lithospheric dynamics and tectonic stratigraphic evolution of the ebro basin we present analysis of two dimensional modeling of the tectonic subsidence in the ebro basin along three profiles crossing the pyrenees the ebro basin and the catalan coastal range to the east and the iberic cordillera to the west the deformation of the foreland basin during tertiary times is simulated using a lithospheric flexure model incorporating laterally varying elastic thicknesses the deflection of the plate is the combined result of pyrenean loading and the loads exerted by the iberic cordillera and catalan coastal range in the eastern part of the ebro basin no extra driving force on the iberian plate is required the flexural modeling supports the hypothesis that underplating of the iberian plate under the european plate is not associated with subduction of old oceanic lithosphere a good fit with the tertiary basin subsidence data and bouguer anomalies is obtained for an elastic plate with local weakness zones under the ebro basin the inferred lateral variation in the elastic rigidity is consistent with heat flow measurements in northern spain and with major mesozoic extension in the iberic cordillera and valencia trough

a scaling law for slow earthquakes with the availability of the global positioning system and other technical advances a growing number of unusual earthquake phenomena occurring at relatively long periods have been recognized they include deep episodic tremor low frequency earthquakes slow slip events and silent earthquakes based on data chiefly from western japan ide et al report that these slow seismic events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes a diverse array of unusual earthquake phenomena occurring at relatively long periods slow events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes indicating that they comprise a new earthquake category recently a series of unusual earthquake phenomena have been discovered including deep episodic tremor1 low frequency earthquakes2 very low frequency earthquakes3 slow slip events4 and silent earthquakes5 6 7 8 9 each of these has been demonstrated to arise from shear slip just as do regular earthquakes but with longer characteristic durations and radiating much less seismic energy here we show that these slow events follow a simple unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes we find that their seismic moment is proportional to the characteristic duration and their moment rate function is constant with a spectral high frequency decay of f 1 this scaling and spectral behaviour demonstrates that they can be thought of as different manifestations of the same phenomena and that they comprise a new earthquake category the observed scale dependence of rupture velocity for these events can be explained by either a constant low stress drop model or a diffusional constant slip model this new scaling law unifies a diverse class of slow seismic events and may lead to a better understanding of the plate subduction process and large earthquake generation

high resolution magnetic stratigraphy across the oligocene miocene boundary in an alluvial lacustrine succession ebro basin northeast spain abstract the study of a late oligocene early miocene 300 m thick section of alluvial and shallow lacustrine sediments in the ebro basin has allowed a high resolution magnetic polarity stratigraphy for the oligocene miocene boundary to be established the samples studied include alluvial sandstones and mudstones as well as shallow lacustrine and paludine micritic and microsparitic limestones two hundred and fifty specimens were stepwise thermally or magnetically demagnetized following standard procedures magnetic imprints of the distinct lithologies present sharp contrasts especially for the stability of the secondary components the vgp data show 18 reversal events defining a sequence of 16 polarity intervals lateral and vertical continuity of the sequences studied has enabled a correspondence between the local paleomastological biozones and the magnetostratigraphic succession to be established the high resolution chronology of this magnetostratigraphic succession provides valuable information that allows the non marine european biochronological scales to be correlated to the global polarity time scale gpts the magnetic polarity zonation of the section has been correlated to the gpts using the distinct sequence and pattern polarity reversals as well as by considering the fossil mammal assemblages as a preliminary result chrons 8 7a 7 and 6c have been identified

continental extension from core complexes to rigid block faulting extension of overthickened continental crust is commonly characterized by an early core complex stage of extension followed by a later stage of crustal scale rigid block faulting these two stages are clearly recognized during the extensional destruction of the alpine orogen in northeast corsica where rigid block faulting overprinting core complex formation eventually led to crustal separation and the formation of a new oceanic backarc basin the ligurian sea here we investigate the geodynamic evolution of continental extension by using a novel fully coupled thermomechanical numerical model of the continental crust we consider that the dynamic evolution is governed by fault weakening which is generated by the evolution of the natural state variables i e pressure deviatoric stress temperature and strain rate and their associated energy fluxes our results show the appearance of a detachment layer that controls the initial separation of the brittle crust on characteristic listric faults and a core complex formation that is exhuming strongly deformed rocks of the detachment zone and relatively undeformed crustal cores this process is followed by a transitional period characterized by an apparent tectonic quiescence in which deformation is not localized and energy stored in the upper crust is transferred downward and causes self organized mobilization of the lower crust eventually the entire crust ruptures on major crosscutting faults shifting the tectonic regime from core complex formation to wholesale rigid block faulting

acoustic properties of neogene carbonates and siliciclastics from the subsurface of the florida keys implications for seismic reflectivity abstract results of measurements of compressional wave velocity and shear wave velocity have been compared with other rock properties xrd and thin section analyses for over fifty minicores from two cores drilled through sedimentary rocks on stock island and long key florida keys the comparisons indicate that sonic velocity in siliciclastics and carbonates is mainly controlled by three factors 1 porosity and primary pore type 2 quartz content and 3 dolomite content in the case of two pliocene prograding formations the combination of depositional fabric and diagenetic alterations produced patterns and values of almost identical impedance for fine grained carbonates and siliciclastics consequently seismic sections can not be used to distinguish between the prograding quartz sands and the prograding fine grained carbonates compressional and shear wave velocities in the limestones are strongly controlled by total porosity and the primary pore type generally high porosity rocks have lower velocities than low porosity rocks but pore types can significantly influence velocities overall an increasing percentage of dolomite in carbonate rocks results in an increase in velocity some dolomitic fabrics deviate from this trend fabric preserving mimetic dolomites yield the highest velocities whereas samples that are of purely sucrosic dolomites produce lower velocities which however are still higher in average than non or only partly dolomitized samples quartz sandstones and quartz bearing limestones have generally low and uniform velocities the low velocities of the sandstones containing 80 quartz is a result of their primary interparticle porosity due to the low diagenetic potential of quartz grains a high quartz content inhibits major diagenetic alterations which would result in cementation and higher velocities synthetic seismograms and nearby seismic sections reveal two major seismic facies as a result of the observed velocity distribution 1 carbonates of the stock island formation and siliciclastics of the long key formation are both characterized by low seismic reflectivity or even seismic transparency this seismic facies is caused by a very similar uniform vertical distribution of low velocities with almost identical impedance values in the two formations thus the transition or an interfingering between the time equivalent siliciclastic long key formation and the carbonate stock island formation might not be detectable on a seismic section 2 the over and underlying shallow marine carbonates in contrast have higher velocities with a wider range of velocities resulting in a succession of high amplitude reflections

the trollheim alluvial fan and facies model revisited widely held fundamental alluvial fan facies concepts generated in past literature based on the trollheim fan deep springs valley california are inconsistent with the actual characteristics of this fan previous publications have established mostly without field study that the trollheim fan consists of debris flow sieve lobe sheetflood and channel facies debris flow and sieve deposits comprise the proximal area giving way to channel or sheetflood deposits distally contrary to these views clayey and gravelly matrix supported debris flow deposits dominate all parts of the trollheim exposures suggesting that this fan has been built almost exclusively by mass wasting events channel fill deposits constitute only a small component of the fan and most are restricted to the proximal area where they have an inset relationship with debris flow sequences the channel facies consists of laterally restricted clast supported gravel lenses formed primarily through the winnowing of debris flow fines by streamflow the most widespread facies on the surface of the fan is a mantle of varnished matrix free pebbles cobbles and boulders that commonly are distributed in radially oriented lobes or levees characteristic of debris flow deposits this mantle was produced by the surficial winnowing of the fine fraction from debris flow deposits primarily by overland water flow in contrast to previous conclusions sheetflood and sieve deposits were not identified anywhere on the fan additionally many of the facies depicted in the widely cited trollheim vertical profile including ripple bedded sand cross bedded sand and overbank mud are not present on or in stratigraphic cuts of the fan after which the profile was named

magnetostratigraphic tests of sequence stratigraphic correlations from the southern california paleogene abstract several sequence stratigraphic analyses have been conducted on the eocene oligocene rocks of the san diego region and of the western transverse ranges in southern california recently developed magnetic stratigraphy and 40ar 39ar dates as well as previously neglected biostratigraphic data provide a high resolution chronostratigraphic framework to test correlation of these sequence stratigraphic interpretations to the global onlap offlap chart haq et al 1987 1988 hardenbol et al 1998 in the san diego area previous stratigraphic analyses miscorrelated nearly all sequences and sequence boundaries to the global time scale some correlations are off by as much as ten million years in the western transverse ranges three contradictory sequence stratigraphic analyses are evaluated the revised dates of the sequence boundaries show poor correlation with the onlap offlap chart of haq et al 1987 1988 or hardenbol et al 1998 and some units are misdated by as much as six million years in both regions few sequences were correctly predicted by the onlap offlap chart suggesting that tectonic controls were more important than eustatic controls in this tectonically active region the errors in so many sequence stratigraphic correlations when tested by high resolution chronostratigraphic data should caution geologists about using sequence stratigraphic age assignments uncritically sequence stratigraphic correlations are only as good as the chronostratigraphy on which they are based

sequence stratigraphy in lacustrine basins a model for part of the green river formation eocene southwest uinta basin utah u s a abstract in the middle green river formation of central nine mile canyon uinta basin utah several lacustrine dominated intervals 10 m thick comprise aggradational carbonate parasequence sets and a progradational clastic parasequence maximum flooding surfaces are best identified within profundal oil shale that caps some of the clastic parasequences these lacustrine transgressive systems tracts therefore exhibit parasequence stacking patterns unlike typical marine sequences two types of sequence boundary are identified type a sequence boundaries display evidence for a basinward shift in facies across a regionally mappable surface that is an angular or rarely parallel unconformity and they typically juxtapose amalgamated braided fluvial channel sandstone late lowstand systems tract onto the profundal oil shale they also bound depositional sequences that show a distinct asymmetry being dominated by transgressive systems tracts 5 80 m thick highstand systems tracts are less than 4 m thick and may be removed completely by erosion on overlying sequence boundaries other surfaces satisfy only some of the standard criteria of sequence boundaries and are termed type b sequence boundaries type a sequence boundaries mark pronounced base level falls following times when the uinta lake had merged with a lake in an adjacent basin to form a much deeper lake such merging permitted the establishment of a new threshold at higher elevation following lake level balancing type b sequence boundaries are interpreted as marking base level falls from a barely merged lake or a lake that had an outflow over a 200 m stratigraphic thickness type a sequence boundaries are more common upsection indicating that with time a pluvial climate became more pronounced or that the adjacent lake was more easily filled type a sequence boundaries also become angular rather than parallel unconformities upsection suggesting increased tilting of the basin margin over time

ten million year history of a thrust sheet the final deformed state of a fold and thrust belt may be reached by an infinite number of kinematic paths two end member kinematic paths are due to continuous or discontinuous rates of deformation we have used a new magnetostratigraphic section from the spanish pyrenees to calibrate the emplacement history over 10 m y of a major thrust sheet the sierras marginales thrust sheet and the deformation of both its hanging wall and footwall six time windows from before 36 5 ma until after 24 7 ma were recognized on the basis of structural and stratigraphic relationships between syntectonic strata and major structures footwall deformation of the sierras marginales thrust sheet occurred continuously on a detachment within the foreland basin sequence 4 5 km net shortening shortening rates steadily increased from 0 14 to 1 5 mm yr with time although the detachments at the base of the foreland and the detachment at the base of the sierras marginales thrust sheet were active coevally the rate of displacement on the sierras marginales detachment decayed with time and shows considerable variability emplacement of the thrust sheet may be divided into three distinct periods a rapid 13 8 km translation from 37 0 to 36 5 ma 27 6 mm yr a gradual climb of the toe of the thrust sheet up a 4 3 km long ramp across the foreland basin succession from 36 5 to 32 0 ma 0 95 mm yr and a final 8 9 km translation from 32 0 to 29 5 ma 3 56 mm yr internal deformation of the thrust sheet occurred only after it reached its present position at some time before 29 5 ma shortening rates steadily decreased from 0 6 mm yr between 29 5 and 27 8 ma to 0 26 mm yr from 27 8 until after 24 7 ma only 1 km of shortening accumulated during each of the two periods the last shortening localized on the most northerly thrust in the study area folding and subsequent faulting above the detachment beneath the foreland suggest that slip was transmitted to its tip point continuously throughout the deformation in contrast translation followed by internal deformation on the hinterland side of the toe of the sierras marginales thrust sheet indicates a successive deactivation of the southern parts of the detachment with time rate of deformation on both detachments was discontinuous and shows substantial variability about the mean in general the spatial and temporal pattern of deformation was distributed and continuous in detail however shortening was spatially and temporally discontinuous above each detachment and structures related to each one display distinctly different deformational patterns rates and styles

iberian plate kinematics a jumping plate boundary between eurasia and africa the rotation of iberia and its relation to the formation of the pyrenees has been difficult to decipher because of the lack of detailed sea floor spreading data although several models have been proposed1 7 here we use detailed aeromagnetic measurements from the sea floor offshore of the grand banks of newfoundland to show that iberia moved as part of the african plate from late cretaceous to mid eocene time with a plate boundary extending westward from the bay of biscay when motion along this boundary ceased a boundary linking extension in the king s trough to compression along the pyrenees came into existence finally since the late oligocene iberia has been part of the eurasian plate with the boundary between eurasia and africa situated along the azores gibraltar fracture zone

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

a complete terrestrial oligocene magnetobiostratigraphy from the ebro basin spain abstract the integrated litho bio and magnetostratigraphic cross correlation of 11 continuous and correlatable sections in the southeastern ebro basin ne spain produced a complete oligocene magnetic polarity stratigraphy ranging from latest eocene to earliest miocene the magnetic polarity zonation of the different alluvial and shallow lacustrine sections has been correlated to the gpts using fossil mammals and the distinct sequence and pattern of polarity reversals the composite magnetic polarity sequence defines a continuous sequence from chron c15n to chron 6cn 2n from 34 8 to 23 7 ma late eocene early miocene in addition a few short normal and reverse polarity events that correlate to cryptochrons in the gpts are found i e in c11n 1r and c8n 1r the resulting regional magneto biostratigraphic framework based on fossil mammals is proposed to refine the dating of the european oligocene biochronological mammal paleogene units and correlate them with the standard oligocene marine stages and the north american land mammal ages the magnetochronology now established enables more precise dating of the late eocene and oligocene paleofloristic and paleofaunistic changes in southwestern europe which were coeval to ongoing global paleoclimatic and paleoceanographic changes on earth caused by high latitude cooling and ice sheet development in eastern antarctica

the 1 april 2014 pisagua tsunami observations and modeling on 1 april 2014 an earthquake with moment magnitude mw 8 2 occurred off the coast of northern chile generating a tsunami that prompted evacuation along the chilean coast here tsunami characteristics are analyzed through a combination of field data and numerical modeling despite the earthquake magnitude the tsunami was moderate with a relatively uniform distribution of runup which peaked at 4 6 m this is explained by a concentrated maximal slip at intermediate depth on the megathrust resulting in a rapid decay of tsunami energy the tsunami temporal evolution varied with locations showing sustained tsunami energy while others showed increased tsunami energy at different times after the earthquake these are the result of the interaction of long period standing oscillations and trapped edge wave activity controlled by inner shelf slopes understanding these processes is relevant for the region which still posses a significant tsunamigenic potential

the 1996 peru tsunamigenic earthquake broadband source process we investigate the spatio temporal complexity of moment release of the february 21 1996 peru earthquake mw 7 5 we use a non linear source tomographic technique based on simulated annealing to invert surface wave source spectra for the slip distribution on a gently dipping fault plane the spectra 5 65 mhz are obtained using an empirical green s function egf method applied to first and second orbit fundamental mode rayleigh waves spectra are well fit by a 110 km bilateral rupture subparallel to the trench updip of the hypocenter with a total moment of 2 0 1020 nm the non linear inversion reveals a 30 30 km major slip patch south the onset where rupture velocities attain 1 5 2 0 km s inversions of teleseismic broadband p and sh waves 10 500 mhz indicate little or no directivity consistent with the surface wave data the average source time functions for both the surface and body wave data are similar in shape and in duration 50 s part of the slip during the 1996 peru event occurred in a region of reduced background seismicity as was the case for the 1992 nicaragua slow event suggesting that the seismogenic potential of low seismicity regions near the trench should be globally reassessed

effect of depth dependent shear modulus on tsunami generation along subduction zones estimates of the initial size of tsunamis generated by subduction zone earthquakes are significantly affected by the choice of shear modulus at shallow depths analysis of over 360 circum pacific subduction zone earthquakes indicates that for a given seismic moment source duration increases significantly with decreasing depth bilek and lay 1998 1999 under the assumption that stress drop is constant the increase of source duration is explained by a 5 fold reduction of shear modulus from depths of 20 km to 5 km this much lower value of shear modulus at shallow depths in comparison to standard earth models has the effect of increasing the amount of slip estimated from seismic moment determinations thereby increasing tsunami amplitude the effect of using depth dependent shear modulus values is tested by modeling the tsunami from the 1992 nicaraguan tsunami earthquake using a previously determined moment distribution ihmle 1996a we find that the tide gauge record of this tsunami is well matched by synthetics created using the depth dependent shear modulus and moment distribution because excitation of seismic waves also depends on elastic heterogeneity it is important particularly for the inversion of short period waves that a consistent seismic tsunami shear modulus model be used for calculating slip distributions

normal and reverse unroofing sequences in syntectonic conglomerates as evidence of progressive basinward deformation when a new mountain belt is generated by tectonics the denudation of the mountain front may cause the development of alluvial fans at its base the retreat of the mountain front by denudation processes and a widening of the drainage network in the source area create adjacent alluvial fan conglomerates with an inverted vertical clast distribution this vertical clast distribution represents a normal unroofing sequence renewed uplift of a previous inverted vertical clast distribution can produce a reverse unroofing sequence if continued shortening occurs in the same area a rejuvenation of the source area and basin margin may produce a new generation of clasts from the source area and a partial or total reworking of previously deposited conglomerates to supply second generation clasts if this type of reworking process is repeated as fault uplift steps basinward several new inverted and stratigraphic vertical clast distributions may arise

kinematic stratigraphic evolution of a growth syncline and its implications for tectonic development of the proximal foreland basin southeastern ebro basin catalunya spain in the southeastern ebro basin of spain analysis of sequential fold history in combination with stacking patterns of conglomerate deposited in a growing syncline demonstrates the impact of local uplift attendant upon fold growth on nonmarine depositional systems in a foreland basin the penyagalera syncline is part of a belt of asymmetric folds developed in proximal paleogene foreland basin deposits by foreland directed propagation of a detachment beneath the basin foreland basin strata form a progradational succession of interbedded siltstone sandstone and evaporite overlain by conglomerate stratal stacking patterns and fold history indicate that conglomerate of the syncline marks the transition within the foreland basin succession from foredeep to wedge top depositional zones the conglomerate is divided into three informal members separated by unconformities the members are divided in turn into lithosomes separated by prominent bounding surfaces lithosomes represent depositional elements deposited by episodic progradation of alluvial fan lobes older conglomerate members are more tightly folded than younger members demonstrating that folding accompanied conglomerate deposition the uplift of opposing limbs of the penyagalera syncline was diachronous the asymmetric syncline comprises an overturned interior southeastern limb and a gently dipping exterior northwestern limb the interior limb rotated to a steep to slightly overturned attitude before significant rotation and uplift of the exterior limb took place rotation of the interior fold limb was episodic and punctuated by periods of erosion of older conglomerate uplift rates during rotation events along the interior limb generally were more rapid than sediment accumulation rates and caused sediment bypass to the foreland basin however sediment accumulation rates overtook uplift rates during late limb rotation causing alluvial fan lithosomes to onlap previously formed unconformities offlap signifying a slight excess of uplift over sediment accumulation rates is not observed in the syncline on the exterior limb sedimentation rates exceeded early limb uplift rates but the relationship of later folding and deposition is not preserved most synclinal closure postdated the youngest preserved lithosomes in the fold young lithosomes occupy a paleocanyon incised deeply into the interior limb of the syncline and mesozoic strata of the thrust belt the paleocanyon was backfilled during late aggradation of the ebro basin an event independent of local folding

the diachroneity of alluvial fan lithostratigraphy a test case from southeastern ebro basin magnetostratigraphy abstract alluvial fan strata contain valuable proxy data for kinematic climatic and sediment flux phenomena associated with high relief source regions proper application of this data is dependent upon acquisition of accurate high resolution chronostratigraphic data best achieved through magnetostratigraphy collection of magnetostratigraphic and other proxy data from composite alluvial fan sections assumes the chronostratigraphic significance of lithostratigraphy we present the first test of this assumption with new magnetostratigraphy collected from paleogene rocks of the southeastern ebro basin we report five new magnetostratigraphic sections that collectively sample 850 m of alluvial fan and associated fluvial strata one hundred meters of lithostratigraphic overlap between these sections reveals equivalent magnetic polarities over short along strike distances 200 2000 m however lithostratigraphic correlation of these sections with the magnetostratigraphy of continuously exposed strata eight km away reveals discrepancies in magnetic polarity trends and age interpretations correlation of our 760 m composite magnetostratigraphic section with the paleogene geomagnetic polarity time scale suggests that this section spans from ca 31 3 to 27 7 ma c12r c9n early to late oligocene this correlation implies steady sedimentation rates of 12 cm ka for fluvial facies and 32 cm ka for alluvial fan facies alternative interpretations that force chronostratigraphic correlation with the lithostratigraphically equivalent interval generate unsteady and or unlikely sedimentation rates in one or both of the stratigraphies and require rejection of multiple well constrained polarity zones the absence of significant surfaces of erosion or paleosol development argue against these alternative interpretations and suggest that even in the best exposed study areas alluvial fan successions may be diachronous and preclude lateral extrapolation of chronostratigraphic and other proxy data interpretations and models based upon data collected from alluvial fan strata may be tenuous unless supported by sufficient spatial overlap to constrain the relationship between time surfaces and rock surfaces

dynamic fluvial systems and gravel progradation in the himalayan foreland although the large scale stratigraphy of many terrestrial foreland basins is punctuated by major episodes of gravel progradation the relationships of such facies to hinterland tectonism and climate change are often unclear structural reentrants provide windows into older and more proximal parts of the foreland than are usually exposed and thus provide key insights to earlier phases of foreland evolution our magnetostratigraphic studies show that although the major lithofacies preserved within the himachal pradesh structural reentrant in northwestern india resemble neogene facies in pakistan they have a much greater temporal and spatial variability from 11 5 to 7 ma major facies boundaries in himachal pradesh vary by as much as 2 3 m y across distances of 20 30 km and are controlled by the interference between a major southeastward flowing axial river and a major southwestward flowing transverse river a thick but highly confined middle to late miocene conglomerate facies includes the oldest extensive siwalik conglomerates yet dated 10 ma and implies the development of significant erosional topography along the main boundary thrust prior to 11 ma our studies document extensive syntectonic gravel progradation with conglomerates extending tens of kilometers into the undeformed foreland during a period of increased subsidence rate and within 1 2 m y of major thrust initiation overall gravel progradation is modulated by the interplay among subsidence sediment supply and the proportion of gravels in rivers entering the foreland

isochronous fluvial systems in miocene deposits of northern pakistan a palacomagnetic isochron dated at about 8 1 myr bp and detailed lithostratigraph of a 40 m interval exposed along strike for 40 km establish the depositional patterns of two contemporaneous interfingering fluvial systems in the upper part of the meddle siwalik sequence the two systems referred to as the buff and blue grey differ in unit shape lithofacies bedding sequence palaeocurrent direction and sand composition interfingering occurs along the south west north east strike of the outcrops with the palaeodrainage directions of the two systems generally perpendicular to this line the axis of the blue grey system which deposited widespread sheet sands and silts lay toward the south west end of the study area the more complex axis of the buff system which deposited shoe string sand bodies and lage volumes of silt and clay lay toward the north east the source area for both systems was the rising himalyan belt to the north and noth east of the study area at maximum extent the blue grey system occupied a channel belt at least 25 km wide channel belt widths and depths for the buff system are 1 3 km and 3 7 m respectively current directions averge 94 for blue grey sands and 136 for buff sands blur grey sands contain 20 more rock fragments and are otherwise less mature than buff sands the buff system shows a verticla pattern of avulsion palaeosol formation and floodplain aggradation which we attribute to autocyclic processes of parallel rivers the blue grey system shows phases of erosion accompaniced laterally by plaeosol formation folowed by valley fill and overfowing of interfluve surfaces theis pattern may be caused by allocyclic presses affecting the source area we interpret the blue grey system as a major drainage from the interior himalayas perhaps the ancestral indus and the buff system as a complex of smaller drinages along the mountain front which were probably ributaries to the bluegrey syste vertebrate fossils including hominoid primates from the area are almost exclusively associated with lithofacies of the buff system and this probably refects both taphonomic and palaeoecological differences between the two systems

magnetostratigraphy and sedimentologically derived geochronology of the quaternary lacustrine deposits of a 3000 m thick sequence in the central qaidam basin western china the qaidam basin is a large basin in western china where the thickness of quaternary deposits has a range of 2000 3000 m at its subsiding depocentre this study investigated the chronology of the quaternary deposits including palaeomagnetics biostratigraphic correlation rates of sediment accumulation seismic reflection surveys and electrical property correlations the results give a full interpretation of ages for the sequence from bottom to top the oldest sequence age was defined by the first appearance of microlimnocythere sinensis huang and was placed in the gauss epoch estimated at approximately 3 ma by extrapolation of accumulation rates the m g boundary occurs at the base of the third fossil zone of ostracoda the first appearance of qinghaicypris crassa huang or at the marker layer k 10 of the electrical log in the sebei anticline area considered here to be 2 48 ma the olduvai event in the fifth fossil zone spanning electrical layers k 4 and k 3 in the sebei area occurs at reflection layer t 0 1 of seismic stratigraphy which could be stratigraphically correlated in the whole basin the boundary of early middle pleistocene such as the brunhes and matsuyama b m boundary falls within the eighth fossil zone and coincides with electrical marker k 0 1 two boundaries corresponding to middle late pleistocene and pleistocene holocene occur at the bases of the 11th and 12th biozones respectively neither of which can be correlated with seismic stratigraphy and electrical logs in the basin due to the lack of widely distributed lacustrine deposits since the middle pleistocene the ages of the boundaries can be tested by deposition rates of different facies derived from the varves and synchronous deposits as a result geochronological sequences of subsurface stratigraphy could be established within a basin wide area on the synchronology of seismic reflectors and correlations of electrical logs as well as biozones c 1998 elsevier science b v all rights reserved

teleseismic inversion for rupture process of the 27 february 2010 chile mw 8 8 earthquake the 27 february 2010 chile m w 8 8 earthquake is the fifth largest earthquake to strike during the age of seismological instrumentation the faulting geometry slip distribution seismic moment and moment rate function are estimated from broadband teleseismic p sh and rayleigh wave signals we explore some of the trade offs in the rupture process estimation due to model parameterizations limited teleseismic sampling of seismic phase velocities and uncertainty in fault geometry the average slip over the 81 500 km 2 rupture area is about 5 m with slip concentrations down dip up dip and southwest and up dip and north of the hypocenter relatively little slip occurred up dip offshore of the hypocenter the average rupture velocity is 2 0 2 5 km s

seismicity and tectonics of the rivera plate and implications for the 1932 jalisco mexico earthquake seismicity on and near the boundaries of the rivera plate is examined in order to determine the subduction regime of the rivera plate and its influence on the earthquake behavior of the northernmost section of the mid america trench in particular we address the question of a rivera cocos boundary there have been several large historic earthquakes in the coastal areas of the mexican states colima and jalisco but the last large event was in june 1932 the 1932 jalisco earthquake ms 8 1 the present quiescence has lasted longer than the average recurrence interval for the mexican subduction zone and the jalisco area is now categorized as a seismic gap however if subduction in this area is dominated by the motion of the rivera plate which is subducting at half the rate of the cocos plate the deficiency of earthquake activity may not be unusual in an attempt to better delineate the rivera cocos boundary intermediate sized earthquakes along and near the rivera fracture zone and the mid america trench were relocated with the joint epicenter determination method we found that in general the catalog locations are fairly accurate with the average change in epicenter upon relocation being 12 km seismicity along the rivera fracture zone follows the physiographic trend of the fracture zone but east of its intersection with the east pacific rise seismicity is more diffuse two intermediate sized earthquakes in this diffuse area have focal mechanisms suggesting that they represent rivera cocos boundary motion reexamination of arrival time data for the 1932 jalisco earthquake yields an epicenter at 19 57 n 104 42 w close to the boundary zone inferred from these two earthquakes we conclude that the possibility that the 1932 jalisco earthquake broke the northernmost section of the cocos north american plate interface as opposed to the rivera north american plate interface cannot be ruled out

cenozoic vertical motions of the catalan coastal ranges ne spain the role of tectonics isostasy and surface transport 1 we analyze the cenozoic topographic evolution of the catalan coastal ranges ne spain and the role of fault activity erosion sedimentation and isostasy in controlling uplift and subsidence a forward numerical model constrained by an extensive geological and geophysical data set is used to examine the temporal and spatial record of cenozoic vertical motions we show that the effect of isostasy erosion and sedimentation is as important as the contribution of fault deformation to the topography of the catalan coastal ranges the model predicts that paleogene topography generation by thrusting was compensated by erosion up to 1 3 km and isostatic subsidence up to 1 2 km resulting in a 1 2 1 9 km high mountain range by the end of compression 29 ma during the neogene strong tectonic subsidence related to normal faulting and the consequent flexural uplift of 0 7 1 2 km surface erosion as much as 1 6 2 3 km and sedimentation up to 4 5 km led to the present landscape configuration extension rates along the barcelona fault controlled flexural uplift and in combination with erosion and sedimentation processes led to the migration of the topographic maximum of the prelitoral range toward the easternmost ebro basin

continuing megathrust earthquake potential in chile after the 2014 iquique earthquake the 2014 iquique event was not the earthquake that had been expected to fill the regional seismic gap given that significant sections of the northern chile subduction zone have not ruptured in almost 150 years it is likely that future megathrust earthquakes will occur south and potentially north of the 2014 iquique sequence two groups publishing in this issue of nature analyse the seismic context of the iquique earthquake that occurred off the coast of northern chile on 1 april 2014 in a seismic zone that had been quiescent since a significant event in 1877 gavin hayes et al identify areas of remaining or elevated earthquake hazard along the megathrust fault in the region and conclude that the 2014 iquique event was not the earthquake that had been anticipated given that significant sections of the northern chile subduction zone have not ruptured in almost 150 years they suggest that it is likely that future megathrust earthquakes will occur south and potentially north of the 2014 iquique sequence bernd schurr et al show that the april 2014 earthquake broke a central fraction of the northern chile seismic gap the last major segment of the south american plate boundary that had yet to rupture in the past century from july 2013 up to the april earthquake they identify three seismic clusters along this part of the plate boundary each lasting a few weeks with earthquakes of increasing peak magnitudes they conclude that these seismic clusters and their slip transients reflect a gradual weakening of the central part of the seismic gap that was instrumental in initiating the final failure the seismic gap theory1 identifies regions of elevated hazard based on a lack of recent seismicity in comparison with other portions of a fault it has successfully explained past earthquakes see for example ref 2 and is useful for qualitatively describing where large earthquakes might occur a large earthquake had been expected in the subduction zone adjacent to northern chile3 4 5 6 which had not ruptured in a megathrust earthquake since a m 8 8 event in 1877 on 1 april 2014 a m 8 2 earthquake occurred within this seismic gap here we present an assessment of the seismotectonics of the march april 2014 iquique sequence including analyses of earthquake relocations moment tensors finite fault models moment deficit calculations and cumulative coulomb stress transfer this ensemble of information allows us to place the sequence within the context of regional seismicity and to identify areas of remaining and or elevated hazard our results constrain the size and spatial extent of rupture and indicate that this was not the earthquake that had been anticipated significant sections of the northern chile subduction zone have not ruptured in almost 150 years so it is likely that future megathrust earthquakes will occur to the south and potentially to the north of the 2014 iquique sequence

high resolution sequence stratigraphy of an alluvial fan fan delta environment stratigraphic and geodynamic implications an example from the keuper chaunoy sandstones paris basin abstract facies analysis of the chaunoy formation conducted as the first stage of this study reveals that the corresponding fluvial system essentially involved bedload deposition 2 d and 3 d megaripple migration and debris flow deposition such processes are characteristic of alluvial fan depositional environments these alluvial fan deposits pass laterally eastward into a shallow lacustrine environment in stage 2 of the study electrofacies are defined by well log analysis and then matched with sedimentary facies defined by core analysis electrofacies associations and depositional environments are then inferred directly from well logs on this basis six electrofacies characterizing the main sedimentary facies associations and depositional environments within the chaunoy formation are defined channel lag deposits channel infilling lake or flood plain overflow deposits and paleosols stage 3 involves establishing correlations based on high resolution sequence stratigraphy within these continental deposits the procedure consists in analysing high frequency fluctuations in baselevel defined from sedimentological studies and calibrated on well log signatures the correlations show that the top of the chaunoy formation is diachronous the formation is subdivided here into three stratigraphic units from base to top chaunoy i ii and iii this study shows that the degree of preservation of continental deposits varies with stratigraphic cycle genetic sequences and genetic sequence sets are asymmetrical with the baselevel rise being better preserved than the baselevel fall while for minor cycle deposits may be similarly preserved during baselevel rise and fall the sequence stratigraphy pattern of the genetic sequences and the genetic sequence sets can result from climatic and or tectonic factors but their effects are difficult to distinguish at the scale of the minor chaunoy i cycle or the chaunoy ii cycle preservation is similar during the baselevel rise and fall that implies that the chaunoy minor cycles were influenced by load discharge resulting in greater accommodation space which could result from climatic or tectonic fluctuations the chaunoy formation was deposited as part of a major baselevel rise during the carnian liassic cycle during this cycle the paris basin was generally tilted to the northwest producing the intra marnes irisees superieures truncation which seems to have been induced by large scale wavelength tectonic deformation detailed isopach maps of minor baselevel cycles in chaunoy i with inferred depositional environments are used to define the extent of depositional environments and fault activity during baselevel rise and fall during emplacement of the braided alluvial fan and lacustrine deposits of the chaunoy formation fault activity which was confined to the western part of the basin controlled the preservation potential i e the thickness of the deposits and depositional environment profiles within the chaunoy i and ii cycles the increased thickness of the sandstone deposits to the northeast and the onlap at the top of chaunoy i can be explained by local fault activity and by the general tilting of the basin the chaunoy iii sandstones are confined to the western part of the basin and seem to have been controlled by local factors only

reply to garces et al comment on the diachroneity of alluvial fan lithostratigraphy a test case from southeastern ebro basin magnetostratigraphy

evidence for and implications of self healing pulses of slip in earthquake rupture dislocation time histories of models derived from waveforms of seven earthquakes are discussed in each model dislocation rise times the duration of slip for a given point on the fault are found to be short compared to the overall duration of the earthquake 10 however in many crack like numerical models of dynamic rupture the slip duration at a given point is comparable to the overall duration of the rupture i e slip at a given point continues until information is received that the rupture has stopped propagating alternative explanations for the discrepancy between the short slip durations used to model waveforms and the long slip durations inferred from dynamic crack models are 1 the dislocation models are unable to resolve the relatively slow parts of earthquake slip and have seriously underestimated the dislocations for these earthquakes 2 earthquakes are composed of a sequence of small dimension short duration events that are separated by locked regions barriers 3 rupture occurs in a narrow self healing pulse of slip that travels along the fault surface evidence is discussed that suggests that slip durations are indeed short and that the self healing slip pulse model is the most appropriate explanation a qualitative model is presented that produces self healing slip pulses the key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity the model has the following features high static strength of materials kilobar range low static stress drops in the range of tens of bars and relatively low frictional stress during slip less than several hundreds of bars it is suggested that the reason that the average dislocation scales with fault length is because large amplitude slip pulses are difficult to stop and hence tend to propagate large distances this model may explain why seismicity and ambient stress are low along fault segments that have experienced large earthquakes it also qualitatively explains why the recurrence time for large earthquakes may be irregular

tectonic and climatic controls on the development of foreland fan deltas montserrat and sant llorenc del munt systems middle eocene ebro basin ne spain abstract along an early cenozoic foreland hinterland boundary in northeastern spain we synthesize the depositional environment climatic conditions structural evolution age catchment geometry and altitudinal characteristics from sedimentologic palynologic stratigraphic structural and paleomagnetic data as the transpressional catalan coastal ranges rose during the paleogene two large fan deltas prograded into the ebro foreland basin adjacent to the northeastern part of the range the apices of the fans likely were localized by lateral ramps or tear faults along which rivers from hinterland catchments debouched into the foreland beginning in the late lutetian proximal debris flow sheetflood and distal fluvial deposits maintained the fan surface at or above sea level despite rapid basin subsidence during the succeeding 4 4 my palynological data suggest that a warm humid climate prevailed throughout this interval the mapped extent of the two fans permits an estimation of their volumes whereas the spatial distribution of distinctive lithologies within the ancestral catalan coastal ranges serves to delimit the approximate catchment areas for each of the fans we estimate mean hinterland denudation rates to range from 100 to 180 m my and mean catchment elevation to range from 700 to 1250 m the steep gradients between these catchments and the low lying fan deltas is attributed to the tectonic style of the ancestral catalan coastal ranges which are characterized by an uplifted basement block along a steep frontal thrust accompanied by folding of cover rocks the considerable topographic relief of these catchments is inferred to have combined with co seismic shaking to produce landslides and rockfalls which were reworked as debris and fluid gravity deposits on the fan surfaces

the chronology of the eocene tectonic and stratigraphic development of the eastern pyrenean foreland basin northeast spain abundant and clearly exposed relationships between structures and syntectonic sedimentary rocks in the southern pyrenees make this area particularly suitable for detailed studies of the sequential development of a collisional orogenic belt during the pyrenean orogeny major shortening occurred in the eastern pyrenees in eocene and early oligocene times until now individual tectonic and depositional events have been only loosely defined temporally by biostratigraphic data in order to provide a more precise chronological framework four new magnetostratigraphic sections spanning 8 km of eocene strata and encompassing 18 m y have been developed in the eastern pyrenees of northern spain the ages of nine major depositional sequences in the eastern pyrenean foreland have been specified within the context of these chronologic data beginning with the early eocene transgression that commenced at 58 ma the timing of numerous tectonic events that occurred during the subsequent 16 m y can also be delineated including the initial emplacement of the pedraforca thrust sheet 58 54 ma the development of the pedraforca breakback thrusts 47 5 40 ma at a mean shortening rate of 2 4 mm yr rotation of the pedraforca footwall three intervals of motion along the vallfogona thrust 42 5 44 0 40 5 41 5 and

comment on the diachroneity of alluvial fan lithostratigraphy a test case from southeastern ebro basin magnetostratigraphy by n swanson hysell and d l barbeau jr

autogenic dynamics of alluvial fans in endorheic basins outcrop examples and stratigraphic significance alluvial fans are relatively simple depositional systems due to the direct coupling of sediment sources and adjacent accumulation areas nonetheless general models of alluvial fan evolution and stratigraphy remain elusive due to the great sensitivity of such systems to allogenic controls and their strongly case specific responses autogenic processes intrinsic to alluvial fan dynamics can complicate stratigraphic architectures with effects not easily distinguishable from those of allogenic forcing a distinction is made here between lateral autogenic dynamics tied to spatial sediment distribution over fan surfaces and vertical autogenic dynamics related to independent incision aggradation cycles autogenic mechanisms have been highlighted recently by modelling studies but remain poorly constrained in field based studies examples are presented here from the margins of the cenozoic teruel and ebro basins spain where alluvial fans accumulated thick successions during phases of basin topographic closure and endorheic drainage which promoted forced aggradation fan successions consist of conformable architectures of stacked clastic sheets laterally continuous and with no evidence of internal unconformities inset architectures fan segmentation or preserved incised channels continuous aggradation in these closed basins strongly inhibited vertical autogenic dynamics in the form of fan head and through fan incision due to the forced rise in geomorphic base level and the creation of positive accommodation furthermore the lack of incised channels favoured widespread sediment transport and aggradation over broad fan sectors in relatively short time spans in contrast to the typical occurrence of active lobes and abandoned fan surfaces caused by lateral autogenic dynamics stratigraphic records of alluvial fans developed in endorheic basins are essentially complete and largely unaffected by autogenic processes the latter characteristic implies that they can be more unambiguously interpreted in terms of allogenic forcing because stratigraphic signatures are not complicated by the effects of complex fan autodynamics

sequence stratigraphy of nonmarine jurassic cretaceous rocks central cordilleran foreland basin system an analysis of the upper jurassic lower cretaceous morrison and cedar mountain formations of utah and colorado has resulted in a general sequence stratigraphic model for nonmarine rocks in this model nonmarine deposition is governed by changes in basin accommodation development and corresponding shifts in depositional base level these fluctuations result in deposition of systematically varying facies and architectural elements that allow nonmarine depositional sequences to be recognized internally nonmarine depositional sequences comprise three systems tracts degradational transitional and aggradational which are analogous to the lowstand transgressive and highstand systems tracts of marine depositional sequences degradational systems tracts overlie sequence bounding unconformities and consist of relatively coarse grained low sinuosity fluvial deposits that are either contained within incised valleys or deposited as widespread thin sheets above shallow erosion surfaces transitional systems tracts represent an increase in basin accommodation development following degradational systems tract deposition they are marked by the transition from laterally continuous low sinuosity fluvial channel sandstones and conglomerates to lenticular and ribbon like meandering and anastomosing channel sandstones aggradational systems tracts are characterized by meandering anastomosing channel sandstones and abundant fine grained overbank and lacustrine deposits the upper jurassic lower cretaceous nonmarine rocks of the study area contain three depositional sequences the first of these the uj 1 sequence consists primarily of an aggradational systems tract overlain by a sequence bounding unconformity however the lower parts of this sequence are transitional with older marine rocks and can be considered the late stages of a marine highstand systems tract the upper morrison sequence uj 2 consists of degradational transitional and aggradational systems tracts above the uj 2 sequence are a sequence bounding unconformity and degradational and transitional systems tracts of the lk 1 sequence represented by the buckhorn conglomerate the buckhorn is overlain by a sequence bounding unconformity and transitional aggradational systems tracts of the lk 2 sequence that is composed of the upper part of the cedar mountain formation the upper jurassic lower cretaceous sequences in utah and colorado can be traced regionally and correlated with nonmarine depositional sequences in central utah and sequences that contain nonmarine transitional and marine rocks in central wyoming these sequences were deposited in the back bulge forebulge and distal foredeep depozones of the late jurassic early cretaceous foreland basin system

a palaeomagnetic analysis of miocene fluvial sediments at pertusa near huesca ebro basin spain the magnetostratigraphy of two logged sections 1 km apart within this system consists of an upper zone of normal polarity and a lower zone of reversed polarity the lithostratigraphy and magnetostratigraphy are parallel the sands and silts are mainly pale yellow brown to dusky yellow and magnetic tests indicate that the magnetization is carried dominantly by ferric oxyhydroxides haematite and goethite the higher temperature natural remanent magnetization is probably due to detrital haematite which would have been partially aligned during fluvial deposition post depositional modification pdrm may have occurred during dewatering haematite pseudomorphing pyrite framboids indicates that early reducing conditions were succeeded by a more oxidizing regime which produced secondary magnetizations associated with fine grained haematite and goethite complete polarity zones are not delineated but the thicknesses present are not excessive compared with other continental miocene deposits the average palaeolatitude of 22 degrees is lower than would be expected for the miocene of northern spain probably due to incomplete averaging of secular variations and other sources of error including possible inclination error modified journal abstract

the 25 october 2010 mentawai tsunami earthquake from real time discriminants finite fault rupture and tsunami excitation 1 the moment magnitude 7 8 earthquake that struck offshore the mentawai islands in western indonesia on 25 october 2010 created a locally large tsunami that caused more than 400 human causalities we identify this earthquake as a rare slow source tsunami earthquake based on 1 disproportionately large tsunami waves 2 excessive rupture duration near 125 s 3 predominantly shallow near trench slip determined through finite fault modeling and 4 deficiencies in energy to moment and energy to duration cubed ratios the latter in near real time we detail the real time solutions that identified the slow nature of this event and evaluate how regional reductions in crustal rigidity along the shallow trench as determined by reduced rupture velocity contributed to increased slip causing the 5 9 m local tsunami runup and observed transoceanic wave heights observed 1600 km to the southeast

sedimentary response to thrusting and fold growing on the se margin of the ebro basin paleogene ne spain abstract the catalan coastal ranges are the alpine structural unit parallel to the mediterranean coast in the ne of the iberian peninsula they shape the southeastern margin of the ebro foreland basin the latest stage of the south pyrenean foreland trough the paleogene sedimentary evolution of this basin margin is closely related to the tectonic evolution of the adjoining catalan coastal ranges a transpressive chain characterized mainly by contractional structures nnw verging folds and thrusts the syntectonic condition of the paleogene deposits of the ebro basin is evidenced by facies directly related to the growth of specific structures thinning fanning and truncation of the sedimentary units towards the growing structures as well as to abrupt changes in the composition of the coarse grained sediments caused by tectonic activity or landslides in the catchment area a tectonosedimentary evolution of approximately 17 ma has been deduced a folds and thrusts involving mesozoic rocks were developed during ypresian resulting in the deposition of mesozoic cover derived breccias b large scale fold growth mostly from lutetian to early bartonian leading to progressive unconformities fanning and growth strata and c out of sequence basement involving thrusting during lutetian and bartonian development of large alluvial fans these events did not take place simultaneously along the 30 km long basin margin studied there is a clear ne to sw migration of the deformation as observed along the whole catalan coastal ranges and the south pyrenean foreland basin

two phase stratigraphic model of foreland basin sequences application of flexural models to nonmarine foreland basin evolution indicates that two different stratigraphic styles of basin fill may develop over time basin subsidence is most rapid during times of thrust load emplacement associated sedimentation is coarse grained immediately adjacent to the thrust front and grades rapidly into fine grained deposits that cover most of the basin the distal part of the basin may also contain deposits derived from streams that flow from beyond the basin toward the thrust belt subsequent removal of the thrust load by erosion and other processes results in flexural rebound of the thrust belt and adjacent foreland basin during this postorogenic phase of adjustment a regional unconformity develops in the proximal part of the foreland basin proximal deposits along with thrust derived sediment are redeposited in the distal foreland basin and beyond this two phase model of foreland sedimentation predicts that coarsening upward sequences in the proximal and distal parts of the basin have reciprocal significance the proximal sequence represents thrust belt advance whereas the distal sequence represents thrust belt cessation

controls on synorogenic alluvial fan architecture beartooth conglomerate palaeocene wyoming and montana late palaeocene uplift of the beartooth range in northwestern wyoming and southwestern montana generated the beartooth conglomerate along the eastern and northeastern flanks of the range systematic unroofing sequences and intraformational unconformities folds and faults in the conglomerate attest to deposition during uplift along the eastern flank at least three ancient alluvial fan systems and a braidplain system can be distinguished on the bases of petrofacies and lithofacies the two southern fans consist of 700 m of sedimentary clast conglomerate and subordinate sandstone dominated by hyperconcentratedflow and stream flow facies the next fan to the north is dominated by plutonic and metamorphic clasts and contains abundant mud matrix supported debris flow facies as well as stream flow facies the northernmost depositional system consists of arkosic channellized fluvial conglomerate and sandstone overbank mudstone and crevasse splay sandstone units palaeocurrent data indicate eastward dispersal away from the beartooth range outstanding exposure of the beartooth conglomerate allows facies to be mapped on lateral photographic mosaics a seven fold hierarchy of bounding surfaces and enclosed lithosomes exists in the beartooth conglomerate first through fourth order surfaces are analogous to first through fourth order surfaces that recently have been documented in sandy fluvial facies with one exception sediment gravity flows are bounded by first order surfaces fifth order surfaces are either erosional e g lateral migration of fanhead trench or accretionary e g aggradation of fan surface during backfilling of trench and construction of lobes on lower fan during entrenchment on upper fan some fifth order surfaces coincide with intraformational angular unconformities and are thus the result of long term fanhead entrenchment following uplift of the upper part of the fan sixth order surfaces bound individual fan packages that are several hundred metres thick and 10 km2 in area the enclosed sixth order lithosomes are distinguishable in terms of petrofacies and lithofacies a single seventh order surface bounds the entire beartooth conglomerate lower order lithosomes are produced by intrinsic processes of fan construction fifth order lithosomes can be attributed to both extrinsic and intrinsic controls sixth and seventh order lithosomes are generated by extrinsic controls

history of the sevier orogenic wedge in terms of critical taper models northeast utah and southwest wyoming problems with applying critical taper models to ancient orogenic wedges are overcome in the late cretaceous late paleocene sevier orogenic wedge in utah and wyoming by a symptomatic approach in which wedge behavior is inferred from the time space distribution of thrust faulting erosion and synorogenic sediment accumulation in association with the orogenic wedge in turn the causes of wedge behavior are interpreted in terms of features that are known about the sevier wedge such as the locations of major decollements and the lithologic constituents of major thrust sheets from coniacian through late paleocene time 35 m y basement and cover rocks in the sevier wedge were shortened by 100 km in three major and one minor events an overall eastward progression of thrusting was punctuated by several episodes of out of sequence and hinterland vergent thrusting over the long term wedge taper was controlled by internal wedge strength initial taper and changes in the durability of the upper surface of the wedge and its internal lithostratigraphy critical taper was maintained by the offsetting effects of basement duplexing in the rear of the wedge and forward imbrication at the front of the wedge while the basal decollement was mainly in basement rocks the wedge was highly tapered and thrust spacing was relatively close 15 km beginning ca 75 ma the basal decollement ramped upward and eastward into weak cambrian shale and jurassic salt thrust spacing increased to 25 45 km and wedge taper decreased drastically the highly tapered rear part of the wedge carried strong basement rocks above moderately weak mylonitic and cataclastic decollements whereas the frontal lower taper part of the wedge carried sedimentary rocks above extremely weak salt and shale decollements through time internal strength of the wedge decreased as it incorporated an increasing proportion of sedimentary rocks the thrust belt was able to advance eastward in spite of its decreasing internal strength and decreasing taper because the basal decollement of the wedge also became weaker through time both by strain softening beneath the rear of the wedge and by propagating along extremely weak rocks beneath the front of the wedge provenance data from associated synorogenic conglomerates indicate that the durability of the upper surface of the wedge probably increased over the long term history of the sevier wedge as an increasing proportion of the erosional surface became occupied by resistant precambrian quartzite and basement rocks this would have had the effect of decreasing the rate of erosion through time and maintaining a steeper surface slope which would have helped the wedge to remain at critical to supercritical taper the sevier wedge also exhibits several shorter term 10 km and 3 was subjected to regional erosion marked by major unconformities that ultimately caught up with tectonic thickening and caused the wedge to stall this cyclicity is attributed to the need for wedges to become supercritical before they can propagate forward over large distances and a lag time between wedge thickening and uplift and wedge erosion erosion eventually catches up to the rate of uplift the wedge stalls and the locus of deformation shifts to the rear of the wedge in order to rebuild taper this analysis suggests that orogenic wedges continually deform and find a way to maintain taper sufficient to allow forward propagation as long as a sufficient push from the rear exists the actual taper value may change substantially through time as lithostratigraphy internal strength upper surface durability and presence absence of weak potential stress guides conspire to maintain a critical taper

magnetostratigraphy of the yaha section tarim basin china 11 ma acceleration in erosion and uplift of the tian shan mountains we report a magnetostratigraphic and rock magnetic study of the yaha section located on the southern flank of the central tian shan mountains asia our results show a two fold increase in sedimentation rate as well as marked changes in rock magnetic characteristics ca 11 ma after 11 ma sedimentation rate remained remarkably constant until at least 5 2 ma these findings are consistent with sedimentary records from other sections surrounding the tian shan we conclude that uplift and erosion of the tian shan accelerated ca 11 ma long after the onset of the collision between india and asia and that the range rapidly evolved toward a steady state geometry via a balance between tectonic and erosion processes

palaeogene evolution of deformation in the northeastern iberian peninsula during the palaeogene alpine compression three units were differentiated in the studied area south of the ebro basin the catalan coastal range dominated by ne sw major basement faults with a sinistral movement the iberian range where the important basement faults have a nw se direction and a reverse movement often with a dextral component the linking zone between these two ranges where an e w dominant structural direction is marked by an array of folds and thrusts with a northward vergence in the mesozoic cover from the analysis of both these major structures and the small scale structures it can be deduced that the compression in the studied area has evolved from a nw se direction lower middle eocene to a n s direction and to a ne sw one uppermost oligocene the major structures are due to the n s compression later the stress field progressively changed to a distensive regime we suggest a relation between the compressive phases and the displacement direction of the iberian plate with reference to the european plate

the 1994 java tsunami earthquake slip over a subducting seamount on june 2 1994 a large subduction thrust earthquake ms 7 2 produced a devastating tsunami on the island of java this earthquake had a number of unusual characteristics it was the first recorded large thrust earthquake on the java subduction zone all of the aftershock mechanisms exhibit normal faulting no mechanisms are similar to the main shock also the large tsunami and the relatively low energy radiated by the main shock have led to suggestions that this earthquake might have involved slow shallow rupture near the trench similar to the 1992 nicaragua earthquake we first relocate the main shock and the aftershocks we then invert long period surface waves and broadband body waves to determine the depth and spatial distribution of the main shock slip a dip of 12 hypocenter depth of 16 km and moment of 3 5 l020 n m mw 7 6 give the best fit to the combined seismic data and are consistent with the plate interface geometry the source spectrum obtained from both body and surface waves has a single corner frequency between 10 and 20 mhz implying a stress drop of 0 3 mpa the main energy release was preceded by a small subevent lasting 12 s the main slip occurred at 20 km depth downdip and to the nw of the hypocenter this area of slip is collocated with a prominent high in the bathymetry that has been identified as a subducting seamount we interpret the java earthquake as slip over this subducting seamount which is a locked patch in an otherwise decoupled subduction zone we find no evidence for slow shallow rupture no thrust aftershocks are expected if the entire locked zone slipped during the main shock but extension of the subducting plate behind the seamount would promote normal faulting as observed it seems probable that such a source model could also explain the size and timing of the observed tsunami

the 17 july 2006 java tsunami earthquake the 17 july 2006 java earthquake involved thrust faulting in the java trench and excited a deadly tsunami 5 8 m that inundated the southern coast of java the earthquake s size estimates vary significantly with seismic wave period very long period signals 300 500 s indicate a seismic moment of 6 7 10 20 nm m w 7 8 m s 20 s 7 2 m b 1 s 6 2 while shaking intensities 3 10 hz were mmiv the large tsunami relative to ms characterizes this event as a tsunami earthquake like previous tsunami earthquakes the java event had an unusually low rupture speed of 1 0 1 5 km s and occurred near the up dip edge of the subduction zone thrust fault most large aftershocks involved normal faulting the rupture propagated 200 km along the trench with several pulses of shorter period seismic radiation superimposed on a smooth background rupture with an overall duration of 185 s

perspectives on the sequence stratigraphy of continental strata this report is the result of a working group on continental sequence stratigraphy that was set up at the 1991 nuna conference in banff canada to date sequence stratigraphic concepts have been applied mainly to the marine realm but unconformity bounded units have long been recognized in nonmarine strata successful application of sequence stratigraphic concepts to continental strata requires careful consideration of controls on base level and sediment supply as with shallow marine environments relative sea level can be considered as the stratigraphic as well as the geomorphic base level for coastal nonmarine settings farther inland stratigraphic base level which determines accommodation space is more complex and takes various forms such as the graded profile for fluvial strata groundwater tables for some eolian strata and lake level for some intermontane sediments sediment supply is also generally a more complex variable for nonmarine environments than in the marine realm because of the proximity to the source area the influence of climate and tectonism on sediment supply can clearly be seen in many continental sediments the fact that the major controls of climate tectonism and eustasy are somewhat interdependent and that a change in one parameter will most likely be reflected in others is also more readily apparent in continental strata although in its infancy sequence stratigraphic concepts have been applied to a wide variety of continental settings in attempts to explain variations in facies architecture of particular interest are studies that have linked fluvial architecture on coastal plains to variations in relative sea level as indicated by coeval marine strata and studies of lacustrine environments that show marked variation in facies between highstand and lowstand deposits the application of sequence stratigraphy to continental strata will likely result in the development of better correlation techniques and models that better predict the location and nature of fluvial and eolian reservoirs

hikurangi margin tsunami earthquake generated by slow seismic rupture over a subducted seamount abstract tsunami earthquakes generate much larger tsunami than their surface wave magnitude would suggest and are a problem for tsunami warning systems they are often not accompanied by intense or even strong ground shaking and hence do not provide a natural warning for self evacuation the lesser known 1947 offshore poverty bay and tolaga bay earthquakes along the east coast of the north island new zealand share many characteristics with other well known tsunami earthquakes including low amplitude shaking long durations and anomalously large tsunami however these two new zealand events are rare in that their source area has been imaged directly by long offset 2d seismic reflection profiles in this contribution we propose a source model for the 1947 offshore poverty bay tsunami earthquake recognising that the hypocentre occurs in a region where seismic reflection and magnetic data support the existence of a shallow m 7 earthquakes with complex low velocity rupture scenarios that enhance tsunami waves and their role in seismic hazard should not be under estimated

complex earthquake rupture and local tsunamis 1 in contrast to far field tsunami amplitudes that are fairly well predicted by the seismic moment of subduction zone earthquakes there exists significant variation in the scaling of local tsunami amplitude with respect to seismic moment from a global catalog of tsunami runup observations this variability is greatest for the most frequently occurring tsunamigenic subduction zone earthquakes in the magnitude range of 7 mw 8 5 variability in local tsunami runup scaling can be ascribed to tsunami source parameters that are independent of seismic moment variations in the water depth in the source region the combination of higher slip and lower shear modulus at shallow depth and rupture complexity in the form of heterogeneous slip distribution patterns the focus of this study is on the effect that rupture complexity has on the local tsunami wave field a wide range of slip distribution patterns are generated using a stochastic self affine source model that is consistent with the falloff of far field seismic displacement spectra at high frequencies the synthetic slip distributions generated by the stochastic source model are discretized and the vertical displacement fields from point source elastic dislocation expressions are superimposed to compute the coseismic vertical displacement field for shallow subduction zone earthquakes it is demonstrated that self affine irregularities of the slip distribution result in significant variations in local tsunami amplitude the effects of rupture complexity are less pronounced for earthquakes at greater depth or along faults with steep dip angles for a test region along the pacific coast of central mexico peak nearshore tsunami amplitude is calculated for a large number n 100 of synthetic slip distribution patterns all with identical seismic moment mw 8 1 analysis of the results indicates that for earthquakes of a fixed location geometry and seismic moment peak nearshore tsunami amplitude can vary by a factor of 3 or more these results indicate that there is substantially more variation in the local tsunami wave field derived from the inherent complexity subduction zone earthquakes than predicted by a simple elastic dislocation model probabilistic methods that take into account variability in earthquake rupture processes are likely to yield more accurate assessments of tsunami hazards

pliocene uplift of the northern tibetan plateau neogene redbeds passing upward into upward coarsening conglomerate and debris flow deposits at the foot of the kunlun mountains record the change in paleoslope related to uplift of the surface of the northern tibetan plateau detailed magnetostratigraphy of a 4 5 km section near yecheng in the western kunlun mountains shows that the change from deposition on distal alluvial plains to proximal alluvial fans occurred during the gilbert reversed chron 4 5 3 5 ma the change in depositional facies was accompanied by an increase in sedimentation rate from an average 0 15 mm yr between the earliest oligocene and the earliest pliocene to 1 4 mm yr in the gauss normal chron 3 6 2 6 ma we interpret the change in depositional facies and increase in sedimentation rate as indicating that the main uplift of the northwestern tibetan plateau began ca 4 5 ma

tsunami generation by horizontal displacement of ocean bottom tsunami generation by an earthquake is generally modeled by water surface displacement identical to the vertical deformation of ocean bottom due to faulting the effect of horizontal deformation is usually neglected however when the tsunami source is on a steep slope and the horizontal displacement is large relative to the vertical displacement the effect becomes significant we show this for two recent earthquakes which generated much larger tsunamis than expected from seismic waves in the case of the 1994 june 2 java indonesia earthquake the focal mechanism was a very shallow dipping thrust and the source was near a very steep trench slope in the case of the 1994 nov 14 mindoro philippines earthquake strike slip faulting extended from ocean to land perpendicular to the coast line in both cases we found that the horizontal motion of slope had an important contribution to the tsunami generation

development of tectonic cyclothems in rift pull apart and foreland basins sedimentary response to episodic tectonism the thickest part of asymmetric rift pull apart and foreland basin fills commonly consists of large scale hundreds to thousands of metres thick tectonically generated cyclothems of fine grained marine lacustrine or longitudinal fluvial deposits and coarse grained transverse braid plain or alluvial fan deposits the appearance of coarse clastics in these basin fills is typically noted as the time of tectonically rejuvenated source area uplift based on the conceptual tie between relief and coarse grain size and on the application of the davis theory of landform development we propose the opposite interpretation that the commencement of fine grained sedimentation above coarse grained deposits in a tectonic cyclothem is the best indicator of renewed tectonic activity this reinterpretation is more consistent with 1 modern examples 2 the consideration of source area and sedimentary basin geomorphology 3 the disparity between the reaction rates of the various environments to subsidence 4 the disparity between the rates of tectonic uplift and erosion and 5 the controls on elastic wedge progradation in our model extensive coarse grained clastic wedge progradation is an indicator of tectonically quiescent phases

interplay between tectonics climate and fluvial transport during the cenozoic evolution of the ebro basin ne iberia 1 three dimensional modeling that integrates fluvial sediment transport crustal scale tectonic deformation and lithospheric flexural subsidence is carried out to simulate the landscape and drainage evolution of the ebro sedimentary basin ne iberia the ebro basin underwent a long period of closed intramountain drainage as a result of tectonic topography generation at the pyrenees the iberian range and the catalan coastal range in the late oligocene the catalan coastal range underwent extension leading to the formation of the valencia trough nw mediterranean but the ebro basin remained closed for nearly 15 myr more before the ebro river cut through the remnants of the topographic barrier this drainage opening caused widespread basin incision that shaped spectacular outcrops of the syntectonic and posttectonic infill here we investigate the processes controlling these major drainage changes the modeling results constrained by a large data set on the tectonic and transport evolution of the area predict a closed phase characterized by a large lake in the central eastern ebro basin dry climatic conditions probably lowered the lake level and contributed together with rift flank uplift to prolong this endorheic basin stage the age and amount of reworked sediment after the opening are consistent with an onset of basin incision between 13 and 8 5 ma as a result of lake capture by escarpment erosion and lake level rise associated with sediment accumulation and wetter climatic conditions sea level changes in the mediterranean had no major impact in the large scale drainage evolution of the ebro basin index terms 1625 global change geomorphology and weathering 1824 1886 1815 hydrology erosion and sedimentation 3210 mathematical geophysics modeling 3344 meteorology and atmospheric dynamics paleoclimatology 8102 tectonophysics continental contractional orogenic belts keywords pyrenees drainage evolution lake sediment budget erosion flexure