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

cosmogenic 36cl accumulation in unstable landforms 1 effects of the thermal neutron distribution cosmogenic nuclides produced in situ within minerals at the surface of the earth are proving to be an effective means of assessing geomorphic histories the use of multiple cosmogenic nuclides permits both exposure times and erosion rates to be determined however if two nuclides are produced only by spallation reactions the systematic differences in their accumulation rates depend only on the differences in their production rates and half lives the relatively small differences that result require a high degree of analytical precision to yield useful results in contrast to other spallogenic nuclides sup 36 cl is also produced by low energy neutron absorption which creates a different pattern of production as a function of depth we have measured the thermal flux with depth in a concrete block using sup 3 he filled neutron detectors the measured thermal neutron profile agrees well with predictions from a simple diffusion based thermal neutron distribution model calculations of sup 36 cl production using the model suggest that the use of sup 36 cl along with a purely spallogenic nuclide to determine erosion rates and exposure times should be less sensitive to analytical error than are determinations from two purely spallogenic nuclides 31 refs 7 figs 3 tabs

partitioning the ongoing extension of the central apennines italy fault slip rates and bulk deformation rates from geodetic and stress data we investigated whether the joint inversion of geodetic and stress direction data can constrain long term fault slip rates in the central apennines and ultimately how extension is partitioned among fault slip and bulk lithosphere permanent strain geodetic velocities are collected in the fault interseismic stage with steady secular deformation thus long term estimates can be derived with a model of elastically unloading seismogenic faults within a viscously deforming lithosphere as the average spacing of permanent global navigation satellite systems gnss stations is similar to the average length of seismogenic faults 25 35 km if not larger we decided to merge permanent and temporary gnss measurements resulting in a denser geodetic data set given that most normal faults in the apennines have slip rates around or below 1 mm a and most campaign gnss velocities carry similar uncertainties simple local back slip models cannot be applied more sophisticated modeling is required to extract reasonable bulk deformation rates and long term fault slip rates at signal to noise ratio of order unity given the spatial distribution of the gnss network we estimated the long term slip rate of seven major fault systems that are in satisfactory agreement with available geological slip rates the resulting spatial distribution of bulk deformation rates locally fits short term transients in other cases they represent the currently unclear signature of tectonic processes like upper crustal viscoplastic deformation and aseismic slip or indicate missing faults in the adopted database we conclude that the time is ripe for determining fault slip rates using geodetic and stress direction data particularly where fault activity rates are hard to determine geologically

patterns and timing of late quaternary faulting in the great basin province and relation to some regional tectonic features large scale surface faulting events each tens of kilometers long and involving more than a meter of displacement of late quaternary age have not been uniformly distributed but have been concentrated in subprovincial and smaller belts and areas within the great basin province furthermore faulting apparently has not been uniformly distributed over time the average recurrence interval of large scale faulting events on individual faults in the province is measured in thousands or tens of thousands of years in contrast to such long recurrence intervals in the central nevada and eastern california seismic belts large scale faulting events have occurred during the last 111 years in an apparently coherent sequential belt filling pulse of activity in which events were separated by only a few years or a few decades the questions are where are other pulses of large scale faulting likely to occur and what controls the localization of such belts and areas characterized by higher rates of faulting two examples of tectonic subprovinces that may play a role in delimiting smaller zones of faulting are the black rock carson sink zone of extension and the central nevada downwarp the central nevada seismic belt lies along the dividing line between these two subprovinces and the northwest margin of the black rock carson sink zone of extension coincides with the margin of a fingerlike belt of dense faulting in northwestern nevada

extensional tectonics of the outer hebrides fault zone south uist northwest scotland the outer hebrides fault zone is a major ese dipping reactivated structure within lewisian basement gneisses of the laurentian craton northwest scotland detailed mapping in south uist reveals important new evidence that contributes to a better understanding of the kinematic evolution of the fault zone large quantities of pseudotachylite which characterize the fault zone on south uist may in part be lithologically controlled and therefore of little value in determining areas of greatest deformation and displacement only limited evidence is preserved for ductile and brittle thrust sense movements along this portion of the fault zone the tectonics of the fault zone on south uist are dominated by structures associated with several episodes of pervasive top down to the se to ene brittle extensional deformation which are progressively overprinted by protophyllonitic and phyllonitic fabrics associated with top down to the e to ene extension a series of late stage high angle normal faults record top down to the ese to ene extension and cut the phyllonites fluid inclusion studies from syntectonic quartz veins constrain the conditions of phyllonite formation at 370 20 c field evidence suggests that this section of the outer hebrides fault zone may have been largely unaffected by sinistral strike slip reactivation as reported along strike to the north suggesting both a varied and compartmentalized tectonic and evolutionary history along the length of the outer hebrides fault zone

morphologic dating of fluvial terrace scarps and fault scarps near west yellowstone montana analysis of fault and fluvial terrace scarps in the west yellowstone basin south of hebgen lake montana indicates that during degradation the gradient of the scarp face and the curvatures of the basal concavity and crestal convexity of the scarp face decrease become more rounded with time the pattern of degradation is identical with that predicted by a simple analytical model for degradation by creep in which the change in elevation at a point on a hillslope is proportional to the curvature of the profile at that point the model therefore provides the basis for morphologic dating a technique for determining the age of a scarp by the extent to which its initial morphology has been degraded in order to date a scarp the coefficient of proportionality c must be known the technique is probably not suitable for use on hillslopes degraded by processes other than creep both the potential and the limitations of morphologic dating are demonstrated via measurements of a sequence of terrace scarps along the madison river the calculated relative ages are in agreement with the known relative ages despite the fact that the gradient of the youngest scarp is significantly less than that of the older scarps to calculate an absolute morphologic age c must be derived from analysis of a scarp of known age having the same aspect must be underlain by the same material and must be within the same climatic zone as the scarp to be dated in the west yellowstone basin a value of c 2 00 0 38 10 3 m 2 yr was calculated from a minimum date of 7100 50 yr b p determined by radiocarbon dating for one of the terrace scarps scarps formed by normal faulting in the west yellowstone basin are much more difficult to date than are terrace scarps because of the possible complexity of their initial morphology fault scarps formed during the 1959 yellowstone earthquake commonly consist of an assemblage of two or more smaller scarps or are superimposed on preexisting scarps formed by one or more previous faulting events by using a selective sampling procedure however one can screen out these fault scarps in this way it was possible to determine an age of 2 800 1 100 yr for a pre 1959 fault scarp in the west yellowstone basin because the fault and terrace scarps in the west yellowstone area do not vary significantly in height the morphologic dating technique proposed earlier by nash 1980a cannot be applied to them the substantially modified procedure developed for the present study does not require a wide range of heights for each scarp to be dated it can be performed using a relatively small number of scarp profiles if c is known it is easy to use and when used with considerable care it is reasonably accurate 36 59 in this study it is potentially applicable to scarps in other areas

complex exposure histories of chert clasts in the late pleistocene shorelines of lake lisan southern israel activities of 26 al and 10 be in five chert clasts sampled from two beach ridges of late pleistocene lake lisan precursor of the dead sea in southern israel indicate low rates of chert bedrock erosion and complex exposure burial and by inference transport histories the chert clasts were derived from the senonian mishash formation a chert bearing chalk which is widely exposed in the nahal zin drainage basin the drainage system that supplied most of the material to the beach ridges simple exposure ages assuming only exposure at the beach ridge sampling sites range from 35 to 354 ky using the ratio 26 al 10 be total clast histories range from 0 46 to 4 3 my unrelated to the clasts current position and exposure period on the late pleistocene beach ridges 160 177 m below sea level optically stimulated luminescence dating of fine sediments from the same and nearby beach ridges yielded ages of 20 0 s 1 4 ka and 36 1 s 3 3 ka these ages are supported by the degree of soil development on the beach ridges and correspond well with previously determined ages of lake lisan which suggest that the lake reached its highest stand around 27 000 cal years bp if the clasts were exposed only once and than buried beyond the range of significant cosmogenic nuclide production then the minimum initial exposure and the total burial times before delivery to the beach ridge are in the ranges 50 1300 ky and 390 3130 ky respectively alternatively the initial cosmogenic dosing could have occurred during steady erosion of the source bedrock back calculating such rates of rock erosion suggests values between 0 4 and 12 m my 1 t he relatively long burial periods indicate extended sediment storage as colluvium on slopes and or as alluvial deposits in river terraces some clasts may have been stored for long periods in abandoned pliocene and early pleistocene routes of nahal zin to the mediterranean before being transported again back into the nahal zin drainage system and washed on to the shores of lake lisan during the late pleistocene copyright 2003 john wiley sons ltd

weathering history of an exposed bedrock fault surface interpreted from its topography abstract morphologic features of bedrock fault scarps are underutilized in studying faulting and weathering history partly because of a lack of accurate quantitative parameters for topography the study employs ground based lidar to measure five patches at different levels on the same fault surface and then calculates roughness in the form of power spectral density in directions parallel and perpendicular to the slip the power spectral density and spatial frequency typically follow a power law for each fault patch showing approximately linear relationships in a log log plot however due to additional power introduced by weathering all spectral curves especially those parallel to the slip can be divided into two segments lower frequency wavelengths of several centimeters several meters and higher frequency wavelengths of several centimeters and below domains this shows that the topographic features at different spatial scales are dominated by different mechanical processes faulting abrasion in the lower frequency domain and the weathering process in the higher frequency domain moreover we develop two parameters to quantify the degree of weathering of a fault outcrop which is significant to describe the evolution of the fault scarp and infer the date of faulting under calibration

cosmogenic 36cl and 10be ages of quaternary glacial and fluvial deposits of the wind river range wyoming we measured cosmogenic 36 cl in 56 samples from boulders on moraines and fluvial terraces in the vicinity of the wind river range wyoming we also measured 10 be in 10 of the same samples most of the 10 be ages were in good agreement with the 36 cl ages indicating that rock surface erosion rates were very low the oldest moraine investigated the type sacagewea ridge site yielded only a limiting minimum age of 232 ka the oldest moraines in the type bull lake complex also could be constrained only to 130 ka the main sequence of type bull lake moraines yielded age distributions indicating deposition within the intervals 130 to 100 ka and 120 to 100 ka the best estimates are closer to the upper limits of these ranges and associated uncertainties are in the range of 10 to 15 these uncertainties could permit deposition in either marine isotope stage 6 or stage 5d we found no evidence of glacial deposits dating to marine isotope stage 4 both bull lake age moraines from fremont lake on the opposite side of the wind river range and boulders on a fluvial terrace above the wind river gave age distributions very similar to that of the second oldest bull lake advance ca 130 to 100 ka the distribution of boulder ages for pinedale moraines at bull lake indicated deposition between 23 and 16 ka nearly identical to the distribution of 10 be ages previously reported for the type pinedale moraines at fremont lake

cosmogenic chlorine 36 production rates in terrestrial rocks abstract chlorine 36 is produced in rocks exposed to cosmic rays at the earth surface through thermal neutron activation of 35cl spallation of 39k and 40ca and slow negative moun capture by 40ca we have measured the 36cl content of 14c dated glacial boulders from the white mountains in eastern california and in a 14c dated basalt flow from utah effective time intergrated production parameters were calculated by simultaneous solution of the 36cl production equations the production rates due to spallation are 4160 310 and 3050 210 atoms 36cl yr 1 mol 139k and 40ca respectively the thermal neutron capture rate was calculated to be 3 07 0 24 105 neutrons kg of rock 1 yr 1 the reported values are normalized to sea level and high geomagnetic latitudes production of 36cl at different altitudes and latitudes can be estimated by appropriate scaling of the sea level rates chlorine 36 dating was performed on carbonate ejecta from meteor crater arizona and late pleistocene morainal boulders from the sierra nevada california calculated 36cl ages are in good agreement with previously reported ages obtained using independent methods

ages of prehistoric earthquakes revealed by cosmogenic chlorine 36 in a bedrock fault scarp at hebgen lake cosmogenic chlorine 36 reveals dates of the multiple prehistoric earthquakes that have produced a scarp on the hebgen lake fault apparent chlorine 36 ages are stratigraphically correct follow a predicted theoretical pattern and produce geologically reasonable model ages of 24 20 7 0 2 6 1 7 and 0 4 thousand years ago this result demonstrates the feasibility of using cosmogenic chlorine 36 to extract paleoearthquake records from bedrock fault scarps

chlorine degassing constrained by cosmogenic 36cl and radiocarbon dating of early holocene rhyodacitic lava domes on erciyes stratovolcano central turkey abstract the erciyes stratovolcano in central turkey has several young rhyodacite lava domes that show evidence of clear exposure histories but have hitherto unknown ages we collected 27 surface samples from three volcanic domes namely karagullu perikartin and dikkartin for cosmogenic 36cl dating the perikartin eruption generated a pyroclastic flow which buried trees that were converted to charcoal the radiocarbon 14c dating yielded an average age of 9728 110 cal years b p calibrated using calib 7 1 we analyzed the cosmogenic 36cl ages however were found that they were probably affected by cl degassing of the magma our study suggests that the radiocarbon age indeed lies between the 0 cl degassing 6 8 0 5 ka under nucleogenic 36cl equilibrium and the 100 degassing conditions 9 9 0 6 ka under nucleogenic 36cl disequilibrium which implies a partial cl degassing 93 during the eruption this value is somewhat higher than earlier estimates and the difference may result from the miscalculated nucleogenic and or low energy neutron production of 36cl uncertainties arising from the corrections due to hydrogen rich cover i e snow of lava surfaces or due to unconsidered geological complications our findings provide a novel approach to estimate the cl degassing on young lavas and deliver a new evidence of the holocene volcano chronology of the central anatolia

style and timing of holocene surface faulting on the meers fault southwestern oklahoma abstract stratigraphic relations and radiocarbon ages of deposits exposed in several trenches and excavations help to establish the timing sense of slip and style of the deformations that resulted from late holocene surface faulting on the meers fault in southwestern oklahoma the eastern half of the scarp is formed on relatively ductile permian hennessey shale and quaternary alluvium whereas the western half is formed on well lithified relatively brittle permian post oak conglomerate in the slick hills

reprint of bedrock fault scarp history insight from t lidar backscatter behaviour and analysis of structure changes abstract this paper provides a research approach and develops a methodology that helps natural weathered bedrock fault scarps to be understood in terms of their structural changes and backscatter behaviour when using terrestrial laser scanning t lidar we tested our approach on the pisia fault in greece that ruptured during the 1981 alkyonides earthquake sequence in corinth gulf the method describes how to correlate fault geometry and structural variations with the backscatter signal of t lidar data from naturally exhumed bedrock fault scarps using this method we are able to reconstruct the past slip history we used t lidar for the analysis of the monochromatic laser beam s backscattered signal to define unsupervised classes of unknown objects on fault surface seven classes were created based on the dendrogram technique using the maximum likelihood method these were used to determine their spatial distribution throughout the scarp height and to calculate the terrain ruggedness index tri in the defined classes the combination of these results shows that i the ruggedness increases with the scarp height and ii the ruggedness and backscattering describe different fault plane conditions we found evidence for past earthquakes on the pisia fault at our study site with average displacements in the range of 30 60 cm with corresponding magnitudes of 6 4 6 6 0 1 ms these results help to reconstruct the recent fault history and potential palaeo events and can also be used i to detect appropriate sample sites on the fault plane for absolute dating and ii as an independent constraint on tracing slip events assisting absolute dating techniques this method can significantly reduce the sampling requirements and costs of cosmogenic absolute dating techniques overall it might be a valuable tool for extracting data regarding the faulting history and slip events for defining seismic hazard parameters

evaluating escarpment evolution and bedrock erosion rates in the western guadalupe mountains west texas and new mexico abstract the guadalupe mountains tower above surrounding plains and basins in western texas and southeast new mexico although this mountain range is extensively studied for the permian stratigraphy related to the petroleum reservoirs in the adjacent delaware basin little is known about the geomorphic history the western escarpment in particular rises abruptly from the salt basin to the west of the range and guadalupe peak rises 1600 m above the surrounding landscape this study investigates how geologic processes create and maintain the steep profile of the escarpment on the western boundary of the guadalupe mountain range in situ produced cosmogenic nuclides were used to quantify erosion rates across the steep western front of the range to assess how tectonic climatic and lithologic forces influence the escarpment profile erosion rates range from 1 to 73 m myr faster erosion rates in the southern area of the escarpment coincide with more frequently mapped faults higher elevations at the top of the rim and locations with colder temperatures and higher precipitation topographic profiles across the western escarpment surfaces indicate greater retreat from the original positions of fault surfaces at the north end of the mountain range faster erosion rates in the mountain range are linked to greater uplift and more recent activity in the southern end of the guadalupe mountains

the accumulation of cosmogenic chlorine 36 in rocks a method for surface exposure dating because of the reaction of cosmic rays with elements in minerals chlorine 36 accumulates in rocks exposed at the earth s surface this suggests that the ratio of chlorine 36 to stable chloride can be used as a geochronometer reasonable agreement has been obtained between measurements of chlorine 36 in volcanic rocks of known age and calculations of chlorine 36 production based on rock composition and cosmicray flux the buildup of chlorine 36 should be a useful means for measuring the surface exposure time of young volcanic rocks and geomorphic features in the age range of 10 3 to 10 6 years

motion on the kaparelli fault greece prior to the 1981 earthquake sequence determined from 36cl cosmogenic dating in february and march 1981 three successive destructive earthquakes occurred at the eastern end of the gulf of corinth the third shock march 4 ms 6 4 ruptured the kaparelli fault about 40 cm of a limestone fault scarp was exhumed by the earthquake each major prehistoric earthquake has added new surface to this cumulative scarp exposing fresh material to cosmic ray bombardment using 36cl cosmic ray exposure dating we have obtained the continuous exposure history for this 4 5 m high limestone surface at two sites about 50 m apart the results suggest that the kaparelli fault has ruptured three times prior to 1981 at 20 3 ka 14 5 0 5 ka and 10 5 0 5 ka with slip amplitudes between 0 6 m and 2 1 m the kaparelli fault appears to have been inactive for 10 thousand years prior to the 1981 event

tessera deformation and the contemporaneous thermal state of the plateau highlands venus abstract geodynamic modeling of tessera deformation at the ancient venusian plateau highlands implies lithospheric thermal gradients exceeding 17 k km 1 regularly spaced contractional ridges in the highlands manifest the unstable growth of perturbations at a dominant wavelength of 20 km controlled by a mechanical layer of relatively uniform thickness we model the deformation as the shortening of a plastic layer over a viscous substrate a layer thickness of less than 6 km is consistent with the observed ridge spacings assuming an anhydrous diabase crustal rheology and a minimum strain rate of 10 16 s 1 the geotherm was at least 17 k km 1 higher strain rates consequently higher thermal gradients are more probable we rule out the possibility that the plateau highlands were locally anomalously hot at the time ridges formed in the tessera that the highlands are dominantly composed of rock more felsic than diabase or that the crust was weak because it was hydrated therefore the average global lithospheric heat flux when the highlands tesserae were deforming was considerably higher than it has been since

dip slip rate determined by cosmogenic surface dating on a holocene scarp of the daju fault yunnan china abstract the daju and lijiang daju fault zones which bound the yulong mountains on its northern and eastern perimeters respectively are segments of a continuous fault system that bends at daju uplift of the yulong mountains the southernmost glacierized mountain range in eurasia resulted from the normal faulting characteristics of the fault system using cosmogenic surface exposure dating with 10 be and 26 al we have measured bedrock exposure ages as a function of elevation along an exposed bedrock scarp of the daju fault 10 be and 26 al exposure ages increase monotonically with elevation ranging from 2 6 to 9 6 ka over the 51 m scarp length giving an average dip slip rate of 7 5 m ka during the holocene period and a vertical uplift rate of 5 7 m ka the 5 7 m ka holocene uplift rate and supporting geomorphic features suggest that the uplift of the yulong mountains mainly occurred in the quaternary the fast slip rate and seismic quiescence for the recent 2 8 ka call attention to the possible recurrence of large magnitude earthquake events along the fault zone

a reevaluation of cosmogenic 36cl production rates in terrestrial rocks we have measured 36cl in a suite of 33 rock samples having well constrained exposure histories and ages the 36cl production parameters were estimated by minimizing the squared deviations between the 36cl and independent ages yielding the following production parameters spallation and muon production from ca 2940 200 atoms 36cl mole ca 1 yr 1 spallation from k 6020 400 atoms 36cl mole k 1 yr 1 and neutron production in air 586 40 fast neutrons g air 1 yr 1 the new production constants for spallation on ca and thermal neutron activation are in good agreement with previous results but that for spallation on k is about 50 larger the past decade has seen a rapid growth in the application of terrestrial cosmogenic nuclides produced by cosmic ray particles within rocks at the earth surface nuclear cross sections particularly for reactions initiated by neutrons and muons are not known with sufficient accuracy so production rates for these nuclides must be empirically calibrated using independently dated geological samples direct production estimates for 36cl were first obtained by zreda et al 1991 who measured 36c1 in mineral separates from granitic boulders on moraine crests at chiatovitch creek in the eastern white mountains of california and nevada this data set was the best available at the time but since then several factors have prompted a reevaluation of the 36cl production rates one is that zreda et al 1994 have shown that there can be significant scatter of the cosmogenic ages of individual glacial boulders toward ages younger than that of the moraine due to soil erosion a second factor is that a much wider range of samples is now available for this purpose finally recent theoretical advances in calculating production by thermal neutron absorption liu et al 1994 now permit more realistic calibration of this reaction

field estimate of paleoseismic slip on a normal fault using the schmidt hammer and terrestrial lidar methods and application to the hebgen fault montana usa