relation between soil age and silicate weathering rates determined from the chemical evolution of a glacial chronosequence long term weathering rates rlt were determined from base cation depletion in soil profiles developed on six granitic glacial moraines varying in age from 0 4 to 297 ka in the wind river mountains wyoming weathering rates were found to decrease with soil age t according to the power law equation rlt 15 t 0 71 where rlt is in meq m 2 yr 1 and t is in ka comparable data from the literature are consistent with this function and it is similar to power law equations describing changes in laboratory weathering rates with time on the basis of our study we predict that for a catchment unaffected by anthropogenic inputs and in a steady state with respect to the organic and cation exchange pools rlt should be higher than present day weathering rates derived from stream fluxes rpd by a factor of about 3 4

aftershock pattern of the july 9 1997 mw 6 9 cariaco earthquake in northeastern venezuela abstract the mw 6 9 cariaco earthquake of july 9 1997 was the strongest earthquake that occurred on the el pilar fault between cumana and the gulf of paria in the 20th century the el pilar fault is the most prominent strike slip fault in the transition zone between the caribbean plate and the south american plate in this region we installed 18 seismic and 10 strong motion stations for recording aftershocks we calculated the hypocenters of 1306 aftershocks with magnitudes between 0 5 and 4 1 most aftershocks concentrated near the documented trace of the el pilar fault the spatial distribution of the aftershocks allowed us to separate the aftershock region on the el pilar fault into six segments with different dip angles we computed and classified fault plane solutions of 222 aftershocks the majority of fault plane solutions are of strike slip type some segments show differences in the dominating type of focal mechanisms from the aftershock distribution and spatial variation of b values we inferred a rupture length of the cariaco earthquake of 60 km and thus an average displacement of 1 3 m during the main shock is estimated two out of four stepovers which were found on this length were seismically activated during the monitoring time interval the b value distribution on the fault plane appears to define two areas of major stress relaxation beneath cariaco and half way between casanay and el pilar close to the surface

geochemical investigation of soils developed in different lithologies in bhutan eastern himalayas within a project studying soil genesis on the southern slopes of the eastern himalayas a comprehensive set of major trace and rare earth element ree contents has been compiled for the first time six saprolites and their associated pedons were sampled on metamorphic migmatitic and leucogranitic parent materials at altitudes ranging from 1520 m to 3770 m metamorphic soils are largely illitic with si decreasing and al and fe increasing with decreasing degree of metamorphism the subsoil of a tourmaline bearing leucogranite is characterised by equally high si but higher contents of k and lower fe mg and ti a migmatitic profile in southern bhutan is dominated by hornblende and is quite distinct from the other lithologies with lower contents of si and k but higher fe mg ca and mn chondrite normalised ree patterns compare with post archaean materials with steep light rare earth lree and flat heavy rare earth hree patterns in comparison to generalised upper crustal composition ucc the bhutanese lithologies show a pronounced eu anomaly whereas the patterns appear rather homogenised in topsoils the influence of the parent materials causes deviations from the general trend with increasing depth the occurrence of marine tethyan sediments is confirmed by a strong positive ce anomaly in the central bhutanese phobjikha valley in the leucogranitic profile ree depletion is attributed to the presence of monazite as corroborated by trace element behaviour because of the hornblende ree patterns of the migmatitic profile are flat and without a eu anomaly chemical indices of alteration cia of between 71 and 92 indicate advanced weathering even at high altitudes correlation analyses show that ree are associated with the silt and clay fraction 63 m at elevations above approximately 3500 m physical weathering causes passive ree enrichment however no differentiation of ree concentrations or patterns within the profile is observed below 3500 m increased chemical weathering and leaching appears to be sufficient to release and translocate rees in this process hree are preferentially translocated whereas ce is more refractory than the other lanthanides this case study confirms that soil weathering and ree behaviour are closely related

changes in failure stress and stress transfer during the 1976 77 friuli earthquake sequence summary coulomb stress changes related to the sequence of strong earthquakes that affected the friuli area northeastern italy during the period 1976 77 have been investigated to explore the possibility of fault interaction and stress transfer mechanisms the seismic sequence that followed the mw 6 4 mainshock of 1976 may 6 consists of 5 events of mw between 5 2 and 6 0 during the same year and one event of mw 5 3 that occurred in 1977 september all characterized by thrust focal mechanisms the area is affected by a regional compressive stress which tends to activate n dipping thrust planes the goal of this study is to analyse and verify the relationship between the stress changes induced by the mainshock and the occurrence of subsequent events our results show that the mainshock induced a variation in the stress field in the area where most of the seismic events occurred our modelling shows a positive correlation between the areas of increased coulomb stress induced by the mainshock and the distribution of seismicity that followed this evidence suggests stress interaction and the possibility that the mainshock promoted the rupture of those faults associated with the event of 1976 may 9 mw 5 1 and the events of 1976 september 11 mw 5 2 and 5 6 1976 september 15 mw 6 0 and 1977 september 16 mw 5 3 the coulomb stress caused by co seismic dislocations decreased in the zone where an mw 5 9 earthquake occurred on september 15 at 03 15 when we included the contribution of the regional tectonic loading in the calculation of coulomb stress changes we found a positive correlation between the hypocentral area of the september 15 03 15 event and the area of coulomb stress increase aftershocks that occurred after the mainshock but before the september 15 03 15 event are also located in the area of coulomb stress increase

geochemistry of the pliocene red clay formation in the chinese loess plateau and implications for its origin source provenance and paleoclimate change abstract recent field observations and sedimentological studies suggest the eolian origin of the late tertiary red clay formation underlying the pleistocene loess soil sequence in the loess plateau thereby extending the wind blown record from 2 6 ma down to 7 0 ma in north central china to address the source provenance of the red clay major and trace element concentrations were analyzed on the samples from a north south loess transect of the loess plateau and a red clay section at jiaxian results show that there is a good agreement of both major and trace element compositions between the last glacial interglacial loess soil units and the jiaxian red clay record the ree distribution patterns of the loess soil and red clay samples are remarkably similar in shape with enriched lree and fairly flat hree profiles and clear negative eu anomaly the geochemical features of the red clay are also identical to those of upper continental crust these chemical characteristics provide further evidence for eolian sedimentation of the red clay from the relations both between na2o al2o3 and k2o al2o3 ratios and between u pb and th pb ratios the eolian loess and red clay materials must have been subject to thorough sedimentary differentiation and moderate chemical weathering in the source area the chemical similarity between soil unit s1 and the red clay implies that such an environment as occurred in the last interglacial period may have already formed in northwestern china during the late tertiary comparison of down section variations in elemental ratios with field observations of pedogenic development of the red clay suggests that cao al2o3 sr rb and sr ba are more sensitive to climate changes than magnetic susceptibility and can be used to reconstruct the climate history of the late cenozoic

the mw 8 1 2014 iquique chile seismic sequence a tale of foreshocks and aftershocks egu2009 11040 schurr b asch g rosenau m wang r oncken o barrientos s salazar p villotte j p 2012 the 2007m7 7 tocopillanorthernchile earthquake sequence implications for along strike and downdip rupture segmentation and megathrust frictional behaviour j geophys res 117 b05305 doi 10 1029 2011jb009030 schurr b et al 2014 gradual unlocking of the plate boundary controlled the initiation of the 2014 iquique earthquake nature 512 7514 299

the andean subduction zone between 22 and 25 s northern chile precise geometry and state of stress abstract one year of seismicity recorded by a local network is used to obtain more precision about the geometry and the stress regime of the andean subduction between 22 and 25 s in the northern chile seismic gap a sharp image of the wadati benioff zone wbz is obtained down to 270 km in depth a seismically quasi quiescent zone is observed in the wbz below the volcanic arc between 150 and 210 km in depth hypocentres of distant intermediate depth earthquakes located with the local network are compared with worldwide seismic network hypocentres in order to evaluate the accuracy of the wbz image at depth greater than 100 150 km in depth no shallow microearthquakes have been observed in the continental crust but some seismic activity is likely to occur locally at the deep root of the atacama fault the stress field and the characteristics of faulting along the subducted slab are investigated underthrusting and localized reverse faulting earthquakes define the seismically coupled plate interface from 20 to 50 km in depth locked zone downdip intra slab normal faulting prevails tensile zone but some strike slip faulting is observed a transition between normal faulting with variable fault azimuth and normal faulting with nearly homogeneous nnw to nw oriented fault plane is found at about 80 km in depth it is found that the stress axes 1 and 3 in the locked zone are oriented in the convergence direction 75 80 e downdip in the tensile zone 3 has a mean azimuth 60 65 e there the slab is hence submitted to a tensional force slab pull oblique relatively to the convergence the transition between seismic underthrusting and intraplate normal faulting downdip occurs at the depth where the continental moho encounters the wadati benioff zone suggesting that a relationship exists between seismic coupling and the presence of continental crust at the plate interface the pre seismic state of this segment of the andean subduction zone is confirmed by the occurrence of strong earthquakes located by the global network around the presumed rupture area and by the stress regime found along the wadati benioff zone

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

engineering and geological characteristics of granite weathering profiles in south china granite weathering profiles are widely distributed in south china their engineering and geological characteristics are major geotechnical subjects that are important in the design and construction of civil engineering projects this paper presents a summary of the weathering characteristics and zoning of granite weathering profiles in south china and discusses their engineering and geological properties a five grade scheme has been adopted in the zoning of a granite weathering profile studies have shown that the completely weathered granites cwg in south china have the following characteristics low moisture content low to medium plasticity w l 22 5 39 0 i p 6 5 11 8 medium void ratio 0 36 1 29 weak shrinkage and medium compressibility a 1 2 0 24 0 8 mpa 1 and high shear strength phi 20 30degrees c 20 40 kpa the cwgs are usually at a low or high plastic state and most of them are over consolidated soils a majority of the physical and mechanical properties have good statistical correlations with the degree of weathering the data presented in the paper are important in geotechnical engineering projects such as slope stability evaluation in china c 2002 elsevier science ltd all rights reserved

neogene weathering and supergene manganese enrichment in subtropical south china an 40ar 39ar approach and paleoclimatic significance deep weathering profiles and associated supergene mn oxides deposits are widely distributed in south china however data on their ages are not available until most recently ar 40 ar 39 laser incremental heating analysis of potassium bearing supergene mn oxides collected from four weathering profiles in the qinzhou fangcheng mn belt guangxi province south china provides for the first time numerical constraints on timing of weathering and supergene mn enrichment thirty eight of 42 cryptomelane grains yield well defined plateau 36 grains or pseudo plateau 2 grains ages ranging from 17 6 0 5 ma to 4 71 0 08 ma 2 sigma the results when combined with data from mn oxides deposits from the adjacent guangdong and hunan provinces document a protracted history of weathering and supergene mn enrichment spanning from the earliest miocene to the latest pliocene in south china this indicates that warm and humid climatic conditions conducive to intense weathering and secondary mineralization prevailed across south china during the whole neogene the climatic conditions inferred from weathering geochronology are consistent with sedimentary records and fossil floral and fauna associations from cenozoic inland and marginal sea basins of south china the weathering geochronology data also provide temporal constraints on the initiation and intensification of the east asian monsoon that has been the cause for the south china s humid climate c 2007 elsevier b v all rights reserved

a rudimentary mechanistic model for soil formation and landscape development ii a two dimensional model incorporating chemical weathering the necessity for a quantitative analysis of pedogenesis has become more compelling in the last few decades in part one of this paper we proposed a rudimentary mechanistic model that considers soil formation spatially at the catena scale this paper extends the model for soil formation in a landscape conditioned by a digital elevation model and further illustrates the application of the model in quantifying pedogenesis the current model states that the change in soil thickness over time depends on the physical weathering rate of rock the loss due to chemical weathering and the transport of soil through erosion the rate of physical weathering or lowering of the bedrock surface is represented as an exponential decline with soil thickness the chemical weathering rate is modelled as a negative exponential function of both soil thickness and time assuming uni dimensional weathering the rate of chemical weathering can be expressed as a reduction in soil thickness the movement of materials in the landscape is characterized by diffusive transport the model is solved numerically using the finite difference approach and applied to a digital elevation model the results for simulation of soil formation in a landscape after 10 000 years shows that the soil accumulates thickens in the gullies and erodes thins in the ridges the soil from the upper slope is transported down slope by the erosion processes and fills the gullies soil thickness is highly correlated with the profile curvature the effect of climate rock type and land management is illustrated by different combinations of weathering rate and erosive diffusivity to illustrate the effect of irregularity and randomness on the stability of the solution and the soil development spatially correlated normally distributed random numbers were added to the initial soil elevation the small randomness appears to cause instability chaos in the system dimensionality analysis of the soil thickness as a function of time confirms the non linear chaotic behaviour of the model rather than merely random noise a difference plot of the soil thickness time series unveiled the presence of a strange attractor alternatively these results may be a result of numerical instability

the effects of source rocks and chemical weathering on the petrogenesis of siliciclastic sand from the neto river calabria italy implications for provenance studies plutonic and gneissic rocks of the sila massif in the uppermost portion of the neto drainage basin calabria southern italy weather and erode under a humid mediterranean climate during the development of weathering profiles a combination of chemical weathering and granular disintegration processes occurred chemical weathering involves a loss of both plagioclase mainly during grus generation and k feldspar mainly during soil formation this loss is attributed to transformation of plagioclase to clay minerals and to leaching and dissolution of k feldspar sand composition is quartzofeldspathic and nearly homogeneous along the main channel of the neto river even where the river cuts across a blanket of sedimentary cover thus fluvial transport does not alter sand composition within the neto drainage basin petrographic indices are effective in 1 discriminating between contributions from similar granite and gneiss source rocks qm f 2 relating the provenance of plutoniclastic and gneissiclastic sand found in the headwaters to grus horizons qm f q rg and 3 distinguishing between upstream first cycle and downstream multicycle sand q rg this last distinction is further emphasized by considering both aphanitic and phaneritic varieties of rock fragments rgrmrs diagram chemical weathering is the main sand producer within the regolithic environment in northern calabria in addition rapid erosion resulting from steep slopes removes weathered products and rapid and short transport leads to minimal sediment maturation in general the f q index is climate and relief dependent thus it should be used in conjunction with palaeoclimatic and palaeophysiographic evidence for provenance interpretations of ancient quartzofeldspathic sandstones

centroid moment tensor solutions for july september 1995 abstract centroid moment tensor solutions are presented for 230 earthquakes that occurred during the third quarter of 1995 the solutions are obtained using corrections for aspherical earth structure represented by a whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward 1992 acoustical imaging plenum press pp 785 797 a new model of anelastic attenuation of durek and ekstrom 1994 eos trans am geophys union spring meet suppl 75 83 is used to predict the decay of the waveforms

near field response of a 1d structure alluvial site abstract we present a case history of the complicated strong motion responses at a site with an almost 1d structure buia in the near field of four m w 5 2 6 0 earthquakes in the friuli plain of italy in one case 15 september 1976 09 21 utc m w 6 0 the 47 m alluvial cover of buia experienced spectral amplitudes lower than its reference site on rock due to the different back azimuths from the source the largest peaks at buia occurred during an m w 5 6 event for practical purposes we tested 1 subjectivity when preparing the 1d models using a blind test with three experts 2 1d linear linear equivalent or nonlinear modeling in common practice and 3 the current seismic regulations we also used noise recordings and the weak motion velocities recorded for local events with digital triplets on the top and the bottom of the alluvial cover buia s response to weak events was more stable than its response to strong ones a simple 1d model five layer under linear conditions with good knowledge of the propagation velocities was able to reproduce the frequencies of the two relative strong motion maxima with an average amplitude underestimation of 1 5 the nonlinear approach simulated the two recorded maxima with slight shifts in frequency because the disaggregation of the seismic hazard showed that the four destructive shocks studied represent the magnitude and distance ranges that dominate the hazard of buia we can conclude that the response spectra of the new italian and european rules were sufficiently preventive notwithstanding the aforementioned complications in the near field

introduction to tectonics of china abstract the continental crust of china is a mosaic of cratonic blocks and orogenic belts containing small cratons and terranes with various tectonic settings they have diverse origins and complex histories of amalgamation and often suffered repeated reworking after multiple episodes of amalgamation in the last three decades extensive geological geochemical and geophysical investigations have been carried out on these cratonic blocks and intervening orogenic belts producing an abundant amount of new data and competing interpretations this provides important insights into understanding the formation and evolution of the chinese continents the papers assembled in this volume present a timely and comprehensive overview on major advancements and controversial issues related to the formation and evolution of continental crust in china complex tectonic histories were experienced not only by the large scale cratonic blocks and orogenic belts but also by small scale terranes and orogens between and inside these blocks nevertheless our understanding of lithotectonic units and geological processes has been greatly advanced by recent studies of zirconology and geochemistry for various rock types from major petrotectonic units in china it has been further advanced from integrated interpretations of geochemical and petrological data for petrogenesis of magmatic rocks an overview of these observations and interpretations provides new insights into understanding the continental plate tectonics and the chemical geodynamics of subduction zones

source parameters and stress release of seismic sequences occurred in the friuli venezia giulia region northeastern italy and in western slovenia abstract the source parameters of the major events of a swarm and of two seismic sequences occurred in the friuli area northeastern italy and in western slovenia were estimated the claut swarm c96 occurred since the end of january to june 1996 with a md 4 3 major shock and it appears composed of three sub sequences the two sequences are the kobarid sequence k98 started on april 12 1998 with a md 5 6 mainshock and the m te sernio s02 sequence caused by the february 14 2002 earthquake md 4 9 acceleration and velocity data recorded by the local seismic network of the istituto nazionale di oceanografia e di geofisica sperimenale ogs and corrected for attenuation were employed to estimate seismic moments and radiated energies source dimensions were inferred from the computed corner frequencies and the stress release was estimated from the brune stress drop the apparent stress and the rms stress drop on the whole seismic moments range from 1 7 1012 to 1 1 1017 n m and radiated energies are in the range 106 1013 j brune stress drops are scattered and do not show any evidence of a self similarity breakdown for sources down to 130 m radius the radiated seismic energy scales as a function of seismic moment with a slope of the scaling relation that decreases for increasing seismic moments the mechanism of stress release was analyzed by computing the parameter of zuniga zuniga r 1993 frictional overshoot and partial stress drop which one bull seismol soc am 83 939 944 the k98 and s02 sequences are characterized by a wide range of the parameter with stress drop mechanism varying from partial locking to overshoot cases the values of the c96 swarm are more homogeneous and close to the orowan s condition the radiated seismic energy and the ratio of stress drop between mainshock and aftershocks appear different among the analyzed cases we therefore investigated the relationship between the stress parameters of the main shock and the energy radiated by the aftershock sequences for this purpose we also estimated the source parameters of two other sequences occurred in the area with mainshocks of md 4 1 and 5 1 respectively we found a positive correlation between the brune stress drop of the mainshock and the ratio between the radiated energy of the mainshock and the summation of the energies radiated by the aftershocks

temperature dependence of silicate weathering in nature how strong a negative feedback on long term accumulation of atmospheric co2 and global greenhouse warming estimation of the temperature dependence of natural feldspar weathering in two catchments at different elevations yields an apparent arrhenius activation energy of 18 4 kcal mol 77 0 kj mol much higher than most laboratory values this finding supports recent suggestions that hydrolytic weathering of silicate minerals may consume carbonic acid and thereby remove atmospheric carbon dioxide more rapidly with increasing temperature than previously thought this result provides a stronger negative feedback on long term greenhouse warming than has been assumed in most models of global carbon cycling the present estimate was determined from the ratio of feldspar weathering rates determined by geochemical mass balance in the southern blue ridge mountains of north carolina united states temperature a function of elevation is the only factor that differs between the two catchments parent rock type aspect hillslope hydrology and vegetation type and successional stage are the same in both

chronology of late paleozoic tectonothermal activity in the southeastern bohemian massif austria moldanubian and moravo silesian zones 40ar 39ar mineral age controls abstract new 40ar 39ar hornblende and muscovite ages from the moldanubian and moravian zones of the southeastern bohemian massif indicate rapid cooling associated with continental underplating during early carboniferous plate collision and closure of the moravo silesian foredeep 40ar 39ar ages have been determined for hornblende concentrates from 1 amphibolite from the moldanubian nappe complex including the dobra gneiss rehberg amphibolite and loosdorf complex all part of the variegated unit 2 micaschist structurally overlying the bittesch gneiss and 3 amphibolite within the bittesch gneiss moravian zone the five hornblende concentrates display variably discordant 40ar 39ar age spectra because of contamination with extraneous argon components however 36ar 40ar vs 39ar 40ar isotope correlations are well defined for the five hornblende concentrates mswd the hornblende and muscovite ages are interpreted to date post variscan metamorphic cooling through ca 500 c and ca 400 c respectively no record of pre variscan thermal events is preserved in either the hornblende or muscovite argon systems however the widespread occurrence of extraneous argon components suggest a pre variscan stage of tectonothermal development the near concordancy of the hornblende and muscovite cooling ages suggest relatively rapid cooling through the contrasting argon closure temperatures and indicate that relatively high crustal levels had likely been attained during the early carboniferous

rapid postseismic transients in subduction zones from continuous gps 1 continuous gps time series from three of four recently measured large subduction earthquakes document triggered rapid postseismic fault creep representing an additional moment release upward of 25 over the weeks following their main shocks data from two mw 8 0 and mw 8 4 events constrain the postseismic centroids to lie down dip from the lower limit of coseismic faulting and show that afterslip along the primary coseismic asperities is significantly less important than triggered deep creep time series for another mw 7 7 event show 30 postseismic energy release but here we cannot differentiate between afterslip and triggered deeper creep a fourth mw 8 1 event which occurred in the broad chilean seismogenic zone shows no postseismic deformation despite coseismic offsets in excess of 1 m for the three events which are followed by postseismic deformation stress transferred to the inferred centroids at 34 60 and 36 km depths by their respective main shock asperities increased reverse shear stress by 0 5 0 8 and 0 2 bar with a comparatively small decrease in normal stress 0 01 bar constraining the coulomb stress increase required to force slip along the metastable plate interface deep triggered slip of this nature is invisible without continuous geodesy but on the basis of these earthquakes would appear to constitute an important mode of strain release from beneath the seismogenic zones of convergent margins these events captured by some of the first permanent gps networks show that deep moment release is often modulated by seismogenic rupture updip and underscore the need for continuous geodesy to fully quantify the spectrum of moment release in great earthquakes index terms 7209 seismology earthquake dynamics and mechanics 3040 marine geology and geophysics plate tectonics 8150 8155 8157 8158 8150 tectonophysics plate boundary general 3040 7230 seismology seismicity and seismotectonics keywords subduction zone earthquake postseismic moment release

the influence of source rock type chemical weathering and sorting on the geochemistry of clastic sediments from the quetico metasedimentary belt superior province canada abstract the geochemistry of clastic sediments is controlled by at least four factors source rock composition weathering of the source rocks sorting of the weathered detritus and post depositional alteration during diagenesis and metamorphism in order to evaluate the relative importance of these factors major trace and rare earth element contents were determined for distal and proximal clastic turbidites from the archaean quetico metasedimentary belt the degree of metamorphism of the samples ranges from middle greenschist to upper amphibolite facies simple mixing of archaean mafic and acidic rocks of similar composition to those found in the adjacent granite greenstone terrains will account for the tio2 feot mgo cr sc y and hree contents of the clastic turbidites the metasediments are enriched in lree relative to the mafic acidic rock mixing line indicating that the acidic source was enriched in the lree compared to archaean terrains from other parts of the world some quetico turbidites have an additional fe rich source component possibly a chemical sediment incorporated at the time of turbidite slumping cao na2o k2o rb and sr form trends on bivariant plots that are oblique to the mafic acidic rock mixing line and hence cannot be accounted for by simple mixing of the source rocks chemical weathering of feldspars prior to deposition can account for cao na2o k2o rb and sr trends since cao na2o and sr are lost to the weathering solutions and k2o and rb are retained on the product clays the higher na 2 o cao k 2 o na 2 o rb k 2 o and sr cao ratios but lower cao content of the distal samples suggest that they were derived from a bulk sediment that had experienced a greater degree of chemical weathering than the proximal sediments sorting is the factor that most strongly influences the composition of individual samples within the proximal sample group the coarse grained metagraywackes with their higher quartz feldspar and heavy mineral contents are enriched in sio2 cao na2o sr lree zr and hf relative to the fine grained clay rich metapelites metapelites are enriched in tio2 al2o3 feot mgo k2o cr zn sc y hree cs and rb as a result of their higher clay contents thus the use of clastic sediment compositions in determining average crustal compositions e g for the ree can only give satisfactory results when all grain size fractions are sampled in their correct relative proportions the chemical differences observed between the high and low grade samples can be accounted for by source rock type chemical weathering of the source rocks or sorting post depositional element mobility does not appear to be an important factor in determining the composition of the quetico metasediments

spatial variability of seismicity parameters in aftershock zones the spatial variability of the b value of the frequency magnitude relationship and the decay rate of aftershocks as described by the p value of the modified omori law is investigated by using dense spatial grids we map out the distribution of b and p values within the landers northridge morgan hill and kobe aftershock sequences considerable spatial variability is found with b values of independent subvolumes ranging from 0 6 to 1 4 and p values ranging from 0 6 to 1 8 these systematic and statistically highly significant differences argue that it is an oversimplification to assign one single p and b value to an aftershock sequence that extends up to 100 km the spatial distribution of these two parameters is compared with the slip distribution during the mainshock suggesting that the areas of largest slip release correlate with high b value regions we hypothesize that the frictional heat created during the event may influence the p value distribution within an aftershock zone while applied shear stress crack density and pore pressure govern the frequency magnitude distribution by investigating the frequency magnitude distribution separately for preseismic and postseismic periods for the morgan hill mainshock we find that only the volume in the vicinity of the highest slip release shows a significant increase in the b value which decays to premainshock values within a year surrounding areas of the aftershock zone show an approximately constant b value with time because the aftershock hazard after a mainshock depends strongly on both the b and p value we propose that aftershock hazard assessment can be improved by taking into account the spatial distribution of the parameters

high resolution image of the oceanic moho in the subducting nazca plate from p s converted waves short period p s converted waves outline the oceanic moho of the descending nazca plate in northern chile at 24 s comparison with hypocentral locations obtained with temporary local seismic networks show that earthquakes inside the subducting oceanic lithosphere of the nazca plate are located predominantly in the oceanic crust at depths between 70 and 120 km and probably in the upper mantle at depths below 120 km the results suggest that dehydration embrittlement as mechanism for intermediate depth earthquakes is active both in the former oceanic crust and upper mantle of subducting lithosphere

timing and duration of supergene mineralization at the xinrong manganese deposit western guangdong province south china cryptomelane 40 ar 39 ar dating supergene mn oxide deposits are widely distributed in guangxi guangdong yunnan and hunan provinces south china accounting for 18 of the total mn reserves in the country direct dating of supergene mn enrichment however is lacking in this paper we present high resolution 40ar 39ar ages of mn oxides from the xinrong mn deposit western guangdong to place numerical constraints on the timing and duration of supergene mn enrichment a total of ten cryptomelane samples spanning a vertical extent of 67 m were dated using the 40ar 39ar laser incremental heating technique with seven samples yielding well defined plateau or pseudo plateau ages ranging from 23 48 0 91 to 2 06 0 05 ma 2 one sample yields a staircase spectrum that does not reach a plateau the spectrum however indicates the presence of two or more generations of mn oxides in the sample whose ages are best estimated at 22 34 0 31 and 10 2 0 86 ma respectively the remaining two samples gave meaningless or uninterpretable results due to significant 39ar recoil and contamination by old phases the 40ar 39ar data thus reveal a protracted history of weathering and supergene mn enrichment that started at least in the end of the oligocene or beginning of miocene and extending into the latest pliocene staircase apparent age spectra resulting from banded or botryoidal samples yield an average growth rate of mn oxides at 0 6 0 7 10 3 mm kyr 1 the values indicate that a 1 mm grain of mn oxides may host minerals precipitated during a time span of ca 1 5 m y and accumulation of mn oxides to form economic deposits under weathering environments may take millions of years the distribution of weathering ages shows that the oldest mn oxides occur on the top of the profile whereas the youngest minerals are found at the bottom suggesting downward propagation of weathering fronts however two samples located at the intermediate depths of the profile yield ages comparable with those occurring at the highest elevations such a complexity of age distribution is interpreted in terms of preferential penetration of mn rich weathering solutions along more permeable fault zones or as a result of multi stages of dissolution and re precipitation of mn oxides a synthesis of geochronological and geological data suggests that formation of the xinrong deposit was a consequence of a combination of favorable lithological climatic and structural conditions because the climatic and structural conditions are similar among the provinces of south china during the cenozoic the geochronological results obtained at xinrong may also have implications for the timing of supergene mn enrichment throughout south china

weathering plants and the long term carbon cycle the chemical weathering of ca mg silicate rocks is the principal process whereby co2 is removed from the atmosphere on long or multimillion year time scales at present vascular land plants exert an important influence on weathering by recycling water and by bringing about the secretion of acids and the buildup of high levels of co2 in soils before the spread of vascular plants on the continents during the mid paleozoic chemical weathering must have been achieved by higher levels of atmospheric co2 and or by the intercession of primitive land biota such as lichens and cyanobacteria from examination of several pre vascular weathering scenarios it is concluded that in order to prohibit unreasonably high levels of atmospheric co2 weathering during the precambrian and early paleozoic must have taken place under essentially closed system abiotic conditions linear feedback or via strong regulation by primitive biota preliminary examination of modern weathering by lichens over tens to thousands of years militates against the latter possibility however much more work needs to be done on the quantitative effect of both primitive biota and vascular plants on the rate of weathering and their response to changes in atmospheric co2 before anything more definitive can be said

chemical weathering of monsoonal eastern china implications from major elements of topsoil major element compositions of 36 bulk samples and 41 clay samples which were obtained from 47 topsoils collected in monsoonal eastern china were investigated with conventional wet chemistry and x ray fluorescence xrf spectrometry respectively based on major element analyses the mobility of major elements and latitudinal distributions of sio2 al2o3 ratio chemical index of alteration cia chemical index of weathering ciw and weathering index of parker wip were analyzed meanwhile the suitability of these chemical weathering indices to topsoils in monsoonal eastern china and its controls were discussed these investigations indicate that na k ca mg and si are relatively depleted while mn p fe and ti are relatively enriched in topsoils of the study area by comparison with their contents in the upper continent crust ucc and that alkali metal na k and alkaline earth metal ca mg elements are generally easier to be depleted from their parent materials than other major elements during chemical weathering the latitudinal distributions of cia ciw and wip show that they are suitable to both bulk and clay samples but sio2 al2o3 is only suitable to clay samples not suitable in bulk ones all these investigations indicate a significant dependence of grain size in major element abundance and latitudinal distributions of sio2 al2o3 cia ciw and wip but parent rock type has little effect on them except its impact on the latitudinal distribution of wip in clay samples the significant grain size dependence probably indicates the presence of unaltered minerals in bulk samples thus we suggest that clay samples are more suitable to investigating chemical weathering of sediments on continents than bulk samples the trivial effect of parent rock type probably indicates a relatively uniform chemical weathering on various parent rocks correlation analyses indicate that climate is the dominant control of chemical weathering of topsoils in the study area and the significant latitude effect indicated by the spatial distributions of chemical weathering indices actually reflect the climate control on chemical weathering of topsoils chemical weathering indices actually reflect the integrated weathering history in the study area besides the dominant control of climate other factors like tectonics parent rock biology landform and soil depth and age might also have some effect on the chemical weathering of topsoils in the study area which needs further research c 2013 elsevier ltd all rights reserved

asperity generating upper crustal sources revealed by b value and isostatic residual anomaly grids in the area of antofagasta chile in our study we show that the locations of largest coseismic slip asperities on the fault plane of the m w 8 0 1995 antofagasta earthquake in northern chile can be mapped by the spatial distribution of the seismic b value obtained from the aftershock sequence of the megathrust earthquake these areas of high seismic moment release and concurrent high b values are congruent with anomalies of the gravity isostatic residual ir field in the antofagasta region they are superimposed on the seismogenic part of the north chilean subduction zone where the strongest coupling of the upper and lower plate is expected the ir anomalies are interpreted to be caused by large jurassic early cretaceous batholiths which intruded into the upper crust the observed positive correlations between high seismic b values ir anomalies and geologic structures enable us to propose a mechanical model for the generation of the asperities in the antofagasta region we suggest that the batholiths in conjunction with buoyant forces acting on the subducted slab of the nazca plate are responsible for locking the interface where the asperities are located this implies long term conditions for the existence of the asperity generating tectonic situation concequently the asperities around antofagasta could be stationary features at least for several seismic cycles hence we propose that the ir anomalies along the north chilean convergent margin can be used as an indicator for high moment release and slip in future large earthquakes

body wave and surface wave analysis of large and great earthquakes along the eastern aleutian arc 1923 1993 implications for future events the 500 km long alaska peninsula and shumagin islands segments of the aleutian arc have a moderate to high probability of rupturing in one or more large or great earthquakes in the next few decades to understand the likely modes of rupture in the next sequence of large and great events and to delineate the current geometry of the plate interface we determine focal mechanisms depths and source time functions from seismic records for the largest events since 1917 the great earthquake of november 10 1938 and seven events with surface wave magnitude ms of 6 9 to 7 5 teleseismic body waves and surface waves are used to estimate the seismic moment and gross rupture characteristics of the great earthquake of november 10 1938 along the alaska peninsula body wave inversion of five p and four sh waves gives a duration of about 110 s in which moment was released in two episodes each of about 50 s duration with the second being larger than the first the first source was located in the general vicinity of the epicenter of the mainshock and the second which occurred about 60 s later was centered about 180 km to the northeast the body wave derived seismic moment is 3 7 1021 n m mw 8 3 we corroborate the body wave results by calculating surface waves by normal mode summation and comparing them with data at periods greater than 50 s an adequate fit to observed seismograms is obtained for either a single point source or two point sources with one located about 180 km northeast of the mainshock epicenter rupture in 1938 appears to have been confined to the alaska peninsula segment uniform rupture into the shumagin region is not supported by the data the ms 6 9 earthquake of may 13 1993 ruptured a small portion of the shumagin gap the earthquake of may 14 1948 ms 7 5 occurred on a shallow dipping thrust fault with a depth of about 31 km not 60 km as originally suggested five ms 7 events in the 1938 rupture zone have locations depths and mechanisms that define a shallow dipping 16 19 plate interface which shallows to 8 under kodiak island subduction of seamounts of the gulf of alaska seamount province may explain the location moment focal mechanism and depth of the five ms 7 events the plate interface dips nearly uniformly between the alaska peninsula and shumagin segments indicating that segmentation if any is not controlled by the orientation of the plate interface a slight warp of the plate interface may form the boundary between rupture zones of great earthquakes along the kodiak and alaska peninsula segments of the arc and may explain why rupture zones of large to great earthquakes rarely cross this tectonic boundary

co seismic slip from the 1995 july 30 mw 8 1 antofagasta chile earthquake as constrained by insar and gps observations summary we analyse radar interferometric and gps observations of the displacement field from the 1995 july 30 mw 8 1 antofagasta chile earthquake and invert for the distribution of slip along the co seismic fault plane using a fixed fault geometry we compare the use of singular value decomposition and constrained linear inversion to invert for the slip distribution and find that the latter approach is better resolved and more physically reasonable separate inversions using only gps data only insar data from descending orbits and insar data from both ascending and descending orbits without the gps data illustrate the complimentary nature of gps and the presently available insar data the gps data resolve slip near gps benchmarks well while the insar provides greater spatial sampling the combination of ascending and descending insar data contributes greatly to the ability of insar to resolve the slip model thereby emphasizing the need to acquire this data for future earthquakes the rake distribution of slip and seismic moment of our preferred model are generally consistent with previous seismic and geodetic inversions although significant differences do exist gps data projected in the radar line of sight los and corresponding insar pixels have a root mean square rms difference of about 3 cm comparison of our predictions of vertical displacement and observed uplift from corraline algae have an rms of 10 cm our inversion and previous results reveal that the location of slip might be influenced by the 1987 mw 7 5 event our analysis further reveals that the 1995 slip distribution was affected by a 1988 mw 7 2 event and might have influenced a 1998 mw 7 0 earthquake that occurred downdip of the 1995 rupture our slip inversion reveals a potential change in mechanism in the southern portion of the rupture consistent with seismic results predictions of the satellite los displacement from a seismic inversion and a joint seismic gps inversion do not compare favourably with the insar observations

accurate hypocentre determination in the seismogenic zone of the subducting nazca plate in northern chile using a combined on offshore network the coupled plate interface of subduction zones commonly called the seismogenic zone has been recognized as the origin of fatal earthquakes a subset of the after shock series of the great antofagasta thrust type event 1995 july 30 mw 8 0 has been used to study the extent of the seismogenic zone in northern chile to achieve reliable and precise hypocentre locations we applied the concept of the minimum 1 d model which incorporates iterative simultaneous inversion of velocity and hypocentre parameters the minimum 1 d model is complemented by station corrections which are influenced by near surface velocity heterogeneity and by the individual station elevations by relocating mine blasts which were not included in the inversion we obtain absolute location errors of 1 km in epicentre and 2 km in focal depth a study of the resolution parameters ale and dspr documents the importance of offshore stations on location accuracy for offshore events based on precisely determined hypo centres we calculate a depth of 46 km for the lower limit of the seismogenic zone which is in good agreement with previous studies for this area for the upper limit we found a depth of 20 km our results of an aseismic zone between the upper limit of the seismogenic zone and the surface correlates with a detachment zone proposed by other studies the results are also in agreement with thermal studies for the antofagasta forearc region

long term stability of global erosion rates and weathering during late cenozoic cooling reports that the geological record of erosion indicates a fourfold increase in global sedimentation rates during the past 5 million years merited a global explanation explanations offered include an increased rate of mountain formation and global cooling now jane willenbring and friedhelm von blanckenburg reanalyse original data sets and use ocean records of beryllium isotope ratios to obtain an indirect measure of past erosion rates and rock weathering they find no clear evidence either for an increase in global erosion or for a pulse of weathered material in the oceans during the past 12 million years they suggest that cenozoic global cooling must have some other cause and the mountain building that did occur had little effect on erosion or weathering flux globally accelerated uplift and global cooling have been suggested as possible causes for a fourfold increase in global sedimentation rates and by inference in erosion rates or weathering fluxes during the past 5 million years here proxy evidence is provided that indicates stable weathering fluxes in the late cenozoic era it is proposed that processes different from an increase in denudation caused cenozoic global cooling over geologic timescales co2 is emitted from the earth s interior and is removed from the atmosphere by silicate rock weathering and organic carbon burial this balance is thought to have stabilized greenhouse conditions within a range that ensured habitable conditions1 changes in this balance have been attributed to changes in topographic relief where varying rates of continental rock weathering and erosion1 2 are superimposed on fluctuations in organic carbon burial3 geological strata provide an indirect yet imperfectly preserved record of this change through changing rates of sedimentation1 2 4 widespread observations of a recent 0 5 myr fourfold increase in global sedimentation rates require a global mechanism to explain them4 5 6 accelerated uplift and global cooling have been given as possible causes2 4 6 7 but because of the links between rates of erosion and the correlated rate of weathering8 9 an increase in the drawdown of co2 that is predicted to follow may be the cause of global climate change instead2 however globally rates of uplift cannot increase everywhere in the way that apparent sedimentation rates do4 10 moreover proxy records of past atmospheric co2 provide no evidence for this large reduction in recent co2 concentrations11 12 here we question whether this increase in global weathering and erosion actually occurred and whether the apparent increase in the sedimentation rate is due to observational biases in the sedimentary record13 as evidence we recast the ocean dissolved 10be 9be isotope system as a weathering proxy spanning the past 12 myr ref 14 this proxy indicates stable weathering fluxes during the late cenozoic era the sum of these observations shows neither clear evidence for increased erosion nor clear evidence for a pulse in weathered material to the ocean we conclude that processes different from an increase in denudation caused cenozoic global cooling and that global cooling had no profound effect on spatially and temporally averaged weathering rates

implications of the 2003 bingol earthquake for the interaction between the north and east anatolian faults aftershocks of the magnitude m w 6 4 bingol earthquake of 1 may 2003 eastern turkey were monitored by a local temporary seismic network the spatial distribution of the aftershocks shows that the earthquake did not occur on the left lateral east anatolian fault but perpendicular to it along a north northwest striking right lateral fault the event ruptured an area of 20 km by 8 km but did not reach the earth s surface the aftershocks of the 2003 bingol earthquake and those of the 1992 erzincan earthquake seem to indicate the existence of a new seismically active right lateral shear zone indeed we show that historical earthquakes along both the north and east anatolian fault led to positive changes in coulomb failure stress for north northwest oriented right lateral strike slip faults in the bingol epicentral area moreover the existence of such faults is supported by remote sensing data online material fault geometry and aftershock data near bingol

constraints on the location and mechanism of the 1511 western slovenia earthquake from active tectonics and modeling of macroseismic data abstract the 1511 western slovenia earthquake m 6 9 is the largest event occurred so far in the region of the alps dinarides junction though it strongly influences the regional seismic hazard assessment the epicenter and mechanism are still under debate the complexity of the active tectonics of the alps dinarides junction is reflected by the presence of both compressional and transpressional deformations this complexity is witnessed by the recent occurrence of three main earthquake sequences the 1976 friuli thrust faulting events the 1998 bovec krn mountain and the 2004 kobarid strike slip events the epicenters of the 1998 and 2004 strike slip earthquakes ms 5 7 and ms 4 9 respectively lie only 50 km far from the 1976 thrust earthquake ms 6 5 we use the available macroseismic data and recent active tectonics studies to assess a possible epicenter and mechanism for the 1511 earthquake and causative fault according with previous works reported in the literature we analyze both a two and a single event case defining several input fault models we compute synthetic seismograms up to 1 hz in an extended source approximation testing different rupture propagations and applying a uniform seismic moment distribution on the fault segments we extract the maximum horizontal velocities from the synthetics and we convert them into intensities by means of an empirical relation a rounded to integer misfit between observed and computed intensities is performed considering both a minimized and a maximized databases built to avoid the use of half degree macroseismic intensity data points our results are consistent with a 6 9 magnitude single event rupturing 50 km of the idrija right lateral strike slip fault with bilateral rupture propagation

direct effects of co2 and temperature on silicate weathering possible implications for climate control a critical uncertainty in models of the global carbon cycle and climate is the combined effect of organic activity temperature and atmospheric co2 on silicate weathering here we present new dissolution rates of anorthite and augite which indicate that silicate weathering in organic rich solutions is not directly affected by soil co2 but is very sensitive to temperature apparently co2 accelerates silicate weathering indirectly by fertilizing organic activity and the production of corrosive organic acids the weathering dependencies highlight the ability of silicate weathering to act as a global thermostat and damp out climate change when used as input in steady state carbon cycle and climate models

geochemistry of the dissolved load of the changjiang basin rivers anthropogenic impacts and chemical weathering abstract this study focuses on the chemical and sr isotopic compositions of the dissolved load of the rivers of the changjiang basin one of the largest riverine systems in the world water samples were collected in august 2006 from the main tributaries and the main changjiang channel the chemical and isotopic analyses indicated that four major reservoirs carbonates silicates evaporites and agriculture urban effluents contribute to the total dissolved solutes the overall chemical weathering carbonate and silicate rate for the changjiang is approximately 40 ton km2 year or 19 mm kyr similar to that of the ganges brahmaputra system and the basin is characterized by carbonate and silicate weathering rates ranging from 17 to 56 ton km2 year and from 0 7 to 7 1 ton km2 year respectively in the lower reach of the changjiang main channel the weathering rates are estimated to be 36 and 2 2 ton km2 year for carbonates and silicates respectively it appears that sulphuric acid may dominate chemical weathering reactions for some sub basins the budgets of co2 consumption are estimated to be 646 109 and 191 109 mol year by carbonate and silicate weathering respectively the contribution of the anthropogenic inputs to the cationic tds of the changjiang is estimated to be 15 20 for the most downstream stations our study suggested that the changjiang is strongly impacted by human activities and is very sensitive to the change of land use

the ciw index a new chemical index of weathering abstract a new chemical index of weathering that can be applied to modern soils and precambrian paleosis is proposed ciw al2o3 the value of this index increases as the degree of weathering increases and the difference between ciw index values of the silicate parent rock and soil or sediment reflects the amount of weathering experienced by the weathered material

crustal deformation and fault slip during the seismic cycle in the north chile subduction zone from gps and insar observations summary the different phases of the earthquake cycle can produce measurable deformation of the earth s surface this work is aimed at describing the evolution of that deformation in space and time as well as the distribution of causal slip on the fault at depth we have applied gps and synthetic aperture radar sar interferometry insar techniques to northern chile where fast plate convergence rates are associated with large subduction earthquakes and extensive crustal deformation the region of northern chile between 18 s and 23 s is one of the most important seismic gaps in the world with no rupture having occurred since 1877 in 1995 the mw 8 1 antofagasta earthquake ruptured the subduction interface over a length of 180 km in the region immediately to the south of this 450 km long gap the coseismic deformation associated with this event has been documented previously here we use gps position time series for 40 benchmarks measured between 1996 and 2000 and ers sar interferograms for the interval between 1995 and 1999 to map both the post seismic deformation following the 1995 event and the ongoing interseismic deformation in the adjacent gap region in the seismic gap the interseismic velocities of 20 30 mm yr 1 to the east with respect to south america are mapped both the gps and the insar measurements can be modelled with 100 per cent coupling of the thrust interface of the subduction to a depth of 35 km with a transition zone extending down to 55 km depth the slip rate in that zone increases linearly from zero to the plate convergence rate south of the gap the interferometric map shows interseismic deformation superimposed with deformation following the 1995 earthquake and covering the same area as the coseismic deformation some 40 per cent of this deformation is related to seismic activity in the 3 3 yr following the 1995 event in particular slip during a mw 7 1 earthquake in 1998 however most of the signal 60 per cent corresponds to post seismic deformation resulting from widespread aseismic slip in the subduction interface the afterslip appears to have occurred down dip in the transition zone at 35 55 km depth and to have propagated laterally northwards at 25 45 km depth under the mejillones peninsula which is a prominent geomorphological feature at the boundary between the 1877 and 1995 rupture zones we propose a simple slip model for the seismic cycle associated with the antofagasta earthquake where the transition zone alternates between aseismic shear and seismic slip

integration of geochemical mass balance with sediment transport to calculate rates of soil chemical weathering and transport on hillslopes 1 we developed a process oriented hillslope soil mass balance model that integrates chemical and physical processes within hillslope soils the model explicitly factors that soil chemical weathering at any hillslope position is related to the flux of soil eroded from upslope as well as soil production from underlying bedrock the model was merged with measurements of soil elemental chemistry and cosmogenic radionuclide based saprolite to soil conversion rates along a 50 m transect of a semiarid granodiorite hillslope in the southeastern australian highlands inverse modeling results in the simultaneous quantification of the rates of soil chemical weathering and soil transport as a function of hillslope position soil chemical weathering rates per land surface area systematically varied along the transect from losses of 0 035 kg m 2 yr 1 on the ridge to gains of 0 035 kg m 2 yr 1 at the lowest slope position the mass loss via soil chemical weathering would have been overestimated by 40 if the impact of soil transport on soil chemistry was ignored the chemical mobility of elements combined with biological nutrient demand controlled the spatial redistribution of individual elements p and ca were preferentially retained relative to si al and fe within the hillslope base the calculated soil transport rate is linearly related to the product of soil thickness and slope gradient instead of slope alone soil residence time was determined by calculating the time length for a 3 dimensional box volume 1 m2 surface area soil thickness to be entirely removed by mass flux of soil transport 4 ka on the ridge to 0 9 ka at the hillslope base these soil residence times combined with soil chemical weathering rates indicate that a 1 m2 area of soil loses 1 800 kg via chemical weathering while passing through the upslope portion of the hillslope but that it regains 90 kg probably via clay precipitation and biological retention of cations during its passage through the lower segments of the transect this study provides a previously unrecognized linkage between physical soil transport and soil chemical weathering that have implications for hillslope evolution as well as biogeochemistry

gps derived deformation of the central andes including the 1995 antofagasta mw 8 0 earthquake in order to study both the interplate seismic loading cycle and the distribution of intraplate deformation of the andes a 215 site gps network covering chile and the western part of argentina was selected monumented and observed in 1993 and 1994 a dense part of the network in northern chile and northwest argentina comprising some 70 sites was re observed after two years in october november 1995 the m w 8 0 antofagasta north chile earthquake of 30th july 1995 took place between the two observations the city of antofagasta shifted 80 cm westwards by this event and the displacement still reached 10 cm at locations 300 km from the trench three different deformation processes have been considered for modeling the measured displacements 1 interseismic accumulation of elastic strain due to subduction coupling 2 coseismic strain release during the antofagasta earthquake and 3 crustal shortening in the sub andes eastward displacement of the sites to the north and to the south of the area affected by the earthquake is due to the interseismic accumulation of elastic deformation assuming a uniform slip model of interseismic coupling the observed displacements at the coast require a fully locked subduction interface and a depth of seismic coupling of 50 km the geodetically derived fault plane parameters of the antofagasta earthquake are consistent with results derived from wave form modeling of seismolog ical data the coseismic slip predicted by the variable slip model reaches values of 3 2 m in the dip slip and 1 4 m in the strike slip directions the derived rake is 66 our geodetic results suggest that the oblique nazca south american plate convergence is accommodated by oblique earthquake slip with no slip partitioning the observed displacements in the back arc indicate a present day crustal shortening rate of 3 4 mm year which is significantly slower than the average of 10 mm year experienced during the evolution of the andean plateau

invited review paper neogene to quaternary tectonics of the coastal cordillera northern chile abstract the extreme aridity of the northern chilean coastal cordillera enables the complete preservation of permanent deformation related to the coupling between nazca and south america the region between antofagasta and arica is characterized by four types of late cenozoic structures ew striking reverse faults ns striking normal faults sparse wnw and nnw striking right lateral strike slip faults and unimodal and bimodal populations of surface cracks the ew reverse faults occur only between 19 and 21 40 s latitude and have been active since at least 6 ma to present a march 2007 earthquake demonstrates that this deformation can occur during the interseismic phase of the plate boundary seismic cycle the ns normal faults are most abundant near antofagasta and mejillones and diminish in significance northward several of these faults in both the antofagasta and the salar grande area have been reactivated as reverse faults causing minor topographic inversion we suggest that normal faults move during both interseismic and coseismic deformation and are fundamentally very weak surface cracks are ubiquitous throughout the region and form by both non tectonic and tectonic mechanisms a significant proportion forms during coseismic deformation and thus may be used to identify long lived rupture segments on the plate boundary overall forearc deformation is very slow with permanent strain rates of 1 5 nstrain year and fault slip rates less than 0 5 mm year

clay mineralogy chemical weathering and landscape evolution in arctic alpine sweden abstract the purpose of this research was to 1 characterize the clay mineralogy of soils in and adjacent to karkevagge a recently deglaciated valley in arctic sweden 2 document chemical weathering in a periglacial environment and 3 use the mineralogy to help explain landscape evolution soil samples were analyzed from 11 sites that differ in elevation parent material drainage slope and vegetation parent materials include residuum alluvium colluvium and glaciofluvial material derived from garnet mica schist plus in one locality a till of granitic origin x ray diffraction xrd was used to characterize the clay size fraction

fault plane structure of the antofagasta chile earthquake of 1995 from a large dataset of aftershocks in the rupture area of the mw 8 0 1995 antofagasta earthquake we derived the spatial distribution of hypocenters and a b value map along the fault plane we further examined various focal mechanisms of the aftershock sequence the b value distribution on the fault plane clearly indicates the heterogeneity of the rupture area we found a positive correlation between the b value variations and the main shock source time function determined by delouis 1996 where zones of high b value are related to high slip with these results we propose to have found evidence for the segmentation of the fault plane and suggest that the mapped inhomogeneities could have played the role of asperities prior to the main shock rupture

long term persistence of subduction earthquake segment boundaries evidence from mejillones peninsula northern chile 1 the mejillones peninsula in northern chile has been recognized as the surface expression of a segment boundary for large subduction zone earthquakes the sharp contact between the rupture planes of two instrumentally recorded earthquakes the mw 8 0 antofagasta 1995 and the mw 7 7 tocopilla 2007 events is located beneath the central part of mejillones peninsula we present new chronostratigraphic and structural data that allow reconstructing the evolution of the peninsula at the surface and correlation of the latter with seismic cycle deformation on the plate interface uplift commenced after 3 4 myr as recorded in the western highland the central graben area on the peninsula started uplifting above sea level as an anticlinal hinge zone prior to 400 kyr ago most probably 790 kyr ago the resulting e w trending hinge exactly overlies the limit between the rupture planes of the antofagasta and tocopilla earthquakes by correlating the uplift data with the slip distribution of the above earthquakes we demonstrate that deformation and uplift is focused during the postseismic and interseismic periods of the megathrust seismic cycle with coseismic deformation opposed to the long term motion additionally the slip deficit beneath the peninsula accumulating between events is probably largely recovered by creep hence we suggest that mejillones peninsula owes its existence to the lateral variation of the propensity for unstable slip at the interface since the latter is a material property the long term spatial stability of the peninsula as a barrier to rupture propagation since at least the middle pleistocene is a necessary consequence

delineation of the geometry of nodes in the alps dinarides hinge zone and recognition of seismogenic nodes m 6 we introduce a new method based on the analysis of the topographical alignments and used to delineate the structural boundaries of the nodes which permits the definition of relatively narrow earthquake prone areas by the pattern recognition approach the structurally bounded nodes capable of earthquakes with m 6 0 identified with pattern recognition in fact cover a significantly smaller area of the study region as compared with that defined by gorshkov et al 2004 who used conventional circles the proposed method thus improves the precision in the location of potential large earthquakes

subducted seafloor relief stops rupture in south american great earthquakes implications for rupture behaviour in the 2010 maule chile earthquake great subduction earthquakes cause destructive surface deformation and ground shaking over hundreds of kilometres their rupture length is limited by the characteristic strength of the subduction plate interface and by lateral variations in its mechanical properties it has been proposed that subduction of topographic features such as ridges and seamounts can affect these properties and stop rupture propagation but the required relief and physical mechanisms of topographic rupture limitation are not well understood here we show that the rupture limits of thirteen historic great earthquakes along the south america nazca plate margin are strongly correlated with subducted topography with relief 1000 m including the juan fernandez ridge the northern limit of rupture in the mw 8 8 maule chile earthquake of 27 february 2010 is located where this ridge subducts analysis of intermediate magnitude earthquakes shows that in most places the subduction of high seafloor relief creates weak aseismic zones at the plate interface which prevent rupture propagation but that the juan fernandez ridge is associated with a locally strong plate interface the maximum rupture length and thus magnitude of great subduction earthquakes is therefore determined by the size and lateral spacing of topographic features where they are present on the subducting plate

the mw 8 1 antofagasta north chile earthquake of july 30 1995 first results from teleseismic and geodetic data a strong mw 8 1 subduction earthquake occurred on july 30 1995 in antofagasta northern chile this is one of the largest events during this century in the region it ruptured the southernmost portion of a seismic gap between 18 s and 25 s in 1992 we had used gps to survey a network with about 50 benchmarks covering a region nearly 500 km long n s and 200 km wide e w part of these marks were re surveyed with gps after the 1995 earthquake comparison with 1992 positions indicate relative horizontal displacement towards the trench reaching 0 7 m the inland subsided several decimeters the mejillones peninsula was uplifted by more than 15 cm teleseismic body wave modelling of vbb records gives a subduction focal mechanism and source time function with three distinct episodes of moment release and southward directivity modelling the displacement field using a dislocation with uniform slip in elastic half space suggests a rupture zone with 19 24 eastward dip extending to a depth no greater than 50 km with n s length of 180 km and an average slip of about 5 m the component of right lateral slip inferred both from the teleseismic and geodetic data does not require slip partitioning at the plate boundary that the well constrained northern end of the 1995 rupture zone lies under the southern part of the mejillones peninsula increases the probability for a next rupture in the gap north of it

correlating variations of b values and crustal deformations during the 1990s may have pinpointed the rupture initiation of the mw 7 4 izmit earthquake of 1999 august 17 summary the b value increases from 1 1 along straight segments to 1 7 along a releasing bend of the north anatolian fault system between 30 1 e and 30 8 e the tensional nature of the bend is corroborated by extension rates of 0 3 strain yr 1 as obtained from global positioning system gps data fault plane solutions in this area change from abundant right lateral strike slip to oblique slip with normal components in the central part of the bend compatible with the formation of a pull apart basin we suggest that this crustal volume is highly fractured corresponding to a short mean crack length due to the superposition of horizontal and normal faulting as a consequence of low normal stress on the existing cracks frictional sliding is assumed to be the predominant mechanism for the generation of seismic events resulting in high b values the lowest b values b 0 8 in the area investigated are found at the junction between the fault bend and the adjoining segment which runs through the epicentre of the 1999 izmit earthquake at the junction a localized stress concentration is expected from numerical models of seismicity along geometrical barriers thus the site of lowest b has been considered to be the most likely place for a major earthquake a conclusion that is confirmed by the izmit earthquake with epicentre located about 13 km from the anticipated site in early 1992 the spatially averaged b value started to increase along the central and northwestern parts of the fault bend and there was a corresponding period of intensified horizontal extension since no large earthquake was recorded in 1992 it is assumed that the anomalous extension and the associated change in stress have been caused by aseismic fault creep in view of the available seismotectonic information surface displacements due to a slow dislocation at depth were calculated the gps data are reasonably explained by a source of normal fault type at a depth of 10 km and equivalent magnitude mw 5 9 stress changes at seismogenic depths are calculated under the assumption that an increase in b is most likely to be observed along those segments where both deviatoric and mean stress are reduced while the coulomb stress change is positive that is the fault is brought closer to failure for right lateral strike slip the stress condition is fulfilled at the sites of the largest b value increase the surface rupture of the izmit earthquake is associated with known fault traces only in the west and in the east of the study area along the fault bend it detaches itself from mapped fault traces and runs through the regions of positive coulomb stress change caused by the inferred 1992 slow event maximum surface slip 5 m is observed in the immediate vicinity of sites of maximum coulomb stress change 3 bar indicating that the 1992 event could have partially unclamped the rupture plane of the subsequent izmit earthquake we propose that the strong differences in b observed along the complex fault bend can be used to characterize different states of tectonic deformation in space and time

clay mineralogy and geochemistry and their palaeoclimatic interpretation of the pleistocene deposits in the xuancheng section southern china a red soil profile in xuancheng anhui province southern china in the middle to lower reaches of the yangtze river was investigated using x ray diffraction x ray fluorescence spec trometer and scanning electron microscopy the mobile components k2o and na2o and trace elements ba and sr of the xuancheng section exhibit a general trend of decrease downward along the red soil profile together with an increase downward of chemical index of alteration cia values suggesting more intense depletion in the lower portion than in the upper portion the major components sio2 a l 2o3 and fe2o3 as well as sio2 al2o3 sio2 fe2o3 and al2o3 fe2o3 ratios show notable fluctuations along the soil profile indicating intense climatic oscillations in the area during the pleistocene age the clay mineral assemblage of the xuancheng section can be generally subdivided into three groups suggesting a general trend of three stages of climate changes the lower portion of 10 4 6 3 m depth has a lower illite content and higher abundance of kaolinite and illite smectite i s clays indicating that a warm and wet climate prevailed over the episode of ca 600 350 ka bp a decrease in abundance of kaolinite and i s clays and increase in illite content at a depth of 6 3 2 2 m probably indicate a transition stage of climate change from warm humid to cool dry in the period ca 350 80 ka bp the higher illite content and lower abundance of kaolinite and i s clays in the upper portion of 2 2 0 m depth suggest that a relatively cool and dry climate dominated since ca 80 ka bp based on changes in clay mineralogy and chemical indices of the sediments seven warm cold fluctuations were determined in the area since the middle pleistocene climate changes documented in the xuancheng section are in agreement with the d 18 o records of sediments from the equatorial pacific core v28 238 and the loess palaeosol sequences in the loess plateau of northwestern china correlated to the episode of s4 and s5 soil units in the loess plateau the period of ca 600 350 ka bp in the xuancheng area was dominated by the particularly strong east asia summer monsoon as indicated by its most abundant kaolinite and i s clays fluctuations in clay mineralogy along the xuancheng soil profile were mainly controlled by both the east asia summer and winter monsoons in response to the global changes in the middle late pleistocene copyright 2009 john wiley sons ltd

the critical role of climate and saprolite weathering in landscape evolution landscapes evolve in response to external forces such as tectonics and climate that influence surface processes of erosion and weathering internal feedbacks between erosion and weathering also play an integral role in regulating the landscapes response our understanding of these internal and external feedbacks is limited to a handful of field based studies only a few of which have explicitly examined saprolite weathering here we report rates of erosion and weathering in saprolite and soil to quantify how climate influences denudation by focusing on an elevation transect in the western sierra nevada mountains california we use an adapted mass balance approach and couple soil production rates from the cosmogenic radionuclide crn 10be with zirconium concentrations in rock saprolite and soil our approach includes deep saprolite weathering and suggests that previous studies may have underestimated denudation rates across similar landscapes along the studied climate gradient chemical weathering rates peak at middle elevations 1200 2000 m averaging 112 3 9 7 t km 2 y 1 compared to high and low elevation sites 46 8 5 2 t km 2 y 1 measured weathering rates follow similar patterns with climate as those of predicted silica fluxes modeled using an arrhenius temperature relationship and a linear relationship between flux and precipitation furthermore chemical weathering and erosion are tightly correlated across our sites and physical erosion rates increase with both saprolite weathering rates and intensity unexpectedly saprolite and soil weathering intensities are inversely related such that more weathered saprolites are overlain by weakly weathered soils these data quantify exciting links between climate weathering and erosion and together suggest that climate controls chemical weathering via temperature and moisture control on chemical reaction rates our results also suggest that saprolite weathering reduces bedrock coherence leading to faster rates of soil transport that in turn decrease material residence times in the soil column and limit soil weathering copyright 2009 john wiley sons ltd

mapping the frequency magnitude distribution in asperities an improved technique to calculate recurrence times we hypothesize that highly stressed asperities may be defined by mapping anomalously low b values along the san andreas fault near parkfield the asperity under middle mountain with its b 0 46 can be distinguished from all other parts of the fault surface likewise along the calaveras fault the northern asperity of the morgan hill 1984 m6 2 rupture can be identified by its low b of 0 5 as a high stress patch along the fault we add further evidence to the observations that the b value of the frequency magnitude relationship of earthquakes is inversely proportional to stress by showing that it decreases with depth in the parkfield segment of the san andreas and along the calaveras fault in both of these areas b values above and below 5 km depth are 1 2 and 0 8 respectively we propose that probabilistic recurrence times tr based on the seismicity parameters a and b should be calculated from their values within asperities only instead of from the values of the entire rupture area of the maximum expected earthquake the strong patches on faults control the time of rupture because they are capable of accumulating larger stresses than the rest of the fault zone which slips along passively when an asperity breaks therefore no information on tr is contained in the passive fault segments only in the asperities at parkfield the probabilistic estimates of tr derived from the data in the whole rupture and in the asperity only are 72 18 24 and 23 12 18 years respectively compared to the historically observed repeat time of 22 years at morgan hill the tr estimates are 122 46 76 and 78 47 110 years respectively compared to the observed repeat time of 72 years

climatic and tectonic controls on weathering in south china and indochina peninsula clay mineralogical and geochemical investigations from the pearl red and mekong drainage basins 1 results of clay mineralogy major element geochemistry and sr and nd isotopes in 93 argillaceous samples collected from drainage basins of the pearl red and mekong rivers reveal different degrees of chemical weathering in southeast asia despite similar climate conditions across these regions the kaolinite illite ratio illite chemistry index and illite crystallinity can be used as indicators of chemical weathering intensity these mineralogical proxies combined with the k2o na2o cao molar ratio chemical index of alteration cia and weathering trends observed from major element results indicate intensive silicate weathering in the pearl river basin moderate to intensive in the mekong river basin and moderate in the red river basin although a significant modification of epsilon nd 0 values in our riverine sediments during chemical weathering and transport is unlikely sr 87 sr 86 ratios are controlled by various states of chemical weathering of high sr minerals such as plagioclase rich in na and ca with a linear decrease trend from the pearl mekong to red river basins our results suggest that it is not the warm climate with heavy monsoon precipitation but tectonics playing the most significant role in controlling weathering and erosion processes in south china and indochina peninsula strong physical erosion caused by tectonic activities and river incision along the eastern margin of the tibetan plateau and along the red river fault system is responsible for high contents of primary minerals in the lowlands of red and mekong river basins

strong tectonic and weak climatic control of long term chemical weathering rates the relationships among climate physical erosion and chemical weathering have remained uncertain because long term chemical weathering rates have been difficult to measure here we show that long term chemical weathering rates can be measured by combining physical erosion rates inferred from cosmogenic nuclides with dissolution losses inferred from the rock to soil enrichment of insoluble elements we used this method to measure chemical weathering rates across 22 mountainous granitic catchments that span a wide range of erosion rates and climates chemical weathering rates correlate strongly with physical erosion rates but only weakly with climate implying that by regulating erosion rates tectonic uplift may significantly accelerate chemical weathering rates in granitic landscapes

local earthquake tomography of shallow subduction in north chile a combined onshore and offshore study selected travel time data from the aftershock series of the great antofagasta earthquake m w 8 0 have been inverted simultaneously for both hypocenter locations and three dimensional v p and v p v s struc ture the data were collected with a dense 44 station seismic network including ocean bottom hydrophones we performed a series of inversions with increasing complexity 1 d 2 d and 3 d this approach was cho sen to account for the heterogeneous seismicity distribution and to obtain a smooth regional model in areas of low resolution special efforts were made to assess the solution quality including standard resolution esti mates and tests with synthetic travel times the subducted plate is imaged between 20 and 50 km in depth as an eastward dipping high v p feature high v p v s ratios within the oceanic crust possibly indicate elevated fluid content underplating of material eroded close to the trench is found beneath the mejillones peninsula the lower crust of the overlying plate is characterized by an average v p of 6 8 6 9 km s and an average to low v p v s ratio large areas of anomalously high v p are found in the lower crust south of the city of antofagasta they are interpreted as remants of magmatic intrusions a zone of high v p v s ratios is found within the rup ture area of the antofagasta main shock just above the subducted slab its location within the region of high est stress release from the main shock suggests that the main shock rupture causes the high v p v s ratio the high v p v s ratio could indicate postseismic fluid migration from the subducted oceanic crust into the overly ing lower crust

full moment tensor retrieval for two earthquake swarms at the alps dinarides junction summary we present the results of the analysis for the seismic source tensor of all events with m d 3 0 belonging to the moggio udinese swarm 1988 february eight events analysed and of the three events of the swarm that occurred between 1993 july 22 and 26 in the tricesimo area the latter sequence is particularly relevant for the assessment of seismic risk of friuli northeast italy since it is close to the densely populated area of udine we use a waveform inversion algorithm which allows us to retrieve the moment tensor rate functions mtrfs that can be factored into a moment tensor and a source time function stf from the orientation of the p axis and of the nodal planes we can hypothesize that the moggio udinese swarm p axis orientated globally between southeast northwest and east west reflects the influence of both the southeastern alpine and external dinaric stress field while in the tricesimo swarm in which the p axis orientations varies between southeast northwest and north south the southeastern alpine stress field seems to act on faults oriented southeast northwest belonging to the external dinaric system

statistical empirical index of chemical weathering in igneous rocks a new tool for evaluating the degree of weathering abstract chemical weathering indices are useful tools in characterizing weathering profiles and determining the extent of weathering however the predictive performance of the conventional indices is critically dependent on the composition of the unweathered parent rock to overcome this limitation the present paper introduces an alternative statistical empirical index of chemical weathering that is extracted by the principal component analysis pca of a large dataset derived from unweathered igneous rocks and their weathering profiles the pca analysis yields two principal components pc1 and pc2 which capture 39 23 and 35 17 of total variability respectively the extent of weathering is reflected by variation along pc1 primarily due to the loss of na 2 o and cao during weathering in contrast pc2 is the direction along which the projections of unweathered felsic intermediate and mafic igneous rocks appear to be best discriminated therefore pc1 and pc2 represent independent latent variables that correspond to the extent of weathering and the chemistry of the unweathered parent rock subsequently pc1 and pc2 were then mapped onto a ternary diagram mfw diagram the m and f vertices characterize mafic and felsic rock source respectively while the w vertex identifies the degree of weathering of these sources independent of the chemistry of the unweathered parent rock the w index has a number of significant properties that are not found in conventional weathering indices first the w index is sensitive to chemical changes that occur during weathering because it is based on eight major oxides whereas most conventional indices are defined by between two and four oxides second the w index provides robust results even for highly weathered sesquioxide rich samples third the w index is applicable to a wide range of felsic intermediate and mafic igneous rock types finally the mfw diagram is expected to facilitate provenance analysis of sedimentary rocks by identifying their weathering trends and thereby enabling a backward estimate of the composition of the unweathered source rock

thrust type subduction zone earthquakes and seamount asperities a physical model for seismic rupture a thrust type subduction zone earthquake of m sub w 7 6 ruptures an area of approximately 6 000 km sup 2 has a seismic slip of approximately 1 m and is nucleated by the rupture of an asperity approximately 25km across a model for thrust type subduction zone seismicity is proposed in which basaltic seamounts jammed against the base of the overriding plate act as strong asperities that rupture by stick slip faulting a m sub w 7 6 event would correspond to the near basal rupture of a approximately 2 km tall seamount the base of the seamount is surrounded by a low shear strength layer composed of subducting sediment that also deforms between seismic events by distributed strain viscous flow planar faults form in this layer as the seismic rupture propagates out of the seamount at speeds of kilometers per second the faults in the shear zone are disrupted after the event by aseismic slow viscous flow of the subducting sediment layer consequently the extent of fault rupture varies for different earthquakes nucleated at the same seamount asperity because new fault surfaces form in the surrounding subducting sediment layer during each fast seismic rupture

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

weathering of the ganga alluvial plain northern india implications from fluvial geochemistry of the gomati river abstract in the northern part of the indian sub continent the ganga alluvial plain gap feeds its weathering products to the ganga brahmaputra river system one of the world s largest fluvial systems the authors present a geochemical study of the gap weathering products transported by the gomati river the ganga river tributary to understand weathering processes of an alluvial plain in a humid sub tropical climate a total of 28 sediment samples were collected during the monsoon season and were analysed by x ray fluorescence spectrometry for 25 major and trace elements bulk chemistry of the channel flood and suspended sediments mostly consists 90 80 and 75 respectively of three elements al si and fe major element concentrations normalised with respect to upper continental crust ucc show strong depletion of highly mobile elements na ca and enrichment of immobile elements ti si silica enrichment in the sand fraction is probably caused by chemical weathering of feldspar mineral sorting during fluvial transportation acts as the single important factor that controls the geochemistry of these weathering products and also strongly influences major and trace element distribution in the individual sediment samples trace element ba cr cu nb ni pb v and zn concentrations were strongly correlated with major element si al fe mn and k concentrations indicating that the abundance of trace elements is controlled by the same processes that control the major element distribution in these sediments the gap weathering products were geochemically distinguished as arkose to litharenite in rock classification chemical mobility normalised with respect to tio 2 in ucc indicates that si na zr ba and sr mainly derived from feldspar muscovite and biotite are lost during weathering iron and zn remained immobile during weathering and were strongly adsorbed by phyllosilicates and concentrated in fine grained sediment fractions the chemical index of alteration indicates that the gap has experienced chemical weathering of incipient to moderate intensity the gap weathering products also demonstrated a progressive incomplete alteration in the alluvial sequence made up of the himalayan derived sediments a model has been proposed to better understand weathering processes and products of the gap in temporary storage of 50 ka in a humid sub tropical climate

seismogenic plane of the northern andean subduction zone from aftershocks of the antofagasta chile 1995 earthquake 1 a temporary seismological network which was located in the antofagasta northern chile region recorded a large part of the aftershocks from a mw 8 0 earthquake in 1995 results from a tomographic inversion show that the aftershocks were concentrated in a plane approximately 3 km thick spatial zone comparison of our results with earlier processed wide angle reflection data shows clearly that this zone is positioned at the top of the oceanic crust therefore it represents the shearing boundary between the subducting oceanic and the continental plate and gives an in situ estimation of the thickness of the boundary outside of this zone events were detected in the continental crust as well as within the oceanic mantle

seismic coupling along the chilean subduction zone underthrusting at subduction zones can cause large earthquakes at shallow depths but is accommodated by aseismic creep below a certain depth the maximum depth of the seismically coupled zone or seismogenic zone is a transition from unstable to stable sliding we have determined the maximum depth of the coupled zone and its variability along the chilean subduction zone the maximum depth of seismic coupling is defined by the depth of large m 6 underthrusting earthquakes that have occurred at the downdip edge of the coupled plate interface earthquake depth is determined with omnilinear waveform inversion of long period p waves the statistical uncertainty in the depth is estimated using bootstrapping omnilinear inversion formally accounts for the scaling incompatibility between the p waveforms and decreases the uncertainty in the depth estimate we have found the depths of 27 earthquakes in the time period from 1961 to 1987 seismic coupling in chile extends down to 48 53 km there is a resolvable change in the maximum depth of coupling around 28 s the region immediately north of this latitude has a coupled zone that extends no deeper than 36 41 km while south of this latitude coupling extends down to 48 53 km this transition is not simply related to the oceanic lithospheric age and plate convergence rate but coincides with a change in several geophysical and geological phenomena with respect to shallower north and deeper south coupling there is a change from active volcanos to no volcanos the dip of the deep slab changes from steep to shallow the thickness of trench sediments changes from thin to thick and the depth of the oceanic basement changes from deeper to shallower at 28 s due to the multiplicity of changes at 28 s there is no clear unique interpretation of what physical mechanism controls the variability in the maximum depth of the seismically coupled zone in chile

climatic and tectonic controls on chemical weathering in the new zealand southern alps abstract climatic and tectonic controls on the relative abundance of solutes in streams draining the new zealand southern alps were investigated by analyzing the elemental and sr isotope geochemistry of stream waters bedload sediment and hydrothermal calcite veins the average relative molar abundance of major cations and si in all stream waters follows the order ca2 50 si 22 na 17 mg2 6 k 5 for major anions the relative molar abundance is hco3 89 so42 7 cl 4 weathering reactions involving plagioclase and volumetrically small amounts of hydrothermal calcite define the ionic chemistry of stream waters but nearly all streams have a carbonate dominated ca2 and hco3 mass balance stream water ca sr and 87sr 86sr ratios vary from 0 173 to 0 439 mol nmol and from 0 7078 to 0 7114 respectively consistent with the ionic budget these ratios lie solely within the range of values measured for bedload carbonate ca sr 0 178 to 0 886 mol nmol 87sr 86sr 0 7081 to 0 7118 and hydrothermal calcite veins ca sr 0 491 to 3 33 mol nmol 87sr 86sr 0 7076 to 0 7097 streams draining regions in the southern alps with high rates of physical erosion induced by rapid tectonic uplift and an extremely wet climate contain 10 more ca2 and 30 more sr2 from carbonate weathering compared to streams draining regions in drier more stable landscapes similarly streams draining glaciated watersheds contain 25 more sr2 from carbonate weathering compared to streams draining non glaciated watersheds the highest abundance of carbonate derived solutes in the most physically active regions of the southern alps is attributed to the tectonic exhumation and mechanical denudation of metamorphic bedrock which contains trace amounts of calcite estimated to weather 350 times faster than plagioclase in this environment in contrast regions in the southern alps experiencing lower rates of uplift and erosion have a greater abundance of silicate versus carbonate derived cations these findings highlight a strong coupling between physical controls on landscape development and sources of solutes to stream waters using the southern alps as a model for assessing the role of active tectonics in geochemical cycles this study suggests that rapid mountain uplift results in an enhanced influence of carbonate weathering on the dissolved ion composition delivered to seawater