using drill cutting separates to estimate the strength of narrow shear zones at safod 1 a technique is presented for estimating frictional strength of narrow shear zones based on hand selection of drillhole cuttings separates tests were conducted on cuttings from the safod scientific drillhole near parkfield california since cuttings are mixed with adjacent material as they travel up the drillhole these fault derived separates give a better representation of the frictional properties of narrow features than measurements from the bulk material alone cuttings from two shear zones one an active trace of the san andreas fault contain a significant weight percent of clay rich grains that exhibit deformation induced slickensides in addition cuttings from the active saf trace contain around 1 serpentine coefficients of friction for clay rich and serpentine grains were 0 3 0 5 and 0 4 0 45 respectively these values are around 0 12 lower than the friction coefficient of the corresponding bulk cuttings providing an improved estimate of the frictional strength of the san andreas fault

lithology and internal structure of the san andreas fault at depth based on characterization of phase 3 whole rock core in the san andreas fault observatory at depth safod borehole abstract we characterize the lithology and structure of the spot core obtained in 2007 during phase 3 drilling of the san andreas fault observatory at depth safod in order to determine the composition structure and deformation processes of the fault zone at 3 km depth where creep and microseismicity occur a total of approximately 41 m of spot core was taken from three separate sections of the borehole the core samples consist of fractured arkosic sandstones and shale west of the saf zone pacific plate and sheared fine grained sedimentary rocks ultrafine black fault related rocks and phyllosilicate rich fault gouge within the fault zone north american plate the fault zone at safod consists of a broad zone of variably damaged rock containing localized zones of highly concentrated shear that often juxtapose distinct protoliths two zones of serpentinite bearing clay gouge each meters thick occur at the two locations of aseismic creep identified in the borehole on the basis of casing deformation the gouge primarily is comprised of mg rich clays serpentinite lizardite chrysotile with notable increases in magnetite and ni cr oxides hydroxides relative to the surrounding host rock the rocks surrounding the two creeping gouge zones display a range of deformation including fractured protolith block in matrix and foliated cataclasite structure the blocks and clasts predominately consist of sandstone and siltstone embedded in a clay rich matrix that displays a penetrative scaly fabric mineral alteration veins and fracture surface coatings are present throughout the core and reflect a long history of syn deformation fluid rock reaction that contributes to the low strength and creep in the meters thick gouge zones

geochemistry of shallow tropical marine sediments from the arafura sea australia abstract tropical shelves have not been the focus of many biogeochemical studies this study presents new data from sediments collected in the arafura sea including headspace gas and lipid contents this allows assessment of modern depositional environments and reconstruction of environmental changes that have affected this tropical carbonate shelf during the last glacial transgression biomarker compositions from surface sediment and core samples from the upper 2 5 m revealed that marine algal input dominated the recently deposited organic matter over the survey area in a region closest to the shore high taraxerol abundance indicated a strong input of mangrove material to samples below 2 5 m indicating strong mangrove development associated with rising sea level during the transgression following the last glacial maximum when sea level stabilized around 6000 bp biomarker data indicate that the terrigenous contribution decreased and that palaeo channels formed during erosion of the continental shelf were infilled with marine dominated material sediments within these palaeo channels contained elevated concentration of dissolved ch4 at the base of the cores the source of the gas was determined to be microbial in origin based on depleted 13c isotopic composition 96 and very low concentration of wet gas components

permeability and frictional strength of cation exchanged montmorillonite 1 smectites such as montmorillonite are abundant throughout the upper crust and are commonly found in fault gouge they are known for their weak frictional strength and low permeability smectites are swellable clays in which the interlayer cation can easily be exchanged in this study we measure permeability and frictional strength of montmorillonite exchanged with na k ca2 and mg2 using a triaxial shear apparatus we find that the interlayer cation influences both permeability and the friction coefficient k montmorillonite is significantly stronger 0 26 than na montmorillonite 0 15 and ca or mg montmorillonite 0 11 permeability for all four clays is between 10 21 and 10 23 m2 in the pressure range between 10 mpa and 100 mpa with k montmorillonite the most permeable clay gouge mg ca and na montmorillonite show relative similar permeabilities of which na montmorillonite is least permeable we relate the higher frictional strength and permeability of k montmorillonite to reduce interlayer water content caused by differences in cation hydration and adsorption the results show that the rapid cation exchange process in montmorillonite can influence macroscale parameters such as permeability and strength which can contribute to changes in local pressure conditions and frictional strength of shallow fault zones

mid holocene palaeolimnological record of a southern hemisphere subtropical lake spanning the last 6000 years lake jennings fraser island australia the study of climate mechanisms in the southern hemisphere during the holocene remains an area of active research that lacks the spatial and temporal connectivity characteristic of northern hemisphere research the subtropical temperate climate transition zone of eastern australia provides a unique location to investigate long term environmental changes during the holocene lake jennings on fraser island was used to investigate climate change in this transition zone using palaeolimnological techniques the beginning of the lake jennings record 6000 to 3500 cal ybp is characterised by fluctuations in geochemical signals an abundance of sponge spicules and a lack of diatom species results suggest gradually increasing precipitation and water depth which affect nutrient cycling however the biological functioning of the lake is difficult to interpret due to the absence of diatoms possibly a result of turbidity dissolution and or predation by freshwater sponges during the late holocene 3500 cal

constraints on the stress state of the san andreas fault with analysis based on core and cuttings from san andreas fault observatory at depth safod drilling phases 1 and 2 stress state constraints on the saf

clay fabrics in safod core samples with optical microscopy scanning electron microscopy sem transmission electron microscopy tem and synchrotron x ray diffraction measurements we analyzed clay microfabrics in ultracataclastic gouge and cataclastic core samples obtained from the main bore hole of the san andreas fault observatory at depth safod the analysis reveals a significant contrast between weak clay fabrics observed in the core samples with synchrotron x ray fabric measurements and strong degree of preferred alignment for clay particles documented with the optical microscope tem and sem observations also show distinct zones of locally aligned and randomly oriented clay minerals the lack of a strong fabric may be attributed to randomly oriented matrix sheet silicates dominating the fault rocks the presence of weak fabrics in intensely strained ultracataclasites fault gouges is attributed to 1 newly formed clay minerals that grew in many orientations 2 folded and kinked clay minerals and 3 clay particles that are wrapped around grains in addition the locally aligned clay particles may act as barriers to fluid flow which in turn decrease porosity expel intergranular pore fluids and consequently may increase fluid pressure

landscape responses to intraplate tectonism quantitative constraints from be 10 nuclide abundances cosmogenic 10 be concentrations in bedrock and alluvium combined with structural studies provide a novel approach for identifying neotectonic forcing of landscape evolution in mildly deforming continental interiors measured 10 be concentrations in the flinders ranges indicate rapid and spatially variable rates of bedrock erosion in a catchment that has incurred at least three large surface rupturing earthquakes since 67 ka 10 be derived erosion rates are lower where late quaternary neotectonic activity is reduced or absent implying that 10 be concentration may act as a tracer for disequilibrium landscapes responding to recent tectonism mechanisms for elevated erosion rates include 1 headward migration of fault generated bedrock knickpoints and resultant oversteepening of stream profiles and catchment hillslopes and 2 liberation of bedrock material from catchment hillslopes via co seismic shaking despite climatic influences on sediment production and transport this study shows that tectonism can provide a dominant control on bedrock erosion rate and relief production in unglaciated mountain belts even in intraplate settings where rates of crustal deformation are mild and earthquake activity is episodic 2007 elsevier b v all rights reserved

frictional properties of simulated fault gouges from the seismogenic groningen gas field under in situ p t chemical conditions we investigated the frictional properties of simulated fault gouges derived from the main lithologies present in the seismogenic groningen gas field ne netherlands employing in situ p t conditions and varying pore fluid salinity direct shear experiments were performed on gouges prepared from the carboniferous shale siltstone substrate the upper rotliegend slochteren sandstone reservoir the overlying ten boer claystone and the basal zechstein anhydrite carbonate caprock at 100 c 40 mpa effective normal stress and sliding velocities of 0 1 10 m s as pore fluids we used pure water 0 5 6 2 m nacl solutions and a 6 9 m mixed chloride brine mimicking the formation fluid our results show a marked mechanical stratigraphy with a maximum friction coefficient of 0 66 for the basal zechstein a minimum of 0 37 for the ten boer claystone 0 6 for the reservoir sandstone and 0 5 for the carboniferous mixed gouges showed intermediate values pore fluid salinity had no effect on frictional strength most gouges showed velocity strengthening behavior with little systematic effect of pore fluid salinity or sliding velocity on a b however basal zechstein gouge showed velocity weakening at low salinities and or sliding velocities as did 50 50 mixtures with sandstone gouge tested with the 6 9 m reservoir brine from a rate and state friction viewpoint our results imply that faults incorporating basal zechstein anhydrite carbonate material at the top of the reservoir are the most prone to accelerating slip that is have the highest seismogenic potential the results are equally relevant to other rotliegend fields in the netherlands and n sea region and to similar sequences globally

rates and timing of earth surface processes from in situ produced cosmogenic be 10 beryllium 10 is the longest lived of the seven known unstable isotopes of be it results mostly from the interaction of cosmic radiation primarily neutrons with a variety of target atoms by spallation the splitting of nuclei lal 1988 it can also be produced at very low levels by radio disintegration of u and th sharma and middleton 1989 although all radioactive be isotopes are produced in the atmosphere via cosmic ray reactions arnold 1956 lal and peters 1967 morris et al chapter 5 this volume in this paper we are most interested in 10be produced in rock which we refer to as in situ produced such in situ produced 10be is a cosmic ray dosimeter functioning as a quantitative monitor of near surface residence time in some geologic situations 10be can be used as a chronometer allowing one to estimate the duration of surface exposure in other settings 10be can be used as a tracer allowing one to estimate the rate distribution and behavior of earth surface processes rates of 10be production are very low in rocks exposed at earth s surface 102 atoms g 1 y 1 resulting in typical in situ produced 10be concentrations termed activities of 103 to 107 atoms g 1 the development of accelerator mass spectrometry ams in the 1980s allowed routine measurement of 10be at levels typical of rocks exposed near earth s surface elmore and phillips 1987 analytical refinements in the 1990s lowered detection limits by an order of magnitude allowing dating of exposure periods 103 years in favorable geologic and geographic situations simple exposure histories at high altitude and latitude most in situ 10be is measured in quartz mineral separates where the primary spallation target is o lal and arnold 1985

extreme dynamic weakening of faults during dehydration by coseismic shear heating the dynamic strength of seismogenic faults has a critical effect on earthquake slip instability and seismic energy release high velocity friction experiments on simulated faults in serpentinite at earthquake slip conditions show a decrease in friction coefficient from 0 6 to 0 15 as the slip velocity reaches 1 1 m s at normal stresses up to 24 5 mpa the extraordinary reduction in fault strength is attributed to flash heating at asperity contacts of gouge particles formed during sliding the rapid heating at asperities causes serpentine dehydration in impermeable fault zones in nature serpentine dehydration and subsequent fluid pressurization due to coseismic frictional heating may promote further weakening this dynamic fault weakening mechanism may explain the lack of pronounced heat flow in major crustal faults such as the san andreas

late quaternary landscape evolution in the keep river region northwestern australia abstract this paper evaluates the late quaternary chronostratigraphic context of archaeological sites in the keep river region northern territory australia cosmogenic dating luminescence dating and sediment characterisation reveal sedimentary processes commencing from erosion of the escarpment and plateaux source through temporary storage in sand sheets to final deposition in alluvial floodplains erosion of the sandstone plateaux 5 mm ka 1 and escarpment faces probably 50 100 mm ka 1 provide the main sediment source for the adjacent sand sheets which have evolved over the past 100 000 years as the product of ongoing cycles of accumulation and denudation the rate of sediment accumulation is lowest near the escarpments on the low energy sediment limited sand sheets 1 and greatest near the main streams 400 mm ka 1 that have more numerous sediment sources collectively luminescence ages indicate an apparent increase in sediment accumulation rate in the sand sheets from 100 mm ka 1 in the late pleistocene to over 200 mm ka 1 in the holocene this most likely reflects enhanced monsoonal activity following postglacial marine transgression palaeosol horizons in the creek profile distinguished by sediment mottling mark potentially significant palaeoenvironmental and palaeoclimatic changes during the quaternary

mineralogical characterization of protolith and fault rocks from the safod main hole 1 washed cuttings provide a continuous record of the rocks encountered during drilling of the main hole of the san andreas fault observatory at depth safod both protolith and fault rocks exhibit a wide variety of mineral assemblages that reflect variations in some combination of lithology p t conditions deformation mechanisms and fluid composition and abundance regions of distinct neomineralization bounded by faults may record alteration associated with fluid reservoirs confined by faults in addition both smectites occurring as mixed layer phases and serpentine minerals are found in association with active strands of the san andreas fault that were intersected during drilling although their rheological influence is not yet fully known faults containing these mineralogical phases are prime candidates for continuous coring during phase 3 of safod drilling in the summer of 2007

frictional behavior of materials in the 3d safod volume 1 we report on frictional properties of rocks within the 3 d crustal volume surrounding the san andreas fault observatory at depth safod samples include lithologies adjacent to the san andreas fault saf in the subsurface safod borehole rocks and synthetic fault gouge composed of talc serpentinite and quartz granodiorite arkosic sandstone and siltstone samples from the safod borehole are frictionally strong 0 56 0 66 sand and clay rich lithologies from outcrop exhibit friction in the range 0 56 0 68 natural serpentinite thought to abut the saf at depth exhibits low friction 0 18 0 26 our results indicate that 1 serpentinite exhibits low strength but is not weak enough to completely satisfy weak fault models 2 all other samples are consistent with a strong fault and crust and 3 if the saf is weak 0 2 due to the presence of serpentinite or talc these minerals would likely need to constitute over 50 by weight of the shear zone

stress rotation across the cascadia megathrust requires a weak subduction plate boundary at seismogenic depths abstract the mendocino triple junction region is the most seismically active part of the cascadia subduction zone the northward moving pacific plate collides with the subducting gorda plate causing intense internal deformation within it here we show that the stress field rotates rapidly with depth across the thrust interface from a strike slip regime within the subducting plate reflecting the pacific plate collision to a thrust regime in the overriding plate we utilize a dense focal mechanism dataset including observations from the cascadia initiative ocean bottom seismograph experiment to constrain the stress orientations to quantify the implications of this rotation for the strength of the plate boundary we designed an inversion that solves for the absolute stress tensors in a three layer model subject to assumptions about the strength of the subducting mantle our results indicate that the shear stress on the plate boundary fault is likely no more than about 50 mpa at 20 km depth regardless of the assumed mantle strength we infer a relatively weak megathrust fault with an effective friction coefficient of 0 to 0 2 at seismogenic depths such a low value for the effective friction coefficient requires a combination of high fluid pressures and or fault zone minerals with low inherent friction in the region where a great earthquake is expected in cascadia

microstructures in landslides in northwest china implications for creeping displacements abstract microstructures mineralogical composition and texture of selected landslide samples from three landslides in the southern part of the gansu province china were examined with optical microscopy transmission electron microscopy tem x ray diffraction xrd and synchrotron x ray diffraction measurements common sheet silicates are chlorite illite muscovite kaolinite pyrophyllite and dickite other minerals are quartz calcite dolomite and albite in one sample graphite and amorphous carbon were detected by tem edx analyses and tem high angle annular dark field images the occurrence of graphite and pyrophyllite with very low friction coefficients in the gouge material of the suoertou and xieliupo landslides is particularly significant for reducing the frictional strength of the landslides it is proposed that the landslides underwent comparable deformation processes as fault zones the low friction coefficients provide strong evidence that slow moving landsliding is controlled by the presence of weak minerals in addition tem observations document that grain size reduction in clayey slip zone material was produced mainly by mechanical abrasion for calcite and quartz grain size reduction was attributed to both pressure solution and cataclasis therefore besides landslide composition the occurrence of ultrafine grained slip zone material may also contribute to weakening processes of landslides tem images of slip zone samples show both locally aligned clay particles as well as kinked and folded sheet silicates which are widely disseminated in the whole matrix small newly formed clay particles have random orientations based on synchrotron x ray diffraction measurements the degree of preferred orientation of constituent sheet silicates in local shear zones of the suoertou and duang he ba landslide is strong this work is the first reported observation of well oriented clay fabrics in landslides

effect of clay content and mineralogy on frictional sliding behavior of simulated gouges binary and ternary mixtures of quartz illite and montmorillonite 1 we investigated the frictional sliding behavior of simulated quartz clay gouges under stress conditions relevant to seismogenic depths conventional triaxial compression tests were conducted at 40 mpa effective normal stress on saturated saw cut samples containing binary and ternary mixtures of quartz montmorillonite and illite in all cases frictional strengths of mixtures fall between the end members of pure quartz strongest and clay weakest the overall trend was a decrease in strength with increasing clay content in the illite quartz mixture the trend was nearly linear while in the montmorillonite mixtures a sigmoidal trend with three strength regimes was noted microstructural observations were performed on the deformed samples to characterize the geometric attributes of shear localization within the gouge layers two micromechanical models were used to analyze the critical clay fractions for the two regime transitions on the basis of clay porosity and packing of the quartz grains the transition from regime 1 high strength to 2 intermediate strength is associated with the shift from a stress supporting framework of quartz grains to a clay matrix embedded with disperse quartz grains manifested by the development of p foliation and reduction in riedel shear angle the transition from regime 2 intermediate strength to 3 low strength is attributed to the development of shear localization in the clay matrix occurring only when the neighboring layers of quartz grains are separated by a critical clay thickness our mixture data relating strength degradation to clay content agree well with strengths of natural shear zone materials obtained from scientific deep drilling projects

quantitative analysis of trace oh in garnet and pyroxenes to calibrate infrared ir spectroscopy for quantitative analysis of trace structural oh in specific minerals we have determined concentrations of h in pure separates of mantle derived pyrope garnet 56 6 ppm h 2o by weight augite 268 8 ppm h 2o and enstatite 217 11 ppm h 2o by manometry after heating the samples and extracting h 2 gas under vacuum ir spectroscopy confirmed the presence of intrinsic oh in these samples prior to extraction and indicated between 86 and 100 removal of h during the extraction procedure the integral specific absorption coefficients of 1 39 0 14 l 7 09 0 32 and 15 6 0 94 ppm h 2o cm 2 for pyrope augite and enstatite respectively allow precise spectroscopic determination of the oh content of upper mantle garnets and pyroxenes to concentration levels of a few parts per million uncertainties in accuracy depend on mineral composition and characteristics of the oh absorption spectrum and are estimated to range between 10 and 50

quaternary structural partitioning within the rigid tarim plate inferred from magnetostratigraphy and sedimentation rate in the eastern tarim basin in china abstract it has been proposed that within the tarim basin tectonic activity has been limited since triassic time however on the basis of magnetostratigraphy from the eastern tarim basin which defines the chronology of sedimentation and structural evolution of the basin we show that the basin interior has been uplifted and partitioned during quaternary the magnetostratigraphy was constructed from 2228 samples that yielded acceptable inclination values characteristic remnant magnetization chrm with both normal n1 n11 and reversed r1 r11 polarity was isolated by thermal demagnetization the data correlate best with polarity chrons c3r to c1n which range from 5 39 ma to recent on the geological time scale 2004 gts2004 an abrupt decrease in the sedimentation rate is observed at 1 77 ma in the ls1 core this change does not overlap with known pleistocene climate change events we attribute this sedimentation rate decrease to a structurally controlled local decrease in accommodation space where basin basement uplifts occur this period of sedimentary environmental change reveals that structural partitioning in the basement of the tarim basin occurred since 1 77 ma and we speculate that tilting of the southeast uplift a sub basin unit within the tarim basin began in early pleistocene time

erosion of an ancient mountain range the great smoky mountains north carolina and tennessee analysis of 10be and 26al in bedrock n 10 colluvium n 5 including grain size splits and alluvial sediments n 59 including grain size splits coupled with field observations and gis analysis suggest that erosion rates in the great smoky mountains are controlled by subsurface bedrock erosion and diffusive slope processes the results indicate rapid alluvial transport minimal alluvial storage and suggest that most of the cosmogenic nuclide inventory in sediments is accumulated while they are eroding from bedrock and traveling down hill slopes spatially homogeneous erosion rates of 25 30 mm ky 1 are calculated throughout the great smoky mountains using measured concentrations of cosmogenic 10be and 26al in quartz separated from alluvial sediment 10be and 26al concentrations in sediments collected from headwater tributaries that have no upstream samples n 18 are consistent with an average erosion rate of 28 8 mm ky 1 similar to that of the outlet rivers n 16 24 6 mm ky 1 which carry most of the sediment out of the mountain range grain size specific analysis of 6 alluvial sediment samples shows higher nuclide concentrations in smaller grain sizes than in larger ones the difference in concentrations arises from the large elevation distribution of the source of the smaller grains compared with the narrow and relatively low source elevation of the large grains large sandstone clasts disaggregate into sand size grains rapidly during weathering and downslope transport thus only clasts from the lower parts of slopes reach the streams 26al 10be ratios do not suggest significant burial periods for our samples however alluvial samples have lower 26al 10be ratios than bedrock and colluvial samples a trend consistent with a longer integrated cosmic ray exposure history that includes periods of burial during down slope transport the results confirm some of the basic ideas embedded in davis geographic cycle model such as the reduction of relief through slope processes and of hack s dynamic equilibrium model such as the similarity of erosion rates across different lithologies comparing cosmogenic nuclide data with other measured and calculated erosion rates for the appalachians we conclude that rates of erosion integrated over varying time periods from decades to a hundred million years are similar the result of equilibrium between erosion and isostatic uplift in the southern appalachian mountains

rock to sediment slope to sea with 10be rates of landscape change abstract measurements of cosmogenic nuclides predominately 10be allow new insights into the ways in which and the rates at which sediment is generated transported and deposited over timescales ranging from 103 to 106 years samples from rock exposures are used to estimate erosion rates at points on the landscape whereas samples of fluvial sediment provide estimates of basin scale rates of denudation integrated over 104 km2 nuclide data show that hilltop bare rock outcrops erode more slowly than basins as a whole suggesting the potential for relief to increase over time as well drained outcrops grow higher more elaborate experiments and interpretive models provide insight into the distribution of hillslope processes including the bedrock to soil conversion rate which appears to increase under shallow soil cover and then decrease under deeper soils changes in average nuclide activity down slopes can be used to estimate grain speed over millennia suggesting for example that sediment o

on the origin of mixed layered clay minerals from the san andreas fault at 2 5 3 km vertical depth safod drillhole at parkfield california a detailed mineralogical study is presented of the matrix of mudrocks sampled from spot coring at three key locations along the san andreas fault observatory at depth safod drill hole the characteristics of authigenic illite smectite i s and chlorite smectite c s mixed layer mineral clays indicate a deep diagenetic origin a randomly ordered i s mineral with ca 20 25 smectite layers is one of the dominant authigenic clay species across the san andreas fault zone sampled at 3 066 and 3 436 m measured depths md whereas an authigenic illite with ca 2 5 smectite layers is the dominant phase beneath the fault sampled at 3 992 m md the most smectite rich mixed layered assemblage with the highest water content occurs in the actively deforming creep zone at ca 3 300 3 353 m true vertical depth of ca 2 7 km with i s 70 30 and c s 50 50 the matrix of all mudrock sam ples show extensive quartz and feldspar both plagioclase and k feldspar dissolution associated with the crystalli zation of pore filling clay minerals however the effect of rock deformation in the matrix appears only minor with weak flattening fabrics defined largely by kinked and fractured mica grains adopting available kinetic models for the crystallization of i s in burial sedimentary envi ronments and the current borehole depths and thermal structure the conditions and timing of i s growth can be evaluated assuming a typical k concentration of 100 200 ppm for sedimentary brines a present day geothermal gradient of 35c km and a borehole temperature of ca 112c for the sampled depths most of the i s minerals can be predicted to have formed over the last 4 11 ma and are probably still in equilibrium with circulating fluids the exception to this simple burial pattern is the occurrence of the mixed layered phases with higher smectite content than predicted by the burial model these minerals which characterize the actively creeping section of the fault and local thin film clay coating on polished brittle slip surfaces can be explained by the influence of either cooler fluids circulating along this segment of the fault or the flow of k depleted brines

time and process rates over the past 100 m y a case for dramatically increased landscape denudation rates during the late quaternary in northern australia a central question in the earth sciences is how rates and styles of landscape evolution have varied over time in response to climate and sea level change tectonic and isostatic uplift and human disturbance the quaternary has been a period of major landscape evolution in many glaciated regions of the world but few data sets of sufficient length are available to assess its significance to the long term development of landscapes in nonglaciated regions analysis of denudation rates over the past 0 5 m y and 100 m y for upland and lowland surfaces in western arnhem land tropical northern australia shows that denudation rates have increased by at least an order of magnitude in the late quaternary compared to the previous 100 m y despite tectonic stability and the absence of glaciation in this region over the past 120 m y the lowlands have undergone denudation rates up to an order of magnitude higher than the uplands so that the landscape has increased in relief independently of the absolute rate of denudation this result is counter to several prominent theories of landscape development that postulate relief reduction over millions of years at least 3 7 of the post cretaceous denudation of this landscape occurred during the most recent 0 5 m y we suggest that the quaternary here was a period of greatly accelerated erosion resulting from changes in climate and sea level accompanying glacial interglacial cycles general sea level regression since the mid cretaceous also likely initiated substantial lowland erosion in this region it appears therefore that the past 100 m y have been punctuated by at least two episodes of accelerated landscape denudation

tectonic geomorphology of australia the australian continent is actively deforming in response to far field stresses generated by plate boundary interactions and buoyancy forces associated with mantle dynamics on the largest scale several 10 3 km the submergence of the northern continental shelf is driven by dynamic topography caused by mantle downwelling along the indo pacific subduction system and accentuated by a regionally elevated geoid the emergence of the southern shelf is attributed to the progressive movement of australia away from a dynamic topography low on the intermediate scale several 10 2 km low amplitude c 100 200 m long wavelength c 100 300 km topographic undulations are driven by 1 anomalous smaller scale upper mantle convection and or 2 lithospheric scale buckling associated with plate boundary tectonic forcing on the smallest scale 10 1 km fault related deformation driven by partitioning of far field stresses has modified surface topography at rates of up to c 170 m ma 21 generated more than 30 50 of the contemporary topographic relief between some of australia s highlands and adjacent piedmonts and exerted a first order control on long term 10 4 10 6 a bedrock erosion although australia is often regarded as tectonically and geomorphologically quiescent neogene to recent tectonically induced landscape evolution has occurred across the continent with geomor phological expressions ranging from mild to dramatic australia is one of the lowest flattest most arid and most slowly eroding continents on earth the average elevation of the continent is only c 330 m above sea level asl maximum local topographic relief is everywhere 1500 m defined by elevation ranges with 100 km radii and two thirds of the con tinent is semi arid to arid with the exception of localized upland areas in the flinders and mt lofty ranges and the eastern highlands bedrock

constraints on the stress state of the san andreas fault with analysis based on core and cuttings from san andreas fault observatory at depth safod drilling phases 1 and 2 1 analysis of field data has led different investigators to conclude that the san andreas fault saf has either anomalously low frictional sliding strength 0 6 arguments for the apparent weakness of the saf generally hinge on conceptual models involving intrinsically weak gouge or elevated pore pressure within the fault zone some models assert that weak gouge and or high pore pressure exist under static conditions while others consider strength loss or fluid pressure increase due to rapid coseismic fault slip the present paper is composed of three parts first we develop generalized equations based on and consistent with the rice 1992 fault zone model to relate stress orientation and magnitude to depth dependent coefficient of friction and pore pressure second we present temperature and pressure dependent friction measurements from wet illite rich fault gouge extracted from san andreas fault observatory at depth safod phase 1 core samples and from weak minerals associated with the san andreas fault third we reevaluate the state of stress on the san andreas fault in light of new constraints imposed by safod borehole data pure talc 0 1 had the lowest strength considered and was sufficiently weak to satisfy weak fault heat flow and stress orientation constraints with hydrostatic pore pressure other fault gouges showed a systematic increase in strength with increasing temperature and pressure in this case heat flow and stress orientation constraints would require elevated pore pressure and in some cases fault zone pore pressure in excess of vertical stress

cosmogenic exposure and erosion history of australian bedrock landforms exceptionally high activities of in situ produced 1 0 be and 2 6 al indicate that australian bedrock surfaces are some of the most stable in the world these cosmogenic nuclides demonstrate that australian granite exposed and sampled at 10 sites along a transect from the eyre peninsula 33 s to the kakadu area in the northern territory 14 s has in some places eroded only decimeters over the past million years however nuclide activities are not saturated in any of the 61 exposed samples we analyzed mandating that the surfaces we sampled are losing mass albeit slowly over time such mass loss indicates that inselbergs are dynamic landforms confounding the assignment of discreet ages to inselberg surfaces nevertheless the differential between slow rates of erosion measured on the very stable uppermost parts of these landforms and the more rapid rates measured below their flanks and below the adjacent grus covered planes suggests that the forms of many large inselbergs which stand meters to tens of meters high must be at least tertiary in age and possibly much older activities of 1 0 be and 2 6 al in 61 exposed australian samples range from 5 1 0 1 10 6 to 5 3 0 6 x 10 5 atoms g 1 and 2 1 0 1 x 10 7 to 3 4 0 5 x 10 6 atoms g 1 respectively normalized to sea level at latitudes of 60 using only neutron scaling activities of 1 0 be and 2 6 al in seven shielded samples 3 5 13 m below the surface are much lower ranging from 3 4 0 2 x 10 4 to 7 0 0 1 x 10 4 atoms g 1 and 1 6 0 1 x 10 5 to 2 8 0 2 x 10 5 atoms g 1 respectively 2 6 al 1 0 be ratios of exposed samples range from 3 89 0 19 to 6 29 0 82 if 2 uncertainty ranges and a nominal sea level high latitude 1 0 be production rate of 5 17 atoms g 1 yr 1 are considered ratio data for all but one surface sample are consistent with continuous surface or near surface exposure and or erosion rock surfaces farther north in australia where the climate is more humid have lower nuclide activities thus we infer that surface stability is inversely related to mean annual precipitation from 61 exposed samples we calculated maximum limiting single nuclide model erosion rates of 0 3 0 1 to 5 7 1 0 m m y and minimum limiting single nuclide model exposure ages of 105 16 to 1310 190 ka by assuming a sea level high latitude 1 0 be production rate of 5 17 atoms g 1 yr 1 seven shielded samples in which the nuclide inventory is muon generated also have nuclide activities consistent with similarly low rates of erosion but over even longer time scales it appears that the eyre peninsula inselbergs have been and are eroding so slowly that they may well be direct descendents of cenozoic and perhaps even mesozoic forms

how plausible are high frequency sediment supply driven cycles in the stratigraphic record abstract this paper is an attempt to quantify the plausible time scales of clastic sediment supply variations at the entrance of sedimentary basins our approach is based on the sedimentary system concept which simplifies natural systems by dividing them into three zones of dominant processes the erosion the transfer and the sedimentation subsystems we examine recent results from geomorphology which show that frequent climate changes can induce high frequency sediment flux variations at the outlet of the source area we put forward the crucial role of the transfer subsystem which conveys sediment from the erosion zone to the basin by applying a diffusive model to a number of worldwide rivers we extend from large 1000 km to intermediate 300 km rivers the previous finding that the transfer subsystem acts as a buffer for short periods sediment pulses tens to hundreds of kiloyears this implies that high frequency stratigraphic cycles in clastic accumulations fed by large drainage systems are unlikely to reflect sediment supply cycles of tens to hundreds of thousands of years of periodicities

frictional properties and sliding stability of the san andreas fault from deep drill core the strength of tectonic faults and the processes that control earthquake rupture remain central questions in fault mechanics and earthquake science we report on the frictional strength and constitutive properties of intact samples across the main creeping strand of the san andreas fault saf california united states recovered by deep drilling we find that the fault is extremely weak friction coefficient 0 10 and exhibits both velocity strengthening frictional behavior and anomalously low rates of frictional healing consistent with aseismic creep in contrast wall rock to the northeast shows velocity weakening frictional behavior and positive healing rates consistent with observed repeating earthquakes on nearby fault strands we also document a sharp increase in strength to values of 0 40 over 1 m distance at the boundary between the fault and adjacent wall rock the friction values for the saf are sufficiently low to explain its apparent weakness as inferred from heat flow and stress orientation data our results may also indicate that the shear strength of the saf should remain approximately constant at 10 mpa in the upper 5 8 km rather than increasing linearly with depth as is commonly assumed taken together our data explain why the main strand of the saf in central california is weak extremely localized and exhibits aseismic creep while nearby fault strands host repeating earthquakes

shallow gas and fluid migration in the northern arafura sea offshore northern australia abstract a variety of shallow gas indicators and fluid migration pathways have been interpreted from new sub bottom profiler multibeam bathymetry side scan sonar and echo sounder data together with geochemical analyses of sampled sediments from the northern arafura sea offshore northern australia this study provides new geological data and a seismic stratigraphy of the youngest units in the money shoal basin in an area that has not been closely studied in over 30 years the shallow gas indicators include pockmarks low frequency enhanced reflectors and acoustic blanking these indicators are supported by gas within shallow cores geochemistry indicates that this gas has a microbial origin but deeper fluid movement is also suggested by the presence of interpreted hydrocarbon slicks based on synthetic aperture radar data a region of likely hydrocarbon seepage is indicated by the clear coincidence of shallow gas indicators with an area of increased faulting and a zone of poor quality seismic data recognised on conventional seismic data together with anomalies interpreted on remote sensing data aligned with mapped deep structures

strength of chrysotile serpentinite gouge under hydrothermal conditions can it explain a weak san andreas fault chrysotile bearing serpentinite is a constituent of the san andreas fault zone in central and northern california at room temperature chrysotile gouge has a very low coefficient of friction 0 2 raising the possibility that under hydrothermal conditions might be reduced sufficiently to 0 1 to explain the apparent weakness of the fault to test this hypothesis we measured the frictional strength of a pure chrysotile gouge at temperatures to 290 c and axial shortening velocities as low as 0 001 m s as temperature increases to 100 c the strength of the chrysotile gouge decreases slightly at low velocities but at temperatures 200 c it is substantially stronger and essentially independent of velocity at the lowest velocities tested we estimate that pure chrysotile gouge at hydrostatic fluid pressure and appropriate temperatures would have shear strength averaged over a depth of 14 km of 50 mpa thus on the sole basis of its strength chrysotile cannot be the cause of a weak san andreas fault however chrysotile may also contribute to low fault strength by forming mineral seals that promote the development of high fluid pressures

late cenozoic increase in accumulation rates of terrestrial sediment how might climate change have affected erosion rates abstract accumulation rates of terrestrial sediment have increased in the past few million years both on and adjacent to continents although not everywhere apparently erosion has increased in elevated terrain regardless of when last tectonically active or what the present day climate in many regions sediment coarsened abruptly in late pliocene time sparser data suggest increased sedimentation rates at 15 ma approximately when oxygen isotopes in benthic foraminifera imply high latitude cooling if climate change effected accelerated erosion understanding how it did so remains the challenge some obvious candidates such as lowered sea level leading to erosion of continental shelves or increased glaciation account for increased sedimentation in some but not all areas perhaps stable climates that varied slowly allowed geomorphic processes to maintain a state of equilibrium with little erosion until 3 4 ma when large oscillations in climate with periods of 20 000 40 000 years developed and de

frictional strength of cuttings and core from safod drillhole phases 1 and 2 1 we investigated the frictional properties of drill cuttings and core obtained from 1 85 3 1 km true vertical depth in the safod scientific borehole in central california triaxial frictional sliding experiments were conducted on samples from primary lithologic units and significant shear zones including the inferred active trace of the san andreas fault the samples were deformed at room temperature under constant effective normal stresses of 10 40 and 80 mpa with axial shortening rates of 0 01 1 0 m s 1 the weakest samples were from shale claystone and siltstone units with friction coefficient 0 4 0 55 stronger samples were from quartzo feldspathic rocks with 0 6 materials tested from two shear zones at 2560 and 3067 m measured depth had 0 4 0 55 and velocity strengthening behavior consistent with fault creep at depths 4 km the coefficient of friction for bulk samples from the inferred trace of the san andreas fault was 0 6

quantification of fabrics in clay gouge from the carboneras fault spain and implications for fault behavior abstract clays in fault rocks have the potential to control fault behavior the formation of frictionally weak clays in fault rocks can lead to fault zone weakening and the development of fabrics through authigenesis and mechanical rotation in clay rich fault rocks can influence fault zone permeability structures the left lateral carboneras fault of southwestern spain is a ca 1 km wide fault zone with anastomosing layers of clay rich gouge up to 50 m thick the gouge derived largely from mica schist is composed of neoformed illite and chlorite anisotropy of magnetic susceptibility 201 measurements and x ray pole figures 144 measurements show comparable oblate clay fabrics with the axis of maximum anisotropy sub parallel to strike this dimensional fabric contrasts with previously published maximum permeability results that are sub vertical this observation coupled with the generally poor clay fabric measured in the samples indicates that the orientation of clays is not likely to be the primary control of the permeability anisotropy of clay rich fault gouge becoming important only when gouge zones are 10s of meters thick which is very unusual even in a fault zone like that of the carboneras fault with thick very clay rich gouge zones with a visible foliations and slip surfaces the degree of clay preferred orientation is low above the millimeter scale showing that any strong clay fabric associated with the foliation are extremely localized phenomena this suggests that processes operating below the millimeter scale may significantly influence fault behavior a result compatible with earlier characterizations of faults in a variety of geologic settings highlighting the importance of understanding how the formation and fabric of fault related authigenic clays influence fault behavior

dating the detachment fault system of the ruby mountains nevada significance for the kinematics of low angle normal faults 1 the mechanics of low angle normal faulting and metamorphic core complexes continue to be a subject of debate we investigate the conditions timing and kinematics of slip in the late upper crustal stages of core complex evolution of the ruby mountains detachment fault at the well exposed secret pass locality with an x ray diffraction xrd and ar ar study of clay gouge samples from three separate faults two from the low angle detachment system and one from a high angle normal fault that soles into the main detachment fault system xrd analysis and modeling of xrd analysis show that authigenic illite rich illite smectite i s in gouge at secret pass is distinguishable from clay phases in hanging wall rocks because the i s in the gouges contains only one water layer as opposed to the more common two water i s phases found in both the hanging wall and footwall ar ar ages for the monomineralic one water i s found in the hanging wall high angle fault the main detachment and a low angle normal fault structurally above the main detachment are 11 6 0 1 ma 12 3 0 1 ma and 13 8 0 2 ma respectively the not quite flat ar ar spectra indicate the gouge illites grew over some interval of time and not in discrete events the nearly overlapping ages indicate that gouge formation and thus the last major period of activity on the detachment were at 11 13 ma and were active coevally as part of a kinematically linked fault system with the main detachment active at dips 45 and possibly as low as 22

spatially variable fault friction derived from dynamic modeling of aseismic afterslip due to the 2004 parkfield earthquake we investigate fault friction from dynamic modeling of fault slip prior to and following the m w 6 0 earthquake which ruptured the parkfield segment of the san andreas fault in 2004 the dynamic modeling assumes a purely rate strengthening friction law with a logarithmic dependency on sliding rate a b ln v v the initial state of stress is explicitly taken into account and afterslip is triggered by the stress change induced by the earthquake source model given a priori we consider different initial stress states and two coseismic models and invert for the other model parameters using a nonlinear inversion scheme the model parameters include the reference friction the friction rate dependency characterized by the quantity a b assumed to be either uniform or depth dependent the model parameters are determined from fitting the transient postseismic geodetic signal measured at continuous gps stations our study provides a view of frictional properties at the kilometers scale over the 0 15 km depth illuminated by the coseismic stress change induced by the parkfield earthquake the reference friction is estimated to be between 0 1 and 0 5 with independent a priori constraints on the amplitude of differential stress the range of possible values narrows down to 0 1 0 17 the friction rate coefficient a b is estimated to be 10 3 10 2 with a hint that it increases upward from about 1 3 10 3 at 3 7 km depth to about 4 7 10 3 at 0 1 km depth it is remarkable that our results are consistent with frictional properties measured on rock samples recovered from the fault zone thanks to the san andreas fault observatory at depth experiment

effects of temperature on the frictional behavior of material from the alpine fault zone new zealand abstract temperature is widely believed to act as a primary control on fault rheology and therefore on the distribution of seismicity along plate boundary faults however there are few detailed measurements of the frictional strength and stability of natural fault gouges at elevated temperatures here we report on a suite of shearing experiments designed to investigate the frictional behavior of fault rocks sampled from depths of 111 5 142 9 m along the alpine fault in new zealand obtained by the international continental scientific drilling program icdp deep fault drilling project dfdp we tested five samples from the dfdp 1b pilot hole two hanging wall chloritic cataclasites two footwall granitic cataclasites and a fault gouge from the principal slip zone psz 1 each sample was sheared at a range of temperatures from 23 to 500 c and at an effective normal stress of 80 mpa the wall rock cataclasites exhibit an increase in the friction coefficient with temperature from 0 45 0 64 at 23 c to 0 87 at 500 c the psz 1 gouge exhibits lower friction coefficient values than the wall rock at temperatures 180 c 0 35 0 46 vs 0 45 0 65 but comparable values 0 87 0 90 at 500 c the variation in frictional strength is accompanied by a transition from velocity strengthening to velocity weakening behavior at temperatures 180 c for all materials extrapolation of the experimentally defined rheological critical stiffness of the fault material and the estimated in situ stiffness of the surrounding crust suggests upper and lower stability boundaries at 1 8 2 5 km and 8 5 8 8 km depth respectively the upper stability boundary is also consistent with the observed depth frequency distribution of earthquakes

origin and behavior of clay minerals in the bogd fault gouge mongolia we analyzed twelve fault gouge samples from the bogd fault in south western mongolia to understand the origin and behavior of clay minerals the investigation relies on x ray powder diffraction xrd scanning electron microscopy sem transmission electron microscopy tem and high energy synchrotron x ray diffraction methods to investigate microstructure and preferred orientation smectite montmorillonite illite smectite mixed layers illite mica and kaolinite are the major clay components in addition to quartz and feldspars which are present in all samples the observations suggest that the protoliths and the fault rocks were highly altered by fluids the fluid rock interactions allow clay minerals to form as well as alter feldspars to precipitate kaolinite and montmorillonite thus newly formed clay minerals are heterogeneously distributed in the fault zone the decrease of montmorillonite component of some of the highly deformed samples also suggests that dehydration processes during deformation were leading to illite precipitation based on synchrotron x ray diffraction data the degree of preferred orientation of constituent clay minerals is weak with maxima for 001 ranging from 1 3 to 2 6 multiples of a random distribution m r d co existing quartz and feldspars have random orientation distributions microstructure and texture observations of the gouges from the foliated microscopic zone alternating with micrometric isotropic clay rich area also indicate that the bogd fault experienced brittle and ductile deformation episodes the clay minerals may contribute to a slip weakening behavior of the fault