the cr renazzo type carbonaceous chondrite group and its implications abstract a petrologic geochemical and oxygen isotopic study of eight meteorites identified as cr renazzo type chondrites reveals that they have a set of similar properties that distinguishes them from other chondrite groups and confirms cr as a carbonaceous chondrite group characteristics of the cr group include 1 1 abundant large multilayered fe ni metal rich type i chondrules 2 2 abundant matrix and dark inclusions di that contain microchondrules microfragments and magnetite framboids and platelets 3 3 unique assemblages of serpentine and chlorite rich phyllosilicates and ca carbonates 4 4 ca carbonate rims on chondrules 5 5 abundant fe ni metal with a positive ni vs co trend and a solar ni co ratio 6 6 low abundance of refractory rich inclusions 7 7 amoeboid olivine aggregates aoa with mn rich and mn poor forsterite and 8 8 oxygen isotopic compositions that form a unique mixing line the cr chondrites are breccias consisting of two major components the large layered chondrules and the matrix dark inclusions al rais is an anomalous member in having a higher abundance of the dark inclusion component 70 vol and this accounts for its having a higher volatile content than other members of the group the conditions that prevailed during aqueous alteration of the cr chondrites differed from those of other hydrated chondrite groups and may be the result of a higher temperature environment than that for the ci and cm chondrites the cr chondrite components chondrules matrix dark inclusions etc experienced aqueous alteration to differing degrees prior to assembly of the host chondrites and dark inclusions represent a lithology that was altered by water to a greater degree than the rest of the meteorite the overall degree of hydration in cr chondrites varies among meteorites with al rais being the most hydrated the oxygen isotopic variation of the whole rocks chondrules and matrices may be related to degree of hydration indicating that cr chondrites interacted with a water rich component having heavy oxygen and that was the same as ci and cm water

origin of zoned metal grains in the que94411 chondrite laser ablation inductively coupled plasma mass spectrometry la icp ms was used to measure distributions of the siderophile elements p v cr fe co ni mo ru rh pd w re os ir and pt in metal grains in the metal rich chondrite que94411 with a spatial resolution of similar to 30 mum the platinum group elements pges except pd exhibit radial zoning in these grains that mimics that previously observed in ni and co the concentrations of these elements decreases from the cores to the rims of the grains the pge distributions support a condensation origin for the enhanced refractory element abundances in the zoned grains the lack of zoning in pd refutes an origin by a redox controlled process and none of the pge ni relationships support an origin by fractional crystallization from a metallic melt several models of grain formation were explored including equilibrium fractional condensation which failed to yield the correct radial zoning the zoning may be the product of a nonequilibrium fractional condensation process in which the refractory siderophiles remained supersaturated in the cooling solar nebula or of diffusion between refractory enhanced fe ni cores and other fe ni metal that may have been deposited later from the solar nebula copyright c 2001 elsevier science ltd

normal faulting earthquakes beneath the outer slope of the japan trench after the 2011 tohoku earthquake implications for the stress regime in the incoming pacific plate 1 after the 2011 mw 9 1 tohoku earthquake numerous intraplate earthquakes occurred beneath the outer slope of the japan trench based on ocean bottom seismograph observations these earthquakes occurred in the oceanic crust and uppermost mantle of the pacific plate at depths shallower than about 40 km and had normal faulting focal mechanisms at all depths before the 2011 earthquake normal faulting earthquakes beneath the outer trench slope occurred only at depths shallower than 20 km whereas those at depths of around 40 km had reverse faulting mechanisms these observations suggest that the stress regime in the pacific plate was changed by the 2011 earthquake the tensional stresses that now extend to depths of about 40 km may play an important role not only in the occurrence of large normal faulting earthquakes but also in hydration of the uppermost mantle of the incoming pacific plate prior to the subduction

long period regional wave moment tensor inversion for earthquakes in the western united states source parameters of moderate to large size mw 4 5 earthquakes in the western united states from 1992 to 1994 are determined by point source moment tensor inversion of complete long period t 35 50 s ground motions recorded at regional distances 1 12 stable long period signals are obtained by low pass filtering records from the very broadband seismometers recently deployed in several networks in the western united states these signals are dominated by fundamental mode rayleigh and love waves which have very simple waveforms due to the limited dispersion on the short paths to regional stations since long period motions are relatively insensitive to the attenuation model and crustal structure used in the inversion they provide robust constraints on the seismic moment and faulting geometry as long as adequate azimuthal coverage is available comparisons of solutions for 21 events with results of other regional and teleseismic wave inversions are made to assess the model dependence and uncertainties of our regional centroid moment tensor rcmt solutions rcmt inversion has limited source depth resolution for shallow crustal events but the focal mechanism and seismic moment determinations prove quite stable over a range of source depths in the crust as well as over a range of crustal propagation models simultaneous waveform inversion of shorter period body wave signals can improve the source depth resolution by applying path corrections for heterogeneous crustal structure shorter period surface wave energy can also be inverted allowing the methodology to be extended to lower magnitude regional events as well the rcmt procedure requires minimal signal processing only a sparse broadband network and a simple laterally homogeneous propagation model thus it can readily be automated and applied in near real time to events in the magnitude range from 4 5 to 7 5 distributed over an area as large as the western united states

outer rise stress changes related to the subduction of the juan fernandez ridge central chile 1 although outer rise seismicity is less common than interplate seismicity in subduction zones a significant level of seismicity has occurred between the nazca trench and juan fernandez ridge in central chile during the past 20 years we first study the 9 april 2001 mw 7 0 event and determine its focal mechanism depth and source time function by body waveform inversion from teleseismic broadband data the results indicate tensional faulting in the upper part of the mechanical lithosphere its strike 41 is similar to those observed in events down dip of the slab at about 100 km depth which could indicate that these earthquakes occur in preexisting structures formed at the trench compressive outer rise events have also occurred during the 1980s in front of the rupture zone of the 1985 mw 7 8 valparaiso earthquake to understand their relation with the state of stress of the lithosphere we construct yield stress envelopes of the oceanic lithosphere including static and dynamic stresses dynamic stresses are due either to slab pull ridge push resistive and drag forces we explain the sequence of compressive and tensional events by the accumulation of stress prior to 1985 when the subduction is assumed to be locked and after by the unlockage of the subduction by the valparaiso interplate event the yield stress envelope analysis enables us to quantify the accumulation of compressive forces before 1985 and the tensional force after

interseismic strain accumulation measured by gps in the seismic gap between constitucion and concepcion in chile the concepcion constitucion area 35 37 s in south central chile is very likely a mature seismic gap since no large subduction earthquake has occurred there since 1835 three campaigns of global positioning system gps measurements were carried out in this area in 1996 1999 and 2002 we observed a network of about 40 sites including two east west transects ranging from the coastal area to the argentina border and one north south profile along the coast our measurements are consistent with the nazca south america relative angular velocity 55 9 n 95 2 w 0 610 ma discussed by vigny et al 2008 this issue which predicts a convergence of 68 mm year oriented 79 n at the chilean trench near

deep crustal structure and flexure of the arabian plate beneath the zagros collisional mountain belt as inferred from gravity observations the zagros mountain belt region a neogene continental collisional zone between arabia and iran that is characterized by a suture a folded belt and a foreland basin is unusual among active mountain belts in that its 6 12 km thick sedimentary cover is shortening predominantly by folding while the basement is apparently thickening along numerous high angle reverse faults we have used over 9000 gravity measurements in the region in conjunction with limited seismological observations and geological cross sections of the uppermost 10 km of crust to infer the deeper crustal structure beneath the region crustal models constrained by the bouguer anomalies and other seismological and geological data are characterized by a moho that dips about 1 to the northeast beneath the folded belt and increases in dip to about 5 near the main zagros thrust mzt the moho depth increases from 40 km beneath the leading edge of the foreland basin the mesopotamian foredeep and persian gulf to as much as 65 km beneath the mzt alternative models that incorporate a subducted oceanic crust that is attached to the underthrusting arabian crust deviate little in their moho configurations from the above simpler models negative isostatic residual anomalies are interpreted to indicate local overcompensation beneath the foreland basin and near the folded belt and beneath the mzt we show that underthrust sedimentary rocks of the converging margins along the suture zone may account for the negative isostatic residual anomalies near the mzt however to explain the rest of the isostatic anomalies requires other forces to be acting on this collisional plate boundary for example elastic flexure models required a combination of topography and subsurface loads or downward force the origin of which is not clear to approximate the bouguer or isostatic residual anomalies associated with the foreland basin and the folded belt the topography load of the zagros mountain belt is insufficient to cause the required deflection of the underthrusting arabian plate a combination of isostatic elastic flexure and horizontal compression forces acting on the edge of the arabian craton and the transitional lithosphere of central iran appears to best model the crust of the zagros region we propose a model in which the lower crust of the converging arabian plate located beneath the zagros is being shortened and thickened plastically between the seismogenic rigid upper crust and a rigid uppermost mantle lid the mantle lid probably decoupled from the lowermost crust un der thrusts the iranian crustal blocks thus confined from below the horizontally compressed plastic lower crust hydraulically depresses the moho and raises the faulted and folded brittle upper crust in isostatic equilibrium

upper lithospheric structure of the subduction zone offshore of southern arauco peninsula chile at 38 s velocities 8 4 km s 1 in the trench outer rise area the top of incoming oceanic plate is pervasively fractured and likely hydrated as shown by extensional faults horst and graben structures and a reduction of both crustal and mantle velocities these slow velocities are interpreted in terms of extensional bending related faulting leading to fracturing and hydration in the upper part of the oceanic lithosphere the incoming mocha fz coincides with an area of even slower velocities and thinning of the oceanic crust 10 15 thinning suggesting that the incoming fracture zone may enhance the flux of chemically bound water into the subduction zone slow mantle velocities occur down to a maximum depth of 6 8 km into the upper mantle where mantle temperatures are estimated to be 400 430c in the overriding plate the tomographic model reveals two prominent velocity transition zones characterized by steep lateral velocity gradients resulting in a seismic segmentation of the marine fore arc the margin is composed of three main domains 1 a 20 km wide frontal prism below the continental slope with vp 3 5 km s 1 2 a 50 km area with vp 4 5 5 5 km s 1 interpreted as a paleoaccretionary complex and 3 the seaward edge of the paleozoic continental framework with vp 6 0 km s 1 frontal prism velocities are noticeably lower than those found in the northern erosional chile margin confirming recent accretionary processes in south central chile

petrology and raman spectroscopy of high pressure phases in the gujba cb chondrite and the shock history of the cb parent body abstract high pressure phases majorite possibly majorite pyropess wadsleyite and coesite are present in the matrix and in barred olivine fragments in the gujba cb chondrite grossular pyrope was also observed in some small inclusions the cb chondrites are metal rich meteorites with characteristics that sharply distinguish them from other chondrite groups all of the cb chondrites contain impact melt regions interstitial to their chondrules fragments and metal and a major impact event or events on the cb chondrite parent body is clearly a significant stage in its history we studied three areas interstitial to chondrules and metal in the gujba cba chondrite from raman spectra the barred olivine fragments and matrix in these regions have various combinations of olivine and low ca pyroxene as well as majorite garnet mg4si4o12 a phase that forms by high pressure transformation of low ca pyroxene and wadsleyite a high pressure product of olivine compositions of the majorite suggest both majorite and majorite pyrope solid solution may be present the mineral assemblage of majorite and wadsleyite suggest minimum shock pressures and temperatures of 19 gpa and 2000 c respectively the occurrences of high pressure phases are variable from one area to another on the scale of millimeters or less suggesting heterogeneous distribution of shock and or back transformation to low pressure polymorphs throughout the meteorite the high pressure phases record a high temperature pressure impact event that is superimposed onto and thus postdates formation of the chondrules and other components in the cb chondrites the barred chondrules and metal in the cb chondrites are primary materials formed prior to the impact event either generated in an earlier planetesimal scale impact event or in the nebula

seismological analyses of the 2010 march 11 pichilemu chile mw 7 0 and mw 6 9 coastal intraplate earthquakes on 2010 march 11 a sequence of large shallow continental crust earthquakes shook central chile two normal faulting events with magnitudes around m w 7 0 and m w 6 9 occurred just 15 min apart located near the town of pichilemu these kinds of large intraplate inland crustal earthquakes are rare above the chilean subduction zone and it is important to better understand their relationship with the 2010 february 27 m w 8 8 maule earthquake which ruptured the adjacent megathrust plate boundary we present a broad seismological analysis of these earthquakes by using both teleseismic and regional data we compute seismic moment tensors for both events via a w phase inversion and test sensitivities to various inversion parameters in order to assess the stability of the solutions the first event at 14 hr 39 min gmt is well constrained displaying a fault plane with strike of n145 e and a preferred dip angle of 55 sw consistent with the trend of aftershock locations and other published results teleseismic finite fault inversions for this event show a large slip zone along the southern part of the fault correlating well with the reported spatial density of aftershocks the second earthquake 14 hr 55 min gmt appears to have ruptured a fault branching southward from the previous ruptured fault within the hanging wall of the first event modelling seismograms at regional to teleseismic distances 10 is quite challenging because the observed seismic wave fields of both events overlap increasing apparent complexity for the second earthquake we perform both point and extended source inversions at regional and teleseismic distances assessing model sensitivities resulting from variations in fault orientation dimension and hypocentre location results show that the focal mechanism for the second event features a steeper dip angle and a strike rotated slightly clockwise with respect to the previous event this kind of geological fault configuration with secondary rupture in the hanging wall of a large normal fault is commonly observed in extensional geological regimes we propose that both earthquakes form part of a typical normal fault diverging splay where the secondary fault connects to the main fault at depth to ascertain more information on the spatial and temporal details of slip for both events we gathered near fault seismological and geodetic data through forward modelling of near fault synthetic seismograms we build a kinematic k 2 earthquake source model with spatially distributed slip on the fault that to first order explains both coseismic static displacement gps vectors and short period seismometer observations at the closest sites as expected the results for the first event agree with the focal mechanism derived from teleseismic modelling with a magnitude m w 6 97 similarly near fault modelling for the second event suggests rupture along a normal fault m w 6 90 characterized by a steeper dip angle dip 74 and a strike clockwise rotated strike 155 with respect to the previous event

short and long term effects of gps measured crustal deformation rates along the south central andes in this study we present the contemporary crustal deformation field along the central and southern andes 17 42 s estimated from four global positioning sys tem gps campaigns conducted in 1994 97 we find that the majority of the observed crustal deformation field is relatively homogenous roughly parallel to the plate conver gence direction with decreasing velocities away from the trench we attribute this type of deformation pattern to the inter seismic phase of an earthquake deformation cycle caused by 100 locking of the thrust interface between the subducting nazca and the overrid ing south american plates we have also detected a strong post seismic deformation sig nal in the vicinity of the 1995 mw8 0 antofagasta 22 26 s and 1960 mw9 5 chile 38 43 s earthquakes this type of deformation can be described as short term in nature compared to geological timescales the above conclusions are based on the results of the 3 d andean elastic dislocation model aedm by subtracting the aedm predicted deformation rates from the observations we obtained a residual velocity field that high lights the post seismic as well as more long term deformation eects for example we find a strong evidence for the continuing crustal shortening across the back arc reach ing its maximum 4 mm yr in the very north of our study area in addition between latitudes 29 34 s there is an indication of e w oriented extension within the fore arc in accordance with the recent geologic findings for the n s oriented normal faulting

nied seismic moment tensor catalogue for regional earthquakes around japan quality test and application abstract we have examined the quality of the national research institute for earth science and disaster prevention nied seismic moment tensor mt catalogue obtained using a regional broadband seismic network freesia first we examined using synthetic waveforms the robustness of the solutions with regard to data noise as well as to errors in the velocity structure and focal location then to estimate the reliability robustness and validity of the catalogue we compared it with the harvard centroid moment tensor cmt catalogue as well as the japan meteorological agency jma focal mechanism catalogue we found out that the nied catalogue is consistent with harvard and jma catalogues within the uncertainty of 0 1 in moment magnitude 10 km in depth and 15 in direction of the stress axes the nied mt catalogue succeeded in reducing to 3 5 the lower limit of moment magnitude above which the moment tensor could be reliably estimated finally we estimated the stress tensors in several different regions by using the nied mt catalogue this enables us to elucidate the stress deformation field in and around the japanese islands to understand the mode of deformation and applied stress moreover we identified a region of abnormal stress in a swarm area from stress tensor estimates

influence of asperities along subduction interfaces on the stressing and seismicity of adjacent areas abstract dmowska r and lovison l c 1992 influence of asperities along subduction interfaces on the stressing and seismicity of adjacent areas in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 23 43 we have investigated the influence of large scale fault inhomogeneities in large subduction earthquakes on the style of deformation and seismic behavior of the incoming oceanic plate and slab at intermediate depths during the earthquake cycle the zones of the large subduction events of rat islands 1965 alaska 1964 and valparaiso 1985 have been searched for earthquakes with m b 5 0 if available and for time periods as long as possible it has been found that in general the seismicity in the incoming oceanic plate clusters in front of asperities areas of highest seismic moment release and strongest locking and is positioned relative to them in the direction of plate motion it is usually lacking in areas adjacent to non asperities that is to zones that slip during the main event but with appreciably smaller seismic moment release and possibly slip seismically aseismically during the whole cycle similar behavior occurs in the downgoing slab at intermediate depths where seismicity during the cycle clusters but less strongly than in the oceanic crust next to asperities and down dip from them we infer that the locking of asperities causes higher stresses associated with the earthquake cycle itself to occur in areas adjacent to asperities both up dip and down dip from them along the direction of plate motion and that such stressing is much less pronounced in the areas adjacent to non asperities this opens the possibility of identifying the areas of highest seismic moment release in future subduction earthquakes and carries implications for where the highest deformation and possibly precursory phenomena and or nucleation of a future event might occur

erratum to back transformation of high pressure phases in a shock melt vein of an h chondrite during atmospheric passage implications for the survival of high pressure phases after decompression earth planet sci lett 217 2003 141 150

seismicity and deformation at convergent margins due to heterogeneous coupling studies of the mechanics of subduction as inferred from earthquake cycle observations suggest that the distribution and style of seismicity in the seafloor between the trench and the outer rise and in the slab at intermediate depth can in some cases serve to identify asperity locations along the thrust interface dmowska and lovison 1992 such asperities identified from seismic wavefield modeling are the zones of highest seismic moment release in large underthrusting events to the extent that asperity locations are relatively stationary from one event to the next their locations provide the zones of highest expected moment release in future large earthquakes and rupture often nucleates at the border of an asperity the region of the thrust interface outside such asperities is apparently less well coupled and releases moment throughout the great earthquake cycle in some combination of aseismic creep and moderate seismicity thus it is reasonable that stress and deformation rates associated with the earthquake cycle should be most pronounced near asperities and that this should have seismic and geodetic consequences three dimensional finite element modeling is used here to understand such stress and deformation patterns and their variation in time in relation to heterogeneity of coupling along thrust interfaces the stress field helps to explain the observed clustering of seafloor seismicity along the strike of the convergent margin in cases of convergence at approximately normal incidence like for the region of the valparaiso chile 1985 thrust event the modeling is consistent with the observation that areas of large earthquakes in the seafloor toward the outer rise and in the slab tend to lie within corridors through thrust zone asperities running perpendicular to the line of the trench we seek to learn if such model stress fields are consistent with observations for the strongly oblique subduction margin of the rat islands western aleutians 1965 event that active areas of the outer rise and slab at intermediate depth are offset along strike from asperity locations modeling results here for the stress in the seafloor raise the possibility that to explain this offset the asperity zones along the thrust interface may have to be strung out along the direction of oblique slip perhaps reflecting the contact path of subducting seamounts or geometric irregularities along the interface shear stress patterns created in the upper plate when there is oblique subduction suggest that favorable areas for back arc strike slip activity following underthrusting as in the adak island central aleutians region of the 1986 andreanof island earthquake ekstrom and engdahl 1989 will also be shifted along strike from asperity locations our analyses show how deformation patterns on the earth s surface above asperities differ from patterns above nonasperities and hence provide tools to identify inhomogeneous coupling from geodetic observations we discuss possible bathymetric topographic and structural signals of strength of coupling and of asperities particularly noting that the density and extent from the trench of seafloor normal faults correlates with seismically inferred zones of strongest coupling in the central aleutians

en echelon and orthogonal fault ruptures of the 11 april 2012 great intraplate earthquakes the magnitude 8 7 earthquake that occurred off the coast of the sumatra subduction zone on 11 april 2012 is shown to have had an extraordinarily complex four fault rupture these great ruptures represent large lithospheric deformation that may eventually lead to a localized boundary between the indian and australian plates on 11 april 2012 two of the largest strike slip earthquakes ever recorded at magnitudes of 8 7 and 8 2 occurred in the northeastern indian ocean a few hundred kilometres off the coast of sumatra three groups now report the analysis of seismic data from the days and months before and after these events as well as the events themselves matthias delescluse and co authors show that these earthquakes are part of the ongoing boost of intraplate deformation between india and australia that followed the aceh 2004 and nias 2005 megathrust earthquakes they conclude that the australian plate driven by slab pull forces at the sunda trench is gradually detaching from the indian plate han yue and colleagues show that the 11 april event involved a complex four fault rupture lasting several minutes followed two hours later by a magnitude 8 2 aftershock these great ruptures on a lattice of strike slip faults that extends through the crust and into the upper mantle represent large lithospheric deformation that may eventually create a localized boundary between the indian and australian plates fred pollitz and colleagues show that in the six days following 11 april the global rate of remote earthquakes with magnitudes greater than 5 5 increased nearly fivefold and events up to magnitude 7 seem to have been triggered the unprecedented delayed triggering power of this earthquake may arise from its strike slip source geometry or because it struck at a time of an unusually low global earthquake rate and increased the number of nucleation sites that were very close to failure the indo australian plate is undergoing distributed internal deformation caused by the lateral transition along its northern boundary from an environment of continental collision to an island arc subduction zone1 2 on 11 april 2012 one of the largest strike slip earthquakes ever recorded seismic moment magnitude mw 8 7 occurred about 100 200 kilometres southwest of the sumatra subduction zone occurrence of great intraplate strike slip faulting located seaward of a subduction zone is unusual it results from northwest southeast compression within the plate caused by the india eurasia continental collision to the northwest together with northeast southwest extension associated with slab pull stresses as the plate underthrusts sumatra to the northeast here we use seismic wave analyses to reveal that the 11 april 2012 event had an extraordinarily complex four fault rupture lasting about 160 seconds and was followed approximately two hours later by a great mw 8 2 aftershock the mainshock rupture initially expanded bilaterally with large slip 20 30 metres on a right lateral strike slip fault trending west northwest to east southeast wnw ese and then bilateral rupture was triggered on an orthogonal left lateral strike slip fault trending north northeast to south southwest nne ssw that crosses the first fault this was followed by westward rupture on a second wnw ese strike slip fault offset about 150 kilometres towards the southwest from the first fault finally rupture was triggered on another en echelon wnw ese fault about 330 kilometres west of the epicentre crossing the ninetyeast ridge the great aftershock with an epicentre located 185 kilometres to the ssw of the mainshock epicentre ruptured bilaterally on a nne ssw fault the complex faulting limits our resolution of the slip distribution these great ruptures on a lattice of strike slip faults that extend through the crust and a further 30 40 kilometres into the upper mantle represent large lithospheric deformation that may eventually lead to a localized boundary between the indian and australian plates

modified frequency wavenumber algorithm for regional seismograms using filon s quadrature modelling of lg waves in eastern north america summary the main focus of this study is to develop an efficient frequency wavenumber code to synthesize high frequency say 10 hz regional seismograms up to a distance of more than 1000 km in a medium consisting of a large number of crustal layers and investigate effects of regional waveguides on lg waves in this newly developed code the frequency wavenumber response is evaluated by using the filon s quadrature at high frequency and the polynomial approximation of bessei s functions implementing trapezoidal integration at low frequency this has reduced the computation time by several folds compared to the time needed for the trapezoidal integration using this algorithm both broad band seismograms at harvard and short period ectn eastern canadian telemetered network seismograms from 1988 november 25 saguenay earthquake were successfully modelled a moment magnitude of 5 9 was used initially an average waveguide was calibrated to successfully excite the regional pnl and snl waves at hrv its near surface structure constrained by matching the recorded frequency content the crust mantle transition zone was constrained by modelling the strength of the broad band snl waves consisting of sn ssmsnsmssms and ssmssms phases relative to the initial pnl waves the model was modified to consist of thin layers with an alternating high and low velocity distribution to match the high frequency ectn lg waves observed from 300 to 600 km away in addition the effect of a near surface irregular receiver structure on the duration of lg waves was also investigated by convolving its response with the regional lg seismograms initial study suggests this method as viable for modelling the entire lg waves including the coda numerical studies suggest that the shapes and peak amplitudes on lg seismograms depend more strongly on the source depth anelasticity and crustal waveguide than do the pnl seismograms

formation of high pressure minerals in shocked l6 chondrite yamato 791384 constraints on shock conditions and parent body size we have studied the high pressure phases observed in yamato 791384 l6 chondrite host meteorite mainly consists of olivine pyroxenes and plagioclase glass mineral fragments observed in the veins and the vein margin region of the host meteorite were partially or totally transformed into high pressure phases ringwoodite majorite akimotoite naalsi3o8 hollandite and jadeite matrix of the shock vein contains majorite pyrope solid solution the spatial distribution indicates that high pressure phases are present in the shock veins and host rocks adjacent to the shock veins investigation of the high pressure phases revealed that in y791384 fragments and adjacent matrix were subjected to pressures around of 18 23 gpa and the vein experienced temperatures around 2300 c during the shock event ringwoodite lamellae were observed in the host olivine adjacent to the vein kinetic investigation for ringwoodite lamellar growth in olivine indicates that the shocked meteorite experienced the pressure for at least 4 s such long duration of the pressure pulse indicates that the size of the parent body was greater than 10 km

discovery of coesite and stishovite in eucrite howardite eucrite diogenite meteorites heds probably originated from the asteroid 4 vesta we investigated one eucrite bereba to clarify a dynamic event that occurred on 4 vesta using a shock induced high pressure polymorph we discovered high pressure polymorphs of silica coesite and stishovite originating from quartz and or cristobalite in and around the shock melt veins of bereba lamellar stishovite formed in silica grains through a solid state phase transition a network like rupture was formed and melting took place along the rupture in the silica grains nanosized granular coesite grains crystallized from the silica melt based on shock induced high pressure polymorphs the estimated shock pressure condition ranged from 8 to 13 gpa considering radiometric ages and shock features the dynamic event that led to the formation of coesite and stishovite occurred ca 4 1 ga ago which corresponds to the late heavy bombardment period ca 3 8 4 1 ga deduced from the lunar cataclysm there are two giant impact basins around the south pole of 4 vesta although the origin of heds is thought to be related to dynamic events that formed the basins ca 1 0 ga ago our findings are at variance with that idea

the portales valley meteorite breccia evidence for impact induced melting and metamorphism of an ordinary chondrite abstract the portales valley h chondrite fall is an annealed impact melt breccia with coarse metal interstitial to angular and subrounded silicate clasts the large metal rich regions exhibit a widmanstatten structure and contain very little troilite we were able to examine a 16 5 kg metal rich specimen of portales valley silicates contain numerous flecks of metallic cu and curvilinear trails of tiny metallic fe ni blebs characteristic of shocked and annealed chondrites one silicate clast appears to have experienced little

acfer 182 search for the location of15n enriched nitrogen in an unusual chondrite abstract acfer 182 an unusual chondrite recovered from the sahara in 1990 is highly enriched in 15 n bulk 15 n ca 600 15 n max 1584 at 900 c reinforcing conclusions that it is related to the very unusual chondrite alh 85085 stepped combustion of whole rock acfer 182 releases 15 n over a wide temperature range excluding a single carrier phase for the 15 n enriched nitrogen the highest relative abundance of 15 n is found in phase n c so far unidentified mineralogically with a c n of ca 8 which releases its nitrogen on combustion of the whole rock at 850 950 c attempts to isolate n c by physical means proved unsuccessful hence a chemical treatment was tried with preparation of an hf hcl resistant residue approximately two thirds of the original amount of nitrogen in the sample was lost on dissolution almost all of component n a the carbonaceous component was removed without significant change in 15 n 950 or c n ratio 75 n b originally thought to be nitrogen in metal was unchanged in abundance 15 n 500 and c n ratio ca 20 indicating that it could not be present in metal unless as an insoluble nitride it might even be an isotopically light entity mixing with residual n a and n c this last component now combusted at a lower temperature than in the whole rock and has a lower 15 n value 1274 a fourth minor component n d is revealed on combustion of the residue which burns above 675 c with 15 n ca 1000 and c n ratio ca 50 the 15 n enriched nitrogen in almost all constituents of acfer 182 is interpreted as emanating from a single source i e interstellar grains which were incorporated within the acfer 182 parent body during aggregation vaporisation condensation and mixing of components caused redistribution of 15 n enriched nitrogen throughout the parent with nitrogen either trapped or implanted into silicates and metal

the cr chondrite clan implications for early solar system processes in this paper we review the mineralogy and chemistry of calcium aluminum rich inclusions cais chondrules feni metal and fine grained materials of the cr chondrite clan including cr ch and the metal rich cb chondrites queen alexandra range 94411 hammadah al hamra 237 bencubbin gujba and weatherford the members of the cr chondrite clan are among the most pristine early solar system materials which largely escaped thermal processing in an asteroidal setting bencubbin weatherford and gujba may be exceptions and provide important constraints on the solar nebula models these constraints include 1 multiplicity of cai formation 2 formation of cals and chondrules in spatially separated nebular regions 3 formation of cais in gaseous reservoir s having o 16 rich isotopic compositions chondrules appear to have formed in the presence of o 16 poor nebular gas 4 isolation of cais and chondrules from nebular gas at various ambient temperatures 5 heterogeneous distribution of al 26 in the solar nebula and 6 absence of matrix material in the regions of cai and chondrule formation

shock metamorphism of ordinary chondrites a revised petrographic classification of progressive stages of shock metamorphism of ordinary chondrites is proposed six stages of shock s1 to s6 are defined based on shock effects in olivine and plagioclase as recognized by thin section microscopy the characteristic shock effects of each shock stage are s1 unshocked sharp optical extinction of olivine s2 very weakly shocked undulatory extinction of olivine s3 weakly shocked planar fractures in olivine s4 moderately shocked mosaicism in olivine s5 strongly shocked isotropization of plagioclase maskelynite and planar deformation features in olivine and s6 very strongly shocked recrystallization of olivine sometimes combined with phase transformations ringwoodite and or phases produced by dissociation reactions s6 effects are always restricted to regions adjacent to melted portions of a sample which is otherwise only strongly shocked in stages s3 to s6 localized melting results from stress and temperature peaks which locally deviate from the equilibration shock pressure due to differences in shock impedance these melting effects are a opaque melt veins shock veins b melt pockets with interconnecting melt veins c melt dikes and d troilite metal deposits in fractures based on a critical evaluation of data from shock recovery experiments a shock pressure calibration for the six shock stages is proposed which defines the s1 s2 s2 s3 s3 s4 s4 s5 and s5 s6 transitions at 5 5 10 15 20 30 35 and 45 55 gpa respectively whole rock melting and formation of impact melt rocks or melt breccias occurs at about 75 90 gpa the symbol for the shock stage may be used in combination with the symbol for the petrologic type to abbreviate the complete classification of a chondrite e g h5 s3 we propose this new shock classification and pressure calibration system to replace previous systems which are out of date with respect to the pressure calibration nominally restricted to l chondrites and based on incomplete and in part illdefined sets of shock effects we have classified seventy six ordinary chondrites using the new classification system and conclude the following 1 1 shock effects and the sequence of progressively increasing degrees of shock metamorphism are very similar in h l and ll groups differences in the frequency distribution of shock stages are relatively minor e g l chondrites appear to have the largest fraction with stages s5 and s6 this suggests that the collisional histories of the h l and ll parent bodies were similar 2 2 petrologic type 3 chondrites are deficient in stages s4 to s6 and with increasing petrologic type the frequency of stages s4 to s6 increases we suggest that the more porous and volatile rich type 3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type volatiles trapped in pores cause shock induced dispersal of the shocked and melted material into small particles which are not expected to survive as meteorites 3 3 stage s3 is the most abundant in nearly all petrologic types 4 4 at shock pressures in excess of about 35 gpa s5 and s6 4he and 40ar are almost completely lost pressures below 10 gpa s1 and s2 do not cause noble gas losses

toward understanding tectonic control on the mw 8 8 2010 maule chile earthquake the maule earthquake of 27th february 2010 m w 8 8 affected similar to 500 km of the nazca south america plate boundary in south central chile producing spectacular crustal deformation here we present a detailed estimate of static coseismic surface offsets as measured by survey and continuous gps both in near and far field regions earthquake slip along the megathrust has been inferred from a joint inversion of our new data together with published gps insar and land level changes data using green s functions generated by a spherical finite element model with realistic subduction zone geometry the combination of the data sets provided a good resolution indicating that most of the slip was well resolved coseismic slip was concentrated north of the epicenter with up to 16 m of slip whereas to the south it reached over 10 m within two minor patches a comparison of coseismic slip with the slip deficit accumulated since the last great earthquake in 1835 suggests that the 2010 event closed a mature seismic gap slip deficit distribution shows an apparent local overshoot that highlight cycle to cycle variability which has to be taken into account when anticipating future events from interseismic observations rupture propagation was obviously not affected by bathymetric features of the incoming plate instead splay faults in the upper plate seem to have limited rupture propagation in the updip and along strike directions additionally we found that along strike gradients in slip are spatially correlated with geometrical inflections of the megathrust our study suggests that persistent tectonic features may control strain accumulation and release along subduction megathrusts c 2012 elsevier b v all rights reserved

isotopically uniform 16o depleted calcium aluminum rich inclusions in ch and cb carbonaceous chondrites abstract in situ oxygen isotope measurements of calcium aluminum rich inclusions cais from the metal rich carbonaceous chondrites isheyevo ch cb like acfer 214 paired with acfer 182 ch que 94411 paired with que 94627 cbb and hammadah al hamra 237 cbb revealed the presence of a common population of igneous isotopically uniform 16o depleted inclusions 17o average 2 standard deviations 7 4 6 5 and 8 3 respectively all cais from cbs and a significant fraction of those from chs and isheyevo are 16o depleted most of the 16o depleted cais consist of ti poor al diopside spinel melilite and forsterite and surrounded by a single and double layered rim of forsterite diopside the 16o depleted cais composed of hibonite grossite melilite and spinel and surrounded by the multilayered melilite diopside forsterite rims are less common some of the 16o depleted refractory igneous inclusions composed of al diopside forsterite and spinel have chondrule like textures skeletal or barred they are mineralogically most similar to al diopside rich chondrules found in metal rich carbonaceous chondrites and composed of al diopside forsterite al rich low ca pyroxene glassy mesostasis and spinel suggesting there is a continuum between these objects we suggest that i most of the isotopically uniform and 16o depleted cais resulted from remelting of pre existing possibly 16o rich refractory inclusions the remelting may have occurred during formation of the magnesian non porphyritic cryptocrystalline and skeletal chondrules in chs cbs and isheyevo either by an unspecified late single stage highly energetic event or in an impact generated plume previously hypothesized for their origin both mechanisms probably occurred in the solar nebula i e in the presence of the nebula gas the forsterite pyroxene rims around 16o depleted cais may have resulted from evaporation recondensation of silicon and magnesium during this event some of the al diopside rich cais may have formed by evaporation of the al rich chondrule melts ii in addition to these components the chs and isheyevo contain a high abundance of chondrules and refractory inclusions formed by the commonly inferred nebular processes evaporation condensation and incomplete melting of dust aggregates during multiple transient heating events these include 16o rich cais amoeboid olivine aggregates and ferromagnesian and aluminum rich chondrules with porphyritic textures such components are also present in cb chondrites but they are exceptionally rare these observations indicate that there are multiple generations of cais in metal rich carbonaceous chondrites iii because the isotopically uniform 16o depleted igneous cais and the magnesian cryptocrystalline and skeletal olivine pyroxene chondrules are found almost exclusively in metal rich carbonaceous chondrites the hypothesized impact plume mechanism of chondrule formation and recycling of cais are not common processes

aftershock seismicity of the 27 february 2010 mw 8 8 maule earthquake rupture zone on 27 february 2010 the mw 8 8 maule earthquake in central chile ruptured a seismic gap where significant strain had accumulated since 1835 shortly after the mainshock a dense network of temporary seismic stations was installed along the whole rupture zone in order to capture the aftershock activity here we present the aftershock distribution and first motion polarity focal mechanisms based on automatic detection algorithms and picking engines by processing the seismic data between 15 march and 30 september 2010 from stations from iris ipgp gfz and university of liverpool we determined 20 205 hypocentres with magnitudes mw between 1 and 5 5 seismic activity occurs in six groups 1 normal faulting outer rise events 2 a shallow group of plate interface seismicity apparent at 25 35 km depth and 50 120 km distance to the trench with some variations between profiles along strike the aftershocks occur largely within the zone of coseismic slip but extend 50 km further north and with predominantly shallowly dipping thrust mechanisms along dip the events are either within the zone of coseismic slip or downdip from it depending on the coseismic slip model used 3 a third band of seismicity is observed further downdip at 40 50 km depth and further inland at 150 160 km trench perpendicular distance with mostly shallow dipping 28 thrust focal mechanisms indicating rupture of the plate interface significantly downdip of the coseismic rupture and presumably above the intersection of the continental moho with the plate interface 4 a deep group of intermediate depth events between 80 and 120 km depth is present north of 36 s within the maule segment a large portion of events during the inter seismic phase originated from this depth range 5 the magmatic arc exhibits a small amount of crustal seismicity but does not appear to show significantly enhanced activity after the mw 8 8 maule 2010 earthquake 6 pronounced crustal aftershock activity with mainly normal faulting mechanisms is found in the region of pichilemu 34 5 s these crustal events occur in a 30 km wide region with sharp inclined boundaries and oriented oblique to the trench the best located events describe a plane dipping to the southwest consistent with one of the focal planes of the large normal faulting aftershock mw 6 9 on 11 march 2010

fault interactions and triggering during the 10 january 2012 mw 7 2 sumatra earthquake the 10 january 2012 mw 7 2 sumatra earthquake in the wharton basin occurred 3 months before the great mw 8 6 and mw 8 2 earthquakes in the same region which had complex ruptures and are the largest strike slip earthquakes ever recorded teleseismic p wave back projection of the mw 7 2 earthquake images a unilateral rupture lasting 40 s without observable frequency dependency low frequency 0 05 0 3 hz high frequency 0 3 1 hz in addition to radiation bursts during the mw 7 2 main shock coherent energy releases from 50 to 75 s and from 100 to 125 s are observed about 143 km northeast of the main shock rupture and landward of the trench analysis of globally recorded p waves in both 0 02 0 05 hz velocity records and 1 5 hz stacked envelope functions confirms the presence of coherent sources during the time windows the observed energy bursts are likely to be large early aftershocks occurring on or near the subduction interface both dynamic and static triggering could have induced these early aftershocks as they initiated after the surface wave passed by and the coulomb stress perturbations from the mw 7 2 main shock promote earthquakes in the observed locations the earthquake sequence is a clear example of a seaward intraplate strike slip earthquake triggering landward intraplate earthquakes in the same region in contrast to previously reported normal reverse or reverse normal interactions at subduction zones

shallow megathrust earthquake ruptures betrayed by their outer trench aftershocks signature abstract for some megathrust earthquakes the rupture extends to the solid earth s surface at the ocean floor this unexpected behaviour holds strong implications for the tsunami potential of subduction zones and for the physical conditions governing earthquakes but such ruptures occur in underwater areas which are hard to observe even with current instrumentation and imaging techniques here we evidence that aftershocks occurring ocean ward from the trench are conditioned by near surface rupture of the megathrust fault comparison to well constrained earthquake slip models further reveals that for each event the number of aftershocks is proportional to the amount of shallow slip a link likely related to static stress transfer hence the spatial distribution of these specific aftershock sequences could provide independent constrains on the coseismic shallow slip of future events it also offers the prospect to be able to reassess the rupture of many large subduction earthquakes back to the beginning of the instrumental era

aftershock seismicity of the 2010 maule mw 8 8 chile earthquake correlation between co seismic slip models and aftershock distribution 1 the 27 february 2010 maule chile mw 8 8 earthquake is one of the best instrumentally observed subduction zone megathrust events here we present locations magnitudes and cumulative equivalent moment of the first 2 months of aftershocks recorded on a temporary network deployed within 2 weeks of the occurrence of the mainshock using automatically determined onset times and a back projection approach for event association we are able to detect over 30 000 events in the time period analyzed to further increase the location accuracy we systematically searched for potential s wave arrivals and events were located in a regional 2d velocity model additionally we calculated regional moment tensors to gain insight into the deformation history of the aftershock sequence we find that the aftershock seismicity is concentrated between 40 and 140 km distance from the trench over a depth range of 10 to 35 km focal mechanisms indicate a predominance of thrust faulting with occasional normal faulting events increased activity is seen in the outer rise region of the nazca plate predominantly in the northern part of the rupture area further down dip a second band of clustered seismicity showing mainly thrust motion is located at depths of 40 45 km by comparing recent published mainshock source inversions with our aftershock distribution we discriminate slip models based on the assumption that aftershocks occur in areas of rapid transition between high and low slip surrounding high slip regions of the mainshock

the 2009 samoa tonga great earthquake triggered doublet great earthquakes having seismic magnitudes of at least 8 usually involve abrupt sliding of rock masses at a boundary between tectonic plates such interplate ruptures produce dynamic and static stress changes that can activate nearby intraplate aftershocks as is commonly observed in the trench slope region seaward of a great subduction zone thrust event1 the earthquake sequence addressed here involves a rare instance in which a great trench slope intraplate earthquake triggered extensive interplate faulting reversing the typical pattern and broadly expanding the seismic and tsunami hazard on 29 september 2009 within two minutes of the initiation of a normal faulting event with moment magnitude 8 1 in the outer trench slope at the northern end of the tonga subduction zone two major interplate underthrusting subevents both with moment magnitude 7 8 with total moment equal to a second great earthquake of moment magnitude 8 0 ruptured the nearby subduction zone megathrust the collective faulting produced tsunami waves with localized regions of about 12 metres run up that claimed 192 lives in samoa american samoa and tonga overlap of the seismic signals obscured the fact that distinct faults separated by more than 50 km had ruptured with different geometries with the triggered thrust faulting only being revealed by detailed seismic wave analyses extensive interplate and intraplate aftershock activity was activated over a large region of the northern tonga subduction zone

crustal extensional faulting triggered by the 2010 chilean earthquake the pichilemu seismic sequence 1 we report a sequence of crustal quakes that began after the mw 8 8 thrust subduction maule earthquake that affected the central chile margin on 27 february 2010 this activity lasted by several months having the most important events on 11 march 2010 mw 6 9 and mw 7 0 with normal focal mechanisms seismicity shows a rupture oriented along a nw striking and sw dipping normal fault from the surface down to the interplate contact seismicity can be correlated with neotectonics extensional structures similarly oriented in the region which have coexisted with nne ssw reverse faults since the late pliocene even though both have older periods of activity since the paleozoic this crustal rupture would have been triggered by the high coulomb stress change produced by the maule earthquake enhanced by likely fluid presence along weakened zones of the forearc crust as evidenced by high vp vs ratio the occurrence of relevant neotectonic activity in coincidence with short term deformation suggests a relationship with long term tectonic features of this region which would have been acting as a barrier during the interseismic period increasing the strain accumulation and triggering contractional faulting in the crust as well as producing high slip patches during great subduction ruptures favoring triggering of crustal extensional faulting crustal faulting in pichilemu suggests that this kind of events should be considered in seismic hazard analysis despite the absence of historical crustal seismic activity before the maule earthquake

reply to discussion of a morphotectonic study of environmental impact on ground water in southern iran and under the persian gulf by g farhoudi and k poll

partial melting of the indarch eh4 meteorite a textural chemical and phase relations view of melting and melt migration to test whether aubrites can be formed by melting of enstatite chondrites and to understand igneous processes at very low o fugacities we have conducted partial melting experiments on the indarch eh4 chondrite at 1000 1500 c silicate melting begins at 1000 c and indarch is completely melted by 1500 c the metal sulfide component melts completely at 1000 c substantial melt migration occurs at 1300 1400 c and metal migrates out of the silicate charge at 1450 c and 50 silicate partial melting as a group our experiments contain three immiscible metallic melts si p and c rich two immiscible sulfide melts fe and femgmnca rich and silicate melt our partial melting experiments on the indarch eh4 enstatite chondrite suggest that igneous processes at low fo2 exhibit several unique features the complete melting of sulfides at 1000 c suggests that aubritic sulfides are not relics aubritic oldhamite may have crystallized from ca and s complexed in the silicate melt significant metal sulfide melt migration might occur at relatively low degrees of silicate partial melting substantial elemental exchange occurred between different melts e g s between sulfide and silicate si between silicate and metal a feature not observed during experiments at higher fo2 this exchange may help explain the formation of aubrites from known enstatite chondrites

lithospheric 3 d flexure modelling of the oceanic plate seaward of the trench using variable elastic thickness summary whendescribingthemechanicalbehaviourofthelithospheremodelledasathinplate themost important parameter corresponds to itsflexural rigidity which is commonly expressed through the effective elastic thickness te this parameter is a measure of the stiffness of the plate and defines the maximum magnitude and wavelength of those surface loads that can be supported without suffering unelastic deformation realistic 3 d models of the flexural response of the lithosphere near the trench are scarce because of the mathematical and computational complexity we present a method for determining the flexure of the lithosphere caused by the combined effect of 3 d seamount loading and bending of the lithosphere near the trench our method consists on solving numerically the flexure equations of the reissner mindlin thin plate theory including variable thickness using the finite element method with mesh adaptation the method was applied to study the flexure of the oceanic nazca lithosphere beneath the o higgins seamount group which lies 70km seaward of the chile trench the results show that an elastic thickness te of 5km under the seamounts a te of 15km far from the trench and a te of 13km near the trench can explain both the down deflection of the oceanic moho and bending of the oceanic lithosphere observed in seismic and gravity profiles in order to study the impact of high trench curvature on the morphology of the outer rise we apply the same methodology to study and model the flexure of the lithosphere in the arica bend region 14 s 23 s results indicate that the te values are overestimated if the 3 d trench curvature is not included in the modelling

type c ca al rich inclusions from allende evidence for multistage formation abstract the coarse grained igneous anorthite rich type c cais from allende studied 100 160 6 1 72 3529 40 cg5 abc ts26 and 93 have diverse textures and mineralogies suggesting complex nebular and asteroidal formation histories cais 100 160 6 1 72 and 3529 40 consist of al ti diopside fassaite 13 23 wt al 2 o 3 2 14 wt tio 2 na bearing akermanitic melilite 0 1 0 4 wt na 2 o ak 30 75 spinel and fine grained 5 10 m anorthite groundmass most of the fassaite and melilite grains have lacy textures characterized by the presence of abundant rounded and prismatic inclusions of anorthite 5 10 m in size lacy melilite is pseudomorphed to varying degrees by grossular monticellite and pure forsterite or wollastonite cai 6 1 72 contains a relict type b cai like portion composed of polycrystalline gehlenitic melilite ak 10 40 fassaite spinel perovskite and platinum group element nuggets the type b like material is overgrown by lacy melilite and fassaite some melilite and fassaite grains in cais 100 and 160 are texturally similar to those in the type b portion of 6 1 72 cais abc and ts26 contain relict chondrule fragments composed of forsteritic olivine and low ca pyroxene cai 93 is overgrown by a coarse grained igneous rim of pigeonite augite and anorthitic plagioclase these three cais contain very sodium rich akermanitic melilite 0 4 0 6 wt na 2 o ak 63 74 and cr bearing al ti diopside up to 1 6 wt cr 2 o 3 1 23 wt al 2 o 0 5 7 wt tio 2 melilite and anorthite in the allende type c cai peripheries are replaced by nepheline and sodalite which are crosscut by andradite bearing veins spinel is enriched in feo the cai fragment cg5 is texturally and mineralogically distinct from other allende type cs it is anorthite poor and very rich in spinel poikilitically enclosed by na free gehlenitic melilite ak 20 30 fassaite and anorthite neither melilite nor pyroxene have lacy textures secondary minerals are absent the al rich chondrules 3655b 2 and 3510 7 contain aluminum rich and ferromagnesian portions the al rich portions consist of anorthitic plagioclase al rich low ca pyroxene and cr bearing spinel the ferromagnesium portions consist of fosteritic olivine low ca pyroxene and opaque nodules we conclude that type c cais 100 160 6 1 72 and 3529 40 formed by melting of coarse grained type b like cais which experienced either extensive replacement of melilite and spinel mainly by anorthite and diopside traces of secondary na bearing minerals e g nepheline or sodalite might have formed as well or addition of silica and sodium during the melting event cg5 could have formed by melting of fine grained spinel melilite cai with melilite and spinel partially replaced anorthite and diopside cais abc 93 and ts 26 experienced melting in the chondrule forming regions with addition of chondrule like material such as forsteritic olivine low ca pyroxene and high ca pyroxene anorthite rich chondrules formed by melting of the al rich type c cai like precursors mixed with ferromagnesian type i chondrule like precursors the allende type c cais and al rich chondrules experienced fluid assisted thermal metamorphism which resulted in pseudomorphic replacement of melilite and anorthite by grossular monticellite and forsterite 100 160 6 1 72 3592 40 or by grossular monticellite and wollastonite abc 93 ts 26 the pseudomorphic replacement was followed or accompanied by iron alkali metasomatic alteration resulting in replacement of melilite and anorthite by nepheline and sodalite enrichment of spinel in feo and precipitation of salite hedenbergite pyroxenes wollastonite and andradite in fractures and pores in and around cais

estimating shock pressures based on high pressure minerals in shock induced melt veins of l chondrites here we report the transmission electron microscopy tem observations of the mineral assemblages and textures in shock induced melt veins from seven l chondrites of shock stages ranging from s3 to s6 the mineral assemblages combined with phase equilibrium data are used to constrain the crystallization pressures which can be used to constrain shock pressure in some cases thick melt veins in the tenhaml6 chondrite contain majorite and magnesiowstite in the center and ringwoodite akimotoite vitrified silicate perovskite and majorite in the edge of the vein indicating crystallization pressure of 25 gpa however very thin melt veins 5 30 m wide in tenham contain glass olivine clinopyroxene and ringwoodite suggesting crystallization during transient low pressure excursions as the shock pressure equilibrated to a continuum level melt veins of umbarger include ringwoodite akimotoite and clinopyroxene in the vein matrix and fe2sio4 spinel and stishovite in sio2 feo rich melt indicating a crystallization pressure of 18 gpa the silicate melt veins in roy contain majorite plus ringwoodite indicating pressure of 20 gpa melt veins of ramsdorf and nakhon pathon contain olivine and clinoenstatite indicating pressure of less than 15 gpa melt veins of kunashak and la lande include albite and olivine indicating crystallization at less than 2 5 gpa based upon the assemblages observed crystallization of shock veins can occur before during or after pressure release when the assemblage consists of high pressure minerals and that assemblage is constant across a larger melt vein or pocket the crystallization pressure represents the equilibrium shock pressure

a morphotectonic study of environmental impact on ground water in southern iran and under the persian gulf the zagros mountain ranges zmr in southern and southwestern iran consisting mainly of limestone are a large and very valuable catchment area which recharges the aquifers in vast areas of iran and of the gulf states beyond the persian gulf the collision resulting from the opening of the red sea and the convergence of arabia towards iran increases the rock porosity and thus the internal drainages this helps to recharge the aquifers but the ground water becomes more vulnerable to the growing landfill another source of ground water contamination is the lower paleozoic salt which crops out in the form of numerous salt plugs

calcium aluminum rich inclusions recycled during formation of porphyritic chondrules from ch carbonaceous chondrites abstract we report on the mineralogy petrography and o isotope compositions of 60 ca al rich inclusions cais incompletely melted during formation of porphyritic chondrules from the ch metal rich carbonaceous chondrites and isheyevo ch cb these include i relict polymineralic cais in porphyritic chondrules ii cais surrounded by chondrule like igneous rims iii igneous pyroxene rich and type c like cais and iv plagioclase rich chondrules with clusters of relict spinel grains 26al 26mg systematics were measured in 10 relict cais and 11 cai bearing plagioclase rich chondrules based on the mineralogy the ch cais incompletely melted during chondrule formation can be divided into grossite rich n 13 hibonite rich n 11 spinel melilite rich n 33 these include plagioclase rich chondrules with clusters of relict spinel grains types mineralogical observations indicate that these cais were mixed with different proportions of ferromagnesian silicates and experienced incomplete melting and gas melt interaction during chondrule formation these processes resulted in partial or complete destruction of the cai wark lovering rims replacement of melilite by na bearing plagioclase and dissolution and overgrowth of nearly end member spinel by chromium and iron bearing spinel only two relict cais and two cai bearing chondrules show resolvable excess of radiogenic 26mg the inferred initial 26al 27al ratios are 1 7 1 3 10 6 3 7 3 1 10 7 1 9 0 9 10 6 and 4 9 2 6 10 6 there is a large range of 17o among the ch cais incompletely melted during chondrule formation from 37 to 5 the unmelted minerals in individual cais however are isotopically uniform and systematically 16o enriched relative to the host chondrules and chondrule like igneous rims which have 17o ranging from 7 to 4 most of the ch cais incompletely melted during chondrule formation are mineralogically and isotopically similar to the ch cais surrounded by wark lovering rims and apparently unaffected by chondrule melting the mineralogy and o isotope compositions of the ch cai bearing chondrules are similar to those of the ch porphyritic chondrules without relict cais we conclude that ch porphyritic chondrules formed by incomplete melting of isotopically diverse solid precursors including mineralogically and isotopically unique cais commonly observed only in ch chondrites therefore the ch porphyritic chondrules must have formed in a distinct disk region where the ch cais were present at the time of chondrule formation because most ch cais avoided chondrule melting we infer that chondrule formation was highly localized these observations preclude formation of ch porphyritic chondrules by splashing of molten planetesimals by impact processing of differentiated planetesimals and by large scale nebular shocks e g shocks driven by disk gravitational instabilities or by x ray flares instead they are consistent with small scale chondrule forming mechanisms proposed in the literature such as nebular processing of dust balls by bow shocks and by current sheets

the fountain hills impact modified cb chondrite and thermal history of the cb asteroid fountain hills is a metal rich chondrite with mineral and whole chondrite oxygen isotope compositions that suggest it is a cb chondrite however its petrologic characteristics suggest that it has been modified by shock and recrystallization to a greater degree than other cb chondrites it differs texturally from the cb chondrites in that its metal is interstitial to the silicate and does not occur as discrete clasts as in the other cb chondrites portions of fountain hills appear to be recrystallized and it contains large mm size olivine rimmed by pyroxene a characteristic of the cb chondrites is the presence of small sulfide blebs in large metal clasts and anomalously heavy 15n enriched nitrogen often associated with metal surrounding the sulfide blebs but fountain hills lacks sulfide and its nitrogen is relatively light the differences between fountain hills and the other cb chondrites can be attributed to a secondary process most likely impact melting and recrystallization that overprinted its primary features and it is inferred that fountain hills is an impact modified cb chondrite

a new metal rich chondrite grouplet abstract a new grouplet of primitive metal rich chondrites here called the cb c carbonaceous b bencubbinite chondrites has been recognized it includes bencubbin weatherford hammadah a1 hamra hh 237 and queen alexandra range que 94411 paired with que 94627 their mineral compositions as well as their oxygen and nitrogen isotopic compositions indicate that they are closely related to the cr and ch chondrites all of which are members of the more inclusive cr clan cb chondrites have much greater metal silicate ratios than any other chondrite group widely increasing the range of metal silicate fractionation recorded in solar nebular processes they also have the greatest moderately volatile lithophile element depletions of any chondritic materials metal has compositional trends and zoning patterns that suggest a primitive condensation origin in contrast with metal from other chondrite groups cb chondrites as well as other cr clan chondrites have much heavier nitrogen higher 15n 14n than that in other chondrite groups the primitive characteristics of the cb chondrites suggest that they contain one of the best records of early nebular processes another chondrite grosvenor mountains 9555 1 is petrographically similar to the cb chondrites but its mineral and oxygen and nitrogen isotope compositions indicate that it formed from a different nebular reservoir

pb pb dating of individual chondrules from the cb a chondrite gujba assessment of the impact plume formation model the cb chondrites are metal rich meteorites with characteristics that sharply distinguish them from other chondrite groups their unusual chemical and petrologic features and a young formation age of bulk chondrules dated from the cba chondrite gujba are interpreted to reflect a single stage impact origin here we report high precision internal isochrons for four individual chondrules of the gujba chondrite to probe the formation history of cb chondrites and evaluate the concordancy of relevant short lived radionuclide chronometers all four chondrules define a brief formation interval with a weighted mean age of 4562 49 0 21 myr consistent with its origin from the vapor melt impact plume generated by colliding planetesimals formation in a debris disk mostly devoid of nebular gas and dust sets an upper limit for the solar protoplanetary disk lifetime at 4 8 0 3 myr finally given the well behaved pb pb systematics of all four chondrules a precise formation age and the concordancy of the mn cr hf w and i xe short lived radionuclide relative chronometers we propose that gujba may serve as a suitable time anchor for these systems

the 2010 mw 8 8 maule megathrust earthquake of central chile monitored by gps large earthquakes produce crustal deformation that can be quantified by geodetic measurements allowing for the determination of the slip distribution on the fault we used data from global positioning system gps networks in central chile to infer the static deformation and the kinematics of the 2010 moment magnitude m w 8 8 maule megathrust earthquake from elastic modeling we found a total rupture length of 500 kilometers where slip up to 15 meters concentrated on two main asperities situated on both sides of the epicenter we found that rupture reached shallow depths probably extending up to the trench resolvable afterslip occurred in regions of low coseismic slip the low frequency hypocenter is relocated 40 kilometers southwest of initial estimates rupture propagated bilaterally at about 3 1 kilometers per second with possible but not fully resolved velocity variations

shallow intraplate seismicity related to the illapel 2015 mw 8 4 earthquake implications from the seismic source abstract the september 16 2015 mw 8 4 illapel chile earthquake is the first large event occurring in north central chile after the 1943 earthquake filling a known seismic gap in the region the earthquake took place in a complex tectonic region nearby an area where transition from erosive to accretionary margin occurs due to the collision of juan fernandez ridge jfr along the chilean margin we inverted the kinematic rupture process of the 2015 mw 8 4 illapel earthquake from the joint inversion of teleseismic body waves and near field data the relative weighting between datasets and the weighting of spatial temporal constraints are objectively estimated by applying the akaike s bayesian information criterion the coseismic slip model yields a total seismic moment of 4 92 1021 nm occurred over 120 s the rupture shows both downdip and updip propagation with slip extending along the thrust interface from 50 km depth to shallow near trench depths

a great earthquake doublet and seismic stress transfer cycle in the central kuril islands temporal variations of the frictional resistance on subduction zone plate boundary faults associated with the stick slip cycle of large interplate earthquakes are thought to modulate the stress regime and earthquake activity within the subducting oceanic plate here we report on two great earthquakes that occurred near the kuril islands which shed light on this process and demonstrate the enhanced seismic hazard accompanying triggered faulting on 15 november 2006 an event of moment magnitude 8 3 ruptured the shallow dipping plate boundary along which the pacific plate descends beneath the central kuril arc the thrust ruptured a seismic gap that previously had uncertain seismogenic potential although the earlier occurrence of outer rise compressional events had suggested the presence of frictional resistance within minutes of this large underthrusting event intraplate extensional earthquakes commenced in the outer rise region seaward of the kuril trench and on 13 january 2007 an event of moment magnitude 8 1 ruptured a normal fault extending through the upper portion of the pacific plate producing one of the largest recorded shallow extensional earthquakes this energetic earthquake sequence demonstrates the stress transfer process within the subducting lithosphere and the distinct rupture characteristics of these great earthquakes illuminate differences in seismogenic properties and seismic hazard of such interplate and intraplate faults

slab1 0 a three dimensional model of global subduction zone geometries 1 we describe and present a new model of global subduction zone geometries called slab1 0 an extension of previous efforts to constrain the two dimensional non planar geometry of subduction zones around the focus of large earthquakes slab1 0 describes the detailed non planar three dimensional geometry of approximately 85 of subduction zones worldwide while the model focuses on the detailed form of each slab from their trenches through the seismogenic zone where it combines data sets from active source and passive seismology it also continues to the limits of their seismic extent in the upper mid mantle providing a uniform approach to the definition of the entire seismically active slab geometry examples are shown for two well constrained global locations models for many other regions are available and can be freely downloaded in several formats from our new slab1 0 website http on doi gov d9arbs we describe improvements in our two dimensional geometry constraint inversion including the use of average active source seismic data profiles in the shallow trench regions where data are otherwise lacking derived from the interpolation between other active source seismic data along strike in the same subduction zone we include several analyses of the uncertainty and robustness of our three dimensional interpolation methods in addition we use the filtered subduction related earthquake data sets compiled to build slab1 0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far concluding that the width of these seismogenic zones is on average 30 larger than previous studies have suggested

a seismological study of the 1835 seismic gap in south central chile we study the possible seismic gap in the concepcion constitucion region of south central chile and the nature of the m 7 8 earthquake of january 1939 from 1 march to 31 may 1996 a seismic network of 26 short period digital instruments was deployed in this area we located 379 hypocenters with rms travel time residuals of less than 0 50 s using an approximate velocity distribution using the velest program we improved the velocity model and located 240 high precision hypocenters with residuals less than 0 2 s the large majority of earthquakes occurred along the wadati benioff zone along the upper part of the downgoing slab under central chile a few shallow events were recorded near the chain of active volcanos on the andes these events are similar to those of las melozas near santiago a few events took place at the boundary between the coastal ranges and the central valley well constrained fault plane solutions could be computed for 32 of the 240 well located events most of the earthquakes located on the wadati benioff zone had slab pull fault mechanism due to tensional stresses sub parallel to the downgoing slab this slab pull mechanism is the same as that of eight earthquakes of magnitude around 6 that are listed in the cmt catalog of harvard university for the period 1980 1998 this is also the mechanism inferred for the large 1939 chilean earthquake a very small number of events in the benioff zone had slab push mechanisms that is events whose pressureaxis is aligned with the slab these events are found in double layered wadati benioff zones such as in northern chile or japan our spatial resolution is not good enough to detect the presence of a double layer but we suspect there may be one 2002 elsevier science b v all rights reserved

back transformation of high pressure phases in a shock melt vein of an h chondrite during atmospheric passage implications for the survival of high pressure phases after decompression abstract we investigated the h6 chondrite yamato 75267 in which a fusion crust cuts a shock melt vein the shock vein region more than 280 m from the fusion crust contains high pressure phases such as ringwoodite majorite pyrope ss garnet and naalsi 3 o 8 hollandite however the shock vein close to the fusion crust entirely consists of the low pressure polymorphs olivine low ca pyroxene and plagioclase glass the boundary between low and high pressure phase regions is parallel to the fusion crust during the atmospheric passage the peripheral part of the chondrite was melted to form the fusion crust our microscopic laser micro raman electron microprobe investigations and calculations indicate an area up to 300 m from the fusion crust experienced a temperature of 1400 c after 3 s during the melting of the peripheral part the high pressure phases would at this conditions quickly transform back to their low pressure polymorphs the result obtained here indicates that post shock temperatures in the interior part of the veins were much lower than 1400 c thus leading to the survival of high pressure phases in heavily shocked chondrites

petrology and oxygen isotopes of nwa 5492 a new metal rich chondrite abstract northwest africa 5492 is a new metal rich chondrite breccia that may represent a new oxygen reservoir and new chondrite parent body it has some textural similarities to cb and ch chondrites but silicates are more reduced sulfides are more common and not associated with metal and metal compositions differ from cb and ch chondrites oxygen isotope ratios indicate that northwest africa nwa 5492 components chondrules and lithic fragments formed in at least two different oxygen reservoirs the more common and presumably host component plots in a region above the terrestrial fractionation line below ordinary chondrite compositions and just above enstatite chondrites in 3 oxygen space the only other chondritic materials that plot in this region are chondrules from the grosvenor mountains gro 95551 ungrouped metal rich chondrite the other rare component plots near the cr cb and ch chondrites based on petrologic characteristics and oxygen isotopic compositions nwa 5492 appears to be related to the ungrouped metal rich gro 95551 chondrite

the condensation origin of zoned metal grains in queen alexandra range 94411 implications for the formation of the bencubbin like chondrites thermodynamic analysis of the compositional profiles across large chemically zoned fe ni metal grains in the bencubbin like chondrite queen alexandra range que 94411 suggests that these grains formed by non equilibrium gas solid condensation under variable oxidizing conditions isolation degree and cr depletion factors the oxidizing conditions must have resulted from the complete vaporization of nebular regions with enhanced dust gas ratios similar to 10 40 x solar because the origin of each of the metal grains studied requires different condensation parameters dust gas ratio isolation degree and cr depletion factor a high degree of heterogeneity in the formation region of the bencubbin like chondrite metal is required to preserve compositional zoning of the metal grains and prevent their melting and sulfidization the grains must have been removed from the hot condensation region into cold regions where the accretion of the bencubbin like asteroidal body took place

mode of occurrence textural settings and nitrogen isotopic compositions of in situ diamonds and other carbon phases in the bencubbin meteorite investigations on a polished thin section pts by reflected light microscopy laser micro raman spectroscopy and cathodoluminescence of the bencubbin meteorite revealed the presence of diamond grains ranging in size from 200 nm to 1 mum in fe ni metal silicates and at metal silicate interfaces most of the diamonds are associated with poorly graphitized carbon pgc nitrogen isotopic measurements with the new generation nanosims 50 ion microprobe indicate the presence of two isotopically distinct types of nitrogen carriers one carrier type consists of diamonds their associated pgcs and diamond free pgcs called group b it is n poor and has isotopically close to normal n the other carrier type consists only of diamond free pgcs called group a is n rich and heavily enriched in n 15 delta 15 n max similar to 1000 parts per thousand the petrographic and raman characteristics of the diamonds are indicative of formation by shock the difference in the n isotopic compositions of diamonds and the associated group b pgcs on the one hand and the group a diamond free pgcs on the other suggests that a n 15 rich component was probably incorporated into the bencubbin parent body in an episode subsequent to the shock event that induced carbon diamond phase transformation from the pristine pgcs with isotopically normal nitrogen in the second episode presumably in a milder shock event significant amounts of n were delivered and redistributed among different phases the isotopically heavy n signature is hence not pristine to the bencubbin parent body but was brought in by a second impactor c 2002 elsevier science b v all rights reserved

primitive feni metal grains in ch carbonaceous chondrites formed by condensation from a gas of solar composition some feni metal grains similar to 150 mu m in apparent diameter in ch carbonaceous chondrites are concentrically zoned in ni similar to 5 10 wt co 0 2 0 4 wt and cr 0 3 0 8 wt silicon is present at the similar to 0 1 wt level these observations are consistent with predicted gas solid condensation from a gas of solar composition at temperatures of similar to 1370 1270 k and total pressure of similar to 10 4 bar estimates of feni metal grain growth and cooling rates in this temperature range are consistent with brief and localized thermal episodes in the solar nebula compositionally similar feni metal grains have also been reported in cr and bencubbin like chondrites because feni metal is highly susceptible to secondary alteration i e metamorphism melting oxidation the observed feni metal condensates in ch bencubbin like and cr chondrites indicate that these meteorites experienced no thermal processing after their lithification and thus are among the most primitive meteorites in our collections

the 1977 sumba earthquake series evidence for slab pull force acting at a subduction zone the great 1977 sumba earthquake occurred at the eastern sunda trench just west of the collision of australian continental lithosphere with the island arc the length of the aftershock zone of this normal faulting earthquake is about 200 km aftershocks are concentrated 65 115 km east of the main shock epicenter with very few aftershocks in a 50 km long segment that spans the main shock epicenter relocated hypocenters and focal mechanism data are consistent with normal faulting throughout the upper 28 km of the oceanic lithosphere there is no evidence for thrust faulting of the deeper aftershocks these data imply that the neutral bending surface must be at least 35 40 km deep a second aftershock zone about 180 km northwest of the main shock became active immediately following the main shock but events were concentrated during days 50 52 this zone is a 70 km long lineation that trends toward the main shock epicenter and reflects right lateral strike slip faulting within the subducted oceanic plate seismicity exists to a depth of about 650 km in the very old plate beneath the sunda banda arc and that plate s negative buoyancy causes very large slab pull forces great interface thrust earthquakes are absent at the sumba region and slab pull forces are inferred to have partially decoupled the subducted plate from the overriding plate this decoupling permits slab pull stresses to be guided updip to the region of the sumba main shock such shallow acting slab pull provides a bending moment at the trench and explains the deformation and timing observed for the entire sumba earthquake series in this model slab pull forces stretch the subducted plate until the increasing stresses at the shallow subduction zone lead to a subduction zone earthquake postseismically the released oceanic plate undergoes a pulse of downdip strain returning the plate to a less extended state the moment of this downdip plate motion could exceed the seismic moment of the main shock

shock metamorphism of carbonaceous chondrites abstract we have studied shock effects in carbonaceous chondrites using optical microscopy of thin sections and find that our petrographic classification of progressive shock metamorphism in ordinary chondrites can also be applied to carbonaceous chondrites we find that sixty nine carbonaceous chondrites can be assigned to four shock stages si to s4 largely on the basis of shock effects in olivine the least shocked chondrite groups are cm2 and co3 thirty six out of thirty eight members are classified as shock stage s1 differences between the mean shock levels of certain groups of chondrites e g co3 and cv3 are probably due to stochastic differences in the sampling of their parent bodies however there is an overall tendency for the mean shock level of carbonaceous chondrites and ordinary chondrites to increase with increasing petrologic type that may reflect real differences in the shock level of near surface materials on their parent bodies caused by intrinsic variations in the chemical and physical properties of these materials petrologic type 2 and 3 chondrites are more porous and richer in volatiles than types 4 to 6 the greater porosity of types 2 3 causes higher post shock temperatures and melting at lower pressures and the higher volatile contents ensure that strongly shocked material is more readily dispersed on release from high pressure we suggest that type 2 3 material shocked above 20 30 gpa normally escapes from the parent asteroids and forms particles that are too small to survive as meteorites in the cv3 group there is a correlation between the degree of chondrule flattening and the intensity of shock metamorphism analogous to that discovered in ordinary chondrites by sneyd et al 1988 suggesting that shock rather than static overburden pressure is responsible for chondrule flattening we infer that the correlations are due to collapse of pores under shock pressures of at least 5 10 gpa and that shock is an important process affecting many physical properties of type 2 4 chondrites

stress transfer and seismic phenomena in coupled subduction zones during the earthquake cycle an elementary mechanical model of a coupled subduction zone is presented it is used to study the transfer of extensional stresses along the underthrusting plate and shear stress interactions between the plate itself and its thrust contact zone with the overriding plate during the earthquake cycle the model assumes an elastic plate which deforms one dimensionally has shear drag interactions treated approximately by the elsasser procedure with a maxwellian viscoelastic mantle and is subject to steady gravitational sinking forces great thrust earthquakes are simulated as sudden stress relieving displacements at the contact zone between the slab and overriding plate the model allows analysis of the space and time variable stresses in the main thrust zone the adjacent oceanic plate and the subducting slab over each earthquake cycle stress variations leading to outer rise events are discussed as well as stress changes responsible for intraplate seismicity downdip from the main thrust zone based on simulations of periodic great earthquakes the results of simulated slow progression of deformation slip from below into the thrust contact zone are also presented such preslip occurring over a time scale that is small in comparison with the whole seismic cycle e g of the order of a tenth or so is shown to transiently slow the rate of buildup of or even relieve extensional stresses in the slab in the absence of preslip those stresses build up steadily in time during the latter part of the cycle the results have implications for induction of sesimic quiescence as well as for explaining patterns of seismicity in relation to spatial position along the underthrusting plate and to time throughout the cycle correlations are reported between the model simulations and seismicity observations from coupled subduction zones around the world the observations include tensional outer rise events after large subduction earthquakes and compressional ones in the latter parts of the cycle normal tensional intraplate earthquakes preceding the main thrust events and positioned downdip from the thrust zones and interlaced periods of seismic activity in the lower part of the main thrust zone and in the descending slab

slip distribution of the february 27 2010 mw 8 8 maule earthquake central chile from static and high rate gps insar and broadband teleseismic data 1 the shallow depth underthrust earthquake of february 27 2010 mw 8 8 ruptured the subduction plate interface in central chile between 34 s and 38 s we retrieve the spatial and temporal distribution of slip during this mega earthquake through a joint inversion of teleseismic records insar and high rate gps hrgps data additionally our model is shown to agree with broadband surface waves rupture initiated at about 32 km depth and propagated bilaterally resulting in two main slip zones located ssw and nne of the hypocenter nucleation did not take place within or at the edge of one of these main asperities but in between during the first 30s slip propagated predominantly southwards later on the rupture evolved more slowly and more symmetrically eventually the northern asperity became predominant with maximum slip reaching about 20 m most of the seismic moment was released within 110s a relatively short time explained by the bilateral propagation the overall average rupture velocity is 2 6 km s but propagation occurred initially faster towards the south 3 2 km s large slip did not reach the trench a result consistent with the moderate size of the tsunami down dip rupture stopped at about 50 km depth in agreement with the lower limit of the locked zone inferred by ruegg et al 2009 from pre seismic gps data

large extensional aftershocks in the continental forearc triggered by the 2010 maule earthquake chile summary the mw 8 8 maule earthquake occurred off the coast of central chile on 2010 february 27 and was the sixth largest earthquake to be recorded instrumentally this subduction zone event was followed by thousands of aftershocks both near the plate interface and in the overriding continental crust here we report on a pair of large shallow crustal earthquakes that occurred on 2010 march 11 within 15 min of each other near the town of pichilemu on the coast of the o higgins region of chile field and aerial reconnaissance following the events revealed no distinct surface rupture we infer from geodetic data spanning both events that the ruptures occurred on synthetic sw dipping normal faults the first larger rupture was followed by buried slip on a steeper fault in the hangingwall the fault locations and geometry of the two events are additionally constrained by locations of aftershock seismicity based on the international maule aftershock data set the maximum slip on the main fault is about 3 m and consistent with field results the onshore slip is close to zero near the surface satellite radar data also reveal that significant aseismic afterslip occurred following the two earthquakes coulomb stress modelling indicates that the faults were positively stressed by up to 40 bars as a result of slip on the subduction interface in the preceding megathrust event in other words the pichilemu earthquakes should be considered aftershocks of the maule earthquake the occurrence of these extensional events suggests that regional interseismic compressive stresses are small several recent large shallow crustal earthquakes in the overriding plate following the 2011 mw 9 0 tohoku oki earthquake in japan may be an analogue for the triggering process at pichilemu

april 2012 intra oceanic seismicity off sumatra boosted by the banda aceh megathrust the two earthquakes of respective magnitudes 8 6 and 8 2 that occurred off the coast of the sumatra subduction zone on 11 april 2012 are shown to be part of a continuing boost of the intraplate deformation between india and australia that followed the aceh 2004 and nias 2005 megathrust earthquakes on 11 april 2012 two of the largest strike slip earthquakes ever recorded at magnitudes of 8 7 and 8 2 occurred in the northeastern indian ocean a few hundred kilometres off the coast of sumatra three groups now report the analysis of seismic data from the days and months before and after these events as well as the events themselves matthias delescluse and co authors show that these earthquakes are part of the ongoing boost of intraplate deformation between india and australia that followed the aceh 2004 and nias 2005 megathrust earthquakes they conclude that the australian plate driven by slab pull forces at the sunda trench is gradually detaching from the indian plate han yue and colleagues show that the 11 april event involved a complex four fault rupture lasting several minutes followed two hours later by a magnitude 8 2 aftershock these great ruptures on a lattice of strike slip faults that extends through the crust and into the upper mantle represent large lithospheric deformation that may eventually create a localized boundary between the indian and australian plates fred pollitz and colleagues show that in the six days following 11 april the global rate of remote earthquakes with magnitudes greater than 5 5 increased nearly fivefold and events up to magnitude 7 seem to have been triggered the unprecedented delayed triggering power of this earthquake may arise from its strike slip source geometry or because it struck at a time of an unusually low global earthquake rate and increased the number of nucleation sites that were very close to failure large earthquakes nucleate at tectonic plate boundaries and their occurrence within a plate s interior remains rare and poorly documented especially offshore the two large earthquakes that struck the northeastern indian ocean on 11 april 2012 are an exception they are the largest strike slip events reported in historical times1 2 and triggered large aftershocks worldwide3 yet they occurred within an intra oceanic setting along the fossil fabric of the extinct wharton basin rather than on a discrete plate boundary4 5 6 7 8 here we show that the 11 april 2012 twin earthquakes are part of a continuing boost of the intraplate deformation between india and australia that followed the aceh 2004 and nias 2005 megathrust earthquakes subsequent to a stress transfer process recognized at other subduction zones9 10 using coulomb stress change calculations we show that the coseismic slips of the aceh and nias earthquakes can promote oceanic left lateral strike slip earthquakes on pre existing meridian aligned fault planes we further show that persistent viscous relaxation in the asthenospheric mantle several years after the aceh megathrust explains the time lag between the 2004 megathrust and the 2012 intraplate events on a short timescale the 2012 events provide new evidence for the interplay between megathrusts at the subduction interface and intraplate deformation offshore on a longer geological timescale the australian plate driven by slab pull forces at the sunda trench is detaching from the indian plate which is subjected to resisting forces at the himalayan front6 8 11

limited overlap between the seismic gap and coseismic slip of the great 2010 chile earthquake the mw 8 8 chile earthquake on 27 february 2010 occurred in a broad region where tectonic loading has been accumulating since the great 1835 earthquake a joint inversion of tsunami and geodetic data suggests that the 2010 earthquake rupture only partly overlapped with the zone of preseismic locking

outer rise seismicity boosted by the maule 2010 mw 8 8 megathrust earthquake abstract the maule 2010 megathrust earthquake mw 8 8 has been characterized by two coseismic high slip patches asperities north and south of the epicenter separated by a region of lower slip here we invert full broadband waveforms to obtain regional moment tensors yielding precise centroid depth and source parameters of outer rise events mw 4 5 including a large mw 7 4 event that occurred just 1 5 h after the maule mainshock outer rise seismicity occurred mainly in two clusters 1 a large number of outer rise events in the subducting plate located just seaward of the northern asperity of the maule earthquake and 2 a second cluster with fewer events seaward of the southern edge of the maule rupture area thus the outer rise seismicity is correlated with the coseismic rupture of the maule earthquake reflecting the stress state of the interplate coupled zone the moment tensor results indicate similar extensional focal mechanisms for all outer rise events in the northern zone in the southern region most of the outer rise events are also extensional except for one strike slip event located near the oceanic mocha fracture zone the centroid depths vary from 5 to 20 km depth and present similar magnitudes many of the outer rise events nucleated near the mocha fracture zone including the mw 7 4 event and one strike slip event the calculated yield strength envelope for the oceanic nazca lithosphere suggests that the centroid depths of intraplate tensional events span almost the entire upper brittle part of the oceanic lithosphere

experimental shock metamorphism of the murchison cm carbonaceous chondrite abstract a series of shock recovery experiments were carried out on the murchison cm carbonaceous chondrite by using a single stage propellant gun the murchison samples were shocked in nine experiments at peak pressures from 4 to 49 gpa the recovered samples were studied in detail by using an optical microscope a scanning electron microscope and an electron probe microanalyzer chondrules are flattened in the plane of the shock front at 4 to 30 gpa the mean aspect ratio of chondrules increases from 1 17 to 1 57 roughly in proportion to the intensity of shock pressure up to 25 gpa at 25 to 30 gpa the mean aspect ratio does not increase further and chondrules show increasingly more random orientations and degrade their preferred orientations and at 35 gpa they are extensively disrupted most coarse grains of olivine and pyroxene are irregularly fractured fracture density increases with increasing shock pressure and at 30 gpa almost all are thoroughly fractured with subgrains of local shock melting occurs as melt veins and pockets at 20 to 30 gpa fracture filling veins of fine grains of matrix are also produced at 25 to 30 gpa the melts and the fine grains seem to result mainly from frictional heating due to displacement along fractures at 35 gpa melting occurs pervasively throughout the matrix the melts are mainly produced from the matrix however they are consistently more enriched in fe s and ca which indicates that these elements are selectively incorporated into the melts the melts contain tiny spherules of fe ni metal fe sulfide and numerous vesicles at 49 gpa the matrix is totally melted and coarse grains of olivine are partially melted the melts contain much larger vesicles 50 300 m in diameter than those in the samples shocked at lower pressures which indicates that much more intense devolatilization and gas expansion took place for the purpose of comparing shock thermal effects between the experimentally shocked samples and naturally shocked targets surface materials in the murchison parent body we calculated internal energy increase for compression by multiple shock wave reflections experimental case and for compression by a single shock wave natural case the results suggest that postshock thermal effects observed at each experiment may be attained by impact on the natural targets at a considerably lower shock pressure than the peak shock pressure from the results of our experiments and calculations we conclude that if the murchison parent body were shocked on the surface at pressures higher than 25 gpa shocked material would probably undergo drastic increase in the degree of comminution and simultaneous generation of strong expansive forces on pressure release thus the results support the hypothesis of scott et al 1992 that volatile rich carbonaceous chondrites shocked above 20 to 30 gpa escaped from the parent body and formed particles that are too small to survive as meteorites

cyclic stressing and seismicity at strongly coupled subduction zones we use the finite element method to analyze stress variations in and near a strongly coupled subduction zone during an earthquake cycle deformation is assumed to be uniform along strike plane strain on a cross section normal to the trench axis and periodic earthquake slip is imposed consistent with the long term rate of plate convergence and degree of coupling simulations of stress and displacement rate fields represent periodic fluctuations in time superimposed on an average field the oceanic plate descending slab and continental lithosphere are assumed here to respond elastically to these fluctuations and the remaining mantle under and between plates is assumed to respond as maxwell viscoelastic in the first part of the analysis we find that computed stress fluctuations in space and time are generally consistent with observed earthquake mechanism variations with time since a great thrust event in particular trench normal extensional earthquakes tend to occur early in the earthquake cycle toward the outer rise but occur more abundantly late in the cycle in the subducting slab downdip of the main thrust zone compressional earthquakes when they occur at all have the opposite pattern our results suggest also that the actual timing of extensional outer rise events is controlled by the rheology of the shallow aseismic portion of the thrust interface the second part of the analysis shows the effects of mantle relaxation on the rate of ground surface deformation during the earthquake cycle models without relaxation predict a strong overall compressional strain rate in the continental plate above the main thrust zone with the strain rate constant between mainshocks however with significant relaxation present a localized region of unusually low compressional or even slightly extensional strain rate develops along the surface of the continental plate above and somewhat inland from the downdip edge of the locked main thrust zone the low strain rate starts in the middle or late part of the cycle depending on position this result suggests that the negligible or small contraction measured on the shumagin islands alaska during 1980 to 1991 may not invalidate an interpretation of that region as being a moderately coupled subduction zone in contrast mantle relaxation causes only modest temporal nonuniformity of uplift rates in the overriding plate and of extensional stress rates in the subducting plate even when the maxwell time is an order of magnitude less than the recurrence interval

historical and recent large megathrust earthquakes in chile abstract recent earthquakes in chile 2014 mw 8 2 iquique 2015 mw 8 3 illapel and 2016 mw 7 6 chiloe have put in evidence some problems with the straightforward application of ideas about seismic gaps earthquake periodicity and the general forecast of large megathrust earthquakes in northern chile before the 2014 iquique earthquake 4 large earthquakes were reported in written chronicles 1877 1786 1615 and 1543 in north central chile before the 2015 illapel event 3 large earthquakes 1943 1880 1730 were reported and the 2016 chiloe earthquake occurred in the southern zone of the 1960 valdivia megathrust rupture where other large earthquakes occurred in 1575 1737 and 1837 the periodicity of these events has been proposed as a good long term forecasting however the seismological aspects of historical chilean earthquakes were inferred mainly from old chronicles written before subduction in chile was discovered here we use the original description of earthquakes to re analyze the historical archives our interpretation shows that a priori ideas like seismic gaps and characteristic earthquakes influenced the estimation of magnitude location and rupture area of the older chilean events on the other hand the advance in the characterization of the rheological aspects that controlled the contact between nazca and south american plate and the study of tsunami effects provide better estimations of the location of historical earthquakes along the seismogenic plate interface our re interpretation of historical earthquakes shows a large diversity of earthquakes types there is a major difference between giant earthquakes that break the entire plate interface and those of mw 8 0 that only break a portion of it

seismic coupling and outer rise earthquakes variation of interplate seismic coupling at subduction zones is a major factor controlling the size of the largest underthrusting events this variation also has a profound effect on the regional intraplate stresses in the vicinity of the subduction zone outer rise seismicity is strongly correlated with variations in interplate coupling reflecting the stress state of the interplate coupled zone over 200 outer rise earthquakes with known focal mechanisms are used to investigate the relationship between stresses in the outer rise and interplate seismic coupling these events occur within the downgoing i e oceanic plate near the bathymetric trench axes and generally fall into the categories of tensional normal or compressional thrust with their tensional or compressional stress axes oriented approximately horizontal and perpendicular to the trench in uncoupled subduction zones only tensional outer rise earthquakes occur which indicates that the outer rise is dominated by tensional stresses associated with plate bending and or slab pull forces in strongly coupled subduction zones both tensional and compressional outer rise events are found these events are related both spatially and temporally to the distribution of large underthrusting earthquakes and are thus an integral part of the earthquake cycle in the strongly coupled regions tensional outer rise events follow large underthrusting events as the outer rise is temporarily in tension due to the underthrusting motion compressional outer rise events take place as compressional stress slowly accumulates oceanward of locked sections of the interplate zone in four instances compressional outer rise earthquakes have been followed by large underthrusting events which have occurred 2 4 7 and 19 years after the associated outer rise event the remaining compressional outer rise events are located in regions that are either known seismic gaps or in regions where the seismic potential is unknown the occurrence of compressional outer rise earthquakes suggests that compressional stress is accumulating in the adjacent interplate region and that there is the potential for a future large underthrusting event in the region thirty compressional outer rise events have been located in trench segments of middle and south america the kurile islands the tonga and kermadec islands the new hebrides arc and the solomon islands regions in both the southern kamchatka and northern new hebrides regions the outer rise seismicity indicates that the stress regimes in the outer rise have changed with time from tensional following a previous large underthrusting event to compressional at present thus three stages of the cycle from underthrusting to tensional outer rise regime to compressional outer rise regime are present requiring only the occurrence of the next underthrusting event to complete the cycle the occurrence of compressional outer rise events is useful for assessing the seismic potential of a region on an intermediate time scale

alh 85085 nitrogen isotope analysis of a highly unusual primitive chondrite alh 85085 is an unusual fine grained primitive chondrite which does not fit into any of the known meteorite classes it shows many chemical similarities to the equally unusual meteorites bencubbin weatherford and renazzo nitrogen isotope analysis shows that alh 85085 like bencubbin weatherford and renazzo contains highly 15 n enriched nitrogen indeed alh 85085 has the highest 15 n measured in any whole rock meteorite totalling to 858 but reaching 1497 in the 850 875 c temperature increment however the distribution of isotopically heavy nitrogen in alh 85085 is different from that observed for bencubbin thus precluding a direct relationship between these meteorites isotopically heavy nitrogen occurs in alh 85085 in two sites carbonaceous material 15 n ca 860 13 c ca 1 c n ca 65 75 and in fine grained fe ni metal or opaque chondritic matrix clasts 15 n ca 990 a third very 15 n enriched nitrogen carrier with 15 n 1500 might also be located in the matrix it is probable that there is only a single component with elevated 15 n 1500 and that it occurs in at least three discrete sites mixed with varying amounts of nitrogen having more isotopically normal 15 n 0 50 the identity of the hosts of the isotopically heavy nitrogen have not been fully determined but it is becoming clear that an increasing number of brecciated meteorites some of which do not seem to be related in other ways show evidence of having sampled a reservoir rich in 15 n this may be a result of the introduction of heavy nitrogen during brecciation its 15 n values and distribution throughout the meteorites brought about by mixing with variable amounts of more isotopically normal nitrogen and subsequent vaporization and re condensation processes

earthquake in a maze compressional rupture branching during the 2012 mw 8 6 sumatra earthquake seismological observations of the 2012 moment magnitude 8 6 sumatra earthquake reveal unprecedented complexity of dynamic rupture the surprisingly large magnitude results from the combination of deep extent high stress drop and rupture of multiple faults back projection source imaging indicates that the rupture occurred on distinct planes in an orthogonal conjugate fault system with relatively slow rupture speed the east southeast west northwest ruptures add a new dimension to the seismotectonics of the wharton basin which was previously thought to be controlled by north south strike slip faulting the rupture turned twice into the compressive quadrant against the preferred branching direction predicted by dynamic coulomb stress calculations orthogonal faulting and compressional branching indicate that rupture was controlled by a pressure insensitive strength of the deep oceanic lithosphere

the chile ridge a tectonic framework a new chile ridge tectonic framework is developed based on satellite altimetry data shipboard geophysical data and primarily 38 500 km of magnetic data gathered on a joint u s chilean aeromagnetic survey eighteen active transforms with fossil fracture zones fzs including two complex systems the chile fz and valdivia fz systems have been mapped between the northern end of the antarctic nazca plate boundary chile ridge at 35 s and the chile margin triple junction at 47 s chile ridge spreading rates from 23 ma to present have been determined and show slowdowns in spreading rates that correspond to times of ridge trench collisions the valdivia fz system previously mapped as two fzs with an uncharted seismically active region between them is now recognized to be a multiple offset fz system composed of six fzs separated by short ridge segments 22 to 27 km long at chron 5a 12 ma the chile ridge propagated from the valdivia fz system northward into the nazca plate through crust formed 5 myr earlier at the pacific nazca ridge evidence for this propagation event includes the friday and crusoe troughs located at discontinuities in the magnetic anomaly sequence and interpreted as pseudofaults this propagation event led to the formation of the friday microplate which resulted in the transferal of crust from the nazca plate to the antarctic plate and in a 500 km northward stepwise migration of the pacific antarctic nazca triple junction rift propagation microplate formation microplate extinction and stepwise triple junction migration are found to occur during large scale plate motion changes and plate boundary changes in the southeast pacific

central chile finally breaks chile is the site of some of the largest earthquakes in the world on average a magnitude 8 earthquake occurs there every 10 years or so these earthquakes take place in the subduction zone either as interplate ruptures at the interface between the south american and nazca plates or as intraplate events within the subducted nazca plate a few times in every century massive plate interface earthquakes break several hundred kilometers in a single shock this is what happened on 27 february 2010 when a major earthquake magnitude 8 8 occurred in the maule and biobio regions in central chile see the first figure this region had last experienced a major subduction earthquake in 1835 when darwin 1 visited the area as part of his voyage on the beagle his description of the earthquake inspired many seismologists and historians of chilean earthquakes 2 3

the 2011 northern kermadec earthquake doublet and subduction zone faulting interactions 1 a large intraslab earthquake doublet 6 july 2011 mw 7 6 21 october 2011 mw 7 4 occurred in the pacific plate beneath the outer trench slope of the northern kermadec subduction zone seaward of an interseismically coupled region of the megathrust the first large event a shallow 24 km centroid depth normal faulting rupture was followed by intraslab aftershocks within minutes and by aftershocks near the megathrust within hours the second large event a deeper 45 km centroid depth thrust faulting rupture below the northern portion of the first rupture plane was also followed by interplate and intraslab aftershocks the last large interplate activity in northern kermadec involved an underthrusting doublet on 14 january 1976 mw 7 8 7 9 previous studies interpret westward movement of the northern kermadec arc relative to the australian plate from gps measurements to be a result of interseismic coupling on the northern kermadec megathrust a locked plate interface in this region should tend to reduce trench slope extensional stresses coulomb stress change calculations using a finite fault model determined from teleseismic body wave inversions for the normal faulting event in the 2011 doublet favor activation of megathrust faulting coulomb stress changes for the october compressional event appear to reduce interplate thrust activity and for a short time reversed the westward motion of the upper plate the net effect of the doublet is a few bar increase of interplate thrust fault driving stress which may have advanced a future large megathrust event intraslab normal faulting may serve as a harbinger not only a response to large megathrust ruptures