lisbon 1755 a case of triggered onshore rupture it has been widely recognized both in classical and in modern studies that the lisbon earthquake of 1755 was a multiple event composed of three shocks separated by a few minutes see e g reid 1914 attempts to constrain the location of the source have led to a diversity of proposals reflecting apparent contradictions in the data the tsunami and damage along the south and southwest iberian coast and in morocco favor an offshore source whereas the presence of an additional zone of strong shaking in the lower tagus valley ltv near lisbon favors a more northerly location by combining the contemporary accounts with intensity data from other earthquakes we favor a compound source with a large distance between the faults we propose that although the mainshock was offshore the resulting stress changes induced the rupture of the ltv fault at a distance on the order of 350 km but subject to large uncertainty in the offshore location a few minutes after the mainshock we favor this model rather than site effects causing high intensities in the lisbon area because the highest intensities show a negative correlation to soft soil several other phenomena described in the eyewitness accounts can also be explained by the local rupture now proposed such as a tsunamilike wave in the tagus river ground deformation affecting the course of the tagus river and the spatial pattern of damaging aftershocks recognition of this missing episode of rupture on the ltv fault significantly changes the hazard estimate for the lisbon area

late pleistocene and holocene palaeogeography of the lower tagus valley portugal effects of relative sea level valley morphology and sediment supply abstract because of the deep glacial incision the lower tagus valley hosts a sedimentary record since 20 000 cal bp making this a unique site along the european atlantic margin with respect to palaeogeographic and sea level changes based on nine cross sections and 55 radiocarbon dates together with a newly created relative sea level curve we constructed five palaeogeographic maps of the infill of the lower tagus valley since 20 000 cal bp we illustrate that relative sea level rise and fluvial sediment supply were the prime forcing factors determining the depositional history and palaeogeographic changes around 20 000 cal bp a deeply incised braided river existed which was directly connected to the ocean across the narrow continental shelf after that 12 000 cal bp the gradually moister and warmer climate caused a change to a single channel river during the following period 12 000 7000 cal bp relative sea level rise resulted in a transgression in the lower tagus valley and the establishment of extensive tidal environments after relative sea level rise had ended 7000 cal bp the valley was progressively filled by a fluvial wedge and tidally influenced bayhead delta since 1000 cal bp the valley fill history was dominated by increased sediment input due to human induced degradation of catchment slopes generally climate was of subordinate importance during the entire studied period merely causing a single channel river resulting from the change from the cold heinrich event 1 to the temperate bolling allerod interstadial despite the tectonic activity in the region neotectonic uplift or subsidence was limited as supported by the horizontal relative sea level curve since 7000 cal bp neotectonics played a minor role due to the large distance from the fennoscandian ice sheet and the narrow continental shelf which prohibited strong glacio and hydro isostatic movements

episodic slow slip events accompanied by non volcanic tremors in southwest japan subduction zone 1 episodic slow slip events have been recognized by means of tilt changes in the western shikoku area southwest japan the crustal tilt deformation was observed repeatedly with a recurrence interval of approximately six months coincident with the occurrences of major non volcanic deep tremor activities in this area observed tilt changes can be explained by slow slip events occurring around the source area of tremors in each episode the source of the slow slip event and tremor migrate simultaneously the spatial and temporal coincidence of tremors and slow slip events indicates that they both may be coupling phenomena reflecting the stress accumulation process at the subducting plate

variety and spatial heterogeneity of tectonic tremor worldwide 1 deep tectonic tremor occurs at various sites worldwide and the source characteristics are heterogeneous even at small scales in this study tremor sources were determined using data sets of seismic waveforms from various locations some of which are not well recognized as being a site of tremor activity the regions of interest are subduction zones at nankai and kyushu japan cascadia in western north america mexico southern chile and new zealand tremor locations are consistent with the geometry of subducting plates and tremor depth tends to be shallower where younger plate is subducting tremor duration shows a negative correlation with tidal sensitivity as reported previously in western shikoku in the nankai subduction zone the duration is also related to the width of the tremor zone in the dip direction of the subducting plate linear structures resembling striations are observed in hypocenter distributions in western shikoku and in the probability of short term migration direction these spatial heterogeneities in tremor activity may be controlled by the heterogeneous frictional properties of the downgoing slab due to long term plate subduction thereby providing information on the maturity of the plate interface

geometry and kinematics of adhesive wear in brittle strike slip fault zones abstract detailed outcrop surface mapping in late paleozoic cataclastic strike slip faults of coastal maine shows that asymmetric sidewall ripouts 0 1 200 m in length are a significant component of many mapped faults and an important wall rock deformation mechanism during faulting the geometry of these structures ranges from simple lenses to elongate slabs cut out of the sidewalls of strike slip faults by a lateral jump of the active zone of slip during adhesion along a section of the main fault the new irregular trace of the active fault after this jump creates an indenting asperity that is forced to plow through the adjoining wall rock during continued adhesion or be cut off by renewed motion along the main section of the fault ripout translation during adhesion sets up the structural asymmetry with trailing extensional and leading contractional ends to the ripout block the inactive section of the main fault trace at the trailing end can develop a sag or half graben type geometry due to block movement along the scallop shaped connecting ramp to the flanking ripout fault leading contractional ramps can develop thrust type imbrication and forces the humpback geometry to the ripout slab due to distortion of the inactive main fault surface by ripout translation similar asymmetric ripout geometries are recognized in many other major crustal scale strike slip fault zones worldwide ripout structures in the 5 500 km length range can be found on the atacama fault system of northern chile the qujiang and xiaojiang fault zones in western china the yalakom hozameen fault zone in british columbia and the san andreas fault system in southern california for active crustal scale faults the surface expression of ripout translation includes a coupled system of extensional trailing ramps as normal oblique slip faults with pull apart basin sedimentation and contractional leading ramps as oblique thrust or high angle reverse faults with associated uplift and erosion the sidewall ripout model as a mechanism for adhesive wear during fault zone deformation can be useful in studies of fault zone geometry kinematics and evolution from outcrop to crustal scales

energy and mass balance observations of the land ice ocean atmosphere system near barrow alaska usa november 1999 july 2002 we present results from a comprehensive field study carried out near barrow alaska usa designed to characterize local to intermediate scale sea ice processes in the arctic coastal zone of central importance to the annual cycle and evolution of the coastal sea ice included in this are the behavior of the snow cover of the ice and adjacent tundra and lake system concurrent studies of mass balance of the sea ice and lake ice interaction of shortwave radiation with the shore fast ice and the adjacent land surfaces evolution of the area coverage and distribution of the various surface types and the resulting regional albedo values maximum snow depths decreased during 2000 02 from 0 38 m to 0 26 m ice melt rates in 2001 were 0 05 and 0 028 m d 1 at the top and bottom of the sea ice respectively two to three times larger than observations from the central arctic detailed surface results combined with aircraft photography were used to calculate regional albedos for the late spring and early summer of 2001 values ranged from 0 8 for all cold snow covered surfaces to approximately 0 4 for melting sea ice and lake ice vs 0 18 for bare tundra regional and surface based values of cumulative shortwave radiation entering the ice were consistent indicating that albedo sampling on a scale of 200 m can provide a useful representation for regional sea ice albedo

simulations of strong ground motion in sw iberia for the 1969 february 28 ms 8 0 and the 1755 november 1 m 8 5 earthquakes i velocity model summary this is the first paper of a series of two concerning strong ground motion in sw iberia due to earthquakes originating from the adjacent atlantic area the aim of this paper is to build and calibrate a velocity model that will be used in the companion paper for seismic intensity modelling of the 1969 m s 8 0 and 1755 m 8 5 8 7 earthquakes taking into account the geological evolution of the region since the palaeozoic we build a 3 d velocity model down to the moho discontinuity substantially different from a simple 1 d layered model the velocity model presented in this paper is built a priori using information originating from a variety of geological and geophysical studies its resolution is sufficient to simulate realistically seismic wave propagation in the low frequency f 0 5 hz range which is the most significant for the study of the destructive effects of large earthquakes at a regional scale to validate the model we compute synthetic seismograms for three recent earthquakes of moderate magnitudes 4 6 m w 5 3 located offshore in the most seismically active area in the region synthetics are generated using a wave propagation code based on the finite difference method which was chosen for its simplicity and accuracy in the frequency range considered in this study 0 1 0 5 hz we compare simulated waveforms with threecomponent seismograms for 9 different stations traveltimes of the direct p waves and the amplitude of ground motion are accurately reproduced at all stations the frequency content of the seismograms fits the observations especially for the lowest frequencies investigated 0 1 0 3 hz for each earthquake the estimated seismic moment is in good agreement with values obtained by other authors using different methods we conclude that the velocity model provides encouraging results for the computation of low frequency seismograms in the region and can be used for the study of larger earthquakes for which the radiated wavefield has a predominant low frequency spectrum

the eastern lower tagus valley fault zone in central portugal active faulting in a low deformation region within a major river environment abstract active faulting in the lower tagus valley central portugal poses a significant seismic hazard that is not well understood although the area has been affected by damaging earthquakes during historical times only recently has definitive evidence of quaternary surface faulting been found along the western side of the tagus river the location geometry and kinematics of active faults along the eastern side of the tagus valley have not been previously studied we present the first results of mapping and paleoseismic analysis of the eastern strand of the lower tagus valley fault zone ltvfz geomorphological paleoseismological and seismic reflection studies indicate that the eastern ltvfz is a left lateral strike slip fault the detailed mapping of geomorphic features and studies in two paleoseismic trenches show that surface fault rupture has occurred at least six times during the past 10 ka the river offsets indicate a minimum slip rate on the order of 0 14 0 24 mm yr for the fault zone fault trace mapping geomorphic analysis and paleoseismic studies suggest a maximum magnitude for the eastern ltvfz of m w 7 3 with a recurrence interval for surface ruptures 1 7 ka at least two events occurred after 1175 95 cal yr bp single event displacements are unlikely to be resolved in the paleoseismic trenches thus our observations most probably represent the minimum number of events identified in the trenches

the anatomy of shallow crustal transpressional structures insights from the archaean carajas fault zone amazon brazil abstract the carajas fault zone cfz is the most prominent structure in the e w trending carajas strike slip system casss an ancient upper crustal fault network of probable late archaean age that cuts across the precambrian amazonian craton in brazil the subvertical faults reactivated pre existing high grade basement shear zone fabrics itacaiunas shear zone and display a complex long lived history of movement 1 ga dominated by oblique and strike slip displacements a postulated early regional phase of dextral movement downfaulted units of low grade to unmetamorphosed basement rocks into dilational bends and offsets in the casss subsequent sinistral transpression ca 2 6 ga led to faulting and folding during partial inversion of the cover rocks in these dilational sites with much of the associated deformation focused in the immediate vicinity

stress pattern in portugal mainland and the adjacent atlantic region west iberia the portuguese mainland territory is located close to the azores gibraltar plate boundary in a tectonic setting responsible for significant neotectonic and seismic activities however few data concerning the present regional lithospheric stress field were available as testified by recently published maps of stress indicators for the europe and mediterranean regions one of the authors already presented a synthesis on this subject cabral 1993 where geological and geophysical stress indicators were considered in this paper we introduce new information mainly a considerable amount of borehole breakout data the updated data set comprises 32 reliable stress indicators showing a mean azimuth of 145 standard deviation 21 for the maximum horizontal stress direction shmax on the average the geological data are rotated clockwise and the focal mechanism data deviated anticlockwise to that azimuth while the borehole elongation results are consistent with the mean shmax trend these differences in stress trend suggest a regional progressive rotation of the shmax direction from nnw sse to wnw ese since the upper pliocene to estimate stress trajectories new and published stress indicators in the adjacent atlantic area and northern africa were also investigated showing a very uniform nw se shmax trend in west iberia a high level of horizontal compressive stress acting oblique to the western portuguese continental margin is inferred and interpreted in view of a proposed regional geodynamical model of activation of this passive margin with the nucleation of a subduction zone in the atlantic sw of iberia at the gorringe submarine bank which is propagating northward along the base of the continental slope at the transition between thinned and normal continental crust

sea ice albedo climate feedback mechanism abstract the sea ice albedo feedback mechanism over the arctic ocean multiyear sea ice is investigated by conducting a series of experiments using several one dimensional models of the coupled sea ice atmosphere system in its simplest form ice albedo feedback is thought to be associated with a decrease in the areal cover of snow and ice and a corresponding increase in the surface temperature further decreasing the areal cover of snow and ice it is shown that the sea ice albedo feedback can operate even in multiyear pack ice without the disappearance of this ice associated with internal processes occurring within the multiyear ice pack e g duration of the snow cover ice thickness ice distribution lead fraction and melt pond characteristics the strength of the ice albedo feedback mechanism is compared for several different thermodynamic sea ice models a new model that includes ice thickness distribution the ebert and curry model the maykut and untersteiner model and the semtner level 3 an

geodynamic models for the azores triple junction a contribution from tectonics abstract the american eurasian and african lithospheric plates meet at the azores triple junction the nature of the northern and southern branches of the junction is well known and uncontroversial the american plate is separated from eurasia and africa by the mid atlantic ridge mar the western group of islands of the azores archipelago flores and corvo lies on the american plate just west of the rift and their tectonic features agree with that location the nature of the third branch of the junction to the east of the mar is however still controversial some authors believe that a ridge ridge ridge junction occurs in the azores area and adopt the structure known as the terceira ridge working as a simple rift boundary as the third branch another model proposes a triangular microplate in the azores region bounded by the mid atlantic rift to the west the east azores fault zone to the south and a fault crossing s miguel and the terceira islands to the northeast in this model the fault zones are pure dextral strike slip boundaries both models would create space problems at gloria fault a well known pure dextral strike slip structure in the first model transtension would be necessary at gloria fault to accommodate plate motion while the second would require a transpressive regime on that structure neotectonic and seismotectonic data in the azores indicate a transtensile regime in the central and eastern island groups in present and recent times this is compatible with a leaky transform structure acting as the third branch of the junction in the azores area a model which has already been presented by several authors in the past stress trajectories deduced from neotectonic studies in some of the islands suggest that the main plate boundary passes between the islands of s jorge and pico south of s miguel and joins gloria fault east of santa maria this model and boundary location is also compatible with seismotectonic and magnetic data

simple constructions for deformation in transpression transtension zones abstract a simple geometrical construction is demonstrated for determining the orientations of the principal axes of the infinitesimal strain ellipsoid in tectonic zones where boundaries obliquely converge or diverge the construction may also be used to determine the relative magnitudes of the principal axes and the ellipsoid shape for infinitesimal and finite transpressional transtensional strains the analysis leads to a tightening of the definitions of the loosely used terms compression wrench and extension applications of the simple construction and convenient graphical solution are illustrated by brief examples

seismic characteristics and identification of negative flower structures positive flower structures and positive structural inversion negative and positive flower structures and positive inverted structures imply specific modes of formation and their distinctive characteristics make them important criteria for the identification of certain structural styles a negative flower structure from the andaman sea consists of a shallow synform bounded by upward spreading strands of a wrench fault that have mostly normal separations paralleling monoclines and oblique en echelon normal faults flank the divergent wrench fault a positive flower structure from the ardmore basin oklahoma consists of a shallow antiform displaced by the upward diverging strands of a wrench fault that have mostly reverse separations en echelon folds are present on either side of this convergent wrench fault flower structures may resemble extensional or contractional fault blocks on individual seismic profiles flower structures are identified by their unique internal fault and fold architecture by their association with a straight and throughgoing zone of deformation and by their lack of a consistent sense of separation or regional upthrown side positive structural inversion at the rambutan oil field south sumatra basin has formed a shallow anticlinorium and has partly uplifted the underlying graben deeper fault segments bounding the graben have retained their normal fault profiles but at shallow levels some of these faults have reverse separations similar changes of separation with depth may be produced by strike slip but sets of faults with listric profiles and nearby blocklike trend patterns identify the inversion as a dip slip event where correlation of reflections is uncertain or deep control is unobtainable positive inverted structures may also resemble contrational fault blocks detached normal fault assemblages and certain negative inverted structures

transpression along the southern san andreas fault durmid hill california transpression is expressed at durmid hill in the development and subsequent rotation of en echelon folds and ongoing vertical uplift the transpression related strain field can be quantified by an analysis of 1 orientation of rotated fold axes which display an angle of about 20 between the san andreas fault and the fold axial traces 2 shortening perpendicular to the fold axes 40 60 3 extension parallel to the fold axes 58 68 measured using a boudinaged ash bed and 4 uplift determined from an antecedent stream 1 1 1 7 mm yr the topographic expression of durmid hill and the exposed stratigraphy the observed deformation may be approximated by a homogeneous transpressional deformation this model suggests that an estimated 9 14 of the total displacement predicted by plate motion models across the san andreas fault has been accommodated by the durmid hill deformation zone adjacent to the fault this off fault deformation is not directly coupled to coseismic or interseismic movement on the fault itself

a review of alpine tectonics in portugal foreland detachment in basement and cover rocks abstract the alpine foreland in portugal was deformed by compressional tectonism during the miocene in the nne ssw oriented lusitanian basin most folds and thrusts in the meso cenozoic cover are oriented ene wsw parallel to the alpine front in the betic cordillera and verge towards the north northwest and south southeast the thrusts are connected by lateral ramps most of these are oriented nne ssw to n s and show sinistral movement and some are transpressional the lateral ramps result from reactivation of older extensional faults related to crustal thinning of the continental margin in the e w oriented algarve basin a simpler basin inversion occurred with older e w normal faults reactivated as essentially pure thrusts in both basins alpine structures formed above decollements in the hettangian evaporite clastic complex variscan basement was also deformed by ene wsw reverse faults during miocene time the similarity in orientation and style of the basement structures to those in the cover suggests that they also occurred by detachment but their larger scale indicates that the detachment is deep and involves much of the crust thus we interpret the central cordillera in which basement rocks are thrust over miocene sediments on both sides as a pop up of crustal scale elevated above downward flattening faults that dip towards each other and merge into a single deep detachment alpine structures in the iberian foreland are therefore similar in structural style to those of the appalachian and laramide forelands of north america and the alpine foreland of northwest europe

seismic and sedimentologic features of oxfordian kimmeridgian syn rift sediments on the eastern margin of the lusitanian basin following deposition of widespread middle oxfordian lacustrine carbonates and evaporites the lusitanian basin was differentiated into a number of sub basins the arruda sub basin is a half graben basin situated some 30 km north of lisbon it accumulated over 2 5 km of kimmeridgian siliciclastic sediments and is bounded to the east by the vila franca de xira fault zone carbonate deposition persisted over horsts along the fault zone from the oxfordian to the early kimmeridgian and in places to the late kimmeridgian and shows a pronounced west east facies zonation with higher energy framestones and grainstones accumulating along the exposed western margins seismic data indicate a major gap between the horst blocks that acted as a conduit through which basement derived siliciclastics were fed westwards into the sub basin to form a submarine fan system the presence of large blocks of framestone carbonates encased in siliciclastics indicates that carbonate sedimentation occurred in abandoned parts of the fan system the rapid changes of sediment thicknesses and facies types along the eastern margin of the arruda sub basin are indicative of contemporaneous strike slip movements

sidewall ripouts in strike slip faults abstract distinctive splay fault configurations in wallrocks associated with pseudotachylyte bearing strike slip fault structures at three different localities are recognized as sidewall ripouts sidewall ripout structures occur as asymmetric doubly tapered fault bounded lenses or slabs adjacent to a dominant planar fault surface scallop shaped lens ripouts develop in isotropic or weakly anisotropic host rocks and elongate slab ripouts develop in strongly anisotropic host rocks the tapered ends of these structures consist of leading contractional p type ramp structures at a low angle to the dominant planar fault surface and trailing extensional r or x type ramp structures at higher angles to the dominant fault surface the formation of ripout structures is attributed to transient variations in the coefficient of friction that cause adhesion between fault surfaces leading to rupture of the sidewalls ripouts are interpreted as large outcrop scale examples of adhesive wear during rupture of the sidewalls developed along planar fault surfaces during slip the asymmetry of the ripout structures in these exposures allows their use as a kinematic indicator where the narrow tapered leading end points in the direction of movement of the ripout lens or slab during adhesion to the opposing fault block wall

slip rate and tremor genesis in cascadia at many plate boundaries conditions in the transition zone between seismogenic and stable slip produce slow earthquakes in the cascadia subduction zone these events are consistently observed as slow aseismic slip on the plate interface accompanied by persistent tectonic tremor however not all slow slip at other plate boundaries coincides spatially and temporally with tremor leaving the physics of tremor genesis poorly understood here we analyze seismic geodetic and strainmeter data in cascadia to observe for the first time a large tremor generating slow earthquake change from tremor genic to silent and back again the tremor falls silent at reduced slip speeds when the migrating slip front pauses as it loads the stronger adjacent fault segment to failure the finding suggests that rheology and slip speed regulated stressing rate control tremor genesis and the same section of fault can slip both with and without detectable tremor limiting tremor s use as a proxy for slip

the spanish portuguese central system an example of intense intraplate deformation and strain partitioning abstract the intraplate deformation of iberia during the cenozoic produced a series of ranges and deformation belts with a wide variety of structural trends the spanish portuguese central system is the most prominent feature crossing over the whole of central iberia it is a large thick skinned crustal pop up with ne sw to e w thrusts however the 500 km long left lateral strike slip messejana plasencia fault also ne sw oriented bends these thrusts to produce ne sw local paleostresses close to the fault which seems to be consistent with a common deformational arrangement this is also supported by the similar sedimentary infilling characteristics found in the surrounding cenozoic basins the moment of the maximum intraplate deformation is registered at the same time in all these basins during the upper priabonian lower chattian as there are two possible sources for the intraplate compressive stresses the pyrenean n s shortening orogen to the north and the betic nw se shortening orogen to the south neither can simply explain both simultaneous movements ne sw strike slip and ne sw thrusting the deduced age of the main deformation indicates a pyrenean origin in contrast the concept of strain partitioning between the two types of faults gives as a result an overall north trending compression existing data do not support crustal detachment from the betics neither from the pyrenees but are consistent with a crustal uplift related to lithospheric folding the subsequent betic related stress field only slightly reworked previously pyrenean related structures except for the portuguese sector where tectonic activity occurred mainly in the upper miocene

disposition of solar radiation in sea ice and the upper ocean a one dimensional sea ice model with an ice thickness distribution is presented to examine the disposition of the incoming surface shortwave radiation within the sea ice and the upper ocean the sea ice model consists of 15 different ice thickness categories and an open water leads category ice growth melting on horizontal and vertical surfaces meltwater pond growth and drainage and snow accumulation evolve independently for each of the ice categories leads melt ponds and thinner ice categories are of particular interest as these features account for nearly all of the solar energy that is transmitted into the upper ocean beneath the ice pack also examined is the surface reflection and absorption internal ice absorption and lateral melting for ponded and pond free ice area averaged results show that 69 of the total annual solar energy is reflected 15 is absorbed by the snow cover 12 is absorbed by the ice and 4 is transmitted to the ocean mixed layer through thin ice and leads

crustal structure beneath the lower tagus valley southwestern iberia using joint analysis of teleseismic receiver functions and surface wave dispersion summary we conducted a joint analysis using a genetic algorithm on body wave teleseismic receiver functions and rayleigh wave phase velocities computed from seismic waveform data recorded at six broadband seismic stations deployed in the lower tagus valley southwestern iberia the study region is located on the central western portuguese mainland a few hundred kilometres north of the africa iberia plate boundary and has a record of historical damage and casualties which are caused by destructive earthquakes occurring either to the southwestern offshore area or onland as a result of intraplate seismic activity the latter may represent a response of old basement fractures to the current convergence between africa and iberia however little is known about the deep structure of the crust beneath this region for this reason we employed the genetic algorithm to analyse the seismic data recorded in the lower tagus valley the crustal thickness beneath the study region varies from 26 to 28 km with an average of 27 5 km which is clearly lower than the global average the crustal thickness shows a tendency of decrease towards the west near the coast of the atlantic ocean being consistent with the extensional tectonic episodes that led to the opening of the atlantic in the middle jurassic

evolution of deformation styles at a major restraining bend constraints from cooling histories mae ping fault zone western thailand the c 500 km long mae ping fault zone trends nw se across thailand into eastern myanmar and has probably undergone in excess of 150 km sinistral motion during the cenozoic a large c 150 km long restraining bend in this fault zone lies on the western margin of the chainat duplex the duplex is a low lying region dominated by north south trending ridges of mesozoic and palaeozoic sedimentary metamorphic and igneous rocks flanked by flat post rift basins of pliocene recent age to the north and south a review of published cooling age data plus new apatite and zircon fission track results indicates that significant changes in patterns of exhumation occurred along the fault zone with time oldest uplift and erosion eocene occurred in the umphang gneiss region west of an inferred thrust dominated restraining bend setting from 36 ma to 30 ma exhumation was strongest north of the duplex along the nw se trending segment of the fault zone at the northern exiting bend of the chainat duplex this region of the fault zone is characterized by a mid crustal level shear zone 5 6 km wide lan sang gneisses that passes to the nw into an apparent strike slip duplex geometry the deformation is interpreted to have occurred during passage around the northern restraining bend which resulted in vertical thickening uplift erosion and extensional collapse of the northern side of the shear zone this concentration of deformation at the bends at the ends of the restraining bend is thought to be a characteristic of strike slip dominated restraining bends following late oligocene early miocene extension there is apatite fission track evidence for 22 18 ma exhumation in the chainat duplex that coincides with a phase of inversion in the phitsanulok basin to the north the miocene recent history of the chainat duplex is one of minor sinistral and dextral displacements related to a rapidly evolving stress field influenced by the numerous tectonic reorganizations that affected se asia during that time

kinematics and paleoseismology of the vernon fault marlborough fault system new zealand implications for contractional fault bend deformation earthquake triggering and the record of hikurangi subduction earthquakes the 40 km long vernon fault in the marlborough fault system of new zealand is characterized by dextral slip with subordinate reverse slip and exhibits abrupt variations in strike of up to 90 onshore fieldwork paleoseismic trenching and offshore high frequency seismic reflection data are integrated together to identify the kinematics and paleoseismic history of three sections of the fault 1 the nne striking vernon hills section which branches off from the awatere fault 2 the ne striking big lagoon section which borders big lagoon to the south and extends 9 km offshore to the east and 3 the e w striking wairau basin section which is entirely submarine the vernon fault can be shown to have a dextral slip rate of 0 8 4 9 mm yr with a preferred estimate of 0 9 mm yr on the big lagoon section we infer that a further unrecognized 3 4 mm yr of dextral slip has been accommodated off fault as a result of accumulated slip on small and or blind reverse faults adjacent to a 6 km wide restraining bend in the main fault the onshore and offshore paleoseismic records are in good agreement these indicate three to five events at eight sites and a mean recurrence interval of 3 9 1 2 ka over the past 16 kyr with the last event taking place at 3 3 ka earthquakes on the vernon fault are responsible for 25 of the holocene subsidence rate of big lagoon over the last 13 ka most of the subsidence of this lagoon has been the result of surface deformation related with southern hikurangi megathrust earthquakes

diverse pliocene quaternary tectonics in a transform environment san francisco bay region california the san francisco bay region occupies part of the diffuse transform boundary zone between the pacific and north american plates although dextral strike slip faulting is dominant the plate motion is expressed in a variety of ways some strike slip faults are parallel with the plate boundary but some are slightly oblique the major strike slip faults are zones in which an interplay occurs between strands some of which are en echelon this interplay may be responsible for some apparent pull apart basins and presumed normal faults along the calaveras fault zone in extensive areas between strike slip fault zones there are many compressional structures folds and reverse faults that are pliocene quaternary in age hence largely coeval with the strike slip faults some of the compressional structures are oblique to and others are parallel with the major strike slip faults we have divided the san francisco bay region into domains on the basis of the types orientations and relationships of structures or in one case lack of strong deformation each domain has responded in its own way to the regional northwest southeast dextral shear imposed by the relative plate motion in an attempt to understand the origin of various structures and the interrelationships among them we compared established models with our observations some observed geometric relationships agree quite well with classical coulomb anderson and simple shear models but others require further explanation models based on fault interaction seem to apply to certain cases for example the east bay hills domain which is between the left stepping calaveras and hayward rodgers creek fault zones is under compression resulting from interaction between the two strike slip zones

similar scaling laws for earthquakes and cascadia slow slip events faults can slip not only episodically during earthquakes but also during transient aseismic slip events1 5 often called slow slip events previous studies based on observations compiled from various tectonic settings6 8 have suggested that the moment of slow slip events is proportional to their duration instead of following the duration cubed scaling found for earthquakes9 this finding has spurred efforts to unravel the cause of the difference in scaling6 10 14 thanks to a new catalogue of slow slip events on the cascadia megathrust based on the inversion of surface deformation measurements between 2007 and 201715 we find that a cubic moment duration scaling law is more likely like regular earthquakes slow slip events also have a moment that is proportional to a3 2 where a is the rupture area and obey the gutenberg richter relationship between frequency and magnitude finally these slow slip events show pulse like ruptures similar to seismic ruptures the scaling properties of slow slip events are thus strikingly similar to those of regular earthquakes suggesting that they are governed by similar dynamic properties a new catalogue of slow slip events on the cascadia megathrust shows that a cubic moment duration scaling law is likely with scaling properties strikingly similar to regular earthquakes

structural and kinematic evolution of a miocene to recent sinistral restraining bend the montejunto massif portugal the montejunto massif lies in the apex of a large scale restraining bend at the southern termination of a sinistral transpressive fault system in the lusitanian basin of portugal cenozoic deformation within the montejunto massif initiated with southerly directed thrusting along the southern boundary of the massif in association with the development of the e w oriented montejunto anticline probably during the langhian deformation switched to the northern boundary of the massif in association with a change to nw directed thrusting and continued development of the montejunto anticline the youngest set of structures within the massif is related to the sinistral reactivation of the arieiro fault system and steeply inclined bedding this late phase of deformation represents the accommodation of a component of sinistral displacement across the restraining bend along mechanical anisotropies formed during this progressive cenozoic deformation event variation in the kinematic style of the main arieiro fault is related to the angle between the fault plane and the displacement vector where 20 abrupt pene contemporaneous switches in displacement direction are recorded along the fault whereas strike slip kinematics predominate where 20 the timing of deformation events in the montejunto massif is uncertain however correlation with the established cenozoic africa europe plate convergence directions may provide potential temporal constraints

strike slip deformation in the confidence hills southern death valley fault zone eastern california usa the confidence hills form a well exposed composite positive flower structure developed in pliocene to recent lacustrine and alluvial fan sediments the structure has developed along the current trace of the southern death valley dextral strike slip fault zone california usa nw se striking fault zones bound the confidence hills in 3d these fault segments are inferred to link at depth to a common basal fault system the flower structure is formed by doubly plunging anticlines that roughly parallel the bounding fault segments fold development was aided by a the presence of a basal salt deposit and numerous detachment horizons within the sedimentary pile and b buttressing and uplift along and against the bounding oblique slip reverse faults structural and palaeomagnetic evidence indicates that the anticlines developed with axial surfaces parallel and sub parallel to the trace of both fault zones folding appears to have initially developed adjacent to and above the southeastern fault segment and then propagated outwards and to the northwest the latest displacements along the current southern death valley fault zone are probably only in the orders of hundreds of metres and as young as 0 9 ma to recent this young fault zone is highly segmented along the length of the floor of southern death valley the high proportion of oblique slip faulting consistent with the strike slip zone being immature the confidence hills structure displays close geometric similarities with other natural examples of positive flower structures and to the features found in scaled analogue sandbox experiments of strike slip faulting