do transcurrent faults guide volcano growth the case of nw bicol volcanic arc luzon philippines this paper shows that although volcanoes can be aligned along transcurrent faults their growth can in reality be controlled by secondary structures that have a different orientation and kinematics assessing the relationships between local structures and volcano growth can be very useful for the evaluation of volcanic hazards and for economic purposes such as geothermal and hydrogeological exploration in the north western bicol volcanic arc luzon philippines the quaternary labo and caayunan volcanoes are aligned with the nw striking transcurrent philippine fault system they are exceptional examples of composite volcanoes mostly comprising lava domes where regional tectonic structures and hydraulic radial fracturing have alternated to control volcano growth field data and analogue modelling demonstrate that apical depressions affecting the domes reflect the geometry of magma feeding fractures these data together with alignments of domes and hot springs and other structural information suggest that magma rose at depth along the nw striking transcurrent faults but that in the uppermost crust magma rose along ne striking fractures parallel to the greatest principal stress

late cenozoic transpressional ductile deformation north of the nazca south america antarctica triple junction abstract the southern andes plate boundary zone records a protracted history of bulk transpressional deformation during the cenozoic which has been causally related to either oblique subduction or ridge collision however few structural and chronological studies of regional deformation are available to support one hypothesis or the other we address along and across strike variations in the nature and timing of plate boundary deformation to better understand the cenozoic tectonics of the southern andes two east west structural transects were mapped at puyuhuapi and aysen immediately north of the nazca south america antarctica triple junction at puyuhuapi 44 s north south striking high angle contractional and strike slip ductile shear zones developed from plutons coexist with moderately dipping dextral oblique shear zones in the wallrocks in aysen 45 46 top to the southwest oblique thrusting predominates to the west of the cenozoic magmatic arc whereas dextral strike slip shear zones develop within it new 40ar 39ar data from mylonites and undeformed rocks from the two transects suggest that dextral strike slip oblique slip and contractional deformation occurred at nearly the same time but within different structural domains along and across the orogen similar ages were obtained on both high strain pelitic schists with dextral strike slip kinematics 4 4 0 3 ma laser on muscovite biotite aggregates aysen transect 45 s and on mylonitic plutonic rocks with contractional deformation 3 8 0 2 to 4 2 0 2 ma fine grained recrystallized biotite puyuhuapi transect oblique slip dextral reverse kinematics of uncertain age is documented at the canal costa shear zone 45 s and at the queulat shear zone at 44 s published dates for the undeformed protholiths suggest both shear zones are likely late miocene or pliocene coeval with contractional and strike slip shear zones farther north coeval strike slip oblique slip and contractional deformation on ductile shear zones of the southern andes suggest different degrees of along and across strike deformation partitioning of bulk transpressional deformation the long term dextral transpressional regime appears to be driven by oblique subduction the short term deformation is in turn controlled by ridge collision from 6 ma to present day this is indicated by most deformation ages and by a southward increase in the contractional component of deformation oblique slip to contractional shear zones at both western and eastern margins of the miocene belt of the patagonian batholith define a large scale pop up structure by which deeper levels of the crust have been differentially exhumed since the pliocene at a rate in excess of 1 7 mm year

strain partitioning and stress rotation at the north anatolian fault zone from aftershock focal mechanisms of the 1999 izmit mw 7 4 earthquake summary we investigate aftershock focal mechanisms of the m w 7 4 izmit earthquake of 1999 august 17 on the western north anatolian fault zone nafz spatial clustering and the orientation of 446 fault plane solutions are analysed the izmit mainshock occurred as a right lateral slip on an ew trending near vertical fault plane aftershock clusters define four individual fault segments focal mechanisms surrounding the epicentres of the izmit and subsequent duzce mainshock m w 7 1 1999 november 12 indicate predominantly strike slip but also normal faulting aftershocks in the area between the izmit and duzce segments are mainly related to ew oriented normal faulting delineating a small pull apart structure beneath the easternmost sea of marmara alignments of aftershocks suggest branching of the nafz into three or more active segments that differ significantly in terms of their focal mechanism characteristics the distribution of aftershock focal mechanisms corresponds to fault segmentation of the nafz in the izmit duzce region produced by coseismic slip areas with large amounts of coseismic slip show aftershocks that are predominantly strike slip but low slip barriers show mostly normal faulting aftershocks stress tensor inversions of the aftershock focal mechanisms show rotations of the local stresses following the izmit mainshock in the izmit sapanca area the maximum horizontal compressive stress axis is horizontally rotated counter clockwise by 8 with respect to the coseismic and long term regional stress field towards the eastern end of the rupture karadere duzce area stresses are rotated clockwise we conclude that the izmit earthquake caused significant stress partitioning along the rupture the direction of stress rotation is related to the orientation of the individual fault segments along the nafz

crustal thickness variations and isostatic disequilibrium across the north anatolian fault western turkey we use teleseismic recordings from a dense array of seismometers straddling both strands of the north anatolian fault zone to determine crustal thickness p s velocity ratio and sedimentary layer thickness to do this we implement a new grid search inversion scheme based on the use of transfer functions removing the need for deconvolution for source normalization and therefore eliminating common problems associated with crustal scale receiver function analysis we achieve a good fit to the data except at several stations located in quaternary sedimentary basins where our two layer crustal model is likely to be inaccurate we find two zones of thick sedimentary material one north of the northern fault branch and one straddling the southern branch the crustal thickness increases sharply north of the northern strand of the north anatolian fault zone nafz where the fault nearly coincides with the trace of the intra pontide suture the velocity ratio changes across the southern fault strand indicating a change in basement composition we interpret these changes to indicate that both strands of the nafz follow preexisting geological boundaries rather than being ideally aligned with the stress field the thick crust north of the northern nafz strand is associated with low topography and so is inconsistent with simple models of isostatic equilibrium requiring a contribution from mantle density variations such as possible loading from underthrust black sea oceanic lithosphere

crustal imaging across the north anatolian fault zone from the autocorrelation of ambient seismic noise seismic images of active fault zones can be used to examine the structure of faults throughout the crust and upper mantle and give clues as to whether the associated deformation occurs within a narrow shear zone or is broadly distributed through the lower crust limitations on seismic resolution within the crust and difficulties imaging shallow structures such as the crust mantle boundary moho place constraints on the interpretation of seismic images in this study we retrieve body wave reflections from autocorrelations of ambient seismic noise the instantaneous phase coherence autocorrelations allow unprecedented ambient noise images of the north anatolian fault zone nafz our reflection profiles show a moho reflected p wave and additional structure within the crust and upper mantle we image a distinct vertical offset of the moho associated with the northern branch of the nafz indicating that deformation related to the fault remains narrow in the upper mantle

distribution of seismic velocities and attenuation in the crust beneath the north anatolian fault turkey from local earthquake tomography we investigate the crustal structure beneath the western part of the north anatolian fault zone nafz an area where at least five damaging earthquakes occurred during the twentieth century this study is based on local earthquake tomography using the data from aftershocks of the izmit event 17 august 1999 m 7 4 recorded by stations of permanent and temporary networks we derive the distribution of v p v s and the v p v s ratio based on the iterative inversion for both v p v s and v p v p v s using the lotos code innovatively in this study we perform an inversion for frequency dependent s wave attenuation 1 q s the reliability of the results is assessed through synthetic tests the distributions of the resulting seismic parameters v p v s v p v s and q s highlight important geodynamical features in the study area the low velocity and high attenuation patterns mostly correlate with the fracturing zones of the nafz low velocities are also observed beneath the main sedimentary basins e g adapazari duzce and kuzuluk high velocity and low attenuation patterns correlate with blocks presumed to be rigid kocaeli armutlu and almacik blocks the rupture traces of the largest earthquakes in this area pass generally in the transition areas between high and low velocities while moderate and weak seismicity is mostly concentrated in low velocity areas based on these results we propose and discuss the role that the almacik block could have played in producing the largest earthquakes in the study area in the twentieth century

geological manifestations of ridge collision evidence from the golfo de penas taitao basin southern chile recent geological and geophysical studies in the southern andes adjacent to the intersection of the chile rise with the peru chile trench ant naz sam triple junction have revealed a number of features and a neogene geologic history that are unique along the pacific margin of south america this history includes 1 development of a tertiary quaternary marine basin with up to 3 km of sediment infill golfo de penas taitao basin gtb 2 disruption of the region by a series of faults with both normal and strike slip movements and 3 localization of silicic near trench volcanism and epizonal plutonism and related hydrothermal activity the northern portion of the gtb began to subside in the late miocene possibly earlier and has subsequently been deformed uplifted and exposed gravity and seismic reflection data suggest that the basin continues offshore where it is still actively subsiding today golfo de penas subsidence and uplift have thus occurred diachronously in the region although it is unclear when subsidence began in the golfo de penas tectonic disruption of the region is likely related to the liquine ofqui fault lof a major ns trending crustal shear zone that curves westward and terminates in the golfo de penas the lof has both down to the west and right lateral offset and separates the main andean cordillera on the east from a large crustal block the chiloe block on the west we hypothesize that the gtb has developed as a pull apart basin in response to northward movement of the chiloe block along the lof we propose a dynamic model whereby a stress gradient that decreases longitudinally away from the chile rise peru chile trench intersection is set up because the youngest most buoyant oceanic lithosphere is being subducted at the triple junction the chile rise is viewed as a type of indenter which is acting to drive the chiloe block northward in front of the northward migrating triple junction this model explains the unique set of geologic features found in the region and suggests that ridge trench interactions may be an important factor in orogenesis at active continental margins

stress modeling of tectonic blocks at cape kamchatka russia using principal stress proxies from high resolution sar new evidence for the komandorskiy block abstract a new data set of 851 lineaments mapped from european remote sensing satellites 1 and 2 full resolution synthetic aperture radar sar data are interpreted as geological proxies for stresses resulting from plate and block collision near the cape kamchatka region of the kamchatka peninsula using a geographical information systems based analysis numerical manifold method nmm analysis is used to model the stress field within the cape kamchatka region resulting from the collision of lithospheric plates and blocks results of our nmm model using different plate motion and plate configuration in the region are compared with orientation data for the mapped set of lineaments these data suggest that the lineaments observed in sar cannot be fully explained by a simple two plate model in this in the cape kamchatka region as an alternative we propose that the data can be explained by the existence of the previously proposed komandorskiy block recent global positioning satellite measurements in the aleutian islands support our lineament derived model and show that the near islands komandorskiy island block of the extreme western aleutians is moving independently of the north american plate

a shallow fault zone structure illuminated by trapped waves in the karadere duzce branch of the north anatolian fault western turkey summary we discuss the subsurface structure of the karadere duzce branch of the north anatolian fault based on analysis of a large seismic data set recorded by a local passcal network in the 6 months following the mw 7 4 1999 izmit earthquake seismograms observed at stations located in the immediate vicinity of the rupture zone show motion amplification and long period oscillations in both p and s wave trains that do not exist in nearby off fault stations examination of thousands of waveforms reveals that these characteristics are commonly generated by events that are well outside the fault zone the anomalous features in fault zone seismograms produced by events not necessarily in the fault may be referred to generally as fault zone related site effects the oscillatory shear wave trains after the direct s arrival in these seismograms are analysed as trapped waves propagating in a low velocity fault zone layer the time difference between the s arrival and trapped waves group does not grow systematically with increasing source receiver separation along the fault these observations imply that the trapping of seismic energy in the karadere duzce rupture zone is generated by a shallow fault zone layer traveltime analysis and synthetic waveform modelling indicate that the depth of the trapping structure is approximately 3 4 km the synthetic waveform modelling indicates further that the shallow trapping structure has effective waveguide properties consisting of thickness of the order of 100 m a velocity decrease relative to the surrounding rock of approximately 50 per cent and an s wave quality factor of 10 15 the results are supported by large 2 d and 3 d parameter space studies and are compatible with recent analyses of trapped waves in a number of other faults and rupture zones the inferred shallow trapping structure is likely to be a common structural element of fault zones and may correspond to the top part of a flower type structure the motion amplification associated with fault zone related site effects increases the seismic shaking hazard near fault zone structures the effect may be significant since the volume of sources capable of generating motion amplification in shallow trapping structures is large

cenozoic evolution of neotethys and implications for the causes of plate motions africa north america eurasia plate circuit rotations combined with red sea rotations and new estimates of crustal shortening in iran define the cenozoic history of the neotethyan ocean between arabia and eurasia the new constraints indicate that arabia eurasia convergence has been fairly constant at 2 to 3 cm yr since 56 ma with slowing of africa eurasia motion to 1 cm yr near 25 ma coeval with the opening of the red sea ocean closure occurred no later than 10 ma and could have occurred prior to this time only if a large amount of continental lithosphere was subducted suggesting that slowing of africa significantly predated the arabia eurasia collision these kinematics imply that africa s disconnection with the negative buoyancy of the downgoing slab of lithosphere beneath southern eurasia slowed its motion the slow steady rate of northward subduction since 56 ma contrasts with strongly variable rates of magma production in the urumieh dokhtar arc implying magma production rate in continental arcs is not linked to subduction rate

the surface rupture and slip distribution of the 17 august 1999 izmit earthquake m 7 4 north anatolian fault the 17 august 1999 izmit earthquake occurred on the northern strand of the north anatolian fault zone the earthquake is associated with a 145 km long surface rupture that extends from southwest of duzce in the east to west of hersek delta in the west detailed mapping of the surface rupture shows that it consists of five segments separated by releasing step overs herein named the hersek karamursel golcuk izmit sapanca lake sapanca akyazi and karadere segments from west to east respectively the hersek segment which cuts the tip of a large delta plain in the western end of the rupture zone has an orientation of n80 the n70 80 e trending karamursel golcuk segment extends along the linear southern coasts of the izmit gulf between karamursel and golcuk and produced the 470 cm maximum displacement in golcuk the northwest southeast striking golcuk normal fault between the karamursel golcuk and izmit sapanca segments has 2 3 m maximum vertical displacement the maximum dextral offset along the izmit sapanca lake segment was measured to be about 3 5 m and its trend varies between n80 e and east west the sapanca akyazi segment trends n75 85 w and expresses a maximum displacement of 5 2 m the karadere segment trends n65 e and produced up to 1 5 m maximum displacement the karadere and sapanca akyazi segments form fan shape or splaying ruptures near their eastern ends where the displacement also diminished

contrasting nature of deformation along an intra arc shear zone the liquine ofqui fault zone southern chilean andes abstract the liquine ofquifault zone lofz cuts the patagonian batholith and the modern volcanic arc of southern chile for ca 1000 km the rock fabric along three transects of the lofz combined with new and published geochronological data suggest marked differences in the nature and timing of deformation along strike in the liquine transect 39 s a 1 km wide northeast striking subvertical mylonitic zone shows north plunging stretching lineations this mylonitic zone has been juxtaposed by high angle reverse faulting against a nearly undeformed miocene granitoid metamorphic assemblages and microstructures in the mylonites indicate greenschist facies conditions and sinistral reverse displacement deformation pre dates a 100 2 ma undeformed porphyritic dike hornblende 40ar 39ar mean age in the reloncavi transect 41 42 s deformation in cretaceous and miocene plutons is predominantly brittle kinematic analysis of two fault populations yields compressional and dextral strike slip stress regimes interpreted as late miocene in age in the hornopiren transect 42 43 s a 4 km wide mylonitic zone developed in plutons and wallrocks shows subhorizontal stretching lineations and dextral displacement a single fault population overprinting the mylonites supports a dextral strike slip stress regime available u pb k ar and 40ar 39ar dates on deformed cenozoic plutons and wallrock range from 9 to 13 ma on hornblende and from 6 to 3 ma on biotite microstructures and mineral assemblages indicate that the youngest ductile fabrics in the plutons formed at greenschist facies similar to the biotite ar closure temperature subparallel magmatic and solid state fabrics combined with geochronology suggest that dextral displacement was continuous during emplacement and cooling of the plutons dextral oblique subduction of the nazca plate beneath western south america has driven long term intra arc deformation at the southern andes plate boundary zone ridge collision in turn has favored dextral displacement at the leading edge of the continent since the pliocene

morphology displacement and slip rates along the north anatolian fault turkey 1 geological and geomorphological offsets at different scales are used to constrain the localization of deformation total displacement and slip rates over various timescales along the central and eastern north anatolian fault naf in turkey the naf total displacement is reevaluated using large rivers valleys 80 15 km and structural markers pontide suture 85 25 km tosya vezirkopru basins 80 10 km these suggest a neogene slip rate of 6 5 mm yr over 13 myr the river network morphology shows offsets at a range of scales 20 m to 14 km across the main fault trace and is also used to estimate the degree to which deformation is localized at a smaller scale the morphology associated with small rivers is offset by 200 m along the naf the age of these features can be correlated with the holocene deglaciation and a slip rate of 18 3 5 mm yr is determined this is consistent with a rate of 18 5 mm yr deduced independently from the 14c dating of stream terrace offsets over the short term gps data gives a similar rate of 22 3 mm yr all our results tend to show that most of the deformation between the anatolian and eurasian lithospheric plates has been accommodated along or very close to the active trace of the naf the difference between the neogene and the holocene slip rate may be due to the recent establishment of the current plate geometry after the creation of the naf

single domain chemical thermochemical and thermal remanences in a basaltic rock summary tiny basaltic samples containing finely grained titanomagnetite with curie temperature less than 100 c were heated in air in weak field 25 100 t at temperatures between 400 c and 560 c for times as long as 32 hr oxyexsolution of titanomagnetite resulted in the crystallization of interacting single domain particles with curie point close to 540 c and the concomitant development of one of two types chemical remanence depending upon thermal treatment isothermal chemical remanence crm or thermochemical remanence tcrm the latter acquired under the combined effects of chemical change and temperature decrease crm and tcrm acquired under various conditions were subjected to thellier type experiments all these treatments were carried out using a vibrating sample thermomagnetometer allowing the continuous recording of magnetization and a very precise temperature control all crm trm and tcrm trm plots were found to be linear over almost the entire trm blocking temperature range whether ptrm checks are positive or not an apparent strength of the acquisition field of crm or tcrm could thus be obtained and divided by the actually applied field to obtain a ratio r which is representative of the crm trm or tcrm trm ratios over most of the unblocking blocking temperature spectrum for crm it is found that r is less than 1 and increases rapidly with acquisition temperature 0 36 0 07 at 400 c 0 66 0 02 at 450 c and 0 90 0 02 at 500 c in qualitative agreement with expressions derived from the theory of non interacting single domain grains thus very large underestimate of geomagnetic field palaeostrength can occur when a natural crm is not recognized as such and is believed to be a natural trm palaeointensity data obtained from geological material prone to the development of secondary minerals as for example baked contacts and volcanic glasses have therefore to be considered with caution in an attempt to mimic deuteric oxyexsolution in cooling magma tcrm was imparted from 560 c to 400 c at a cooling rate of 0 1 c min in contrast to the crm case r is found to slightly exceed 1 1 11 0 05 according to theoretical considerations this finding suggests that in practice tcrm approximates to trm

postmagmatic cooling and late cenozoic denudation of the north patagonian batholith in the los lagos region of chile 41 42 15 s zircon and apatite fission track ft thermochronology was applied to investigate the history of cooling and denudation of the southern andes between 41 and 42 15 s in relation to the late cenozoic activity of the liquine ofqui fault zone lofz and the northward migration of the chile triple junction ctj fifty six zircon and 51 apatite ft ages plus 37 apatite confined track length distributions were obtained mainly from plutonic rocks of the north patagonian batholith npb in the main andean cordillera apatite ft ages and track lengths indicate a stage of rapid cooling at 5 3 ma along both sides of the lofz whereas older miocene ages with monotonous cooling histories were obtained further away from the fault zircon ft ages range from cretaceous to pliocene with marked differences observed along and across the lofz three different types of temperature time histories characterise the post magmatic cooling of the npb in the region deep intrusions with moderate and steady cooling rates intrusions in the upper crust with very slow cooling rates following a stage of initial rapid cooling and rapidly cooled and exhumed shallow intrusions the latter with younger ages towards the fault zone the most prominent denudation episode along the lofz is late miocene to pliocene coeval with plate tectonic reconstructions for the arrival and subduction of the chile rise beneath the taitao peninsula

late cenozoic geomorphic and tectonic evolution of the patagonian andes between latitudes 42 s and 46 s an appraisal based on fission track results from the transpressional intra arc liquine ofqui fault zone fission track ft thermochronology has been applied to investigate the low temperature cooling and denudation history of the patagonian andes along the southern part of the intra arc transpressional liquine ofqui fault zone between 42 and 46 s the liquine ofqui fault is shown to have been the focus of enhanced cooling and denudation initiated between ca 16 and 10 ma several fault blocks with different cooling histories are identified these are separated by major oblique or reverse slip faults proposed to form the eastern part of a major crustal scale dextral transpression zone local very fast rates of cooling and denudation between ca 7 and 2 ma were coeval with collision of the chile rise an active mid oceanic ridge with the peru chile trench between 47 and 48 s this location is close to the southern termination of the liquine ofqui fault implying that the collision of the ridge was a major force driving late cenozoic transpression the lack of significant cooling and denudation before ca 16 ma is indicative of pure strike slip or transtensional movement along the liquine ofqui fault before the collision of the ridge digital landscape analysis supports glacial and periglacial erosion as the main contributor to denudation since ca 7 ma leading to restriction of topographic development the combination of transpression induced rock uplift and glacial erosion is shown to be very effective at causing localized denudation anomalously young ft ages along the liquine ofqui fault are attributed to the existence of a late cenozoic localized heat flow anomaly along the fault

the link between volcanism and tectonics in the southern volcanic zone of the chilean andes a review abstract the nature of the interplay between tectonics and volcanism is a major question in continental margin tectonics the southern andes volcanic zone svz located at the obliquely convergent nazca south america plate margin between 33 s and 46 s offers a unique opportunity to address this question because of along strike changes in crustal thickness tectonic style and well constrained long term and short term kinematic history the complex interaction between tectonic and magmatic processes is evidenced by both the architecture and geochemical signature of volcanic systems main first order factors accounting for the along strike variations in the nature and composition of volcanism are crustal thickness and the existence of a major intra arc fault system the liquine ofqui fault zone lofz second order factors include the local nature of the volcanic arc basement two main categories of volcano tectonic associations have been identified according to the spatial distribution and internal organization of individual volcanoes and clusters of volcanoes with respect to both the overall strike of the volcanic arc and the first and second order active inactive basement faults kinematically coupled associations those that are directly related to the current dextral transpressional tectonic regime include ne trending volcanic alignments of stratovolcanoes and or monogenetic cones kinematically uncoupled associations in which coupling with the current regime is not required include stratovolcanoes built on top of ancient reverse and strike slip faults of the volcanic arc basement and monogenetic cones lying along master faults of the lofz whereas mostly primitive magmas are found in the first category more evolved terms can occur genetically associated with the second category we propose a simplified three dimensional model for the magma plumbing system along and across the svz that integrates kinematically coupled and kinematically uncoupled volcano tectonic associations within the framework of first and second order geological and structural constraints

chemical gradient at diffusive interfaces in magma chambers the results of high pressure experiments on diffusion and soret separation in natural silicate melts show that the diffusive behaviour between natural silicic and mafic magmas can be approximately modelled as if the system were a binary mixture of sio2 and other components such as mgo feo cao steady state compositional profiles across a diffusive interface between silicic and mafic magma layers are calculated on the basis of phenomenological relationships for the fluxes of chemical species and heat in the binary mixtures using the experimental data of diffusion and soret coefficients in natural silicate melts the compositional profiles show a curvature with a minimum sio2 value within the interface due to the soret effect and temperature dependence of diffusion coefficient the compositional gradient at the lower half of the diffusive interface is similar to that resulting from the soret separation of a mafic melt regardless of the composition of the silicic magmas these results suggest that picritic magma can be formed in the interfacial region between the mafic and silicic magma layers the compositional gradient explains chemical variation of mafic to picritic inclusions in a mixed andesite of the abu volcano group japan

the motion of crustal blocks driven by flow of the lower lithosphere and implications for slip rates of continental strike slip faults geodetic measurements in actively deforming areas of the continents reveal the pattern of deformation in the lithosphere if the dominant forces acting on crustal blocks are tractions at their bases then the long term motion of each block will be given by the average velocity of the underlying lithosphere slip rates between blocks estimated in this way from recent geodetic measurements across fault zones in the south island of new zealand and southern california are in good agreement with slip rates estimated geologically

cu and fe diffusion in rhyolitic melts during chalcocite dissolution implications for porphyry ore deposits and tektites copper diffusion plays an important role in natural processes such as metal transport during the formation of magmatic hydrothermal porphyry type ore deposits and cu isotope fractionation during tektite formation copper diffusion data in natural silicate melts however are limited in this study chalcocite cu 2 s dissolution experiments were carried out using chalcocite rhyolite diffusion couples to study cu and s diffusion in rhyolitic melts instead of chalcocite dissolution as initially expected our experiments show that cu is transferred from the chalcocite crystal to the rhyolitic melt and fe is transferred from the rhyolitic melt to chalcocite whereas the s concentration profile in the rhyolitic melt is essentially flat from the cu and fe exchange profiles in the rhyolitic melts cu diffusivities and fe diffusivities are obtained and reported copper diffusivity in rhyolitic melts containing 0 10 to 5 95 wt h 2 o at temperatures of 750 to 1391 c and pressures of 0 5 to 1 0 gpa can be described as d cu rhy exp 14 75 0 35 0 23 0 10 w 11647 491 698 117 w t which allows the estimation of an activation energy for diffusion in dry rhyolitic melts to be 96 8 4 1 kj mol in the above equation diffusivity d is in m 2 s t is the temperature in k w is the h 2 o concentration in the rhyolitic melts in wt and all errors reported are at 1 level combining cu diffusion data from this study and previous data in basaltic melt gives a general equation for cu diffusivity in natural silicate melts d cu exp 17 3 0 9 3 8 1 5 si al h 4403 1094 9700 1921 si al h t where si al h is the cation mole fraction of si plus al minus h in the silicate melt on a wet basis iron diffusivities obtained in this study in anhydrous to 6 wt h 2 o rhyolite are combined with previous data to get a general equation for fe diffusion in rhyolitic melts d fe rhy exp 16 1 1 7 19859 2541 1218 135 w t our data demonstrate that cu diffusion is faster than h 2 o or cl in rhyolitic melts containing 6 wt water which indicates that the scavenging and transport of cu by a magmatic volatile phase during formation of porphyry type ore deposits is not limited by diffusion of cu based on our experimental data cu diffusivity is almost four orders of magnitude higher than zn in anhydrous rhyolitic melts which supports the explanation of more diffusive loss of cu leading to more fractionated cu isotopes than zn isotopes in tektites

accelerating seismicity and stress accumulation before large earthquakes the stress field that existed before a large earth quake can be calculated based on the known source parame ters of the event this stress field can be used to define a region that shows greater seismic moment rate changes prior to the event than arbitrarily shaped regions allowing us to link two previously unrelated subjects coulomb stress interactions and accelerating seismicity before large earthquakes as an example we have examined all m 6 5 earthquakes in california since 1950 while we illustrate the model using seismicity in california the technique i s general and can be applied to any tectonically active re gion we show that where sufficient knowledge of the re gional tectonics exists this method can be used to aug ment current techniques for seismic hazard estimation

finite element modelling of crustal deformation in the baikal rift zone new insights into the active passive rifting debate abstract the origin of the forces responsible for crustal extension in the baikal rift zone siberia is the object of a debate between passive rifting models where crustal extension is primarily caused by horizontal forces related to the kinematics of asia india eurasia collision and active rifting models where crustal extension is primarily caused by a diapiric mantle upwelling in this work we used a two dimensional visco elastic finite element model in order to determine whether horizontal forces alone can account for the present day deformation in the baikal rift zone we tested a number of kinematic boundary conditions and compared predictions of various models against the observed stress and strain field deduced from seismotectonic data earthquake focal mechanisms and microtectonic analyses by adjusting the kinematic boundary conditions and using a three plate model with a differential displacement between the mongolian and amurian plates we found a best fit model that correctly accounts for the observed strain and stress field over the entire baikal rift zone the fact that our model does not take into account vertical forces but still explains most of the observed deformation suggests that the present day opening of the baikal rift is essentially controlled by horizontal forces related to the regional kinematics these forces could have their origin in the india eurasia collision zone further south this result does not imply that the asthenosphere played no role in the rifting process in particular before the fast rifting stage of the baikal rift evolution 3 4 ma but might suggest a recent plio quaternary triggering effect of the india asia collision on the deformation in the baikal rift

possible worst case tsunami scenarios around the marmara sea from combined earthquake and landslide sources this study evaluates tsunami hazards in the marmara sea from possible worst case tsunami scenarios that are from submarine earthquakes and landslides in terms of fault generated tsunamis seismic ruptures can propagate along the north anatolian fault naf which has produced historical tsunamis in the marmara sea based on the past studies which consider fault generated tsunamis and landslide generated tsunamis individually future scenarios are expected to generate tsunamis and submarine landslides could be triggered by seismic motion in addition to these past studies numerical modeling has been applied to tsunami generation and propagation from combined earthquake and landslide sources in this study tsunami hazards are evaluated from both individual and combined cases of submarine earthquakes and landslides through numerical tsunami simulations with a grid size of 90 m for bathymetry and topography data for the entire marmara sea region and validated with historical observations from the 1509 and 1894 earthquakes this study implements tunami model with a two layer model to conduct numerical tsunami simulations and the numerical results show that the maximum tsunami height could reach 4 0 m along istanbul shores for a full submarine rupture of the naf with a fault slip of 5 0 m in the eastern and western basins of the marmara sea the maximum tsunami height for landslide generated tsunamis from small medium and large of initial landslide volumes 0 15 0 6 and 1 5 km3 respectively could reach 3 5 6 0 and 8 0 m respectively along istanbul shores possible tsunamis from submarine landslides could be significantly higher than those from earthquakes depending on the landslide volume significantly these combined earthquake and landslide sources only result in higher tsunami amplitudes for small volumes significantly because of amplification within the same tsunami amplitude scale 3 0 4 0 m waveforms from all the coasts around the marmara sea indicate that other residential areas might have had a high risk of tsunami hazards from submarine landslides which can generate higher tsunami amplitudes and shorter arrival times compared to istanbul

the liquine ofqui fault zone a long lived intra arc fault system in southern chile abstract plate reconstructions for the cenozoic document relatively steady right oblique subduction of the farallon nazca plate beneath the chilean continental margin the kinematic signature recorded along the intra arc liquine ofqui fault zone lofz a major feature of the southern andes may help to understand the way in which the nazca south america slip vector has been partitioned into strain and displacement along and across the continental margin the lofz consists of two nne trending right stepping straight lineaments a strike slip duplex at the right step and curved features which splay off the straight lineaments toward the northwest the lofz runs mostly through heterogeneously deformed cenozoic plutonic rock of the north patagonian batholith and patchy metamorphic wall rock early cenozoic volcano sedimentary rocks and dyke swarms found in close spatial association with the strike slip duplex are believed to have developed in strike slip related basins quaternary volcanoes are aligned parallel to the lofz both ductile and brittle kinematic indicators within centimeter to meter wide high strain zones document late cenozoic dextral shear deformation contrasting left lateral deformation recorded on older and wider mylonitic zones suggests that the lofz may be a long lived shear zone that accommodated continental scale deformation arising from the farallon nazca south america plate convergence a block rotation pattern as indicated by paleomagnetic data is consistent with the geometry and cenozoic kinematics of the lofz

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

space geodetic estimation of the nazca south america euler vector abstract gps data from four sites in the nazca plate easter island galapagos robinson crusoe and san felix islands and from five sites in the stable core of the south american plate enabled us to estimate the euler vector of the nazca plate with respect to south america the observed velocities of easter island 6 6 cm yr at 102 3 galapagos 5 1 cm yr at 90 0 robinson crusoe 6 6 cm yr at 80 1 and san felix 6 0 cm yr at 82 1 are significantly slower than the global plate model nuvel 1a velocites for those four sites our estimated euler pole is located at 48 8 n 91 7 w with a rate of 0 59 m y the nuvel 1a and earlier space geodetic studies give rotation rates that are 20 faster

multicomponent diffusion in a basaltic melt temperature dependence abstract eighteen successful diffusion couple experiments in 8 component sio2 tio2 al2o3 feo mgo cao na2o k2o basaltic melts were conducted at 1260 c and 0 5 gpa and at 1500 c and 1 0 gpa these experiments are combined with previous data at 1350 c and 1 0 gpa guo and zhang 2018 to study the temperature dependence of multicomponent diffusion in basaltic melts effective binary diffusion coefficients of components with monotonic diffusion profiles were extracted and show a strong dependence on their counter diffusing component even though the average or interface compositions are the same the diffusion matrix at 1260 c was obtained by simultaneously fitting diffusion profiles of all diffusion couple experiments as well as appropriate data from the literature all features of concentration profiles in both diffusion couples and mineral dissolution are well reproduced by this new diffusion matrix at 1500 c only diffusion couple experiments are used to obtain the diffusion matrix eigenvectors of the diffusion matrix are used to discuss the diffusion exchange mechanism and eigenvalues characterize the diffusion rate diffusion mechanisms at both 1260 and 1500 c are inferred from eigenvectors of diffusion matrices and compared with those at 1350 c reported in guo and zhang 2018 there is indication that diffusion eigenvectors in basaltic melts do not depend much on temperature but complexity is present for some eigenvectors the two slowest eigenvectors involve the exchange of sio2 and or al2o3 with nonalkalis the third slowest eigenvector is due to the exchange of divalent oxides with other oxides the fastest eigenvector is due to the exchange of na2o with other oxide components some eigenvalues differ from each other by ti oxide mineralization

determining the geometry of the north anatolian fault east of the marmara sea through integrated stress modeling and remote sensing techniques abstract the 1200 km long north anatolian fault naf is part of an east west trending dextral shear zone naf system along the boundary between the anatolian and eurasian plates that widens to the west this widening zone of deformation complicates potential earthquake rupture paths and highlights the importance of understanding the geometry of active fault systems in the central portion of the naf system just west of the town of bolu the naf splits into two major faults the northern and southern strands these two faults diverge almost converge and then diverge again to border the marmara sea earthquake data from the region where the two faults converge indicate that they may be linked by an active fault we model the active fault geometries with and without the linking fault to explore its impact on the output regional stress field from a finite element model these results are compared to focal mechanism records and lineament analyses to determine which geometry best simulate the stress field in a regional model our results show that a linking fault between the northern and southern strands of the naf system is necessary to best match the primary stress orientations of the model with the maximum paleostress orientations inferred from deformation patterns and observed in earthquake focal mechanisms furthermore the linking fault should be a significant component in future models of the naf system within the region

the north anatolian fault a new look dedicated to the memory of three pioneers ihsan ketin sirri erinc and melih tokay and a recent student aykut barka who burnt himself out in pursuit of the mysteries of the north anatolian fault abstract the north anatolian fault naf is a 1200 km long dextral strike slip fault zone that formed by progressive strain localization in a generally westerly widening right lateral keirogen in northern turkey mostly along an interface juxtaposing subduction accretion material to its south and older and stiffer continental basements to its north the naf formed approximately 13 to 11 ma ago in the east and propagated westward it reached the sea of marmara no earlier than 200 ka ago although shear related deformation in a broad zone there had already commenced in the late miocene the fault zone has a very distinct morphological expression and is seismically active since the seventeenth century it has shown cyclical seismic behavior with century long cycles beginning in the east and progressing westwa

the north anatolian fault in the sea of marmara 1 using the detailed geometry and tectonics of the main marmara fault that connects the gulf of izmit fault with the ganos fault established by le pichon et al 2001 and the new gps data set recently analyzed by meade et al 2002 we confirm the existence of a marmara block delimited to the north by the northern branch of the north anatolian fault the marmara branch and to the south by the southern branch the kinematics of this block indicate that the marmara branch that crosses the sea of marmara is close to pure dextral strike slip at a rate of 23 mm yr on its whole length the short cinarcik section is the only one where a significant extensional component is predicted a simple kinematic model accounts for slip partitioning there with 8 10 mm yr of extension to the south of the basin and 23 mm yr of dextral strike slip along the northern cinarcik margin the new gps data demonstrate the existence of important asymmetric elastic loading along the main marmara fault that may have significant implications for the seismotectonics of the area the expected future large earthquake may rupture the whole main marmara fault the partitioning in the cinarcik basin may produce magnitude 7 normal faulting earthquakes if their repetition time is about 250 years the 1896 earthquake may have been one of these normal fault earthquakes the marmara block is less than 1 ma prior to its formation it was part of the anatolian block at this time the ganos fault was already a dextral strike slip fault but the fault system in the sea of marmara would have been affected by an extensional component increasing toward the east that accounts for the increasing size of the sedimentary basins eastward

the role of magma mixing in the genesis of pge mineralization in the bushveld complex thermodynamic calculations and new interpretations the elegant magma mixing model for the formation of the platinum group elements pge mineralization associated with chromite and sulfide in the bushveld complex proposed by naldrett and von gruenewaldt 1989 has recently been questioned by cawthorn 1999 based on his own calculation cawthorn concluded that the concave upward sulfur solubility curve of a fractionated basaltic magma which is central to the model does not exist cawthorn 1999 pointed out that both the hanging wall and footwall sequences of the merensky reef formed from sulfide undersaturated magmas instead of sulfide saturated magmas as predicted by the model cawthorn argued that there is a mass balance problem with the model if these rocks did not contribute pge to the sulfides in the reef our thermodynamic calculations indicate that the concave upward curve of s solubility though different in detail from the original is very much in evidence our calculations also indicate that the content of s dissolved in the residual magma may fall below the s solubility curve when the rate of s increase in the magma due to the removal of silicate cumulates is less than the rate of increase in its s solubility due to the change in its temperature and composition during fractional crystallization mixing of such fractionated and yet sulfide undersaturated magma with appropriate amounts of a primitive magma is still capable of achieving sulfide oversaturation in the hybrid once the immiscible sulfides settle out of the magma the content of s dissolved in the hybrid may fall below its solubility curve again during further crystallization thus no sulfide segregation is expected in the rocks crystallized subsequently r factor assessment needs to consider the consequence of sulfide suspension in magma small quantities of sulfide droplets formed during the normal course of fractional crystallization may remain suspended in magma until the next replenishment and in this case they can be redissolved in the hybrid when the proportion of a new input is large enough because there is no early sulfide liquid segregation both the residual and new magmas will not be depleted in pge and are equally important for contributing pge to the sulfide liquid segregated during a subsequent magma mixing event

tectonic consequences of the collision of the arabian and eurasian plates finite element models abstract the tectonic consequences of northward motion of the arabian plate and its push against the anatolian plate are modeled using a two dimensional plane stress finite element scheme interaction of four plates african arabian anatolian and eurasian and rupture of major faults inside and around anatolia are investigated by assigning northward motions to the arabian 5 cm yr and the african 3 cm yr plates a number of boundary conditions are used to match the known fault motions with theoretical models the faults are modeled as weak zones which could fail by slip strike slip faulting and or separation normal faulting numerical models show that northward convergence of the arabian and african plates alone cannot explain movements on all known faults an additional driving force that would produce about 2 cm yr westward motion of the anatolian plate is required with such a boundary condition added the finite element models produce movements along five major faults north anatolian east anatolian dead sea or levant fracture tuz golu and ecemis with current magnitudes and directions

westward propagation of the north anatolian fault into the northern aegean timing and kinematics we present new evidence for the propagation processes of the north anatolian fault folding in the dardanelles straits region allows us to document the timing of the deformation preceding and the finite displacement after the passage of the propagating tip of the fault the accuracy of the observations is due to interplay between deformation and the sea level changes in the mediterranean the well known messinian regression followed by the pliocene transgression the long term kinematics around the sea of marmara pull apart total displacement of about 85 km over the past 5 m y is similar to the present day kinematics deduced from space geodesy at a larger scale westward propagation of the north anatolian fault over nearly 2000 km in the past 10 m y appears to be associated with strain recovery suggesting that the continental lithosphere retains long term elasticity

kinetics of anorthite dissolution in basaltic melt abstract we report convection free anorthite dissolution experiments in a basaltic melt at 1280 1500 c and 0 5 gpa on two different crystallographic surfaces 1 2 1 and 3 0 2 to investigate dissolution kinetics the anisotropy of the anorthite dissolution rate along these two surfaces is negligible time series experiments at 1280 c show that anorthite dissolution is mainly controlled by diffusion in the melt within experimental uncertainty analytical solutions were used to model the dissolution and diffusion processes and to obtain the diffusivities and the saturation concentrations of the equilibrium determining component al2o3 for anorthite dissolution into the basaltic melt for the first time we are able to show the physical and chemical characteristics of quench growth effect on the near interface melt using high spatial resolution 0 3 m eds analyses for anorthite an 90 saturation in a melt with 39 53 wt sio2 and 0 4 wt h2o the concentration of al2o3 in wt depends on temperature as follows ln c s al 2 o 3 8 032 0 192 7882 287 t where t is temperature in k and errors are given at 1 level al2o3 diffusivity in basaltic melt during plagioclase dissolution can be expressed as ln d al 2 o 3 ebd plag diss 13 69 1 57 19 313 2485 t where d is in m2 s and the activation energy is 161 21 kj mol these results are applied to model the convective dissolution of anorthite in basaltic melts the model indicates that though anorthite crystals can survive for a longer time compared to olivine crystals of the same size in the same melt the former would rise for a much smaller distance compared to the olivine sinking distance due to the smaller density contrast between anorthite and melt

paleomagnetism of the north patagonian batholith southern chile an exercise in shape analysis abstract over 100 sites in granitic country rock mafic inclusions within granitic rock and mafic dikes were sampled in the northernmost 550 km of the patagonian batholith after magnetic cleaning some sites were rejected as magnetically unstable and others were combined because they were contiguous and carried similar directions hence probably representing duplicate samplings of the same direction of the geomagnetic field a total of 42 well determined directions 29 from granitic country rock and inclusions and 13 from dikes survived to be included in the interpretation most of these had a normal magnetic polarity probably indicating that a disproportionate fraction of the north patagonan batholith formed during the mid cretaceous long normal interval tectonic interpretation of paleomagnetic directions from intrusive rocks often is difficult because paleohorizontal indicators in such rocks are usually lacking rather than struggle against this limitation we yielded to it and elected to concentrate on the shapes of our various data sets the method used is simple and straightforward involving bingham statistics and small circle fitting from this analysis it appears that the main structural feature within the north patagonian batholith npb the liquine ofqui fault zone is a site of crustal detachment a sliver of south america west of the fault is detached from the rest of the continent and has moved relatively northward because the main strands of the liquine ofqui fault are curved and concave to the west northward movement was accompanied by counterclockwise rotation east of the fault the npb appears to have been the locus of distributed shear mainly dextral the principal period of deformation of the batholith appears to have been mid or late cenozoic and may have been initiated by the arrival of the south america nazca farallon phoenix aluk triple junction

asymmetric slip partitioning in the sea of marmara pull apart a clue to propagation processes of the north anatolian fault between 1939 and 1999 the north anatolian fault naf experienced a westward progression of eight large earthquakes over 800 km of its morphological trace the 2000 km long north anatolian transform fault has also grown by westward propagation through continental lithosphere over a much longer timescale 10 myr the sea of marmara is a large pull apart that appears to have been a geometrical mechanical obstacle encountered by the naf during its propagation the present paper focuses on new high resolution data on the submarine fault system that forms a smaller pull apart beneath the northern sea of marmara between two well known strike slip faults on land izmit and ganos faults the outstandingly clear submarine morphology reveals a segmented fault system including pull apart features at a range of scales which indicate a dominant transtensional tectonic regime there is no evidence for a single continuous purely strike slip fault this result is critical to understanding of the seismic behaviour of this region of the naf close to istanbul additionally morphological and geological evidence is found for a stable kinematics consistent both with the long term displacement field determined for the past 5 myr and with present day anatolia eurasia motion determined with gps however within the sea of marmara region the fault kinematics involves asymmetric slip partitioning that appears to have extended throughout the evolution of the pull apart the loading associated with the westward propagation process of the naf may have provided a favourable initial geometry for such a slip separation

the relationship between strain rates crustal thickening palaeomagnetism finite strain and fault movements within a deforming zone the deformation of continental lithosphere generally does not occur on a single fault but is distributed over a zone up to a few hundred kilometers wide if the deformation rate is constant throughout the zone and if the velocity is continuous everywhere and does not change with time the deformation gradient tensor can be obtained analytically this tensor directly determines the amount of crustal thickening and is related in a complicated manner to the finite strain tensor the declination of remnant magnetization measured within the zone can also be rotated by the deformation because palaeomagnetic measurements are generally made on rigid blocks which have not been deformed there is no simple relationship between such rotations and the finite strain expressions for all these quantities are obtained in terms of the velocity gradients which are taken to be constant the history of western north america is used to illustrate the relationship between the present deformation by strike slip and thrust motions the rotations of the remnant magnetization vectors and the shape of accreted terranes at the surface distributed deformation is taken up by motion on faults which separate the zone into blocks the displacement rate on the faults their strike and the finite rotations of the blocks are all controlled by the velocity gradients analytic expressions relating these quantities are obtained a deforming zone containing normal faults which crosses central greece takes up both strike slip and extension and illustrates the relationship between the structures within and the motion across the zone a similar but more complicated zone in northeastern iran involves both strike slip and shortening

surface rupture and slip distribution of the 12 november 1999 duzce earthquake m 7 1 north anatolian fault bolu turkey the 12 november 1999 earthquake m 7 1 occurred on the duzce fault a splay of the north anatolian fault in the bolu basin approximately three months after the 17 august 1999 m 7 4 earthquake the surface rupture was 40 km long and the maximum right lateral offset was 500 5 cm averaging 300 cm the 9 km of the westernmost part of the rupture along the southern margin of the eften lake had a 350 cm maximum vertical displacement normal faulting some of which was already ruptured during the 17 august 1999 event with few tens of centimeters the surface rupture has a generally simple narrow deformation zone of 0 5 5 m however in some places it widens to 50 m transtensional and transpressional structures were observed within releasing and restraining step over areas respectively the larger dextral offsets on some streams indicate previous events the dextral slip measurements along the rupture reflect a symmetric distribution the eastern connection of this rupture zone with the main trace of north anatolian fault remains unclear because the bakacak and elmalik fault which are connecting faults had no surface rupture manuscript received 14 november 2000

reflection image spectroscopy across the andean subduction zone abstract this paper presents new insights into the south american subduction zone from reprocessed seismic images we applied a 3d kirchhoff prestack depth migration scheme to data sets containing different narrow frequency ranges in order to extract additional details from seismic reflection images this approach accounts for the effects of scattering on the seismic image especially for structures below a heterogeneous overburden the reflection image in such environments will differ significantly when focusing on different frequency ranges due to the frequency dependence of scattering that is likely to be present the narrow frequency range images uncover reflectors in one frequency range that are masked in another range furthermore the images enable for instance the characterization of the medium in terms of scatterer concentration and thus improve the structural interpretation the analysis of these images might help to distinguish between small scale structures in the high frequency band and large scale structures in the low frequency band we call this imaging approach reflection image spectroscopy ris we applied the ris approach to the ancorp 96 data set an onshore deep seismic reflection profile across the south american central andes the narrow frequency range images revealed additional details that we interpret as features directly linked to fluid migration processes in the subduction zone furthermore structural details of the oceanic crust and the overlying mantle and crust are revealed from the narrow frequency range images we interpret that the top of the so called nazca reflector at 70 km depth marks the upper limit of the hydrated mantle wedge whereas the bottom of the reflector represents the top of the subducted oceanic crust the compilation of our results with local earthquake data confirms this interpretation similar features observed in another deep seismic profile precorp 95 support this interpretation too furthermore the ris images show a highly reflective heterogeneous zone between the nazca reflector at 70 km depth and a prominent mid crustal bright spot quebrada blanca bright spot at about 30 km depth we associate this zone with a complex network of ascending fluids or partial melts initiated by ascending fluids released from the subducted oceanic plate this observation links the quebrada bright spot directly to the dehydrating oceanic plate

the reflection seismic survey of project tipteq the inventory of the chilean subduction zone at 38 2 s summary we describe results of an active source seismology experiment across the chilean subduction zone at 38 2 s the seismic sections clearly show the subducted nazca plate with varying reflectivity below the coast the plate interface occurs at 25 km depth as the sharp lower boundary of a 2 5 km thick highly reflective region which we interpret as the subduction channel that is a zone of subducted material with a velocity gradient with respect to the upper and lower plate further downdip along the seismogenic coupling zone the reflectivity decreases in the area of the presumed 1960 valdivia hypocentre the plate interface itself can be traced further down to depths of 50 60 km below the central valley we observe strong reflectivity at the plate interface as well as in the continental mantle wedge the sections also show a segmented forearc crust in the overriding south american plate major features in the accretionary wedge such as the lanalhue fault zone can be identified at the eastern end of the profile a bright west dipping reflector lies perpendicular to the plate interface and may be linked to the volcanic arc

deformation partitioning in flat subduction setting case of the andean foreland of western argentina 28 s 33 s 1 the andean foreland of western argentina 28 s 33 s corresponds to back arc deformations associated with the ongoing flat subduction of the nazca plate beneath the south american lithosphere in this paper short and long term tectonic regimes for this andean region are investigated and compared to nuvel 1 and the new gps derived velocity field for the andes mountains from this comparison it appears that 1 the slight convergence obliquity at the plate boundary is accommodated by the subduction zone itself precluding any deformation partitioning at lithospheric scale 2 clockwise rotation of 1 and p axes within the andean foreland of western argentina suggests that plio quaternary deformation partitioning may occur in the upper plate at crustal scale and 3 comparison of seismic rates of shallow deformations determined from moderate to large earthquakes localized between 22 s and 36 s shows that the amount of shortening is about the same 2 4 cm yr 1 between the forearcs of the 30 dipping slab segments and the back arc of the flat segment all together those observations are in close agreement with the idea that interplate coupling in flat subduction settings may play a key role in the present day transfer of plate boundary forces consequently the andean back arc of western argentina might be regarded as an obliquely converging foreland where plio quaternary deformations are partitioned between strike slip and thrust motions that are localized in the east verging thin skinned argentine precordillera and west verging thick skinned pampean ranges respectively

paleoseismological evidence of recent earthquakes on the 1967 mudurnu valley earthquake segment of the north anatolian fault zone this study contributes paleoseismological data on the recent history of surface rupturing earthquakes on the southern main branch of the north anatolian fault zone nafz turkey west of the bolu basin we focused on the fault segment that ruptured during the 1967 mudurnu valley earthquake m s 7 1 which preceded the devastating earthquakes of 1999 in the sequence of westward migrating nafz earthquakes since 1939 geomorphological mapping was carried out in a search for trenching sites on the central part of the 22 july 1967 earthquake segment in the absence of locations in sedimentary environments best suited for paleoseismological interpretation of faulted holocene deposits we trenched fluvial channel deposits at a terrace of the gravel dominated mudurnu river the most conservative interpretation of the trench stratigraphy and faulting evidence suggests that at least one paleoearthquake most probably two occurred after a d 1693 the 1967 earthquake segment has ruptured at least once since the historical earthquake of a d 1668 which was previously considered to be a likely candidate for the penultimate event and before 1967 it is not possible to confidently assign the penultimate event to one of the post a d 1693 historical earthquakes in the broader area around the mudurnu valley e g the earthquake of a d 1719 because the historical data published so far do not provide conclusive information about when past ruptures of the mudurnu valley branch of the nafz a secluded area did or did not take place

a community benchmark for subduction zone modeling we have developed a suite of benchmarks to facilitate the comparison of numerical models for the dynamics and thermal structure of subduction zones the benchmark cases are based on a thermomechanical approach in which the slab is prescribed kinematically and the wedge flow is computed dynamically we propose various cases to investigate the influence of boundary conditions and rheology on wedge flow and resulting thermal structure a comparison between the codes suggest that accurate modeling of the thermal field requires a good implementation of the velocity discontinuity along the seismogenic zone and high resolution in the thermal boundary layers a minor modification to the boundary conditions of the wedge flow is also necessary to avoid a pressure singularity that exists in analytical solutions of the cornerflow model

surface fault breaks aftershock distribution and rupture process of the 17 august 1999 izmit turkey earthquake the results obtained from field studies of surface fault breaks on land aftershock studies and analysis of complex teleseismic body waves of the 17 august 1999 izmit earthquake m w 7 4 indicate that the northern strand of the north anatolian fault zone had been ruptured between 29 1 e and 31 1 e with a maximum total fault rupture length of about 200 km the 12 november 1999 duzce earthquake m w 7 2 extended the surface fault break an additional 41 km to the east alignment of the aftershocks delineates the fault rupture on land and extends it to the west of the hersek delta well into the marmara sea to 29 1 e longitude we have identified six fault rupture segments two of them are located to the west of the hersek delta and four are located to the east rupture process analysis suggests two stages of rupture separated in space and time with an estimated total scalar seismic moment of 2 42 1020 n m the first stage initiated at the epicenter near izmit and propagated asymmetrically first eastward and then westward with a total scalar moment of 1 6 1020 n m showing predominantly right lateral strike slip faulting followed by a minor subevent extending the rupture further east the second stage took place at the western and eastern ends of the source area rupturing two segments within the marmara sea west of the hersek delta and two segments between akyazi and golyaka the rupture process analysis indicates that six fault segments were ruptured during the mainshock four of them on land and two within the marmara sea the major moment release of 1 2 1020 n m is found on the 64 km long sapanca segments located between the easternmost tip of the gulf of izmit and akyazi with an estimated maximum slip of 5 3 m the moment release on the golcuk segment with a length of 30 km is about 3 7 1019 n m and the estimated slip on this segment is 4 1 m rupture process analysis suggests two 20 km long segments between akyazi and golyaka striking n70 e the scalar moment releases on these segments are 2 7 1019 and 1 9 1019 n m with estimated offsets of 2 2 and 1 6 m respectively the last two subevents took place to the west of the hersek delta on the yalova segment and within the marmara sea with estimated offsets of 1 3 and 1 0 m respectively manuscript received 20 august 2000

kinematic constraints on intra arc shear and strain partitioning in the southern andes between 38 s and 42 s latitude 1 on the basis of structural field work fault kinematic analysis and the analysis of digital imagery we describe the northern part of the southern andean intra arc liquine ofqui fault zone lofz as an sc like fault zone system accommodating part of the nazca south american plate convergence obliquity kinematic modeling suggests that the lofz accommodated 124 24 21 km of dextral displacement between 40 s and 42 s and 67 13 11 km between 38 s and 40 s since the pliocene associated vertical axis rotations are 31 4 clockwise and 9 1 counterclockwise along synthetic and antithetic faults respectively mean pliocene to recent shear rates along the lofz decrease northward from 32 6 mm yr to 13 3 mm yr compatible with partitioning of half of the convergence obliquity into the intra arc zone north of 40 s and complete partitioning to the south the displacement gradient along the intra arc zone results in margin parallel shortening of the fore arc

postseismic deformation near the izmit earthquake 17 august 1999 m 7 5 rupture zone we present and interpret the results of postseismic global positioning system monitoring of the first 298 days following the 17 august 1999 izmit earth quake whereas the data suggest some spatial and temporal complexity in the post seismic motions the overall pattern can be characterized by time dependent relaxa tion functions and suggests exponential decay with an estimated 57 day relaxation time the very rapid deformation during the first few weeks following the mainshock suggests rapid afterslip on and below the coseismic rupture segments the exponen tial decay of the postseismic deformations through the end of the observation period suggests contributions from the lower crustal viscoelastic relaxation

the role of magma mixing in the genesis of pge mineralization in the bushveld complex thermodynamic calculations and new interpretations a discussion sir the concept of magma mixing producing sulfide mineralization especially any enriched in platinum group elements such as the merensky reef has become well entrenched naldrett and von gruenewaldt 1989 presented calculations for the saturation limit of sulfur in the presumed parental magma of the bushveld complex and derivative liquids based on well established phase relationships for that magma as with most phase boundaries it is curved with a convexity such that mixing between two points straddling the curved boundary could lead to a mixed magma that was sulfur oversaturated a revised version was presented by li et al 2001a plotting data from the bushveld complex on a zr versus s diagram however whatever two compositional axes are used in a binary diagram they cannot completely define the sulfur solubility limits for multicomponent magmas such solubility limits on a binary diagram are only valid for the very specific compositions for which the curve was constructed but will not be applicable if different compositions are projected onto the diagram in both models it is assumed that the magma evolution trend and hence sulfur solubility defined by fractionation is exactly the same as that produced during magma mixing the first issue discussed here is why such an assumption is incorrect it was also suggested by li et al 2001a that during norite fractionation the magma may become sulfur undersaturated this interpretation of their phase diagram also requires reexamination finally the actual composition of the magmas calculated by li et al 2001a must be questioned in an erratum li et al 2001b published in response to a draft of this manuscript these errors were recognized however the brief retraction does not explain the reasons why such models calculations and interpretations are not applicable there are differences between magma series produced by fractionation and those produced

seismic observations at an overstep of the western north anatolian fault abant sapanca region turkey the course of the active north anatolian fault system from lake abant to lake sapanca was traced by its high micro earthquake activity if approaching from the east this section includes a broad south to north overstep fault offset of the main fault

the 1999 izmit earthquake sequence in turkey seismological and tectonic aspects the izmit duzce earthquake sequence is the largest sequence recorded by modern digital networks in the history of turkish earthquakes the m w 7 4 izmit mainshock occurred at 29 967 e and 40 729 n and 13 km depth at 00 hr 01 min 38 7 sec utc on 17 august 1999 and was preceded by at least eight immediate foreshocks of magnitude m l 3 0 aftershock locations show that a large region has become seismically very energetic following the mainshock and that most of the aftershock zone developed quickly in the first 3 days the distribution of the aftershocks illuminates numerous seismotectonic structures associated with the various branches of the north anatolian fault naf in the aftershock zone the seismicity pattern defines a rupture plane that extends about 80 km east and 75 km west of the mainshock epicenter confirming bilateral rupture during the mainshock the western aftershock activity is almost entirely located offshore extending along the axis of the izmit bay we show that the westernmost extent of the mainshock rupture reached the offshore region just 10 km south of the princes islands the dominance of strike slip motion is one of the main characteristics of the izmit sequence a number of significant aftershock clusters occur off the inferred mainshock rupture plane the spatial and temporal occurrence of these clusters show that they are triggered by the complex redistribution of stresses and dynamic strains imposed by the dislocation of the mainshock the focal mechanisms of the events located in the western end of the rupture zone show both strike slip and normal faulting mechanisms we infer that the yalova cluster was triggered by the mainshock the dominance of the normal faulting mechanisms supports the notion that dynamic extensional strains played a major role in triggering this cluster four events located off the princes islands indicate similar source mechanisms characterized by right lateral strike slip motion parallel to the strike of the northern boundary fault nbf and local trend of aftershock distribution this observation leads to a first order seismotectonic evidence that the nature of the nbf which is known to be a transtensional feature at the surface is dominated by strike slip motion at depth the coexistence of strike slip and extensional seismotectonic features in the sea of marmara highlights the importance of strain partitioning amongst shallow transtentional structures accommodating north south extension and deeper structures associated with the naf accommodating east west right lateral shear manuscript received 22 september 2000

stress tensor inversions along the westernmost north anatolian fault zone and its continuation into the north aegean sea summary gephart forsyth s method has been applied to estimate stress orientations from earthquake fault plane solutions of the westernmost north anatolian fault zone nafz its westward continuation in the northern aegean sea where it interacts with the normal faulting of central greece and of the western coastal parts of anatolia in total 163 fault plane solutions were used to invert for the stress tensor of 9 seismotectonic subregions magnitudes range from 1 1 to 7 4 all events have shallow focal depths most occurred in the uppermost 15 km and very few in the 15 to 40 km depth range the region studied is characterized by strike slip nafz by transtension central greece and western anatolia and by a strong signature of transpression in the marmara area from nafz to central greece the 3 axis changes continuously and smoothly its orientation from n35 e in the westernmost nafz to nearly north south in continental central greece and the maximum horizontal stress hmax changes from wnw ese to e w the total angle of lateral variation in the direction of either hmax or 3 is 40 in central western anatolia the orientation of 3 is nne ssw n10 e while in southern western anatolia it is nnw sse n33 w in both cases the development of the major grabens simav gediz menderes is in agreement with the resolved stress tensor at the termination of the nafz against central greece the regime is complex the dextral shear motion transferred from the east crosses the pilion peninsula and northern evia island where it interacts with the major normal faults of continental greece these faults have variable orientations the e w trending quaternary fault system and the nw se trending fault system which is inherited from the past the latter faults under the presently acting stress field are reactivated either as strike slip faults with sinistral strike slip component when oriented at small angle in respect to 3 or as normal faults with small sinistral strike slip component when oriented at high angle in respect to 3 the occurrence of the recent 2001 july 26 skyros event which was clearly connected to a nnw sse fault with sinistral strike slip motion provides strong seismological evidence that the old structures can equally well be reactivated under the presently active stress field

seismicity and source parameters for small scale earthquakes along the splays of the north anatolian fault naf in the marmara sea summary major discrepancy between present day fault models in the marmara sea is closely related to structural development of depression areas beneath the sea therefore in this study the marmara sea and especially its major basins are investigated by means of recent seismological observations consisting of microseismicity 1 2 md 3 6 2002 may 2006 may focal mechanisms 2 4 md 5 0 1999 2006 and stress analysis based on the focal mechanisms in the cinarcik basin where either pull apart model or negative flower structure is proposed northeastern margin is represented by strike slip sources having a nw alignment probably corresponding to a cross basin strike slip fault developing in a matured pull apart basin this suggestion is directly relevant to experiments of sand box analogue models these experiments indicate that such a cross basin strike slip fault is produced after the pull apart basins attain their mature stage eventually resulting in less vertical displacements attributed to normal faults bounding the basin this experimental decline may be corroborated by the paucity of normal mechanisms in the basin extensional motion in this region is more influential outside of the basin especially to the area where an onshore seismic activity is monitored on the land on the other hand another strike slip activity in the cinarcik basin is distributed on a possible strand parallel to the northern coastline of the marmara sea in the armutlu peninsula this may indicate that one or more short strands of the northern splay extend to the west by bounding the basin from the south in the central basin the existence of a right lateral strike slip faulting on an east west trending fault is supported by similar strike slip focal mechanisms located at both extremities of the basin to the west dominant style of deformation gradually shifts from strike slip faulting to transpression along the western coastline of the marmara sea where the northern splay joins with the offshore continuation of the ganos fault finally focal mechanisms in the marmara sea are inverted for the best fitting stress tensor characterized by a subvertical 2 axis and two subhorizontal stress axes of 1 and 3 oriented nw se and ne sw respectively conclusively this study infers that the current tectonics of the marmara sea is mainly governed by a strike slip regime ascribed to both submarine splays of the naf and partly dominated by extensional and compressional features indicating shallow processes at local scales

are s c structures duplexes and conjugate shear zones different manifestations of the same scale invariant phenomenon abstract by measuring s spacing c spacing and the s c angle in deformed rocks this paper investigates the geometry of previously published examples of s c and s c like structures on a scale range between micrometres and several hundred kilometres the results indicate that common s c fabrics of thin section hand specimen and outcrop scale and conjugate fault mylonite zones of map scale define a simple function c spacing 2 s spacing which depicts a scale invariant geometry over ten orders of magnitude logarithmic plots of cumulative frequency suggest that the s c fractal set d 0 13 is restricted to the scale range between 600 800 m and 1 km where genuine s c structures characterized by antithetic shear on the s planes can be formed below 600 800 m grain scale processes seem to influence the development of s c structures above the upper limit 1 km only s c like structures with duplex kinematics synthetic shear on s planes occur the s c and s c c fractals are envisaged as self similar structures where the foliations work as both s or c planes depending on which scale is considered

compressional and transpressional stress pattern for pliocene and quaternary brittle deformation in fore arc and intra arc zones andes of central and southern chile kinematic analysis of fault slip data for stress determination was carried out on late miocene to quaternary rocks from the fore arc and intra arc regions of the chilean andes between 33 and 46 south latitudes studies of neogene and quaternary infilling the central depression as well as plutonic rocks of the north patagonian batholith along the liquine ofqui fault zone have revealed various compressional and or transpressional states of stress in the pliocene the maximum compressional stress 1 was generally oriented east west during the quaternary the deformation was partitioned into two coeval distinctive states of stress in the fore arc zone the state of stress was compressional with 1 oriented in a n s to nne ssw direction in the intra arc zone the state of stress was transpressional with 1 striking ne sw along the coast in one site 37 30 s the quaternary strain deformation is extensional with an e w direction which can be explained by a co seismic crustal bending readjustment

slip rate variability and distributed deformation in the marmara sea fault system the slip rate along a fault controls the accumulation of strain that is eventually released during an earthquake estimates from a three dimensional geomechanical model of the slip rate on the main marmara fault near istanbul turkey reconcile geodetic and geological observations and indicate smaller values and higher variability than previously thought the slip rate along a fault controls the accumulation of strain that is eventually released during an earthquake1 along a 150 km long stretch of the north anatolian fault near istanbul turkey strain has been building up2 since the last large earthquake in 1766 estimates of the geodetic slip rates along the main marmara fault vary widely ranging between 17 and 27 9 mm yr 1 refs 2 3 4 5 this slip rate is difficult to quantify because of the lack of satellite observations offshore and the complexity of the submarine fault system that includes the main marmara fault2 6 7 here we estimate the right lateral slip rate on the main marmara fault using a three dimensional geomechanical model that incorporates these structural complexities from our simulations we infer slip rates between 12 8 and 17 8 mm yr 1 our estimates are smaller and more variable than previous results primarily because of slip partitioning and internal deformation our model results reconcile geodetic observations and geological fault slip rates8 9 10 which had been considered conflicting previously we suggest that the inferred variability in slip rate on the main marmara fault favours segmented release of seismic moment during consecutive events over the failure of the whole seismic gap in one large earthquake

speculations on the geometry of the initiation and termination processes of earthquake rupture and its relation to morphology and geological structure earthquake initiation and termination processes are commonly described in terms of barriers and asperities barriers fall into two classes geometric barriers are associated with places where the orientation of a failure surface changes and relaxation barriers where stress is low because aseismic creep processes outpace tectonic loading geometric barriers fall into conservative and nonconservative subgroups according to whether finite fault motion can proceed without the creation of new structures or whether it demands the creation of new faulting or void space the multiple faulting or fragmentation associated with some nonconservative barriers can disrupt fault planes and form asperities by means of selected examples it is shown that a description in terms of these barriers can help one to visualise the processes of earthquake rupture and its relation to the geological environment

global positioning system constraints on plate kinematics and dynamics in the eastern mediterranean and caucasus we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1997 at 189 sites extending east west from the caucasus mountains to the adriatic sea and north south from the southern edge of the eurasian plate to the northern edge of the african plate sites on the northern arabian platform move 18 2 mm yr at n25 5 w relative to eurasia less than the nuvel 1a circuit closure rate 25 1 mm yr at n21 7 w preliminary motion estimates 1994 1997 for stations located in egypt on the northeastern part of africa show northward motion at 5 6 2 mm yr also slower than nuvel ia estimates 10 1 mm yr at n2 4 e eastern turkey is characterized by distributed deformation while central turkey is characterized by coherent plate motion internal deformation of 2 mm yr involving westward displacement and counterclockwise rotation of the anatolian plate the anatolian plate is de coupled from eurasia along the right lateral strike slip north anatolian fault naf we derive a best fitting euler vector for anatolia eurasia motion of 30 7 0 8 n 32 6 0 4 e 1 2 0 1 myr the euler vector gives an upper bound for naf slip rate of 24 1 mm yr we determine a preliminary gps arabia anatolia euler vector of 32 9 1 2 n 40 3 1 1 e 0 8 0 2 myr and an upper bound on left lateral slip on the east anatolian fault eaf of 9 1 mm yr the central and southern aegean is characterized by coherent motion internal deformation of 2 mm yr toward the sw at 30 1 mm yr relative to eurasia stations in the se aegean deviate significantly from the overall motion of the southern aegean showing increasing velocities toward the trench and reaching 10 1 mm yr relative to the southern aegean as a whole

paleomagnetic evidence of complex tectonic rotation pattern in the nw anatolian region implications for the tectonic history since the middle eocene abstract the kinematic evolution of the almacik block and the armutlu region which are surrounded by the branches of the north anatolian fault is not completely understood because of incompatible paleomagnetic data a previous paleomagnetic study in the almacik block indicated that there have been large rotations associated with the rotation as a whole coherent block and another study postulated a more complex tectonic evolution the aim of this study was to obtain paleomagnetic directions on middle eocene volcanic volcanoclastic rocks at 25 sites in nw anatolia and to determine the tectonic deformation process along the north anatolian fault zone after rock magnetic measurements and stepwise thermal and alternating field demagnetisation most of the samples taken were characterised by one component of magnetisation after the removal of viscous magnetisation a characteristic remanent magnetisation was obtained at 500 580 c showing evidence of magnetite and titanomagnetite with a small amount of ti however in some cases a high temperature component was isolated between 600 and 650 c indicating a titanohematite composition the mean direction obtained from the istanbul zone d 191 5 i 47 1 95 7 1 indicated no tectonic rotation relative to the reference direction of the stable eurasian plate d 191 0 i 53 2 95 5 0 besse and courtillot 2002 torsvik et al 2008 in the middle eocene the paleomagnetic directions in the almacik block and the armutlu region suggest counterclockwise rotations of 22 3 7 8 and 17 7 14 6 respectively relative to the istanbul zone when integrated together with previous studies our paleomagnetic results indicate that both the armutlu region and the almacik block were emplaced in the same area during the middle eocene the deformation of the northern branch of the north anatolian fault resulted in a bend and an overstep fault offset of 25 km between lake sapanca and lake abant during this process both the almacik block and the armutlu region were separated distinctly from each other with a counter clockwise rotation with respect to the istanbul zone in addition within some parts of the almacik block an internal deformation with large declination anomalies ranging from 160 to 250 was observed in this study and in previous studies these different declinations could be the result of chemical remagnetisation of hydrothermal events stress related magnetisation or small block rotations

3d mechanical modeling of the gps velocity field along the north anatolian fault the north anatolian fault naf extends over 1500 km in a complex tectonic setting in this region of the eastern mediterranean collision of the arabian african and eurasian plates resulted in creation of mountain ranges i e zagros caucasus and the westward extrusion of the anatolian block in this study we investigate the effects of crustal rheology on the long term displacement rate along the naf heat flow and geodetic data are used to constrain our mechanical model built with the three dimensional finite element code adeli the fault motion occurs on a material discontinuity of the model which is controlled by a coulomb type friction the rheology of the lithosphere is composed of a frictional upper crust and a viscoelastic lower crust the lithosphere is supported by a hydrostatic pressure at its base representing the asthenospheric mantle we model the long term deformation of the surroundings of the naf by adjusting the effective fault friction and also the geometry of the surface fault trace to do so we used a frictional range of 0 0 0 2 for the fault and a viscosity varying between 10 19 and 10 21 pa s one of the most striking results of our rheological tests is that the upper part of the fault is locked if the friction exceeds 0 2 by comparing our results with geodetic measurements mcclusky et al j geophys res b 105 2000 5695 5719 and tectonic observations we have defined a realistic model in which the displacement rate on the naf reaches v17 mm yr for a viscosity of 10 19 pa s and a fault friction of 0 05 this strongly suggests that the naf is a weak fault like the san andreas fault in california adding topography with its corresponding crustal root does not induce gravity flow of anatolia rather it has the counter intuitive effect of decreasing the westward anatolian escape we find a poor agreement between our calculated velocity field and what is observed with gps in the marmara and the aegean regions we suspect that the simple lithosphere model is responsible for this discrepancy taking into account the weaknesses of these deforming regions should allow us to build a more realistic model that would match ground observations more appropriately on the other hand our results fit well gps measurements in central anatolia setting the basis of modeling crustal strain in turkey b 2003 elsevier science b v all rights reserved

depth dependent geometry of the liquine ofqui fault zone and its relation to paths of slab derived fluids using a non homogeneous elastic model for the south chile subduction zone we calculate the depth dependent geometry of the liquine ofqui fault zone lofz considering that faults develop where shear stress is maximum shear stress develops due to the oblique subduction process depending on shear modulus which varies as a function of the amount of fluids within the overriding plate regions with different values of shear modulus are obtained by the geometries of isotherms calculated from a thermal model based on the principle that fluids move from higher to lower pressure regions we calculate paths of fluids from the subducting slab towards the free surface in the vicinity of the volcanic arc the obtained fluid paths agree with the geometry of the lofz suggesting that margin parallel strike slip faults could serve as pathways for fluids through the overriding plate in oblique subduction zones

earthquakes and lineament infrastructure a further result attending to the disturbances of the surface of the earth has been to produce rents or fissures in the rocks which have been subject to their violent movements and to convert them into receptacles of metallic ores accessible by the labours of men reverend william buckland geology and mineralogy with reference to natural theology london william pickering 1836 analyses of the nucleation propagation and stopping of moderate to large earthquake ruptures coupled with high precision studies of background and aftershock microearthquake activity are yielding insights into the infrastructure of major transcurrent fault zones within the seismogenic regime curvature and echelon segmentation of a principal slip surface within a ca 1 km wide main fault zone appear to exert major controls on the starting and stopping of ruptures geometrical irregularities of this kind transverse to the direction of rupture propagation may be usefully classified into dilational and antidilational jogs referring to the area change in the plane defined by the slip vector and the pole to planar segments of the fault extensional fracture systems linking echelon fault segments across dilational jogs allow long term transfer of fault slip but appear to play an especially important role as kinetic barriers impeding or arresting rapid rupture propagation in fluid saturated crust the rapid transfer of slip is opposed by suctions arising from rupture induced differential fluid pressures delayed slip transfer delineated by intense aftershock activity may then occur as fluid pressures re equilibrate fossil examples of such linking extensional fracture systems are characterized by multi episode hydraulic implosion breccias dilational zones of this kind may migrate along faults or remain fixed for relatively long time periods they serve as particularly favourable sites for hydrothermal mineralization and may also localize magmatic activity along major lineaments

strike slip fault geometry in turkey and its influence on earthquake activity the geometry of turkish strike slip faults has been reviewed and described from this data set it appears that fault geometry the distribution of discontinuities such as bends and stepovers along the main fault trace plays an important role in controlling the location of large earthquake rupture segments along the fault zones large earthquake ruptures generally do not propagate past individual stepovers that are wider than 5 km or bends that have angles greater than about 30 more important than the size of each discontinuity however is the total geometric pattern i e the distribution of adjacent bends and stepovers based not only on distance from one another but also on relative discontinuity size certain geometric patterns restraining single or double bends are particularly common and can be viewed as responsible for strain accumulation along portions of the fault zone fault geometry not only plays a role in the extent of earthquake rupture but also in characteristics of earthquake behavior for example large earthquake epicenters often occur near restraining bends or double bends furthermore aftershocks and swarm activity can often be associated with releasing areas areas along the strike slip fault that are undergoing a relatively large amount of extension

gps constraints on continental deformation in the africa arabia eurasia continental collision zone and implications for the dynamics of plate interactions 1 the gps derived velocity field 1988 2005 for the zone of interaction of the arabian african nubian somalian and eurasian plates indicates counterclockwise rotation of a broad area of the earth s surface including the arabian plate adjacent parts of the zagros and central iran turkey and the aegean peloponnesus relative to eurasia at rates in the range of 20 30 mm yr this relatively rapid motion occurs within the framework of the slow moving 5 mm yr relative motions eurasian nubian and somalian plates the circulatory pattern of motion increases in rate toward the hellenic trench system we develop an elastic block model to constrain present day plate motions relative euler vectors regional deformation within the interplate zone and slip rates for major faults substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below 1 2 mm yr including central and eastern anatolia turkey the southwestern aegean peloponnesus the lesser caucasus and central iran geodetic slip rates for major block bounding structures are mostly comparable to geologic rates estimated for the most recent geological period 3 5 myr we find that the convergence of arabia with eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the caucasus and zagros mountain belts around the periphery of the collision zone in addition we find that the principal boundary between the westerly moving anatolian plate and arabia east anatolian fault is presently characterized by pure left lateral strike slip with no fault normal convergence this implies that extrusion is not presently inducing westward motion of anatolia on the basis of the observed kinematics we hypothesize that deformation in the africa arabia eurasia collision zone is driven in large part by rollback of the subducting african lithosphere beneath the hellenic and cyprus trenches aided by slab pull on the southeastern side of the subducting arabian plate along the makran subduction zone we further suggest that the separation of arabia from africa is a response to plate motions induced by active subduction

the morphology of strike slip faults examples from the san andreas fault california fault zones are seldom straight nor are fractures within them continuous permanent strain fields are imprinted near a fault of complex geometry as a result of continued slip these strain fields may be manifest as vertical deformation near the fault strain fields that increase area result in subsidence and strain fields that reduce area result in uplift although these effects are modified by erosion and deposition the general features of fault zone morphology are a consequence of the geometry and slip distribution along strike graphical views of strain fields associated with simple vertical strike slip faults are derived using boundary element methods if the fault is straight and parallel to the applied shear strain the hills and valleys resulting from finite fault rupture are separated by the fault trace this is rarely observed in nature instead strike slip faults cut through hills and valleys apparently of their own making we show this to be a consequence of segments of the fault being nonparallel to each other and to the overall applied shear strain coseismic strains are large but transient since they are substantially annulled by rupture on contiguous fault segments we test our theory with examples from parts of the san andreas fault system in california the morphologies of the parkfield region and the southern san andreas fault in the coachella valley are shown to be consistent with plausible distributions of slip on mapped surface faults the location of the salton sea appears to be a consequence of a reduction of slip on the san andreas fault toward the brawley seismic zone

the chile ridge a tectonic framework a new chile ridge tectonic framework is developed based on satellite altimetry data shipboard geophysical data and primarily 38 500 km of magnetic data gathered on a joint u s chilean aeromagnetic survey eighteen active transforms with fossil fracture zones fzs including two complex systems the chile fz and valdivia fz systems have been mapped between the northern end of the antarctic nazca plate boundary chile ridge at 35 s and the chile margin triple junction at 47 s chile ridge spreading rates from 23 ma to present have been determined and show slowdowns in spreading rates that correspond to times of ridge trench collisions the valdivia fz system previously mapped as two fzs with an uncharted seismically active region between them is now recognized to be a multiple offset fz system composed of six fzs separated by short ridge segments 22 to 27 km long at chron 5a 12 ma the chile ridge propagated from the valdivia fz system northward into the nazca plate through crust formed 5 myr earlier at the pacific nazca ridge evidence for this propagation event includes the friday and crusoe troughs located at discontinuities in the magnetic anomaly sequence and interpreted as pseudofaults this propagation event led to the formation of the friday microplate which resulted in the transferal of crust from the nazca plate to the antarctic plate and in a 500 km northward stepwise migration of the pacific antarctic nazca triple junction rift propagation microplate formation microplate extinction and stepwise triple junction migration are found to occur during large scale plate motion changes and plate boundary changes in the southeast pacific

complex patterns of fluid and melt transport in the central andean subduction zone revealed by attenuation tomography abstract we present a high resolution 3 d model of p wave attenuation q p 1 for the central andean subduction zone data from 1500 mostly intermediate depth 60 250 km earthquakes recorded at three temporary seismic networks covering the forearc arc and backarc around 23 s were used for tomographic inversion the forearc is characterised by uniformly high q p values indicating low temperature rocks in accordance with low surface heat flow values prominent low q p anomalies are found beneath the magmatic arc and the backarc in the crust and mantle continuous regions of low q p connect earthquake clusters at 100 km and 200 km depth with zones of active volcanism in the arc and backarc fluids fluxed from the subducted oceanic lithosphere into the overlying mantle wedge where they induce melting explain our observations we propose that low q p regions indicate source and ascent pathways of metamorphic fluids and partial melts ascent of fluids and melts as imaged by seismic q p are not vertical as is often implicitely assumed instead sources of fluids are located at different depth levels and ascent paths are complex and exhibit significant variation within the study area the largest quaternary backarc volcano cerro tuzgle is fed by mantle melts which are imaged as a plume of low q p material that reaches to the strong earthquake cluster at 200 km depth

geomechanical model of the marmara sea region ii 3 d contemporary background stress field summary we present the contemporary 3 d background stress field of the marmara sea region derived from a geomechanical model the background stress field i e the component of the absolute stress state that is time independent over the seismic cycle primarily depends on the distribution of density and elastic parameters on the acting far field stresses from plate boundary forces and on fault geometries we take these into account to predict the 3 d background stress field including its spatial variations technically our model concept involves the definition of an appropriate initial stress state accounting for the gravitational reference stress state of the crust which is then changed by plate tectonics until the 3 d background stress field has evolved the modelled stress field agrees well with observations from earthquake focal mechanism solutions and their formal stress inversion with orientation of maximum horizontal stress and with the distribution of seismicity in the marmara sea in particular in the vicinity of fault bends the stress field deviates considerably from the regional nw se oriented maximum horizontal stress and exhibits variability of the stress regime our model results are consistent not only with dynamic observations but also with kinematic ones various kinematic observations are understandable from the stress field we show that a stress regime that indicates normal faulting in the basins is nonetheless reconcilable with almost pure strike slip motion on the main marmara fault the distribution of seismicity in the marmara sea can be explained in first order by the distribution of critical differential stress which is closely related to local fault geometries we refer the wide absence of seismicity between the bend of the main marmara fault near istanbul and the central basin to the relatively plane fault geometry of that segment normal stress on the main marmara fault is highly variable along strike which makes segment wise rupture more likely than a rupture of the seismic gap at once comparably low normal stress on the prince s islands segment indicates a shorter interevent time for this fault segment than for the central segment of the main marmara fault