3 d inhomogeneities in the upper mantle abstract the method developed by aki christofferson and husebye for determining a 3 d seismic image of the earth s interior from the travel time data obtained at a 2 d array has been applied to seventeen arrays around the world by various authors the most outstanding results from these works are that small scale lateral velocity anomalies exist in the lower crust and upper mantle everywhere studied the reality of these deep seated anomalies is supported by 1 1 significant reduction of residual variance 2 2 resolution analysis for decoupling from shallower anomalies and 3 3 error analysis for the significance of anomalies in this paper we try to strengthen the credibility of these deep seated anomalies by drawing attention to those found where they were expected namely low velocity bodies under several geothermal areas and high velocity anomalies associated with the subducting plate

thermochronology of the high pressure metamorphic rocks of crete greece implications for the speed of tectonic processes new fission track thermochronologic data from the high pressure p low temperature t rocks of crete greece combined with pressure temperature and stratigraphic constraints reveal that their subduction began between 36 and 29 ma metamorphism took place in western crete at peak conditions of 10 2 kbar and 400 50 c between 24 and 19 ma and rapid exhumation to 10 km and 300 c at a minimum rate of 4 km m y was completed before 19 ma constraints from the thermal history of the plate above the inferred extensional detachment reveal that tectonic unroofing contributed 85 to 90 of the overall exhumation of the high p low t rocks of crete we propose that the hellenic subduction zone has acted as a retreating plate boundary since at least the early oligocene and collision and extension during this time were driven by roll back associated with slab pull rather than by gravitational collapse as a consequence of crustal thickening the speed of subduction and exhumation of the high p low t rocks of crete within 10 m y has important implications for other orogenic belts showing that rocks can be subducted metamorphosed at high pressure and exhumed despite slow overall plate convergence within the uncertainties of many paleontologic and isotopic age data

geochemistry and u pb protolith ages of eclogitic rocks of the asis lithodeme piaxtla suite acatlan complex southern mexico tectonothermal activity along the southern margin of the rheic ocean recent data indicating that the piaxtla suite acatlan complex southern mexico underwent eclogite facies metamorphism and exhumation during the devono carboniferous suggest an origin within the rheic ocean rather than the iapetus ocean the asis lithodeme piaxtla suite consists of polydeformed metasediments and eclogitic amphibolites that are intruded by megacrystic granitoid rocks u pb zircon data indicate that the metasediments were deposited after c 700 ma and before intrusion of c 470 420 ma quartz augen granite the metasedimentary rocks contain abundant mesoproterozoic detrital zircons c 1050 1250 ma and a few zircons in the range of c 900 992 and c 1330 1662 ma their geochemical and sm nd isotopic signature is typical of rift related passive margin sediments derived from an ancient cratonic source which is interpreted to be the adjacent mesoproterozoic oaxacan complex megacrystic granites were derived by partial melting of a c 1 ga crustal source similar to the oaxacan complex amphibolitic layers exhibit a continental tholeiitic geochemistry with a c 0 8 1 1 ga source t dm age and are inferred to have originated in a rift related environment by melting of lithospheric mantle in the ordovician this rifting may be related to the early ordovician drift of peri gondwanan terranes e g avalonia from gondwana and the origin of the rheic ocean

systematic survey of high resolution b value imaging along californian faults inference on asperities understanding and forecasting earthquake occurrences is presumably linked to understanding the stress distribution in the earth s crust this cannot be measured instrumentally with useful coverage however the size distribution of earthquakes quantified by the gutenberg richter b value is possibly a proxy to differential stress conditions and could therewith act as a crude stress meter wherever seismicity is observed in this study we improve the methodology of b value imaging for application to a high resolution 3 d analysis of a complex fault network in particular we develop a distance dependent sampling algorithm and introduce a linearity measure to restrict our output to those regions where the magnitude distribution strictly follows a power law we assess the catalog completeness along the fault traces using the bayesian magnitude of completeness method and systematically image b values for 243 major fault segments in california we identify and report b value structures revisiting previously published features e g the parkfield asperity and documenting additional anomalies e g along the san andreas and northridge faults combining local b values with local earthquake productivity rates we derive probability maps for the annual potential of one or more m6 events as indicated by the microseismicity of the last three decades we present a physical concept of how different stressing conditions along a fault surface may lead to b value variation and explain nonlinear frequency magnitude distributions detailed spatial b value information and its physical interpretation can advance our understanding of earthquake occurrence and ideally lead to improved forecasting ability

meltwater circulation and permeability of arctic summer sea ice derived from hydrological field experiments abstractpermeability and meltwater flow have been studied in sea ice in the siberian and central arctic during the summers of 1995 and 1996 a bail test technique has been adapted to allow for measurements of in situ permeability found to range between 1011 and 108 m2 permeability varied by about a factor of 2 between 1995 above normal melt rates and 1996 below normal melt rates release of fluorescent tracers fluoresceine rhodamine furthermore allowed the derivation of flow velocities and assessment of the relevant driving forces hydraulic gradients in rough ice and wind stress in ponded ice were found to be particularly important driving meltwater over distances of several m day1 the mid to late summer ice was found permeable enough to completely divert meltwater from the surface into the ice interior it could be shown however that lower permeabilities of the upper ice layers as well as refreezing of meltwater are associated with significantly lower permeabilities in particular during the early melt season fostering development of surface melt ponds

size distribution of parkfield s microearthquakes reflects changes in surface creep rate s u m m a r y the nucleation area of the series of m6 events in parkfield has been shown to be characterized by low b values throughout the seismic cycle since low b values represent high differential stresses the asperity structure seems to be always stably stressed and even unaffected by the latest main shock in 2004 however because fault loading rates and applied shear stress vary with time some degree of temporal variability of the b value within stable blocks is to be expected we discuss in this study adequate techniques and uncertainty treatment for a detailed analysis of the temporal evolution of b values we show that the derived signal for the parkfield asperity correlates with changes in surface creep suggesting a sensitive time resolution of the b value stress meter and confirming near critical loading conditions within the parkfield asperity

subduction zone metamorphism calc alkaline magmatism and convergent margin crustal evolution abstract at the dawn of the age of plate tectonics akiho miyashiro published a seminal paper in which he drew attention to significant differences in regional metamorphic phase assemblages described contrasting geologic occurrences and inferred their characteristic ranges of physical conditions he advanced the paired metamorphic belt concept involving an oceanward narrow high p low t blueschist zone intimately intermixed with ophiolites and a landward broad low p high t realm associated with arc volcanic plutonic rocks more recent studies have illuminated the following 1 two main types of convergent plate junction can be distinguished pacific underflow of thousands of km of oceanic lithosphere and alpine closure of an intervening oceanic basin leading to continental collision 2 plate descent carries mafic felsic lithologies to depths of 35 120 km or more at relatively low temperatures producing high pressure hp pacific type and ultrahigh pressure uhp alpine type metamorphic terranes respectively 3 exhumed hp uhp complexes display low aggregate bulk densities reflecting chiefly buoyancy driven ascent of quartzofeldspathic allochthons 4 at a depth of 35 km in a warm lithosphere subduction zone sialic crust should melt if an aqueous fluid were abundant it does not hence the activity of h2o must be low at such depths 5 global observations indicate that volcanic plutonic arcs are sited 100 20 km above subducting oceanic plates devolatilization of sinking hydrated oceanic crust mantle promotes the generation of calc alkaline arc melts in this magmagenic zone 6 pacific type underflow of basaltic crust capped plates produces new and recycled continental crust whereas alpine type convergence reshuffles collided terranes but does not generate juvenile sialic crust

lu hf geochronology of mississippian high pressure metamorphism in the acatlan complex southern mexico abstract since the first discovery of eclogite in the acatlan complex in southern mexico the age of the high pressure metamorphism has been a matter of debate several attempts to date high pressure metamorphic rocks of the acatlan complex have been made using the u pb and 40 ar 39 ar methods the resulting dates however do not correspond unambiguously to the time of eclogite facies metamorphism in this study the age of high pressure metamorphism in the acatlan complex has been determined by lu hf garnet whole rock geochronology this paper presents four high precision 4 to 7 point garnet whole rock isochrons of amphibolitized eclogite from the piaxtla suite and the asis lithodeme in the acatlan complex the four dates agree within uncertainties yielding a weighted mean of 352 5 1 6 ma which we interpret to be the age of eclogite facies metamorphism in the piaxtla suite and the asis lithodeme marking active subduction in the acatlan complex in the carboniferous mississippian high pressure metamorphism in turn might be related to the closure of the rheic ocean and the assembly of pangea

evolution of the rheic ocean the rheic ocean which separated laurussia from gondwana following the closure of iapetus is arguably the most important ocean of the palaeozoic its suture extends from mexico to turkey and its closure produced the climactic variscan alleghanian ouachita orogeny that assembled the supercontinent pangaea following protracted cambrian rifting that represented a continuum from neoproterozoic orogenic processes the rheic ocean opened in the early ordovician with the separation of several neoproterozoic arc terranes from the continental margin of northern gondwana separation occurred along the line of a former neoproterozoic suture following the onset of subduction in the outboard iapetus ocean the timing of rift drift transition and drive for subsequent spreading was likely governed by slab pull accounting for the rapid rate 8 10 cm yr at which the rheic ocean widened during the ordovician the ocean broadened at the expense of iapetus and attained its greatest width 4000 km in the silurian by which time baltica had sutured to laurentia and the neoproterozoic arc terranes had accreted to laurussia closing iapetus in the process closure of the rheic ocean began in the devonian and was facilitated by northward subduction beneath southern baltica and southward subduction beneath northwest gondwana closure was largely complete by the mississippian as gondwana and laurussia sutured to build pangaea north africa colliding with southern europe to create the variscan orogen in the devonian carboniferous and west africa and south america suturing to north america to form the alleghanian and ouachita orogens respectively during the carboniferous permian the rheic ocean consequently plays a dominant role in the basement geology of southern europe in the appalachian ouachita orogeny of north america and in the palaeozoic sedimentary structural and tectonothermal record from middle america to the middle east with its closure the ocean brought about the assembly of pangaea and brought the palaeozoic era to an end

high pressure rocks of the acatlan complex southern mexico large scale subducted ordovician rifted passive margin extruded into the upper plate during the devonian carboniferous abstract high pressure hp rocks in the paleozoic acatlan complex of southern mexico occur in a median belt extruded into the complex which is the root zone of a klippe to the west these hp rocks are predominantly clastic metasedimentary rocks and include a bimodal suite of amphibolites and granitoids u pb la icpms zircon dating indicates that one of the amphibolites was intruded at or before 461 2 ma and a megacrystic granitoid yielded an intrusive age of 488 8 7 ma which is within the 490 450 ma range of other dated hp megacrystic granitoids the amphibolites have a tholeiitic transitional to alkalic within plate chemistry derived from a heterogeneous mantle by various degrees of partial melting the host metasedimentary rocks contain detrital zircons derived both from the acatlan granitoids and the ca 1 0 1 3 ga oaxacan complex and are inferred to represent rifted passive margin sediments an age of 348 4 1 ma from zircons in a migmatized amphibolite is interpreted as the time of migmatization and dates decompression melting following peak pressure at depths of 45 55 km retrogression from 530 c to 370 c occurred between 343 and 335 ma the predominance of reasonably coherent rifted passive margin rocks over a surface area of 10 90 km suggests removal of a large slice of the upper plate during flat slab subduction this slice was subducted to depths of ca 45 55 km where it was underplated and transferred to the overriding plate the absence of oaxacan complex rocks in the hp belt suggests the oaxacan basement was subducted to greater depths underplating was followed by extrusion facilitated by extension in the upper plate that produced mississippian rift basins east of the median hp belt westward overthrusting of the hp rocks produced a klippe that overrode mississippian clastic wedge sediments

u pb geochronological constraints on the triassic jurassic ayu complex southern mexico derivation from the western margin of pangea a abstract we present la icp ms laser ablation inductively coupled plasma mass spectrometry u pb detrital and igneous zircon data of poly deformed metamorphic and igneous rocks of the ayu area southern mexico these rocks were previously inferred to be part of the late paleozoic acatlan complex but new age data indicate that they formed in the mesozoic and should be placed in the newly designated ayu complex the ayu complex comprises polydeformed metasedimentary rocks chazumba lithodeme of a turbidite like protolith that are intercalated with boudinaged ortho amphibolites with transitional arc to morb tholeiitic geochemistry in the south the metasedimentary sequence is affected by a ca 171 ma partial melting which formed the magdalena migmatite migmatization was accompanied by 171 168 ma intrusions of granodioritic dioritic and granitic dikes and sheets as well as pegmatite bodies which are characterized by inherited zircon populations of ca 260 290 320 360 420 480 880 990 and 1080 1250 ma that are also found in the chazumba lithodeme u pb detrital zircon dating of seven metasedimentary samples from the migmatized and unmigmatized chazumba lithodeme yielded youngest detrital zircons and clusters of 192 198 214 250 266 and 291 ma and are interpreted to reflect the late triassic middle jurassic deposition of turbiditic rocks the transitional arc tholeiitic geochemistry of the chazumba amphibolites is consistent with turbidite sedimentation in a back arc environment along a rifted passive margin close to a contemporaneous magmatic arc inferred flattening of the subduction zone led to subduction erosion during the early middle jurassic and underthrusting of the chazumba lithodeme to depths equivalent to amphibolite facies metamorphism steepening of the subducting slab and diachronous rifting within the gulf of mexico contributed to extensional tectonics recorded on the mexican mainland and facilitated the tectonic exhumation of the chazumba lithodeme by normal faulting along the reactivated providencia shear zone during the middle late jurassic more generally the documentation of arc back arc assemblages in the ayu complex requires deposition adjacent to a subducting ocean and thus supports a pangea a reconstruction that was synchronous with the breakup of pangea

evolution history of the neoproterozoic eclogite bearing complex of the muya dome central asian orogenic belt constraints from zircon u pb age hf and whole rock nd isotopes abstract u pb dating and hf isotope analysis of zircons and whole rock nd isotope analyses were carried out on country rocks of the eclogite gneiss complex of the north muya dome in the anamakit muya zone of the baikal muya accretionary fold belt zircons from garnet biotite gneisses qtz kfsp pl bt grt and garnet biotite muscovite schist pl kfsp bt mu grt qtz were dated using the la icp ms technique based on u pb isotope data and cl images zircon grains were divided into three groups detrital magmatic and metamorphic zircons metamorphic zircons display no zoning or the cloudy zoning the grains morphology together with the well developed oscillatory zoning clearly identifies the igneous origin of magmatic zircons the metamorphic zircons ages 576 680 ma have th u ratios varying from 0 271 to 0 004 whereas the ratio in magmatic zircons ranges from 0 779 to 0 11 magmatic zircons from granite gneisses of the north muya dome exhibit a relatively narrow spread in the crystallization age with the major peak at ca 764 ma younger ages are interpreted as due to the partial resetting of u pb system during the subsequent metamorphic evolution detrital zircons from two mica schist sample mu 93 10 give ages of 1 88 2 66 ga the oldest detrital zircon from this sample plots near concordia and has a 207 pb 206 pb age of 3 2 ga zircons from this sample are characterized by the widest scatter of hf t values from 13 9 to 15 3 and t dm c model ages 0 82 3 86 ga zircons from other samples have a much narrower ranges of hf t 11 6 to 0 7 and t dm c 0 85 1 52 ga the involvement of older crustal material is also evident from the whole rock nd isotopic compositions the gneisses and schists exhibit a range of nd isotopic compositions with nd t values ranging from 3 5 to 3 6 and t nd dm from 1 64 to 1 09 ga the integration of the hf isotope data with the age spectra provides with the first evidence for the existence of mesoarchean crust in the baykal muya sector of the central asian orogenic belt

chlorinity salinity distribution patterns in experimental granular sea ice this work investigates the possibility of brine channel formation and development during the freezing of granular ice from a loose frazil ice suspension in an nacl solution at sea water concentration three experiments were performed at various constant growth rates in a purpose built vessel with computer controlled thermal driving high resolution chlorinity measurements are used as a proxy for the bulk salinity of the samples these show clear brine segregation processes in the ice with very high salinity gradients for the fast 10 mm h 1 to medium 2 mm h 1 freezing rates provided that a suitable sampling scale is adopted weak segregation was found at the low freezing rate 0 5 mm h 1 the spatial distribution of the bulk salinity fits the visual appearance of brine channels in the ice adequately in both horizontal and vertical sections in a similar way to columnar congelation sea ice the number of brine channels significantly decreases with growth rate but the density of channels is systematically lower in the granular ice than that found at equivalent freezing rates in the columnar ice this is attributed to the lower geometrical constraints on brine transport in the granular medium contrasts between brine channel geometry and density at different growth rates are discussed in light of the mushy layer concept adapted to sea ice growth from the solidification of alloys

statistical analyses of great earthquake recurrence along the cascadia subduction zone goldfinger et al 2012 interpreted a 10 000 year old sequence of deep sea turbidites at the cascadia subduction zone csz as a record of clusters of plate boundary great earthquakes separated by gaps of many hundreds of years we performed statistical analyses on this inferred earthquake record to test the temporal clustering model and to calculate time dependent recurrence intervals and probabil ities we used a monte carlo simulation to determine if the turbidite recurrence in tervals follow an exponential distribution consistent with a poisson memoryless process the latter was rejected at a statistical significance level of 0 05 we performed a cluster analysis on 20 randomly simulated catalogs of 18 events event t2 excluded using ages with uncertainties from the turbidite dataset results indicate that 13 cata logs exhibit statistically significant clustering behavior yielding a probability of clus tering of 13 20 or 0 65 most 70 of the 20 catalogs contain two or three closed clusters a sequence that contains the same or nearly the same number of events and the current cluster t1 t5 appears consistently in all catalogs analysis of the 13 cat alogs that manifest clustering indicates that the probability that at least one more event will occur in the current cluster is 0 82 given that the current cluster may not be closed yet the probabilities of an m 9 earthquake during the next 50 and 100 years were estimated to be 0 17 and 0 25 respectively we also analyzed the sensitivity of results to including event t2 whose status as a full length rupture event is in doubt the inclusion of t2 did not change the probability of clustering behavior in the csz turbidite data but did significantly reduce the probability that the current cluster would extend to one more event based on the statistical analysis time independent and time dependent recurrence intervals were calculated

neoarchean evolution of differing convergent margin assemblages in the wabigoon subprovince geochemical and geochronological evidence from the lake of the woods greenstone belt superior province northwestern ontario abstract the neoarchean lake of the woods greenstone belt is subdivided into three lithostratigraphic assemblages a lowermost mafic volcanic assemblage a compositionally diverse predominantly volcanic middle assemblage and a predominantly sedimentary uppermost assemblage the secular evolution and geodynamic settings of these assemblages are constrained with detailed geochronological and geochemical data the lower keewatin is the oldest assemblage with a zircon u pb age of 2738 2 0 ma it consists of mg and fe tholeiitic basalts mg number 30 65 with flat to slightly enriched rare earth elements ree la yb cn 0 9 1 6 elevated large ion lithophile elements lile and undepleted high field strength elements hfse the tholeiites do not appear to have exact modern analogs but do have some similarities to primitive arc tholeiites and back arc basin basalts suggesting an archean destructive margin setting the upper keewatin assemblage disconformably overlies the lower keewatin assemblage it consists of volcanic and sedimentary groups two geochemically distinct volcanic suites are recognized the dominant suite consists of compositionally diverse calc alkalins basalt to rhyolite felsic end members have yielded zircon u pb ages ranging from 2712 to 2723 ma the suite exhibits highly fractionated ree la yb cn 4 35 elevated lile and nb and ta depletion anomalies which are very similar to modern island arc volcanic rocks developed in proximity to continental margins a coeval suite of mafic to ultramafic volcanic rocks consists of mg tholeiite komatiitic basalt and ultramafic komatiite mg numbers 45 80 the suite exhibits depleted lree la yb cn 0 6 1 0 slightly elevated lile and undepleted to slightly enriched hfse suggesting that this geochemically primitive suite was produced by partial melting of a refractory mantle source perhaps as second stage melts of the same mantle source from which the lower keewatin assemblage basalts were previously derived the electrum assemblage unconformably overlies the upper keewatin assemblage in the northern part of the belt it consists of conglomerates sandstones and minor volcanic rocks having detrital ages indicating deposition after 2699 ma the volcanic rocks consists of andesite to rhyolite with shoshonitic to calc alkaline geochemical affinity as indicated by highly fractionated ree la yb cn 12 112 highly enriched lile and pronounced nb ta and ti depletion anomalies samples from the syenitic falcon island pluton appear to be coeval with electrum assemblage volcanics having an u pb isotopic age of 2694 ma and similar but even more alkaline chemistry consisting of highly fractionated lree and lile trace elements with very pronounced nb ta and ti depletion anomalies these late tectonic suites are geochemically similar to modern shoshonites with a continental influence formed in the late stages of a mature island arc or a continental arc setting

late paleozoic subduction and exhumation of cambro ordovician passive margin and arc rocks in the northern acatlan complex southern mexico geochronological constraints abstract the origin and age of high pressure hp rocks are crucial for paleogeographic reconstructions because they either define an oceanic suture or an extrusion zone within the upper plate hp rocks in the san miguel las minas area in the northern part of the acatlan complex southern mexico have been inferred to be of early paleozoic age and to mark oceanic sutures however blueschists in the northern part of the complex have yielded mississippian 40ar 39ar plateau ages of 344 5 ma for glaucophane and 338 3 ma and 337 2 ma for muscovite these ages are slightly younger than recently published ages a u pb zircon age of 353 1 ma from associated eclogite and a 347 3 ma muscovite age from the tectonically overlying greenschist facies las minas unit taken together these data indicate rapid cooling between 700 and 340 c in ca 17 myr on the other hand associated ordovician anacahuite amphibolite cooled through ca 500 c at 299 6 ma 40ar 39ar on hornblende suggesting a second permian phase of exhumation protoliths of the high grade rocks include cambrian ordovician rift passive margin psammites pelites and tholeiitic dykes an ordovician mafic intrusion anacahuite amphibolite dated at 470 10 ma u pb zircon and megacrystic granite dated at 492 12 ma u pb zircon and arc related mafic rocks of unknown age these rocks are interpreted to have been part of the upper plate rocks that was removed by subduction erosion and taken to depths between 35 and 55 km where they underwent blueschist eclogite facies metamorphism this was followed by rapid extrusion along a channel bounded by an easterly dipping mississippian listric normal shear zone and a thrust modified by a permian dextral fault rocks above and below the extrusion zone are mainly cambro ordovician rift passive margin units but a small vestige of the arc is preserved as dikes cutting rocks lying unconformably beneath the fossiliferous latest devonian lower permian patlanoaya group since faunal data indicate that pangea had begun amalgamation by the mississippian at which time the acatlan complex lay 1500 2000 km south of the ouachita collisional orogen between gondwana and laurentia it is inferred that subduction and extrusion of the high pressure rocks occurred on the active western margin of pangea

randomness of megathrust earthquakes implied by rapid stress recovery after the japan earthquake the 2011 tohoku oki earthquake released stress within a subduction zone analysis of seismic data shows that stresses returned to pre quake levels within a few years implying that large quakes could occur more often than previously thought

the high pressure iberian czech belt in the variscan orogen extrusion into the upper gondwanan plate a siluro devonian high pressure hp belt the iberian czech or ic belt extends from iberia cordoba coimbra shear zone through armorica and the massif central to the bohemian massif iberian czech ic belt and includes arc and periarc rocks morb and supra subduction ophiolites and passive margin sequences it has generally been interpreted to be either a a suture of the galician south brittany massif central and moldanubian ocean b a nappe rooted to the north in the rheic ocean or c the result of post collisional strike slip shuffling of the gondwanan margin during which a slice of the rheic ocean was inserted into the gondwanan margin we agree with a rheic ocean origin but propose that the ic belt represents a pre collisional part of the gondwanan continental oceanic margin that was removed by subduction erosion underwent hp metamorphism and was then extruded into the overlying gondwanan plate this model explains i the lack of paleolatitudinal and faunal differences across the ic belt ii the juxtaposition of active margin tectonics within synchronous passive margin sequences and iii the pre collisional age of most of the hp metamorphism the complete range of hp rocks in the ic belt from blueschist to hot eclogites indicates that previous correlations with b and a type subduction respectively cannot be sustained

earthquake recurrence models fail when earthquakes fail to reset the stress field 1 parkfield s regularly occurring m6 mainshocks about every 25 years have over two decades stoked seismologists hopes to successfully predict an earthquake of significant size however with the longest known inter event time of 38 years the latest m6 in the series 28 sep 2004 did not conform to any of the applied forecast models questioning once more the predictability of earthquakes in general our study investigates the spatial pattern of b values along the parkfield segment through the seismic cycle and documents a stably stressed structure the forecasted rate of m6 earthquakes based on parkfield s microseismicity b values corresponds well to observed rates we interpret the observed b value stability in terms of the evolution of the stress field in that area the m6 parkfield earthquakes do not fully unload the stress on the fault explaining why time recurrent models fail we present the 1989 m6 9 loma prieta earthquake as counter example which did release a significant portion of the stress along its fault segment and yields a substantial change in b values

decade scale decrease inb value prior to the m9 class 2011 tohoku and 2004 sumatra quakes 1 the gutenberg richter frequency magnitude distribution of earthquakes has become well established in seismology the slope of the relation between frequency and magnitude b value is typically 1 but it often shows variations around 1 based on an analysis of seismicity prior to the 2011 tohoku and 2004 sumatra earthquakes both in magnitude m 9 class we show that the pronounced decade scale decrease inbvalue was a common precursor to both mega quakes around their hypocenters this is the first report onm9 class quakes to confirm a change inb value which has been predicted based on the results of laboratory experiments we propose that the b value is an important indicator of an impending great earthquake and has great potential in terms of predicting a future large quake off the pacific coast of hokkaido japan

solidification of leads theory experiment and field observations thin sea ice plays a central role in the surface heat and mass balance of the arctic ocean in order to develop understanding of these balances we describe and analyze highly resolved temperature data taken through the air sea ice interface during the transition from an ice free to an ice covered arctic ocean surface the data were taken to observe the thermodynamic evolution of a lead a process that has previously only been accessible to measurement techniques confined to the lead edge our detailed analysis of the field data is guided by recent theoretical and experimental advances in understanding the phase dynamics of directionally solidified alloys because of the dearth of direct observations we also present time series of the relevant heat fluxes inferred from our data and demonstrate the controlling influence that the internal phase evolution has on these quantities we have previously examined the stability of the brine trapped in a growing sea ice matrix both theoretically and experimentally and now find that haline convection driven from within the growing layer is consistent with this previous work and with the nature of direct turbulence measurements the importance of this process is that although ice growth is continuous the local brine flux commences abruptly only after some time in contrast to what had previously been supposed hence the ice growth process itself is a source of intermittency in oceanic boundary layer turbulence furthermore we find that in this particular situation the sea ice growth is not simply a square root function of time in contrast to the model typically used in numerical simulations by far the most practical methods of studying lead convection are numerical simulations and laboratory models and a strong conclusion of this study is the importance of the proper treatment of the boundary conditions describing the buoyancy flux

fore arc deformation controls frequency size distribution of megathrust earthquakes in subduction zones 1 seismotectonic deformation in subduction zones seems to follow rather simple spatiotemporal patterns with fore arc basins overlying the areas of large slip during quasiperiodic megathrust earthquakes to study the possible coupling between long term deformation and earthquake behavior we use compressive granular wedges overlying a rate and state dependent frictional interface as analogue models of subduction zone fore arcs overlying a seismogenic megathrust for different seismogenic zone geometries we analyze deformation time series with respect to the accumulation of permanent strain and frequency size distributions of episodic slip events equivalent to great m 8 earthquakes we observe that permanent deformation in the wedges localizes at the periphery of unstable slip at depth over tens of simulated seismic cycles for updip limited seismogenic zone models this leads to structural wedge segmentation characterized by an elastic domain overlying the zone of unstable basal slip along with the evolution of segmentation the frequency size distributions of episodic slip events develop from more random gutenberg richter like events b value 0 6 toward more periodic characteristic events b value 0 1 corresponding coefficients of variation cv of recurrence intervals decrease from cv 0 6 in deforming wedges to cv 0 3 in segmented wedges from the experiments we thus infer a positive feedback between fore arc tectonics and megathrust seismogenesis which brings the system from a stochastic to a more deterministic state our experimental observations imply that the quasiperiodic recurrence of great subduction earthquakes evident from existing earthquake records is a long term feature intrinsically related to the seismotectonic segmentation of the fore arc wedges

late ordovician early silurian continental collisional orogeny in southern mexico and its bearing on gondwana laurentia connections new zircon and monazite u pb data tectonic mapping and petrologic studies in key units of the acatlan complex show a previously undocumented phase of continental collision orogeny of late ordovician early silurian age in southern mexico the event involved the partial eclogitization of oceanic lithosphere and continental crust which traveled westward more than 200 km over siliciclastic metasedimentary rocks of the trench forearc of an opposing continental margin the overriding eastern margin was the oaxaquia microplate attached to gondwana and the western overridden margin is considered to have been the eastern margin of laurentia this event which we name the acatecan orogeny was roughly synchronous with the possible closure of iapetus along the appalachian margin which involved according to current models either the docking of peri gondwanan terranes such as avalonia and carolina or the direct collision between gondwana and laurentia the permanence of oaxaquia in northwestern gondwana until the end of the silurian as suggested by tremadocian to silurian marine faunas in the cover of oaxaquia is more consistent with the direct collision of gondwana and laurentia at the end of the ordovician forming the acatlan complex between

some premonitory phenomena of the 1995 hyogo ken nanbu kobe earthquake seismicity b value and fractal dimension abstract this paper presents a detailed and complex analyses of the spatio temporal evolution of seismic activity between 1976 and 1998 in a broad area surrounding the epicentre of the 1995 hyogo ken nanbu kobe earthquake as well as in the source area various precursory changes in seismicity such as quiescence followed by increased seismic activity b value and fractal dimension correlation dimension d2 anomalies appear approximately two years before the occurrence of the major event an increased level of background seismicity is clearly observed after the occurrence of the kobe earthquake particularly in the northeast extension of the source area all these anomalous changes in seismic activity before and after the occurrence of the 1995 hyogo ken nanbu earthquake appear in a relatively large region surrounding the epicentre of the main shock as well as in the source area

late cretaceous shortening and early tertiary shearing in the central sierra madre del sur southern mexico insights into the evolution of the caribbean north american plate interaction 1 a wide region in the central part of the sierra madre del sur sms southern mexico records two deformational phases between the late cretaceous and early tertiary the first is a progressive approximately e w shortening phase that spans from the coniacian to earliest paleocene and involves deformation of cretaceous marine sedimentary units the second phase corresponds to paleocene to early eocene deformation that also affects continental sediments and is characterized by gentle folding and counterclockwise rotation of previous shortening structures associated with strike slip faulting here we present geologic geochronologic and structural data of two key areas of the sierra madre del sur the guerrero morelos platform gmp and the huajuapan tamazulapan area in western oaxaca to describe the geometry kinematics and timing of the late cretaceous and early tertiary deformation two regional magmatic episodes constrain the deformational history 1 the first between the maastrichtian and the paleocene 68 57 ma documents the end of late cretaceous shortening in the gmp and 2 the second between the late eocene and early oligocene 37 29 ma has a more regional distribution the time and space analysis of deformation and magmatism in southern mexico led us to exclude flat subduction or collision of the guerrero terrane to the west as the cause for late cretaceous shortening in the gmp considering the similarity in the time and style of deformation with that of the northern chortis block we favor an interpretation in which the tectonic evolution of the central and eastern sms is the result of progressive interaction of the caribbean plate with the southernmost edge of north america since the late cretaceous

seismic gap hypothesis ten years after the seismic gap hypothesis states that earthquake hazard increases with time since the last large earthquake on certain faults or plate boundaries one of the earliest and clearest applications of the seismic gap theory to earthquake forecasting was by mccann et al 1979 who postulated zones of high medium and low seismic potential around the pacific rim in the 10 years since there have been over 40 large m 7 0 earthquakes enough to test statistically the earlier forecast we also analyze another forecast of long term earthquake risk that by kelleher et al 1973 the hypothesis of increased earthquake potential after a long quiet period can be rejected with a large confidence the data suggest that contrary to these forecasts places of recent earthquake activity have larger than usual seismic hazard whereas the segments of the circum pacific belt with no large earthquakes in recent decades have remained relatively quiet the clustering of earthquake times does not contradict the plate tectonic model which constrains only the long term average slip rate not the regularity of earthquakes

laser probe 40 ar 39 ar ages of early and late stage alteration assemblages rosario porphyry copper molybdenum deposit collahuasi district i region chile sensibly identical laser probe 40 ar 39 ar dates of 32 9 or 0 5 2sigma and 32 9 or 0 6 ma are determined for respectively early stage hydrothermal biotite and late stage hydrothermal muscovite from the giant rosario porphyry copper deposit in the collahuasi district of northern chile the age determinations were carried out on ca 1 cm 2 1 to 0 5 mm thick wafers of altered rock or on smaller chips broken therefrom obviating the requirement for mineral separation and permitting direct petrographic control of the analytical procedure the age data although not unambiguous imply that this extremely large hydrothermal center was emplaced over a short interval hydrothermal activity in this central andean transect migrated eastward over a period of ca 3 to 4 m y from copaquire through quebrada blanca to rosario the intensity of mineralization increasing with time rosario chuquicamata and la escondida the largest of the west fissure domeyko fault system array were apparently emplaced coevally in the terminal stage of the late eocene early oligocene metallogenic episode

the juchatengo complex an upper level ophiolite assemblage of late paleozoic age in oaxaca southern mexico the juchatengo complex jc suite is located between the proterozoic oaxacan complex to the north and the xolapa complex to the south and was amalgamated by late paleozoic magmatism it consists of mafic and sedimentary rocks that have oceanic affinities with internal pseudostratigraphic structural and metamorphic characteristics which resemble a typical upper level ophiolite assemblage new u pb zircon and previous hornblende k ar analyses yield ages of ca 291 313 ma u pb for plagiogranites and ca 282 277 ma for tonalites intruding the entire sequence including pelagic sediments at the top with a maximum deposition age of ca 278 ma and noteworthy local provenance these data constrain the age of the jc to the late pennsylvanian early permian period hf isotopic analyses obtained from zircons in the jc plagiogranite and tonalite show that they come from a similar primitive mantle source 176hf 177hf 0 282539 0 283091 hf t 3 2 to 15 0 hf t values from near 0 to 2 8 in the tonalites indicate a contribution from the continental crust trace elements and ree patterns in whole rock and zircons point to a primitive mantle source for differentiated mafic plagiogranite dykes and tonalitic plutons geochronological and geochemical data address the generation of new oceanic crust above the subduction zone probably in a backarc setting in this tectonic scenario the jc ophiolite originated due to the convergence of the paleo pacific plate below the already integrated oaxacan and acatlan complexes in western pangea the dextral displacement places the deformation in a transtensional regime during the late paleozoic age

statistical evaluation of characteristic earthquakes in the frequency magnitude distributions of sumatra and other subduction zone regions 1 if subduction zone earthquakes conform to a characteristic model in which persistent segments fail at predictable stress levels due to the steady accumulation of tectonic loading historical seismicity may constrain the occurrence of future events we test this model for earthquakes on the sumatra andaman megathrust and other subduction zones using frequency magnitude distributions using simulations we show that poisson confidence intervals correctly account for the counting errors of histogram data these confidence intervals demonstrate that we cannot reject the gutenberg richter distribution in favor of a characteristic model in any of the real catalogues tested a visual bias in power law count data at high magnitudes combined with a sample bias for large earthquakes is sufficient to explain candidate characteristic events this result implies that historical earthquakes are likely poor models for future events and that monte carlo simulations will provide a better assessment of earthquake and associated hazards

tectonometamorphic evolution of the acatlan complex eclogites southern mexico the acatlan complex of southern mexico is linked to the evolution of the appalachian caledonian chains and records events related to the taconian acadian and alleghanian orogenies of northeastern north america mafic eclogites and garnet amphibolites from two selected localities are used to partially reconstruct the tectonometamorphic evolution of this complex eclogites contain garnet almandine ca na pyroxene phengitic mica zoisite clinozoisite quartz ca na amphibole barroisite katophorite albitic plagioclase rutile phase and textural relationships thermobarometric determinations and available radiometric ages indicate that eclogite facies metamorphism took place during the ordovician at temperatures around 560 60 c and pressures between 11 and 15 kbar 1 kbar 100 mpa eclogites underwent widespread retrogression to epidote amphibolite then greenschist facies during exhumation most probably during devonian times epidote amphibolite facies include the critical assemblage cal

rupture process of the 2011 tohoku oki earthquake and absolute elastic strain release 1 on 11 march 2011 the tohoku oki earthquake in eastern japan and the devastating tsunami that followed it caused severe damage and numerous deaths to clarify the rupture process of the earthquake we inverted teleseismic p wave data applying a novel formulation that takes into account the uncertainty of green s function which has been a major error source in waveform inversion the estimated seismic moment is 5 7 1022 nm mw 9 1 associated with a fault rupture 440 km long and 180 km wide along the plate interface the source process is characterized by asymmetric bilateral rupture propagation but we also found continuous slips up dip from the hypocenter which led to a large maximum slip 50 m long slip duration 90 s and a large stress drop 20 mpa the long slip duration large stress drop extensional normal faulting aftershocks in a previously compressional stress regime and low angle normal slips at approximately the depth of the plate interface suggest that the earthquake released roughly all of the accumulated elastic strain on the plate interface owing to exceptional weakening of the fault the stress accumulated on the plate interface was about 20 mpa near the trench and 0 10 mpa in the down dip source region

static stress drop in the mw 9 tohoku oki earthquake heterogeneous distribution and low average value static stress drop distribution and its average value over the rupture area contain important information on the mechanics of large earthquakes here we derive static stress drop distributions from 40 published rupture models for the 2011 mw 9 tohoku oki earthquake that are based on various multidisciplinary observations average stress drop value over the fault area encompassed by the 5 m coseismic slip contour is not unusually large for each rupture model the mean for the 40 models is 2 3 1 3 mpa assuming a uniform rigidity 40 gpa the value for the entire rupture zone and with a more realistic rigidity structure will be even lower in the majority of the models local stress drop in parts of the rupture zone well exceeds 20 mpa the heterogeneous stress change distribution with large stress drop being accompanied by large stress increase leads to the small average for the earthquake

the largest aftershock how strong how far away how delayed 1 proposed in the 1950 s bath s law states that the largest aftershock has a magnitude that is typically 1 2 less than that of the mainshock thirty years of the global earthquake catalog allow us to extend bath s law in time space and focal mechanism on average reverse faults have a smaller magnitude and distance from the mainshock to largest aftershock than strike slip faults the distribution of the time intervals between mainshocks and their largest aftershocks obeys power law but with a somewhat faster rate of decay than for aftershocks in general this implies that the largest aftershocks are more likely to occur earlier rather than later in a given sequence of aftershocks

buoyancy driven rapid exhumation of ultrahigh pressure metamorphosed continental crust abstract preservation of ultrahigh pressure uhp minerals formed at depths of 90 125 km require unusual conditions our subduction model involves underflow of a salient 250 150 km wide 90 125 km long of continental crust embedded in cold largely oceanic crust capped lithosphere loss of leading portions of the high density oceanic lithosphere by slab break off as increasing volumes of microcontinental material enter the subduction zone buoyancy driven return toward midcrustal levels of a thin 2 15 km thick low density slice finally uplift backfolding normal faulting and exposure of the uhp terrane sustained over 20 million years rapid 5 mm year exhumation of the thin aspect ratio uhp sialic sheet caught between cooler hanging wall plate and refrigerating downgoing lithosphere allows withdrawal of heat along both its upper and lower surfaces the intracratonal position of most uhp complexes reflects consumption of an intervening ocean basin and introduction of a sialic promontory into the subduction zone uhp metamorphic terranes consist chiefly of transformed yet relatively low density continental crust compared with displaced mantle material otherwise such complexes could not return to shallow depths relatively rare metabasaltic metagabbroic and metacherty lithologies retain traces of phases characteristic of uhp conditions because they are massive virtually impervious to fluids and nearly anhydrous in contrast h2o rich quartzofeldspathic gneissose schistose more permeable metasedimentary and metagranitic units have backreacted thoroughly so coesite and other uhp silicates are exceedingly rare because of the initial presence of biogenic carbon and its especially sluggish transformation rate uhp paragneisses contain the most abundantly preserved crustal diamonds

crustal emplacement of exhuming ultra high pressure rocks will that be pro or retro side ultra high pressure u hp rocks form and exhume from deep within subduction channels but subsequent horizontal transport in the shallower orogenic crust makes it difficult to reconstruct their tectonic histories we use a conceptual framework and numerical models to show that buoyant exhumation from within a subduction conduit formed during one sided subduction may lead to emplacement of u hp rocks into either the lower plate prowedge or upper plate retrowedge of an orogen depending on whether the upper plate crust deforms or acts as a backstop during exhumation both modes may operate at different positions or different times within an orogen leading to emplacement of u hp rocks into both plates without changing subduction geometry we propose that retrotransport during exhumation may explain some u hp rocks e g liverpool land situated in the upper plate of the greenland norwegian caledonides

slab1 0 a three dimensional model of global subduction zone geometries 1 we describe and present a new model of global subduction zone geometries called slab1 0 an extension of previous efforts to constrain the two dimensional non planar geometry of subduction zones around the focus of large earthquakes slab1 0 describes the detailed non planar three dimensional geometry of approximately 85 of subduction zones worldwide while the model focuses on the detailed form of each slab from their trenches through the seismogenic zone where it combines data sets from active source and passive seismology it also continues to the limits of their seismic extent in the upper mid mantle providing a uniform approach to the definition of the entire seismically active slab geometry examples are shown for two well constrained global locations models for many other regions are available and can be freely downloaded in several formats from our new slab1 0 website http on doi gov d9arbs we describe improvements in our two dimensional geometry constraint inversion including the use of average active source seismic data profiles in the shallow trench regions where data are otherwise lacking derived from the interpolation between other active source seismic data along strike in the same subduction zone we include several analyses of the uncertainty and robustness of our three dimensional interpolation methods in addition we use the filtered subduction related earthquake data sets compiled to build slab1 0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far concluding that the width of these seismogenic zones is on average 30 larger than previous studies have suggested

earthquake statistics at parkfield 1 stationarity of b values 1 in this paper paper 1 we quantitatively show that the heterogeneous pattern of b values of the gutenberg richter relation in the parkfield segment of the san andreas fault is to a high degree stationary for the past 35 years this prepares the grounds for paper 2 where we test the hypothesis that our model of spatially varying b values forecasts future seismicity more accurately than the approach in which one assumes a constant b value equal to the average regional value the method we develop to measure stationarity in the presence of spatial heterogeneity consists of the following steps 1 determine the optimal dimensions of the sampling volume by mapping b values with a wide range of radii and selecting the largest radius that gives the most detailed resolution of the b value heterogeneity along the selected fault segment the high data density permits the definition of the dominant dimensions of the seismotectonic fabric which is about 8 10 km 2 map the difference in b value between two periods selecting numerous possible catalog divisions 3 identify significant changes of b values by the utsu test utsu 1992 along the studied fault segment of 110 km length only one patch of radius 5 km showed a significant increase in b from below average to above as a function of time this change in b initiates around 1993 and thus correlates in space and time with a well documented episode of creep at depth using the derived spatial variable b value distributions we find that the highest probability for earthquakes with magnitude m 6 is in the middle mountain asperity where the 1966 parkfield earthquake nucleated and where all m 4 5 events in the data set occurred in contrast if only the regional average b value of 0 92 is used to predict future seismicity the creeping segment north of parkfield should produce major earthquakes most frequently a conclusion that contradicts the observations

observations of platelet ice growth and oceanographic conditions during the winter of 2003 in mcmurdo sound antarctica 1 platelet ice is the name given to ice crystals that nucleate in the ocean and grow either at depth or loosely attached to the ice water interface related to the proximity of ice shelves it is known to form in supercooled seawater this study details the conditions for its growth during the austral winter of 2003 in mcmurdo sound antarctica a key finding is that the presence of platelet ice in the sea ice cover is conclusively linked to the time history of the appearance of ice crystals in the water column monitored using the strength of the backscattered signal from an acoustic doppler current profiler as a proxy generally these crystals appeared from mid may as water near the interface became supercooled this near surface supercooling appears to be related to a simultaneous abrupt change in the structure of the upper 250 m of the water column from one that behaved dynamically and contained both the warmest and coolest measured temperatures to one in which the water was essentially isothermal near its surface freezing temperature near surface ocean temperature was also affected by tidal mixing and by an increase in the thickness and density over the course of winter of the surface mixed layer created by salt rejection during ice growth these processes allowed cold water trapped by buoyancy in a band at the base of the mixed layer in early winter to gain access to the ice water interface by midwinter this band of cold water probably had its origin beneath the mcmurdo ice shelf

extensional late paleozoic deformation on the western margin of pangea patlanoaya area acatlan complex southern mexico abstract new mapping in the northern part of the paleozoic acatlan complex patlanoaya area records several ductile shear zones and brittle faults with normal kinematics previously thought to be thrusts these movement zones separate a variety of units that pass structurally upwards from i blueschist eclogitic metamorphic rocks piaxtla suite and mylonitic megacrystic granites columpio del diablo granite ordovician granites elsewhere in the complex ii a gently e dipping listric normal shear zone with top to the east kinematic indicators that formed under upper greenschist to lower amphibolite conditions iii the middle late ordovician las minas quartzite upper greenschist facies psammites with minor interbedded pelites intruded by mafic dikes and a leucogranite dike from the columpio del diablo granite unconformably overlain by the otate meta arenite lower greenschist facies psammites and pelites roughly temporal equivalents are the middle late ordovician mal paso and ojo de agua units interbedded metasandstone and slate and metapelite and mafic minor intrusions respectively some of these units are intruded by the massive 461 2 ma palo liso megacrystic granite decussate contact metamorphic muscovite yielded a 40 ar 39 ar plateau age of 440 4 ma iv a steeply moderately e dipping normal fault v latest devonian middle permian sedimentary rocks patlanoaya group here elevated from formation status the upward decrease in metamorphic grade is paralleled by a decrease in the number of penetrative fabrics which varies from i three in the piaxtla suite through ii two in the las minas unit e trending sheath folds deformed by ne trending subhorizontal folds with top to the southeast asymmetry both associated with a solution cleavage iii one in the otate mal paso and ojo de agua units steeply se dipping ne sw plunging open close folds to iv none in the patlanoaya group 40 ar 39 ar analyses of muscovite from the earliest cleavage in the las minas unit yielded a plateau age of 347 3 ma and show low temperature ages of 260 ma post dating all of these structures and the patlanoaya group are ne plunging subvertical folds and kink bands an e w vertical normal fault juxtaposes the low grade rocks against the anacahuite amphibolite that is cut by megacrystic granite sheets both of which were deformed by two penetrative fabrics amphibole from this unit has yielded a 40 ar 39 ar plateau age of 299 6 ma which records cooling through 490 c and is probably related to a permo carboniferous reheating event during exhumation the extensional deformation is inferred to have started in the latest devonian 360 ma during deposition of the basal patlanoaya group lasting through the rapid exhumation of the piaxtla suite at 350 340 ma synchronous with cleavage development in the las minas unit deposition of the patlanoaya group with active fault related exhumation suggested by mississippian and early permian conglomerates 340 and 300 ma respectively and continuing at least into the middle permian 260 ma muscovite ages the continuity of mid continent mississippian fauna from the usa to southern mexico suggests that this extensional deformation occurred on the western margin of pangea after closure of the rheic ocean

palaeozoic to early jurassic history of the northwestern corner of gondwana and implications for the evolution of the iapetus rheic and pacific oceans abstract the palaeozoic to mesozoic igneous and metamorphic basement rocks exposed in the merida andes of venezuela and the santander massif of colombia are generally considered to define allochthonous terranes that accreted to the margin of gondwana during the ordovician and the carboniferous however terrane sutures have not been identified and there are no published isotopic data that support the existence of separate crustal domains a general paucity of geochronological data led to published tectonic reconstructions for the evolution of the northwestern corner of gondwana that do not account for the magmatic and metamorphic histories of the basement rocks of the merida andes and the santander massif we present new zircon u pb icp ms data from 52 igneous and metamorphic rocks which we combine with whole rock geochemical and pb isotopic data to constrain the tectonic history of the precambrian to mesozoic basement of the merida andes and the santander massif these data show that the basement rocks of these massifs are autochthonous to gondwana and share a similar tectono magmatic history with the gondwanan margin of peru chile and argentina which evolved during the subduction of oceanic lithosphere of the iapetus ocean the oldest palaeozoic arc magmatism is recorded at 500 ma and was followed shortly by barrovian metamorphism peak metamorphic conditions at upper amphibolite facies are recorded by anatexis at 477 ma and the intrusion of synkinematic granitoids until 472 ma subsequent retrogression resulted from localised back arc or intra arc extension at 453 ma when volcanic tuffs and interfingered sedimentary rocks were deposited over the amphibolite facies basement continental arc magmatism dwindled after 430 ma and terminated at 415 ma coevally with most of the western margin of gondwana after pangaea amalgamation in the late carboniferous to early permian a magmatic arc developed on its western margin at 294 ma as a result of subduction of oceanic crust of the palaeo pacific ocean intermittent arc magmatism recorded between 294 and 225 ma was followed by the onset of the andean subduction cycle at 213 ma in an extensional regime extension was accompanied by slab roll back which led to the migration of the arc axis into the central cordillera of colombia in the early jurassic

fine scale isotopic heterogeneities and fluids in the deep crust a40ar 39ar laser ablation and tem study of muscovites from a granulite eclogite transition zone spectacular exposures on holsnoy island western norway reveal that eclogites formed in situ from adjacent anhydrous granulites as a result of the localized infiltration of fluids stepwise and laser40ar 39ar experiments on muscovite from the eclogites have been used in conjunction with electron microprobe and transmission electron microscopy tem analysis to examine the behavior of argon under high pressure metamorphism and subsequent cooling muscovites with 0 10 0 17na na k yield40ar 39ar plateau and integrated ages in the range 450 465 ma 20 35 myr older than40ar 39ar muscovite plateau ages from adjacent eclogite samples laser40ar 39ar analyses on 75 m spots across two single muscovite grains from these samples are approximately uniform at 444 2 1 9 21 spots and 443 3 1 7 ma 26 spots however incremental heating of high sodic 0 18 0 32 na na k muscovite failed to yield a plateau laser40ar 39ar analyses of 100 areas from two single grains from this sample reveal complex two dimensional patterns with variable apparent ages in the range of 445 625 ma electron microprobe measurements obtained from one of the grains reveal that the paragonite content is also highly variable both parallel and perpendicular to 001 all the tem bright field images obtained from this mica yield information consistent with a single homogeneous phyllosilicate phase yet several of the selected area electron diffraction saed analyses document locally intergrown muscovite and sodic muscovite possibly in an exsolution relationship on a unit cell scale analytical electron microscopy aem analyses obtained over a 5 100 nm scale on the same sample reveal great range and heterogeneity inna k including pure muscovite although no separate paragonite domains were found in contrast muscovite grains with consistent laser spot fusion and plateau ages show little heterogeneity inna k at the microprobe level these data provide evidence of variable fluid mediated incorporation of excess40ar under high pressure eclogite facies conditions at the time of the development of the sodic muscovite compositions the data indicate that fine scale heterogeneities in argon isotopic compositions were generated during eclogite facies equilibration and were preserved as the rocks were cycled back to the surface despite the influx of free fluids in the rocks at high pressure the heterogeneities are best reconciled with local buffering and limited mobility of the fluids at least during the final stages of equilibration

ordovician earliest silurian rift tholeiites in the acatlan complex southern mexico evidence of rifting on the southern margin of the rheic ocean abstract the acatlan complex of southern mexico is a vestige of a paleozoic ocean inferred to be either the cambro ordovician iapetus and or the ordovician carboniferous rheic oceans ordovician granitoids in the complex have been interpreted as either the products of dehydration melting arc or rift magmatism however the geochemistry of felsic rocks is inconclusive the geochemistry of a recently discovered major ordovician earliest silurian mafic igneous suite associated with these granitoids is critical to defining the tectonic setting of the igneous event and to paleogeographic reconstructions such data from three areas in the acatlan complex xayacatlan patlanoaya and cuaulote document tholeiitic within plate characteristics with a source in either primitive mantle or mantle previously modified by subduction related magmatism possibly combined with crustal contamination this combined with their occurrence as a dike swarm intruding rift passive margin clastic sedimentary rocks indicates rifting of a continental margin mafic dikes at xayacatlan yielded a concordant u pb tims zircon age of 442 1 ma and a 40 ar 39 ar hornblende plateau age of 434 3 ma the age of mafic magmatism at other localities is defined by the ages of associated granitoids intruded at ca 461 ma and by the age of the youngest detrital zircon in the host rocks 496 25 ma at patlanoaya previously published age data suggest that this igneous event may have started earlier at 478 5 ma early ordovician although the life spans of the iapetus and rheic oceans overlap during the ordovician subduction and collision characterize the former whereas the latter was in a rift drift mode thus this ordovician earliest silurian magmatism is more consistent with rifting along the southern margin of the rheic ocean initiation of rifting at ca 480 ma is contemporaneous with separation of peri gondwanan terranes such as avalonia and carolinia from amazonia oaxaquia subsequent rifting may be analogous to mesozoic cenozoic western north america where transtensional deformation is related to dispersal of terranes e g baja california and cretaceous baja british columbia leading to a gradual collapse of the inboard continental margin

formation and structure of refrozen cracks in land fast first year sea ice 1 this study characterizes the healing process and structure of undeformed linear parallel sided flooded cracks in land fast sea ice field investigations and refreezing experiments were performed in mcmurdo sound ross sea antarctica between 1998 and 2002 data from a two dimensional thermistor array are used to show that the ice water interface of freezing cracks is arch shaped due to bidirectional heat flow to the surrounding ice cover and to the atmosphere ice growing laterally into the crack is found to desalinate over a prolonged period of time until the isotherms are approximately horizontal superposition of heat flow to the atmosphere and to the host sea ice sheet allows the refreezing progress to be modeled analytically close to the ice air interface the salinity is higher at the sides of wide refrozen cracks than it is at the center however deeper down and in narrower cracks in general the salinity is higher at the center than at the sides a finite volume computational fluid dynamics cfd model reproduces the generally arch shaped alignment of brine pockets this pattern is attributed to convection in the mushy layer crystals are found to grow upstream into the crack due to a salinity gradient in the buoyant convective flow

u pb neoproterozoic ordovician protolith age constraints for high to medium pressure rocks thrust over low grade metamorphic rocks in theixcamilpa area acatlan complex southern mexico high grade and high pressure rocks in acatlan complex southern mexico are inferred to have been emplaced either during the convergence and collision between laurentia and gondwana or during subduction on the western margin of pangea in the ixcamilpa area such rocks occur in a synformal nappe and are subdivided into 1 the neoproterozoic ordovician piaxtla suite metapsammite meta pelite and amphibolite that passes structurally upwards from blueschist through eclogite to amphibolite facies intruded by 2 cambro ordovician megacrystic granitoids both of which were thrust westwards over 3 the carboniferous zumpango unit consisting of clastic and meta volcanic rocks laser ablation inductively coupled plasma mass spectrometry la icp ms u pb zircon geochronology yielded age population peaks at i 435 490 ma probably derived from acatlan granitoids ii 500 700 ma likely derived from the yucatan peninsula and brasiliano orogens iii 800 900 ma with provenance in the goias arc of easter

990 and 1100 ma grenvillian tectonothermal events in the northern oaxacan complex southern mexico roots of an orogen inliers of f1 0 1 3 ga rocks occur throughout mexico and form the basement of the oaxaquia microcontinent in the northern part of the largest inlier in southern mexico rocks of the oaxacan complex consist of the following structural sequence of units from bottom to top which protolith ages are 1 huitzo unit a 1012f12 ma anorthosite mangerite charnockite granite amcg suite 2 el catro n unit z1350 ma orthogneiss migmatized at 1106f6 ma and 3 el marquez unit z1140 ma para and orthogneisses these rocks were affected by two major tectonothermal events that are dated using u pb isotopic analyses of zircon a the 1106f6 ma olmecan event produced a migmatitic or metamorphic differentiation banding folded by isoclinal folds and b the 1004 978f3 ma zapotecan event produced at least two sets of structures z1 recumbent isoclinal class 1c 3 folds with gently nw plunging fold axes that are parallel to mineral and stretched quartz lineations under granulite facies metamorphism and z2 tight upright subhorizontal wnw to nne trending folds accompanied by development of brown hornblende at upper amphibolite facies metamorphic conditions cooling through 500 jc at 977f12 ma is documented by 40 ar 39 ar analyses of hornblende fold mechanisms operating in the northern oaxacan complex under zapotecan granulite facies metamorphism include flexural and tangential longitudinal strain accompanied by intense flattening and stretching parallel to the fold axes subsequent phanerozoic deformation includes thrusting and upright folding under lower grade metamorphic conditions the zapotecan event is widespread throughout oaxaquia and took crustal rocks to a depth of f25 30 km by orogenic crustal thickening and is here designated as zapotecan orogeny modern analogues for zapotecan granulite facies metamorphism and deformation occur in middle to lower crustal portion of subduction and collisional orogens contemporaneous tectonothermal events took place throughout oaxaquia and in various parts of the genvillian orogen in laurentia and amazonia d 2003 elsevier science b v all rights reserved

pressure temperature time evolution of paleozoic high pressure rocks of the acatlan complex southern mexico implications for the evolution of the iapetus and rheic oceans new thermobarometric and u pb and 40 ar 39 ar geochronologic data coupled with ages obtained from the acatlan complex the basement of the mixteco terrane of southern mexico reveal the existence of three distinctive high pressure metamorphic events of early to middle paleozoic age each recorded in a separate lithological suite xayacatlan suite eclogites with oceanic affinity underwent peak metamorphism at 609 491 c and 13 12 kb during the early ordovician ca 490 477 ma u pb zircon followed by a partial overprint at 600 c and 9 6 kb and then at 500 c and 6 7 kb an overprinting event at 525 500 c and 9 5 kb is ascribed to the devonian the pressure temperature p t path of the xayacatlan suite indicates a subduction exhumation process followed by tectonically related reburial ixcamilpa suite blueschists with oceanic affinity underwent epidote blueschist metamorphism t 200 390 c p 6 9 kb and then epidote amphibolite t 390 580 c p 9 6 kb events ascribed to the late ordovician early silurian esperanza suite eclogites with continental affinity underwent peak metamorphism at 830 730 c and 17 15 kb amphibole from eclogite yields a 430 5 ma 40 ar 39 ar age dating the high pressure hp event p t paths of high temperature ht eclogites like those of the esperanza suite have been related to the collision of continental blocks partial overprinting occurred at 690 640 c and 14 10 kb prior to 374 2 ma 40 ar 39 ar phengite the three hp suites were tectonically juxtaposed at different times before the mississippian period resulting in the closure of the iapetus ocean phengite 40 ar 39 ar geochronology reveals the existence of a widespread tectonothermal event between 345 and 323 ma which may be related to the juxtaposition of the hp composed block and the gondwanan affinity cosoltepec suite causing the closure of the rheic ocean the tectonothermal events in the acatlan complex coincide in time physical conditions and tectonic setting with events in the appalachian caledonian orogen suggesting their relation on that basis the geology of the acatlan complex can lead to a more comprehensive understanding of the tectonic evolution of the appalachian orogen and of the gondwana laurentia interactions preceding the pangean assembly

mapping the frequency magnitude distribution in asperities an improved technique to calculate recurrence times we hypothesize that highly stressed asperities may be defined by mapping anomalously low b values along the san andreas fault near parkfield the asperity under middle mountain with its b 0 46 can be distinguished from all other parts of the fault surface likewise along the calaveras fault the northern asperity of the morgan hill 1984 m6 2 rupture can be identified by its low b of 0 5 as a high stress patch along the fault we add further evidence to the observations that the b value of the frequency magnitude relationship of earthquakes is inversely proportional to stress by showing that it decreases with depth in the parkfield segment of the san andreas and along the calaveras fault in both of these areas b values above and below 5 km depth are 1 2 and 0 8 respectively we propose that probabilistic recurrence times tr based on the seismicity parameters a and b should be calculated from their values within asperities only instead of from the values of the entire rupture area of the maximum expected earthquake the strong patches on faults control the time of rupture because they are capable of accumulating larger stresses than the rest of the fault zone which slips along passively when an asperity breaks therefore no information on tr is contained in the passive fault segments only in the asperities at parkfield the probabilistic estimates of tr derived from the data in the whole rupture and in the asperity only are 72 18 24 and 23 12 18 years respectively compared to the historically observed repeat time of 22 years at morgan hill the tr estimates are 122 46 76 and 78 47 110 years respectively compared to the observed repeat time of 72 years

pre collisional high pressure metamorphism and nappe tectonics at active continental margins a numerical simulation the evolution of a subduction channel and orogenic wedge is simulated in 2d for an active continental margin with p t paths being displayed for selected markers in our simulation subduction erosion affects the active margin and a structural pattern develops within a few tens of millions of years with four zones from the trench into the forearc i an accretionary complex of low grade metamorphic sedimentary material ii a wedge of nappes with alternating upper and lower crustal provenance and minor interleaving of oceanic or hydrated mantle material iii a megascale melange composed of high pressure hp and ultra high pressure uhp metamorphic rocks extruded from the subduction channel and iv the upward tilted frontal part of the remaining lid the p t paths and time scales correspond to those typically recorded in orogenic belts the simulation shows that hp uhp metamorphism of continental crust does not necessarily indicate collision but that the material can be derived from the active margin by subduction erosion and extruded from the subduction channel beneath the forearc during ongoing subduction

mode switching in volcanic seismicity el hierro 2011 2013 the gutenberg richter b value is commonly used in volcanic eruption forecasting to infer material or mechanical properties from earthquake distributions such studies typically analyze discrete time windows or phases but the choice of such windows is subjective and can introduce significant bias here we minimize this sample bias by iteratively sampling catalogs with randomly chosen windows and then stack the resulting probability density functions for the estimated b value to determine a net probability density function we examine data from the el hierro seismic catalog during a period of unrest in 2011 2013 and demonstrate clear multimodal behavior individual modes are relatively stable in time but the most probable b value intermittently switches between modes one of which is similar to that of tectonic seismicity multimodality is primarily associated with intermittent activation and cessation of activity in different parts of the volcanic system rather than with respect to any systematic inferred underlying process

caltepec fault zone an early permian dextral transpressional boundary between the proterozoic oaxacan and paleozoic acatlan complexes southern mexico and regional tectonic implications 1 the tectonic boundary between the grenville age oaxacan and paleozoic acatlan crystalline complexes in southern mexico named the caltepec fault zone cfz is characterized for the first time as a dextral transpressional nnw trending and ene dipping ductile fault zone of early permian age the complexes are welded by a syntectonic magmatic epidote bearing granite along the entire length of the cfz from east to west the 2 6 km wide cfz consists of disrupted and retrograded banded gneisses of the oaxacan complex quartz feldspar mylonite and the syntectonic magmatic epidote bearing cozahuico granite czg with huge xenoliths up to several kilometers long and up to 600 m wide of the proterozoic gneisses thrust westward over metasedimentary tectonites of the acatlan complex the czg shows magmatic fabrics that represent a transition to solid state deformation characterized by subvertical foliation subhorizontal nne and sse dipping mineral stretching lineation and dextral kinematics the megaxenoliths underwent partial melting developing banded migmatites with layers of epidote bearing granitic neosome the parallelism of fabrics in these anatexitic rocks and in the enclosing deformed granite suggests that ductile deformation migmatization of xenolithic gneisses and granite emplacement along the cfz were coeval the neosome yielded a u pb zircon concordant age of 275 6 1 ma probably dating the peak of the tectonothermal event we interpret the cfz as a major terrane boundary accommodating transpressional interaction between the acatlan and oaxaquia blocks which were amalgamated in an oblique convergent setting by early permian time as the leading edge of gondwana impinged onto the southern margin of laurentia along the marathon ouachita suture to form pangea

constraints on the subduction erosion extrusion cycle in the paleozoic acatlan complex of southern mexico geochemistry and geochronology of the type piaxtla suite abstract the type high pressure hp piaxtla suite in the acatlan complex of southern mexico consists of retrogressed eclogite amphibolite megacrystic granitoids and high grade meta sedimentary rocks exhumation of these hp rocks has recently been interpreted as the result of extrusion into the upper plate rather than by return flow up the subduction zone geochemical analyses of the retrograde eclogites indicate that they have a rift tholeiitic transitional alkalic composition these are closely associated with a megacrystic meta granitoid that has yielded an intrusive age of 452 6 ma concordant u pb zircon analyses with inherited zircon populations at ca 800 950 ma and 1000 1200 ma derived from the underlying basement probably the oaxacan complex which borders the acatlan complex to the east the bimodal nature of these igneous rocks and their spatial and temporal close association with continentally derived sedimentary rocks is similar to most hp rocks in the acatlan complex derived from a rifted passive margin the youngest detrital zircon population in a meta psammite sample yielded a u pb age of 365 15 ma with older analyses distributed along a chord with an upper intercept of 1287 29 ma the ca 365 ma age provides a maximum age for the time of deposition of this sample 40 ar 39 ar ages from the retrogressed eclogites provided hornblende plateau ages of 342 2 ma and 344 2 ma whereas muscovite from the granitoid and meta psammite yielded 334 2 ma plateau ages these data constrain the subduction erosion extrusion cycle to 35 ma during which the rocks were taken to a depth of ca 40 km at a rate of 2 7 km ma and back to the surface at 2 4 km ma such exhumation rates are slower than those in continent continent collision zones but similar to those in the iberia czech variscan belt where tectonic interpretation also suggests extrusion into the upper plate

normalized rupture potential for small and large earthquakes along the pacific plate off japan we combine temporal variability in local seismic activity rates and size distributions to estimate the evolution of a gutenberg richter based metric the normalized rupture potential nrp comparing differences between smaller and larger earthquakes for the pacific plate off japan we study both complex spatial patterns and how they evolve over the last 18 years and more detailed temporal characteristics in a simplified spatial selection i e inside and outside the high slip zone of the 2011 m9 tohoku earthquake we resolve significant changes in particular an immediate nrp increase for large events prior to the tohoku event in the subsequent high slip patch a very rapid decrease inside this high stress release area coupled with a lasting increase of nrp in the immediate surroundings even in the center of the tohoku rupture the nrp for large magnitudes has not dropped below the 12 year average and is not significantly different from conditions a decade before the m9 event

modelling tectonic styles and ultra high pressure uhp rock exhumation during the transition from oceanic subduction to continental collision the tectonic styles of the transition from oceanic subduction to continental collision and their implications for exhumation of uhp material are tested in a series of numerical thermal mechanical models that address subduction collision dynamics at constant convergence rate reference models examine the sensitivity to continental mantle lithosphere density pro continental margin temperature and rheology and retro continental margin rheology three tectonic styles are observed 1 continental subduction without significant deformation of the over riding continent favoured by relatively dense mantle lithosphere and a strong retro continental margin 2 deformation and subduction of the leading edge of the retro continent favoured by low density mantle lithosphere and strong retro continental crust and 3 backthrusting of the retro continental margin and subsequent double subduction favoured by low density mantle lithosphere and weak retro continental crust continental u hp material is formed in all three tectonic styles although it is only efficiently exhumed in the first case three mechanisms contribute to u hp exhumation their importance depending on the evolving geometry of the subduction zone the strength of the continental margin crust and the density of the subducting mantle lithosphere weaker hotter continental margins decouple in the subduction channel and are subsequently exhumed by buoyancy and or driven circulation of material and or forced expulsion in response to insertion of strong continent into the subduction channel plunger effect stronger colder continental material is subducted without detachment and is then transported laterally underplating the retro continental mantle lithosphere neither surface erosion nor slab break off are required for uhp exhumation

comparison of short term and time independent earthquake forecast models for southern california we have initially developed a time independent forecast for southern california by smoothing the locations of magnitude 2 and larger earthquakes we show that using small m 2 earthquakes gives a reasonably good prediction of m 5 earthquakes our forecast outperforms other time independent models kagan and jackson 1994 frankel et al 1997 mostly because it has higher spatial resolution we have then developed a method to estimate daily earthquake probabilities in south ern california by using the epidemic type earthquake sequence model kagan and knopoff 1987 ogata 1988 kagan and jackson 2000 the forecasted seismicity rate is the sum of a constant background seismicity proportional to our time independent model and of the aftershocks of all past earthquakes each earthquake triggers aftershocks with a rate that increases exponentially with its magnitude and decreases with time following omori s law we use an isotropic kernel to model the spatial distribution of aftershocks for small m 5 5 mainshocks for larger events we smooth the density of early aftershocks to model the density of future aftershocks the model also assumes that all earthquake magnitudes follow the gutenberg richter law with a uniform b value we use a maximum likelihood method to estimate the model parameters and test the short term and time independent forecasts a retro spective test using a daily update of the forecasts between 1 january 1985 and 10 march 2004 shows that the short term model increases the average probability of an earthquake occurrence by a factor 11 5 compared with the time independent forecast

reliability of coulomb stress changes inferred from correlated uncertainties of finite fault source models 1 static stress transfer is one physical mechanism to explain triggered seismicity coseismic stress change calculations strongly depend on the parameterization of the causative finite fault source model these models are uncertain due to uncertainties in input data model assumptions and modeling procedures however fault model uncertainties have usually been ignored in stress triggering studies and have not been propagated to assess the reliability of coulomb failure stress change cfs calculations we show how these uncertainties can be used to provide confidence intervals for co seismic cfs values we demonstrate this for the mw 5 9 june 2000 kleifarvatn earthquake in southwest iceland and systematically map these uncertainties a set of 2500 candidate source models from the full posterior fault parameter distribution was used to compute 2500 cfs maps we assess the reliability of the cfs values from the coefficient of variation cv and deem cfs values to be reliable where they are at least twice as large as the standard deviation cv 0 5 unreliable cfs values are found near the causative fault and between lobes of positive and negative stress change where a small change in fault strike causes cfs values to change sign the most reliable cfs values are found away from the source fault in the middle of positive and negative cfs lobes a likely general pattern using the reliability criterion our results support the static stress triggering hypothesis nevertheless our analysis also suggests that results from previous stress triggering studies not considering source model uncertainties may have lead to a biased interpretation of the importance of static stress triggering

structural and tectonic evolution of the acatlan complex southern mexico its role in the collisional history of laurentia and gondwana 1 correlation of deformational phases and thermal events in the acatlan complex permits definition of nine major tectonic events seven events are related to the evolution of the iapetus and rheic oceans by the early ordovician the xayacatlan suite of laurentian affinity was metamorphosed to eclogite facies and exhumed before colliding with the el rodeo suite from the late ordovician to silurian the upper ordovician ixcamilpa suite with peri gondwanan affinity was metamorphosed to blueschist facies exhumed and subsequently was overthrust by the xayacatlan el rodeo block part of the esperanza suite is an early silurian intra iapetian continental arc that collided with and subducted beneath continental crust generating a silurian eclogitic event by the late devonian collision of the three high p t suites closed the iapetus ocean the resulting composite terrain was thrust over the gondwana bordering cosoltepec suite to close the rheic ocean during the earliest mississippian the collision of the acatlan complex and the oaxaca terrane uplifted and deformed the composite terrane by the early permian deposition of the chazumba suite occurred in a pull apart basin a latest early permian event produced thrust shear zones with n s directed shortening during the middle jurassic plume rise caused regional doming magmatism and amphibolite facies metamorphism during the late cretaceous paleogene folds and thrust faults overprint the acatlan complex most events in the acatlan complex correlate with events in the appalachian chain suggesting that the acatlan complex was located near the appalachians until the jurassic when it was displaced by the gulf of mexico opening

geology and geochronology of paleozoic rocks in western acatlan complex southern mexico evidence for contiguity across an extruded high pressure belt and constraints on paleozoic reconstructions the acatlan complex straddles a high pressure belt previously interpreted as either 1 a suture zone within the iapetus or the rheic oceans which would have a contrasting geological record across the suture or 2 a tectonic slice extruded into the upper plate which would imply contiguity across the complex distinguishing between these hypotheses is critical to paleogeographic reconstructions examination of the western acatlan complex reveals the following 1 deposition of clastic rocks between 654 and 464 ma 2 intrusion of bimodal ordovician bodies at ca 464 ma 3 high grade deformation with cooling through 400 c by 360 335 ma 4 deposition of clastic rocks and pillow lavas after 350 400 ma 5 deformation accompanied by greenschist facies metamorphism at ca 335 ma 6 deposition of clastic and bimodal volcanic rocks at ca 327 ma 7 320 270 ma subgreenschist deformation 8 deposition of the middle upper permian sedimentary rocks and 9 intrusion of a 61 1 ma diorite followed by early cenozoic laramide ene folding and faulting zircon ages 350 400 570 505 827 890 ma 0 9 1 3 ga suggest both local and amazonian sources with deposition above a local mesoproterozoic oaxacan basement on the southern margin of the rheic ocean this geological record is very similar to that of the eastern acatlan complex which supports the extrusion hypothesis a model that may be applicable to other orogens

growth of and brine drainage from nacl h2o freezing a simulation of young sea ice 1 a numerical simulation is used to predict the early time evolution of the solidification and brine drainage of a binary nacl h2o mixture the mathematical formulation is based on continuum mixture theory as outlined by bennon and incropera 1987 and medjani 1993 results yield a simple relationship between surface temperature and cumulative salt mass draining from the ice additionally a scaling analysis of the energy equation leads to a simple parameterization for ice thickness results compare well with existing laboratory measurements however the delay in onset of brine drainage reported in the literature is not supported by these results images generated using continuum salinity and liquid fraction data overlaid with streamlines generated from velocity data provide a reasonable qualitative resemblance to laboratory observations of nacl h2o ice growth

stress release process along an intraplate fault analogous to the plate boundary a case study of the 2017 m5 2 akita daisen earthquake ne japan stress accumulation and release in the crust remains poorly understood compared to that at the plate boundaries spatiotemporal variations in foreshock and aftershock activities can provide key con