the present day stress field of australia abstract the unusual present day crustal stress pattern of the australian continent has been the subject of scientific debate for over 25 years the orientation of maximum horizontal present day stress s hmax in continental australia is unlike all other major tectonic plates in that the stress pattern shows regional variability and it is not oriented sub parallel to the direction of absolute plate motion previous studies on the stress pattern of australia revealed that the complex stress pattern of the continent is controlled at a first order by the superposition of plate tectonic forces exerted at the plate boundaries however prior analysis of the contemporary australian crustal stress pattern have been unable to model or explain the stress pattern observed in most of eastern australia and has not extensively addressed the numerous smaller scale variations in stress orientation the recent development of unconventional reservoirs in australia has resulted in a greatly increased amount of new data for stress analysis in previously unstudied or poorly constrained areas in eastern australia in addition stress analysis in conventional hydrocarbon mineral and geothermal exploration in all other parts of the continent provides the opportunity to review and update the australian stress map asm this study presents the new release of the asm with a total of 2150 stress data records in australia increased from 594 data records in 2003 the 2016 asm contains 1359 data records determined from the interpretation of drilling related stress indicators 650 from earthquake focal mechanism solutions 139 from shallow engineering measurements and two from geological indicators the results reveal four distinct regional trends for the s hmax orientation in australia including a nne ssw s hmax trend in northern and northwestern australia which rotates to a prevailing e w orientation in most western and south australia the orientation of s hmax in eastern australia is primarily ene wsw and swings to nw se in southeastern australia a comparison between the new asm database and neotectonic features further confirms the role of contemporary stress in recent deformation of the australian crust the 2016 asm reveals significant discrepancies between newly observed s hmax orientations and predictions by published geomechanical numerical models for the australian continent forces generated at the boundary of indo australian plate remain the major control on the regional crustal stress pattern in continental australia however the increased data density particularly in eastern australia reveals numerous local perturbations of the stress field that were not previously clearly captured hence the key findings of the new release are that local intra plate stress sources are more significant than previously recognized particularly in eastern australian basins and cause substantial local scale rotations of the present day crustal stress pattern that have not been factored into existing australian stress models

the dynamics of motion of the south american plate observations of the intraplate stress field as compiled and evaluated in the context of the world stress map project can be compared with stress modelling results to increase our understanding of the dynamics of motion of the lithospheric plates in this paper we investigate the driving and resistive plate tectonic forces acting on the south american plate in order to establish a detailed basis for future stress modelling our basic assumption is that the plate is in mechanical equilibrium that is the net torque of the forces acting on the plate vanishes the complexity of the forces exerted along the margins of the south american plate requires the dynamical analysis to be performed step wise incorporating the forces which are expected to be of major importance a first order model is defined the effect of additional plate boundary forces is subsequently examined in terms of superpositions onto the first order model with the first order model the relation between three resistive forces and shear stress on the base of the lithosphere is derived the ridge push force driving the motion of the south american plate can be quantified independently and is included in the calculations as a known quantity solutions are obtained using four different determinations of the euler vector of absolute motion of the south american plate which is taken to define the orientation of the basal shear stress the results demonstrate that the concept of a basal shear stress actively driving plate motion cannot be discarded on the basis of a dynamical analysis further with the assumption that basal drag is entirely concentrated below the continental pan of the lithosphere estimates of the maximum amount of continental basal shear resistance are derived evaluation of an alternative model for the south american plate excluding the northernmost pan of the andes demonstrates the significance of the resistive force exerted on the south american plate due to convergence with the caribbean plate it is to be expected that comparison of theoretical distributions of intraplate stress computed on the basis of the present dynamical analysis with observations of the actual state of stress will further constrain the range of feasible force models

gravitational potential energy and regional stress and strain rate fields for continental plateaus examples from the central andes and colorado plateau abstract the commonly observed extension in areas of elevated and thickened crust is an expected consequence of having excess gravitational potential energy gpe compared to the low gpe of the surrounding crust while this conceptual model is well founded it is less clear how well gpe related stress orientations compare quantitatively to observed stress and strain rate orientations and what any inconsistency tells us about the presence of other competing forces we estimate the gpe distribution for the central andes and the greater colorado plateau area using topography and crustal thickness variations respectively and compare the related stress fields with the world stress map as well as with a geodetic strain rate field for the colorado plateau only in both areas deviatoric stresses associated with gpe variations alone cannot fully account for the observed deformation rate field for the central andes only a combination of deviatoric stresses associated with gpe and relative plate motions can account for the near n s tensional stress observed in the peruvian andes and the margin normal compressional stress along the eastern cordillera and sub andean fold and thrust belt the observed deformation field around the colorado plateau shows e w extension largely inconsistent with the deviatoric stresses associated with gpe variations except for the area east of the rio grande rift the ne sw oriented stress observed on the southwestern colorado plateau is consistent with the orientations of tensional deviatoric stresses associated with gpe variations we argue that this consistency could be haphazard stress observations may not reflect the current state of stress due to inherited structure or could result from the relative high strength of colorado plateau that allows for regional gpe variations and possibly basal shear to be more significant forces than far field plate interactions for the central andes and colorado plateau stresses associated with gpe variations have a strong influence on the total stress field and can thus be used to calibrate the overall level of deviatoric stress acting within the lithosphere

uplift history of the central and northern andes a review the elevation of the andean cordillera is a crucial boundary condition for both climatic and tectonic studies the andes affect climate because they form the only barrier to atmospheric circulation in the southern hemisphere and they intrigue geologists because they have the highest plateau on earth formed at a noncollisional plate margin the altiplano puna yet until recently few quantitative studies of their uplift history existed this study presents both 1 a review of the quantitative paleoelevation estimates that have been made for the central and colombian andes and 2 an examination of the source and magnitude of error for each estimate in the central andes paleobotanical evidence suggests that the altiplano puna had attained no more than a third of its modern elevation of 3700 m by 20 ma and no more than half its modern elevation by 10 7 ma these data imply surface uplift on the order of 2300 3400 m since the late miocene at uplift rates of 0 2 0 3 mm yr paleobotanical and geomorphological data suggest a similar uplift history for the eastern cordillera namely no more than half the modern elevation present by 10 ma no evidence exists for an exponential increase in uplift rate as has been interpreted from fissiontrack data these uplift rates mostly reflect mean surface uplift rather than rock uplift that is uplift of material points because little dissection of the western eastern cordillera has occurred south of lat 19 s and of the altiplano puna thus the central andean plateau appears to be young in the colombian andes paleobotanical data imply rapid uplift of the eastern cordillera between 2 and 5 ma at rates on the order of 0 6 3 mm yr however some of this uplift is likely rock uplift due to erosion driven isostatic rebound rather than mean surface uplift

beach ridges and prograded beach deposits as palaeoenvironment records abstract beach ridges are landforms commonly developed on prograded coasts with beach shorelines a sequence of beach ridges coupled with their subsurface deposits can be regarded as a time series of coastal evolution methodological advances in field surveying and chronology applicable to beach ridges have led to detailed palaeoenvironmental reconstructions to be derived from such sequences this paper reconsiders the basic aspects of beach ridges and deposits which need to be properly understood for their comprehensive interpretation in a palaeo environmental context it also reviews case studies in which beach ridge sequences have been used to unveil past sea level history catastrophic events and climate changes proposed formative processes of beach ridges include 1 progradation of sandy beach and berm formations in relation to fairweather waves coupled with aeolian foredune accumulation 2 building of gravel ridges by storm waves 3 welding of longshore bars beach ridge formation through sea level oscillation is thought to be questionable and caution is suggested for this process when undertaking palaeoenvironmental reconstruction beach deposit stratification is known to dip either landwards or seawards but landward dips are uncommon seaward dipping stratification is formed in relation to beachface progradation and is usually dissected in places by erosion surfaces resulting from episodic beach retreat the boundary between the foreshore and the underlying shoreface is well defined only in the case that longshore bars lead to complex bedding structure relative to that of the foreshore reliable chronology of beach ridges can be determined by radiocarbon and optically stimulated luminescence osl dating radiocarbon dating of articulated shells which are considered not to be extensively reworked provides robust results but osl dating is more useful as it enables direct dating of sediment grains it is noted that there are restrictions in chronological resolution and continuity inherent to beach ridge and beach deposits the plan view geomorphic expression of beach ridges typically consists of ridge sets with multi decadal intervals whereas their internal sedimentary structures define shorter time scales records of beach sedimentation and erosion are likely to be reworked by episodic high magnitude beach retreat and the resultant record of the net progradation is likely to be sporadic and discontinuous the height of sandy beach ridges is often variable due to differing degrees of aeolian sand accumulation and they are thus not used as sea level indicators unless purely wave built gravel ridge height is a relatively reliable indicator of sea level but can vary in response to storminess fluctuations subsurface sediment facies boundaries are preferred as sea level indicators and those proposed include boundaries of aeolian beach foreshore shoreface and upper lower shorefaces catastrophic events are expressed in both erosional and depositional records erosion surfaces or scarp imprints revealed in a cross section of beach deposits indicate storm or tsunami events however erosional events are likely to rework previous records of sedimentation and even other erosional events and thus the apparent history decoded from the resultant deposits tends to be biased several attempts for estimating the frequency and intensity of prehistoric cyclones rely on assumed relationships between the level of coarse sand beach ridges and cyclone inundation the formative process of coarse sand ridges remains uncertain and needs to be clarified as it constitutes the fundamental basis of these attempts the growth rates of beach ridge systems are expected to reflect fluctuations in river sediment discharge to the coast and in aeolian sand flux due to onshore winds both of which are affected by climate change assessment of the growth rate is potentially improved by ground penetrating radar survey of subsurface structure and by detailed chronology orientation of beach ridges reflects long term trends in wave direction inferred relationships between beach ridges and cyclic fluctuations of sea level and climate rely on weak assumptions and are not substantiated by rigid chronological evidence and thus remain highly questionable correlation between the inherently decadal signal of beach ridge intervals and possible climate cycles such as sunspot activity is probably coincidental as it lacks causal explanations

holocene estuary development in the algarve region southern portugal a reconstruction of sedimentological and ecological evolution this paper presents a reconstruction of the former coastal estuaries of the quarteira and carcavai estuaries in southern portugal based on sedimentological geochemical and palynological analyses of holocene sediment cores the results show that each estuary developed differently depending on the morphology of the palaeovalley environmental conditions and especially the influence of the sea and the formation of barrier systems both estuaries were flooded between 7000 and 5500 cal bp by sea level rise and were almost completely filled by sediment by the beginning of the roman occupation 226 bc 2176 cal bp a clear change in sedimentological processes is evident in both estuaries between 5500 and 3000 cal bp and is interpreted as an erosion phase or evidence of high energy events such as storms or tsunamis

geomorphic imprints of repeated tsunami waves in a coastal valley in northeastern japan abstract devastating tsunami waves induced by the 2011 off the pacific coast of tohoku earthquake severely inundated valleys along the ria type notched rocky coast in northeastern japan causing erosion of bedrock on valley side slopes using high resolution topographic data obtained by terrestrial and airborne laser scanning we investigated detailed morphology of the eroded valley in a typical site at aneyoshi we found several characteristic features likely affected by tsunami wave erosion 1 a series of small cliffs on the valley side slopes related to the tsunami flow depth 2 an inverse asymmetry of side slopes at ingrown meander bends 3 an exceptionally wide valley bottom near the coast and 4 a knickpoint located around the maximum tsunami run up point far back from the coast these topographic features are ascribable to repeated tsunami wave erosion since the mid holocene

temporal variation of the stress field during the construction of the central andes constrains from the volcanic arc region 22 26 s western cordillera chile during the last 20 ma in order to understand the response of the stress field state to intrinsic processes during the construction of the andes such as thickening of the continental crust lithospheric delamination and or thermal weakening we investigate the stress field evolution of the arc region since the last 20 my in the central andes 22 26 5 s the 43 reduced paleostress tensors derived from inversion of 682 fault slip data reveal a complex pattern of stress states during the last episode of orogenic construction and topographic uplift we identify two geodynamic stages the first stage corresponds to the construction of the altiplano puna plateau and the second one to its gravitational collapse four stress states that have prevailed in the altiplano puna plateau since middle miocene times characterize the transition from one stage to the other along the study latitudes a spatiotemporal change in stress state is clearly observed which led to an understanding that a change in the stress field may be related not only to the boundary conditions but also to intrinsic factors associated with the construction of the andean orogeny our results suggest that ca 13 10 ma and ca 8 5 ma in the southern altiplano and northern puna and in the southern puna respectively regional elevation and crustal thicknesses reached threshold values necessary to generate the orogenic collapse

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

the mechanical state of the lithosphere in the altiplano puna segment of the andes abstract information about topography the shape of the geoid seismicity neogene deformation and volcanism in the region of altiplano puna of western south america is used to analyse the state of stress across the convergent plate margin in terms of the effects of topography and simple models of its compensation an average elevation near 4 km is consistent with compensation by a yet unresolved combination of crustal root and hot uppermost mantle producing a geoid high of 22 27 meters average horizontal compressive stress in excess of a reference sea level lithostatic value of 390 bars in a 150 km thick lithosphere and an average shear stress of 170 bars along a 30 dipping interplate boundary the basis for these estimates is evidence for a neutral to extensional stress regime within the high plateau contrasted with a compressional regime on the eastern slopes and along the interplate boundary itself comparison with other plateaus in a convergent plate tectonic setting suggests an evolutionary sequence from compressional to extensional tectonics as elevation of the plateau increases

tsunamigenic incisions produced by the december 2004 earthquake along the coasts of thailand indonesia and sri lanka field observations and satellite images indicate that tsunami waves exhibit specific patterns during flooding and recession forming characteristic incisions in the coastal landscape to study these incisions we analyze high resolution remote sensing images of the coastline of indonesia thailand and sri lanka impacted by the tsunami of december 26th 2004 the analysis sheds light on the different mechanisms by which currents scour incisions during the flooding and receding phases of a tsunami during flooding the high velocity flow indents the levees of existing tidal channels and bays leaving short flood scours the receding water then dissects the coastline with equally spaced return channels widening toward the coast

shells a thin shell program for modeling neotectonics of regional or global lithosphere with faults the thin plate method of modeling neotectonics uses isostasy and vertical integration of lithospheric strength to reduce three dimensional problems to two dimensions we introduce new thin shell continuum elements and fault elements which satisfy the completeness and compatibility requirements and permit extension of these methods to the lithospheres of spherical planets even a coarse grid of these elements with elastic rheology can reproduce low order toroidal free oscillations in the program shells a realistic frictional dislocation creep rheology is handled by iteration this method converges to solutions which can be numerically tested to confirm that they satisfy both local equilibrium and the balance of torques on whole plates because this code can incorporate both natural plate shapes with internal faults and realistic rheologies it yields models that are readily tested by their predictions of geodetic velocities stresses and fault slip rates

internal structure of the aeolian sand dunes of el fangar spit ebro delta tarragona spain this paper presents an analysis of the dune field dynamics of el fangar spit in the ebro delta spain associating it with the internal structure of dunes carried out with ground penetrating radar and supported by data from topographic dgps these analyses are of great importance to ascertain the state of the internal structure of dunes as an important element in their stability and therefore in their evolution the internal structure shows accretion and progradation sequences of dunes over beach deposits which depend on dune morphology height crest orientation and location as well as the processes acting on them

the world stress map database release 2016 crustal stress pattern across scales abstract knowledge of the present day crustal in situ stress field is a key for the understanding of geodynamic processes such as global plate tectonics and earthquakes it is also essential for the management of geo reservoirs and underground storage sites for energy and waste since 1986 the world stress map wsm project has systematically compiled the orientation of maximum horizontal stress shmax for the 30th anniversary of the project the wsm database has been updated significantly with 42 870 data records which is double the amount of data in comparison to the database release in 2008 the update focuses on areas with previously sparse data coverage to resolve the stress pattern on different spatial scales in this paper we present details of the new wsm database release 2016 and an analysis of global and regional stress pattern with the higher data density we can now resolve stress pattern heterogeneities from plate wide to local scales in particular we show two examples of 40 60 shmax rotations within 70 km these rotations can be used as proxies to better understand the relative importance of plate boundary forces that control the long wave length pattern in comparison to regional and local controls of the crustal stress state in the new wsm project phase iv that started in 2017 we will continue to further refine the information on the shmax orientation and the stress regime however we will also focus on the compilation of stress magnitude data as this information is essential for the calibration of geomechanical numerical models this enables us to derive a 3 d continuous description of the stress tensor from point wise and incomplete stress tensor information provided with the wsm database such forward models are required for safety aspects of anthropogenic activities in the underground and for a better understanding of tectonic processes such as the earthquake cycle

stress modeling in the andes constraints on the south american intraplate stress magnitudes regions of high topography which exhibit both compressional and extensional deformation provide a natural laboratory to place constraints on horizontal intraplate stress magnitudes an elastic finite element analysis of the lithospheric stress field in the cordillera bianca region of peru has been used to evaluate the lithospheric stress state and constrain the south american intraplate stress magnitudes the orthogonal orientation of the andean high topography to the east west regional stress field in conjunction with the well documented change in deformation style from compression to extension across the cordillera provides a unique setting for the stress modeling a two dimensional finite element grid consisting of an assembly of isotropic elastic quadrilateral elements in a state of plane strain was used to represent the lithosphere an isostatically balanced crustal density model was used to calculate the stresses associated with the lateral density variations between the andean topography and the brazilian shield in some models horizontal stress was concentrated at midcrustal depths by including vertical variation in young s modulus the modeling results indicate bounds of 10 and 75 mpa for the magnitude of the average horizontal stress averaged over a 100 km thick lithosphere a preferred value of 25 mpa is obtained on the basis of fitting all of the data for the rheological models considered and predicting a transition from extension to compression near the 3000 m elevation contour such a far field average stress is consistent with a ridge push origin because the modeling performed in this study assumes that the topographic load is entirely compensated by the buoyancy of the deflected moho these estimates represent upper bounds the effect of incorporating thermal support for the topographic load of the cordillera bianca would be to further reduce our estimate of the intraplate stress magnitudes analysis of the distribution of calculated stress with depth indicates that previous assumptions about the vertical plane shear stress within the lithosphere being negligible are acceptable for the geometry of the andes

basement fabric controls rift nucleation and postrift basin inversion in the continental margin of ne brazil abstract in passive continental margins the brittle reactivation of shear zones and their role in the deformation and deposition of sedimentary basins are still a matter of debate in this research we investigated the role of the brittle reactivation of precambrian shear zones in the nucleation of rift and postrift faults in the onshore portion of the sergipe alagoas and pernambuco basins in northeastern brazil we combine and interpret a dataset of aeromagnetic and topographic data associated with reflection seismic and borehole data to analyze the evolution of a portion of the atlantic continental margin of brazil our results indicate that in the crystalline basement the magnetic lineaments are correlated with ductile structures as shear zones and the continuity of these lineaments in the sergipe alagoas and pernambuco basins is interpreted as the shear zones below the sedimentary cover of these basins we document the following phases of the brittle reactivation of basement shear zones 1 the opening of the south atlantic ocean in the early cretaceous under an extensional stress regime and 2 tectonic inversion induced by the mid atlantic ridge push and the andean cordillera rise in the neogene quaternary under a predominantly strike slip stress regime during the rift phase the brittle reactivation of the shear zones controlled the locations and architectures of the rifts these structures acted as zones of weakness and were reactivated as normal faults the brittle reactivation of shear zones was still active during the postrift phase and was responsible for the development of compressional structures the reverse faulting and related folding pattern indicate tectonic inversion in the late cretaceous cenozoic the structures formed during the postrift phase under a strike slip regime are consistent with the present day stress field indicating that tectonic inversion is an active phase of the brazilian margin

ground penetrating radar facies of inferred tsunami deposits on the shores of the arabian sea northern indian ocean abstract the occurrence of tsunami waves that affected the shores of the arabian sea including the gulf of oman coastline has been proven by historical reports and sedimentological investigations the damaging effect of such extensive events should not be underestimated in this region in our study we present an investigation of coarse to fine grained marine tsunami deposits in the vicinity of fins sultanate of oman using ground penetrating radar gpr the sedimentary setting along the beach section preserves evidence boulder block deposits as well as trenching results for possible high energy wave impacts the investigated area s environment is representative of conditions which lead to the best possible gpr data quality arid conditions no interference due to electrical power lines and an elevated study area 5 10 m a m s l which eliminates the low frequency noise of the ground and the possibility of salt water in the gpr data 3d visualisation of gpr results from four study areas show e g wedging out of sediments and fining inland features as well as several erosion features at the base of the deposit these findings corroborate the hypothesis of inferred tsunami deposits furthermore the presented gpr investigation technique provides new insights regarding the spatial distribution and internal architecture of palaeo tsunami deposits in comparable tsunami prone regions worldwide

a 1500 yr record of north atlantic storm activity based on optically dated relict beach scarps understanding of long term dynamics of intense coastal storms is important for determining the frequency and impact of these events on sandy coasts we use optically stimulated luminescence osl dates on relict scarps within a prograded barrier sequence to reconstruct the chronology of large magnitude erosional events in the western gulf of maine osl dates obtained on quartz rich sediments immediately overlying relict scarps indicate severe beach erosion and retreat due to erosional events ca 1550 390 290 and 150 cal yr b p our data provide new evidence of increased storm activity most likely frequency and or intensity of extratropical storms during the past 500 yr which was preceded by a relatively calm period lasting 1000 yr the width of the coastal sequence preserved between successive paleoscarps shows strong correlation with the time interval elapsed between storms our fi ndings indicate that diagnostic geophysical and sedimentological signatures of severe erosional events offer new opportunities for assessing the impact and timing of major storms along sandy coasts

stress observations and driving force models for the south american plate stress observations are compared to predictions of driving force models for the south american plate stress observations have the potential to give detailed information about the forces driving the plates in that sets of forces with the same net torque can produce quite different stress patterns for a two dimensional vertical section model of a plate there are three conditions for dynamical equilibrium the net forces and the net torque about any point must all be zero these conditions are used to estimate the magnitudes of forces as a function of age with ridge push and slab pull as active forces and plate drag and slab resistance as passive forces the results are consistent with earlier published models and indicate that the primary balance for an oceanic plate is between slab pull and the resisting drag forces we generalize the model for the possible forces driving the south american plate and compare with observed stress measurements and kinematics the south american plate has a small slab pull component amounting to about one fifth the ridge push force with the other components reasonably isolated geographically thus the plate balance is largely between ridge push and plate drag this gives an opportunity of resolving the effects of trench suction or collision at the subduction zones most remarkable is the nearly uniform e w orientation of the regional stress field shmax directions which is extensional in the high andes a second feature is the n s orientations in the amazon basin the two dimensional horizontal stress patterns are compared for successive models of combinations of driving forces models with ridge push slab pull at the scotia and caribbean arcs and trench suction near the west coast balanced by plate drag produce similar stress patterns to those observed the magnitude of a possible trench suction force is estimated using a model with an eddy between the nazca slab and the overlying south american plate

topography growth drives stress rotations in the central andes observations and models 1 recent numerical models that couple global mantel circulation with lithosphere dynamics show that growth of the central andes controls the 30 reduction of convergence velocity between the nazca and south america plates observed over the past 10 ma the increase of gravitational potential energy due to topographic growth is also a major control on the stress pattern here we use numerical models which reproduce the nazca south america convergence history to predict the change of stress pattern in the central andes for the past 10 ma comparison of the modeled stress orientations at present day with the observed ones results in 23 9 mean deviation based on this good agreement we attempt to predict paleostress orientations 10 ma ago interestingly the modeled stress orientations 3 2 ma ago are very similar to the present day orientations from this result we infer that stress rotations occurred between 10 and 3 2 ma ago when topography was considerably lower

bending the bolivian orocline in real time global positioning system gps data from the central andes record vertical axis rotations that are consistently counterclockwise in peru and bolivia north of the bend in the mountain belt and clockwise to the south in southern bolivia argentina and chile these geologically instantaneous rotations have the same sense as rotations that have accrued over millions of years and are recorded by paleomagnetic and geologic indicators the change in sign of the rotation at both decadal and million year time scales occurs across the axis of topographic symmetry that defines the bolivian orocline when extrapolated to a common time interval the magnitudes of rotation from geologic features and from gps are surprisingly similar given that a significant part of the instantaneous deformation field is probably elastic and due to interseismic locking of the plate boundary some of the interseismic deformation field must reflect permanent deformation and or some of the current elastic deformation will be converted to upper plate permanent deformation over time rather than be recovered by elastic rebound during interplate earthquakes we suggest that the spatial patterns of the elastic and the permanent modes of bending are similar because they are driven by the same stress field

plate boundary forces are not enough second and third order stress patterns highlighted in the world stress map database 1 the world stress map project compiles a global database of contemporary tectonic stress information of the earth s crust early releases of the world stress map project demonstrated the existence of first order plate scale stress fields controlled by plate boundary forces and second order regional stress fields controlled by major intraplate stress sources such as mountain belts and zones of widespread glacial rebound the 2005 release of the world stress map project database provides for some areas high data density that enables us to investigate third order local stress field variations and the forces controlling them such as active faults local inclusions detachment horizons and density contrasts these forces act as major controls on the stress field orientations when the magnitudes of the horizontal stresses are close to isotropic we present and discuss examples for venezuela australia romania brunei western europe and southern italy where a substantial increase of data records demonstrates some of the additional factors controlling regional and local stress patterns

zircon u pb ages major and trace elements and hf isotope characteristics of the tiantangzhai granites in the north dabie orogen central china tectonic implications cretaceous granites are widespread in the north dabie orogen central china but their emplacement sequence and mechanism are poorly known the tiantangzhai complex in the north dabie complex is the largest cretaceous granitic suite consisting of six individual intrusions in this study zircon u pb ages are used to constrain the crystallization and protolith ages of these intrusions the shigujian granite is a syn tectonic intrusion with an age of 141 ma this granite was emplaced under a compressional regime oscillatory rims of zircons have yielded two peaks at 137 1 ma and 125 1 ma the 137 1 ma peak represents the beginning of orogenic extension and tectonic collapse whereas the 125 1 ma peak represents widespread granitic magmatism zircon cores have yielded concordant ages between 812 and 804 ma which indicate a crystallization age for the protolith the tiantangzhai granites show relatively high sr contents and high la yb and sr y ratios the shigujian granite has positive eu anomalies resulting from partial melting of a plagioclase rich source in an over thickened crust correspondingly in situ lu hf analyses from zircons yield high negative e hf t values from 24 8 to 26 6 with two stage hf model ages from 2748 34 to 2864 40 ma suggesting that the magmas were dominantly derived from partial melting of middle to lower crustal rocks the dabie orogen underwent pervasive nw se extension at the beginning of the early cretaceous associated with subduction of the palaeo pacific plate beneath eastern china

efficient computation of surf zone waves using the nonlinear shallow water equations with non hydrostatic pressure abstract a numerical method for non hydrostatic free surface irrotational flow governed by the nonlinear shallow water equations including the effects of vertical acceleration is presented at the aim of studying surf zone phenomena a vertical boundary fitted grid is used with the water depth divided into a number of layers a compact finite difference scheme is employed for accurate computation of frequency dispersion requiring a limited vertical resolution and hence capable of predicting the onset of wave breaking a novel wet dry algorithm is applied for a proper handling of moving shoreline mass and momentum are strictly conserved at discrete level while the method only dissipates energy in the case of wave breaking the numerical results are verified with a number of tests and show that the proposed model using two layers without ad hoc assumptions enables to resolve propagating nonlinear shoaling breaking waves and wave run up within the surf and swash zones in an efficient manner

analysis of the south american intraplate stress field the first order south american intraplate stress field was modeled through a finite element analysis to evaluate the relative contribution of plate boundary forces and intraplate stress sources the finite element mesh consisted of 3100 nodes in a network of 5993 equal area triangular elements which provided a spatial resolution of about 1 at the equator an important aspect of our modeling is the inclusion of topographic forces due to the cooling oceanic lithosphere along the mid atlantic ridge e g ridge push the continental margins along the east coast of brazil and argentina and the elevated continental crust e g the andean cordillera predicted intraplate stresses for two representations of the western collisional boundary forces are evaluated pinned collisional boundaries and applied collisional boundary forces constraint for the modeling was provided by information about the orientation of the maximum horizontal compressive stress shmax provided by 217 stress indicators from the world stress map project as well as by shmax magnitude estimates and torque information from previous investigations our modeling results demonstrate that the first order features of the observed stress field can be explained with simple tectonic models which balance the torque acting on the plate either with a fixed western margin or drag forces applied along the base of the plate the predicted intraplate stress field is characterized by a nearly uniform e w shmax orientation throughout most regions of the plate with stress magnitudes generally less than 20 mpa averaged over a 100 km thick lithosphere significant perturbation of this regional stress field occurs in the western part of the plate in response to forces associated with the high topography of the andes although the magnitude of the collisional boundary forces acting along the western margin remains poorly constrained we estimate a plausible upper bound on the force per unit length acting along the peru chile trench to be about 2 5 1012 n m 1 while some of our models are consistent with a driving basal drag to balance the torques acting on the plate the magnitude of the drag torque is small compared to the contribution from other sources of stress such as the ridge push force

evidence for storm dominated early progradation of castle neck barrier massachusetts usa abstract washovers dune scarps and flattened beach profiles with concentrations of coarse grained sediment or heavy minerals are the diagnostic geological signatures of large storms on barriers today it is clear that storms are a major force driving transgressive barriers onshore but what is not as well understood is the role these powerful erosive events play in the evolution of prograding barriers application of ground penetrating radar gpr and a combination of coring techniques have significantly improved our ability to image barrier architecture results of these studies reveal a more complex evolution than previously recognized it is now possible to precisely locate and map storm deposits within prograded barrier lithosomes a comprehensive study of northern castle neck massachusetts was performed using 15 km of gpr surveys a 120 m long seismic line 11 cores and several radiocarbon dates storm related layers are the most prominent horizons contained in the barrier stratigraphy the geometry and sedimentology of these layers closely resembles those of a present day post storm beach twenty closely spaced curvilinear heavy mineral layers imaged in the landward portion of the barrier suggest that the castle neck barrier was heavily influenced by storms during its initial phase of progradation beginning 4000 years bp approximately 1800 years bp two intense storms impacted the coast depositing two extensive coarse grained units these layers mimic the flat lying sand and gravel deposits that occur in front of a nearby eroding till outcrop following major storms the great number of storm deposits in the early history of castle neck is related to either a period of greater storm activity and or a slow rate of barrier progradation the occurrence and preservation of these earlier storm layers are likely a product of the exposure of nearby drumlins resulting in greater availability of iron oxide and ferromagnesian sands the supply of heavy mineral sands has gradually diminished as the barrier prograded and the proximal drumlin source was buried by beach and dune sands

cenozoic shift from compression to strike slip stress regime in the high andes at 30 s during the shallowing of the slab implications for the el indio tambo mineral district in the high andes of central chile above the flat slab segment analysis of more than 1 000 fault slip data from miocene outcrops provides evidence for a change of the regional tectonic regime from compressional to strike slip this shift in tectonic regime occurred during the waning stages of arc volcanism between 14 and 11 ma as a result of the shallowing of the nazca plate in conjunction with the migration of deformation to the precordillera during the early to middle miocene a compressive regime with horizontal 1 axis n86 e was responsible for reverse slip along nne to n striking faults during the late miocene a shift to strike slip tectonics took place due to an increase in the absolute magnitude of the vertical stress component as the crust thickened and the gravitational potential energy increase we argue that instead of the previously accepted highly compressional setting in the arc region during the slab flattening the change to a strike slip regime was the main control on mineralization mineralization was controlled by the promotion of fluid expulsion from the magma chambers along active sub vertical strike slip fault systems with a high slip tendency and focusing of fluids in localized areas undergoing extension under this strike slip regime the el indio tambo and la despensa fault systems formed as dextral strike slip systems the tips and jog sites along these faults experienced local extensional stress fields forming the el indio and tambo mineral districts

new constraints on the evolution of carolina bays from ground penetrating radar ground penetrating radar gpr data for the savannah river site srs in the upper coastal plain of south carolina combined with geological archaeological and ecological data place new constraints on the evolution of carolina bays extant srs bay morphology formed mainly during the holocene and did not involve migration of bays across the landscape multiple periods of bay rim accretion with intervening intervals of erosion may characterize the longer term evolution of the bays bay evolution however did not involve significant modification of the upland unit underlying the region during fluctuating but generally open water conditions breaking waves along bay shorelines eroded and transported sediment which was subsequently exposed for deflation during periods of low water deflation and transport of sand into standing vegetation along the margin of the bay depression created a rim in the form of a parabolic dune lacking obvious internal stratification simultaneously infilling occurred by shoreline erosion and transport from adjacent elevated surfaces this coupled with growth of emergent vegetation resulted in decreased hydroperiod wave energy shoreline modification and rim accretion transport of some rim sediments back into the bays via alluvial and colluvial activity created wedges of infilling sediment during waning stages of evolution the apparent contradiction of bay orientation with respect to prevailing winds might reflect seasonal changes in water level and wind direction southwesterly winds during spring high water causes nw se elongation of the bays whereas northwesterly winds during lower water in the fall and winter account for nearshore deflation and rim accretion along the east southeastern bay margins

the sedimentary architecture of a holocene barrier spit sylt german bight swash bar accretion and storm erosion abstract the southern german north sea coast was shaped by the last post glacial sea level rise that caused a significant retreat of the coastline approximately 5 ka bp the rate of sea level rise decreased providing space for the formation of the frisian islands which line the coast this study is focused on the island of sylt located at the german north sea coast close to the danish border here two sandy spit systems developed during the holocene combining ground penetrating radar studies and sedimentological investigations based on shallow cores new aspects on the sedimentary history of this holocene spit system have been revealed the data indicate that strong erosional events alternated with phases of progradation and growth the welding of swash bars is shown to be the predominant process during progradational phases of the spit system during these periods progradation was not restricted to linear growth along the spit axis but also included a seaward directed component major erosion surfaces which delimit progradational sediment packages are interpreted to reflect exceptionally severe storms the fossilization potential of this sedimentary record was controlled by a positive net long term sediment balance and the position of the ground water table which controlled eolian deflation only with a stable or rising sea level and associated ground water table position are sediments protected from deflation the proposed sedimentary model may serve as a template for interpretation of comparable settings in the geological record

a tsunami record in the sedimentary archive of the central algarve coast portugal characterizing sediment reconstructing sources and inundation paths this study describes sedimentation associated with the tsunami generated by the lisbon earthquake of ad 1755 it is argued here that the tsunami deposited a sand sheet across the lagoa dos salgados

sedimentary architecture of a spit end salisbury beach massachusetts the imprints of sea level rise and inlet dynamics abstract in the vicinity of tidal inlets the facies architecture of barrier islands is largely controlled by inlet channel shifting and the transfer of sand between the ebb tidal delta and the adjacent shore including processes of inlet sediment bypas sing merrimack river inlet is situated in a mixed energy setting and is characterized by episodic shifting of the ebb channel prior to being stabilized in 1881 here we delineate the internal structure and evolution of the updrift barrier spit terminus by integrating data obtained from ground penetrating radar transects and sediment cores to document the effects of inlet associated sedimentation processes our results document complex radar and sedimentological facies which define two distinctive associations of facies the inlet distal and proximal within the core of the present barrier these facies are associated with three phases of barrier terminus evolution i barrier retrogradation characterized by the preservation of washover and backbarrier marsh facies deposited during sea level rise ii downdrift barrier progradation characterized by channel fill and swash platform deposits overlain by foreshore deposits generated by long shore currents and swash bars migrating to the foreshore from the swash platform and iii foreshore seaward progradation characterized by cross beds this study illustrates the highly complex nature of inlet associated spit ends of barriers likewise our results shed light on the mechanisms of spit elongation and recurving in a setting where the estuary opening is narrowing

joint modeling of lithosphere and mantle dynamics evaluation of constraints from global tomography models with the advances in technology seismological theory and data acquisition a number of high resolution seismic tomography models have been published however discrepancies between tomography models often arise from different theoretical treatments of seismic wave propagation different inversion strategies and different data sets using a fixed velocity to density scaling and a fixed radial viscosity profile we compute global mantle flow models associated with the different tomography models and test the impact of these for explaining surface geophysical observations geoid dynamic topography stress and strain rates we use the joint modeling of lithosphere and mantle dynamics approach of ghosh and holt 2012 to compute the full lithosphere stresses except that we use hc for the mantle circulation model which accounts for the primary flow coupling features associated with density driven mantle flow our results show that the seismic tomography models of s40rts and saw642an provide a better match with surface observables on a global scale than other models tested both of these tomography models have important similarities including upwellings located in pacific eastern africa iceland and mid ocean ridges in the atlantic and indian ocean and downwelling flows mainly located beneath the andes the middle east and central and southeast asia

historical tsunamis and storms recorded in a coastal lowland shizuoka prefecture along the pacific coast of japan four sand units deposited by tsunamis and one sand unit deposited by storm surge s were identified in a muddy marsh succession in a narrow coastal lowland along the pacific coast of central japan tsunamis in ad 1498 1605 1707 and 1854 that were related to large subduction zone earthquakes along the nankai trough and storm surges in 1680 and or 1699 were responsible for the deposition of these sand units these sand units are distinguished by lithofacies sedimentary structures grain size and mineral composition and radiocarbon ages their ages are supported by events in local historical records the tsunami deposits in the study area are massive or parallel laminated sands with associated intraclasts gravels draping mud layers and rarely a return flow subunit the storm surge deposits are devoid of these characteristics and are composed of groups of thin current ripple laminated sand layers the differences in sedimentary structures between the tsunami and storm surge deposits are attributed to the different characteristics of tsunami and storm waves

relating rapid plate motion variations to plate boundary forces in global coupled models of the mantle lithosphere system effects of topography and friction abstract recent high resolution models of past plate motions and their comparison with plate motion models inferred from space geodetic techniques reveal a number of short term variations in global plate velocities over the past 10 myrs such variations serve as powerful probe into the nature and magnitude of plate boundary forces because they are unlikely to originate from changes in mantle buoyancy forces which evolve on longer time scales here we explore the constraints of the velocity record using a novel coupled modeling approach of global neo tectonic simulations combined with realistic plate driving forces obtained from mantle circulation models mcms to arrive at simple global budgets of mantle lithosphere and plate boundary forces we focus on three plate boundary systems along the nazca south america plate margin the aleutian trench and the india australia plate boundary to show that gravitational spreading from high topography in the andes and tibet contributes substantially to the global plate tectonic force balance and that this contribution is sufficient to explain some 35 of recent velocity changes over the earth s surface including among others the observed 30 convergence reduction between the nazca south america plates our models make a number of specific predictions such as significant lateral variations in plate coupling forces along a given margin revealed by trench parallel gravity and bathymetry anomalies and the occurrence of large earthquakes as well as differences by as much as a factor of five from margin to margin they also support the notion of a relatively young plate boundary separating the india and australia plates which has been previously suggested based on independent observations importantly we find that the modeled nazca south america convergence reduction explains recent spreading rate variations in the south atlantic and south pacific which points to the importance of far field effects on the adjacent continents in explaining the spreading record of oceanic basins our numerical results demonstrate a that detailed budgets of forces acting upon plates can be obtained and b support the notion of strong forcing along weak plate boundaries

ridge forces absolute plate motions and the intraplate stress field torque poles are calculated for a variety of possible forces acting on the plates including ridge push slab pull and collisional resistance these torque poles are then compared to the directions of absolute plate motions there is a strong correlation between ridge torque poles and the azimuth of absolute plate motions for the north american south american pacific cocos and eurasian plates simple slab pull torques correlate well with absolute motion azimuths for the pacific nazca and cocos plates and moderately well with the absolute motion azimuth of the indoaustralian plate collisional resistance torque poles correlate with the absolute motion azimuth of the eurasian plate only the correlations are presented as further evidence that the absolute reference frame for plate motion is determined by the surface plates themselves torque poles for various forces are also compared with several long wavelength features of the global intraplate stress field that also tend to be aligned with absolute motion directions in general ridge torque directions agree well with the orientations of maximum horizontal stresses for stable north america western europe and south america and provide an alternative explanation for the alignment in terms of ridge push forces rather than basal drag collisional resistance forces can also explain the alignment of stresses in western europe for the indoaustralian plate the torque pole for collisional resistance forces is consistent with the general pattern of stresses in at least the western half of the plate but is not a good predictor of the entire data set for the plate other processes in addition to collisional resistance must be important for the indo australian plate ridge push forces may account for a significant portion of the long wavelength features of the intraplate stress field especially away from continental collisions such a conclusion is consistent with negative buoyancy of the slab being an important component of the driving mechanism as previously suggested slab forces may be largely balanced within the subducted slab itself and thus have limited effect on deformation of the surface plates

effects of density contrasts on the orientation of stresses in the lithosphere relation to principal stress directions in the transverse ranges california the influence of stresses arising from horizontal density contrasts on the orientation and relative magnitudes of principal stresses in an otherwise uniform lithospheric stress field is investigated a simple model is constructed in which a local deviatoric stress due to a density anomaly embedded within or just below the lithosphere and a regionally constant deviatoric stress field are each approximated by biaxial tensors the net stress field is obtained from the sum of the two both the relative magnitudes of principal stresses and the magnitude of the angular difference in principal stress direction of the summed tensor compared with that obtained in the absence of buoyancy forces depend on two parameters the first is the ratio where is a measure of the magnitude of the regional deviatoric stress and is the magnitude of the stress arising from buoyancy forces associated with the density anomaly the second parameter is the angle between the trend of the density anomaly and the direction of maximum compressional stress that obtains in the absence of any perturbation by the local buoyancy forces the directions of the principal axes of the total stress field are found to differ by up to 90 from those of the reference stress field the model is applied to the transverse ranges california where the observed 23 difference in orientation of principal horizontal compressive stress compared with the principal compressive stress direction in central california constrains the predicted value of to be approximately 0 4 this is consistent with an independently calculated range of in which is inferred from seismological constraints on the magnitude of density variations underneath the transverse ranges and is inferred from observations of heat flow along the san andreas fault in central california the agreement between the two estimates of supports the hypothesis that the observed differences in horizontal principal stress orientation in california can be explained by the combined influence of a local negative buoyancy force under the transverse ranges and a regional stress field associated with transcurrent deformation within the pacific north american plate boundary zone the observed counterclockwise angular difference in principal horizontal stress direction in the transverse ranges compared with central california implies that the plane of maximum right lateral shear stress is also rotated counterclockwise relative to that in central california this supports the possibility that the big bend in the san andreas fault may be a consequence of the negative buoyancy forces acting in the transverse ranges and not the cause of transverse ranges formation as has often been assumed

holocene sea level fluctuations and coastal evolution in the central algarve southern portugal in armacao de pera bay southern portugal environmental changes during the holocene can be interpreted based on the morphological and sedimentological similarities between older geomorphic features cemented beach and dune rocks and present coastal features using knowledge of the present beach and dune processes we propose a two step model for the evolution of armacao de pera bay first during the rapid sea level rise between about 8 800 and 6 600 yr cal bp the bay changed from a positive to a negative budget littoral cell and transgressive dunes formed favoured by drought conditions at about 5 000 yr cal bp during a sea level maximum beach width was less than the critical fetch and dunes stabilized and underwent cementation during the wetter atlantic climatic event the second phase of dune accumulation started at about 3 200 yr cal bp due to a regression of sea level during which the bay changed back to a positive budget littoral cell in which beach width was greater than the critical fetch currently the beach width is less than the critical fetch dunes are inactive and the sedimentary budget is negative due to sediment storage in local river systems

geomorphological effects of tsunami run up and backwash abstract geomorphological processes associated with tsunami run up and backwash are highly complex to date most studies have considered the sedimentology of palaeo tsunamis while almost no detailed studies have been undertaken in areas known to have been affected by tsunamis in recent times research on contemporary tsunamis show that coastal landscapes may be greatly altered not only by direct tsunami run up orthogonal to the shoreline but also by episodes of vigorous backwash and by water flow sub parallel to the coastline the combined effect of these processes produces hitherto unrecognised coastal landforms that are dominated by the effects of high magnitude erosion and deposition deposition of large boulders is also associated with severe tsunamis while in adjacent areas run up processes often result in the deposition of continuous and discontinuous sediment sheets in many instances the upper limit of sediment deposition lies well below the upper limit of wave run up which is frequently marked by a well defined zone of stripped vegetation and soil the processes described have considerable implications for models of coastal evolution it may even be the case that the evolution of particular stretches of coastline are dominated by such high magnitude low frequency events

contemporary recent extension and compression in the central andes abstract although extension in the high andes vs compression in the lowlands has already been widely discussed in the literature for the first time we recognized both extensional and contractional structures that developed contemporaneously during late pliocene quaternary times in a wide area of the central andean chain about 90 000 km 2 where crustal earthquake data are missing this area comprises north eastern chile south western bolivia and north western argentina and extends from the puna plateau to the altiplano volcanic belt late pliocene quaternary folds with hinge lines trending nne ssw to n s are mostly located along the westernmost part of the volcanic belt and the eastern part of the western cordillera locally there are coeval reverse faults parallel to the folds which reach up to the surface particularly the miscanti ridge tolocha fault and la casualidad ridge may be the morphostructural expression of tens km long fault propagation folds which locally show topographic scarps hundreds of meters high north and east of the contractional structures we found evidence of late pliocene quaternary normal faults striking n s in the southern part of the study area and nw se in the northern part well developed grabens are present in the higher areas of the volcanic belt and in the transition zone with the puna plateau the surface rupture zones of normal fault swarms range 8 24 km in length with single fault strands up to 18 km long which are typical of tectonic structures the distribution in space and time of the studied contractional and extensional structures indicates that they originated in the same time period we thus address the challenging question regarding the possible origin of the stress sources by analysing possible causes such as volcanotectonics high topography orogeny collapse and gravitational spreading of the orogen in relation also with the role played by inherited structures we finally analyse the relations between the different structures and magma upwelling and the potential for seismic hazard

the strength of faults in the crust in the western united states abstract the strength of secondary faults within plate boundary zones and of master faults like the san andreas has been controversial for decades we use a global finite element code with a variable resolution grid and global plate driving forces to determine whether the effective friction on the san andreas fault is high 0 6 1 intermediate 0 3 0 5 or low 0 2 whether a single value of can be used for all mapped faults within california and whether weakening of the ductile lower crust associated with faulting is important we compare our model results with existing data on fault slip rates gps velocities stress field and earthquake depth distribution the comparison indicates that all faults are weak 0 2 and that additional weakening of major faults is important all viable solutions also indicate that weakening of the lower crust below major faults is necessary the strongest faults in the region have in the range 0 2 0 05 the san andreas fault is a very weak fault among weak faults with

seismic driving of nationwide changes in geomorphology and prehistoric settlement a 15th century new zealand example abstract we propose a model for the seismic driving of environmental changes and illustrate it using a case study from new zealand dated to the 15th century ad a seismic staircase shows a chronological progression of environmental outcomes that includes tsunami rock avalanches vegetation disturbance rapid coastal dune building river aggradation and abandonment of prehistoric coastal settlements the 15th century event appears to be unique in the past millenium and is most notable for its period of rapid coastal dune building the coincidence of a catastrophic el nino episode in the mid 15th century ad may have served to move sediments rapidly through the terrestrial system thus delimiting clearly separate geomorphological after effects we contend that seismic driving is a major factor in determining paleoenvironmental change in tectonically active areas during the holocene and provides the palaeoenvironmental context within which smaller scale events operate

hydro and morpho dynamic modeling of breaking solitary waves over a fine sand beach part i experimental study abstract the objectives of this work are 1 to examine the mechanisms that influence tsunami erosion and deposition mechanisms in the littoral zone via physical simulations of breaking solitary waves over a fine sand beach and 2 to provide experimental data for validation of numerical models to predict tsunami erosion and deposition processes the experiments were carried out in a 48 8 m 2 16 m 2 1 m wave flume the flume was instrumented to observe free surface elevations cross shore velocities suspended sediment concentrations vertical and cross shore pore pressure gradients near the shoreline and morphological changes in addition wave sediment interactions were observed via underwater video cameras the results are systematically analyzed to investigate the roles of wave breaking bore runup wave drawdown and wave induced pore pressure variations on tsunami erosion and deposition processes the studies showed that the wave plunging on a thin layer of water prior to reaching the shoreline did not cause much sediment suspension while the waterjet impinging directly on the beach entrained substantial amounts of sand the suspended sediments were subsequently pushed up the slope by fluid momentum as the broken wave transformed to a turbulent bore a small net deposition region was observed near the maximum runup point where both the flow velocity and the water depth were near zero a significant amount of the sediment transport occurred during the wave drawdown in the form of thick sheet flow which resulted in net erosion of the shore face and the beach a hydraulic jump formed near the wave breaking region toward the end of the drawdown which caused most of the suspended sand to deposit in the wave breaking region consequently breaking solitary waves over a sloping fine sand beach led to net erosion of the shore face and the beach net deposition in a small region immediately seaward of the max excursion point and net deposition in the wave breaking zone

changes in the tectonic regime above a subduction zone of andean type the andes of peru and bolivia during the pliocene pleistocene this paper adresses the changes in the tectonic regime in the peruvian and bolivian andes that have occurred since the upper miocene when the present day elevation of the cordillera above sea level has been almost reached the stress patterns are deduced essentially from a field study of fault kinematics and a numerical inversion of the slip vector data measured on the fault planes the cuzco fault system in southern peru is chosen as an example to illustrate the methodology used in this region striations on both active and holocene faults are in agreement with a n s extension but faults affecting early pleistocene deposits exhibit two families of striations the younger results from the previous n s extension the older involving reverse motions results from either an e w or a n s compression faults affecting pliocene formations often show an oldest family of striations resulting from a ne sw or an e w trending extension thus three tectonic regimes are demonstrated which are also supported by regional unconformities and sedimentological data 1 a pliocene extensional regime 2 a lower pleistocene compressional regime and 3 a mid pleistocene present day extensional regime similar analyses conducted in the pacific and sub andean lowlands allow sketching of the successive pliocene pleistocene stress patterns in the central andes the quaternary and present day stress pattern is characterized by a n s extension in the high andes and in the pacific lowlands and by an e w compression in the sub andean lowlands and at the contact between the nazca and south american plates this stress pattern is interpreted at a large wavelength 100 km as an effect of compensated topography this model supposes that the vertical lithospheric stress zz increases with the topography the crustal thickness and the low density mantle beneath and that the lithospheric maximum compressional horizontal stress hmax trending e w roughly parallel to the convergence is fairly constant on both edges of the andes the tectonics being compressional zz is 3 and hmax is 1 in the high andes zz becomes 1 then the e w trending hmax is 2 and hmin trending n s is 3 allowing extension to occur in this direction the pliocene stress pattern was characterized by a ne sw or an e w trending extension in the high andes in the pacific lowlands and possibly in the sub andean lowlands this stress pattern was clearly different from the present day one because the e w trending stress was hmin this required a weak push or eventually tractional boundary forces acting on the south american lithosphere it is suggested that this might result from a strong slab pull due to a long steeply dipping slab which decreased the value of the xx stress transmitted to the overriding plate the early pleistocene state of stress was compressional since the elevation of the andes had not markedly decreased during this period this required an increase of the e w trending stress value this resulted from a strong coupling between the two lithospheric plates possibly due to a rupture of a long slab under its own weight other spatial changes in the stress pattern are related to the particular situation of the forearc to the subduction of the buoyant nazca ridge and to the different dips of the slab extension in the high andes is of small magnitude of the order of 1 during the last 1 2 m y in a few basins it may have attained 40 during the pliocene 5 3 m y

cenozoic climate change as a possible cause for the rise of the andes causal links between the rise of a large mountain range and climate have often been considered to work in one direction with significant uplift provoking climate change here we propose a mechanism by which cenozoic climate change could have caused the rise of the andes based on considerations of the force balance in the south american lithosphere we suggest that the height of and tectonics in the andes are strongly controlled both by shear stresses along the plate interface in the subduction zone and by buoyancy stress contrasts between the trench and highlands and shear stresses in the subduction zone depend on the amount of subducted sediments we propose that the dynamics of subduction and mountain building in this region are controlled by the processes of erosion and sediment deposition and ultimately climate in central south america climate controlled sediment starvation would then cause high shear stress focusing the plate boundary stresses that support the high andes

cenozoic global plate motions cenozoic global plate motions relative to the hot spots are investigated and compared to plate motions in a mean lithosphere reference frame plate motions were analyzed over six time intervals divided by ages 10 25 43 48 and 56 ma chosen as much as possible to coincide with key plate reorganizations alternative motion circuits and rotational parameters were considered and evaluated with paleomagnetic data from the pacific and north american plates the circuit found to be in best agreement with the paleomagnetic data is one in which the hot spots in the atlantic region are assumed to be fixed relative to the hot spots in the pacific region throughout the cenozoic the hot spot and mean lithosphere reference frames have been in continual slow relative motion the rate of motion is nonuniform however most of the motion having occurred during the middle cenozoic the net cenozoic rotation of the lithosphere relative to the hot spots is described by a right handed rotation of 7 about a euler pole at 46 s 87 e which yields a 5 displacement of the north poles of the two reference frames this motion is small enough that inferences drawn about plate speeds in one reference frame should be valid in the other analysis of the global motions resulting from our preferred model showed that many characteristics of current plate motions have persisted throughout the cenozoic plate speeds correlate with latitude plates moving faster near the equator than near the poles throughout the cenozoic as at present continental plates except for the indian plate moved slower than oceanic plates throughout the cenozoic even the structure of the velocity fields as revealed in a contour of root mean square velocities in equatorial bands persists throughout the cenozoic the migration of the paleomagnetic axis over time is also compared to the hot spot and mean lithosphere reference frames the paleomagnetic axis has shifted 5 10 relative to the hot spot frame and a lesser amount relative to the mean lithosphere frame

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

how did the ad 1755 tsunami impact on sand barriers across the southern coast of portugal idl pest oe cte la0019 2013 plani2c ed481b 2014 132 0 post doc eu fp7 research project risc kit ga 2013 603458 e fct investigator program ref if 01047 2014

joint modeling of lithosphere and mantle dynamics sensitivity to viscosities within the lithosphere asthenosphere transition zone and d layers abstract although mantle rheology is one of the most important properties of the earth how a radial mantle viscosity structure affects lithosphere dynamics is still poorly known particularly the role of the lithosphere asthenosphere transition zone and d layer viscosities using constraints from the geoid plate motions and strain rates within plate boundary zones we provide important new refinements to the radial viscosity profile within the key layers of the lithosphere asthenosphere transition zone and d layer we follow the approach of the joint modeling of lithosphere and mantle dynamics ghosh and holt 2012 ghosh et al 2013b 2019 wang et al 2015 to show how the viscosities within these key layers influence lithosphere dynamics we use the viscosity structure sh08 steinberger and holme 2008 as a starting model the density variations within the mantle are derived from the tomography models which based on prior modeling had provided a best fit to the surface observables wang et al 2015 our results show that narrow viscosity ranges of moderately strong lithosphere 2 6 5 6 1022 pa s and moderately weak transition zone 5 9 3 1020 pa s as well as slightly large ranges of moderately weak asthenosphere 5 34 1019 pa s and d layer 4 8 18 1020 pa s are necessary to match all the surface observables we also find that a very strong lithosphere 8 6 1022 pa s along with a weak asthenosphere

stress balance above subduction application to the andes the frequent changes in tectonic and morphological evolutions of active plate margins suggest that similar processes drive apparently antagonistic tectonics we address the problem by a thin viscous sheet approach where the governing stresses are restricted to interplate traction buoyancy and viscous stresses various cases are explored from compression to extension leading to dismiss corner flow driven models and to favor interplate traction driven models from the topography of the andes we determine the magnitude and profiles of the current stresses beneath the andes at various locations the total transmitted force is about 9 1012 n m 1 shear stresses at the boundaries of the deforming lithosphere range between 25 and 110 mpa and almost balance the buoyancy stresses due to crustal thickening the remaining difference being the viscous stresses the deviatoric stress is less than 10 mpa and the effective viscosity of the andean lithosphere is as low as 3 1021 pa s maximum compression is located in the eastern side of the andes matching the geological observations but we find that the current stress regime is insufficient to explain the present day elevation this suggests that interplate traction was slightly stronger in the past when the neogene plate convergence was faster and this decrease in interplate traction implies that high and steep parts of the andes cannot be sustained anymore the shape of the altiplano can be explained by a weak lateral variation of the viscosity which allows the high plateau to be constructed in the characteristic time span of andean building

optically stimulated luminescence dating of young sediments a review optically stimulated luminescence osl dating of young 1000 years sediments is used increasingly in a wide variety of late holocene studies as a mean of establishing contemporary sedimentation rates or the timing of sediment deposition this paper provides a summary of the basic principles of osl dating outlines the problems specific to the dating of young material and then uses recent applications to young sediments to illustrate the greatly increased scope and potential of the method in geomorphology and the geology of recent deposits the overall reliability of this new generation of osl ages is examined by comparing where possible osl ages with independent age control it is concluded that the osl ages are accurate in that there is no evidence for systematic over or under estimation it is our conclusion that osl dating should be regarded as a reliable chronological tool for determining the time of deposition of water lain sediments from the coastal zone and aeolian deposits from both coastal and inland environments our conclusion is supported by the growing popularity of osl dating in geomorphology and geology

feedback between mountain belt growth and plate convergence while it is generally assumed that global plate motions are driven by the pattern of convection in the earth s mantle the details of that link remain obscure bouyancy forces associated with subduction of cool dense lithosphere at zones of plate convergence are thought to provide significant driving force but the relative magnitudes of other driving and resisting forces are less clear as are the main factors controlling long term changes in plate motion the ability to consider past as well as present plate motions provides significant additional constraints because changes in plate motion are necessarily driven by changes in one or more driving or resisting forces which may be inferred from independent data here we present for the first time a model that explicitly links global mantle convection and lithosphere models to infer plate motion changes as far back as miocene time by accurately predicting observed convergence rates over the past 10 m y we demonstrate that surface topography generated at convergent margins is a key factor controlling the long term evolution of plate motion specifically the topographic load of large mountain belts and plateaus consumes a significant amount of the driving force available for plate tectonics by increasing frictional forces between downgoing and overriding plates

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

seismic driving of sand beach ridge formation in northern honshu japan abstract the coastal sendai plain consists of an extensive sand beach ridge system that was inundated by the 2011 tohoku oki tsunami the spatial and temporal extent of these beach ridges appears to match well with the record of past earthquakes and tsunamis in the region and it is proposed that they could have formed as a result of a process called seismic driving this process recognises the widespread and catastrophic disruption of the environment caused by a large earthquake a series of immediate and delayed after effects created by a cascade of geomorphological processes linking the earthquake with beach ridge formation is examined for the sendai plain the significance of the role played by volcanic eruptions smaller earthquakes and climate related high intensity and duration rainfall activity is also highlighted at a region wide scale the beach ridge systems of ishinomaki akita aomori and tanabu are also considered alongside those of the sendai plain throughout northern honshu there appears to be synchronous beach ridge formation albeit based upon a moderately poor chronological resolution further data indicate that there may also be contemporaneous evidence on hokkaido to the north more detailed research is now needed in order to secure a higher resolution dataset of the spatial and temporal extent of beach ridges throughout the region in order to determine whether they preserve a record of the magnitude and frequency of earthquakes and potentially tsunamis related to activity on both the japan and kuril trenches if strong seismic driving linkages can be proven it offers the intriguing possibility of being able to develop a far more comprehensive record of past earthquakes and tsunamis local regional and distant than currently exists records could be based on both tsunami deposits in the low lying swales and the spatial and temporal extent of the intervening beach ridges

topographic constraints on deviatoric stress field in the indo eurasian collision region seismo tectonic implications the deviatoric stress field are computed from the inversion of gravitational potential energy gpe for the indo eurasian plate collision region including the himalaya and the tibet plateau the resulting stress pattern in combination with stress and strain rates obtained by inverting respectively the focal mechanism solution of large earthquakes and gps derived plate motions are used to study the nature of the present day deformations a narrow belt bordering the himalayan collision zone from the south is characterized by strong compressive stresses the variations in stress pattern along this belt coincide with arc normal ridges extending into the himalaya and are able to explain arc parallel segmentation of seismicity gravitational collapse seems to play an important role in the southeastern tibet plateau depth sensitivity of the seismic derived stresses and gps derived surface strain rates coupled with evidence of arcuate shaped high electrical conductivity favour strong ductile flow around the eastern himalaya syntaxis ehs at mid crustal depth the deflection of crustal flow indicted by the viscous resistance offered by the rigid sichuan basin adds to the traction stresses to cause clockwise rotation of the block around ehs

low temperature thermochronology in the peruvian central andes implications for long term continental denudation timing of plateau uplift canyon incision and lithosphere dynamics abstract in peru the western edge of the 4 5 km high western cordillera is cut by a 3 km deep canyon to understand incision by the cotahuasi ocona river and the regional uplift history of this orogenic plateau capped by volcanic rocks 26 crystalline rock samples were collected for low temperature thermochronology from vertical profiles parallel and perpendicular to the canyon rock cooling histories confirm that most plateau denudation had occurred prior to 24 ma but plateau incision peaked after c 14 9 ma in response to rapid surface uplift the abrupt occurrence of a rock heating event is also detected during middle miocene time this was either a response to the emplacement of low conductivity regionally extensive ignimbritic caprock or a response to crustal scale fluid circulation caused by wet melting of the overriding plate when magmatism resumed c 24 ma the potential for thermochronology to provide information on past geothermal gradients is discussed showing how it can be used as a proxy for understanding change in subducting slab dynamics with oscillations in subduction angle having perhaps been the main on off switch for magmatism in this cordilleran setting supplementary material fission track and apatite u th he results and apatite chemistry indicators are available at http www geolsoc org uk sup18405

geomechanical model of the marmara sea region ii 3 d contemporary background stress field summary we present the contemporary 3 d background stress field of the marmara sea region derived from a geomechanical model the background stress field i e the component of the absolute stress state that is time independent over the seismic cycle primarily depends on the distribution of density and elastic parameters on the acting far field stresses from plate boundary forces and on fault geometries we take these into account to predict the 3 d background stress field including its spatial variations technically our model concept involves the definition of an appropriate initial stress state accounting for the gravitational reference stress state of the crust which is then changed by plate tectonics until the 3 d background stress field has evolved the modelled stress field agrees well with observations from earthquake focal mechanism solutions and their formal stress inversion with orientation of maximum horizontal stress and with the distribution of seismicity in the marmara sea in particular in the vicinity of fault bends the stress field deviates considerably from the regional nw se oriented maximum horizontal stress and exhibits variability of the stress regime our model results are consistent not only with dynamic observations but also with kinematic ones various kinematic observations are understandable from the stress field we show that a stress regime that indicates normal faulting in the basins is nonetheless reconcilable with almost pure strike slip motion on the main marmara fault the distribution of seismicity in the marmara sea can be explained in first order by the distribution of critical differential stress which is closely related to local fault geometries we refer the wide absence of seismicity between the bend of the main marmara fault near istanbul and the central basin to the relatively plane fault geometry of that segment normal stress on the main marmara fault is highly variable along strike which makes segment wise rupture more likely than a rupture of the seismic gap at once comparably low normal stress on the prince s islands segment indicates a shorter interevent time for this fault segment than for the central segment of the main marmara fault