a microearthquake study of the mygdonian graben northern greece during march and april 1984 a temporary network of 29 portable stations was operated in the region of the mygdonian graben near thessaloniki northern greece where a destructive earthquake ms 6 5 had occurred in the summer of 1978 during a period of six weeks we recorded 540 earthquakes with magnitudes ranging from 0 2 to 3 0 from this set of data 254 events are selected which according to us have a precision in epicenter and depth better than 1 5 km a total of 54 single event focal mechanisms have been determined the seismicity and focal mechanisms show a rather complex pattern there are no clear individual faults but the e w and nw se striking zones show n s extension zones striking nne ssw show dextral strike slip motion but nw se zones with sinistral strike slip are also observed in the center of the graben where the 1978 earthquake was located we observe several thrust mechanisms distributed in two groups showing either nw se or e w compression these earthquakes seem to be located 2 km above the earthquakes showing normal mechanisms the mean direction of the t axes found from the focal mechanisms trends n15 and dips sub horizontal we propose a model for the formation and evolution of a complex graben system comprising several stages in the initial stage the deformation occurs along pre existing nw se or nne ssw faults with normal or strike slip movements in the second stage a new e w trending group of normal faults is formed over the ancient fault network these new faults have a direction perpendicular to the mean t axis and accommodate better the actual state of stress at this stage the initial faults adjust to the deformation produced by the e w trending new faults and may constitute geometric barriers to the evolution of the new normal faults

ocean bottom profiling with ambient noise a model for the passive fathometer a model is presented for the complete passive fathometer response to ocean surface noise interfering discrete noise sources and locally uncorrelated noise in an ideal waveguide the leading order term of the ocean surface noise contribution produces the cross correlation of vertical multipaths and yields the depth of sub bottom reflectors discrete noise incident on the array via multipaths give multiple peaks in the fathometer response these peaks may obscure the sub bottom reflections but can be attenuated with use of minimum variance distortionless response mvdr steering vectors the seabed critical angle introduces discontinuities in the spatial distribution of distant surface noise and may introduce spurious peaks in the passive fathometer response these peaks can be attenuated by beamforming within a bandwidth limited by the array geometry and critical angle

the relationship between current and paleo groundwater base levels abstract base levels are basically divided into two categories oceanic and marine base levels and continental terminal endorheic ones the marine domain serves as the ultimate base level for both surface and groundwater drainage systems continental inland depressions very often serve as terminal endorheic base levels to both surface drainage and groundwater systems many of the current both marine and inland base levels served also in the past as paleo base levels fluctuations of base level elevations affect the adjoined groundwater system in several ways such as changes in groundwater levels location of divides depths of fresh saline water interfaces and the amount of flow to the base levels this paper provides examples from many different parts of the world that describe the relationship between current and paleo base levels the examples include marine base levels as well as inland endorheic ones both currently above and below sea level close to and distant from the sea

stratigraphic record of basin development within the san andreas fault system late cenozoic fish creek vallecito basin southern california the fish creek vallecito basin contains a 5 5 km thick section of late miocene to early pleistocene sedimentary rocks exposed in the hanging wall of the west salton detachment fault these deposits preserve a high fidelity record of late cenozoic subsidence and basin filling that resulted from deformation in the san andreas fault system of southern california existing and new paleomagnetic data combined with new u pb zircon ages of two tuffs high in the section show that the section ranges in age from ca 8 0 0 4 ma at the base to ca 0 95 ma at the top geohistory analysis reveals 1 moderate subsidence 0 46 mm yr from ca 8 0 to 4 5 ma 2 rapid subsidence 2 1 mm yr from 4 5 to 3 1 ma 3 moderate subsidence 0 40 mm yr from 3 1 to 0 95 ma and 4 rapid uplift and erosion that has exhumed the section since ca 1 ma onset of sedimentation at ca 8 0 0 4 ma records earliest extension or transtension in the area possibly related to localization of the pacific north america plate boundary in the salton trough and gulf of california alternatively marine incursion at 6 3 ma may be the earliest record of plate boundary deformation in the gulf of california salton trough region a thick interval higher in the section records progradation of the colorado river delta into and across the basin starting ca 4 9 ma progradation continued during an abrupt increase in subsidence rate at 4 5 ma and fluvial deltaic conditions persisted for 1 4 m y during the rapid subsidence phase indicating that delta progradation was driven by a large increase in rate of sediment input from the colorado river uplift and inversion of the basin starting ca 1 0 ma record initiation of strike slip faults that define the modern phase of dextral wrench tectonics in the western salton trough

bayesian ambient noise inversion for geoacoustic uncertainty estimation the noise produced by wind driven breaking waves in shallow water provides a method for probing the seabed and drifting vertical arrays have been deployed for remote sensing of geoacoustic parameters by estimating the frequency and angle dependent reflection coefficients in addition techniques such as spectral factorization allow obtaining the impulse response of the multilayered seabed environment this impulse response carries information of the sediment acoustic properties that can be extracted and passed as prior information to a bayesian framework for the estimation of geoacoustic parameters and its corresponding uncertainties which ultimately determine the resolution of the method the bayesian formulation estimates a joint posterior probability density function from which marginal density functions moments and covariances between geoacoustic parameters of interest can be quantified in this work bayesian inversion based on markov chain monte carlo sampling is applied to simulated ambient n

estimating seabed scattering mechanisms via bayesian model selection a quantitative inversion procedure is developed and applied to determine the dominant scattering mechanism surface roughness and or volume scattering from seabed scattering strength data the classification system is based on trans dimensional bayesian inversion with the deviance information criterion used to select the dominant scattering mechanism scattering is modeled using first order perturbation theory as due to one of three mechanisms interface scattering from a rough seafloor volume scattering from a heterogeneous sediment layer or mixed scattering combining both interface and volume scattering the classification system is applied to six simulated test cases where it correctly identifies the true dominant scattering mechanism as having greater support from the data in five cases the remaining case is indecisive the approach is also applied to measured backscatter strength data where volume scattering is determined as the dominant scattering mechanism comparison of inversion results with core data indicates the method yields both a reasonable volume heterogeneity size distribution and a good estimate of the sub bottom depths at which scatterers occur

the neogene genus streptochilus bronnimann and resig 1971 from the gulf of california abstract four species of the planktonic foraminiferal genus streptochilus from key neogene marine localities are documented in relation to the evolution of the gulf of california s globigerus s latus s macdougallae sp nov and s inglei sp nov planktonic foraminiferal bioevents and strontium isotopes in the bouse tirabuzon carmen and ojo de buey lithostratigraphic units constrain the local distribution range between 6 and 5 3 ma for the last three species whereas s globigerus appears locally at 5 5 ma and disappears between 3 79 and 3 46 ma in the imperial and trinidad formations the last occurrence of streptochilus latus and the first and last occurrences of s globigerus in the ancient gulf of california are correlated with bioevents calibrated in the equatorial pacific therefore they can be used as reliable local biostratigraphic markers the presence of streptochilus in the ancient gulf of california seems to correlate with upwelling in a pattern similar to that observed in the modern oceans

euro seistest determination of the geological structure of the volvi basin and validation of the basin response the volvi basin northern greece is a 5 km wide graben of neogene age it has been chosen by european union directorate general xii for science research and development in climatology and natural hazards as a test site euro seistest for studying site effects in one of europe s most seismic active areas the site is located in the epicentral area of the 1978 ms 6 5 earthquake that struck the city of thessaloniki the geometry velocity and stratigraphy of the basin were not well known consequently a number of geophysical and geotechnical studies were performed to determine the 2d geometry and the dynamic characteristics vp vs qs of the valley investigations included 78 refraction tests 20 surface wave inversions and 8 borehole seismic tests as well as geotechnical tests this article presents the methodology used for the geophysical investigation and the results in its center the graben depth reaches 190 m and at least four normal faults have been located along the section the overall graben structure and the fault locations have been confirmed by the records of a shot generated at one edge of the valley and by the measurements of a local earthquake wave propagation appears to be strongly influenced by the thickness of the sediments which in turn is controlled by fault displacements simple 2d modeling of the basin response was performed and the results are in good agreement with weak motion data confirming the validity of the seismic structure inferred from seismic prospecting

evidence for paleoseismic slip on a continental low angle normal fault tectonic pseudotachylyte from the west salton detachment fault ca usa abstract the potential of continental low angle normal faults lanf to nucleate large 6 0 m w earthquakes at low angles remains unclear despite much focused research we document evidence for ancient seismicity along a continental lanf detachment fault that formed and slipped at low angles and produced tectonic pseudotachylyte these thick and laterally persistent pseudotachylyte accumulations along the west salton detachment fault wsdf salton trough usa preserve convincing evidence for a frictional melt origin including spherulitic microlites ductile flow structures preservation of high temperature phases as clasts and injection veins cumulative thickness of pseudotachylyte along the fault ranges from 0 1 to 1 5 m and pseudotachylyte cataclasite in the fault core and damage zone are exposed along 2 6 km length of the fault reworked fragments of pseudotachylyte in cataclasites and multiple generations of cataclasites provide evidence for the preservation of multiple earthquake cycles the limited exposure

the influence of burial heating on the u th he system in apatite grand canyon case study article history thermochronological data can constrain the cooling paths of rocks exhumed through the uppermost 1 2 km of earth s crust and have thus been pivotal in illuminating topographic development over timescales 0 1 ma however in some cases different methods have led to conflicting conclusions about timing of valley scale exhumation here we investigate the case of western grand canyon usa where different thermochronological datasets have been interpreted to record very different timings of canyon incision 70 ma versus 5 ma we present a method to assess key assumptions in these constraints and demonstrate that burial heating conditions of basement rocks in the mesozoic can result in incomplete annealing of radiation damage in apatite in turn this has a dramatic effect on the temperature sensitivity of the apatite u th he system and its ability to record post burial exhumation the possibility of incomplete annealing resolves the apparent conflict in time temperature paths inferred over the last 70 ma although it requires temperatures during burial that are lower than predicted by apatite fission track data a refinement of parameters that prescribe the kinetics of damage annealing and related control on 4 he diffusivity in apatite would account for this discrepancy specifically if alpha recoil damage anneals at a lower rate than fission tracks at a given temperature these effects will be important for any application of the apatite u th he system in geologic settings that experienced prolonged residence 10 ma between 50 150 c the approaches developed here provide means to assess these effects

tectonic stresses on the mainland of greece in situ measurements by overcoring abstract direct in situ measurements of the horizontal stresses in continental greece indicate a predominantly n s extensive stress considerable scatter of the azimuth of the axis of extension is found in thrace in contrast to a more homogeneous pattern in macedonia and peloponnesus these results are obtained with an overcoring technique in boreholes of a few meters they can be compared with neotectonic and seismic data to evaluate the present deformation process in this basin

particle filtering for passive fathometer tracking seabed interface depths and fathometer amplitudes are tracked for an unknown and changing number of sub bottom reflectors this is achieved by incorporating conventional and adaptive fathometer processors into sequential monte carlo methods for a moving vertical line array sediment layering information and time varying fathometer response amplitudes are tracked by using a multiple model particle filter with an uncertain number of reflectors results are compared to a classical particle filter where the number of reflectors is considered to be known reflector tracking is demonstrated for both conventional and adaptive processing applied to the drifting array data from the boundary 2003 experiment the layering information is successfully tracked by the multiple model particle filter even for noisy fathometer outputs

influence of climate change and uplift on colorado plateau paleotemperatures from carbonate clumped isotope thermometry the elevation history of earth s surface is key to understanding the geodynamic processes responsible for the rise of plateaus we investigate the timing of colorado plateau uplift by estimating depositional temperatures of tertiary lake sediments that blanket the plateau interior and adjacent lowlands using carbonate clumped isotope paleothermometry a measure of the temperature dependent enrichment of 13 c 18 o bonds in carbonates comparison of modern and ancient samples deposited near sea level provides an opportunity to quantify the influence of climate and therefore assess the contribution of changes in elevation to the variations of surface temperature on the plateau analysis of modern lake calcite from 350 to 3300 m elevation in the southwestern united states reveals a lake water carbonate temperature lct lapse rate of 4 2 0 6 c km analysis of miocene deposits from 88 to 1900 m elevation in the colorado river drainage suggests that the ancient lct lapse rate was 4 1 0 7 c km and temperatures were 7 7 2 0 c warmer at any one elevation than predicted by the modern trend the inferred cooling is plausible in light of pliocene temperature estimates off the coast of california and the consistency of lapse rates through time supports the interpretation that there has been little or no elevation change for any of the samples since 6 ma together with previous paleorelief estimates from apatite u th he data from the grand canyon our results suggest most or all of the plateau s lithospheric buoyancy was acquired 80 60 ma and do not support explanations that ascribe most plateau uplift to oligocene or younger disposal of either the farallon or north american mantle lithosphere

6 ma age of carving westernmost grand canyon reconciling geologic data with combined aft u th he and 4he 3he thermochronologic data conflicting hypotheses about the timing of carving of the grand canyon involve either a 70 ma old or 6 ma young grand canyon this paper evaluates the controversial westernmost segment of the grand canyon where the following lines of published evidence firmly favor a young canyon 1 north derived paleocene hindu fanglomerate was deposited across the present track of the westernmost grand canyon which therefore was not present at 55 ma 2 the 19 ma separation point basalt is stranded between high relief side canyons feeding the main stem of the colorado river and was emplaced before these tributaries and the main canyon were incised 3 geomorphic constraints indicate that relief generation in tributaries and on plateaus adjacent to the westernmost grand canyon took place after 17 ma 4 the late miocene pliocene muddy creek formation constraint shows that no river carrying far traveled materials exited at the mouth of the grand canyon until after 6 ma interpretations of previously published low temperature thermochronologic data conflict with these lines of evidence but are reconciled in this paper via the integration of three methods of analyses on the same sample apatite u th he ages ahe 4he 3he thermochronometry 4he 3he and apatite fission track ages and lengths aft hefty software was used to generate time temperature t t paths that predict all new and published 4he 3he ahe and aft data to within assumed uncertainties these t t paths show cooling from 100 c to 40 60 c in the laramide 70 50 ma long term residence at 40 60 c in the mid tertiary 50 10 ma and cooling to near surface temperatures after 10 ma and thus support young incision of the westernmost grand canyon a subset of ahe data when interpreted alone i e without 4he 3he or aft data are better predicted by t t paths that cool to surface temperatures during the laramide consistent with an old grand canyon however the combined aft ahe and 4he 3he analysis of a key sample from separation canyon can only be reconciled by a young canyon additional new aft 5 samples and ahe data 3 samples in several locations along the canyon corridor also support a young canyon this inconsistency which mimics the overall controversy of the age of the grand canyon is reconciled here by optimizing cooling paths so they are most consistent with multiple thermochronometers from the same rocks to do this we adjusted model parameters and uncertainties to account for uncertainty in the rate of radiation damage annealing in these apatites during sedimentary burial and the resulting variations in he retentivity in westernmost grand canyon peak burial conditions temperature and duration during the laramide were likely insufficient to fully anneal radiation damage that accumulated during prolonged near surface residence since the proterozoic we conclude that application of multiple thermochronometers from common rocks reconciles conflicting thermochronologic interpretations and the data presented here are best explained by a young westernmost grand canyon samples spread along the river corridor also suggest the possibility of variable mid tertiary thermal histories beneath north retreating cliffs

how sediment promotes narrow rifting application to the gulf of california 1 if the gravitational stress changes related to crustal thinning are large enough to affect the mode of extension then sedimentation should also affect that mode we propose that the weight of sediments reduces the difference in crustal buoyancy forces caused by local crustal thinning allowing a rift to extend more easily in a narrow rift mode we examine the effect of deposition of large amounts of nonlocally derived sediment on extensional style using two dimensional regional scale numerical experiments of extending thick continental crust with varied initial thermal conditions geometries rheological parameters and sedimentation properties depending on initial model conditions the onset of rifting in thick continental crust occurs in the narrow rifting wide rifting or core complex mode with continued extension all cases eventually transition to a narrow rifting mode for a system in wide rift mode moderate to fast sedimentation shortens the time needed to transition to a narrow rift in the gulf of california changes in extensional style correlate with sediment thickness with an earlier transition to narrow rifting in the north versus the south we compare our model results to the extensional history of the gulf of california where sediments may have caused the northern and north central domain of the gulf delfin tiburon and guaymas segments to transition to narrow rifting before the south central domains alarcon segment

detailed evaluation of site response estimation methods across and along the sedimentary valley of volvi euro seistest using records from the euro seistest area near thessaloniki greece we studied empirically the amplification effects of a sedimentary valley one of the main advantages of this site is the very detailed knowledge of the near subsurface structure due to exhaustive geophysical and geotechnical measurements and data analyses jongmans et al 1998 the uniqueness of the seismological data set is the very dense network 31 stations were installed perpendicular and parallel to the valley axis with minimum interstation distances of 250 m the mean ampli fications along both axes estimated from 13 local events were imaged using the traditional spectral ratio technique variations of the mean amplifications due to the choice of different data subsets were tested by the use of up to 89 local events supplemented by four teleseismic events offering good low frequency resolution results obtained using the traditional spectral ratio technique were compared with results from a generalized inversion technique the h v ratio technique a coda wave technique and nakamura s technique advantages and disadvantages of each method are outlined especially from a practical point of view

pleistocene brawley and ocotillo formations evidence for initial strike slip deformation along the san felipe and san jacinto fault zones southern california abstract we examine the pleistocene tectonic reorganization of the pacific north american plate boundary in the salton trough of southern california with an integrated approach that includes basin analysis magnetostratigraphy and geologic mapping of upper pliocene to pleistocene sedimentary rocks in the san felipe hills these deposits preserve the earliest sedimentary record of movement on the san felipe and san jacinto fault zones that replaced and deactivated the late cenozoic west salton detachment fault sandstone and mudstone of the brawley formation accumulated between 1 1 and 0 6 0 5 ma in a delta on the margin of an arid pleistocene lake which received sediment from alluvial fans of the ocotillo formation to the west southwest our analysis indicates that the ocotillo and brawley formations prograded abruptly to the east northeast across a former mud dominated perennial lake borrego formation at 1 1 ma in response to initiation of the dextral oblique san felipe fault zone the 25 km long

lithosphere thickness in the gulf of california region abstract the gulf of california has a long tectonic history before the subduction of the guadalupe and magdalena plates ceased extension of the gulf began to the east at the basin and range province later it was focused west of the sierra madre occidental and the opening of the gulf started currently the gulf rifting has different characteristics to the north than to the south in this study we analyze the lithosphere thickness in the gulf of california region by means of p wave and s wave receiver functions we grouped our lithosphere thickness estimates into five froups 1 north of the gulf with a thin lithosphere 50 km related to the extension observed in the salton through region 2 the northwestern part of baja california with a thicker lithosphere 80 km thinning towards the gulf due to the extension and opening processes 65 km 3 central baja california with no converted phase corresponding to the lithosphere asthenosphere boundary but evidence of the presence of a slab remnant 4 the southern baja california peninsula showing a shallow lithosphere astenosphere boundary lab

three stage evolution of the los angeles basin southern california we propose that an episode of transtension dominated development of the los angeles basin area from 12 to 6 ma following middle miocene transrotation and prior to the modern transpressional regime transtension resulted from the releasing bend of the san gabriel chino hills cristianitos fault which acted as the primary transform boundary in southern california during this episode such an interpretation implies that significant transform motion did not occur on the southern san andreas fault prior to 6 ma and that the gulf of california has opened primarily since 6 ma we propose a three stage model for evolution of the los angeles basin and vicinity within the evolving transform fault system transrotation 18 12 ma transtension 12 6 ma and transpression 6 0 ma timing of these stages correlates with microplate capture events which occurred during conversion from a convergent margin to a transform margin

inversion of teleseismic body waves for the moment tensor of the 1978 thessaloniki greece earthquake seismograms from wwssn and canadian network stations were modeled to determine the source parameters of the 20 june 1978 thessaloniki greece earthquake m s 6 4 the depth of the initial rupture was constrained to 11 1 km by comparison of the arrival times of surface reflections with synthetic short period seismograms a focal sphere plot of first motion polarities provided little constraint on other focal parameters except to indicate that predominantly normal faulting was involved a generalized inverse technique utilizing the moment tensor formalism was applied to teleseismic p and sh waves for six increments of depth the moment tensor obtained indicated a nearly horizontal n trending tension axis and a nearly vertical compression axis and yielded the following double couple source parameters strike 280 7 dip 55 3 rake 65 5 seismic moment 5 7 1025 dyne cm and a skewed triangular source time function with a rise time of about 1 sec and duration of 6 to 8 sec due to indications of multiple or finite source effects for this event and the assumption in the moment tensor formalism of a point source a low pass filter was applied to the data and the inversions were repeated the results were nearly identical with those of the original inversion suggesting that any individual sources had similar mechanisms or that the point source model is sufficient for this earthquake

colorado river chronostratigraphy at lee s ferry arizona and the colorado plateau bull s eye of incision abstractlee s ferry arizona united states lies at an important geo logic transition between the grand canyon margin and the canyon lands center of the colorado plateau it marks a knickpoint along the colorado river at the top of the steep grand canyon and it is central to debate about the patterns of erosion and sources of uplift in this famous landscape new chronostratigraphic data from the suite of ll terraces here indicate a strong uvial response to climate driv ers superimposed upon an integrated mid to late pleistocene incision rate of 350 m m y a regional compilation of well constrained results over the same timescale reveals that this is intermediate between slower rates downstream in grand canyon and even faster rates in the central colorado plateau which taper off again farther upstream near the plateau s eastern edge this bull s eye pattern of rapid inci sion in the central colorado plateau does not match proposed sources of uplift from mantle dynamics at the south and west ank of the pla teau nor patterns of river steepness and energy instead we suggest that this incision pattern is primarily driven by transient response to drainage integration and isostatic feedback from the deep exhuma tion of weak rocks in the central plateau introduction

rates of late cenozoic tectonism in the vallecito fish creek basin western imperial valley california the kinetics of continental rifting are recorded in the late neogene sediments of the western imperial valley california the gulf of california opened in its present form about 4 m y ago capturing the colorado river some 5 km of deltaic and fluvial sediments accumulated in the vallecito fish creek area during the interval 4 3 0 9 m y ago initial sedimentation rates were 5 5 mm yr 1 which diminished in an exponential fashion to 0 5 mm yr 1 when isostatic adjustments are accounted for this implies tectonic subsidence rates of 1 5 mm yr 1 decreasing systematically to 0 1 mm yr 1 after 0 9 m y ago right lateral shearing along the elsinore fault zone cut across the basin causing it to be tilted and uplifted at a mean rate of 5 9 mm yr 1 the basin was concurrently rotated as a unit 35 clockwise the dissected pediments and badlands that now characterize the area were formed and eroded in the past 0 9 m y

chronology of miocene pliocene deposits at split mountain gorge southern california a record of regional tectonics and colorado river evolution late miocene to early pliocene deposits at split mountain gorge california preserve a record of basinal response to changes in regional tectonics paleogeography and evolution of the colorado river the base of the elephant trees formation magnetostratigraphically dated as 8 1 0 4 ma provides the earliest well dated record of extension in the southwestern salton trough the oldest marine sediments are ca 6 3 ma the nearly synchronous timing of marine incursion in the salton trough and northern gulf of california region supports a model for localization of pacifi c north america plate motion in the gulf ca 6 ma the fi rst appearance of colorado river sand at the miocene pliocene boundary 5 33 ma suggests rapid propagation of the river to the salton trough and supports a lake spillover hypothesis for initiation of the lower colorado river

steady 10be derived paleoerosion rates across the plio pleistocene climate transition fish creek vallecito basin california rates of erosion over time provide a valuable tool for gauging tectonic and climatic drivers of landscape evolution here we measure 10be archived in quartz sediment from the fish creek vallecito basin to resolve a time series of catchment averaged erosion rates and to test the hypothesis that aridity and increased climate variation after ca 3 ma led to an increase in erosion rates in this semi arid ice free setting the fish creek vallecito basin located east of the peninsular ranges in southern california is an ideal setting to derive a plio pleistocene paleo erosion rate record the basin has a rapid sediment accumulation rate a detailed magnetostratigraphic age record and its stratigraphy has been exposed through recent rapid uplift and erosion a well defined source region of uniform lithology and low erosion rate provides a high reproducible 10be signal we find that paleo erosion rates were remarkably consistent between 1 and 4 ma averaging 38 24 m myr 2 modern catchment averaged erosion rates are similar to the paleo erosion rates the uniformity of erosion over the past 4 myr indicates the landscape was not significantly affected by late pliocene global climate change nor was it affected by a local long term increase in aridity

the continuity of active fault systems in greece summary evidence from geomorphology the distribution of large earthquakes and geodetic measurements suggests that the active faulting in mainland greece and the north aegean sea is concentrated into a small number of discrete linear zones that bound relatively rigid blocks on land the zones are most clearly identified where the faulting is associated with large escarpments particularly in hard footwall rocks the zones can become indistinct and diffuse near their ends sometimes because they enter high unstable topography where landsliding obscures the fault morphology but mostly because the extension rates decrease along strike as a consequence of the relative rotation of the blocks they bound the main graben systems of chalkidiki southern thessaly and the north gulf of evia all seem to connect with the strike slip faulting in the offshore aegean and to die out in the west a configuration related to clockwise rotations in east central greece by contrast the gulf of corinth which is the fastest opening graben system in greece opens more rapidly in the west than the east both these features of the gulf of corinth are consequences of the motion of the south aegean and peloponnese as a single block late pliocene and quaternary geology and geomorphology indicate that the boundaries of the rigid blocks in central greece have changed over that time with faulting migrating into the hanging walls sometimes changing in orientation these changes are probably related to the way faulting in the seismogenic layer adapts to block rotation so as to maintain the general features of a velocity field that is controlled by larger scale effects such as buoyancy forces and the seaward migration of the subducting slab beneath crete the image of greece as a mosaic of rigid blocks whose boundaries change with time is a useful framework for seismic hazard evaluation but we emphasize that some moderate sized earthquakes do occur away from the main fault zones within the relatively rigid blocks and especially near their diffuse ends

eroding dynamic topography 1 geological observations of mantle flow driven dynamic topography are numerous especially in the stratigraphy of sedimentary basins on the contrary when it leads to subaerial exposure of rocks dynamic topography must be substantially eroded to leave a noticeable trace in the geological record here we demonstrate that despite its low amplitude and long wavelength and thus very low slopes dynamic topography is efficiently eroded by fluvial erosion providing that drainage is strongly perturbed by the mantle flow driven surface uplift using simple scaling arguments as well as a very efficient surface processes model we show that dynamic topography erodes in direct proportion to its wavelength we demonstrate that the recent deep erosion experienced in the colorado plateau and in central patagonia is likely to be related to the passage of a wave of dynamic topography generated by mantle upwelling

paleocurrent evidence for lateral displacement of the pliocene colorado river delta by the san andreas fault system southeastern california more than 600 paleocurrent measurements from fluvial paleochannels of the early colorado river delta plain preserved in the palm spring formation in the fish creek vallecito fcv section of southern california indicate that the fcv section was on the gulf of california southeastern flank of the delta plain as recently as 2 8 ma these measurements imply 130 km of tectonic translation to the northwest since 2 8 ma which can be accounted for by the displacement histories of baja california and component faults of the san andreas system stratigraphic data from the fcv section and other neogene localities when plotted on a palinspastic base indicate 1 marine transgression of a narrow gulf of california rift basin and bouse embayment site of modern lower colorado river by 5 5 ma and 2 uplift of the bouse embayment initiation of the lower colorado river and southward progradation of the delta to essentially its present position by 4 ma

continental rupture and the creation of new crust in the salton trough rift southern california and northern mexico results from the salton seismic imaging project a refraction and wide angle reflection seismic profile along the axis of the salton trough california and mexico was analyzed to constrain crustal and upper mantle seismic velocity structure during active continental rifting from the northern salton sea to the southern imperial valley the crust is 17 18 km thick and approximately one dimensional the transition at depth from colorado river sediment to underlying crystalline rock is gradual and is not a depositional surface the crystalline rock from 3 to 8 km depth is interpreted as sediment metamorphosed by high heat flow deeper felsic crystalline rock could be stretched preexisting crust or higher grade metamorphosed sediment the lower crust below 12 km depth is interpreted to be gabbro emplaced by rift related magmatic intrusion by underplating low upper mantle velocity indicates high temperature and partial melting under the coachella valley sediment thins to the north and the underlying crystalline rock is interpreted as granitic basement mafic rock does not exist at 12 18 km depth as it does to the south and a weak reflection suggests moho at 28 km depth structure in adjacent mexico has slower midcrustal velocity and rocks with mantle velocity must be much deeper than in the imperial valley slower velocity and thicker crust in the coachella and mexicali valleys define the rift zone between them to be 100 km wide in the direction of plate motion north american lithosphere in the central salton trough has been rifted apart and is being replaced by new crust created by magmatism sedimentation and metamorphism

thick deltaic sedimentation and detachment faulting delay the onset of continental rupture in the northern gulf of california analysis of seismic reflection profiles 1 the transition from distributed continental extension to the rupture of continental lithosphere is imaged in the northern gulf of california across the obliquely conjugate tiburon upper delfin basin segment structural mapping on a 5 20 km grid of seismic reflection lines of petroleos mexicanos demonstrates that 1000 extension is accommodated on a series of nne striking listric normal faults that merge at depth into a detachment fault the detachment juxtaposes a late neogene marine sequence over thinned continental crust and contains an intrabasinal divide due to footwall uplift two northwest striking dextral oblique faults bound both ends of the detachment and shear the continental crust parallel to the tectonic transport a regional unconformity in the upper 0 5 s two way travel time and crest erosion of rollover anticlines above the detachment indicates inversion and footwall uplift during the lithospheric rupture in the upper delfin and lower delfin basins the maximum length of new crust in both delfin basins is less than 40 km based on the lack of an acoustic basement and the absence of a lower sedimentary sequence beneath a wedge shaped upper sequence that reaches 5 km in thickness a fundamental difference exists between the tiburon delfin segment and the guaymas segment to the south in terms of presence of low angle normal faults and amount of new oceanic lithosphere which we attribute to thermal insulation diffuse upper plate extension and slip on low angle normal faults engendered by a thick sedimentary lid

comment on apatite 4he 3he and u th he evidence for an ancient grand canyon flowers and farley reports 21 december 2012 p 1616 published online 29 november 2012 propose that the grand canyon is 70 million years old starkly contrasting models for the age of the grand canyon 70 versus 6 million years can be reconciled by a shallow paleocanyon that was carved in the eastern grand canyon 25 to 15 million years ago ma negating the proposed 70 ma and 55 ma paleocanyons cooling models and geologic data are most consistent with a 5 to 6 ma age for western grand canyon and marble canyon

sedimentation and crustal recycling along an active oblique rift margin salton trough and northern gulf of california transtensional basins embedded in the san andreas fault system of southern california united states and northwestern mexico are fi lled with sediment derived from the colorado river which drains a large area of the western u s interior the sediment is rapidly buried heated and mingled with intrusions in the deep basins to form a new generation of recycled crust along the active plate boundary using a range of values for total basin depth relative volume of mantle derived intrusions and composition of early rift deposits the volume of colorado river derived sediment in the basins is bracketed between 2 2 and 3 4 10 5 km 3 similar to the volume of rock that likely was eroded from the colorado river catchment over the past 5 6 m y the volumetric rate of crustal growth by sedimentation is 80 130 km 3 m y km comparable to growth rates in subductionrelated island arcs and slow seafl oor spreading centers sedimentary and basinal processes thus play a major role in crustal evolution and recycling in this setting and may be important at other rifted margins where a large river system is captured following tectonic collapse of a prerift orogenic highland

a late miocene early pliocene chain of lakes fed by the colorado river evidence from sr c and o isotopes of the bouse formation and related units between grand canyon and the gulf of california we report strontium isotopic results for the late miocene hualapai limestone of the lake mead area arizona nevada and the latest miocene to early pliocene bouse formation and related units of the lower colorado river trough arizona california nevada together with parallel oxygen and carbon isotopic analyses of bouse samples to constrain the lake overflow model for integration of the colorado river sr isotopic analyses on the basal 1 5 cm of marl in particular along a transect over a range of altitude in the lowest altitude basin that contains freshwater brackish and marine fossils document the 87 sr 86 sr of first arriving bouse waters results reinforce the similarity between the 87 sr 86 sr of bouse formation carbonates and present day colorado river water and the systematic distinction of these values from neogene marine sr basal bouse samples show that 87 sr 86 sr decreased from 0 7111 to values in the range 0 7107 0 7109 during early basin filling 87 sr 86 sr values from a recently identified marl in the las vegas area are within the range of bouse sr ratios 87 sr 86 sr values from the hualapai limestone decrease upsection from 0 7195 to 0 7137 in the approach to a time soon after 6 ma when hualapai deposition ceased and the colorado river became established through the lake mead area bouse formation 18 o values range from 12 9 to 1 0 vienna pee dee belemnite vpdb and 13 c between 6 5 and 3 4 vpdb negative 18 o values appear to require a continental origin for waters and the trend to higher 18 o suggests evaporation in lake waters sr and stable isotopic results for sectioned barnacle shells and from bedding planes of the marine fish fossil colpichthys regis demonstrate that these animals lived in saline freshwater and that there is no evidence for incursions of marine water either long lived or brief in duration lack of correlation of sr and o isotopic variations in the same samples also argue strongly against systematic replacement of sr in bouse carbonates after deposition our results reinforce the conclusion that the bouse formation was deposited in a descending series of basins connected by overflow of colorado river water the hualapai limestone records a separate and earlier lake that may have been progressively influenced by colorado river water as the time of river integration approached

dating of pliocene colorado river sediments implications for cosmogenic burial dating and the evolution of the lower colorado river we applied cosmogenic 26 al 10 be burial dating to sedimentary deposits of the ancestral colorado river we compared cosmogenic burial ages of sediments to the age of an independently well dated overlying basalt flow at one site and also applied cosmogenic burial dating to sediments with less precise independent age constraints all dated gravels yielded old ages that suggest several episodes of sediment burial over the past 5 3 m y comparison of burial ages to the overlying 4 4 ma basalt yielded good agreement and suggests that under the most favorable conditions cosmogenic burial dating can extend back 4 5 m y in contrast results from other sites with more broadly independent age constraints highlight the complexities inherent in burial dating these complexities arise from unknown and complicated burial histories insufficient shielding postburial production of cosmogenic isotopes by muons and unknown initial 26 al 10 be ratios nevertheless and in spite of the large range of burial ages and large uncertainties we identify samples that provide reasonable burial age constraints on the depositional history of sediment along the lower ancestral colorado river these samples suggest possible sediment deposition and burial at ca 5 3 4 7 and 3 6 ma our calculated basinwide erosion rate for sediment transported by the modern colorado river 187 mm k y 1 is higher than the modern erosion rates inferred from the historic sediment load 80 100 mm k y 1 in contrast basinwide paleo erosion rates calculated from pliocene sediments are all under 40 mm k y 1 the comparatively lower denudation rates calculated for the pliocene sediment samples are surprising given that the sampled time intervals include significant pliocene aggradation and may include much incision of the grand canyon and its tributaries this conflict may arise from extensive storage of sediment along the route of the colorado river slower paleobedrock erosion or the inclusion of sediments that were derived preferentially from higher elevations in the watershed

does slab window opening cause uplift of the overriding plate a case study from the gulf of california abstract complete subduction of an oceanic plate results in slab window opening a key uncertainty in this process is whether the higher heat flux and asthenospheric upwelling conventionally associated with slab window opening generate a detectable topographic signature in the overriding plate we focus on the baja california peninsula which incorporates the western margin of the gulf of california rift the topography and tectonics of the rift flank along the peninsula are strongly bimodal north of the puertecitos accommodation zone the primary drainage divide attains a mean elevation of ca 1600 m above sea level asl above an asthenospheric slab window opened by pacific farallon spreading ridge subduction along this section of the trench at ca 17 15 ma to the south mean topography decreases abruptly to ca 800 m asl excluding the structurally distinct los cabos block at the southern tip of the peninsula above fragments of the oceanic farallon slab which stalled following slab tear off at ca 15 14 ma along the peninsula a low relief surface established atop miocene subduction related volcaniclastic units has been incised by a west draining canyon network in response to uplift these canyons exhibit cut and fill relationships with widespread post subduction lavas here we utilise landsat and digital elevation model dem data integrated with previously published k ar and 40ar 39ar lava crystallisation ages to constrain the onset of rift flank uplift to ca 9 5 ma later than slab window formation in the north and ca 11 10 ma later in the south these greatly exceed response time estimates of ca 2 ma or less for uplift triggered by slab window opening instead uplift timing of the high elevation northern region is consistent with lower lithospheric erosion driven by rift related convective upwelling to the south stalled slab fragments likely inhibited convective return flow preventing lithospheric erosion and limiting uplift to the isostatic response to crustal unloading during rifting

late miocene extension in coastal sonora mexico implications for the evolution of dextral shear in the proto gulf of california oblique rift abstract the timing kinematics and processes responsible for the rapid transition from subduction to oblique rifting and the localization of the pacific north america plate boundary in the gulf of california are not well understood well exposed volcanic rocks deposited between 15 and 10 ma in the sierra bacha coastal sonora mexico preserve a record of late miocene deformation on the eastern rifted margin of the gulf of california and offer new insights into the timing and kinematic evolution of oblique rifting detailed geologic mapping fault kinematic analysis u pb and 40ar 39ar geochronology and paleomagnetic data reveal that the 2 km thick composite volcanic section is cut by a series of southwest dipping domino style normal faults and uniformly tilted down to the northeast palinspastic cross section restoration suggests that the region experienced ca 55 60 northeast southwest directed extension between 11 7 and 10 9 ma fault kinematic data reflect relatively minor dextral transtension either following or during the later stages of extension paleomagnetic results indicating modest clockwise vertical axis block rotation suggest that dextral shear was concentrated in the southwest of the study area near the modern coastline these results support an emerging model in which dextral strain was not ubiquitous across sonora and did not initiate immediately following the 12 5 ma transition from subduction to oblique rifting instead strain east of the baja california microplate at this latitude evolved from extension dominated transtension prior to 8 ma to dextral shear dominated transtension by 7 6 ma the onset of dextral shear in coastal sonora likely resulted from an increase in rift obliquity due to a change in relative plate motion direction at 8 ma the increase in rift obliquity and resultant onset of significant strike slip faulting played a crucial role in facilitating subsequent plate boundary localization and marine incursion in the northern gulf of california by 6 ma and continental rupture at 2 1 ma

rapid n s extension in the mygdonian graben northern greece deduced from repeated geodetic surveys in november 1994 a geodetic network situated on the mygdonian graben 30 km ne of thessaloniki greece was remeasured using the gps technique this network was established in 1979 in the epicentral area of the 1978 earthquake ms 6 5 and was measured using triangulation techniques seven times between 1979 and 1989 the comparison between 1979 and 1994 data shows that this part of the mygdonian graben experienced about 8 cm of n s horizontal extension most of the extension is concentrated in a narrow one or two kilometers e w zone located on the southern boundary of the graben furthermore the analysis of repeated triangulation surveys suggests a rate of extension of 5 7 1 3 mm y that remained constant with time between 1979 and 1994 this extension could result from long term postseismic relaxation processes or from continous aseismic slip within the graben

systematic heat flow measurements across the wagner basin northern gulf of california abstract a primary control on the geodynamics of rifting is the thermal regime to better understand the geodynamics of rifting in the northern gulf of california we systematically measured heat flow across the wagner basin a tectonically active basin that lies near the southern terminus of the cerro prieto fault the heat flow profile is 40 km long has a nominal measurement spacing of 1 km and is collocated with a seismic reflection profile heat flow measurements were made with a 6 5 m violin bow probe although heat flow data were collected in shallow water where there are significant temporal variations in bottom water temperature we use ctd data collected over many years to correct our measurements to yield accurate values of heat flow after correction for bottom water temperature the mean and standard deviation of heat flow across the western central and eastern parts of the basin are 220 60 99 14 889 419 mw m 2 respectively corrections for sedimentation would increase measured heat flow across the central part of basin by 40 to 60 we interpret the relatively high heat flow and large variability on the western and eastern flanks in terms of upward fluid flow at depth below the seafloor whereas the lower and more consistent values across the central part of the basin are suggestive of conductive heat transfer moreover heat flow across the central basin is consistent with gabbroic underplating at a depth of 15 km and suggests that continental rupture here has not gone to completion

matched field processing geoacoustic inversion and source signature recovery of blue whale vocalizations matched field processing mfp and global inversion techniques have been applied to vocalizations from four whales recorded on a 48 element tilted vertical array off the channel islands in 1996 global inversions from selected whale calls using as few as eight elements extracted information about the surrounding ocean bottom composition array shape and the animal s position these inversion results were then used to conduct straightforward mfp on other calls the sediment sound speed inversion estimates are consistent with those derived from sediment samples collected in the area in general most animals swam from the east to west but one animal remained within 500 m of its original position over 45 min all whales vocalized between 10 and 40 m depth three acoustic sequences are discussed in detail the first illustrating a match between an acoustic track and visual sighting the second tracking two whales to ranges out to 8 km and the final sequence demonstrating high resolution dive profiles from

quaternary evolution of the corinth rift and its implications for the late cenozoic evolution of the aegean summary we present geological and morphological observations at different scales to constrain rates of faulting and the distribution of deformation in the seismically active aegean region we focus first on the 130 km long corinth rift an asymmetric graben where a flight of terraces of marine origin are uplifted we show that the edges of the terraces lie in the footwall of the normal fault bounding the corinth rift and correspond to sea level highstands of laic pleistocene age using a detailed analysis of aerial and spot imagery supported by field observations we have mapped 10 terrace platforms and strandlines ranging in elevation from 10 to 400 m over distances of 2 to 20 km from the fault the elevation of the terraces inner edges was estimated at 172 sites with an error of 5m this data set contains a precise description of the uplift and flexure of 10 different palaeohorizontal lines with respect to the present sea level to date the deformation we correlate the corinth terraces with late pleistocene oxygen isotope stages of high sea level stands and with global sea level fluctuations using a thick elastic plate model consistent with our current understanding of the earthquake cycle and a boundary element technique we reproduce the geometry of the shorelines to constrain both mechanical parameters and the slip on the fault we show that the seismogenic layer behaves over the long term as if its elastic modulus were reduced by a factor of about 1000 all the terraces are fitted for fault slip increasing in proportion to terrace age and the component of regional uplift is found to be less than 0 3 mm yr 1 the best fits give a slip rate of 11 3 mm yr 1 on the main rift bounding fault over the last 350 kyr other geological and morphologic information allows us to estimate the total age of the main fault 1 ma and to examine the mechanical evolution of the corinth rift the minimum observed sediment thickness in the gulf places an extreme check on the results of the modelling and a lower bound on slip rate of 6 7 mm yr 1 40 per cent less than estimated with modelling even this slip rate is nearly 10 times higher than for comparable features in most of the aegean and elsewhere in the world at a larger scale the spacing and asymmetry of the rift systems in the aegean suggest strain localization in the upper mantle with slow extension starting 15 myr ago or earlier the more recent 1 myr rapid phase of rifting in corinth partly reactivated this earlier phase of extension the younger faulting in corinth appears to result from its present location in the inhomogeneous stress field process zone of the south westward propagating tip of the southern branch of the north anatolian fault we extend these relations to propose a mechanical model for the late cenozoic evolution of the aegean as the arabia europe collision progressed in eastern turkey it caused anatolia to move to the west and the north anatolian fault to propagate into the aegean where the early slow extension started to be modified about 5 ma ago the process of propagation dramatically increased the activity of some but not all of the earlier rifts the model we present is compatible with tectonic observations as well as with the seismicity the palaeomagnetic rotations and the displacement field now observed with gps and slr

early pleistocene initiation of the san felipe fault zone sw salton trough during reorganization of the san andreas fault system structural and stratigraphic analyses along the western margin of the salton trough show that the san andreas fault system was reorganized in early pleistocene time from a system dominated by two fault zones the san andreas fault and the west salton detachment fault to a network of dextral faults that include the san andreas and at least four dextral faults to the southwest the san felipe fault zone one of these dextral faults has 5 8 2 8 km of right separation and consists of three principal faults in the peninsular ranges these are the san felipe fault in the wnw sunset fault in the middle and fish creek mountains fault in the ese they form a left stepping array and bound domains in which the sunset conglomerate the older west salton detachment fault and cretaceous mylonitic rocks below the detachment are folded about wnw trending folds a complex flower structure within the left stepovers probably produced this fault parallel folding because all the rocks within stepovers of the san felipe fault zone from cretaceous to pleistocene are deformed about wnw trending folds and record broadly similar shortening strains we infer a quaternary age of deformation parts of the san felipe fault zone cut latest pleistocene to holocene surficial deposits and the fault zone is likely active evidence for early pleistocene initiation of the san felipe fault zone is preserved in conglomerate ne of the sunset fault poorly sorted angular boulder conglomerate and pebbly sandstone of the sunset conglomerate are 600 m thick and lie in angular unconformity on the pliocene palm spring group the conglomerate coarsens upward and toward the fault and is dominated by plutonic clasts derived from sw of it conglomerate beds contain up to 10 sandstone clasts recycled from older basin fill and accumulated in proximal to medial alluvial fans that were shed to the ne from uplifted rocks along the then active sunset fault based on lithologic stratigraphic structural and compositional similarities we correlate the sunset conglomerate to the pleistocene ocotillo formation clasts of recycled sandstone record erosion of detachment related basin fill that predates the san felipe fault and once covered the vallecito and fish creek mountains these crystalline cored mountain ranges first emerged from beneath basin fill during early slip above the nascent san felipe fault ca 1 1 1 3 ma later the san felipe fault zone cut upward folded cut across and deactivated the west salton detachment fault within a 9 km wide contractional bend and pair of left steps areas that accumulated sediment within this step over zone between ca 1 1 and ca 0 6 ma are currently being inverted and folded initiation of the san felipe fault in early pleistocene time was a significant event in the reorganization of the southern san andreas fault system the quaternary dextral faults broadened the plate boundary zone south westward from roughly 25 km during coeval slip on the san andreas fault and west salton detachment fault to 50 70 km and mark a change in the dominant structural style from transtension to distributed dextral faulting south of the big bend

marine incursion synchronous with plate boundary localization in the gulf of california volcanic strata on southwest isla tiburon define the age of interstratified marine rocks and through revision of existing correlations the age of the proto gulf of california marine incursion a 5 7 0 2 ma ash flow was emplaced at the base of the marine section a rhyodacite dike and its related lava flow dated as 11 2 1 3 ma 3 7 0 9 ma and 4 2 1 8 ma intrudes and overlies respectively the marine rocks the 11 2 ma age which was the core datum for a middle miocene proto gulf of california origin for the underlying rocks is discordant with all other isotopic and microfossil ages an alternative interpretation utilizing all available geologic and geochronologic data except this discordant age is that marine strata on isla tiburon are latest miocene to early pliocene age reinterpretation of these strata supports a simplified history of marine incursion into the gulf of california marine rocks as old as 8 2 ma in the southern gulf of california indicate an early marine incursion perhaps flooding a region of more intense proto gulf of california continental extension flooding of the entire basin by 6 5 6 3 ma correlates to the sudden onset of significant pacific north american plate boundary motion within the gulf of california

latest miocene transtensional rifting of northeast isla tiburon eastern margin of the gulf of california abstract details about the timing and kinematics of rifting are crucial to understand the conditions that led to strain localization continental rupture and formation of the gulf of california ocean basin we integrate detailed geologic and structural mapping basin analysis and geochronology to characterize transtensional rifting on northeastern isla tiburon a proximal onshore exposure of the rifted north america margin adjacent to the axis of the gulf of california slip on the kunkaak normal fault tilted its hanging wall down to the east 70 and formed the non marine tecomate basin deposited across a 20 angular unconformity from 7 1 6 4 ma the hanging wall tilted at 35 5 myr while non marine sandstone and conglomerate accumulated at 1 4 0 2 mm yr at least 1 8 0 1 km of sediments and pyroclastic deposits accumulated in the tecomate basin concurrent with clockwise vertical axis block rotation and 2 8 km of total dip slip motion on the kunkaak fault linear extrapolation of tilting and sedimentation rates suggests that faulting and basin deposition initiated 7 6 7 4 ma but an older history involving initially slower rates is permissible the kunkaak fault and tecomate basin are truncated by nw striking dextral oblique structures including the yawassag fault which accrued 8 km of post 6 4 ma dextral displacement the coastal sonora fault zone on mainland sonora which accrued several tens of kilometers of late miocene dextral offset continues to the northwest across northeastern isla tiburon and offshore into the gulf of california the establishment of rapid latest miocene transtension in the coastal sonora fault zone was synchronous with the 8 7 ma onset of transform faulting and basin formation along the nascent pacific north america plate boundary throughout northwestern mexico and southern california plate boundary strain localized into this gulf of california shear zone a narrow transtensional belt that subsequently hosted the marine incursion and continental rupture in the gulf of california

early neogene continental sedimentation in the vallecito and fish creek mountains western salton trough california abstract lower neogene sedimentary rocks in the vallecito and the fish creek mountains along with locally intercalated basalts were deposited in a half graben basin and range setting three depositional environments are recognized 1 braided stream 2 alluvial fan and 3 landslide a platte type braided stream system with local accumulation of seif dunes drained a westward tilted pediment surface coarse sand was deposited as transverse and linguoid bars sand dunes and flat beds and gravel was deposited as longitudinal bars modified by tractive flow in broad shallow channels this system joined a donjek type northward flowing axial drainage characterized by channels with marked topographic relief deep channel reaches were infilled with longitudinal gravel bars and massive granular very coarse sand from concentrated dispersions giant sand waves were rarely present in deeper channel reaches in shallower channel tracts coarse sand was deposited as transverse bars sand dunes and flat beds and gravel was deposited as small longitudinal bars the alluvial fan deposits accumulated along the faulted western margin of the basin and prograded eastward over the axial drainage they consist of debris flow sheetflood and donjek type channel fill deposits subenvironments are defined by the distribution of these deposits and their bedding geometries the upper fan above the intersection point is characterized by debris flow and channel fill deposits with numerous internal erosional contacts and laterally discontinuous beds the middle fan below the intersection point is marked by crudely developed thickening upward cycles of laterally continuous repetitively interbedded very thick debris flow and thinner bedded sheetflood deposits the lower fan is represented by interbedded debris flow and sheetflood deposits that are thinner bedded and less organized than the middle fan subfacies the landslide deposits locally top the sequence they are massive laterally continuous sedimentary megabreccias containing clasts that are up to 5 m in diameter and display a distinctive jigsaw puzzle texture these breccias formed as two cataclysmically emplaced air cushioned landslides one was dislodged from the vallecito mountains and traveled eastward while the other was released from the fish creek mountains and traveled westward

quaternary rift flank uplift of the peninsular ranges in baja and southern california by removal of mantle lithosphere 1 regional uplift in southern california usa and northern baja california mexico is interpreted to result from flexure of the elastic lithosphere driven largely by heating and thinning of the upper mantle beneath the gulf of california and eastern peninsular ranges the geometry and timing of faulting in the salton trough and gulf of california the history of recent rock uplift along the pacific coastline and geophysical data constrain models of lithospheric heating and thinning based on unloading of a continuous elastic plate high topography that marks the 400 km long rift shoulder in northern baja california mimics the pattern of uplift observed along the pacific coastline as defined by marine terraces we interpret this to indicate that recent rock uplift has occurred across the entire width of northern baja peninsula and increases from west to east pliocene strata deposited at sea level along the pacific coastline in southern california have not been uplifted significantly above quaternary marine terrace deposits this suggests the onset of rock uplift along the pacific coast here is post pliocene and occurs after miocene crustal extension in the salton trough and gulf of california strong heating of the mantle lid beneath the peninsular ranges in northern baja california thus coincides with crustal extension limited to localized oceanic spreading in the gulf of california citation mueller k g kier t rockwell and c h jones 2009 quaternary rift flank uplift of the peninsular ranges in baja and southern california by removal of mantle lithosphere tectonics 28 tc5003 doi 10 1029 2007tc002227

slip history of the la cruz fault development of a late miocene transform in response to increased rift obliquity in the northern gulf of california abstract the gulf of california rift has accommodated oblique divergence of the pacific and north america plates in northwestern mexico since miocene time due to its infancy its rifted margins preserve a rare onshore record of early continental break up processes and an opportunity to investigate the role of rift obliquity in strain localization we map rift related structures and syn tectonic basins on southern isla tiburon a proximal onshore exposure of the rifted north america margin we integrate analysis and geochronology of syn tectonic sedimentary basins and mapping of crosscutting relationships to characterize the style and timing of fault activity on southern isla tiburon an early phase of extension initiated between 19 17 ma and 12 2 ma subsequently these normal faults and related basins were cut by the la cruz strike slip fault and buried by deposits of the la cruz basin an elongate fault controlled trough coextensive with the la cruz fault crosscutting relationships show that the nw striking la cruz fault accrued 5 2 km of dextral slip 8 4 ma the la cruz fault and parallel tiburon transform were kinematically linked to detachment faulting that accommodated latest miocene to pliocene oblique opening of the offshore upper tiburon pull apart basin the onset of strike slip faulting on isla tiburon was synchronous with the 8 6 ma onset of transform faulting and basin formation along 1000 km of the reconstructed pacific north america plate boundary this transition coincides with the commencement of a clockwise azimuthal shift in pacific north america relative plate motion that increased the obliquity of the gulf of california rift and formed the gulf of california shear zone the record from the proto gulf of california illustrates how highly oblique rift geometries where transform faults are kinematically linked to pull apart basins enhance the ability of continental lithosphere to rupture and ultimately hasten the formation of new oceanic rift basins

a linear inverse method to reconstruct paleo topography abstract landscape evolution provides insight into the tectonic and erosional processes that have shaped the topography observed today however in many cases an estimate of an earlier topography is required to make first order interpretations about volumes of sediment eroded or depths of fluvial incision or to serve as an initial condition in landscape evolution models this paper presents a means to reconstruct paleo topography in two dimensions in areas that have experienced an increase in incision using available topographic remnants or areas of low erosion rate the approach is based on an analytical solution to the steady state stream power model in which a single elevation within the drainage network is a function of the integrated channel steepness and the normalized landscape response time or values the branching structure of a drainage network provides redundant information that can be exploited to infer spatial variations in channel steepness and a base level parameter a single elevation pixel can be written as a sum of channel steepness multiplied by values and a set of elevation pixels can be combined as a system of equations in order to improve efficiency channel steepness is parameterized using pixels of constant values by incorporating smoothness constraints on the channel steepness pixels using a laplacian operator a stable solution to the inverse problem can be obtained to infer the channel steepness values in space a base level parameter and in turn paleo topography this approach is explored with examples from the inyo mountain range usa grand canyon usa and the karrat region in western greenland

comment on age and evolution of the grand canyon revealed by u pb dating of water table type speleothems polyak et al reports 7 march 2008 p 1377 reported speleothem data leading to their inference that the western grand canyon incised much earlier than previously thought this contradicts several lines of published geological knowledge in the region hinges upon unjustified hydrogeological assumptions and is based on two anomalous data points for which we offer alternative explanations

analyzing lateral seabed variability with bayesian inference of seabed reflection data this paper considers bayesian inversion of seabed reflection coefficient data for multi layer geoacoustic models at several sites with the goal of studying lateral variability of the seabed rigorous uncertainty estimation is carried out to resolve lateral variability of the sediments from inherent inversion uncertainties the uncertainty analysis includes bayesian model selection comprehensive quantification of data error statistics and a markov chain monte carlo approach to transforming data uncertainties to model uncertainties model selection is addressed using the bayesian information criterion to ensure parsimony of the parametrizations data error statistics are quantified by estimating full covariance matrices from data residuals with posterior statistical validation a metropolis hastings sampling algorithm is used to compute posterior probability densities four experiment sites are considered along a track located on the malta plateau mediterranean sea and the inversion results are compared to cores taken at each site differences between profile marginal probability distributions at adjacent sites are quantified using the bhattacharyya coefficient differences that exceed the estimated geoacoustic uncertainties are interpreted as spatial variability of the seabed the results are compared to an interpretation of geologic features evident in a chirp sub bottom profiler section

breaching of strike slip faults and successive flooding of pull apart basins to form the gulf of california seaway from ca 8 6 ma

postseismic deformation associated with the 1992 m ω 7 3 landers earthquake southern california following the 1992 m 7 3 landers earthquake a linear array of 10 geodetic monuments at roughly 5 km spacing was established across the emerson fault segment of the landers rupture the array trends perpendicular to the local strike of the fault segment and extends about 30 km on either side of it the array was surveyed by global positioning system 0 034 0 048 0 381 1 27 1 88 2 60 and 3 42 years after the landers earthquake to measure both the spatial and temporal character of the postearthquake relaxation the temporal behavior is described roughly by a short term decay time 84 23 days exponential relaxation superimposed upon an apparently linear trend because the linear trend represents motions much more rapid than the observed preseismic motions we attribute that trend to a slower decay time greater than 5 years postseismic relaxation the curvature of which cannot be resolved in the short run 3 4 years of postseismic data about 100 mm of right lateral displacement and 50 mm of fault normal displacement accumulated across the geodetic array in the 3 4 year interval covered by the postseismic surveys those displacements are attributed to postseismic right lateral slip in the depth interval 10 to 30 km on the downward extension of the rupture trace the right lateral slip amounted to about 1 m directly beneath the geodetic array and the fault normal displacement is apparently primarily a consequence of the curvature of the rupture these conclusions are based upon dislocation models fit to the observed deformation however no dislocation model was found with rms residuals as small as the expected observational error

geoacoustic inversion of ambient noise a simple method the vertical directionality of ambient noise is strongly influenced by seabed reflections therefore potentially geoacoustic parameters can be inferred by inversion of the noise in this approach using vertical array measurements the reflection loss is found directly by comparing the upward with the downward going noise theory suggests that this simple ratio is in fact the power reflection coefficient potentially a function of angle and frequency modeling and parameter searching are minimized and the method does not require a detailed knowledge of the noise source distribution the approach can handle stratified environments and is believed to tolerate range dependence experimental data from five sites four in the mediterranean one on the new jersey shelf are described most of the mediterranean sites had temporally varying noise directionality yet yielded the same reflection properties as one would hope one site was visited in conditions of very low surface noise this paper concentrates on an experimental demonstration of the feasibility of the method and data quality issues rather than automatic search techniques for geoacoustic parameters

a trans dimensional polynomial spline parameterization for gradient based geoacoustic inversion this paper presents a polynomial spline based parameterization for trans dimensional geoacoustic inversion the parameterization is demonstrated for both simulated and measured data and shown to be an effective method of representing sediment geoacoustic profiles dominated by gradients as typically occur for example in muddy seabeds specifically the spline parameterization is compared using the deviance information criterion dic to the standard stack of homogeneous layers parameterization for the inversion of bottom loss data measured at a muddy seabed experiment site on the malta plateau the dic is an information criterion that is well suited to trans d bayesian inversion and is introduced to geoacoustics in this paper inversion results for both parameterizations are in good agreement with measurements on a sediment core extracted at the site however the spline parameterization more accurately resolves the power law like structure of the core density profile and provides smaller overall uncertainties in geoacoustic parameters in addition the spline parameterization is found to be more parsimonious and hence preferred according to the dic the trans dimensional polynomial spline approach is general and applicable to any inverse problem for gradient based profiles work supported by onr

buried rhyolites within the active high temperature salton sea geothermal system abstract previously unrecognized pulses of rhyolite volcanism occurred in the salton trough between 420 8 ka and 479 38 ka 2 based on high spatial resolution u pb zircon geochronology presently these rhyolite lavas tuffs and shallow subvolcanic sills are buried to depths between 1 6 and 2 7 km at ambient temperatures between 200 and 300 c and are overprinted by propylitic to potassic hydrothermal alteration mineral assemblages consisting of finely intergrown quartz k feldspar chlorite epidote and minor pyrite alteration resistant geochemical indicators whole rock nd isotopes zircon oxygen isotopes reveal that these rhyolites are derived from remelting of morb type crust that was chilled and hydrothermally altered by deep circulating hydrothermal waters u pb zircon dating confirms the presence of bishop tuff in well state 2 14 at 1 7 km depth approximately 5 km ne of the geothermal wells that penetrated the buried rhyolites these results indicate accelerated subsidence towards the center of the salton trough increasing from 2 2 mm a to 3 8 mm a based on these results the present day salton sea geothermal field is identified as a focus zone of episodic rhyolitic volcanism intense heat flow and metamorphism that predates present day geothermal activity and holocene volcanism by at least 400 ka

an uplift history of the colorado plateau and its surroundings from inverse modeling of longitudinal river profiles 1 it is generally agreed that a region encompassing the colorado plateau has been uplifted by sub crustal processes admittance calculations tomographic studies and receiver function analyses suggest that dynamic support is generated by some combination of convective upwelling and lithospheric thickness changes notwithstanding advances in our understanding of present day setting uplift rate histories are poorly constrained and debated an improved history will aid discrimination between proposed models here we show that a regional uplift rate history can be obtained by inverting longitudinal river profiles we assume that the shape of a river profile is controlled by uplift rate and moderated by erosion in our model uplift rate is allowed to vary smoothly as a function of space and time upstream drainage area is invariant with time simultaneous inversion of river profiles from the colorado rio grande columbia and mississippi catchments shows that three phases of regional uplift occurred the first phase occurred between 80 and 50 myrs when 1 km of uplift was generated at a rate of 0 03 mm yr a second phase occurred between 35 and 15 myrs when 1 5 km of uplift was generated at a faster rate of 0 06 mm yr a final phase of uplift commenced 5 myrs ago these distinct phases of late cretaceous and oligocene uplift are corroborated by stratigraphic considerations by thermochronometric data and by stratigraphic evidence of periodic clastic efflux delivered into the gulf of mexico an episodic uplift history is consistent with staged removal of thick lithospheric mantle beneath a large region which is currently centered on yellowstone

stratigraphic record of pleistocene faulting and basin evolution in the borrego badlands san jacinto fault zone southern california sedimentary rocks in the borrego badlands southern california contain a record of pleistocene crustal deformation during initiation and evolution of the san jacinto fault zone we used detailed geologic stratigraphic and paleomagnetic analysis to determine the age and geometry of the deposits and reconstruct the history of fault controlled sedimentation in this area the base of the 300 to 500 m thick ocotillo formation is a paraconformity to abrupt conformable contact that records a brief hiatus followed by rapid progradation of coarse alluvial sediment over lacustrine facies of the borrego formation at 1 05 0 03 ma this coincides with regional scale progradation of ocotillo formation sand and gravel and appears to record initiation of strike slip faults in the southwestern salton trough at ca 1 1 ma thickness trends clast compositions paleocurrents and distribution of paleosols provide evidence for initiation of the east coyote mountain fault at ca 1 05 ma followed by onset of nne ward basin tilting obliquely toward the santa rosa segment of the clark fault at ca 1 0 ma stratigraphic omission of the ocotillo formation and progressively older units southwest of the coyote creek fault beneath the fonts point sandstone provides evidence that tilting to the northnortheast was related in part to growth of the san felipe anticline during deposition of the ocotillo formation map and stratigraphic data suggest that the coyote creek fault in the western borrego badlands postdates ocotillo deposition and thus appears to have propagated southeast into the study area at ca 0 6 ma the fonts point sandstone is a thin sheetlike alluvial deposit that records the end of deposition and onset of transpressive deformation in the borrego badlands the base of the fonts point sandstone changes from a conformable contact in a narrow belt southeast of the inspiration point fault where it is dated at 0 6 0 02 ma to an angular unconformity on the folded ocotillo formation northwest of the fault the pattern of stratal truncation records initiation of the inspiration point fault at ca 0 6 ma this coincides with a major structural reorganization in the san jacinto fault zone that initiated the modern phase of north south shortening and erosion in the southwestern salton trough

a karst hydrology model for the geomorphic evolution of grand canyon arizona usa abstract the evolution of grand canyon started 85 ma when the southwestern hualapai plateau section of the colorado plateau began uplifting this uplift initiated a northeast trending drainage canyon system laramide paleo grand canyon that was to constrain all later routes including that of the colorado river this drainage proceeded down dip but up the stratigraphic section so that northward incision intersected progressively younger paleozoic to mesozoic rock we propose a capture of groundwater by the karstic redwall limestone at rm 197 that shifted the drainage direction of this early canyon along a n60 e trending section to rm 130 uplift of the kaibab arch at 80 65 ma forced coconino plateau drainage to divert around the west side of the arch rather than northeast across it in the mid tertiary an arizona river in the western grand canyon transported shinumo clasts to the california sespe formation and a magmatism tectonic volcanism episode occurred on and south of the hualapai plateau by 17 ma basin and range down faulting furthered earlier miocene canyon headward erosion eastward and then northward into utah causing a complete regional drainage reversal southward this miocene western paleo grand canyon river incised into the redwall muav karst aquifer so as to supply the 12 6 ma hualapai limestone with high 87sr 86sr carbonate spring water a 6 0 5 5 ma final connection between the east and west sides of the kaibab arch was accomplished by karst piracy drainage traversing under the arch this complexity of origin separate canyon sections joined drainage reversals and a final karst connection is why grand canyon remains enigmatic to geologists

bayesian geoacoustic inversion using wind driven ambient noise this paper applies bayesian inversion to bottom loss data derived from wind driven ambient noise measurements from a vertical line array to quantify the information content constraining seabed geoacoustic parameters the inversion utilizes a previously proposed ray based representation of the ambient noise field as a forward model for fast computations of bottom loss data for a layered seabed this model considers the effect of the array s finite aperture in the estimation of bottom loss and is extended to include the wind speed as the driving mechanism for the ambient noise field the strength of this field relative to other unwanted noise mechanisms defines a signal to noise ratio which is included in the inversion as a frequency dependent parameter the wind speed is found to have a strong impact on the resolution of seabed geoacoustic parameters as quantified by marginal probability distributions from bayesian inversion of simulated data the inversion method is also applied to experimental data coll

initiation of the southern elsinore fault at 1 2 ma evidence from the fish creek vallecito basin southern california 1 strike slip faults west of the san andreas fault saf accommodate more than half of the modern pacific north america plate motion in southern california yet their age kinematic evolution and long term slip rates are incompletely understood the southern elsinore fault is part of this zone and occupies the boundary between mesozoic crystalline rocks of the peninsular ranges and late cenozoic sedimentary rocks of the salton trough depocenter the fish creek vallecito basin a recently inverted western sub basin of the salton trough contains a thick succession of plio pleistocene sedimentary rocks that preserve a record of crustal subsidence and uplift in response to evolving tectonic controls deposits older than 1 2 ma accumulated during transtension and subsidence in the hanging wall of the low angle west salton detachment fault a fanning dip interval high in the section dated at 1 2 1 0 ma accumulated during tilting caused by earliest motion on the elsinore and earthquake valley faults total offset of 1 2 km yields a lifetime slip rate of about 1 2 mm yr for the southern elsinore fault similar to a late pleistocene rate in the coyote mountains but slower than published estimates for the northern elsinore fault this difference likely results from long term transfer of slip from the northern elsinore fault to the san felipe and san jacinto fault zones farther east initiation of the elsinore fault at 1 2 ma coincides with a major tectonic reorganization that terminated slip on the detachment fault and formed the modern network of strike slip faults west of the saf

asymmetrical inversely graded upstream migrating cyclic steps in marine settings late miocene early pliocene fish creek vallecito basin southern california abstract cyclic steps are ubiquitous in modern sedimentary environments yet their recognition remains sparse in the rock record here we interpret three sets of undulating backsets 1 to 3 recognized in the late miocene early pliocene latrania formation in the anza borrego desert the fish creek vallecito basin southern california usa as the first cm to dm scale outcrop record of cyclic steps based on asymmetrical cross sections upstream migration and inversely graded laminae upstream migration and asymmetrical cross sections of backsets and concomitant backset laminae are attributed to supercritical to subcritical flow transitions through weak hydraulic jumps which are composed of i thin tens of centimetres and slower reported as flow velocities of 0 45 to 1 45 m s 1 with mean value of 0 89 m s 1 subcritical represented by internal froude numbers fr of 0 67 to 0 99 with mean value of fr 0 84 turbidity currents on the stoss sides and ii thin tens of centimetres and faster reported as of 0 99 to 4 03 m s 1 with mean value of 2 24 m s 1 supercritical represented by fr of 1 84 to 3 07 with mean value of fr 2 42 turbidity flows on the lee sides the inversely graded laminae in the troughs of backsets are 2 to 5 cm thick and consist of two discrete divisions i 1 to 2 cm thick lower finer grained divisions made up of parallel laminated siltstones overlain by very fine to fine grained sandstones and ii 2 to 3 cm thick upper divisions composed of medium to coarse grained sandstones with sporadic occurrence of subrounded pebbles these inversely graded laminae are related to stratified collisional and or frictional traction carpets under conditions of high fall out rates due to the poor preservation potential of cyclic steps the rock record of cyclic steps is generally considered to be rare the present outcrop based study presents a detailed analysis of sedimentary facies growth patterns and flow dynamics of marine cyclic steps thereby contributing to better understand architectural styles and lithological properties of cyclic steps in the geological record

geodetic strain of greece in the interval 1892 1992 a first order triangulation of greece was carried out in the 1890s reoccupation using global positioning system receivers of 46 of the 93 original markers yielded estimates of the deformation of the region over the intervening interval broad regions have similar geodetic strain over the 100 year time span strain north of the gulf of korinthos is predominantly north south extension though with a significant east west component the central peloponnisos is relatively stable whereas the gulfs of the southern peloponnisos are all characterized by uniaxial east west extension the seismic expression of strain for the entire region calculated from the seismic moment tensors of earthquakes of m s 5 8 during the past 100 years accounts for only 20 50 of the geodetically determined strain at a scale of 50 100 km the fraction of the strain that is expressed seismically varies much more than this range in particular whereas seismic strain in the eastern gulf of korinthos over the past 100 years is commensurate with the geodetic strain there is rapid extension across the western gulf of korinthos 0 3 strain yr 1 with negligible seismic strain for the 100 year period prior to 1992 the egion earthquake of june 1995 in the western gulf of korinthos released only a small proportion 20 of the elastic strain that had accumulated in that region the observed distribution of displacements can be explained by the relative rotation of two plates with a broad accommodation zone between them but it is equally consistent with the deformation that would be expected of a sheet of fluid moving toward a low pressure boundary at the hellenic trench a simple calculation implies that if the region does behave as a fluid then its effective viscosity is 10 22 10 23 pa s such viscosities are consistent with the deformation of a lithosphere obeying a rheological law similar to that obtained for olivine in the laboratory

a source study of the thessaloniki northern greece 1978 earthquake sequence summary the thessaloniki northern greece earthquake sequence appears to have occurred along faults forming a graben structure this graben situated in the border region between the serbomacedonian massif and the vardar zone is bounded to the south west by clearly exposed north west striking north east dipping normal faults relative hypocentre determinations fault plane solutions surface faulting and the aftershock distribution suggest that some of these faults have been reactivated during the 1978 earthquakes the source parameters of the mainshock mb 6 1 ms 6 4 were determined by computing body wave synthetic seismograms in the time domain and comparing them with the observed this modelling constrained the orientation of faulting determined by the p wave fault plane solution it also constrained the source depth to 6 mp 2 km similar depths were calculated by a relative relocation method for the other three large events of the sequence the dislocation time function required for the far field had a total duration of 9 mp 1 5 s the body wave moment was 5 2 mp 1 8 times 1025 dyne cm for a fault length of 35 km and a fault width of 17 km both estimated from the aftershock distribution the static stress drop was found to be 4 bar an accelerograph record of the mainshock shows two distinct events 3 4 s apart these two events were unresolved by the long period data in the far field but the unusually long duration of the mainshock time function suggests an overall slow energy release which probably occurred as a sequence of events close in space and time seismic energy released in this fashion can account for waveform complexities observed at some stations

miocene pliocene exhumation along the west salton detachment fault southern california from u th he thermochronometry of apatite and zircon 1 the salton trough is the northernmost segment of the active gulf of california oblique rift system the main rift related structure in the western salton trough is the low angle west salton detachment fault wsdf footwall and hanging wall apatite and zircon u th he ages record a significant contrast in thermal history across the wsdf confirming pliocene normal slip along the fault apatite u th he ages record rapid exhumational cooling from 5 to 2 ma consistent with the timing of accelerated tectonic subsidence recorded in wsdf hanging wall sedimentary strata and consistent with the initiation age of dextral plate boundary slip on the southern san andreas fault in the salton trough our results indicate that the wsdf caused at least 2 3 4 km of exhumation and 8 10 km of approximately e directed horizontal extension since 5 ma slip rate of the wsdf at yaqui ridge was likely in the range of 2 3 5 km ma from 7 to 2 ma the wsdf may have been active well before 5 ma middle miocene apatite u th he ages from samples at high elevations have steep age elevation gradients and suggest that exhumation may have initiated by 12 ma about when subduction ceased along a large segment of the baja california margin and consistent with the age of onset of extension in northeastern baja california

initiation evolution and extinction of pull apart basins implications for opening of the gulf of california abstract we present a model for the origin crustal architecture and evolution of pull apart basins the model is based on results of three dimensional upper crustal elastic models of deformation field observations and fault theory and is generally applicable to basin scale features but predicts some intra basin structural features geometric differences between pull apart basins are inherited from the initial geometry of the strike slip fault step over which results from the forming phase of the strike slip fault system as strike slip motion accumulates pull apart basins are stationary with respect to underlying basement and the fault tips propagate beyond the rift basin increasing the distance between the fault tips and pull apart basin center because uplift is concentrated near the fault tips the sediment source areas may rejuvenate and migrate over time rift flank uplift results from compression along the flank of the basin with increasing strike slip movement the basins deepen and lengthen field studies predict that pull apart basins become extinct when an active basin crossing fault forms this is the most likely fate of pull apart basins because basin bounding strike slip systems tend to straighten and connect as they evolve the models show that larger length to width ratios with overlapping faults are least likely to form basin crossing faults and pull apart basins with this geometry are thus most likely to progress to continental rupture in the gulf of california larger length to width ratios are found in the southern gulf which is the region where continental breakup occurred rapidly the initial geometry in the northern gulf of california and salton trough at 6 ma may have been one of widely spaced master strike slip faults lower length to width ratios which our models suggest inhibits continental breakup and favors straightening of the strike slip system by formation of basin crossing faults within the step over as began 1 2 ma when the san jacinto and elsinore cerro prieto fault systems formed

structural analysis of recent and active faults and regional state of stress in the epicentral area of the 1978 thessaloniki earthquakes northern greece during spring and summer 1978 macedonia greece suffered damaging seismic activity during the two main shocks which occurred on may 23 mb 5 7 and june 20 mb 6 1 seismic open cracks and faults were formed in the epicentral area 25 km nne from thessaloniki they have been mapped and their kinematics analyzed these studies have shown that they result from the reactivation of existing faults of pleistocene recent and historical age and that the crust is stretching along a n s to nne ssw direction in that part of the north aegean principal stress directions have been computed from the slip vectors measured on recent neotectonic faults and seismic cracks and faults this computation utilizing a simple mechanical model homogeneous deformation through the addition of small and independent displacements of rigid blocks in a highly fractured body a striking feature of this analysis is that the tensional directions 3 deduced from seismic faulting and from recent neotectonic faulting are nearly the same they are compatible with the regional tension axis deduced from focal mechanisms of north aegean and with the focal mechanisms of the 1978 thessaloniki main shocks they are also compatible with in situ stress measurements in this region studies of superficial seismic faulting strongly support previous assumptions proposed from aftershock distribution the 1978 thessaloniki earthquakes resulted from reactivation of several different faults situated within the same ne dipping fault zone of upper eocene lower oligocene age and older separating the serbo macedonian massif from the peonias east vardar zone

the aegean sea we summarize briefly the main features of a kinematic model of evolution of the aegean area since 13 ma the formation of the aegean sea by extensional tectonics is related to the subduction of the mediterranean floor below the hellenic arc we then make a quantitative estimate of vertical movements in the aegean area on the basis of geological data and demonstrate that the outer arc was built since the beginning of this episode of subduction by vertical uplift the easiest way to explain the uplift is by underplating finally we discuss briefly the dynamics of the subduction marginal sea formation processes in this continental collision framework

trans dimensional geoacoustic inversion of wind driven ambient noise this letter applies trans dimensional bayesian geoacoustic inversion to quantify the uncertainty due to model selection when inverting bottom loss data derived from wind driven ambient noise measurements a partition model is used to represent the seabed in which the number of layers their thicknesses and acoustic parameters are unknowns to be determined from the data exploration of the parameter space is implemented using the metropolis hastings algorithm with parallel tempering whereas jumps between parameterizations are controlled by a reversible jump markov chain monte carlo algorithm sediment uncertainty profiles from inversion of simulated and experimental data are presented

pre pliocene extension around the gulf of california and the transfer of baja california to the pacific plate late miocene 12 5 ma extension around the edges of the gulf of california has been alternatively attributed to basin and range extension back arc extension or development of the pacific north america plate boundary this extension was ene directed and similar in structural style to extension in the basin and range province timing constraints permit nearly synchronous onset of this deformation in a belt extending sse from northernmost baja california to the mouth of the gulf where this extensional faulting continued through pliocene time to the present synchronous with motion on the modern transform plate boundary in the gulf of california no change in direction of extension can be resolved revised constraints on pacific north america plate motion support the development of this late miocene extension as a component of pacific north america displacement that could not be accommodated by strike slip displacement along the existing plate boundary west of the baja california peninsula this scenario implies that transfer of baja california from the north america plate to the pacific plate was a gradual process beginning about 12 10 ma when motion of the pacific plate relative to north america was partitioned into separate regimes of strike slip and dip slip displacement on opposite sides of baja california