data covering the axial portion of the northern basins we conclude that the northern sea of marmara is at present cut by an active continuous strike slip fault system that we call the marmara fault it links the 270 izmit portion of the northern branch of the north anatolian fault to the east of the sea to the 245 ganos fault to the west the marmara fault itself consists of two main parts the western one is a single 80 km long fault it follows a 265 direction that differs by 20 from the direction of the ganos fault at its northeastern extremity it turns toward the northern margin of the cinarcik basin this western part of the fault is seismically quite active the eastern part is more complex it extends over 65 km in a 280 direction there is thus a 10 clockwise rotation with respect to the 270 izmit fault strand that should result in a slight extensional component within the eastern cinarcik basin this part of the marmara fault has two parallel branches 10 km apart the northern one near the foot of the northern slope the southern one near the foot of the southern slope a shortening zone occupies the northwestern corner of the cinarcik basin and much of the adjacent eastern central high and separates the northern branch from the western one the southern branch on the other hand may cross the eastern central high along a narrow 280 valley the data we have provide no definitive evidence on which of these two branches carries most of the motion the establishment of the present trace of the fault through the marmara basin is contemporaneous with a recent phase of deposition of deep giant ripples parallel to the bathymetric slope contours and adjacent to the turbidites basin deposits the base of these deep basins sedimentary deposits is marked by a widespread erosional unconformity below which lies a gently folded sedimentary sequence that may consist of shallow thrace basin deposits

surface strain anomaly induced by the storage and drainage of englacial water in koryto glacier kamchatka russia to investigate short term flow pattern variations of a temperate glacier longitudinal surface strain was measured with a wire strainmeter in the ablation area of koryto glacier kamchatka russia strain rate anomalies were observed in late summer 2000 that were triggered by a water overflow from a moulin near the measurement site followed by the drainage of accumulated water the strain event started with compressive strain rates of 10 3 d 1 lasting for 6 hours which then became tensile similar strain rate variations were observed again on the next day during the event basal sliding speed measured at the margin in the lower reach of the glacier fluctuated by about 50 of the daily mean smaller and larger sliding speeds corresponded to the compressive and tensile surface strains respectively these measurements suggest that the storage and sudden drainage of water caused spatially non uniform water pressure fluctuations along the glacier changing the sliding regime over short time periods

on the effect of digital elevation model accuracy on hydrology and geomorphology this study compares published cartometric and photogrammetric digital elevation models dems of various grid spacings with a ground truth data set obtained by ground survey and studies the implications of these differences on key hydrologic statistics inferred catchment sizes and stream networks from published dems were found to be significantly different than those from the ground truth in most instances furthermore the width functions and cumulative area relationships determined from the published dems were found to fall consistently outside the 90 confidence limits determined from the ground truth for more than 60 of the relationship suggesting that these hydrologic properties are poorly estimated from published dems however the slope area relationships determined from published dems were found to be less sensitive to catchment shape size and stream network with the relationship falling outside the 90 confidence limits for less than 40 of the relationship for all catchments identified from the published dems a published relationship linking the horizontal resolution with the vertical accuracy of the dem was tested predicting a horizontal resolution of about 10 m for the published dems tested

predicting the topographic limits to a gully network using a digital terrain model and process thresholds a digital terrain model is used with process thresholds to predict the extent of a stable gully network in a 5 km2 catchment of the southeastern highlands of australia the model developed by dietnch et al 1992 1993 predicts the topographic controls on channel networks and interprets these in terms of a critical shear stress for channel incision c applied by saturation overland flow we adapt the model slightly to compare the shear stress applied by hortonian overland flow to that applied by saturation overland flow the limits to gully erosion in the catchment are controlled strongly by a topographic threshold that has an inverse relationship between upslope catchment area and local gradient the topographic threshold for channel incision is reproduced using a simple model of hortonian overland flow and a c appropriate for incision into a degraded grass surface c 245 dyn cm2 this is consistent with historical evidence for the timing of gully erosion the study confirms a strong topographic control on the extent of the channel network in a catchment significantly different from the western north america catchments where the topographic threshold was first demonstrated despite its simplicity the model for incision by overland flow appears capable of distinguishing the hydrological processes responsible for channel incision when these are reflected in the relationship between channel network and landscape morphology the model requires relatively simple inputs suggesting it may be useful for mapping gully erosion hazard in actively eroding catchments

short term variations in flow velocity of glaciar soler patagonia chile short term variations in ice flow velocity were obtained at intervals of a few hours and a few days in the ablation area of glaciar soler patagonia chile in november 1985 a maximum flow rate was measured at about four times the minimum value a good correlation with a time lag of 7 5 h was found between the ice flow velocity in the lower reaches and the amount of water discharge from the glacier terminus it was concluded therefore that the velocity variations should have resulted from the variations in basal sliding velocity which is strongly controlled by the subglacial water pressure

dynamic behavior of glaciar perito moreno southern patagonia frontal oscillations since the beginning of the 20th century are known at glaciar perito moreno an eastward outlet glacier of hielo patagonico sur southern patagonia ice field in 1900 the calving front was located about 1 km from the opposite bank from 1935 to 1988 ruptures of ice dams occurred at intervals of 1 5 years although this glacier has thus oscillated it can be regarded as having been in a rather stable condition during the last half century ice thickness in the ablation area has also remained unchanged from 1990 to 1996 the near steady behavior of glaciar perito moreno may be attributed to a regulating effect of the calving rate namely a decrease in the ablation amount due to calving with a retreat of the glacier using 12 m long ablation poles ice flow velocities at the ablation area were measured several times in 1993 and 1994 the velocity in the early summer november was found to be slightly larger than the annual mean it is concluded that basal sliding is significant throughout the year at this temperate glacier with large fluctuations within a short period

observations of a reversal in vertical and horizontal strain rate regime during a motion event on unteraargletscher bernese alps switzerland during a motion event on unteraargletscher bernese alps switzerland in spring 1996 surface velocities were measured up to eight times a day at four different locations along the central flowline using global positioning system equipment in addition accumulated vertical strains over the uppermost 50 and 100 m were measured at a location where the total ice thickness is 260 m the motion event was accompanied by high horizontal and vertical strain rates as compared to annual mean values a reversal in strain regime was observed with horizontal strain rates changing to extension while vertical strain rates became compressive this strain rate reversal coincided within the temporal resolution of the data with a maximum in vertical ice displacement at the surface within a day variations in vertical strain from 0 04 a 1 to 0 06 a 1 were observed over the uppermost 100 m vertical stretching is estimated to have contributed to at least 20 of the anomalous vertical ice movement at the surface there were significant differences between measured longitudinal strain averaged over a distance corresponding to a few ice thicknesses and measured vertical strain in spring 1997 a similar but more detailed set of measurements was collected at the same measuring site and vertical strain rates were found to vary non uniformly with depth with the largest values closest to the surface

utilization of 6 6 cm format vertical aerial photographs for repetitive mapping of surface morphology and measurement of flow velocities of a small glacier in a remote area glaciar soler hielo patagonico norte chile

scaling regimes of local slope versus contributing area in digital elevation models four scaling regimes are observed in digital elevation models dems when the average local slope is calculated for pixels grouped according to the values of the contributing area threshold criteria proposed by various researchers to identify the extent of the channel network are examined relative to the slope area scaling diagram the scaling response observed in dems is reproduced with a landscape evolution and channel network growth model originally developed by willgoose et al 1989 the threshold criterion proposed in this model is a useful tool to separate two different slope area scaling regimes observed in dem data

localized amplification of seismic waves and correlation with damage due to the northridge earthquake evidence for focusing in santa monica abstract the analysis of seismograms from 32 aftershocks recorded by 98 seismic stations installed after the northridge earthquake in the san fernando valley the santa monica mountains and santa monica california indicates that the enhanced damage in santa monica is explained in the main by focusing due to a lens structure at a depth of several kilometers beneath the surface and having a finite lateral extent the diagnosis was made from the observation of late arriving s phases with large amplitudes localized in the zones of large damage the azimuths and angles of incidence of the seismic rays that give rise to the greatest focusing effects correspond to radiation that would have emerged from the lower part of the rupture surface of the mainshock thus the focusing and hence the large damage in santa monica were highly dependent on the location of the northridge event and an earthquake of similar size located as little as one source dimension away would not be likely to repeat this pattern we show from coda wave analysis that the influence of surface geology as well as site effects on damage in santa monica is significantly smaller than are the focusing effects

reversal of ice motion during the outburst of a glacier dammed lake on gornergletscher switzerland during the outburst flood of a glacier dammed lake on gornergletscher switzerland in july 2004 the drained lake water triggered anomalous glacier motion at the onset of the outburst the ice flow direction in the vicinity of the lake became closer to the central flowline when the lake discharge magnitude decreased the flow direction altered such that the ice moved back to the azimuth of the initial motion at one of the survey points where the ice flows parallel to the central flowline the ice accelerated along the pre event flow direction followed by a 1808 backward motion that lasted over 2 days these observations indicate the impact of the lake outburst on the subglacial and englacial stress conditions however the reversal in the flow direction is difficult to explain by drawing on our current understanding of glacier mechanics the timing and the timescale of the flow direction changes suggest that the elastic glacier motion and its rebound played a role under the rapidly changing stress conditions but the young s modulus of ice is too large to cause the observed ice motion other processes including basal separation and subglacial sediment deformation are discussed as possible mechanisms for the reversal of the ice motion

glacier calving observed with time lapse imagery and tsunami waves at glaciar perito moreno patagonia calving plays a key role in the recent rapid retreat of glaciers around the world however many processes related to calving are poorly understood since direct observations are scarce and challenging to obtain when calving occurs at a glacier front surface water waves arise over the ocean or a lake in front of glaciers to study calving processes from these surface waves we performed field observations at glaciar perito moreno patagonia we synchronized time lapse photography and surface waves record to confirm that glacier calving produces distinct waves compared with local noise a total of 1074 calving events were observed over the course of 39 d during austral summer calving occurred twice more frequently than in spring the cumulative distribution of calving interevent time interval followed exponential model implying random occurrence of events in time we further investigated wave properties and found that source to sensor distance can be estimated from wave dispersion within 20 error we also found that waves produced by different calving types showed similar spectra in the same frequency range between 0 05 0 2 hz and that the amplitude of surface waves increased with the size of calving this study demonstrates the potential of surface wave monitoring for understanding calving processes

glacier hydromechanics early insights and the lasting legacy of three works by iken and colleagues the association between basal hydrology and glacier sliding has become nearly synonymous with the early work of almut iken and colleagues their research published in the journal of glaciology from 1981 to 1986 made an indelible impact on the study of glacier hydromechanics by documenting strong correlations between basal water pressure and short term ice flow variations with a passion for elucidating the physics of glacier bed processes iken herself made fundamental contributions to our theoretical and empirical understanding of the sliding process from the theoretical bound on basal shear stress to the inferences drawn from detailed horizontal and vertical velocity measurements the work of iken and colleagues continues to inform the interpretation of data from alpine glaciers and has found increasing relevance to observations from the ice sheets

short term velocity variations on hansbreen a tidewater glacier in spitsbergen spatial and temporal variations of the flow of hansbreen a tidewater glacier in southern spitsbergen svalbard are investigated during summer 1999 surface flow velocities were measured in the ablation zone of hansbreen with a temporal reso lution of 3 4 hours short events with strongly increased surface velocities and a typical duration of 1 2 days were observed these speed up events are related to periods of strongly increased water input to the glacier due to rainfall or enhanced surface melt a close relation is found between the surface velocities and water pressure recorded in a moulin however there are indications from a short time lag between velocity and water pressure peak as well as from observed vertical surface uplifts that basal motion is related to basal water storage rather than directly to basal water pressure the observed short term velocity variations and associated processes on hansbreen are very similar to those observed on land based valley glaciers and suggest that the relevant mechanisms and physical processes that control the flow and its temporal variations are similar in contrast to the flow of land based glaciers sliding velocities on hansbreen are observed to be high all year round and velocities increase towards the calving front

erosion thresholds and land surface morphology we propose a graphical technique to analyze the entirety of landforms in a catchment to define quantitatively the spatial variation in the dominance of different erosion processes high resolution digital elevation data of a 1 2 km2 hilly area where the channel network had been mapped in the field were used in the digital terrain model topog to test threshold theories for erosion the land surface was divided into 20 m2 elements whose shapes were then classified as convergent planar or divergent the entire landscape plotted on a graph of area per unit contour length against surface gradient shows each planform plotting as a separate field a simple steady state hydrologic model was used to predict zones of saturation and areas of high pore pressure to mimic the extreme hydrologic events responsible for erosive instability of the land surface the field observation that saturation overland flow is rare outside convergent zones provided a significant constraint on the hydrologic parameter in the model this model was used in threshold theories to predict areas of slope instability and areas subject to erosion by saturation overland flow both of which can contribute to channel initiation the proportion of convergent elements predicted to exceed the threshold varies greatly with relatively small changes in surface resistance demonstrating a high sensitivity to land use such as cattle grazing overall the landscape can be divided using erosion threshold lines into areas prone to channel instability due to runoff and stable areas where diffusive transport predominates

gully position characteristics and geomorphic thresholds in an undisturbed catchment in northern australia gullying is a significant process in the long term dynamics and evolution of both natural and rehabilitated i e post mining landscapes from a landscape management perspective it is important that we understand gully initiation and development as it is well recognized that catchment disturbance can result in the development of gullies that can be very difficult to rehabilitate this study examines gully position using geomorphic statistics relating to features such as depth width and length in a catchment undisturbed by european activity in the northern territory australia the results demonstrate that gullying occurs throughout the catchment and that a slope area threshold does not exist and that gully position broadly follows the catchment area slope relationship simple relationships relating catchment area and slope to gully depth width and length provide poor results despite these relationships having been found to apply for ephemeral gullies in cropland the results suggest that gully initiation thresholds are low as a result of an enhanced fire regime a threshold model for gully position that uses catchment area and slope to switch between gully and hillslope was evaluated and found broadly to capture gully position copyright 2006 john wiley sons ltd

high resolution measurements of spatial and temporal variations in surface velocities of unteraargletscher bernese alps switzerland data from automated in situ measurements of surface displacements on unteraargletscher bernese alps switzerland made a few times a day from late june until late october 1998 are presented two short term speed up events were observed and partial evidence for a third motion event was seen short term motion events are thus not limited to the start of the melting season strong correlation between the timing of the motion events and periods of heavy rainfall in conjunction with the large size of the area of the glacier which becomes activated during the events both point towards an external triggering mechanism in the time periods between two motion events surface velocities do not vary significantly with time after a motion event surface velocities do not return to previous values suggesting that the events have a lasting effect on the structure of the subglacial drainage system

mapping of glacial motion and surface topography of hielo patagonico norte chile using satellite sar l band interferometry data the first topographic and ice motion maps of the northwestern flank of hielo patagonico norte hpn northern patagonia icefield in chile were produced using satellite synthetic aperture interferometric radar data acquired by nasa s spaceborne imaging radar c instrument in october 1994 the topographic map has a io m vertical precision with a 30 m horizontal spacing which should be sufficient to serve as a reference for monitoring future mass changes of the icefield the ice motion map is accurate to within 4 mm d or 1 ma the radar derived surface topography and ice velocity are used to estimate the ice discharge from the accumulation area of four outlet glaciers and the calving flux and mass balance of glaciar san rafael the results demonstrate the use of sar interferometry for monitoring glaciological parameters on a spatial and temporal scale unattainable by any other means

large amplitude moho reflections sms from landers aftershocks southern california closely spaced aftershocks of the 28 june 1992 landers earthquake m w 7 3 were used to make event record sections that show the transverse components of s and sms arrivals at a distance of 70 to 170 km for the data recorded toward the north in the mojave desert large sms phases are observed with amplitudes 2 to 5 times greater than the direct s for similar distances to the south the sms arrival is comparable to or smaller than the s comparisons to synthetic seismograms indicate that the large amplitude sms phases are produced by the simple crustal structure of the mojave desert that allows a large moho reflection in contrast the more complex geologic structure to the south partitions the seismic energy into a more complicated set of seismic phases so that the moho reflection is diminished in amplitude the large sms phases observed in the mojave enhance the overall ground motions by a factor of 2 to 3 this suggests that when damaging earthquakes occur in other regions of simple crustal structures moho reflections will produce amplified strong motions at distance ranges around 100 km depending on the local structure

surface ice motion deviating toward the margins during speed up events at gornergletscher switzerland 1 high frequency ice flow measurements during speed up events in gornergletscher switzerland revealed intriguing ice motion which has never been reported in detail before during the summer 2005 more than a 100 flow speed increase was observed three times at four gps stations installed across gornergletscher the speed ups were accompanied by a decimeter scale surface uplift two of the events were triggered by intensive surface melt and rainfall while the third one was due to the outburst of gornersee a glacier dammed lake located 2 km upglacier an interesting observation was ice motion deviating toward the side margins during the events as the glacier accelerated a transverse cross glacier velocity component was generated turning the flow direction away from the central flow line toward the margins when the glacier decelerated the transverse velocity component reversed so that the ice flowed back to the azimuth of the initial flow direction in the most significant case the trajectory of the survey stake deviated from the original track by 0 2 m in the transverse direction we hypothesize that the observed lateral ice motion was caused by locally elevated subglacial water pressure when the ice sole decoupled from the bed at a part of the glacier a point source of vertical displacement was transmitted to the surface through viscous ice this caused the transverse as well as vertical surface motion as observed in ground motion during magma intrusion the hypothesis was tested with a two dimensional ice flow model applied to the transverse glacier cross section the model confirmed that the surface ice would move toward the margins as observed in gornergletscher if subglacial water pressure exceeded the ice overburden pressure over a limited part of the bed

the influence of critical moho reflections on strong ground motions recorded in san francisco and oakland during the 1989 loma prieta earthquake the amplitudes of strong ground motions from the loma prieta earthquake recorded in the san francisco and oakland areas exceeded the levels predicted by standard empirical attenuation relations preliminary analysis of accelerograms having known trigger times strongly suggests that the elevation of ground motion amplitudes in the distance range of approximately 40 to 100 km was due to critical reflections from the base of the crust these reflections which are identified on the basis of their arrival times and phase velocity and by comparison with simulated accelerograms were large and occurred at relatively close range because of the deep focal depth of the earthquake and the strong velocity gradient at the base of the crust these motions were further amplified presumably by impedance contrast effects at soft soil sites in san francisco and oakland the effect of the critical reflections in amplifying peak accelerations of the loma prieta earthquake in the san francisco and oakland regions was as large as the effect of soft soil site conditions focal depth has an important influence on strong motion attenuation at distances beyond about 40 km and empirical attenuation relations derived from shallow crustal earthquakes may underpredict the ground motions of deeper crustal events in this distance range further analyses using an expanded data base that includes recordings of aftershocks are required to rigorously test the proposed explanation of the ground motions recorded in san francisco and oakland and the conclusions drawn from that explanation

glacier velocity and water input variability in a maritime environment franz josef glacier new zealand short term glacier velocity variations typically occur when a water input is accommodated by an increase in the subglacial water pressure although these velocity variations have been well documented on many glaciers few studies have considered them on glaciers where heavy rain and glacier melt occur year round this study investigates the relationship between water inputs and glacier velocity on franz josef glacier new zealand we installed six gnss stations across the lower glacier during austral summer 2010 11 and one station during summer 2012 13 glacier velocity remained elevated at all stations for 7 days following large rain events during diurnal melt events we find velocity variations in the early afternoon 12 00 16 00 at 600 m a s l and in the late evening 20 00 01 00 at 400 m a s l we hypothesize that the late evening velocity variations occurred as an upstream region of high subglacial water pressures and accelerated ice motion propagated downstream this mechanism may also explain the increased longitudinal compression and transverse extension across the lower glacier during speed up events our results indicate that the subglacial drainage system likely decreases in efficiency upstream and that the water input variability can still cause short term velocity variations despite the large year round water inputs

channel head location and characteristics using digital elevation models the drainage network is the conduit through which much surface water and sediment are routed within a catchment in a catchment the position of where hillslopes begin and channels end has long been considered the position of transition between diffusive processes upslope and the more incisive fluvial processes downslope consequently understanding channel head location is an important issue in understanding catchment hydrology and geomorphology this study examines channel head position and characteristics in a catchment in arnhem land northern territory australia in this study the position of channel heads was mapped within the catchment and plotted on a reliable digital elevation model of the catchment it was found that the majority of channel heads have relatively small source areas and that graphical catchment descriptors such as the area slope relationship and cumulative area distribution can provide reliable measures of the field position of the heads of first order streams and the transition from hillslope to channel the area slope relationship and cumulative area distribution are also shown to be good tools for determining digital elevation model grid size which can capture hillslope detail and the transition from hillslope to channel copyright 2005 john wiley sons ltd

mapping high pn velocity beneath the colorado plateau constrains uplift models the massive international seismological centre data set of the past 20 years and the two station method are used to determine pn velocities in the mantle lid beneath the colorado plateau in this method the event is located at distances where pn is the first arrival 2 16 and the path is in or very near the azimuth of the two station pair and crosses the plateau this technique to a large extent minimizes the hypocenter mislocation effect and possible errors due to variations in the crustal structure near the source since only the difference in travel times at the two stations is used however this technique has a few underlying assumptions and possible sources of errors such as the quality of the pn data base and station delays caused by varying crustal structure that require an extremely careful application of the method a detailed study of the source of errors and a methodology of selection of the data are presented application of this method to the colorado plateau using all possible two station pairs from 53 stations located within or along the margin of the plateau yields an average high pn velocity of 8 12 0 09 km s this value is considerably larger than the average value of 7 83 km s based on available but very limited seismic refraction profiles but is remarkably similar to the average value of 8 1 km s for the relatively stable midcontinent region our new pn velocity for the colorado plateau eliminates the paradox in the literature that emphasizes the rather close similarity between average pn velocities beneath the colorado plateau and the basin and range province while their tectonic and magmatic cenozoic history is dramatically different previous models for the structure and evolution of the plateau have used the low pn velocity as an important constraint on density and thermal state of the lithosphere hence such models should be reexamined on the basis of this new uppermost mantle pn velocity determination there are two main models that have been proposed to explain the 2 km uplift of the colorado plateau one is based on a combination of thermal thinning of the lithosphere and crustal thickening and the other involves a combination of the delamination of the subducted subhorizontal farallon oceanic plate from the overriding north american plate and crustal thickening we show that the delamination model is more readily consistent not only with our velocity determination and the elevation of the plateau but also with varied geological observations reported in the literature that concern the cenozoic evolution of western north america

patterns of rock fragment cover generated by tillage erosion abstract intensively cultivated areas in the upper part of the guadalentin catchment southeast spain show a systematic spatial pattern of surface rock fragment cover rc the objective of this paper is to quantify and to explain this spatial rock fragment cover pattern therefore a map of an intensively cultivated area of 5 km2 was digitised and for each pixel total topographic curvature was calculated next rock fragment cover was determined photographically at 35 sites with a range of total slope curvatures a linear relation between total curvature and rock fragment cover was found except for narrow concavities it was hypothesised that this pattern can be explained by a significant net downslope movement of rock fragments and fine earth by tillage the displacement distances of rock fragments by tillage with a duckfoot chisel were measured by monitoring the displacement of tracers painted rock fragments and aluminium cubes on 5 sites having different slopes the rare of tillage erosion for one tillage pass with a duckfoot chisel expressed by the diffusion constant k equals 282 kg m for up and downslope tillage and only 139 kg m for contour tillage nomograms indicate that mean denudation rates in almond groves due to tillage erosion 3 to 5 tillage passes per year can easily amount to 1 5 2 6 mm year for contour tillage and up to 3 6 5 9 mm year for up and downslope tillage for a field 50 m long and having a slope of 20 these figures are at least one order of magnitude larger than reported denudation rates caused by water erosion in similar environments hence tillage erosion contributes significantly to land degradation the downslope soil flux induced by tillage not only causes considerable denudation on topographic convexities hill tops and spurs and upper field boundaries but also an important sediment accumulation in topographic concavities hollows and valley bottoms and at lower field boundaries kinetic sieving i e the upward migration of rock fragments by the tines of the duckfoot chisel also concentrates the largest rock fragments in the topsoil in such a way that a rock fragment mulch develops in narrow valleys and at the foot of the slopes these results clearly indicate that tillage erosion is the main process responsible for the observed rock fragment cover pattern in the study area since the study area is representative for many parts of southern spain where almond groves have expanded since 1970 the results have a wider application they show to what extent intensive tillage of steep slopes has contributed to the increase in soil degradation to changes in hillslope morphology i e strong denudation of convexities development of lynchets and rapid infilling of narrow valley bottoms and to the development of rock fragment cover patterns which control the spatial variability of the hydrological and water erosion response within such landscapes

glacier surge mechanism 1982 1983 surge of variegated glacier alaska the hundredfold speedup in glacier motion in a surge of the kind the kind that took place in variegated glacier in 1982 1983 is caused by the buildup of high water pressure in the basal passageway system which is made possible by a fundamental and pervasive change in the geometry and water transport characteristics of this system the behavior of the glacier in surge has many remarkable features which can provide clues to a detailed theory of the surging process the surge mechanism is akin to a proposed mechanism of overthrust faulting

active faults and evolving strike slip basins in the marmara sea northwest turkey a multichannel seismic reflection study abstract the north anatolian fault is a 1200 km long transform fault forming the boundary between the anatolian and eurasian plates near its western end it strikes through the marmara sea and is responsible for the creation of three deep marine depressions the north anatolian fault system and the linked basins in the eastern marmara sea were studied using newly acquired multi channel seismic reflection data in the marmara sea the north anatolian fault consists of a main strand and a few subsidiary branches the main strand is made up of the ganos 15 km long central marmara 105 km and north boundary 45 km fault segments the north boundary fault joins in the east to the izmit segment which was ruptured during the m s 7 4 earthquake on 17 8 1999 the north boundary fault is highly oblique to the regional displacement vector which results in the generation of a symmetrical fault wedge basin this cinarcik basin is a wedge shaped deep marine depression south of istanbul it is about 50 km long up to 20 km wide and 1250 m deep and is filled with pliocene to quaternary sediments over 3 km thick the north boundary fault joins in the west to the transpressional central marmara fault around the restraining segment boundary the syntransform sediments are being deformed into a large anticlinorium the cinarcik basin started to form when the westward propagating north anatolian fault intersected a northwest trending pre existing fault zone during the pliocene and bifurcated into nw and sw trending segments forming a transform transform transform type triple junction dextral strike slip movement along the arms of the triple junction led to the development of the cinarcik basin the present fault geometry in the marmara region was achieved later during the mid pliocene following the termination of the triple junction geometry south of the main north anatolian fault system there is a second active strike slip fault in the marmara sea made up of several segments a highly asymmetrical fault bend basin comprising pliocene quaternary sediments over 2 5 km thick is forming along a releasing fault segment of this south boundary fault system

variations in the surface velocity of an alpine cirque glacier following pioneering work in norway cirque glaciers have widely been viewed as rigidly rotating bodies this model is incorrect for basin filling cirque glaciers as we have demonstrated at west washmawapta glacier a small glacier in the canadian rocky mountains here we report observations at the same glacier that assess whether complex temporal variations of flow also occur for parts of three summers we measured daily displacements of the glacier surface in one year four short duration speed up events were recorded three of the events occurred during the intervals of warmest weather when melt was most rapid the fourth event occurred immediately following heavy rain we interpret the speed up events as manifestations of enhanced water inputs to the glacier bed and associated slip lubrication by increased water volumes and pressures no further speed ups occurred in the final month of the melt season despite warm temperatures and several rainstorms the dominant subglacial water system likely transformed from one of poorly connected cavities to one with an efficient channel network the seasonal evolution of hydrology and flow resembles behaviors documented at other larger temperate glaciers and indicates that analyses of cirque erosion cannot rely on simple assumptions about ice dynamics

slope area relationships and sediment dynamics in two alpine streams the paper focuses on the channel network of alpine basins attempting to interpret channel reaches in terms of response to erosion and deposition processes two basins in the dolomites north eastern italy were considered the rio cordon 5 km2 and the upper boite river 163 km2 the channel network was extracted from raster type digital elevation models dem using a slope area threshold criterion a contribution area index cai which combines drainage area a and local slope s cai a0 5s was used to identify channel heads the channel network extracted from the dem was then analysed to recognize cells showing a value of cai lower than the threshold adopted for channel initiation contiguous cells with low values of cai define channel reaches with low transport efficiency field surveys carried out for some selected cases showed a good agreement between prevailing sediment deposition predicted by the analysis of the channel network and observed channel morphological features sediment sources mapped in two study basins were also analysed in relation to the location of channels with high potential for sediment deposition this made it possible to classify the potential role of different types of sediment sources with regard to basin sediment yield topographic characteristics of the channel network expressed by cai were compared with a classification of channel morphology in the rio cordon it was found that cells with low values of cai frequently occur in the riffle pool reaches whereas the percentage significantly decreases in step pool and bedrock channels copyright 2003 john wiley sons ltd

combined measurements of subglacial water pressure and surface velocity of findelengletscher switzerland conclusions about drainage system and sliding mechanism interpretation des mesures de pression dans les forages et des vitesses superficielles la comparaison avec les modeles suggere que l on a neglige le frottement du aux debris dans les modeles et qu il n existe jamais de chenaux cylindriques rectilignes