u pb trace element and lu hf properties of unique dissolution reprecipitation zircon from uhp eclogite in sw sulu terrane eastern china abstract a unique dissolution reprecipitation zircon has been identified for the first time in a qtz and phe bearing eclogite from the drill hole ccsd mh southwestern sulu uhp terrane by using laser raman and cathodoluminescence cl imaging combined with trace element analyses and u pb and lu hf isotope data relic inherited domains of partially dissolved zircon show magmatic features and preserve mineral inclusions of cpx pl qtz ap whereas newly formed zircons crystallized around or along cracks of the inherited magmatic domains and contain mineral inclusions of coe grt omp phe ap typical for uhp metamorphism in addition primary fluid inclusions were identified in the coesite bearing zircon domains characterized by a single h2o phase or co2 h2o phase indicating the presence of fluids during uhp conditions strongly dissolved inherited magmatic zircons yielded shrimp 206pb 238u ages of 782 588 ma with an upper intercept age of 780 14 ma new recrystallized or metamorphic zircons yielded consistent triassic uhp ages around 238 225 ma with a weighted mean of 229 2 2 3 ma zircon trace element and hf isotope compositions and mineral inclusions classify the protolith of the sulu eclogite as an intermediate to mafic neoproterozoic igneous rock which was subducted to mantle depth and experienced uhp metamorphism in middle triassic times the juvenile ehf 780 ma value of 7 4 2 9 in inherited magmatic zircon points to a significant input from the depleted mantle to the dabie sulu uhp terrane during middle neoproterozoic new uhp zircon domains have low lu hf th u and significantly higher 176hf 177hf ratios than the inherited magmatic zircons consistent with formation during recrystallization and fractionation of the lu hf system during uhp metamorphism

dehydration melting of amphibolite at 10 kbar the effects of temperature and time we have simulated the dehydration melting of a natural low k calcic amphibolite 67 4 hornblende 32 5 anorthite in piston cylinder experiments at 10 kbar and 750 1000 c for 1 9 days the solidus temperature is lower than 750 c garnet appears at 850 c the overall reaction is hb p l cpx al hb ca hb ga opx three stages of reaction are 1 melting dominated by the growth of clinopyroxene and garnet with little change in composition of liquid or garnet 2 a reversal of this reaction between 875 c and 900 c with decreases in the amounts of liquid and garnet and 3 a large increase in liquid along with the loss of hornblende and decrease of plagioclase while clinopyroxene and garnet increase garnet is enriched in pyrope and zoned from fe cores to mg edges range 3 mol pyrope liquid composition is enriched first in an to 950 c and then in ab the liquids are more calcic and aluminous than natural tonalites which is attributed to the plagioclase composition an90 the formation of peraluminous liquid from the metaluminous amphibolite is caused by anorthite not h2o saturated conditions the results are consistent with an amphibolite phase diagram with relatively high solidus temperatures in the garnet absent field 900 1000 c but with a solidus backbend at 7 9 kbar coincident with the garnet in boundary hornblende breakdown due to garnet formation in a closed system must make h2o available for h2o undersaturated melting right down to the h2o saturated solidus below 700 c which defines a large low temperature pt area where hydrous granitoid melts can be generated with residual garnet and hornblende

two stage collision related extrusion of the western dabie hp uhp metamorphic terranes central china evidence from quartz c axis fabrics and structures abstract the western dabie orogen also known as the hong an block forms the western part of the dabie sulu hp uhp belt central china rocks of this orogen have been subjected to pervasive ductile deformation and include numerous quartz schists and felsic mylonites cropping out in ductile shear zones quartz textures in these mylonites contain important clues for understanding the movement sense of late collisional extrusion and exhumation of high pressure ultrahigh pressure hp uhp rocks from the lower crustal level to the upper crustal level during middle triassic and early jurassic the orientation and distribution of quartz crystallographic axes were used to confirm the regional shear sense across the orogen the asymmetry of c axis patterns consistently indicates top to the southeast thrusting across the orogen in early structural stages later stages of deformation show different senses of movement in northern and southern parts of the orogen with top to the northwest sinistral shearing recorded in rocks north of the xinxian hp uhp eclogite facies belt and top to the southeast dextral shearing south of the same unit based on our study on quartz c axis fabrics and marco to micro scale structures simultaneous southeastward shearing within a large part of the orogen and normal faulting north of the xinxian hp uhp unit is explained by upward extrusion in early stages of deformation the extrusion process has been attributed to syn and late collisional processes accounting for some earlier deformation in the western dabie orogen such as metamorphic sequences around the core of the xinxian hp uhp eclogite facies unit much higher pressure of deformation is also indicated in the aligned glaucophane and omphacite from blueschist and eclogite in the field an orogen parallel eastward extrusion of the xinxian hp uhp eclogite facies unit however occurred diachronously in later stages of deformation therefore a tectonic model combining an early upward extrusion with a later eastward extrusion is presented two different stages and types of extrusion for exhumation of hp uhp rocks are suitable to all of east central china geochronological data shows that the first upward extrusion occurred during middle triassic the second eastward extrusion occurred during late triassic to early jurassic these two extrusions are correlative with two stages of rapid exhumation of the dabie hp uhp rocks respectively these two stage late collisional middle triassic to early jurassic extrusion events bridge the gap between syn collisional early to middle triassic vertical extrusion and post collisional cretaceous eastward directed lateral escape and provide vital clues to understanding the more detailed processes of exhumation of hp uhp rocks

mesozoic large scale lateral extrusion rotation and uplift of the tongbai dabie shan belt in east china the tectonic convergence between the south china block and qinling belt that occurred in mesozoic time was not homogeneous along strike it was mainly concentrated in the shengnongjia and hannan domes which formed a pair of indentors along which the south china block penetrated the qinling belt as a consequence the tongbai dabie shan belt the eastern part of the qinling orogenic belt may have undergone large scale eastward extrusion clockwise rotation and uplift as indicated by its boundary deformation features it was originally located beneath the narrowest part of the qinling belt where it underwent ultrahigh pressure metamorphism in the early triassic

regional earthquake likelihood models i first order results abstract the regional earthquake likelihood models relm working group designed a 5 year experiment to forecast the number spatial distribution and magnitude distribution of subsequent target earthquakes defined to be those with magnitude 4 95 m 4 95 in a well defined california testing region included in the experiment specification were the description of the data source the methods for data processing and the proposed evaluation metrics the relm experiment began on 1 january 2006 and involved 17 time invariant forecasts constructed by seismicity modelers by the end of the experiment on 1 january 2011 31 target earthquakes had occurred we analyze the experiment outcome by applying the proposed consistency tests based on likelihood measures and additional comparison tests based on a measure of information gain we find that the smoothed seismicity forecast by helmstetter et al 2007 based on m 2 earthquakes since 1981 is the best forecast regardless of whether aftershocks are included in the analysis the relm experiment has helped to clarify ideas about testing that can be applied to more wide ranging earthquake forecasting experiments conducted by the collaboratory for the study of earthquake predictability csep online material figures and tables showing the relm testing region and collection region definitions numerical results associated with the relm experiment and the uncorrected forecast by ebel et al 2007

a new view of italian seismicity using 20 years of instrumental recordings in this paper we show the seismicity of the past 20 years that occurred in italy and surrounding regions hypocentral locations have been obtained by using p and s wave arrival times from the ingv national and several regional permanent seismic networks more than 48 000 events selected from an original data set of about 99 780 are used to reconstruct the most complete seismic picture of the italian region so far the seismicity distribution allows inference on seismotectonics of this complex region of subduction versus continental collision our results clearly reveal the geometry of the adria and the ionian subduction and a continuous normal fault belt in the upper crust following the apennines mountain range the depth of the seismogenic layer is computed from the cut off of seismicity at depth and shows large variations along and across the seismic active regions earthquakes are generated by the different velocity of slab retreat and the subsequent asthenospheric upwelling d 2004 elsevier b v all rights reserved

temporal variation of seismic velocity and anisotropy before the 2009 mw 6 3 l aquila earthquake italy we describe a set of seismological observations of the foreshock sequence preceding the 6 april 2009 m w 6 3 l9aquila earthquake the dense configuration of the seismic network in the epicenter area and the occurrence of a long foreshock sequence provide the opportunity for a detailed reconstruction of the preparatory phase of the main shock approaching the earthquake we observed clear variations in the seismic wave propagation properties the elastic properties of rocks in the fault region underwent a sharp change about a week before the earthquake from our observations we infer that a complex sequence of dilatancy diffusion processes takes place and that fluids play a key role in the fault failure process

pore pressure migration along a normal fault system resolved by time repeated seismic tomography in this study we outline the space and time variations of body wave velocities during one of the best documented series of normal faulting earthquakes the 1997 umbria marche sequence in central italy we show the first ever observations of rock fracturing and fluid overpressure propagation along a fault system by using space time resolved variations of vp vs anomalies four dimensional variations that accompany earthquake migration and precede large aftershocks the vp vs increase observed before the mid october earthquakes was related to a pore pressure increase on fluid filled cracks in the volume around the fault we also document that such variations are measurable only by using s and p wave arrival times

fluid flow during exhumation of deeply subducted continental crust zircon u pb age and o isotope studies of a quartz vein within ultrahigh pressure eclogite quartz veins in high pressure to ultrahigh pressure metamorphic rocks witness channelized fluid flow that transports both mass and heat during collisional orogenesis this flow can occur in the direction of changing temperature pressure during subduction or exhumation shrimp u pb dating of zircon from a kyanite quartz vein within ultrahigh pressure eclogite in the dabie continental collision orogen yields two age groups at 212 7 and 181 13 ma which are similar to two groups of la icpms age at 210 4 and 180 5 ma for the same sample these ages are significantly younger than zircon u pb ages of 224 2 ma from the host eclogite thus the two age groups from the vein date two episodes of fluid flow involving zircon growth the first due to decompression dehydration during exhumation and the second due to heating dehydration in response to a cryptic thermal event after continental collision laser fluorination o isotope analyses gave similar 18o values for minerals from both vein and eclogite indicating that the vein forming fluid was internally derived synchronous cooling between the vein and eclogite is suggested by almost the same quartz mineral fractionation values with regularly decreasing temperatures that are in concordance with rates of o diffusion in the minerals while the quartz veining was caused by decompression dehydration at 700 650 c in a transition from ultrahigh pressure to high pressure eclogite facies retrogression the postcollisional fluid flow was retriggered by heating dehydration at 500 c without corresponding metamorphism in either case the kyanite quartz vein formed later than the peak ultrahigh pressure metamorphic event at the middle triassic pointing to focused fluid flow during exhumation rather than subduction the growth of metamorphic zircon in the eclogite appears to have depended on fluid availability so that their occurrence is a type of geohygrometer besides geochronological applicability to dating of metamorphic events in orogenic cycles

seismic swarms and diffuse fracturing within triassic evaporites fed by deep degassing along the low angle alto tiberina normal fault central apennines italy

on varying b values with depth results from computer intensive tests for southern california summary the gutenberg richter b value is thought to reflect the stress conditions in the crust therefore spatial and or temporal variations of the b value can provide important information regarding crustal tectonics we investigate the variation of b value with depth in seven selected areas of southern california a previous study provided a detailed mapping of the variations of b with depth in california our study is less systematic than this study our approach is more similar to the regional one used by mori abercrombie in comparison to these previous studies our investigation indicates that the variability of b is often not statistically significant and that the decrease of b with depth should be interpreted with caution the seismic catalogues used are subsets of a set of about 100 000 seismic events recorded by the southern california seismic network scsn and relocated by richards dinger shearer we study the performance of utsu s test compared to bootstrap tests for comparison of b values the results of our investigation also raise the question of the relevancy of utsu s test when comparing b values both simulations and real cases show that the utsu s test is biased towards rejection of the null hypothesis in favour of the hypothesis that b values are significantly different

carbon dioxide earth degassing and seismogenesis in central and southern italy 1 we present the first regional map of co2 earth degassing from a large area most of central and south italy derived from the carbon of deep provenance dissolved in the main springs of the region the investigation shows that a globally significant amount of deeply derived co2 10 of the estimated global co2 emitted from subaerial volcanoes is released by two large areas located in western italy the anomalous flux of co2 suddenly disappears in the apennine in correspondence to a narrow band where most of seismicity concentrates here at depth the gas accumulates in crustal traps generating co2 overpressurized reservoirs which induce seismicity

high sr y and la yb ratios the meaning of the adakitic signature abstract the name of adakite is used to describe a far too large group of rocks whose sole common feature is high sr y and la yb ratios however such a signature can be achieved via different processes melting of a high sr y and la yb source deep melting with abundant residual garnet fractional crystallization or afc or interactions of felsic melts with the mantle causing selective enrichment in lree and sr over hree a database of the compositions of adakitic rocks including high silica and low silica adakites martin h smithies r h rapp r p moyen j f champion d c 2005 an overview of adakite tonalite trondhjemite granodiorite ttg and sanukitoid relationships and some implications for crustal evolution lithos 79 1 2 1 24 continental adakites and archaean adakites was assembled geochemical modeling of the potential processes is used to interpret it and reveals that 1 the classical model of slab melting provides the best explanation for the genesis of high silica adakites 2 low silica adakites are explained by garnet present melting of an adakite metasomatized mantle i e at depths greater than 2 5 gpa 3 continental adakites is a term encompassing a huge range of rocks with a corresponding diversity of petrogenetic processes and most of them are different from both low and high silica adakites 4 archaean adakites show a bimodal composition range with some very high sr y examples similar to part of the ttg suite reflecting deep melting 2 0 gpa of a basaltic source with a relatively high sr y while lower sr y rocks formed by shallower 1 0 gpa melting of similar sources comparison with the archaean ttg suite highlights the heterogeneity of the ttgs whose composition spreads the whole combined range of hsa and archaean adakites pointing to a diversity of sources and processes contributing to the ttg suite

the long precursory phase of most large interplate earthquakes many earthquakes are preceded by foreshocks however the mechanisms that generate foreshocks and the reason why they occur before some earthquakes and not others are unknown here we use seismic catalogues from the best instrumented areas of the north pacific to analyse the foreshock sequences preceding all earthquakes there between 1999 and 2011 of magnitude larger than 6 5 and at depths shallower than 50 km the data set comprises 31 earthquakes at plate boundaries and 31 in plate interiors we find that there is a remarkable contrast between the foreshock sequences of interplate compared with intraplate earthquakes most large earthquakes at plate interfaces in the north pacific were preceded by accelerating seismic activity in the months to days leading up to the mainshock in contrast foreshocks are much less frequent in intraplate settings we suggest that at plate boundaries the interface between the two plates begins to slowly slip before the interface ruptures in a large earthquake this relatively long precursory phase could help mitigate earthquake risk at plate boundaries

earth science microseismicity data forecast rupture area on 28 september 2004 there was an earthquake of magnitude 6 0 at parkfield california here we show that the size distribution of the micro earthquakes recorded in the decades before the main shock occurred allowed an accurate forecast of its eventual rupture area applying this approach to other well monitored faults should improve earthquake hazard assessment in future

lack of spatiotemporal localization of foreshocks before the 1999 mw 7 1 duzce turkey earthquake we use a matched filter technique to detect small seismic events before the m w 7 1 duzce earthquake that are not included in the regular catalog the study employs extensive waveform dataset recorded by a 10 station fault zone array near the epicenter of the duzce earthquake deployed about three months before the event we use 3134 earthquakes within 20 km of the duzce epicenter listed in the local catalog as templates to scan through waveforms recorded within 65 hours before the duzce earthquake the analysis reveals 262 newly detected events in this time interval which is 5 times more than the 55 events listed in the original catalog most of the events occur to the west of the duzce epicenter which was initiated between a more active western and relatively quite eastern fault segments the results do not indicate a localizing foreshock process that accelerates in time and or involves progressive concentration of activity around the mainshock hypocenter during the preceding 65 hour period instead we find that the duzce source region becomes less active during the 20 hours immediately before the mainshock our results together with other recent studies suggest that progressive acceleration and localization of foreshocks around the mainshock epicenter is not a general phenomenon online material figures of timing of recorded waveforms peak ground velocities foreshock activity seismicity rate and temporal evolution of earthquake activity vertical waveforms and distribution of template events

porewater ph and authigenic phases formed in the uppermost sediments of the santa barbara basin abstract in this paper porewater and solid phase analyses are used in combination with in situ o 2 and ph microelectrode measurements to characterize early diagenetic processes in the uppermost sediments of the santa barbara basin california rapid reduction of dissolved oxygen nitrate solid phase manganese and iron and dissolved sulfate is observed between sediment depths of 0 and 2 cm reductive solubilization of ferric iron phases releases fe 2 adsorbed phosphate and fluoride to the porewaters and contributes to a sharp increase in porewater ph between 2 and 4 cm sulfate reduction rates peak ph levels off and acid volatile sulfides and pyrite become the dominant forms of solid phase iron saturation state calculations which depend largely on ph indicate that the porewaters of the santa barbara basin become saturated with respect to carbonate fluorapatite and calcite within the first 0 25 mm of the sediment and are highly supersaturated by and below 2 cm in spite of this result porewater evidence of phosphate and fluoride removal into a solid phase is observed only in the first 5 cm of some cores whereas dissolved ca profiles suggest dispersed calcite precipitation throughout the sediment column this finding is interpreted as an indication of the nonsteady state nature of the surface reactions that may given sufficient nucleation sites and time lead to carbonate fluorapatite genesis in anoxic sediments finally microelectrode ph profiles from two other basins in the california borderlands are presented these demonstrate that the porewaters of the santa barbara basin are more alkaline than those of other basins this outcome is attributed to the lack of particle mixing and a unique interplay between fe liberation and fes precipitation reactions in the santa barbara basin

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

geochemical evidence for origin of magma mixing for the triassic monzonitic granite and its enclaves at mishuling in the qinling orogen central china abstract whole rock major trace elements and sr nd isotopes mineral chemistry and zircon u pb and lu hf isotope compositions are reported for i type monzogranite and its mafic microgranular enclaves from the triassic mishuling granite in the qinling orogen central china zircon u pb dating yields an age of 212 5 ma for the mafic enclaves and 213 3 ma for the host monzogranite whole rock major trace elements sr nd isotopes and zircon hf isotopes preclude simple crystal fractionation or restite unmixing for a genetic link between the enclaves and the monzogranite mixing between mafic and felsic magmas is compatible with the geochemical data the monzogranite displays an enriched lile and lree pattern high 87sr 86sr i ratios of 0 7068 to 0 7071 and low end t values of 9 2 to 5 7 suggesting a crustal origin its high mg 47 6 to 50 7 cr and ni contents clearly indicate its derivation from mafic refractory lower crust most of the zircons in the monzogranite have negative ehf t values of 12 5 to 0 1 and two stage hf model ages of 1049 to 1683 ma and some zircons in the host monzogranite have positive ehf t values of 0 3 to 4 8 and single stage hf model ages of 665 to 845 ma this indicates that the monzogranite is most likely to be formed by partial melting of a proterozoic lower continental crust the mafic enclaves have fine grained igneous textures and contain abundant acicular apatite that indicates rapid cooling they also have a high 87sr 86sr i ratio of 0 7071 and a low end t value of 6 5 suggesting a derivation from ancient subcontinental lithosphere mantle sclm zircons in the mafic microgranular enclaves have ehf t values of 1 6 to 5 1 and single stage hf model ages of 700 to 910 ma suggesting a possible origin from partial melting of the neoproterozoic sclm that may form in association with contemporaneously supercontinental rifting in the south china block therefore the mishuling i type granite may form by anatexis of meso neoproterozoic lower crust with mixing between the mafic and felsic magmas in particular we interpret the positive ehf t values as being derived from reworking of neoproterozoic juvenile lithosphere in response to tectonic extension in the late stage of the triassic continental collision between the south china block and the north china block

very detailed seismic pattern and migration inferred from the april 2010 pietralunga northern italian apennines micro earthquake sequence abstract we propose a very detailed picture of seismicity that occurred in the proximity of the alto tiberina fault atf northern italian apennines a low angle normal fault by presenting the pattern and evolution of a seismic sequence on the hanging wall of the atf in the first months of 2010 that was characterized by about 1000 events with m l ranging from 0 7 to 3 8 to capture the rupture kinematics of the investigated area a cross correlation technique was initially applied to calculate very accurate time shifts among the events of the sequence and then to relocate them the whole sequence was relocated with the double difference method which includes both absolute travel time measurements and cross correlation differential travel times the new locations confirm that the seismic activity was mainly arranged along a nw se oriented structure that ranged in depth from 4 km to 6 km with dipping towards ne at an angle of ca 65 in comparison with geological data the position of the seismic sequence is compatible with the evaporite triassic layer the main nodal planes are consistent with the spatial evolution of the aftershocks and with the tensional state of stress in the area an analysis of waveform similarity was performed at a reference station by merging the capability of the cross correlation technique and the bridging algorithm the detected mutiplets allow us to emphasize the anisotropic spatial and temporal migrations of the seismicity that occurred along a 307 n strike direction with an averaged propagation velocity of ca 0 4 km day we explain the highlighted anisotropic behavior of the migration with the hypothesized presence of overpressured fluids and with physical properties of triassic evaporites this suggests the importance of such very detailed relocation of weak and micro seismicity for improvement of our knowledge of fault system geometry and its evolution

heterogeneities along the 2009 l aquila normal fault inferred by the b value distribution 1 in this study we map the distribution of the b value of the gutenberg richter law as well as complementary seismicity parameters along the fault responsible for the 2009 mw6 1 l aquila earthquake we perform the calculations for two independent aftershock sub catalogs before and after a stable magnitude of completeness is reached we find a substantial spatial variability of the b values which range from 0 6 to 1 3 over the fault plane the comparison between the spatial distribution of the b values and the main shock slip pattern shows that the largest slip occurs in normal to high b values portion of the fault plane while low b value is observed close to the main shock nucleation no substantial differences are found in the b value computed before and after the main shock struck in the small region of the fault plane populated by foreshocks

four magmatic fabrics in the tuolumne batholith central sierra nevada california usa implications for interpreting fabric patterns in plutons and evolution of magma chambers in the upper crust for the first time four distinct magmatic fabrics are documented in a composite plutonic body the tuolumne batholith central sierra nevada california usa one type of fabric was formed by strain caused by highly localized magma flow type 1 whereas the other three chamber wide fabrics recorded strain increments during boundary processes along batholith margins type 2 superimposed by increments of heterogeneous regional tectonic strain types 3 and 4 our present work indicates that in contrast to studies that consider magmatic fabrics to be simple structures formed by a single process magmatic lineations and foliations in plutons may reflect accumulated finite strain and form as composite structures recording multiple strain increments in relatively static actively deforming and rheologically complex crystal mushes at lower melt percentages we demonstrate that multiple magmatic fabrics in a single batholith may record remarkably different processes and thus preserve a temporal record of strain in the batholith from strain during internal chamber processes to postem placement regional tectonic strain however it may be commonly very problematic to infer the exact nature of flow or even fabric forming process from the preserved rock record our study also exemplifies how examination of magmatic fabric patterns in plutons complemented with geochronology may provide crucial constraints on the interplay among successive magma emplacement fabric preservation temporal evolution of strain fields in a crystallizing magma chamber and the development of crystal mush zones

geochemical and nd pb isotopic characteristics of the tethyan asthenosphere implications for the origin of the indian ocean mantle domain abstract it is unclear why the pb nd and sr isotopic composition of the modern mid ocean ridge basalts morb from the indian ocean is different from that of the north atlantic and pacific oceans a possible explanation for this is that the indian morb type isotopic signature is a long lived regional feature of the mantle as evidently shown by the isotopic composition of the 350 ma morb like mian lue northern ophiolite which was formed in the same region presently occupied by the indian ocean however this hypothesis is in conflict with the lack of indian morb type isotopic signature in a number of 150 ma tethyan and indian ocean crusts to further constrain the origin of the indian morb type isotopic signature we analyze the geochemical and pb nd and sr isotopic composition of representative mafic rocks from four tethyan ophiolites ranging in age from 90 to 360 ma the sr isotopic composition of the samples is unreliable due to alteration but the age corrected nd and pb isotopic ratios and geochemical data indicate that these tethyan rocks were derived from a geochemically depleted asthenospheric source that had a clear indian morb type isotopic signature we therefore conclude that the bulk of the indian suboceanic mantle was most probably inherited from the tethyan asthenosphere a few regions in both the tethyan and indian oceans however are most probably underlain by pacific and north atlantic morb type mantle and vice versa because of the flow of the asthenosphere in response to tectonic plate reorganizations that lead to openings and closures of ocean basins the indian morb type isotopic signature of the western pacific marginal basin crusts could be due to either flow of the indian ocean mantle into the western pacific or to endogenous production of such an isotopic signature from delaminated east asian sublithospheric materials during closure of the tethys ocean

continuity of the north qilian and north qinling orogenic belts central orogenic system of china evidence from newly discovered paleozoic adakitic rocks abstract adakitic intrusive rocks of 430 450 ma were discovered in the north qilian orogenic belt the western section of the central orogenic system cos in china these adakitic rocks were lower crust melts rather than slab melts as indicated by their crustal ce pb nb u ti eu and nd sm ratios and radiogenically enriched 87sr 86sr i of 0 7053 0 7066 and end t of 0 9 to 1 7 while they are all characterized by low yb 65 and la yb n 13 7 ratios these adakitic rocks are classified into the low mgo ni cr and high mgo ni cr groups the low mgo samples were derived from partial melting of thickened lower crust whereas the high mgo samples were melts from delaminated lower crust which subsequently interacted with mantle peridotite upon ascent adakitic rocks from the adjacent north qinling orogenic belt also originated from thickened lower crust at 430 ma in addition the north qilian and north qinling orogenic belts both consist of lithological assemblages varying from subduction accretionary complexes at south to central arc assemblages which include adakitic rocks then to backarc phases at north such a sequence reflects northward subduction of the qilian and qinling oceans in these two orogenic belts the occurrence of adakitic rocks of common origin and ages together with the similarities in tectonic configurations and lithological assemblages are considered to be the evidence for the continuity between eastern qilian and western qinling forming a 1000 km early paleozoic orogenic belt in such a tectonic configuration the qilian and qinling oceans that subducted from south possibly represent parts of the large proto tethyan ocean this inference is supported by the coexistence of early paleozoic coral and trilobite specimens from asia america and australia in the north qilian orogenic belt post 400 ma volcanic rocks occur in the north qinling orogenic belt but are absent in the north qilian orogenic belt indicating that these two orogenic belts underwent distinct evolution history after the closure of the proto tethyan ocean 420 ma

collision leading to multiple stage large scale extrusion in the qinling orogen insights from the mianlue suture abstract the geologic framework of the phanerozoic qinling dabie orogen was built up through two major suturing events of three blocks from north to south these include the north china craton including the north qinling block the qinling dabie microblock and the south china craton including the bikou block separated by the shangdan and mianlue sutures the mianlue suture zone contains evidence for mesozoic extrusion tectonics in the form of major strike slip border faults surrounding basement blocks a late paleozoic ophiolite and a ca 240 200 ma thrust belt that reformed by 200 150 ma thrusts during a type intracontinental subduction the regional map pattern shows that the blocks are surrounded by complexly deformed devonian to early triassic metasandstones and metapelites forming a regional scale block in matrix melange fabric five distinct tectonic units have been recognized in the belt 1 basement blocks including two types of precambrian basement crystalline and transitional 2 continental margin slices including early paleozoic strata and late paleozoic fluviodeltaic sedimentary rocks proximal and distal fan clastics reflecting the development of a north facing rift margin on the edge of the south china plate 3 out of sequence oceanic crustal slices including strongly deformed postrift deep water sedimentary rocks sheeted dikes basalts and mafic ultramafic cumulates of a late paleozoic ophiolite suite developing independent of the rift margin in a separate basin 4 out of sequence island arc slices 5 accretionary wedge slices all the tectonic units were deformed during three geometrically distinct deformation episodes d 1 d 2 and d 3 during 240 200 ma units 2 4 involved southward thrusting and vertical then southward extrusion of about 20 km of horizontal displacement above the autochthonous basement during the d 1 episode thrust slices 20 km south of the mianlue suture are related to this vertical extrusion due to the same rock assemblages ages and kinematics the d 2 and d 3 episodes folded all the units in a thick skinned style about east west d 2 and west northwest d 3 axes in the mianlue suture zone an early foreland propagating sequence of accretion of late paleozoic rocks deposited above the yangtze craton is not involved in d 1 deformation but is temporally equivalent to the d 2 and d 3 deformation in the mianlue suture two stages of strike slip faulting mainly occurred at the end of d 2 and d 3 respectively during d 2 deformation the bikou block was obliquely indented to the ese into the mianlue suture rather than being thrust over the mianlue suture from the north as a part of the qinling dabie microblock during d 3 deformation however the bikou block was bounded by the south boundary fault of the mianlue suture and the yangpingguan fault on the south these faults are coeval strike slip faults but of opposite senses and accommodated minor southwestward extrusion of the bikou block into songpan ganze orogen the other basement blocks north of the mianlue suture were extruded eastward by about 20 km of lateral displacement based on the offset of the wudang dome during the d 3 episode due to the northeastward indentation of the hannan complex of the south china craton post d 3 emplacement of granite cutting across the strike slip faults such as the mianlue suture provides a minimum age of 200 ma for d 3 deformation therefore based on insights from the evolution of the mianlue suture the d 2 and d 3 episodes in the mianlue suture and its neighbors are not responsible for and associated with the two stage extrusion of the dabie uhp hp terranes from the foping dome to the present erosional surface more than 350 km

spatial and temporal b value anomalies preceding the devastating off coast of nw sumatra earthquake of december 26 2004 1 spatial and temporal variations of b values are studied by means of 624 earthquakes in the andaman nicobar islands region during a five year period preceding the giant shock on december 26 2004 sliding time and space windows containing 50 events are used temporal variations reveal two significant drops in b value which coincide with the occurrence of two large shocks ms 7 0 towards the end of 2002 and with the mw 9 0 event in 2004 the spatial distribution shows accumulation of stresses low b around the epicentres of the 2002 and 2004 events and an event in north andaman the area of high stress around the 2004 epicenter extends in nnw sse direction over an area about 450 km long

tectonics of the qinling central china tectonostratigraphy geochronology and deformation history abstract the qinling orogen preserves a record of late mid proterozoic to cenozoic tectonism in central china high pressure metamorphism and ophiolite emplacement songshugou ophiolite assembled the yangtze craton including the lower qinling unit into rodinia during the 1 0 ga grenvillian orogeny the lower qinling unit then rifted from the yangtze craton at 0 7 ga subsequent intra oceanic arc formation at 470 490 ma was followed by accretion of the lower qinling unit first to the intra oceanic arc and then to the sino korea craton subduction then imprinted a 400 ma andean type magmatic arc onto all units north of the northern liuling unit oblique subduction created silurian devonian wnw trending sinistral transpressive wrench zones e g lo nan shang dan and late permian early triassic subduction reactivated them in dextral transpression lo nan shang xiang shang dan and subducted the northern edge of the yangtze craton exhumation of the cratonal edge formed the wudang metamorphic core complex during dominantly pure shear crustal extension at 230 235 ma post collisional south directed shortening continued through the early jurassic cretaceous reactivation of the qinling orogen started with nw se sinistral transtension coeval with large scale early cretaceous crustal extension and sinistral transtension in the northern dabie shan it presumably resulted from the combined effects of the siberia mongolia sino korean and lhasa west burma qiangtang indochina collisions and pacific subduction regional dextral wrenching was active within a ne sw extensional regime between 60 and 100 ma an early cretaceous andean type continental magmatic arc with widespread early cretaceous magmatism and back arc extension was overprinted by shortening related to the collision of yangtze indochina block with the west philippines block strike slip and normal faults associated with eocene half graben basins record paleogene nne ssw contraction and wnw ese extension the neogene is characterized by normal faults and nne trending sub horizontal extension pleistocene quaternary nw se extension and ne sw contraction comprises sinistral strike slip faults and is part of the nw se extension imposed across eastern asia by the india asia collision

geologic framework and tectonic evolution of the qinling orogen central china abstract the geologic framework of the qinling orogen was built up through interplay of three blocks the north china block including the north qinling the south qinling and the south china block separated by the shangdan and mianlue sutures the shangdan suture resulted from middle paleozoic collision of the north china block and the south qinling the mianlue suture resulted from late triassic collision of the south qinling and the south china block present upper crust of the qinling is structured dominantly by thrust fold systems the north qinling displays thick skinned deformation with crystalline basement involved whilst the south qinling is characterized by thin skinned thrusts and folds detached above the lower sinian two types of precambrian basement crystalline and transitional are defined according to lithology and metamorphic grade and different in age stratigraphic and sedimentary architecture is characterized by distinct zonation the qinling orogen experienced a prolonged continental divergence and convergence between blocks during the period from late neoproterozoic to early paleozoic times the south qinling was the northern margin of the south china block and the north qinling was the southern margin of the north china block separated by a proto tethyan qinling ocean the north qinling evolved into an active margin when the proto tethyan qinling ocean subducted northward during ordovician time collision of the south and north qinling took place in middle paleozoic along the shangdan suture synchronous with the collision rifting occurred at the southern rim of the south qinling and was followed by the opening of the paleo tethyan qinling ocean during the late paleozoic resulting in the splitting of the south china block from the south qinling collision of the south qinling and the south china block came about in the late triassic along the mianlue suture the late triassic collisional orogeny caused extensive fold and thrust deformation and granitoid intrusions throughout the qinling and led to final amalgamation of the north and south china blocks

improved tests reveal that the accelerating moment release hypothesis is statistically insignificant 1 we test the hypothesis that accelerating moment release amr is a precursor to large earthquakes using data from california nevada and sumatra spurious cases of amr can arise from data fitting because the time period area and sometimes magnitude range analyzed before each main shock are often optimized to produce the strongest amr signal optimizing the search criteria can identify apparent amr even if no robust signal exists for both 1950 2006 california nevada m 6 5 earthquakes and the 2004 m9 3 sumatra earthquake we can find two contradictory patterns in the pre main shock earthquakes by data fitting amr and decelerating moment release we compare the apparent amr found in the real data to the apparent amr found in four types of synthetic catalogs with no inherent amr when spatiotemporal clustering is included in the simulations similar amr signals are found by data fitting in both the real and synthetic data sets even though the synthetic data sets contain no real amr these tests demonstrate that apparent amr may arise from a combination of data fitting and normal foreshock and aftershock activity in principle data fitting artifacts could be avoided if the free parameters were determined from scaling relationships between the duration and spatial extent of the amr pattern and the magnitude of the earthquake that follows it however we demonstrate that previously proposed scaling relationships are unstable statistical artifacts caused by the use of a minimum magnitude for the earthquake catalog that scales with the main shock magnitude some recent amr studies have used spatial regions based on hypothetical stress loading patterns rather than circles to select the data we show that previous tests were biased and that unbiased tests do not find this change to the method to be an improvement the use of declustered catalogs has also been proposed to eliminate the effect of clustering but we demonstrate that this does not increase the statistical significance of amr given the ease with which data fitting can find desired patterns in seismicity future studies of amr like observations must include complete tests against synthetic catalogs that include spatiotemporal clustering

multi stage granitic magmatism during exhumation of subducted continental lithosphere evidence from the wulong pluton south qinling abstract detailed petrology and zircon u pb dating data indicate that the wulong pluton is a zoned granitic intrusive formed from successive increments of magmas an age range of at least 30 ma is recorded from the 225 235 ma quartz diorite on the pluton margin the ca 218 ma granodiorite in the intermediate zone and the ca 207 ma monzogranite at the pluton center all the granitoids display evolved sr nd pb isotopic compositions with 87 sr 86 sr i of 0 7044 0 7062 unradiogenic nd e nd t values of 6 1 to 3 0 nd model ages of 1 1 1 3 ga and moderately radiogenic pb compositions 206 pb 204 pb i 17 500 17 872 207 pb 204 pb i 15 513 15 549 208 pb 204 pb i 37 743 38 001 in combination with variations in zircon hf isotopic compositions with e hf t values in each stage span 12 units and the hf isotopic model ages of 800 1600 ma these features suggest that the granitoids might have been derived from the reworking of an old lower crust mixed with paleozoic and proterozoic materials the rocks also display an adakitic affinity with sr 479 973 ppm high sr y ratios mostly 60 and negligible eu anomalies eu eu 0 78 0 97 but low rb sr ratios low y 4 6 17 ppm hree yb 0 95 1 7 ppm yb lu 6 7 and dy yb 1 9 2 4 ratios suggesting the absence of plagioclase and presence of garnet amphibole in their residue considering a large gap among their crystallization ages we propose that the geochemical evolution from pluton margin to center was controlled mainly by melting conditions and source compositions rather than fractional crystallization mafic enclaves that were hosted in the quartz diorite and granodiorite are mainly syenogabbroic to syenodioritic in composition and are metaluminous and enriched in lree and liles but are depleted in hfse and display an evolved sr nd pb isotopic composition suggesting that they may have been derived from the partial melting of an enriched mantle lithosphere which was metasomatized by adakitic melts and fluids from a subducted continental crust in combination with the results of the triassic ultra high pressure metamorphic rocks in the dabie orogenic belt we apply a model involving the exhumation of subducted continental crust to explain the formation of the wulong pluton at the first stage a dense and refractory mafic lower crust that was trapped at mantle depth by continental subduction witnessed melting under high temperature conditions to produce the quartz diorite magma characterized by low sio 2 60 65 63 98 wt and high tio 2 0 39 0 86 wt the magma subsequently interacted with mantle peridotite leading to high mg 57 67 and the metasomatism of the overriding mantle wedge at the second stage an asthenosphere upwelling that was probably caused by slab break off at ca 220 ma melted the enriched sub continental lithospheric mantle sclm to produce mafic magmas represented by the mafic enclaves that are hosted in the quartz and granodiorite resulting in the partial melting of the shallower subducted crust and generating the granodiorite that is distinguished by high sio 2 69 16 70 82 wt high al 2 o 3 15 33 16 22 wt and a cnk values mostly 1 05 at the third stage the final collapse of the triassic qinling dabie orogenic belt at ca 215 205 ma caused extensive partial melting of the thickened orogenic lower crust to produce the monzogranite which is characterized by high sio 2 67 68 70 29 wt low tio 2 mostly

non poissonian earthquake occurrence in coupled stress release models and its effect on seismic hazard summary most seismic hazard estimations are based on the assumption of a poisson process for earthquake occurrence even though both observations and models indicate a departure of real seismic sequences from this simplistic assumption instrumental earthquake catalogues show earthquake clustering on regional scales while the elastic rebound theory predicts a periodic recurrence of characteristic earthquakes on longer timescales for individual events recent implementations of time dependent hazard calculations in california and japan are based on quasi periodic recurrences of fault ruptures according to renewal models such as the brownian passage time model however these renewal models neglect earthquake interactions and the dependence on the stressing history which might destroy any regularity of earthquake recurrences in reality to explore this we investigate the coupled stress release model a stochastic version of the elastic rebound hypothesis in particular we are interested in the time variability of the occurrence of large earthquakes and its sensitivity to the occurrence of gutenberg richter type earthquake activity and fault interactions our results show that in general large earthquakes occur quasi periodically in the model the occurrence probability of large earthquakes is strongly decreased shortly after a strong event and becomes constant on longer timescales although possible stress interaction between adjacent fault zones does not affect the recurrence time distributions in each zone significantly it leads to a temporal clustering of events on larger regional scales the non random characteristics especially the quasi periodic behaviour of large earthquakes are even more pronounced if stress changes due to small earthquakes are less important the recurrence time distribution for the largest events is characterized by a coefficient of variation from 0 6 to 0 84 depending on the relative importance of small earthquakes

the preparatory phase of the 2009 mw 6 3 l aquila earthquake by improving the detection capability of low magnitude foreshocks we explored the detection capability of low magnitude earthquakes before the 6 april 2009 mw 6 3 l aquila event by using a matched filter technique and 512 foreshocks as templates we analyzed continuous waveforms from 10 broadband seismic stations in a 60 km radius from the epicenter and for 3 months before the main shock more than 3000 new events mostly located on the main shock fault were detected to define the spatial temporal evolution of micro seismicity the foreshock sequence was active northwest of the mw 6 3 hypocenter in january then migrated toward it at a speed of 0 5 km day in middle of february at that time in a 4 km2 patch close to the main shock nucleation point the cumulative number of earthquakes gradually increased until the mw 6 3 event this patch characterized by a low b value played a key role in controlling the preparation stage to the 2009 l aquila main rupture

recent seismicity of italy active tectonics of the central mediterranean region and seismicity rate changes after the mw 6 3 l aquila earthquake abstract in this paper we present a new image of the instrumental seismicity of italy obtained by refining hypocentral determinations for about 100 000 earthquakes that occurred in the period 2005 2012 the improved locations yield new constraints on active tectonics of the central mediterranean area where prolonged interaction between nested plates and continental slivers led to the development of the alpine and apennines systems intermediate depth and deep earthquakes define a lateral heterogeneous process of delamination and sinking of the continental lithosphere active beneath the mountain belts shallow seismicity prevalently occurs beneath elevated topography and correlates with low velocity mantle anomalies suggesting a superposition of gravity related forces to the eurasia africa plate convergence the delamination process drives a paired system of compression and extension that stretches the mountain range while shortening the external side of the belts the updated seismic catalog permits us to resolve a sharp variation of seismic rates that occurred in recent years timely after the 2009 mw 6 3 l aquila earthquake the increase of seismic rates is reasonably due to regional scale perturbation of the stress field induced by fluid flow and pore pressure variations within the crust probably related to deep dehydration processes active beneath the mountain belt

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

when and why the continental crust is subducted examples of hindu kush and burma abstract the indian subcontinent has been colliding against asia along the himalayas hindu kush and burma in this collision zone have intermediate depth seismicities beneath them with most of the continental crust subducted into a few hundred km depth the subduction not collision in these regions is an enigma long time we show that the continental lithosphere subducted beneath hindu kush and burma traveled over the reunion and kerguelen hotspots from 100 ma to 126 ma and is likely to have been metasomatized by upwelling plumes beneath those hotspots the devolatilization of the metasomatized lithosphere impinging on the collision boundary would have provided a high pore fluid pressure ratio at the thrust zones and made the subduction of the continental lithosphere in these regions possible the subducted lithosphere could give intermediate depth seismicities by devolatilization embrittlement such subduction of hotspot affected lithosphere without accompanying any oceanic plate would be one candidate for producing ultrahigh pressure metamorphic rocks by deep subduction of the continental crust

stressing of fault patch during seismic swarms in central apennines italy persistent seismic swarms originate along the normal faulting system of central apennines italy in this study we analyze the space time energy distribution of one of the longer and more intense of these swarms active since august 2013 in the high seismic risk area of the gubbio basin our aim is to verify if information relevant to constraint short term earthquake occurrence scenarios is hidden in seismic swarms during the swarm the seismic moment release first accelerated with a rapid migration of seismicity along the fault system and suddenly dropped we observe a decrease of the b value along the portion of the fault system where large magnitude events concentrated possibly indicating that a fault patch was dynamically stressed this finding suggests that the onset of seismic swarms might help the formation of critically stressed patches

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

spatial and temporal variations of aftershock activity of the 23 october 2011 mw 7 1 van turkey earthquake abstract on 23 october 2011 an m w 7 1 earthquake struck the van lake region of eastern turkey causing vast damage in the cities of van and ercis the mainshock was followed by a large number of aftershocks which define a 60 70 km long and 30 35 km wide northeast southwest trending structure in agreement with the source rupture models derived for the main event in this paper we take advantage of this large data set to examine the spatial and temporal properties of the van earthquake aftershock activity we derive the spatial distribution of b value of the gutenberg richter law as well as complementary seismicity parameters along the surface projection of the fault plane recent studies have been published on the same issue presenting controversial and sometimes opposite results with respect to previous studies we rely on a possibly higher quality catalog of relocated earthquakes furthermore we adopt a more conservative approach excluding from the analysis the first few days of data until the m c reaches a stable completeness threshold finally we conduct statistical tests in order to check the significance of the spatial and temporal variation of b value across the fault plane calculations are made for the complete catalog and for two independent aftershock subcatalogs after which a stable magnitude of completeness m c is reached for each catalog we correlate the observed b value patterns with slip distribution models of the mainshock obtained through the inversion of seismological and geodetic data overall the b values vary from 0 9 to 1 5 along the van rupture fault zone the higher b values 1 1 are observed around the epicenter of the mainshock characterizing the higher coseismic slip area on the fault projection low b values are concentrated at the peripheral portion of the fault away from high slip patches moreover the b value distribution over the fault plane undergoes significant variation throughout the aftershock sequence

the effect of uncertainties on estimates of background seismicity rate abstract identifying changes in the rate of background earthquakes is a common method to detect transients in seismic activity rates and these transients can often be linked to changes in physical properties of the crust or to the recording homogeneity of seismic networks in this article we consider the effect that various sources of uncertainty have on seismicity rate estimation and we describe a monte carlo method to compute the statistical significance of seismicity rate changes we consider real earthquake catalogs and synthetic catalogs that represent poissonian background seismicity we find that the choice of declustering algorithm and the variation in the related parameter values have the greatest impact on seismicity rate change calculations this sensitivity is a direct consequence of the fact that there is no unique or universally applied approach to separate aftershocks and foreshocks from background events hypocenter location uncertainty also influences the statistical significance of seismicity rate changes its relevance depends on the ratio of the location uncertainty to the extension of the seismicity rate anomaly we find that magnitude uncertainty and edge effects associated with seismicity declustering have less impact than the other factors but their influence is not negligible in an example application we suggest that when uncertainties are considered the reported seismicity rate changes prior to the 1992 landers and big bear mainshocks decrease significantly