a scaling law for slow earthquakes with the availability of the global positioning system and other technical advances a growing number of unusual earthquake phenomena occurring at relatively long periods have been recognized they include deep episodic tremor low frequency earthquakes slow slip events and silent earthquakes based on data chiefly from western japan ide et al report that these slow seismic events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes a diverse array of unusual earthquake phenomena occurring at relatively long periods slow events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes indicating that they comprise a new earthquake category recently a series of unusual earthquake phenomena have been discovered including deep episodic tremor1 low frequency earthquakes2 very low frequency earthquakes3 slow slip events4 and silent earthquakes5 6 7 8 9 each of these has been demonstrated to arise from shear slip just as do regular earthquakes but with longer characteristic durations and radiating much less seismic energy here we show that these slow events follow a simple unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes we find that their seismic moment is proportional to the characteristic duration and their moment rate function is constant with a spectral high frequency decay of f 1 this scaling and spectral behaviour demonstrates that they can be thought of as different manifestations of the same phenomena and that they comprise a new earthquake category the observed scale dependence of rupture velocity for these events can be explained by either a constant low stress drop model or a diffusional constant slip model this new scaling law unifies a diverse class of slow seismic events and may lead to a better understanding of the plate subduction process and large earthquake generation

inversion of fluvial channels for paleorock uplift rates in taiwan the transient response of erosion to changes in rock uplift rate leads to the preservation of rock uplift history in the long profiles of rivers however extracting this information is nontrivial as changes in channel steepness are the result of both spatial and temporal changes in rock uplift rate as well as other factors such as climate and rock type we exploit an analytical linear solution for river channel profile evolution in response to erosion and tectonic uplift to investigate the rock uplift history of taiwan the analytical approach allows us to solve the linear inverse problem efficiently extracting rock uplift as a function of space and time from digital elevation data we assess the potential of fluvial topography to resolve rock uplift rates using three approaches 1 a synthetic resolution test 2 analysis of the forward model to demonstrate where in space and time the fluvial topography constrains rock uplift rate and 3 interpretation of the model resolution matrix furthermore the potential to analyze large data sets reduces the influence of stochastic processes such as landslides small scale river network reorganization and also local lithological variability in taiwan our analysis suggests that current rock uplift rates exceed erosion rates across much of the island and that there has been an increase in rock uplift rates since 0 5 ma across the central range

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

numerical modeling of frontal and basal accretion at collisional margins 1 we investigate the deformation of orogenic wedges that form in the early stages of continent continent collisions using a two dimensional numerical model limited to the upper lithosphere our models show that deformation at the plate margins is influenced by rheology surface processes and the balance between inward mass flux and outward subduction flux as controlled by the subduction load which represents the effects of slab pull and resistive forces and flexural downbending we find three characteristic deformation modes 1 near pure subduction with little or no accretion 2 frontal accretion with development of an accretionary wedge built up by offscraping of the sediment layer at shallow depth and 3 independent frontal and basal accretion where a retrothrust allows stacking of basement nappes at crustal to mantle depths near pure subduction is enabled for ordinary rheology materials characterized by brittle and viscous material behavior approximating a christmas tree type depth profile and almost zero friction along the subduction shear zone frontal accretion occurs when slightly increased friction along the subduction shear zone allows offscraping of the sediment layer from the subducting plate independent frontal and basal accretion develops in strong rheology models with an almost fully brittle material behavior major surface erosion or a reduction of the subduction load promote the development of large basement nappes frontal accretion is favored by major sedimentation during convergence a large backstop and in the case of a lateral transition from a strong rheology to an ordinary rheology subducting plate our numerical models develop first order characteristics as observed in natural orogenic wedges for example upper crustal nappe stacks frontal and basal accretion or extension in the core of an orogen frontal and basal accretion are interdependent and tend to stabilize the subduction system

erosion rates for taiwan mountain basins new determinations from suspended sediment records and a stochastic model of their temporal variation abstract we estimate erosion rates from suspended sediment records for 11 basins in the eastern central range ecr of taiwan using methods based on mean measured sediment discharge a rating curve of sediment and water discharge and a rating curve corrected for periods of limited sediment due to the lack of landslide supplied sediment the preferred method for any basin depends on record length and sampling frequency with higher quality records being analyzed by the latter method erosion rate estimates range from 2 2 to 8 3 mm yr for records with varying sampling frequencies and durations between 8 and 27 yr this variation in erosion rates does not seem to reflect lithology tectonic environment or climate we interpret the variation in terms of natural stochastic variation in water discharge and sediment supply to assess the quality of the erosion rate estimates and to better understand the dependence of uncertainty on the duration and frequency of sampling we construct a stochastic model of sedi

very low frequency earthquakes related to small asperities on the plate boundary interface at the locked to aseismic transition 1 very low frequency vlf seismic signals observed in southwestern japan are evidently radiated from shear slips on the upper surface of the subducting philippine sea plate we used grid moment tensor inversion and centroid moment tensor inversion to calculate 242 moment tensor solutions with moment magnitudes between 3 1 and 3 8 from continuous seismograms recorded over a 5 year period by using a very dense broadband seismic network at least 5 10 sequences of repetitive activity were observed during the 5 years the vlf events formed clustered distributions along the 35 km isodepth contour of the subducting plate surface the nodal planes which dip landward of moment tensor solutions of the vlf events reflected the configuration of the subducting plate interface the slip vectors were consistent with the direction of movement of the subducting plate the dip and strike of the slip vectors clearly reflected the configuration of the upper surface of the subducting plate we found that the rates of seismic moment release per unit area associated with five major vlf clusters were very similar although both the seismic magnitudes and sizes of the clusters varied considerably the rate of seismic moment released from detectable vlf sources was 0 1 of the rates of short term slow slip events suggesting that the source areas occupied only 0 1 of the fault segment on which the short term slow slip events occurred

supply and removal of sediment in a landslide dominated mountain belt central range taiwan abstract a strong coupling between hillslope and valley systems is often inferred for mountain landscapes dominated by bedrock landsliding we reveal the nature of this link using data sets on landsliding and sediment transport from two montane catchments draining the eastern central range of taiwan here the magnitude frequency distribution of landslides can be modeled by a robust power law but this scale invariance is not mirrored in the sediment discharge at the mountain front instead downstream sediment loads reflect a complex response to both sediment supply and ambient hydraulic conditions the rivers do not transport significant amounts of sediment unless it is provided by hillslope mass wasting in the catchment removal of landslide debris is a function of the transport capacity of the stream at the site of entry thus there is a dual supply and transport control on sediment loads in bedrock floored streams over a monitoring period of 25 yr the bulk of the sediment leaving the mountain bel

mechanism of deep low frequency earthquakes further evidence that deep non volcanic tremor is generated by shear slip on the plate interface 1 we study the mechanism of low frequency earthquakes lfes in the nankai trough in western shikoku japan precise locations have previously suggested that they represent shear slip on the plate boundary in this paper we examine the mechanism of these events due to the low signal to noise ratio we analyze stacked lfe waveforms and compare them with the waveforms of nearby earthquakes of known mechanism within the subducting philippine sea plate analysis of both the focal mechanism using p wave first motions and the moment tensor using s waveforms indicates that lfes represent shear slip on a low angle thrust fault dipping to the northwest namely the plate interface together with reports that deep tremor consists of a swarm of lfes our results suggest that deep tremor is generated directly by shear slip on the plate interface and as such represents a seismic signature of the accompanying slow slip events

effects of bedrock landslides on cosmogenically determined erosion rates abstract the successful quantification of long term erosion rates underpins our understanding of landscape formation the topographic evolution of mountain ranges and the mass balance within active orogens the measurement of in situ produced cosmogenic radionuclides crns in fluvial and alluvial sediments is perhaps the method with the greatest ability to provide such long term erosion rates although deep seated bedrock landsliding is an important erosional process in active orogens its effect on crn derived erosion rates is largely unquantified we present a numerical simulation of cosmogenic nuclide production and distribution in landslide dominated catchments to address the effect of bedrock landsliding on erosion rates results of the simulation indicate that the temporal stability of erosion rates determined from crn concentrations in sediment decreases with increased ratios of landsliding to bedrock weathering rates within a given catchment area and that as the frequency of landsliding increases larger catchment areas must be sampled in order to accurately evaluate long term erosion rates in addition results of this simulation suggest that sediment sampling for crns is the appropriate method for determining long term erosion rates in regions dominated by mass wasting processes whereas bedrock surface sampling for crns may generally underestimate long term erosion rates response times of crn concentrations to changes in erosion rate indicate that climatically driven cycles of erosion may be detected but that complete equilibration of crn concentrations to new erosional conditions may take tens of thousands of years comparison of simulated crn derived erosion rates with a new data set of such rates from the nepalese himalaya underscore the conclusions drawn from the model results

complexity of the deep san andreas fault zone defined by cascading tremor seismic tremors can be used to distinguish plate boundaries analysis of tremors occurring deep beneath the san andreas fault may identify the boundary between the north american plate and the preserved remnant of a subducted slab

tremor genic slow slip regions may be deeper and warmer and may slip slower than non tremor genic regions slow slip events sses are observed worldwide and often coincide with tectonic tremor notable examples of sses lacking observed tectonic tremor however occur beneath k lauea volcano hawaii the boso peninsula japan near san juan bautista on the san andreas fault california and recently in central ecuador these sses are similar to other worldwide sses in many ways e g size or duration but lack the concurrent tectonic tremor observed elsewhere instead they trigger swarms of regular earthquakes we investigate the physical conditions that may distinguish these non tremor genic sses from those associated with tectonic tremor including slip velocity pressure temperature fluids and fault asperities although we cannot eliminate the possibility that tectonic tremor may be obscured in highly attenuating regions slip velocities of sses at k lauea volcano 10 6 m s and boso peninsula 10 7 m s are among the fastest sses worldwide k lauea volcano the boso peninsula and central ecuador are also among the shallowest sses worldwide and thus have lower confining pressures and cooler temperatures in their respective slow slip zones fluids also likely contribute to tremor generation and no corresponding zone of high vp vs has been noted at k lauea or boso we suggest that the relatively faster slip velocities at k lauea volcano and the boso peninsula result from specific physical conditions that may also be responsible for triggering swarms of regular earthquakes adjacent to the slow slip while different conditions produce slower sse velocities elsewhere and trigger tectonic tremor

how fast is the denudation of the taiwan mountain belt perspectives from in situ cosmogenic 10be quantifying denudation rates in a wide range of climatic and tectonic settings at various time and space scales is a critical step in calibrating and validating landscape evolution models focusing on taiwan we quantified centennial rates of denudation at the scale of the whole orogen using in situ 10be concentrations measured in stream sediments collected at the outlets of major rivers to assess denudation rates that are statistically significant we applied both the mean square weighted deviation approach and the bootstrap technique for the central segment of the belt where the collision is considered to be near mature the orogen scale pattern of denudation shows a two fold pattern 1 higher denudation values on the order of 4 5 mm yr characterize the eastern side of the belt i e retro wedge with a slight increase towards the south and 2 lower denudation values on the order of 1 3 mm yr on the western side of the belt pro wedge with a minimum value centered on the main recess of the deformation front to the north and to the south of the central segment the denudation rates converge towards lower values on the order of 2 3 mm yr at the scale of the mountain belt drainage basin metrics such as relief hypsometric index and slope values seem to explain the observed variance in the data population conversely to the first order average precipitation pattern suggesting a strong tectonic control on the regional pattern of denudation rates applied to the whole orogen such field based approach thus provides important input data to validate and calibrate the parameters to be supplied to landscape evolution models

mountain building in taiwan a thermokinematic model the taiwan mountain belt is classically viewed as a case example of a critical wedge growing essentially by frontal accretion and therefore submitted to distributed shortening however a number of observations call for a significant contribution of underplating to the growth of the orogenic wedge we propose here a new thermokinematic model of the taiwan mountain belt reconciling existing kinematic thermometric and thermochronological constraints in this model shortening across the orogen is absorbed by slip on the most frontal faults of the foothills crustal thickening and exhumation are sustained by underplating beneath the easternmost portion of the wedge tananao complex tc where the uplift rate is estimated to 6 3 mm a 1 and beneath the westernmost internal region of the orogen hsueshan range units hr where the uplift rate is estimated to 4 2 mm a 1 our model suggests that the tc units experienced a synchronous evolution along strike despite the southward propagation of the collision it also indicates that they have reached a steady state in terms of cooling ages but not in terms of peak metamorphic temperatures exhumation of the hr units increases northward but has not yet reached an exhumational steady state presently frontal accretion accounts for less than 10 of the incoming flux of material into the orogen although there is indication that it was contributing substantially more 80 before 4 ma the incoming flux of material accreted beneath the tc significantly increased 1 5 ma ago our results also suggest that the flux of material accreted to the orogen corresponds to the top 7 km of the upper crust of the underthrust chinese margin this indicates that a significant amount 76 of the underthrust material has been subducted into the mantle probably because of the increase in density associated with metamorphism we also show that the density distribution resulting from metamorphism within the orogenic wedge explains well the topography and the gravity field by combining available geological data on the thermal and kinematic evolution of the wedge our study sheds new light onto mountain building processes in taiwan and allows for reappraising the initial structural architecture of the passive margin

controls on the strength of coupling among climate erosion and deformation in two sided frictional orogenic wedges at steady state 1 many important insights regarding the coupling among climate erosion and tectonics have come from numerical simulations using coupled tectonic and surface process models however analyses to date have left the strength of the coupling between climate and tectonics uncertain and many questions unanswered we present an approximate analytical solution for two sided orogenic wedges obeying a frictional rheology and in a condition of flux steady state that makes explicit the nature and sensitivity of the coupling between climate and deformation we make the simplifying assumption that the wedge grows in a self similar fashion consistent with airy isostasy such that topographic taper is invariant with orogen width tectonic influx rate and climate we illustrate first how and why the form of the erosion rule matters to orogen evolution and then derive a physically based orogen scale erosion rule we show that steady state orogen width crest elevation and crustal thickness are controlled by the ratio of accretionary flux to erosional efficiency to a power dictated by the erosion process remarkably we show that for most combinations of parameters in the erosion law rock uplift rate is more strongly controlled by erosional efficiency than it is by the accretionary flux further assuming frontal accretion with no underplating the spatial distribution of erosional efficiency dictates the relative rock uplift rates on the pro wedge and retro wedge and the time averaged trajectories of rocks through the orogen the restriction to invariant frictional properties is conservative in these respects systems subject to positive feedback between erosion and rheology will exhibit even stronger coupling among climate erosion and deformation than shown here

episodic slow slip events accompanied by non volcanic tremors in southwest japan subduction zone 1 episodic slow slip events have been recognized by means of tilt changes in the western shikoku area southwest japan the crustal tilt deformation was observed repeatedly with a recurrence interval of approximately six months coincident with the occurrences of major non volcanic deep tremor activities in this area observed tilt changes can be explained by slow slip events occurring around the source area of tremors in each episode the source of the slow slip event and tremor migrate simultaneously the spatial and temporal coincidence of tremors and slow slip events indicates that they both may be coupling phenomena reflecting the stress accumulation process at the subducting plate

evidence for a scale limited low frequency earthquake source process we calculate the seismic moments for 34 264 low frequency earthquakes lfes beneath the olympic peninsula washington lfe moments range from 1 4 1010 to 1 9 1012 n m mw 0 7 2 1 while regular earthquakes follow a power law moment frequency distribution with a b value near 1 the number of events increases by a factor of 10 for each unit increase in mw we find that while for large lfes the b value is 6 for small lfes it is 1 the magnitude frequency distribution for all lfes is best fit by an exponential distribution with a mean seismic moment characteristic moment of 2 0 1011 n m the moment frequency distributions for each of the 43 lfe families or spots on the plate interface where lfes repeat can also be fit by exponential distributions an exponential moment frequency distribution implies a scale limited source process we consider two end member models where lfe moment is limited by 1 the amount of slip or 2 slip area we favor the area limited model based on the observed exponential distribution of lfe moment and geodetically observed total slip we estimate that the total area that slips within an lfe family has a diameter of 300 m assuming an area limited model we estimate the slips subpatch diameters stress drops and slip rates for lfes during episodic tremor and slip events we allow for lfes to rupture smaller subpatches within the lfe family patch models with 1 10 subpatches produce slips of 0 1 1 mm subpatch diameters of 80 275 m and stress drops of 30 1000 kpa while one subpatch is often assumed we believe 3 10 subpatches are more likely

the control mechanisms of erosion and weathering at basin scale from cosmogenic nuclides in river sediment the study of a sample of river sediment enables the determination of spatially averaged denudation rates that provide an exceptional perspective on erosion and weathering processes that have taken place within a landscape these measurements are done with in situ produced cosmogenic nuclides e g 10be 26al mostly in quartz from alluvial sediment cosmogenic nuclides are produced when secondary cosmic rays interact with the very uppermost layer of the earth s surface they are produced within a characteristic depth scale of about 1 m which means that the measured concentrations record an integrated denudation history while material passed through this depth interval depending on the denudation rate the resulting integration time scales are 103 to 105 years and one obtains a robust long term estimate of natural denudation that is relatively insensitive to short term changes the last 10 years have seen significant research activity using these methods and an array of fascinating tectono geomorphologic and geochemical insights are emerging amongst these is the ability to identify the physical and chemical processes with which a landscape responds to tectonic activity or climate change a compilation of world wide denudation rates in non glaciated areas that however does not yet include some of the world s most active mountain belts has resulted in the following findings some of which have been unexpected 1 no obvious relationship between precipitation or mean annual temperature and total denudation is apparent 2 topographic relief alone does not result in high rates of denudation 3 denudation rates are high in areas of landscape rejuvenation that is triggered and controlled by tectonic activity faulting escarpment formation and retreat rifting surface uplift 4 rates of weathering using a combination of cosmogenic nuclides and zirconium normalised cation loss balances co vary primarily with physical erosion rates and much less with temperature or precipitation 5 in some areas of high land use short term rates from river load gauging exceed those from cosmogenic nuclides by several orders of magnitude which serves to highlight the severity of geomorphic change caused by human action in the future the control mechanisms over denudation will be determined on all spatial scales ranging from the single soil section to entire river basins the same analysis can be done back through time on well dated terraces lake records and marine sediment cores which is possible with 10be for the past 1 2 my the rates obtained will be used to develop a quantitative understanding of tectonic geomorphologic and geochemical landscape processes which in turn is a prerequisite to design and calibrate models of the response of landscapes to tectonic climate and anthropogenic forcing

a large silent earthquake in the guerrero seismic gap mexico 1 geodetic measurements from a network of permanent gps stations along the pacific coast of mexico reveal a large silent earthquake along the segment of the cocos north american plate interface identified as the guerrero seismic gap the event began in october of 2001 and lasted for 6 7 months average slip of 10 cm produced measurable displacements over an area of 550 250 km2 the equivalent moment magnitude of the event was mw 7 5 recognition of this and previous slow event here indicate that the seismogenic portion of the plate interface is not loading steadily as hitherto believed but is rather partitioning the stress buildup with episodic as opposed to steady state or periodic slip downdip of the seismogenic zone this process increases the stress at the base of the seismogenic zone bringing it closer to failure these results call for a reassessment of the seismic potential of guerrero and other seismic gaps in mexico

a cosmic trip 25 years of cosmogenic nuclides in geology terrestrial cosmogenic nuclides produced by secondary cosmic ray interactions in the atmosphere and in situ within minerals in the shallow lithosphere are widely used to date surface exposure of rocks and sediments to estimate erosion and weathering rates and to date sediment deposition or burial their use has transformed geomorphology and quaternary geology for the first time allowing landforms to be dated and denudation rates to be measured over soil forming time scales the application of cosmogenic nuclides to geology began soon after the invention of accelerator mass spectrometry ams in 1977 and increased dramatically with the measurement of in situ produced nuclides in mineral grains near earth s surface in the 1980s the past 25 yr have witnessed the development of cosmogenic nuclides from their initial detection to their prevalence today as a standard geochronological and geochemical tool this review covers the major developments of the past 25 yr by comparing the state of the field in 1988 with that of today and by identifying key advances in that period that moved the field forward we emphasize the most commonly used in situ produced nuclides measured by ams for geological applications but we also discuss other nuclides where their applications overlap our review covers ams instrumentation cosmogenic nuclide production rates the methods of surface exposure dating measurement of erosion and weathering and burial dating and meteoric 10 be in memoriam devendra lal 1929 2012 whose vision inspired the field

the source scanning algorithm mapping the distribution of seismic sources in time and space summary we introduce a new method which we call the source scanning algorithm ssa for imaging the distribution of seismic sources in both time and space using trial locations and origin times the method calculates the brightness function by summing the absolute amplitudes observed at all stations at their respective predicted arrival times the spatial and temporal distribution of sources is then identified by a systematic search throughout the model space and time for the maximum brightness the greatest advantages of this method are that 1 it exploits waveform information both arrival times and relative amplitudes without the need to calculate highfrequency synthetic seismograms and 2 it requires neither pre assembled phase picking data nor any a priori assumptions about the source geometry a series of tests using synthetic data have shown that this method is robust and can faithfully recover the input source configuration to within 1 grid interval finally we demonstrate the value of the algorithm by locating a typical tremor event with emergent waveforms that occurred during the recent episodic tremor and slip ets sequence in the northern cascadia subduction zone

ongoing exhumation of the taiwan orogenic wedge revealed by detrital apatite thermochronology the impact of effective mineral fertility and zero track grains abstract in clastic detritus derived from the erosion of young active orogens the geologic interpretation of apatite fission track aft data is hampered by the occurrence of grains without spontaneous tracks and by contributions from multiple eroding sources with different apatite fertilities here we use the taiwan orogen as a test case to illustrate how to overcome these problems and deal with zero track grains in detrital aft studies following long established principles of fission track statistics our results support the effectiveness of raman spectroscopy for a reliable identification of apatite grains we found that zero track grains are dominant in taiwan modern sands and generally contain enough u to provide useful aft age constraints to exhumation the absence of spontaneous tracks in most of these grains is due to a short residence time below the temperature of total aft annealing rather than to low u concentration detrital aft data shows that the extent of the taiwan aft reset zone previously inferred from bedrock data was partly underestimated the revised aft reset zone includes the southernmost part of the island and when combined with published zft data supports a scenario of southward progressing exhumation during arc continent collision the application of the taiwan lesson to clastic detritus derived from the himalaya resolves paradoxical interpretations of detrital fission track data sets recently published in the framework of iodp expedition 354 pointing to a major role of the namche barwa syntaxis as a source of apatite grains shed to the bengal fan

orogeny and orography the effects of erosion on the structure of mountain belts a numerical model of the coupled processes of tectonic deformation and surface erosion in convergent orogens is developed to investigate the nature of the interaction between these processes crustal deformation is calculated by a two dimensional finite element model of deformation in response to subduction and accretion of continental crust erosion operates on the uplifted surface of this model through fluvial incision which is taken to be proportional to stream power the relative importance of the tectonic and erosion processes is given by a dimensionless erosion number relating convergence velocity rock erodibility and precipitation rate this number determines the time required for a system to reach steady state and the final topographic shape and size of a mountain belt fundamental characteristics of the model orogens include asymmetric topography with shallower slopes facing the subducting plate and an asymmetric pattern of exhumation with the deepest levels of exhumation opposite to subduction these characteristics are modified when the regional climate exhibits a dominant wind direction and orographically enhanced precipitation on one side of the mountain belt the two possible cases are dominant wind in the direction of motion of the subducting plate and dominant wind direction in the opposite direction of the subducting plate velocity models of the former case predict a broad zone of exhumation with maximum exhumation in the orogen interior models of the latter case predict a focused zone of exhumation at the margin of the orogen and at high erosion number a reversal in the topographic asymmetry natural examples of these two cases are presented the southern alps of new zealand exhibits the climate and exhumation asymmetry characteristic of wind in the direction opposite to motion of the subducting plate the asymmetry of topography suggests that erosion is not efficient enough to have reversed the topographic asymmetry the contrasting example of dominant wind in the direction of subduction motion is provided by the olympic mountains of washington state in this case exhumation of deep levels of the cascadia accretionary wedge shows a broad domal pattern consistent with the observed orographic precipitation

cascadia tremor located near plate interface constrained by s minus p wave times nonvolcanic tremor is difficult to locate because it does not produce impulsive phases identifiable across a seismic network an alternative approach to identifying specific phases is to measure the lag between the s and p waves we cross correlate vertical and horizontal seismograms to reveal signals common to both but with the horizontal delayed with respect to the vertical this lagged correlation represents the time interval between vertical compressional waves and horizontal shear waves measurements of this interval combined with location techniques resolve the depth of tremor sources within 2 kilometers for recent cascadia tremor the sources locate near or on the subducting slab interface strong correlations and steady s p time differences imply that tremor consists of radiation from repeating sources

the frequency size scaling of non volcanic tremors beneath the san andreas fault at parkfield possible implications for seismic energy release abstract we analyse the frequency size distribution of non volcanic tremors observed along the parkfield section of the san andreas fault we suggest that these non volcanic tremors follow a power law scaling typical of scale invariant stick slip tectonic earthquakes but with an unusually high scaling exponent of more than 2 0 and a systematic depth dependency while each individual non volcanic tremor releases only a minuscule amount of energy and slip this is more than compensated by their sheer numbers consequently the integrated contribution of this largely invisible seismicity non volcanic tremors and nano earthquakes is non negligible and could potentially account in selected patches along the san andreas fault for up to 100 of the plate motion

slow slip on the northern hikurangi subduction interface new zealand 1 in october 2002 a surface displacement episode of 20 30 mm magnitude was observed over a 10 day period on two continuous global positioning system gps instruments near gisborne north island new zealand we interpret this to result from slow slip on the northern hikurangi subduction interface using ten years of regional campaign gps 1995 2004 and recent continuous gps data we estimate the recurrence interval for similar events to be 2 3 yrs in november 2004 a similar slow slip event occurred within this recurrence period the 2002 event can be modeled by 18 cm of slow slip near the down dip end of the seismogenic zone on the subduction interface offshore of gisborne the campaign gps data show that the 2002 slow slip event had little effect on regional strain patterns

numerical and analytical models of cosmogenic radionuclide dynamics in landslide dominated drainage basins 1 in many tectonically active regions on earth landslides dominate sediment delivery to channels while cosmogenic radionuclides crn represent a valuable tool to document basin averaged erosion rates a better understanding of crn dynamics in these systems is required before erosion rates can be reliably inferred from crn concentrations the stochastic nature of landslides results in variability of crn concentrations in both alluvial and hillslope samples that is both difficult to document and poorly understood to guide sampling strategies we developed a 2 d plan view model to simulate the influence of landslides on crn dynamics we employ a sediment mixing model in which concentrations of crns from material eroded by both landslides and steady processes are combined to evaluate how best to infer erosion rates from crn concentrations this model is further used to test a new analytical solution for the distribution of crn concentrations on hillslopes in a landslide prone system results suggest that for landscapes dominated by deep 5 m landslides only large drainage basins 100 km2 provide consistently reliable estimates of erosion rates from crn concentrations for landscapes dominated by shallow landslides 0 7 2 m smaller basins can produce reliable estimates results further suggest that the distribution of concentrations from hillslope samples could be used to deduce the relative contribution of material derived from landslide and steady processes these findings underscore the need to consider carefully the sources of natural variability in sampling and analyzing crns if properly done the variability can reveal useful information about geomorphic processes in landslide prone areas

examination of surface exposure ages of antarctic moraines using in situ produced 10be and 26al concentrations of 10be t12 1 5 106 y and 26a1 t12 0 72 106 y have been determined by accelerator mass spectrometry ams in a suite of quartz samples taken from sandstone boulders in several moraines in arena valley a dry valley adjacent to the taylor glacier in the quatermain mountains southern victoria land east antarctica these isotopes are produced in surficial quartz by cosmic ray spallation of o and si the concentrations in these samples ranged from 6 1 105 to 3 0 107 at g 1 for 10be and from 9 4 106 to 1 2 108 at g 1 for 26a1 depending upon the extent of exposure at the surface analyses of 10be in several samples from a single moraine at altitudes ranging from 1300 to 1650 m permitted an estimation of the air attenuation pathlength of cosmic ray neutrons the value of 142 96 41 g cm 2 is consistent with other published values production rates of 17 6 4 at g 1 y 1 for 10be and 113 54 16 at g 1 y 1 for 26a1 at 1300 m and 87 s and a 26al 10be production ratio of 6 5 1 3 1 3 were calculated from the data these values correspond to sea level production rates at high geomagnetic latitude of 6 4 at g 1 y 1 and 41 7 at g 1 y 1 for 10be and 26a1 respectively consistent with determinations based on 11 ky glacially polished surfaces in the sierra nevada in california these production rates imply exposure ages for the various moraines ranging from 50 ky to 2 5 my in accordance with other geological evidence the 10be and 26al ages of these rocks compare favorably with those found using a similar dating method based on in situ production of 3he examination of the 3he concentrations in conjunction with the present data set yields an estimate of 3he production of 230 8540 at g 1 y 1 corresponding to 85 31 15 at g 1 y 1 at sea level this is lower than previously reported values of 240 60 at g 1 y 1 and 190 at g 1 y 1 scaled to sea level and high geomagnetic latitude based respectively on volcanic flows less than 2000 years old at low latitude and samples collected from 14 400 year old volcanic flows this discrepancy is likely due to diffusive losses which may become significant up to 50 for surface exposure ages on the order of 2 0 my nevertheless the general correlations among the three isotopes suggest that 3he does not suffer gross losses through diffusion

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

estimating seismic moment magnitude mw of tremor bursts in northern cascadia implications for the seismic efficiency of episodic tremor and slip 1 we develop a method to estimate the seismic moments of deep non volcanic tremor bursts observed in northern cascadia for each tremor burst the maximum amplitudes at individual stations within a time window 5 s around the predicted arrivals of the s phase are measured and compared to the maximum s amplitudes measured from synthetic seismograms the proposed method is thoroughly calibrated using 464 local earthquakes and the results show excellent consistency between the reported ml and the estimated mw we apply the method to northern cascadia tremors and infer that most bursts have mw 1 0 1 7 the corresponding b value appears to be 1 consistent with that of ordinary earthquakes but over a narrower mw range comparison of cumulative tremor mw and the mw estimated from the accompanying slow slip suggests that the seismic efficiency of the episodic tremor and slip ets is of the order of 0 1 or less

northern cascadia episodic tremor and slip a decade of tremor observations from 1997 to 2007 1 we analyze continuous seismic and gps records collected in the last decade 1997 2007 to establish the most comprehensive observational basis for northern cascadia episodic tremor and slip ets events a simple ets scale system using a combination of a letter and a digit is proposed to quantitatively characterize the spatial and temporal dimensions of ets events clear correlation between gps and tremor signals is observed for all a b class episodes but the gps signature is less obvious for minor ones regular ets recurrence can be established only for a b class episodes in southern vancouver island halting and jumping are very common in ets migration patterns and along strike migration can happen in both directions a prominent tremor gap is observed in midisland around 49 5 n this gap coincides with the epicenters of the only two large earthquakes beneath vancouver island ets tremors also tend to occur in places where the local seismicity is relatively sparse the tremor depth distribution shows a peak in the 25 35 km range where strong seismic reflectors i e the e layer are documented detailed waveform analysis confirms the existence of shallow tremors above the currently interpreted plate interface our results suggest that a significant portion of the tremor activity and perhaps associated shearing are taking place along well developed structures such as the e layer while fewer tremor bursts are generated elsewhere in response to the induced stress variation throughout the source volume

erosional control of the kinematics and geometry of fold and thrust belts imaged in a physical and numerical sandbox 1 we investigate the effect of systematically varying erosion intensity k on the geometry and kinematics of fold and thrust belts modeled using equivalent conditions in physical and numerical experiments similar material properties and boundary conditions were used to compare numerical experiments to those modeled in the sandbox using an erosion rule that removes mass from the scaled sand wedges according to rates expected from bedrock fluvial incision the geometry of both modeling approaches is quantitatively compared with that expected from analytical theory the fold and thrust belt growth rate is inversely proportional to k and is well predicted by theory except for the high erosion case in which both the numerical and the experimental sandbox grows supercritically a direct relationship exists between the erosion intensity and the number of fore shear bands and shear strain magnitude the number of fore shear bands decreases and their strain increases with erosion intensity the results indicate that realistic and mechanistic erosion rules can be applied to physical experiments to model mass removal and this approach opens up the possibility of calibrating strain history to erosion intensities for predictions in natural settings quantitative comparisons between the physical and numerical sandbox experiments indicate that deformation style and geometry of the thrust and fold belts are similar when identical rheologies and boundary conditions are used this benchmarking suggests that numerical experiments realistically model conditions observed in the simple cohesionless rheologies commonly employed in sandbox experiments this suggests that numerical simulation may reliably model experimental deformation in geological situations that are difficult to represent in scaled experiments because of the different scales and rheologies of natural orogenic wedges

landslides control the spatial and temporal variation of channel width in southern taiwan implications for landscape evolution and cascading hazards in steep tectonically active landscapes

erosion and exhumation in accretionary orogens experimental and geological approaches 1 this study examines the role of erosion on exhumation and deformation history of accretionary orogens through experimental and geological methods fault propagation kinematics and exhumation rates in an eroded thrust wedge are analyzed through scaled sandbox simulations by testing different parameters friction rheologic layering and sediment input output ratio a model coulomb wedge is submitted to erosion under flux steady state conditions that is the volume of eroded material remains equal to the volume of newly accreted material maintaining a constant surface slope during shortening results show that the way of exhumation depends on the internal dynamics of thrust wedges and conversely on how this dynamics is modified by erosion in the eroded thrust wedges the diversity of exhumation patterns is controlled by the mode of fault propagation depending on the basal friction high or low the vertical component of exhumation is generally higher for the wedges with high basal friction than for low friction wedges the uplift of material occurs along a cluster of subvertical thrusts in the middle part of the eroded thrust wedge with low basal friction the material is exhumed along a series of inclined 20 50 thrusts in the rear of the high friction wedge the zone of maximum exhumation is generally localized in the middle part of the thrust wedge and migrates toward the backstop with continued shortening the vertical exhumation rate increases with time and the material accreted later is rapidly transferred to the main exhumation zone compared to the material accreted during the early stages the exhumation occurs at rates 2 times faster in the wedges with half the thickness than in full thickness wedges the total quantity of eroded material at the end of convergence constitutes 36 50 of initial model area for the thrust wedges with low basal friction and 20 40 for the high basal friction wedges the extent of basal underplating increases with total shortening the area of basal underplated material constitutes up to 30 and 40 of the eroded thrust wedge area for the models with low and high basal friction respectively presence of decollements in the accreted series allows underplating of thrust units developing an anticlinal stack whose growth and location is favored by erosion our results are compared to different present day active and ancient convergent orogens himalaya taiwan southern alps of new zealand and cascadia orogen allowing the different specific exhumation processes to be characterized

taiwan mountain building insights from 2 d thermomechanical modelling of a rheologically stratified lithosphere summary the taiwan orogen has long been regarded as a case example for studying mountain building in association with subduction processes in this paper we present a fully coupled thermomechanical modelling of the taiwan collision based on a realistic viscous elastic plastic rheology it satisfactorily reproduces available thermochronometric data long short term deformation patterns heat flux and erosion sedimentation distribution across the taiwan orogeny we found that a deep seated flux of asian crustal material into the orogenic wedge should be invoked to counter balance observed exhumation and erosion in the central range however in contrast with recent thermokinematic models of exhumation and deformation suggesting that underplating plays a significant role we show that most constraints on exhumation and deformation can be more straightforwardly interpreted by the frontal accretion of the rheologically layered asian crust we finally infer that such a model is in better agreement with the basic expectation that the hot young and buoyant chinese continental margin should hardly be subducted beneath the cold old and dense oceanic plate of the philippines sea

a thermomechanical wedge model of taiwan constrained by fission track thermochronometry abstract we present 31 new apatite fission track aft ages for the island of taiwan that when combined with existing aft and zircon fission track zft data provide regional spatial coverage of the island with respect to low temperature thermochronometry the overall pattern of zft and aft ages in taiwan exhibits unreset ages in the southern and western portions of the island and reset ages predominantly in the central range and eastern taiwan this pattern supports interpretations of the orogen kinematics as reflecting a crustal scale wedge with a southward propagating collision zone in this model new material is accreted to the wedge from the west and is transferred to the east with the greatest exhumation occurring along the eastern margin as recorded in the reset ages in the east and unreset ages in the west the southward propagating collision is consistent with reset ages in the north where erosional exhumation has been ongoing for longer and unreset ages in the south where the younger collision implies less time for erosional exhumation despite the variation in the age of the collision along the strike of the island the widths of the aft and zft reset age zones remain nearly constant between 23 00 n to 24 00 n and 23 20 n to 24 00 n respectively suggesting that the orogen is in an exhumational steady state over these regions with respect to the aft and zft thermochronometers we use the fission track data in conjunction with observations of crustal structure crustal fabric and heat flow measurements to constrain a time dependent two dimensional thermomechanical model of orogen evolution by accounting for the heat transfer tectonic and erosion processes needed to predict aft and zft ages we are able to investigate the relationship between the measured ages and the tectonic characteristics of the orogen with our model we conclude that 1 roughly half of the material accretion in taiwan occurs through underplating over an approximately 40 km wide region 2 current average erosion rates are 3 3 mm yr in the eastern central range and 2 3 mm yr over the whole island 3 the collision has been propagating southward at a rate between 20 and 51 km ma over the past 2 3 ma and 4 central taiwan is in a topographic thermal and exhumational steady state

production of cosmogenic radionuclides at great depth a multi element approach abstract for the last two decades in situ produced cosmogenic nuclides are increasingly applied in earth sciences to quantify surface processes in parallel significant reduction of the analytical uncertainties linked to advances in accelerator mass spectrometry ams allows more precise measurements however among all the published works on cosmogenic nuclides only few studies are dedicated to a better understanding of their production systematic or to a better constrain of the physical parameters involved in their production thus an approach to investigate in situ produced cosmogenic nuclides 10 be 26 al and 36 cl along a single 11 meter long core drilled from the surface and composed of carbonates and quartzose conglomerates has been launched these measurements have been used to quantify muon induced productions based on natural samples for each studied nuclide contrary to the current most oftenly used calculation of muon induced production parameters which are based on irradiation experiments at discrete energies productions based on natural samples are considering the entire energy range of particles reaching the ground surface the evolution of 36 cl concentrations with depth needs to agree with those parameters deduced from 10 be and 26 al data this is optimized when considering a fast muon induced 36 cl production contribution and a spallation production rate at sea level high latitude slhl of 42 0 2 0 atoms 36 cl g ca 1 a 1 1 sigma uncertainty

erosion rates and orogenic wedge kinematics in taiwan inferred from fission track thermochronometry new apatite and zircon fission track ages and previously published thermochronometric data are used to evaluate erosion rates and particle paths within the active taiwan arc continent collision we present 20 new apatite fission track ages and 6 new zircon fission track ages apatite and zircon ages are all reset in the northern and eastern parts of taiwan although the region of reset apatite ages is larger we interpret this pattern as resulting from crustal accretion at the western margin of the orogenic wedge combined with southward propagation of the collision zone a onedimensional thermal model including erosion provides prediction of the fission track ages the distribution of reset ages is best explained with an erosion rate of 4 6 mm yr given a propagation velocity of 60 mm yr this erosion rate implies that nearly 25 km of material has been eroded from northern taiwan the lack of reset 40 ar 39 ar ages from muscovite and biotite suggests that rockparticle paths have a large horizontal component a result consistent with an eroding orogenic wedge model

pyrrhotite as a tracer for denudation of the taiwan orogen 1 the use of pyrrhotite as an index mineral to delineate metamorphic isograds has long been proposed however details of the occurrence of pyrrhotite in different metamorphic facies and its implications have rarely been explored here by simple characterization of magnetic properties and mineral identification we demonstrate that pyrrhotite is widely distributed in low grade metamorphic terranes of taiwan s central range and in sediments derived therefrom by coupling the distribution of pyrrhotite in rocks with that in dated sediment strata we have studied the denudation history of taiwan s orogen from a source to sink perspective we suggest that pyrrhotite is a potential tracer for studying surface processes in orogens with high denudation rates similar to that in taiwan

modern vertical deformation rates and mountain building in taiwan from precise leveling and continuous gps observations 2000 2008 1 to characterize the present day vertical displacement field in the active taiwan orogenic belt 1843 precise leveling and 199 continuous gps measurements from 2000 to 2008 are collected and analyzed in this study vertical velocities derived from the leveling data are placed in a reference frame of the chinese continental margin using continuous gps observations at nearby sites the leveling and gps vertical velocities generally reveal a dome shaped pattern with uplift of 0 2 18 5 mm yr in the interior of the mountain range and subsidence on the flanks of the mountains and coastal plains modern uplift rates in the active fold and thrust belt are generally consistent with geologic uplift rates however present day uplift rates in the central range are faster than the million years averaged exhumation rates the modern subsidence rates are generally consistent with geologic rates except for the rates in western coastal areas due to groundwater pumping present day subsidence in the southern central range and northern coastal range is however inconsistent with long term uplift which may reflect interseismic elastic strain accumulation across faults present day subsidence in northern taiwan occurs in a region of postcollisional orogenic collapse we model the present day and geologic vertical velocities and published gps horizontal velocity data across southern taiwan using a 2 d lithospheric model the model suggests a combined slip rate of 40 mm yr on the frontal thrusts and 45 mm yr on the longitudinal valley fault the model requires an additional source of crustal thickening under the central range to match the observed present day uplift rates

imaging slow slip fronts in cascadia with high precision cross station tremor locations 1 we apply a new method to obtain accurate locations of tremor sources beneath southern vancouver island unlike more standard cross time methods which compare waveforms from different time windows at the same station this cross station method compares waveforms from the same time window at widely separated stations it performs well relative to cross time methods when the response to an impulsive tremor source is dominated by the main arrival rather than coda and when multiple colocated sources are active within the time window examined we focus on a region roughly 10 km across that was monitored by the polaris deployment from 2003 to 2006 relative location errors appear to be 1 km allowing us to image in great detail rapid and small scale tremor migrations that arise behind the main slow slip front the secondary fronts tend to a start at or within about 1 km of the main tremor front and propagate back along strike at rates of 10 20 km h b less commonly do the reverse ending at the main front or c propagate up or downdip at or within 1 2 km of the main front estimated stress drops in the secondary events are comparable to that in the main event implying that their 25 50 times greater propagation speed results from a similarly greater slip speed

scaling factors for the rates of production of cosmogenic nuclides for geometric shielding and attenuation at depth on sloped surfaces abstract the decrease in rates of production of cosmogenic nuclides occurs because of shielding of cosmic rays by mountains sloped surfaces and local rock formations that block them when a large part of the sky is blocked this correction is large and requires detailed model calculations this paper considers three geometries a rectangular obstruction a triangular obstruction and a sloped surface other geometries can be considered as a combination of these the results are presented in terms of formulas and graphs so that the reader can easily apply them to common field situations any use of cosmogenic nuclides in the study of geomorphic processes or forms must consider factors that introduce variations in the production of nuclides

slow earthquakes coincident with episodic tremors and slow slip events we report on the very low frequency earthquakes occurring in the transition zone of the subducting plate interface along the nankai subduction zone in southwest japan seismic waves generated by very low frequency earthquakes with seismic moment magnitudes of 3 1 to 3 5 predominantly show a long period of about 20 seconds the seismicity of very low frequency earthquakes accompanies and migrates with the activity of deep low frequency tremors and slow slip events the coincidence of these three phenomena improves the detection and characterization of slow earthquakes which are thought to increase the stress on updip megathrust earthquake rupture zones

earthquakes triggered by silent slip events on kīlauea volcano hawaii silent earthquakes or slow slip events happen so slowly that they cannot be detected by conventional seismographs but now the availability of gps data means that they can be followed in detail segall et al report on a series of small earthquakes on k lauea volcano hawaii the earthquakes at depths of 7 to 8 km appear to be triggered by otherwise silent slow slips though small triggered earthquakes of this type can be used to help quantify the increased hazard due to slow slip events slow slip events or silent earthquakes have recently been discovered in a number of subduction zones including the nankai trough1 2 3 in japan cascadia4 5 and guerrero6 in mexico but the depths of these events have been difficult to determine from surface deformation measurements although it is assumed that these silent earthquakes are located along the plate megathrust this has not been proved slow slip in some subduction zones is associated with non volcanic tremor7 8 but tremor is difficult to locate and may be distributed over a broad depth range9 except for some events on the san andreas fault10 slow slip events have not yet been associated with high frequency earthquakes which are easily located here we report on swarms of high frequency earthquakes that accompany otherwise silent slips on k lauea volcano hawaii for the most energetic event in january 2005 the slow slip began before the increase in seismicity the temporal evolution of earthquakes is well explained by increased stressing caused by slow slip implying that the earthquakes are triggered the earthquakes located at depths of 7 8 km constrain the slow slip to be at comparable depths because they must fall in zones of positive coulomb stress change triggered earthquakes accompanying slow slip events elsewhere might go undetected if background seismicity rates are low detection of such events would help constrain the depth of slow slip and could lead to a method for quantifying the increased hazard during slow slip events because triggered events have the potential to grow into destructive earthquakes

increase of human over natural erosion rates in tropical highlands constrained by cosmogenic nuclides we quantify the difference between the human caused sediment yield and the natural rates of soil production and bedrock erosion in a now largely deforested tropical highland the present day rate of soil loss in the upper mahaweli catchment sri lanka is calculated by using suspended river load fluxes these data provide spatially averaged sediment yields of 130 2100 t km 2 yr 1 local rates of soil loss from agricultural plots on hillslopes are as high as 7000 t km 2 yr 1 by comparison natural rates of sediment generation as determined by measuring cosmogenic 1 0 be in quartz from sediments and soils are only 13 30 t km 2 yr 1 the natural rates presented here provide a benchmark against which recent erosion rates determined by various sediment gauging techniques can be referenced in the sri lankan highlands these results suggest that soil is now being lost 10 100 times faster from agriculturally utilized areas than it is being produced

determination of predevelopment denudation rates of an agricultural watershed cayaguas river puerto rico using in situ produced 10be in river borne quartz accurate estimates of watershed denudation absent anthropogenic effects are required to develop strategies for mitigating accelerated physical erosion resulting from human activities to model global geochemical cycles and to examine interactions among climate weathering and uplift we present a simple approach to estimate predevelopment denudation rates using in situ produced cosmogenic 10be in fluvial sediments denudation processes in an agricultural watershed cayaguas river basin puerto rico and a matched undisturbed watershed icacos river basin were compared using 10be concentrations in quartz for various size fractions of bed material the coarse fractions in both watersheds bear the imprint of long subsurface residence times fine material from old shallow soils contributes little however to the present day sediment output of the cayaguas this confirms the recent and presumably anthropogenic origin of the modern high denudation rate in the cayaguas basin and suggests that pre agricultural erosional conditions were comparable to those of the present day icacos

thrust wedges with decollement levels and syntectonic erosion a view from analog models abstract analog sandbox models have been set up to study the impact of syntectonic erosion on thrust wedges with one and two decollement levels different accretion mechanisms are activated depending on interactions between surface processes and wedge mechanics frontal accretion backthrusting underthrusting and underplating due to decollement induced duplex formation at depth these mechanisms may function simultaneously being located at different parts across the wedge for all the experiments a high friction is imposed at the base of models and the volume of eroded material remains equal to the volume of newly accreted material maintaining a constant surface slope during the shortening erosion limits the forward propagation of thrust wedges and favors the underthrusting of basal layers allowing duplex formation erosion promotes development of major backthrusts in the thrust wedges without or with one decollement but no backthrusts was formed in the wedges with two decollements slow erosion allows lower extent of basal underthrusting in comparison with regular rate erosion variations in the erosion taper lead to changes in duplex geometry and exhumation rate in thrust wedges with one or two decollements the 6 erosion taper promotes formation of antiformal stack at the rear part of thrust wedge high rate of basal underthrusting and high extent of erosional removal the cover layers are nearly completely eroded above the antiformal stack and form the synformal klippe in frontal part of thrust wedges the 8 erosion taper allows development of individual ramp anticlines and active forward thrusting of cover layers above the decollement and low rate of basal underplating below it with consequent low extent of erosional removal the results of our experiments support the observations on structural evolution and erosion in the alberta foothills of the canadian rockies

rates of cooling and denudation of the early penglai orogeny taiwan as assessed by fission track constraints abstract as an attempt to define the timing of the peak temperature of the penglai orogeny and estimate the early cooling and denudation rates of the taiwan mountain belt fission track dating of zircon and apatite was conducted on several key metamorphic rock samples the zircon fission track ages for the metasandstone clasts collected from the central and northern parts of the coastal range were determined as 4 0 0 5 and 3 6 0 3 ma respectively both of the clasts were identified as from the ancient central range which was metamorphosed at temperatures high enough to cause a complete reset of the zircon fission track system during 1 2 ma they were exhumed and deposited in the coastal range basin due to the later penglai orogeny of taiwan obviously they have not further been annealed since their deposition in the coastal range the difference between the above fission track ages and the stratigraphical age of the host sedimentary formation represent the ancient cooling ages when they were exposed on the early central range these ancient cooling ages are comparable with the zircon fission track age of a present day outcrop of the tananao schist 1 8 0 2 ma this accordance implies that at ca 5 ma the northern and central parts of the central range achieved the peak temperature of the penglai orogeny and then they began to emerge above sea level accepting this scenario we calculate the rates of denudation and cooling of the central range to be ca 2 5 4 6 mm yr 1 and 120 c m y 1 respectively for the last 4 ma

mountain erosion over 10 yr 10 k y and 10 m y time scales we used cosmogenic 10 be to measure erosion rates over 10 k y time scales at 32 idaho mountain catchments ranging from small experimental watersheds 0 2 km 2 t o large river basins 35 000 km 2 these long term sediment yields are on average 17 times higher than stream sediment fluxes measured over 10 84 yr but are consistent with 10 m y erosion rates measured by apatite fission tracks our results imply that conventional sediment yield measurements even those made over decades can greatly underestimate long term average rates of sediment delivery and thus overestimate the life spans of engineered reservoirs our observations also suggest that sediment delivery from mountainous terrain is extremely episodic sporadically subjecting mountain stream ecosystems to extensive disturbance

denudation rates determined from the accumulation of in situ produced 10be in the luquillo experimental forest puerto rico we present a simple method for estimation of long term mean denudation rates using in situ produced cosmogenic 10be in fluvial sediments procedures are discussed to account for the effects of soil bioturbation mass wasting and attenuation of cosmic rays by biomass and by local topography our analyses of 10be in quartz from bedrock outcrops soils mass wasting sites and riverine sediment from the icacos river basin in the luquillo experimental forest puerto rico are used to characterize denudation for major landform elements in that basin the 10be concentration of a discharge weighted average of size classes of river sediment corresponds to a long term average denudation of 43 m ma 1 consistent with mass balance results

denudation rate changes along a fast eroding mountainous river with slate headwaters in taiwan from 10 be meteoric 9 be ratios

neotectonic characteristics along the eastern flank of the central range in the active taiwan orogen inferred from fluvial channel morphology the tectonic activity of the taiwan orogenic belt has been studied by different methods over various timescales constraints on tectonic characteristics over timescales of 103 105 years however are rather limited to further understand the tectonic forcing over this timescale we analyzed 20 major river basins along the eastern flank of the central range the mountainous core of the orogen the results of river steepness index ksn values and the distribution patterns of knickpoints are consistent with the patterns of tectonic evolution in taiwan on both ends of the orogen the rivers have low ksn values that indicate low uplift rates throughout the area in the central part of the island where the orogen is under rapid collisional processes the rivers are steeper and are characterized by many tectonic knickpoints our results show different patterns from both short term and long term uplift and denudation rate patterns this suggests that these rates change temporally and spatially moreover the steepness indexes of rivers in the taiwan orogen show the same increasing trend with erosion rates as those in other active orogens but correspond to significantly higher erosion rates this is likely produced by the frequent debris flow and landslide events in taiwan a character that makes the island distinctive from other active orogens in the world

spatial temporal patterns of seismic tremors in northern cascadia 1 we study in detail the two consecutive episodic tremor and slip ets events that occurred in the northern cascadia subduction zone during 2003 and 2004 for both sequences the newly developed source scanning algorithm ssa is applied to seismic waveform data from a dense regional seismograph array to determine the precise locations and origin times of seismic tremors in map view the majority of the tremors occurred in a limited band bounded approximately by the surface projections of the 30 km and 50 km depth contours of the plate interface the horizontal migration of tremor occurrence is from southeast to northwest with an average speed of 5 km d in cross section tremors in both sequences span a depth range of over 40 km across the interface with the majority occurring in the overriding continental crust in particular 50 55 of them are located within 2 5 km from the strong seismic reflector bands above the plate interface the lack of vertical migration implies that a slow diffusion process in the vertical direction cannot be responsible for tremor occurrences the source spectra of tremors clearly lack high frequency content 5 hz relative to local earthquakes we propose two possible models to explain the relationship between slip and tremors the first one regards ets tremors as the manifestation of hydroseismogenic processes in response to the temporal strain variation associated with the episodic slip along the lower portion of the plate interface downdip from the locked zone in the second model tremors and slip are associated with the same process along the same structure in a distributed deformation zone across the plate interface neither model can be dismissed conclusively at this stage

spatially averaged long term erosion rates measured from in situ produced cosmogenic nuclides in alluvial sediment spatially averaged erosion rates of small catchments can be accurately inferred from the concentrations of cosmogenic nuclides in stream sediment here we test this technique at two catchments by comparing erosion rates inferred from cosmogenic nuclides with rates of alluvial fan deposition over the past 16 000 years these two independent estimates agree within one standard error demonstrating that cosmogenic nuclide signatures of stream sediment can be used to measure spatially averaged long term erosion rates using this technique we show that long term erosion rates are an exponential function of average hillslope gradient at these sites

10be study of rapid erosion in taiwan cosmogenic 10be was measured using accelerator mass spectrometry in soils and sediments to study the erosion of taiwan which has the highest denudation rate in the world the river sediments in taiwan have very low 10be concentrations around 5 million atoms per gram about 145 the world wide average this is the direct consequence of its high sediment yield of more than 1000 mg cm2 yr 70 times the world average combining these values we found that for taiwan as a whole the 10be output to the sea only slightly exceeds the input from the rain a situation typical of many areas around the world therefore even in this example of extremely rapid erosion 10be seems to remain a useful indicator for erosion status the total 10be inventory found in a soil profile from a geologically stable area is at least 18 of the maximum possible inventory the minimum age thus estimated for the soil is 0 11 ma in reasonable agreement with estimates from other means the maximum erosion rate for this area thus estimated is at most 0 14 mg cm2 yr four orders of magnitude slower than the average value observed for taiwan we also demonstrate that the shelf sediments around taiwan have received the admixing of a 10be rich component from the ocean and would give a poor estimate for material eroded from taiwan

topographic and lithologic control on catchment wide denudation rates derived from cosmogenic 10be in two mountain ranges at the margin of ne tibet abstract fault bounded mountain ranges with along strike variations in mean slope angle and local relief offer the opportunity to investigate how denudation depends on these topographic parameters we determined catchment wide denudation rates along two actively growing fault bounded mountain ranges the yumu and western longshou shan from 10be concentrations in quartz from stream sediments both ranges expose 1 low grade metamorphic paleozoic rocks in their center and 2 unmetamorphosed cretaceous red beds near the tips of the range bounding thrust faults field observations document debris flows shallow landsliding and surface wash as dominant mechanisms of mass transport on the hillslopes denudation rates obtained for the paleozoic metasediments range from 100 to 300 mm ka 1 and correlate linearly with mean slope angle and local relief in contrast cretaceous sediments exhibit mainly higher and more variable denudation rates between 30 and 500 mm ka 1 although slope and relief values are lower for these catchments the higher denudation rates in the cretaceous red beds are interpreted as resulting from their lower mechanical strength as compared to the resistant paleozoic rocks this important lithologic control on denudation demonstrates that uniform catchment lithologies and rock strength are essential for deciphering the effect of topographic indices on the rate of denudation

climate induced denudational changes during the little ice age inferred from 10be meteoric 9be ratio a case study from the core monsoon zone of india abstract denudation rates are often estimated with high uncertainty using the average mass of material discharged through a drainage basin or considering the rate of surface processes estimating long term denudation rates through these conventional methods requires the assumption that the surficial processes have remained constant throughout time since the earth s surface has been obliterated throughout the geological time by climate tectonics or the recent anthropogenic activities the present rate of change may not represent past processes this study presents changes in denudation rate using the 10be meteoric 9be ratio for the past 600 years from anshupa lake sediment record in the core monsoon zone of india paleodenudation rate estimated using 10be meteoric 9be varies from 392 42 to 95 6 t km2 yr intense indian summer monsoon ism during the periods of solar maxima which caused decadal scale floods in the indian sub continent favored a higher rate of denudation than the periods of solar minima that experienced droughts in the indian sub continent due to weakening of ism

estimating rates of denudation using cosmogenic isotope abundances in sediment we propose as a testable hypothesis a basin scale approach for interpreting the abundance of in situ produced cosmogenic isotopes an approach which considers explicitly both the isotope and sediment flux through a drainage basin unlike most existing models which are appropriate for evaluating in situ produced cosmogenic isotope abundance at discrete points on earth s surface our model is designed for interpreting isotope abundance in sediment because sediment is a mixture of materials in favourable cases derived from throughout a drainage basin we suggest that measured isotope abundances may reflect spatially averaged rates of erosion we investigate the assumptions and behaviour of our model and conclude that it could provide geomorphologists with a relatively simple means by which to constrain the rate of landscape evolution if a basin is in isotopic steady state and if sampled sediments are well mixed

revisiting the hypsometric curve as an indicator of form and process in transport limited catchment hypsometry has historically been used as an indicator of geomorphic form of catchments and landforms yet there has been little work aimed at relating hypsometry to landform process and scale this paper uses the siberia catchment evolution model to explore linkages between catchment process and hypsometry siberia generates results that are qualitatively and quantitatively similar to observed hypsometric curves for physically realistic parameters however we show that not only does the hypsometry reflect landscape runoff and erosion process but it is strongly dependent on channel network and catchment geometry we show that the width to length ratio of the catchment has a significant influence on the shape of the hypsometric curve though little on the hypsometric integral for landforms dominated by fluvial sediment transport the classic strahler mature hypsometric curve is only generated for catchments with roughly equal width and length narrow catchments show a hypsometric curve more similar to strahler s monadnock form for landscapes dominated by diffusive transport the simulated hypsometric curve is concave down everywhere this being consistent with curves reported for some example catchments in france because the transition between diffusive dominance to fluvial is scale dependent with larger catchments exhibiting greater fluvial dominance then the hypsometric curve is a scale dependent descriptor of landforms experimental results for simulated landforms from a small scale rainfall erosion simulator are reported it is shown that siberia yields satisfactory fits to the data confirming its ability to predict the form of the hypsometric curve from a simple model of geomorphic processes 1998 john wiley sons ltd

two sided orogen collision and erosion from the sandbox to the southern alps new zealand in continental collision zones the indentor is of approximately the same vertical dimension as the material being deformed thereby allowing material to move over the indentor and out of the deforming orogen this simple constraint on the height of the indentor differs from that imposed by the bulldozer model of wedge deformation and results in the formation of an orogen with two opposite dipping topographic slopes these two wedges are mechanically coupled and the mechanics are strongly influenced by the erosion conditions imposed on the wedge where the growing mountains perturb prevailing moisture laden winds the erosion pattern is highly asymmetric erosional work being concentrated at the toe of the steep wedge facing the indentor the inboard wedge concentration of erosional energy results in concentration of mechanical energy in the same region and produces the distinctive geological and geophysical patterns associated with continental collision these include rapid uplift and exposure of deep crustal assemblages adjacent to the indentor accompanied by high crustal heat flow and anomalously low seismicity the outcrop pattern along the inboard wedge evolves from that of a crustal cross section currently exposed in the southern alps to one dominated by repetitive nappe structures consisting predominantly of lower crustal units as in the western alps of europe the other wedge the outboard wedge undergoes relatively little erosion is broad with a more gentle surface slope and maintains an outcrop pattern consisting of upper crustal material

transient fault slip in guerrero southern mexico the guerrero region of southern mexico has ac cumulated more than 5 m of relative plate motion since the last major earthquake in early 1998 a continuous gps site in guerrero recorded a transient displacement modeling indicates that anomalous fault slip propagated from east to west along strike of the subduction megathrust campaign gps and leveling data corroborate the model the moment release was equivalent to an mw 6 5 earthquake no m 5 earthquakes accompanied the event indicating the frictional regime is velocity strengthening at the location of slip

automated detection and location of cascadia tremor 1 a new autonomous seismic location and detection methodology enables real time opportunities for high resolution spatio temporal monitoring of non volcanic tremor combining a unique cross correlation technique with epicenter clustering analysis in northern cascadia automatically yields thousands of tremor epicenters from the may 2008 episodic tremor and slip ets event while routinely detecting and locating inconspicuous inter ets tremor bursts although ets events in this area produce about two weeks of continuous tremor we find a nearly equal amount of tremor during the last 15 month inter ets period the resulting ets and inter ets epicenters occur in the slow slip region where the plate interface is 30 45 km deep and have a sharp well resolved updip boundary about 75 km east of the downdip edge of the seismogenic megathrust zone this ability to track tremor with high spatio temporal resolution facilitates automatic tremor monitoring and the mapping of the transition zone and regions of locked zone stress accumulation

cascadia tremor polarization evidence for plate interface slip 1 new seismic measurements of the repeated phenomenon of episodic tremor and slip in northern cascadia indicate identical source processes of tremor and slow slip predicted polarization directions of upgoing s waves radiated from shear slip on the plate interface align with the relative motion between the juan de fuca and north american plates seismic observations from small aperture array data on the olympic peninsula of the cascadia subduction zone show uncharacteristically stable linear particle motion coincident with the passage of tremor sources beneath the array the azimuth of this horizontal ground motion matches expected polarizations from slip on the plate interface this finding suggests that cascadia tremor is shear slip on the plate interface implying that as in japan geodetically observed slow slip and seismically observed tremor are manifestations of the same phenomenon

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

improved discrimination of subglacial and periglacial erosion using 10be concentration measurements in subglacial and supraglacial sediment load of the bossons glacier mont blanc massif france deciphering the complex interplays between climate uplift and erosion is not straightforward and estimating present day erosion rates can provide useful insights glaciers are thought to be powerful erosional agents but most published glacial erosion rates combine periglacial subglacial and proglacial erosion processes within a glaciated catchment sediments found in subglacial streams originate either from glacial erosion of substratum or from the rock walls above the glacier that contribute to the supraglacial load terrestrial cosmogenic nuclides tcn are produced by interactions between cosmic ray particles and element targets at the surface of the earth but their concentration becomes negligible under 15 m of ice measuring tcn concentrations in quartz sand sampled in subglacial streams and in supraglacial channels is statistically compliant with stochastic processes e g rockfalls and may be used to discriminate subglacial and periglacial erosion results for two subglacial streams of the bossons glacier mont blanc massif france show that the proportion of sediments originating from glacially eroded bedrock is not constant it varies from 50 to 90 n 6 the difference between the two streams is probably linked to the presence or absence of supraglacial channels and sinkholes which are common features of alpine glaciers therefore most of the published mean catchment glacial erosion rates should not be directly interpreted as subglacial erosion rates in the case of catchments with efficient periglacial erosion and particularly rockfalls the proportion of sediments in the subglacial stream originating from the supraglacial load could be considerable and the subglacial erosion rate overestimated here we estimate warm based subglacial and periglacial erosion rates to be of the same order of magnitude 0 39 0 33 and 0 29 0 17 mm a 1 respectively

partitioning sediment flux by provenance and tracing erosion patterns in taiwan we critically evaluate the potential and limitations of an alternative way to calculate erosion rates based on petrographic and mineralogical fingerprints of fluvial sediments coupled with gauged sediment fluxes our approach allows us to apportion sediment loads to different lithological units and consequently to discriminate erosion rates in different tectonic domains within each catchment our provenance data on modern taiwanese sands indicate focused erosion in the backbone range and tananao complex of the retrowedge lower rates are inferred for the northern part of the island characterized by tectonic extension and for the western foothills in the prowedge the principal factor of uncertainty affecting our estimates is the inevitably inaccurate evaluation of total sediment load because only the suspended flux was measured another is the assumption that suspended load and bed load are derived from the same sources in fixed proportions additional errors are caused by the insufficiently precise definition of lithologically similar compositional end members and by the temporal variability of sediment composition at the outlet of each catchment related to the spatial variability of erosional processes and triggering agents such as earthquakes typhoons and landslides to evaluate the robustness of our findings we applied a morphometric technique based on the stream power model the results obtained are broadly consistent with local discrepancies ascribed to poorly constrained assumptions and choices of scaling parameters our local erosion estimates are consistent with gps uplift rates measured on a decadal timescale and generally higher than basin wide results inferred from cosmogenic nuclide and thermochronology data

seasonal dependence of large scale birkeland currents the seasonal dependence of large scale birkeland currents has been determined from the analysis of vector magnetic field data acquired by the triad satellite in the northern hemisphere statistical characteristics of single sheet i e net currents and double sheet birkeland currents were determined from 555 triad passes during the summer and 408 passes during the winter more complicated multiple sheet current systems were not included in this study the average kp value for the summer events is 1 9 and for the winter events is 2 0 the principal results include the following 1 the single sheet birkeland currents are statistically observed more often than the double sheet currents in the dayside of the auroral zone during any season the single sheet currents are also observed more often in the summer than in the winter as much as 2 to 3 times as often depending upon the mlt sector 2 the intensities of the single and double sheet birkeland currents on the dayside from approximately 1000 mlt to 1800 mlt are larger during the summer in comparison to winter by a factor of about 2 3 the intensities of the double sheet birkeland currents in the nightside the dominant system in this local time do not show a significant difference from summer to winter 4 the single and double sheet currents in the dayside between 0600 and 1800 mlt appear at higher latitudes by about 1 to 3 during the summer in comparison to the winter these characteristics suggest that the birkeland current intensities are controlled by the ionospheric conductivity in the polar region the greater occurrence of single sheet birkeland currents during the summertime supports the suggestion that these currents close via the polar cap when the conductivity there is sufficiently high to permit it since the intensities of birkeland currents are larger during periods of greater ionospheric conductivity an important source but perhaps not the only source of these currents must be a voltage generator in the magnetosphere possibly related to the convective electric field

a silent slip event on the deeper cascadia subduction interface continuous global positioning system sites in southwestern british columbia canada and northwestern washington state usa have been moving landward as a result of the locked state of the cascadia subduction fault offshore in the summer of 1999 a cluster of seven sites briefly reversed their direction of motion no seismicity was associated with this event the sudden displacements are best explained by 2 centimeters of aseismic slip over a 50 kilometer by 300 kilometer area on the subduction interface downdip from the seismogenic zone a rupture equivalent to an earthquake of moment magnitude 6 7 this provides evidence that slip of the hotter plastic part of the subduction interface and hence stress loading of the megathrust earthquake zone can occur in discrete pulses

neotectonic architecture of taiwan and its implications for future large earthquakes the disastrous effects of the 1999 chi chi earthquake in taiwan demonstrated an urgent need for better knowledge of the island s potential earthquake sources toward this end we have prepared a neotectonic map of taiwan the map and related cross sections are based upon structural and geomorphic expression of active faults and folds both in the field and on shaded relief maps prepared from a 40 m resolution digital elevation model augmented by geodetic and seismologic data the active tandem suturing and tandem disengagement of a volcanic arc and a continental sliver to and from the eurasian continental margin have created two neotectonic belts in taiwan in the southern part of the orogen both belts are in the final stage of consuming oceanic crust collision and suturing occur in the middle part of both belts and postcollisional collapse and extension dominate the island s northern and northeastern flanks both belts consist of several distinct neotectonic domains seven domains kaoping chiayi taichung miaoli hsinchu ilan and taipei constitute the western belt and four domains lutao lanyu taitung hualien and ryukyu make up the eastern belt each domain is defined by a distinct suite of active structures for example the chelungpu fault source of the 1999 earthquake and its western neighbor the changhua fault are the principal components of the taichung domain whereas both its neighboring domains the chiayi and miaoli domains are dominated by major blind faults in most of the domains the size of the principal active fault is large enough to produce future earthquakes with magnitudes in the mid 7 values