modeling depth distributions of overland flows smith m w cox n j bracken l j 2011 modeling depth distributions of overland flows geomorphology 125 3 402 413

analyzing earthquake clustering features by using stochastic reconstruction 1 on the basis of the epidemic type aftershock sequence etas model and the thinning procedure this paper gives the method about how to classify the earthquakes in a given catalogue into different clusters stochastically the key points of this method are the probabilities of one event being triggered by another previous event and being a background event making use of these probabilities we can reconstruct the functions associated with the characteristics of earthquake clusters to test a number of important hypotheses about the earthquake clustering phenomena we applied this reconstruction method to the shallow seismic data in japan and also to a simulated catalogue the results show the following assertions 1 the functions for each component in the formulation of the space time etas model are good enough as a first order approximation for describing earthquake clusters 2 a background event triggers less offspring in expectation than a triggered event of the same magnitude 3 the magnitude distribution of the triggered event depends on the magnitude of its direct ancestor 4 the diffusion of the aftershock sequence is mainly caused by cascades of individual triggering processes while no evidence shows that each individual triggering process is diffusive and 5 the scale of the triggering region is still an exponential law as formulated in the model but not the same one for the expected number of offspring

gully annealing by aeolian sediment field and remote sensing investigation of aeolian hillslope fluvial interactions colorado river corridor arizona usa abstract processes contributing to development of ephemeral gully channels are of great importance to landscapes worldwide and particularly in dryland regions where soil loss and land degradation from gully erosion pose long term land management problems whereas gully formation has been relatively well studied much less is known of the processes that anneal gullies and impede their growth this study of gully annealing by aeolian sediment spanning 95 km along the colorado river corridor in glen marble and grand canyon arizona usa employed field and remote sensing observations including digital topographic modelling results indicate that aeolian sediment activity can be locally effective at counteracting gully erosion gullies are less prevalent in areas where surficial sediment undergoes active aeolian transport and have a greater tendency to terminate in active aeolian sand although not common examples exist in the record of historical imagery of gullies that underwent infilling by aeolian sediment in past decades and evidently were effectively annealed we thus provide new evidence for a potentially important interaction of aeolian hillslope fluvial processes which could affect dryland regions substantially in ways not widely recognized moreover because the biologic soil crust plays an important role in determining aeolian sand activity and so in turn the extent of gully development this study highlights a critical role of geomorphic ecologic interactions in determining arid landscape evolution

importance of small earthquakes for stress transfers and earthquake triggering 1 we estimate the relative importance of small and large earthquakes for static stress changes and for earthquake triggering assuming that earthquakes are triggered by static stress changes and that earthquakes are located on a fractal network of dimension d this model predicts that both the number of events triggered by an earthquake of magnitude m and the stress change induced by this earthquake at the location of other earthquakes increase with m as similar to 10 dm 2 the stronger the spatial clustering the larger the influence of small earthquakes on stress changes at the location of a future event as well as earthquake triggering if earthquake magnitudes follow the gutenberg richter law with b d 2 small earthquakes collectively dominate stress transfer and earthquake triggering because their greater frequency overcomes their smaller individual triggering potential using a southern california catalog we observe that the rate of seismicity triggered by an earthquake of magnitude m increases with m as 10 alpha m where alpha 1 05 0 05 we also find that the magnitude distribution of triggered earthquakes is independent of the triggering earthquake s magnitude m when alpha approximate to b small earthquakes are roughly as important to earthquake triggering as larger ones we evaluate the fractal correlation dimension d of hypocenters using two relocated catalogs for southern california the value of d measured for distances 0 1 r 5 km is d 1 54 for the shearer et al catalog and d 1 73 for the hauksson et al catalog the value of d reflects both the structure of the fault network and the nature of earthquake interactions by considering only those earthquake pairs with interevent times larger than 1000 days we can largely remove the effects of short term clustering then d approximate to 2 close to the value d 2 alpha 2 1 predicted by assuming that earthquake triggering is due to static stress the value d approximate to 2b implies that small earthquakes are as important as larger ones for stress transfers between earthquakes and that considering stress changes induced by small earthquakes should improve models of earthquake interactions

relations between rainfall runoff induced erosion and aeolian deposition at archaeological sites in a semi arid dam controlled river corridor process dynamics in fluvial based dryland environments are highly complex with fluvial aeolian and alluvial processes all contributing to landscape change when anthropogenic activities such as dam building affect fluvial processes the complexity in local response can be further increased by flood and sediment limiting flows understanding these complexities is key to predicting landscape behavior in drylands and has important scientific and management implications including for studies related to paleoclimatology landscape ecology evolution and archaeological site context and preservation here we use multi temporal lidar surveys local weather data and geomorphological observations to identify trends in site change throughout the 446 km long semi arid colorado river corridor in grand canyon arizona usa where archaeological site degradation related to the effects of upstream dam operation is a concern using several site case studies we show the range of landscape responses that might be expected from concomitant occurrence of dam controlled fluvial sand bar deposition aeolian sand transport and rainfall induced erosion empirical rainfall erosion threshold analyses coupled with a numerical rainfall runoff soil erosion model indicate that infiltration excess overland flow and gullying govern large scale centimeter to decimeter scale landscape changes but that aeolian deposition can in some cases mitigate gully erosion whereas threshold analyses identify the normalized rainfall intensity defined as the ratio of rainfall intensity to hydraulic conductivity as the primary factor governing hydrologic driven erosion assessment of false positives and false negatives in the dataset highlight topographic slope as the next most important parameter governing site response analysis of 4 years of high resolution four minute weather data and 75 years of low resolution daily climate records indicates that dryland erosion is dependent on short term storm driven rainfall intensity rather than cumulative rainfall and that erosion can occur outside of wet seasons and even wet years these results can apply to other similar semi arid landscapes where process complexity may not be fully understood copyright 2015 john wiley sons ltd

global seismicity of 2001 centroid moment tensor solutions for 961 earthquakes abstract centroid moment tensor cmt solutions are presented for 961 earthquakes occurring during 2001 the solutions are obtained using corrections for aspherical earth structure represented by the whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward a m dziewonski r l woodward acoustic imaging at the planetary scale in h emert h p harjes eds acoustical imaging vol 19 plenum press new york 1992 pp 785 797 the model of anelastic attenuation of durek and ekstrom bull seism soc am 86 1996 144 is used to predict the decay of the waveforms

3 d rotation of double couple earthquake sources summary we discuss 3 d rotations by which one double couple earthquake source can be rotated into another arbitrary double couple due to the symmetry of double couple sources there are four such rotations an algorithm is obtained in analytical form which is also available as a computer program solving the inverse problem of 3 d rotation of double couple earthquake sources i e for each pair of focal mechanisms or seismic moment tensor solutions the program finds all four rotations which rotate one mechanism into another this algorithm may be used in a wide variety of studies of stress field causing earthquakes investigations of the relationship between the focal mechanisms and the tectonic features of a seismogenic region etc the same inversion algorithm can be used to study the 3 d rotation of any symmetric second rank tensor such as the stress or strain tensor

millimeter scale microrelief affecting runoff yield over microbiotic crust in the negev desert abstract the negative effect of microrelief upon runoff yield explained by the increase in water storage and the slowdown in flow velocity is a known phenomenon however research concerning surface roughness hitherto focused on decimeter or centimeter scale microrelief owing to the heterogeneous character of many natural plots the effect of centimeter scale microrelief was mainly shown under controlled sprinkling experiments whereas no data was yet made available concerning the possible effect of a millimeter scale microrelief upon runoff yield under natural field conditions when runoff yield was measured over crusted i e surfaces covered by 1 3 mm of cyanobacterial crust and scalped 2 6 m 2 plots at the hallamish dune field negev desert israel during 5 winter seasons 1990 1995 no runoff was generated from the scalped plots during the first year following scalping while meagre quantities were received during the second year nevertheless during the third season and onward runoff yield at the scalped plots was consistently and significantly higher than that of the crusted control plots and this was so albeit the fact that the crust chlorophyll content of the scalped plots during the third season was as low as half the amount of the crusted plots these findings appeared to contradict previous findings that showed the existence of a positive linear relationship between the crust chlorophyll content and runoff yield the apparent contradiction was explained by the differences in the plot microrelief indicating that minute differences even of a millimeter scale may greatly affect runoff yield and thus may compensate for lower crust chlorophyll content surface smoothness which characterizes many of the arid zones may thus explain at least partially the high runoff yield obtained in deserts

biological soil crust effects must be included to accurately model infiltration and erosion in drylands an example from tabernas badlands in dryland ecosystems runoff is mainly generated in bare areas which are also more susceptible to water erosion than vegetated areas these bare areas are often covered and protected by biological soil crusts bscs which modify numerous physicochemical surface properties involved in runoff and erosion processes bscs are considered as one of the most important stabilizing factors in the soil surface but most previous research has concentrated only on patch or hillslope scale effects of bscs and their effect at coarser scales has rarely been studied in this article we present a new approach based on previous surface cover quantification for including the effects of bscs in physically based runoff and erosion modeling the limburg soil erosion model lisem was used to parameterize and simulate the effects of bscs on runoff and erosion in a small semiarid catchment characterized by fine textured soils and predominantly covered by bscs paired model simulations under two scenarios with and without including the effects of bscs were run under different rainfall intensities to evaluate the effect of bscs on runoff and erosion under different rainfall conditions runoff and erosion rates recorded in the field at the catchment outlet were predicted much more accurately when bscs were included because there was less overestimation of runoff rate maximum runoff peaks and erosion rates in the areas dominated by bscs the proposed approach enables bscs to be included in spatially distributed runoff and erosion models improving their predictions and may be used for evaluating how the effect of human activity on bscs affects catchment scale water erosion

generalized omori law for aftershocks and foreshocks from a simple dynamics a theory of the time dependence of earthquake foreshocks and aftershocks is presented the theory involves the response to sudden forcing of a dynamics of self driven acceleration to failure the empirically observed omori law which says that the rate of aftershocks as a function of time falls as a power law in time is derived theoretically the exponent of the falloff in time is shown to generically give a value close to one for rapidly accelerating dynamics to see if the theory is consistent with other features of real data foreshocks and aftershocks of small magnitude mainshocks are analyzed in a catalogue of real earthquakes results show that the spatial and temporal distribution of aftershocks is separable into a dependence on space and a dependence on time that the spatial distribution of aftershocks is consistent with the hypothesis that stress changes from the mainshock cause aftershocks and that the number of foreshocks approaches the number of aftershocks as the magnitude of the mainshock becomes smaller

microbiotic crust control of runoff generation on sand dunes in the negev desert 1 the general belief that dune sands in arid regions are not likely to generate runoff and that runoff necessitates wet conditions is examined runoff generation was measured within an arid dune field in the western negev desert israel during 1990 1994 on 16 plots 1 2 6 6 m2 constructed along a continuum of crust covered crust the relationships between chlorophyll a and carbohydrates of the microbiotic crust and runoff yield were studied whereas chlorophyll a 15 45 mg m 2 and carbohydrates 4 9 17 6 g m 2 of the cyanobacterial crusts showed positive linear relationships with runoff coefficients a significant reduction in runoff yield was obtained once the moss dominated crust with 53 54 5 mg m 2 chlorophyll a and 28 5 28 9 g m 2 of carbohydrates which inhabited the wettest habitat within the dune field was also included in the analysis contrary to previous assumptions that an increase in runoff generation occurs on arid and semiarid sand dunes in wet climates wet climates may lead to the establishment of moss dominated crusts that in turn decrease runoff yield

quantifying relationships of burning roughness and potential dust emission with laser altimetry of soil surfaces at submeter scales abstract decrease in surface roughness by the reduction of vegetation is one mechanism by which fire can promote aeolian transport in a variety of landscapes the extent to which fire might alter the roughness of the soil surface at fine spatial scales and the effect of this alteration on post fire aeolian response is not well known we examined relationships in the field between dust emissions and subcentimeter level soil surface roughness at submeter spatial scales with a terrestrial laser scanner and portable wind tunnel analog based on aeolian theory we hypothesized that observed relationships would differ from those determined in previous studies with laser altimetry at landscape scales meter kilometer length scales we examined four semiarid shrublands in southern idaho usa containing a distinct pattern of undershrub and interspace microsites including recently burned and unburned conditions mixed models were used to determine effects of burning on surface roughness and the response of dust emissions to changes in surface roughness results indicated that burned soil surfaces were rougher than unburned soil surfaces dust emissions were enhanced by increases in roughness on burned soil surfaces and in the absence of nonerodible roughness elements i e plants this finding is expectedly in contrast to previous work that demonstrated an inverse relationship between soil erosion and surface roughness determined with lidar light detection and ranging at landscape scales vegetated and unvegetated surfaces relationships of lidar derived roughness and aeolian emissions are scale dependent and vary with environmental factors of fire and vegetation these findings are integral for future research that attempts to parameterize model based predictions of aeolian emissions with lidar derived roughness

a strong correlation between induced peak dynamic coulomb stress change from the 1992 m7 3 landers california earthquake and the hypocenter of the 1999 m7 1 hector mine california earthquake the 1992 m7 3 landers earthquake may have played a role in triggering the 1999 m7 1 1 hector mine earthquake as suggested by their close spatial 20 km proximity current investigations of triggering by static stress changes produce differing conclusions when small variations in parameter values are employed here i test the hypothesis that large amplitude dynamic stress changes induced by the landers rupture acted to promote the hector mine earthquake i use a flat layer reflectivity method to model the landers earthquake displacement seismograms by requiring agreement between the model seismograms and data i can constrain the landers main shock parameters and velocity model a similar reflectivity method is used to compute the evolution of stress changes i find a strong positive correlation between the hector mine hypocenter and regions of large 4 mpa dynamic coulomb stress changes peak f t induced by the landers main shock a positive correlation is also found with large dynamic normal and shear stress changes uncertainties in peak f t 1 3 mpa are only 28 of the median value 4 6 mpa determined from an extensive set 160 of model parameters therefore the correlation with dynamic stresses is robust to a range of hector mine main shock parameters as well as to variations in the friction and skempton s coefficients used in the calculations these results imply dynamic stress changes may be an important part of earthquake trigging such that large amplitude stress changes alter the properties of an existing fault in a way that promotes fault failure

microbiotic crusts in the high equatorial andes and their influence on paramo soils although microbiotic crusts are known from many lowland deserts they have apparently never been reported from alpine areas this paper describes microbiotic crusts from an equatorial high andean location paramo de piedras blancas in venezuela the main objectives are to describe the basic characteristics of the crusts to examine the properties of the soils on which they occur and to discuss their possible geomorphic significance for paramo soils properties of crusts and of the soils beneath them were compared with those of adjacent bare soils at three sites between 4360 and 4550 m altitude measurements on unconfined soil compressive strength and infiltration rates were taken in the field crust specimens were also gathered and later examined and sectioned under a microscope to ascertain micromorphological details laboratory data included soil texture organic matter content color ph water storage at field capacity and stability of soil aggregates crusts formed discontinuous garland like patches parallel to contours or covered small round soil buds produced by frost sorting microbiotic crusts contained many plants including an unclassified hepatic genus marsupella dumort a moss grimmia longirostris hook and several lichen species crusts consisted of a thin organic layer 5 35 mm overlying mineral soil and showed three parallel bands with diffuse boundaries the outer layer had green reddish brown live plant shoots and stems with few fine mineral grains the middle layer had anatomically recognizable dark brown plant material and a greater content of mineral grains the light colored basal layer had little organic matter mixed with coarse mineral particles it also contained many small orthovughs vesicles and some larger arched chambers caused mainly by frost activity soils with a microbiotic crust were darker than bare soils organic matter content in crust areas was two to three times higher than in adjacent bare soil ph dropped 0 3 units below crusts soils with crust had finer texture than bare ground the content of fines in crusts was 1 5 times higher than in bare soils but gravel in these was four times higher than below cryptogams indices of particle concentration showed that grains 0 5 1 mm were more abundant in crusts finer soils in crusts may result from a combination of a prior random texture variation b cryptogam colonization of fine soil patches sorted by frost c interception and capture of aeolian dust by cryptogams especially by mosses and d reduction of fine particle erosion by crusts as coarse grains are lost mean particle size within crusts drops geomorphic effects of crusts were also significant a infiltration rates were 70 greater in crust than in noncrust soils 67 0 vs 40 4 mm min b crust soils stored more water at field capacity 48 7 88 4 than bare areas 20 5 42 c crust soils had a higher resistance to raindrop erosion than bare areas 47 5 drops 0 1 g vs 10 2 drops 0 1 g undisturbed crust specimens were even more effective in resisting drop impact surviving up to 1100 drops 0 1 g d cryptogams increased soil compressibility more than 200 from 54 g cm2 in bare soils to 118 1 g cm2 in crust areas all these geomorphic changes should result in lower rates of soil erosion in paramo areas with dense crusts

secondary aftershocks and their importance for aftershock forecasting the potential locations of aftershocks which can be large and damaging are often forecast by calculating where the mainshock increased stress we find however that the mainshock induced stress field is often rapidly altered by aftershock induced stresses we find that the percentage of aftershocks that are secondary aftershocks or aftershocks triggered by previous aftershocks increases with time after the mainshock if we only consider aftershock sequences in which all aftershocks are smaller than the mainshock the percentage of aftershocks that are secondary also increases with mainshock magnitude using the california earthquake catalog and monte carlo trials we estimate that on average more than 50 of aftershocks produced 8 or more days after m 5 mainshocks and more than 50 of all aftershocks produced by m 7 mainshocks that have aftershock sequences lasting at least 15 days are triggered by previous aftershocks these results suggest that previous aftershock times and locations may be important predictors for new aftershocks we find that for four large aftershock sequences in california an updated forecast method using previous aftershock data and neglecting mainshock induced stress changes can outperform forecasts made by calculating the static coulomb stress change induced solely by the mainshock manuscript received 20 november 2002

triggering of seismicity at short timescales following californian earthquakes 1 a method for measuring seismicity rate changes caused by the occurrence of major earthquakes in the surrounding crust is proposed it is based on a nonstationary poisson modeling of earthquake activity an estimate of the seismicity rate change and a probability measure of seismicity triggering following a large shock are derived and the removal of the influence of independent aftershock sequences of other nearby previous earthquakes is attempted without using more traditional declustering techniques the seismicity rate change estimator is corrected for its natural bias in favor of positive changes at short timescales that has so far strongly hindered measures of seismicity quiescences three californian earthquakes are examined using this method the 1989 m7 1 loma prieta the 1992 m7 3 landers and the 1994 m6 7 northridge earthquakes positive triggering is very commonly observed as expected but quiescence is however more seldomly obtained for timescales up to 100 days after the main shock this relative absence of quiescence as compared to typical predictions of coulomb modeling for example is also independently observed through direct correlation analyses of californian seismicity the possibility that the stresses caused by the main shock are spatially highly variable may explain these observations

effects of biological soil crusts on surface roughness and implications for runoff and erosion abstract soil surface roughness has a strong influence on runoff and erosion affecting surface storage capacity water flow routing and velocity and modifying runoff rates it also reduces soil detachment by raindrops and the shear effect of water flow on the soil surface in arid and semiarid ecosystems biological soil crusts bscs commonly appear in clearings between plants depending on the dominant component in the bsc community the roughness of the soil surface may vary considerably changing the hydrologic and erosive response of the soil the aim of this study is to determine the effect of physical and biological crusts on soil surface roughness and their influence on runoff and erosion for this purpose we set up open plots containing different bsc types and treatments and recorded runoff and total erosion from all the events for 18 months micro topographic indexes were calculated from high resolution digital surface models of the plots built from terrestrial laser scanner height data after comparing different spatial resolutions and indexes we concluded that only the local random roughness index in a 40 mm moving window provided a precise estimation of the roughness induced by bscs though it did not have a direct effect on runoff response the best relationship between microtopography and runoff on biologically crusted soils was found for surface storage capacity which appears as a powerful predictor of the runoff coefficient on long temporal scales sediment yield was not well predicted by any of the micro topographic indexes studied the only index that was significantly related to sediment yield was the local random roughness in a 40 mm moving window but even this explained only a third of the erosion variance

estimating aerodynamic roughness over complex surface terrain 1 surface roughness plays a key role in determining aerodynamic roughness length zo and shear velocity both of which are fundamental for determining wind erosion threshold and potential while zo can be quantified from wind measurements large proportions of wind erosion prone surfaces remain too remote for this to be a viable approach alternative approaches therefore seek to relate zo to morphological roughness metrics however dust emitting landscapes typically consist of complex small scale surface roughness patterns and few metrics exist for these surfaces which can be used to predictzofor modeling wind erosion potential in this study terrestrial laser scanning was used to characterize the roughness of typical dust emitting surfaces playa and sandar where element protrusion heights ranged from 1 to 199mm over which vertical wind velocity profiles were collected to enable estimation of zo our data suggest that although a reasonable relationship r 2 0 79 is apparent between 3 d roughness density and zo the spacing of morphological elements is far less powerful in explaining variations in zo than metrics based on surface roughness height r 2 0 92 this finding is in juxtaposition to wind erosion models that assume the spacing of larger scale isolated roughness elements is most important in determining zo rather our data show that any metric based on element protrusion height has a higher likelihood of successfully predicting zo this finding has important implications for the development of wind erosion and dust emission models that seek to predict the efficiency of aeolian processes in remote terrestrial and planetary environments

seismicity alert probabilities at parkfield california revisited for a decade the u s geological survey has used the parkfield earthquake prediction experiment scenario document to estimate the probability that earthquakes observed on the san andreas fault near parkfield will turn out to be foreshocks followed by the expected magnitude 6 mainshocks during this time we have learned much about the seismogenic process at parkfield about the long term probability of the parkfield mainshock and about the estimation of these types of probabilities the probabilities for potential foreshocks at parkfield are reexamined and revised in light of these advances as part of this process we have confirmed both the rate of foreshocks before strike slip earthquakes in the san andreas physiographic province and the uniform distribution of foreshocks with magnitude proposed by earlier studies compared to the earlier assessment these new estimates of the long term probability of the parkfield mainshock are lower our estimate of the rate of background seismicity is higher and we find that the assumption that foreshocks at parkfield occur in a unique way is not statistically significant at the 95 confidence level while the exact numbers vary depending on the assumptions that are made the new alert probabilities are lower than previously estimated considering the various assumptions and the statistical uncertainties in the input parameters we also compute a plausible range for the probabilities the range is large partly due to the extra knowledge that exists for the parkfield segment making us question the usefulness of these numbers

rainfall runoff relationship over encrusted dune surfaces nizzana western negev israel a thin microbial crust covers the lower part of longitudinal dunes in the western negev where average annual rainfall is 95 mm in order to study the effect of the microbial crust on rainfall runoff relationships under natural rainfall conditions runoff plots equipped with pressure gauges were established on opposite north and south facing slopes that differ in their vegetal cover and crust properties the study covered four years 1990 94 the first two years were wet and the following two years relatively dry one to five flow events were recorded per year no correlation was found between runoff yield rain amount and rain intensity unlike many microbial crusts reported in the literature the microbial crust in the western negev is not hydrophobic infiltration rate is high under dry surface conditions and of the order of 9 12 mm h 1 when the crust is saturated the high final infiltration rate is explained by the occurrence of large pores that do not seal when the crust is saturated typical hydrographs have very steep rising and falling limbs pointing at a limited contributing area most flows last less than 10 min and runoff volumes collected are on the whole very small owing to differences in crust properties runoff is higher on north than on south facing slopes 1997 john wiley sons ltd

prediction probabilities from foreshocks when any earthquake occurs the possibility that it might be a foreshock increases the probability that a larger earthquake will occur nearby within the next few days clearly the probability of a very large earthquake ought to be higher if the candidate foreshock were on or near a fault capable of producing that very large mainshock especially if the fault is towards the end of its seismic cycle we derive an expression for the probability of a major earthquake characteristic to a particular fault segment given the occurrence of a potential foreshock near the fault to evaluate this expression we need 1 the rate of background seismic activity in the area 2 the long term probability of a large earthquake on the fault and 3 the rate at which foreshocks precede large earthquakes as a function of time magnitude and spatial location for this last function we assume the average properties of foreshocks to moderate earthquakes in california 1 the rate of mainshock occurrence after foreshocks decays roughly as t 1 so that most foreshocks are within three days of their mainshock 2 foreshocks and mainshocks occur within 10 km of each other and 3 the fraction of mainshocks with foreshocks increases linearly as the magnitude threshold for foreshocks decreases with 50 of the mainshocks having foreshocks with magnitudes within three units of the mainshock magnitude within three days we apply our results to the san andreas hayward san jacinto and imperial faults using the probabilities of large earthquakes from the report of the working group on california earthquake probabilities 1988 the magnitude of candidate event required to produce a 1 probability of a large earthquake on the san andreas fault within three days ranges from a high of 5 3 for the segment in san gorgonio pass to a low of 3 6 for the carrizo plain

anomalous stress diffusion in earthquake triggering correlation length time dependence and directionality 1 it has been recently suggested that moderate and large earthquakes can be triggered by similarly sized events at very long range here we study the main characteristics of earthquake triggering by determining its correlation length time dependence and directionality the problem is examined at a global level by using the harvard centroid moment tensor catalogue our results show that the correlation lengths depend only weakly on the magnitude thresholds involved no significant systematic triggering is observed for distances greater than the lithospheric thickness 100 150 km and the correlation length magnitude is similar to the seismogenic thickness 10 20 km the mean triggering distance and correlation length both increase with time very slowly compared with what would be expected from a normal diffusion process this is consistent with a clock advance on the failure time based on the constitutive rules for subcritical crack growth following a transient change in the loading stress the power law scaling disappears after a few months a functional form for the probability of triggering as a function of time and distance is proposed on the basis of the properties of near critical point systems the model fits the data well and could be used to calculate conditional probabilities for time dependent seismic hazard due to earthquake triggering an apparent directionality effect that was observed in the data set can be attributed to an artefact of poor depth determination these results do not preclude individual long range triggering with a potential directionality effect but they do rule out a statistical correlation at distances much greater than the thickness of the lithosphere

the age of the permian triassic boundary abstract the 5 cm boundary clay bed in the chinese stratotype section through the permian triassic boundary has been recognised as a bentonite shrimp ion microprobe dating of zircons in the bentonite indicates a magmatic age of 251 2 3 4 ma 2 this is the first direct constraint on the numerical age of the permian triassic boundary future refinements of ages at this important but poorly constrained level of the phanerozoic timescale may depend on re analysis of this uniquely placed volcanic horizon and other bentonites in the fossiliferous chinese upper permian and lower triassic the utility of defining the permian triassic boundary in the chinese stratotype section in the vicinity of known dateable horizons should be considered

small earthquakes tectonic forces earthquake scaling and frequency of occurrence relations require that small earthquakes be just as important as larger ones in redistributing the forces that drive relative displacements across active faults of any dimension including plate boundaries

toggling of seismicity by the 1997 kagoshima earthquake couplet a demonstration of time dependent stress transfer 1 two m 6 well recorded strike slip earthquakes struck just 4 km and 48 days apart in kagoshima prefecture japan in 1997 providing an opportunity to study earthquake interaction aftershocks are abundant where the coulomb stress is calculated to have been increased by the first event and they abruptly stop where the stress is dropped by the second event this ability of the main shocks to toggle seismicity on and off argues that static stress changes play a major role in exciting aftershocks whereas the dynamic coulomb stresses which should only promote seismicity appear to play a secondary role if true the net stress changes from a sequence of earthquakes might be expected to govern the subsequent seismicity distribution however adding the stress changes from the two kagoshima events does not fully capture the ensuing seismicity such as its rate change temporal decay or migration away from the ends of the ruptures we therefore implement a stress transfer model that incorporates rate state friction in which seismicity is treated as a sequence of independent nucleation events that are dependent on the fault slip slip rate and elapsed time since the last event the model reproduces the temporal response of seismicity to successive stress changes including toggling decay and aftershock migration nevertheless the match of observed to predicted seismicity is quite imperfect due perhaps to inadequate knowledge of several model parameters however to demonstrate the potential of this approach we build a probabilistic forecast of larger earthquakes on the expected rate of small aftershocks taking advantage of the large statistical sample the small shocks afford not surprisingly such probabilities are highly time and location dependent during the first decade after the main shocks the seismicity rate and the chance of successive large shocks are about an order of magnitude higher than the background rate and are concentrated exclusively in the stress triggering zones

viscoelastic stress triggering of the 1999 hector mine earthquake by the 1992 landers earthquake the 1999 mw 7 1 hector mine earthquake occurred only 20 km from the 1992 mw 7 3 landers earthquake fault the close spacing between the two earthquakes suggests that the landers earthquake trigger the hector mine event based on an elastic half space model scientists from the usgs scec and cdmg 2000 have found a negative coulomb stress change at the hector mine hypocenter due to landers this negative stress change is inconsistent with the hypothesis of static stress triggering in this paper i show evidence of stress triggering of the hector mine earthquake by landers due to a process governed by viscoelastic flow in the lower crust this visoelastic flow has produced broad scale postseismic rebound observed by gps and insar measurements the result of this study is that viscoelastic flow has significantly modified the regional stress field in the mojave desert after the landers earthquake the evolving stress field including viscoelastic flow has gradually moved the coulomb stress change at the hector mine hypocenter to a positive level the increase in coulomb stress exceeded 1 bar right before the hector mine earthquake bringing the hector mine ruptures to the proximity of catastrophic failure

the influence of competition between lichen colonization and erosion on the evolution of soil surfaces in the tabernas badlands se spain and its landscape effects article i nfo badlands often contain a mosaic of soil surface types with contrasting hydrological behaviour which drives their short term geomorphic evolution the tabernas badlands in semiarid se spain show a complex mosaic of bare ground biological soil crusts and plant covered patches and high variability of covers and morphologies previous work has identified the surfaces that act as sources of runoff and sediments and those that act as sinks the pathways of runoff between surfaces and the runoff and erosion at catchment scale however surfaces without vascular plants can be quite dynamic with important effects on geomorphic processes this work aims to generate hypotheses about the dynamics of both bare soil 34 of the area and biological soil crusts 33 and to provide a first estimation of the growth rate of terricolous lichens as increase of coverage and their geomorphological implications the dynamics of ten representative soil surfaces were photographically monitored over 13 years recording the cover and pattern of bare soil and of the two main kinds of biological soil crust brown crust and white crust erosion deposition were measured by erosion pins in unbounded plots and the hydrological and erosional behaviour monitored in bounded plots under natural and simulated rainfall biological colonization and crust growth were studied from 2004 within cleared plots in four crust communities microclimate was continuously monitored in each community after 13 years net erosion was recorded only in previously eroded slopes and divides vegetated sites and those covered by biological soil crust remained more or less invariant or recorded sedimentation in all white crust surfaces whole crust cover increased by 3 on average while macrolichen cover increased by nearly 30 within the driest brown crust macrolichen cover increased by 7 while the whole crust decreased by 3 according to previous work lichen cover particularly of white crust is often greater in north to east facing orientations because of the higher slope stability and the longer duration of moisture however the increase of the whole biological soil crust can depend more on species composition and previous cover and less or not at all on the aspect although certain species do grow faster in particular orientations within the plots cleared in 2004 the greatest increase occurred in the pioneering brown crust which reached an average of 26 cover after one year in spite of it receiving the most insolation significant microclimatic differences exist among the communities mainly in radiation soil moisture and thallus surface temperature terricolous lichen crusts primary colonizers of bare sufficiently stable areas can grow quickly and by increasing soil stability and development and modifying surface hydrology they can influence surface dynamics and ultimately landform dynamics crust growth rate probably decreases as its cover increases and it probably also oscillates with microclimatic oscillations however the high potential growth rate recorded allows detection not only of climatic changes but also short term possibly seasonal periods of stability extensive lichen crusts indicate low erosion rates and particular climatic conditions variations of crust cover could indicate climatic or land use variations

earthquake hazard after a mainshock in california after a strong earthquake the possibility of the occurrence of either significant aftershocks or an even stronger mainshock is a continuing hazard that threatens the resumption of critical services and reoccupation of essential but partially damaged structures a stochastic parametric model allows determination of probabilities for aftershocks and larger mainshocks during intervals following the mainshock the probabilities depend strongly on the model parameters which are estimated with bayesian statistics from both the ongoing aftershock sequence and from a suite of historic california aftershock sequences probabilities for damaging aftershocks and greater mainshocks are typically well constrained after the first day of the sequence with accuracy increasing with time

the evaluation of unmanned aerial system based photogrammetry and terrestrial laser scanning to generate dems of agricultural watersheds article i nfo agricultural watersheds tend to be places of intensive farming activities that permanently modify their microtopography the surface characteristics of the soil vary depending on the crops that are cultivated in these areas agricultural soil microtopography plays an important role in the quantification of runoff and sedi ment transport because the presence of crops crop residues furrows and ridges may impact the direction of water flow to better assess such phenomena 3 d reconstructions of high resolution agricultural watershed to pographyareessential fine resolutiontopographicdatacollectiontechnologiescanbeusedtodiscernhighlyde tailed elevation variability in these areas knowledge of the strengths and weaknesses of existing technologies used for data collection on agricultural watersheds may be helpful in choosing an appropriate technology this study assesses the suitability of terrestrial laser scanning tls and unmanned aerial system uas photogrammetry for collecting the fine resolution topographic data required to generate accurate high resolution digital elevation models dems in a small watershed area 12 ha because of farming activity 14 tls scans 25 points m 2 were collected without using high definition surveying hds targets whic ha re generally used to mesh adjacent scans to evaluate the accuracy of the dems created from the tls scan data 1098 ground control points gcps were surveyed using a real time kinematic global positioning system rtk gps linear regressions were then applied to each dem to remove vertical errors from the tls point elevations errors caused by the non perpendicularity of the scanner s vertical axis to the local horizontal plane and errors correlated with the distance to the scanner s position the scans were then meshed to generate a demtls with a1 1m spatial resolution the agisoft photoscan and micmac software packages were used to process the aerial photo graphsand generate a dempsc agisoftphotoscan anddemmcm micmac respectively with spatial resolutions of 1 1 m comparing the dems with the 1098 gcps showed that the demtls was the most accurate data prod uct with a root mean square error rmse of 4 5 cm followed by the demmcm and the dempsc which had rmse values of 9 0 and 13 9 cm respectively the dempsc had absolute errors along the border of the study area that ranged from 15 0 to 52 0 cm indicating the presence of systematic errors although the derived demmcm was accurate an error analysis along a transect showed that the errors in the demmcm data tended to increase in areas of lower elevation compared with tls uas is a promising tool for data collection because of its flexibility and low operational cost however improvements are needed in the photogrammetric processing of the aerial photographs to remove non linear distortions

aftershock zone scaling we investigate the distribution of aftershock zones for large earthquakes scalar seismic moment m 10 19 5 n m moment magnitude m 7 mainshocks are selected from the harvard centroid moment tensor catalog and aftershocks are selected from the preliminary determination of epicenters neic catalog the aftershock epicenter maps are approximated by a two dimensional gaussian distribution the major ellipse axis is taken as a quantitative measure of the mainshock focal zone size the dependence of zone length l on earthquake size is studied for three representative focal mechanisms thrust normal and strike slip although the numbers of mainshocks available for analysis are limited maximum a few tens of events in each case all earthquakes show the same scaling m l 3 no observable scaling break or saturation occurs for the largest earthquakes m 10 21 n m m 8 therefore it seems that earthquake geometrical focal zone parameters are self similar

properties and spatial distribution of microbiotic crusts in the negev desert israel abstract playing a cardinal role in surface stabilization and in carbon and nitrogen fixation microbiotic crusts play a crucial role in arid regions where they may serve as useful biomarkers for wind power and wetness duration this is especially the case on relatively unstable and infertile sand dunes in the negev desert where high correlations between the crust chlorophyll content and the daytime wetness duration were found yet only scarce data are available as to the possible link between the chlorophyll content and other physical color thickness strength crack density surface roughness and infiltrability and biological protein carbohydrate organic matter and species composition factors which determine in turn the crust type and its effect upon geomorphological and ecological processes no data are available on crust type distribution these were the aims of the current research when a cluster analysis was performed five types of microbiotic crusts were defined four of which were cyanobacterial a d and one moss dominated crust e the crusts differed in their physical and biological properties they showed an increase in chlorophyll content protein carbohydrates and organic matter from a to e with concomitant increase in species diversity thickness roughness and strength but with some variables crack density and infiltrability showing a reversed trend at the moss dominated crust the increase in the biomass components of the crust and the gradual change of the physical properties are explained by the improved physical conditions primarily wetness duration which facilitates longer hours of photosynthetic activity and consequently the introduction of additional more mesic species such as green algae lichens and mosses extended wetness duration was found to shift the crust type from cyanobacterial to moss dominated crust the spatial distribution of the crusts as verified by crust mapping coincided with the daylight surface duration which in turn was controlled by topography aspect angle and slope position it implies that whereas initial physical conditions dictates species composition and thus crust type the crust type in turn is responsible for characterizing the physical properties of the surface which may largely affect ecological and geomorphological processes

effects of microbiotic crusts under cropland in temperate environments on soil erodibility during concentrated flow several studies illustrate the wind and water erosion reducing potential of semi permanent microbiotic soil crusts in arid and semi arid desert environments in contrast little is hitherto known on these biological crusts on cropland soils in temperate environments where they are annually destroyed by tillage and quickly regenerate thereafter this study attempts to fill the research gap through a a field survey assessing the occurrence of biological soil crusts on loess derived soils in central belgium in space and time and b laboratory flume 2 m long experiments simulating concentrated runoff on undisturbed topsoil samples 0 4 0 1 m2 quantifying the microbiotic crust effect on soil erosion rates three stages of microbiotic crust development on cropland soils are distinguished 1 development of a non biological surface seal by raindrop impact 2 colonization of the soil by algae and gradual development of a continuous algal mat and 3 establishment of a well developed microbiotic crust with moss plants as the dominant life form as the silt loam soils in the study area seal quickly after tillage microbiotic soil crusts are more or less present during a large part of the year under maize sugar beet and wheat representing the main cropland area on average the early successional algae dominated crusts of stage 2 reduce soil detachment rates by 37 whereas the well developed moss mat of stage 3 causes an average reduction of 79 relative soil detachment rates of soil surfaces with microbiotic crusts compared with bare sealed soil surfaces are shown to decrease exponentially with increasing microbiotic cover b 0 024 for moss dominated and b 0 006 for algae dominated crusts in addition to ground surface cover by vegetation and crop residues microbiotic crust occurrence can therefore not be neglected when modelling small scale spatial and temporal variations in soil loss by concentrated flow erosion on cropland soils in temperate environments copyright 2007 john wiley sons ltd

depressional storage for markov gaussian surfaces processes during rain events such as infiltration runoff soil erosion and crust formation are influenced in part by depressional storage and surface roughness if the surface topography is known its potential depressional storage can be calculated the objective of this paper was to relate the statistical parameters for quantifying surface roughness to depressional storage analysis of topographic data sets digitized at millimeter grids by a laser scanner showed that soil roughness can be quantified by a markov gaussian m g type random process a monte carlo simulation procedure was used to find the mean ponding characteristics from simulated m g surfaces depressional storages were found to be functions of two m g parameters two sample length scales and the slope steepness the markov parameters are the global variance 2 and the correlation length scale l and the sample length scales are grid spacing x and side length ls after proper scaling all storage functions collapsed into two nondimensional relationships 1 storage at zero slope as a function of relative sample length scale and 2 storage as a function of scaled slope when l 0 simulated surfaces followed the random gaussian model and the nondimensional storage was only a function of scaled slope storages calculated from digitized elevation data sets with m g type statistics agreed well with results obtained from simulated surfaces

are aftershocks of large californian earthquakes diffusing we analyze 21 aftershock sequences of california to test for evidence of space time diffusion aftershock diffusion may result from stress diffusion and is also predicted by any mechanism of stress weakening here we test an alternative mechanism to explain aftershock diffusion based on multiple cascades of triggering in order to characterize aftershock diffusion we develop two methods one based on a suitable time and space windowing the other using a wavelet transform adapted to the removal of background seismicity both methods confirm that diffusion of seismic activity is very weak much weaker than reported in previous studies a possible mechanism explaining the weakness of observed diffusion is the effect of geometry including the localization of aftershocks on a fractal fault network and the impact of extended rupture lengths which control the typical distances of interaction between earthquakes

flow threads in surface run off implications for the assessment of flow properties and friction coefficients in soil erosion and hydraulics investigations soil surface microtopography produces non uniform surface run off in which narrow threads of relatively deep and fast ow move within broader shallower slower moving regions this kind of ow is probably widespread given that microtopography is itself common methods used to record the properties of surface run off include grid or transect based depth observations with a single mean ow speed derived by calculation from v q wd and the use of dye timing to estimate velocity with an effective mean depth calculated from d q wv because these methods allow only single ow eld mean values to be derived for v or d neither is well suited to non uniform ows the use of depth data to derive a ow eld mean v furthermore implicitly applies area weighting to the depth data likewise the use of dye speeds for v inherently overestimates mean v because dye dominantly follows the faster ow threads the associated errors in derived parameters such as friction coef cients are not readily quanti ed and appear not to have been addressed previously new eld experiments made on untilled soil surfaces in arid western nsw australia explore these circumstances and the implications for deriving meaningful measures of ow properties including friction coef cients on surfaces deliberately chosen for their very subtle microtopography average thread velocities are shown to be commonly 2 5 times greater than the ow eld mean and locally 6 7 times greater on the other hand non thread ow speeds lie below the ow eld mean on average reaching only 84 per cent of this value and often considerably less flow eld means conceal the existence of regions of the ow eld whose properties are statistically distinct results con rm that a reliance on ow eld average depths yields estimates of friction coef cients that are biased toward the shallower high roughness parts of the ow while if dye speeds are relied upon the results are biased toward the deeper smoother threads of ow a new approach to the evaluation of friction coef cients in non uniform ows is advanced involving the determination of separate coef cients for threads and non thread zones of the ow eld in contrast ow eld friction coef cients as they are customarily derived in run off plot experiments subsume these distinct coef cients in proportions that are generally unknown the value of such coef cients is therefore questionable copyright 2004 john wiley sons ltd

sensitivity of static stress calculations to the earthquake slip distribution 1 the apparent strong correlation between coulomb stress changes and the spatial distribution of aftershocks suggests the possibility of making near real time estimations of areas at risk of experiencing off fault aftershocks in order to do this in practice a number of issues must first be addressed including the extent to which the main shock slip must be known in detail before a meaningful stress map can be constructed here we investigate this issue by constructing a time ordered sequence of slip solutions for the landers earthquake computing coulomb stress changes for each solution and quantitatively comparing the stress field with the observed aftershocks by 1 resolving the coulomb stress change onto the aftershock nodal planes and calculating the percentage of events consistent with triggering and 2 constructing a two dimensional map of coulomb stress and computing the correlation coefficient between the positive and negative areas and the locations of the aftershocks we find that slip solutions based on empirical relations and either focal mechanism or moment tensor data produce stress fields inconsistent with the observed spatial distribution of aftershocks whereas slip solutions incorporating the correct rupture geometry but greatly simplified slip produce stress fields consistent with the aftershock distribution when very near fault events are excluded we further find that resolving stress perturbations onto earthquake nodal planes and computing the percentage of events experiencing positive coulomb stress provides a poor measure of success because of the limited range of structures on which events occur and the compatibility of the main shock stress field with these structures our results support the hypothesis that coulomb stress changes affect the spatial distribution of aftershocks and suggest that meaningful calculations of coulomb stress can be made as soon as an earthquake s rupture geometry is well constrained

topographic controls on the spatial distribution of ground cover in the tabernas badlands of se spain abstract the relationships between the spatial distribution of ground cover and terrain attributes were examined in the tabernas badlands se spain in order to understand the terrain dependent driving forces of the spatially heterogeneous ground cover ground cover was mapped in the field and terrain attributes were derived from a 1 m resolution digital elevation model dem the association of spatial distribution of the landforms resulting from a regionalisation using a nonhierarchical classification of the topographic overlays and the ground cover pattern was proved from the analysis of relationships between terrain attributes and proportional abundance of ground cover types it was found that ground cover is arranged along topographic gradients plant covered surfaces are more abundant on low slope angles concave slopes relatively large contributing areas and with low length slope factor values unvegetated surfaces show contrary trends and lichens are associated with intermediate conditions relationships with local terrain attributes such as slope angle or elevation are more pronounced than those with terrain attributes related to sediment and water transfer such as contributing area wetness index or length slope factor which could be explained by the heterogeneity of runoff that is usually shorter than the hillslope length the relationships established between the spatial distribution of ground cover types and terrain attributes provide the basis for future development of a tool for mapping spatial distribution of ground cover in similar areas from only topographic information

effect of depression storage capacity on overland flow generation for rough horizontal surfaces water transfer distance and scaling overland flow triggering on rough surfaces was investigated using an understanding oriented model the model was based on conditioned walker technique and developed to simulate and analyse the evolution of puddle connection on numerically generated rough surfaces the percolation theory gave a theoretical framework to formalize model outputs and to study overland flow scaling overland flow triggering appeared consistent with a percolation process a scale change exponent was suggested new insights based on the concept of transfer distance of water were emphasized transfer distance enabled us to analyse the water redistribution inside a field and helped to define rainfall efficiency when infiltration occurred copyright 2002 john wiley sons ltd

statistical model for standard seismicity and detection of anomalies by residual analysis abstract a statistical point process model is derived to describe the standard activity of earthquake occurrences by assuming that general seismicity is given by the superposition of aftershock sequences the parameters are estimated ty the maximum likelihood method using the estimated model the residual point process of the data is defined and used to find the anomalies which are included in the data set but not captured in the considered model for the standard seismicity for instance seismic quiescences can be measured quantitatively by using the residual process some examples are provided to illustrate such analyses furthermore a time series of the magnitudes on the residual point process is considered to investigate its dependence either on the time or on the history of the seismicity by assuming the exponential distribution at each time and modelling of the b value we can examine such dependences and estimate them two practical examples are shown

the role of crust thickness in runoff generation from microbiotic crusts contrary to humid areas where runoff takes place following the saturation of the soil column runoff in arid and semiarid zones takes place when rain intensities exceed the infiltration capability of the upper soil crust whether physical crust or microbiotic crust mc this type of overland flow known as hortonian overland flow hof is not fully understood especially in the case of mc in particular little is known regarding the effect of crust thickness and its fine silt and clay content on runoff generation with some scholars claiming that runoff generation is positively correlated with crust thickness and fine content in an attempt to determine the effect of crust thickness and to assess the role played by the silt and clay on runoff generation a set of field and lab experiments were undertaken on mcs inhabiting sand dunes in the negev desert israel these included sprinkling experiments coupled with measurements of the physical thickness silt and clay and biological chlorophyll protein total carbohydrates properties of 0 5 10 mm thick crusts the data showed that runoff generation took place on surfaces as thin as 0 5 0 7 mm only and was not correlated with the fine silt and clay content the implications for hof and for arid ecosystems are discussed copyright 2014 john wiley sons ltd

estimating total horizontal aeolian flux within shrub invaded groundwater dependent meadows using empirical and mechanistic models 1 wind erosion is a significant environmental problem that removes soil resources from sensitive ecosystems and contributes to air pollution in regions of shallow groundwater friable puffy soils are maintained through capillary action surface evaporation of solute rich soil moisture and protection from mobilization by groundwater dependent grasses and shrubs when a reduction in vegetation cover occurs through any disturbance process there is potential for aeolian transport and dust emission we find that as mean gap size between vegetation elements scaled by vegetation height increases total horizontal aeolian sediment flux increases and explains 58 of the variation in total horizontal aeolian sediment flux we also test a probabilistic model of wind erosion based on gap size between vegetation elements scaled by vegetation height the okin model which predicts measured total horizontal aeolian sediment flux more closely than another commonly used model based on the average plant area observed in profile raupach model the threshold shear velocity of bare soil appears to increase as gap size between vegetation elements scaled by vegetation height increases reflecting either surface armoring or reduced interaction between the groundwater capillary zone and surface sediments this work advances understanding of the importance of measuring gap size between vegetation elements scaled by vegetation height for empirically estimating q and for structuring process based models of desert wind erosion in groundwater dependent vegetation

post fire hillslope log debris dams for runoff and erosion mitigation in the semiarid ebro basin abstract the hydrologic effects of hillslope log debris dams were analyzed in areas of the castejon mountains semiarid ebro basin ne spain affected by a wildfire four experimental sites showing differences in the soil composition calcareous and gypseous and the aspect of the steep slopes north and south facing were selected all of the experimental sites were located along planar hillslopes where aleppo pine forest had burned in 2009 in the four sites per triplicate runoff and sediment yields were measured for two consecutive years 2012 2013 after the construction of log dams on partially re vegetated sites in 2011 in 2012 log dam installation significantly decreased soil erosion from 8 51 mg ha 1 year 1 to 0 76 mg ha 1 year 1 with a log dam performance of approximately 90 being obtained similarly the log dams caused a significant reduction of runoff from 6 9 to 3 3 mm year 1 presenting a performance of 52 both differences decreased one year later approximately 75 of the soil loss from 2012 was collected in only one clean out period when rainfall was almost half of annual rainfall the quality of the eroded sediments and water runoff was related to the composition of the ah horizon log dams reduced soil erosion in three of the four sites tested during the first year however in the second year only one site showed statistically significant differences which was the site with the greatest amount of bare soil these findings indicate that in semi arid areas post fire active restoration measures are still active four years after a fire on south facing slopes with poor soils and slow ground cover recovery

slope channel coupling between pipes gullies and tributary channels in the mocatan catchment badlands southeast spain the dispersive nature of the highly sodic silts of the triassic rich unit of the gochar formation plays a fundamental role in the erosion of the mocatan catchment badlands in almeria where a rejuvenating pipe and incised channel network is rapidly evacuating slope materials referring to concepts of medium and long term landscape evolution and incorporating contemporary thoughts on the role of connectivity in system evolution from the geomorphological literature this paper attempts to develop a conceptual model of the way geologic topographic material property and ecological factors combine to explain the complex geomorphological evolution of the site an electronic distance measurement edm survey was undertaken using a leica tc3100 to produce a detailed topographic map this database was supplemented by geomorphological geological and ecological data derived from ground survey and remote sensing and further morphometric analysis undertaken preferred orientations of channel segments and the topographic distribution of pipe roof collapse features and outfalls in relation to known stratigraphic controls suggests that once coupled to the slope base channel pipe networks develop in a systematic sequential way a wave of incision moving up the main channel reconnects channels with slopes and the resulting increased hydraulic gradients on sideslopes encourage extensive deep pipe development for the first time in these materials once major pipe development is possible three dimensional pipe networks enlarge and then collapse to form an extensive partially coupled steep sided gully network from this perspective the coupling of the pipe to a rejuvenating channel is a significant intrinsic threshold event and the main reason that badlands have developed locally in these dispersive materials it is concluded that erosion in this landscape will only be suppressed after a considerable period of slope base stability which could allow a gradual loss of sodium from the surface by leaching or organic exchanges both theoretical and management implications are explored

effect of natural restoration time of abandoned farmland on soil detachment by overland flow in the loess plateau of china vegetation restoration has significant effects on soil properties and vegetation cover and thus affects soil detachment by overland flow few studies have been conducted to evaluate this effect in the loess plateau where a great green project was implemented in the past decade this study was carried out to quantify the effects of age of abandoned farmland under natural vegetation restoration on soil detachment by overland flow and soil resistance to erosion as reflected by soil erodibility and critical shear stress the undisturbed soil samples were collected from five abandoned farmlands with natural restoration age varying from 3 to 37 years the samples were subjected to flow scouring in a 4 0 m long by 0 35 m wide hydraulic flume under six different shear stresses ranging from 5 60 to 18 15 pa the results showed that the measured soil detachment capacities in currently cultivated farmland were 24 1 to 35 4 times greater than those of the abandoned farmlands for the abandoned farmlands soil detachment capacities fluctuated greatly due to the complex effects of root density and biological crust thickness and could be simulated well by flow shear stress and biological crust thickness with a power function nse 0 851 soil erodibility of abandoned farmlands decreased gradually with restoration age and reached a steady stage when restoration age was greater than 28 years the critical shear stress of the natural abandoned farmlands declined when restoration age was less than 18 years and then increased due to the episodic influences of vegetation recovery and biological crust development more studies in the loess plateau are necessary to quantify the relationship between soil detachment capacity and biological crust thickness for better understanding the mechanism of soil detachment under natural vegetation restoration copyright 2013 john wiley sons ltd

quantifying the surface covering binding and bonding effects of biological soil crusts on soil detachment by overland flow biological soil crusts bscs have impacts on soil detachment process through surface covering and binding and bonding b b mechanisms which might vary with successional stages of bscs this study was conducted to quantify the effects of surface covering binding and bonding of bscs on soil detachment capacity by overland flow in a 4 m long hydraulic flume with fixed bed two dominant bsc types developed well in the loess plateau the early successional cyanobacteria and the later successional moss were tested using natural undisturbed soil samples collected from the abandoned farmlands two treatments of undisturbed crusts and one treatment of removing the above ground tissue of bscs were designed for each bsc type for comparison bare loess soil was used as the baseline the collected soil samples were subjected to flow scouring under six different shear stresses ranging from 6 7 to 21 2 pa the results showed that soil detachment capacity dc and rill erodibility kr decrease with bsc succession and the presence of bscs obviously increased the critical shear stress especially for the later successional moss crust for the early successional cyanobacteria crust dc was reduced by 69 2 compared to the bare loess soil where 37 7 and 31 5 are attributed to the surface covering and b b respectively for the later successional moss crust dc decreased by 89 8 compared to the bare loess soil where 68 9 and 20 9 contributed to the surface covering and b b respectively these results are helpful in understanding the influencing mechanism of bscs on soil erosion and in developing the process based erosion models for grassland and forestland copyright 2017 john wiley sons ltd

penetration resistance of biological soil crusts and its dynamics after crust removal relationships with runoff and soil detachment abstract soil sealing and crusting are common widespread processes in arid and semiarid soils that strongly affect runoff and erosion in these soils biological soil crusts bscs are an essential surface component known to have an important role in water processes and are also strong erosion protection agents however these crusts are also highly vulnerable to disturbances which seriously affect their pedological and ecological roles the aims of this study were to examine whether penetration resistance pr depends on bsc developmental stage and how removal of bscs affects pr under dry and wet soil conditions and to analyse the relationship between pr and runoff and soil detachment in these soils this research was conducted in two semiarid ecosystems representative of crusting processes in se spain el cautivo and las amoladeras almeria province four pairs of plots containing the main bsc types identified at both sites were selected and two treatments were considered one in each plot in the pair i unaltered bsc and ii bsc removal by scraping two intense rainfall simulation experiments were performed one after another in these plots runoff was measured during both and water samples were collected for further determination of sediment yield pr was measured in undisturbed bsc and scalped soil on dry soil prior to rainfall on wet soil after the first and second rainfalls and on dry soil seven months after bsc removal crust pr was higher at las amoladeras 3 13 0 54 kg cm 2 than at el cautivo 1 52 0 74 kg cm 2 due to soil compaction from trampling by livestock in the former pr varied with bsc development with less developed cyanobacteria bscs showing higher resistance under dry and wet conditions than more developed lichen bscs bsc removal was followed by the formation of a new seal physical crust upon raining which however did not result in increased pr no significant relationship was found between pr and runoff but there was a weak negative relationship between pr and soil detachment because in bscs which had higher prs soil detachment rates were much lower than in recently scalped soils seven months after bsc removal pr was significantly higher in scalped soils than for undisturbed bscs our results show that pr was not a good indicator of hydrological and soil detachment response of bscs or the soil sealing during rain immediately after bsc removal but it was a good indicator of physical soil crust formation in scalped soils over time

global omori law decay of triggered earthquakes large aftershocks outside the classical aftershock zone 1 triggered earthquakes can be large damaging and lethal as evidenced by the1999 shocks in turkey and the 2001 earthquakes in el salvador in this study earthquakes with ms 7 0 from the harvard centroid moment tensor cmt catalog are modeled as dislocations to calculate shear stress changes on subsequent earthquake rupture planes near enough to be affected about 61 of earthquakes that occurred near defined as having shear stress change 0 01 mpa the ms 7 0 shocks are associated with calculated shear stress increases while 39 are associated with shear stress decreases if earthquakes associated with calculated shear stress increases are interpreted as triggered then such events make up at least 8 of the cmt catalog globally these triggered earthquakes obey an omori law rate decay that lasts between 7 11 years after the main shock earthquakes associated with calculated shear stress increases occur at higher rates than background up to 240 km away from the main shock centroid omori s law is one of the few time predictable patterns evident in the global occurrence of earthquakes if large triggered earthquakes habitually obey omori s law then their hazard can be more readily assessed the characteristic rate change with time and spatial distribution can be used to rapidly assess the likelihood of triggered earthquakes following events of ms 7 0 i show an example application to the m 7 7 13 january 2001 el salvador earthquake where use of global statistics appears to provide a better rapid hazard estimate than coulomb stress change calculations

importance of direct and indirect triggered seismicity in the etas model of seismicity 1 using the simple etas branching model of seismicity which assumes that each earthquake can trigger other earthquakes we quantify the role played by the cascade of triggered seismicity in controlling the rate of aftershock decay as well as the overall level of seismicity in the presence of a constant external seismicity source we show that in this model the fraction of earthquakes in the population that are aftershocks is equal to the fraction of aftershocks that are indirectly triggered and is given by the average number of triggered events per earthquake previous observations that a significant fraction of earthquakes are triggered earthquakes therefore imply that most aftershocks are indirectly triggered by the mainshock

soil surface roughness measurement methods applicability and surface representation abstract in a laboratory rainfall simulator study soil surface roughness was measured using contact roller chain pin meter and noncontact devices laser scanner photogrammetry soil surfaces with two initial roughness conditions aggregates as for the contact methods resolution cm range and precision mm range is limited which constrains their application to calculation of simple surface parameters resolution and precision in the sub millimeter range could be obtained with the laser scanner while for the photogrammetric method the measurement uncertainty was approximately 1 2 mm measurement time was highest 90 min for the pin meter technique though data were ready to use for analyses laser scanner measurements took 34 min several steps of data post processing required 30 more minutes data acquisition was fastest for photogrammetry 5 min but expert knowledge as well as special hard and software were necessary for time consuming photo analyses taking about 120 min the chain and pin meter were compared using a profile index profile lengths matched well for smooth surfaces on rough surfaces the chain meter gave shorter profile lines between profile index from chain measurements and the random roughness derived from pin meter data a polynomial regression could be found parameters of distributions of elevations as well as inclinations and depressions were used to compare the laser scanner and the photogrammetric technique generally the laser scanner was able to reproduce small aggregates as well as voids in between them while dem from stereophotos was smoothed between major aggregates this led to skewed distributions of elevations and inclinations as well as to a lower surface area up to 39 and a lower depression volume up to 68 shapes of depressions were significantly different as well the used photogrammetric technique is supposed to be successful in producing adequate dems for already smoothed surfaces e g after rainfall events the study revealed different fields of application and limitations of the compared devices using a non adequate technique for certain situations will definitely have implications on further analyses concerning connectivity of runoff pathways surface protection from raindrop impact or runoff detachment and sediment transport

the potential roles of biological soil crusts in dryland hydrologic cycles biological soil crusts bscs are the dominant living cover in many drylands of the world they possess many features that can influence different aspects of local hydrologic cycles including soil porosity absorptivity roughness aggregate stability texture pore formation and water retention the influence of biological soil crusts on these factors depends on their internal and external structure which varies with climate soil and disturbance history this paper presents the different types of biological soil crusts discusses how crust type likely influences various aspects of the hydrologic cycle and reviews what is known and not known about the influence of biological crusts on sediment production and water infiltration versus runoff in various drylands around the world most studies examining the effect of biological soil crusts on local hydrology are done by comparing undisturbed sites with those recently disturbed by the researchers unfortunately this greatly complicates interpretation of the results applied disturbances alter many soil features such as soil texture roughness aggregate stability physical crusting porosity and bulk density in ways that would not necessarily be the same if crusts were not naturally present combined these studies show little agreement on how biological crusts affect water infiltration or runoff however when studies are separated by biological crust type and utilize naturally occurring differences among these types results indicate that biological crusts in hyperarid regions reduce infiltration and increase runoff have mixed effects in arid regions and increase infiltration and reduce runoff in semiarid cool and cold drylands however more studies are needed before broad generalizations can be made on how biological crusts affect infiltration and runoff we especially need studies that control for sub surface soil features such as bulk density micro and macropores and biological crust structure unlike the mixed effects of biological crusts on infiltration and runoff among regions almost all studies show that biological crusts reduce sediment production regardless of crust or dryland type copyright 2006 john wiley sons ltd

theory of time dependent rupture in the earth at a velocity x which is a well defined function of k this propagation is stable and quasi static and is referred to as subcritical crack growth we shall use the terms stable quasistatic and subcritical to mean propagation at velocities much less than the sonic velocities of the medium this behavior results from stress induced corrosion at the crack tip the principal corrodent for the present application being h20 this behavior has been firmly established in the laboratory for mode i tensile cracks in a wide variety of materials ineluding silicates and silicate glasses see cholz 1968a 1972a martin 1972 wiederhorn and bolz 1970 atkinson 1979 lawn and wilshaw 1975 knott 1973 the form of the relationship between k and x does not vary significantly with the material only the parameters in the law vary as an example we show in figure 1 data on subcritical crack growth in quartz after atkinson 1979 the empirical relationship is found to take the form