the 1986 1988 intraplate earthquake sequence near joao câmara northeast brazil evolution of seismicity abstract the 1986 1988 intraplate earthquake sequence near joao c mara 5 5 s 35 7 w has been among the most significant in northeast brazil this century some 14 000 events were recorded in the 18 months from august 1986 including fifteen above magnitude 4 0 and one of 5 1 4000 buildings were damaged a local network of four portable seismographs was operated during most of the period augmented by a nine station telemetric network between may 1987 and april 1988 the temporal and spatial distribution of this seismicity is examined and determination of unusually good hypocentres is made possible by the simple velocity structure good signal transmission and impulsive p and s arrivals on most seismograms activity has been closely confined to a 28 km linear zone with a strike of 040 except for some small events along a parallel zone displaced laterally by 12 km neither zone has been related to any surface feature some unusual characteristics have raised concern about possible future seismicity the largest event occurred four months after the onset of activity and after several weeks of relative quiescence a 5 km intermediate section of the inferred fault has so far experienced only a few very small events

liquefaction evidence for strong earthquakes of holocene and latest pleistocene ages in the states of indiana and illinois usa abstract sand and gravel filled clastic dikes of seismic liquefaction origin occur throughout much of southern indiana and illinois nearly all of these dikes originated from prehistoric earthquakes centered in the study area in this area at least seven and probably eight strong prehistoric earthquakes have been documented as occurring during the holocene and at least one during the latest pleistocene the recognition of different earthquakes has been based mainly on timing of liquefaction in combination with the regional pattern of liquefaction effects but some have been recognized only by geotechnical testing at sites of liquefaction most paleo earthquakes presently recognized lie in indiana but equally as many may have occurred in illinois studies in illinois have not yet narrowly bracketed the age of clastic dikes at many sites which sometimes causes uncertainty in defining the causative earthquake but even in illinois the largest paleo earthquakes probably have been identified prehistoric magnitudes were probably as high as about moment magnitude m 7 5 this greatly exceeds the largest historic earthquake of m 5 5 centered in indiana or illinois the strongest paleo earthquakes struck in the vicinity of the concentration of strongest historic seismicity elsewhere paleo earthquakes on the order of m 6 7 have occurred even where there has been little or no historic seismicity both geologic and geotechnical methods of analysis have been essential for verification of seismic origin for the dikes and for back calculating prehistoric magnitudes methods developed largely as part of this study should be of great value in unraveling the paleoseismic record elsewhere

neotectonic evolution of the brazilian northeastern continental margin based on sedimentary facies and ichnology abstract quaternary post barreiras sediments are widespread along brazil s passive margin these deposits are well exposed in the onshore paraiba basin which is one of the rift basins formed during the pangean continental breakup in this area the post barreiras sediments consist of sandstones with abundant soft sediment deformation structures related to seismicity contemporaneous with deposition the trace fossils thalassinoides and psilonichnus are found up to 38 m above modern sea level in sandstones dated between 60 0 1 4 and 15 1 1 8 ka the integration of ichnological and sedimentary facies suggests nearshore paleoenvironments such deposits could not be related to eustatic sea level rise as this time coincides with the last glaciation hence an uplift of 0 63 mm yr or 1 97 mm yr if sea level was 80 m lower in the last glaciation would have been required to ascend the post barreiras sediments several meters above the present day sea level during the last 60 ka this would suggest that the post rift stage of the south american eastern passive margin may have experienced tectonic reactivation more intense than generally recognized although more complete data are still needed the information presented herein may play an important role in studies aiming to decipher the quaternary evolution of this passive margin

the northeast brazilian rift system the northeast brazilian rift basins provide important data critical to the understanding of continental rifting processes associated with the opening of the south atlantic these basins represent the locus of intersection of the southern and equatorial branches and some basins yield substantial chronostratigraphic data that constrain the temporal and spatial interaction of the rift phases similar data are not found in its counterpart in africa especially for the neocomian these early cretaceous rift basins of northeast brazil illustrate key three dimensional geometries of intracontinental rift systems mainly controlled by the basement structural framework during the main rift phase syn rift ii neocomian early barremian extensional deformation was distributed over three main rift axes 1 the gabon sergipe alagoas gsa trend 2 the reconcavo tucano jatoba rtj trend and 3 the cariri potiguar cp trend during this phase extensional deformation jumped west from the easternmost basins gsa trend to a series of ne trending intracratonic basins rtj and cp trends characterized by a set of asymmetric half grabens separated by basement highs transfer faults and or accommodation zones these basins are typically a few tens of kilometers wide and trend ne sw roughly perpendicular to the main extension direction during the neocomian preexisting upper crustal weakness zones like the dominantly ne sw trending shear zones of the brazilian pan african orogeny controlled the development of intracrustal listric normal faults internal transverse structures such as transfer faults and accommodation zones were also controlled by the local basement structural framework the megashear zones of pernambuco brazil and ngaundere africa seem to have behaved like a huge accommodation zone accommodating extensional deformation along the rtj gsa trends with simultaneous extension along the cp trend during the late barremian syn rift phase iii a significant change in rifting kinematics occurred when the cp trend was aborted and major rifting initiated at the equatorial branch during the aptian while the equatorial branch and benue trough africa experienced the main rift phase the rtj trend was aborted and the gsa trend developed a transitional phase between the rift and drift stage the gsa trend and the offshore potiguar basin represent the site of continued evolution into passive margin basins following the main rift episode

clastic dykes in east belgium evidence for upper pleistocene strong earthquakes west of the lower rhine rift segment fissures of seismic origin are described from terrace deposits of the meuse river in the liege maastricht area west of the lower rhine roer rift segment though associated with hydroplastic deformation of the sediments they are not injection structures they are interpreted as tension cracks resulting from local deformation of susceptible layers inferred to be due to cyclic loading by seismic waves the fissures have been tilled afterwards from above by vertically laminated sands and silts the distribution of the fissured areas and the special features of some ground cracks suggest that they could be linked to more than one earthquake between 650 and l00 ka bp by comparison with liquefaction phenomena described in relation to actual earthquakes the failure of the meuse terrace deposits could have been produced by seismic events of m l 6 5

late pleistocene holocene evolution of the doce river delta southeastern brazil implications for the understanding of wave influenced deltas abstract brazil s coast displays many wave influenced deltas that are still incompletely understood despite their significance for reconstructing the history of late pleistocene holocene sea level changes in this region and the potential to advance in the knowledge of wave influenced deltas among them the doce river delta is the most expressive given its larger geographic extension the present work shows that this is a wave influenced delta that evolved within the context of late pleistocene holocene sea level fluctuations rather than a mid holocene lagoonal delta as proposed elsewhere the delta had an initial progradation at an osl age of 132 7 9 1 ka after the marine isotope stage mis 5e which was followed by major progradation between 45 775 49 391 and 29 678 29 226 cal yr bp beach ridges spits formed during these phases were in part destroyed during an ensuing transgression between 8161 7933 and 4974 4850 cal yr bp the central delta remained dominated by fluvial processes which kept pace with the rising sea level due to relatively high rainfall in the doce river drainage basin the doce river delta started to grow again after the late holocene transgression a process still on going at the present time during this evolution the doce river was deflected northward and then southward a process that did not result in any significant facies change when the updrift and downdrift sides of the river s mouth are compared such a pattern is in disagreement with previously proposed asymmetry index models for wave influenced deltas which predict an uneven distribution of sandy or muddy rich deposits in the updrift and downdrift sides of the river s mouth respectively several other deltas along the brazilian coast also display facies configuration similar to the doce river delta or have patterns opposed to those proposed by the asymmetry index models based on these analogs it can be stated that the geometries and facies patterns of wave dominated deltas are not determined simply by the interplay of fluvial and marine processes instead they can be strongly influenced by the fluvial influx sea level changes and or tectonic reactivations as it appears to be the case of brazilian wave influenced deltas including the doce river delta such a conclusion calls for a word of caution when applying processes based facies models to reconstruct wave influenced deltas in the sedimentary record

experimental studies of the fluidization of layered sediments and the formation of fluid escape structures experiments demonstrate that fluid escape structures can be produced as a result of unstable fluidization behaviour where a lower base layer of granular material is inhibited from fluidizing by the presence of an overlying non fluidizing top layer before the base layer can fluidize the weight of the overlying material must be balanced and this is accomplished by base layer material pressing against the bottom surface of the confining top layer forming a static layer this static layer allows the top layer to lift away from the base layer which is then free to fluidize a water filled crack forms below the static layer and as this grows instability causes the static layer and top layer to bend and conical voids to form below the antiformal sections rupture occurs at the apex of the water void allowing the underlying water and fluidizing material to burst out through the top layer the fluidized base layer material then flows through the rupture until all of this material except that in the static layer is deposited above the previously overlying layer and a stable fluidization system results the top layer material is bent upwards around the rupture and the resulting pillar type escape structure is preserved if flow then ceases the vigour of the burst out is greatest when the base layer material has a grain size 15 of the top layer material if the base layer grain size is less than 8 of the top layer then base layer material will pass through the top layer pore spaces without forming an escape structure if cohesive material is present escape structures form when a layer of fine grained cohesive material overlies a layer of cohesionless material at low flow rates small pipes with scattered angular bends pierce the top layer and base layer material passes through them the base layer material is ejected on to the top layer and builds up around the mouth of each pipe to form constructional structures sand volcanoes this is in contrast to the cohesionless experiments where the weight of material being deposited on the top layer caused an ejecta filled depression to form around the rupture if flow then ceases both the pipes and the sand volcanoes are preserved at high flow rates where the base layer fluidizes the top cohesive layer becomes fragmented small fragments circulate within the fluidizing base layer and are preserved as floating clasts large fragments sink to the bottom of the fluidizing base layer erosion of the bottom surface of these larger fragments causes this surface to become convex downward the experimentally derived structures are similar to pillar type structures observed in the field and the processes described can be used to investigate the development of these structures fluidization experiments also demonstrate the genesis of dish structures and the cohesive behaviour can be applied to the deformation of these structures after initial formation

earthquake magnitude frequency epicentral distance and soft sediment deformation in sedimentary basins abstract empirical equations available for earthquake magnitude frequency and the maximum epicentral distance of liquefied sites versus magnitude are combined with the characteristic instantaneous sediment deposition rate at a station in a sedimentary basin to form a model for the local stratigraphic frequency of earthquake induced soft sediment deformation structures both the style of sedimentation and the characteristics of the earthquake source combine to determine the pattern of incidence of the structures in a basin the model is probably most directly applicable to the geodynamic interpretation of fluvial basins in which substantial volumes of readily liquefied sands accumulate at high local short term rates

clastic dykes in over consolidated tills evidence for subglacial hydrofracturing at killiney bay eastern ireland abstract a swarm of vertical gravel filled dykes up to 6 m high and several decimetres wide cut through an over consolidated till at killiney bay the dykes are rooted in a gravel layer and many display plumes of clastic debris ejected into the overlying sediments burst out structures such features have not previously been described these clastic dykes are interpreted as the infillings of hydrofractures which formed when water pressures in the basal gravel layer exceeded the overburden pressure and tensile shear strength of the capping till the burst out structures extend up to 7 m from the tops of the dykes and provide strong evidence for forceful upward flow evidence suggests that the hydrofractures formed subglacially probably during a minor re advance their presence in late devensian 26 13 ka bp tills with an irish sea provenance irish sea till may have important implications for the subglacial hydrology of the last irish sea ice sheet these hydrofractures cannot form in unconsolidated glacimarine sediment and their presence precludes a glacimarine origin for these deposits they greatly affect the geotechnical properties of irish sea tills in particular providing very permeable routes through otherwise impermeable layers with important consequences in situations elsewhere in the irish sea basin where they have been used as aquicludes in landfill and low level nuclear waste disposal sites

late quaternary sedimentation in the paraiba basin northeastern brazil landform sea level and tectonics in eastern south america passive margin abstract late quaternary deposits in the northeastern brazil have been scarcely investigated despite their relevance to the discussion of the post rift evolution of the south american passive margin within the context of landform sea level and tectonic deformation sedimentological stratigraphic and morphological characterization of these deposits referred as post barreiras sediments led to their distinction from underlying early middle miocene strata based on optically stimulated luminescence osl dating two sedimentary units pb1 and pb2 were recognized and related to the time intervals between 74 8 9 3 and 30 8 6 9 ka and 8 8 0 9 and 1 8 0 2 ka respectively unit pb1 consists of indurated sandstones and breccias either with massive bedding or complex types of soft sediment deformation structures generated by contemporaneous seismic activity unit pb2 is composed of massive sands or sands related to structures developed by dissipation of dunes the present work focusing on the post barreiras sediments discusses landform sea level and tectonics of the eastern south american passive margin during the latest quaternary non deposition and sub aerial exposure related to the tortonian worldwide low sea level combined with tectonic quiescence followed the miocene transgression tectonic deformation in the latest pleistocene created space to accommodate unit pb1 in downthrown faulted blocks and perhaps also synclines produced by strike slip deformation although deposition of this unit was simultaneous with the progressive fall in sea level that followed the last interglacial maximum punctuated rises combined with land subsidence led to marine deposition close to the modern coastline renewed subsidence in the holocene gave rise to accommodation of the post barreiras sediments most of unit pb2 was deposited during the holocene transgression but it is not composed of marine sediments which suggests either an insignificant rise in relative sea level or aeolian reworking of thin transgressive sands the data presented here lead to a review of the evolution of the south american passive margin based on assumptions of uniform sedimentation and undeformed planation surfaces over a wide coastal area of the northeastern brazil

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

extensive soft sediment deformation structures in the early darriwilian middle ordovician shallow marine siliciclastic sediments formed on the baltoscandian carbonate ramp northwestern estonia abstract the nearshore middle ordovician early darriwilian deposits of the baltoscandian basin formed on the flank of tectonically stable fennoscandian shield comprise numerous soft sediment deformation structures the areal extent of the deformed interval extends up to 9000 km 2 from nw estonia to se sweden the deformation structures occur within a meter scale sandstone horizon that includes load casts flame structures ball and pillow morphologies up to 2 m wide sedimentary dykes autoclastic breccias sand volcanoes and other related soft sediment deformation structures evidently these deformation structures formed during a single seismic event that caused liquefaction and fluidization of the water saturated unconsolidated shallow marine sediments within almost the entire sandstone unit pakri formation probably a unique catastrophic earthquake of magnitude 7 or higher occurred in this region penecontemporaneously with the deposition of these sediments the ultimate cause of seismic event of such magnitude in the tectonically stable baltoscandian basin is unclear however deposition and deformation of the pakri formation fall within the middle ordovician meteoritic bombardment period which resulted from the disruption of a large parent body in the asteroid belt approximately 470 ma ago this in turn suggests a potential impact origin for the single catastrophic earthquake in the tectonically stable study region although impact crater of suitable age is currently not known from the region then previous studies have documented some impact metamorphic shock lamellae i e pdfs and abundant extraterrestrial chromite grains from the deformed sediments

the unsteady post rift stage of the south american passive margin based on the tectono sedimentary evolution of the onshore paraiba basin ne brazil abstract the post rift tectono sedimentary history of passive margins has been an issue of increased interest after the perception of their unsteady nature during the neogene and quaternary the evolution of the eastern south america margin might be benefited from investigations of the sedimentary record in a number of marginal basins the paraiba basin is of particular interest to discuss the post rift evolution of the south american passive margin because it represents the last bridge with the african plate this work aims to analyze the post rift sedimentary record of the onshore paraiba basin as a contribution to discuss the neotectonic history of the south american passive margin surface and subsurface data were integrated from outcrops deep stratigraphic profiles airborne geophysical maps and remote sensing products the depositional and denudational processes in this basin were a result of tectonic subsidence and uplifting tectonics after the main rifting phase are indicated by abundant structures including normal reverse and strike slip faults as well as folds that affected the neogene and late pleistocene sedimentary deposits the ductile and brittle deformation resulted mainly from multiple reactivations of e w ne sw and nw se trending basement shear zones the deformation mechanism included distension and compression under a strike slip regime tectonic reactivations even during the late pleistocene support an unsteady south atlantic passive continental margin throughout the post rifting stage

quaternary fault control on the coastal sedimentation and morphology of the sao francisco coastal plain brazil abstract the role of neotectonic faulting in shaping topography and controlling sediment deposition has been increasingly documented along the stable continental margin of south america but the level of the present day tectonic stability of this margin is still a matter of debate this paper presents an investigation of the effects of quaternary fault reactivation on the sao francisco coastal plain sfcp this feature is a 56 km long progradational coastal plain located in the sergipe alagoas basin along the continental margin of brazil the sfcp is bounded on the west by a system of normal faults striking n s to ne sw the horst that bounds this plain is capped by the miocene barreiras formation and quaternary debris flow and fluvial deposits whereas the graben is filled with braided stream deposits and sandy beach ridge sediments the faulting contributed to the generation of accommodation space for the deposition of coastal sediments on the plain these processes started with the reactivation of cretaceous faults during the miocene during the quaternary fault reactivation and associated soft sediment deformation occurred between 82 and 8 3 ka with minor pulses between 1700 and 60 cal yr bp several faults along this margin are tectonically active and may represent the onshore continuation of gravitational collapses that have been documented offshore along the continental shelf and slope

soft sediment deformation structures interpreted as seismites in the uppermost aptian to lowermost albian transgressive deposits of the chihuahua basin mexico several levels of soft sediment deformation structures s s d s cut by synsedimentary normal faults have been observed in the transition beds between the las vigas and la virgen formations cretaceous in the northeastern part of the chihuahua basin in mexico these structures consisted of four kinds of motifs floating breccias flame like structures large pillow structures and wavy structures they are restricted to five stratigraphic levels 1 5 and surrounded by undeformed beds in fluvio lacustrine and tidal deposits and can be traced over a distance of several hundred meters this deformation is interpreted to have resulted from the combined effects of liquidization and shear stress in soft sediments due to local earthquakes in the area which could have been generated during the rifting stage of the chihuahua basin new constraints placed on the age of the las vigas formation bracketed by late aptian charophytes at the bottom and colomiellids of late aptian to earliest albian age at the top suggest that this synrift tectonism lasted at least until the end of the aptian

sediment deformation in miocene and post miocene strata northeastern brazil evidence for paleoseismicity in a passive margin abstract stratigraphic intervals characterized by varied and complex styles of soft sediment deformation structures are well preserved in miocene and late pleistocene to holocene deposits of a sedimentary basin located in northeastern brazil the miocene strata represented by the barreiras formation record only brittle structures including numerous faults and fractures with straight and high angle dipping planes that are often filled with sands derived from overlying beds folds consisting of broad anticlines and synclines are also present in this unit the late pleistocene to holocene deposits named post barreiras sediments contain an indurated sandy package with a large variety of ductile and brittle deformation structures i e massive sandstones with isolated sand fragments and breccias undulatory strata sand dykes and diapirs sinks and bowls pebbly pockets plunged sediment mixtures fitted sand masses cone shaped cracks fault grading and sedimentary enclaves these features confined to sharp based stratigraphic horizons that progressively grade downward into undisturbed deposits are related to seismic shocks of high surface wave magnitude i e ms 5 or 6 amalgamated seismites suggest that previously formed seismites were affected by subsequent seismic wave propagation seismic waves caused by activity along one or most likely several tectonic structures would have propagated throughout the depositional environment producing laterally extensive seismites the close proximity to earthquake epicenters would have promoted pervasive re sedimentation due to pore overpressure resulting high volumes of massive sandstones and breccia the similarity between deposits with correlatable strata from many other areas along the brazilian coast allows raise the hypothesis that the seismic episodes might have affected sedimentation patterns in a large i e extension of several hundreds of kilometers geographic area thus the modern seismicity recorded along northeastern brazil was recurrent during the quaternary and perhaps also in the pliocene the estimated high magnitude of the seismic events and the great regional extent of the affected area demonstrate that the brazilian coast experienced tectonic stress through the last geological episodes of its evolution which would have favored sediment accumulation and penecontemporaneous re sedimentation this geological context is unexpected in a passive margin inducing to revisit the debate on how active is a passive margin

streambank erosion rates and loads within a single watershed bridging the gap between temporal and spatial scales abstract the importance of streambank erosion to watershed scale sediment export is being increasingly recognized however few studies have quantified bank erosion and watershed sediment flux at the basin scale across temporal and spatial scales in this study we evaluated the spatial distribution extent and temporal frequency of bank erosion in the 5218 ha walnut creek watershed in iowa across a seven year period we inventoried severely eroding streambanks along over 10 km of stream and monitored erosion pins at 20 sites within the watershed annual streambank recession rates ranged from 0 6 cm yr during years of hydrological inactivity to 28 2 cm yr during seasons with high discharge rates with an overall average of 18 8 cm yr the percentage of total basin export attributed to streambank erosion along the main stem of walnut creek ranged from 23 to 53 large variations in individual site annual rates and percentage of annual load suggested that developing direct relationships between streambank erosion rates and total sediment discharge may be confounded by the timing and magnitude of discharge events storage of sediments within channel system and the remobilization of eroded material

soft sediment deformation structures in the earth s oldest seismites abstract the chaibasa formation in eastern india which was deposited between 2100 and 1600 million years ago shows deformations that must have formed when the sediments were not yet consolidated some of these deformation structures have never been described before here they are described depicted and their origin is analysed we show that they must be the result of shocks which can only be explained satisfactorily as triggered by earthquakes the layers containing these deformation structures are termed seismites they are among the earliest records of earthquakes known in the earth s history

earthquake induced structures in young sediments abstract soft sediment deformational structures have been identified in several plio quaternary horizons near burdur in southwest turkey these horizons satisfy criteria for correlating such structures with seismic events and it is proposed that the structures were formed by earthquake induced liquefaction the deformational structures are thus interpreted to represent seismic events which occurred up to 2 3 ma ago

tsunami induced conglomerates in miocene upper bathyal deposits chita peninsula central japan abstract the tsubutegaura conglomeratic tsunamiites occur in the middle section of the miocene storm related sand silt alternation system in the chita peninsula central japan deposition of the system in the upper bathyal environment in a bay and synsedimentary seismic activity has been elucidated by palaeontological palaeogeographical and sedimentological studies two coupled units each built up by a conglomerate layer with an overlying sandstone layer and the alignment of lenticular sedimentary bodies are exceptional in this sequence some typical lenticular bodies confined within sedimentary troughs consist of a boulder bearing conglomerate layer and calcareous sandstone layer of the lower couple and another conglomerate layer of the upper couple the tuffaceous sandstone layer of the upper couple is distributed more widely than the other lithologies the framework gravels in the coupled conglomerates form a clast supported fabric and are quite notably monomictic the clasts are angular and imbricated partly forming peculiar gravel clusters due to traction current transportation conspicuous laminations develop in the coupled sandstone layers antidunes with chute and pool structure in the upper couple sandstone layer indicate deposition from an upper flow regime current on the other hand the calcareous composition of the lower couple sandstone layer reveals shallow water provenance thixotropic deformations and diastasis cracks in the siltstone bed immediately beneath the layers of the couples show that a severe earthquake tremor and a rapid change of water pressure occurred just before the deposition of the tsunamiites submarine debris flows due to collapse of a fault scarp in a shallow bank and the ensuing wash by two pulses of the tsunami induced ebb current comprise the scenario for the formation of the tsubutegaura conglomeratic tsunamiites

late oligocene miocene transgressions along the equatorial and eastern margins of brazil abstract the seaboard of brazil is a highly favorable setting for studying episodes of worldwide sea level rise because of its passive nature previous studies of the equatorial coast of brazil have led to the recognition of extensive oligo miocene and miocene marine influenced deposits but these deposits have been overlooked in other coastal areas of brazil the aim of the present study is to show the origin and evolution of late oligocene and miocene marine influenced strata exposed in more than 5000 km of coastal areas along the wnw trending equatorial and nne trending eastern brazilian continental margins we review the most relevant data concerning the strata of these ages exposed along the equatorial and eastern margins of brazil and combine them with new data based on these occurrences we analyze the history of sea level fluctuations and show that marine influenced strata are more widespread in these margins than originally thought our main results indicate that a marine influence is not only imprinted in the deposits exposed along the equatorial margin but it is also widespread in several areas of the eastern margin for a long geological time interval ranging from the end of the cretaceous or paleogene up to the late oligocene most of the brazilian coast remained a non depositional site exposed to subaerial erosion and lateritic soil development the combination of sea level rise and tectonic subsidence promoted sediment accumulation in the onshore portion of several basins two transgressive episodes occurred one in the oligo miocene and another in the early middle miocene the latter gave rise to deposition of the barreiras formation however during the supposedly middle miocene eustatic sea level highstand in coastal brazil there was a renewed and extensive phase of non deposition and subaerial erosion with lateritic soil formation a process that lasted up to the late quaternary this mismatching of the sedimentary record with other south american and continental areas is discussed herein as in many other areas of south america and of the world the regressive transgressive events recorded along the brazilian coast most likely responded to a combination of eustatic sea level fluctuations and local factors such as tectonic activity intraplate stresses and changes in dynamic topography during the post rift history of the eastern south american plate

neogene quaternary fault reactivation influences coastal basin sedimentation and landform in the continental margin of ne brazil we investigate the role of reactivation of precambrian basement fabric in the tectono sedimentary and geomorphological evolution of the paraiba basin continental margin of northeastern brazil during the cretaceous neogene and quaternary this basin represents part of the last bridge between south america and africa before the last breakup stage of the south atlantic rifting in the early cretaceous the paraiba basin infill is composed of siliciclastic and carbonate cretaceous units as well as aeolian fluvial and marine quaternary units we used shuttle radar imagery aeromagnetic wellbore and field data the reduced to the pole magnetic map rtp indicates the continuity of the steeply dipping precambrian basement shear zones beneath the paraiba basin the combined analysis of surface and subsurface data shows that ne sw and e w striking shear zones were subjected to brittle reactivation in the aptian middle albian during the basin opening and again in the neogene quaternary forming a system of horsts and grabens along the basin some of these structures such as the e w oriented pernambuco shear zone present modern day seismicity n s and mainly nw se striking transfer faults cut across aptian middle albian to neogene quaternary strata these four main fault directions control main river channels and alluvial valleys up to 2 km wide topographic breaks up to 50 m were created by late reactivation of rift faults which mark the boundary between horsts and grabens along the basin in addition structural data evidence syn tectonic faulting with vertical offsets up to 80 m in the cretaceous and up to 70 m in the neogene quaternary we conclude that shear zones across the study area are long lived structures that have behaved as weakness zones their neotectonic brittle reactivation has controlled sediment deposition and landform development which continued through the neogene quaternary

shallow marine massive sandstone sheets as indicators of palaeoseismic liquefaction an example from the ordovician shelf of central bolivia abstract the middle to upper ordovician siliciclastic succession in central bolivia provides excellent exposures of up to 1 m thick massive sandstone beds produced by liquefaction induced sediment remobilisation these fine grained massive sandstones occur in shallow marine nearshore facies that were deposited above storm wave base vertical to steeply inclined clastic dykes which penetrate up to 1 5 m of the overlying sediment pile feed into the basal parts of massive sandstone sheets these dykes are interpreted as pathways used by liquefied sediment during upward directed escape from a subsurface horizon the relatively short lateral spacing of 5 to 25 m between the individual dykes initiated lateral coalescence of ejected individual sediment bodies as a result massive sandstone sheets formed and can be traced laterally over several kilometres while undeformed sandy deposits contain between 5 to 10 dispersed clay the average clay content in massive sandstone sheets is 15 the elongated sometimes s shaped form of the sandy laminated fragments reflects squeezing during movement showing that they have been deformed under shear stress during flow the axis of maximum elongation of the fragments indicates local flow direction as the massive sandstone sheets are likely the products of seismic shocks they provide the first evidence of tectonic activity in this part of the basin during the middle to late ordovician

soft sediment deformation structures induced by rapid sedimentation in early cretaceous turbidites lingshan island eastern china turbidites of the early cretaceous lingshandao formation on lingshan island eastern china show numerous soft sediment deformation structures the turbidites accumulated in a rift basin plain on the distal part of a low energy fan together with autochthonous fine grained sediments that settled from suspension occasionally sets of both types of sediments slumped down the basin slope the turbidites were studied in two sections paleocurrent directions measured from sole marks at the base of the sandy turbidites indicate a slope from se to nw this is consistent with the dip direction of the axial planes of the major slump folds among the numerous types of soft sediment deformation structures that are present two types are of special interest because of their specific genesis viz rip up clasts and dome structures it appears that rapid sedimentation must be considered as the main trigger behind these deformations the rapid accumulation of particularly the sandy turbidites resulted in overloading

soft sediment deformation structures in a lacustrine sedimentary succession induced by volcano tectonic activities an example from the cretaceous beolgeumri formation wido volcanics korea abstract the cretaceous beolgeumri formation is composed of laminated mudstones intercalated with sandstones chert and a bed of lapilli tuff that were deposited in a lacustrine environment at the terminal part of a regional strike slip fault systems on the southwestern korean peninsula the beolgeumri formation contains various types of soft sediment deformation ssd structures that are characterized by a wide extent

diurnal and semidiurnal variations in global surface wind and divergence fields diurnal and semidiurnal variations in surface winds and wind divergence over the globe 50 s 70 n are documented using 3 hourly wind observations from 10 000 land stations and available marine reports during 1976 1997 a strong diurnal cycle in surface winds is found over land areas strongest over high terrain and in summer with an amplitude of 0 6 1 1 m s for wind speed and 0 5 0 7 m s for the zonal and meridional wind components surface wind speed peaks in the early afternoon over most of the globe it is suggested that increased downward turbulent mixing of momentum during the day could be one of the main causes for the early afternoon maximum of surface wind speed the diurnal anomalies of surface wind divergence tend to be out of phase in adjacent regions in particular land areas except for extreme inland locations exhibit maximum divergence around dawn 0600 0800 local solar time lst while nearby oceanic regions have their maximum divergence in the evening 1700 1900 lst thus there is evidence for a large scale diurnal circulation in which surface air rises and converges over the continents and sinks and diverges over nearby oceans in the afternoon and early evening and the opposite occurs in the early morning over the tropical atlantic and pacific oceans 10 s 10 n a zonally coherent pattern of maximum convergence divergence north south of the equator around 0900 1200 lst is generally similar to the latitudinal profile of the mean daily divergence indicative of an enhancement of the local hadley cell around 1030 lst relative to the daily mean another zonally coherent north south dipole occurs over the north pacific with maximum surface wind divergence convergence around 0600 0800 lst in the subtropics midlatitudes this phase pattern correlates with cloud cover over the two regions over the united states surface divergence peaks around 0600 lst in the west and the east and around 2000 lst in the center

methodology for a regional tidal model evaluation with application to central california abstract observations from disparate observational assets including tide gauges moorings and high frequency hf radars were used to depict the tidal variability and to evaluate model tidal simulations for a region off central california including the monterey bay for this study the hydrodynamic model was forced only with tides derived from a large scale model for the northeast pacific ocean homogeneous density and initially horizontally uniform density stratification cases were considered the model successfully reproduced tidal sea surface height variations within the model domain as determined by comparisons with sea level or bottom pressure measured at six locations to achieve tidal currents with realistic amplitudes as determined from hf radar and moored measurements it was found that barotropic velocity as well as sea level from the large scale regional tidal model must be included in specifying the open boundary condition however even with such forcing the model with homogeneous density field under predicted the semidiurnal and diurnal barotropic currents as estimated from depth averaged currents measured at 11 locations in the diurnal frequency band the observed surface and nearshore depth averaged currents are likely influenced by meteorological forcing which was not included in the model the hf radar measured surface tidal currents both semidiurnal and diurnal are consistent from year to year and between the winter season and the entire year semidiurnal surface tidal currents derived from year long hf radar measurements do not resemble either the modeled or measured barotropic current fields rather they exhibit amplitudes and small scale spatial variability indicative of the presence of internal tides thus indicating that model derived barotropic tidal currents cannot be validated over large spatial extents using long time series of hf radar derived surface currents with initially horizontally uniform vertical density stratification the model produced surface currents with spatial variability and amplitude range comparable to what was derived from hf radar surface current measurements but the point by point comparisons are not impressive for this region of complex topography likewise the subsurface current comparisons performed at four deepwater locations show considerable model data differences possible reasons for these disparities include the effects of atmospheric forcing spatially and temporally varying stratification remotely generated coastally trapped waves and remotely generated internal tides

tsunami sedimentary facies deposited by the storegga tsunami in shallow marine basins and coastal lakes western norway sedimentary successions in small coastal lakes situated from 0 to 11 m above the 7000 year bp shoreline along the western coast of norway contain a distinctive deposit very different from the sediments above and below the deposit is interpreted to be the result of a tsunami inundating the coastal lakes an erosional unconformity underlies the tsunami facies and is traced throughout the basins with most erosion found at the seaward portion of the lakes the lowermost tsunami facies is a graded or massive sand that locally contains marine fossils the sand thins and decreases in grain size in a landward direction above follows coarse organic detritus with rip up clasts here termed organic conglomerate and finer organic detritus the tsunami unit generally fines and thins upwards the higher basins 6 11 m above the 7000 year shoreline show one sand bed whereas basins closer to the sea level 7000 years ago may show several sand beds separated by organic detritus these alternations in the lower basins may reflect repeated waves of sea water entering the lakes in basins that were some few metres below sea level at 7000 years bp the tsunami deposit is more minerogenic and commonly present as graded sand beds but also in some of these shallow marine basins organic rich facies occur between the sand beds the total thickness of the tsunami deposit is 20 100 cm in most studied sites an erosional and depositional model of the tsunami facies is developed

debris flow and glacioisostatic induced soft sediment deformation structures in a pleistocene glaciolacustrine fan the southern baltic sea coast poland abstract middle pleistocene glaciolacustrine fan sediments are exposed along a cliff at the baltic sea coast where plastic and brittle soft sediment deformation structures ssds commonly occur 1 fold structures various types of folds and flexures 2 load structures load casts pseudonodules and flame structures 3 water escape structures wes and 4 brittle deformation structures such as faults medium and small scale reverse and normal and fragments of broken up laminae the origins of the ssds can be linked to gravitational processes promoted by shear stresses in subaqueous debris flows on the glaciolacustrine fan and by the weight of overlying sediments and or to the glacial rebound of earth s crust during deglaciation because in the pleistocene the baltic sea and surrounding areas were covered by ice sheets many times the question investigated here concerns recognition of the trigger mechanisms responsible for the development of ssds and the criteria needed to recognize those mechanisms based on the lithological and deformational features of the sediments involved some types of ssds can look similar regardless of trigger mechanisms but some occur more often as a result of a specific mechanism is it possible to distinguish ssds of seismic origin in a glaciolacustrine fan succession affected by multiple debris flows and of ssds that evolved as a consequence of slope processes we suggest criteria to recognize ssds triggered by the glacioisostatic rebound as well as those which can develop as a result of the rebound and slope processes

liquefaction and fluidization of lacustrine deposits from lahaul spiti and ladakh himalaya geological evidences of paleoseismicity along active fault zone abstract soft sediment deformational structures are important diagnostic features of paleoseismic studies these seismites result from local vigorous fluidization and hydroplastic deformation formed during liquefaction as a direct consequence of permanent deformation of ground surface due to earthquakes of large magnitude the region of eastern ladakh spiti basin and the upper sutlej river basin record a concentration of earthquakes in a well defined ne trending seismic zone sub parallel to the strike of leo pargil horst and the kaurik chango fault zone soft sediment deformational studies of the fluvial and fluvio lacustrine sequences near sumdo village along sangla valley of himachal pradesh and near saspol village of ladakh indicate that the kaurik chango fault zone is a seismogenic fault causing liquefaction and fluidization as the consequence of earthquake activity in the past thermal luminescence tl date of the deformational structures near the sumdo village constrains the paleoseismic activities of large magnitude between 90 000 years third activity to 26 000 years last geological evidence with a recurrence interval of approximately 10 000 years during the quaternary period

paleosurfaces from northeastern amazonia as a key for reconstructing paleolandscapes and understanding weathering products the characterization and mapping of paleoweathering surfaces as well as their associated deposits throughout the northeastern amazonia can be a useful tool for inter basin stratigraphic correlations and for establishing the evolution of landscapes and climates through time this type of investigation has led to the recognition of five weathering surfaces developed from the upper cretaceous through the quaternary designated here as s1 to s5 surface s1 occurs at the top of late cretaceous deposits represented by the ipixuna cujupe succession as well as on older precambrian and paleozoic rocks surface s2 marks the top of an indurated massive semi flint1 unit for cases in which surfaces s1 and s2 are amalgamated a thick lateritic paleosol displaying hexagonal branched concretions is present surface s3 occurs at the top of the pirabas and lower portion of the barreiras formations of late oligocene early miocene age and it is also associated with paleosol but has no lateritization when surface s3 is amalgamated with surfaces s1 and s2 bauxite is present in association with the underlying laterites surface s4 bounds the top of the middle to upper barreiras formation of middle miocene age as well as correlatable deposits known as the belterra clay this surface is marked by a lateritic paleosol having columnar concretions surface s5 occurs between a lower unit consisting of massive light red sands of the plio pleistocene post barreiras 1 sediments and an upper unit of yellow eolian sands of the holocene post barreiras 2 sediments the paleoweathering surfaces present in the northeastern amazonia enable the reconstruction of several depositional episodes represented by thin only few meters thick sedimentary units from the late cretaceous to the quaternary the creation of new accommodation space on subsiding areas gave rise to sediment accumulation during transgressions intervening weathering surfaces formed during significant falls in relative sea level associated with tectonically stable episodes the overprinting of weathering surfaces formed during different times and thus under different climatic conditions seems to have been crucial for the development of the various weathering products observed throughout the region which include economically important laterites bauxites semi flint beds and kaolin deposits this paper shows that the genesis of these deposits was controlled by the complex interplay of tectonics climate sediment deposition and erosion resulting in a complex evolution of paleolandscapes

archeological and pedological evidence for large prehistoric earthquakes in the new madrid seismic zone central united states prehistoric liquefaction features have been identified by careful observation of their structural and stratigraphic relations to native american occupation horizons and their subtle soil characteristics the ages of these liquefaction features have been estimated from radiocarbon dating of wood associated with the features and native american artifacts found within bounding occupation horizons at three sites near blytheville arkansas in the central part of the new madrid seismic zone one sand blow crater formed between a d 800 and 1400 two sand blow deposits formed between a d 800 and 1670 and three possibly four sand dikes formed since 4035 b c where not found in association with native american occupation horizons and artifacts prehistoric liquefaction features can be difficult to distinguish from features that formed during the great new madrid earthquakes of a d 1811 and 1812 this raises the possibility that prehistoric liquefaction features may have been misinterpreted during previous studies in the area nevertheless a paleoearthquake chronology is beginning to emerge for the new madrid seismic zone our findings are consistent with paleoseismological studies in the northern part of the seismic zone and suggest a recurrence interval of hundreds of years for earthquakes large enough to induce liquefaction in this region m 6 4 by mapping the age distribution of liquefaction features a more accurate assessment of the long term earthquake potential of the region will be possible

the role of precambrian mylonitic belts and present day stress field in the coseismic reactivation of the pernambuco lineament brazil abstract the pernambuco lineament is a steeply dipping continental scale ductile shear zone rooted within the precambrian lithosphere of intraplate northeastern brazil it was formed during the brasiliano orogeny 600 ma and reactivated during the pangea breakup in the cretaceous when it controlled fault propagation and sediment accumulation in several rift basins the region is now under an e w trending horizontal compression and n s trending extension and faulting occurs predominantly in a strike slip regime we investigated two aftershock sequences and the preexisting tectonic fabrics along the pernambuco lineament in order to evaluate the role of these fabrics in the coseismic reactivation of continental scale structures the lineaments consist of a main ene wsw trending mylonitic belt about 2 3 km wide and two secondary ne trending mylonitic belts about 100 m wide they both present steeply dipping mylonitic foliations and shallowing plunging stretching lineations the mylonites present granitoid protoliths and mineral parageneses that range from amphibolite to greenschist facies brittle deformation overprints the ductile fabric in all mylonitic belts in 1991 coseismic reactivation nucleated along the ene wsw striking 3 3 5 6 km deep normal fault of less than 1 km in length in the main mylonitic belt in 2002 seismicity migrated to a ne trending secondary mylonitic branch and moved as a right lateral strike slip 1 2 km long 3 8 4 9 km deep fault plane both fault segments reactivated the mylonitic foliation and form part of a major system we conclude that the interplay between the present day stress field and preexisting fabrics controls seismogenic fault location attitude and kinematics the pernambuco lineament is an example of a long lived continental scale structure where selective reactivation has occurred other shear zones in the region also show a long history of brittle reactivation and present similar orientation in relation to the present day stress axes they might be dormant structures prone for reactivation under the present day stress field

impact of synsedimentary metre scale normal fault scarps on sediment gravity flow dynamics an example from the gres d annot formation se france abstract synsedimentary faults result in the direct interaction between tectonic and sedimentary processes at similar spatio temporal scales sedimentological analysis of sediment laden gravity flows in the northern part of the gres d annot formation sanguiniere sub basin col de la moutiere tete ronde has revealed the presence of fault scarps of metre scale height these synsedimentary fault scarps were sufficient to disturb the sediment gravity flow dynamics resulting in i a strong variation of the erosive behaviour of a concentrated flow and ii the transformation of a strongly stratified laminar hyperconcentrated flow into a turbulent flow in short distance less than 500 m these disturbances develop without the flows being deviated by the fault scarps but produce great facies heterogeneity the least homogeneous facies mixing sand and clay being localized on the upstream obstacle side the most homogeneous massive sand downstream

mechanisms and controls on the formation of sand intrusions sandstone intrusions are found in all sedimentary environments but have been reported most commonly from deep water settings they also appear to be more frequently developed in tectonically active settings where applied tectonic stresses facilitate development of high fluid pressures within the sediments a variety of mechanisms have been cited as triggers for clastic intrusions these include seismicity induced liquefaction application of tectonic stresses excess pore fluid pressures generated by deposition related processes and the influx of an overpressured fluid from deeper within the basin into a shallow sand body the formation of sandstone dykes and sills is investigated here by considering them as natural hydraulic fractures when the seal on an unconsolidated overpressured sand body fails the resulting steep hydraulic gradient may cause the sand to fluidize the fluidized slurry can then inject along pre existing or new fractures to form clastic intrusions the scale and the geometry of an intrusive complex is governed by the stress state depth and pre existing joints or faults within the sedimentary succession as well as the nature of the host sediments for the simplest tectonic setting where the maximum stress in a basin is vertical gravitational loading small irregular intrusions commonly result in the formation of sills at shallow depths within a few metres of the surface whereas at greater depth dykes and sills forming clastic intrusion networks are more typical a simple relationship is derived to calculate the maximum burial depth at which a dyke sill complex forms as a function of the source bed to sill height the bulk density of the surrounding sediments and the ratio of the vertical to horizontal effective stresses k 0 when applied to three examples of large scale dyke sill complexes developed within paleocene and eocene deep water reservoir sand bodies of the north sea maximum burial depths in a range of 375 to c 500 m 450 700 m and 550 850 m are estimated for intrusion of each of the three complexes

liquefaction induced structures in quaternary alluvial gravels and gravelly sediments ne brazil abstract we have identified numerous well preserved elutriation and fluidization structures probably induced by liquefaction in quaternary gravels and gravelly sediments of braided fluvial channel deposits in the rio grande do norte and ceara states northeastern brazil they show evidence of upward directed water escape after sediment deposition and before sediment compaction among the several types of structures observed the most frequent are pillars pockets and dikes these structures range in width from a few centimeters to as much as 4 m and in height from 60 cm to 4 m dikes pillars and pockets are systematically associated clastic dikes vented large quantities of sand to the upper layers or the surface pebbles and cobbles from the host rock sank into the dikes and formed pillars and pockets pockets form the root part pillars form the intermediate part and dike the upper part of the composite structure the morphology of the structures in sectional and plan views indicates a 3d geometry composed of a tabular dike and pillar that present a downward continuous transition to a bowl shaped pocket this stratigraphy of liquefaction features is different from that usually presented in the current literature field data suggest that both the location and the geometry of the features were controlled by sedimentary properties rather than joints and small faults the size and abundance of these features suggest that they were formed by great events rather than localized mechanisms field evidence also indicates that these features are the product of fluidization and elutriation and may have been induced by liquefaction processes associated with seismic shaking a nonseismic origin related to elutriation processes however cannot be ruled out for some of the features

experimental soft sediment deformation structures formed by the liquefaction of unconsolidated sands and some ancient examples the effects of liquefaction in saturated sand bodies under a variety of driving forces are described from shaking table experiments and structures from the geological record are presented which are analogous to the experimental structures the collapse of sloping heaps of cross bedded sand under a gravitational body force generates low angle essentially uncontorted stratification a basal zone of shearing may be present with steepened and folded foresets stretching of foresets may be accommodated on normal faults and bottomsets may be contorted into inclined folds in natural systems the substrate may also liquefy causing deformation driven by an unevenly distributed confining load stratification in the surface bedform is flattened and stratification in the substratum contorted experiments failed to produce relative displacement at the interface between stacked sand bodies liquefaction of gravitationally unstable systems in sands generates load structures comparable to those from sand mud systems recumbent folded deformed cross bedding is formed by current shear over a liquefied bed as has been inferred from field and theoretical analyses shear of nonliquefied sand forms angular folds other deformation mechanisms such as fluidization or seepage may generate structures similar to all of these local water escape structures driven by fluidization occur in the upper parts of some liquefied sand bodies they include cusps sand volcanoes and clastic dykes transient cavities formed in some experiments and seemed to be preserved as breached cusps although the experiments tried to isolate individual driving forces driving forces may operate together and there may be a continuum between deformation driven by water escape and deformation driven by loading different structures from those described here may form where liquefaction develops in a buried layer as opposed to at the sediment surface

seismic induced slump in early pleistocene deltaic deposits of the baza basin se spain abstract early pleistocene lacustrine deposits of the baza basin in se spain show a 2 m thick sheet with deformation structures intercalated within horizontal strata along a 180 m exposure we recognise an alternation of compressional thrusts and extensional normal faults and tensional joints structures these structures are interpreted as a planar slump analysis of the different structures together with the sedimentary facies indicates that this slump moved towards the north in a subaqueous deltaic environment 2 5 m deep with a paleoslope of

numerical study of the role of wind forcing and freshwater buoyancy input on the circulation in a shallow embayment gulf of trieste northern adriatic sea 1 this paper investigates the role of wind forcing and river discharge on a small scale shallow embayment the gulf of trieste the qualitative and quantitative analysis of these dominant processes is carried out using a high resolution numerical model initialized and forced with experimental data the simulations are focused on short term transient events which occurred during the stratification season spring and summer two significant case studies are analyzed in detail a strong wind event during summer and a river flood during spring the model output is also checked against the results of a nondimensional scale analysis and against buoy and satellite observed data these comparisons show a good correlation validating the numerical simulations for the two case studies the model shows that strong wind events blowing on stably stratified water cause coastal upwelling and almost entirely mix the water column in a few hours strong wind driven currents can flush the whole basin in almost 3 days on the contrary river floods affect mainly the upper layer down to 5 m the circulation is estuarine with a sharp vertical density gradient and horizontal fronts at the interface between plume freshwater and ambient salty water given the length scale of the basin the effect of rotation is weak and a local coastal current in geostrophic balance is not formed during the simulated time period 20 days

diurnal period wind stress and current fluctuations over the continental shelf off northern california diurnal period wind stress and current fluctuations measured over the continental shelf off northern california during the coastal ocean dynamics experiment in the summers of 1981 and 1982 are examined the diurnal currents are strongly surface intensified with amplitudes of up to 20 cm s 1 at depths of less than 35 m the diurnal currents are nonstationary and their amplitude is well correlated with the amplitude modulation of the local diurnal wind stress beneath the surface layer the diurnal current vectors rotate clockwise with ellipse semi major axes of 1 to 3 cm s 1 a mixed layer model driven with diurnal wind stress and surface heat flux produces currents similar to those observed in the upper water column the deeper currents are consistent with the combination of a freely propagating kelvin and first mode coastal trapped wave and over the inner shelf with the interior flow forced by the diurnal wind stress in the presence of a coast

tidal currents in the northwestern adriatic high frequency radio observations and numerical model predictions the results of a two year long deployment of high frequency radars along the italian coast of the northern adriatic are analyzed to characterize the surface tidal currents m2 and k1 ellipses are aligned with the basin axis and exhibit large eccentricities in the middle of the basin decreasing toward the italian coast comparisons are made with a 3d finite element non linear numerical model of the tides complex correlations between modeled and observed tidal currents show a remarkable agreement in the middle of the basin with magnitudes reaching 0 985 and average phases of 6 4 deg however the magnitudes drop to 0 5 within 20 30 km from the italian coast where the modeled currents amplitudes are underestimated by 2cm s and the phases lag the observed phases by 60 deg this shallow region less than 30 m deep is characterized by low salinity water originating at the po river and laterally sheared coastal flows the radars may have captured the influence of stratification or mean sheared flows both absent from the model the model parameterization of bottom friction may also inadequately represent the effects of real bottom friction on the vertical current shear

seismites an attempt at critical analysis and classification abstract the main types of seismites are reviewed following the proposed classification and are illustrated by our own case studies the large variety of seismites depends on the sedimentologic hydrodynamic and diagenetic characters of the deposits subject to seismic shocks on a given site generally different types of seismites cane be related to the same seismic event these peculiar but widespread sedimentary structures are not always univocal and may often be related to different causes therefore the structures discussed must necessarily be placed in a detailed geological context

tsunami sedimentation associated with the 1923 kamchatka earthquake abstract the kuril kamchatka region is notorious for the occurrence of earthquake tsunamis and historical documents show that they have caused repeatedly considerable damage since the 1750s the great tsunami generated in april 1923 around the northern kamchatka trench flooded the coast of ust kamchatsk depositing a thin sand layer which is traceable up to 3 km or more inland beyond the present coastline local government documents indicate that the 1923 tsunami flooded low lying coastal areas covered by thick snow the unusual process of tsunami run up without loss of tractive load is interpreted to have resulted from the smoothing of fields by the ice covered surface we conclude that the tsunami flooded snowfields and deposited an extensive sheet of sand a mixture of snow and seawater flooded over the area and caused damage to vegetation

comparison of observed hf radar adcp and model barotropic tidal currents in the new york bight and block island sound abstract a three dimensional primitive equation model is used to simulate the barotropically forced semidiurnal tidal currents in the new york bight nyb and block island sound bis model tidal velocity ellipses are verified at historical current meter locations and with measurements from acoustic doppler current profilers adcps and hf radar codar the model reproduces well the regional tidal flow pattern as well as the vertical tidal velocity structure the model misfits typically are 2 4 cm s in amplitude and 5 7 in orientation through comprehensive skill assessment the model s capacity of simulating the three dimensional barotropic tidal currents is clearly demonstrated moreover it is shown that the integrity of hf radar measurements can be assured by verifying with model tidal ellipses

neotectonic reactivation of shear zones and implications for faulting style and geometry in the continental margin of ne brazil abstract the eastern continental margin of south america comprises a series of rift basins developed during the breakup of pangea in the jurassic cretaceous we integrated high resolution aeromagnetic structural and stratigraphic data in order to evaluate the role of reactivation of ductile neoproterozoic shear zones in the deposition and deformation of post rift sedimentary deposits in one of these basins the paraiba basin in northeastern brazil this basin corresponds to the last part of the south american continent to be separated from africa during the pangea breakup sediment deposition in this basin occurred in the albian maastrichtian eocene miocene and in the late quaternary however our investigation concentrates on the miocene quaternary which we consider the neotectonic period because it encompasses the last stress field this consisted of an e w oriented compression and a n s oriented extension the basement of the basin forms a slightly seaward tilted ramp capped by a late cretaceous to quaternary sedimentary cover 100 400 m thick aeromagnetic lineaments mark the major steeply dipping ductile e w to ne striking shear zones in this basement the ductile shear zones mainly reactivated as strike slip normal and oblique slip faults resulting in a series of miocene quaternary depocenters controlled by ne e w and a few nw striking faults faulting produced subsidence and uplift that are largely responsible for the present day morphology of the valleys and tablelands in this margin we conclude that precambrian shear zone reactivation controlled geometry and orientation as well as deformation of sedimentary deposits until the neogene quaternary

soft sediment deformation structures in late albian to cenomanian deposits sao luis basin northern brazil evidence for palaeoseismicity soft sediment deformation structures from the alc ntara formation late albian to cenomanian sao luis basin northern brazil consist of 1 contorted structures which include convolute folds ball and pillow structures concave up paths with consolidation lamination recumbently folded cross stratification and irregular convolute stratification that grades into massive beds 2 intruded structures which include pillars dykes cusps and subsidence lobes and 3 brittle structures represented by fractures and faults displaying planes with a delicate ragged morphology and sharp peaks these structures result from a complex combination of processes mostly including reverse density gradients fluidization and liquefaction reverse density gradients promoted by differential liquefaction associated with different degrees of sediment compaction led to the genesis of convolute folds more intense deformation promoted the development of ball and pillow structures subsidence lobes and sand rolls which are attributed to denser and thus more compacted less liquefied portions that sank down into less dense more liquefied sediments irregular convolute stratification that grades into massive beds would have formed at periods of maximum deformation the subsidence of beds was accompanied by lateral current drag and fluid escape from water saturated sands in addition the fractures and faults record brittle deformation penecontemporaneous with sediment deposition all these mechanisms were triggered by a seismic agent as suggested by a combination of criteria including 1 the position of the study area at the edge of a major strike slip fault zone that was reactivated several times from the albian to the holocene 2 a relative increase in the degree of deformation in sites located closer to the fault zone 3 continuity of the deformed beds over large distances several kilometres 4 restriction of soft sediment deformation structures to single stratigraphic intervals bounded by entirely undeformed strata 5 recurrence through time and 6 similarities to many other earthquake induced deformational structures

quaternary tectonics in a passive margin marajo island northern brazil marajoisland is located in a passive continental margin that evolved from rifting associated with the opening of the equatorial south atlantic ocean in the late jurassic early cretaceous period this study based on remote sensing integrated with sedimentology as well as subsurface and seismographic data available from the literature allows discussion of the significance of tectonics during the quaternary history of marginal basins results show that eastern marajoisland contains channels with evidence of tectonic control mapping of straight channels defined four main groups of lineaments i e nne ssw ne sw nw se and e w that parallel main normal and strike slip fault zones recorded for the amazon region additionally sedimentological studies of late quaternary and holocene deposits indicate numerous ductile and brittle structures within strati graphic horizons bounded by undeformed strata related to seismogenic deformation during or shortly after sediment deposition this conclusion is consistent with subsurface bouguer mapping suggestive of eastern marajoisland being still part of the marajograben system where important fault reactivation is recorded up to the quaternary together with the recognition of several phases of fault reactivation these data suggest that faults developed in association with rift basins might remain active in passive margins imposing important control on development of depositional systems copyright 2007 john wiley sons ltd

use of liquefaction induced features for paleoseismic analysis an overview of how seismic liquefaction features can be distinguished from other features and how their regional distribution and properties of source sediment can be used to infer the location and strength of holocene paleo earthquakes abstract liquefaction features can be used in many field settings to estimate the recurrence interval and magnitude of strong earthquakes through much of the holocene these features include dikes craters vented sand sills and laterally spreading landslides the relatively high seismic shaking level required for their formation makes them particularly valuable as records of strong paleo earthquakes this state of the art summary for using liquefaction induced features for paleoseismic interpretation and analysis takes into account both geological and geotechnical engineering perspectives the driving mechanism for formation of the features is primarily the increased pore water pressure associated with liquefaction of sand rich sediment the role of this mechanism is often supplemented greatly by the direct action of seismic shaking at the ground surface which strains and breaks the clay rich cap that lies immediately above the sediment that liquefied discussed in the text are the processes involved in formation of the features as well as their morphology and characteristics in field settings whether liquefaction occurs is controlled mainly by sediment grain size sediment packing depth to the water table and strength and duration of seismic shaking formation of recognizable features in the field generally requires a low permeability cap above the sediment that liquefied field manifestations are controlled largely by the severity of liquefaction and the thickness and properties of the low permeability cap criteria are presented for determining whether observed sediment deformation in the field originated by seismically induced liquefaction these criteria have been developed mainly by observing historic effects of liquefaction in varied field settings the most important criterion is that a seismic liquefaction origin requires widespread regional development of features around a core area where the effects are most severe in addition the features must have a morphology that is consistent with a very sudden application of a large hydraulic force this article discusses case studies in widely separated and different geological settings coastal south carolina the new madrid seismic zone the wabash valley seismic zone and coastal washington state these studies encompass most of the range of settings and the types of liquefaction induced features likely to be encountered anywhere the case studies describe the observed features and the logic for assigning a seismic liquefaction origin to them also discussed are some types of sediment deformations that can be misinterpreted as having a seismic origin two independent methods for estimating prehistoric magnitude are discussed briefly one method is based on determination of the maximum distance from the epicenter over which liquefaction induced effects have formed the other method is based on use of geotechnical engineering techniques at sites of marginal liquefaction in order to bracket the peak accelerations as a function of epicentral distance these accelerations can then be compared with predictions from seismological models

neotectonics in the south american passive margin evidence of late quaternary uplifting in the northern paraiba basin ne brazil abstract the relief evolution of several areas of northeastern brazil has been increasingly related to tectonic events this is the case for the paraiba basin where an abundance of faults and folds were recorded in neogene and even late pleistocene holocene deposits we tested whether dome like morphologies in the northern sector of this basin where geological exposures are scarce were also formed by tectonic deformation the work combined limited geological data with qualitative and quantitative analyses of the relief applying the 1 arc second digital elevation model provided by the shuttle radar topography mission the geomorphic indices of basin asymmetry factor af swath topographic profiles enhanced transverse hypsometry index thi and normalized river long profiles were used for validating a neotectonic origin for the dome like morphologies this interpretation was also supported by other morphological evidence of the dome relief including recurving channels featured in radial to recurved trellis patterns tectonically controlled drainage sub basins high relative relief values related to increased fluvial incision and anomalous river long profiles indicative of ungraded rivers the domic structures were attributed to fault and fold related strike slip deformation during the late quaternary this record supports the proposal that the south american passive margin remained under tectonic stress long after the main rifting in the late jurassic early cretaceous

surface current patterns in front of the venice lagoon abstract surface patterns of the low frequency current in a 20 30 km region in front of the venice lagoon were analysed from a 13 month long hf radar data set surface circulation was related to prevalent wind regimes in the area and to the tidal flow through the lagoon inlet three different categories of wind forcing were defined bora ne wind sirocco se wind and finally the category containing all other wind directions and calms winds lower than 3 m sec mean flow and vorticity spatial distributions were discussed for different wind conditions the coastal area about 5 km wide is characterized by a flow field with maximum vorticity outside the coastal boundary layer the interior flow is part of the adriatic basin wide cyclonic circulation two counter rotating vortices of the dimension of about 4 5 km were evidenced in the average flow field in front of the lagoon inlet malamocco inlet in all situations except for the bora the vortex pair is probably associated with the tidal flow through the inlet the bora wind induces a strong southward coastal jet detached from the coast by about 5 km homogenizing the flow and eliminating the dipole the average coastal flow pattern in calm wind conditions was also analysed as a function of the strong inflow outflow currents in the inlet 0 7 m s 1 from the lagoon inlet in both cases the vorticity pattern is similar with the negative vorticity to the left of the inlet and positive to the right looking seaward

source parameters of the anjar earthquake of july 21 1956 india and its seismotectonic implications for the kutch rift basin abstract the kutch rift basin is a major seismic region in india characterized by a low earthquake occurrence rate but a very high maximum intensity the largest event in the region is the great kutch earthquake of 1819 estimated m w 7 8 however lacking instrumental data its exact source parameters are not well known the anjar or rann of kutch earthquake of july 21 1956 m w 6 0 took place very close to the 1819 kutch event and caused considerable damage and casualties our modeled waveforms of teleseismic p and sh waves and p wave first motions determine a reverse faulting mechanism strike 235 dip 46 5 and rake 85 as well as source parameters for the anjar earthquake a previous strike slip mechanism for this event has been eliminated on the basis of waveform constraints the two nodal planes of our solution both strike northeast sub parallel to the trend of the kutch rift very close to the trend of the isoseismals the seismic moment is 1 19 10 25 dyne cm the focal depth and the stress drop are 15 km and 162 bar respectively the anjar reverse fault may represent a reactivated normal fault undergoing tectonic inversion in the kutch rift zone under present day compressional stress two larger earthquakes adjacent to anjar but outside of the kutch rift are also found to be mainly reverse faulting with a minor strike slip component judging from available information the great kutch event of 1819 is most likely a reverse faulting event

surface circulation in the gulf of trieste northern adriatic sea from radar model and adcp comparisons 1 high resolution high frequency hf radar observations of surface currents in the gulf of trieste got are presented and compared to moored subsurface current measurements and to high resolution simulations from the northern adriatic princeton ocean model napom oceanographic model dominant circulation modes of the got were resolved and numerical model capabilities in reconstructing them were assessed the time frame covers march 2011 through october 2012 napom reconstructs the dominant surface circulation features observed by the radar such as the general basin wide cyclonic circulation scheme and the coastal jet outflowing the got but is in general less energetic than radar currents comparisons between radar adcp and model currents suggest that the model underestimates originate within the low frequency diurnal semidiurnal and inertial bands and that both radar and model currents do not reproduce the diurnal tidal ellipse structure observed by the moored current meter however radar model results for the semidiurnal tides are spatially consistent using empirical orthogonal function eof decomposition the coherent spatial scales and corresponding temporal scales were extracted findings suggest that hf radar current observations complement model simulations in regions of enhanced topographic variability where variance of model currents at the surface is distorted by the effects of the sigma layer grid on the contrary model results complement radar observations in areas with poor radar coverage and furthermore provide spatial and temporal continuity of ocean state forecasts

the adriatic sea general circulation part ii baroclinic circulation structure abstract in the second part of the paper dedicated to the adriatic sea general circulation the horizontal structure of the hydrographic parameters and dissolved oxygen fields is described on a seasonal timescale maps of temperature and salinity climatological fields reveal the enhanced seasonal variability of the adriatic sea which at the surface is associated with the major dilution effects of river runoff the density and derived dynamic height fields show for the first time the baroclinic geostrophic structure of the general circulation winter is dominated by compensation effects between temperature and salinity fronts along the western coastline the resulting baroclinic circulation is weak and suggests the presence of barotropic current components not accessible by the dataset spring and summer seasons have the smallest spatial scales in the temperature and salinity fields and stronger subbasin scale gyres and current systems which have been classified in a schematic representation of the circu