geochemistry and petrogenesis of intrusive and extrusive ophiolitic plagiogranites central anatolian crystalline complex turkey plagiogranites associated with the sarikaraman ophiolite of the central anatolian crystalline complex turkey closely resemble other plagiogranites from supra subduction zone type ophiolites of neotethys the ophiolite is remarkable in displaying a higher proportion of the plagiogranite suite ca 10 by volume than is usually associated with such bodies the sarikaraman plagiogranites are represented by intrusive sheets and netvein trondhjemites largely developed at the top of the upper gabbros and as multiphase dykes within the sheeted dyke complex the plagiogranite dykes are considered to feed extrusive silicified rhyolites associated with the basaltic lavas in the volcanic section of the ophiolite field relations suggest that the trondhjemites were probably generated from the roof section of a dynamic and evolving gabbroic magma chamber both the deep seated trondhjemites and the volcanic rhyolites constitute the sarikaraman plagiogranite suite geochemically there is complete overlap between the intrusive trondhjemites and extrusive rhyolites which are characterised by morb normalized low hfs element contents with small negative nb ta anomalies and variably enhanced lil element abundances unlike other plagiogranites however the sarikaraman suite is not characterized by consistently low k2o contents a feature that reflects the variable mobilization of the lil elements under lower greenschist facies conditions the ree are uniformly enriched relative to the basic components of the complex but have similar normalized patterns exhibiting mild light ree depletion in terms of their origin the initial or most primitive plagiogranite melts could have been generated by either fractional crystallization 70 85 of clinopyroxene feldspar amphibole or partial melting 5 15 batch melting of a gabbroic source material although only the first process can produce most of the range of the plagiogranite compositions as a group the plagiogranites exhibit some degree of internal variation which can be generated by further fractionation largely dominated by feldspar with minor apatite and amphibole

second round of evaluations of proposed earthquake precursors this review summarizes the result of the second round of nominations for the iaspei preliminary list of significant precursors currently this list contains five cases of precursors 1 foreshocks 2 preshocks 3 seismic quiescence before major aftershocks 4 radon decrease in ground water and 5 ground water level increase a list of four cases that could not be accepted nor rejected by the panels reviewing them contains three on crustal deformations and one on seismic quiescence in the second round 10 nominations were evaluated nine new ones and one which had been considered previously two were accepted for the list two were placed in the category of undecided cases to date a total of 40 nominations have been evaluated by iaspei for 37 of these the nominations the mail reviews the panel opinions and where supplied the author s reply were published this evaluation process remains active throughout the international decade for natural hazards reduction additional nominations are invited

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

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

precursory seismic quiescence seventeen cases of precursory seismic quiescence to mainshocks with magnitudes fromml 4 7 toms 8 0 are summarized the amount of rate decrease ranges from 45 to 90 the significance of these changes varies between 90 and 99 99 the assumption that the background rate is approximately constant is fulfilled in most crustal volumes studied all quiescence anomalies seem to have abrupt beginnings and the rate during the anomalous period is fairly constant the duration of the precursors ranges from 15 to 75 months and it is not clear what factors determine that time at least three successful predictions have been based on seismic quiescence these cases have shown that mainshocks can be predicted based on quiescence but they have also shown that the interpretation of the data in real time is difficult and nonunique if a false alarm is defined as a period of quiescence with a significance level larger than a precursory quiescence in the same tectonic area then we estimate based on searches in four areas that the false alarm rate may be on the order of 50 failure to predict may be expected in perhaps 50 of mainshocks even in carefully monitored areas quiescence cannot be used as a precursor in tectonic environments with low seismic activity most characteristics of the phenomenon are still poorly defined but data exist which probably permit at least a doubling of the presently available data on case histories

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

comment on continental geochemical signatures in dacites from iceland and implications for models of early archaean crust formation by willbold m hegner e stracke a and rocholl a

pattern informatics and its application for optimal forecasting of large earthquakes in japan pattern informatics pi technique can be used to detect precursory seismic activation or quiescence and make an earthquake forecast here we apply the pi method for optimal forecasting of large earthquakes in japan using the data catalogue maintained by the japan meteorological agency the pi method is tested to forecast large magnitude m 5 earthquakes spanning the time period 1995 2004 in the kobe region visual inspection and statistical testing show that the optimized pi method has forecasting skill relative to the seismic intensity data often used as a standard null hypothesis moreover we find in a retrospective forecast that the 1995 kobe earthquake m 7 2 falls in a seismically anomalous area another approach to test the forecasting algorithm is to create a future potential map for large m 5 earthquake events this is illustrated using the kobe and tokyo regions for the forecast period 2000 2009 based on the resulting kobe map we point out several forecasted areas the epicentral area of the 1995 kobe earthquake the wakayama area the mie area and the aichi area the tokyo forecast map was created prior to the occurrence of the oct 23 2004 niigata earthquake m 6 8 and the principal aftershocks with 5 0 m we find that these events were close to in a forecasted area on the tokyo map the pi technique for regional seismicity observation substantiates an example showing considerable promise as an intermediate term earthquake forecasting in japan

true k feldspar granites in oceanic crust masirah ophiolite sultanate of oman a upb and smnd isotope study abstract this paper presents u pb and sm nd isotope data of various rock types from the masirah ophiolite sultanate of oman the study aimed at delineating the source and genesis of k feldspar granites which are emplaced in the oceanic crust theses granites clearly intruded the sequence prior to its obduction and show initial pb and nd isotopic compositions which exclude significant continental crust contribution during their generation both geochronological and geochemical data are in conflict with the assumption of a continuous differentiation process for granite generation i e the granites are not the final differentiation chain products of oceanic crust generation their emplacement into previously thinned oceanic crust and their possible genetic relationship with partly explosive alkaline volcanism suggest that the masirah granites were generated by partial melting at depth as a consequence of transtensional movements associated with transform faults these faults may have favored deep hydration of the crust which initiated melting probably enhanced by heat transfer from a nearby hotspot

evidence for mogi doughnut behavior in seismicity preceding small earthquakes in southern california 1 we examine the average space time behavior of seismicity preceding m 2 5 earthquakes in southern california from 1981 to 2005 using a high resolution catalog and identify regions of enhanced activity in a 1 day period preceding larger earthquakes at distances comparable to their predicted source radii the difference in precursory behavior between large and small earthquakes is subtle but statistically significant when averaged over many earthquakes and it has similarities to the mogi doughnut seismicity pattern observed to occur prior to some m 6 and larger earthquakes these results indicate that many standard earthquake triggering models do not account for all of the processes involved in earthquake occurrence

silicic magmas from the emeishan large igneous province southwest china petrogenesis and their link with the end guadalupian biological crisis abstract the emeishan large igneous province in sw china comprises a bimodal mafic silicic suite with the silicic rocks occurring at the uppermost part of the thick lava sequence the silicic rocks have an age of 257 263 ma and are thus roughly coeval with the guadalupian loping g l boundary event most silicic rocks trachyte and rhyolite from the emeishan province have rather uniform e nd values 1 to 2 9 that are comparable with the uncontaminated high ti basalts this fact and the remarkably narrow ranges of incompatible element ratios e g zr nb of the basalt silicic suite indicate a genetic relationship between basalt and silicic members the significant difference between the emeishan rocks and the experimental melts of hydrated basaltic crust suggests the fractional crystallization of basaltic magma rather than crustal melting as the major petrogenetic process for the formation of silicic rocks indeed their major and trace element trends can be modeled by fractionation of the observed mineral phases feldspar clinopyroxene fe ti oxide and apatite in contrast to the virtually closed system differentiation processes associated with trachytes the rhyolites may have experienced interaction with upper crustal material during ascent the geochemical characteristics and recent assessment of timing of the emeishan volcanism suggest the emeishan rhyolites as the potential source of the widespread clay bed at the g l boundary in south china this enhanced the causal link between the emeishan eruption and the end guadalupian biological crisis

precursory seismic activation and critical point phenomena in this paper we relate the behavior of seismicity prior to a characteristic earthquake to the excitation in proximity to a spinodal instability we illustrate the spinodal instability as the upper limit of superheated water prior to a steam explosion we draw an analogy between the steam explosion and a characteristic earthquake and show that the power law activation associated with the spinodal instability is essentially identical to the power law increase in benioff strain observed prior to characteristic earthquakes we find that theory and actual data give very similar results

case 23 nomination of precursory seismic quiescence as a significant precursor several cases of extremely strong quiescences have been investigated in great detail and it was found that they are statistically highly significant and that they cannot be reasonably explained by catalog heterogeneity several additional cases of quantitatively measured quiescence have been documented the method of measuring quiescence has progressed from using visual means to using a quantitative approach and the understanding of the noise sources has significantly advanced during the last few years therefore i feel that quiescence is a real phenomenon and the method to detect it has matured to a point that is acceptable for the list of significant precursors although considerably more work needs to be done to understand this parameter and its role in the earthquake generation process

seismic quiescence before the m 7 1988 spitak earthquake armenia a detailed analysis of the 35 yr of seismicity between 1962 and 1997 using a gridding technique shows that the m7 spitak earthquake of 1988 december 7 was preceded by a quiescence anomaly that started at approximately 1984 0 5 and lasted about 5 0 5 yr up to the main shock this quiescence anomaly had a radius of about 20 3 km estimated from circular areas with 75 per cent rate decrease centred at the point of maximum significance of the anomaly the quiescence was clearly present in the aftershock volume during the 5 yr before the 1988 main shock but its statistically strongest expression was located 30 km nw of the epicentre this anomaly fulfills the association rules between precursory quiescence anomalies and main shocks even for a tight definition and is therefore proposed as a case of precursory quiescence the largest value of the standard deviate z found by random selection of samples by gridding was z 14 for a time window of tw 3 yr using a sample size of n 300 events this makes this anomaly the strongest observed so far and it is the first documented in an environment of continental collision there are no false alarms exceeding in significance the precursor the armenian earthquake catalogue used for this study had 4600 earthquakes with m mmin 2 2 in the area bounded by 39 5 to 42 n 42 5 to 47 e from the point of view of homogeneous reporting this is the best catalogue we have analysed so far the limits of the data used and the density of the grid are dictated by the data and have no influence on the results the choice of free parameters does not influence the results significantly within the following limits 100 n 500 2 tw 7 2 2 mmin 2 8

how can one test the seismic gap hypothesis the case of repeated ruptures in the aleutians the test that kagan and jackson 1991 1995 applied to the seismic gap hypothesis did not bring us closer to understanding the generation of large earthquakes on the contrary it led some to the conclusion that the rebound theory of earthquake generation should be rejected we disagree with this point of view and argue that a global test of the simplified gap hypothesis cannot be done because it cannot account for differences in the slip history of fault segments and tectonic differences between separate plate boundaries kagan and jackson did show however that the original gap hypothesis was oversimplified and should be refined we propose that consideration of all the facts including slip history and seismicity patterns in the andreanof islands show that the concept of seismic gaps and the elastic rebound theory are correct for that segment of the plate boundary the coseismic slip in the m w 8 7 earthquake that broke this plate boundary segment in 1957 was only 2 m as published before the repeat earthquake of 1986 m w 8 and thus using a plate convergence rate of 7 3 cm year the return time in this cycle was expected to be less than 30 years unless substantial aseismic creep occurs this supports the time predictable model of mainshock recurrence in addition kisslinger et al 1985 and kisslinger 1986 noticed a seismic quiescence in the subsequent source volume before the 1986 earthquake and attempted to predict it the specific parameters he estimated were not entirely correct although his interpretation of the observed quiescence as a precursor was we conclude that the 1986 m w 8 andreanof earthquake was not an example that disproves the seismic gap hypothesis on the contrary it shows that the hypothesis that plate motions reload plate boundaries after most of the elastic energy is released in great ruptures was correct in this case this suggests that great earthquakes occur preferably in mature gaps we believe the testing of the seismic gap hypothesis by algorithm on a global scale is an example that illustrates that overly simplified tests can lead to erroneous conclusions to make progress in the actual understanding of the physics of the process of great earthquake ruptures one must consider all the facts known for case histories

la sio2 and yb sio2 systematics in mid ocean ridge magmas implications for the origin of oceanic plagiogranite analytical expressions for the variation in d la and d yb with increasing liquid sio2 for olivine plagioclase augite hornblende orthopyroxene magnetite and ilmenite brophy in contrib mineral petrol 2008 online first have been combined with numerical models of hydrous partial melting of mid ocean ridge mor cumulate gabbro melting and fractional crystallization of slightly hydrous mid ocean ridge basalt morb magma to assess a melting versus fractionation origin for oceanic plagiogranite for felsic magmas 63 wt sio2 the modeling predicts the following mor cumulate gabbro melting should yield constant or decreasing la and constant yb abundances with increasing liquid sio2 the overall abundances should be similar to those in associated mafic magmas morb fractional crystallization should yield steadily increasing la and yb abundances with increasing sio2 with overall abundances significantly higher than those in associated mafic magmas application to natural occurrences of oceanic plagiogranite indicate that both mor cumulate gabbro melting and morb fractionation are responsible application of the model results to icelandic rhyolites strongly support a fractional crystallization rather than a crustal melting origin

statistical physics approach to understanding the multiscale dynamics of earthquake fault systems 1 earthquakes and the faults upon which they occur interact over a wide range of spatial and temporal scales in addition many aspects of regional seismicity appear to be stochastic both in space and time however within this complexity there is considerable self organization we argue that the occurrence of earthquakes is a problem that can be attacked using the fundamentals of statistical physics concepts of statistical physics associated with phase changes and critical points have been successfully applied to a variety of cellular automata models examples include sandpile models forest fire models and particularly slider block models these models exhibit avalanche behavior very similar to observed seismicity a fundamental question is whether variations in seismicity can be used to successfully forecast the occurrence of earthquakes several attempts have been made to utilize precursory seismic activation and quiescence to make earthquake forecasts some of which show promise

b o th isotope systematics in icelandic tephra abstract we report new boron concentrations and isotope compositions measured by ion microprobe on holocene tephra samples from 6 icelandic volcanoes the b concentrations range over almost a factor of 10 from 1 50 0 10 to 13 10 0 10 ppm in basalt and obsidian respectively the highest 11b 16 9 2 2 and 6 1 1 6 measured in rhyolites from the rift related askja and krafla volcanoes in contrast the lowest 11b values 5 3 and 5 2 observed in samples with the some of the highest 18o 4 92 and 5 18 respectively and 230th 232th 1 067 and 1 030 respectively correspond to a normal mantle signature the variations of boron isotope compositions in the icelandic tephra and their negative correlations with both 18o and 230th 232th strongly support the mixing between mantle derived basalts and crustal rhyolites produced from anatexis of hydrothermally altered basaltic crust the low 18o in combination with high 11b values in rhyolite is best explained by the presence of seawater derived b in a hydrothermal fluid that is mostly of meteoric origin

the recent isla san luis volcanic centre petrology of a rift related volcanic suite in the northern gulf of california mexico abstract isla san luis one of the most recent eruptive centres in the gulf of california presents a complete magma evolution trend from basaltic andesites to rhyolites the less evolved lavas are palagonite tuffs related to surtseyan type activity which characterized the emergent stage of the island subaerial lava flows and later high energy hydromagmatic eruptions are dacites which make up the tuff rings of the southeastern corner of the island rhyolites are the latest erupted products and the development of the younger dome in the centre of the island was preceded by ash and pumice fallout containing quenched bombs with an obsidian crust and a pumiceous core basaltic andesites contain olivine fo87 80 calcium rich plagioclase and sparse clinopyroxene microphenocrysts the typical mineralogy of dacitic and rhyolitic lavas is plagioclase two pyroxenes major and trace elements vary regularly with mgo taken as a differentiation index isla san luis lavas are enriched in lile and depleted in nb ta and ti their characteristics are intermediate between tholeiitic and calc alkaline lavas they are also lree enriched and the la yb n ratios steepen slightly with differentiation such an evolution is better explained by combined fractional crystallization and assimilation processes

modification of an oceanic plateau aruba dutch caribbean implications for the generation of continental crust the generation of the continental crust may be connected to mantle plume activity however the nature of this link and the processes involved are not well constrained an obstacle to understanding relationships between plume related mafic material and associated silicic rocks is that later tectonic movements are liable to obscure the original relationships particularly in ancient greenstone belts studies of younger analogous regions may help to clarify these relationships on the island of aruba in the southern caribbean a sequence of partly deformed mafic volcanic rocks intruded by a predominantly tonalitic batholith is exposed the mafic lavas show geochemical and isotopic affinities with other basaltic picritic and komatiitic rocks that crop out elsewhere in the caribbean these are well documented as belonging to an 88 91 ma plume related oceanic plateau which is allochthonous with respect to the americas and is thought to have been formed in the pacific region the 85 to 82 ma tonalitic rocks share some geochemical characteristics high sr and ba low nb and y with archaean tonalite trondhjemite granodiorite ttg suites field relationships suggest that deformation of the plateau sequence possibly related to collision with a subduction zone was synchronous with intrusion of the aruba batholith new incremental heating 40ar 39ar dates combined with existing palaeontological evidence show that cooling of the batholith occurred shortly after eruption of the plateau basalt sequence sr nd isotopic data for both rock suites are uniform 87sr 86sri 0 7035 endi 7 whereas pb isotopes are more variable plateau sequence 206pb 204pb 18 6 19 1 207pb 204pb 15 54 15 60 208pb 204pb 38 3 38 75 aruba batholith 206pb 204pb 18 4 18 9 207pb 204pb 15 51 15 56 208pb 204pb 38 0 38 5 this suggests that there has been a minor sedimentary input into the source region of the batholith however the limited time interval between basaltic and tonalitic magmatism makes a normal subduction related origin for the tonalites improbable instead models involving derivation of tonalite from partial melting of the plateau sequence or alternatively genesis in an unusual subduction zone environment are investigated

interevent times in a new alarm based earthquake forecasting model summary this study introduces a new earthquake forecasting model that uses the moment ratio mr of thefirst to second order moments of earthquake interevent times as a precursory alarm index to forecast large earthquake events this mr model is based on the idea that the mr is associated with anomalous long term changes in background seismicity prior to large earthquake events in a given region the mr statistic is defined as the inverse of the index of dispersion or fano factor with mr values or scores providing a biased estimate of the relative regional frequency of background events here termed the background fraction to test the forecasting performanceofthisproposedmrmodel acompositejapan wideearthquakecatalogueforthe years between 679 and 2012 was compiled using the japan meteorological agency catalogue for the period between 1923 and 2012 and the utsu historical seismicity records between 679 and 1922 mr values were estimated by sampling interevent times from events with magnitude m 6 using an earthquake random sampling ers algorithm developed during previous research three retrospective tests of m 7 target earthquakes were undertaken to evaluate the long intermediate and short term performance of mr forecasting using mainly molchan diagrams and optimal spatial maps obtained by minimizing forecasting error defined by miss and alarm rate addition this testing indicates that the mr forecasting technique performs well at long intermediate and short term the mr maps produced during longterm testing indicate significant alarm levels before 15 of the 18 shallow earthquakes within the testing region during the past two decades with an alarm region covering about 20percent alarm rate of the testing region the number of shallow events missed by forecasting was reduced by about 60percent after using the mr method instead of the relative intensity ri forecasting method at short term our model succeeded in forecasting the occurrence region of the 2011 mw 9 0 tohoku earthquake whereas the ri method did not cases where a period of quiescent seismicity occurred before the target event often lead to low mr scores meaning that the target event was not predicted and indicating that our model could be further improved by taking into account quiescent periods in the alarm strategy

structure of the scandes lithosphere from surface to depth abstract in this review we give an overview of geophysical data and models available for the scandinavian mountains and adjacent areas as they are of relevance to the debate about the existence and cause of neogene uplift emphasis is given to potential field and petrophysical data of which the earth science communities of norway and sweden have a long tradition of acquisition and interpretation this is reflected in the wealth and dense coverage of data available the topography of the scandes mountain chain correlates to a large degree with a bouguer gravity low which suggests isostatic compensation but comparison with magnetic and petrophysical data shows that the gravity low is partly influenced by the trans scandinavian igneous belt signals due to the effects of surface geology can be further eliminated by considering the near surface density distribution as provided by petrophysical sampling to illuminate the entire lithospheric structure active and passive seismic and magnetotelluric data can be used recent and ongoing experiments are aimed at improving the existing models of the lithosphere integration of these different geophysical data sets allows the structure of the lithosphere of the scandes and its surroundings to be addressed seismic models show no pronounced crustal root below the scandes which could provide isostatic compensation but instead an increase of crustal thickness towards the central fennoscandian shield from the integrated model isostatic compensation is inferred to be largely controlled by the density distribution of the crust and that a high density lower crust to the east of the scandes is necessary to achieve isostatic equilibrium on a regional scale we demonstrate the typical crustal structure with profiles crossing from the scandes into the shield and a combined onshore offshore basement map

widespread seismicity excitation throughout central japan following the 2011 m 9 0 tohoku earthquake and its interpretation by coulomb stress transfer 1 we report on a broad and unprecedented increase in seismicity rate following the m 9 0 tohoku mainshock for m 2 earthquakes over inland japan parts of the japan sea and izu islands at distances of up to 425 km from the locus of high 15 m seismic slip on the megathrust such an increase was not seen for the 2004 m 9 1 sumatra or 2010 m 8 8 chile earthquakes but they lacked the seismic networks necessary to detect such small events here we explore the possibility that the rate changes are the product of static coulomb stress transfer to small faults we use the nodal planes of m 3 5 earthquakes as proxies for such small active faults and find that of fifteen regions averaging 80 by 80 km in size 11 show a positive association between calculated stress changes and the observed seismicity rate change 3 show a negative correlation and for one the changes are too small to assess this work demonstrates that seismicity can turn on in the nominal stress shadow of a mainshock as long as small geometrically diverse active faults exist there which is likely quite common

origin of k feldspar megacrysts in rhyolites from the emeishan large igneous province southwest china abstract silicic rocks occur in the uppermost units of the longest volcanic succession 5000 m thick in the binchuan area of the permian emeishan flood basalt province of sw china they are predominantly rhyolites and to a lesser extent trachytes both containing potassium feldspar megacrysts as the dominant phenocryst phase up to approximately 20 mm in size these megacrysts contain domains of albite arranged in vein like networks likely formed by post magmatic alteration crystal size distributions csd suggest that these megacrysts grew in a stable magmatic system consistent with relatively uniform core to rim compositional k 2 o 14 16 wt and isotopic profiles 208 pb 206 pb ratios 2 06 2 08 0 005 both whole rock trace elements and pb isotope ratios of these silicic rocks are similar to the emeishan basalts suggesting a common source for both mafic and felsic units and a limited role of crustal melting in genesis of the felsic units major and trace element models further indicate that these rocks could not have formed exclusively by re melting of old crust or solidified basaltic rock but must have formed through crystal fractionation from the flood basalts or possibly partial melting of basaltic rock followed by fractional crystallization k feldspar bearing rhyolites are also observed in the last stages of other large igneous provinces we suggest that they represent final melt fractions and their appearance in the magmatic system coincides with waning of voluminous magmatic activities