relocation and assessment of seismicity in the iran region summary more than 2000 instrumentally recorded earthquakes occurring in the iran region during the period 1918 2004 have been relocated and reassessed with special attention to focal depth using an advanced technique for 1 d earthquake location a careful review of starting depths association of teleseismic depth phases and the effects of reading errors on these phases are made and when necessary waveforms have been examined to better constrain ehb focal depths uncertainties in ehb epicentres are on the order of 10 15 km in the iran region owing to the earth s lateral heterogeneity and uneven station distribution uncertainties of reviewed ehb focal depth estimates are on the order of 10 km as compared to about 4 km for long period p and sh body waveform inversions nevertheless these ehb depth estimates are sufficiently accurate to resolve robust differences in focal depth distribution throughout the iran region and within their errors show patterns that are in agreement with the smaller number of earthquakes whose depths have been confirmed by body wave modelling or local seismic networks the importance of this result is that future earthquakes with apparently anomalous depths can easily be identified and checked if necessary most earthquakes in the iranian continental lithosphere occur in the upper crust with the crustal shortening produced by continental collision accommodated entirely by thickening and distributed deformation in the zagros mountains nearly all earthquakes are confined to the upper crust depths 20 km and there is no evidence for a seismically active subducted slab dipping ne beneath central iran by contrast in southeastern iran where the arabian seafloor is being subducted beneath the makran coast low level earthquake activity occurs in the upper crust as well as to depths of at least 150 km within a northward dipping subducting slab near the oman line a region transitional between the zagros and the makran seismicity extends to depths of up to 30 45 km in the crust consistent with low angle thrusting of arabian basement beneath central iran in north central iran along the alborz mountain belt seismic activity occurs primarily in the upper crust but with some infrequent events in the lower crust particularly in the western part of the belt the talesh where the south caspian basin underthrusts nw iran earthquakes that occur in a band across the central caspian following the apscheron balkhan sill between azerbaijan and turkmenistan have depths in the range 30 100 km deepening northwards these are thought to be connected with either incipient or remnant northeast subduction of the south caspian basin basement beneath the east west trending apscheron balkhan sill curiously in this region of genuine mantle seismicity there is no evidence for earthquakes shallower than 30 km

region specific key seismic parameters for earthquakes in northern iran strong motion accelerograms recorded within northern iran are used to examine the propagation characteristics of shear wave including geometric spreading behavior q value j 0 and horizontal to vertical h v ratio these region specific key seismic parameters are estimated from 259 three component records of 22 earth quakes with magnitude ranging from m 4 9 to m 7 4 in northern iran the geometric spreading follows a trilinear behavior with a strong postcritical reflection from the moho the first and second hinges of the trilinear behavior are at 75 and 150 km respectively the associated q value based on the vertical component is q 87 f 1 46 j0 value for vertical and horizontal components are 0 03 and 0 05 respec tively because of lack of station specific site information the h v ratio is considered to be a rough estimation of generic site amplification the obtained region specific parameters are used to estimate the average stress drop based on three stochastic modeling approaches stochastic point source modeling suggests a brune stress drop of 125 bars whereas stochastic finite fault modeling based on static and dynamic corner frequency approaches suggests a stress drop of 68 bars

rare earth thhfta and large ion lithophile element variations in metabasites from the proterozoic amphibolite granulite transition zone at arendal south norway abstract the proterozoic arendal metabasites are minor intrusions which possess wholly metamorphic textures and mineral assemblages data are presented for eight selected samples chondrite normalised ree patterns are relatively flat between 10 and 20 chondrite abundances they are characterised by 1 ce n yb n n nd n 1 normalised to primordial mantle values the incompatible elements reveal variable enrichment in the large ion lithophile elements except th and low ta they are similar to many destructive plate margin basalts on a th hf ta diagram the rocks plot in a sub linear trend reflecting variation in th hf samples with high th hf ratios come from the zone of highest metamorphic grade where the host gneisses are deficient in th consequently the patterns in the metabasites could not have been produced by any secondary metamorphic fractionation or by bulk contamination by the country rocks there is no evidence for any post magmatic mobility of any of the elements except rb which is depleted in the highest grade rocks relative to their lower grade counterparts the trace element distributions are largely reflecting those of the parental magmas but consideration of bulk distribution coefficients shows how they may have been modified in some aspects e g ce n nd n by the imposition of the metamorphic mineralogies the data are consistent with a model involving a derivation from a mantle source region which had been affected by subduction related hydrous metasomatism or partial melting and b crystallisation of the magmas directly under the high grade conditions

stochastic simulation of strong motion records from the 2012 ahar varzaghan dual earthquakes northwest of iran here the generalized inversion of s wave amplitude spectra is employed for deriving the site response and s wave attenuation quality factor in the northwest region of iran a total of 279 strong motion accelerograms recorded at distances below 200 km from 41 earthquakes with moment magnitudes ranging from m w 3 8 to 6 5 are used to determine the region speci c attenuation model the site responses have been determined for all 54 stations individually the bulk of strong motion data i e 184 records comes from the 2012 ahar varzaghan dual earthquakes in northwest iran and their aftershocks also the modified finite fault method which is able to model nonuniform stress distribution on the fault plane is employed to investigate the coseismic stress parameter for the first and second ahar varzaghan dual earthquakes by minimizing the difference between the synthesized and observed pseudospectral accelerations for 5 damping results denote a concentration of stress drops on the northwestern part of the first event s fault and on the central and eastern part of the second fault stochastic simulations using the calibrated stress distribution have been performed on a regular grid covering the study area for both rock and soil site conditions in total 651 points the results show that the maximum of peak ground accelerations pgas during the ahar varzaghan dual earthquakes for the rock site condition reached 557 cm s s and the largest peak ground velocities pgvs were estimated around 76 cm s in general comparisons between simulated data and empirical ground motion prediction equations gmpes show that the stochastic predictions pgas and pgvs are higher than those predicted by the empirical gmpes for distances less than 30 km and are smaller for distances more than 30 km the simulated data are also consistent with the modi ed mercalli intensity observations and show reasonable agreement this can be considered as another validation of the method

a ground motion predictive model for iran and turkey for horizontal pga pgv and 5 damped response spectrum investigation of possible regional effects we present a ground motion prediction equation gmpe for turkey and iran to investigate the possible regional effects on ground motion amplitudes in shallow active crustal earthquakes the proposed gmpe is developed from a subset of the recently compiled strong motion database of the earthquake model of the middle east region project see data and resources 1 a total of 670 turkish and 528 iranian accelerograms with depths down to 35 km are used to estimate peak ground acceleration peak ground velocity and 5 damped elastic pseudospectral acceleration ordinates of 0 01 s t 4 s the moment magnitude range of the model is 4 m w 8 and the maximum joyner boore distance is r jb 200 km the functional form considers three major fault mechanisms strike slip normal and reverse the nonlinear soil behavior is a function of v s 30 average shear wave velocity in the upper 30 m of soil profile our observations from empirical and estimated ground motion trends advocate regional differences in the territories covered by iran and turkey that originate from the differences in q factors kappa and near surface velocity profiles these factors eventually affect the magnitude and distance dependent scaling of spectral amplitudes in iran and turkey in essence the ground motion amplitudes of these two neighboring countries would draw patterns different than the ground motion estimates of gmpes developed from the strong motion databases of shallow active crustal earthquakes from multiple countries online material matlab code and regression coefficients for computing the response spectrum and distance scaling 1 sec 7

oxide and sulphide minerals in highly oxidized rb depleted archaean granulites of the shevaroy hills massif south india oxidation states and the role of metamorphic fluids the shevaroy hills of northern tamil nadu southern india expose the highest grade granulites of a prograde amphibolite facies to granulite facies deep crustal section of late archaean age these highly oxidized quartzofeldspathic garnet charnockites generally show minor high tio2 biotite and amphibole as the only hydrous minerals and are greatly depleted in the incompatible elements rb and th peak metamorphic temperatures garnet orthopyroxene and pressures garnet orthopyroxene plagioclase quartz are near 750 degrees c and 8 kbar respectively pervasive veinlets of k feldspar exist throughout dominant plagioclase in each sample and show clean contact with orthopyroxene they are suggested to have been produced by a low h2o activity migrating fluid phase under granulite facies conditions most likely a concentrated chloride carbonate brine with high alkali mobility accompanied by an immiscible co2 rich fluid silicate oxide and sulphide mineral assemblages record high oxygen fugacity pyroxenes in the felsic rocks have high mg mg fe 0 5 0 7 the major oxide mineral is ilmenite with up to 60 mole per cent exsolved hematite utilizing three independent oxygen barometers ferrosilite magnetite quartz ferrosilite hematite quartz and magnetite hematite in conjunction with garnet orthopyroxene exchange temperatures samples with x hm ilm 0 1 yield a consistent oxygen fugacity about two log units above fayalite stability less oxidized samples x hm ilm 0 4 pyrite is the dominant sulphide and pyrrhotite is absent pyrite grains in these samples have marginal alteration to magnetite along the rims signifying a high temperature oxidation event moderately oxidized samples 0 1 x hm ilm 0 4 have abundant co existing pyrrhotite pyrite and magnetite the most reduced granulite samples have pyrrhotite as the dominant sulphide with little or no pyrite and no coexisting magnetite chalcopyrite is a common accessory mineral of pyrite and pyrrhotite in all the samples textures in some samples suggest that it formed as an exsolution product from pyrrhotite extensive vein networks of magnetite and pyrite associated principally with the pyroxene and amphibole give evidence for a pervasive highly oxidizing fluid phase thermodynamic analysis of the assemblage pyrrhotite pyrite and magnetite yields consistent high oxidation states at 700 800 degrees c and 8 kbar the oxygen fugacity in our most oxidized pyrrhotite bearing sample is 10 12 65 bar at 770 degrees c there are strong indications that the shevaroy hills granulites recrystallized in the presence of an alkali rich low h2o activity fluid probably a concentrated brine it cannot be demonstrated at present whether the high oxidation states were set by initially oxidized protoliths or effected by the postulated fluids the high correspondence of maximally rb depleted samples with the highest recorded oxidation states suggests that the rb depletion event coincided with the oxidation event probably during breakdown of biotite to orthopyroxene k feldspar we speculate that these alterations were effected by exhalations from deep seated alkali basalts which provided both heat and high oxygen fugacity low a h2o fluids it will be of interest to determine whether greatly rb depleted granulites in other precambrian terranes show similar highly oxidizing signatures

sea99 a revised ground motion prediction relation for use in extensional tectonic regimes we present sea99 a revised predictive relation for geometric mean horizontal peak ground acceleration and 5 damped pseudovelocity response spec trum appropriate for estimating earthquake ground motions in extensional tectonic regimes which we demonstrate to have lower ground motions than other tectonic regimes sea99 replaces sea96 a relation originally derived by spudich et al 1996 1997 the data set used to develop sea99 is larger than that for sea96 and minor errors in the sea96 data set have been corrected in addition a one step regression method described by joyner and boore 1993 1994 was used rather than the two step method of joyner and boore 1981 sea99 has motions that are as much as 20 higher than those of sea96 at short distances 5 30 km and sea99 s motions are about 20 lower than sea96 at longer periods 1 0 2 0 sec and larger distance 40 100 km sea99 dispersions are significantly less than those of sea96 sea99 rock motions are on the average 20 lower than motions predicted by boore et al 1994 except for short distances at periods around 1 0 sec where sea99 motions exceed those predicted by boore et al 1994 by as much as 10 com parison of ground motions from normal faulting and strike slip events in our data set indicates that normal faulting horizontal ground motions are not significantly different from extensional regime strike slip ground motions

petrologic evidence for k feldspar metasomatism in granulite facies rocks abstract we present evidence for k feldspar metasomatism in charnockitic granulites from two well known terranes the shevaroy hills massif s india 750 c 8 kbars and the bamble sector s e norway 790 c 7 5 kbars in the form of k feldspar veins principally along plagioclase and quartz grain boundaries and in the form of highly variable antiperthitic patches of k feldspar in an uneven scattering of plagioclase grains with one exception orthopyroxene or amphibole grains in contact with these k feldspar veins show no alteration to secondary biotite indicating that the h 2 o activity of the fluids responsible for these veins must have been relatively low a high ba concentration in these veins also suggests a metasomatic origin point counted back scattered electron photomicrographs along with microprobe analyses provide reintegrated k feldspar and plagioclase compositions for 8 to 12 predetermined random areas per thin section for three samples from bamble and three samples from the shevaroy hills these reintegrated feldspar compositions plot over a range of temperatures on the feldspar ternary for each sample and indicate saturation temperatures above the mean temperature for either region with a few reintegrated compositions above the 1000 c isotherm and with the lower cut off temperatures at 700 c and 600 c for the shevaroy and bamble samples respectively these patterns suggest that exsolution alone could not have been responsible for the formation of the k feldspar veins and patches in these rocks we suggest that these veins are due to the influx of complex supercritical low h 2 o activity brines shortly after peak metamorphic conditions that this influx continued during the initial phases of post peak metamorphic uplift and that these fluids represent the first stage in a series of fluid influxes in which the h 2 o activity increased as uplift continued reaction of these brines with potassium undersaturated plagioclase grains formed k feldspar veins along grain boundaries and fractures as well as diffusing into the plagioclase which became supersaturated and exsolved k feldspar as antiperthite patches during uplift and cooling formation of secondary biotite halos around orthopyroxene in one sample associated with these k feldspar veins can be explained by heightened h 2 o activity in the brines due to enrichment in h 2 o emplacement of the veins at lower pressure during uplift or both compared to the other shevaroy and bamble samples

aftershock decay rates in the iranian plateau motivated by the desire to have more information following the occurrence of damaging events the main purpose of this article is to study aftershock sequence parameters in the iranian plateau to this end the catalogue of the iranian earthquakes between 2002 to the end of 2013 has been collected and homogenized among which 15 earthquakes have been selected to study their aftershock decay rates for different tectonic provinces the completeness magnitudes mc of the earthquake catalogue have been calculated in different time intervals also the mc variability in spatial and temporal windows has been determined for each selected event for major iranian earthquakes catalogue of aftershocks has been collected thanks to three declustering methods first the classical windowing method of gardner and knopoff bull seismol soc am 64 1363 1367 1974 second a modified version of this using spatial windowing based on the wells and coppersmith bull seismol soc am 84 974 1002 1994 relations and third the burkhard and grunthal swiss j geosci 102 149 188 2009 scheme effects of the temporal windows also have been investigated using the time periods of 1 month 100 days and 1 year in the declustering method of gardner and knopoff bull seismol soc am 64 1363 1367 1974 in the next step the modified omori law coefficients have been calculated for the 15 selected earthquakes the calibrated regional generic model describing the temporal and magnitude distribution of aftershocks is of interest for time dependent seismic hazard forecasts the regional characteristics of the aftershock decay rates have been studied for the selected iranian earthquakes in the alborz zagros and central iran regions considering their different seismotectonics regimes however due to the lack of sufficient data no results have been reported for the kopeh dagh and makran seismotectonic regions

site amplifications for generic rock sites seismic shear wave velocity as a function of depth for generic rock sites has been estimated from borehole data and studies of crustal velocities and these velocities have been used to compute frequency dependent amplifications for zero attenuation for use in simulations of strong ground motion we define a genetic rock site as one whose velocity at shallow depths equals the average of those from the rock sites sampled by the borehole data most of the boreholes are in populated areas for that reason the rock sites sampled are of particular engineering significance we consider two genetic rock sites rock corresponding to the bulk of the borehole data and very hard rock such as is found in glaciated regions in large areas of eastern north america or in portions of western north america the amplifications on rock sites can be in excess of 3 5 at high frequencies in contrast to the amplifications of less than 1 2 on very hard rock sites the consideration of unattenuated amplification alone is computationally convenient but what matters for ground motion estimation is the combined effect of amplification and attenuation for reasonable values of the attenuation parameter k 0 the combined effect of attenuation and amplification for rock sites peaks between about 2 and 5 hz with a maximum level of less than 1 8 the combined effect is about a factor of 1 5 at 1 hz and is less than unity for frequencies in the range of 10 to 20 hz depending on t using these amplifications we find provisional values of about ao 70 bars and k 0 0 035 sec for rock sites in western north america by fitting our empirically determined response spectra for an m 6 5 event to simulated values the borehole data yield shear velocities 033o of 618 and 306 rrdsec for rock and soil sites respectively when averaged over the upper 30 m from this we recommend that v30 equals 620 and 310 m sec for applications requiring the average velocity for rock and soil sites in western north america by combining the amplifications for rock sites and the site factors obtained from our analysis of strong motion data we derive amplifications for sites with 17 3o 520 m sec nehrp class c corresponding to a mix of rock and soil sites and v3o 310 and 255 m sec average soil and nehrp class d sites respectively for the average soil site the combined effect of amplification and attenuation exceeds a factor of 2 0 for frequencies between 0 4 and about 4 hz with a peak site effect of 2 4 the peak of the nehrp class d site effect is 2 7

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

on two characteristic frequencies of acceleration spectra patch corner frequency and fmax abstract we examine two issues related to the radiation of tectonic earthquake sources i the complexity of the shape of observed source spectra and ii the effect of recording site characteristics on the cut off frequency f max of acceleration spectra beyond which spectral amplitudes diminish sharply we compute the far field spectra of the 1979 imperial valley and the 1984 morgan hill earthquakes from the slip functions that were inferred from detailed inversion studies of strong motion and teleseismic data of these two california strike slip events these spectra along with data from the 1983 central japan sea earthquake sequence main shock and aftershocks demonstrate the existence of the so called patch corner frequency which is related to the scale length of heterogeneities of the fault plane such a frequency is a distinct feature of the source spectrum of the specific barrier model of papageorgiou and aki by analyzing accelerograms of the san fernando earthquake of 1971 we found that f max determined from records at soil stations is nearly the same as that determined from records at hard rock stations

estimates of shear wave q and κ0 for unconsolidated and semiconsolidated sediments in eastern north america measured and calculated values of the effective quality factor qef and the site attenuation parameter 0 for unconsolidated and semiconsolidated sediments in eastern north america ena indicate that the latter is strongly dependent on sediment thickness estimates of 0 for national earthquake hazard reduction program nehrp bc site profiles sediment plus hard rock in the mississippi embayment and the atlantic coastal plain were found to increase from about 9 to 31 msec for sedi ment thicknesses ranging from 116 to 600 m stochastic simulations using the 175 m thick hypothetical nehrp bc site profile used to estimate ena ground motions in the nationalseismichazardmapsbytheu s geologicalsurvey usgs indicatethat 0 20 msec provides a smaller estimate of amplification that agrees more closely with the low strain short period site coefficients in the nehrp recommended provisions for seismic regulations for new buildings and other structures nehrpprovisions than the10msecvalueusedbytheusgs alinearregressionofthe 0 estimatescompiledin this study indicates that 0 20 msec corresponds to a relatively thick bc sediment thickness of 460 116 m these same stochastic simulations indicate that the rela tivelyshallowusgssiteprofileprovidesestimatesofamplificationthataresmallerthan thelow strainlong periodsitecoefficientsinthenehrpprovisions thedependenceof bothsiteattenuationandsiteamplificationonsedimentthicknesssuggeststhattheuseof a single reference site condition for hazard mapping might not be appropriate instead theseresultsimplythateitheraregionalsetofreferencesiteprofilesshouldbedeveloped or that a more uniform site condition such as hard rock should be used to define a more stable reference site condition in ena

a reappraisal of earthquake focal mechanisms and active shortening in the zagros mountains of iran summary the zagros mountains of sw iran are one of the most seismically active intra continental fold and thrust belts on earth and an important element in the active tectonics of the middle east surface faulting associated with earthquakes is extremely rare and so most information about the active faulting comes from earthquakes we use long period teleseismic p and sh body waves to determine the orientation and depth of faulting in 16 new earthquakes and then evaluate and synthesize all the available teleseismic data on earthquake source parameters in the zagros we use this information to investigate the style and distribution of active faulting in the zagros and how it contributes to the n s shortening of the arabia eurasia collision when the data are ranked in quality and carefully evaluated simple patterns are seen that are not apparent when routine catalogue data are taken at face value an important change in the fault configuration occurs along strike of the belt in the nw overall convergence is oblique to the trend of the belt and the surface anticlines and is achieved by a spatial separation partitioning of the orthogonal strike slip and shortening components on separate parallel fault systems by contrast in the se overall convergence is orthogonal to the regional strike and achieved purely by thrusting in the central zagros between these two structural regimes deformation involves parallel strike slip faults that rotate about vertical axes allowing extension along the strike of the belt the overall configuration is similar to that seen in other curved shortening belts such as the himalaya and the java sumatra trench all the zagros earthquakes we have been able to check have centroids shallower than 20 km and are confined to the upper crust many of the larger earthquakes are likely to occur in the basement beneath the sedimentary cover which is active even beneath areas of known shallow structural decollement such as the dezful embayment the dominant style of shortening is high angle reverse faulting with dips 30 though some lower angle thrusting occurs in places active thrust and reverse faulting is relatively confined to the lower topography on the sw edge of the belt today and only strike slip faulting affects the higher topography profound vertical changes in structural and stratigraphic level indicate that a similar style of deformation was once active across the width of the simple folded belt but has progressively migrated sw over the last 5 ma there is no evidence for a seismically active structural decollement such as a low angle thrust beneath the zagros nor is there any seismic evidence for active subduction either beneath the zagros or beneath central iran instead the arabian margin seems to have shortened by distributed thickening of the basement only in the syntaxis of the oman line at the se end of the zagros is there any evidence for a low angle thrust of regional extent here earthquakes continue 50 km north of the zagros thrust line the geological suture between the arabian margin and central iran reaching depths of 30 km and may represent thrusting of arabian basement beneath central iran to this extent

test of goodness of the nga ground motion equations to predict the strong motions of the 2012 ahar varzaghan dual earthquakes in northwestern iran in the first part of this study a set of 87 ground motion records with closest distance to the rupture plane r rup less than 200 km and averaged shear wave velocity over the top 30 m of the subsurface v s 30 between 175 and 1400 m s recorded during the 2012 ahar varzaghan dual earthquakes m w1 6 4 m w2 6 3 were taken into account to examine the predictive capabilities of the next generation attenuation nga ground motion prediction equations gmpes via a set of comparative analyses and tests the first applied method to assess the performance of the nga gmpes is based on the intraevent residual analysis the primary database i e 87 records was also used to develop an event specific gmpe in the case of the ahar varzaghan dual earthquakes by means of regression analyses the derived event specific gmpe has been compared with the nga gmpes for two different site conditions that is v s 30 375 m s rock site and v s 30 375 m s soil site the residual analysis results indicate that the nga gmpes perform better in predicting data recorded at rock sites compared to soil sites for soil sites and at large periods t 2 0 s the observed spectral accelerations are overpredicted by the nga gmpes furthermore as the second part of this study to select the most adequate gmpes 14 strong motion records from the 1997 ardebil earthquake m w 6 1 were added to the primary database the implementation of the likelihood lh and log likelihood methods as modern lh based ranking assessment techniques as well as the nash sutcliffe index reveal that the nga gmpes show good compatibility at short medium periods t 1 0 s on the basis of the data recorded during the 2012 ahar varzaghan dual and 1997 ardebil earthquakes i e 101 records however in the long period range the dispersion in the data does not allow the authors to draw a comprehensible conclusion

co2transfer between the upper mantle and the atmosphere temporary storage in the lower continental crust the co2 atmospheric content has shown large variations over geological times high contents up to one order of magnitude more than present day values ultimately correspond to discrete episodes of mantle degassing either juvenile or subduction related carbon recycling a number of arguments e g the continuous volume increase of carbonate bearing sediments with time suggest that throughout the earth s history juvenile co2 has formed a major contribution to the global carbon budget of the earth the absence of a direct relationship between major volcanic episodes and the average co2 atmospheric content suggests that volcanoes might not be the only way by which mantle co2 is transported to the surface it is proposed that large quantities of juvenile co2 could temporarily be stored in the lower continental crust during major episodes of granulite formation these are primarily caused by magmatic underplating and they result in a vertical accretion of the crust by accumulation of co2 bearing mantle derived magmas most of the co2 migrates through the crust during post metamorphic evolution and isostatic restoration of the normal continental thickness however large quantities of co2 can still be present in some areas notably as high density fluids enclosed in minerals

anomalously low temperature orthopyroxene spinel and sapphirine occurrences in metasediments from the bamble amphibolite to granulite facies transition zone south norway possible evidence for localized action of saline fluids a reply the question has been raised whether isolated granulite facies islands which occur throughout the amphibolite facies of the regional amphibolite to granulite facies transition zone in the central part of the bamble sector southern norway are the result of prograde or retrograde metamorphism we have studied one of these islands the sapphirine granulites at hauglandsvatn despite the preponderance of amphibolite facies assemblages in the surrounding rocks and the small scale of distribution of the granulite facies assemblages the current assemblage is considered to be prograde and has developed at the expense of biotite in the regional main foliation leaving relict biotite separated from quartz by a continuous corona of orthopyroxene and k feldspar other high temperature low ah2o reactions resulted in the formation of spinel corundum albite oligoclase symplectites at the expense of biotite and sillimanite the symplectites have partially been replaced by symplectites of tiny blue sapphirine

simultaneous study of the source path and site effects on strong ground motion during the 1989 loma prieta earthquake a preliminary result on pervasive nonlinear site effects we considered the effects of source propagation path and local site conditions on strong ground motion from the loma prieta earthquake in the following steps first the local site effect was removed from the strong motion records applying the weak motion amplification factors estimated from nearby stations of usgs regional network using the coda method then we confirmed the approximate validity of the 1 r law of geometrical spreading factor for the crustal model applicable to the region and we determined the attenuation parameter q f and source spectrum s f empirically from the site effect corrected spectral amplitude both q f and s f are consistent with the results obtained earlier for major california earthquakes we then synthesized the time history of ground acceleration by applying the stochastic simulation technique the agreement between the observed and predicted records was good for duration and spectral content we found however a strong systematic discrepancy with regard to peak acceleration namely for distances less than 50 km the predicted peak acceleration consistently overestimated the observed for sediment sites and underestimated it for the franciscan formation sites since the above systematic discrepancy applies to all the available stations within about 50 km from the hypocenter it is unlikely that the effect is due to the radiation pattern near source structure or topography it appears that the strong difference in the amplification factor between the franciscan and the sediment sites observed for weak motion disappears at acceleration levels higher than about 0 1 to 0 3 g if this is due to the nonlinear response of the sediment sites it is in the range expected from geotechnical engineering studies

earthquake source scaling relationships from 1 to 5 ml using seismograms recorded at 2 5 km depth the scaling relationships of earthquake sources less than about magnitude 3 have been the subject of considerable controversy over the last two decades studies of such events have shown a tendency for the constant stress drop self similarity of larger earthquakes to breakdown at small magnitudes and an apparent minimum source dimension of about 100 m has been observed other studies showed that this apparent breakdown in scaling could be an artifact of severe near surface attenuation limiting the spatial resolution of surface data in this study source parameters are determined for over 100 nearby tectonic earthquakes from recordings at a depth of 2 5 km in granite in the cajon pass scientific drill hole southern california comparison of the seismograms recorded at this depth with those at the wellhead clearly demonstrates the effect of the severe attenuation in the upper kilometers of the earth s crust source parameters are calculated by spectral modeling of three component p and s waves assuming four source models based on the brune 2 n 2 model in model l n 2 is fixed and q of p and s waves is determined to be 912 581 1433 and 1078 879 1323 respectively the numbers in parentheses are 1 standard deviation in model 2 qp qs 1000 is assumed and n is allowed to vary the 2 model is a good average for the data set but there is some real scatter supported by the data in model 3 qp qs 1000 is also assumed and 2 is constrained and in model 4 attenuation is ignored and n is allowed to vary source dimensions of less than 10m are observed for all four models 10 times smaller than the proposed minimum no breakdown in constant stress drop scaling is seen in the downhole data approximately ml 1 to 5 5 m0 109 1016 nm the ratio between radiated seismic energy estimated by integrating the velocity squared spectra with adequate signal bandwidth and seismic moment appears to decrease gradually with decreasing moment in the magnitude range 1 to 7 this is not incompatible with a constant stress drop but could result from errors in calculating energy the ratio of the s wave energy to that radiated by the p waves is about 14 after correction for attenuation this low value is consistent with the corner frequency shift of about 1 3 this corner frequency shift is observed for all four source models and therefore is interpreted as being source controlled

a predictive equation for vertical to horizontal response spectral ratios in northern iran abstract the importance of the vertical component of ground motion in damage infliction on a variety of structural systems has been shown in recent years however the available models for ground motion prediction equations gmpes for this component of earthquakes are limited and most of the existing gmpes have been specifically developed for the horizontal component of ground motion alternatively in some cases it is proposed to scale the horizontal spectrum of the earthquake to the vertical one using vertical to horizontal response spectral ratios vhsrs in this work the applicability of some global and regional vhsr models for northern iran are evaluated using several existing statistical approaches the results of these evaluations show inadequate correlation between these models and the observed vhsrs in this region consequently a new vhsr model has been proposed to convert the horizontal earthquake spectrum to the vertical one in the studied region in order to determine the regression coefficients for the proposed vhsr model some 712 three component records with distances less than 300 km from the source from 79 earthquakes with the magnitude ranging from m w 4 1 to 7 3 were used regression coefficients for peak ground acceleration and pseudospectral acceleration for 5 damped systems are determined using a random effect approach a series of comparative studies on the proposed model with respect to the existing vhsrs was performed using the median residuals for the spectral periods in the 0 1 3 s range the results of such investigation show significant reduction of the variability for the proposed model at least 50 compared with the other vhsrs online material database of strong motion records

titaniferous magnetite ilmenite thermometry and titaniferous magnetite ilmenite orthopyroxene quartz oxygen barometry in granulite facies gneisses bamble sector se norway implications for the role of high grade co 2 rich fluids during granulite genesis oxygen fugacities have been estimated for a wide distribution of samples from the granulite facies terrane region c of the bamble sector se norway using both the titaniferous magnetite ilmenite and orthopyroxene titaniferous magnetite quartz oxygen barometers these oxygen fugacities are estimated using temperatures calculated from the titaniferous magnetite ilmenite thermometer of ghiorso and sack 1991 and are both internally consistent with each other as well with the thermometer in samples for which the estimated temperature is high the two oxygen barometers show good agreement whereas agreement is poor for low temperature samples in these low temperature samples oxygen fugacities estimated from titaniferous magnetite ilmenite are considerably less than those estimated from orthopyroxene titaniferous magnetite quartz an increase in this discrepancy with decrease in temperature appears to reflect preferential resetting of the hematite component in the ilmenite grains without significant alteration of the more numerous titaniferous magnetite grains this is due in part to greater re equilibration of the ilmenite grains during retrograde interoxide resetting between the ilmenite grains and the titaniferous magnetite grains the mean temperature for the non reset samples 791 17 c 1 is in good agreement with temperatures obtained from garnet orthopyroxene kd exchange thermometry in the same region 785 795 c 1 harlov 1992 2000a most non reset oxygen fugacities range from log10 f o2 14 to 11 8 or approximately 0 5 1 5 log units above quartz fayalite magnetite at 7 5 kbar both these temperatures and the range of oxygen fugacities are in good agreement with those estimated using the titaniferous magnetite ilmenite thermometer oxygen barometer of andersen et al 1991 the quilp equilibrium quartz ulvospinel ilmenite pyroxene is used to project self consistent equilibrium temperatures and oxygen fugacities for samples reset due to hematite loss from the ilmenite grains these projected temperatures and oxygen fugacities agree reasonably well with the non reset samples the mean projected quilp temperature is 823 6 c 1 this result supports the conclusion that low titaniferous magnetite ilmenite temperatures down to 489 c and accompanying low oxygen fugacities are the result of hematite loss from the ilmenite grains non reset oxygen fugacities lie approximately 1 5 log10 units above the upper graphite stability curve indicating that the stable c o h fluid phase interacting with these gneisses whether regionally or locally was co2 this is borne out by the presence of numerous co2 rich fluid inclusions in these rocks

multiple plagioclase crystal populations identified by crystal size distribution and in situ chemical data implications for timescales of magma chamber processes associated with the 1915 eruption of lassen peak ca products of the 1915 lassen peak eruption reveal evidence for a magma recharge magma mixing event that may have catalyzed the eruption and from which four compositional members were identified light dacite black dacite andesitic inclusion and dark andesite crystal size distribution textural and in situ chemical major and trace element and sr isotope data for plagioclase from these compositional products define three crystal populations that have distinct origins phenocrysts long axis40 5 mm that typically have core an contents between 34 and 36 mol microphenocrysts long axis between 0 1 and 0 5 mm that have core an contents of 66 69 and microlites long axis50 1mm with variable an core contents from 64 to 52 phenocrysts are interpreted to form in an isolated dacitic magma chamber that experienced slow cooling based on textural compositional and isotopic data for the magma represented by the dacitic component magma recharge was not an important process until just prior to the 1915 eruption average residence times for phenocrysts are in the range of centuries to millennia microphenocrysts formed in a hybrid layer that resulted from mixing between endmember reservoir dacite and recharge magma of basaltic andesite composition high thermal contrast between the two end member magmas led to relatively high degrees of undercooling which resulted in faster crystal growth rates and acicular and swallowtail crystal habits some plagioclase phenocrysts from the dacitic chamber were incorporated into the hybrid layer and underwent dissolution precipitation seen in both crystal textures and rim compositions average microphenocryst residence times are of the order of months microlites may have formed in response to decompression and or syn eruptive degassing as magma ascended from the chamber through the volcanic conduit chemical distinctions in plagioclase microlite an contents reveal that melt of the dark andesite was more mafic than the melt of the other three compositions we suggest that mixing of an intruding basaltic andesite and reservoir dacite before magma began ascending in the conduit allowed formation of a compositionally distinct microlite population melt in the other three products was more evolved because it had undergone differentiation during the months following initial mixing as a consequence melt and microlites among these three products have similar compositions the results of this study highlight the integrated use of crystal size distribution textural and in situ chemical data in identifying distinct crystal populations and linking these populations to the thermal and chemical characteristics of complex magma bodies

petrology and geothermobarometry of granulite facies metapelites from the hisoy torungen area south norway new data on the sveconorvegian p t t path of the bamble sector the high grade rocks metapelite quartzite metagabbro of the hisoy torungen area represent the south westernmost exposures of granulites in the proterozoic bamble sector south norway the area is isoclinally folded and a metamorphic p t t path through four successive stages m1 m4 is recognized petrological evidence for a prograde metamorphic event m1 is obtained from relict staurolite chlorite albite staurolite hercynite ilmenite cordierite sillimanite fine grained felsic material quartz and hercynite biotite sillimanite within metapelitic garnet the phase relations are consistent with a pressure of 3 6 0 5 kbar and temperatures up to 750 850 c m1 is connected to the thermal effect of the gabbroic intrusions prior to the main m2 sveconorwegian granulite facies metamorphism the main m2 granulite facies mineral assemblages quartz plagioclase k feldspar garnet biotite sillimanite are best preserved in the several metre wide al rich metapelites which represent conditions of 5 9 9 1 kbar and 790 884 c these p t conditions are consistent with a temperature increase of 80 100 c relative to the adjacent amphibolite facies terranes no accompanying pressure variations are recorded up to 1 mm wide fine grained felsic veinlets appear in several units and represent remnants of a former melt formed by the reaction bt sil qtzgrt lq this dehydration reaction together with the absence of large scale migmatites in the area suggests a very reduced water activity in the rocks and xh2o 0 25 in the c o h fluid system was calculated for a metapelitic unit a low but variable water activity can best explain the presence or absence of fine grained felsic material representing a former melt in the different granulitic metapelites the strongly peraluminous composition of the felsic veinlets is due to the reaction grt former melt silcrd bt qtz h2o which has given poorly crystalline cordierite aggregates intergrown with well crystalline biotite the cordierite and biotite producing reaction constrains a steep first stage retrograde relative to m2 uplift path decimetre to metre wide strongly banded metapelites quartz plagioclase biotite garnet sillimanite inter layered with quartzites are retrograded to m3 amphibolite facies assemblages a p t estimate of 1 7 5 6 kbar 516 581 c is obtained from geothermobarometry based on rim rim analyses of garnet biotite plagioclase sillimanite quartz assemblages and can be related to the isoclinal folding of the rocks m4 greenschist facies conditions are most extensively developed in millimetre wide chlorite rich calcite bearing veins cutting the foliation

high grade k feldspar veining in granulites from the ivrea verbano zone northern italy fluid flow in the lower crust and implications for granulite facies genesis we present observations of extensive networks of k feldspar microveins associated with quartz and plagioclase in granulite facies rocks from the ivrea verbano zone northern italy back scattered electron images of the granulite facies samples show a continuous system of k feldspar veins along quartz plagioclase and plagioclase plagioclase grain boundaries that can be traced across the entire length of a thin section quartz grain rims in contact with these veins show evidence of extensive corrosion in contrast contact between the veins and the orthopyroxene and garnet grains is very clean with no signs of secondary alteration k feldspar quartz plagioclase of the same compositions as the veins are commonly found as near rim inclusions within garnet microprobe traverses from the interiors of the k feldspar veins to their rims show increasing ba indicating a metasomatic origin some veins display a boudinaged texture possibly related to the d2 deformation event in the ivrea verbano zone and the

p t conditions for the arendal granulites southern norway implications for the roles of p t and co2in deep crustal lile depletion the orthopyroxene clinopyroxene garnet orthopyroxene and garnet clinopyroxene geothermometers and the garnet orthopyroxene plagioclase garnet clinopyroxene plagioclase and anorthite ferrosilite grossular almandine quartz geobarometers are applied to metabasites and the garnetplagioclase sillimanite quartz geobarometer is applied to a metapelite from the proterozoic arendal granulite terrain bamble sector norway p t conditions of metamorphism were 7 3 0 5 kbar and 800 60 c this terrain shows a regional gradation from the amphibolite facies into normal lile content granulite facies rocks and finally strongly lile deficient granulite facies gneisses neither p nor t vary significantly across the entire transition zone the change in grade parallels the increasing dominance of co2 over h2o in the fluid phase lile depletion is not a pre condition of granulite facies metamorphism granulites may have either depleted or normal chemistries the results presented herein show that lile deficiency in granulite facies orthogneisses is not necessarily related to variations in either p or t the important mechanisms in the arendal terrain were a direct synmetamorphic crystallization from magma with primary lile poor mineralogies imposed by the prevailing fluid regime and b metamorphic depletion involving scavenging of liles during flushing by mantle derived co2 rich fluids the latter process is constrained by u pb and rb sr isotopic work to have occurred no later than 50 ma after intrusion of the acid intermediate gneisses and was probably associated with contemporary basic magmatism in a tectonic environment similar to a present day cordilleran continental margin

simulation of strong ground motion in northern iran using the specific barrier model summary in this study based upon the calibrated specific barrier model sbm against the latest available strong motion data ground motion prediction equations for soil and rock sites in northern iran are developed the sbm may provide the most complete simple and self consistent description of the faulting process which is applicable in both near fault and far field regions consequently the sbm may provide consistent ground motion simulations over the entire necessary frequency range and for all distances of engineering interests to determine source parameters in this study we used 163 three component records of 32 earthquakes with magnitude ranging from mw 4 9 to 7 4 in northern iran in the database records with hypocentral distances less than 200 km are chosen and only earthquakes whose moment magnitude estimates are available have been used furthermore using the best available information recording sites are classified into two main geologic categories rock and soil because of the lack of site amplification information in the most regions of the world including iran we used the h v ratio method for estimating the site amplification moreover the kappa factor that shows diminishing the high frequency amplitude is determined in this study two data sets are considered for determining the source parameters g and l and the h v ratio and the kappa factor only s wave part of signals is used in each analysis regression analysis is performed using random effects method that considers both interseismic event to event and coseismic within event variabilities to effectively deal with the problem of weighting observations from different earthquakes the residuals are controlled against available northern iranian strong ground motion data to verify that the model predictions are unbiased and that there are no significant residual trends with magnitude and distance at first it is assumed that no sign of self similarity breakdown is observed between the source radius and its seismic moment after controlling the results the modified sbm should be used as some deviations have been observed to verify the robustness of the results the number of observations is changed by removing various randomly selected data sets from the original database which results in unchanged results of the model stochastic simulations are then implemented to predict peak ground motion and response spectra parameters the stochastic sbm predictions are in relatively good agreement with other available attenuation relationships proposed for iran europe and middle east it has been shown that the proposed sbm of this study provides unbiased ground motion estimates over the entire frequency range of most engineering applications it provides a reliable and physically realistic yet computationally efficient way to model strong ground motions

oblique terrane assembly in the late paleoproterozoic during the labradorian gothian orogeny in southern scandinavia the earliest deformation of the curved kongsberg bamble belt in norway produced a northwestward directed tectonic wedge suggesting oblique nw se collision during the labradorian gothian orogeny in southern scandinavia oblique terrane assembly with the outboard western units colliding last explains the trapping of the ostfold marstrand island arc formed at c 1760 ma between younger 1700 1600 ma terranes the apparent lack of svecofennian crust west of the trans scandinavian igneous belt and the apparent lack of labradorian gothian age crust in the british isles the labradorian of north america may have also resulted from oblique terrane assembly

halogen geochemistry of fluid during amphibolite granulite metamorphism as indicated by apatite and hydrous silicates in basic rocks from the bamble sector south norway abstract the halogen chemistry of apatites biotites amphiboles and titanites from metabasites in the proterozoic bamble sector amphibolite granulite facies transition zone norway has been studied to gather data on the behaviour of halogens during original magmatism and subsequent metamorphism three groups of apatites could be recognized 1 f oh apatites with more than 50 mole f and virtually no cl 2 f oh apatites with up to 15 mole of cl 3 cl rich apatites with up to 6 73 wt cl the latter are the most cl rich metamorphic apatites ever reported the f contents of coexisting biotite do not follow this division but their cl contents do log z sfnc hf z sfnc h 2 o values for the coexisting fluid phase calculated from biotite are slightly lower than those calculated from apatite log z sfnc hcl z sfnc h 2 o values in the coexisting fluid phase calculated from biotite are substantially higher than those calculated from apatite the log z sfnc hf z sfnc h 2 o reflects the composition of the peak metamorphic fluid phase the apatites show three types of patterns of f contents 1 w shaped 2 rimward increasing and 3 rimward decreasing pattern 2 reflects progressive metamorphism pattern 3 is thought to reflect growth starting near peak metamorphism and going on during retrograde dilution of the peak metamorphic fluid by a newly introduced aqueous one some apatites show local resorption effects along cracks no regional trend in calculated log z sfnc hf z sfnc h 2 o values is present as different from other granulite terrains the bamble biotites and amphiboles from granulite facies samples do not have higher halogen contents as those from the amphibolite facies area the samples show that halogen bearing fluids were controlled at a very restricted scale during peak as well as retrograde metamorphism

high density carbonic fluid inclusions in charnockites from eastern ghats india petrologic implications abstract charnockite rocks a significant litho unit in eastern ghats granulite belt eggb are characterized by the presence of dry mineral assemblage the anhydrous conditions required for the formation of ganulites are believed to be controlled by the lowering of water activity through the influx of co2 bearing fluids here we present the results of systematic petrographic and microthermometric studies characterizing the nature composition and density of co2 rich fluid inclusions in charnockitic rocks from gangarajumadugula in this study we have combined mineralogic thermobarometry with microthermometric data of the carbonic fluid inclusion population of high density in the charnockite samples from gangarajumadugula area to substantiate desiccation of lower crustal environment producing anhydrous conditions in the eastern ghats granulite belt close to peak pressure temperature calculations for core composition using convergence technique in present study indicate that these charnockites have experienced maximum p t around 860 c at 9 kbar which is broadly consistent with independent p t estimates inferred for gangarajumadugula area the reaction textures preserved by these charnockites and the thermobarometric data characterize decompression followed by cooling history high density carbonic fluid inclusions 1 08 g cm3 in quartz provide potential evidence for the involvement of co2 rich fluid during granulite facies metamorphism in eggb occurrence of co2 rich inclusions and elevated p t conditions open up the possibility favoring the mechanism of vapour deficient dehydration melting accompanied by co2 infiltration to account for charnockite formation from precursor crustal rocks our study documents that fluid inclusions in high grade metamorphic rocks have enormous potential in retaining worthwhile information of peak metamorphic conditions and understanding the metamorphic processes

global comparisons of earthquake source spectra a key question in earthquake seismology is whether earthquake sources in different tectonic regions are functionally equivalent in terms of radiated ground motion this article compares the apparent earthquake source radiation for six different regions japan mexico turkey california british columbia b c western canada and eastern north america ena the source path and site effects were consistently separated to the extent possible to allow interregional comparisons of apparent source radiation large fourier spectra databases were created for both horizontal and vertical components for earthquakes with magnitude between 2 5 and 7 5 regional parameters characterizing source path and site properties including crustal and near surface site amplifications were investigated to isolate apparent source spectra based on the vertical component spectra at a reference distance of 1 km a new magnitude scale m 1 was defined from the spectral level at 1 hz the magnitude scale m 1 is a natural complement to existing magnitude scales that measure the low frequency and high frequency spectral amplitudes moment magnitude m and high frequency m hf respectively in all regions the apparent source spectra for small to moderate earthquakes m 6 show good agreement with the single corner brune 1970 1971 point source model 2 spectrum suggesting a stress parameter of about 100 bars 10 mpa a two corner source model better matches the spectra for large magnitude earthquakes m 6 especially at intermediate frequencies for small to moderate events the two source models are nearly equal apparent source spectra from small to moderate earthquakes e g m 1 3 5 6 5 suggest a general similarity between the different tectonic regions studied although minor discrepancies appear in some cases there are no noticeable regional characteristics no evident depth effects were found on the apparent source spectra manuscript received 1 april 2001

calibration of the specific barrier model to earthquakes of different tectonic regions the specific barrier model proposed and developed by papageorgiou and aki 1983a b 1985 provides the most complete yet parsimonious self consis tent description of the faulting process it applies both in the near fault and in the far field region thus allowing for consistent ground motion simulations over the entire frequency range and for all distances of engineering interest the model has been implemented in the stochastic method and calibrated with extended databases of response spectral amplitudes from earthquakes of intraplate regions mainly east ern north america events interplate regions and regions of tectonic extension spu dich et al 1999 database the ensemble average value of a key parameter of the specific barrier model the local stress drop dr l i s 161 bars for interplate earth quakes 114 bars for extensional regime earthquakes and 180 bars for intraplate earthquakes the high frequency source spectral levels of interplate and extensional regime earthquakes deviate significantly from self similar scaling the deviation is most likely caused by the effective source area and or irregularities in the rupture kinematics we account for their overall effects through a high frequency source complexity factor f in the source spectrum of the specific barrier model as a result inter and intraplate source spectra show similar high frequency levels at moderate magnitudes but intraplate earthquakes have higher spectral levels at the larger mag nitudes the interplate soil residuals show clear signs of nonlinear site response whereas only slight signs of such nonlinearity are observed for the extensional data set the regional models calibrated in this study are in reasonably good agreement with other regional attenuation relationships and provide a reliable and physically realistic yet computationally efficient way to model strong ground motions with implications for seismic hazard and risk analysis online material strong motion station and event station pair information

the redox state of pinatubo dacite and the ilmenite hematite solvus the oxidation state of the 1991 pinatubo dacite and many other oxidized silicic arc volcanic rocks has been overestimated we reproduce the compositions of magnetite and ferrian ilmenite found in pinatubo dacite by doing crystallization experiments at 780 degrees c 2 2 kbar and nno 1 7 or 0 2 log units the extra components in igneous ilmenite notably geikielite expand the solvus in a way that is not correctly accommodated in current formulations of the iron titanium oxide thermobarometer

an empirical study of earthquake source spectra for california earthquakes we generalize source path and site effects for california earthquakes as functions of magnitude and distance based on regression analysis of 1000 fourier acceleration spectra from 43 california earthquakes in the moment magnitude range from 4 4 to 7 4 recorded at rupture distances from 1 to 200 km empirically derived source spectra for california earthquakes are generally inconsistent with the spectral shape implied by a brune omega squared point source model this is manifested by magnitude and frequency dependence of the brune model parameters for ex ample the brune stress parameter that best matches the data at high frequencies decreases from a value of about 120 bars at m5 5 to a value near 50 bars at m7 5 at frequencies below 1 hz though source spectra have much lower spectral ampli tudes than predicted by the brune point source model for these values of stress this discrepancy grows with increasing magnitude finite fault simulations indicate that this is a consequence of the breakdown of the validity of the point source approxi mation for large ruptures a stochastic finite fault model in which the fault is dis cretized as a number of subfaults each of which is represented by a brune omega squared point source correctly matches the observed spectral shapes and amplitudes the spectral decay parameter kappa representing average near surface attenuation of high frequency motion at rock sites increases with increasing magnitude from values near 0 035 sec at m5 5 to 0 050 sec at m7 5 magnitude dependence of kappa may be interpreted as evidence of nonlinearity for typical california sites subjected to strong ground motion comparisons of our empirical source spectra for california to corresponding spec tra for eastern north america suggest that the spectral amplitudes are similar in the two regions for low frequency motions f 2 hz for m5 5 f 0 5 hz for m7 5 for equivalent crustal conditions the eastern events appear to have enhanced high frequency near source amplitudes relative to the california events this is particularly pronounced for large magnitude earthquakes

comparative oxygen barometry in granulites bamble sector se norway oxygen fugacities have been estimated for the high grade portion of the bamble granulite facies terrane se norway using both titaniferous magnetite ilmenite and orthopyroxene titaniferous magnetite quartz oxygen barometers the two oxygen barometers show good agreement for samples indicating high titaniferous magnetite ilmenite temperatures whereas agreement is poor for low temperature samples oxygen fugacities estimated from titaniferous magnetite ilmenite are considerably lower than those estimated from orthopyroxene titaniferous magnetite quartz this discrepancy increases with a decrease in temperature which appears to reflect preferential resetting of the hematite content in the ilmenite grains without much alteration of the more numerous titaniferous magnetite or orthopyroxene grains the mean temperature for the non reset samples 795 60 c 1 agrees well with temperatures obtained from garnet orthopyroxene k d exchange thermometry in the same region 785 60 c 1 most non reset o

mobilization of gold in the deep crust evidence from mafic intrusions in the bamble belt norway abstract the location of mesothermal gold deposits in the upper part of major transcurrent shear zones suggests that gold was derived from the deep wider portions of the shears the 30 km wide bamble belt south norway is a deep shear belt metamorphosed to upper amphibolite and granulite grade at about 1 1 ga preliminary studies showed that its rocks are strongly depleted in gold and other chalcophile elements mafic rocks were chosen for more detailed study of the mobilization of gold during metamorphism gold in mafic rocks largely partitions into the sulphide phase which is mainly comprised of pyrrhotite modification of this phase was required to liberate gold bamble has two main groups of mafic rock the first metabasites intruded before peak metamorphism are uniformly low in gold their o2 at peak metamorphism obtained from ilmenite orthopyroxene equilibria indicates a strongly oxidized mineral assemblage well above fmq pyrrhotite was stable at peak temperature of 800 c but on cooling below 600 c internal mineralogical buffering by the oxidized assemblage caused the o2 to cross into the stability field of pyrite following conversion of pyrrhotite to pyrite the latter was partly replaced by magnetite these serial changes in the mineralogical form of iron sulphide was conducive to the extraction of gold as was the oxidized nature of the mineral assemblage that would have buffered metamorphic fluids to high o2 the second group of mafic rocks hyperites intruded after peak metamorphism record intermediate steps in the extraction of gold these intrusions of coronitic gabbro were metamorphosed in whole or in part to amphibolite there is a decrease in gold and other chalcophile elements across a hyperite dyke from the pyrrhotite bearing coronitic gabbro interior to the pyrite bearing amphibolite margin

global variations of stress drop for moderate to large earthquakes 1 we investigate the global variation of earthquake stress drops using spectra of about 2000 events of mb 5 5 between 1990 and 2007 we use an iterative least squares method to isolate source displacement spectra from travel path and receiver contributions based on a convolutional model the observed p wave source spectra are corrected with a globally averaged empirical correction spectrum and estimates of near source attenuation assuming a brune type source model we estimate corner frequencies and compute stress drops stress drop estimates for individual earthquakes range from about 0 3 to 50 mpa but the median stress drop of about 4 mpa does not vary with moment implying earthquake self similarity over the mw 5 2 to 8 3 range of our data a comparison of our results with previous studies confirms this observation over most of the instrumentally observable magnitude range while the absolute values of our estimated stress drops depend upon the assumed source model we identify relative regional variations of stress drop that are robust with respect to the processing parameters and modeling assumptions which includes an inherent assumption of constant rupture velocity we find a dependence of median stress drop on focal mechanism with a factor of 3 5 times higher stress drops for strike slip earthquakes and also find a factor of 2 times higher stress drops for intraplate earthquakes compared to interplate earthquakes

what we can and cannot learn about earthquake sources from the spectra of seismic waves earthquake sources are commonly viewed as shear dislocations this imposes distinct limitations on what source parameters can be realistically determined from radiated shear wave spectra first the slip velocity on the fault is the real parameter that controls the strength of the high frequency radiation it can be directly determined from acceleration spectra by fitting their high frequency level second the relationship between corner frequency of the spectrum and the radius of the source is fundamentally unclear as a result the source dimensions cannot be accurately determined from the spectra such an estimate would be as accurate as any other informed guess third the stress drop only serves as a proxy for the source radius in the relationship between the radius and the corner frequency it thus cannot be reliably determined from the spectra the quantity usually obtained from the spectra and referred to as the stress drop is a poorly defined parameter that may bear little relevance to the actual stresses acting on faults this parameter has little meaning unless converted to the maximum slip velocity which is the only quantity that can be accurately determined from the spectra the typical value of stress drop of 100 bars established from the spectra of california events may imply that the typical slip velocities have been on the order of 0 5 m sec although it is more accurate to determine slip velocities directly from the spectra

seismicity parameters and spatially smoothed seismicity model for iran abstract in the present study seismicity parameters seismic activity value and maximum regional magnitude of the iranian plateau are computed for sites equally distributed all over the country on a grid of 1 1 decimal degree the most complete available catalog including historical and instrumental earthquakes of the plateau from 734 b c to a d 2011 is first prepared from numerous resources earthquakes within a 200 km buffer surrounding each grid point are selected and historical and instrumental parts are more accurately specified based on the completeness test of stepp 1972 the instrumental part is also analyzed to identify the various completeness intervals and the minimum completeness magnitude for each interval is determined by the maximum curvature method next the seismicity parameters are calculated from uncertain and incomplete data by the maximum likelihood procedure of kijko and sellevoll 1989 1992 and kijko 2004 after removing aftershocks and foreshocks the spatial variation of seismicity parameters is illustrated in the form of contour maps over the whole iranian plateau for the first time the value corresponding to the magnitudes m w 4 varies over the plateau from 0 7 to 23 4 and the highest values are located in the zagros and alborz mountains confirming that a large portion of the seismic deformation in the plateau is accommodated in these regions the estimated values for all points lie between 1 3 and 2 9 this spatial distribution of values demonstrates the crustal heterogeneity over the plateau low values in northeast and east iran also indicate high probability of large earthquake occurrence it is observed that the estimated m max is between m w 6 5 and 8 and hence most of that part of the country may experience large earthquakes the obtained results are important for two aspects 1 new seismotectonic models could be proposed by combining the presented maps with geological geodetic and tectonic data and 2 these results together with a detailed geological data describing potential seismogenic sources can be used directly to evaluate ground motion hazard for engineering design and generate seismic hazard maps an approximate and gross estimate of peak ground acceleration pga level at bedrock for 2 and 10 probabilities of exceedance in a 50 year period is also computed using an area source model characterized by the presented seismicity parameters the regional distribution of the estimated pga sheds a new light on facilitating risk management and allocating national resources for mitigating potential losses at a country based level online material table of completeness magnitude and seismicity parameters

average seismic source parameter relations for mid plate earthquakes mid plate earthquakes which are defined as having their epicenters at least 500 km from plate margins represent a small portion of the total global seismicity however because those occurring within continental interiors are characterized by anomalously large damage areas they are of particular interest empirical mb ms and m o data are used to develop scaling relations for mid plate earthquakes from them it is found that the corner period t o2 of their far field displacement spectra varies as the one fourth power of the seismic moment which indicates that average stress drop increases as seismic moment increases by use of savage s 1972 rectangular bilateral dislocation model the derived spectra of mid plate earthquakes yield estimates of fault rupture length and width average fault displacement and source rise time as a function of seismic moment these relations show that large mid plate earthquakes such as the 1886 south carolina and 1811 and 1812 new madrid events do not require large fault rupture length

scaling differences between large interplate and intraplate earthquakes a study of large intraplate earthquakes with well determined source parameters shows that these earthquakes obey a scaling law similar to large interplate earthquakes in which m 0 l 2 or u l where l is rupture length and u is slip in contrast to interplate earthquakes for which 1 10 5 for for the intraplate events 6 10 5 which implies that these earthquakes have stress drops about 6 times higher than interplate events this result is independent of focal mechanism type this implies that intraplate faults have a higher frictional strength than do plate boundaries and hence that faults are velocity or slip weakening in their behavior this factor may be important in producing the concentrated deformation that creates and maintains plate boundaries

metamorphic fluids in the deep crust most of the inferences about fluid action in the deep crust are drawn from field petrographic and geochemical studies in the granulite facies terrains deductions on the nature of fluids are made from major and minor element distributions and isotopic patterns in metamorphic rocks calculations of fluid mineral equilibria based on observed assemblages fluid inclusions and field evidence of fluid pathways discussion of these features has focused attention on several major problems concerning the timing flow mechanisms and origin of the fluids a key issue concerns episodicity versus secular activity of fluids there are strong arguments that most fluid action in the deep crust is linked to thermal deformational events including magmatism and regional meta morphism discrete radiometric ages of high grade terrains often define relatively short periods of crystallization or recrystallization the late archean granulite facies metamorphism of southern india is an example where u pb systems of zircons buhl et al 1983 whole rock u pb data peucat et al 1 987 and sm nd systems of whole rocks and minerals bernard griffiths et al 1 987 all show a major high temperature recrys tallization event inferred by several workers to have involved pervasive fluid action centered closely around 2 5 ga another geochemical indi cation of episodic fluids comes from stable isotope studies of progressive metamorphic sequences as in the damara orogen namibia where whole rock b 180 increases slightly at isograds representing arrested dehydration events but is monotonous between isograds hoernes hoffer 1 985

the seismic radiation from composite models of faulting abstract the failure of an asperity i e the dynamic rupture of a small fault area with finite stress drop surrounded by a broken or weak fault area which has no stress drop but which slips after the asperity fails is proposed as a model for the rupture process of a subevent in a composite earthquake the rupture area of the composite earthquake surrounding the subevent is modeled by the weak fault area surrounding the asperity in the subevent model the resulting seismic moment of the subevent is proportional to the stress drop and the rupture area of the subevent as well as the radius of the composite earthaquake by setting the stress drops of the asperity models equal to the dynamic stress drops of the subevents the composite earthquake can be modeled as the sum of a set of subevents which cover the rupture area of the composite earthquake the scaling of the high and low frequency radiation from composite earthquakes composed of asperities is commensurate with generally observed spectral scaling laws in contrast to composite earthquakes composed of cracks or smaller earthquakes a simple filtering strategy is proposed for filtering the waveforms radiated by cracks to approximate the waveforms radiated by asperities the p and s waves radiated by an m l 5 2 earthquake which occurred on 9 may 1983 at coalinga california are simulated using the p and s waves radiated by an m l 3 6 aftershock the aftershock waveforms are first filtered to approximate the radiation from asperities with the appropriate rupture areas and then the waveforms of 12 asperity subevents are summed together to simulate the waveforms and spectra of the composite earthquake

the ilmenite titano magnetite assemblage kinetics of re equilibration abstract compositions of coexisting ilmenite and titano magnetite commonly have been used to establish the conditions of formation for igneous and metamorphic rocks buddington lindsley geothermometer oxybarometer temperatures so determined for some rocks are lower than might be expected for magmatic crystallization these low temperatures are the result of re equilibration of the fe ti oxides during slow cooling this process is one in which titano magnetites are oxidized and ilmenites are reduced upon cooling along a buffer curve or in the presence of a fluid of constant composition textural studies indicate that the reduction of the ilmenite hematite phase may be the slower reaction consequently the rate controlling step of the re equilibration the kinetics of the reduction reactions in the two phase region between the joins for the ilmenite hematite and magnetite ulvospinel solid solution series were studied by thermogravimetric analysis at controlledfo2 with experiments conducted near the ni nio and qfm buffers annealed ilmenite ss synthetic charges were reduced isothermally the temperature range for the experiments was 900 1250 c with total gas flow rates of 0 35 and 1 0 cm s kinetic data were collected by measuring the weight change during each experiment as a function of time additionally a cooling rate 0 5 c hr experiment was conducted near the qfm buffer from 1150 to 985 c starting with an ilmenite saturated spinel phase at 1200 c and 0 35 cm s flow rate the reaction mechanism is an interfacial process where mass transport of the reacting gases is the rate controlling step in isothermal experiments at 1100 c and lower diffusion of reactants through a solid product layer was the controlling mechanism the activation energy for this diffusion process is 59 6 kcal mole significant enhancement of diffusion occurs along grain boundaries although the individual phases may re equilibrate internally upon cooling the fe ti contents must remain unchanged for proper use of this mineral indicator i e no external re equilibration it is imperative that the kinetics of the situation be appreciated these preliminary kinetic experiments indicate that extreme caution must be exercised when applying this ilmenite titano magnetite geothermometer oxybarometer these phases may only truly quench in the parameters of formation in the case of certain hypabyssal and extrusive occurrences

juvenile co2in enderbites of tromoy near arendal southern norway a fluid inclusion and stable isotope study the enderbites from tromoy in the central granulite facies part of the proterozoic bamble sector of southern norway contain dominantly co2 and n2 fluid inclusions co2 from fluid inclusions in quartz segregations in enderbites was extracted by mechanical crushing and thermal decrepitation and the 13c measured measurement was also made on samples washed in 10 hcl oxidized with cuo at high temperatures and step wise extracted with progressive heating results between the different techniques are systematic the main results show 13c of 4 5 1 5 for crushing and 7 2 for thermal decrepitation 13c is about constant for co2 extracted at different temperatures and points to a homogeneous isotopic composition due to the presence of carbonate particles and or induced contaminations for the extraction by thermal decrepitation the results for the crushing experiments are assumed the most reliable for fluid inclusion co2 very low values of 13c have not been found in enderbite samples and 13c combined with 18o of the host quartzes 8 11 indicates juvenile values in addition the fluid inclusions were examined by microthermometry and raman analysis and host quartz by acoustic emission and cathodoluminescence co2 fluid inclusions have varying densities with a frequency maximum of 0 92 g cm 3 and generally do not concur with trapping densities at granulite conditions textures show that co2 must have been trapped in fluid inclusions in one early event but transformed to different extents during late isothermal uplift without important fractionation of isotope compositions the present data support a model of intrusion and crystallization of a co2 rich enderbitic magma at granuiite conditions

simulation of ground motion in the zagros region of iran using the specific barrier model and the stochastic method abstract physically based ground motion prediction equations for soil and rock sites in the zagros region have been developed based on the specific barrier model sbm used within the context of the stochastic model instead of direct time domain simulation random vibration theory was used to estimate measures of peak motion in terms of the pseudospectral velocity of anelastic harmonic oscillator with 5 viscous damping to avoid the uncertainties calibration of the source model uses a database of carefully selected strong motion data without ambiguity about the site condition therefore only rock sites are selected for determining source parameters also to avoid any inconsistencies caused by magnitude conversion formulas we restricted the dataset only to events with available moment magnitudes regression analysis is performed using the random effects model that considers both interevent and intraevent variabilities to effectively deal with the problem of an unequal number of records from different earthquakes no sign of self similarity breakdown is observed between the source radius and its seismic moment the local and global stress drops derived for the zagros region 39 and 116 bars respectively are more consistent with the values obtained by other authors for an interplate regime than the values for an intraplate region however from the viewpoint of source heterogeneity as the ratio of the stress drops is an indicator of the complexity of the source and heterogeneity of slip on the fault the zagros events which have a stress drop ratio of about three are more homogeneous than other interplate events stochastic simulations are then implemented to predict peak ground motion and response spectra parameters for rock and soil site conditions online material catalog tables of earthquakes and attenuation tables