radiated energy from the mid niigata japan earthquake of october 23 2004 and its aftershocks 1 the mid niigata earthquake of october 23 2004 is a shallow reverse faulting event with mw 6 6 we analyze transverse component accelerograms of the main shock and four aftershocks mw 4 0 5 5 recorded at 29 strong motion observation stations the epicenters of the four aftershocks are located within 5 km from that of the main shock the stations are well distributed around the epicenters and their epicentral distances are between 15 and 60 km we calculate spectral ratio between records of the main shock and each of the aftershocks in order to obtain source spectral ratio by empirically removing the effects of wave propagation path and surface layers at the stations thus obtained source spectral ratio is inconsistent with that expected from the self similar omega square model fitting omega square source spectral ratio with variable corner frequency to the observed spectral ratio radiated energy and corner frequency are estimated radiated energy from the main shock is 3 2 1014 j although energy to moment ratios for the main shock and the aftershocks are all distributed within a narrow range from 8 10 6 to 4 10 5 they definitely increase with the event size this scale dependence is quite similar to that obtained previously for strike slip events in japan the relationship between the seismic moment m0 and the corner frequency f0 is m0 f0 3 3 0 2 these results suggest a break in self similarity

scale dependence of seismic energy to moment ratio for strike slip earthquakes in japan we analyzed four pairs of a large m w 6 and a small m w 3 5 to 4 shallow strike slip earthquakes to investigate the scale dependence of the seismic energy to moment ratio an important macroscopic parameter which reflects the basic physical process of seismic slip these earthquakes occurred in the south western part of japan and high quality close in records epicentral distance 50 km are available for both the small and large earthquakes the paired events have almost the same focal mechanism and hypocenter location we used the spectral ratio of the paired events in order to remove the effects of attenuation along the wave propagation path and the station site response we then estimated the seismic energy from the source spectra estimated from the spectral ratio the energy to moment ratio increases with the earthquake size this scale dependence is very similar to that found earlier for earthquakes in southern california

estimation of radiated energy using the kik net downhole records old method for modern data we use kik net nied down hole records to estimate the radiated energy er of 29 japanese inland earthquakes with a magnitude range from mw 5 6 to 7 0 the method is based on the work of gutenberg and richter in which the time integral of s wave ground motion velocity squared is measured as a basic metric of the radiated energy only stations within a distance of 100 km are used to minimize complex path and attenuation effects unlike the teleseismic method that uses mainly p waves the use of s waves which carry more than 95 per cent of the radiated energy allows us to obtain robust results we calibrate the method using synthetic seismograms to modernize and improve the gutenberg richter method we compute synthetic seismograms for a source model of each event with a given source function i e known er the actual mechanism and the source station geometry then we compare the given er with the computed energy metric to correct for the unknown effect of wave propagation and the mechanism the use of down hole records minimizes the uncertainty resulting from the site response our results suggest that the currently available estimates of er from teleseismic data are probably within a factor of 3 on average of the absolute value the scaled energy er er m0 is nearly constant at about 3 10 5 over a magnitude range from mw 5 6 to 7 0 with a slight increasing trend with mw we found no significant difference in er between dip slip and strike slip events

evidence for non constant energy moment scaling from coda derived source spectra 1 we present two lines of evidence showing the ratio of seismically radiated energy er to seismic moment mo increases with increasing moment for crustal events spanning 5 orders in seismic moment this ratio often referred to as the scaled energy er m0 has been elusive and the subject of recent debate within the seismological community because significant frequency dependent corrections must be made to account for source and path heterogeneity it is not uncommon that energy estimates of the same event by different researchers have significantly different values to minimize some of the potential problems we used the regional coda methodology outlined by mayeda et al 2003 on 4 large earthquake sequences mw 7 4 and 7 2 izmit duzce mw 7 2 gulf of aqaba mw 7 3 landers and mw 7 2 hector mine this methodology has been shown to provide the lowest variance estimate of the source spectrum when compared against traditional direct wave estimates in our first approach we made energy estimates from coda derived spectra and observed that increases with increasing moment for 3 7 mw 7 4 in our second approach we used the simple idea outlined by prieto et al 2004 to directly test for self similarity under self similarity earthquake source spectra scaled by 3 should have the same shape to test this one needs very stable spectra either through spectral stacking of direct wave spectra or by the use of stable coda derived spectra for all sequences we found that the mainshocks and larger aftershocks had significantly different spectral shapes than the smaller events the scaled 3 spectra of the larger events represented an upper bound having larger amplitudes near the corner frequency in fact an 3 5 scaling moved the larger events closer to the mean of the spectral population though the spectral shape differences persisted these results strongly suggest that earthquakes are not scaling self similarly and that complexities in the rupture process such as variable slip velocity exist between small and large events

validation of non self similar source scaling using ground motions from the 2008 wells nevada earthquake sequence abstract the behavior of earthquake source scaling has been the topic of significant debate in the earthquake source community over the past two decades and validating recent results has been difficult in this study we focus on high quality records from the 21 february 2008 m w 5 9 wells nevada earthquake and its aftershocks which provide an unprecedented opportunity to take an in depth look at the source scaling and ground motions for this earthquake sequence conflicting scaling relations were reported in two previous studies baltay et al 2010 mayeda and malagnini 2010 in addition recent comparisons of the ground motion prediction equations gmpes with this data set have shown significant overestimation of ground motions for the aftershocks while being in rough agreement with the mainshock ground motions petersen et al 2011 in order to evaluate the reported scaling relationships and better understand the observed discrepancy in the gmpe s we chose to revisit the wells nevada earthquake sequence we investigate the source parameters of the earthquakes using the s wave and coda spectral ratio methods mayeda et al 2007 and find that the stress drops of the aftershocks are 2 5 times lower than that of the mainshock we compute pseudospectral acceleration psa ratios using direct s waves from broadband records and compare with theoretical source ratios assuming the self similar and non self similar source scaling assumptions as well as ratios derived from state of the art gmpe estimates we find that we can only simultaneously match source ratios between the mainshock and selected aftershocks if we use non self similar scaling accounting for the significant differences in the stress drop between small and large earthquakes will help to enhance the prediction capability of ground motions for this region by validating the source scaling with psa ratios these results can be used as constraints in stress parameterization used in the gmpe s

a new spectral ratio method using narrow band coda envelopes evidence for non self similarity in the hector mine sequence 1 the use of local and regional s wave coda is shown to provide stable amplitude ratios that better constrains source differences between event pairs we first compared amplitude ratio performance between local and near regional s and coda waves in the san francisco bay region for moderate sized events then applied the coda spectral ratio method to the 1999 hector mine mainshock and its larger aftershocks we find 1 average amplitude ratio standard deviations using coda are 0 05 to 0 12 roughly a factor of 3 smaller than direct s waves for 0 2 f 15 0 hz 2 coda spectral ratios for the mw 7 0 hector mine earthquake and its aftershocks show a clear departure from self similarity consistent with other studies using the same datasets and 3 event pairs green s function and target events can be separated by 25 km for coda amplitudes without any appreciable degradation in sharp contrast to direct waves

end permian to mid triassic termination of the accretionary processes of the southern altaids implications for the geodynamic evolution phanerozoic continental growth and metallogeny of central asia the altaids is one of the largest accretionary orogenic collages in the world with the highest rate of phanerozoic continental growth and significant metallogenic importance it is widely accepted that subduction related orogenesis of the altaids started in the late precambrian and gradually migrated southward present coordinates however it is uncertain when and how the building of the altaids was finally completed based on structural geology geochemical geochronological and paleomagnetic data this paper presents late paleozoic to early mesozoic accretionary tectonics of two key areas north xinjiang in the west and inner mongolia in the east together with neighboring mongolia the late paleozoic tectonics of north xinjiang and adjacent areas were characterized by continuous southward accretion along the wide southern active margin of siberia and its final amalgamation with the passive margin of tarim which may have lasted to the end permian to early mid triassic in contrast in inner mongolia and adjacent areas two wide accretionary wedges developed along the southern active margin of siberia and the northern active margin of the north china craton which may have lasted to the mid triassic the final products of the long lived accretionary processes in the southern altaids include late paleozoic to permian arcs late paleozoic to mid triassic accretionary wedges composed of radiolarian cherts pillow lavas and ophiolitic fragments and high pressure ultrahigh pressure metamorphic rocks permian alaskan type zoned mafic ultramafic complexes intruded along some major faults of the tien shan we define a new tarim suture zone immediately north of the tarim craton that is probably now buried below the tien shan as a result of northward subduction of the tarim block in the cenozoic the docking of the tarim and north china cratons against the southern active margin of siberia in the end permian to mid triassic resulted in the final closure of the paleoasian ocean and terminated the accretionary orogenesis of the southern altaids in this part of central asia this complex geodynamic evolution led to formation of giant metal deposits in central asia and to substantial continental growth

u pb zircon dating of granulite metamorphism in the sludyanskiy complex eastern siberia abstract conventional multigrain and single grain zircon u pb ages were obtained for syn and post metamorphic granitoids from the sludyanskiy complex in the south western baikal region regarded as a classical precambrian terrain in the eastern siberia single grains of magmatic zircon from the syn metamorphic hypersthene bearing biotite trondhjemite and two pyroxene trondhjemite have yielded concordant u pb ages of 488 5 0 6 ma and 488 0 5 ma concordant u pb data for zircons of metamorphic origin in the syn metamorphic two pyroxene trondhjemite yield an age for the peak of the granulite facies metamorphism in the sludyanskiy complex as 477 6 2 ma the pattern of multigrain magmatic zircon samples from syn metamorphic granitoids reflects significant pb loss during the metamorphic episode this came to an end before 471 1 2 ma as demonstrated by concordant zircon data for the intrusion of post metamorphic amphibole two pyroxene quartz syenite our zircon data establish that the granulite facies reworking of the sludyanskiy complex took place during the palaeozoic and not during the paleoproterozoic as was previously suggested the age span between the intrusions of syn metamorphic and post metamorphic granitoids constrains the duration of the metamorphic episode to about 20 ma

geological setting and controls on the development of graphite sillimanite and phosphate mineralization within the jiamusi massif an exotic fragment of gondwanaland located in north eastern china abstract china is the world s biggest producer and exporter of graphite and also possesses the world s largest reserves of crystalline graphite one of the main production areas is in northeastern china around jixi in heilongjiang province where graphite sillimanite and phosphate form in original sedimentary horizons within the mashan group the mashan group is composed of khondalitic metasediments and tectonically interleaved orthogneisses all metamorphosed to granulite facies the peak conditions have been calculated at 800 850 c at 5 3 6 2 kb and the p t t path defines a tight clockwise loop involving simultaneous decrease in temperature and pressure falling to 410 490 c at less than 3 kb this metamorphic event is interpreted as resulting from continent continent collision with emplacement of mantle derived mafic magma and possible delamination at the base of the crust metamorphism has been precisely dated at 500 ma using u pb zircon shrimp techniques it appears likely that this terrane formed part of an originally more extensive orogenic belt of late pan african age rocks of similar age are recorded from east antarctica western australia india and sri lanka suggesting that the mashan group was most likely juxtaposed with these areas within gondwanaland the mechanism by which the mashan group arrived at its present position between the siberian and north china cratons is poorly constrained but it appears likely that along with the north china south china and tarim blocks it underwent a northward drift from an initial location off northern australia to finally dock with the siberian craton in the late permian to late jurassic

source rupture process of the 2007 noto hanto japan earthquake estimated by the joint inversion of strong motion and gps data abstract the source rupture process during the 2007 noto hanto earthquake which was a reverse faulting event located near the western coast of the noto peninsula in central japan was estimated by the kinematic linear waveform inversion method the waveform inversion was conducted by jointly using velocity waveforms recorded at 12 near source strong motion stations and static horizontal displacements recorded at 19 global positioning system gps stations in order to implement reliable green s functions into the inversion a one dimensional underground velocity structure for each individual strong motion station was modeled through waveform modeling of an aftershock the waveform inversion result showed the following image of the source rupture process the larger slip concentrated in the vicinity of the hypocenter and it extended to the shallow portion of the source fault with a maximum slip of 5 1 m the whole source process was characterized by the total seismic moment of 1 57 10 19 n m m w 6 7 with the rupture duration of approximately 9 s the obtained source model explained observed strong ground motions and gps measured static horizontal displacements well the slip distribution correlated well with the spatiotemporal aftershock distribution and the northeast end of the rupture was blocked by the resistive structure in the crust from these facts the 2007 noto hanto earthquake could be concluded as reactivation of preexisting seafloor active faults f14 and f15 which were reported by the previous geophysical and geological surveys off the shore of the noto peninsula

early paleozoic metamorphic rocks of the erguna block in the great xing an range ne china evidence for the timing of magmatic and metamorphic events and their tectonic implications abstract the erguna block is a crustal unit located along the eastern margin of the central asian orogenic belt caob in the far north of china it contains a variety of khondalitic rocks that include sillimanite and garnet bearing gneiss biotite plagioclase gneiss and carbonate in association with hornblende plagioclase gneiss and a variety of granitic orthogneisses these rocks are collectively referred to as the mohe complex and make up the basement rocks in this poorly exposed terrane four samples were analyzed for this study including two samples of biotite plagioclase gneiss one sample of garnet sillimanite gneiss and a sample of hornblende plagioclase gneiss all samples provide evidence of metamorphism in the form of discrete zircon grains or metamorphic rims around detrital cores and they record remarkably consistent 206 pb 238 u ages between 495 2 ma and 497 6 ma detrital zircon cores with oscillatory zoning from the two biotite plagioclase gneiss samples yield magmatic ages that range from 608 8 ma to 1015 12 ma whereas those in the garnet sillimanite gneiss range from 678 8 to 1373 17 ma these results establish that a range of meso to neoproterozoic magmatic rocks were present in the source area and contributed to the sedimentary protoliths the youngest zircon core with an age of 608 8 ma limits the maximum possible age of deposition indicating that the rocks of the mohe complex cannot be late archean to early proterozoic as previously considered the 500 ma age for the granulite facies metamorphic event in the mohe complex is identical to that recorded in the mashan complex of the jiamusi block and the hutou complex of the khanka block 1000 km to the south southeast implying that an extensive early paleozoic khondalite belt extended across much of the eastern caob rocks of similar age and metamorphic grade have also been recorded from the sayang baikal orogen along the southern margin of the siberia craton 1000 km to the west it is unclear at present whether these two belts are directly related but whatever the relationship it is evident that extensive tracts of khondalitic rocks were present in the eastern caob they were subsequently affected by high grade metamorphism in the early paleozoic forming collisional accretionary terranes that were accreted during the late pan african global event

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

empirical green s function analysis of recent moderate events in california i use seismic data from portable digital stations and the broadband terrascope network in southern california to investigate radiated earthquake source spectra and discuss the results in light of previous studies on both static stress drop and apparent stress applying the empirical green s function egf method to two sets of m 4 6 1 events i obtain deconvolved source spectra estimates and corner frequencies the results are consistent with an 2 source model and constant brune stress drop however consideration of the raw spectral shapes of the largest events provides evidence for a high frequency decay more shallow than 2 the intermediate f 1 slope cannot be explained plausibly with attenuation or site effects and is qualitatively consistent with a model incorporating directivity effects and a fractional stress drop rupture process as suggested by haddon 1996 however the results obtained in this study are not consistent with the model of haddon 1996 in that the intermediate slope is not revealed with egf analysis this could reflect either bandwidth limitations inherent in egf analysis or perhaps a rupture process that is not self similar i show that a model with an intermediate spectral decay can also reconcile the apparent discrepancy between the scaling of static stress drop and that of apparent stress drop for moderate to large events

emplacement ages geochemical and sr nd hf isotopic characterization of mesozoic to early cenozoic granitoids of the sikhote alin orogenic belt russian far east crustal growth and regional tectonic evolution abstract the sikhote alin range of the russian far east is an important accretionary orogen of the western pacific orogenic belt in order to study the formation and tectonic evolution of the orogen we performed zircon u pb dating as well as geochemical and sr nd hf isotopic analyses on 24 granitoid samples from various massifs in the primorye and khabarovsk regions the zircon dating revealed that the granitoids were emplaced from 131 to 56 ma cretaceous to paleogene in the primorye region granitoids in the coastal sikhote alin intruded the cretaceous taukha accretionary terrane from ca 90 to 56 ma whereas those along the central sikhote alin fault zone intruded the jurassic samarka accretionary terrane during ca 110 75 ma the oldest monzogranite 131 ma was emplaced in the lermontovka area of the nw primorye region granitoid massifs along the central sikhote alin fault zone in the khabarovsk region formed from 109 to 58 ma thus the most important tectonothermal events in the sikhote alin orogen took place in the cretaceous geochemical analysis indicates that most samples are i type granitoids they have initial 87sr 86sr ratios ranging from 0 7040 to 0 7083 and initial nd isotopic ratios expressed as end t values from 3 0 to 5 0 mostly 0 to 5 the data suggest that the granitoid magmas were generated by partial melting of sources with mixed lithologies including the subducted accretionary complex hidden paleozoic proterozoic basement rocks based on whole rock nd isotopic data we estimated variable proportions 36 77 of juvenile component mantle derived basaltic rocks in the generation of the granitic magmas furthermore zircon hf isotopic data ehf t 0 to 15 indicate that the zircon grains crystallized from melts of mixed sources and that crustal assimilation occurred during magmatic differentiation the quasi continuous magmatism in the sikhote alin orogen suggests that the paleo pacific plate subduction was very active in the late cretaceous the apparently regular progression of granitic intrusion ages from 80 to 56 ma in the taukha terrane may reflect oblique underflow of the paleo pacific plate beneath the eurasian continental margin subduction was not only manifested by granitic intrusion but also by abundant silicic volcanism the late cretaceous paleo pacific plate motion probably changed from parallel or sub parallel to oblique relative to the continental margin of the sikhote alin leading to the change of magmatic source region and geochemical characteristics of the derived igneous rocks late cretaceous rapid sea floor spreading at ca 100 ma induced highly active subduction and led to voluminous magmatism in the entire circum pacific realm finally the present age and isotopic study lends support to the hypothesis of geologic and tectonic correlation between sikhote alin and sw japan

variability in earthquake stress drop and apparent stress 1 we apply empirical green s function coda based analysis to four earthquake sequences in japan that span a magnitude range of 1 8 to 6 9 to measure radiated energy corner frequency and stress drop we find no systematic dependence of apparent stress or stress drop on seismic moment for these sequences and find they both are log normally distributed however we identify several anomalous events both energetic and enervated that show sharply different spectral signatures from the rest of the population these events indicate that much of the variation in apparent stress and stress drop is statistically significant which may have important implications for seismic hazard analysis

pan african metamorphic and magmatic rocks of the khanka massif ne china further evidence regarding their affinity the khanka massif is a crustal block located along the eastern margin of the central asian orogenic belt caob and bordered to the east by late jurassic early cretaceous circum pacific accretionary complexes of the eastern asian continental margin it consists of graphite sillimanite and cordierite bearing gneisses carbonates and felsic paragneisses in association with various orthogneisses metamorphic zircons from a sillimanite gneiss from the hutou complex yield a weighted mean 206 pb 238 u age of 490 4 ma whereas detrital zircons from the same sample give ages from 934 610 ma magmatic zircon cores in two garnet bearing granite gneiss samples also collected from the hutou complex yield weighted mean 206 pb 238 u ages of 522 5 ma and 515 8 ma whereas their metamorphic rims record 206 pb 238 u ages of 510 500 ma these data indicate that the hutou complex in the khanka massif records early palaeozoic magmatic and metamorphic events identical in age to those in the mashan complex of the jiamusi massif to the west the older zircon populations in the sillimanite gneiss indicate derivation from neoproterozoic sources as do similar rocks in the jiamusi massif these data confirm that the khanka massif has a close affinity with other major components of the caob to the west of the dun mi fault based on these results and previously published data the khanka massif is therefore confirmed as having formed a single crustal entity with the jiamusi and possibly the bureya massif since neoproterozoic time

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

apparent break in earthquake scaling due to path and site effects on deep borehole recordings 1 we reexamine the scaling of stress drop and apparent stress rigidity times the ratio between seismically radiated energy to seismic moment with earthquake size for a set of microearthquakes recorded in a deep borehole in long valley california in the first set of calculations we assume a constant q and solve for the corner frequency and seismic moment in the second set of calculations we model the spectral ratio of nearby events to determine the same quantities we find that the spectral ratio technique which can account for path and site effects or nonconstant q yields higher stress drops particularly for the smaller events in the data set the measurements determined from spectral ratios indicate no departure from constant stress drop scaling down to the smallest events in our data set mw 0 8 our results indicate that propagation effects can contaminate measurements of source parameters even in the relatively clean recording environment of a deep borehole just as they do at the earth s surface the scaling of source properties of microearthquakes made from deep borehole recordings may need to be reevaluated

primary uranium sources for sedimentary hosted uranium deposits in ne china insight from basement igneous rocks of the erlian basin carboniferous permian triassic and jurassic igneous basement rocks around the erlian basin in northeast china have been investigated through detailed mineralogical whole rock geochemistry geochronological data and sm nd isotope studies carboniferous permian biotite granites and volcanic rocks belong to a calc alkaline association and were emplaced during the late carboniferous early permian 313 1 286 2 ma these rocks are characterised by positive end t 3 3 5 3 and fairly young t dm model ages 485 726 ma suggesting a dominant derivation from partial melting of earlier emplaced juvenile source rocks triassic biotite granites belong to a high k calc alkaline association and were emplaced during the middle triassic 243 3 233 2 ma their negative end t 2 to 0 1 and higher t dm model ages 703 893 ma suggest a contribution from precambrian crust during the magma generation processes leading to a strong enrichment in k and incompatible elements such as th and u highly fractionated magmas crystallised in u rich biotite up to 21 ppm u and two mica granites in biotite granite the major u bearing minerals are uranothorite and allanite they are strongly metamict and the major part of their uranium 90 has been released from the mineral structure and was available for leaching mass balance calculations show that the triassic biotite granites may have at least liberated 14 000 t u km3 and thus correspond to a major primary uranium source for the u deposits hosted in the erlian basin

organic geochemical and paleoenvironmental characterization of the brown shale formation kiliran sub basin central sumatra basin indonesia abstract the central sumatra basin csb formed during the late eocene to early oligocene is the most prolific hydrocarbon basin in indonesia the brown shale formation of the pematang group is the sole known source rock for the tens of billions of barrels of oil located in the csb samples analyzed in this study were from the karbindo coal mine in the kiliran graben of the kiliran sub basin located on the western side of the csb this study incorporates advanced organic geochemical and petrographical data of samples from the brown shale formation as well as interpretations from previous studies at this location to construct a detailed paleoenvironment model for this tertiary lake the lacustrine source rock was deposited under fresh water conditions with subtle changes in the environment that resulted in significant changes in ecologies based on new data from organic petrography biomarkers microscale sealed vessel pyrolysis and characterization of the polyaromatic hydrocarbons the organic matter in the brown shale formation was determined to be sourced primarily from lacustrine organisms with a small amount of terrestrial plant input 4 methylsterane concentrations and n alkane distributions indicate that non marine dinoflagellates and botryococcus braunii a race were likely a significant portion of the local biosphere

the emplacement time of the hegenshan ophiolite constraints from the unconformably overlying paleozoic strata abstract controversy has long surrounded the emplacement time of the hegenshan ophiolite that is considered to mark a suture zone called the hegenshan heihe suture resulting from the closure of a back arc basin in the paleo asian ocean the hegenshan ophiolite in the xiaobaliang area is unconformably overlain by a sequence of paleozoic strata called the zhesi formation that consists of conglomerate sandstone siltstone and limestone some of which contain permian marine fossils of brachiopods therefore the ages of these paleozoic strata can be used to constrain the emplacement time of the hegenshan ophiolite four samples of the zhesi formation collected in the xiaobaliang area yield the detrital zircon u pb ages of 285 272 ma with the peak at 279 ma 315 288 ma with a peak at 300 ma 320 358 ma with a peak at 336 ma and 406 3 ma of which the 280 and 300 ma age groups are remarkably similar to the ages of latest carboniferous early permian gegenaobao dashizai formation or a type granites which formed under a post collisional setting however the age groups of 320 to 358 ma with a peak at 336 ma show the features of mafic ultramafic zircons in cl image most likely derived from local mafic ultramafic rocks of the hegenshan ophiolite in the xiaobaliang area which is supported by the fact of the ophiolite unconformably overlain by the middle permian zhesi formation therefore we propose that the emplacement time of the hegenshan ophiolite must have happened at some time before the middle permian 280 ma most likely between 300 and 335 ma not in the silurian devonian or mesozoic as previously considered

evidence for non self similarity and transitional increment of scaled energy in the 2005 west off fukuoka seismic sequence 1 we investigated seismic scaling relations of the 2005 west off fukuoka seismic sequence in japan using a coda based methodology two independent methods such as coda source spectrum method and coda spectral ratio method were applied to seismic waveform data recorded at four broadband seismic stations located around the epicenter of the mainshock the corner frequencies determined from both methods are consistent with each other and the scaling relations between the corner frequencies and the corresponding seismic moments are clearly non self similar in both cases moreover the scaled energy obtained from the coda source spectrum method shows that there is a transitional change in the scaled energy with seismic moment the scaled energy is larger for events with mw 5 0 than for events with mw 4 0 for events larger than mw 5 0 the scaled energy is almost constant and it means that they obey self similar scaling for events smaller than about mw 4 0 the scaled energy is more or less constant but it is difficult to decide whether it follows self similar or non self similar scaling because of scatter and the limitation of the minimum moment magnitude mw 3 4 the most important observation is a linear increment of the scaled energy between about mw 4 0 and 5 0 these observations imply that the rupture dynamics for larger and smaller earthquakes are different and that the change in dynamics may occur continuously between about mw 4 0 and 5 0 in this seismic sequence

age of palaeozoic granites and metamorphism in the tuvino mongolian massif of the central asian mobile belt loss of a precambrian microcontinent abstract the tuvino mongolian massif tmm was previously interpreted as a precambrian block within the central asian mobile belt according to this idea it consists of tectonic slices composed of metamorphic rocks of pre mesoproterozoic basement that experienced two episodes of regional metamorphism and mesoproterozoic cover rocks that were reworked together with the basement during high grade metamorphism zircon u pb dating of granitoids from all metamorphic complexes demonstrates that the earliest metamorphic event occurred at 536 6 ma significantly later than the deposition of the cover rocks regional upper amphibolite facies metamorphism which affected all metasedimentary units of the tmm occurred in the short time interval of 497 4 to 489 3 ma we propose that there is no simple basement cover relationship in the tuvino mongolian massif instead the massif consists of tectonic domains composed of heterogeneous metasedimentary successions with distinct pre metamorphic and pre tectonic histories that were juxtaposed by thrusting prior to 497 ma and then metamorphosed under upper amphibolite facies conditions we suggest that this thrusting event was associated with early palaeozoic collisional processes related to amalgamation of the central asian mobile belt our new model for the evolution of the tmm implies derivation of neoproterozoic terrigeneous metasediments from 800 900 ma granitoids formed in an andean type active continental margin setting

radiation efficiency and apparent stress of small earthquakes in a south african gold mine 1 nine triaxial borehole accelerometers were installed within 200 m along a 2650 m deep haulage tunnel in the mponeng gold mine in south africa we analyzed the high sample rate recordings 15 khz to determine source parameters of small earthquakes in the mine to study the source processes we carried out multiple time window waveform inversions for five larger events 0 8 m 1 4 that occurred within 150 m of the stations from the inversion results we could determine the fault planes for all five events and estimate the range of rupture speed we can conclude that rupture speeds were faster than 2 5 km s 65 of the shear wave velocity the radiation efficiency is written as a function of the rupture speed and becomes greater with increasing rupture speed this study indicates that radiation efficiencies of small earthquakes in the south african gold mine are almost equal to those of larger natural earthquakes we also calculated radiated seismic energies and static stress drops of the five events to investigate their apparent stresses apparent stresses of the five events were from 1 to 10 mpa and static stress drops were 1 to 20 mpa we found that the source parameters rupture speed apparent stress radiation efficiency and static stress drop did not largely differ from values for larger natural earthquakes this suggests that the dynamic rupture processes of these small events were similar to those of the larger natural earthquakes

u pb ages of detrital zircon of the paleozoic sedimentary rocks new constraints on the emplacement time of the hegenshan ophiolite ne china abstract the hegenshan ophiolite in the solonker hegenshan belt is the largest ophiolite in the central asian orogenic belt caob despite its significance in constraining regional tectonic evolution the emplacement time of the hegenshan ophiolite is still under debate in this study we provide new detrital zircon ages of the paleozoic sedimentary rocks that unconformably overlie the wusinihei ophiolite northeastern part of the hegenshan ophiolite to constrain the lower limit emplacement time of the hegenshan ophiolite the zircon ages obtained from the paleozoic sedimentary rocks range from 298 8 to 363 7 ma and show bimodal distribution at 300 320 ma peak at 308 ma and 320 360 ma peak at 330 ma the age group of 300 320 ma coincides with the age range of the volcanic rocks of the late paleozoic gegenaobao formation the age group of 320 360 ma with a peak at 330 ma may be linked to local mafic ultramafic rocks of the hegenshan ophiolite accordingly we suggest that the emplacement time of the hegenshan ophiolite should have occurred earlier than the deposition of the gegenaobao formation most likely during the time between 308 and 330 ma instead of the silurian devonian or mesozoic as previously considered

geodynamics of the western part of the mongolia okhotsk collisional belt trans baikal region russia and mongolia abstract after the western edge of the mongolian microcontinent joined the siberian continent in the region of central mongolia in the earliest permian these two continental blocks remained turned at an angle of about 120 with respect to each other and separated on greater extent of their present day boundary by an enormous gulf of the paleopacific called the mongolia okhotsk ocean closure of this ocean at the early middle jurassic boundary led to the complete collision of siberia and mongolia which by then had already become part of the mongolia north china continent this main collisional episode which lasted through the middle and late jurassic involved thrusting folding and magmatism and produced the mongolia okhotsk belt the onon island arc which was located in the mongolia okhotsk ocean was squeezed between the two major continents inasmuch as the third element the island arc was involved in the collision it is reasonable to distinguish two branches of the mongolia okhotsk suture these branches control the spatial distribution of gold mineralization in the trans baikal region on the southeastern periphery of siberia the crust thickened considerably after the collision and a plateau like uplift formed in the early cretaceous when compression ceased the collisional uplift collapsed and the thrusts were transformed into low angle normal faults the motions on which were responsible for the formation of rift basins and exhumation of metamorphic core complexes

the metamorphic characteristics of metapelites of the mashan group in mashan area eastern heilongjiang province china constraint on the crustal evolution of the jiamusi massif abstract mashan complex in the southeastern margin of the jiamusi massif has traditionally been interpreted to be the oldest stratigraphic sequence in eastern ne china here we investigated the mashan complex in the ximashan area and present lots of new la icp ms zircon u pb petrological and mineralogical chemical data in addition with phase equilibria modeling to constrain the timing of metamorphism p t conditions and the p t path of the mashan complex and furthermore to deduce the crustal evolution of the jiamusi massif the protoliths of the metapelites from the mashan complex in the ximashan area are clay rocks and sandstones whose provenance is dominantly felsic rocks which formed from a continental island arc three metamorphic generation assemblages m2 m4 are recognized in the studied samples a peak granulite facies stage a post peak near isothermal decompression stage and a late near isobaric cooling stage which together define a clockwise p t path it reveals important information related to the collision orogeny subsequent uplift and post collision process zircon u pb dating of two metapelitic samples yielded metamorphic ages of the older group varying from 535 6 to 480 5 ma which can be perfectly correlated with the age range 501 6 to 498 6 ma of magmatic activities recorded by the gneissic granite sample the data presented here together with those published allow us to preliminarily infer that the peak of the granulite facies metamorphism in the ximashan area of the jiamusi massif might have occurred at 530 500 ma the younger of the metamorphic ages 476 453 ma should be regarded as the age of late stage therefore a collision orogeny regime is favored to interpret the metamorphic evolution of metapelites of the mashan group in the mashan area

moment energy stress drop and source spectra of western united states earthquakes from regional coda envelopes we present a new method to estimate stable seismic source parameters such as energy moment and orowan stress drop using regional coda envelopes from as few as one broadband station we use the method to compute path and site corrected seismic moment rate spectra for 117 recent western united states earthquakes empirical green s function corrections were applied to our surface and body wave coda envelope measurements to generate s wave source spectra these source spectra provide stable single station estimates of radiated seismic energy es and seismic moment mo that for common events are in excellent agreement with network averaged estimates obtained using local and regional data teleseismic moment estimates are compatible with our regional results but teleseismic energy estimates appear to be nearly an order of magnitude low we estimated the seismic moment of events ranging between mw 2 2 and 7 3 and energy estimates for which we had measured at least 70 of the total energy generally events above mw 3 3 we use these estimates to examine the behavior of derived parameters such as the orowan stress drop 2 es mo while the earthquakes we studied have a small range in orowan stress drop generally between 0 1 and 20 mpa they show a strong tendency for orowan stress drop to increase with moment approximately as mo0 25 we believe this is a source effect and is not due to inadequate bandwidth or attenuation correction and note that this trend appears to continue for microearthquakes as described in a recent deep borehole study in southern california many of the large high stress drop earthquakes show complexity in their moment rate spectra near the corner frequency and cannot be fit by a simple square model instead above the first corner frequency the spectral decay ranges between f 1 0 and f 1 5 this leads to larger estimates of radiated energy than predicted with a simple square model and has implications for seismic hazard estimation coda envelopes have three main advantages over direct arrivals for estimating seismic moment and energy 1 coda amplitudes vary little with geology and source radiation anisotropy and allow accurate single station applications 2 path corrected coda amplitude measurements can be applied to very large regions allowing a comparison of source parameters throughout the western united states using a common methodology and stations 3 because long period coda can last for hours for large local and regional events it allows the analysis of seismograms with clipped early arrivals

permian geodynamic setting of northeast china and adjacent regions closure of the paleo asian ocean and subduction of the paleo pacific plate abstract northeast china and adjacent regions are located in the central east asian continent and consist tectonically of both the paleo asian and paleo pacific orogens between the siberian platform and sino korean north china block this paper discusses some hotly debated issues concerning the permian geodynamic setting of these regions based on a comprehensive analysis of available geological geochemical paleobiogeographical and paleomagnetic data spatial and temporal distribution of ophiolites and associated continental marginal sequences permian sedimentary sequences spatial distribution and geochemistry of permian magmatic rocks and the evolution of paleobiogeographical realms imply 1 that the permian marine basins in northeast china and adjacent regions include remnants of the paleo asian ocean in southeastern inner mongolia and central jilin province and active continental margins of the paleo pacific ocean 2 that the suture between the siberian and sino korean paleoplates was finally emplaced in the permian and is located in areas from suolunshan solonker eastwards through regions north to the xar moron river in southeastern inner mongolia and then central jilin province to the yanji area and 3 that the permian crustal evolution of northeast china and adjacent regions as well as parts of the siberian paleoplate was influenced by subduction of the paleo pacific oceanic plate finally the permian tectonic framework and paleogeography of northeast china and adjacent regions in central east asia are discussed briefly and early and late permian palinspastic reconstruction maps are provided

spectral ratio analyses of explosion earthquakes at sakurajima volcano japan abstract it s quite important to clarify what physical parameters control the magnitude of volcanic explosion to understand magma processes in the conduit analyses of explosion earthquakes which are associated with vulcanian eruptions enable us to quantitatively evaluate dynamic process of the explosive eruptions in the present study we analyze hundreds of explosion earthquakes recorded at sakurajima volcano japan during 2012 2013 applying a spectral ratio method that can retrieve the source spectral information without being disturbed by heterogeneous structure to three component seismograms recorded at three stations operated by japan meteorological agency we examine scaling relations in explosion earthquakes to obtain an averaged feature we group the observed explosion earthquakes into five classes i ii iii iv v according to their maximum amplitudes and calculate the spectral ratios between the five classes because vulcanian eruptions continue to effuse volcanic ash for several to tens of minutes spectral amplitude ratios are calculated by shifting a time window of 10 s for five successive 10s long time windows from the onset to coda wave the results show that the spectral amplitude ratios are characterized by the low and high corner frequencies about 2 hz and 3 5 hz respectively with increasing the magnitude of explosion earthquakes amplitude ratios at low and high frequency ranges which are 0 5 2 hz and 3 5 10 hz respectively increase while the corner frequencies do not significantly change since the explosion earthquakes at sakurajima volcano occur at a same crater without changing the vent radius the observed spectral amplitude ratio change may be attributed to pressure changes in the conduit another finding is that the amplitudes of spectral ratio gradually decrease with lapse time keeping the corner frequencies such a lapse time dependence of spectral ratios is completely different from those of tectonic earthquakes in which direct and coda waves show a same spectral amplitude ratio we infer that the early part of the seismic waves of explosion earthquakes is generated by an initial rapid pressure release in the conduit while coda waves are by successive oscillations of the magma system during continuous ash emission

source scaling of inland crustal earthquake sequences in japan using the s wave coda spectral ratio method we estimate corner frequencies and stress drops for 298 events ranging from m w 3 2 7 0 in 17 inland crustal earthquake sequences in japan to investigate the source scaling and variation in stress drops we obtain the source spectral ratio from observed records by the s wave coda spectral ratio method the advantage of using the s wave coda is in obtaining much more stable source spectral ratios than using direct s waves we carefully examine the common shape of the decay of coda envelopes between event pair records the corner frequency and stress drop are estimated by modeling the observed source spectral ratio with the omega square source spectral model we investigate the dependences of stress drops on some tectonic effects such as regionality focal mechanism and source depth the principal findings are as follows 1 a break in self similar source scaling is found in our dataset events larger than m w 4 5 show larger stress drops than those of smaller events 2 stress drops of aftershocks are mostly smaller than those of mainshocks in each sequence 3 there are no systematic differences between stress drops of events occurring inside and outside the niigata kobe tectonic zone in japan 4 clear dependence of the faulting type on stress drops cannot be seen 5 stress drops of aftershocks depend on their source depth 6 the crack size obtained from the corner frequency corresponds to the total rupture area of heterogeneous slip models for large events

comparison of direct and coda wave stress drop measurements for the wells nevada earthquake sequence 1 i calculate the corner frequencies and stress drops of the seven largest earthquakes m4 6 in the wells nevada sequence 2008 using both coda and direct waves i use spectral ratio empirical green s function egf and methods to investigate whether differences and uncertainties in the analyses could affect the calculated source parameters i find that the source spectral ratios from the coda and direct s waves are similar for the same pairs of earthquakes but that the source spectra and corresponding source parameters depend systematically on whether the earthquake of interest is the larger or smaller within the spectral ratio mayeda and malagnini 2009a calculated coda spectral ratios between the m6 main shock and six large aftershocks m 4 and performed a combined inversion to calculate source parameters they found that the main shock had a higher stress drop than the large aftershocks i model the identical spectral ratios individually in the manner that i use for direct waves i find that the choice of source model and fitting procedure produces significant random scatter but no systematic biases i calculate direct wave ratios for the same earthquake pairs and find higher variability but no systematic difference in the results lastly i use m2 8 3 2 aftershocks as egfs for the large aftershocks these spectral ratios yield significantly higher corner frequencies and stress drops for the large aftershocks than when the same earthquakes are the denominator in ratios with the main shock to improve the quality of egf analyses i propose strict objective criteria for acceptance of a spectral ratio fit 1 observable source pulse 2 the amplitude ratio of the low to high frequency limits of the fit is at least 5 and 3 the corner frequency only varies by 50 when the variance is within 5 of the minimum

seismic scaling relations and aftershock activity from the sequences of the 2004 mid niigata and the 2005 west off fukuoka earthquakes mw 6 6 in japan 1 we investigate seismic scaling relations and seismic activity using two japanese earthquake sequences the 2004 mid niigata prefecture earthquake mnpe and the 2005 west off fukuoka prefecture earthquake wofe sequences although the mainshocks of the two sequences have the same mw of 6 6 the aftershock activities are different from each other in term of moment release the mnpe produced a large number of aftershocks including six events with mw 5 5 over a period of about two weeks on the other hand the wofe sequence did not produce aftershocks that exceeded mw 5 5 in the scaling relationship of seismic moment m0 versus corner frequency fc obtained from the mnpe sequence the fc s tend to decrease with decreasing m0 between mw 3 5 and 6 6 and the best fit line determined in a least squares sense is m0 fc 3 41 in the wofe sequence the best fit line is m0 fc 3 06 in the same mw range the fc range of small aftershocks is lower in the mnpe sequence than in the wofe sequence moreover the m0 fc relations for small events 3 5 mw 4 0 in the mnpe sequence are different between the events on the main faults m0 fc 3 53 and the off main fault events m0 fc 4 44 these results suggest that there is difference or variation in the scaling relation even in the same mw range probably reflecting different tectonic or seismogenic conditions

low stress drop earthquakes in the rupture zone of the 1992 nicaragua tsunami earthquake tsunami earthquakes events that generate larger than expected tsunami and are deficient in high frequency seismic radiation are rare but hazardous to coastal populations one model for these events is shallow rupture through low strength materials we calculate seismic moment corner frequency and stress drop for 216 earthquakes 2 1 mw 4 7 november 2005 june 2006 within and external to the 1992 nicaragua tsunami earthquake rupture zone to test the hypothesis that differences in fault zone properties defined the limits of the 1992 tsunami rupture zone and continue to produce spatial variations in earthquake source properties mean stress drop of events within the rupture area is 1 2 mpa and 5 5 mpa for events just outside of the rupture zone with similar magnitude earthquakes in each group our results demonstrate different source parameter characteristics for microseismicity in the region of a past tsunami earthquake

stress drops and radiated energies of aftershocks of the 1994 northridge california earthquake we study stress levels and radiated energy to infer the rupture characteristics and scaling relationships of aftershocks and other southern california earthquakes we use empirical green functions to obtain source time functions for 47 of the larger m 4 0 aftershocks of the 1994 northridge california earthquake m6 7 we estimate static and dynamic stress drops from the source time functions and compare them to well calibrated estimates of the radiated energy our measurements of radiated energy are relatively low compared to the static stress drops indicating that the static and dynamic stress drops are of similar magnitude this is confirmed by our direct estimates of the dynamic stress drops combining our results for the northridge aftershocks with data from other southern california earthquakes appears to show an increase in the ratio of radiated energy to moment with increasing moment there is no corresponding increase in the static stress drop this systematic change in earthquake scaling from smaller to larger m3 to m7 earthquakes suggests differences in rupture properties that may be attributed to differences of dynamic friction or stress levels on the faults

detrital zircon u pb geochronology and stratigraphy of the cretaceous sanjiang basin in ne china provenance record of an abrupt tectonic switch in the mode and nature of the ne asian continental margin evolution abstract the age spectra obtained from 505 spots of detrital zircon u pb ages of five representative sandstone samples from the sanjiang basin in ne china point to a significant change in its provenance during the coniacian santonian the predominant detrital source for the sanjiang basin during the early cretaceous was the zhangguangcai range magmatic belt and jiamusi block along its western and southern periphery whereas it changed in the late cretaceous to its eastern periphery the timing of these inferred changes in the detrital source regions and drainage patterns nearly coincide with the age of a regional unconformity in and across the basin the time interval of non deposition and unconformity development was coeval with a transitional period between an extensional tectonic regime in the early cretaceous and a contractional deformation episode in the late cretaceous the sanjiang basin evolved during this time window from a backarc to a foreland basin the migration of the coastal orogenic belt and the fold and thrust belt development farther inland during the late cretaceous marked the onset of regional scale shortening and surface uplift in the upper plate of a flat or very shallow dipping subduction zone the stratigraphic record the detrital source and geochronology of the basinal strata and the internal structure of the sanjiang basin present therefore an important record of a tectonic switch in the nature of continental margin evolution of northeast asia during the late mesozoic

coda derived source parameters of earthquakes and their scaling relationships in the korean peninsula we applied the coda derived source spectrum method of mayeda et al 2003 to earthquakes in and around the korean peninsula after empirical calibra tions we derived source spectra of the earthquakes from the coda derived spectra we estimated valuable source parameters such as the seismic moment corner frequency and radiated energy for small events with mw 3 5 we derived simple linear relation ships between the coda spectral amplitudes and local magnitudes reported from the korea meteorological administration and korea institute of geoscience and mineral resources these relationships can be used to estimate stable local magnitudes for future earthquakes using a small number of stations to investigate whether the earth quakes occurring in this region obey self similarity we examined the scaling relation ships between dynamic and static source parameters such as the corner frequency radiated energy and scaled energy versus seismic moment the scaling relationship between the corner frequency and seismic moment showed clear nonself similarity with a scaling parameter of 0 54 this value is more or less consistent with previous results for different regions scaling relations of radiated energy and scaled energy versus the seismic moment also show size dependent behavior that cannot be explained by self similarity this result implies that the rupture dynamics of small and large earthquakes are different in this region our observation provides further evidence supporting the nonself similarity of earthquakes

apparent stress and corner frequency variations in the 1999 taiwan chi chi sequence evidence for a step wise increase at mw 5 5 1 apparent stress and corner frequencies are measured for the chi chi taiwan sequence beginning with the mw 7 6 mainshock on 20 september 1999 using the coda source ratio method we obtained stable source ratio estimates using broadband stations on taiwan we find the following 1 for the mainshock and 3 of the larger aftershocks apparent stress is clustered around 0 8 mpa 0 1 mpa 2 events below mw 5 5 exhibit lower apparent stress with larger scatter ranging between 0 08 and 0 8 mpa and are spatially variable 3 the brune 1970a 1970b omega square source model fits the spectral shape for events 4 7 mw 7 6 however a step wise break in self similarity exists at mw 5 5 we hypothesize that larger events are subject to the regional state of stress whereas smaller aftershocks are sensitive to the local state of stress from stress field redistribution following the mainshock and or fault zone lubrication that affects only larger events

the hulan group its role in the evolution of the central asian orogenic belt of ne china the hulan group of central jilin province northeastern ne china consists of felsic volcanic and sedimentary rocks that underwent sub greenschist to amphibolite facies metamorphism and multiple phases of deformation during formation of the central asian orogenic belt young nd model ages of 1100 ma obtained in this study do not support earlier models that the hulan group was either rifted from the north china craton to the south or from the jiamusi block to the north since both these blocks have much older nd model ages detrital zircon u pb ages from a meta sedimentary rock of the hulan group define a maximum age of deposition of 287 6 ma not early palaeozoic as previously believed rb sr mineral isochron data indicate that metamorphism of the hulan group occurred at 250 ma this conclusion is further supported by an age of 248 4 ma for the dayushan granite which intruded the hulan group these new isotopic data together with evaluation of the regional geology indicate that final oceanic closure in the chinese segment of the central asian orogenic belt took place in the late permian the hulan area is located along the solonker xra moronchangchun suture that extends from inner mongolia across to central jilin province it is this zone that marks the final ocean closure resulting in the amalgamation of the north china and siberian cratons 2007 elsevier ltd all rights reserved