the measurement and modelling of rill erosion at angle of repose slopes in mine spoil the process of rill erosion causes significant amounts of sediment to be moved in both undisturbed and disturbed environments and can be a significant issue for agriculture as well as mining lands rills also often develop very quickly from a single rainfall event to a season and can develop into gullies if sufficient runoff is available to continue their development this study examines the ability of a terrestrial laser scanner to quantify rills that have developed on fresh and homogeneous mine spoil on an angle of repose slope it also examines the ability of the siberia erosion model to simulate the rill s spatial and temporal behaviour while there has been considerable work done examining rill erosion on rehabilitated mine sites and agricultural fields little work has been done to examine rill development at angle of repose sites results show that while the overall hillslope morphology was captured by the laser scanner with the morphology of the rills being broadly captured the characteristics of the rills were not well defined the digital elevation model created by the laser scanner failed to capture the rill thalwegs and tops of the banks therefore delineating a series of ill defined longitudinal downslope depressions these results demonstrate that an even greater density of points is needed to capture sufficient rill morphology nevertheless siberia simulations of the hillslope demonstrated that the model was able to capture rill behaviour in both space and time when correct model parameters were used this result provides confidence in the siberia model and its parameterization the results demonstrate the sensitivity of the model to changes in parameters and the importance of the calibration process copyright 2007 john wiley sons ltd

catchment reconstruction erosional stability at millennial time scales using landscape evolution models abstract an important part of planning for the rehabilitation of a mine site is the design of stable final landforms for waste rock dumps or spoil piles whilst able to be assessed over the short term years to decades the longer term behaviour centuries to millennia of such landscapes is not within any meaningful human time frame of observation predictive numerical models therefore form an important tool with which current landscape behaviour and longer term trajectory can be assessed however an important issue associated with the use of models is the ability to assess the reliability and accuracy of the model here the siberia and caesar lisflood landscape evolution models lems are used to simulate and assess the geomorphic stability of a conceptual rehabilitated landform of the ranger uranium mine in the northern territory australia for a simulated period of up to 1000 years utilising both models in this study enabled an independent assessment of likely landscape processes and evolution as well as each model results show that siberia and caesar lisflood produce erosion rates and patterns that are broadly similar at millennial time scales short term processes such as gullying appear to be the dominant erosion features in the proposed landforms and may produce substantial erosion in terms of size and amount of hillslope material eroded and transported downslope vegetation was found to have a major effect on the erosion potential of the landform surface overall both models produce very similar results

control of seafloor roughness on earthquake rupture behavior earthquake rupture complexity is described for three recent large underthrusting earthquakes along the costa rican subduction zone the 1983 osa 1990 nicoya gulf and 1999 quepos events these earthquakes occurred in regions characterized by distinctly different morphologic features on the subducting plate the 1990 and 1999 events occurred along linear projections of subducting seamount chains and had fairly simple earthquake rupture histories both events are interpreted as failure of the basal contact of closely spaced isolated seamounts acting as asperities in contrast the 1983 event occurred along the subducting cocos ridge and had a complex rupture history comparison of rupture characteristics of these large underthrusting earthquakes with size and location of subducting features provides evidence that seamounts can be subducted to seismogenic depths and that variations in seafloor bathymetry of the subducting plate strongly influence the earthquake rupture process

a 1 d morphodynamic model for rill erosion 1 the key objective of this paper is to develop a 1 d hydrodynamic and sediment transport model namely rill1d that handles transcritical flows over abrupt changes e g formation of pool crests and width change in a single rill and also predicts changes in rill bed elevation replication of rill conditions in terms of flow and bed evolution changes necessitated the use of an enhanced tvd maccormack scheme with implementation of tseng s surface gradient method to provide an oscillation free solution over formed pool crests the model at the end of each time step calculates the flow depth velocity and bed shear stress and provides changes in bed elevation and grain size distribution within a cell the hydrodynamic performance of rill1d is evaluated by comparing its results with either analytical solutions or experimental observations from various benchmark tests with rigid bed conditions that include 1 formation of a hydraulic jump in a rectangular channel 2 steady subcritical and transcritical flow without a shock over a hump 3 formation of a hydraulic jump in a converging diverging frictionless channel and 4 flows over step pools it is shown that the enhanced tvd maccormack scheme adequately simulates transcritical flows by preserving the mass conservation and reducing the artificial numerical error the scheme also approximates satisfactorily depth and velocity for a single rill with a fixed bed consisting of steps and pools except near the pool headwalls where a backroller forms with negative velocities the sediment component of rill1d is evaluated by two field investigations of single rills with mobile beds with the field data the code is tested for its ability to reproduce measured values of sediment transport rates a sensitivity analysis is performed to assess the effects of cell size and critical erosional strength in the predictive ability of the model rill1d performs reasonably well in these simulations in terms of sediment prediction rates and fared adequately in terms of replicating rill bed morphology

effect of raindrop splash and transversal width on soil erosion laboratory flume experiments and analysis with the hairsine rose model the parameter consistency of the one dimensional hairsine rose h r erosion model under conditions of significant rainfall splash was examined to account for the splash characteristic length scale and its interaction with the transverse erosion width experiments were carried out using erosion flumes of the same length 6 m but different widths with sediment concentrations measured at the flume exits total sediment concentration and the concentration of seven size fractions 1000 m were measured at high rainfall intensity 60 mm h and with a gentle slope 2 2 the conditions employed ensured that erosion was predominantly precipitation driven the experimental results showed that raindrop splash affected particularly the sediment breakthrough from the wider flumes flumes 1 and 2 1 and 0 5 m wide respectively however the raindrop splash effect was less significant in observed sediment concentrations from the narrower flumes flumes 3 and 4 both 0 25 m wide for these flumes the detached sediment was affected by the transversal width of the flume in that an amount of detached sediment adhered to the barriers instead of being removed in the overland flow the one dimensional h r model was fitted to the experimental results and good agreement was found in particular for the finer size classes the data for the coarser grain sizes were more scattered suggesting sediment motion by mechanisms other than as a suspension in the overland flow e g rolling along the soil surface the optimized parameters indicated that the shield layers where the shield consists of redeposited eroded sediment of the wider flumes 1 and 2 developed within 5 10 min from the start of the experiment whereas in the narrower flumes 3 and 4 they never fully developed the optimized detachment rates were consistent with previous findings but the estimated thickness of the deposited layer was too small to provide complete protection of the original soil against raindrop detachment indicating that the shield was not uniform the experimental design allowed us to investigate directly the effect of flow non uniformity on soil erosion by inclusion of an offset drainage point in flume 4 the observations taken during and after the experiment as well as surface elevation data confirmed the noticeable impact of non uniform flow on the erosion process

the use of digital elevation models in the identification and characterization of catchments over different grid scales this study examines the ability of well known hydrological and geomorphological descriptors and statistics to differentiate between catchments with spatially varying geology size and shape subject to the same climate in the northern territory australia the effect of digital elevation model grid resolution on these statistics is also examined results demonstrate that catchment descriptors such as the area slope relationship cumulative area distribution and hypsometric curve can differentiate between catchments with different geology and resultant morphology but catchment network statistics are insensitive to differences in geology examination of the effects of digital elevation model grid scale demonstrates that while considerable catchment information can be gained at digital elevation grids greater than 10 m by 10 m hillslope and hydrological detail can be lost geomorphic descriptors such as the area slope relationship cumulative area distribution width function and strahler statistics were shown to be sensitive to digital elevation model grid scale but the hypsometric curve was not consequently caution is needed when deciding on an appropriate grid resolution as well as the interpretation and analysis of catchment properties at grid scales greater than that for optimal hillslope and area aggregation definition copyright 2005 john wiley sons ltd

measuring rill erosion using structure from motion a plot experiment abstract in this paper the results of a plot experiment on rill erosion are reported the rill network manually incised on the soil and further shaped by a clear inflow discharge was surveyed using the three dimensional photo reconstruction 3d pr technique which allows to obtain a digital terrain model dtm by a large series of oblique images of the channel from consumer un calibrated and non metric cameras the three dimensional 3d dtm and the quasi tridimensional 2 5d model were generated by agisoft photoscan software for a single rill channel the reliability of the 3d image based ground measurements of morphological and hydraulic variables was positively tested by the corresponding measurements carried out on the rill gypsum cast moreover the morphological and hydraulic variables were measured at 11 transects of the plot by a profilometer p the 2 5d and 3d models using the 3d model as reference the analysis showed that the reliability of the measurements by p and 2 5d methods was comparable and the error was generally lower than 15 the rill measurements carried out by the three methods agreed with the available literature measurements and supported the applicability of both the empirical relationship between rill length and its eroded volume and the theoretical dimensionless relationship among the morphological variables describing the channelized erosion process the analysis also showed that the effect of the distance between two consecutive cross sections on the rill volume measurement by 3d model is negligible finally the shaping effect of different flow discharges on three straight rills incised into the plot was tested in particular three increasing flow discharges 0 15 0 35 and 0 5 l s 1 were used sequentially in two rills while the maximum discharge of the sequence 0 5 l s 1 was used into the third rill both the grain size distribution of the eroded sediment and the total amount of soil loss were affected by the discharge sequence

fine scale partitioning of contemporary strain in the southern walker lane implications for accommodating divergent strike slip motion treating the crust as a micropolar continuum and inverse modeling a high quality catalog of earthquake focal mechanisms reveals that km scale heterogeneous strain is partitioned at km scales into pairs of plane strains with sub perpendicular principal axes these earthquakes occurred in a shallow crustal volume centered on the western indian wells valley of eastern california the site of divergent right lateral strike slip motion along the boundary between the sierran microplate and the southern basin and range province the seismic events defining the plane strains occur in a diffuse seismic source zone and cannot be additionally subdivided on the basis of the type of strain they accommodate the results indicate that seismic moment release for background earthquakes is partitioned into events associated with either fault zone perpendicular extension by normal faults or horizontal shearing by conjugate strike slip faults the spatial scales over which this partitioning occurs suggest that outcrop scale brittle faults may in some cases record nearly perpendicular plane strains related to a single continuous deformation

effects of subducting seafloor roughness on upper plate vertical tectonism osa peninsula costa rica 1 subduction of seamounts and ridges along thinly sedimented convergent margins results in deformation of the overriding forearc exposures of newly recognized late pleistocene shallow water deposits i e marenco formation record intervals of rapid subsidence and uplift across the costa rican forearc inboard of the subducting cocos ridge in general the marenco formation is a fining upward fossiliferious late pleistocene marine sand disconformably overlying beveled surfaces cut across the competent osa melange basement the 50 to 27 ka age of the marenco formation is constrained by 12 accelerator mass spectrometry and two conventional 14c dates obtained on marine macrofossils the deposition of this sequence coincident with a general fall in sea level during oxygen isotope stage 3 requires 6 mm yr 1 subsidence inboard of the northwest flank of the subducting cocos ridge presently exposures of the marenco formation are found at 75 m above sea level requiring uplift rates in excess of 6 mm yr 1 we interpret the down and up history of vertical tectonism recorded by the marenco formation as the response of the upper plate to variations in the elevation of the subducting cocos ridge on the basis of a model where the upper plate deforms through bends because of roughness on a rigid downgoing plate the rate duration and spatial distribution of vertical tectonism across the forearc are determined by the magnitude of the orthogonal component of the relative convergence vector and the bathymetry of the underthrusting plate application of this model to bathymetric data for the cocos plate offshore yields a broad agreement between predicted future rates of subsidence and uplift and rates over the last 50 kyr recorded by the marenco formation furthermore analysis suggests that the arrival of the blunt tipped leading edge of the cocos ridge 0 5 3 ma resulted in an initial period of very rapid 30 mm yr 1 uplift

post mining landform evolution modelling 2 effects of vegetation and surface ripping computer simulations of the topographic evolution of the proposed post mining rehabilitated landform for the era ranger mine showed that for the unvegetated and unripped case the landform at 1000 years would be dissected by localized erosion valleys maximum depth 7 6 m with fans maximum depth 14 8 m at the outlet of the valleys valley form simulated by siberia has been recognized in nature this indicates that siberia models natural processes efficiently for the vegetated and ripped case reduced valley development maximum 1000 year depth 2 4m and deposition maximum 1000 year depth 4 8m occurred in similar locations as for the unvegetated and unripped case i e on steep batter slopes and in the central depression areas of the landform for the vegetated and ripped condition simulated maximum valley depth in the capping over the tailings containment structure was c 2 2 m by modelling valley incision decisions can be made on the depth of tailings cover required to prevent tailings from being exposed to the environment within a certain time frame a reduction in thickness of 1 m of capping material over tailings equates to c 1 000 000 mm3 over a 1 km2 tailings dam area this represents a saving of c 1 500 000 in earthworks alone incorporation of siberia simulations in the design process may result in cost reduction while improving confidence in environmental protection mechanisms copyright 2000 environmental research institute of the supervising scientist commonwealth of australia

the march 25 1990 mw 7 0 ml 6 8 earthquake at the entrance of the nicoya gulf costa rica its prior activity foreshocks aftershocks and triggered seismicity on march 25 1990 a large earthquake mw 7 0 ml 6 8 occurred at the entrance of the nicoya gulf costa rica at 1322 55 6 utc producing considerable damage in central costa rica and generating much interest about whether or not the nicoya seismic gap nishenko 1989 had broken the local country wide seismographic network recorded 6 years of activity prior to this large earthquake 16 hours of foreshocks the mainshock and its aftershocks this network is operated jointly by the costa rica volcanological and seismological observatory at the national university ovsicori una and the charles f richter seismological laboratory at the university of california santa cruz cfrsl ucsc we obtained high resolution locations from this network and located the mainshock at 9 38 5 n 84 55 6 w depth is 20 0 km and the largest foreshock mw 6 0 march 25 1990 at 1316 05 8 utc at 9 36 4 n 84 57 1 w depth is 22 4 km we find that the aftershock zone abuts the southeast boundary of the nicoya seismic gap suggesting that the seismic gap did not rupture since the installation of the local network in april 1984 to march 24 1990 nearly 1900 earthquakes with magnitudes from 1 7 to 4 8 318 with magnitude 3 0 or larger have been located at the entrance of the nicoya gulf one of the most active regions in costa rica the march 25 earthquake occurred at the northwest edge of this region where a sequence of foreshocks began 16 hours prior to the mainshock the spatial temporal distribution of aftershocks and directivity analysis of the mainshock rupture process using teleseismic records both indicate a southeast propagating rupture the mainshock ruptured an asperity of approximately 600 km2 of area with this area expanding to 4000 km2 after 7 days we present evidence that suggests that the ruptured asperity is produced by the subduction of a seamount inversion of teleseismic broadband and long period p and sh waves yields a thrust faulting mechanism with the shallow plane striking 292 dipping 26 and with a rake of 88 in agreement with the subduction of the cocos plate under the caribbean plate local first motions for the largest foreshock and the mainshock agree with this solution we also present evidence suggesting that the march 25 1990 earthquake triggered and reactivated several seismic swarms in central costa rica and temporally decreased the activity in the epicentral area of the july 3 1983 ms 6 2 perez zeledon earthquake

depth distribution of interrill overland flow and the formation of rills a gumbel distribution for maxima is proposed as a model for the depths of interrill overland flow the model is tested against three sets of field measurements of interrill overland flow depths obtained on shrubland and grassland hillslopes at walnut gulch experimental watershed southern arizona the model is found to be a satisfactory fit to 81 of the 90 measured distributions the shape and location parameters of all fitted distributions are strongly correlated with discharge however whereas a common relationship exists between discharge and for all depth distributions the relationships with vary systematically downslope using the gumbel distribution as a model for the distribution of overland flow depths a probabilistic model for the initiation of rills is developed drawing upon the previous work of nearing as an illustration of this approach we apply this model to the shrubland and grassland hillslopes at walnut gulch it is concluded that the presence of rills on the shrubland but not on the grassland is due to the greater runoff coefficient for the shrubland and or the greater propensity of the shrubland for soil disturbance compared with the grassland finally a generalized conceptual model for rill initiation is proposed this model takes account of the depth distribution of overland flow the probability of flow shear stress in excess of local soil shear strength the spatial variability in soil shear strength and the diffusive effect of soil detachment by raindrops copyright 2005 john wiley sons ltd

sediment transport capacity of sheet and rill flow application of unit stream power theory theoretical equations for calculating the unit stream power of both sheet and rill flow were developed and used to predict the sediment transport capacity of such flows independent data sets from three sources representing both finely aggregated clay soils and coarse textured nonaggregated soils sheet rill and composite sheet rill flow systems and a range of slopes were used to test the utility of the method the results were very good and demonstrated the simplicity and robustness of the method for shallow overland flow the best results were obtained when the critical unit stream power at incipient sediment motion was treated as a constant value that was independent of slope the results also suggest that a unique value of critical unit stream power for rill initiation exists that is independent of soil type for noncohesive loams or fine sands and finely aggregated clay soils the sediment transport capacity can be accurately predicted from a knowledge of the physical characteristics of the soil or bed material alone for aggregated clay soils this requires information on the aggregate size distribution and the effects of soil particle size differentiation as flow rates and unit stream powers increase with the transition from sheet to rill flow

the steeply subducting edge of the cocos ridge evidence from receiver functions beneath the northern talamanca range south central costa rica the deep structure of the south central costa rican subduction zone has not been studied in great detail so far because large parts of the area are virtually inaccessible we present a receiver function study along a transect of broadband seismometers through the northern flank of the cordillera de talamanca south costa rica below moho depths the receiver functions image a dipping positive conversion signal this is interpreted as the subducting cocos plate slab compatible with the conversions in the individual receiver functions in finite difference modeling a dipping signal such as the one imaged can only be reproduced by a steeply 80 dipping structure present at least until a depth of about 70 100 km below this depth the length of the slab cannot be determined because of possible scattering effects the proposed position of the slab agrees with previous results from local seismicity local earthquake tomography and active seismic studies while extending the slab location to greater depths and steeper dip angle along the trench no marked change is observed in the receiver functions suggesting that the steeply dipping slab continues until the northern flank of the cordillera de talamanca in the transition region between the incoming seamount segment and cocos ridge considering the time predicted for the establishment of shallow angle underthrusting after the onset of ridge collision the southern costa rican subduction zone may at present be undergoing a reconfiguration of subduction style where the transition to shallow underthrusting may be underway but still incomplete

effect of antecedent conditions and fixed rock fragment coverage on soil erosion dynamics through multiple rainfall events the effect of antecedent conditions and specific rock fragment coverage on precipitation driven soil erosion dynamics through multiple rainfall events was investigated using a pair of 6 m 1 m flumes with 2 2 slope four sequential experiments denoted e1 e2 e3 and e4 involved 2 h precipitation rates of 28 74 74 and 28 mm h 1 respectively and 22 h without rainfall were conducted in each experiment one flume was bare while the other had 40 rock fragment coverage the soil was hand cultivated and smoothed before the first event e1 only and left untouched subsequently sediment yields at the flume exit reached steady state conditions over time scales that increased with sediment size experiments were designed such that both steady and non steady effluent sediment yields were reached at the conclusion of e1 results from subsequent experiments showed that short time soil erosion was dependent on whether steady state erosion was achieved during the preceding event although consistent steady state effluent sediment yields were reached for each sediment size class steady state erosion rates were however dependent on the rainfall intensity and its duration if steady state sediment yields were reached for a particular size class that class s effluent sediment yield peaked rapidly in the next rainfall event the early peak was followed by a gradual decline to the steady state condition on the other hand for size classes in which steady state was not reached at the end of the rainfall event i e e1 in the following event e2 the sediment yields for those classes increased gradually to steady state i e the sharp peak was not observed the effect of rock fragment cover 40 on the soil surface was also found to be significant in terms of the time to reach steady state i e their presence reduced the time for steady conditions to be attained effluent sediment yields for the bare and rock fragment covered flumes e1 showed steady conditions were reached for the latter in contrast to the former we used the hairsine rose h r model to simulate the experimental data as it explicitly models soil particle size classes experiments e1 and e2 involved soil compaction by raindrops and in this case the model predictions were found to be unsatisfactory however compaction was effectively completed by the end of experiment e2 and the model provided reasonable predictions for experiments e3 and e4

soil erosion rates on sloping cultivated land on the loess plateau near ansai shaanxi province china an investigation using 137cs and rill measurements sediment yields from the rolling hills area of the loess plateau in northern china 10 000 25 000 t km 2 yr 1 are amongst the highest in the world the sediment is believed to derive from both the deep gullies that dissect the rolling plateau and the steep cultivated fields on the slopes of the mounds between the gullies however there are few reliable data for erosion rates on the cultivated fields and it is suspected that current estimates 10 000 16 000 t km 2 yr 1 based on empirical relationships derived from erosion plot studies exceed the true values this study sought to address the need for more information concerning erosion of the cultivated fields through derivation of erosion rates from measurements of rill volume and caesium 137 cs 137 inventories for typical fields near the village of ansai shaanxi province the derived erosion rates are discussed and compared with estimates based on empirical relationships derived from erosion plot data where erosion rate estimates based on both rill volume data and cs 137 inventories are available they show good agreement in the pattern of downslope variation both show a sharp decline in erosion rates at a slope length of c 50 m this is tentatively attributed to a change from transport limited to detachment limited conditions where rill incision reaches the undisturbed loess at the base of the plough layer no such decline is visible in the predictions based on empirical relationships derived from erosion plot data further evidence is presented that supports the suggestion that these empirical relationships overestimate erosion rates at slope lengths in excess of c 50 m it is tentatively suggested that the rates of soil erosion from sloping cultivated fields in the rolling hills area are more likely to lie in the range 8000 10 000 t km 2 yr 1 than in the higher range suggested by the empirical relationships c 1998 john wiley sons ltd

quaternary uplift and seismic cycle deformation peninsula de nicoya costa rica differing rates and styles of quaternary deformation along the costa rican fore arc reflect segmentation of the trench corresponding with three contrasting domains of subducting sea floor offshore rapid upward flexure of the southern fore arc segment results from the subduction of the buoyant cocos ridge whereas moderate deformation along the central fore arc segment reflects the subduction of buoyant seamounts in contrast the northern costa rican fore arc deforms in response to the subduction of relatively dense sea floor devoid of major bathymetric anomalies quaternary geomorphic evidence and earthquake oral histories from the peninsula de nicoya within the northern costa rican fore arc demonstrate arcward tilting of the fore arc crust with discrete uplift events occurring during large subduction earthquakes uplift rates calculated from the late holocene cabuya terrace along the peninsula s trench perpendicular southeastern coast decrease systematically toward the arc from 4 5 m k y at cabuya to 1 7 m k y at montezuma 8 km to the northeast an uplifted carbonate beachrock horizon radiocarbon age 4500 5200 yr b p correlated between cabuya and montezuma is tilted 0 1 downward toward the arc although quaternary uplift is evident as far arcward as tambor 10 km northeast of montezuma uplifted terraces are absent between tambor and the golfo de nicoya a submerged archaeological site radiocarbon age 2500 yr b p located along the golfo de nicoya coast 30 km northeast of montezuma demonstrates late holocene subsidence of 0 5 m k y these data indicate net late holocene arcward tilting of the peninsula at an angular rotation rate of between 0 01 and 0 02 k y oral histories describing the m 7 7 nicoya subduction earthquake of 5 october 1950 provide evidence of seismic cycle deformation along the peninsula s southwestern coast between puerto carrillo and nosara interviews with 48 residents show that coseismic uplift of at least 1 m affected this coastline and that a significant fraction of this uplift has subsequently been reversed during four decades of gradual subsidence the coseismic deformation pattern estimated from a uniform slip dislocation model for the 1950 earthquake is consistent with both geomorphic and oral history evidence these observations suggest that seismic cycle deformation functions as an important mechanism of vertical tectonism within the costa rican fore arc arcward rotation and doming of the peninsula de nicoya during the quaternary may reflect repeated cycles of sudden coseismic deformation followed by gradual postseismic and or interseismic crustal movement

crude oil in a shallow sand and gravel aquifer iii biogeochemical reactions and mass balance modeling in anoxic groundwater abstract crude oil floating on the water table in a sand and gravel aquifer provides a constant source of hydrocarbons to the groundwater at a site near bemidji minnesota the degradation of hydrocarbons affects the concentrations of oxidized and reduced aqueous species in the anoxic part of the contaminant plume that developed downgradient from the oil body the concentrations of fe2 mn2 and ch4 eh measurements and the 13c ratios of the total inorganic c indicate that the plume became more reducing ver a 5 a period however the size of the contaminant plume remained stable during this time field data coupled with laboratory microcosm experiments indicate that benzene and the alkylbenzenes are degraded in an anoxic environment in anaerobic microcosm experiments conducted under field conditions almost complete degradation 98 was observed for benzene in 125 d and for toluene in 45 d concentrations of aqueous fe2 and mn2 increased in these experiments indicating that the primary reactions were hydrocarbon degradation coupled with fe and mn reduction mass transfer calculations on a 40 m flowpath in the anoxic zone downgradient from the oil body indicated that the primary reactions in the anoxic zone are oxidation of organic compounds precipitation of siderite and a ferroan calcite dissolution of iron oxide and outgassing of ch4 and co2 the major difference in the two models presented is the ratio of co2 and ch4 that outgasses both models indicate quantitatively that large amounts of fe are dissolved and reprecipitated as ferrous iron in the anoxic zone of the contaminant plume

central costa rica deformed belt kinematics of diffuse faulting across the western panama block fault kinematics seismicity and geodetic data across central costa rica reveal a diffuse fault zone here named the central costa rica deformed belt ccrdb the ccrdb defines the western margin of the panama block and links the north panama deformed belt npdb along the caribbean coast with the middle america trench mat along the pacific coast the junction of the ccrdb and the mat coincides with an abrupt transition from smooth to rough crust on the subducting cocos plate rough smooth boundary shallow subduction of rough thickened oceanic crust associated with the cocos ridge shifts active shortening into the volcanic arc along faults of the ccrdb variable fault kinematics along this zone may reflect three combined deformation mechanisms horizontal shortening and shear from oceanic ridge indentation basal traction from shallow subduction and localized block uplift from subducting seamount roughness within the forearc domain 1 mesoscale faults express transtension where steep ne striking regional scale faults intersect the pacific coast across the volcanic arc domain 2 mesoscale faults exhibit mostly sinistral and dextral slip on ne and nw striking conjugate faults respectively approaching the npdb in the back arc domain 3 transcurrent faulting is modified by transpression and crustal thickening fault kinematics are consistent with earthquake focal mechanisms and global positioning system gps measurements radiometric age constraints confirm that faulting postdates the late neogene onset of shallow subduction the ensuing deformation front has propagated northward into the volcanic arc to its present position along the seismically active ccrdb within the forearc the effect of shallow subduction is overprinted by local uplift related to underthrusting seamounts

active strike slip faulting in el salvador central america several major earthquakes have affected el salvador central america during the past 100 yr as a consequence of oblique subduction of the cocos plate under the caribbean plate which is partitioned between trench orthogonal compression and strike slip deformation parallel to the volcanic arc focal mechanisms and the distribution of the most destructive earthquakes together with geomorphologic evidence suggest that this transcurrent component of motion may be accommodated by a major strike slip fault el salvador fault zone we present field geological structural and geomorphological data collected in central el salvador that allow the constraint of the kinematics and the quaternary activity of this major seismogenic strike slip fault system data suggest that the el salvador fault zone consists of at least two main e w fault segments san vicente and berlin segments with associated secondary synthetic wnw ese and antithetic nnw sse riedel shears and nw se tensional structures the two main fault segments overlap in a dextral en echelon style with the formation of an intervening pull apart basin our original geological and geomorphologic data suggest a late pleistocene holocene slip rate of 11 mm yr along the berlin segment in contrast with low historical seismicity the kinematics and rates of deformation suggested by our new data are consistent with models involving slip partitioning during oblique subduction and support the notion that a trench parallel component of motion between the caribbean and cocos plates is concentrated along e w dextral strike slip faults parallel to the volcanic arc

middle miocene to present plate tectonic history of the southern central american volcanic arc abstract new mid miocene to present plate tectonic reconstructions of the southern central american volcanic arc cava reveal that the inception of cocos ridge subduction began no earlier than 3 ma and possibly as late as 2 ma the cocos ridge has been displaced from the malpelo ridge to the southeast since 9 ma along the panama fracture zone pfz system ambiguous pfz and coiba fracture zone cfz interaction since 9 ma precludes conclusively establishing the age of initial cocos ridge subduction detailed reconstructions based on magnetic anomalies offshore reveal several other variations in subduction parameters beneath southern central america that preceded subduction of the cocos ridge including southeastward migration of the nazca cocos caribbean triple junction along the middle america trench mat from 12 ma to present and subduction of 2 km high scarps both parallel and perpendicular to the trench from 6 to 1 ma the timing of changes in subduction processes has commonly been determined by and correlated with geologic changes in the upper plate however reliable 40 ar 39 ar dating of these events has become available only recently abstr programs geol soc am 2002 these new dates better constrain the magmatic and structural history of southern costa rica observations from this data set include a gap in the volcanic record from 11 to 6 ma which coincides temporally with emplacement of most plutons in southern costa rica normal arc volcanism ceased after 3 5 ma in southern costa rica and pliocene mostly 1 5 ma adakite volcanism was widely distributed from central panama to southern costa rica though volumetrically insignificant this new data reveals that many geologic phenomena commonly attributed to subduction and underplating of the buoyant cocos ridge in fact precede inception of cocos ridge subduction and seem to correlate more favorably in time with earlier tectonic events adakite volcanic activity corresponds in space and time with the subduction of a large scarp associated with a tectonic boundary off southern panama regional unconformities and an 11 6 ma gap in arc volcanism match temporally with oblique subduction of the nazca plate beneath central and southern costa rica cessation of volcanic activity low temperature cooling of plutons in the cordillera de talamanca ct and rapid increases in sedimentation in the fore arc and back arc basins coincide with passage of the nazca cocos caribbean triple junction and initiation of subduction of rough crust associated with cocos nazca rifting 3 5 ma closely followed by initial subduction of the cocos ridge 2 3 ma none of the aforementioned geologic events occurred at a time that would allow for underplating by the cocos ridge rather they are probably related to complex interactions with subduction of complicated plates offshore all of the aforementioned events indicate that the southern central american subduction system has been in flux since at least 12 ma

runoff generation and routing on artificial slopes in a mediterranean continental environment the teruel coalfield spain the aim of this study was to identify the mechanisms of runoff generation and routing and their controlling factors at the hillslope scale on artificial slopes derived from surface coal mining reclamation in a mediterranean continental area rainfall and runoff at interrill and microcatchment scales were recorded for a year on two slopes with different substrata topsoil cover and overburden cover runoff coefficient and runoff routing from interrill areas to microcatchment outlets were higher in the overburden substratum than in topsoil and greater in the most developed rill network rainfall volume is the major parameter responsible for runoff response on overburden suggesting that this substratum is very impermeable at least during the main rainfall periods of the year late spring and autumn when the soil surface is sealed in such conditions most rainfall input is converted into runoff regardless of its intensity results from artificial rainfall experiments conducted 3 and 7 years after seeding confirm the low infiltration capacity of overburden when sealed the hydrological response shows great seasonal variability on the overburden slope in accordance with soil surface changes over the year rainfall volume and intensities i30 i60 explain runoff at the interrill scale on the topsoil slope where rainfall experiments demonstrated a typical hortonian infiltration curve however no correlation was found at the microcatchment level probably because of the loss of functionality of the only rill as ecological succession proceeded the runoff generation mechanism on the topsoil slope is more homogeneous throughout the year runoff connectivity defined as the ratio between runoff rates recorded at the rill network scale and those recorded at the interrill area scale in every rainfall event was also greater on the rilled overburden slope and in the most developed rill network the dense rill networks of the overburden slope guarantee very effective runoff drainage regardless of rainfall magnitude rills drain overland flow from interrill sealed areas reducing the opportunity of reinfiltration in areas not affected by siltation runoff generation and routing on topsoil slopes are controlled by grass cover and soil moisture content whereas on overburden slopes rill network density and soil moisture content are the main controlling factors copyright 2002 john wiley sons ltd

inversion of field data in fault tectonics to obtain the regional stress iii a new rapid direct inversion method by analytical means summary a new method for determining the reduced stress tensor with four degrees of freedom the orientations of the three principal stress axes as well as the ratio of principal stress differences using fault slip data or focal mechanisms of earthquakes is presented from a computational point of view the inversion of fault slip data is made in a direct way by purely analytical means as a result the determination process is extremely fast and adaptable on small microcomputers from a physical point of view the method aims at simultaneously i minimizing the angles between theoretical shear stress and actual slip vector and ii having relative magnitudes of shear stress large enough to induce slip despite rock cohesion and friction examples of application to actual fault slip data sets with good or poor variety of fault slip orientations are shown the double significance of the basic criterion adopted results in a more realistic solution of the inverse problem than the single minimization of the shear stria angle

fast ground water mixing and basal recharge in an unconfined alluvial aquifer konza lter site northeastern kansas abstract ground water chemistry and water levels at three levels in a well nest were monitored biweekly for two and a half years in a shallow unconfined floodplain aquifer in order to study the dynamics of such shallow aquifers the aquifer in northeastern kansas consists of high porosity low hydraulic conductivity fine grained sediments dominated by silt and bounded by fractured limestone and shale bedrock results show that the aquifer underwent chemical stratification followed by homogenization three times during the study period the length of time between maximum stratification and complete homogenization was 3 5 months the chemical parameters most useful for demonstrating the mixing trends were dissolved nitrate and sulfate higher nitrate concentrations were typical of unsaturated zone water and were sourced from fertilizer applied to the cultivated fields on the floodplain variations in sulfate concentrations are attributed to dissolution of rare gypsum in limestone bedrock and variable evapoconcentration in the unsaturated zone the mixing of three chemically different waters entrained unsaturated zone water water entering the base of the floodplain aquifer and water in residence before each mixing event was simulated the resident water component for each mixing event was a fixed composition based on measured water chemistry in the intermediate part of the aquifer the entrained water composition was calculated using a measured composition of the shallow part of the aquifer and measurements of soil water content in the unsaturated zone the incoming basal water composition and the fractions of each mixing component were fitted to match the measured chemistry at the three levels in the aquifer a conceptual model for this site explains 1 rapid water level rises 2 water chemistry changes at all levels in the aquifer coincident with the water level rises 3 low measured hydraulic conductivity of the valley fill and apparent lack of preferential flow pathways 4 minuscule amounts of unsaturated zone recharge and 5 dissolved oxygen peaks in the saturated zone lagging water level peaks we postulate that rainfall enters fractures in bedrock adjacent to the floodplain this recharge water moves rapidly through the fractured bedrock into the base of the floodplain aquifer the recharge event through the bedrock causes a rapid rise in water level in the floodplain aquifer and the chemistry of the deepest water in the floodplain aquifer changes at that time the rising water also entrains slow moving nitrate rich unsaturated zone water altering the chemistry of water in the shallow part of the aquifer vertical chemical stratification in the aquifer is thus created by the change in water chemistry in the upper and lower parts of the saturated zone as the water level begins to decline the aquifer undergoes mixing that eventually results in homogeneous water chemistry the rise in water level from the recharge event also displaces gas from the unsaturated zone that is then replaced as the water level declines following the recharge event this new oxygen rich vadose zone air equilibrates rapidly with saturated zone water resulting in a dissolved oxygen pulse in the ground water that peaks one half to 2 months after the water level peak this oxygen pulse subsequently declines over a period of 2 6 months

seismogenic deformation field in the mojave block and implications for tectonics of the eastern california shear zone from the aftershocks of the 1992 landers earthquake we infer the orientation of the principal strain rate axes d 1 d 2 d 3 d 1 lengthening their relative magnitude and the relative spin of fault blocks by using a micropolar continuum model to invert the seismic p and t axes the seismogenic deformation is consistent with the geodetic measurements of the coseismic displacement and with the secular deformation of the central mojave block regionally the aftershock data define two major domains within the central mojave block 1 the western mojave block including the san bernardino mountains and the epicentral area of the big bear earthquake which is characterized by e w d 1 lengthening and n s d 3 shortening and 2 the central mojave block including the landers surface rupture zone which is characterized by nw se d 1 and ne sw d 3 inversion for the principal strain axes of geodetically measured coseismic displacements across the big bear and landers seismogenic zones gives results similar to the aftershock inversions for those areas indicating that the aftershocks accommodate a deformation similar to the main rupture and do not reflect elastic rebound or residual stresses the background seismicity for 1981 to 1991 shows the same characteristic d 1 and d 3 orientations for the two domains indicating that the secular seismogenic strain has the same regional geometry as the 1992 coseismic deformation the micropolar inversion also provides values of the relative vorticity parameter w which reflects a difference between the vorticity of a shearing continuum and the vorticity of fault bounded blocks rotating within tabular seismogenic shear zones the observed fault geometry along the kickapoo fault suggests a pinned block model for the local block rotation that is consistent with the values of w obtained from our inversions we interpret the regional nw se orientation of d 1 in the central mojave block to be characteristic of the dextral eastern california shear zone which transfers approximately 22 of the pacific north american plate motion from the san andreas system to the walker lane belt in eastern california our results and geodetic determinations of the secular shear strain in the central mojave block indicate that the locus of nw dextral shear generally lies between the san bernardino mountains and the pisgah fault

effect of subducting sea floor roughness on fore arc kinematics pacific coast costa rica fault kinematics and uplift in the costa rican fore arc of the middle america convergent margin are controlled to a large extent by roughness on the subducting cocos plate along the northwest flank of the incoming cocos ridge seafloor is characterized by short wavelength roughness related to northeast trending seamount chains onland projection of the rough subducting crust coincides with a system of active faults oriented at high angles to the margin that segment the fore arc thrust belt and separate blocks with contrasting uplift rates trunk segments of pacific slope fluvial systems typically follow these margin perpendicular faults regionally developed marine and fluvial terraces are correlated between drainages and across faults along the costa rican pacific coast terrace separations across block bounding faults reveal a pattern of fore arc uplift that coincides roughly with the distribution of incoming seamounts magnitude and distribution of quaternary uplift along the costa rican pacific coast suggests that despite a thin incoming sediment pile the inner fore arc shows an accumulation of mass a characteristic that may be due to underplating of seamounts beneath the fore arc high

emergence and erosion a model for rill initiation and development soil erosion by overland flow resulting from infiltration excess rainfall generates rill networks on hillslope areas the way in which these networks emerge and develop suggests that hillslope erosion functions as a self organizing dynamic system based upon this argument a model for soil erosion rillgrow 1 has been developed this operates at the spatial scale of raindrops and microtopography in this paper the second generation of the model rillgrow 2 is described and applied to four different soil surfaces results suggest that even at this early stage in its development rillgrow 2 is capable of replicating the success of the earlier model and in some cases of extending them the success of both models suggests that this self organizing view of rill generation may capture some fundamental aspects of the operation of real erosional systems copyright 2000 john wiley sons ltd

seismotectonics of the coso range indian wells valley region california transtensional deformation along the southeastern margin of the sierran microplate

fault propagation folds induced by gravitational failure and slumping of the central costa rica volcanic range implications for large terrestrial and martian volcanic edifices long sublinear ridges and related scarps located at the base of large volcanic structures are frequently interpreted as normal faults associated with extensional regional stress in contrast the ridges bordering the central costa rica volcanic range ccrvr are the topographic expression of hanging wall asymmetric angular anticlines overlying low angle thrust faults at the base of the range these faults formed by gravitational failure and slumping of the flanks of the range due to the weight of the volcanic edifices and were perhaps triggered by the intrusion of magma over the past 20 000 years the thrust fault underlying alajuela ridge rises from a depth of 700 m at a dip of 15 over a distance of a few kilometers it ramps up at 600 m depth on a 40 slope and terminates in the axis of the forward syncline 400 m below the surface the hanging wall of this fault has been thrusted about 200 m away from the volcanic range axis thrusting on the lower flanks of the ccrvr is compensated by extension on the range axis with formation of summit grabens shallow seismicity in the volcanic range suggests that thrusting is still active we postulate that at kilauea volcano hawaii the gravity and magma induced slumping of the southern flank on low angle thrust faults generates hanging wall anticlines similar to those observed in costa rica these anticlines are hypothesized to occur along the base of the volcano where the thrust faults ramp up toward the sea bottom ridges and scarps between 2000 and 5000 m below sea level are interpreted as the topographic expression of these folds we further suggest that the scarps of the ccrvr and kilauea are valid scaled terrestrial analogs of the perimeter scarp of the martian volcano olympus mons we suggest that the crust below olympus mons has failed under the load of the volcano triggering the radial slumping of the flanks of the volcano on basal thrusts the thrusting would have in turn formed the anticlinal ridges and scarps that surround the edifice the thrusting seems to be preferential toward the northwest and southeast and a northeast southwest rift zone seems to have developed perpendicular to the regional topographic gradient the thrust faults may extend all the way to the base of the martian crust about 40 km and they may have been active until almost the end of the volcanic activity we suggest that gravitational failure and slumping of the flanks of volcanoes is a process common to most large volcanic edifices in the ccrvr and at kilauea this slumping of the flanks is a slow intermittent process but it could evolve to rapid massive avalanching leading to catastrophic eruptions thus monitoring of uplift and displacement of the folds related to the slump tectonics could become an additional effective method for mitigating volcanic hazards

paleosol evidence for quaternary uplift and for climate and ecosystem changes in the cordillera de talamanca costa rica abstract a noncalcareous volcanic paleosol succession from the upper montane rain forest of the cordillera de talamanca costa rica lat 9 41 03 3 n long 83 53 45 9 w 2507 m elev provides evidence for changing quaternary elevation climate and ecosystems basal deposits crb horizons are saprolitized porphyritic andesite enriched in si al and fe and depleted in base cations which record an earliest period of very intense weathering forming a leached residuum of smectite kaolinite and fe oxides or oxyhydroxides on a mature paleolandscape probably in tropical lowlands paleo saprolite deposits are sharply overlain by interbedded lapilli tuffs and two paleosols with dark colored organic c rich 2 3 wt ab horizons one containing abundant grass pollen interpreted as mollic epipedons of grassland soils andic mollisol like paleosols with 13c values 24 5 pdb that record a former c3 grassland ecosystem possible pedogenic carbonate btkb horizons with all carbonate removed by overprinting by younger pedogenic processes provide evidence of former drier and drained conditions uppermost buried soils mainly btb horizons are non calcareous clay rich andic ultisol like paleosols that record pedogenesis under climates similar to current conditions with highly weathered clay mineral suites ams dating of charcoal from the upper btb paleosol constrains a latest glacial age 36 640 650 14c yr bp ages for two additional deeper samples were 43 48 ka for the 2btb paleosol uplift rates of the cordillera de talamanca are estimated as 1 km 1 ma consequently the described paleosols provide evidence for 1 initial lowland pedogenesis perhaps at 2 3 ma 2 regional uplift and major unconformity volcanism and development of a grassland ecosystem that has 13c values similar to those measured in modern high elevation paramo sites in the cordillera 24 4 to 26 3 pdb but formed mollic epipedons and pedogenic carbonates which do not characterize modern paramo soils followed by 3 continued late pleistocene volcanism and pedogenesis in environments similar to current oak dominated montane rain forest conditions the paleosol succession provides a valuable record of dynamic climate ecosystem change and uplift history in the cordillera de talamanca that can complement and extend existing bog and lake sediment records

collision versus sliver transport in the hanging wall at the middle america subduction zone constraints from background seismicity in central costa rica earthquake focal mechanism solutions for 135 small magnitude events are inverted for best fitting partial strain rate tensors that characterize contemporary strain in five areas that span the western margin of the panama microplate in central costa rica the results indicate the predominance of subhorizontal maximum stretching subparallel to the middle america trench mat and provide constraints on the role of cocos ridge collision at the mat the trajectory of maximum stretching changes 25 45 over several tens of kilometers from the central costa rica deformed belt ccrdb where it is nearly e w to the area inboard of the cocos ridge where it is nw se this change suggests that background seismogenic deformation reflects the transition from the trailing edge of a fore arc sliver to an area of the upper plate affected by ridge collision this diffuse deformation may be localized in part on conjugate strike slip faults of the ccrdb

tomographic evidence for a subducted seamount beneath the gulf of nicoya costa rica the cause of the 1990 mw 7 0 gulf of nicoya earthquake 1 tomographic images constrain the existence of a subducted seamount beneath the gulf of nicoya costa rica the subducted seamount is found at a depth of 30 km within the rupture area of the march 25 1990 mw 7 0 gulf of nicoya earthquake the gulf of nicoya earthquake was a typical thrust type subduction earthquake and occurred on a shallow dipping thrust fault parallel or along the boundary between the subducting cocos plate and the overriding plate precise relocation of the mainshock and its aftershocks in a 3 d p wave velocity model shows that the area of the mainshock rupture is coincident with the imaged subducted seamount most of the aftershocks are relocated within or close to the inferred subducted seamount above the subducting oceanic plate we interpret the subducted seamount as an asperity whose rupture caused the 1990 gulf of nicoya earthquake

deducing the distribution of terminal electron accepting processes in hydrologically diverse groundwater systems the distribution of microbially mediated terminal electron accepting processes teaps was investigated in four hydrologically diverse groundwater systems by considering patterns of electron acceptor nitrate sulfate consumption intermediate product hydrogen h sub 2 concentrations and final product ferrous ion sulfide and methane production in each hydrologic system a determination of predominant teaps could be arrived at but the level of confidence appropriate for each determination differed in a portion of the lacustrine aquifer of the san joaquin valley for example all three indicators sulfate concentrations decreasing h sub 2 concentrations in the 1 2 nmol range and sulfide concentrations increasing along flow paths identified sulfate reduction as the predominant teap leading to a high degree of confidence in the determination in portions of the floridan aquifer and a petroleum hydrocarbon contaminated aquifer sulfate reduction and methanogenesis are indicated by production of sulfide and methane and hydrogen concentrations in the 1 4 nmol and 5 14 nmol range respectively however because electron acceptor consumption could not be documented in these systems less confidence is warranted in the teap determination in the black creek aquifer no pattern of sulfate consumption and sulfide production were observed but h sub 2 concentrations indicated sulfate reduction as the predominant teap in this case more where just a single line of evidence is available the least confidence in the teap diagnosis is justified because this methodology is based on measurable water chemistry parameters and upon the physiology of microbial electron transfer processes it provides a better description of predominant redox processes in groundwater systems than more traditional eh based methods less

two approaches to modeling the initiation and development of rills in a man made catchment 1 surface erosion rills are dominant structures in young developing ecosystems and as such they fundamentally affect water flows for example by channeling surface runoff or by locally changing the infiltration capacity of the soil to successfully model the systems hydrology it is indispensable to take the development of erosion rills into account the goal of this study was to model the emergence of an erosion rill network with total length of 6 km formed during the last few years in the 6 ha large artificial catchment chicken creek near cottbus germany the length and connectivity of the evolving network were quantified from aerial images this analysis showed that the major rill network established already during the first year of ecosystem development we adapted two model approaches to simulate the emergence of erosion rills first we used a self organized critical network approach with soil erosion and sediment deposition governed by a local critical shear stress the second approach based on manning s equation was developed to compare the results of the self organized critical network approach with results from a simple but more physically based approach erosion was triggered in the case of high local shear stress and deposition was calculated from settling velocity of the suspended particles both models were able to reproduce the observed rill network geometric characteristics such as network length and rill depth were simulated in the right order of magnitude the models also managed to describe the position and temporal evolution of the main erosion rills in the catchment

structure deformation and strength of the loma prieta fault northern california usa as inferred from the 1989 1990 loma prieta aftershock sequence analysis of aftershock focal mechanisms of the october 1989 m 7 1 loma prieta earthquake reveals details of structure and deformation aftershocks below 4 6 km define an alignment plane oriented 131 65 this alignment includes three planar segments defining a restraining bend in a blind strike slip fault dextral strike slip dominates in the south and reverse dextral slip dominates in the north a distribution similar to slip during the main shock above this fault dominantly reverse faults striking roughly 110 lie en echelon along the main fault trend in the 17 sets of spatially clustered aftershocks a more complex substructure is defined by local planar hypocenter alignments and by preferred orientations of aftershock shear planes the maximum shortening axes make angles with the normal to these planes that average 46 and 53 respectively these angles are incompatible with a weak fault for which 0 20 orientations of preferred aftershock shear planes resemble riedel shears relative to local hypocenter alignment planes the similarity of slip distributions inferred from the aftershock inversions and from the main shock implies that the stress drop during the main shock was incomplete and thus that the loma prieta fault is not unusually weak triaxial brittle deformation is partitioned into a pair of plane strains rotated relative to each other about a common principal axis the shape of the triaxial strain ellipsoid determines the angle of rotation evidence supports our micropolar model of brittle deformation which predicts that the antisymmetric part of the seismic moment tensor records effects of block rotations

use of a landscape simulator in the validation of the siberia catchment evolution model declining equilibrium landforms this paper presents a study to test the ability of the current generation of landscape evolution models to correctly predict landscape form from measured erosion processes landscapes generated by the siberia landscape evolution model were compared to experimental model landscapes in declining equilibrium the model simulations were compared using geomorphologically and hydrologically significant parameters comparisons of the simulated landscapes with the experimental landscapes were carried out using the hypsometric curve width function cumulative area distribution and area slope relationship these comparisons demonstrate that siberia can correctly simulate the experimental model landscape at declining equilibrium the simulation showed sensitivity to the spatial distribution of the rainfall particularly with respect to hypsometry using the correct measured distribution of rainfall was necessary rather than using a spatially uniform rainfall distribution the results also highlighted the importance of digital terrain map dtm error in deriving geomorphic statistics the observed landform had a consistently larger width function than the simulation only when the simulations were corrupted with elevation errors with statistical properties of the errors in the experimental landscape dtm as measured by photogrammetry did the observed and simulated width functions match

active thrusting in the inner forearc of an erosive convergent margin pacific coast costa rica 1 structural and geomorphic analyses of the fila costena thrust belt in southwest costa rica indicate active thrusting within the inner forearc the fila costena exposes three major thrust faults that imbricate the late tertiary forearc basin sequence of the terraba basin the frontal thrust of the fila costena marks the boundary between an uplifting inner forearc and a subsiding outer forearc with only local uplift astride the indenting cocos ridge on the basis of surface constraints a cross section across the thrust belt suggests that all three thrusts flatten into parallelism with a low angle decollement horizon near the contact between the basement and the cover sequence of the terraba basin this decollement lies at a depth of 4 km the minimum shortening recorded by restoration of fault related folds is 17 km or 45 observations of late tertiary marine sediments tilted and faulted late quaternary fluvial terraces and raised holocene marine terraces indicate that fila costena uplift was likely initiated in the quaternary and is ongoing given that the coastal mountains are separated from the talamanca range by a valley the decollement that delaminates the forearc basin from the underthrusting forearc must continue as a flat beneath the valley but must link with the plate boundary along a crustal scale ramp system a structural geometry that has resulted in uplift of the talamanca range the highest peaks in central america the dichotomy between uplift in the inner forearc and subsidence in the outer forearc is explained in terms of the response of an arcward thickening wedge to rough subducting crust index terms 8150 tectonophysics plate boundary general 3040 8123 tectonophysics dynamics seismotectonics 8010 structural geology fractures and faults 8015 structural geology local crustal structure 8005 structural geology folds and folding

seismic cycle and plate margin deformation in costa rica gps observations from 1994 to 1997 global positioning system gps observations in costa rica from 1994 to 1997 reveal a complex pattern of motion consistent with the superposition of seismic cycle and secular plate margin deformation in the south velocity vectors are consistent with motion of the panama block plus postseismic deformation following the 1991 limon earthquake and interseismic strain due to partial locking of the middle america trench mat thrust in the northwest sites west of the volcanic arc are moving to the nw as a forearc sliver superimposed on this sliver motion are vertical and horizontal interseismic deformations from the adjacent nicoya segment of the mat we apply two different inverse methods to understand the source of the seismic strain in nw costa rica we compare fault locking models derived using a singular value decomposition inversion with that of a simulated annealing global optimization approach both methods yield similar models for partial locking of the thrust interface beneath the nicoya peninsula our results define an area of nearly fully locked fault beneath the outer coast of the southern portion of the peninsula with somewhat lower coupling beneath the northern half and with low coupling elsewhere these initial results show the promise for detailed imaging of the locked portion of a thrust interface responsible for future large subduction zone earthquakes

the april 22 1991 valle de la estrella costa rica mw 7 7 earthquake and its tectonic implications a broadband seismic study the rapture process of a large back arc thrusting earthquake the april 22 1991 valle de la estrella costa rica mw 7 7 earthquake is investigated using broadband body waves and long period surface waves we find the source process to be relatively simple with the source models separately obtained from body and surface waves being very consistent the event occurred on a shallow southwest dipping rapture plane on which most energy is released updip of the hypocentral location 10 20 km deep high frequency radiation appears to have been released over a relatively small source area our preferred model has a focal mechanism with strike 102 10 dip 17 14 and rake 63 17 a seismic moment of 3 8 1 5 1020 n m and a total rupture duration of 40 6 s the earthquake appears to be associated with the north panama deformed belt npdb a thrust and fold complex that has accommodated the oroclinal deformation of panama this event along with previous large events north of panama in 1882 and 1916 indicates that there is substantial convergence along the npdb marking the npdb as a probable emerging plate boundary it remains difficult to gauge the earthquake hazard in the region because of the tectonic complexity

comparison of gully erosion estimates using airborne and ground based lidar on santa cruz island california abstract gully erosion removes comparatively large volumes of soil from small areas it is often difficult to quantify the loss of soil because the footprint of individual gullies is too small to be captured by most generally available digital elevation models dems such as the usgs national elevation dataset airborne lidar light detection and ranging has the potential to provide the required data density but an even newer class of ground based sensors may provide better local resolution at lower cost in this study we compared digital elevation models produced by airborne and ground based lidar systems with ground based geomorphic and geodetic survey data to determine their utility in quantifying volumetric soil loss due to gully erosion in a heavily degraded watershed 7 55 10 2 km 2 on southwestern santa cruz island in southern california volumetric estimates of the eroded sediment were produced by comparing the lidar derived dems of the gully system to a modeled pre erosion surface average point densities were significantly higher for the ground based lidar system and provided more detailed information however its limited scanning footprint and side looking orientation presented serious challenges in collecting continuous data from deeply incised gullies making the airborne system preferable for this type of investigation and likely for most applications where heavy topographic shadowing is prevalent

a physical explanation of an observed link area slope relationship an observed log log linear relationship between channel slope and contributing area is explained by the erosional physics that lead to catchment form it is postulated that tectonic uplift is in balance with the fluvial erosion down wasting that dominates catchment erosion and it is shown that this relationship results in the observed log log linear relationship at dynamic equilibrium in addition it has been observed that there are deviations from this log log linear relationship near the catchment divide with observed slopes being lower than those predicted from the relationship this is explained by noting that for small areas fluvial erosion effects are dominated by soil creep and rain splash modeled by diffusive physics the area at which this deviation from log log linearity occurs is that point on the hillslope at which diffusive physics like soil creep and rain splash begin to dominate fluvial erosion these predictions are confirmed by numerical simulations using a catchment evolution model

bookshelf faulting in nicaragua oblique subduction at a high rate of convergence along much of the middle america trench results in northwest directed trench parallel block motion accommodation of this motion along northwest striking dextral strike slip faults has been postulated however in nicaragua such faults are not well developed we suggest instead that this motion is accommodated by bookshelf faulting that includes northeast striking left lateral faults we present earthquake epicenter and focal mechanism data and mapped fracture and fault data consistent with this model trenchward migration of the volcanic arc since the miocene and reactivation of northeast striking miocene structures may have led to the development of this arc and trench normal fault system

the mw 6 4 damas costa rica earthquake of 20 november 2004 aftershocks and slip distribution the earthquake of 20 november 2004 was located north of damas island in the pacific coast of costa rica within the costa rica deformed belt the earthquake was located at 24 km depth and reported with a magnitude m w of 6 4 and a strike slip mechanism with a large normal dip slip motion this mechanism agrees with mapped faults in the area that suggest transtensional deformation on the forearc and the entire western boundary of the panama microplate aftershock locations do not delineate a preferable plane to distinguish between the two nodal planes and are distributed between 15 and 25 km depth the slip distribution during the mainshock modeled after teleseismic and local data pictured a circular rupture 8 km in radius and 0 25 m of average displacement the fault plane cannot be distinguished from the two nodal planes from the slip distribution because of the lack of directivity and resolution for this magnitude earthquake weak evidence from empirical green s function analysis suggests that the dextral northwest oriented fault could be the causative fault depth to the top of the slab hypocenter location of the mainshock its slip distribution depth distribution of the aftershocks and quaternary fault activity at the surface suggest that deformation takes place throughout the whole thickness of the crust this extended deformation might be caused by seamount subduction and strong basal friction on the upper plate due to subduction of a thick young and buoyant oceanic plate rough seafloor and underplating of large seamounts

characterizing the primary material sources and dominant erosional processes for post fire debris flow initiation in a headwater basin using multi temporal terrestrial laser scanning data abstract wildfire dramatically alters the hydrologic response of a watershed such that even modest rainstorms can produce hazardous debris flows relative to shallow landslides the primary sources of material and dominant erosional processes that contribute to post fire debris flow initiation are poorly constrained improving our understanding of how and where material is eroded from a watershed during a post fire debris flow requires 1 precise measurements of topographic change to calculate volumetric measurements of erosion and deposition and 2 the identification of relevant morphometrically defined process domains to spatially constrain these measurements of erosion and deposition in this study we combine the morphometric analysis of a steep small 0 01 km 2 headwater drainage basin with measurements of topographic change using high resolution 2 5 cm multi temporal terrestrial laser scanning data made before and after a post fire debris flow the results of the morphometric analysis are used to define four process domains hillslope divergent hillslope convergent transitional and channelized incision we determine that hillslope divergent and hillslope convergent process domains represent the primary sources of material over the period of analysis in the study basin from these results we conclude that raindrop impact induced erosion ravel surface wash and rilling are the primary erosional processes contributing to post fire debris flow initiation in the small steep headwater basin further work is needed to determine 1 how these results vary with increasing drainage basin size 2 how these data might scale upward for use with coarser resolution measurements of topography and 3 how these results change with evolving sediment supply conditions and vegetation recovery

effect of embedded rock fragments on slope soil erosion during rainfall events under simulated laboratory conditions abstract quantifying the role of embedded rock fragments in soil water processes on a slope is crucial for the application of rock fragments in soil and water conservation practice in this study a laboratory runoff and erosion experiment was conducted in the soils embedded with rock fragments including five rock fragment contents rc of 0 0 1 0 2 0 3 and 0 4 kg kg 1 in a metal flume under three slopes 5 10 and 15 results showed that the mean steady infiltration rate in the soil without rock fragment null was lower than that in the soils containing rock fragments low rock fragment contents of 0 1 0 2 kg kg 1 and high rock fragment contents of 0 3 0 4 kg kg 1 labelled as low and high respectively as slope gradient 5 but was higher than the latter two soils as slope gradients 10 and 15 initial infiltration rate significantly increased with rc p

inner forearc response to subduction of the panama fracture zone southern central america abstract subduction of the right lateral panama fracture zone along the convergent margin of central america creates abrupt lateral variations in convergence rate obliquity and subducting crustal thickness at its intersection with the middle america trench this intersection known as the panama co nz ca triple junction is migrating to the southeast at a rate of 55 mm yr and currently coincides with the lateral termination of the fila costena thrust belt in the inner forearc of the overriding plate mapping in the inner forearc in the area that straddles the subducting panama fracture zone reveals that cocos caribbean convergence west of the triple junction leads to the development of an inner forearc thrust belt inboard of the colliding cocos ridge while little deformation is evident inboard of nazca caribbean convergence east of the triple junction this results in the lateral termination of the fila costena thrust belt in the region of the forearc that projects over the panama fracture zone where four out of five mapped thrust faults tip out and are buried by lahars three new balanced cross sections indicate a steep gradient in shortening from the center of the thrust belt to its southeastern termination the short term history of the inner forearc recorded in the landscape and topography of the fila costena is consistent with the southeastward migration of the thrust belt and the panama triple junction throughout the past 3 ma with evidence for the growth of a new topographic divide and reorganization of stream channel networks

geodetic and seismic constraints on some seismogenic zone processes in costa rica new seismic and geodetic data from costa rica provide insight into seismogenic zone processes in central america where the cocos and caribbean plates converge seismic data are from combined land and ocean bottom deployments in the nicoya peninsula in northern costa rica and near the osa peninsula in southern costa rica in nicoya inversion of gps data suggests two locked patches centered at 14 2 and 39 6 km depth interplate microseismicity is concentrated in the more freely slipping intermediate zone suggesting that small interseismic earthquakes may not accurately outline the updip limit of the seismogenic zone the rupture zone for future large earthquakes at least over the short 1 year observation period we also estimate northwest motion of a coastal sliver block at 8 3 mm yr probably related to oblique convergence in the osa region to the south convergence is orthogonal to the trench cocos caribbean relative motion is partitioned here with 8 cm yr on the cocos panama block boundary including a component of permanent shortening across the fila costena fold and thrust belt and 1 cm yr on the panama block caribbean boundary the gps data suggest that the cocos plate panama block boundary is completely locked from 10 50 km depth this large locked zone as well as associated forearc and back arc deformation may be related to subduction of the shallow cocos ridge and or younger lithosphere compared to nicoya with consequent higher coupling and compressive stress in the direction of plate convergence

slope aspect affects geomorphic dynamics of coal mining spoil heaps in belgium abstract after the abandonment of coal mining in belgium in the 1960s 1980s many coal tips have been left to themselves increasingly these coal tips are regarded as socio cultural heritage and protected for their environmental value this research analyses the spatial distribution of the main geomorphic processes sheet and rill erosion landsliding rock fragment movement and root throw occurring on coal tips in belgium through mapping of the processes and their causal factors five spoil heaps spread over the major coal basins were studied in detail the spoil heaps were subdivided in homogeneous land units especially with regard to slope gradient vegetation cover and slope aspect qualitative and quantitative observations were done on processes and potential causal factors regressions showed that generally the expression of slope processes on the studied coal tips is 1 strongly dependent on westerly aspect of the slopes 2 independent of slope gradient which presents a narrow range 3 impeded by grass cover and 4 not fully predictable due to variability in type and age of dumped mine spoil

analysis of fault slip inversions do they constrain stress or strain rate fault slip data commonly are used to infer the orientations and relative magnitudes of either the principal stresses or the principal strain rates which are not necessarily parallel or equal at the local scale of an individual fault the shear plane and slip direction define the orientations of the local principal strain rate axes but not in general the local principal stress axes at a large scale the orientations of p and t axes maxima for sets of fault slip data do not provide accurate inversion solutions for either strain rate or stress the quantitative inversion of such fault slip data however provides direct constraints on the orientations and relative magnitudes of the global principal strain rates to interpret the inversion solution as constraining the global principal stresses requires that 1 the fault slip pattern must have a characteristic symmetry no lower than orthorhombic 2 the material must be mechanically isotropic and 3 there must be a linear constitutive relationship between the global stress and the global strain rate isotropic linear elastic constitutive equations are appropriate to describe the local deformation surrounding an individual slip discontinuity fault slip inversions however constrain the characteristics of a large scale cataclastic flow which is described by constitutive equations that are probably but to an unknown degree anisotropic and nonlinear such material behavior would not strictly satisfy the requirements for the stress interpretation thus at the present state of knowledge fault slip inversion solutions are most reliably interpreted as constraining the principal strain rates

modelling landscape evolution geomorphology is currently in a period of resurgence as we seek to explain the diversity origins and dynamics of terrain on the earth and other planets in an era of increased environmental awareness yet there is a great deal we still do not know about the physics and chemistry of the processes that weaken rock and transport mass across a planet s surface discovering and refining the relevant geomorphic transport functions requires a combination of careful field measurements lab experiments and use of longer term natural experiments to test current theory and develop new understandings landscape evolution models have an important role to play in sharpening our thinking guiding us toward the right observables and mapping out the logical consequences of transport laws both alone and in combination with other salient processes improved quantitative characterization of terrain and process and an ever improving theory that describes the continual modification of topography by the many and varied processes that shape it together with improved observation and qualitative and quantitative modelling of geology vegetation and erosion processes will provide insights into the mechanisms that control catchment form and function this paper reviews landscape theory in the form of numerical models of drainage basin evolution and the current knowledge gaps and future computing challenges that exist copyright 2010 john wiley sons ltd

seismogenic zone structure of the southern middle america trench costa rica 1 the shallow seismogenic portion of subduction zones generates damaging large and great earthquakes this study provides structural constraints on the seismogenic zone of the middle america trench offshore central costa rica and insights into the physical and mechanical characteristics controlling seismogenesis we have located 300 events that occurred following the mw 6 9 20 august 1999 quepos costa rica underthrusting earthquake using a three dimensional velocity model and arrival time data recorded by a temporary local network of land and ocean bottom seismometers we use aftershock locations to define the geometry and characteristics of the seismogenic zone in this region these events define a plane dipping at 19 that marks the interface between the cocos plate and the panama block the majority of aftershocks occur below 10 km and above 30 km depth below sea level corresponding to 30 35 km and 95 km from the trench axis respectively relative event relocation produces a seismicity pattern similar to that obtained using absolute locations increasing confidence in the geometry of the seismogenic zone the aftershock locations spatially correlate with the downdip extension of the oceanic quepos plateau and reflect the structure of the main shock rupture asperity this strengthens an earlier argument that the 1999 quepos earthquake ruptured specific bathymetric highs on the downgoing plate we believe that subduction of this highly disrupted seafloor has established a set of conditions which presently limit the seismogenic zone to be between 10 and 35 km below sea level

using beryllium 7 to monitor the relative proportions of interrill and rill erosion from loessal soil slopes in a single rainfall event quantifying the relative proportions of soil losses due to interrill and rill erosion processes during erosion events is an important factor in predicting total soil losses and sediment transport and deposition beryllium 7 7 be can provide a convenient way to trace sediment movement over short timescales providing information that can potentially be applied to longer term larger scale erosion processes we used simulated rainstorms to generate soil erosion from two experimental plots 5 m 4 m 25 degrees slope containing a bare hand cultivated loessal soil and measured 7 be activities to identify the erosion processes contributing to eroded material movement and or deposition in a flat area at the foot of the slope based on the mass balance of 7 be detected in the eroded soil source and in the sediments the proportions of material from interrill and rill erosion processes were estimated in the total soil losses the deposited sediments in the flat area and in the suspended sediments discharged from the plots the proportion of interrill eroded material in the discharged sediment decreased over time as that of rill eroded material increased the amount of deposited material was greatly affected by overland flow rates the estimated amounts of rill eroded material calculated using 7 be activities were in good agreement with those based on physical measurements of total plot rill volumes although time lags of 45 and 11 minutes existed between detection of sediment being removed by rill erosion based on 7 be activities and observed rill initiation times our results suggest that the use of 7 be tracer has the potential to accurately quantify the processes of erosion from bare loessal cultivated slopes and of deposition in flatter downslope areas that occur in single rainfall events such measurements could be applied to estimate longer term erosion occurring over larger areas possessing similar landforms copyright c 2010 john wiley sons ltd

forearc response to subduction of the cocos ridge panama costa rica stratigraphic paleontologic and structural data from two panama costa rica forearc peninsulas located landward of the aseismic cocos ridge along the southernmost middle america trench document rapid pliocene subsidence and basin infilling followed by quaternary deformation and uplift on the burica peninsula an approximately 3 000 m thick pliocene pleistocene clastic sedimentary sequence characterized by fine grained turbidite deposits and volumetrically minor coarser grained channel fill slump and debris flow deposits bears depth diagnostic foraminifera that document rapid pliocene subsidence and deposition on a south dipping paleoslope new paleobathymetric and age estimates from foraminifera in these rocks indicate shallowing of depositional paleodepths from 2 000 to 1 200 m during the late pliocene present day exposure of these rocks indicates an average quaternary uplift rate of 1 mm yr the turbidite section on the burica peninsula is interpreted to represent a trench slope deposit and is correlated to a similar marine sedimentary section on the adjacent osa peninsula of costa rica structures developed within pliocene pleistocene strata of the outer forearc burica and osa peninsulas record minor 5 subhorizontal margin perpendicular shortening and margin perpendicular extension bedding orientations on the osa and burica peninsulas generally record arcward tilting by 10 30 of these outer forearc blocks on the burica peninsula the medial fault zone a north striking high angle right lateral strike slip fault has truncated and reoriented the pliocene pleistocene sedimentary sequence by fault bend forced folding a linear margin parallel fault herein named the ballena celmira fault zone bounds the arcward side of the osa and burica peninsulas and has accommodated vertical displacements between the outer forearc burica osa area and inner forearc terraba area throughout the tertiary structural and seismicity observations from the forearc region suggest that neogene deformation of the leading edge of the arc in this area reflects the effects of isostatic uplift and possibly increased interplate shear stresses as a result of subduction of the cocos ridge beneath this part of the arc since 1 m y ago

distribution of terminal electron accepting processes in an aquifer having multiple contaminant sources abstract concentrations of electron acceptors electron donors and h2 in groundwater were measured to determine the distribution of terminal electron accepting processes teaps in an alluvial aquifer having multiple contaminant sources upgradient contaminant sources included two separate hydrocarbon point sources one of which contained the fuel oxygenate methyl tertbutyl ether mtbe infiltrating river water was a source of dissolved no3 so4 and organic carbon doc to the downgradient part of the aquifer groundwater downgradient from the mtbe source had larger concentrations of electron acceptors dissolved o2 and so4 and smaller concentrations of teap end products dissolved inorganic c fe2 and ch4 than groundwater downgradient from the other hydrocarbon source suggesting that mtbe was not as suitable for supporting teaps as the other hydrocarbons measurements of dissolved h2 indicated that so4 reduction predominated in the aquifer during a period of high water levels in the aquifer and river the predominant teap shifted to fe3 reduction in upgradient areas after water levels receded but remained so4 reducing downgradient near the river this distribution of teaps is the opposite of what is commonly observed in aquifers having a single contaminant point source and probably reflects the input of doc and so4 to the aquifer from the river results of this study indicate that the distribution of teaps in aquifers having multiple contaminant sources depends on the composition and location of the contaminants and on the availability of electron acceptors

spatial organization of soil depths using a landform evolution model 1 the evolution of soil depths is investigated by modeling the interaction between soil production and surface erosion within a landform evolution model an enhanced version of the landform evolution model siberia that incorporates a soil evolution module is used to simulate evolving landforms and soils depths over geologic timescales the spatial and temporal evolution of soil depths are examined at the hillslope scale though it is widely accepted among the geomorphology community that soil water enhances chemical physical and biological weathering processes its effect has not been explicitly included in published models of soil production the main scientific questions that we address are 1 what are the implications of incorporating soil moisture dependency in the soil production function and 2 what type of soil production dynamics is needed to generate a bedrock topography that has a different spatial pattern from that of the ground surface a range of physics for the soil production model is explored the effect of soil moisture is included using the wetness index obtained from drainage analysis of either surface elevations or the bedrock topography the results show that the various soil production functions that incorporate either a wetness index or subsurface flow depth based on the bedrock topography give rise to soils that self organize with well defined spatial patterns and bedrock elevations with spatial organization significantly different from that of the surface the model that incorporates the influence of subsurface water on soil production is able to naturally generate a soil production rate with a maximum value for a nonzero soil depth and overcomes an inconsistency of previously published humped soil production models

impact of rock fragment size on erosion process and micro topography evolution of cone shaped spoil heaps abstract spoil heaps in sites disturbed by construction cause severe acceleration of erosion threatening environment quality and personal safety rock fragments rfs are a common component of spoil heaps therefore this study was conducted to evaluate the effects of different size classes of rfs on cone shaped spoil heap erosion a 3d laser scanner was used to capture the surface micro topography evolution a multi day rainfall simulation experiment at 1 5 mm min 1 rainfall intensity was conducted with 30 mass percent of rfs of different diameters 1 3 5 3 5 7 7 10 10 15 cm the results showed that rfs reduced runoff by 13 0 relative to the bare soil spoil heap among which the rfs of the 7 10 cm size class performed best only the initial surface micro topography factors increased with rf size the stable micro topography factors of 1 3 5 cm rf treatment were 59 2 larger than those for other rf treatments on average because of the slope slump spoil heaps containing small size 1 3 5 rfs more easily slumped with an area of 0 895 m2 and showed obvious changes in micro topography rfs in different size classes influenced soil loss of spoil heaps via runoff yield and effects on slope stability larger roughness increment and runoff rate were associated with greater soil loss rate r2 0 828 but time varying roughness had no effect on runoff overall the results of this study provide a better understanding of the impact of rfs on spoil heap erosion

kinematics of postseismic relaxation from aftershock focal mechanisms of the 1994 northridge california earthquake geodetic observations of surface deformation associated with the 1994 northridge southern california earthquake generally are reproduced by simple models of a large scale elastic dislocation on a blind or buried thrust fault the smaller scale aftershocks of the northridge earthquake are distributed throughout much of the volume of crust that appears to have deformed elastically during the mainshock these aftershocks averaged over volumes that are large relative to their rupture radii reflect a distributed permanent deformation that is accommodated by local brittle fracture we use a micropolar continuum model to invert the aftershocks in such volumes for the average incremental strain and we compare that deformation both with the elastic strain from the dislocation model of the mainshock and with geodetically measured strain aftershock deformation that occurred at depths below about 6 km and which is associated with the primary rupture zone is consistent with slow continuation of the southwest side up reverse slip on the blind northridge thrust fault in contrast aftershock deformation from the upper 5 7 km of the hanging wall block directly above the thrust fault can be characterized by horizontal ne sw shortening and horizontal nw se i e fault parallel extension this pattern of deformation is similar to that associated with the mainshock as observed geodetically and as calculated from the elastic dislocation model we interpret that the aftershock activity in the hanging wall represents the quasi ductile accommodation by brittle deformation mechanisms of a permanent strain distributed through the hanging wall block the aftershocks along the mainshock rupture zone are interpreted as resulting from either 1 the time dependent release along a weakened fault zone of part of the remaining accumulated elastic strain in the upper crust or 2 the continued slip in the weakened fault zone driven by the deformation of a ductile elastic lower crustal layer that relaxes under the stress transferred by the coseismic loss of cohesion in the upper crust in either case the aftershock activity suggests that the crust undergoes quasi ductile flow as a brittle elastic material and is not a strictly elastic material

subduction zone structure and magmatic processes beneath costa rica constrained by local earthquake tomography and petrological modelling summary a high quality data set of 3790 earthquakes were simultaneously inverted for hypocentre locations and 3 d p wave velocities in costa rica tests with synthetic data and resolution estimates derived from the resolution matrix indicate that the velocity model is well constrained in central costa rica to a depth of 70 km northwestern and southeastern costa rica are less well resolved owing to a lack of seismic stations and seismicity maximum h2o content and seismic wave speeds of mid ocean ridge basalt and harzburgite were calculated for metamorphic phase transformations relevant to subduction both the 3 d p wave velocity structure and petrological modelling indicate the existence of low velocity hydrous oceanic crust in the subducting cocos plate beneath central costa rica intermediate depth seismicity correlates well with the predicted locations of hydrous metamorphic rocks suggesting that dehydration plays a key role in generating intermediate depth earthquakes beneath costa rica wadati benioff zone seismicity beneath central costa rica shows a remarkable decrease in maximum depth toward southeastern costa rica the presence of asthenosphere beneath southeastern costa rica which entered through a proposed slab window may explain the shallowing of seismicity due to increased temperatures and associated shallowing of dehydration of the slab tomographic images further constrain the existence of deeply subducted seamounts beneath central costa rica large low p wave velocity areas within the lower crust are imaged beneath the southeasternmost volcanoes in central costa rica these low velocities may represent anomalously hot material or even melt associated with active volcanism in central costa rica tomographic images and petrological modelling indicate the existence of a shallow possibly hydrated mantle wedge beneath central costa rica

results from a new model of river basin evolution this paper briefly describes a model of the erosional development of catchments and their channel networks the model differentiates between the dominant transport processes in hillslope and channels the development of channels and hillslopes occurs in an integrated manner as a function of physically observable mechanisms the growth of a river basin is qualitatively described the model concepts are used to study the basin during periods of growth transient periods as well as during dynamic equilibrium this leads to hypotheses about the relationship between slopes relief tectonic uplift erodability runoff and catchment area it is shown that the model leads to very reasonable and desirable behaviour of hillslopes during retreat and degradation

holocene forearc block rotation in response to seamount subduction southeastern peninsula de nicoya costa rica the southeastern tip of the peninsula de nicoya costa rica on the caribbean plate margin lies inboard of the rough bathy metric terrain on the subducting cocos plate and along the land ward projection of the convergence vector for the fisher seamount group the southern tip of the peninsula has nearly orthogonal coastlines and extensive well preserved holocene marine terraces

post mining landform evolution modelling 1 derivation of sediment transport model and rainfall runoff model parameters data were collected from three sites on the waste rock dump at era ranger mine 1 the cap site which was unvegetated and unripped with a surface slope of 2 8 per cent 2 the batter site surface slope 20 7 per cent also unvegetated and unripped but with a covering of coarse rock material and 3 the soil site surface slope 1 2 per cent which had c 90 per cent vegetation cover of low shrubs and grasses and had been topsoiled and surface ripped natural rainfall events were monitored on the sites to collect rainfall runoff and soil loss data to parameterize a sediment transport model of the form t s q dt and the distfw rainfall runoff model low frequency high intensity events resulted in the greatest soil loss to accurately predict sediment loss during high intensity events storms with a range of intensities were selected to derive the sediment transport model distfw hydrology model parameters were derived by fitting four monitored events simultaneously the selected parameters for the vegetated and ripped case may overpredict discharge for some rainfall events resulting in conservative design of erosion control features on rehabilitated landforms copyright 2000 environmental research institute of the supervising scientist commonwealth of australia

sediment transport in rill flow under deposition and detachment conditions the understanding of soil erosion processes and the development of accurate erosion prediction models require understanding of detachment deposition and sediment transport in rills the objectives of this study were to determine whether sediment transport capacity is a unique value for given soil flow rate and slope and to determine if equilibrium sediment concentration in the rill obtained by detachment was different from that observed under depositional conditions experiments on a carmi loam fine mixed mesic typic hapludalf simulated rill erosion under net detachment and net deposition conditions two discharge rates of 6 and 9 l min 1 and two sediment input regimes of 0 and excess of transport capacity were tested on soil beds with lengths of 2 4 6 7 and 8 m at 7 slope sediment load reached steady state conditions within the 8 m distance on the rill at 9 l min 1 discharge 8 m length and excess sediment added to the flow sediment delivery was 71 g l 1 versus 31 g l 1 for the corresponding case with no sediment added overall for the conditions tested rill flow transported two times more sediment than it could detach the flow did not reach its maximum potential transported load through detachment of soil due in part to changes in the sediment size distribution under deposition and possibly to the protective action of bedload particles moving along the rill bottom and or changes in flow turbulence associated with sediment laden flow d 2003 elsevier science b v all rights reserved

a catchment scale evaluation of the siberia and caesar landscape evolution models landscape evolution models provide a way to determine erosion rates and landscape stability over times scales from tens to thousands of years the siberia and caesar landscape evolution models both have the capability to simulate catchment wide erosion and deposition over these time scales they are both cellular operate over a digital elevation model of the landscape and represent fluvial and slope processes however they were initially developed to solve research questions at different time and space scales and subsequently the perspective detail and process representation vary considerably between the models notably caesar simulates individual events with a greater emphasis on fluvial processes whereas siberia averages erosion rates across annual time scales this paper describes how both models are applied to tin camp creek northern territory australia where soil erosion rates have been closely monitored over the last 10 years results simulating 10 000 years of erosion are similar yet also pick up subtle differences that indicate the relative strengths and weaknesses of the two models the results from both the siberia and caesar models compare well with independent field data determined for the site over different time scales representative hillslope cross sections are very similar between the models geomorphologically there was little difference between the modelled catchments after 1000 years but significant differences were revealed at longer simulation times importantly both models show that they are sensitive to input parameters and that hydrology and erosion parameter derivation has long term implications for sediment transport prediction therefore selection of input parameters is critical this study also provides a good example of how different models may be better suited to different applications or research questions copyright 2010 john wiley sons ltd and commonwealth of australia

a new estimate for present day cocos caribbean plate motion implications for slip along the central american volcanic arc velocities from 153 continuously operatinggps sites on the caribbean north american and pacic plates arecombinedwith61newlyestimatedpacic cocosseafloor spreading rates and additional marine geophysical data to deriveanewestimate of present daycocos caribbean plate motion acomparisonofthepredictedcocos caribbean di rectiontoslipdirectionsofnumerousshallow thrustsubduc tion earthquakes from the middle america trench between costa rica and guatemala shows the slip directions to be deflected 10 clockwise from the plate convergence direc tion supporting thehypothesisthatfrequentdextralstrike slip earthquakes along the central american volcanic arc result from partitioning of oblique cocos caribbean plate convergence linear velocity analysis for forearc locations in nicaragua and guatemala predicts 14 2m m yr 1 of northwestward trench parallel slip of the forearc relative to thecaribbean plate possibly decreasing inmagnitude inel salvador and guatemala where extension east of the vol canic arc complicates the tectonic setting

accuracy constraints of terrestrial lidar data for soil erosion measurement application to a mediterranean field plot abstract applications of terrestrial laser scanning tls to measure soil erosion are yet limited although this topographic mapping method allows for large area coverage with high resolution and reliable precision however restricting factors are accurate and stable references for multi temporal change detection and adverse scanning geometries at agricultural fields the plot is usually situated on gentle slopes provoking low viewing angles of the scanning device onto the surface which inherits the risk of high data noise in this study tls is exploited from a high tripod to measure soil erosion at an andalusian hillslope 2 1000 m2 in the mediterranean sediment yield reveals discontinuous pattern and tls is a promising method to quantify these surface changes a stable reference system is defined resulting in multi temporal registration accuracy better than 7 mm further an mm accurate calibration plot 60 m2 is designed to evaluate scan geometry and radiometry i e incidence angle footprint and intensity in dependence of distance related errors a lookup table is determined to correct systematic errors of the field data the andalusian field plot is captured during a winter season and during single precipitation events estimated erosion rates amount 10 and 2 4 t ha 1 respectively surface changes with magnitudes larger 1 5 cm are reliably measured tls can be implemented to estimate soil erosion with cm resolution if errors are carefully accounted for

dendrogeomorphic assessment and sediment transfer of natural vs mining induced debris flow activity in călimani mountains eastern carpathians romania abstract during the second half of the twentieth century in the central part of the c limani mountains the mining activities for sulfur rich ore extraction and processing produced significant landscape changes sediment transfers across the affected catchments started during the mining period and are still ongoing today more than two decades after the cessation of the mining activities in 1997 subsequently neither rehabilitation works nor erosion control measures were undertaken to stabilize the spoil heap deposits and natural reforestation also material consolidation was impeded by the highly unstable talus slopes moreover little is known about the frequency of the hydrogeomorphic processes responsible for sediment transfers and their consequences dendrogeomorphic investigations grain size analyses and topographic surveys were carried out to document the history of hydrogeomorphic activity the volume of material stored behind the retention dams and the rate of sediment accumulation tree ring analysis allowed us to reconstruct ten debris flow events in the natural environment as well as in mining disturbed environment for the period 1931 2017 and 1970 2017 respectively triggering of debris flows appears related to spring and summer precipitation originating from short duration convective systems or long lasting rainfalls in these remote mining areas the reconstructed frequency of debris flows return intervals of 8 1 and 4 7 years might be explained by the rainwater accumulation on the spoil heap platform and the availability of sediments which flow down the talus and then follow the stream channels to reach one of the sediment retention reservoirs 7 4 8 4 cm y 1

the seismic source parameters of the 1991 costa rica aftershock sequence evidence for a transcurrent plate boundary the april 22 1991 valle de la estrella costa rica earthquake ms 7 6 was a back arc thrusting event associated with the underthrusting of the caribbean plate beneath central america a network of three passcal type portable instruments was deployed to monitor the aftershock activity in southern costa rica 2 to 6 weeks after the main shock the waveforms recorded on three component midperiod seismometers were used to recover source information for 15 small aftershocks magnitudes between 3 2 and 4 4 with a linear moment tensor inversion method we conducted several tests to investigate the effects of unknown structure and event mislocation on source parameter recovery the longer period waveforms in general are less sensitive to the effects of the structural details so that the essential source information can be successfully extracted from the waveform data the earlier part of the seismic wave forms has proven to be the most important carrier of the source information a gross crustal model can be used to describe the structure for the source study the small changes in the waveform character resulting from the mislocation of the events or inexact green s functions generated from the oversimplified crustal model do not prohibit us from the recovery of the source orientation at local distances in contrast the determination of the focal depth is subject to uncertainty because of the lack of detailed structural information our focal mechanisms are generally in good agreement with p wave first motion fault plane solutions determined from a local short period network the aftershocks show a clear spatial segmentation based on focal mechanism type most aftershocks near or southeast of the main shock were thrusting events with focal mechanisms similar to the main shock in contrast a cluster of aftershocks northwest of the main shock showed dominantly left lateral strike slip motion on a northeasterly striking nodal plane this suggests that a diffuse deformation zone exists in central costa rica and is characterized by left lateral strike slip motion this diffuse transcurrent deformation zone coincides with several geologic and geophysical features and perhaps is a result of the slower subduction rate of the buoyant cocos ridge than its adjacent segments along the middle america trench mat the diffuse transcurrent boundary may intersect with the north panama deformed belt npdb near limon costa rica and is very likely a plate boundary for the proposed panama block

a simulation model for unified interrill erosion and rill erosion on hillslopes a mathematical model was developed for simulating runoff generation and soil erosion on hillslopes the model is comprised of three modules one for overland flow one for soil infiltration and one for soil erosion including rill erosion and interrill erosion rainfall and slope characteristics affecting soil erosion on hillslopes were analysed the model results show that the slope length and gradient time distribution rainfall and distribution of rills have varying influence on soil erosion erosion rate increases nonlinearly with increase in the slope length a long slope length leads to more serious erosion the effect of the slope gradient on soil erosion can be both positive and negative thus there exists a critical slope gradient for soil erosion which is about 45 for the rate of erosion at the end of the slope and about 25 for the accumulated erosion copyright 2005 john wiley sons ltd

review of earth science research using terrestrial laser scanning abstract the application of advanced remote sensing technologies including terrestrial laser scanning tls to the earth sciences has increased rapidly in the last two decades improving the spatial and temporal resolution of data terrestrial laser scanning units have evolved into a common tool in studies of spectral and structural geology seismology natural hazards geomorphology and glaciology special consideration of the advantages and limitations of tls in each of these fields is discussed in depth in the context of important work published in each field the workflow used in a tls survey is crucial to the success of the survey and field specific earth science workflows are therefore also discussed products based on tls data such as triangulated irregular networks tin and digital surface models dsm are commonplace tools throughout the earth sciences and the use of these tools to measure slip distributions fault geometries aeolian transport river bed morphologies and flows and other research problems is expanded on where appropriate the review concludes with a discussion of recent trends in tls instrument development and their potential impact on the use of tls in the earth sciences in the future

runoff characteristics and soil erosion dynamic processes on four typical engineered landforms of coalfields an in situ simulated rainfall experimental study abstract large engineered landform tracts formed during coalfield development and construction cause serious soil erosion and threaten the ecological security of the coalfield area a series of in situ simulated rainfall experiments with rainfall intensities ranging from 1 0 to 3 0 mm min 1 were conducted to explore the runoff characteristics and erosion dynamic processes of four engineered landforms namely waste slag heap with more gravel wsg waste slag with more sand wss waste soil heap wsh and disturbed land dl with undisturbed land ul as the control ck compared with ul the wss wsg and wsh runoff rates rrs increased by 38 83 71 39 and 63 16 respectively but decreased by 9 25 for dl the slope flow of ul was in the subcritical laminar and subcritical transition flow regimes while the four engineered landform flow regimes were mainly subcritical transition and subcritical turbulent flow regimes the ul and dl soil loss rates slrs followed a declining fluctuating levelling off trend while the wss wsg and wsh slrs followed a trend of multiple early stage peaks and valleys before levelled off the mean wss wsg wsh and dl slrs were 11 19 times 138 67 times 73 47 times and 2 82 times that of ul respectively ul disturbance significantly increased the runoff ability to detach sediments by 2 48 94 90 times based on the relationships between runoff rate and soil loss rate the shear stress stream power and unit stream power up critical values initiating dl soil erosion were 58 86 37 06 and 56 67 lower than those of ul respectively while higher critical hydrodynamic values were required to detach wsg wss and wsh particles the rainfall intensity ri slope gradient median particle size d50 fractal dimension fd and up were employed to develop an empirical model for predicting engineered landform slrs

the long term stability of engineered landforms of the ranger uranium mine northern territory australia application of a catchment evolution model there is a need to assess the long term stability of engineered landforms associated with the rehabilitation of ranger uranium mine northern territory australia as it is a requirement that mill tailings must be contained for periods in excess of 1000 years the geomorphic model siberia is calibrated on hydrologic and erosion data collected by a combination of monitoring and rainfall simulation experiments on the waste rock dumps of ranger preliminary analysis of ranger s preferred above grade option suggests that erosion of the order of 7 to 8 m will occur on the structure in a period of 1000 years this depth of erosion may be sufficient to compromise the integrity of containment it is shown that siberia has significant advantages over steady state erosion models suggestions are made for the design that will enhance the stability of the structure and extend the structural life of the containment 1998 john wiley sons ltd

digital outcrop models applications of terrestrial scanning lidar technology in stratigraphic modeling abstract laser ranging is extremely accurate and efficient terrestrial scanning lidar light detection and ranging applied to outcrop stratigraphic mapping enables researchers to capture laser range data at a rate of thousands of individual x y z and laser intensity points per second these data in conjunction with complementary remotely and directly sampled data are used to conduct high precision facies characterization and to construct 3d geological computer models outcrop data are presented here to explain our workflow and to discuss the construction of rock based 3d digital outcrop models doms reproducibility and quantification are the drivers of this methodology high resolution terrestrial lidar acquisition processing interpretation and visualization are discussed and applied to mapping of geological surfaces in three dimensions laser generated models offer scientists an unprecedented visualization medium in a quantitative 3d arena applications of this technology include constructing and visualizing complex 3d earth models from outcrops for improved reservoir modeling flow simulation in hydrocarbon and aquifer systems and property modeling to constrain forward seismic modeling

quaternary uplift astride the aseismic cocos ridge pacific coast costa rica the pacific coast of costa rica lies within the central american forearc and magmatic arc region that was created by northeastward subduction of the cocos plate beneath the caribbean plate at the middle america trench from the peninsula de nicoya south eastward toward the peninsula de osa and the peninsula de burica on the panamanian border the middle america trench loses its physiographic expression where it intersects the aseismic cocos ridge interaction between subduction of the buoyant aseismic cocos ridge and the overriding caribbean plate is invoked to explain the variation in rates of vertical crustal uplift along a coastal transect from nicoya to burica the pliocene and pleistocene stratigraphic record and holocene marine terraces and beach ridge complexes indicate that maximum rates of crustal uplift have occurred on the peninsula de osa immediately landward of the aseismic cocos ridge crustal uplift rates decrease northwest toward the peninsula de nicoya and to a lesser extent southwest toward the peninsula de burica the late quaternary stratigraphy on the peninsula de osa is subdivided into two major chronostratigraphic sequences from groupings of radiocarbon dates crustal uplift rates calculated from these sequences systematically decrease from 6 5 to 2 1 m ka north east across the peninsula deformation of the peninsula is modeled as uplifted and down to the northeast tilted fault blocks with an angular rotation rate of 0 03 to 0 06 per thousand years although less well constrained crustal uplift rates on the peninsula de nicoya 200 km to the northwest of the peninsula de osa vary from 1 m ka for pliocene and pleistocene sediments to 2 5 m ka for holocene marine terraces in the quepos region 100 km to the northwest of the peninsula de osa calculated uplift rates derived from incision of late quaternary fluvial terraces range from 0 5 to 3 0 m ka on the peninsula de burica only 60 km to the southwest of the peninsula de osa calculated uplift rates range from 4 7 m ka for a late holocene marine terrace to 1 2 m ka for post late pliocene deep sea sediments the variations in calculated uplift rates on the peninsula de osa constrain a dynamic model for subduction of the cocos ridge and the resulting uplift of the overriding caribbean plate deflection of the caribbean plate is modeled using various effective elastic thicknesses as the response of an elastic plate to the buoyant force of the subducted cocos ridge because the shape of the subducted end of the cocos ridge is unknown two scenarios are evaluated 1 a radially symmetric ridge with a slope similar to the slope of the flanks of the ridge and 2 a ridge where the subducted end was truncated by the panama fracture zone the best fit model utilizes a truncated ridge that has been subducted during the past 0 5 m y 50 km beneath the overriding caribbean plate which has an effective elastic thickness of 5 km the model predicts that the highest uplift rate should be 3 7 m ka and occur on the southwest coast of the peninsula de osa the rate of uplift slows considerably to the northeast and indicates that the peninsula de osa is tilting to the northeast which agrees with observations in that region the predicted uplift rate attributed to aseismic ridge subduction also decreases along the coast both north and south of the peninsula de osa resulting in little uplift that can be attributed to cocos ridge subduction in the northwestern portions of the peninsula de nicoya

a statistic for testing the elevation characteristics of landscape simulation models there is an urgent need to test recently constructed conceptual models of landscape evolution and geomorphology against field data many statistics that have commonly been used such as strahler statistics are poorly suited to this testing being unable to potentially falsify the models when applied in controlled conditions the relations between these statistics and catchment mass movement processes are in many cases indirect moreover they are sensitive to unknowable inputs e g initial conditions one of the main differences among the competing landscape evolution models is their representation of mass movement and erosion processes so that statistics that are directly linked to these processes or their geomorphic signature are needed this paper examines the use of a log log linear relation between catchment area slope and elevation this relation has been previously derived quantitatively from the catchment erosion and hydrologic processes for dynamic and declining geomorphic equilibria using a catchment evolution model this paper shows that the relation is robust against deviations from the assumptions of spatial and temporal homogeneity of erosion climate and tectonic uplift made in its derivation the sensitivity of the geomorphology to time varying tectonic uplift and climate and spatially variable soil erodability is examined it is thus asserted that the relation between area slope and elevation is suitable for testing of models against field data where spatial and temporal homogeneity of erosion climate and tectonic uplift are only approximately true in the case of variable soil erodability planar drainage patterns exhibit self organization with the high elevation regions of the catchment having low soil erodability consequently a downstream increasing erodability of the soil material consistent with a downstream fining type of behavior is observed it is further argued that the equilibria relation is fundamental and uniquely defines the elevation form of catchments so that all other elevation statistics are derived from it

landscape evolution within a retreating volcanic arc costa rica central america subduction of hotspot thickened seafloor profoundly affects convergent margin tectonics strongly affecting upper plate structure volcanism and landscape evolution in southern central america low angle subduction of the cocos ridge and seamount domain largely controls landscape evolution in the volcanic arc field mapping stratigraphic correlation and 4 0 ar 3 9 ar geochronology for late cenozoic volcanic rocks of central costa rica provide new insights into the geomorphic response of volcanic arc landscapes to changes in subduction parameters slab thickness roughness dip late neogene volcanism was focused primarily along the now extinct cordillera de aguacate quaternary migration of the magmatic front shifted volcanism northeastward to the caribbean slope creating a new topographic divide and forming the valle central basin stream capture across the paleo aguacate divide led to drainage reversal toward the pacific slope and deep incision of reorganized fluvial networks pleistocene caldera activity generated silicic ash flows that buried the valle central and descended the tarcoles gorge to the orotina debris fan at the coast growth of the modern cordillera central accentuated relief along the new divide establishing the valle central as a pacific slope drainage basin arc migration relocation of the pacific caribbean drainage divide and formation of the valle central basin resulted from slab shallowing as irregular hotspot thickened crust entered the subduction zone the geomorphic evolution of volcanic arc landscapes is thus highly sensitive to changes in subducting plate character

testing of the siberia landscape evolution model using the tin camp creek northern territory australia field catchment the siberia landscape evolution model was used to simulate the geomorphic development of the tin camp creek natural catchment over geological time measured hydrology erosion and geomorphic data were used to calibrate the siberia model which was then used to make independent predictions of the landform geomorphology of the study site the catchment located in the northern territory australia is relatively untouched by europeans so the hydrological and erosion processes that shaped the area can be assumed to be the same today as they have been in the past subject to the caveats regarding long term climate fluctuation a qualitative or visual comparison between the natural and simulated catchments indicates that siberia can match hillslope length and hillslope profile of the natural catchments a comparison of geomorphic and hydrological statistics such as the hypsometric curve width function cumulative area distribution and area slope relationship indicates that siberia can model the geomorphology of the selected tin camp creek catchments copyright 2002 environmental research institute of the supervising scientist commonwealth of australia

geochemistry of dissolved inorganic carbon in a coastal plain aquifer 1 sulfate from confining beds as an oxidant in microbial co2 production a primary source of dissolved inorganic carbon dic in the black creek aquifer of south carolina is carbon dioxide produced by microbially mediated oxidation of sedimentary organic matter groundwater chemistry data indicate however that the available mass of inorganic electron acceptors oxygen fe iii and sulfate and observed methane production is inadequate to account for observed co2 production although sulfate concentrations are low approximately 0 05 0 10 mm in aquifer water throughout the flow system sulfate concentrations are greater in confining bed pore water 0 4 20 mm the distribution of culturable sulfate reducing bacteria in these sediments suggests that this concentration gradient is maintained by greater sulfate reducing activity in sands than in clays calculations based on fick s law indicate that possible rates of sulfate diffusion to aquifer sediments are sufficient to explain observed rates of co2 production about 10 5 mmoll 1 year 1 thus eliminating the apparent electron acceptor deficit furthermore concentrations of dissolved hydrogen in aquifer water are in the range characteristic of sulfate reduction 2 6 nm which provides independent evidence that sulfate reduction is the predominant terminal electron accepting process in this system the observed accumulation of pyrite and calcite cemented sandstones at sand clay interfaces is direct physical evidence that these processes have been continuing over the history of these sediments