accelerating seismic crustal deformation in the north aegean trough greece summary a recently developed algorithm has been applied to define regions of the northern aegean in which accelerating seismic crustal deformation is currently occurring an elliptical such region has been found in the western part of the north aegean accelerating deformation which started three decades ago and has been released by the generation of intermediate magnitude earthquakes m 4 5 is still occurring based on these observations we can assume that this region is now in a state pre shock deformation that will lead to a critical point main shock the estimated basic parameters of this impending main shock are 39 7 n 23 7 e for the epicentre m 6 0 for the moment magnitude and tc 2001 1 for the origin time the corresponding uncertainties are less than 100 km for the epicentre 0 4 for the magnitude and 1 5 yr for the origin time

u pb detrital zircon and 39ar 40ar muscovite ages from the eastern parts of the karagwe ankole belt tracking paleoproterozoic basin formation and mesoproterozoic crustal amalgamation along the western margin of the tanzania craton abstract the karagwe ankole belt forms part of a complex system of orogenic belts in central east africa that record the amalgamation of archaean and or paleoproterozoic continental kernels in the proterozoic the actual timing of tectonic processes including initial basin formation and subsequent deformation is only poorly constrained so that the geodynamic significance of the karagwe ankole belt within the broader system of proterozoic orogens in central east africa is not well understood this paper presents u pb ages of detrital zircons constraining the age of sediments of the eastern parts of the karagwe ankole fold belt overlying the western tanzania craton and 39ar 40ar muscovite ages from mylonites and phyllonites associated with the main phase of subsequent shortening and fold and thrust tectonics d2 39ar 40ar muscovite ages from the main detachment between archaean basement gneisses and imbricated cover rocks of the kagera supergroup in the eastern frontal parts of the karagwe ankole belt constrain the timing of the main fabric forming event and thrusting d2 to 1326 10 ma this age is at the young end of the age range for the main phase of granite plutonism and mafic dyke emplacement that have previously been related to crustal extension and associated intracontinental rifting if correct and representative for the main phase of deformation in the rest of the karagwe ankole belt the ages may rather point to a collisional event between the congo and tanzania cratons west of the karagwe ankole belt in mesoproterozoic times indicating a closer correlation with rocks of the kibara belt sensu stricto to the immediate south u pb detrital zircon ages for the older muyaga and overlying bukoba group of the kagera supergroup confirm the paleoproterozoic timing of sedimentation from ca 1780 ma but before ca 1568 ma the presence of a distinct group of ca 1750 1790 ma zircons in the bukoba group indicate uplift erosion and subsequent reworking of sediments and volcanic units contained in the lower muyaga group to the west the ages also suggest a correlation between the bwezigoro group of sw uganda and the bukoba group indicating the presence of a far more extensive paleoproterozoic and or early mesoproterozoic foreland basin overlying the western margin of the archaean tanzania craton and paleoproterozoic uganda block

evaluation of the results for an intermediate term prediction of the 8 january 2006 mw 6 9 cythera earthquake in the southwestern aegean during the past few decades the critical earthquake model which is based on observations concerning accelerating seismic deformation and concepts of the critical point dynamics has been proposed by various seismologists as a useful tool for intermediate term earthquake prediction a refined approach of this model has been previously applied to search for preshock critical regions in the southern aegean using all available data until the middle of 2002 a critical region corre sponding to a large mainshock had been identified papazachos et al 2002a b in the southwestern part of the aegean near the cythera island the predicted in 2002 parameters for this ensuing earthquake are u 36 5 n k 22 7 e for the epicental geographic coordinates with a model uncertainty of 120 km focal depth 100 km moment magnitude m 6 9 0 5 and origin time tc 2006 4 2 0 the generation of the strong cythera earthquake on 8 january 2006 with m 6 9 epicenter coordinates u 36 2 n and k 23 4 e and a focal depth of h 65 km satisfies this intermediate term prediction the region where significant macroseismic effects were anticipated from the predicted mainshock cythera south peloponnesus west crete and west cyclades corresponds to the area where damage by the 8 january 2006 strong earthquake has been observed the verification of this prediction is strong evidence that the intermediate term prediction of strong earthquakes is potentially feasible but additional forward testing of the model is needed to validate this result

the evolution of regional seismicity between large earthquakes 1 we describe a simple model that links static stress coulomb modeling to the regional seismicity around a major fault unlike conventional coulomb stress techniques which calculate stress changes we model the evolution of the stress field relative to the failure stress background seismicity is attributed to inhomogeneities in the stress field which are created by adding a random field that creates local regions above the failure stress the inhomogeneous field is chosen such that when these patches fail the resulting earthquake size distribution follows a gutenburg richter law immediately following a large event the model produces regions of increased seismicity aftershocks where the overall stress field has been elevated and regions of reduced seismicity where the stress field has been reduced stress shadows the high stress levels in the aftershock regions decrease due to loading following the main event combined with the stress shadow from the main event this results in a broad seismically quiet region of lowered stress around the epicenter pre event seismicity appears as the original stress shadows finally fill as a result of loading the increase in seismicity initially occurs several fault lengths away from the main fault and moves inward as the event approaches as a result of this effect the seismic moment release in the region around the future epicenter increases as the event approaches synthetic catalogues generated by this model are virtually indistinguishable from real earthquake sequences in california and washington

the mechanics of continental extension in western north america implications for the magmatic and structural evolution of the great basin abstract a finite element model of continental extension within a rheologically stratified lithosphere is used to examine the structural and magmatic consequences of extensional collapse of thickened crust within the early tertiary north american cordillera crustal thickening creates a weakness in the upper mantle in the model which focuses strain within the great basin during extension marginal highlands corresponding to the sierra nevada and colorado plateau develop near the edges of the weakened region where abrupt changes in the strength of the lithosphere create large gradients in the amount of strain the great thickness of the crust results in widespread ductile flow in the lower crust within the interior of the great basin favoring the formation of metamorphic core complexes during the early stages of extension ductile flow becomes inhibited as the crust thins and cools possibly contributing to the change in the style of extension from low angle detachment faulting to high angle normal faulting during the middle miocene as the lithosphere cools the strength of the uppermost mantle increases after about 10 m y the upper mantle becomes stronger beneath the great basin than beneath adjacent unextended regions strain then begins to migrate outward from the interior of the great basin onto the marginal highlands and their interior edges begin to collapse and are incorporated into the widening great basin after 40 m y of extension the highest rates of strain are localized at the edges of the great basin in positions corresponding to the walker lane tectonic belt of western nevada and the colorado plateau transition zone the weight of the marginal highlands in the model is partially supported by flexure of the strong layer in the uppermost mantle portions of the uppermost mantle which have been flexed upward cool more rapidly than deeper portions creating periodical variations in the strength of the lithosphere which eventually develop into crustal and lithospheric boudinage with a wavelength similar to that observed in regional gravity studies rapid thinning of the model lithosphere during the first 10 m y of extension results in nearly adiabatic decompression of the lithospheric mantle partial melting of the lower lithospheric mantle is likely during this period if volatile phases or mafic lithologies were present this mechanism may account for widespread silicic magmatism in the great basin during the middle tertiary as the region undergoing extension widens the rate of lithospheric thinning decreases and the mantle beneath the great basin begins to cool this leads to a cessation of melting within the lithosphere and waning of silicic volcanism 15 20 m y after the onset of extension the appearance of predominantly basaltic and bimodal volcanic suites in the great basin during the last 5 10 ma correlates well with the onset of decompression melting in the asthenosphere if the mantle potential temperature is greater than about 1350 c approximately 70 c warmer than typical mantle potential temperature

extension during continental convergence with application to the tibetan plateau the tibetan plateau is the product of crustal thickening caused by the collision between india and asia and is the largest active example of extensional tectonics in a zone of continental collision throughout most of the tertiary the tectonics of the plateau were dominated by north south shortening a significant proportion of which took place on east west striking thrust faults for the last 5 m y or so the plateau has been thinning by the mechanism of extension on north south trending normal faults previous investigations of the collision have been able to account for the large scale features of the tertiary deformation but have failed to explain the transition in the late tertiary to quaternary strain rate field of the plateau from north south compression to east west extension the transition could in principle be effected by a reduction in the rate of convergence between india and asia or by a uniform reduction in strength of the whole continental lithosphere of asia it could not however be effected by a reduction in strength of the elevated region alone this produces increased compressional strain rates in the weakened zone an alternative explanation for the transition to extension comes from considering the thermal evolution of thickened continental lithosphere the lower part of the lithosphere consists of a thermal boundary layer which when thickened by horizontal shortening is colder and denser than its surroundings convective instability of the thickened thermal boundary layer and its replacement by hot asthenosphere would rapidly raise the surface elevation and gravitational potential energy of the overlying part of the lithosphere the convective instability would happen in a time brief compared with the collision time scale 50 m y in the case of india and asia but would only occur after there had already been substantial thickening of the lithosphere numerical experiments show that for a range of lithospheric parameters the increase in surface height as much as 2 km and of potential energy 5 to 10 1012 n m 1 resulting from convective instability of the lower lithosphere are sufficient for east west extension to replace north south compression as the dominant feature of the stress field of the tibetan plateau

evolving geographic patterns of cenozoic magmatism in the north american cordillera the temporal and spatial association of magmatism and metamorphic core complexes four maps are presented here that show the location and extent of magmatic fields between eastern alaska and northern mexico during the successive time intervals of 55 40 40 25 25 10 and 10 0 ma and four others show the distribution of metamorphic core complexes during the same cenozoic time intervals the maps are based on u s geological survey and canadian cordilleran data bases contining about 6000 isotopic dates and extensive literature review for nearly 60 ma the development of metamorphic core complexes has coincided with the locus of a really extensive and voluminous intermediate composition magmatic fields the association is suggestive of a close link between magmatism and core complex formation namely that magma directly and indirectly lowers the strength of the crust magmatism thus controls the location and timing of core complex formation the stresses responsible may be inherited from mesozoic crustal thickening locally created by uplift and magmatic thickening of the crust and imposed by the global pattern of plate motions and driving forces since the miocene rates of magmatism extension and core complex formation have declined the modern basin and range province is not a suitable model for the situation that existed during major magmatic culminations the singular event of early miocene time the merging of two large magmatic fields extinguishing the laramide magmatic gap explains several disconnected observations the hyperextension episode of the colorado river corridor rapid reorientation of stress patterns across much of western north america and subsequent rapid tectonic movements in california magma triggered breakup of western north america lithosphere coincided with development of the san andreas transform system thermal destruction of the laramide magmatic gap created a california microplate about 22 ma ago that moved rapidly away from north america thus two plate tectonic processes thermal destruction of the lithosphere bridge and northward growth of a transform system interacted to produce miocene and later tectonic patterns and events

kibaran a type granitoids and mafic rocks generated by two mantle sources in a late orogenic setting burundi in the mesoproterozoic northeastern kibaran belt of burundi central africa two distinct late kibaran magmatic suites coexist both including a type granitoids they are located along the boundary zone between the kibaran mobile belt western internal domain and the archaean tanzanian craton overlain by mesoproterozoic foreland deposits eastern external domain intense deformation high temperature metamorphism and intrusion of abundant peraluminous anatectic crustal granites occur only in the former domain whereas the mesoproterozoic sedimentary cover of the latter is much less or even nearly undeformed nor metamorphosed the first late kibaran magmatism 350 km long kabanga musongati with an emplacement age of 1275 ma u pb on zircon is mainly composed of mafic and ultramafic layered rocks with subordinate a type acidic differentiates moderately enriched in incompatible elements initial isotopic ratios srlr 0 708 nd 8 indicate an old continental lithospheric mantle origin the emplacement of these late kibaran magmatic rocks was controlled by late lateral shear possibly contemporaneous with the latest intrusions of the kibaran peraluminous synkinematic granites of the western internal domain 1330 1260 ma the second late kibaran magmatism 40 km long gitega makebuko and bukirasazi alignment with an emplacement age of 1249 s ma u pb on zircon is limited in volume it is mainly granitic in composition a type can be strongly enriched in incompatible elements and comprises both syenites and mafic rocks initial isotopic ratios srlr 0 702 na 4 5 to 1 4 point to an oib type asthenospheric lower continental lithospheric mantle origin with only slight contamination by the lower crust during differentiation this group was also intruded during the late lateral shear in both groups liquid lines of descent can be reconstructed although some of the rocks have been strongly albitized this indicates that the granites are produced by differentiation of less evolved magmas and not by crustal anatexis upwelling of the asthenosphere along the tanzanian craton can generate by adiabatic pressure release the oibtype basic melts and provide the heat necessary to melt the continental lithospheric mantle sources this mechanism assigns a major role to a lithosphere scale late kibaran shear event occurring at the end of the regional compressive deformation between two rheologically contrasted domains ascent of the asthenosphere continental lithospheric mantle delamination and late orogenic extensional collapse of the western internal domain are suggested as a possible geodynamic model for the entire northeastern kibaran belt additional work is however necessary to test this model finally our results indicate that in the northeastern kibaran belt the kibaran orogeny ended at 1250 ma despite various reactivation events occurring later e g at 1137 ma

accelerating seismic crustal deformation before the izmit nw turkey large mainshock of 1999 august 17 and the evolution of its aftershock sequence summary the large izmit nw turkey mainshock 1999 august 17 mw 7 6 followed by another large earthquake on 1999 november 12 mw 7 2 caused extensive damage and loss of life in a zone approximately 170 km long along the coastal area of the gulf of izmit and further east to adapazari and duzce on the basis of the critical earthquake concept and by applying a recently developed optimization algorithm an elliptical area surrounding the 1999 august 17 mainshock epicentre was identified in which accelerating moderate magnitude seismic activity started in 1981 and culminated in the generation of the mainshock on the other hand the space and time distribution of the aftershocks of the first mainshock 1999 august 17 and the time variations of the b value of the gutenberg richter recurrence law and the mean aftershock magnitude suggest that the second mainshock 1999 november 12 might have been anticipated

a distributed temperature index ice and snowmelt model including potential direct solar radiation hourly melt and discharge of storglaciaren a small glacier in sweden were computed for two melt seasons applying temperature index methods to a 30 m resolution grid for the melt component the classical degree day method yielded a good simulation of the seasonal patient of discharge but the pronounced melt induced daily discharge cycles were not captured modelled degree day factors calculated for every hour and each gridcell from melt obtained from a distributed energy balance model varied substantially both diurnally and spatially a new distributed temperature index model is suggested attempting to capture both the pronounced diurnal melt cycles and the spatial variations in melt due to the effects of surrounding topography this is accomplished by including a radiation index in terms of potential clear sky direct solar radiation and thus without the need for other data besides air temperature this approach improved considerably the simulation of diurnal discharge fluctuations and yielded a more realistic spatial distribution of melt rates the incorporation of measured global radiation to account for the reduction in direct solar radiation due to cloudiness did not lead to additional improvement in model performance

accelerated preshock deformation of broad regions in the aegean area twenty four regions where accelerating deformation has been observed for a few decades before corresponding strong m 6 0 7 5 mainshocks are identified in the broader aegean area to a first approximation these preshock regions have elliptical shapes and the radius r in km of a circle with an area equal to the corresponding ellipse is related to the moment magnitude m of the mainshock by the equation log r 0 42 m 0 68 the dimension of each preshock region is about seven to ten times larger than the rupture zone fault length of the corresponding mainshock the time variation of the cumulative benioff strain was satisfactorily fitted by a power law relation which is predicted by statistical physics if the mainshock to which accelerating strain rates leads is considered as a critical point the duration t in years of the accelerating benioff strain release period is given by the relation log t 5 94 0 75 log s r where s r is the mean benioff strain rate release per year for 104 km2 in the preshock region calculated by the complete available data m 5 2 for the entire instrumental period 1911 1998 the importance of identifying and investigating such regions for better understanding the dynamics of the active part of the lithosphere as well as for earthquake prediction and time dependent seismic hazard assessment is discussed

petrology and geochemistry of the lyngdal granodiorite southern norway and the role of fractional crystallisation in the genesis of proterozoic ferro potassic a type granites abstract in south western norway the sveconorwegian orogenic thickening 1024 970 ma is followed by an important post collisional magmatism 950 930 ma divided in two suites vander auwera et al 2003 the anorthosite mangerite charnockite suite amc suite and the hornblende biotite granitoids suite hbg suite the hbg suite displays a continuous trend from gabbronorites to granites this paper presents the petrography and geochemistry major and trace elements sr nd isotopes of the lyngdal granodiorite and associated massifs tranevag and red granite massifs which belong to the hbg suite although being very close to the anorthosite massifs mafic microgranular enclaves mme resulting from magma mingling can be abundant and probably correspond to the parent magma of the studied plutons the lyngdal granodiorite and associated massifs are subalkaline metaluminous a type granitoids with high feo t feo t mgo ratio and k 2 o content forming a ferro potassic a type continuous trend from quartz monzodiorite to granite 56 72 wt sio 2 in harker diagrams the lyngdal tranevag plutons share the proterozoic rapakivi granites trend that they extend to lower sio 2 content major and trace element modelling as well as sr nd isotopes show that fractional crystallisation without assimilation is the differentiation process for lyngdal tranevag fractionating minerals are clinopyroxene hornblende plagioclase oxides biotite apatite zircon and allanite the red granite 71 75 wt sio 2 does not belong to this trend probably due to a different initial magma composition this study shows that ferro potassic a type granitoids can be derived by fractional crystallisation from mafic magmas

retrospective on the accelerating seismic release asr hypothesis controversy and new horizons abstract the hypothesis that large earthquakes may be preceded by a period of accelerating seismicity or accelerating seismic release asr was proposed about twenty years ago a compilation of almost one hundred peer reviewed publications on this topic since the late 1980s to the present day shows that the rate of asr studies increased gradually until 2004 but decreased afterwards this negative trend is amplified by a recent increase in the number of negative results and criticisms of the asr hypothesis the author suggests that much of the recent negativity regarding this topic is due to the formulation of this hypothesis as a power law fit to cumulative seismicity series this approach is intrinsically linked to the consensus for criticality evident from an overview of the asr literature to explain the emergence of power laws in earthquake populations the holistic view of the earth s crust as a complex system restricts seismicity pattern analyses to the study of main features such as power laws while a reductionist view would allow for more refined ones such a paradigm shift or sea change might be under way in the asr literature where in 2007 a new approach was proposed to explain the asr power law from combined concepts of elastic rebound and geometry reductionism versus holism is a fundamental problem that not only applies to the study of asr but also to the broader field of earthquake physics and earthquake predictability science

geochemistry of crustally derived leucocratic igneous rocks from the ulugh muztagh area northern tibet and their implications for the formation of the tibetan plateau this is the published version copyright 2012 american geophysical union all rights reserved

comment on columbia river volcanism the question of mantle heterogeneity or crustal contamination by r w carlson g w lugmair and j d macdougall abstract strontium and neodymium isotopic data on basalts from the columbia river province are consistent with an unfractionated source for the magmas and do not necessarily indicate large amounts of crustal contamination this conclusion is based on the observation that 1 1 the nd values of 99 of the basalts are positive and sharply bounded at nd 0 2 2 the trace element patterns can be modelled without crustal assimilation 3 3 there is no associated rhyolitic volcanism and 4 4 the isotopic ratios correlate with geographic position as well as chemical composition

u pb zircon calendar for namaquan grenville crustal events in the granulite facies terrane of the o okiep copper district of south africa s xvi geokongres geological society of south africa stellenbosch pp 160 163 van zyl d 1978 a petrological approach towards the ore bearing potentialities of the okiep basic intrusives in namaqualand in verwoed w j ed mineralization in metamorphic terranes geological society of south africa special publication 4 323 329 vellet v 1958 the geology of the copper district namaqualand cape province south africa unpublished report of the o okiep copper company 110 pp waters d j 1989 metamorphic evidence for the heating and cooling path of namaqualand granulites in daly j s cliff r a yardley b w d eds evolution of metamorphic belts geological society london special publication 43 357 363 williams i s claesson s 1987 isotopic evidence for the precambrian provenance and caledonian metamorphism of high grade paragneisses from the seve nappes scandinavian caledonides ii ion microprobe zircon u th pb contributions to mineralogy and petrology 97 205 217 clifford et al crustal events in o okiep district

positive degree day factors for ablation on the greenland ice sheet studied by energy balance modelling ice ablation is related to air temperature by the positive degree day factor variations of the positive degree day factor in west greenland are studied using an energy balance model to simulate ablation under different conditions degree day factors for simulated and measured ice ablation at nordbogletscher and qaman rssup sermia agree well with values around 8 mm d 1 c 1 degree day factors for snow are less than half those for ice energy balance modelling shows that degree day factors vary with summer mean temperature surface albedo and turbulence but there is only evidence of large positive degree day factors at lower temperatures and with low albedo 0 3 the greatest effect of albedo variations 0 3 0 7 is at lower temperatures while variations in turbulence have greater effect at higher temperatures current models may underestimate runoff from the greenland ice sheet by several tenths because they use a degree day factor for melting ice that is too small for the colder parts of the ice sheet i e the upper ablation area and the northerly margin

seismicity variations in the southern aegean greece before and after the large m7 7 1956 amorgos earthquake due to evolving stress the largest earthquake m0 4 9 1027 dyn cm of the 20th century in the territory of greece occurred south of amorgos island causing extensive destruction in the southern aegean area it occurred on an ene trending normal fault that is seated parallel to the island s southern coastline changes in the rates of moderate size earthquakes m 5 0 that occurred before and after the amorgos earthquake within circular regions centered on its epicenter with radii of 100 150 and 200 km are investigated the rate for moderate size events just before the main shock appears to be considerably increased when compared to those of either preceding or subsequent periods further inspection reveals that more evident seismicity fluctuations are attributed to distances exceeding 100 km these changes may be indicative of a broad region that is approaching a high stress state prior to an eventual large earthquake close to the main event that is within the 100 km radius a remarkable quiescence period lasting about two decades before its occurrence was observed changes in seismicity are discussed in combination with static stress changes calculated by the application of the stress evolutionary model that takes into account the coseismic slip associated with the larger events m 6 5 since the beginning of the 20th century and the tectonic loading on the major faults in the study area these larger events as with the intermediate magnitude seismicity taking place at distances exceeding 100 km and which encircled the quiescent area observed during the last 22 years before the amorgos earthquake are well correlated with stress enhanced areas in each stage of the evolutionary model

seismic activity on neighbouring faults as a long term precursor to large earthquakes in the san francisco bay area activity in moderate size earthquakes accelerated in the several decades before the large california earthquakes of 1989 1906 and 1868 this type of precursor seems to require the presence of several major faults in close enough proximity to one another that moderate size shocks are selectively triggered on surrounding faults during the latter stages of the cycle of strain buildup to large earthquakes it may be possible to use quantitative aspects of similar seismic precursors to make predictions of large earthquakes on timescales of a few years to one decade

40ar39ar thermochronological constraints on the structural evolution of the mesoproterozoic natal metamorphic province se africa abstract ten 40 ar 39 ar age spectra are presented for hornblende grains separated from mylonitized and weakly deformed amphibolites from the mesoproterozoic 1 2 1 0 ga natal metamorphic province nmp since the proposal of the sweat hypothesis the nmp has become a crucial area in which to study grenville aged locally termed namaquan accretion in this part of rodinia gondwana unlike many segments of the world s 1 1 ga belts the nmp is particularly suited to such studies since it is devoid of a high temperature pan african 500 ma overprint in this study we have dated hornblendes from within the earliest d1 ne directed thrust dominated structural domains of the belt the d1 domains are characterized by ne directed recumbent fold and thrust nappes and a pervasive generally s to sw dipping metamorphic foliation with down dip stretching lineations the new data constrain the minimum age of this early event which includes obduction of the northernmost tugela terrane onto the kaapvaal craton to 1135 9 ma in the d1 domains of the mzumbe terrane to the south cooling to below 550 c had only been attained by 1005 ma we also dated amphibolites from the later d2 structural domains which are characterized by sub vertical sinistral mylonite belts with sub horizontal to oblique stretching lineations our data show that d2 oblique shearing commenced at 1050 1035 ma in the mzumbe terrane and only terminated at 980 ma the youngest movements also included reactivation of major d1 structures such as the melville thrust mzumbe margate terrane boundary at 990 ma finally indications of minor pan african resetting was detected during the first 5 of the ar ar spectra from mylonites of the lilani matigulu shear zone tugela mzumbe terrane boundary indicating the polyphase nature of this major structure it has been suggested that the d1 event records the early ne sw directed arc continent collision history of the belt whilst the d2 event represents a continuation of essentially the same convergence vectors after extensive crustal thickening the new data place important time constraints on the major tectonic events in the nmp which appear comparable in many ways to other parts of the global grenvillian orogen

accelerating seismic crustal deformation in the southern aegean area a region of intense accelerating seismic crustal deformation has been identified in the southwestern part of the hellenic arc broader area of cythera island the identification is performed using a detailed parametric grid search of the broader southern aegean area for accelerating energy release behavior the identified region has similar properties with past preshock critical regions which have been identified for strong mainshocks in the aegean area based on such observations which suggest that this region is at a critical state that can lead to a critical point that is to the generation of a mainshock an estimation is made of the possible epicenter coordinates magnitude and origin time of this oncoming large m 7 0 earthquake the estimation procedure is validated on the basis of retrospective analysis of strong events in the aegean area as well as by appropriate application on synthetic random catalogs these results the existence of similar observations of accelerating seismic deformation in eastern part of southern aegean and independent information on the time distribution of large earthquakes m 6 8 for the whole southern aegean indicate that the generation of strong earthquakes in this area in the next few years must be considered as very probable

intermediate term prediction of occurrence times of strong earthquakes pattern recognition procedures for infrequent events are adapted to the problem of identifying patterns of clustering of small and intermediate scale seismicity before large earthquakes identification procedures derived from analysis of large california and nevada earthquakes yield a high success rate when applied to other parts of the world

late orogenic gold mineralization in the western domain of the karagwe ankole belt central africa auriferous quartz veins from the byumba deposit rwanda abstract gold mineralization in the kab karagwe ankole belt of central africa dominantly occurs as quartz lode and ferruginous breccia systems primary gold mineralization in the kab is possibly linked to a deformational event in the early neoproterozoic which is accompanied by shear movements and post compressional magmatism the byumba deposit is chosen due to its position in the kab mesoproterozoic metasedimentary stratigraphy akanyaru supergroup interesting structural trend nw trending shear zone and its closeness to magmatic intrusions explorative drillings from the byumba deposit in rwanda were logged and sampled for further petrographic investigation in situ rb sr geochronology laser ablation inductively coupled plasma triple quadrupole mass spectrometry and micro x ray fluorescence xrf major and trace element mapping distinct phases of folding and shear deformation are present at byumba and three main phases of quartz veining are identified pre syn post folding the first quartz vein generation is layer parallel and folded along the bedding indicative of a pre folding origin v1 generation a second generation of quartz veins v2a is concentrated in fold hinges and related to the primary folding of the layers cleavage parallel and often boudinaged v2b quartz veins are emplaced during late stage folding post folding v3 massive or sigmoidal quartz veins crosscut the folds and cleavage element mapping of the gold by using xrf shows that chlorite rich quartz veins v3 host the primary gold mineralization in the form of sub micron gold and of small disseminated blebs cores additionally recorded a supergene enrichment phase of gold at reduction zone boundaries in situ rb sr geochronology on white mica of the crosscutting post folding quartz veins v3 point towards an early neoproterozoic age of 900 ma the gold mineralization at byumba is interpreted to be related to the regional early neoproterozoic compressional deformation event based on 1 the post folding timing of the auriferous veins 2 the observation of shear related textures both in the host rock and the veins and 3 the location of the byumba deposit within a regional shear structure this association with compressional shearing points towards an orogenic origin for gold mineralization however a magmatic hydrothermal influence from contemporaneous granitic magmatism cannot be excluded

probabilities of activation of seismic faults in critical regions of the aegean area summary properties of the accelerating seismic crustal deformation pattern and of the intermediateterm seismic quiescence pattern have been combined to identify faults in the aegean area 34 n 43 n 19 e 30 e that have a considerable probability of generating strong earthquakes m 6 4 during the next 5 yr period eight groups of such faults have been identified and the probability of each fault being activated during this time period has been estimated three of these groups are located in southern greece hellenic arc two in central greece east central greece ionian islands two in northwestern turkey and one in the area of the borders of albania greece and the former yugoslav republic of macedonia the importance of these results for intermediate term seismic hazard assessment is discussed

identification of seismic precursors before large earthquakes decelerating and accelerating seismic patterns 1 a useful way of understanding both seismotectonic processes and earthquake prediction research is to conceive seismic patterns as a function of space and time the present work investigates seismic precursors before the occurrence of an earthquake it does so by means of a methodology designed to study spatiotemporal characteristics of seismicity in a selected area this methodology is based on two phenomena the decelerating moment release dmr and the accelerating moment release amr as they occur within a period ranging from several months to a few years before the oncoming event the combination of these two seismic sequences leads to the proposed decelerating accelerating moment release damr earthquake sequence which appears as the last stage of loading in the earthquake cycle this seismic activity appears as a foreshock sequence and can be supported by the stress accumulation model sam the damr earthquake sequence constitutes a double seismic precursor identified in space and time before the occurrence of an earthquake and can be used to improve seismic hazard assessment research in this study the developed methodology is applied to the data of the 1989 loma prieta california the 1995 kobe japan and the 2003 lefkada greece earthquakes the last part of this study focuses on the application of the methodology to the ionian sea western greece and forecasts two earthquakes in that area

neoproterozoic glacial deposits from the aracuai orogen brazil age provenance and correlations with the sao francisco craton and west congo belt article i nfo glacigenic diamictite successions of the macaubas group are widespread in the western domain of the aracuai orogen east of the sao francisco craton brazil diamictites also occur on this craton and in the african counterpart of the aracuai orogen the west congo belt detrital zircon grains from the matrix of diamictites and sandstones from the macaubas group were dated by the u pb shrimp technique the geochronological study sets the maximum depositional age of the glacial diamictites at 900 ma and indicates multiple sources for the macaubas basin with ages ranging from 900 to 2800 ma sm nd tdm model ages determined on whole rock samples range from 1 8 ga to 2 5 ga and get older up section comparison of our data with those from the cratonic area suggest that these glacial deposits can be correlated to the jequitai and carrancas diamictites in the sao francisco craton and to the lower mixtite formation of the west congolian group exposed in africa the 900 1000 ma source is most probably represented by the zadinian mayumbian volcanic rocks and related granites from the west congo belt however one of the most voluminous sources with ages in the 1 1 1 3 ga interval has not been detected in the sao francisco congo craton possible sources for these grains could occur elsewhere in africa or possibly from within the brasilia belt in western central brazil

increased long range intermediate magnitude earthquake activity prior to strong earthquakes in california we study the space time relationships between strong earthquakes in california and the intermediate magnitude earthquakes that both precede and follow them all 11 earthquakes in california with nominal magnitudes greater than or equal to 6 8 from 1941 to 1993 were preceded by an increase in the rate of occurrence of earthquakes having magnitudes greater than 5 1 ten of the 11 earthquakes occurred when or shortly after the intermediate magnitude activity was greater than its 75th percentile three of these strong earthquakes are in a conventional space time foreshock aftershock relationship with others of the 11 strong events the precursory activity is concentrated in regions having linear dimensions of the order of a few hundred kilometers these dimensions are significantly larger than the estimated fracture lengths of the ensuing strong earthquakes the correlations are ill defined for smaller earthquakes and are almost unidentifiable for earthquakes with magnitudes less than about 4 6 the precursors to the strong earthquakes appear over a time interval of the order of 5 to 10 years before the strong earthquake although the onset was about 25 years before the san francisco earthquake in the case of the loma prieta and san francisco earthquakes the onset of increased activity appears to be relatively abrupt the increased activity is either switched off abruptly to distances of the order of hundreds of kilometers shortly after the occurrence of a strong earthquake or the strong events are themselves part of a precursory pattern of continuing high activity before a second strong earthquake that takes place soon thereafter with subsequent extinction of activity after it thus the intermediate magnitude precursors do not directly influence the time and location of the subsequent strong event but the strong event has a strong influence on the stress field in the vicinity of intermediate magnitude earthquakes to distances of the order of many times the scale size of the strong earthquake

snow accumulation and ice flow at dome du gouter 4300 m mont blanc french alps glaciological experiments have been carried out at dome du gouter 4300 m a s l mont blanc in order to understand the flow of firn ice in this high altitude alpine glacierized area accumulation measurements from stakes show a very strong spatial variability and an unusual feature of mass balance fluctuations for the alps i e the snow accumulation does not show any seasonal patterns measured vertical velocities which should match with long term mean mass balance are consistent with observed accumulations therefore the measurement of vertical velocities seems a good way of quickly obtaining reliable mean accumulation values for several decades in such a region a simple flow model can be used to determine the main flowlines of the glacier and to propose snow ice age of core samples from the two boreholes drilled down t the bedrock in june 1994 these results coincide with radioactivity measurements made to identify the well known radioactive snow layers of 1963 and 1986 we can hope to obtain ice samples 55 60 years old about 20 or 30 m above the bedrock 110 m deep below the deformation of the ice layers is loo great to be dated accurately

deformation and related radiochronology in a late pan african mylonitic shear zone adrar des iforas mali the influence of a deformation on the zircon u pb system was studied using the example of the western margin of the iforas granulitic unit mali where undeformed sub alkaline leptynites have evolved to strongly foliated mylonites and then to ultramylonites the deformation episod was late pan african and occurred at low temperature zircons show evidences of a brittle behavior with microcracks development then fracturation of the crystals and dispersion of the fragments in the ductile matrix an equilibrium grain size was reached which probably depended of the stress but was independant of the initial size of the zircons and of the strain

an observational test of the origin of accelerating moment release before large earthquakes 1 a progressive increase of seismic activity distributed over a wide region around a future earthquake epicenter is termed accelerating moment release amr this phenomenon has been observed in several studies over the last 15 years although there is no consensus about the physical origin of the effect in a recent hypothesis known as the stress accumulation sa model the amr is thought to result from the last stage of loading in the earthquake cycle in this view the increasing seismicity is due to minor stress release as the whole region becomes sufficiently stressed for the major event to occur the stress accumulation model makes specific predictions about the distribution of events in an amr sequence because the amr is predicted to be a result of loading on the main fault the precursory activity should be concentrated in the positive lobes of the far field stresses calculated by a backslip dislocation model of the main shock to test this model amr is first found in optimal circular regions around the epicenters of each of the m w 6 5 earthquakes in central and southern california since 1950 a backslip dislocation model is then used to determine which of the precursory events occur in the regions predicted by stress accumulation amr is shown to occur preferentially in the lobes of the backslip stress field predicted by the stress accumulation model

time variation of parameters related to the accelerating preshock crustal deformation in the aegean area the time variation of two parameters related to accelerating seismic deformation before strong earthquakes in the aegean area is examined the first is the b parameter of the gutenberg richter relation and the second is the curvature parameter c which is a measure of deviation of the accelerating preshock deformation from a linear time variation of this deformation following two different procedures it was found that the b value exhibits a decreasing trend prior to the oncoming earthquake in agreement with the results of laboratory experiments and other independent observations c values also show a decreasing trend before main shocks these results indicate that such time variations of these parameters can be considered as precursory phenomena of ensuing strong earthquakes

the energy release in earthquakes energy calculations are generally made through an empirical application of the familiar gutenberg richter energy magnitude relationships the precise physical significance of these relationships is somewhat uncertain we make use here of the recent improvements in knowledge about the earthquake source to place energy measurements on a sounder physical basis for a simple trapezoidal far field displacement source time function with a ratio x of rise time to total duration t 0 the seismic energy e is proportional to 1 x 1 x 2 m 0 2 t 0 3 where m 0 is seismic moment as long as x is greater than 0 1 or so the effect of rise time is not important the dynamic energies thus calculated for shallow events are in reasonable agreement with the estimate e 5 10 5 m 0 based on elastostatic considerations deep events despite their possibly different seismological character yield dynamic energies which are compatible with a static prediction similar to that for shallow events studies of strong motion velocity traces obtained near the sources of the 1971 san fernando 1966 parkfield and 1979 imperial valley earthquakes suggest that even in the distance range of 1 to 5 km most of the radiated energy is below 1 to 2 hz in frequency far field energy determinations using long period wwssn instruments are probably not in gross error despite their band limited nature the strong motion record for the intermediate depth bucharest earthquake of 1977 also suggests little teleseismic energy outside the pass band of a long period wwssn instrument

short lived eburnian orogeny in southern mali geology tectonics u pb and rb sr geochronology abstract this work is based on a comprehensive field survey including mapping of the massigui degree sheet in southern mali the investigated area belongs to the northern part of the man shield which is mainly composed of lower proterozoic volcano sedimentary sequences birimian and of large areas of granitoids the whole being affected by the eburnian orogeny structural and geochronological u pb and rb sr results from this study point to a short period of time 30 ma for the eburnian orogenesis between 2100 and 2070 ma the events recorded later 1984 30 ma being due to tectonic reactivations on the other hand no trace of events older than 2100 ma have been found coupled with geochemical and rb sr isotopic systematics this leads to invoke a fundamental link between birimian volcanics and eburnian granitoids both being high k calc alkaline in composition and coming from a single evolving mantle source in a palaeo environment which has some of the characteristics of modern subduction including back arc or docking zones the main regional structure of the area strikes roughly nne ssw with an important strike slip component escorted by a greenschist metamorphism the deformation is the most intense in the n40 to n10 5 km large banifin shear zone where metamorphism reached the lower amphibolite facies here one observes subvertical strong foliation non cylindrical folding locally sheath folds and subhorizontal pencil lineations the deformation being regionally recorded by light subisoclinal folds with subvertical axes compatible with a sinistral movement this regional shear tectonics d2 2074 9 8 ma is preceded by an isoclinal deformation d1 bracketed between 2098 5 ma and d2 only known as relics from which it likely derived a later phase d3 occurred along the banifin shear belt at a more superficial level even if still ductile generated by a dextral movement and having induced retrograde metamorphism this last tectonic phase which is not accompanied by plutonism nor volcanism has been dated at 1982 30 ma being responsible for the complete resetting of the rb sr isotopic system in the plutons present in the banifin corridor

evolving towards a critical point a review of accelerating seismic moment energy release prior to large and great earthquakes there is growing evidence that some proportion of large and great earthquakes are preceded by a period of accelerating seismic activity of moderate sized earthquakes these moderate earthquakes occur during the years to decades prior to the occurrence of the large or great event and over a region larger than its rupture zone the size of the region in which these moderate earthquakes occur scales with the size of the ensuing mainshock at least in continental regions a number of numerical simulation studies of faults and fault systems also exhibit similar behavior the combined observational and simulation evidence suggests that the period of increased moment release in moderate earthquakes signals the establishment of long wavelength correlations in the regional stress field the central hypothesis in the critical point model for regional seismicity is that it is only during these time periods that a region of the earth s crust is truly in or near a self organized critical soc state such that small earthquakes are capable of cascading into much larger events the occurrence of a large or great earthquake appears to dissipate a sufficient proportion of the accumulated regional strain to destroy these long wavelength stress correlations and bring the region out of a soc state continued tectonic strain accumulation and stress transfer during smaller earthquakes eventually re establishes the long wavelength stress correlations that allow for the occurrence of larger events these increases in activity occur over longer periods and larger regions than quiescence which is usually observed within the rupture zone of a coming large event the two phenomena appear to have different physical bases and are not incompatible with one another

occurrences of evaporitic salts in bugesera region burundi and relation to hydrogeochemical evolution of groundwater several studies conducted on occurrences of evaporitic salts in various parts of the world often interpret the formation of such salts as the result of the evaporation of subsurface brines saline lake waters and sea water contaminated groundwater on one hand and the deposition of sea sprays and wind transported salts on the other hand this study seeks to understand processes governing the formation of evaporitic salts in a humid tropical context and to establish a link between the occurrence of these salts and the different processes controlling the hydrogeochemical evolution of groundwater in bugesera region in north eastern burundi unlike previous studies salt occurrences in the study area occur in a continental and humid tropical environment where chemical analyses of water samples from several small lakes reveal rather fresh water while salt incrustations reported in the western burundi occur in a sedimentary basin which is made up of a mixture of lacustrine and fluviatile sediments the evaporitic salts in the depression of bugesera appear in the upper layers of the weathered overburden developed on precambrian basement rocks these facts suggest that the lithological nature and setting of the area may not be the key factor controlling the formation of these salt deposits x ray diffraction xrd analyses performed on saline soils from two quarries in bugesera region confirm the presence of salt minerals including particularly gypsum caso4 2h2o halite nacl and thenardite na2so4 other minerals identified such as goethite kaolinite muscovite and quartz may be part of the soil matrix chemical analyses on leachates of soil samples from the 2 quarries in bugesera region confirm their saline nature as evidenced by high tds 1826 17 679 mg l and ph values 8 3 8 5 the predominance of na mg2 ca2 k so42 cl in the chemical composition of the dissolved salts clearly reflects their mineralogical composition this study clearly demonstrates that these evaporitic salts originate from the combination of three processes namely the dissolution of aluminosilicate minerals which enrich groundwater in different salt forming ions the capillary rise which lifts the shallow groundwater and the dissolved ions up to the reach of evaporation and ultimately the evapoconcentration which precipitates the salts following well established pathways these findings are well supported by the results of the simulation of the evapoconcentration process with the phreeqc hydrochemical model

climate warming revealed by englacial temperatures at col du dome 4250 m mont blanc area 1 temperatures were measured in two deep boreholes drilled at the same location in the ice at col du dome 4250 m in 1994 and 2005 providing clear evidence of atmospheric warming the 1994 temperature profile was already far from steady state conditions results from a heat transfer model reveal that the englacial temperature increase cannot be explained solely by atmospheric temperature rise the latent heat produced by the refreezing of surface meltwater below the surface also contributes to the englacial temperature increase although surface melting is normally very low at this altitude this contribution became significant after 1980 for temperatures at the top of the borehole simulations for different climatic scenarios show that glaciated areas located between 3500 and 4250 m could become temperate in the future this warming could have a major impact on the stability of hanging glaciers frozen to their beds if the melting point is reached

a note on the prediction of the september 13 1986 strong earthquake in kalamata southwest peloponnesus greece abstract a comparison between the observed focal parameters of the september 13 1986 kalamata greece strong shock and the predicted ones shows that the prediction was quite successful as far as time of occurrence location and focal depth are concerned the discrepancy between the observed m s 6 2 and predicted m s 6 5 7 6 magnitude is attributed to the use of old seismological information and the lack of systematic observation of non seismic earthquake precursors precursors of this type observed by local people before some recent greek shocks including the kalamata earthquake indicate that their systematic monitoring could substantially contribute toward earthquake prediction in greece assuming the random model the probability that the kalamata earthquake occurred in the specified target area by chance is 0 65

vein type tungsten deposits in rwanda rutsiro area of the karagwe ankole belt central africa abstract the rutsiro w sn nb ta deposit consists of vein hosted metal ores occurring within a black schist dominated formation of the rwandan proterozoic metasediments supergroup the collected samples revealed that the mineralised veins are mostly composed of quartz and ferberite the ore microscopy studies of the polished sections of the mineralised vein material confirmed ferberite as the main w mineral in the quartz veins ilmenite occurs within the ferberite crystals as inclusions in addition to quartz the concentrate samples contain a variety of minerals including cassiterite crystals tourmaline and free ilmenite and rutile crystals which came from the hosting black schists the sem eds analysis showed that free crystals of ree minerals such as monazite and xenotime are common in the concentrate samples electron probe microanalysis using wavelength dispersive spectrometry wds confirmed the composition of w and sn minerals to correspond to ferberite as the main w ore mineral together with some scheelite and cassiterite for tin ore mineral the microprobe analysis also revealed the occurrence of columbite tantalite and the association of indium and molybdenum traces with scheelite the analysed monazites fall into two groups monazite ce and monazite nd the proposed mineralisation history suggests that there is a replacement stage of scheelite ca2 by hydrothermal fe2 to produce reinite which is a ferberite polycrystalline pseudomorph the occurrence of sulphides such as arsenopyrite pyrite and pyrrhotite implies at least one sulphide phase in later stages of mineralisation the occurrence of tourmaline as inclusions within cassiterite crystals and the tourmalinisation of the country rocks close to the mineralised veins confirm tourmaline as an important pathfinder for w sn mineralisation the rutsiro w sn mineralisation is classified as a vein type deposit however two granitic cupolas underneath the deposit which are probably greisenised are suggested as source of the metal rich mineralising fluids geophysical works are required to investigate the presence of these cupolas

u pb monazite ages of the kabanga mafic ultramafic intrusions and contact aureoles central africa geochronological and tectonic implications mafic ultramafic rocks of the kabanga musongati alignment in the east african nickel belt occur as bushveld type layered intrusions emplaced in metasedimentary sequences the age of the mafic ultramafic intrusions remains poorly constrained though they are regarded to be part of ca 1375 ma bimodal magmatism dominated by voluminous s type granites in this study we investigated igneous monazite and zircon from a differentiated layered intrusion and metamorphic monazite from the contact aureole the monazite shows contrasting crystal morphology chemical composition and u pb ages monazite that formed by contact metamorphism in response to emplacement of mafic ultramafic melts is characterized by extremely high th and u and yielded a weighted mean 207pb 206pb age of 1402 9 ma which is in agreement with dates from the igneous monazite and zircon the ages indicate that the intrusion of ultramafic melts was substantially earlier by 25 m y 95 confidence than the prevailing s type granites calling for a reappraisal of the previously suggested model of coeval bimodal magmatism monazite in the metapelitic rocks also records two younger growth events at ca 1375 ma and ca 990 ma coeval with metamorphism during emplacement of s type granites and tin bearing granites respectively in conjunction with available geologic evidence we propose that the kabanga musongati mafic ultramafic intrusions likely heralded a structurally controlled thermal anomaly related to nuna breakup which culminated during the ca 1375 ma kibaran event manifested as extensive intracrustal melting in the adjoining karagwe ankole belt producing voluminous s type granites the grenvillian aged ca 990 ma tin bearing granite and related sn mineralization appear to be the far field record of tectonothermal events associated with collision along the irumide belt during rodinia assembly since monazite is a ubiquitous trace phase in pelitic sedimentary rocks in contact aureoles of mafic ultramafic intrusions and in regional metamorphic belts our study highlights the potential of using metamorphic monazite to determine ages of mafic ultramafic intrusions and to reconstruct postemplacement metamorphic history of the host terranes georef subject absolute age africa east africa gabbros igneous rocks intrusions mesoproterozoic metamorphic rocks metamorphism metasedimentary rocks monazite neoproterozoic nesosilicates norite orthosilicates phosphates plutonic rocks precambrian proterozoic silicates tanzania u pb ultramafics upper precambrian zircon zircon group

geochemical and isotopic sr nd and pb evidence on the origin of the anorthosite bearing anorogenic complexes of the air province niger abstract abundant leucogabbro and anorthosite associated with other felsic rocks occur in seven high level ring complexes of ofoud type in central air the leucogabbroic rocks are plagioclase cumulates whereas troctolites and melatroctolites in the meugueur meugueur ring dyke are olivine cumulates the plagioclase cumulates are strongly laminated but generally unlayered and have positive europium anomalies fine grained marginal gabbros and monzogabbros without europium anomalies are interpreted as having been close to magmatic liquids as are the other felsic rocks which have complementary negative europium anomalies the fine grained basic rocks are mildly alkaline with a troctolitic tendency with high ti p and incompatible elements and low transition elements cumulus mineral compositions an65 and fo65 55 are moderately differentiated the felsic syenites and granites are alkaline to rarely peralkaline strontium isotopic initial ratios sri in the leucogabbroic rocks calculated assuming ages for each intrusion based on whole rock isochrons for felsic rocks range from 0 7035 to about 0 707 whereas end t varies sympathetically from 2 6 to 4 2 although there is a spread in values each intrusion has a distinct isotopic signature bous and the marginal facies of meugueur meugueur having the highest end t and lowest sri whereas rocks from the others have lower end t and higher sri sri in the felsic rocks obtained from isochrons ages in the range 400 490 ma are considerably larger and vary from 0 7084 for abontorok and tagueito 0 7138 for bonus end t varies from 7 5 to 14 4 the initial lead isotopic ratios for the leucogabbroic rocks show a narrow range of values 206pb 204pb 16 7 17 75 207pb 204pb 15 45 15 53 while the felsic rocks have less ratiogenic ratios down to 206pb 204pb 16 4 and 207pb 204pb 15 32 the parental basic magma fractionated olivine and ortho pyroxene but not plagioclase which must have accumulated prior to intrusion at moderately shallow depths the inferred parental magma probably had characteristics suggesting an origin by minor contamination of a slightly depleted oib type source the other felsic rocks are not comagmatic and could have arisen by crustal contamination of a residual felsic melt the ofoud type complexes are similar to labrador type massif anorthosites

a mathematical formulation of accelerating moment release based on the stress accumulation model large earthquakes can be preceded by a period of accelerating seismic activity of moderate sized earthquakes this phenomenon usually termed accelerating moment release has yet to be clearly understood a new mathematical formulation of accelerating moment release is obtained from simple stress transfer considerations following the recently proposed stress accumulation model this model based on the concept of elastic rebound simulates accelerating seismicity from theoretical stress changes during an idealized seismic cycle in this view accelerating moment release is simply the consequence of the decrease due to loading of the size of a stress shadow due to a previous earthquake we show that a power law time to failure equation can be expressed as a function of the loading rate on the fault that is going to rupture we also show that the m value which is the power law exponent can be defined as m d 3 with d a parameter that takes into account the geometrical shape of the stress lobes and the distribution of active faults in the stress accumulation model the power law is not due to critical processes

determination of earthquake energy release and ml using terrascope we estimated the energy radiated by earthquakes in southern california using on scale very broadband recordings from terrascope the method we used involves time integration of the squared ground motion velocity and empirical determination of the distance attenuation function and the station corrections the time integral is typically taken over a duration of 2 min after the p wave arrival the attenuation curve for the energy integral we obtained is given by q r cr n exp kr r 2 2 h ref 2 with c 0 49710 n 1 0322 k 0 0035 km 1 and h ref 8 km where is the epicentral distance a similar method was used to determine m l using terrascope data the station corrections for m l are determined such that the m l values determined from terrascope agree with those from the traditional optical wood anderson seismographs for 1 5 6 5 m l saturates the ratio e s m 0 m 0 seismic moment a measure of the average stress drop for six earthquakes the 1989 montebello earthquake m l 4 6 the 1989 pasadena earthquake m l 4 9 the 1990 upland earthquake m l 5 2 the 1991 sierra madre earthquake m l 5 8 the 1992 joshua tree earthquake m l 6 1 and the 1992 landers earthquake m w 7 3 are about 10 times larger than those of the others that include the aftershocks of the 1987 whittier narrows earthquake the sierra madre earthquake the joshua tree earthquake and the two earthquakes on the san jacinto fault the difference in the stress drop between the mainshock and their large aftershocks may be similar to that between earthquakes on a fault with long and short repeat times the aftershocks which occurred on the fault plane where the mainshock slippage occurred had a very short time to heal hence a low stress drop the repeat time of the major earthquakes on the frontal fault systems in the transverse ranges in southern california is believed to be very long a few thousand years hence the events in the transverse ranges may have higher stress drops than those of the events occurring on faults with shorter repeat times such as the san andreas fault and the san jacinto fault the observation that very high stress drop events occur in the transverse ranges and the los angeles basin has important implications for the regional seismic potential the occurrence of these high stress drop events near the bottom of the seismogenic zone strongly suggests that these fault systems are capable of supporting high stress that will eventually be released in major seismic events characterization of earthquakes in terms of the e s m 0 ratio using broadband data will help delineate the spatial distribution of seismogenic stresses in the los angeles basin and the transverse ranges

precursory accelerating seismic crustal deformation in the northwestern anatolia fault zone abstract we present the results of a systematic search for the identification of accelerating seismic crustal deformation in the broader northern aegean area and in northwestern turkey we found that accelerating seismic deformation release expressed by the generation of intermediate magnitude earthquakes is currently observed in nw turkey on the basis of the critical earthquake model and by applying certain constraints which hold between the basic quantities involved in this phenomenon it can be expected that this accelerating seismic activity may culminate in the generation of two strong earthquakes in this area during the next few years the estimated epicenter coordinates of the larger of these probably impending earthquakes are 39 7 n 28 8 e its magnitude is 7 0 and its occurrence time tc 2003 5 the second strong event is expected to occur at tc 2002 5 with a magnitude equal to 6 4 and epicenter coordinates 40 0 n 27 4 e the uncertainties in the calculated focal parameters for these expected events are of the order of 100 km for the epicenter 0 5 for their magnitude and 1 5 years for their occurrence time

gulf of guinea continental slope and congo zaire deep sea fan sr pb isotopic constraints on sediments provenance from zaiango cores abstract sediment accumulation in the continental margin of equatorial central africa is mostly derived from terrigenous flux of the larger congo ex zaire and smaller coastal rivers in order to determine the present day respective contributions of these different sources we analysed the pb sr isotopic compositions of late quaternary sediments accumulated on the continental margin and congo deep sea fan the isotopic data of eight piston cores from the zaiango project ifremer total show a strong geochemical similarity between sediments from distant cores situated on the slope near the congo estuary that can be explained by the spreading of the congo sediment plume over extensive areas of the margin however the core located at the northern boundary of the congo river influence has higher 87 sr 86 sr ratio suggesting a melange with a more radiogenic source probably provided by the small but numerous rivers of this coast the differences observed between present day samples from congo channel and from the terminal depositional lobe suggest a segregation of the sand along the channel during the transit which creates a pb isotopic fractionation therefore the comparison between sr and pb isotopes shows a strong discrimination of pb according to sedimentation processes while sr isotopes seem directly influenced by the coastal rivers contributions

which empirical model is best suited to simulate glacier mass balances based on an extensive dataset of surface mass balances smb from four glaciers in the french alps for the period 1995 2012 and in the framework of enhanced temperature index models we investigate the sensitivity of seasonal glacier smb to temperature solar radiation precipitation and topographical variables our results reveal strong correlations between winter smb and precipitation although the precipitation gradient cannot explain the high accumulation rates based on the available point measurements we found no relevant relationship between winter smb and topographical variables temperature was found to be the main driver of ice snow ablation while solar radiation was found to strongly influence the spatial distribution of summer smb we compared the ability of several enhanced temperature index models to accurately simulate point smb and glacier wide mb our analyses revealed that the uncertainties in the simulated annual smb due to winter smb uncertainties are larger than differences between models and prevented us from concluding which model is the most suitable in contrast with results of previous studies including solar radiation in melt models did not improve the performances when modelling glacier wide mb we conclude that a classical degree day model is sufficient to simulate the long term glacier wide mb if the underlying processes are not required to be resolved

direct evidence for archean crust in the western domain of the karagwe ankole belt rwanda implications for neoarchean to paleoproterozoic crustal evolution abstract neoarchean orthogneiss dated at 2629 9 ma by sims zircon u pb has been discovered in the rusizian terrane of the western domain of the karagwe ankole belt rwanda redefining the nw margin of the tanzania craton metamorphism of the orthogneiss at 1959 4 ma was associated with paleoproterozoic granitic arc magmatism in the rusizian terrane over the period ca 2000 1840 ma the major and trace element composition of the peraluminous calc alkalic orthogneiss is consistent with magmatism in an arc setting at an active continental margin its nd depleted mantle model age of ca 2800 ma is consistent with derivation by partial melting and reworking of older crust at the nw margin of the tanzania craton the paleoproterozoic thermal event was related to the accretional collision between the congo and tanzania cratons during the assembly of the nuna supercontinent future tectonic modelling of the karagwe ankole belt must take into account the presence of archean basement beneath the western domain

a type granite and the red sea opening abstract miocene oligocene a type granite intrudes the eastern side of the red sea margin within the zone of extension from jiddah saudi arabia south to yemen the intrusions developed in the early stages of continental extension as arabia began to move slowly away from africa around 30 20 ma within the narrow zone of extension silicic magmas formed dikes sills small plutons and extrusive equivalents in the jabal tirf area of saudi arabia these rocks occur in an elongate zone consisting of late precambrian basement to the east which is gradually invaded by mafic dikes the number of dikes increases westward until an igneous complex is produced parallel to the present red sea axis the jabal tirf igneous complex consists of diabase and rhyolite granophyre sills 20 24 ma although these are intrusine intrusive rocks their textures indicate shallow depths of intrusion the alkali granites of yemen consist primarily of perthitic feldspar and quartz with some minor alkali amphiboles and acmite these granites represent water poor hypersolvus magmas generated from parent alkali basalt magmas the granophyric two feldspar granites associated with the mafic dike swarms and layered gabbros formed by fractional crystallization from tholeiitic basalt parent developed in the early stages of extension initial 87sr 86sr ratios of these rocks and their bulk chemistry indicate that production of peralkaline and metaluminous granitic magmas involved both fractionation and partial melting as they ascended through the late precambrian crust of the arabian plate

surface mass balance of glaciers in the french alps distributed modeling and sensitivity to climate change a new physically based distributed surface mass balance model is presented for alpine glaciers based on the crocus prognostic snow model it resolves both the temporal 1 hour time step and spatial 200 m grid step variability of the energy and mass balance of glaciers mass balance reconstructions for the period 1981 2004 are produced using meteorological reconstruction from the safran meteorological model for glacier de saint sorlin and glacier d argentiere french alps both glaciers lost mass at an accelerated rate in the last 23 years the spatial distribution of precipitation within the model grid is adjusted using field mass balance measurements this is the only correction made to the safran meteorological input to the glacier model which also includes surface atmospheric temperature moisture wind and all components of downward radiation independent data from satellite imagery and geodetic measurements are used for model validation with this model glacier sensitivity to climate change can be separately evaluated with respect to a full range of meteorological parameters whereas simpler models such as degree day models only account for temperature and precipitation we provide results for both mass balance and equilibrium line altitude ela using a generic alpine glacier the sensitivity of the ela to air temperature alone is found to be 125 m c 1 or 160 m c 1 if concurrent stefan boltzmann longwave radiation change is taken into account

late orogenic post orogenic and anorogenic granites distinction by major element and trace element chemistry and possible origins granites classified into four categories based solely on tectonics of occurrence and associated rock types also have compositional characteristics that are consistent within groups and different am

the geochemistry metasomatism and petrogenesis of the granites of the english lake district new geochemical data for the carrock threlkeld ennerdale shap skiddaw and eskdale granites of the lake district are presented and discussed with particular reference to the metasomatism and petrogenesis of the intrusions the caledonian granites of the lake district have more associated hydrothermal activity and mineralization than their equivalents north of the iapetus suture in scotland pervasive high temperature metasomatism which affects the shap skiddaw and eskdale intrusions is accompanied by remobilization of the large ionic lithophile elements k rb sr u and li and b although high field strength elements including the rare earth elements remain unaffected except near greisen and mineral veins the threlkeld intrusion appears to have suffered loss of a ba and sr during a low temperature event however there is no consistent relationship between granite composition hydrothermal activity and mineralization which could be used to support the granite cupola model for mineralization in the province rather the episodic mineralization which affects the lake district may be related more to the broad geothermal field consequent upon the emplacement of the deeper lake district batholith identified from geophysical data despite the variable metasomatic perturbations of their primary chemistry three distinct groups of intrusions can be recognized on geochemical grounds the carrock granophyre is a product of tholeiitic fractionation and the threlkeld and ennerdale bodies are more typical calc alkaline intrusions whereas the eskdale shap and skiddaw plutons show a progressive evolution towards more complex geochemical patterns suggesting decreasing hornblende but increasing plagioclase control of fractionating processes the culmination of this trend may have been the emplacement of a large high heat production granite beneath the lake district at the end of the caledonian orogeny the suggestion made on geophysical grounds that the eskdale intrusion is a cupola of the lake district batholith cannot be simply reconciled with geochemical modelling none of the lake district granites has geochemical or isotopic characteristics which are convincingly s type i e formed by partial melting of a sedimentary protolith and a model of subcrustal magmagenesis beneath an evolving arc or continental margin appears to be more appropriate

provenance of the vazante group new u pb sm nd lu hf isotopic data and implications for the tectonic evolution of the neoproterozoic brasilia belt abstract the vazante group show varied u pb provenance patterns along the basin zircon ages range from 936 to 3409 ma but paleo and mesoproterozoic terrains constitute the main sources of the original sediments the youngest population 930 ma establishes the maximum depositional age of the group sm nd t dm data show the predominance of paleoproterozoic ages 1 90 2 08 ga and also indicate some input from younger sources in rocks of the lapa formation 1 67 to 2 0 ga in the upper part of the group whereas rocks of the serra do garrote formation present the oldest model ages 2 03 to 2 76 ga hf isotopic compositions of the detrital zircons indicate that they were derived mainly from recycled paleoproterozoic crust with a minor mesoproteroic juvenile component terranes within the sao francisco craton represent the main sources of detrital sediments of this group and reinforce the interpretation that it may be a passive margin sequence developed along the western margin of the original continent however the origin of mesoproterozoic grains remains uncertain slightly younger sm nd model ages in the lapa formation however are not entirely consistent with derivation solely from the craton and may indicate contribution from younger sources such as the neoproterozoic goias magmatic arc

role of crustal thickening and extensional collapse in the tectonic evolution of the sevier laramide orogeny western united states the effects of crustal thickening and extensional collapse of continental crust combined with variations in plate convergence forces provide a coherent explanation for evolution of the cretaceous early tertiary sevier laramide orogeny crustal thickening of the sevier laramide hinterland region was triggered by the combination of compressive plate convergence forces and subduction induced conductive heating of the crust eastward progradation of the locus of sevier laramide deformation through time reflects the progressive widening of the region of crustal thickening the region of maximum crustal thickening migrated outward until about 80 to 75 ma when it encountered excessively strong lithosphere of the colorado plateau the locus of deformation was then transmitted laterally across both a hinterland that had attained maximum crustal thickness and the rigid colorado plateau into the laramide rocky mountain foreland an episode of vigorous extensional collapse of orogenically thickened crust affected the southern cordillera between about 75 and 35 ma early tertiary waning of plate convergence rates and continued subduction induced conductive heating of thickened crust allowed extensional collapse along the southern cordillera region to drive the colorado plateau block northward the result was the late laramide phase of rocky mountain foreland deformation because of this compressive deformation in the central and southern laramide rocky mountain region continued through eocene time rather than ceasing at 56 ma as it did in the northern cordillera

implications of oxygen isotope data and trace element modeling for a large scale mixing model for the columbia river basalt current debate regarding the origin of the columbia river basalt group centers on whether the considerable geochemical diversity in these basalts is the result of derivation from a heterogeneous mantle or of extensive interaction of the magmas with crustal rocks compositionally diverse rocks such as the pomona and elephant mountain members of the saddle mountains formation have identical 87 sr 86 sr ratios 0 7078 0 7080 these radiogenic rocks have nearly identical 18 o values 6 24 6 36 to those of picture gorge 6 24 the least radiogenic of the columbia river basalts 87 sr 86 sr 0 7038 this suggests that the mantle beneath the columbia plateau is heterogeneous at least with respect to sr and probably other components basalts with low 18 o values 6 19 6 36 can be found in all formations of the columbia river basalt an observation not compatible with models requiring extensive assimilation of upper crustal rocks to explain isotopic differences between formations evidence for crustal contamination for some flow rocks in the grande ronde wanapum and saddle mountains basalts does exist contamination however seems to have affected isolated members of formations rather than formations as a whole this conclusion is consistent with the results of trace element modeling which suggests that the grande ronde and saddle mountains basalts were produced as numerous independent magmas from a heterogeneous mantle the magmas ascended following independent paths some undergoing crustal contamination others not

forecasting southern california earthquakes since 1978 and 1979 california has had a significantly higher frequency of moderate to large earthquakes than in the preceding 25 years in the past such periods have also been associated with major destructive earthquakes of magnitude 7 or greater and the annual probability of occurrence of such an event is now 13 percent in california the increase in seismicity is associated with a marked deviation in the pattern of strain accumulation a correlation that is physically plausible although great earthquakes magnitude greater than 7 5 are too infrequent to have clear associations with any pattern of seismicity that is now observed the san andreas fault in southern california has accumulated sufficient potential displacement since the last rupture in 1857 to generate a great earthquake along part or all of its length

current accelerating seismic excitation along the northern boundary of the aegean microplate according to previous observations geophys res lett 27 2000 3957 the generation of large mz7 0 earthquakes in the western part of the north anatolian fault system marmara sea is followed by strong earthquakes along the northern boundary of the aegean microplate nab northwestermost anatolia northern aegean central greece ionian islands therefore it can be hypothesized that a seismic excitation along this boundary should be expected after the occurrence of the izmit 1999 earthquake m 7 6 we have applied the method of accelerating seismic crustal deformation which is based on concepts of critical point dynamics in an attempt to locate more precisely those regions along the nab where seismic excitation is more likely to occur for this reason a detailed parametric grid search of the broader nab area was performed for the identification of accelerating energy release behavior three such elliptical critical regions have been identified with centers along this boundary the first region a is centered in theeasternpartofthisboundary 40 2jn 27 2je southwestofmarmara thesecondregion b hasacenterinthemiddlepartof the boundary 38 8jn 23 4je east central greece and the third region c in the westernmost part of the boundary 38 2jn 20 9je ionian islands the study of the time variation of the cumulative benioff strain in two of the three identified regions a and b revealed that intense accelerating seismicity is observed especially after the occurrence of the 1999 izmit mainshock therefore it can be suggested that the seismic excitation at least in these two regions has been triggered by the izmit mainshock estimations of the magnitudes and origin times of the expected mainshocks in these three critical regions have also been performed assuming that the accelerating seismicity in these regions will lead to a critical point that is to the generation of mainshocks

the o okiep copper district namaqualand south africa a review of the geology with emphasis on the petrogenesis of the cupriferous koperberg suite the o okiep copper district is the oldest formal mining area in south africa between 1852 and 2002 the 2 500 km2 area yielded two million tons of copper from 32 mines ranging in ore tonnages from 140 000 to 37 million tons this paper summarizes the calendar of events from the formation of the first primitive crust 1 700 2 000 ma ago to early cambrian times 500 ma ago with particular emphasis on the namaquan grenville orogeny notably the o okiepian episode 1 180 1 210 ma ago of alpine type folding regional granite plutonism and granulite facies metamorphism and the klondikean episode 1 020 1 040 ma ago of open and tight folding and the intrusion of the rietberg granite and the koperberg suite almost all of the copper in the o okiep district occurs in the koperberg suite of which there are 1 700 small bodies that constitute 0 7 of the outcrop area the suite comprises jotunite anorthosite biotite diorite and hypersthenic rocks ranging from leuconorite to hypersthenite and it is one of only two world examples of economic copper mineralization in rocks of the anorthosite charnockite kindred the second example is caraiba brazil high isr and low end for a 1 030 ma intrusion age and high 2 of 10 1 for koperberg rock types indicate a crustal progenitor for the suite and the presence of jotunite suggests a subducted crustal source at ca 40 50 km depth the magmatic sulphide paragenesis in the koperberg suite is chalcopyrite pyrrhotite narrap type ore that in a number of ore bodies has been inverted under upper amphibolite facies conditions to bornite ti free magnetite carolusberg type ore meteoric fluids resulted in supergene cu enrichment in koperberg bodies to 500 m below the pre nama peneplane and lower greenschist facies metamorphism 500 570 ma ago is reflected by inter alia hoits type ore bearing second generation bornite chalcopyrite covellite chalcocite

crustal deformation in the central ionian islands greece results from dgps and dinsar analyses 1995 2006 abstract ground deformation studies based on differential gps dgps and differential interferometric sar dinsar analyses have been conducted in the seismically active area of the central ionian islands local gps networks were installed in cephallonia 2001 and zakynthos 2005 the cephallonian network has been remeasured five times and zakynthos once as of july 2006 the studies have yielded detailed information regarding both local and regional deformations that are occurring in the area for lefkas island dinsar analysis march to september 2003 revealed 56 mm of uplift in the central and western parts and is attributed to the august 2003 earthquake mw 6 3 that occurred offshore to the west synthetic dinsar modelling of the magnitude and extent of deformation is consistent with the seismologically deduced parameters for the ruptured segment along the lefkas transform fault subsidence for cephallonia island dinsar analysis 1995 to 1998 indicated ground deformation up to 28 mm located in small sections of the island further interferometric analysis for the period 2003 to 2004 encompassing the occurrence of the lefkas earthquake in august 2003 indicated 28 mm of uplift in the northern part while during the next two years 2004 to 2005 further uplift of at least 56 mm had taken place at the western and northern part of the island dgps measurements for the period 2001 to 2006 revealed a clockwise rotation of the island with respect to a centrally located station on aenos mt the horizontal component of deformation generally ranged from 6 to 34 mm with the largest values at the western and northern parts of the island considering the vertical deformation two periods are distinguished the first one 2001 to 2003 is consistent with anticipated motions associated with the main geological and tectonic features of the island the second one 2003 to 2006 has been tentatively attributed to dilatancy in which relatively small uplift 20 40 mm occurred along the southern and southeastern parts of the island while larger magnitudes 50 mm happened at the western part paliki peninsula these large magnitudes of uplift over an extended area 50 km in conjunction with an accelerated benioff strain determined from the analysis of the seismicity in the broader region are consistent with dilatancy this effect commenced some time after 2003 and is probably centered in the area between zakynthos and cephallonia if this interpretation is correct it may foreshadow the occurrence of a very strong earthquake s sometime during 2007 to 2008 in the above designated region

new observational information on the precursory accelerating and decelerating strain energy release recent reliable data are used to study the behavior of seismic activity before 46 strong shallow earthquakes m 6 0 which correspond to five complete samples of mainshocks these samples include 6 mainshocks m 6 0 7 1 that occurred in western mediterranean since 1980 17 mainshocks m 6 0 7 2 which occurred in the aegean greece and surrounding area since 1980 5 mainshocks m 6 4 7 5 that occurred in anatolia since 1980 12 mainshocks m 6 0 7 3 that occurred in california since 1980 and 6 mainshocks m 7 0 8 3 that occurred in japan since 1990 in all 46 cases a similar precursory seismicity pattern is observed specifically it is observed that accelerating benioff strain square root of seismic energy release caused by preshocks occurs in a broad circular region critical region with a radius about eight times larger than the fault length of the mainshock in agreement with results obtained by various research groups during the last two decades however in a much smaller circular region seismogenic region with a radius about four times the fault length the corresponding preshock strain decelerates with the time to the mainshock the time variation of the strain follows in both cases a power law but the exponent power is smaller than unit m 0 3 in the case of the accelerating preshock strain and larger than unit m 3 0 in the case of the decelerating preshock strain predictive properties of this decelerating in accelerating out strain model are expressed by empirical relations the possibility of using this model for intermediate term earthquake prediction is discussed and the relative model uncertainties are estimated

mixing of magmatic hydrothermal and metamorphic fluids and the origin of peribatholitic sn vein type deposits in rwanda abstract the fluid sources of granite related sn quartz vein deposits are commonly obscured by fluid mixing or fluid rock interactions as a result fluid inclusions minerals and isotopes in these veins indicate an intermediate composition between magmatic and metamorphic but the degree of mixing between these endmembers is currently unquantified this study presents a novel quantitative approach to assess the degree of mixing between magmatic hydrothermal and external metamorphic fluids in the formation of peribatholitic sn quartz veins in particular fluid mixing in the sn mineralized rwamagana musha ntunga pegmatite quartz vein field in east rwanda has been evaluated by the following four methods quartz stable isotopes muscovite geochemistry fluid inclusion microthermometry and la icp ms and geochemical modelling the quartz stable isotope data 18o 13 1 to 15 8 v smow d 27 6 to 59 7 v smow cannot uniquely differentiate between a metamorphic fluid origin or an initial magmatic hydrothermal fluid origin with subsequent metamorphic fluid mixing or host rock interaction however granitophile element concentrations in magmatic muscovite from pegmatites and hydrothermal muscovite from associated sn quartz veins are equally high indicating a close genetic link rb 530 8740 ppm li 110 1990 ppm sn 87 810 ppm cs 62 420 ppm primary h2o co2 n2 nacl medium saline magmatic fluid inclusions in quartz of pegmatites 12 7 wt nacleq and h2o co2 n2 nacl low saline fluid inclusions in barren metamorphic quartz veins 4 9 wt nacleq were analyzed by la icp ms these results show an enrichment in li rb sn and cs for the magmatic fluid while the metamorphic fluid is characterized by low granitophile element concentrations and high sr and ba contents the expected rb cs and rb sn signature of the sn quartz vein muscovite was modelled using the measured fluid endmember compositions confirming mixing between magmatic and metamorphic fluids in the formation of the veins the quantification suggests that the hydrothermal sn quartz vein fluid contains 5 80 of an external metamorphic fluid component

sr and nd isotopic compositions age and petrogenesis of a type granitoids of the vernon supersuite new jersey highlands usa abstract voluminous late mesoproterozoic monzonite through granite of the vernon supersuite underlies an area of approximately 1300 km2 in the highlands of northern new jersey the vernon supersuite consists of hastingsite biotite bearing granitoids of the byram intrusive suite bis and hedenbergite bearing granitoids of the lake hopatcong intrusive suite lhis these rocks have similar major and trace element abundances over a range of sio2 from 58 to 75 wt are metaluminous to weakly peraluminous and have a distinctive a type chemistry characterized by high contents of y nb zr lree and ga al ratios and low mgo cao sr and hree whole rock rb sr isochrons of bis granite yield an age of 1116 41 ma and initial 87 sr 86 sr ratio of 0 70389 and of lhis granite an age of 1095 9 ma and initial 87 sr 86 sr ratio of 0 70520 both suites have similar initial 143 nd 144 nd ratios of 0 511267 to 0 511345 bis and 0 511359 to 0 511395 lhis values of end are moderately high and range from 1 21 to 2 74 in the bis and 2 24 to 2 95 in the lhis petrographic evidence field relationships geochemistry and isotopic data support an interpretation of comagmatism and the derivation of both suites from a mantle derived or a juvenile lower crustal parent with little crustal assimilation both suites crystallized under overlapping conditions controlled by p t fh2o lake hopatcong magma crystallized at a liquidus temperature that approached 900 c and a pressure of about 6 kbar and remained relatively anhydrous throughout its evolution initial p t conditions of the byram magma were 850 c and about 5 5 kbar bis magma was emplaced contemporaneous with or slightly preceding lhis magma and both magmas were emplaced during a compressional tectonic event prior to granulite facies metamorphism that occurred in the highlands between 1080 and 1030 ma

global observational properties of the critical earthquake model the preshock critical regions of 20 mainshocks with magnitudes between 6 4 and 8 3 which occurred recently since 1980 in a variety of seismotectonic regimes greece anatolia himalayas japan california were identified and investigated all these strong earthquakes were preceded by accelerating time to mainshock seismic crustal deformation benioff strain the time variation of the cumulative benioff strain follows a power law with a power value m 0 3 in very good agreement with theoretical considerations we observed that the dimension of the critical region increased with increasing mainshock magnitude and with decreasing long term seismicity rate of the region an increase of the duration of this critical preshock phenomenon with decreasing long term seismicity rate was also observed this spatial and temporal scaling expresses characteristics of the critical earthquake model which are of importance for earthquake prediction research we also showed that the critical region of an oncoming mainshock coincides with the preparing region of this shock where other precursory phenomena can be observed

mountain snow distribution governed by an altitudinal gradient and terrain roughness 1 the heterogeneous mountain snow cover is challenging the eye and the analytical mind of the observer the snow distribution affects water resources natural hazards such as avalanches and ecology while a lot of recent research has helped to better understand this snow distribution and the processes that cause the heterogeneity it has not yet been possible to predict snow distribution satisfactorily on the basis of terrain parameters alone we present a model of the mean snow depth in topographic control units as a function of two terrain parameters the conventional elevation plus a fractal roughness parameter for this we used a unique data set of high resolution measurements of snow depth from an airborne laser scanner the model captures the heterogeneous snow distribution by merely analysing the terrain and the mean precipitation this unusually simple relationship holds for clusters of the snow depths of small topographical units by applying fractal analysis we describe the roughness of the terrain and use this parameter for the prediction of snow deposition rougher terrain holds less snow than smoother terrain this finding is important not only for avalanche warning or eco hydrological applications but also for reliably predicting how snow water storage may change in the light of the pronounced climate change already ongoing in mountain regions

seismicity trends and potential for large earthquakes in the alaska aleutian region the high likelihood of a gap filling thrust earthquake in the alaska subduction zone within this decade is indicated by two independent methods analysis of historic earthquake recurrence data and time to failure analysis applied to recent decades of instrumental data recent may 1993 earthquake activity in the shumagin islands gap is consistent with previous projections of increases in seismic release indicating that this segment along with the alaska peninsula segment is approaching failure based on this pattern of accelerating seismic release we project the occurrence of one or morem 7 3 earthquakes in the shumagin alaska peninsula region during 1994 1996 different segments of the alaska aleutian seismic zone behave differently in the decade or two preceding great earthquakes some showing acceleration of seismic release type a zones while others show deceleration type d zones the largest alaska aleutian earthquakes in 1957 1964 and 1965 originated in zones that exhibit type d behavior type a zones currently showing accelerating release are the shumagin alaska peninsula delarof and kommandorski segments time to failure analysis suggests that the large earthquakes could occur in these latter zones within the next few years

a chronostratigraphic framework for the north central kaapvaal craton the bushveld complex and the vredefort structure abstract sufficient geochronological data are available pertaining to the north central part of the kaapvaal craton to construct a chronostratigraphic framework for the rock units involved in the vredefort event from the basement rocks at 3170 ma to the waterberg soutpansberg groups deposited between 2025 and 1425 ma the resulting framework forms a convenient chronological guide to the geological evolution of this area and the timing of events such as that at vredefort the basement on which the supracrustal rocks were deposited stabilised from 3170 to 3060 ma but metamorphism and metasomatism of these rocks occurred up to 2800 m y ago in different parts of the craton the first unit of the wits triad the volcaniclastic dominion group was deposited at 3060 ma on the stabilising basement this was followed by the dominantly clastic witwatersrand supergroup and the overlying ventersdorp supergroup the dominantly volcanic ventersdorp rocks are 2700 m y old and form the last unit of the wits triad a considerable time gap of 200 300 ma separates the triad from the lowermost units of the overlying transvaal sequence the age of these volcanic and clastic protobasinal rocks is poorly constrained between 2500 and 2300 ma they may in fact represent eroded remnants of a more extensive depositional cycle the mainly clastic sedimentary part of the transvaal sequence pretoria group has been dated at 2224 ma the upper part of the transvaal sequence rooiberg group is only constrained by the age of the intrusive bushveld complex the bushveld basic layered rocks are well dated at 2060 ma as are the subsequent granites at 2050 ma the vredefort event which post dates the bushveld complex is reasonably well constrained by the age of the bronzite granophyre at 2000 ma deposition of the waterberg and soutpansberg groups which post date the bushveld complex is poorly constrained between the age of the bushveld granites and younger alkaline intrusives at 1425 ma but these sediments and volcanics were probably formed between 2025 and 1752 ma the waterberg group may therefore contain debris from the vredefort structure

intermediate term earthquake prediction using precursory events in the new madrid seismic zone abstract earthquake prediction may be possible for some mainshock events the time to failure method described by varnes 1989 and bufe and varnes 1990 uses precursory events foreshocks to define an accelerated energy release curve by fitting an equation to the data a predicted time of failure and magnitude can be calculated until recently this method has been used in only a few studies in tectonically active areas and for moderate to large magnitude mainshock events using the microearthquake network data set from the new madrid seismic zone nmsz which is reasonably complete for earthquakes of magnitude 1 5 in the area of interest the method has yielded predicted values of past events as small as m b 3 5 the network data set used in this evaluation covers the time interval from 29 june 1974 to 20 july 1995 for the nmsz there have been 36 earthquakes of magnitude 3 5 over the 21 yr period in which the network has been operating because precursory events are required for the application of the time to failure method mainshocks that occurred before 1980 do not have enough data to adequately define the accelerated energy release curve therefore we utilized the 26 earthquakes that occurred after 1980 and that had a magnitude 3 5 sixteen of the 26 mainshock events were modeled in most cases the precursory sequences yielded predicted times of failure and magnitudes that were reasonably close to the actual mainshock values the remaining mainshocks including those occurring before 1980 could not be modeled due to either 1 not enough events to adequately define the precursory sequence or 2 interfering events that disrupt the accelerated energy release curve in addition two events were modeled from the nuttli catalog nuttli 1979 along with one that used a combination of both catalogs nineteen earthquakes with magnitudes 3 5 were evaluated using the time to failure method the first calculation using the time to failure method gave predicted results with large error bounds essentially no upper bound on the predicted magnitude an empirical relationship between parameters has helped to constrain the range of the predicted magnitude and to a lesser extent the estimated time of failure this relationship modifies the time to failure equation and yields predicted values for magnitudes that have an upper limit another empirical relationship suggests that the logarithm of the moment of the mainshock increases linearly with the logarithm of the size of the precursory event search diameter the relative seismicity of the region also influences the optimum search diameter used to find precursory events in addition to the evaluation of the acceleration sequences associated with the mainshocks an analysis of the occurrence of false positive acceleration sequences acceleration sequences that do not end in a mainshock was conducted the preliminary false positive analysis was conducted by randomly selecting potential mainshock locations the results yielded a false positive acceleration sequence occurrence rate of 2 with the incorporation of the empirical relationships into the time to failure method the potential for future intermediate term earthquake predictions for the nmsz is encouraging

structural controls of fluid flow and gold mineralization in the easternmost parts of the karagwe ankole belt of north western tanzania abstract gold mineralization in the biharamulo region of western tanzania is confined to the sheared low angle basement cover contact between archaean basement gneisses of the tanzania craton and the structurally overlying low grade metamorphic metasediments of the mesoproterozoic karagwe ankole belt regional scale fluid flow along this detachment is indicated by the pervasive silicification and retrogression of wall rocks to pervasively foliated phyllonites and pyritization of particularly metasediments commonly graphite rich in the hanging wall of the shear zone gold mining centres on specific structural sites along the detachment but also in stratigraphically higher sections in the structurally overlying metasediments zones of gold mineralization along the detachment correlate with ne trending ramp structures dip angles 20 35 that are most ideally orientated for slip and reactivation within the low angle phyllonitic detachment repeatedly overprinted auriferous quartz vein stockworks in quartzofeldspathic gneisses immediately below the detachment indicate brittle fracturing of the competent footwall lithotypes during slip along the weaker detachment in cases of massive silicification up to 50 m thick quartz blows are formed along the contacts between detachment phyllonites and footwall gneisses the multiple overprinting relationships of successive quartz vein generations in these zones of massive silicification suggests that the quartz blows acted as competent blocks in the weak detachment causing the repeated overprint of earlier silicification by later fracturing and quartz veining events gold mineralization above the detachment and in stratigraphically higher metasediments is closely associated with fold structures that form part of the low grade metamorphic fold and thrust belt veining is particularly abundant in competent lithotypes such as quartzite and chemically reactive ferruginous mafic sills overprinting relationships between quartz vein sets illustrate fluid flow during fold amplification and importantly the final lock up stage of folds during which much of the mineralization was introduced oxygen isotope values for quartz veins indicate fluids were likely derived from clastic mainly metapelitic sedimentary sequences of the karagwe ankole fold belt the data also implies that the partially reworked archaean granitoid greenstone basement of the tanzania craton has not contributed to the fluid evolution and possibly gold mineralization the extent 100 km of the basement cover detachment and associated alteration is indicative for a regional scale fluid system gold mineralization is however controlled by local structures and lithological contrasts that require the detailed mapping and sampling of the regional structure

the ages of the kabanga north and kapalagulu intrusions western tanzania a reconnaissance study the kabanga north and kapalagulu intrusions form part of a 500 km belt of intrusions within the kibaran orogenic belt of central africa some of the intrusions within the belt host important ore deposits notably ni sulfides at kabanga and ni laterites at musongati and kapalagulu despite the economic significance of the intrusions their ages have remained unclear here we present shrimp ii u pb zircon ages interpreted as magmatic ages of crystallization for the kabanga north intrusion 1403 14 ma and for the kapalagulu intrusion 1392 26 ma these data along with other geochronological and petrological data support a model of a broadly coeval and cogenetic suite of mafic ultramafic intrusions throughout the kibaran orogenic belt from northwest tanzania through burundi and possibly as far south as the democratic republic of congo

predictive modeling of the seismic cycle of the greater san francisco bay region the seismic cycle for the san francisco bay region is synthesized by a model combining the pre and post 1906 seismic histories the long term acceleration of seismic release seismic moment benioff strain release or event count in the seismic cycle and the shorter term accelerations preceding the larger earthquakes within that cycle are modeled using an empirical predictive technique called time to failure analysis in which rate of seismic release is proportional to an inverse power of the remaining time to failure the exponent of time to failure in the accelerating sequences appears to be scale invariant and the length of the full cycle is estimated at 269 50 years the 1989 loma prieta earthquake which is the culmination of the first subcycle in the present long term seismic cycle should have been predictable with an uncertainty of 2 years in time and 0 5 in magnitude although the specific location at loma prieta was not predictable by this technique if our model is correct and if the loma prieta earthquake is the culmination of a subcycle the san francisco bay region should be entering a relatively long 20 50 years period of seismic quiescence above magnitude 6 a great earthquake such as the 1906 san francisco event would appear to be more than a century in the future

mineralogical and geochemical study of the rare earth element mineralization at gakara burundi abstract the rare earth element ree mineralization of gakara burundi has first been discovered in 1936 and has periodically been the subject of geological studies at times when the exploitation of bastnasite ce and monazite ce was economically interesting this study focuses on the establishment of a mineral paragenesis for gakara with special attention to the ree bearing phases to understand the formation history of the deposit the paragenesis can be subdivided into 3 stages primary ore deposition brecciation stage and supergene alteration evidence for fenitization processes i e pinkish red cathodoluminescence of k feldpar brecciation stage and the strong enrichment of light rees in bastnasite and monazite substantiate the hypothesis of a structurally controlled hydrothermal mineralization with a strong carbonatitic affinity this likely confirms the association of the gakara ree deposit with the neoproterozoic alignment of alkaline complexes and carbonatites along the present day western rift it suggests a direct link with a currently unidentified carbonatitic body at depth possibly derived from a predominantly metasomatized lithospheric mantle

earthquake rupture as a critical point consequences for telluric precursors abstract earthquakes are related to rupture phenomena in complex statistical systems of cracks we first review some available information suggesting that rupture in earthquakes is a critical point the consequences of this hypothesis on several phenomena are then discussed in particular we focus our attention on a simple theory of electroseismic activity based on mechano electrical transduction effects such as the piezoelectric or the pressure induced polarization effect the neighbourhood of the rupture threshold is characterized by a specific response which could correspond to telluric wave activity observed as precursors of earthquakes

exhumation of high pressure rocks a review of concepts and processes the exhumation of high pressure metamorphic rocks requires either the removal of the overburden that caused the high pressures or the transport of the metamorphic rocks through the overburden exhumation cannot be achieved simply by thrusting or strike slip faulting it may be caused by erosion of shortened and thickened crust but this is unlikely to be the only mechanism for exhuming rocks from depths greater than about 20 km one or more of the following additional mechanisms may be involved 1 corner flow of low viscosity material trapped between the upper and lower plates in a subduction zone can cause upward flow of deeply buried rock and may explain some occurrences of high pressure tectonic blocks in melange this process does not however appear to be adequate to explain the exhumation of regional high pressure terrains 2 buoyancy forces acting directly on metamorphic rock bodies may cause them to rise relative to more dense surroundings this is likely to be the most important mechanism of exhumation of crustal rocks subducted into the mantle but cannot explain the emplacement of coherent tracts of high density metamorphic rock into shallow crustal levels some high pressure blocks emplaced at shallow levels in accretionary terrains may have been entrained in diapiric intrusions of low density mud or serpentinite 3 extension driven by the forces associated with contrasts in surface elevation may explain the exhumation and structural setting of many high pressure terrains extension may occur in the upper part of an accretionary wedge thickened by underplating or it may affect the whole lithosphere in a region of intracontinental convergence if surface elevation has been increased by the removal of a lithospheric root in the second case extension may be accompanied by magmatism and an evolution towards higher temperature during decompression of the metamorphic terrain

decelerating precursory seismicity in vrancea abstract preshock seismic excitation followed by seismic quiescence has been observed in the seismogenic region of strong shallow mainshocks the strain released by such preshocks is decelerating with the time to the mainshock and is fitted by a power law with a power value larger than unit this model is tested in the present work for the intermediate depth earthquakes of the vrancea region generated in an isolated seismogenic zone proper for such testing a backward application of this decelerating preshock strain model for the case of 4 3 1977 m 7 5 earthquake for which reliable data are available shows a good fit of the power law pattern to the seismic activity preceding the main shock the occurrence rate of recent intermediate depth shocks in vrancea indicates that this region is currently in a state of decelerating seismic deformation which may lead to the generation of a strong intermediate depth mainshock there at about the beginning of the third decade of the present century the respective uncertainties are unknown due to lack of previous relative studies