observations and modeling of strong ground motions for the 9 october 1995 mw 8 colima jalisco mexico earthquake abstract the colima jalisco cj region in northwestern mexico has generated large magnitude earthquakes at least since 1800 for example during the last century three large destructive shallow thrust subduction earthquakes occurred on 3 and 18 june 1932 with m s of 8 2 and 8 respectively and on 9 october 1995 m w 8 m s 7 4 this historical seismicity and the lack of seismic recordings in the cj region pose important constraints for the computation of reliable seismic hazard studies for sites in this region of mexico towards this aim we have used a hybrid method to generate broadband bb synthetics for the m w 8 cj 1995 earthquake for the recording sites of the near mz intermediate cg and far col fields the low frequency lf 0 5 hz synthetics were simulated by applying a 3d finite difference method and the high frequencies hf 0 5 hz were generated by the empirical green s function technique finally matched filters were applied to the lf and hf synthetics to obtain the bb time series the lf synthetics were computed from a finite fault description of the source with four asperities in a 2 5d model constrained by gravity and seismological data our preferred model includes an approximation of a thin accretionary prism for the hf modeling we also used the four asperity source model as well as the recordings of the foreshock and aftershock of the m w 8 1995 mainshock based on the comparisons of the bb synthetics with the observed strong ground motions for the 1995 cj earthquake at the three stations we believe that our hybrid method is a first step toward the generation of more reliable estimates of the seismic hazards in cj region further improvement in the hazard estimates depends on the urgent deployment of seismological and strong ground motion infrastructure in the cj region

the late cretaceous to recent tectonic history of the pacific ocean basin abstract a vast ocean basin has spanned the region between the americas asia and australasia for well over 100 myr represented today by the pacific ocean its evolution includes a number of plate fragmentation and plate capture events such as the formation of the vancouver nazca and cocos plates from the break up of the farallon plate and the incorporation of the bellingshausen kula and aluk phoenix plates which have been studied individually but never been synthesised into one coherent model of ocean basin evolution previous regional tectonic models of the pacific typically restrict their scope to either the north or south pacific and global kinematic models fail to incorporate some of the complexities in the pacific plate evolution e g the independent motion of the bellingshausen and aluk plates thereby limiting their usefulness for understanding tectonic events and processes occurring in the pacific ocean perimeter we derive relative plate motions with 95 uncertainties for the pacific farallon vancouver kula pacific bellingshausen pacific and early pacific west antarctic spreading systems based on recent data including marine gravity anomalies well constrained fracture zone traces and a large compilation of magnetic anomaly identifications we find our well constrained relative plate motions result in a good match to the fracture zone traces and magnetic anomaly identifications in both the north and south pacific in conjunction with recently published and well constrained relative plate motions for other pacific spreading systems e g aluk west antarctic pacific cocos recent pacific west antarctic spreading we explore variations in the age of the oceanic crust seafloor spreading rates and crustal accretion and find considerable refinements have been made in the central and southern pacific asymmetries in crustal accretion within the overall pacific basin where both flanks of the spreading system are preserved have typically deviated less than 5 from symmetry and large variations in crustal accretion along the southern east pacific rise i e pacific nazca farallon spreading appear to be unique to this spreading corridor through a relative plate motion circuit we explore the implied convergence history along the north and south america s where we find that the inclusion of small tectonic plate fragments such as the aluk plate are critical for reconciling the history of convergence with onshore geological evidence

seismicity and structure in central mexico evidence for a possible slab tear in the south cocos plate the morphology of the transition from flat to normal subduction in eastern central mexico is explored using intraslab earthquakes recorded by temporary and permanent regional seismic arrays observations of a sharp transition in slab dip near the abrupt end of the trans mexican volcanic belt tmvb suggest a possible slab tear located within the subducted south cocos plate the eastern lateral extent of a thin ultra slow velocity layer usl imaged atop the cocos slab in recent studies along the meso america subduction experiment array is examined here using additional data we find an end to this usl which is coincident with the western boundary of a zone of decreased seismicity and the end of the tmvb near the sharp transition in slab dip waveform modeling of the 2 d structure in this region using a finite difference algorithm provides constraints on the velocity and geometry of the slab s seismic structure and confirms the location of the usl analysis of intraslab seismicity patterns reveals clustering sudden increase in depth variable focal mechanism orientations and faulting types and alignment of source mechanisms along the sharp transition in slab dip the seismicity and structural evidence suggests a possible tear in the south cocos slab this potential tear together with the tear along the orozco fracture zone to the northwest indicates a slab rollback mechanism in which separate slab segments move independently allowing for mantle flow between the segments

hadrosaurid edmontosaurus bonebeds from the horseshoe canyon formation horsethief member at drumheller alberta canada geology preliminary taphonomy and significance three monodominant hadrosaurid bonebeds in the horsethief member of the horseshoe canyon formation uppermost campanian in southern alberta canada are documented each bonebed is hosted by a dec

a model for attenuation of backscatter due to sediment accumulations and its application to determine sediment thicknesses with gloria sidescan sonar where the seafloor consists of a highly backscattering surface covered with a drape of fine grained sediment and where the sediment does not contribute significantly to the backscattered signal the sediment thickness can potentially be inferred from the amount of signal attenuation in the sediment layer a first order acoustical model is proposed in which the signal strength is reduced by an amount proportional to the sediment thickness and attenuation rate in the sediments data collected with geological long range inclined azdic gloria are used to develop and test this model at an acoustic frequency of 6 5 khz the range of sediment thickness that the sonar can potentially recover is 0 20 m a range that is often below the resolution of vertical profilers in the first example the signal variation with grazing angle over a uniformly buried surface is analyzed for attenuation which is expected to increase toward shallow grazing angles and longer attenuating paths through the sediment layer the surface is a lava flow north of hawaii covered by 1 2 m of fine grained sediments clague et al 1990 and gloria data analyzed with the model suggest an attenuation coefficient of 0 2 0 4 db m a value consistent with results from laboratory and field measurements of sediment attenuation in the second example a rocky surface is buried by varying amounts of sediment which is analyzed at almost constant grazing angle the surface is the volcanic basement of the southeast indian ridge and gloria data reveal the thickening of the sediment cover with distance away from the spreading center this is used to derive an average sedimentation rate of 6 mm ka which is generally consistent with results from other studies and suggests that this technique may be used to study differences in sedimentation rates between different regions furthermore the model is used to calculate from image amplitude distributions the sediment thickness distribution which represents the accumulation of sediments in ponds and the exposure of abyssal hills these sedimentary processes are also reflected in the standard deviation of sediment thickness which increases with seafloor age i explore the various sources of error in estimating sediment thickness using this technique and propose a model for nonuniform sediment drapes the first order model assumes a uniform thickness at the subfootprint scale

mechanisms of lithospheric extension at mid ocean ridges summary we examine the extensional deformation of oceanic plates at mid ocean ridges especially within an axial yield zone where pervasive faulting occurs thermal models of ridges are developed which include the effects of lithospheric thickening on the mantle flow the heat of magmatic crustal accretion at the ridge axis and the hydrothermal cooling due to seawater circulation in the crust when hydrothermal circulation occurs the brittle lithospheric plate at slow spreading ridges could be as thick as 8 9 km thicker than the crust while the plate at fast spreading ridges is only 1 2 km for a typical slow spreading ridge several kilometres of plate thickening are expected within a distance of 15 km from the ridge axis when subjected to the extensional force due to horizontal stretching shear failure by normal faulting will occur pervasively in an axial zone where the lithospheric plate is the thinnest adopting perfectly plastic rheology as a continuum description of deformation on the distributed faults we obtain approximate solutions for the stress distribution in the yield zone within this yield zone sea floor topography increases significantly away from the ridge axis so that the resuiting gravity sliding force balances the differential horizontal extensional force due to the thickening of the lithospheric plate basal stresses induced by the viscously deforming asthenosphere could significantly influence the stresses inside the lithospheric plate only if the mantle viscosity beneath the ridge is on the order of 10 pa s significantly higher than generally accepted values of 10 pa s model calculations reveal that although the seafloor topography at the mid atlantic ridge at 13 15 on is regionally compensated it is locally supported by stresses in the lithospheric plate the deviation of the lithospheric plate from its thermal isostatic equilibrium position can be explained by necking due to plastic stretching in the axial yield zone and elastic deflection of strong plates outside the yield zone the best fit models require the yield zones to have a half width of 10 15 km we find systematic variations in the gravity and topography of the east pacific rise which indicate strong influence of plate spreading rate on the ridge thermal and mechanical structure at the 16 17 on area where the half spreading rate is 4 3 cm yr a prominent axial topographic high and an axial mantle bouguer gravity low exist implying a crustal or sub crustal low density body the gravity low disappears at the 20 21 n area where the half spreading rate is 3 6 cm yr as the plate spreading rate decreases from 4 3 cm yr at the 16 17 on area to 2 7 cm yr at the 22 23 on area axial ridge topography changes from higher than the thermal isostatic equilibrium position to lower than the isostatic position the low axial topography at the 22 23 n area can be explained by the existence of a low amplitude median valley

faunal assemblages from the upper horseshoe canyon formation an early maastrichtian cool climate assemblage from alberta with special reference to the albertosaurus sarcophagus bonebed the faunal assemblage from the early maastrichtian portion of the horseshoe canyon formation is described on the basis of four new vertebrate microfossil localities and remains from the albertosaurus bonebed all of the localities sampled were deposited during a cool dry climate at a palaeolatitude of 58 n thus these assemblages provide insight into a northern cool climate assemblage in the early maastrichtian of western north america this fauna is characterized by the presence of taxa with more northern affinities such as holostean a champsosaurs troodon and toothed birds warm climate taxa such as crocodylians large and diverse turtles and albanerpetontids are notable in their absence the albertosaurus bonebed locality at the top of unit 4 of the horseshoe canyon formation was deposited during the initial stages of a trend to a warmer and wetter climate that is represented in unit 5 the bonebed shares many taxa with the underlying vertebrate microfossil localities however a notable diffe

temporal evolution of overlapping spreading centers at 16 20 n on the east pacific rise abstract a compilation of sea beam data on the right stepping overlapping spreading center osc at 16 20 n on the east pacific rise epr and in the surrounding region is presented sea beam data from the rise flanks at 16 20 n reveal three deep basins at least one of which is flanked by a curved ridge whose morphology is similar to that at the offset the widths of these offaxis basins range from 8 to 13 km and allow an estimate to be made of the sizes of the offsets at which they were formed it is proposed that they represent traces on the rise flank which provide a record of the development of the offset and a basis for prediction of its future evolution the repeated pattern of abandoned overlap basins and cuspate ridges supports the notion that oscs are episodic on a time scale of approximately 200 000 years and are cyclic in nature it also reveals an alternation of dominance between the southern and northern segments which have shifted the location of the discontinuity along the axis so as to create zig zag traces of basins on the ridge flanks

a taphonomic analysis of a multitaxic bonebed from the st mary river formation uppermost campanian to lowermost maastrichtian of alberta dominated by cf edmontosaurus regalis ornithischia hadrosauridae with significant remains of pachyrhinosaurus canadensis ornithischia ceratopsidae scabby butte is an isolated exposure of upper cretaceous uppermost campanian to lowermost maastrichtian strata of the st mary river formation these rocks have produced a diverse assemblage of b

p wave velocity tomography from local earthquakes in western mexico in western mexico the subduction of the rivera and cocos plates beneath the north america plate has deformed and fragmented the overriding plate forming several structural rifts and crustal blocks to obtain a reliable subsurface image of the continental crust and uppermost mantle in this complex area we used p wave arrivals of local earthquakes along with the fast marching method tomography technique we followed an inversion scheme consisting of 1 the use of a high quality earthquake catalog and corrected phase picks 2 the selection of earthquakes using a maximum location error threshold 3 the estimation of an improved 1 d reference velocity model and 4 the use of checkerboard testing to determine the optimum configuration of the velocity nodes and inversion parameters surprisingly the tomography results show a very simple vp distribution that can be described as being controlled by geologic structures formed during two stages of the separation of the rivera and cocos plates the earlier period represents the initial stages of the separation of the rivera and cocos plates beneath western mexico the later period represents the more advanced stage of rifting where the rivera and cocos plates had separated sufficiently to allow melt to accumulate below the colima volcanic complex during the earlier period 14 or 10 1 6 ma ne sw oriented structures lineaments such as the southern colima rift were formed as the two plates separated during the second period 1 6 ma to the present the deformation is attributed to magma generated within and above the tear zone between the rivera and cocos plates rising beneath the region of the colima volcanic complex the rising magma fractured the overlying crust forming a classic triple rift junction geometry this triple rift system is confined to the mid to lower crust perhaps indicating that this rifting process is still in an early stage this fracturing along with fluid circulation and associated heat advection within the fractures can easily explain the observed distribution of vp as well as many of the results of previous seismological studies also surprisingly we find no evidence at deep crustal depths to support either a trenchward migration of the volcanic arc or toroidal asthenospheric flow through the slab tears bounding the jalisco block to the nw and se

east pacific rise from siqueiros to orozco fracture zones along strike continuity of axial neovolcanic zone and structure and evolution of overlapping spreading centers we have used the sea beam multibeam echo sounding system to survey the east pacific rise epr from 8 20 n to 18 30 n obtaining complete coverage of the epr axial neovolcanic zone and all intervening transform faults here we focus on the epr neovolcanic zone and the definition of overlapping spreading centers ocs s between the orozco and siqueiros transform faults the neovolcanic zone is narrow 0 5 2 0 km and continuous along strike and occurs within and near a strike continuous axial summit graben the neovolcanic zone and summit graben reside along the crest of a volcanic axial high which is 2 10 km wide and which continues uninterrupted along strike for 40 140 km within 20 50 km of an intersection with a transform fault the axial neovolcanic zone narrows and deepens and within only 3 6 km of the intersection the neovolcanic zone turns sharply into the transform valley at seven locations between the siqueiros and orozco transform faults the axial neovolcanic zone is discontinuous and is laterally offset a short distance 1 15 km in contrast with a classic ridge transform ridge plate boundary however offset rise terminations overlap each other by a distance approximately 3 times greater than their offset they curve toward each other and often one merges into the other along strike separating the osc s is an elliptical overlap basin up to 600 m deep whose long axis is subparallel to the adjacent spreading centers the overlap basin is characterized by volcanic constructional edifices a key difference between these offsets and small transform faults in the atlantic is that there are no transform fault structures in the overlap basin which link the offset rise axes a continuous axial depth profile reveals a long wavelength 20 60 km undulation of the rise axis which may be associated with variations in the magmatic budget along strike the lowest points in the axial depth profile occur near transform faults and at osc s suggesting that these features are associated with along strike minima in the magmatic budget we suggest that major phases of volcanic activity propagate episodically along the axis away from centers of magmatic inflation and that osc s develop where magmatic pulses fail to meet due to misalignment of fracture systems sinuous bends in the rise axis or other heterogeneities transform faults fail to develop on fast spreading centers where the lateral offsets are small 15 km because the lithosphere is too thin and weak to maintain a classic rigid plate ridge transform fault pattern the osc geometry is unstable and evolves rapidly and the overlapping rises may propagate at rates faster than the local spreading rate one of the two osc s prevails while the other is abandoned while the locations of osc s may not be fixed relative to the rise axis they may tend to recur near the same place creating scars in older lithosphere which resemble fracture zones but whose fine scale structure is quite different there is excellent agreement between the observed structure of osc s and laboratory studies of osc s using wax models photoelastic studies of overlapping cracks and boundary element modeling of overlapping cracks seismic refraction and reflection near two osc s suggests that large offset osc s have separate magma chambers beneath the offset rise axes while small offset osc s may share a single axial magma chamber three dimensional inversion of magnetic anomalies suggests that significant petrologic anomalies may occur near some osc tips waxing and waning of overlapping magma chambers may give rise to the eruption of highly fractionated feti basalts and associated magnetic anomalies

crustal processes at spreading centers recent discoveries and research on mid ocean ridges mor s in the last four years have greatly increased our knowledge of this fundamental type of plate boundary the last iugg review of mor research was in 1975 aumento et al 1975 and its omission as a topic in 1978 may have reflected a feeling that spreading centers were reasonably well understood since that time however there has been a surfeit of important new observations and exciting research and there is now a turmoil of innovative ideas about the processes which create and leave their imprint on two thirds of the earth s crust new seismic measurements have been made and interpreted as evidence for the existence of shallow axial magma chambers amc beneath intermediate total opening rate 5 9 cm yr and fast 9 18 cm yr spreading centers fig 1 yet there is controversy as to whether they are steady state whether they persist beneath slow ridges as well in the steady state what the dimensions and shape of the chamber are its relation to oceanic crustal stratigraphy and its relation to observations in ophiolites black smoker hydrothermal vents have been discovered in the pacific spewing forth 350 c fluids blackened by polymetallic sulfide precipitates this discovery is embroiled in debate as to how long the vents last whether they occur at slow spreading rates as well whether the enormous heat flux of the vents freeze the magma chamber even at fast spreading rates their influence on geochemical balances in the ocean and the value of the sulfide deposits commercially it has been found that our initial view of mor s as two dimensional linear structures has served us well as an initial working model but must be significantly modified to account for variations in tectonic volcanic and hydrothermal activity along strike as well as for episodicity of these processes deep sea drilling project dsdp samples have raised fundamental questions about formation of the magnetic source layer hydrothermal circulation and fault mechanisms along the mor spreading centers which penetrate existing lithosphere along strike as propagating rifts have modified our views of how plate boundaries reorient themselves and how v shaped magnetic and topographic trends are formed we have also found that transform faults may modify spreading center processes for some distance away from their intersections with mor s and that rigid plate transform faults may fail to develop at fast spreading centers under certain conditions resulting in en echelon overlapping of spreading centers this review will focus on these developments and several others only example references to these topics will be given in the text and many important topics will not be discussed directly e g petrology and geochemistry mantle convection research on lithosphere older than 1 m y however i have tried to compile and have included an extensive bibliography for u s research on a broader range of mor topics for mid 1978 to mid 1982 which is the main purpose of this report pre 1978 references are occasionally included where appropriate abstracts are not included

miocene spreading centre south of isla guadalupe the juan de fuca rivera cocos and nazca plates in the eastern pacific are small fragments remaining from the fragmentation and partial subduction of the long narrow farallon plate which began as early as 55 myr ago1 this fragmentation apparently resulted from interaction of the very irregular pacific farallon ridge with the uneven coastlines of the american plate1 4 and involved the formation of ridge trench transforms5 creation of new spreading centres6 ridge jumps1 7 8 deactivation of subduction zones2 and other phenomena1 we present here magnetic evidence that a fifth small fragment of the farallon plate is preserved in the eastern pacific off the coast of baja california its preservation is the result of an eastward jump of the pacific farallon ridge 12 5 myr ago which was preceded by asymmetric spreading and perhaps pivotal subduction1 menard1 first suggested this idea and showed that anomaly 5b is symmetric and parallel to a linear trough trending southwards from guadalupe island he named the small fragment of the farallon plate preserved between this trough and the margin of baja california to the east the guadalupe plate1 we show that both anomalies 5b and 5c symmetrically flank the guadalupe trough our results and conclusions are not based on new magnetic data but rather on reinterpretation of aeromagnetic profiles published by taylor et al 9

microearthquake activity on the orozco fracture zone preliminary results from project rose we present preliminary hypocenter determinations for 52 earthquakes recorded by a large multi institutional network of ocean bottom seismometers and ocean bottom hydrophones in the orozco fracture zone in the eastern pacific during late february to mid march 1979 the network was deployed as part of the rivera ocean seismic experiment also known as project rose the orozco fracture zone is physiographically complex and the pattern of microearthquake hypocenters at least partly reflects this complexity all of the well located epicenters lie within the active transform fault segment of the fracture zone about half of the recorded earthquakes were aligned along a narrow trough that extends eastward from the northern rise crest intersection in the approximate direction of the cocos pacific relative plate motion these events appear to be characterized by strike slip faulting the second major group of activity occurred in the central portion of the transform fault the microearthquakes in this group do not display a preferred alignment parallel to the direction of spreading and several are not obviously associated with distinct topographic features hypocentral depth was well resolved for many of the earthquakes reported here nominal depths range from 0 to 17 km below the seafloor

controlled source electromagnetic sounding of the oceanic lithosphere the attenuation of ionospheric signals in the frequency range 0 06 24 hz by sea water effectively precludes using the magnetotel luric method to study the electrical structure of the upper oceanic lithosphere we have carried out a dipole dipole electromagnetic sounding in the north pacific by injecting electromagnetic signals into the ocean and sea bed the crust at the site is 25 myr old and has a thin sediment cover the technique similar to that used in earlier work1 2 involves dragging a horizontal dipole antenna along the sea floor the electric fields that propagated through the resistive basement were detected by seafloor receivers at ranges of 10 65 km as the ambient electric field is very small varying from 10 18 v2 m 2 hz 1 at 0 1 hz to 10 24 v2 m2 hz 1 above 1 hz ref 3 the controlled source signals could be easily monitored our data are consistent with a simple one dimensional earth model consisting of a 3 7 km thick crustal layer of moderate conductivity 0 001 s m 1 underlain by a thicker region of very low conductivity 2 10 5 s m 1 the results suggest an upper mantle water content of at most 0 1 by volume

kinematic evolution of the northern cocos plate as the east pacific rise approached and impinged upon the western margin of north america the farallon plate began to break into multiple smaller plates whose relative movements changed strongly from those before breakup movements of the northern cocos plate inferred from magnetic lineations show rapidly changing rates and pole positions which may be characteristic of other small remnants of the farallon plate finite difference poles and rates for cocos pacific relative motion during the time intervals 2 5 5 7 7 10 and 10 14 m y have been determined from the geometry of magnetic isochrons prior to about 2 m y the cocos pacific pole was 10 to 20 south of its present location and angular rates were 2 4 times the present rate from 10 7 m y we deduce a large degree of oblique convergence between the cocos and north american plates which may be an important constraint on the evolution of the structure of the continental margin of southwestern mexico the tehuantepec ridge originated as the ridge ridge transform which generated the clipperton fracture zone spreading rate estimates for the southern part of the cocos plate suggest the possibility that the tehuantepec ridge was reactivated as a ridge trench transform between the two cocos plate fragments prior to about 7 m y

northern east pacific rise evolution from 25 m y b p to the present the northeast pacific topography and magnetic lineations 25 m y b p to the present record the traces of three major spreading reorganizations only one spreading center is observed today but there is evidence for several ephemeral episodes of twin spreading accompanying the evolution from an extensive pacific guadalupe plate boundary to a much shortened pacific cocos and pacific rivera plate boundary the 25 m y b p plate reorganization culminated with the formation of the guadalupe plate bound by the murray fracture zone to the north and the cocos nazca spreading ridge to the south between 25 and 12 5 m y b p spreading continued while the plate retained the same general outline the 12 5 11 m y b p reorganization resulted in the creation of a much shortened pacific cocos plate boundary located in its early stages over the mathematician seamounts and a much reduced cocos plate the last reorganizaton 6 5 3 5 m y b p resulted in the abandonment of the mathematician spreading ridge as a pacific cocos plate boundary in favor of the east pacific rise

rivera ocean seismic experiment rose overview the rivera ocean seismic experiment rose was designed as a combined sea and land seismic program to utilize both explosive and earthquakes to study a number of features of the structure and evolution of a mid ocean ridge a major oceanic fracture zone and the transition region between ocean and continent the primary region selected for the experiment included the rivera fracture zone the crest and eastern flank of the east pacific north of the rivera and adjacent areas of baja california and mainland mexico the experiment included 1 study of the east pacific rise south of the orozco fracture zone primarily using ocean bottom recording and explosive sources 2 a seismicity program at the orozco and 3 a land based program of recording natural events along the coastal region of mexico a considerable amount of useful data was obtained in each of the three subprograms in the marine parts of the experiment we were able to address a variety of problems including structure and evolution of young oceanic crust and mantle structure and dynamics of the east pacific rise seismicity of the orozco fracture zone and partitioning of energy transmission between the ocean volume and the crust lithosphere on land the fortuitousmore occurrence of the petatlan m7 6 earthquake of march 14 1979 permitted the acquisition of an excellent data set of foreshocks and aftershocks of this large event which provide new insight into the filling of a major seismic gap in the region this overview describes the scientific rationale and the design of the experiments along with some general results less

albertosaurus dinosauria theropoda material from an edmontosaurus bonebed horseshoe canyon formation near edmonton clarification of palaeogeographic distribution tyrannosaurid cranial bones including a maxilla dentary and pterygoid were collected from a monodominant edmontosaurus bonebed in the horseshoe canyon formation exposed near the city of edmon

crustal structure of an extinct rift axis in the labrador sea preliminary results from a seismic refraction survey abstract a preliminary crustal structure for the extinct rift axis in the labrador sea is presented based on a one dimensional analysis of ocean bottom seismometer obs refraction profiles within the extinct rift low p wave velocities are observed for crustal 3 6 6 3 km s and upper mantle 7 3 8 1 km s refractors the velocity depth structures for obss sampling crust within the extinct rift suggest a marked thinning and variability in crustal thickness from 4 7 km to 2 6 km in comparison to typical thicknesses of 6 4 km observed in the adjacent flanks the crustal structures at the extinct rift resemble those observed at the active and inactive transforms of oceanic fracture zones following arguments for crustal thinning at fracture zones we speculate that the first order thinning of the lower crust is due to a reduction in the supply of partial melt to the accretionary axis at the extinct rift the reduced supply is attributed to changes in the thermal field and spreading rate as rifting ceased this is consistent with thermal models which predict that crustal thickness decreases appreciably for spreading rates less than 20 mm yr when plate spreading predominates over buoyancy in driving mantle upwelling

breaking new ground estimates of crack depth along the axial zone of the east pacific rise 9 12 54 n using simple fracture mechanics models the depths of fissures that were observed along the axial zone of the east pacific rise epr from 9 12 to 54 n with the deep towed argo z vehicle are estimated the widest cracks 4 8 m along this fast spreading portion of the epr are the deepest and are spatially correlated with the broadest youngest and most hydrothermally active portions of the ridge crest if the widest deepest cracks are not primarily eruptive they should be most abundant in areas of older lava flows having increased in width with time this is not observed some of the widest cracks are located where the 1991 eruption of the ridge crest occurred at 9 45 52 n and may be deep enough to reach the sheeted dikes of layer 2b these cracks may have tapped melt during the eruption and facilitated the flux of vapor rich hydrothermal fluids through overlying lava flows the narrowest presumably shallowest cracks correspond to the narrowest oldest and least hydrothermally active portions of the ridge crest we interpret the wide deep cracks as primarily eruptive in origin and suggest that they may be associated with the inflation of an axial magma chamber whereas the narrow shallow cracks are interpreted as primarily tectonic and are thought to be associated more with far field plate stresses

quantifying tooth variation within a single population of albertosaurus sarcophagus theropoda tyrannosauridae and implications for identifying isolated teeth of tyrannosauridsthis article is one of a series of papers published in this special issue on the theme albertosaurus documenting variation in theropod dinosaurs is usually hindered by the lack of a large sample size and specimens representing several ontogenetic stages here variation within 140 disassociated and seven in situ tyrannosaur teeth from the upper cretaceous lower maastrichtian monodominant albertosaurus sarcophagus theropoda tyrannosauridae bonebed is documented this sample represents the largest data set of teeth from one population of a sarcophagus containing both adult and juvenile specimens tooth variation was assessed using multivariate analyses principal component discriminant and canonical variate analyses heterodonty in the teeth of a sarcophagus contributes to the large amount of variation in the data set premaxillary teeth are significantly different from maxillary and dentary teeth but there is no quantifiable difference between a priori identified maxillary and dentary teeth juvenile and adult teeth of a sarcophagus show apparent quantitative differences that are size dependen

dynamic modelling of the subduction zone of central mexico summary in central mexico some significant normal faulting events have occurred within the subducted oceanic cocos plate just below or near the down dip edge of the strongly coupled interface these normal faulting shocks followed large shallow thrust earthquakes in other subduction zones such events generally precede the up dip thrust events a vertical 2 d finite element modelling has been used to simulate the subduction of the cocos plate beneath the north american plate when the slab is driven by an active convergence velocity or slab pull we find that the latter mechanism plays only a minor role due to shallow subduction the modelling results show that the stress pattern is very sensitive to the geometry of the plates in particular normal faulting earthquakes that follow large thrust events can be explained on the basis of the flexural response of the overriding and subducting plates to the peculiar geometry of this subduction zone where the subducting slab becomes horizontal at about 100 km from the trench this horizontal part of the subducting plate down dip with respect to the main thrust zone is under an extensional stress field this provides an alternative explanation to the slab pull for the occurrence of normal faulting intraplate earthquakes in order for normal faulting earthquakes to occur in the early part of the seismic cycle it is necessary that the large up dip thrust events have a partial stress drop we find that for small fractional stress drop a wide region of extension remains below the down dip edge of the main fault plane following a large thrust earthquake thus the main thrust earthquakes do not invert the polarity of the active stress field which is compressional and extensional up dip and down dip respectively with respect to the main thrust fault larger fractional stress drops result in larger delays in the occurrence of normal faulting events after the main thrust events

the morphology of propagating spreading centers new and old recent seabeam investigations over the east pacific rise in the northeast pacific have shown the existence of a propagating spreading center at 18 n the propagating and dying spreading centers are joined by a zone of orthogonal lineations which appear to be the traces of a continuously migrating transform fault similar orthogonal lineations occur at 16 n 107 30 w on the western side of the trace of a 5 m y old propagating spreading center the amplitude and the complexity of the topographic signature over the earlier propagating spreading center are higher and greater than over the presently active center suggesting that the relief of the earlier center may owe its origin to differential subsidence of thermally contrasting segments of lithosphere analogous to fracture zone topography of similar origin traces of former propagating spreading centers are thus a combination of two sets of landforms those resulting from propagation and those resulting from the juxtaposition of two blocks of lithosphere of different thickness

on gregarious behavior in albertosaurusthis article is one of a series of papers published in this special issue on the theme albertosaurus one century ago a field party from the american museum of natural history discovered a bonebed in the upper cretaceous horseshoe canyon formation of alberta canada excavations by that museum th

the orthogonality of subduction an empirical rule abstract measurement of the angle of plate convergence obliquity of subduction along twenty one trench and transform boundaries reveals that the direction of plate convergence is not randomly distributed but rather is strongly bimodal plate convergence is most commonly taken up along a system of strike slip faults and trench segments in which the direction of plate convergence is approximately normal to the trench axis orthogonal subduction slip vectors measured along these trench segments confirm the observation that in general oceanic lithosphere is subducted nearly perpendicular to the trench axis plate boundaries evolve often by forming new plate boundaries in ways that tend to maintain this pattern of orthogonal subduction

palaeoenvironmental and palaeoclimatic reconstruction of the upper cretaceous late campanian early maastrichtian horseshoe canyon formation alberta canada abstract pedogenic features and geochemical signatures of paleosol profiles exposed in the horseshoe canyon formation hcfm were studied to reconstruct the ancient environments and climates that prevailed at high latitude 60 n in the north american western interior during the late campanian to early maastrichtian eight pedotypes representing hydromorphic moderately drained and well drained paleosols were recognized when considered within their stratigraphic context these paleosols show that palaeoenvironmental and palaeoclimatic changes occurred either gradually between major lithological subdivisions of the hcfm or relatively rapidly within subdivisions hydromorphic paleosols predominant in the coal bearing stratigraphic interval at the base of the hcfm were gradually replaced by well drained paleosols in the overlying coal poor interval while climate remained warm and humid during this change in soil drainage conditions mean annual temperature and precipitation dropped rapidly higher in section shortly prior to the campanian maastrichtian boundary without concomitant lithological or pedological changes a brief return of poorly drained paleosols in the middle of the hcfm coincides with a regional marine transgression drumheller marine tongue well drained palaeoenvironments associated with a warm and dry climate persisted through the upper part of the hcfm until a gradual return to poorly drained conditions and to a warm humid climate occurred at the top of the formation an important decline in turtle diversity through the hcfm previously attributed to climate is shown to coincide instead with changes in soil drainage conditions where aridity landscape instability and migratory barriers possibly acted as secondary limiting factors to faunal recovery

northern east pacific rise magnetic anomaly and bathymetric framework the oceanic crust in the eastern pacific between 7on and 30on and east of 127ow contains a fairly complete history of the spreading centers associated with the east pacific rise since 25 m y b p late oligocene in this paper we have summarized the seafloor spreading magnetic anomaly data and the bathymetric data that reflect the record of this tectonic history the well defined magnetic lineations north of the clarion fracture zone in the mouth of the gulf of california and on the east flank of the east pacific rise epr are carefully examined and used to provide a guide for interpreting the spreading pattern between the clarion and clipperton fracture zones southward of the rivera fracture zone over the mathematician ridge and over the entire epr east of the mathematician ridge between the rivera and siqueiros fracture zones the bathymetric data provide a trace of the fracture zone pattern in each of the above mentioned areas the fracture zone bathymetry and the seafloor spreading magnetic lineations on the epr south of the rivera fracture zone have a distinctive fanning pattern caused by close poles of rotation and plate boundary reorganizations all these data provide a good record of the plate reorganizations in the middle miocene at magnetic anomaly 5a time 12 5 to 11 m y b p in the late miocene at magnetic anomaly 3 4 time 6 5 m y b p and in the pliocene at magnetic anomaly 2 3 time 3 5 m y b p several abandoned spreading centers including the mathematician ridge were left behind as a result of these reorganizations the mathematician ridge is shown to be a set of ridges and trough whose origin is related to the tectonic activity associated with each of the above mentioned reorganizations since anomaly 5a

provenance of the sedimentary rakaia sub terrane torlesse terrane south island new zealand the use of igneous clast compositions to define the source abstract the permian to late triassic rakaia sub terrane part of the torlesse superterrane of the new zealand eastern province is an accretionary complex that comprises an enormous volume of quartzofeldspathic sandstones and mudstones with subsidiary conglomerates plus minor oceanic assemblages the field of provenance analysis has undergone a revolution with the development of single crystal isotope dating techniques using mainly silt to sand sized single mineral grains fine sand and mud may be transported over thousands of kilometres with potential problems for provenance studies reinforcing the need for caution when interpreting provenance evidence from single heavy mineral grains this study focuses on coarser grained rocks notably conglomerates which involve much shorter transport distances and therefore may be used to trace proximal sources a detailed rock sampling programme and geochronological geochemical and sr nd isotope analysis of igneous clasts from four conglomerates boundary creek te moana mckenzie pass and lake hill have broadly characterised the igneous source for the rakaia sub terrane shrimp u pb zircon ages of rakaia sub terrane igneous clasts define three distinct periods of magmatic crystallisation the first period ranges in age from 292 to 243 ma permian to middle triassic with two clusters recognisable a minor early permian one ranging in age from 292 to 277 ma and a major late permian to middle triassic one from 258 to 243 ma all these clasts are confined to the kazanian permian te moana the dorashamian permian mckenzie pass and the carnian late triassic lake hill conglomerates the clasts which are subduction related calc alkaline to high k calc alkaline and metaluminous to peraluminous range in lithology from andesite to rhyolite and their plutonic equivalents many clasts at lake hill have chemical compositions characteristic of partial melts of a source of basaltic composition in equilibrium with amphibole pyroxene garnet adakites indicative of a thick crust in the clast source area the second period comprises carboniferous calc alkaline metaluminous to weakly peraluminous clasts of the permian boundary creek conglomerate ranging in age from 356 to 325 ma the third group consists of two cambrian clasts a monzogranite from te moana c 497 8 ma and a dacite from lake hill c 517 ma geochronology geochemistry and sr nd isotopes of rakaia igneous clasts correlate broadly with those of permian to triassic plutons and volcanics from the amundsen and ross provinces of marie byrd land thus the antarctic sector of the panthalassan margin of gondwana is the probable source for the rakaia sub terranes as opposed to the other postulated sources in eastern australia

crustal age between the clipperton and clarion fracture zones magnetic anomalies of 52 80 ma age have been mapped in the equatorial pacific in a region where they were previously unrecognized these anomalies now at 7 n are best modeled with crustal rocks of negative inclination apparently because the crust was formed at a spreading ridge that was south of the magnetic equator in late cretaceous early tertiary time magnetic anomalies recorded along a 5900 km trackline that follows a flowline of crustal generation show one long period from 12 to 31 ma of apparent constant half spreading rate over the 0 to 80 ma represented

gravity and structure of the continental margins of southwestern mexico and northwestern guatemala geophysical measurements over the eastern end of the tehuantepec ridge and adjacent continental margins of southern mexico and northern guatemala indicate that the ridge is a fracture zone and that it marks the boundary between two different subduction provinces a positive free air gravity anomaly which extends northwestward along the outer continental shelf of guatemala curves abruptly landward in the gulf of tehuantepec the positive shelf anomaly is on trend with the positive anomaly of the nicoya peninsula costa rica and suggests that rocks genetically related to cretaceous rocks of the nicoya complex extend northwestward along the continental shelf to the gulf of tehuantepec a crustal and subcrustal cross section of the continental margin of guatemala constrained by gravity magnetic and seismic refraction data indicates that the rock strata causing the outer shelf gravity high dip landward consistent with imbricate thrusting of the oceanic crust beneath and into the continental margin a model crustal cross section of the continental margin of southern mexico north of the tehuantepec ridge shows a markedly different margin structure with a relatively small amount of continental accretion and a continental crustal block extending to within approximately 25 km of the trench axis

three dimensional seismic imaging of the costa rica accretionary prism structural diversity in a small volume of the lower slope conventional two dimensional seismic reflection investigations have been generally relied upon to provide images of large to medium scale structural features in accretionary prisms we undertook a three dimensional seismic reflection survey of a small part of a prism arcward of the middle america trench off costa rica to more correctly image structure and to use the improved structural information to examine the processes of accretion this survey reveals small features with dimensions of hundreds of meters while also defining features thousands of meters in lateral extent both of which were underappreciated in conventional two dimensional data from the same area we have imaged active off scraping at the trench and both duplexing and out of sequence faulting a few kilometers arcward of the trench fault spacing and reflector geometry vary dramatically over a space of several hundred meters some of these variations are related to visible changes in morphology of the underlying oceanic basement but others are not so easily documented fault surface reflections define an architecture which may control gross fluid motion through the prism this architecture is apparently formed by duplexing and out of sequence faulting and has been maintained by periodic motion on some of the out of sequence faults the slope sediment apron records multiple phases of deformation abundant small offset reverse faults break the seafloor and indicate recent shortening of a broad region of the underlying prism a primary result of this survey is appreciation of the structural diversity across a small width of an accretionary prism

taphonomy of the danek bonebed a monodominant edmontosaurus hadrosauridae bonebed from the horseshoe canyon formation alberta the danek bonebed horsethief member horseshoe canyon formation late campanian is dominated by the remains of at least 12 edmontosaurus regalis skeletal remains of a tyrannosaurid and ceratopsid are also known the predominantly disarticulated remains were interred on a periodically inundated floodplain and although the cause of death is unknown a sudden catastrophic death explains the demographic spread faunal diversity rare greenstick fractures and homogeneous weathering abrasion categories of the assemblage the danek bonebed shares a similar taphonomic signature to the liscomb bonebed prince creek formation alaska but it is unique among all other described hadrosaurid bonebeds in the unusually high proportion of bite marked bones 30 suggesting scavenging played a major role in the reworking of the assemblage the highest frequency of bite marks is found on small often unidentifiable and commonly ignored bone fragments underscoring the role that such fragments can play in taphono

evidence for geomagnetic excursions recorded in brunhes and matuyama chron lavas from the trans mexican volcanic belt 1 this study presents paleomagnetic data from 59 independent lava flows from the trans mexican volcanic belt tmvb with ages from 6 4 ma to recent 52 being younger than 1 ma and 11 new 40ar 39ar age determinations most remanence carriers are ti poor titanomagnetite of pseudosingle domain magnetic structure nine lavas contain small amounts of titanomaghemite and four lavas additional titano hematite paleosecular variation of lava flows younger than 1 7 ma is consistent with latitude dependent model g and also in agreement with other pleistocene paleomagnetic data from the tmvb the directional record of brunhes and matuyama chrons lavas was correlated to the geomagnetic polarity timescale and there is evidence for at least four geomagnetic excursions one lava flow dated at 592 20 ka has a fully reversed paleodirection and most likely erupted during the big lost excursion another fully reversed flow dated at 671 12 ka gives new volcanic evidence for the delta stage 17 excursion this excursion is supported by a reversed intermediate direction of another flow from a different volcanic field but of very close age of 673 10 ka from the matuyama age lavas one flow with normal polarity magnetization dated at 949 37 ka could either be related to the kamikatsura or the santa rosa excursion and a normal polarity flow dated at 1628 56 ka could have been emplaced during the gilsa excursion the results presented here confirm in one case but disagree in four cases with results presented in two previous studies of the same lava flows and interpreted as geomagnetic excursions

dinosaur biostratigraphy of the edmonton group upper cretaceous alberta canada evidence for climate influence a high resolution biostratigraphic analysis of 287 dinosaurian macrofossils and 138 bonebeds in the edmonton group upper cretaceous of southern alberta provides evidence for at least three dinosa

stratigraphy of the danek bonebed upper cretaceous horseshoe canyon formation central alberta and correlations with strata in the drumheller and grande prairie regions although considerable work has been conducted on the stratigraphy and dinosaur assemblages of the horseshoe canyon formation of southern alberta equivalent strata and assemblages in central alberta remain poorly understood data from the danek bonebed edmonton alberta are beginning to fill this gap the bonebed occurs 4 m above the 9 big island coal seam this stratigraphic position lies just below the middle of the horseshoe canyon formation in the edmonton region and also lies below a thick stratigraphically significant non coaly interval that is expressed throughout central and southern alberta the stratigraphic position of the danek bonebed equates best with the uppermost horsethief member of the horseshoe canyon formation in the drumheller region and the upper part of unit 4 of the wapiti formation in the grande prairie region in both drumheller and grande prairie the correlated position of the bonebed underlies a zone of marine transgression drumheller marine tongue which in turn incl

the danek edmontosaurus bonebed new insights on the systematics biogeography and palaeoecology of late cretaceous dinosaur communities1 vertebrate bonebeds are rich sources of palaeontological information throughout the world rogers et al 2007 and they have long been sources of information on dinosaur anatomy behaviour ecology growth and variability although dinosaur dominated bonebeds have been known in alberta for a long time brown 1919 sternberg 1970 they received relatively little attention during the first seven decades that dinosaurs were collected in the province this was primarily because collectors came to alberta for the relatively common well preserved articulated dinosaur skeletons that produced both new species and spectacular museum displays currie 1981 1987 since the beginning of the 1980s the dinosaur bonebeds of dinosaur provincial park have received considerable attention currie and dodson 1984 visser 1986 ryan 1992 andersen 2000 ryan et al 2001 ryan 2003 ryan and russell 2005 eberth and getty 2005 however younger bonebeds from farther north in the province have enjoyed less attention ryan et al 1995 1998 2011 eberth et al 2013 two notable exceptions are the albertosaurus bonebed near dry island buffalo jump provincial park currie and koppelhus 2010 and the pachyrhinosaurus lakustai bonebed along pipestone creek near grande prairie currie et al 2008 in and around edmonton in particular dinosaur remains have been largely ignored in the published literature bell and campione 2014 despite easy access to outcrops along the north saskatchewan river and its associated streams and creeks this special issue of the canadian journal of earth sciences increases our knowledge of edmonton s urban dinosaurs especially the iconic and serendipitously named hadrosaurid

trench parallel fluid flow in subduction zones resulting from temperature differences differences in the thermal state of subducting crust along the trench of a subduction zone cause differences in subduction zone temperature that persist to tens of kilometers down dip of the trench the resulting differences in fluid viscosity permeability and hydraulic conductivity can lead to trench parallel variations in fluid pressure on the plate boundary fault temperature differences in locations with low decollement temperature 75 c at the trench result in large differences in fluid viscosity and fluid flow from the cold to the hot side of the system margins characterized by high decollement temperature at the trench are probably dominated by temperature controlled differences in intrinsic permeability resulting in fluid flow from the hot to the cold side of the system margins with large trench parallel temperature differences support considerable trench parallel fluid flow and the effect is accentuated for cases where compaction driven dewatering is concentrated near the trench type locations for along strike hydrologic differences include margins with subducting crust with differences in plate age along the trench or patchy hydrothermal circulation in such cases the three dimensional pattern of subduction zone fluid flow should be considered when inferring the location of the source of fluids sampled from boreholes or seeps additionally trench parallel differences in fluid pressure control effective stress on the plate boundary fault reduced effective stress on the plate boundary on the low hydraulic conductivity side of a subduction zone reduces the effective friction coefficient which both reduces frictional heating and may delay the onset of frictional instability

a revised life table and survivorship curve for albertosaurus sarcophagus based on the dry island mass death assemblagethis article is one of a series of papers published in this special issue on the theme albertosaurus in 1910 a crew from the american museum of natural history discovered a bone bed composed primarily of the large tyrannosaurid albertosaurus sarcophagus in what is now dry island buffalo jump provincial park in alberta canada study of the remains from the site allowed the first life table and survivorship curve for a non avian dinosaur to be created these have served as a model for subsequent studies of dinosaurian population biology since 2006 the discovery and preparation of hundreds of new elements from the bone bed stand to substantially increase the minimum number of individuals mni represented this would allow testing of previous conclusions regarding the population biology of these animals and refinement of our understanding of the patterns of survivorship here four formerly unrecognized individuals from the dry island assemblage are revealed and a revised life table presented as in the previous analysis a left skewed age distribution and sigmoidal survivorship pattern were found annua

the memory of the accreting plate boundary and the continuity of fracture zones a detailed aeromagnetic anomaly map of the mesozoic seafloor spreading lineations southwest of bermuda reveals the dominant magnetic grain of the oceanic crust and the character of the accreting boundary at the time of crustal formation the magnetic anomaly pattern is that of a series of elongate lobes perpendicular to the fracture zone flowline trends the linear sets of magnetic anomaly peaks and troughs have narrow regions of reduced amplitude anomalies associated with the fracture zones during the period of mesozoic geomagnetic polarity reversals when 1200 km of central north atlantic seafloor formed the atlantic accreting boundary consisted of stationary elongate spreading center cells that maintained their independence even though sometimes only minor spatial offsets existed between cells normal oceanic crustal structure was formed in the spreading center cells but structural anomalies and discontinuities characteristic of fracture zones were formed at their boundaries which parallel flowlines of mesozoic relative plate motion in the central north atlantic we suggest that the memory for a stationary pattern of independent spreading center cells resides in the young brittle lithosphere at the accreting boundary where the lithosphere is weakest here each spreading center cell independently goes through its cylce of stress buildup stress release and crustal accretion after which its memory is refreshed the temporal offset between the peaks of the accretionary activity that takes place within each cell may provide the mechanism for maintaining the independence of adjacent spreading center cells through times when no spatial offset between the cells exists

a new centrosaurine ceratopsid from the oldman formation of alberta and its implications for centrosaurine taxonomy and systematics centrosaurus brinkmani sp nov is distinguished from centrosaurus apertus by key features of its cranial ornamentation including the shape and orientation of the postorbital horn and parietal ornamentation at parietal locus 3 the shape of the parietal ornamentation at locus 2 and the possession of accessory parietal ossifications developed as short spines on the caudal parietal ramus this species is restricted to the oldman formation of southern alberta and is the oldest ceratopsid represented by diagnostic material in canada phylogenetic analysis of the centrosaurinae suggests that the development of spike like ornamentation at the parietal locus 3 parietal locus is inversely related to the development of the p1 parietal ornamentation

comparison of a stochastic seafloor model with seamarc ii bathymetry and sea beam data near the east pacific rise 13 15 n a recent seamarc ii survey along the hanks and crest of the east pacific rise between 13 and 15 n edwards et al 1988 provides us with a unique opportunity to compare stochastic models of the seafloor against bathymetric data stochastic models can be used to quantitatively characterize intermediate to small scale 100 km seafloor features such as abyssal hills in a recent paper goff and jordan 1988 introduced a model for the two point covariance function having five free parameters which describe the amplitude orientation characteristic wavelengths and hausdorff fractal dimension of seafloor topography these parameters can be estimated from multibeam data such as sea beam by inverting auto and cross covariance functions for the beams the stochastic model can be used to generate synthetic topography to arbitrary resolution and scale by assuming appropriate sea beam noise and response characteristics we can use the synthetic topography to produce synthetic data sets comparison of real and synthetic data is an important means of assessing the performance of the stochastic model unfortunately the limited spatial extent of sea beam in the across track direction and lack of 100 coverage over large areas severely limit our ability to compare the full two dimensional stochastic model with real seafloor morphology especially with respect to abyssal hill length characteristics the recent seamarc ii survey included sufficient off axis topography over 100 km 70 000 km2 to permit a comparison of a complete two dimensional synthetic topographic field with a region of abyssal hill terrain that has close to 100 data coverage we have estimated stochastic models for various regions of the seamarc ii survey area from several sea beam tracks which cross it synthetic fields are generated from these models using a fourier method these comparisons indicate the extent to which the model succeeds in characterizing seafloor topography and the directions we will need to take to improve our modeling a change in ridge complexity at 14 n and the location of a propagator pseudofault appear to be correlated with changes in stochastic character modeled in this region such correlations may provide important new constraints on the understanding of ridge processes

apparent polar wander of the mean lithosphere reference frame summary apparent polar wander in the mean lithosphere no net rotation no net torque uniform drag reference frame is compared with apparent polar wander in the hotspot reference frame over the past 100 myr palaeomagnetic poles and plate rotations previously used to determine an apparent polar wander path for the hotspot reference frame are here used to determine an apparent polar wander path in the mean lithosphere reference frame we find that the two paths are similar especially for late cretaceous time when a 10 20 shift of the pole occurred to first order the hotspots and lithosphere as a whole moved in unison relative to the palaeomagnetic axis during late cretaceous time a non dipole field explanation for the apparent shift can probably be excluded however either motion of the time averaged geomagnetic axis relative to the spin axis or polar wandering could have caused this shift the latter being the more likely explanation

marine tectonics processes at mid ocean ridges the use of multibeam echo sounders and various side looking sonar systems has greatly increased our knowledge and understanding of mid ocean ridge mor processes since the last iugg review on mid ocean ridge research macdonald 1983 the extensive use of swath mapping tools such as sea beam deep tow seamarc i and ii the application of multichannel seismic reflection techniques to the detection of axial magma chambers and the use of satellite data in the study of oceanic lithosphere have rejuvenated marine tectonics and have generated and stimulated a large number of important contributions this review will focus on what we feel were the major developments in marine tectonics with an emphasis on mid ocean ridges in the last four years certain topics such as marine seismicity and satellite studies are only briefly mentionned for reference and will be covered in greater detail in other reviews because of the exponential growth in the number of publications related to mors during 1982 1986 only a few references pertinent to each of the major research topics will be quoted in the text as examples but the reader will find an extensive bibliography at the end of the text references published prior to 1982 were added only where appropriate

intraslab seismicity and thermal stress in the subducted cocos plate beneath central mexico we present a model of the subducting cocos slab beneath central mexico that provides an explanation for stresses causing the occurrence of the majority of the intraslab earthquakes which are concentrated in a long flat segment based on the recently developed thermal models for the central mexico subduction zone the thermal stresses due to non uniform temperature contrast in the subducting slab are calculated using a finite element approach the slab is considered purely elastic but due to high temperature at its bottom the behavior is considered as ductile creep the calculation results show a 20 km slab core characterized by a tensional state of stress with stresses up to 70 mpa on the other hand the top of the slab experiences high compressive thermal stresses up to 110 mpa depending on the elastic constants used and location along the flat part of the subducting plate these compressive stresses at the top of the slab are not consistent with the exclusive normal fault intraslab earthquakes and two different sources of stress are proposed the trenchward migration of the mexican volcanic arc for the last 7 ma indicates an increase of the slab dip through time this observation suggests that the gravity torque might exceed the suction torque considering the flat slab as an embedded plate subject to an applied clockwise net torque of 0 5 10 16 1 5 10 16 n m the upper half would exhibit tensional stresses of 40 110 mpa that can actually balance the compressive thermally induced stresses an alternative stress source might come from the slab pull force caused by the slab positive density anomaly based on our density anomaly estimations 75 20 kg m 3 a 350 km slab length dipping at 20 into the asthenosphere induces a slab pull force of 1 7 10 12 4 6 10 12 n m this force produces a tensional stress of 41 114 mpa sufficient to balance the compressive thermal stresses at the top of the flat slab the linear superposition of the thermally and torque or slab pull induced stresses shows tensile stresses up to 60 180 mpa inside the flat slab core also our results suggest that the majority of the intraslab earthquakes inside the flat slab are situated where the resultant stresses are larger than 40 80 mpa this study provides a reasonable explanation for the existence of exclusively normal fault intraslab earthquakes in the flat slab beneath central mexico and also it shows that thermal stresses due to non uniform reheating of subducting slabs play a considerable role in the total stress field

palaeopathological changes in a population of albertosaurus sarcophagus from the upper cretaceous horseshoe canyon formation of alberta canadathis article is one of a series of papers published in this special issue on the theme albertosaurus over the past decade excavations of a monodominant theropod bonebed from the lower maastrichtian beds of the horseshoe canyon formation have recovered a minimum number of 26 individuals of the tyrannosaur albertosaurus sarcophagus examination of skeletal elements from the bonebed revealed a small number of abnormalities from at least two individuals these include bony spurs enthesophytes of unknown origin on three pedal phalanges well healed fracture calluses are present on two rib shafts and a gastralia element the left dentary of one adult preserves both healed and unhealed parallel bite marks and a perforative lesion attributable to a partially healed mechanically induced puncture wound unfortunately the limited range in the types and frequencies of pathological changes provides only little information on the distribution of such phenomena but may be suggestive of the overall health of the population

hadrosaurid and lambeosaurid bone beds from the upper cretaceous two medicine formation of montana taphonomic and biologic implications numerous dinosaur bone beds have been found in the upper cretaceous two medicine formation taphonomy and size frequency profiles for the most common skeletal elements of six predominantly hadrosaurid and or lambeosaurid assemblages were compared all six localities are single highly concentrated bone horizons within silty mudstones most are monospecific with some degree of skeletal association parautochthonous and likely the result of mass mortality four are associated with small lacustrine or waterhole environments and may be the result of drought related mortality within the two medicine formation drought was apparently a common mechanism for generating fossil assemblages both hadrosaurids and lambeosaurids appear to have been gregarious lack of association between small total length 3 m and larger individuals suggests either that juvenile growth rates were as rapid as large ungulates or less likely that juveniles had a period of noninteraction with adults perhaps dwelling in strictly ju

a taxonomic assessment of the type series of albertosaurus sarcophagus and the identity of tyrannosauridae dinosauria coelurosauria in the albertosaurus bonebed from the horseshoe canyon formation campanian maastrichtian late cretaceous the type series of albertosaurus sarcophagus consisting of a type cmn 5600 and a paratype cmn 5601 is inadequately established since it has not been demonstrated that the specimens represent the same taxon this problem has arisen because the original diagnostic characters have a wider distribution among tyrannosauridae or they are in error and both specimens consist of incomplete and damaged skulls the type series was studied to test for the presence of diagnostic characters in the type specimen and if so to provide a rationale for referring the paratype to the taxon of the bones shared between the skulls only five could be compared one character the enlarged posterior pneumatic recess of the palatine is shared between the two specimens this condition differs from the situation seen in other tyrannosaurids this character provided the rationale for assessing the identity of the specimens collected from the albertosaurus bonebed from which one palatine was collected that exhibits the diag

taphonomy of debris flow hosted dinosaur bonebeds at dalton wells utah lower cretaceous cedar mountain formation usa abstract a taphonomic study of the lower cretaceous dalton wells dw dinosaur bonebeds near moab utah provides insight into the origins preservational biases and paleobiological significance of one of the richest and most diverse early cretaceous dinosaur sites known the bonebeds occur in a stacked succession of debris flows at the base of the yellow cat member of the cedar mountain formation which was deposited in a seasonally dry alluvial lacustrine setting although only 5 of the locality has been collected more than 4200 bones were recovered representing an assemblage overwhelmingly dominated by dinosaurs with a minimum of 67 individuals that represent at least eight genera the assemblage also includes eight elements from four non dinosaurian reptiles the dinosaur fauna is sauropod dominated mni minimum number of individuals 41 a basal macronarian mni 15 venenosaurus mni 3 a camarasaurid mni 2 and a large number mni 21 of generically unassigned sauropod elements other dinosaurs include the theropods utahraptor mni 9 nedcolbertia mni 2 a possible ornithomimid mni 2 plus a large iguanodontid mni 4 and the ankylosaurid gastonia mni 9 patterns of skeletal articulation and clustering ontogenetic representation and bone surface modification indicate that the assemblage accumulated and was exposed for more than a year as the result one or more multiple mass mortality events likely droughts that culled large numbers of subadults from the biocoenose carcasses and disarticulated elements were reworked then later transported a short distance and buried by a succession of debris flows skeletal representation data patterns of sorting breakage burrows abrasion and scratch marks provide evidence for sorting trampling and scavenging prior to debris flow reworking pre debris flow sorting is attributed to earlier hydraulic winnowing of easily transported elements the intensity and thoroughness of breakage involving 97 of the elements suggest highly focused high load impacts compatible with trampling by sauropods and iguanodontids lightly abraded and vertically displaced elements indicate episodes of trampling in soft mud trampling occurred before and after debris flow transport theropod tooth marks are uncommon but bone scavenging by osteophagous insects was common and severe resulting in substantial damage to articular surfaces comparisons of dw and other debris flow hosted bonebeds indicate that there are few consistent patterns among fossil assemblage and bone modification data however there are numerous similarities in the geological and spatial taphonomy datasets from these sites resulting from the similar physico hydraulic conditions under which elements were transported reworked and buried geologically and taphonomically dalton wells is similar to the blagoveshchensk monodominant hadrosaur bonebed in the udurchukan formation of eastern russia which also is interpreted as a debris flow hyperconcentrated flow deposit dalton wells also shares geologic and taphonomic characteristics with four bonebeds southeast of the town of green river utah and all occur at the base of the yellow cat member the uniform stratigraphic occurrences of the dalton wells blagoveshchensk and the green river sites resting on an unconformity and their shared sedimentologic and taphonomic features indicate that these sites originated in response to similar tectonic depositional and biostratinomic factors

volcanic eruption of the mid ocean ridge along the east pacific rise crest at 9 45 52 n direct submersible observations of seafloor phenomena associated with an eruption event in april 1991 in april 1991 we witnessed from the submersible alvin a suite of previously undocumented seafloor phenomena accompanying an in progress eruption of the mid ocean ridge on the east pacific rise crest at 9 45 n 52 n the volume of the eruption could not be precisely determined although comparison of pre and post eruption seabeam bathymetry indicate that any changes in ridge crest morphology resulting from the eruption were 10 m high effects of the eruption included 1 increased abundance and redistribution of hydrothermal vents disappearance of numerous vent communities and changes in characteristics of vent fauna and mineral deposits within the eruption area since december 1989 2 murkiness of bottom waters up to tens of meters above the seafloor due to high densities of suspended mineral and biogenic particulates 3 destruction of a vent community by lava flows mass wasting and possible hydrovolcanic explosion at a site known as tubeworm barbecue in the axial summit caldera asc at 9 50 6 n 4 near critical temperatures of hydrothermal vent fluids ranging up to 403 c 5 temporal variations over a 2 week interval in both temperatures and chemical isotopic compositions of hydrothermal fluids 6 unusual compositions of end member vent fluids with ph values ranging to a record low of 2 5 salinities ranging as low as 0 3 wt nacl one twelfth that of seawater and dissolved gases reaching high concentrations 65 mmol l for both co2 and h2s 7 venting at temperatures above 380 c of visually detectable white vapor that transformed to plumes of gray smoke a few centimeters above vent orifices 8 disorganized venting of both high temperature fluids black and gray smoke and large volumes of cooler diffuse hydrothermal fluids directly from the basaltic seafloor rather than from hydrothermal mineral constructions 9 rapid and extensive growth of flocculent white bacterial mats species unknown on and under the seafloor in areas experiencing widespread venting of diffuse hydrothermal fluid and 10 subseafloor downslope migration of magma normal to the ridge axis in a network of small scale 1 5 m diameter lava tubes and channels to distances at least 100 200 m outside the asc we suggest that in april 1991 intrusion of dikes in the eruption area to 200 m beneath the asc floor resulted in phase separation of fluids near the tops of the dikes and a large flux of vapor rich hydrothermal fluids through the overlying rubbly cavernous lavas low salinities and gas rich compositions of hydrothermal fluids sampled in the eruption area are appropriate for a vapor phase in a seawater system undergoing subcritical liquid vapor phase separation boiling and phase segregation hydrothermal fluids streamed directly from fissures and pits that may have been loci of lava drainback and or hydrovolcanic explosions these fissures and pits were lined with white mats of a unique fast growing bacteria that was the only life associated with the brand new vents the prolific bacteria which covered thousands of square meters on the ridge crest and were also abundant in subseafloor voids may thrive on high levels of gases in the vapor rich hydrothermal fluids initially escaping the hydrothermal system white bacterial particulates swept from the seafloor by hydrothermal vents swirled in an unprecedented biogenic blizzard up to 50 m above the bottom the bacterial proliferation of april 1991 is likely to be a transient bloom that will be checked quickly either by decline of dissolved gas concentrations in the fluids as rapid heat loss brings about cessation of boiling and or by grazing as other organisms are re established in the biologically devastated area

gabbroic rocks from the mathematician ridge failed rift plutonic rocks from the ocean crust provide direct evidence on the petrological processes leading to its formation and evolution the nature of such rocks is important for interpreting the origin of on land ophiolites so far oceanic plutonic rocks have been mainly recovered from slow spreading ridges and their associated fractures1 13 and from trenches14 15 here we report the results of petrological studies of a suite of gabbros and related plutonic and volcanic rocks dredged from the mathematician ridge mr which was a fast spreading ridge 43 mm yr 1 until it was abandoned 3 5 myr ago16 textures and mineral chemistry of the rocks together with structural considerations indicate that before abandonment the mr produced fractionated mid ocean ridge basalt morb and fractionated gabbros the gradual decrease of spreading rate during abandonment resulted in morphological change eruption of more primitive morb and possibly tectonic emplacement of the older ferrogabbros alternatively the latter could have been tectonically emplaced after abandonment

motion of the rivera plate since 10 ma relative to the pacific and north american plates and the mantle abstract to better understand the influence of rivera plate kinematics on the geodynamic evolution of western mexico we use more than 1400 crossings of seafloor spreading magnetic lineations along the pacific rivera rise and northern mathematician ridge to solve for rotations of the rivera plate relative to the underlying mantle and the pacific and north american plates at 14 times since 9 9 ma our comparison of magnetic anomaly crossings from the undeformed pacific plate to their counterparts on the rivera plate indicates that significant areas of the rivera plate have deformed since 9 9 ma dextral shear along the southern edge of the plate from 3 3 2 2 ma during a regional plate boundary reorganization deformed the rivera plate farther into its interior than previously recognized in addition seafloor located north of two rupture zones within the rivera plate sutured to north america after 1 5 ma anomaly crossings from these two deformed regions thus cannot be used to reconstruct motion of the rivera plate finite rotations that best reconstruct pacific plate anomaly crossings onto their undeformed counterparts on the rivera plate yield stage spreading rates that decrease gradually by 10 between 10 and 3 6 ma decrease rapidly by 20 after 3 6 ma and recover after 1 ma the slowdown in pacific rivera seafloor spreading at 3 6 ma coincided with the onset of dextral shear across the then incipient southern boundary of the rivera plate with the pacific plate the available evidence indicates that the rivera plate has been an independent microplate since at least 10 ma contrary to published assertions that it fragmented from the cocos plate at 5 ma motion of the rivera plate relative to north america has changed significantly since 10 ma in concert with significant changes in pacific rivera motion a significant and robust feature of rivera north america motion not previously recognized is the cessation of margin normal convergence and thus subduction from 2 6 to 1 0 ma along the entire plate boundary followed by a resumption of trench normal subduction along the southern half of the rivera north america plate boundary after 1 0 ma motion of the rivera plate relative to the underlying mantle since 10 ma has oscillated between periods of landward motion and seaward motion the evidence suggests that the torque exerted by slab pull on this young and hot oceanic plate is either minimal or is effectively counterbalanced by forces that resist its motion

fluvial sequence stratigraphy the wapiti formation west central alberta canada abstract outcrop exposures and high resolution subcrop data allow the description and mapping of four stratigraphic discontinuities in the fully nonmarine strata of the campanian maastrichtian wapiti formation western interior foreland basin alberta canada this framework defines four unconformity bounded depositional sequences a d based on sequence stratigraphic methodology well log patterns and facies analysis in ascending order sequence a records the transition from the underlying marine facies of the puskwaskau formation into the wapiti fluvial facies and consists of strongly progradational and aggradational stacking patterns sequences b and c show a similar pattern of basal amalgamated channel fill deposits that grade upwards into floodplain dominated strata finally sequence d is dominated by channelized sediments and extensive overbank facies an aggradational stacking pattern suggests deposition under high accommodation conditions maximum flooding surfaces are interpreted within fine grained deposits in the upper portions of sequences c and d they are tied to regionally extensive coals that accumulated more than 250 km away from the coeval shoreline this study provides new evidence that major coal seams may represent the extension of marine maximum flooding surfaces into the downstream controlled fluvial realm furthermore the new stratigraphic framework of subaerial unconformities and maximum flooding surfaces provides the means of subdividing the previously undifferentiated fully nonmarine wapiti formation into depositional sequences and component systems tracts

taphonomy age and paleoecological implication of a new pachyrhinosaurus dinosauria ceratopsidae bonebed from the upper cretaceous campanian wapiti formation of alberta canada the grande prairie region alberta canada includes some of the richest cretaceous fossil sites in north america including the recently described bonebed of pachyrhinosaurus lakustai at the pipes

source characteristics of hypothetical subduction earthquakes in the northwestern united states historic earthquake sequences on subduction zones that are similar to the cascadia subduction zone are used to hypothesize the nature of shallow subduction earthquakes that might occur in the northwestern united states based on systematic comparisons of several physical characteristics including physiography and seismicity subduction zones that are deemed most similar to the cascadia subduction zone are those in southern chile southwestern japan and colombia these zones have all experienced very large earthquake sequences and if the cascadia subduction zone is also capable of storing elastic strain energy along its greater than 1000 km length then earthquakes of very large size m w 8 1 2 must be considered circumstantial evidence is presented that suggests but does not prove that large subduction earthquakes along the cascadia subduction zone may have an average repeat time of 400 to 500 yr

geophysical study of the east pacific rise 15 n 17 n an unusually robust segment bathymetric side scan sonar magnetic and gravity data from the east pacific rise epr between 15 and 17 n are used to establish the spreading history and examine melt delivery to an unusually robust spreading segment the axial ridge between the orozco transform fault 15 30 n and the 16 20 n overlapping spreading center osc has an average elevation of 2300 m which is 300 m shallower than typical epr depths and its cross sectional area is double the average value for the northern epr the total opening rate is 86 km myr but the inflated segment appears to have spread faster to the east by more than 20 since 0 78 ma the orientation of magnetic isochrons and lineaments in the side scan sonar indicates a 3 counterclockwise rotation of the spreading direction since 1 8 ma c2 and reflects a change in the pacific cocos plate motion the side scan lineaments also show that the percentage of inward facing faults 83 and the spacing between faults 1 5 km are consistent with the spreading rate dependence shown by carbotte and macdonald 1994 however the mean fault length 4 8 km is 1 5 km shorter than expected for the spreading rate and suggests that extensive off axis volcanism has draped the faults gravity analysis shows that the inflated segment has a 12 mgal bull s eye shaped low in residual mantle bouguer anomaly we offer several possible end member models for the anomaly including a prism of 10 partial melt in the mantle and lower crust or a crustal thickness anomaly of 2 25 km kinematic modeling that is based on structure and magnetic data suggests that two large magmatic pulses occurred at approximately 0 8 ma and 0 3 ma and have reshaped the plate boundary geometry and inflated the segment

transport induced abrasion of fossil reptilian teeth implications for the existence of tertiary dinosaurs in the hell creek formation montana the experimental transport induced abrasion of five fossil teeth from a crocodilian and the tyrannosaurid dinosaur albertosaurus demonstrates that enamel coated teeth are minimally affected by abrasion associated with sediment transport processes after the equivalent of 360 480 km of transport two teeth showed slight loss of weight scratches were developed on the surface of one tooth there were slight enlargements of the areas between adjacent serrations of one tooth and a pit in the exposed dentine of one tooth was abraded smooth these changes would have been difficult to recognize if the teeth had not been examined before the start of the experiment our results suggest that dinosaur teeth are abraded so slowly by transport processes that they provide equivocal evidence for limited transport and reworking

analysis of marrow cavity fillings as a tool to recognise diverse taphonomic histories of fossil reptile bones implications for the genesis of the lower muschelkalk marine bone bearing bed middle triassic żyglin s poland abstract the bone bearing bed from yglin s poland which likely represents the oldest lower muschelkalk accumulation of reptile remains in the se part of the germanic basin has been investigated in order to determine its genesis the basic methods were supported by petrographic analysis of the marrow cavity and large inter trabecular pore space fillings of fossil bones which was used to check its usefulness to identify the environments where the bones were initially deposited and to decipher taphonomic histories of the remains the bone bearing bed is a composite deposit which consists of three distinct layers from bottom to top micritic limestone mudstone bioturbated autochthonous mud crinoidal limestone grainstone to packstone calcirudite and shell rich limestone packstone to wackstone calcirudite the crinoidal limestone layer the main bone bearing bed is recognised as the proximal tempestite deposited in the mid ramp zone the petrographic analysis of the fillings reveals the prevalence of minute ostracod carapaces accompanied by other grains embedded together with micrite to microspar such compositions suggest that these sediments may have been inserted into the bone pore spaces in lagoons and tidal flat ponds features of some bones record their early diagenetic burial and lithification before the final redeposition the isopachous spar blocky spar and weathered pyrite document changes in the chemical composition of fluids that flowed into the bone interiors the burrow found in the marrow cavity of specimen iguam zov 7 provides evidence that some remains were inhabited by minute or juvenile invertebrates all recognised features indicate that both invertebrate and vertebrate bioclasts included in the tempestite were initially deposited in various settings of the carbonate ramp and in the end redeposited as a result of a heavy storm or a hurricane the examined bone bearing bed represents time averaged assemblage which originated due to hydraulic concentration of the vertebrate bioclasts the petrographic analysis of the fillings is a valuable tool to identify complex taphonomic pathways of vertebrate bioclasts

magma intrusion near volcan tancitaro evidence from seismic analysis abstract between may and june 2006 an earthquake swarm occurred near volcan tancitaro in mexico which was recorded by a temporary seismic deployment known as the mars network we located 1000 events from this seismic swarm previous earthquake swarms in the area were reported in the years 1997 1999 and 2000 we relocate and analyze the evolution and properties of the 2006 earthquake swarm employing a waveform cross correlation based phase repicking technique hypocenters from 911 events were located and divided into eighteen families having a correlation coefficient at or above 0 75 90 of the earthquakes provide at least sixteen phase picks we used the single event location code hypo71 and the p wave velocity model used by the jalisco seismic and accelerometer network to improve hypocenters based on the correlation adjusted phase arrival times we relocated 121 earthquakes which show clearly two clusters between 9 10 km and 3 4 km depth respectively the average location error estimates are

a plate kinematic framework for models of caribbean evolution abstract we define the former relative positions and motions of the plates whose motions have controlled the geological evolution of the caribbean region newly determined poles of rotation defining the approximate spreading histories of the central north and the south atlantic oceans are given for the late jurassic early cretaceous anomaly sequence of the central north atlantic we have used previously published definitions of fracture zone traces and magnetic anomaly picks redetermining the pole positions and angular rotations for various isochrons on an evans and sutherland interactive graphics system for magnetic anomalies younger than the cretaceous quiet period in both oceans we 1 used seasat altimeter data to help define fracture zone traces and 2 identified and used marine magnetic anomalies to determine the positions of spreading isochrons along the flowlines indicated by the fracture zones by the finite difference method the relative paleopositions and the relative motion history between north and south america were computed this analysis defines the size and shape and the rate at which the size and shape changed of the interplate region between north and south america since the middle jurassic thus a plate kinematic framework is provided for the larger plates pertaining to the caribbean region in which can be derived more detailed scenarios for gulf of mexico and caribbean evolution north and south america diverged to approximately their present relative positions from late triassic to early campanian about 84 m y ago time this is the period during which the gulf of mexico and a proto caribbean seaway were formed since the campanian only minor relative motion has occurred from early campanian through to middle eocene times south america diverged only another 200 km and since the middle eocene minor n s convergence has occurred these very minor post early campanian motions have probably been accommodated by imperfect shear and compression along the atlantic fracture zones to the east of the lesser antilles and along the northern and southern borders of the caribbean plate accordingly it is suggested that from campanian time to the present the relative motions between the north and south american plates have had only minor effects on the structural development of the caribbean region primarily using the data of engebretson et al the convergence history of pacific plates with north america was calculated for two points near the western caribbean by completing finite difference solutions the convergence history of the pacific plates with the caribbean and south american plates can be approximated the direction and rate of convergence of the pacific plates with the americas may have controlled the style of subduction and possible microplate migration along the north american south american and western caribbean boundaries that define the eastern pacific plate margin

holocene emerged notches and tectonic uplift along the jalisco coast southwest mexico this paper presents the preliminary results from a study of holocene emerged shorelines marine notches and their tectonic implications along the jalisco coast the pacific coast of jalisco sw mexico is an active tectonic margin this coast has been the site of two of the largest earthquakes to occur in mexico this century the 1932 mw 8 2 jalisco earthquake and the 1995 mw 8 0 colima earthquake measurement and preliminary radiocarbon dating of emergent paleoshorelines along the jalisco coast provide the first constraints upon the timing for tectonic uplift along this coastline uplifted holocene marine notches and wave cut platforms occur at elevations ranging from ca 1 to 4 5 m amsl in situ intertidal organisms dated with radiocarbon the first ever reported for the jalisco area provide preliminary results that record tectonic uplift during at least the past 1300 years bp at an average rate of about 3 mm year we propose a model in which coseismic subsidence produced by offshore earthquakes is rapidly recovered during the postseismic and interseismic periods the long term period is characterized by slow tectonic uplift of the jalisco coast we found no evidence of coastal interseismic and long term subsidence along the jalisco coast