mechanics of low stress forearcs nankai and cascadia the nankai and cascadia subduction zones have low stress forearcs where the margin normal horizontal compressive stress is similar to or less than the vertical stress except in the accretionary prisms in the absence of active back arc spreading the forearc margin normal stress is controlled mainly by the total shear force along the subduction fault or the plate coupling force and the gravitational force the plate coupling force creates compression and the gravitational force in the presence of margin topography creates lateral tension we give a simple expression that relates the forearc stress to topography and average fault strength with the latter represented by an effective coefficient of friction we also use a finite element model of two converging plates in frictional contact to model the forearc stresses the analyses indicate that a low stress forearc requires not only the subduction fault to be very weak but also the mechanically coupled fault area to be narrow in the downdip direction and shallow in depth for nankai and cascadia where the coupled fault areas are narrow and shallow because of the young and hot subducting plates is about 0 05 or less and in any case less than 0 09 the low fault strength is probably not a unique property of low stress forearcs since the same low values combined with wider and deeper coupled areas can be shown to create large margin normal compression in addition there does not seem to be any relation between subduction earthquake magnitudes and plate coupling forces great earthquakes occur at subduction zones having low stress forearcs such as nankai and cascadia

splay fault activity revealed by aftershocks of the 2010 mw 8 8 maule earthquake central chile splay faults large thrust faults emerging from the plate boundary to the seafloor in subduction zones are considered to enhance tsunami generation by transferring slip from the very shallow dip of the megathrust onto steeper faults thus increasing vertical displacement of the seafloor these structures are predominantly found offshore and are therefore difficult to detect in seismicity studies as most seismometer stations are located onshore the mw moment magnitude 8 8 maule earthquake on 27 february 2010 affected 500 km of the central chilean margin in response to this event a network of 30 ocean bottom seismometers was deployed for a 3 month period north of the main shock where the highest coseismic slip rates were detected and combined with land station data providing onshore as well as offshore coverage of the northern part of the rupture area the aftershock seismicity in the northern part of the survey area reveals for the first time a well resolved seismically active splay fault in the submarine forearc application of critical taper theory analysis suggests that in the northernmost part of the rupture zone coseismic slip likely propagated along the splay fault and not the subduction thrust fault while in the southern part it propagated along the subduction thrust fault and not the splay fault the possibility of splay faults being activated in some segments of the rupture zone but not others should be considered when modeling slip distributions

coesite and pure pyrope in high grade blueschists of the western alps a first record and some consequences a pyrope quartzite originally described by vialon 1966 from the dora maira massif was resampled and reinvestigated garnet up to 25 cm in size phengite kyanite talc and rutile are in textural equilibrium in an undeformed matrix of polygonal quartz the garnet is a pyrope almandine solid solution with 90 to 98 mol mg end member it contains inclusions of coesite which has partially inverted to quartz resulting in a typical radial cracking of the host garnet around the inclusions several lines of evidence show that coesite crystallised under nearly static pressure conditions and that the whole matrix has once been coesite

kinematic models of dewatering accretionary prisms steady state two dimensional analytical solutions are derived for sediment velocity and rate of fluid expulsion in a thickening accretionary prism with smooth upper and lower surfaces two different kinematic assumptions lead to two similar sets of solutions in one case the sediment flow lines are assumed to diverge uniformly landward in the other case the horizontal velocity of any given sediment column is assumed uniform by further assuming zero horizontal darcy velocity in the prism expressions can be obtained for the approximate vertical fluid velocity and pore fluid pressure fields results from applying these solutions to the cascadia accretionary prism off vancouver island show the importance of modeling the effects of lateral as well as vertical porosity variation on the hydrogeology of the prism these solutions provide a means to estimate fluid flow and pore pressure distribution for prisms with realistic geometry the rate of fluid expulsion can also be incorporated into numerical models as the fluid source term

convergence rate across the nepal himalaya and interseismic coupling on the main himalayan thrust implications for seismic hazard we document geodetic strain across the nepal himalaya using gps times series from 30 stations in nepal and southern tibet in addition to previously published campaign gps points and leveling data and determine the pattern of interseismic coupling on the main himalayan thrust fault mht the noise on the daily gps positions is modeled as a combination of white and colored noise in order to infer secular velocities at the stations with consistent uncertainties we then locate the pole of rotation of the indian plate in the itrf 2005 reference frame at longitude 1 34 3 31 latitude 51 4 0 3 with an angular velocity of 0 5029 0 0072 myr the pattern of coupling on the mht is computed on a fault dipping 10 to the north and whose strike roughly follows the arcuate shape of the himalaya the model indicates that the mht is locked from the surface to a distance of approximately 100 km down dip corresponding to a depth of 15 to 20 km in map view the transition zone between the locked portion of the mht and the portion which is creeping at the long term slip rate seems to be at the most a few tens of kilometers wide and coincides with the belt of midcrustal microseismicity underneath the himalaya according to a previous study based on thermokinematic modeling of thermochronological and thermobarometric data this transition seems to happen in a zone where the temperature reaches 350 c the convergence between india and south tibet proceeds at a rate of 17 8 0 5 mm yr in central and eastern nepal and 20 5 1 mm yr in western nepal the moment deficit due to locking of the mht in the interseismic period accrues at a rate of 6 6 0 4 10 19 nm yr on the mht underneath nepal for comparison the moment released by the seismicity over the past 500 years including 14 m w 7 earthquakes with moment magnitudes up to 8 5 amounts to only 0 9 10 19 nm yr indicating a large deficit of seismic slip over that period or very infrequent large slow slip events no large slow slip event has been observed however over the 20 years covered by geodetic measurements in the nepal himalaya we discuss the magnitude and return period of m 8 earthquakes required to balance the long term slip budget on the mht

shear stresses on megathrusts implications for mountain building behind subduction zones 1 shear stresses on a subduction megathrust play an important role in determining the forces available for mountain building adjacent to a subduction zone in this study the temperatures and shear stresses on megathrusts in 11 subduction zones around the pacific rim hikurangi tonga izu ogasawara western nankai northeastern japan aleutians western alaska cascadia northern chile southern chile and se asia northern sumatra have been determined the main constraint is that vertical normal stresses beneath the highlands behind the subduction zone are nearly equal to horizontal normal stresses in the plane of a trench or arc normal section for a typical brittle and ductile megathrust rheology frictional shear stress gz for depth z and ductile shear stress a exp b rt at temperature t where a b are rheological parameters treated as constants rheological constants common to all the megathrusts crust mantle b are determined by simultaneously solving for the force balance in the overlying wedge and megathrust thermal structure using a simplex minimization algorithm taking account of the induced mantle corner flow at depth 65 15 km 2 and constant radiogenic heating 0 65 0 3 w m 3 2 throughout the crust the a constants are solved individually for each subduction zone assuming that the maximum depth of interplate slip earthquakes marks the brittle ductile transition the best fit solution shows two groupings of megathrusts with most subduction zones having a low mean shear stress in the range 7 15 mpa crust 0 032 0 006 mantle 0 019 0 004 and unable to support elevations 2 5 km for a typical frictional sliding coefficient 0 5 the low effective coefficients of friction suggest high pore fluid pressures at 95 lithostatic pressure tonga and northern chile require higher shear stresses with crust 0 095 0 024 mantle 0 026 0 007 suggesting slightly lower pore fluid pressures at 81 lithostatic ductile shear in the crust is poorly resolved but in the mantle appears to show a strong power law dependency with b 36 18 kj mol 1 amantle values are sensitive to the precise value of b but are in the range 1 20 kpa the power law exponent n for mantle flow is poorly constrained but is likely to be large n 4 the brittle ductile transition in the crust occurs at temperatures in the range 370 c 512 c usually close to the base of the crust and in the mantle at much lower temperatures 180 c 300 c possibly reflecting a marked change in pore fluid pressure or quasi ductile and subfrictional properties in subduction zones where the subducted slab is older than 50 ma a significant proportion of the integrated shear force on the megathrust is taken up where it cuts the mantle and temperatures are 300 c in much younger subduction zones the stress transmission is confined mainly to the crust the shear stresses particularly in the crust may be kept low by some sort of lubricant such as abundant water rich trench fill which lowers the frictional sliding coefficient or effective viscosity and or raises pore fluid pressure the unusual high stress subduction zone in northern chile lacks significant trench fill and may be poorly lubricated with a mean shear stress 37 mpa required to support elevations 4 km in the high andes however where the crust is thin in sediment starved and poorly lubricated subduction zones such as tonga the mean shear stress will still be low sediment may lubricate megathrusts accommodating underthrusting of continental crust such as in the himalayas or eastern central andes which have a low mean shear stress 15 mpa

fuzzy based spatial modeling approach to predict island karst distribution a conceptual model previous studies have shown that island karst could successfully indicate paleoclimate change in the quaternary period however because of the relative inaccessibility of carbonate islands and their rural settings the exploration of island karst features has been limited to enhance future research remote sensing and geospatial modeling were used in this study to improve the island karst exploration record the results showed that fuzzy based spatial modeling could successfully predict the island karst distributions on a simple carbonate island the accuracy of the model was above 90 this method could apply to other coastal karst regions and carbonate islands in the future

coastal and inland karst morphologies driven by sea level stands a gis based method for their evaluation sea level is the base level for groundwater circulation in coastal aquifers the evolution of karst surface landforms and subsurface drainage systems in these aquifers has been conditioned in geological time by tectonics and glacio eustatic sea level changes present morpho structural settings and the type distribution of karst surface and subsurface forms have developed in different carbonate formations according to differences in lithology climate and exposure time all driving the intensity of morphologic and karst processes the repeated and significant changes of groundwater level linked to sea level changes have had the most important role in driving the continuous evolution of karstic drainage systems and has resulted in most cases in a multiphase karst this study aims at defining a general method for identifying in karst coastal settings the elevations of flat or low topographic gradient surfaces using morphometric analysis of digital elevation models dems and geographical information systems giss and their comparison with elevations of distinctive karstic levels passages lateral solution cavities observed in vertical shafts and horizontal caves of the elevations of flat or low topographic gradient surfaces only those agreeing within 10 m or 20 m with elevation ranges marked by the high frequency of distinctive karst levels were considered as representative of the more probable past sea level stands the method is applied to a regional coastal carbonate formation in southern italy by using a 10 m dem and information on 140 complex caves and 85 shafts of the 15 elevations indicated by dem analysis 620 600 470 450 425 385 355 315 270 250 205 180 150 110 and 70 m above sea level a s l 13 match clearly those highlighted by significant frequencies of distinctive karstic levels these elevations are validated by comparison to the elevation of terraces and karst plains indicated in the literature copyright 2012 john wiley sons ltd

inferences on sediment strength and fault friction from structures at the aleutian trench the structural relations of conjugate thrust faults and the master decollement imaged in a research level processed multichannel seismic reflection record across the eastern aleutian trench allow quantitative estimates of the sediment strength and friction across thrust boundaries of the subduction zone these estimates are derived from geometric relations between faults and from the overall geometry of accreted prisms they suggest the presence of high pore fluid pressures that result in low levels of friction along a master decollement and on the main bounding thrust faults in the accreted sediment therefore coupling in the immediate trench area apparently does not contribute significantly to the generation of horizontal compression upslope

high precision mass spectrometric uranium series dating of cave deposits and implications for palaeoclimate studies calcite deposits in caves known as speleothem can provide valuable palaeoenvironmental information1 4 in particular because speleothem are deposited only in air filled caves gaps in deposition in coastal caves record high stands of sea level here we report the use of isotope dilution mass spectrometry to date speleothem by the uranium series method the use of mass spectrometry in uranium series dating was first applied to corals5 and has greatly improved the precision of this dating method the speleothem dated here a flowstone from 15 m below modern sea level in a bahamian cave records changes in sea level over the past 280 000 years the dated hiatuses in deposition indicate high sea level stands that are in general agreement with data from deep sea oxygen isotope stratigraphy6 and other estimates for the timing of high stands and glacial minima1 3 7

revealing the deep structure and rupture plane of the 2010 maule chile earthquake mw 8 8 using wide angle seismic data the 27 february 2010 maule earthquake mw 8 8 ruptured 400 km of the nazca south america plate boundary and caused hundreds of fatalities and billions of dollars in material losses here we present constraints on the fore arc structure and subduction zone of the rupture area derived from seismic refraction and wide angle data the results show a wedge shaped body 40 km wide with typical sedimentary velocities interpreted as a frontal accretionary prism fap landward of the imaged fap the velocity model shows an abrupt velocity contrast suggesting a lithological change which is interpreted as the contact between the fap and the paleo accretionary prism backstop the backstop location is coincident with the seaward limit of the aftershocks defining the updip limit of the co seismic rupture and seismogenic zone furthermore the seaward limit of the aftershocks coincides with the location of the shelf break in the entire earthquake rupture area 33 s 38 5 s which is interpreted as the location of the backstop along the margin published seismic profiles at the northern and southern limit of the rupture area also show the presence of a strong horizontal velocity gradient seismic backstop at a distance of 30 km from the deformation front the seismic wide angle reflections from the top of the subducting oceanic crust constrain the location of the plate boundary offshore dipping at 10 the projection of the epicenter of the maule earthquake onto our derived interplate boundary yielded a hypocenter around 20 km depth this implies that this earthquake nucleated somewhere in the middle of the seismogenic zone neither at its updip nor at its downdip limit

lithologic mapping in the mountain pass california area using advanced spaceborne thermal emission and reflection radiometer aster data abstract evaluation of an advanced spaceborne thermal emission and reflection radiometer aster image of the mountain pass california area indicates that several important lithologic groups can be mapped in areas with good exposure by using spectral matching techniques the three visible and six near infrared bands which have 15 m and 30 m resolution respectively were calibrated by using in situ measurements of spectral reflectance calcitic rocks were distinguished from dolomitic rocks by using matched filter processing in which image spectra were used as references for selected spectral categories skarn deposits and associated bright coarse marble were mapped in contact metamorphic zones related to intrusion of mesozoic and tertiary granodioritic rocks fe muscovite which is common in these intrusive rocks was distinguished from al muscovite present in granitic gneisses and mesozoic granite quartzose rocks were readily discriminated and carbonate rocks were mapped as a single broad unit through analysis of the 90 m resolution five band surface emissivity data which is produced as a standard product at the eros data center three additional classes resulting from spectral angle mapper processing ranged from 1 a broad granitic rock class 2 to predominately granodioritic rocks and 3 a more mafic class consisting mainly of mafic gneiss amphibolite and variable mixtures of carbonate rocks and silicate rocks

using alsm to map sinkholes in the urbanized covered karst of pinellas county florida 1 methodological considerations comparison of a database of interpreted sinkholes made using airborne laser swath mapping alsm with databases of sinkholes made from interpretation of aerial photographs reveals substantial disagreement the discrepancies involve the location number areas and circularity of interpreted sinkholes methodological factors that contribute to the discrepancies include blockage of alsm laser returns in thick vegetation multi path reflections and misrepresentation of the true extent of sinkholes comparison of two alsm derived databases made 1 independently from versus 2 in combination with earlier air photo analysis in undeveloped regions had the following result one fourth of the sinkholes interpreted by using the composite method were missed by the independent analysis and one third of the sinkholes that were interpreted from the independent analysis were not interpreted as sinkholes using the composite method subjective interpretation leads to a high level of uncertainty such that the results of the remote sensing studies are suspect if not invalid

quaternary cave levels in peninsular florida abstract the hypothesis that caves in the florida peninsula are tied to quaternary sea levels was proposed by hydrogeologists without data some 40 years ago the hypothesis is a version of glacial control of cave levels which is the logical combination of the water table theory of speleogenesis and the concept that base level positions the water table at the usa type example of glacial control of cave levels mammoth cave in the paleozoic rocks of kentucky the intermediary is base level determined by rivers by hypothesis the intermediary for florida is glacioeustatic sea level this paper presents elevation data that supports this hypothesis recent cave surveys in the air filled caves and spot elevations from archived maps reveal prominent levels of passages centered at 5 12 21 and 30 m above sea level over broad areas they do not follow the large scale structure of the floridan aquifer instead they align with nearby coastal marine terraces identified as modal peaks on frequency plots from various topographic data bases levels matching with the three highest terraces wicomico penholoway and talbott are particularly clear lower levels if they accord with sea level stands are likely composites data from cavities encountered in drilled wells e g bit drops and spot elevations from archived underwater cave maps demonstrate passage levels at depths of 15 30 70 and 90 120 m below the modern water table the depths below water table are similar to the depths below sea level of distant submerged terraces and paleoshoreline features identified using multibeam bathymetric data in the gulf of mexico the cave bit drop and terrace data are all consistent with the concept that quaternary sea level is the fundamental control on the cave scale porosity within the floridan aquifer this conclusion does not rule out the possibility that lithologically favored positions paleokarst features and confining units and mixing zones are also involved in the location of caves levels in this near coastal environment

splay fault slip during the mw 8 8 2010 maule chile earthquake splay faults are thrusts that emerge from the plate boundaries of subduction zones such structures have been mapped at several convergent margins and their activity commonly ascribed to large megathrust earthquakes however the behavior of splay faults during the earthquake cycle is poorly constrained because typically these structures are located offshore and are difficult to access here we use geologic mapping combined with space and land geodesy as well as offshore sonar data to document surface fault ruptures and coastal uplift at isla santa maria in south central chile 37 s caused by the 27 february 2010 maule earthquake m w 8 8 during the earthquake the island was tilted parallel to the margin and normal faults ruptured the surface and adjacent ocean bottom we associate tilt and crestal normal faulting with growth of an anticline above a blind reverse fault rooted in the nazca south america plate boundary which slipped during the maule earthquake the splay fault system has formed in an area of reduced coseismic plate boundary slip suggesting that anelastic deformation in the upper plate may have restrained the 2010 megathrust rupture surface fault breaks were accompanied by prominent discharge of fluids our field observations support the notion that splay faulting may frequently complement and influence the rupture of subduction zone earthquakes

stress orientations in subduction zones and the strength of subduction megathrust faults subduction zone megathrust faults produce most of the world s largest earthquakes although the physical properties of these faults are difficult to observe directly their frictional strength can be estimated indirectly by constraining the orientations of the stresses that act on them a global investigation of stress orientations in subduction zones finds that the maximum compressive stress axis plunges systematically trenchward consistently making an angle of 45 to 60 with respect to the subduction megathrust fault these angles indicate that the megathrust fault is not substantially weaker than its surroundings together with several other lines of evidence this implies that subduction zone megathrusts are weak faults in a low stress environment the deforming outer accretionary wedge may decouple the stress state along the megathrust from the constraints of the free surface

a 1000 year climate ice core record from the guliya ice cap china its relationship to global climate variability in 1992 an american chinese expedition successfully recovered three ice cores 308 6 93 2 and 34 5m from the guliya ice cap summit 6710 m a s l in the far western kunlun on the qinghai tibetan plateau china guliya resembles a polar icecap with 10 m 200 m and basal temperatures of 15 6 5 9 and 2 1 c respectively the 308 6 m core to bedrock is the longest ice core retrieved from an elevation greater than 4000 m a s l and provides the first ice core history from the western side of the qinghai plateau the plateau experiences a pronounced annual precipitation cycle during which 70 80 of annual total precipitation falls in the summer monsoon season this leads to a marked visible stratigraphy in the glaciers which allows accurate dating of the ice cores and reconstruction of the net mass accumulation this paper presents 1 the results of the geophysical program to determine ice thickness ice flow and surface topography 2 an assessment of net accumulation from stake measurements snow pits and shallow core samples and 3 the analyses of the upper 100 m of the 308 6 m core which provide a 1000 year history including the little ice age which is compared with chinese historical records extended periods of positive accumulation on guliya are closely contemporaneous with dry periods in eastern china a trans pacific teleconnection is suggested by the strong temporal coherence between extended wet and dry phases on guliya and on the quelccaya ice cap peru

initiation and development of the pennine basal thrust swiss alps a structural and geochronological study of an exhumed megathrust abstract the pennine basal thrust pbt is an exhumed megathrust developed during continental collision from late eocene to miocene to trace its evolution five samples with indications for up to three microstructurally diachronous white mica generations were investigated by laser in situ and step heating 40 ar 39 ar dating three deformation related crystallization ages can be distinguished 1 d 1 characterized in the pbt hanging wall by an s 1 foliation defined by white mica chloritoid began at or before 38 0 ma 2 d 2 formed a pervasive s 2 cleavage and synchronous white mica rich veins dated at 27 ma 3 d 3 produced an s 3 crenulation cleavage and chlorite white mica veins dated at 23 ma older ages of 96 ma footwall and 115 ma hanging wall are interpreted as minimum ages for the detrital component finally discrete faulting produced fault gouge with an illite k ar age of 19 ma a simplified back restored reconstruction provides a tectonic context for the dated structures in this framework d 1 occurred during middle to late eocene tectonic accretion after late eocene initiation of continental collision d 2 reflects oligocene top to nw shearing with both in and out of sequence thrusting d 3 then developed from 23 to 19 ma during the progressive deactivation of the pbt

toward understanding tectonic control on the mw 8 8 2010 maule chile earthquake the maule earthquake of 27th february 2010 m w 8 8 affected similar to 500 km of the nazca south america plate boundary in south central chile producing spectacular crustal deformation here we present a detailed estimate of static coseismic surface offsets as measured by survey and continuous gps both in near and far field regions earthquake slip along the megathrust has been inferred from a joint inversion of our new data together with published gps insar and land level changes data using green s functions generated by a spherical finite element model with realistic subduction zone geometry the combination of the data sets provided a good resolution indicating that most of the slip was well resolved coseismic slip was concentrated north of the epicenter with up to 16 m of slip whereas to the south it reached over 10 m within two minor patches a comparison of coseismic slip with the slip deficit accumulated since the last great earthquake in 1835 suggests that the 2010 event closed a mature seismic gap slip deficit distribution shows an apparent local overshoot that highlight cycle to cycle variability which has to be taken into account when anticipating future events from interseismic observations rupture propagation was obviously not affected by bathymetric features of the incoming plate instead splay faults in the upper plate seem to have limited rupture propagation in the updip and along strike directions additionally we found that along strike gradients in slip are spatially correlated with geometrical inflections of the megathrust our study suggests that persistent tectonic features may control strain accumulation and release along subduction megathrusts c 2012 elsevier b v all rights reserved

twentieth century climatic warming in china in the context of the holocene development of an annual mean temperature series of china for the period of ad 1880 1998 indicated that 1998 was thie wanrest year since 1880 during 1998 temperature was 1 38c higher than the normal 1961 90 annual mean temperatures of china were found using a weighted average of 10 regional series whliich covei ed the xvhole lanid ai ea of the coutliry fromii xinjiang and tibet ii the west to tailwan i the ecast gaps in temperatture obseivations were filled by using ice core i 0 and tie iing data for thice regions in the west and docuimenitary data for scven regions in the east since 1 951 only obser x ational data were usecl fiftyyear mean teiimperatture anomnalies were calculated trom the ninth to trwentietlh cernturies the series do not show any conisistenit warm peiliod in west china durinig the mediaeval warmii period ad 900 to 1300 but temiperatures in east china in at 850 1099 anid 1200 99 were abouit 0 2c higher than the average for recent years centurv mean ternperatures combin

aftershock seismicity of the 27 february 2010 mw 8 8 maule earthquake rupture zone on 27 february 2010 the mw 8 8 maule earthquake in central chile ruptured a seismic gap where significant strain had accumulated since 1835 shortly after the mainshock a dense network of temporary seismic stations was installed along the whole rupture zone in order to capture the aftershock activity here we present the aftershock distribution and first motion polarity focal mechanisms based on automatic detection algorithms and picking engines by processing the seismic data between 15 march and 30 september 2010 from stations from iris ipgp gfz and university of liverpool we determined 20 205 hypocentres with magnitudes mw between 1 and 5 5 seismic activity occurs in six groups 1 normal faulting outer rise events 2 a shallow group of plate interface seismicity apparent at 25 35 km depth and 50 120 km distance to the trench with some variations between profiles along strike the aftershocks occur largely within the zone of coseismic slip but extend 50 km further north and with predominantly shallowly dipping thrust mechanisms along dip the events are either within the zone of coseismic slip or downdip from it depending on the coseismic slip model used 3 a third band of seismicity is observed further downdip at 40 50 km depth and further inland at 150 160 km trench perpendicular distance with mostly shallow dipping 28 thrust focal mechanisms indicating rupture of the plate interface significantly downdip of the coseismic rupture and presumably above the intersection of the continental moho with the plate interface 4 a deep group of intermediate depth events between 80 and 120 km depth is present north of 36 s within the maule segment a large portion of events during the inter seismic phase originated from this depth range 5 the magmatic arc exhibits a small amount of crustal seismicity but does not appear to show significantly enhanced activity after the mw 8 8 maule 2010 earthquake 6 pronounced crustal aftershock activity with mainly normal faulting mechanisms is found in the region of pichilemu 34 5 s these crustal events occur in a 30 km wide region with sharp inclined boundaries and oriented oblique to the trench the best located events describe a plane dipping to the southwest consistent with one of the focal planes of the large normal faulting aftershock mw 6 9 on 11 march 2010

solution conduits as indicators of late quaternary sea level position abstract solution conduits or caves can provide a measure of glacio eustatic sea level position for the quaternary in high latitudes cave deposits contain artifacts fossils and sediments that reflect surface conditions with respect to climate secondary calcite deposits most notably stalagmites record growth episodes during ice minima and non growth during ice maxima they provide an indirect estimate of areal ice cover at high latitudes and are an indirect measure of sea level in low latitudes stable carbonate platforms contain caves that provide a direct measure of past sea level position solution conduits developing in a fresh water lens will record the position of the lens and therefore sea level as sea level fluctuates fresh water lens horizons and conduit development horizons will shift preserving a record of past sea level position cave wall rock and cave deposits can produce a chronology for given conduit positions secondary calcite deposits notably stalagmites record growth periods during sea level low stands or ice maxima and record growth hiatuses during flooding by sea level high stands or ice minima the inverse of high latitude stalagmites lighthouse cave san salvador island bahamas records a sea level high stand at 1 to 6 m for some time period between 85 000 and 70 000 years ago based on position and timing of conduit development and records sea level at present elevation for some time period between 49 000 and 37 000 years ago based on a stalagmite with a marine overgrowth

sea level oscillations during the last interglacial highstand recorded by bahamas corals whether sea level was stable during the last interglacial remains a subject of debate an analysis of the u th ages of coral reefs in the bahamas corrected for open system behaviour confirms the presence of at least one oscillation within the sea level highstand

miocene paleotopography of the central alps abstract reconstructing surface elevation surface uplift and relief histories is fundamental to understanding the growth of mountain ranges to explore their topographic limits and relate these to the interplay between geodynamic and earth surface processes here we aim to quantify miocene paleoelevation of the central european alps through stable isotope paleoaltimetry the novelty of our approach which renders our analysis less sensitive to past climate change is that stable isotope proxies of identical age are analyzed from both the high internal parts of the alpine orogen and the adjacent foreland basin whereas the foreland basin was at or near sea level and traces the combined effects of upstream changes in rainfall amount and composition the high alpine site additionally records the effect of elevation on stable isotopes in precipitation we compare hydrogen isotopic ratios d in mica and chlorite that interacted with meteoric water along the simplon detachment a major normal fault that developed at high elevations with meteoric water compositions deduced from carbonate bearing paleosols of the north alpine foreland basin d values of muscovite 126 and chlorite 135 from the brittle hanging wall and of recrystallized muscovite 108 and biotite 140 from adjacent footwall mylonites provide unequivocal evidence for localized syntectonic meteoric water interaction along the simplon detachment detailed 40 ar 39 ar and fission track geochronology constrains the timing of isotopic exchange to ca 14 5 ma when the footwall mylonites passed through the ductile to brittle transition age equivalent oxygen isotope ratios 18 o measured within pedogenic carbonate from north alpine foreland paleosols that developed near miocene sea level serve as our low elevation point of reference 18 o values in these paleosols dated with ca 100 ka precision vary between 19 and 25 smow with average values of 20 at ca 14 5 ma using the relative differences between meteoric water compositions in the foreland basin and the high alpine simplon detachment our isotope data are consistent with a mid miocene minimum average elevation difference of 2350 700 500 m for the simplon region our results indicate that miocene alpine elevations were at least comparable to those of today and are likely to have acted as an important barrier to atlantic derived moisture transport into central europe and eurasia since that time

accretionary prisms in subduction earthquake cycles the theory of dynamic coulomb wedge 1 we expand the theory of critically tapered coulomb wedge for accretionary prisms by considering stress changes in subduction earthquake cycles building on the coulomb plasticity of the classical theory we assume an elastic perfectly coulomb plastic rheology and derive exact stress solutions for stable and critical wedges the new theory postulates that the actively deforming most seaward part of an accretionary prism the outer wedge overlies the updip velocity strengthening part of the subduction fault and the less deformed inner wedge overlies the velocity weakening part the seismogenic zone during great earthquakes the outer wedge is pushed into a compressively critical state with an increase in basal and internal stresses and pore fluid pressure after the earthquake the outer wedge returns to a stable state the outer wedge geometry is controlled by the peak stress of the updip velocity strengthening part of the subduction fault achieved in largest earthquakes the inner wedge generally stays in the stable regime throughout earthquake cycles acting as an apparent backstop and providing a stable environment for the formation of forearc basins the new theory has important implications for the studies of the updip limit of the seismogenic zone the evolution of accretionary prisms and forearc basins activation of splay faults and tsunami generation evolution of the fluid regime and mechanics of frontal prisms at margins dominated by tectonic erosion

rotation and exhumation of a thrust plane apatite fission track data from the glarus thrust switzerland apatite fission track ages and track length measurements are presented from 22 samples from the glarus alps eastern switzerland where maximum temperatures of 100 to 350 c along an alpine thrust plane were reached during late tertiary metamorphism with the exception of the northernmost sample apatite ages are fully reset and range between 5 and 12 ma apatite fission track data along a vertical profile and a horizontal profile indicate that isothermal planes were oriented parallel to the glarus thrust plane and that the thrust plane cooled below a mean apatite fission track closure temperature of 110 c at 9 ma the metamorphic pattern and fission track data indicate a south dipping thrust plane during the times of peak metamorphic conditions postmetamorphic thrusting over a distance of 10 km and gradational exhumation of the plane to a horizontal position at ca 9 ma ongoing rotation of the plane is reflected by the present dip of about 7 nnw

noncohesive critical coulomb wedges an exact solution active fold and thrust belts or submarine accretionary complexes can be modeled as critically tapered wedges of material on the verge of coulomb failure everywhere overlying a basal decollement where frictional sliding is occurring ignoring cohesion the four strength parameters needed to describe a critical coulomb wedge are its internal and basal coefficients of friction and b and its internal and basal hubbert rubey fluid pressure ratios and b an exact relation between surface slope and basal dip of a noncohesive critical wedge with uniform properties is derived the state of stress within such a wedge has the same orientation everywhere and is constant if is and vice versa a coefficient of internal friction 1 1 is consistent with the known surface slope basal dip and pore fluid pressures in the active fold and thrust belt of western taiwan assuming that byerlee s law b 0 85 is valid on the base the wide variety of tectonic styles observed to occur along convergent margins including subduction erosion active accretion subduction without accretion and even extension and normal faulting may be controlled by relatively small spatial or temporal variations in either b or b

determination of the pore fluid pressure ratio at seismogenic megathrusts in subduction zones implications for strength of asperities and andean type mountain building 1 we construct the differential stress profile across the fore arc in a subduction zone from the force balance between the shear stress at seismogenic megathrust and the lithostatic pressure we assume that is written by 1 n where is the pore fluid pressure ratio is the coefficient of static friction and n is the normal stress given a density structure of the fore arc wedge we determine by comparing calculated fore arc stresses with observed ones as 0 95 0 98 in shikoku miyagi peru north chile and south chile and 0 90 0 93 in south vancouver island and washington the parameter averaged over the seismogenic megathrust is of the order of 10 mpa stress drops of great earthquakes in these zones occupy 14 87 and not a constant fraction of they on the other hand increase linearly with 1 we propose a simple fault model in which the area of asperities as a fraction of the total fault area is proportional to 1 variation of fractional area of asperities thus may explain the observed correlation and the regional variation of assuming that the differential stress at summit of the andean mountains is zero not at the coast as observed at present we determine to be 0 84 in north chile in the mountain building stage such a smaller value of along with 0 9 in subduction zones would suggest that variation of controls the tectonic style of the earth

megathrust friction determined from mechanical analysis of the forearc in the maule earthquake area the seismogenic potential of a given fault depends essentially on its frictional properties and on the mechanical properties of the medium determining the spatio temporal variations of frictional properties is therefore a key issue in seismotectonics this study aims to characterize the friction on the south america megathrust in the 2010 mw 8 8 maule earthquake area from mechanical analysis of the forearc structure and morphology based on the critical taper theory we first show that the rupture area of the maule earthquake also shown to be locked in the interseismic period coincides with the stable part of the wedge in the surrounding area the wedge is critical a finding consistent with various evidence for active deformation there this is in particular true for the arauco peninsula area which seems to have arrested the maule earthquake s rupture to the south this observation lends support to the view that the seismic rupture is inhibited when propagating beneath a critical area the geometry of the critical portion of the wedge suggests a standard internal friction int 0 7 0 13 and a hydrostatic pore pressure within the wedge the effective friction beneath the critical outer wedge is estimated to be eff b 0 27 0 03 this could be related to intrinsically low friction minerals clay or high pore pressure along the megathrust we next use the limit analysis approach to constrain the variation of the effective friction along the megathrust based on the location and geometry of internal faulting within the forearc a low effective friction is found within the rupture area eff b 0 14 to explain the reactivation of thrust fault such as the santa maria updip of the coseismic rupture or the activation of normal splay faults downdip of the rupture area the low effective friction found there could reflect strong dynamic weakening

u th dating of marine isotope stage 7 in bahamas slope sediments in order to understand the driving forces for pleistocene climate change more fully we need to compare the timing of climate events with their possible forcing in contrast to the last interglacial marine isotope stage mis 5 the timing of the penultimate interglacial mis 7 is poorly constrained this study constrains its timing and structure by precise u th dating of high resolution n 18 o records from aragonite rich bahamian slope sediments of odp leg 166 sites 1008 and 1009 the major glacial interglacial cycles in n 18 o are distinct within these cores and some mis 7 substages can be identified these sediments are well suited for u th dating because they have uranium concentrations of up to 12 ppm and very low initial 230 th contributions with most samples showing 230 th 232 th activity ratio of s 75 u and th concentrations and isotope ratios were measured by thermal ionisation mass spectrometry and multiple collector inductively coupled plasma mass spectrometry with the latter providing dramatically better precision twenty nine of the 41 samples measured have a n 234 u value close to modern seawater suggesting that they have experienced little diagenesis ages from 27 of the 41 samples were deemed reliable on the basis of both their u and their th isotope ratios ages generally increase with depth although we see a repeated section of stratigraphy in one core extrapolation of constant sedimentation rate through each substage suggests that the peak of mis 7e lasted from v237 to 228 ka and that 7c began at 215 ka this timing is consistent with existing low precision radiometric dates from speleothem deposits the beginning of both these substages appears to be slightly later than in orbitally tuned timescales the end of mis 7 is complex but also appears to be somewhat later than is suggested by orbitally tuned timescales although this event is not particularly well defined in these cores fl 2002 elsevier science b v all rights reserved

constraining the strength of megathrusts from fault geometries and application to the alpine collision zone abstract using coulomb wedge solutions we show that the effective strength of megathrusts b can be determined from the geometry of out of sequence thrusts cutting through an accretionary or orogenic wedge the method is first tested on central chilean margin for which it yields a frictional strength of b 0 053 0 043 0 024 the inferred value agrees well with previous strength estimates and with the tectonic response of the central chilean wedge to 2010 m w 8 8 maule earthquake we then use the approach to constrain the strength of the collision megathrust of the central european alps 30 20 million years ago we find that the collision megathrust had a strength of b 0 065 0 035 0 026 which is similarly low than the strength of subduction megathrusts the result is integrated into a static force balance model to examine potential implications of a weak megathrust for the alpine orogeny the model results suggest that the alpine megathrust supported a mean maximum elevation of 2 000 m and that growth of the wedge up to this elevation supported a switch from contractional to extensional tectonics in the interior of the alps around 20 ma finally using the example of the himalayas we show how the strength of megathrusts may be also derived from the geometry of crustal ramps which provides a valuable alternative if details on out of sequence thrusts are missing

stress buildup in the himalaya the seismic cycle on a major fault involves long periods of elastic strain and stress accumulation driven by aseismic ductile deformation at depth ultimately released by sudden fault slip events coseismic slip distributions are generally heterogeneous with most of the energy being released in the rupture of asperities since on the long term the fault s walls generally do not accumulate any significant permanent deformation interseismic deformation might be heterogeneous revealing zones of focused stress buildup the pattern of current deformation along the himalayan arc which is known to produce recurring devastating earthquakes and where several seismic gaps have long been recognized might accordingly show significant lateral variations providing a possible explanation for the uneven microseismic activity along the himalayan arc by contrast the geodetic measurements show a rather uniform pattern of interseismic strain oriented consistently with long term geological deformation as indicated from stretching lineation we show that the geodetic data and seismicity distribution are reconciled from a model in which microseismicity is interpreted as driven by stress buildup increase in the interseismic period the uneven seismicity pattern is shown to reflect the impact of the topography on the stress field indicating low deviatoric stresses 35 mpa and a low friction 0 3 on the main himalayan thrust arc normal thrusting along the himalayan front and east west extension in southern tibet are quantitatively reconciled by the model

hydrogeology and mechanics of subduction zone forearcs fluid flow and pore pressure at subduction zones fluid flow pore pressure and tectonic processes are tightly interconnected excess pore pressure is driven by tectonic loading and fluids released by mineral dehydration and it has profound effects on fault and earthquake mechanics through its control on effective stress the egress of these overpressured fluids which is in part governed by the presence of permeable fault zones is a primary mechanism of volatile and solute transport to the oceans recent field measurements new constraints gained from laboratory studies and numerical modeling efforts have led to a greatly improved understanding of these coupled processes here we summarize the current state of knowledge of fluid flow and pore pressure in subduction forearcs and focus on recent advances that have quantified permeability architecture fluxes the nature and timing of transience and pressure distribution thus providing new insights into the connections between fluid metamorphic mechanical and fault slip proc

climatic and hydrologic changes in the tien shan central asia abstract the authors analyze climatic and hydrologic data from 110 sites collected from the middle of the twentieth century to the present in the tien shan one of the largest mountain systems of central asia in spite of a few confounding interregional variations in the temporal changes of surface air temperature precipitation runoff glacier mass and snow thickness in the tien shan it has been possible to establish statistically significant long term trends in these key hydroclimatic variables the average rise in air temperature was 0 01 c yr 1 over the range with slightly lower values below 2000 m elevation the precipitation in the tien shan increased 1 2 mm yr 1 over the past half century the precipitation increase is larger at low altitudes in the northern and western regions than at altitudes above 2000 m a decrease in snow resources occurred almost everywhere in the tien shan the maximum snow thickness and snow duration have decreased on average 10 cm and 9 days respectively the annual

coastal deformation and great subduction earthquakes isla santa maria chile 37 s isla santa maria at the active margin of south central chile is the result of earthquake related uplift and deformation in the forearc since at least late pleistocene time field mapping dating of key depositional horizons and analysis of seismic refl ection profi les reveal ongoing deformation in this sector of the chilean forearc the 30 km 2 island is located 12 km above the interplate seismogenic zone and 75 km landward of the trench it is situated near the southern termination of the concepcion earthquake rupture segment where charles darwin measured 3 m of coseismic uplift during a m 8 megathrust earthquake in 1835 permanent postearthquake deformation from this earthquake and an earlier event in 1751 is registered by emerged landward tilted abrasion surfaces uplift at 2 m k y and tilting at 0 025 k y of the island have been fairly constant throughout the late quaternary and have resulted in emergence of the island above sea level 31 k y ago the island is composed of a late pleistocene upper tilted surface with two asymmetric tilt domains and holocene lowlands characterized by uplifted and tilted strandlines industry offshore seismic refl ection profi les covering an area of 1800 km 2 and crustal seismicity reveal active reversefault cored anticlines surrounding isla santa maria the principal fault apparently roots in the plate interface thrust these reverse faults in the upper plate result from inversion of late cretaceous to early pliocene normal faults and rift structure of the arauco forearc basin positive inversion of these inherited structures started between 3 6 and 2 5 ma and resulted in continuous shortening rates of 0 8 mm yr the seismic refl ection profi les show that the asymmetric tilt domains and progressive syntectonic sedimentation are linked to the position of the island in the forelimbs of two converging anticlines whereas their backlimbs have been removed by cliff retreat the 2 m uplift contour of the 1835 earthquake is parallel to the strike of active faults and antiforms in the arauco concepcion region the close relation among the asymmetric uplift and tilt of the island modern deformation patterns and reverse faults rooted in the plate interface suggests that slip on the plate interface thrust infl uences localizes and segments surface deformation during large interplate earthquakes furthermore the link between positive inversion of pre existing structures uplift and tilt patterns in the forearc emphasizes the importance of inherited structural fabrics in guiding plate boundary deformation

neogene lateral extension during convergence in the central alps evidence from interrelated faulting and backfolding around the simplonpass switzerland abstract the simplon fault zone occurs at the western end of the lepontine metamorphic dome in the central alps and represents a major low angle 25 dip normal fault associated with wsw ene directed lateral extension movement began in the early miocene and continued until at least 3 ma accumulating a total vertical throw of around 10 km corresponding to 24 km displacement parallel to the fault this displacement is partitioned between a broad zone of ductile mylonites in the footwall and a more discrete cataclastic detachment fault the simplon line in the central region simplon village to zwischbergen some 3 km of the total vertical displacement is accommodated by the discrete cataclastic zone due to the higher exposed structural level the importance of the cataclastic component increases towards the northwest in the northern steep belt around the simplonpass retrograde greenschist facies mylonite formation and younger cataclastic faulting associated with lateral extension occurred contemporaneously with sse vergent large scale backfolding representing nnw sse shortening and crustal thickening the combined effect was an overall shortening across the orogen accommodated by an extension parallel to the orogen allowing lateral escape of continental material normal faulting and the resultant lateral escape was not just superficial it extended to depths of at least 15 km and probably to depths exceeding 25 km the overall geometry and kinematics of the simplon fault zone and in particular the interplay between folding and faulting is very similar to that described from the metamorphic core complexes and detachment faults of the cordillera of the southwestern usa within the central alps extension was associated with rapid exhumation of the lepontine metamorphic dome as evidenced by very rapid cooling rates determined from mineral ages in the footwall similar to the cenozoic tectonics of the himalayas and tibet orogen parallel extension in the mountain belt may have been promoted by an overall reduction in the horizontal compressive stress in this direction more limited extension of the same age and orientation is known from a large area of the european foreland greater extension in the mountain belt compared with the foreland was accommodated by major strike slip transfer fault systems and was linked to coeval overthrusting of the lowlands towards the southwest in the external southwestern alps of haute provence france coeval folding and orogen parallel extension such as at the simplonpass were developed in a dextral transpressive regime due to oblique wnw ese convergence across the alps during the neogene

thermal history of the central gotthard and aar massifs european alps evidence for steady state long term exhumation 1 quantifying long term exhumation rates is a prerequisite for understanding the geodynamic evolution of orogens and their exogenic and endogenic driving forces here we reconstruct the exhumation history of the central aar and gotthard external crystalline massifs in the european alps using apatite and zircon fission track and apatite u th he data age elevation relationships and time temperature paths derived from thermal history modeling are interpreted to reflect nearly constant exhumation of 0 5 km ma since 14 ma a slightly accelerated rate 0 7 km ma occurred from 16 to 14 ma and again from 10 to 7 ma faster exhumation between 16 and 14 ma is most likely linked to indentation of the adriatic wedge and related thrusting along the alpine sole thrust which in turn caused uplift and exhumation in the external crystalline massifs the data suggest nearly steady moderate exhumation rates since 14 ma regardless of major exogenic and endogenic forces such as a change to wetter climate conditions around 5 ma or orogen perpendicular extension initiated in pliocene times recent uplift and denudation rates interpreted to be the result of climate fluctuations and associated increase in erosional efficiency are nearly twice this 0 5 km ma paleoexhumation rate

solution mass transfer deformation adjacent to the glarus thrust with implications for the tectonic evolution of the alpine wedge in eastern switzerland abstract we have studied aspects of absolute finite strain of sandstones and the deformation history above and below the glarus thrust in eastern switzerland the dominant deformation mechanism is solution mass transfer smt which resulted in the formation of a semi penetrative cleavage our analysis indicates that the verrucano and melser sandstones which lie above the thrust were deformed coaxially with pronounced contraction in a subvertical z direction and minor extension in a subhorizontal x direction trending at 200 most of the contraction in z was balanced by mass loss volume strains averaging 36 below the glarus thrust sandstones of the north helvetic flysch have smaller principal strains but similar volume strains deformation there was also approximately coaxial the x direction is horizontal and trends 160 which is different by 40 from the x direction in the hanging wall the hanging wall of the glarus thrust verrucano and melser sandstones was deformed first after it was accreted deep beneath the alpine wedge continued northward advance of the wedge accomplished in part by motion on the glarus thrust allowed the wedge to override and accrete the north helvetic flysch which then started to form an smt cleavage the difference in x directions may reflect a change in transport direction but this conclusion is difficult to accept since extension was minor and was accommodated by coaxial flattening and not simple shear our work indicates that mass loss volume strains were important in sandstones of the helvetic nappes the missing mass cannot be accounted for at the local scale and appears to have been transported beyond the helvetic zone

andean growth and the deceleration of south american subduction time evolution of a coupled orogen subduction system article i nfo present day orography at the andean margin is a result of isostasy tectonic accretion and erosional processes the resulting excess mass of the andes gives rise to frictional stresses on the seismogenic plate interface that resist the sinking of the subducting slab into the upper mantle thus subduction rates should be sensitive to the time dependent dynamics of a back arc orogen as well as erosional or accretional processes that affect orogen growth here we develop a two dimensional coupled orogen slab model that allows for the prediction of orogen size and plate motion in response to both tectonic and erosional forcing we find that the frictional force exerted by the orogen on the subducting slab grows quadratically with orogen width and that the frictional resistance typically balances 10 50 of the slab pull force the time evolution of the coupled orogen subduction zone system is largely controlled by the rate of orogen growth which is controlled by the rate of convergence and the erosivity of the climate state in the case of the andean margin our models show that miocene aridification leads to reduced erosion increased orogen growth greater frictional resistance to subduction and ultimately to a 50 reduction in the convergence rate between the nazca and south american plates

late holocene variation of the raigorodskogo glacier and climate change in the pamir alai central asia during the late holocene the raigorodskogo glacier in the pamir alai central asia expanded before 3215 after 1545 and at 310 cal years bp as dated by the 14c calibrated ages of wood samples from moraine deposits and terrace exposures the glacier expansions which were accompanied by increased melt water run off over the terrace surface were confined to the proglacial area the terrace deposits with intercalated buried soil layers provide evidence of two obvious warm periods when the glacier abruptly retreated during the late holocene shortly before 1545 cal years bp and again sometime before ca 500 cal years bp fallen juniperus turkestanica broken by moraine deposits suggests that the largest glacial expansion during the little ice age occurred 310 cal years bp the glacier expansion in the little ice age was on roughly the same scale as that which occurred in the cold period after 1545 cal years bp observational records of the glacier terminus and moraine positions indicate that recent glacier advances occurred in the years 1908 1911 sometime in 1911 1934 and in 1960 1977 these advances were small while the glacier recessions were larger in the 1900s with large recessions also sometime in 1911 1934 and in 1977 1998 the glacier recession rate of 27 m year in 1911 1934 was faster than the rates of 13 m year in 1977 1990 and 21 m year in 1990 1998 however the glacier recession rate has been accelerating recently particularly after 1990 this recession reflects recent climate warming in inland asia

the accretion of foreland basin sediments during early stages of continental collision in the european alps and similarities to accretionary wedge tectonics we present structural observations from foreland basin sediments that were incorporated into the orogenic wedge of the central european alps during early stages of continental collision our analysis focuses on the prograde evolution and considers the full history of the sediments ranging from their deposition in the basin to deep burial and metamorphism at temperatures of 320 c the tectonic evolution is matched with constraints on the diagenetic alteration of the sediments for this purpose we calculate the temperatures and depths of sediment compaction and illitization as well as the associated fluid liberation the data set highlights that the tectonic incorporation of the sediments into the orogenic wedge was strongly controlled by their diagenetic state earliest deformation took place during imbrication and frontal accretion of unconsolidated and fluid saturated sediments ductile folding of the sediments occurred already at this stage and was assisted by particulate flow with the progressive consolidation of the sediments the elastic strength increased which resulted in an overall embrittlement this rheological change is recorded by the onset of out of sequence thrusting brittle faulting and the formation of massive quartz calcite veins which took place in the approximate temperature range of the seismogenic zone i e 150 350 c moreover widespread pressure solution resulted in the formation of a penetrative cleavage and records slow but long lasting deformation at low background strain rates in summary the prograde tectonic evolution of the frontal alpine wedge exhibits many similarities with the structural and mechanical evolution of accretionary wedges at active subduction zones

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

locking of the chile subduction zone controlled by fluid pressure before the 2010 earthquake large subduction zone earthquakes are thought to occur where the down going and overriding tectonic plates are strongly locked analysis of geodetic and seismic data collected in the decade before the 2010 chile earthquake shows that variations in pore fluid pressure correlate with the degree of plate interface locking and may therefore control earthquake rupture

large scale subduction of continental crust implied by india asia mass balance calculation continental crust is buoyant compared with its oceanic counterpart and resists subduction into the mantle when two continents collide the mass balance for the continental crust is therefore assumed to be maintained here we use estimates of pre collisional crustal thickness and convergence history derived from plate kinematic models to calculate the crustal mass balance in the india asia collisional system using the current best estimates for the timing of the diachronous onset of collision between india and eurasia we find that about 50 of the pre collisional continental crustal mass cannot be accounted for in the crustal reservoir preserved at earth s surface today represented by the mass preserved in the thickened crust that makes up the himalaya tibet and much of adjacent asia as well as southeast asian tectonic escape and exported eroded sediments this implies large scale subduction of continental crust during the collision with a mass equivalent to about 15 of the total oceanic crustal subduction flux since 56 million years ago we suggest that similar contamination of the mantle by direct input of radiogenic continental crustal materials during past continent continent collisions is reflected in some ocean crust and ocean island basalt geochemistry the subduction of continental crust may therefore contribute significantly to the evolution of mantle geochemistry buoyant continental crust is thought to resist subduction calculation of the crustal mass balance during the collision between india and eurasia indicates that about 50 of pre collisional continental crust has been subducted into the mantle

characterizing the main himalayan thrust in the garhwal himalaya india with receiver function ccp stacking abstract we use common conversion point ccp stacking of ps receiver functions to image the crustal structure and moho of the garhwal himalaya of india our seismic array of 21 broadband seismometers spanned the himalayan thrust wedge at 79 80 e between the main frontal thrust and the south tibet detachment in 2005 2006 our ccp image shows the main himalayan thrust mht the detachment at the base of the himalayan thrust wedge with a flat ramp flat geometry seismic impedance contrasts inferred from geologic cross sections in garhwal imply a negative impedance contrast velocity decreasing downward for the upper flat located beneath the lower himalaya and a positive impedance contrast velocity increasing downward for the ramp located beneath the surface trace of the munsiari thrust or mct i at the lower flat located beneath the higher himalaya spatially coincident measurements of very high electrical conductivities require the presence of free fluids and we infer a negative impedance contrast on the mht caused by ponding of these fluids beneath the detachment our seismic image indicates that the upper flat of the mht is 10 km below sea level and dips north at 2 connecting to a mid crustal ramp which is 10 km high and dips at 16 the lower flat is 20 25 km below sea level and dips at 4 the main central thrust mct appears as a negative impedance contrast dipping at 16 the moho is nearly horizontal at 35 45 km depth beneath the sub himalaya and lower himalaya deepening to 50 km or more beneath the higher himalaya this depth is 10 25 km shallower than in the nw indian himalaya and 5 10 km shallower than in central nepal requiring significant along strike variations in crustal thickness the observed thickness of subducted indian crust in garwhal is 20 28 km

global variations of stress drop for moderate to large earthquakes 1 we investigate the global variation of earthquake stress drops using spectra of about 2000 events of mb 5 5 between 1990 and 2007 we use an iterative least squares method to isolate source displacement spectra from travel path and receiver contributions based on a convolutional model the observed p wave source spectra are corrected with a globally averaged empirical correction spectrum and estimates of near source attenuation assuming a brune type source model we estimate corner frequencies and compute stress drops stress drop estimates for individual earthquakes range from about 0 3 to 50 mpa but the median stress drop of about 4 mpa does not vary with moment implying earthquake self similarity over the mw 5 2 to 8 3 range of our data a comparison of our results with previous studies confirms this observation over most of the instrumentally observable magnitude range while the absolute values of our estimated stress drops depend upon the assumed source model we identify relative regional variations of stress drop that are robust with respect to the processing parameters and modeling assumptions which includes an inherent assumption of constant rupture velocity we find a dependence of median stress drop on focal mechanism with a factor of 3 5 times higher stress drops for strike slip earthquakes and also find a factor of 2 times higher stress drops for intraplate earthquakes compared to interplate earthquakes

temperatures heat flux and frictional stress near major thrust faults we examine the two dimensional advective and conductive transport of heat in a region of thrust faulting both simple theoretical considerations and numerical experiments show that the steady state temperatures near the fault are reduced by a divisor s 1 b z vsin below what they would be with the same heat sources but in the absence of advection in this expression z is the depth to the fault v is the slip rate is the component of the dip of the fault in the direction of underthrusting is thermal diffusivity and b is a dimensionless factor that is essentially equal to one for most forms of heating initial changes in temperatures near the fault are given by t z t t z 0 12vsin t z 0 z these simple formulae are successful because of the neglible influence of lateral conduction of heat at least for slip rates of a few mm yr or more two time constants govern the transition from the initial change in temperature to steady state t1 u v where u is the distance along the fault in the direction of underthrusting from the surface to the depth in question and t2 z 2 2 where z is the depth to the fault when elapsed times exceed the sum of these two time constants temperatures differ from their steady state values by only about 10 percent the numerical experiments indicate that the simple formulae are sufficiently accurate that sophisticiated numerical modeling of temperatures in specific regions is unwarranted putain an application of these simple formulae to measurements of conductive heat flow at island arcs implies that shear stresses at island arcs approach 100 mpa and are greater than 30 mpa calculations of temperatures appropriate for the himalaya suggest that shear stresses of 100 mpa on the main central thrust probably are required to account for the tertiary granites of the region if melting took place after slip began on the thrust similarly the cut off in seismicity at a depth of about 15 km in the himalaya if due to temperatures exceeding 350 to 450 c implies a deviatoric stress close to 100 mpa

estimates of stress drop and crustal tectonic stress from the 27 february 2010 maule chile earthquake implications for fault strength 1 the great 27 february 2010 mw 8 8 earthquake off the coast of southern chile ruptured a 600 km length of subduction zone in this paper we make two independent estimates of shear stress in the crust in the region of the chile earthquake first we use a coseismic slip model constrained by geodetic observations from interferometric synthetic aperture radar insar and gps to derive a spatially variable estimate of the change in static shear stress along the ruptured fault second we use a static force balance model to constrain the crustal shear stress required to simultaneously support observed fore arc topography and the stress orientation indicated by the earthquake focal mechanism this includes the derivation of a semianalytic solution for the stress field exerted by surface and moho topography loading the crust we find that the deviatoric stress exerted by topography is minimized in the limit when the crust is considered an incompressible elastic solid with a poisson ratio of 0 5 and is independent of young s modulus this places a strict lower bound on the critical stress state maintained by the crust supporting plastically deformed accretionary wedge topography we estimate the coseismic shear stress change from the maule event ranged from 6 mpa stress increase to 17 mpa stress drop with a maximum depth averaged crustal shear stress drop of 4 mpa we separately estimate that the plate driving forces acting in the region regardless of their exact mechanism must contribute at least 27 mpa trench perpendicular compression and 15 mpa trench parallel compression this corresponds to a depth averaged shear stress of at least 7 mpa the comparable magnitude of these two independent shear stress estimates is consistent with the interpretation that the section of the megathrust fault ruptured in the maule earthquake is weak with the seismic cycle relieving much of the total sustained shear stress in the crust

strength of stick slip and creeping subduction megathrusts from heat flow observations subduction faults called megathrusts can generate large and hazardous earthquakes the mode of slip and seismicity of a megathrust is controlled by the structural complexity of the fault zone however the relative strength of a megathrust based on the mode of slip is far from clear the fault strength affects surface heat flow by frictional heating during slip we model heat flow data for a number of subduction zones to determine the fault strength we find that smooth megathrusts that produce great earthquakes tend to be weaker and therefore dissipate less heat than geometrically rough megathrusts that slip mainly by creeping

active shortening within the himalayan orogenic wedge implied by the 2015 gorkha earthquake the himalaya grow as the indian plate is thrust beneath tibet analysis of surface deformation caused by the 2015 gorkha earthquake suggests slip on smaller scale faults at the foot of the high himalaya help build earth s highest peaks

conditions for a crustal block to be sheared off from the subducted continental lithosphere what is an essential factor to cause features associated with collision 1 crustal blocks are detached from the subducting lithosphere at various depths i call such phenomena shearing off and investigate the mechanical conditions for shearing off to occur in the continental lithosphere the buoyancy of the crustal block does not work selectively as a driving force until it has been sheared off and i suppose that shearing off occurs when the shear traction at the thrust whose maximum value is calculated from the strength along the thrust overcomes the strength of the boundary faults of the block and determine the depth of the leading edge of the subducted crustal block when shearing off occurs the temperatures of the slab and at its surface are calculated by the steady state formula of molnar and england 1990 as a function of the surface heat flow dip angle and convergence velocity of the subducted continental plate as the shear stress and temperature at the ductile part of the thrust zone are consistent with the flow law the shear stress at the brittle part is a strong function of the pore fluid pressure ratio i show that shearing off of an upper crustal block is possible only for a small value of such as 0 4 when the surface heat flow value is 70 mw m2 i suggest that the essential factor to cause shallow offscraping of crustal blocks in collision zones is not a buoyancy of the continental crust but a low value of which would result from a little amount of dehydration from the subducted continental plate

probing the transition between seismically coupled and decoupled segments along an ancient subduction interface the transition zone at the downdip end of seismic coupling along subduction interfaces is often the site of megathrust earthquake nucleation and concentrated postseismic afterslip as well as the focus site of episodic tremor and slip features exhumed remnants of the former alpine subduction zone found in the swiss alps allow analyzing fluid and deformation processes near the transition zone region 30 40 km paleodepth the dent blanche thrust dbt is a lower blueschist facies shear zone interpreted as a fossilized subduction interface where granitic mylonites overlie a metamorphosed accretionary wedge we report field observations from the dbt region where multiple several tens of meters thick foliated cataclastic networks are interlayered within the basal dbt mylonites petrological results and microstructural observations indicate that the various cataclasis events took place at near peak metamorphic conditions 400 500 c 1 1 1 3 gpa during subduction of the tethyan seafloor in eocene times 42 48 ma some of these networks exhibit mutual crosscutting relationships between mylonites foliated cataclasites and vein systems indicating mutual overprinting between brittle deformation and ductile creep whole rock chemical compositions in situ 40ar 39ar age data of recrystallized phengite and sr isotopic signatures reveal that dbt rocks also underwent multiple hydrofracturing and metasomatic events via the infiltration of fluids mainly derived from the oceanic metasediments underneath the dbt from the rock fabrics we infer strain rate fluctuations of several orders of magnitude beyond subduction strain rates 10 12 s 1 accompanied by fluctuation of supralithostatic and quasi lithostatic fluid pressures 1 0 95 dbt brittle plastic deformation switches highlight the diversity of deformation processes and fluid rock interactions in the transition zone region of the subduction interface

splay fault triggering by great subduction earthquakes inferred from finite element models we have investigated the influence that megathrust earthquake slip has on the activation of splay faults using a 2 d finite element method fem taking into account the effects of gravity and variations in the frictional strength properties of splay faults we simulated both landward dipping and seaward dipping splay fault geometries and imposed depth variable slip distributions of subduction events our results indicate that the two types of splay fault exhibit a similar behavior with variations in frictional properties along the faults affecting only the seismic magnitude the triggering process is controlled by a critical depth megathrust slip concentrated at depths shallower than the critical depth will favor normal displacement while megathrust slip concentrated at depths deeper than the critical depth is likely to result in reverse motion our results thus provide a useful tool for predicting the activation of secondary faults and may have direct implications for tsunami hazard research

three dimensional geometry and tectonostratigraphy of the pennine zone central alps switzerland and northern italy abstract continental collision during alpine orogenesis entailed a polyphase deformation history d1 d5 in the pennine zone of the central alps the regional tectonostratigraphy was basically developed during d1 and d2 characterised by isoclinal typically north closing recumbent anticlines separated by pinched in synclines on the scale of tens of kilometres later deformation phases d3 and d4 warped the stack into wavy to open folds exhumation of this zone resulted locally in later vertical shortening and folding of already steep fabrics d5 three dimensional models of the nappe pile were constructed based on geostatistical assessment of the regional foliation field and considering the abundant structural field data these models indicate the existence of five principal tectonostratigraphic levels developed during d1 and thus equivalent to nappe units s str the gotthard the leventina antigorio the maggia simano and probably the monte leone as well as the composite lepontine series lebendun soja and adula cima lunga levels all these tectonic units formed part of the passive continental margin of europe prior to the onset of the alpine orogenesis individual isoclinal post nappe folds reflect relative displacements on the order of 40 km or more the most prominent d2 post nappe structure is the wandfluhhorn fold structurally equivalent to the northern closure of the leventina lucomagno antiform the lebendun and monte leone folds are of similar magnitudes and also affect the whole nappe pile whereas the smaller mogno and molare synforms only refold the maggia simano nappe internally principal d3 and d4 structures are the tight mergoscia synform directly north of the insubric fault between bellinzona and locarno southern steep belt the maggia steep zone forming the steep western limb of the campo tencia synform and subdividing the lepontine dome into the simplon and ticino subdomes the chiera synform steepening the dominant foliation in the north northern steep belt and the vanzone and claro antiforms steepening the dominant foliation in the south southern steep belt the current geometry of the northern and southern steep belts reflects an interplay between d4 and d3 involving both fold interference and reactivation tightening

combining digital elevation data srtm aster high resolution satellite imagery quickbird and gis for geomorphological mapping a multi component case study on mediterranean karst in central crete abstract remote sensing data have become more and more popular for geomorphological investigations because their steadily increasing level of detail and accessibility opens up new potentials in this context this paper examines the application and quality of digital elevation models srtm and aster dems high resolution satellite imagery quickbird and gis techniques for the detection and mapping of karst landforms mainly enclosed depressions at different scales in the ida mountains of central crete besides discussing methodological issues and evaluating suitability potentials we conducted an exemplary case study based on spatial analysis of the regional karst morphology different input datasets and processing methods are applied gis based analysis land cover classification raster calculations etc in order to carry out an area wide surveying and mapping of karst depressions the findings are supported and validated by auxiliary field studies due to the level of detail and occasional data errors an exclusive use of satellite imagery or digital elevation models for automatic karst landform detection performs insufficiently our results demonstrate that mapping karst features through remote sensing is significantly dependent on scale of interest existing environmental conditions and data quality a semi automatic data integration approach on the basis of digital datasets generated by combined satellite image processing and dem analysis yields the best results especially when indirect karst indicating variables like iron oxide rich sediments are included as detection criteria the multi component application presented in this paper provides a time saving and effective tool for meso to macro scale object detection and extensive study areas however the potential of fully automated karst feature mapping still needs to be explored in future work concerning the spatial dimension of karstification in central crete the gis based results allow differentiating further geomorphological characteristics e g by indicating a significant altitudinal change of karst forms within the study area size and shape of depressions dolines uvalas and poljes vary considerably due to the geological setting climatic impacts neotectonics and elevation

megathrust shear force controls mountain height at convergent plate margins the shear force along convergent plate boundary faults megathrusts determines the height of mountain ranges that can be mechanically sustained1 4 however whether the true height of mountain ranges corresponds to this tectonically supported elevation is debated4 7 in particular climate dependent erosional processes are often assumed to exert a first order control on mountain height5 12 although this assumption has remained difficult to validate12 here we constrain the shear force along active megathrusts using their rheological properties and then determine the tectonically supported elevation using a force balance model we show that the height of mountain ranges around the globe matches this elevation irrespective of climatic conditions and the rate of erosion this finding indicates that mountain ranges are close to force equilibrium and that their height is primarily controlled by the megathrust shear force we conclude that temporal variations in mountain height reflect long term changes in the force balance but are not indicative of a direct climate control on mountain elevation

protracted continental collisions argue for continental plates driven by basal traction abstract in plate tectonic theory collision between two continents should quickly terminate because of continental buoyancy if convergence is to continue it should do so at a new subduction zone where oceanic crust can be consumed the protracted continental collisions in the alps zagros and himalayas which have continued to deform continental crust since the early or middle cenozoic are therefore anomalies in standard plate tectonic theory it is commonly held that plates are driven by slab pull but this does not account for the continuing tethyan collisions where the descending slab has detached from the subducting continent these protracted continental collisions are better explained by horizontal traction of the mantle on the base of deep continental roots dragging the northern and southern continents together along a tethyan axis of mantle convergence continental undertow thus resolves the collision anomaly in plate tectonics

phasing and amplitude of sea level and climate change during the penultimate interglacial the penultimate interglacial period was punctuated by three sea level highstands uranium thorium ages obtained from speleothems in italian caves show that the relationship between the timing of the peaks in sea level and northern hemisphere insolation is dependent on the previous extent of continental ice sheets

sea level controls sedimentation and environments in coastal caves and sinkholes abstract quaternary climate and sea level research in coastal karst basins caves cenotes sinkholes blueholes etc generally focuses on analyzing isotopes in speleothems or associating cave elevations prior sea level highstands the sediments in coastal karst basins represent an overlooked source of climate and sea level information in the coastal zone but to accurately interpret these sediments first requires an understanding of the forcing mechanisms that emplace them in this study we hypothesize that coastal karst basins transition through vadose littoral anchialine and finally into submarine environments during sea level rise because groundwater and sea level oscillate in near synchrony in the coastal zone causing each environment to deposit a unique sedimentary facies to test this hypothesis the stratigraphy in twelve sediment cores from a bermudian underwater cave green bay cave was investigated and temporally constrained with twenty radiocarbon dates the results indicate that we recovered the first succession spanning the entire holocene from an underwater cave 13 ka to present the sediments were characterized with x radiography fossil remains bulk organic matter organic geochemistry 13corg c n and grain size analysis four distinct facies represent the four depositional environments i vadose facies 7 7 ka calcite rafts lithofacies ii littoral facies 7 7 to 7 3 ka calcite rafts and mud lithofacies iii anchialine facies 7 3 to 1 6 ka slackwater and diamict lithofacies and iv submarine facies