paleoseismology along the 1980 surface rupture of the irpinia fault implications for earthquake recurrence in the southern apennines italy the irpinia fault was the source of the ms 6 9 1980 irpinia earthquake and produced the first unequivocal historical surface faulting in italy trenching of the 1980 fault scarp at piano di pecore a flat intermontane basin about 5 km south of the 1980 instrumental epicenter provides the first data on earthquake recurrence intervals slip per event and slip rate on a major normal fault in the southern apennines fault zone the trenches exposed evidence of four pre 1980 paleoearthquakes that occurred during the past 8600 years a best estimate average recurrence interval is 2150 years although the time interval between individual events varies by as much as a factor of 2 each paleo earthquake is similar to the 1980 surface rupture in amount of slip and style of deformation which suggests that the 1980 event is characteristic for the irpinia fault slip per event values average 61 cm the net vertical displacement of 2 12 2 36 m since 8600 cal year b p observed in the trenches gives a vertical slip rate of 0 25 0 35 mm yr a dip slip rate of 0 29 0 40 mm yr and an extension rate of 0 14 0 20 mm yr although fault behavior data are only available for the irpinia fault they provide a starting point for evaluating earthquake recurrence and rates of deformation in southern apennines they suggest that 1 fault specific earthquake recurrence intervals based on the historical seismic record overestimates the occurrence of large magnitude m7 earthquakes and 2 the holocene rate of extension across the apennines is 1 mm yr the 1980 earthquake and the paleoseismologic observations show that repeated and localized surface faulting occurs in southern apennines and leaves subtle but distinct geomorphic evidence that can be detected with detailed and careful investigation

organism substrate interactions and astrobiology potential models and methods abstract organism substrate interactions and their products biogenic structures are important biosignatures on earth this study discusses the application of ichnology the study of organism substrate interactions to the search for present and past life beyond earth three main questions are addressed 1 why to look for biogenic structures i e traces and ichnofabrics beyond earth 2 what biogenic structures to expect on other planets moons and asteroids 3 how to study extraterrestrial biogenic structures review of terrestrial evidence highlights a set of properties that make traces and ichnofabrics important for the search of potential extraterrestrial life trace fossils preserve the activity of soft bodied organisms biogenic structures are resilient to processes that obliterate other biosignatures i e mechanical and chemical degradation diagenesis tectonism and metamorphism traces are very visible biosignatures traces indicate environment and behaviour traces can be universal biosignatures i e biosignatures ideally suited for detecting any type of life a model of organism substrate interactions beyond earth is here proposed expected extraterrestrial traces are those that manifest behaviours that allow to maintain homeostasis excavations meandering traces and biodeposition structures most of the existing rovers and orbiters provide basic instruments for searching these traces it is here suggested that the search for extraterrestrial biogenic structures by rovers would also benefit from artificial adjustable lighting gpr lidar and drilling equipment with optical televiewer in this study open access databases of rover and orbiter imagery have been searched for traces and ichnofabrics but no unquestionable evidence of biogenic structures beyond earth has been found besides those produced by humans this sounds along the lines of the famous fermi paradox if the universe is teeming with aliens where are their traces results of this search show that habitable environments are not the only place to look for biogenic structures non habitable environments such as moons without atmosphere can favour the preservation of shallow tier traces the better preservation potential of traces compared to other biosignatures greatly widens the issue of planetary protection including the interaction between astronauts or vehicles and the substrate may produce disturbances although this study highlights a new direction of study with the tools and concepts of ichnology dialogue between the astrobiological and ichnological communities is needed to use its full potential and possibly answer one of the major questions of science does life exist beyond earth

coulomb stress changes caused by repeated normal faulting earthquakes during the 1997 umbria marche central italy seismic sequence 1 we investigate fault interaction through elastic stress transfer among a sequence of moderate magnitude main shocks 5 mw 6 which ruptured distinct normal fault segments during a seismic sequence in the umbria marche region central apennines we also model the spatial pattern of aftershocks and their faulting mechanisms through coulomb stress changes we compute stress perturbations caused by earthquake dislocations in a homogeneous half space our modeling results show that seven out of eight main shocks of the sequence occur in areas of enhanced coulomb stress implying that elastic stress transfer may have promoted the occurrence of these moderate magnitude events our modeling results show that stress changes caused by normal faulting events reactivated and inverted the slip of a secondary n s trending strike slip fault inherited from compressional tectonics in its shallowest part 1 3 km of the 1517 available aftershocks 82 are located in areas of positive stress changes for optimally oriented planes oops for coulomb failure however only 45 of the 322 available fault plane solutions computed from polarity data is consistent with corresponding focal mechanisms associated with the oops the comparison does not improve if we compute the optimally oriented planes for coulomb failure by fixing the strike orientation of oops using information derived from structural geology our interpretation of these modeling results is that elastic stress transfer alone cannot jointly explain the aftershock spatial distribution and their focal mechanisms

a drying upward aeolian system of the bohdasin formation early triassic sudetes of ne czech republic record of seasonality and long term palaeoclimate change abstract the record of aeolian processes was studied in early triassic sandstones of the upper part of the bohdasin formation ne bohemia an isolated erosional relict of a triassic fluvial aeolian succession in the sudetes block of the bohemian massif central europe the aeolian system exposed in the dev t k i quarry near cerven kostelec provides a significant addition to the generally poorly preserved record of early triassic palaeoclimate and palaeowind regime in central europe two mutually interbedded facies occur in the aeolian succession 1 dune facies comprising cross strata that show interdune reactivation and superimposition bounding surfaces and 2 interdune facies formed by horizontally stratified commonly mud draped sandstones which display a number of indicators of damp to wet conditions and fluctuations in water table the succession of the dev t k i sandstones is interpreted as a record of migration and climb of dunes with intervening interdune flats which replaced an underlying fluvial system it is likely that a coeval fluvial system existed near the dev t k i dune field providing available sand in dry periods and flooding in wet periods dominant palaeowind directions are southwestward and northward in present day coordinates repeated reversals of palaeowind direction interpreted as seasonal are recorded in changes in the internal structure of the cross strata reworking and reactivation in the dune migration direction at least some episodes of dune reworking occurred simultaneously with episodes of water table rise a drying upward trend in the aeolian succession is interpreted from evidence for increased availability of sand through time the upward transition from a braided fluvial to a wet drying upward aeolian system within the bohdasin formation represents a shift toward maximum aridity of the palaeoenvironment which marks also the peak arid conditions in the long term palaeoclimatic evolution of the carboniferous triassic succession of the sudetes region and correlates with the establishment of aeolian settings in other regions of central europe during the early triassic the record of changing palaeowind directions documented in several cases to have been coupled with episodes of rapid rise in water table is taken as evidence for pronounced climatic seasonality and brings additional support to the models predicting strong monsoonal circulation during the early triassic affecting particularly the eastern subequatorial coast of pangaea and adjoining regions

tropical westerlies over pangaean sand seas cross equatorial westerly winds are key features of tropical circulation in monsoonal regions although prominent in numerical climate models of pangaea the supercontinent straddling earth s equator late palaeozoic to early mesozoic such flow has not been confirmed previously by migration directions of ancient dunes wind blown sandstones that span 100 million years of earth history are widely exposed in south western usa if recent palaeomagnetic data from the colorado plateau are used to correct mesozoic palaeogeographic maps the plateau is placed about 10 further south than previously assumed and the prevailing north westerly surface winds recorded by dune deposited sandstones are explicable as cross equatorial westerlies the hallmark of modern monsoon circulation permian to early jurassic dunes were driven by north westerlies produced by a steep pressure gradient spanning the supercontinent during december january february although winds are light in most modern near equatorial settings the east african jet accounts for more than half the cross equatorial flow in june july august the thicknesses of annual depositional cycles within the navajo sandstone indicate that the near equatorial north westerly winds that drove these particular dunes were stronger than the modern east african jet the early jurassic dunes that deposited the thick cycles were positioned west of the dominant southern hemisphere thermal low and against highlands to the west a setting very similar to the east african jet the mountains along the western coast of pangaea not only enhanced wind strength but also cast a rain shadow that allowed active dunes to extend very close to the palaeoequator

a new ichnotaxon classification of large mammaliform trackways from the lower cretaceous botucatu formation parana basin brazil abstract during the early cretaceous a large area in brazil and other south american countries was covered by an extensive paleoerg field the botucatu desert the araraquara county sao paulo state brazil contains some of the most diverse ichnological assemblages in the botucatu formation mammaliform trace fossils from the botucatu formation are of great interest as they may represent the only record of lower cretaceous mammaliamorpha from brazil these trace fossils can be grouped into two distinct classes based on the dimensions of the footprints the larger morphotype is described and classified as a new ichnotaxon aracoaraichnium leonardii igen nov isp nov with a discussion of preservational features and paleoecological aspects this morphotype can be differentiated from brasilichnium leonardi 1981 by digit morphology with digits iii and iv being larger and sub equal in size the tracks are mesaxonic unlike brasilichnium which is ectaxonic and the stride is proportionally smaller suggesting a trackmaker with shorter limbs in relation to body length another characteristic that reinforces the new ichnotaxon is the larger size of the footprints of aracoaraichnium igen nov footprints representing intermediate ontogenetic stages between brasilichnium and the larger morphotype are not observed suggesting that the two track types were made by different taxa compared with others tetrapod ichnotaxa the new ichnotaxon is characterized by differences in the number and morphology of the digits track morphology the degree of heteropody and locomotor parameters tracks with good preservation quality were likely originally produced in the humid subsurface below the surficial dry sand layer tracks with smaller dimensions and trackways with the presence or absence of the manus may be due to variable degrees of impression into subsurface layers and substrate heterogeneity the aracoaraichnium igen nov trackmakers probably inhabited areas near the desert making occasional incursions into desert areas while brasilichnium trackmakers may have been mostly nocturnal residents of the desert environment

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

mid cretaceous aeolian desert systems in the yunlong area of the lanping basin china implications for palaeoatmosphere dynamics and paleoclimatic change in east asia abstract the mid cretaceous constitutes a period of worldwide atmospheric and oceanic change associated with slower thermohaline circulation and ocean anoxic events possible polar glaciations and by a changing climate pattern becoming controlled by a zonal planetary wind system and an equatorial humid belt during the mid cretaceous the subtropical high pressure arid climate belt of the planetary wind system controlled the palaeolatitude distribution of humid belts in asia as well as the spatial distribution of rain belts over the massive continental blocks at mid low latitudes in the southern and northern hemispheres additionally the orographic effect of the andean type active continental margin in east asia hindered the transportation of ocean moisture to inland regions with rising temperatures and palaeoatmospheric conditions dominated by high pressure systems desert climate environments expanded at the inland areas of east asia including those accumulated in the mid cretaceous of the simao basin the sichuan basin and the thailand s khorat basin and leading the late cretaceous erg systems in the xinjiang basin and jianghan basin this manuscript presents evidences that allow to reinterpret previously considered water laid sediments to be accumulated as windblown deposits forming part of extensive erg sandy desert systems using a multidisciplinary approach including petrological sedimentological and architectural observations the mid cretaceous albian turonian nanxin formation from the yunlong region of lanping basin formerly considered to aqueous deposits is here interpreted as representing aeolian deposits showing local aeolian fluvial interaction deposits the palaeowind directions obtained from the analysis of aeolian dune cross beddings indicates that inland deserts were compatible with a high pressure cell hpc existing in the mid low latitudes of east asia during the mid cretaceous compared with the early cretaceous the mid cretaceous had extremely lower temperatures and pressure gradients more arid climate which is in accordance with the existing morphology of hpc and the hpc was stable with little movement simultaneously the deserts controlled by the mid cretaceous hpc were closer to the equator indicating the shrinkage of the hadley cell relative to the early cretaceous

depositional model for a prograding oolitic wedge upper jurassic iberian basin abstract facies architecture and bedding patterns of the kimmeridgian pozuel formation iberian basin evidence that this 50 70 m thick oolitic grainstone unit conforms to the infralittoral prograding wedge ilpw model instead of the classic models used for interpreting oolitic grainstones sandbodies on carbonate ramps or platforms i e bank margin shoal complexes beaches and beach ridges ten lithofacies have been distinguished in the pozuel formation 5 10 dipping clinobedded oolitic grainstone foresets passing to tabular oolitic packstones grainstones which interfinger the muddy basinal bottomsets landwards the clinobeds pass into subhorizontal topsets composed of trough cross bedded to structureless oolitic grainstones oolitic skeletal grainstones with stromatoporoids and coral stromatoporoid microbial mounds siliciclastic lithofacies and oncolitic peloidal packstones occur at the innermost position these lithofacies stack in strike elongated 5 20 m thick 0 5 2 km dip oriented wide aggradational progradational packages with complex sigmoid oblique geometries lithofacies depositional geometries and stacking pattern permit to summarize the main characteristic of such upper jurassic oolitic infralittoral prograding wedge potentially to be applied in other oolitic sandbodies both in outcrops and subsurface 1 sediment production within the wave action zone 2 grainstone dominated textures 3 prograding basinward onto basinal muds 4 laterally strike extensive paralleling the shoreline 5 variable thickness commonly of few tens of meters 6 broadly sigmoidal to oblique internal architecture with topsets foresets and bottomsets 7 dip of foresets close to the angle of repose 8 topsets deposited in shallow water extending through the shoreface from the shoreline down to the wave base 9 mounds either microbial or skeletal may occur in the topsets the coated grains factory was along the high energy wave dominated outer platform topset beds from where the mud was winnowed and the grains transported both landward to the platform interior and seaward to the platform edge from were the grains cascaded down the slopes as grain flows and mass flows forming clinobeds this genetic model can be applied to other grain dominated lithosomes some of them forming hydrocarbon reservoirs e g the jurassic hanifa formation and some arab d e g qatif field in arabia the smackover formation in northern louisiana and south arkansas the aptian shuaiba formation e g bu hasa field and the cenomanian mishrif formation e g umm adalkh field of the arabian gulf

physical and stochastic models of earthquake clustering abstract the phenomenon of earthquake clustering i e the increase of occurrence probability for seismic events close in space and time to other previous earthquakes has been modeled both by statistical and physical processes from a statistical viewpoint the so called epidemic model etas introduced by ogata in 1988 and its variations have become fairly well known in the seismological community tests on real seismicity and comparison with a plain time independent poissonian model through likelihood based methods have reliably proved their validity on the other hand in the last decade many papers have been published on the so called coulomb stress change principle based on the theory of elasticity showing qualitatively that an increase of the coulomb stress in a given area is usually associated with an increase of seismic activity more specifically the rate and state theory developed by dieterich in the 90s has been able to give a physical justification to the phenomenon known as omori law according to this law a mainshock is followed by a series of aftershocks whose frequency decreases in time as an inverse power law in this study we give an outline of the above mentioned stochastic and physical models and build up an approach by which these models can be merged in a single algorithm and statistically tested the application to the seismicity of japan from 1970 to 2003 shows that the new model incorporating the physical concept of the rate and state theory performs not worse than the purely stochastic model with two free parameters only the numerical results obtained in these applications are related to physical characters of the model as the stress change produced by an earthquake close to its edges and to the a and parameters of the rate and state constitutive law

a new tetrapod ichnotaxon from botucatu formation lower cretaceous neocomian brazil with comments on fossil track preservation on inclined planes and local paleoecology abstract botucatu formation is a paleoerg worldwide famous for its vertebrate and invertebrate ichnofossils among botucatu formation tetrapod tracks ichnogenus brasilichnium leonardi 1981 is well known being generally attributed to mammaliform trackmakers in this study a new ichnotaxon is described brasilichnium saltatorium isp nov characterized by a hopping locomotion in phases the new ichnotaxon differs from b elusivum leonardi 1981 mainly for the locomotion pattern it also differs from other ichnotaxa by indicating hopping progression regarding limb morphology and track configuration fossil evidence shows b saltatorium and b elusivum could be produced by the same organism and represent an alternation in locomotory behavior neoichnological experiments were conducted to better understand track preservation and aspects of saltatorial dynamics on inclined planes it was observed differences in heteropody degree may be related to movement direction and locomotion effort on ascending or descending the incluned plane due to extramorphological features heteropody is more evident when the producer climbs the simulated dune also when the movement is ascendent lack of handprints can occur this can be explained by total overlap of pes and manus impression and subsurface hand impression comparing with recent organisms living in similar environments and conditions the botucatu formation b saltatorium producer should have been a generalist organism likely with an omnivorous habit it may have adopted hopping locomotion to gain velocity when hunting escaping predators or to facilitate progression on inclined planes and hot sand sao bento quarry represents a paleodesert environment with relative high humidity where temporary lagoons may have formed during pluvial events paleo rain episode evidence is preserved through raindrops impact craters on local sandstone sao bento quarry paleoenvironment sustained a rich paleofauna represented by abundant ichnofossils this local diversity suggests a punctual productive desert paleocommunity with several paleoecological interactions where brasilichnium producer was one of the fundamental elements

relationships between fault geometry slip rate variability and earthquake recurrence in extensional settings field observations and modelling indicate that elastic interaction between active faults can lead to variations in earthquake recurrence intervals measured on timescales of 102 104 yr fault geometry strongly influences the nature of the interaction between adjacent structures as it controls the spatial redistribution of stress when rupture occurs in this paper we use a previously published numerical model for elastic interaction between spontaneously growing faults to investigate the relationships between fault geometry fault slip rate variations and the statistics of earthquake recurrence these relationships develop and become systematic as a long term consequence of stress redistribution in individual rupture events even though on short timescales earthquake activity appears to be stochastic we characterize fault behaviour using the coefficient of variation cv of earthquake recurrence intervals and introduce a new measure slip rate variability srv that takes into account the size and time ordering of slip events cv generally increases when the strain is partitioned on more than one fault but the relationship between long term fault slip rate srmean and cv is poorly defined in contrast srv increases systematically where faulting is more distributed and srmean is lower to first order srv is inversely proportional to srmean we also extract earthquake recurrence statistics and compare these to previously published probability density functions used in earthquake forecasting the histograms of earthquake recurrence vary systematically as a function of fault geometry and are best characterized by a weibull distribution with fitting parameters that vary from site to site along the fault array we explain these phenomena in terms of a time varying geometrical control on stress loading of individual faults arising from the history of elastic interactions and compare our results with published data on srv and earthquake recurrence along normal faults in new zealand and in the italian apennines our results suggest that palaeoseismic data should be collected and analysed with structural geometry in mind and that information on srv cv and srmean should be integrated with data from earthquake catalogues when evaluating seismic hazard

a frictional population model of seismicity rate change 1 we study models of seismicity rate changes caused by the application of a static stress perturbation to a population of faults and discuss our results with respect to the model proposed by dieterich 1994 these models assume a distribution of nucleation sites e g faults obeying rate state frictional relations that fail at constant rate under tectonic loading alone and predicts a positive static stress step at time t0 will cause an immediate increased seismicity rate that decays according to omori s law we show one way in which the dieterich model may be constructed from simple general ideas illustrated using numerically computed synthetic seismicity and mathematical formulation we show that seismicity rate changes predicted by these models 1 depend on the particular relationship between the clock advanced failure and fault maturity 2 are largest for the faults closest to failure at t0 3 depend strongly on which state evolution law faults obey and 4 are insensitive to some types of population heterogeneity we also find that if individual faults fail repeatedly and populations are finite at timescales much longer than typical aftershock durations quiescence follows a seismicity rate increase regardless of the specific frictional relations for the examined models the quiescence duration is comparable to the ratio of stress change to stressing rate which occurs after a time comparable to the average recurrence interval of the individual faults in the population and repeats in the absence of any new load perturbations this simple model may partly explain observations of repeated clustering of earthquakes

the 2009 l aquila earthquake italy what s next in the region hints from stress diffusion analysis and normal fault activity abstract this work aims at defining the contribution in terms of earthquake probability assessment of the integration of coulomb stress diffusion analysis related to an earthquake with geological studies on fault activities investigating the case of the april 6 2009 l aquila central italy earthquake mw 6 3 the analysis of the coulomb stress diffusion induced by this earthquake has revealed a stress increase along two poorly investigated active normal faults in the apennines the subequana fault and the middle aterno valley fault no strong seismic events have been attributed to these tectonic structures over the past 800 1000 yr and they have therefore been considered as probable seismic gaps geological and paleoseismological investigations have since indicated that these tectonic structures belong to the same 25 30 km long fault system that ruptured twice during the late holocene the last activation occurred between the 4th 1st century b c and the past millennium probably during the 2nd 1st century b c with the penultimate between 6381 30 bp and 3511 37 bp the data obtained indicate that this fault system might rupture in up to magnitude 6 8 earthquakes and that the 2009 seismic event has brought these tectonic structures about 200 yr closer to failure

palaeowind patterns during the latest jurassic earliest cretaceous in gondwana evidence from aeolian cross strata of the botucatu formation brazil abstract the direction of sediment transport in the aeolian sandstones of the botucatu formation latest jurassic earliest cretaceous of the parana basin has been interpreted on the basis of cross strata dip directions which allowed the reconstruction of regional wind patterns in midwestern gondwana regionally cross strata dip directions indicate variations of palaeowind directions across the outcrop area of the botucatu palaeoerg the northern portion of the palaeoerg was characterized by palaeowinds blowing from the nne whereas the southern portion was under the influence of palaeowinds coming from the sw a wind convergence zone occurred at palaeolatitudes around 24 to 26 s the identified wind pattern agrees with general circulation models for the late jurassic which predict that during the summer months december through february strong monsoonal winds to the s existed at low latitudes in gondwana southerly winds converged at the itcz at around 24 s with winds blowing toward the northeast

wind directions predicted from global circulation models and wind directions determined from eolian sandstones of the western united states a comparison panfish j t and peterson f 1988 wind directions predicted from global circulation models and wind directions determined from eolian sandstones of the western united states a comparison in g kocurek editor late paleozoic and mesozoic eolian deposits of the western interior of the united states sediment geol 56 261 282 wind directions for middle pennsylvanian through jurassic time are predicted from global circulation models for the western united states these predictions are compared with paleowind directions interpreted from eofian sandstones of middle permsylvanian through jurassic age predicted regional wind directions correspond with at least three quarters of the paleowind data from the sandstones the rest of the data may indicate problems with correlation local effects of paleogeography on winds and lack of resolution of the circulation models the data and predictions suggest the following paleoclimatic developments through the time interval studied predominance of winter subtropical high pressure circulation in the late pennsylvanian predominance of summer subtropical high pressure circulation in the permian predominance of summer monsoonal circulation in the triassic and earliest jurassic and during the remainder of the jurassic influence of both summer subtropical and summer monsoonal circulation with the boundary between the two systems over the western united states this sequence of climatic changes is largely owing to paleogeographic changes which influenced the buildup and breakdown of the monsoonal circulation and possibly owing partly to a decrease in the global temperature gradient which might have lessened the influence of the subtropical high pressure circulation the atypical humidity of triassic time probably resulted from the monsoonal circulation created by the geography of pangaea this circulation is predicted to have been at a maximum in the triassic and was likely to have been powerful enough to draw moisture along the equator from the ocean to the west

eolian deposits of the northern margin of the south china jianghan basin reconstruction of the late cretaceous east asian landscape in central china abstract the late cretaceous honghuatao formation includes a succession of thick clastic sedimentary sequences which are widely exposed in northwestern jianghan basin central china here detailed sedimentological and facies architectural analyses are performed allowing to re interpret and identify the controversy for sedimentary environment and to investigate the paleoclimatic condition the honghuatao stratigraphic sequence includes eolian dunes and dry interdunes deposits with fluvial channel deposits at the bottom and top the vertical change between fluvial and eolian systems indicates alternating wet and dry climate at the same time the provenance analysis combined with the paleocurrents from the w nw and ne indicates that huangling dome south qinling belt and dabie orogen supply the main detrital source for the honghuatao formation the late cretaceous first rifting subsidence in the jianghan basin provided accommodation space for the preservation of the aeolian accumulation moreover the existence of the mountain belts around the basin that is the orographic effect precluded the winds from transporting humidity to the interior of the jianghan basin generating the desert system this study shows that the formation of eolian deposits in the honghuatao formation and coeval strata in numerous adjacent basins was a sedimentary response to the prevailing desert climate in the mid to low latitude areas of the northern hemisphere during the late cretaceous which was predominately controlled by the subtropical high pressure system on a planetary scale

climate of the supercontinent pangea numerous climate models predict that the geography of the supercontinent pangea was conducive to the establishment of a megamonsoonal circulation in general geologic evidence supports the hypothesis of a megamonsoon that reached maximum strength in the triassic pangea in the late carboniferous had widespread peat formation in what is now central and eastern north america and europe and relatively dry conditions on the colorado plateau the equatorial region of the continent became drier through the end of the carboniferous by the permian the equatorial region of pangea was dry and indicators of aridity and rainfall seasonality became more widespread wind directions from colorado plateau eolian sandstones are consistent with an increasing influence of monsoonal circulation at this time in the triassic climate in the colorado plateau region became relatively wet though still seasonal and the few eolian sandstones indicate a major shift in wind direction at that time in addition sedimentation

stratigraphy and volcanic facies architecture of the torres syncline southern brazil and its role in understanding the parana etendeka continental flood basalt province abstract the torres syncline is a large structure that constitutes the eastmost outcrop of the parana etendeka cfb in south american side and this work focuses the stratigraphy and facies architecture of the volcanic pile in the syncline the volcanic sequence along the study area permits the division of three regions main valley intermediate zone and south hinge each of them with distinct stratigraphy which probably reflects the structural evolution of the syncline the stratigraphy of the torres syncline is composed by 1 botucatu palaeoerg 2 basic volcanic episode i 3 basic volcanic episode ii 4 acidic volcanic i 5 basic volcanic episode iii and 6 acidic volcanic episode ii the five volcanic episodes recognized in study area can be related to five volcanic facies architecture compound braided tabular classic tabular lobate escoriaceous dome field acidic lavas and tabular flows acidic lavas the basic episode i is composed by pahoehoe flows with a compound braided facies architecture that covered the botucatu palaeoerg the basic episode ii is a tabular classic facies architecture predominantly composed by simple flows 10 20 m thick reaching the total thickness of 500 m in main valley the acidic episode i is exposed in main valley and south hinge and is composed by acidic lavas forming lava dome field facies architecture with a thickness of 150 m the basic episode iii is predominantly constituted by a flows with tabular lobate escoriaceous facies architecture the acidic episode ii is constituted by tabular flow volcanic facies acidic flows and outcrops all along the study area the torres syncline constitute the eastmost on shore exposures of the parana etendeka cfb in south american side and detailed stratigraphic volcanological and structural studies in these area coupled with correlation with huab basin nw namibia africa will aim the understanding of the gondwana breakup process and the early stages of the south atlantic margin opening

basaltic ring structures of the serra geral formation at the southern triângulo mineiro agua vermelha region brazil abstract the serra geral formation constitutes a continental magmatic province on the southern part of south america within the parana basin basaltic magmatism of the serra geral formation occurred as extrusions at around 134 5 to 131 5 my ago the formation is part of the parana etendeka large igneous province spanning south america and southwestern africa the main extrusion mechanism was probably through fissures related to extensional regime during the breakup of gondwana in the cretaceous basaltic ring structures brs with tens of meters of diameter cropping out downstream of grande river at agua vermelha hydroelectric dam in southern tri ngulo mineiro region enable the study of the mechanism of extrusion the origin of the brs has been subject to differing interpretations in the past either collapsed lava flows or central conduits detailed geological mapping at 1 1000 scale stratigraphic petrographic and gravimetric analysis of the most well preserved of the brs with a 200 m diameter has enabled the description of thirteen different basalt lava flows along with single a central lava lake and a ring dyke structure the central flow interpreted as a preserved lava lake comprises vesicle and amygdale rich basalt spatter ropy and degassing structures the most basal of the thirteen lava flows has massive basalt containing geodes filled with quartz above the lava flows show massive basalt with vertical columnar jointing where is possible to identify the top and bottom of each individual flow with gentle dips towards the perimeter of the structure a prominent ring dyke dipping towards the lava lake presents horizontal columnar jointing and cuts the basal and central flows the gravimetric analysis shows a weak negative bouguer anomaly on the center of the brs the proposed model describes the volcanism of the region in three main steps 1 fissure flow occurs with lava input 2 this lava cools and crystallizes cementing most of the fissures promoting the formation of localized central conduits and 3 the presence of dissolved gas in lava produces ring and radial fractures around the solidified lava lake the magma uses some of the ring fissures to ascend and the following lava flows assume the ring shape of the dyke vent thus the brs in agua vermelha region can be interpreted as remnants of central conduits representing the late stage magmatism of the serra geral formation

seismicity and mean magnitude variations correlated to the strongest earthquakes of the 1997 umbria marche sequence central italy 1 nearby faults can interact affecting the timing of a future earthquake a large earthquake can alter the static stress surrounding faults possibly activating an aftershock sequence here we test the hypothesis of earthquake triggering by examining the earthquakes that affected the umbria marche region central italy during september 1997 to april 1998 the analysis was performed combining information contained in parameters a and b of the gutenberg richter relationship before and after the strongest main shocks using a catalog of 6211 earthquakes m 1 5 by analyzing the changes in space of the a parameter we found that colfiorito main shocks mw 5 7 and 6 0 on 26 september 1997 increased the seismicity rate within 40 50 km of the epicenter we interpret this behavior as the effect of stress redistribution after analyzing the b value changes in space and time we found the strongest increase in mean magnitude in the sellano area between the colfiorito shocks and the two strong events mw 5 2 and 5 6 respectively which hit this region on 12 and 14 october 1997 this area was also the location of the strongest increase in change of the local occurrence rate density on the basis of these observations we postulate that temporal variations in both a and b values indicate a probable causal connection between the largest earthquakes in the sequence

climate sediment supply and tectonics as controls on the deposition and preservation of the aeolian fluvial etjo sandstone formation namibia deposition and subsequent preservation of the jurassic cretaceous etjo sandstone formation of namibia represents a complex interplay between climatic and tectonic factors and related variations in extrabasinal sediment supply the aeolian and fluvial deposits indicate semi arid to arid climatic conditions throughout the deposition of four distinct sedimentary units the succession records either an upward increase in aridity or an upward increase in aeolian sediment supply represented by a transition from a fluvially dominated basal unit through a marginal fluvial aeolian unit to an exclusively aeolian unit a combination of inherited palaeotopography and syndepositional extensional faulting provided the space necessary for the accumulation of much of the succession a basinwide unconformity super surface divides the succession this hiatus resulted partly from a lack of available preservation space and partly from a shutdown in aeolian activity related to a regional climatic reorganization a subsequent shift in the palaeowind direction from northwesterly to southwesterly exploited sand reserves in the parana basin of south america and led to the resumption of aeolian sedimentation across the region variations in preserved bedform thickness were directly controlled by differential amounts of tectonic subsidence across the basin a second major super surface towards the top of the succession resulted from the regional shutdown of large tracts of the aeolian system following the eruption of etendeka flood basalts across the region

recalculated probability of m 7 earthquakes beneath the sea of marmara turkey 1 new earthquake probability calculations are made for the sea of marmara region and the city of istanbul providing a revised forecast and an evaluation of time dependent interaction techniques calculations incorporate newly obtained bathymetric images of the north anatolian fault beneath the sea of marmara le pichon et al 2001 armijo et al 2002 newly interpreted fault segmentation enables an improved regional a d 1500 2000 earthquake catalog and interevent model which form the basis for time dependent probability estimates calculations presented here also employ detailed models of coseismic and postseismic slip associated with the 17 august 1999 m 7 4 izmit earthquake to investigate effects of stress transfer on seismic hazard probability changes caused by the 1999 shock depend on marmara sea fault stressing rates which are calculated with a new finite element model the combined 2004 2034 regional poisson probability of m 7 earthquakes is 38 the regional time dependent probability is 44 18 and incorporation of stress transfer raises it to 53 18 the most important effect of adding time dependence and stress transfer to the calculations is an increase in the 30 year probability of a m 7 earthquake affecting istanbul the 30 year poisson probability at istanbul is 21 and the addition of time dependence and stress transfer raises it to 41 14 the ranges given on probability values are sensitivities of the calculations to input parameters determined by monte carlo analysis 1000 calculations are made using parameters drawn at random from distributions sensitivities are large relative to mean probability values and enhancements caused by stress transfer reflecting a poor understanding of large earthquake aperiodicity index terms 7223 seismology seismic hazard assessment and prediction 7230 seismology seismicity and seismotectonics 8150 tectonophysics plate boundary general 3040 keywords earthquake probability sea of marmara seismic hazard turkey stress interaction north anatolian fault

forecasting where larger crustal earthquakes are likely to occur in italy in the near future a forecast of future occurrences of larger m 5 9 crustal earthquakes in italy is made on the basis of historic and instrumental seismicity and following a seismotectonic regionalization recently derived on the basis of geological evidence combined with earthquake epicenters and focal mechanisms completeness problems in the seismic catalog allow one to study only 20 regions out of 58 large crustal seismicity within each seismogenic region is modeled as either a periodic gauss process or a random poisson process according to the experimental coefficient of variation of the series of past occurrences in each region return times are estimated directly from the series of m 4 5 earthquakes if they are sufficient in number or from the gutenberg richter law applied to lower magnitude seismicity m 4 5 otherwise the immediate probability of an m 5 9 crustal seismic event is esti mated to be very low in all regions except southeastern sicily and appennino abrnz zese in the near future next 20 yr the estimated probability is high above 65 also in the appennino forlivese and naso capo d orlando regions in addition to detailed seismic risk reevaluations these regions represent the best bet for a program of intensive monitoring to gather a record of the process of strain accumulation and seismic release

global tectonics and eustasy for the past 2 billion years abstract continental freeboard and eustasy as gauged by the relative position of the world shelf break with respect to sea level have varied by 250 m from today s ice free shelf break depth of 200 m during the past 600 ma assuming constant or uniformly accreting continental crust and ocean water volume in an ice free world sea level fluctuations can be attributed to variation in the world ocean basin volume caused by changes in either its area or its depth relative to the world shelf break an increase in volume and lowering of sea level occur as 1 the world ocean floor ages cools and subsides 2 accreting continents collide thicken and decrease in area and 3 poorly conductive continental platforms become thermally elevated due to a size induced stasis over the mantle conversely a decrease in the age of the world ocean floor attenuation of continental crust during rifting and an increase in continent number and mobility will reduce the world ocean basin volume and raise sea level theoretical sea level calculated from these principles correlates well with calibrated first order cycles of eustatic sea level change for the phanerozoic the record closely fits a simple model of retardation and acceleration of terrestrial heat loss during alternating periods of supercontinent accretion and fragmentation calibrated to sea level highstands successive first order marine transgressions and orogenic pangea regressions characterize a self sustaining 440 ma plate tectonic cycle for the late precambrian and phanerozoic the cycle can be recognized as far back as 2 ga from the tectonic evidence of continental collision and rifting recorded in global orogenic peaks and mafic dike swarms and may be related to major episodes of glaciation and evolutional biogenesis

comparison of characteristic and gutenberg richter models for time dependent m 7 9 earthquake probability in the nankai tokai subduction zone japan summary earthquake forecasts are usually underinformed and can be plagued by uncertainty in terms of the most appropriate model and parameter values used in that model in this paper we explore the application of two different models to the same seismogenic area the first is a renewal model based on the characteristic earthquake hypothesis that uses historical palaeoseismic recurrence times and fixed rupture geometries the hazard rate is modified by the coulomb static stress change caused by nearby earthquakes that occurred since the latest characteristic earthquake the second model is a very simple earthquake simulator based on plate motion or fault slip rates and adoption of a gutenberg richter magnitude frequency distribution this information is commonly available even if historical and palaeoseismic recurrence data are lacking the intention is to develop and assess a simulator that has a very limited parameter set that could be used to calculate earthquake rates in settings that are not as rich with observations of large earthquake recurrence behaviour as the nankai trough we find that the use of convergence rate as a primary constraint allows the simulator to replicate much of the spatial distribution of observed segmented rupture rates along the nankai tonankai and tokai subduction zones although we note rate differences between the two forecast methods in the tokai zone we also see enough similarities between simulations and observations to suggest that very simple earthquake rupture simulations based on empirical data and fundamental earthquake laws could be useful forecast tools in information poor settings

late cretaceous climbing erg systems in the western xinjiang basin palaeoatmosphere dynamics and east asia margin tectonic forcing on desert expansion and preservation abstract this study reassesses the terrestrial deposits of the late cretaceous tangbian formation in the western xinjiang basin of the south china block originally considered to be aqueous deposits we reinterpret these strata as representing an extensive aeolian system in a desert environment this paper suggests that the development of aeolian deposits in the tangbian fm represents the culmination of the late cretaceous desertification that followed the relatively humid early late cretaceous epoch in the interior of south china the area was dominated by subtropical high pressure systems on a planetary scale combined with coastal mountains caused by sustained orogenic activity the interaction between subtropical high pressure systems and topographic conditions ultimately caused the development of a tropical desert climate characterized by an extensive dry climbing aeolian dune system we propose that the coastal mountains not only blocked moisture transport from the ocean and led to the aridification of south china interior but also exerted a control and transformed the original prevailing surface wind pattern

significance of stress transfer in time dependent earthquake probability calculations 1 a sudden change in stress is seen to modify earthquake rates but should it also revise earthquake probability data used to derive input parameters permit an array of forecasts so how large a static stress change is required to cause a statistically significant earthquake probability change to answer that question effects of parameter and philosophical choices are examined through all phases of sample calculations drawing at random from distributions of recurrence aperiodicity pairs identifies many that recreate long paleoseismic and historic earthquake catalogs probability density functions built from the recurrence aperiodicity pairs give the range of possible earthquake forecasts under a point process renewal model consequences of choices made in stress transfer calculations such as different slip models fault rake dip and friction are tracked for interactions among large faults calculated peak stress changes may be localized with most of the receiving fault area changed less than the mean thus to avoid overstating probability change on segments stress change values should be drawn from a distribution reflecting the spatial pattern rather than using the segment mean disparity resulting from interaction probability methodology is also examined for a fault with a well understood earthquake history a minimum stress change to stressing rate ratio of 10 1 to 20 1 is required to significantly skew probabilities with 80 85 confidence that ratio must be closer to 50 1 to exceed 90 95 confidence levels thus revision to earthquake probability is achievable when a perturbing event is very close to the fault in question or the tectonic stressing rate is low

on the handling of uncertainties in estimating the hazard of rupture on a fault segment uncertainties in data and parameter values have often been ignored in hazard estimates based on historic and prehistoric records of rupture on fault segments a mixture of distributions approach is appropriate to handle uncertainties in parameters of recurrence time distributions estimated from the geological and historical earthquake record of a fault segment and a mixture of hazards approach is appropriate for data uncertainties and for uncertainties in parameters estimated from a set of similar faults the former approach admits updating of the distributions for uncertainty as time passes the aim is to present the hazard as a single value which takes account of both data and parameter uncertainties conditional only on modeling assumptions the proposed methods are described in detail for the exponential and lognormal recurrence time models for fault rupturing earthquakes and applied by way of illustration to selected fault segments namely the mojave segment of the san andreas fault california and the wellington hutt valley segment of the wellington fault new zealand

random stress and earthquake statistics spatial dependence summary we calculate the 3 d stochastic rotations of focal mechanisms disorientations caused by stresses arising from the presence of many small random point defects that may surround the tip of an earthquake fault these random stresses can be shown to be distributed according to a cauchy distribution as a consequence the next episode of fracture of a fault cannot be planar the disorientation of focal mechanisms of these new rupture episodes is closely approximated by a rotational cauchy distribution as observed previously the geometry of fault systems for natural earthquakes is consistent with these observations since it too can be modelled by the cauchy distribution these observations indicate how the 3 d rupture process in rocks and other materials can be modelled we also calculate distributions of disorientations caused by a uniformly random 3 d rotation of sources these distributions are governed by symmetry properties of earthquake focal mechanisms to take into account the source symmetry we compare the cauchy distribution which is due to influence of random stresses to the distributions caused by random rotations

m 7 earthquake rupture forecast and time dependent probability for the sea of marmara region turkey we forecast time independent and time dependent earthquake ruptures in the marmara region of turkey for the next 30 years using a new fault segmentation model we also augment time dependent brownian passage time bpt probability with static coulomb stress changes cff from interacting faults we calculate mw 6 5 probability from 26 individual fault sources in the marmara region we also consider a multisegment rupture model that allows higher magnitude ruptures over some segments of the northern branch of the north anatolian fault zone beneath the marmara sea a total of 10 different mw 7 0 to mw 8 0 multisegment ruptures are combined with the other regional faults at rates that balance the overall moment accumulation we use gaussian random distributions to treat parameter uncertainties e g aperiodicity maximum expected magnitude slip rate and consequently mean recurrence time of the statistical distributions associated with each fault source we then estimate uncertainties of the 30 year probability values for the next characteristic event obtained from three different models poisson bpt and bpt cff using a monte carlo procedure the gerede fault segment located at the eastern end of the marmara region shows the highest 30 year probability with a poisson value of 29 and a time dependent interaction probability of 48 we find an aggregated 30 year poisson probability of m 7 3 earthquakes at istanbul of 35 which increases to 47 if time dependence and stress transfer are considered we calculate a twofold probability gain ratio time dependent to time independent on the southern strands of the north anatolian fault zone

layered seismogenic source model and probabilistic seismic hazard analyses in central italy we defined a seismogenic model for central italy based on three layers of sources and computed the relative seismic hazard maps one layer is constituted by individual structures liable to generate major earthquakes m 5 5 we defined them as seismogenic boxes by using geological information in terms of plan projec tion of active faults the seismicity rates associated with an individual source are based on the geometry and kinematics of the fault the recurrence model is controlled by the earthquake source association and when possible we defined the occurrence time of the last major event using it in a time dependent approach another layer is given by the instrumental seismicity analysis of the past two decades which allows us to evaluate the background seismicity m 5 5 using a sliding window selec tion of events we defined a model of regular adjacent cells of variable a and b values of the gutenberg richter relation the last layer utilizes all the instrumental earth quakes and the historical events not correlated to known structures 4 5 m 6 by separating them into seismotectonic provinces shaped on a geological structural basis the seismic hazard computations first use this layered model in a traditional probabilistic scheme the results indicate a narrow belt of peak ground acceleration pga higher than 0 30g with standard deviation in attenuation functions in the axial part of the apennine chain with a maximum spot of pga 0 40g southeast of the area damaged by the 1997 1998 umbria marche sequence pga expected not to be exceeded in 50 years at 90 probability level the background seismicity gives a nonnegligible contribution to the hazard at least for first damage levels then a simplified time dependent hypothesis has been introduced for the individual sources alone computing the conditional probability of occurrence of characteristic earth quakes for each source by brownian passage time distributions adopting equivalent fictitious seismicity rates we obtained maps referring to the next 50 years by using traditional codes these results show that the contribution of the recently active sources vanishes and the most hazardous sites are now located south of l aquila and in the sulmona area we consider that the methodology and results obtained are useful for seismic risk reduction strategies

3d shear wave velocity structure beneath the southeastern tibetan plateau from ambient noise we perform high resolution 3d shear wave structures of the crust and upper mantle using continuous wave data recorded at 170 stations from national and regional networks in the southeastern tibetan plateau first empirical green s functions are obtained between all the possible station pairs then rayleigh wave group velocity and phase velocity dispersion curves are retrieved using the frequency time analysis method the rayleigh wave group velocity images at periods from 8 to 50 s and phase velocity images at periods from 8 to 40 s are inverted on a 1 1 grid finally the 1d shear wave structure beneath each grid and the 3d shear wave velocity structure are acquired by linear interpolation our results indicate that low velocity layers lvls are ubiquitous in the middle lower crust beneath the southeastern tibetan plateau but vary in depth 20 35 km thickness 5 20 km and strength 5 4 10 8 velocity reduction in different blocks the 3d geometry of the lvls is complex and cannot be interpreted as a model with a uniform flow channel the shear velocity in the chuandian block is unevenly distributed indicating that the block is inhomogeneous the 12 may 2008 wenchuan and 20 april 2013 lushan earthquake sequences m s 3 0 all occurred in the crustal layers in which lvls are inhibited by the strong sichuan basin and in which the topography and crustal thickness vary sharply this formed the earthquake preparation environment of the two earthquakes the ningnan qiaojia pull apart region is characterized by low shear wave velocity in the shallow crust which agrees well with the sedimentary features of the upper crust a relatively high velocity is observed in the central part of the low velocity sichuan basin in the shallow layers indicating the basement beneath the sichuan basin may be uplifted around the central part of the basin

cyclic cross bedding in the eolian dunes of the sergi formation upper jurassic reconcavo basin inferences about the wind regime abstract the upper jurassic sergi formation displays eolian cyclic cross bedding composed of a regular intercalation of grain flow and wind ripple packages forming 1 3 m thick cycles each cycle is bound by erosive downwind surfaces and it comprises a sequence of lower angle wind ripple laminae followed by steeper grain flow strata that built out upon the wind ripple wedges in the migration direction the cross strata mean vectors dip consistently towards sw these cycles are related to seasonal changes in wind direction the cyclic stratification pattern suggests an alternation of northeasterly transverse winds responsible for slipface evolution and dune migration followed by reverse transversal or oblique winds overall southerly winds these winds caused dune degradation and reworking and led to the formation of reactivation surfaces and the related deposition of wind ripple wedges the wind pattern inferred from the eolian cyclic cross bedding is consistent with the quantitative atmospheric circulation model that indicates that a monsoonal wind regime operated in the low latitudes of gondwana during the late jurassic

crustal velocity and strain rate fields in italy and surrounding regions new results from the analysis of permanent and non permanent gps networks summary we present a new geodetic velocity solution for italy and the surrounding areas obtained from an analysis of continuous and survey mode global positioning system observations collected between 1991 and 2002 we have combined local regional and global networks into a common reference frame velocity solution providing a new detailed picture of the regional scale deformation field in the central mediterranean our velocity estimates are computed with respect to a new stable eurasian reference frame constraining the kinematics of the greater african eurasian plate boundary system in the study area we provide strain rate values for the main seismotectonic districts which are in good agreement with the seismic deformation inferred from earthquake focal mechanisms the southern tyrrhenian area calabria the apennines the southeastern alps the southern dinarides and the albanides display deformation rates at the order of 20 30 nanostrain yr 1 the corsica sardinia block moves according to eurasian plate motions and there is no indication that the opening of the tyrrhenian is still active the pelagian and sicilian domains are separated by a northwest southeast discontinuity the sicily channel rifted area and marginally significant relative motion between the pelagian plateau and the african plate is also observed the southern tyrrhenian is affected by north south compression and accommodates up to 50 per cent of the africa eurasia relative plate motion whereas the calabrian arc exhibits 2 mm yr 1 northwest southeast extension the observed deformation pattern suggests the presence of a major approximately north south tectonic discontinuity separating the sicilian and calabrian domains an extensional boundary observed along peninsular italy coincides with the distribution of seismogenic faults along the axis of the apennines this boundary separates a tyrrhenian and an adriatic domain with diverging velocities orientated north nnw ward and northeastward respectively the apennines are extending perpendicularly to the chain axis at rates of less than 3 mm yr 1 and only in the outer northern apennines indications of active shortening are observed insignificant deformation is observed in the western po plain and the western alps while the central and eastern alps display north south shortening the eastern adriatic domain is shortening perpendicular to the dinaric front with strain rates increasing from north to south the locus of collision between the aegean balkan system and the adriatic and ionian domains is marked by the kephalonia fault system which accommodates up to 20 1 mm yr 1 of right lateral motion the deformation pattern observed in the peri adriatic domain is well described by a counter clockwise rotation of the adriatic microplate around a pole located in the western alps

stratigraphic evolution of a fluvial eolian succession the example of the upper jurassic lower cretaceous guara and botucatu formations parana basin southernmost brazil abstract the guara and botucatu formations comprise an 80 to 120 m thick continental succession that crops out on the western portion of the rio grande do sul state southernmost brazil the guara formation upper jurassic displays a well defined facies shift along its outcrop belt on its northern portion it is characterised by coarse grained to conglomeratic sandstones with trough and planar cross bedding as well as low angle lamination which are interpreted to represent braided river deposits southwards these fluvial facies thin out and interfinger with fine to medium grained sandstones with large scale cross stratification and horizontal lamination interpreted as eolian dune and eolian sand sheets deposits respectively the botucatu formation is characterised by large scale cross strata formed by successive climbing of eolian dunes without interdune and or fluvial accumulation dry eolian system the contact between the guara and the botucatu formations is delineated by a basin wide deflation surface supersurface the abrupt change in the depositional conditions that took place across this supersurface suggests a major climate change from semi arid upper jurassic to hyper arid lower cretaceous conditions a rearrangement of the parana basin depocenters is contemporaneous to this climate change which seems to have changed from a more restrict accumulation area in the guara formation to a wider sedimentary context in the botucatu formation

the database of individual seismogenic sources diss version 3 summarizing 20 years of research on italy s earthquake geology abstract this paper describes the main characteristics the evolution and the structure of the database of individual seismogenic sources diss and particularly of its release of early 2007 the database contains the results of the investigations of the active tectonics in italy during the past 20 years the first two sections of this paper document the recent evolution in mapping and archiving italian active fault data in relation to important achievements in the understanding of italian tectonics some of which were spurred by significant earthquakes the central sections describe the current structure of the database the reasons for its assumptions and data categories its current contents its evolution through several years of improvements the last section describes how the current contents of the database correspond with the existing strain and stress data available from focal mechanism borehole breakout and gps data for the whole of italy the database supplies a fresh and unified view of active and seismogenic processes in italy by building on basic physical constraints concerning rates of crustal deformation on the continuity of deformation belts and on the spatial relationships between adjacent faults both at the surface and at depth

preservation of aeolian genetic units by lava flows in the lower cretaceous of the parana basin southern brazil the lower cretaceous geological record of the intracratonic parana basin in southern brazil comprises a thick succession of aeolian sandstones and volcanic rocks the intercalation between aeolian sandstone and volcanic floods allowed the preservation of distinct aeolian genetic units each genetic unit represents an accumulation episode bounded by supersurfaces that coincides with the base of lava flood events the entire package can be subdivided into a lower genetic unit which corresponds to aeolian sandstones preserved below the initial lava flows botucatu formation and an upper set of genetic units which comprises interlayered aeolian deposits and lava floods serra geral formation the lower genetic unit is up to 100 m thick its base is composed of ephemeral stream and aeolian sand sheet deposits that are overlain by cross bedded sandstones whose origin is ascribed to simple locally composite crescentic and complex linear aeolian dunes aeolian accumulation of the lower unit was possible as a result of the existence of a wide topographic basin which caused wind deceleration and a large sand availability that promoted a positive net sediment flux the upper genetic units comprise isolated sand bodies that occur in two different styles 1 thin lenses 3 m thick formed by aeolian sand sheets and 2 thick sand lenses 3 15 m comprising cross bedded cosets generated by migration and climbing of simple to locally composite crescentic aeolian dunes accumulation of the aeolian strata was associated with wind deceleration within depressions on the irregular upper surface of the lava floods the interruption of sedimentation in the lower and upper genetic units and related development of supersurfaces occurred as a result of widespread effusions of basaltic lava preservation of both wind rippled topset deposits of the aeolian dunes and pahoehoe lava imprints indicates that lava floods covered active aeolian dunes and hence protected the aeolian deposits from erosion thus preserving the genetic units

mid cretaceous desert system in the simao basin southwestern china and its implications for sea level change during a greenhouse climate abstract paleoclimatic indicators suggest that the mid cretaceous was one of the warmest intervals of the phanerozoic the period of the mid cretaceous super greenhouse also experienced an equator to pole temperature gradient much lower than that of the present day implying greater meridional heat transport by the atmosphere and or oceans however reconstructions of cretaceous atmospheric circulation have been hindered by a lack of relevant datasets based on reliable proxies or direct geological evidence aeolian deposits provide direct information about paleoclimate as well as the direction and intensity of paleo wind in the interiors of continents using petrologic and sedimentologic observations this study reassesses the terrestrial deposits of the mid cretaceous mangang formation in the simao basin of southwestern china originally considered to be aqueous deposits we reinterpret these strata as representing aeolian transport in a desert environment we suggest that the development of aeolian deposits in the mangang formation and coeval strata in adjacent basins was a local response to the prevailing desert climate in the mid to low latitudes of the northern hemisphere during the mid cretaceous which were dominated by subtropical high pressure systems on a planetary scale in addition with the closure of the mesotethys ocean the intermontane basins of the south china simao and indochina blocks became more isolated from atmospheric circulation bidirectional subduction of the bangong nujiang oceanic crust and the izanagi plate beneath east asia led to the development of andean type margins which created a rain shadow effect in continental east asia these factors caused the development of a tropical desert climate characterized by aeolian dunes and evaporite deposition we speculate that the severe depletion of groundwater reservoirs via the desertification of east asia may represent a previously unrecognized trigger for short term sea level changes during the ice free cretaceous greenhouse interval

pennsylvanian to jurassic eolian transportation systems in the western united states peterson f 1988 pennsylvanian to jurassic eolian transportation systems in the western united states in g kocurek editor late paleozoic and mesozoic eolian deposits of the western interior of the united states sediment geol 56 207 260 the direction of sediment transport in eolian sandstones of permsylvanian to jurassic age was interpreted from crossbedding resultants vector means obtained from studies of eolian rocks in the western u s supplemented by data from the few eolian units of eastern north america these were compiled from the published or unpublished theses hterature from unpublished fidd data contributed by colleagues or from measurements made for this study in addition new paleogeographic maps were compiled to evaluate the influence of geographic features on the atmospheric circulation patterns that are inferred from the crossbedding studies regionally the crossbedding indicates northeasterly northerly or northwesterly winds present coordinates from pennsylvanian through most of middle jurassic time a rather abrupt change in wind directions occurred in late middle jurassic time late part of the cauovian age when westerly wind patterns developed by the late jurassic the winds shifted to southwesterly calculations of the consistency factor vector mean strength made from region wide analyses of the resultants indicate fairly unidirectional winds from the permsylvanian through the early jurassic middle jurassic circulation was more varied judging from crossbedding studies in the lower part of the entrada sandstone crossbedding in upper jurassic eolian rocks of wyoming and south dakota yielded a random pattern but upper jurassic rocks farther south on the colorado plateau and adjoining areas show a return to a fairly unidirectional pattern comparing the resultants with their reconstructed paleogeographic setting shows surprisingly little influence of major geographic features on overall circulation patterns however the greatest amount of local variation occurred at or near highly indented shorelines where the temperature contrast between land and water produces local wind currents that may vary appreciably from regional circulation patterns although they do not cause noticeable horizontal deflections in wind patterns small and low topographic highs appear to be able to promote the development of a dune field if a source of sand is available and if streams do not enter the growing dune field

suppression of large earthquakes by stress shadows a comparison of coulomb and rate and state failure stress shadows generated by california s two most recent great earthquakes 1857 fort tejon and 1906 san francisco substantially modified 19th and 20th century earthquake history in the los angeles basin and in the san francisco bay area simple coulomb failure calculations which assume that earthquakes can be modeled as static dislocations in an elastic half space have done quite well at approximating how long the stress shadows or relaxing effects should last and at predicting where subsequent large earthquakes will not occur there has however been at least one apparent exception to the predictions of such simple models the 1911 m 6 0 earthquake near morgan hill california occurred at a relaxed site on the calaveras fault we examine how the more complex rate and state friction formalism based on laboratory experiments might have allowed the 1911 earthquake rate and state time to failure calculations are consistent with the occurrence of the 1911 event just 5 years after 1906 if the calaveras fault was already close to failure before the effects of 1906 we also examine the likelihood that the entire 78 years of relative quiet only four m 6 earthquakes in the bay area after 1906 is consistent with rate and state assumptions given that the previous 7 decades produced 18 m 6 earthquakes combinations of rate and state variables can be found that are consistent with this pattern of large bay area earthquakes assuming that the rate of earthquakes in the 7 decades before 1906 would have continued had 1906 not occurred these results demonstrate that rate and state offers a consistent explanation for the 78 year quiescence and the 1911 anomaly although they do not rule out several alternate explanations

magmatism and continental break up in the south atlantic high precision40ar 39ar geochronology abstract a detailed ar ar study of the parana etendeka continental flood basalts cfb has been undertaken using laser spot analysis data provide information not only on the age of the samples but also on the variability of the non radiogenic ar component and state of alteration the results indicate the parana etendeka cfb were erupted over 10 million years between 137 and 127 ma providing a minimum overall eruption rate of 0 1 km3 yr 1 this is an order of magnitude less than that previously proposed for this the deccan and siberian cfb provinces but it is similar to estimates for hawaii iceland and the columbia river cfb in detail the new ar ar analyses indicate that magmatism within the parana etendeka province migrated from nw to se prior to and during the opening of the south atlantic providing an explanation for the asymmetry of the cfb lavas about the south atlantic moreover chemically defined magma types were erupted at different times in different places and so within the paranathey may not be used as reliable chronostratigraphic units rather such magmatic units may reflect the extent of compositionally distinct source regions in the uppermost mantle and indicate that partial melting took place over a wide area under the paranabasin the nw se migration of the onset of magmatism might be interpreted as a plume trace but the inferred rate of movement is 3 times faster than that inferred from subsequent magmatism on the rio grande rise it is argued that the onset of magmatism reflected extensional tectonics normal to the ponta grossa dyke swarm given that magmatism preceded the main phase of rifting and that extension across the ponta grossa was moderate current plume models have difficulty in predicting sufficient melting within the asthenosphere

the role of viscoelastic stress transfer in long term earthquake cascades insights after the central italy 2016 2017 seismic sequence central italy is characterized by a network of active faults that interact in a complex manner coseismic coulomb stress changes have been invoked by several authors to explain the concentration of moderate to strong earthquakes in this region but none has considered the time dependent viscoelastic relaxation of the lower crust and upper mantle as a possible additional source of stress changes at a regional scale here starting from the 1915 m w 6 9 0 2 fucino earthquake we calculated the coseismic plus postseismic coulomb failure stress changes cfs due to eight moderate to strong earthquakes that have struck central italy in the last century and culminated with the 2016 2017 sequence results from this modeling coupled with some synthetic tests simulating normal fault earthquakes with different magnitudes allowed us to highlight the importance of postseismic processes in particular the viscoelastic stress transfer due to events of m w 6 5 can modify the spatial distribution of cfs on a centennial timescale and therefore trigger events at larger distances in addition using these results we identified other earthquake clusters in the historical catalogue last 618 years which like the 1915 2017 series were potentially modulated by both coseismic and postseismic processes finally considering our calculations combined with historical and paleoseismological data we suggest that several faults in central italy may be at present close to failure

earthquake recurrence on the south hayward fault is most consistent with a time dependent renewal process 1 elastic rebound and stress renewal are important components of earthquake forecasting because if large earthquakes can be shown to be periodic then rupture probability is time dependent while renewal models are used in formal forecasts it has not been possible to exclude the alternate view that repeated large earthquakes can happen in rapid succession without requiring time for stress regeneration here a consistency test between time dependent and time independent recurrence distributions is made using a monte carlo method to replicate the paleoseismic series on the south hayward fault time dependent distributions with recurrence interval of 210 years and coefficient of variation of 0 6 reproduce the event series on the south hayward 5 times more often than any exponential distribution a highly significant difference as determined using a two tailed z test for relative proportions therefore large hayward fault earthquakes are quasi periodic and are most consistent with a stress renewal process

circum pacific seismic potential 1989 1999 the seismic potential for 96 segments of simple plate boundaries around the circum pacific region is presented in terms of the conditional probability for the occurrence of either large or great interplate earthquakes during the next 5 10 and 20 years i e 1989 1994 1989 1999 and 1989 2009 this study represents the first probabilistic summary of seismic potential on this scale and involves the comparison of plate boundary segments that exhibit varying recurrence times magnitudes and tectonic regimes presenting these data in a probabilistic framework provides a basis for the uniform comparison of seismic hazard between these differing fault segments as well as accounting for individual variations in recurrence time along a specific fault segment and uncertainties in the determination of the average recurrence time

bedform alignment in directionally varying flows many kinds of sediment bedforms are presumed to trend either normal or parallel to the direction of sediment transport for this reason the trend of bedforms observed by remote sensing or by field observations is commonly used as an indicator of the direction of sediment transport such presumptions regarding bedform trend were tested experimentally in bidirectional flows by rotating a sand covered board in steady winds transverse oblique and longitudinal bedforms were created by changing only two parameters the angle between the two winds and the proportions of sand transported in the two directions regardless of whether the experimental bedforms were transverse oblique or longitudinal as defined by the bedform trend relative to the resultant transport direction they all had trends that yielded the maximum gross transport across the bedforms the fact that many of the experimental bedforms were neither transverse nor parallel to the resultant transport direction suggests that transport directions cannot be accurately determined by presuming such alignment

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

a mutually consistent seismic hazard source model for southern california abstract a previous attempt to integrate geological geodetic and observed seismicity data into a probabilistic hazard source model predicted a rate of magnitude 6 to 7 earthquakes significantly greater than that observed historically one explanation was that the discrepancy or apparent earthquake deficit is an artifact of the upper magnitude limit built into the model this was controversial however because removing the discrepancy required earthquakes larger than are seen in the geological record and larger than implied from empirical relationships between fault dimension and magnitude although several articles have addressed this issue an alternative integrated source model without an apparent deficit has not yet appeared we present a simple geologically based approach for constructing such a model that agrees well with the historical record and does not invoke any unsubstantiated phenomena the following factors are found to be influential the b value and minimum magnitude applied to gutenberg richter seismicity the percentage of moment released in characteristic earthquakes a round off error in the moment magnitude definition bias due to historical catalog incompleteness careful adherence to the conservation of seismic moment rate uncertainty in magnitude estimates obtained from empirical regressions allowing multi segment ruptures cascades and the time dependence of recurrence rates the previous apparent deficit is shown to have resulted from a combination of these factors none alone caused the problem nor solves it the model presented here is relatively robust with respect to these factors

stress interaction effect on the occurrence probability of characteristic earthquakes in central apennines 1 in this study we compute the effect of stress change due to previous historical earthquakes on the probability of occurrence of future earthquakes on neighboring faults following a methodology developed in the last decade we start from the estimate of the probability of occurrence in the next 50 years for a characteristic earthquake on known seismogenic structures based on a time dependent renewal model then a physical model for the coulomb stress change caused by previous earthquakes on these structures is applied the influence of this stress change on the occurrence rate of characteristic earthquakes is computed taking into account both permanent clock advance and temporary rate and state perturbations we apply this method to the computation of earthquake hazard of the main seismogenic structures recognized in the central and southern apennines region for which both historical and paleoseismological data are available this study provides the opportunity of reviewing the problems connected with the estimate of the parameters of a renewal model in case of characteristic earthquakes characterized by return times longer than the time spanned by the available catalogues and the applicability of the concept of characteristic earthquake itself the results show that the estimated effect of earthquake interaction in this region is small compared with the uncertainties affecting the statistical model used for the basic time dependent hazard assessment

earthquake nucleation on faults with rate and state dependent strength abstract dieterich j h 1992 earthquake nucleation on faults with rate and state dependent strength in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 115 134 faults with rate and state dependent constitutive properties reproduce a range of observed fault slip phenomena including spontaneous nucleation of slip instabilities at stresses above some critical stress level and recovery of strength following slip instability calculations with a plane strain fault model with spatially varying properties demonstrate that accelerating slip precedes instability and becomes localized to a fault patch the dimensions of the fault patch follow scaling relations for the minimum critical length for unstable fault slip the critical length is a function of normal stress loading conditions and constitutive parameters which include dc the characteristic slip distance if slip starts on a patch that exceeds the critical size the length of the rapidly accelerating zone tends to shrink to the characteristic size as the time of instability approaches solutions have been obtained for a uniform fixed patch model that are in good agreement with results from the plane strain model over a wide range of conditions above the steady state stress the logarithm of the time to instability linearly decreases as the initial stress increases because nucleation patch length and premonitory displacement are proportional to dc the moment of premonitory slip scales by d3c the scaling of dc is currently an open question unless dc for earthquake faults is significantly greater than that observed on laboratory faults premonitory strain arising from the nucleation process for earthquakes may by too small to detect using current observation methods excluding the possibility that dc in the nucleation zone controls the magnitude of the subsequent earthquake then the source dimensions of the smallest earthquakes in a region provide an upper limit for the size of the nucleation patch

paleoclimate of the kimmeridgian tithonian late jurassic world i results using a general circulation model abstract the kimmeridgian tithonian 154 7 145 6 ma middle and late late jurassic was a time of expanded continental rifting increased sea floor spreading and a relatively high eustatic sea level stand these processes collectively caused the fragmentation and flooding of the megacontinent pangea as well as the alteration of the global paleoclimate using a version of the community climate model ccm from the national center for atmospheric research we report two kimmeridgian tithonian paleoclimate seasonal simulations with geologically inferred paleotopography one using a co 2 concentration of 280 ppm pre industrial level and the other 1120 ppm increasing the co 2 four fold warms virtually the entire planet the greatest warming occurs over the higher latitude oceans and the least over the equatorial and subtropical regions simulation of a warmer planet with an elevated greenhouse effect fits the distribution of paleoclimatically sensitive faunas floras and sedimentary rocks model results indicate that sea ice was restricted to the high latitudes of the boreal and austral seas making landfall only in restricted areas the trade winds bring heavy rainfall in december january february to eastern gondwana and in june july august to the tethys sea margins a strong june july august monsoon occurs over southeast asia the distribution of coals correlates to precipitation sufficient to maintain gymnosperm forests and coastal areas where water saturated sediments are a result of eustatic high stands of sea level evaporites are localized to areas of negative precipitation evaporation runoff is restricted to regions of intense precipitation overall the 1120 ppm co 2 simulation provides a reasonable paleoclimate for the kimmeridgian tithonian and provides a standard until a ccm with oceanic heat transport a coupled atmospheric oceanic model or one with a finer grid cell configuration is available the results need further scrutiny in areas with more detailed geologic information

oscillating redox conditions in the middle late jurassic alpine tethys insights from selected geochemical indices and 57fe mossbauer spectroscopy abstract the middle late jurassic greenhouse conditions included co2 levels that have been estimated to be four to five times higher than they are presently by analysing the pattern of selected trace elements as redox proxies v u and mo and the variations in the chemical state of iron using 57fe mossbauer spectroscopy we demonstrate the occurrence of major changes in sediment redox conditions from the late bajocian through the late oxfordian in the pelagic environment of the alpine tethys in its carpathian domain our interpretation is based on analysis of siliceous limestones rich in radiolarians intercalated with red nodular limestones of ammonitico rosso type facies from the kri na nappe in the eastern part of the tatra mountains poland the presented redox potential eh values shows its changeable pattern along the section from 0 74 v to 0 16 v the low values of eh from 0 74 v to 0 4 v create the long term ca 7 myr trend of the medium scale fluctuations comprising the upper bajocian through the lower oxfordian interval of predominately grey and green radiolarian siliceous limestones this interval comprises the three short term less than 0 5 myr periods of slightly increasing eh from 0 35 v to 0 17 v observed in the uppermost bajocian lower bathonian and lower callovian as well as the significant changes in sediment redox conditions from oxic to dysoxic in the upper bajocian the overlying succession corresponding to the middle upper oxfordian ca 4 myr is characterized by red radiolarian siliceous limestones with positive eh values that indicate deposition under more oxic conditions than those during any other period in the study section the negative values of eh attributed to the upwelling periods coincide with the decreasing sea surface water temperature sst and increasing organic matter flux the largest negative shift is noted in the upper callovian which coincided with the cool climatic phase the positive eh values indicate oxic conditions due to the lowering of organic matter input coinciding with an increased sst caused by surface water stratification based on the observed long term variation in the redox we postulate thermally driven east west atmospheric circulation along the equatorial tethys ocean caused by the sharp contrast in sea surface temperature similar to the walker circulation operating across the modern pacific this phenomenon would have been the dominant periodical mode over the tropics and subtropics regions of the nw tethys during the middle late jurassic global warming reduces the long term strength of the mean tropical atmospheric circulation leading to sea water stratification near the surface and consequently lowering the organic matter flux however additional seaways of heat transport could also exist as they are associated with the opening closing of the hispanic corridor

pangaean climate during the early jurassic gcm simulations and the sedimentary record of paleoclimate results from new simulations of the early jurassic climate show that increased ocean heat transport may have been the primary force generating warmer climates during the past 180 m y the simulations conducted using the general circulation model gcm at the goddard institute for space studies include realistic representations of paleocontinental distribution topography epeiric seas and vegetation in order to facilitate comparisons between model results and paleoclimate data three major features of the simulated early jurassic climate include the following 1 a global warming compared to the present of 5 c to 10 c with temperature increases at high latitudes five times this global average average summer temperatures exceed 35 c in low latitude regions of western pangaea where eolian sandstones testify to the presence of vast deserts 2 simulated precipitation and evaporation patterns agree closely with the moisture distribution interpreted from evaporites and coal deposits high rainfall rates are associated primarily with monsoons that originate over the warm tethys ocean unlike the megamonsoons proposed in previous studies these systems are found to be associated with localized pressure cells whose positions are controlled by topography and coastal geography 3 decreases in planetary albedo occurring because of reductions in sea ice snow cover and low clouds and increases in atmospheric water vapor are the positive climate feed backs that amplify the global warming similar to other mesozoic climate simulations our model finds that large seasonal temperature fluctuations occurred over mid and high latitude continental interiors refuting paleoclimate evidence that suggests more equable conditions sensitivity experiments suggest that some combination of ocean heat transport increase high levels of co2 and improved modeling of ground hydrological schemes may lead to a better match with the geologic record we speculate also that the record itself is biased toward equable climatic conditions a suggestion that may be tested by comparing gcm results with more detailed phytogeographic analyses

eolian dunes computer simulations and attractor interpretation a simple computer simulation algorithm for the transport of sand by wind produces forms resembling barchan crescentic ridge linear and star natural dune classes sand is moved as slabs composed of many grains that are picked up at random transported in a specified direction and deposited 1 with a probability that depends on the local presence or absence of sand or 2 in shadow zones in the lee of dunes the simulated dune fields are interpreted as complex systems with sand dune classes being dynamical attractors of these systems the evolution of dunes once formed becomes decoupled from the details of eolian sand transport

a constitutive law for rate of earthquake production and its application to earthquake clustering seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress ing history control the timing of earthquakes the model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties this yields a general state variable constitutive formulation for rate of earthquake production resulting from an applied stressing history to illustrate and test the model some characteristics of seismicity following a stress step have been explored it is proposed that various features of earthquake clustering arise from sensi tivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate earthquake data appear to support a model prediction that aftershock duration defined as the time for rates to return to the back ground seismicity rate is proportional to mainshock recurrence time observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen dence of stress changes of the first event of the pair and stress sensitive time dependent nucleation applications of the constitutive formulation are not restricted to the simple stress step models investigated here it may be applied to stressing histories of arbitrary complexity the apparent success at modeling clustering phenomena suggests the possibil ity of using the formulation to estimate short to intermediate term earthquake probabil ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress

stress transferred by the 1995 mw 6 9 kobe japan shock effect on aftershocks and future earthquake probabilities the kobe earthquake struck at the edge of the densely populated osaka kyoto corridor in southwest japan we investigate how the earthquake transferred stress to nearby faults altering their proximity to failure and thus changing earthquake probabilities we find that relative to the pre kobe seismicity kobe aftershocks were concentrated in regions of calculated coulomb stress increase and less common in regions of stress decrease we quantify this relationship by forming the spatial correlation between the seismicity rate change and the coulomb stress change the correlation is significant for stress changes greater than 0 2 1 0 bars 0 02 0 1 mpa and the nonlinear dependence of seismicity rate change on stress change is compatible with a state and rate dependent formulation for earthquake occurrence we extend this analysis to future mainshocks by resolving the stress changes on major faults within 100 km of kobe and calculating the change in probability caused by these stress changes transient effects of the stress changes are incorporated by the state dependent constitutive relation which amplifies the permanent stress changes during the aftershock period earthquake probability framed in this manner is highly time dependent much more so than is assumed in current practice because the probabilities depend on several poorly known parameters of the major faults we estimate uncertainties of the probabilities by monte carlo simulation this enables us to include uncertainties on the elapsed time since the last earthquake the repeat time and its variability and the period of aftershock decay we estimate that a calculated 3 bar 0 3 mpa stress increase on the eastern section of the arima takatsuki tectonic line attl near kyoto causes fivefold increase in the 30 year probability of a subsequent large earthquake near kyoto a 2 bar 0 2 mpa stress decrease on the western section of the attl results in a reduction in probability by a factor of 140 to 2000 the probability of a mw 6 9 earthquake within 50 km of osaka during 1997 2007 is estimated to have risen from 5 6 before the kobe earthquake to 7 11 afterward during 1997 2027 it is estimated to have risen from 14 16 before kobe to 16 22

mesozoic deposits of sw gondwana namibia unravelling gondwanan sedimentary dispersion drivers by detrital zircon the namibian mesozoic successions may be remnant of a high dynamic sedimentary system that is characterized by multiple stages of sediment accumulation and erosion with contemporaneous homogenization starting with the deposition of the permo carboniferous dwyka group strata and continues at least until the lower cretaceous the lower cretaceous sedimentary system is interpreted to have involved at least an area covering the whole sw gondwana documenting the sedimentary history during the evolution from an ice house environment to an arid desert to test the sediment homogenization hypothesis we applied a combination of isotopic and morphometric data on detrital zircon grains as well as whole rock geochemical data of selected mesozoic sandstones from namibia as a base for the interpretation of the detrital zircon age data we compiled a zircon age dataset with c 44 000 analyses for the southern african region all samples reveal a major detrital pan african zircon age peak of c 0 5 0 7 ga sourced from the pan african magmatic events occurring around the kalahari craton margin the lowermost triassic is characterized by the occurrence of additional mesoproterozoic and paleoproterozoic age peaks of c 1 0 1 2 ga and 1 8 2 0 ga with a majority of zircon grains showing angular shapes the protosource of these grains is interpreted to possibly be the namaqua metamorphic complex and other paleoproterozoic structural units deformed in course of the namaqua orogeny in contrast other samples show a prominent permo triassic age peak and completely rounded zircon grains putatively derived from within the gondwanides volcanic arc the disparity in the zircon age pattern may point towards a change in provenance and also a change in the whole system of zircon recycling during the mesozoic southern gondwana the lower triassic neu loore fm are constrained to more local bedrock sources and short zircon transport distance in contrast zircon grains of the middle triassic omingonde the jurassic etjo und the cretaceous twyfelfontein formations are an expression for a major recycling and sediment homogenization system the system was facilitated by an interplay between fluvial and eolian sedimentary transport systems