influence of chemical denudation on hillslope morphology 1 models of hillslope evolution involving diffusion like sediment transport are conventionally presented as an equation in which the changes in land surface elevation or soil thickness are balanced by the divergence of soil transport and tectonic uplift soil production or both these models typically do not include the loss or gain of mass in hillslope soils due to processes of chemical weathering and deposition we formulate a more general depth integrated equation for the conservation of soil mass on a hillslope that includes a term representing chemical deposition or denudation this general depth integrated equation is then simplified to determine the one dimensional form of a steady state hillslope which experiences both mechanical and chemical denudation the differences in morphology between hillslopes only experiencing diffusion like mechanical sediment transport and hillslopes experiencing both diffusion like mechanical sediment transport and chemical denudation are explored under the conditions of a downslope increase in local soil lowering rate due to chemical weathering the hillslope profile will depart from the parabolic shape predicted by models that incorporate only linear diffusion like mechanical sediment transport in addition hillslopes that experience both chemical and mechanical denudation may have a convex concave profile at steady state a necessary condition for such steady state profiles is that the chemical denudation rate must exceed the mechanical denudation rate we further suggest that combinations of other physical parameter values such as total denudation rate average soil depth sediment diffusivity and the increase in soil depth away from the divide that lead to steady state convex concave hillslope profiles may exist in a wide variety of natural settings

active fault related folding in the epicentral area of the december 25 1222 io ix mcs brescia earthquake northern italy seismotectonic implications abstract a dense grid of petroleum industry seismic reflection profiles coupled with field mapping exploratory trenching and geomorphic and structural analysis are used to characterize the quaternary growth history of the capriano del colle fault system one of several inferred active buried thrusts that extend across the po plain in northern italy shortening is characterized here by a deeply buried south vergent forethrust and an associated north vergent backthrust whose upward propagation is expressed by fault propagation folding near the surface structural interpretation based on seismic data suggests that strain is accommodated at very shallow levels by secondary flexural slip thrusts and reverse faults developed on synclinal flanks that emanate from active axial surfaces analysis of syntectonic growth strata document maximum rates of dip slip of 3 45 0 66 mm yr 1 6 myr 1 2 myr and 0 47 0 22 mm yr during a more recent time period 0 89 myr present a quarry excavation at capriano del colle allows a preliminary paleoseismologic analysis of coseismic surface faulting and liquefaction exposed near the core of an active mid pleistocene to holocene anticline these features are interpreted to be generated during strong local earthquakes consistent with the environmental effects and ground motions of an event similar to the december 25 1222 brescia earthquake io ix mcs this indicates for the first time that compressive folds and blind thrusts in the po plain are currently accommodating slow rates of modern contraction in an active zone of the southern alps that extends from lake garda to varese we thus argue that earthquakes similar to the december 25 1222 brescia event are likely to occur in this region and pose a direct threat to such a densely populated and developed area

evidence for large holocene earthquakes on the compton thrust fault los angeles california 1 we demonstrate that the compton blind thrust fault is active and has generated at least six large magnitude earthquakes mw 7 0 7 4 during the past 14 000 years this large concealed fault underlies the los angeles metropolitan area and thus poses one of the largest deterministic seismic risk in the united states we employ a methodology that uses a combination of high resolution seismic reflection profiles and borehole excavations to link blind faulting at seismogenic depths directly to near surface fault related folding deformed holocene strata record recent activity on the compton thrust and are marked by discrete sequences that thicken repeatedly across a series of buried fold scarps we interpret the intervals of growth as occurring after the formation of now buried paleofold scarps that formed during uplift events on the underlying compton thrust ramp minimum uplift in each of the scarp forming events which occurred at 0 7 1 75 ka event 1 0 7 3 4 ka or 1 9 3 4 event 2 5 6 7 2 ka event 3 5 4 8 4 ka event 4 10 3 12 5 ka event 5 and 10 3 13 7 ka event 6 ranged from 0 6 to 1 9 m indicating minimum thrust displacements of 1 3 to 4 2 m such large displacements are consistent with the occurrence of large magnitude earthquakes mw 7 this multidisciplinary methodology provides a means of defining the recent seismic behavior and therefore the hazard for blind thrust faults that underlie other major metropolitan regions around the world

slip rates on the chelungpu and chushiang thrust faults inferred from a deformed strath terrace along the dungpuna river west central taiwan the chelungpu fault produced the september 1999 m w 7 6 chi chi earthquake central taiwan the shortening rate accommodated by this structure integrated over several seismic cycles and its contribution to crustal shortening across the taiwanese range have remained unresolved to address the issues we focus our study on the chelungpu and chushiang thrust faults within the southernmost portion of the chi chi rupture area structural measurements and available seismic profiles are used to infer the subsurface geometry of structures the chushiang and chelungpu faults appear as two splay faults branching onto a common ramp that further north connects only to the chelungpu surface trace we survey a deformed strath terrace along the dungpuna river buried under a 11 540 309 years old fill deposit given this age the dip angles of the faults and the vertical throw determined from the offset of the strath terrace across the surface fault traces we estimate slip rates of 12 9 4 8 and 2 9 1 6 mm yr on the chelungpu and chushiang faults respectively these yield a total shortening rate of 15 8 5 1 mm yr to be absorbed on their common decollement at depth this total value is an upper bound for the slip rate on the chelungpu fault further north where the chushiang fault disappears and transfers shortening to adjacent faults combining these results with the recently constrained shortening rate on the changhua blind thrust reveals that all these frontal faults presently absorb most of the long term horizontal shortening across the taiwanese range they thus stand as the major sources of seismic hazards in this heavily populated area the return period of earthquakes similar to the chi chi event over a 80 km long stretch of the western foothills is estimated to be 64 years this value is an underestimate because it assumes that all the faults locked during the interseismic period slip only during such large events comparison with historical seismicity suggests that episodic aseismic deformation might also play a major role in accommodating shortening

tree root mounds and their role in transporting soil on forested landscapes the growth and decay of tree roots can stir and transport soil this is one process that contributes to the mass movement of soil on hillslope to explore the efficiency of this process we document the mounding of soil beside ponderosa and lodgepole pine trees in the forests that dominate the mid elevations of colorado s boulder creek watershed mounds are best expressed around ponderosa pines reaching vertical displacements above the far field slopes of order 10 20 cm fading into the slope by roughly 100 cm distance from the trunks with common diameters of 30 cm positive mounding occurs on all sides of trees on slopes indicating that the mounding is not attributable to deflection of a creeping flow of soil around the tree but rather to the insertion of root volume on all sides in the subsurface mounding is commonly asymmetric even on cross slope profiles significant variation in the mound sizes results in no clear relationship between tree diameter and root volume displaced these observations motivated the development of a discrete element model of tree root growth using the liggghts model in which grains we specified to be root cells were allowed to enlarge within the simulated granular matrix mounding could be reproduced with the majority of the vertical displacement of the surface being attributable to reduction of the bulk density due to dilation of the granular matrix during root enlargement finally we develop a previous analysis of the role of roots in transporting soil during growth and decay cycles we find that even in shallow soils the root cycle can drive significant soil transport down forested montane slopes copyright 2013 john wiley sons ltd

coevolution of nonlinear trends in vegetation soils and topography with elevation and slope aspect a case study in the sky islands of southern arizona 1 feedbacks among vegetation dynamics pedogenesis and topographic development affect the critical zone the living filter for earth s hydrologic biogeochemical and rock sediment cycles assessing the importance of such feedbacks which may be particularly pronounced in water limited systems remains a fundamental interdisciplinary challenge the sky islands of southern arizona offer an unusually well defined natural experiment involving such feedbacks because mean annual precipitation varies by a factor of five over distances of approximately 10 km in areas of similar rock type granite and tectonic history here we compile high resolution spatially distributed data for effective energy and mass transfer eemt the energy available to drive bedrock weathering above ground biomass soil thickness hillslope scale topographic relief and drainage density in two such mountain ranges santa catalina scm pinaleno pm strong correlations exist among vegetation soil topography variables which vary nonlinearly with elevation such that warm dry low elevation portions of these ranges are characterized by relatively low above ground biomass thin soils minimal soil organic matter steep slopes and high drainage densities conversely cooler wetter higher elevations have systematically higher biomass thicker organic rich soils gentler slopes and lower drainage densities to test if eco pedo geomorphic feedbacks drive this pattern we developed a landscape evolution model that couples pedogenesis and topographic development over geologic time scales with rates explicitly dependent on vegetation density the model self organizes into states similar to those observed in scm and pm our results highlight the potential importance of eco pedo geomorphic feedbacks mediated by soil thickness in water limited systems

horizontal coseismic deformation of the 1999 chi chi earthquake measured from spot satellite images implications for the seismic cycle along the western foothills of central taiwan 1 the 1999 chi chi earthquake mw 7 6 broke a major thrust fault along the western foothills of the central range of taiwan we have measured the horizontal coseismic displacement field by correlating optical satellite images acquired before and after the earthquake these data reveal the fault trace and a clockwise rotation of surface displacements toward the north with much larger displacements and strain in the hanging wall at the surface coseismic slip increases from 5 6 m near the epicenter to 10 11 m to the north in the epicentral area we observe a left lateral strike slip zone trending n125 e and farther north a fault zone trending n s with a right lateral component the data were modeled using elastic dislocations the fault geometry consists of a shallow

local erosion rates versus active tectonics cosmic ray exposure modelling in provence south east france over the past decade in situ produced cosmogenic nuclides have revolutionised the study of landscape evolution in particular numerous studies have demonstrated that in active tectonic settings cosmic ray exposure dating of deformed or displaced geomorphic features makes it possible to quantify long term deformation rates in western european countries erosion due to climatically driven processes and human activities is probably the factor that most limits the accuracy of exposure ages and landscape modification rates in this study we present the results of a depth profiling technique applied to alluvial terraces located along the rhone and the moyenne durance rivers the expected decrease with depth of the measured 10be concentrations has been modelled using a 2 inversion method in order to constrain the exposure history of the alluvial sediments the results suggest that 1 over the quaternary the local surface erosion rates including both regional uplift and climatically driven processes acting on landforms are on the order of 30 m myr in southeastern france and 2 providing a fairly good bracketing of the exposure age the modelled abandonment age of alluvial terraces affected by the moyenne durance fault allows estimating incision rates comparing the alluvial terrace elevations with topographic river profiles and a minimum vertical slip rate value of roughly 0 02 mm yr for the southern segment of the moyenne durance fault

estimates of the rate of regolith production using and from an alpine hillslope abstract the production of regolith is a fundamental geomorphic process because most surface processes transport only unconsolidated material we use concentrations of the cosmogenic radionuclides crns 10 be and 26 al in regolith and bedrock to deduce the rate of production of regolith on an alpine hillslope in the wind river range wy these calculations are based on a theoretical model which we develop here this model shows that it is important to consider dissolution of regolith in regolith production and in basin averaged erosion rate studies rates of production of regolith are uniform along the hillslope and the mean rates for the entire hillslope deduced from 10 be and 26 al are 14 3 4 0 and 13 0 4 0 m ma 1 respectively rates of production of regolith deduced from 10 be concentrations in regolith mantled bedrock support the rates deduced from regolith concentrations in the alpine environment examined here the rate of production of regolith beneath 90 cm of regolith is nearly twice as fast as the average rate of production of regolith on bare rock surfaces which small et al small e e anderson r s repka j l finkel r 1997 erosion rates of alpine bedrock summit surfaces deduced from in situ 10 be and 26 al earth and planetary science letters 150 413 425 previously documented rock mantled with regolith probably weathers more rapidly than bare rock because the water required for frost weathering is limited on bare rock surfaces because the hillslope examined here is convex with constant curvature and regolith production and thickness are uniform down the slope the regolith volume flux must be proportional to the local slope of the hillside therefore our results are consistent with gilbert s gilbert g k 1909 the convexity of hilltops journal of geology 17 344 350 steady state hillslope hypothesis if tor height and the difference between rates of weathering on bare and regolith mantled rock provide a fair estimate of the age of summit flats steady state hillslope conditions have been attained in less than several million years

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

spatio temporal slip and stress level on the faults within the western foothills of taiwan implications for fault frictional properties we use preseismic coseismic and postseismic gps data of the 1999 chi chi earthquake to infer spatio temporal variation of fault slip and frictional behavior on the chelungpu fault the geodetic data shows that coseismic slip during the chi chi earthquake occurred within a patch that was locked in the period preceding the earthquake and that afterslip occurred dominantly downdip from the ruptured area to first order the observed pattern and the temporal evolution of afterslip is consistent with models of the seismic cycle based on rate and state friction comparison with the distribution of temperature on the fault derived from thermo kinematic modeling shows that aseismic slip becomes dominant where temperature is estimated to exceed 200 at depth this inference is consistent with the temperature induced transition from velocity weakening to velocity strengthening friction that is observed in laboratory experiments on quartzo feldspathic rocks the time evolution of afterslip is consistent with afterslip being governed by velocity strengthening frictional sliding the dependency of friction l on the sliding velocity v is estimated to be ol o ln v 8 10 3 we report an azimuthal difference of about 10 20 between preseismic and postseismic gps velocities which we interpret to reflect the very low shear stress on the creeping portion of the decollement beneath the central range of the order of 1 3 mpa implying a very low friction of about 0 01 this study highlights the importance of temperature and pore pressure in determining fault frictional sliding

quantification of soil production and downslope creep rates from cosmogenic 10be accumulations on a hillslope profile average soil transport rates over a period of 3500 yr on a convex soil mantled hillslope have been quantified using a mass balance model that incorporates the soil concentration of the cosmogenic isotope 10 be the 10 be model results support the assumption used in most geomorphic models that the soil creep rate is proportional to surface gradient the predicted diffusion coefficient is 360 55 cm 3 yr 1 cm 1 contour length and the average rate of soil production is 0 026 0 007 cm yr within the uncertainty of this technique the data do not reject g k gilbert9s hypothesis that some hillslopes may exist in a condition of dynamic equilibrium with a uniform soil production rate however the model does not require an assumption of dynamic equilibrium and may be an approach that uniquely allows the quantification of a local soil production rate law

numerical modeling of trishear fault propagation folding in contrast to kink band migration modeling methods trishear numerical models produce fault propagation folds with smooth profiles and rounded hinges modeled fold hinges tighten and converge downward within a triangular zone of distributed deformation which is focused on the fault tip such features have been reported from field studies and are also seen in analogue models of compressional deformation however apart from its initial application to laramide folds little quantitative work has been undertaken on trishear fault propagation folding in other settings in addition no study has been undertaken into the growth strata which might be associated with such structures this paper uses an equivalent velocity description of the geometric model of trishear together with models of erosion and sedimentation to investigate trishear fault propagation folding of both pregrowth and growth strata the trishear model is generalized to include a variety of fault propagation to slip ratios and fault propagation from a flat decollement the models show continuous rotation of the forelimb with the characteristic development of cumulative wedges within growth strata when total slip on a structure is high the model predicts overturned pregrowth and growth strata during the initial stages of deformation beds in the forelimb thicken but later thin when they become steep or overturned the effect of variations in fault propagation to slip ratios on two dimensional finite strain in the models is assessed by the use of initially circular strain markers high fault propagation to slip p s ratios lead to narrow zones of high finite strain while lower p s ratios lead to more ductile deformation and broader zones of high strain in all cases hanging wall anticlines and footwall synclines originate as early ductile folds which are later cut by the propagating fault modeled structures are compared with natural examples

coseismic thrusting and folding in the 1999 mw 7 6 chi chi earthquake a high resolution approach by aerial photos taken from tsaotun central taiwan we used aerial photos taken before and after the 21 september 1999 m w 7 6 chi chi earthquake in central taiwan to measure the near field ground deformation a total of 12 pairs of images were processed with co registration of optically sensed images and correlation to produce a horizontal displacement map of a 10 km 10 km area near tsaotun using pairs of images with different viewing angles both the horizontal and vertical slip across the fault zone can be measured our measurements when resampled into lower resolution are consistent with lower resolution measurements of horizontal displacements obtained from spot images as well as with vertical displacements obtained from repeated leveling measurements and field observations horizontal strain is strongly localized along the chelungpu fault clpf and along a secondary scarp that runs parallel to the clpf about 2 km to the east the ailiao fold scarp alf this pattern closely matches the surface ruptures mapped in the field horizontal strain across clpf correlates remarkably well with the topographic features produced by long term deformation the cumulative horizontal shortening across the clpf and alf amounts to 4 9 0 4 and 6 1 0 6 m respectively and fault parallel displacement is 3 4 0 4 m the pattern of surface strain is consistent with the interpretation of the alf as a fold scarp formed over an active axial hinge zone this study shows that even in this compressional setting most surface deformation is localized within narrow fault zones or active axial hinges

lateral variations in the long term slip rate of the chelungpu fault central taiwan from the analysis of deformed fluvial terraces the chelungpu fault ruptured during the september 1999 mw 7 6 chi chi earthquake in central taiwan this event was characterized by coseismic displacements increasing along strike and updip from south to north previous studies suggested that such lateral variations also existed in the long term fault slip rate but this has not yet been clearly documented to address this we investigate deformed fluvial terraces along the choushui and tatu wu rivers in the southern and central segments of the thrust fault optical ages of 13 ka to 38 ka obtained for these terraces enable estimation of fault slip rates of 5 8 2 0 and 10 3 1 6 3 0 mm yr for the southern and central segments respectively we combine these findings with the fault slip rate determined by other authors for the northern segment statistical analysis of the data suggests lateral variations in the long term fault slip rate with values increasing toward the north this pattern in the slip rate averaged over approximately tens of thousand years is similar to that observed for coseismic displacements during the chi chi earthquake the similarities in the deformation pattern observed for one earthquake or cumulated over several events suggest that the chi chi earthquake could be characteristic of the earthquakes breaking the chelungpu fault with respect to slip distribution our results also allow for discussing the plausible evolution of major rivers draining the foothills of central taiwan over the last 40 60 kyr

1999 chi chi earthquake a case study on the role of thrust ramp structures for generating earthquakes the 21 september 1999 chi chi earthquake m w 7 6 occurred on east dipping shallow thrust faults that produced a high relief surface rupture extraordinary surface breaks appeared that could be clearly traced for about 100 km across many counties these thrust faults the chelungpu and shihkang are part of an active fold and thrust belt related to ongoing recent arc continent collision measurement of slip vectors along the earthquake rupture indicates that the orientation of the maximum shear stress changed from a westward direction n70 90 w on the chelungpu fault to a northwestward direction n30 40 w on the shihkang fault the stress field underwent a clockwise rotation of about 40 during the chi chi earthquake near rupture vertical displacements in the hanging wall of the shihkang fault have more cumulative displacement than on the chelungpu fault which is consistent with global positioning system gps measurements maximum vertical offset on the rupture was found to be about 10 m by the surficial rupture and gps measurements in addition analysis of crustal deformation by gps measurements on the hanging wall defines a coseismic uplift related to a fault ramp structure our synthesis of geological and geodetic analyses shows the importance of ramp structures associated with thrust faults for generating large earthquakes and provides a general framework for understanding earthquake in fold and thrust belts large surficial coseismic uplift and strong asperities appear to be a function of fault ramp geometry our analysis also indicates that in general ramp structures in fold and thrust belts may have a high potential in generating large earthquakes manuscript received 14 november 2000

styles and rates of long term denudation in carbonate terrains under a mediterranean to hyper arid climatic gradient abstract carbonate minerals unlike silicates have the potential to dissolve almost completely and with high efficiency thus in carbonate terrains denudation rate and style the governing process of denudation mechanical or chemical should be more sensitive to climatic forcing using 36 cl measurements in 39 carbonate bedrock and sediment samples we calculate long term denudation rates across a sharp climatic gradient from mediterranean to hyper arid conditions our samples were collected along the arugot watershed which drains the eastern flank of the judea range central israel to the dead sea and is characterized by a pronounced rain shadow denudation rates of flat lying bedrock outcrops sampled along interfluves differ by an order of magnitude from 20 mm ka 1 in the mediterranean zone to 1 3 mm ka 1 in the hyper arid zone these rates are strongly correlated with precipitation and thus reflect the importance of carbonate mineral dissolution in the overall denudation process in contrast denudation rates of steep bedrock surfaces depend on the hillslope gradient but only in the hyper arid climate zone indicating that mechanical processes dominate the overall hillslope denudation within this zone the dominance of slope dependent mechanical erosion in the hyper arid zone is also reflected by an increase in spatially average denudation rates from 17 19 mm ka 1 in the mediterranean semi arid zones to 21 25 mm ka 1 in the hyper arid zone these higher rates are attributed to clast contribution from steep slopes under arid climate this suggests an increased importance of mechanical processes to the overall denudation in the hyper arid zone we demonstrate that the transition between chemically dominated denudation to mechanically dominated denudation occurs between 100 and 200 mm of mean annual precipitation long term denudation rates across the judea range indicate that between mediterranean and hyper arid climates chemical weathering rates are limited by precipitation nevertheless in more humid climates chemical weathering rates are apparently limited by the rates of carbonate mineral dissolution this study demonstrates that carbonate terrains have the capacity to shift between mechanically and chemically dominated denudation in response to changes in precipitation similar transitions in response to changes in temperature or the level of tectonic activity have been previously reported we suggest that the abrupt nature of such transitions can be primarily attributed to the efficiency of carbonate dissolution processes and the competition between surface and subsurface drainage systems in carbonate terrains

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

a vertical exposure of the 1999 surface rupture of the chelungpu fault at wufeng western taiwan structural and paleoseismic implications for an active thrust fault we mapped and analyzed two vertical exposures exposed on the walls of a 3 to 5 m deep 70 m long excavation and a smaller 3 m deep 10 m long excavation across the 1999 rupture of the chelungpu fault the primary exposure revealed a broad anticlinal fold with a 2 5 m high west facing principal thrust scarp contained in fluvial cobbly gravel beds and overlying fine grained overbank deposits sequential restoration of the principal rupture requires initial failure on the basal east dipping thrust plane followed by wedge thrusting and pop up of an overlying symmetrical anticline between two opposing secondary thrust faults net vertical offset is about 2 2 m across the principal fault zone from line length changes we estimate about 3 3 m of horizontal shortening normal to fault strike the ratio of these values yields a total slip of 4 0 m and an estimate of about 34 for the dip of the fault plane below the excavation this value is nearly the same as the 35 average dip of the fault plane from the surface to the hypocenter restoration of the exposed gravelly strata and adjacent overbank sediments deposited prior to the 1999 event around the principal rupture suggests the possible existence of a prior event a buried 30 m wide anticlinal warp beneath the uplifted crest of the 1999 event is associated with three buried reverse faults that we interpret as evidence for an earlier episode of folding and faulting in the site the prior event is also recorded in the smaller excavation which is located 40 m south and is oriented parallel to the larger excavation radiocarbon dating of samples within the exposed section did not place tight constraints on the date of the previous event available data are interpreted as indicating that the previous event occurred before the deposition of the less than 200 14 c yr b p overbank sands and after the deposition of the much older fluvial gravels we interpret the previous event as the penultimate event relative to the 1999 chi chi earthquake we estimated the long term slip rate of the chelungpu fault to be 10 15 mm yr during the last 1 ma based on previously published retrodeformable cross sections this rate is however significantly higher than geodetic rates of shortening across the chelungpu thrust where two pairs of permanent global positioning system stations suggest 7 10 mm yr of shortening across the fault given the 4 m of average slip the long term slip rate yields an interseismic interval of between 267 and 400 yr for the chelungpu fault

a dislocation model for the earthquake cycle at convergent plate boundaries summary a kinematic model for the earthquake cycle at convergent plate boundaries has been constructed on the basis of dislocation theory we model the lithosphere asthenosphere system by a stratified semi infinite medium under gravity consisting of an elastic surface layer an intervening layer with maxwell viscoelasticity and an elastic substratum the steady motion of plate convergence is naturally represented by uniform slip at a constant rate on the upper boundary of the descending oceanic plate the occurrence of interplate earthquakes is regarded as a perturbation of the steady state plate motion and represented by a periodic sequence of step slips on a finite seismic zone of the plate interface based on dislocation theory we can show that the steady slip on the interface deeper than the lithosphereasthenosphere boundary does not contribute to surface deformation in the steady state accordingly the surface deformation associated with the earthquake cycle is given by the superposition of viscoelastic responses to the steady slip on the interface shallower than the lithosphere asthenosphere boundary the steady backslip on the seismic zone and the periodic sequence of seismic slips we have computed cyclic patterns of vertical displacements at the free surface for two representative cases taking account of gravity effects the patterns of vertical displacements differ notably in the latter stage of the cycle depending on whether or not the seismic zone extends through the entire thickness of the lithosphere after the completion of one earthquake cycle our model yields a certain amount of permanent deformation resulting from the steady plate convergence the pattern of the permanent deformation that is characterized by steep uplift on the continental side sharp subsidence at the plate boundary and gentle uplift on the oceanic side is irrespective of the cyclic process of stress accumulation and release repeated on the seismic zone the earthquake cycle model developed here provides a possible explanation for the formation of earthquake origin marine terraces

an assessment of human versus climatic impacts on holocene soil erosion in ne peloponnese greece soil erosion is a natural geomorphological process which can be triggered by both natural climate tectonics or both and anthropogenic e g agriculture perturbation of the ecosystem evidence has accrued that the holocene climate experienced large fluctuations in amplitude and suggestions of human impact on the ecosystem provided by the neolithic revolution dating back to the early holocene have been made the question of whether man or climate was the dominant factor responsible for holocene soil erosion remains unresolved to resolve the reasons for holocene sediment redistribution high resolution chronometric data on sediments derived from colluvial and alluvial archives from southern greece were obtained and combined with available archaeological and paleoclimatic data from the eastern mediterranean these data show a significant correlation between sedimentation rates and settlement history climatic fluctuations are only weakly correlated with sedimentation history the results show high sedimentation rates during the early neolithic 7th millennium bc in southern greece suggesting that holocene soil erosion was triggered by human activity and then amplified by enhanced precipitation this would explain the high sedimentation rates during the early neolithic in connection with enhanced precipitation in the eastern mediterranean which continued until the mid holocene

paleoseismology of the chelungpu fault during the past 1900 years abstract the 1999 earthquake brought about 80 km long surface ruptures along the shihkang chelungpu and tajienshan faults central taiwan several trenches have been excavated across the chelungpu fault of the middle segment the surface ruptures display clear scarps ranging from 0 2 to 4 m high showing a complex geomorphic pattern due to coseismic faulting and folding in the study measurement of the vertical offset or structural relief was taken with reference to the hanging wall beyond the trishear deformation zone therefore we suggest that for the measurement of offset we should disregard the trishear zone and that structural relief on the hanging wall should be represented as a real vertical offset the net slip is then calculated from the structural relief and dip angle of the thrust on a vertical plane along the slip direction through the excavation of a pineapple field across the chelungpu fault we are able to provide evidence of at least four earthquake events for the past about 1900 years including the 1999 earthquake furthermore based on the radiocarbon dates and historical record the timing of the penultimate event is bracketed to be between 430 and 150 years ago and the average recurrence interval is less than 700 years these data indicate that the average slip rate is about 8 7 mm yr for the past 1900 years

growth of bending moment faults due to progressive folding insights from sandbox models and paleoseismological implications abstract bending moment normal faults bmf form during outer arc extension of a folding layer these faults observed in contractional and extensional tectonic environments can represent the only tectonic features potentially available for paleoseismological investigations i e trenching in order to date the movement of deeper structures yet the reliability of bmf as a paleoseismological feature is debated in terms of its potential to continuously record coseismic deformation and their relationship with progressive flexure we made use of analogue modeling in order to explore a simple model of progressive orthogonal flexure and the development of bmf we collected data on mode of bmf inception and growth by analyzing time series of cross section deformation measuring dip parallel bmf displacement profiles and constructing a three dimensional model of fault architecture by slicing of the experiment our results point to a model of bmf development typical of mechanically constrained faults where limits on self similar growth of faults is imposed once a maturity stage of displacement accumulation is attained the bmf can accumulate displacement until the structure reaches a maturity stage when further slip is inhibited this could result in an incomplete paleoseismological record of further fold movements however this fault stage can be recognized by the d shaped displacement profile typical of mature bmf a simple two dimensional constant area balancing model is proposed allowing us to derive incremental changes in flexuring given the area of the collapsed sector with bmf and the thickness of the faulted layer these results support the use of bmf as a paleoseismological proxy for deeper structures

continuous catchment scale monitoring of geomorphic processes with a 2 d seismological array 1 distributed activity of geomorphic processes with different spatiotemporal scales is hard to monitor in detail with conventional methods but might be detected with seismometers from july to september 2010 we deployed 14 seismometers to evaluate the ability of a two dimensional array with small interstation distances 11 km to continuously monitor geomorphic processes in a mountain catchment 370 km2 in taiwan spectral analysis of seismic records highlights different sources with high frequency content 1 hz consistent with hillslope and river processes using a common detection algorithm and a location technique based on the timing of seismic amplitude we have located 314 near surface events most of which 69 occurred during daily convective storms event activity was positively correlated with the precipitation intensity but this relation was not uniform in the catchment high resolution satellite images and air photos did not show geomorphic change during the study which did not have any episodes of extreme precipitation a majority of events 61 were collocated with preexisting geomorphic features landslide scars gullies within the uncertainty on location 9 of interstation distance the combination of event location and timing suggests a geomorphic source of recorded signals and most events had the seismic characteristics of rockfall debris avalanches or slides reactivation of prior erosion sites by such processes is difficult to detect with imagery but can possibly be resolved by seismic monitoring when proven this approach will allow a spatially comprehensive survey of geomorphic activity at the catchment scale with temporal detail sufficient to evaluate the exact meteorological conditions under which process events occur

prolonged seismically induced erosion and the mass balance of a large earthquake large earthquakes deform the earth s surface and drive topographic growth in the frontal zones of mountain belts they also induce widespread mass wasting reducing relief the sum of these two opposing effects is unknown using a time series of landslide maps and suspended sediment transport data we show that the mw7 6 chi chi earthquake in taiwan was followed by a period of enhanced mass wasting and fluvial sediment evacuation peaking at more than five times the background rate and returning progressively to pre earthquake levels in about six years therefore it is now possible to calculate the mass balance and topographic effect of the earthquake the choshui river has removed sediment representing more than 30 of the added rock mass from the epicentral area this has resulted in a reduction of surface uplift by up to 0 25 m or 35 of local elevation change and a reduction of the area where the chi chi earthquake has built topography for other large earthquakes erosion may evolve in similar predictable ways reducing the efficiency of mountain building in fold and thrust belts and the topographic expression of seismogenic faults prolonging the risk of triggered processes and impeding economic regeneration of epicentral areas

evidence for prehistoric coseismic folding along the tsaotun segment of the chelungpu fault near nan tou taiwan 1 taiwan s 1999 mw 7 6 earthquake generated over 85 km surface rupture along the chelungpu thrust fault paleoseismic studies at the shi jia site near nantou city reveal folding as the predominant form of deformation stratigraphic relations across the 1999 fold scarp show the style and degree of deformation caused by the penultimate event is similar to observed 1999 deformation a boring transect across the fold scarp provides additional evidence of an earlier earthquake investigations at the shi jia site revealed three prehistoric events accelerator mass spectrometry ams radiocarbon ages indicate that the penultimate earthquake occurred between 1160 and 1440 a d paleoseismic studies north of the shi jia site reveal much younger penultimate earthquakes suggesting a 1999 type event may not be characteristic along the tsaotun segment of the chelungpu fault

evolution of coseismic fault related folds induced by the chi chi earthquake a case study of the wufeng site central taiwan by using 2d distinct element modeling abstract coseismic fault propagation folds are generally associated with blind faults which are of considerable academic interest and have recently been recognized as critical for assessing seismic hazards the wufeng excavation site was characterized by a major east dipping basal thrust exhibiting a dip angle of 34 and 2 opposing vergent thrusts generated a pop up anticlinal fold in soil cover induced by the 1999 chi chi earthquake mw 7 6 in order to represent the soft soil behavior we set up a direct shear simulation test to obtain valid parameters for soil a series of 2d distinct element models possessing different bonding types and strengths was conducted to determine the deformation pattern near the surface and the evolution of the fault tip propagation the coseismic deformation features of soft and plastic soil cover like the mutative limb thickness complex ruptures and the overturned forelimbs in small scale caused by the propagation of the blind fault tip were accurately predicted by contact bond model in which grains were allowed to rotate and slip without cements breaking our results show that the alternative thrusts and pop up structure developed before the main basal thrust fault ruptured through the ground surface at the wufeng excavation site we evaluated the slipping distance of the main fault at approximately 6 m in wufeng during the 1999 chi chi earthquake

from mass wasting to slope stabilization putting constrains on a tectonically induced transition in slope erosion mode a case study in the judea hills israel calcrete coated remnants of landslide debris and alluvial deposits are exposed along the presently stable hillslopes of the soreq drainage judea hills israel these remnants indicate that a transition from landslide dominated terrain to dissolution controlled hillslope erosion had occurred this transition possibly occurred due to the significant decrease in tectonic uplift during the late cenozoic the study area is characterized by sub humid mediterranean climate the drainage hillslopes are typically mantled by thick calcrete crusts overlying upper cretaceous marine carbonate rocks using tt osl dating of aeolian quartz grains incorporated in the calcrete which cements an ancient landslide deposit we conclude that incision of 100 m occurred from 1056 262 to 688 86 ka due to 0 3 westward tilt of the region such incision invoked high frequency of landslide activity in the drainage the ages of a younger landslide remnant alluvial terrace and alluvial fan all situated only a few meters above the present level of the active streambed range between 688 86 ka and 244 25 ka and indicate that since 688 86 the soreq base level had stabilized and that landslide activity decreased significantly by the middle pleistocene copyright 2012 john wiley sons ltd

spatial slip distribution of the september 20 1999 chi chi taiwan earthquake mw7 6 inverted from teleseismic data the teleseismic waveforms of the mw7 6 september 20 1999 chi chi earthquake were examined to obtain the quick information on the fault rupture process the deconvolution results show the fault ruptured from south to the north and revealed the west movement of the hanging wall to the footwall on the eastern dipping plane the spatial slip distribution shows that the earthquake was mainly composed by a large asperity with a dimension of about 45km 15km the maximum slip was about 8 m located at about 45 km to the north of the epicenter the slip distributions obtained in this study have a good agreement with the observed surface breaks the comparable static and the dynamic stress drops of about 11 mpa in the large slip region indicate that the melting fluid pressurization might have taken place in this earthquake it reduces the dynamic friction and results in the large slip observed

estimating the return times of great himalayan earthquakes in eastern nepal evidence from the patu and bardibas strands of the main frontal thrust the return times of large himalayan earthquakes are poorly constrained despite historical devastation of cities along the mountain range definitive links between events and specific segments of the main frontal thrust mft are not established and paleoseismological records have not documented the occurrence of several similar events at the same location in east central nepal however recently discovered primary surface ruptures of that megathrust in the a d 1255 and 1934 earthquakes are associated with flights of tectonically uplifted terraces we present here a refined longer slip history of the mft s two overlapping strands patu and bardibas thrusts in that region based on updated geomorphic neotectonic mapping of active faulting two 1 3 km long shallow seismic profiles and logging of two river cut cliffs three paleoseismological trenches and several pits with constraints from 74 detrital charcoals and 14 cosmogenic nuclide ages the amount of hanging wall uplift on the patu thrust since 3650 450 years requires three more events than the two aforementioned the uplift rate 8 5 1 5mm yr thrust dip 25 5 n and apparent characteristic behavior imply 12 17 5m of slip per event on the bardibas thrust discrete pulses of colluvial deposition resulting from the coseismic growth of a flexural fold scarp suggest the occurrence of six or seven paleo earthquakes in the last 4500 50 years the coeval rupture of both strands during great himalayan earthquakes implies that in eastern nepal the late holocene return times of such earthquakes probably ranged between 750 140 and 870 350 years

weathering limited hillslope evolution in carbonate landscapes understanding topographic evolution requires integrating elementary processes acting at the hillslope scale into the long wavelength framework of landscape dynamics recent progress has been made in the quantification of denudation of eroding landscapes and its links with topography despite these advances data is still sparse in car bonate terrain which covers a significant part of the earth s surface in this study we measured both long term denudation rates using in situ produced 36 cl concentrations in bedrock and regolith clasts and surface convexity at 12 sites along ridges of the luberon carbonate range in provence southeastern france starting from 30 mm ka for the lowering of the summit plateau surface denudation linearly increases with increasing hilltop convexity up to 70 mm ka as predicted by diffusive mass transport theory beyond this point denuda tion rates appear to be insensitive to the increase in hilltop convexity we interpret this constant denudation as indicating a transition from a regime where hillslope evolution is primarily controlled by diffusive downslope regolith transport toward a situation in which denuda tion is limited by the rate at which physical and chemical weathering processes can produce clasts and lower the hilltop such an abrupt transition into a weathering limited dynamics may prevent hillslope 1 denudation from balancing the rate of base level fall imposed by the river network and could potentially explain the development of high local relief in many mediterranean carbonate landscapes

progressive offset and surface deformation along a seismogenic blind thrust in the po plain foredeep southern alps northern italy here we present for the first time in the po plain foredeep northern italy the middle to late pleistocene growth history of an outcropping secondary fold and related faults whose progressive deformation over an intermediate time window 105 years is driven by an underlying seismogenic blind thrust we trenched and logged an outcropping decametric secondary anticline related to a deeper blind compressional structure which deforms fluvial sediments and an overlying loess paleosol sequence folded units were dated using radiocarbon and optically stimulated luminescence methods to the late pleistocene holocene and tentatively correlated with glacial interglacial phases occurring during the time interval from marine isotope stage 6 to the present a multistep retrodeformation of the fold allowed us to calculate uplift rates for this secondary and shallow anticline varying between 0 02 and 0 1 mm yr since circa 200 kyr trishear forward deformation modeling of the fold indicates that the amplification of the observed fold could be caused by two shallow thrusts formed through a break backward activation this generated a decametric surface fold whose most recent growth was associated with bending moment normal faulting in the crestal and forelimb region our observations demonstrate that near surface compressive tectonics can be caused by blind thrusting via a complex array of fault and folds upward strain propagation and generation of shallow low angle thrust and related folding seem to be mainly due to secondary fold related faulting according to an out of syncline thrusting mechanism

inferring a thrust related earthquake history from secondary faulting a long rupture record of la laja fault san juan argentina abstract trenches excavated across the surface rupture of the 15 january 1944 m w 7 san juan argentina earthquake show evidence for repeated rupture of la laja fault in the late pleistocene and holocene the 1944 rupture extended for about 7 km striking n35 e and dipping 42 e parallel to neogene bedding with a maximum east side up vertical displacement of 30 cm we interpret nine discrete colluvial wedges each capped by a soil as evidence for nine surface ruptures in the past 32 35 ka our topographic profile of the t3 terrace surface projected across the fault suggests these nine events collectively produced 10 3 m of dip displacement we used radiocarbon and optically stimulated luminescence dating to define the timing of past events yielding an average recurrence interval of 3 9 0 3 ka the average estimate for displacement per event is about 1 1 m compared with the 0 5 m of dip slip that occurred in 1944 using a fault related fold model that infers 28 m of shortening based on the axial surface migration for the t 3 terrace along with the 35 ka age of the terrace yields a shortening rate of 0 8 mm yr by the 1944 source thrust fault which is about 20 of the global positioning system constrained total shortening rate across the precordillera using this shortening rate and an assumed fault dip of 30 implies a fault slip rate of about 1 1 mm yr which combined with the average recurrence interval implies 4 m of average slip per event on the causative fault at depth online material unit descriptions from the trenches stepwise reconstruction from trench 1 and annotated photographs of the la laja region

structure from motion photogrammetry a low cost effective tool for geoscience applications abstract high resolution topographic surveying is traditionally associated with high capital and logistical costs so that data acquisition is often passed on to specialist third party organisations the high costs of data collection are for many applications in the earth sciences exacerbated by the remoteness and inaccessibility of many field sites rendering cheaper more portable surveying platforms i e terrestrial laser scanning or gps impractical this paper outlines a revolutionary low cost user friendly photogrammetric technique for obtaining high resolution datasets at a range of scales termed structure from motion sfm traditional softcopy photogrammetric methods require the 3 d location and pose of the camera s or the 3 d location of ground control points to be known to facilitate scene triangulation and reconstruction in contrast the sfm method solves the camera pose and scene geometry simultaneously and automatically using a highly redundant bundle adjustment based on matching features in multiple overlapping offset images a comprehensive introduction to the technique is presented followed by an outline of the methods used to create high resolution digital elevation models dems from extensive photosets obtained using a consumer grade digital camera as an initial appraisal of the technique an sfm derived dem is compared directly with a similar model obtained using terrestrial laser scanning this intercomparison reveals that decimetre scale vertical accuracy can be achieved using sfm even for sites with complex topography and a range of land covers example applications of sfm are presented for three contrasting landforms across a range of scales including an exposed rocky coastal cliff a breached moraine dam complex and a glacially sculpted bedrock ridge the sfm technique represents a major advancement in the field of photogrammetry for geoscience applications our results and experiences indicate sfm is an inexpensive effective and flexible approach to capturing complex topography

observations of basin ground motions from a dense seismic array in san jose california we installed a dense array of 41 digital seismographs in san jose california to evaluate in detail the effects of a deep sedimentary basin and shallow sedimentary deposits on earthquake ground motions this urban array is located near the eastern edge of the santa clara valley and spans the evergreen sedimentary basin identified by gravity data average station spacing is 1 km with three stations initially spaced 110 m apart despite the high noise urban environment the stations of the array successfully triggered on and recorded small local earthquakes m 2 5 2 8 at 10 25 km distance and larger regional events such as the m 5 0 bolinas earthquake 90 km distance m 4 6 5 6 earthquakes near mammoth lakes 270 km distance m 4 9 5 6 events in western nevada 420 km distance and the m 7 1 hector mine earthquake 590 km distance maps of spectral ratios across the array show that the highest amplitudes in all frequency bands studied 0 125 8 hz are generally observed at stations farther from the eastern edge of the santa clara valley larger spectral amplitudes are often observed above the western edge of the evergreen basin snapshots of the recorded wavefield crossing the array for regional events to the east reveal that large low frequency 0 125 0 5 hz arrivals after the s wave travel from south to north across the array a moving window cross correlation analysis finds that these later arrivals are surface waves traveling from the south the timing and propagation direction of these arrivals indicates that they were likely produced by scattering of incident s waves at the border of the santa clara valley to the south of the array it is remarkable that the largest low frequency phases at many of the valley sites for regional events to the east are basin surface waves coming from a direction about 70 degrees different from that of the epicenters basin surface waves emanating from the eastern edge of the valley are also identified by the cross correlation analysis

mean bedrock to saprolite conversion and erosion rates during mountain growth and decline abstract weathering and associated atmospheric co2 consumption are thought to increase during the erosion of uplifting mountain ranges but the effect of enhanced erosion on weathering is still the subject of active debate we explore the possibility that erosion heterogeneity in uplifting landscapes significantly impacts the temporal relationships among mean uplift erosion and weathering using a 3d landscape evolution model applied to a synthetic surface with different uplift and climate scenarios although we do not strictly simulate the weathering outflux of the mountain we analyze the weathering response through the evolution of the mountain mean saprolite production rate and compare it to the mountain mean erosion rate through time the parametrical analysis shows that the temporal relationship between the mean erosion and saprolite production rates depends mainly on the ratio of the maximum saprolite production rate and the uplift rate wm u we explore two end members 1 when wm u 1 which corresponds to mountain ranges under a hot and humid climate the mean erosion and saprolite production rates vary at the same rate during the uplift and after once the uplift is stopped when the uplift is stopped the mean saprolite production increases and then decreases locally at different times this heterogeneity induces an overall decrease in the mean saprolite production rate 2 when wm u

coseismic fold scarps and their kinematic behavior in the 1999 chi chi earthquake taiwan 1 discrete scarps that are created or reactivated during large earthquakes are a locus of concentrated hazard a number of the coseismic scarps activated in the 1999 chi chi earthquake are actually fold scarps which display several types of ground deformation characterized by localized folding and are distinct from classic fault scarps which form by a fault cutting the surface this paper documents and analyzes fold scarps that formed or reactivated in the 1999 chi chi taiwan earthquake our results show the chi chi fold scarps can be generally divided into two types 1 those associated with folding ahead of the tip of a blind thrust fault at shallow depths and 2 those associated with folding by kink band migration above fault bends at substantial depths ranging from 0 8 to 5 km the previously published trishear model can be applied to model the former type while a new curved hinge kink band migration model is provided to describe the behavior of the latter type a key feature of fold scarps of the second type is that hinge zones are typically wide 25 100 m relative to the displacement in a single earthquake 1 10 m which exerts a significant control on fold scarp morphology and evolution because the coseismic strains of both types of fold scarps display relatively wide deformation zones 10 100 m relative to fault scarps wider set back zones might be appropriate from a public policy point of view to alleviate the risk to structural damage and collapse resulting from permanent ground deformation

pleistocene alluvial deposits dating along frontal thrust of changhua fault in western taiwan the cosmic ray exposure point of view abstract to tackle the history of active thrusts it is necessary to open the observation window on time scales on the order of 104 105 years by studying the surface morphologies resulting from their activities because fluvial systems are particularly sensitive to recent environmental changes geomorphic features such as alluvial terraces are frequently used as markers to gauge tectonic deformation together with the measurement of cumulative displacements the chronological framework of emplacement and abandonment of these geomorphic markers is thus fundamental to determine long term fault slip rates in taiwan the geomorphic features associated with fault activity have been studied in detail with a high level of resolution however the use of deformed and partially preserved alluvial terraces is often hampered by the absence of well documented ages the purpose of this paper is two fold first we take the opportunity to review the chronological constraints that have been published in taiwan so far second we present how the cosmogenic dating method in situ produced 10be can be used to constraint the chronological framework of alluvial deposits over a pleistocene time scale thanks to a comparison of our cosmogenic derived ages with existing data we present a consistent regional chronological framework for the pakua tadu area along the changhua fault one of the most active frontal thrusts in the western foothills of the taiwan mountain belt we also discuss its relationships with global eustatism and its tectonic implications for the timing of propagation of the deformation front during the last 450 kyr