an experimental study of the kinetics of decompression induced crystallization in silicic melt 1 experiments were conducted to study the temporal evolution of feldspar crystallization kinetics during isothermal decompression pinatubo dacite was held at 780 c 220 mpa fo2 nno 2 h2o saturated conditions for an equilibration period decompressed to final pressures pf ranging from 175 to 5 mpa and then held for 0 3 931 hours according to the plagioclase liquidus curve in ph2o t space for the relevant melt composition these decompressions impose effective undercoolings teff of 34 266 c growth of preexisting phenocrysts and newly formed sparse microlites dominate crystallization at 75 pf 150 mpa teff 34 93 c and equilibrium crystal modes are achieved in 168 hours microlite nucleation is the dominant transformation process for 10 pf 50 mpa teff 125 241 c and chemical equilibrium is not attained by 168 hours under these conditions slow steady decompressions typically produced normally zoned euhedral and planar faceted feldspar crystals although anhedral morphologies were produced at very low pf contrary to expectation slowly decompressed samples were usually further from chemical equilibrium than rapidly decompressed samples after similar durations below the initial pressure although counterintuitive these trends are consistent with new constraints on the relative rates of feldspar nucleation and growth controlled by teff and melt viscosity experienced during each decompression path analysis of liquid to solid transformation kinetics using ttt style diagrams shows that crystallization occurs most rapidly at 100 mpa by a crystal growth mechanism the next most efficient crystallization conditions are at 25 mpa in a crystal nucleation dominated regime

kinematics of the north american caribbean cocos plates in central america from new gps measurements across the polochic motagua fault system 1 the polochic motagua strike slip fault system in guatemala marks the on land plate boundary between the north american na and the caribbean ca plates gps observations in 1999 and 2003 show that the far field velocity across the system na ca relative velocity is 20 mm yr this is significantly higher than the nuvel 1a velocity but is consistent with the gps based ca na velocity proposed by demets et al 2000 the observations are modeled by a fault centered on the motagua fault locked at a depth of 20 km with a slip rate decreasing from eastern to central guatemala from 20 to 12 mm yr towards the na ca cocos triple junction this decrease is accommodated by 8 mm yr of e w extension in the westernmost part of ca south of the motagua fault about 10 mm yr of dextral slip is observed across the mid american volcanic arc the na ca cocos triple junction is thus a complex 400 km wide wedge shaped area

tsunami from the mariana earthquake of april 5 1990 its abnormal propagation and implications for tsunami potential from outer rise earthquakes the tsunami generated by the mariana earthquake of april 5 1990 was observed on the japanese and pacific islands as far as hawaii the observed tsunami amplitudes are not a simple function of distance from the source but vary with large scale bathymetry numerical computations of tsunami propagation are made for actual bathymetry and the computed amplitudes are compared with the observations from the comparisons the seismic moment is estimated to be 1 4 1020nm very similar to that from seismic waves and indicates that the seismic waves and tsunami are equally excited the numerical computations also show that the tsunami propagated toward the japanese coast through two different paths one is through the trench system with high velocity and small amplitude the other along the ridge system with low velocity but large amplitude the two kinds of tsunami are identified on recently installed ocean bottom pressure gauges since the mariana earthquake was an outer rise earthquake in a weakly coupled subduction zone where the size of outer rise event is larger than underthrusting events it is possible that even larger earthquakes occur in this region the tsunami potential from such events must be considered including the unusual tsunami propagation

centroid depth and mechanism of trench outer rise earthquakes trench outer rise earthquakes occur by reactivation or creation of normal faults caused as the oceanic lithosphere approaches a subduction zone and bends into the deep sea trench these faults may cut deep enough into the mantle to allow sea water to penetrate into the lithosphere causing serpentinization the amount of water carried into the mantle is linked to the maximum depth that the tensional faults cut into the lithosphere which in turn is directly linked to the maximum focal depths of outer rise normal faulting earthquakes we analysed teleseismic p and s waves of seven earthquakes from the trench outer rise offshore of central america using teleseismic waveform inversion of broad band data for the computation of green s functions for waveform inversion probabilistic earthquake locations were calculated to study the rupture process earthquake centroid depths and focal mechanisms for a sequence of subevents were calculated both hypocentral depths from the relocation process and the estimated centroid depths from the waveform inversion show that all events occur at shallow depths 30 km furthermore the locations of the subevents relative to each other suggest that fault planes for mw 6 are in the order of 50 km in length and only 5 10 km in width rupture generally propagates downdip and the focal mechanisms change for most events from normal faulting to strike slip or oblique thrusting with time the depth at which this mechanism change is observed may represent the depth of the nodal plane between tensional and compressional regions in the incoming plate

flowgo a kinematic thermo rheological model for lava flowing in a channel we present a kinematic self adaptive numerical model to describe the down flow thermal and rheological evolution of channel contained lava as our control volume of lava advances down a channel it cools and crystallizes an increasingly thick and extensive surface crust grows and its heat budget and rheology evolve by estimating down flow heat and velocity loss our model calculates the point at which the control volume becomes stationary giving the maximum distance lava flowing in the channel can extend modeled effusion rates velocities widths surface crust parameters heat budget cooling temperature crystallinity viscosity and yield strength all compare well with field data collected during eruptions at mauna loa k lauea and etna modeled lengths of 25 27 2 5 5 7 and 0 59 0 83 km compare with measured lengths of 25 27 4 and 0 75 km for the three flows respectively over proximal flow portions we calculate cooling crystallization viscosity and yield strength of 1 10 c km 1 0 001 0 01 volume fraction km 1 103 104 pa s and 10 3 102 pa respectively at the flow front cooling crystallization viscosity and yield strength increase to 100 c km 1 0 1 volume fraction km 1 106 107 pa s and 103 104 pa respectively all of which combine to cause the lava to stop flowing our model presents a means of a analyzing lava flow thermo rheological relationships b identifying important factors in determining how far a channel fed flow can extend c assessing lava flow hazard and d reconstructing flow regimes at prehistoric unobserved or remote flows

crystal morphologies in pillow basalts implications for mid ocean ridge processes abstract we present the results of a detailed petrological study of a sparsely phyric basalt mapco ch98 dr11 dredged along the mid atlantic ridge 30 41 n the sample contains microphenocrysts of olivine that display four different rapid growth morphologies comparison of these morphologies with those obtained in dynamic crystallization experiments allows us to constrain the thermal history of the sample the dendritic morphology swallowtail chain and lattice olivine is directly related to the final quenching during magma seawater interaction in contrast the three other morphologies namely the complex polyhedral crystal the closed hopper and the complex swallowtail morphology result from several cycles of cooling heating corresponding to a maximum degree of undercooling of 20 25 c during crystal growth these thermal variations occurred before eruption and are interpreted to be the result of turbulent convection in a small magmatic body beneath the ridge the results suggest that the mid atlantic ridge is underlain by a mush zone that releases batches of liquid during tectonic segregation aphyric basalts are emitted during eruptions controlled by the tectonic activity whereas phyric basalts correspond to small fractions of magma from the mush zone mobilized by reinjections of primitive magmas

tsunamigenic potential of outer rise normal faults at the middle america trench in central america the middle america trench is formed by the subduction of the cocos and rivera plates under the caribbean and north american plates the subduction interface presents low coupling in central america showing its seismicity a high frequency of outer rise normal fault earthquakes these outer rise earthquakes are generated on the inherited structures of the seafloor spreading fabric during the subducting plate bending we analyze focal mechanism data in combination with the available structural data of the outer rise normal faults in order to constrain the rupture characteristics of the outer rise normal earthquakes a new empirical scaling relationship is developed to define earthquake magnitudes from normal fault dimensions in the outer rise context we numerically model the tsunami wave propagation due to the worst outer rise tsunamigenic source in the area to estimate its damaging potential wave elevations higher than 2 m are common at the coast in front of the fault extent with maximum wave elevations of 8 m the capability of these faults to generate ocean wide tsunamis is low however they can produce significant tsunamis locally

source characteristics of the nicaraguan tsunami earthquake of september 2 1992 a large ms 7 2 shallow earthquake took place off the pacific coast of nicaragua on september 2 1992 and set off large tsunamis the ground motion of the main shock was very weak along the whole nicaraguan coast a tsunami as high as 10 m was observed at el transito whereas a height of about 2 m is empirically expected for an earthquake of ms 7 2 the tsunami magnitude mt is estimated to be 7 9 from tide gage data the nicaraguan event is a tsunami earthquake which generates unusually large tsunamis for its earthquake magnitude the source mechanism is studied in detail by using waveforms of body waves and surface waves recorded on global broadband seismographs the possibility of single force source is ruled out from radiation patterns and the amplitude ratio of rayleigh and love waves the main shock is interpreted as a low angle thrust fault with strike 302 dip 16 and slip 87 the cocos plate underthrusting beneath the caribbean plate the seismic moment from surface wave analysis is 3 0 1020 nm mw 7 6 the source dimension is estimated to be 200 km 100 km from the aftershock area the inversion results of body waves suggest bilateral rupture with rupture velocity as low as 1 5 km s and duration time of about 100 s the source process time is unusually long indicating that the associated crustal deformation has a long time constant

seismic moment catalog of large shallow earthquakes 1900 to 1989 we compile a worldwide catalog of shallow depth 70 km and large ms 7 earthquakes recorded between 1900 and 1989 the catalog is shown to be complete and uniform at the 20 sec surface wave magnitude ms 7 0 we base our catalog on those of abe 1981 1984 and abe and noguchi 1983a b for events with ms 7 0 those catalogs however are not homogeneous in seismicity rates for the entire 90 year period we assume that global rates of seismicity are constant on a time scale of decades and most inhomogeneities arise from changes in instrumentation and or reporting we correct the magnitudes to produce a homogeneous catalog the catalog is accompanied by a reference list for all the events with seismic moment determined at periods longer than 20 sec using these seismic moments for great and giant earthquakes and a moment magnitude relationship for smaller events we produce a seismic moment catalog for large earthquakes from 1900 to 1989 the catalog is used to study the distribution of moment released worldwide although we assumed a constant rate of seismicity on a global basis the rate of moment release has not been constant for the 90 year period because the latter is dominated by the few largest earthquakes we find that the seismic moment released at subduction zones during this century constitutes 90 of all the moment released by large shallow earthquakes on a global basis the seismic moment released in the largest event that occurred during this century the 1960 southern chile earthquake represents about 30 to 45 of the total moment released from 1900 through 1989 a frequency size distribution of earthquakes with seismic moment yields an average slope b value that changes from 1 04 for magnitudes between 7 0 and 7 5 to b 1 51 for magnitudes between 7 6 and 8 0 this change in the b value is attributed to different scaling relationships between bounded large and unbounded small earthquakes thus the earthquake process does have a characteristic length scale that is set by the downdip width over which rupture in earthquakes can occur that width is typically greater for thrust events at subduction zones than for earthquakes along transform faults and other tectonic environments

textural difference between pahoehoe and aa lavas of izu oshima volcano japan an experimental study on population density of plagioclase the groundmass textures of 1778 a d pahoehoe and 1986 a d aa lavas of izu oshima volcano japan differ in population density of plagioclase by about two orders of magnitude the pahoehoe lavas are coarser grained and have a population density of lo cme3 while the aa lavas are finer grained and have a population density of 109 3 cma3 the groundmasses of these texturally different lavas however have nearly the identical chemical compositions one atmosphere melting crystallization experiments on the lavas showed that a 20 c difference in initial melting temperature near the liquidus temperature can cause about five orders of magnitude difference in the population density of plagioclase after annealing at about 100 c below the liquidus temperature yet more than two orders of magnitude difference in cooling rate of the experiments only bring about less than one order of magnitude difference in population density the large effect of the initial melting temperature on the population density of plagioclase is interpreted to reflect nucleation induced by the transformation of polymerized clusters in the melt into crystal nuclei by a reduction in the critical size of the nuclei the initial size distribution of clusters in the melt largely affects the population density of plagioclase during natural eruptive processes degassing of magmas produces strongly undercooled conditions and it is proposed that a slight difference in the degree of undercooling of magmas before final degassing and eruption may have caused the large difference in the population density of plagioclase of the pahoehoe and aa lavas

on estimating crystal shape for crystal size distribution analysis abstract the accurate determination of three dimensional crystal habit long intermediate short axis is a requirement to enable correct stereological conversion of 2d crystal size measurements to true 3d crystal size distributions csds in this contribution we introduce a database and spreadsheet program which provides an objective estimate of true crystal habit from raw 2d measurements the database compares the sample s 2d measurements with 2d shape curves for random sections through 703 different habits the output gives the five best match curves and corresponding crystal habits based on a least squares fit between sample and database the minimum sample size required to give good shape estimates from 2d data is tested using random runs of sections through known shapes with different population densities at minimum 75 crystal sections are required to robustly determine crystal habit for csd measurements if crystals are tabular in shape with more acicular shapes requiring a minimum of 250 sections suggesting a sample size of 250 sections to be used for shape determination in natural examples where the true 3d shape is unknown the crystal habit of the best match shape can then be used to provide a more robust csd analysis which in turn can be used to investigate magmatic processes with more certainty

coseismic and postseismic stress changes in a subducting plate possible stress interactions between large interplate thrust and intraplate normal faulting earthquakes 1 a large intraplate normal faulting earthquake mw 7 5 occurred in 1999 in the subducting cocos plate below the downdip edge of the ruptured thrust fault of the 1978 oaxaca mexico earthquake mw 7 8 this situation is similar to the previous case of the 1997 normal faulting event mw 7 1 that occurred beneath the rupture area of the 1985 michoacan mexico earthquake mw 8 1 we investigate the possibility of any stress interactions between the preceding 1978 thrust and the following 1999 normal faulting earthquakes for this purpose we estimate the temporal change of the stress state in the subducting cocos plate by calculating the slip distribution during the 1978 earthquake through teleseismic waveform inversion the dynamic rupture process and the resultant coseismic stress change together with the postseismic stress variations due to plate convergence and the viscoelastic relaxation process to do this we calculate the coseismic and postseismic changes of all stress components in a three dimensional space incorporating the subducting slab the overlying crust and uppermost mantle and the asthenosphere for the coseismic stress change we solve elastodynamic equations incorporating the kinematic fault slip as an observational constraint under appropriate boundary conditions to estimate postseismic stress accumulations due to plate convergence a virtual backward slip is imposed to lock the main thrust zone the effects of viscoelastic stress relaxations of the coseismic change and the back slip are also included the maximum coseismic increase in the shear stress and the coulomb failure stress below the downdip edge of the 1978 thrust fault is estimated to be in the range between 0 5 and 1 5 mpa and the 1999 normal faulting earthquake was found to take place in this zone of stress increase the postseismic variations during the 21 years after the 1978 event modify the magnitude and patterns of the coseismic stress change to some extent but are not large enough to overcome the coseismic change these results suggest that the coseismic stress increase due to the 1978 thrust earthquake may have enhanced the chance of occurrence of the 1999 normal faulting event in the subducting plate if this is the case one of the possible mechanisms could be static fatigue of rock materials around preexisting weak planes involved in the subducting plate and it is speculated that that one of these planes might have been reactivated and fractured because of stress corrosion cracking under the applied stress there for 21 years

magnetic and petrologic characterization of synthetic martian basalts and implications for the surface magnetization of mars 1 a suite of synthetic martian basalts is generated with the objective of providing fundamental material properties data for use in modeling and interpretation of mission data we systematically evaluate the effects of major element composition oxygen fugacity fo2 and cooling rate on phase chemistry and magnetic mineralogy grain size and intensity of remanent magnetization the range of experimental compositions and fo2 are chosen to bracket the range expected in the martian crust our results should therefore span the range of possible mineralogies textures and magnetic properties in rapidly cooled mars crustal materials two starting compositions are used for the sample synthesis 1 an fe rich al poor composition patterned after snc basaltic meteorites and 2 a composition based on thermal emission spectrometer tes data with a much lower fe al ratio the resulting magnetic phase in samples generated at the quartz fayalite magnetite qfm buffer is a spinel structured oxide with varying amounts of cr ti mg and al compositional differences depend on bulk composition cooling rate differences in crystallization sequence and the kinetics of silicate mineral nucleation and growth oxide abundance and magnetic intensity are most strongly influenced by fo2 with more subtle composition and cooling rate effects moderately oxidizing qfm conditions result in an intense magnetization 2 3 10 5 am2 kg 1 to 1 4 10 2 am2 kg 1 especially in the meteorite derived basalts however an increase of magnetic grain size into the multidomain range meteorite type and or low unblocking temperatures resulting from increased cr substitution tes type may affect the long term stability of the remanence in qfm samples

late holocene hydrous mafic magmatism at the paint pot crater and callahan flows medicine lake volcano n california and the influence of h2o in the generation of silicic magmas this paper characterizes late holocene basalts and basaltic andesites at medicine lake volcano that contain high pre eruptive h2o contents inherited from a subduction related hydrous component in the mantle the basaltic andesite of paint pot crater and the compositionally zoned basaltic to andesitic lavas of the callahan flow erupted approximately 1000 14c years before present 14c years b p petrologic geochemical and isotopic evidence indicates that this late holocene mafic magmatism was characterized by h2o contents of 3 to 6 wt h2o and elevated abundances of large ion lithophile elements lile these hydrous mafic inputs contrast with the preceding episodes of mafic magmatism from 10 600 to 3000 14c years b p that was characterized by the eruption of primitive high alumina olivine tholeiite haot with low h2o 0 2 wt lower lile abundance and different isotopic characteristics thus the mantle derived inputs into the medicine lake system have not always been low h2o primitive haot but have alternated between haot and hydrous subduction related calc alkaline basalt this influx of hydrous mafic magma coincides temporally and spatially with rhyolite eruption at glass mountain and little glass mountain the rhyolites contain quenched magmatic inclusions similar in character to the mafic lavas at callahan and paint pot crater the influence of h2o on fractional crystallization of hydrous mafic magma and melting of pre existing granite crust beneath the volcano combined to produce the rhyolite fractionation under hydrous conditions at upper crustal pressures leads to the early crystallization of fe mg silicates and the suppression of plagioclase as an early crystallizing phase in addition h2o lowers the saturation temperature of fe and mg silicates and brings the temperature of oxide crystallization closer to the liquidus these combined effects generate sio2 enrichment that leads to rhyodacitic differentiated lavas in contrast low h2o haot magmas at medicine lake differentiate to iron rich basaltic liquids when these fe enriched basalts mix with melted granitic crust the result is an andesitic magma since mid holocene time mafic volcanism has been dominated primarily by hydrous basaltic andesite and andesite at medicine lake volcano however during the late holocene h2o poor mafic magmas continued to be erupted along with hydrous mafic magmas although in significantly smaller volumes

analysis of the tsunami generated by the great 1977 sumba earthquake that occurred in indonesia abstract the great outer rise earthquake m w 8 3 occurred near the sunda trench indonesia on 19 august 1977 the earthquake has been previously studied using seismological data the earthquake generated a large tsunami that caused severe damage in sumbawa and sumba islands in indonesia the tsunami was also observed at tide gauges in australia we numerically computed a far field tsunami and we compared the observed tsunami waveforms on three tide gauges with the computed waveforms we also numerically computed the tsunami inundation and compared the observed tsunami run up of 8 m and tsunami inundation distance of 500 m in lunyuk on sumbawa island with the computed ones to explain the observed tsunami waveforms tsunami run up and tsunami inundation distance the slip amount is found to be 3 m on the assumed fault model with a fault length of 200 km and fault width of 70 km the rigidity is assumed to range between 6 0 and 6 8 10 10 n m 2 and the range of the total seismic moment is calculated to be between 2 5 and 2 9 10 21 n m m w 8 2 which is similar to those estimated by the previous seismological studies additionally we calculated the ratio between the observed tsunami run up and the computed maximum tsunami height along the coastline of lunyuk this ratio called the amplification factor may possibly be used to roughly estimate the tsunami run up from a tsunami numerical calculation result on a coarse grid system

petrology and chemistry of mil 03346 and its significance in understanding the petrogenesis of nakhlites on mars antarctic meteorite miller range mil 03346 is a nakhlite composed of 79 clinopyroxene 1 olivine and 20 vitrophyric intercumulus material we have performed a petrological and geochemical study of mil 03346 demonstrating a petrogenetic history similar to previously discovered nakhlites quantitative textural study of mil 03346 indicates long 1 x 101 yr residence times for the cumulus augite whereas the skeletal fe ti oxide fayalite and sulfide in the vitrophyric intercumulus matrix suggest rapid cooling probably as a lava flow from the relatively high forsterite contents of olivine up to fo43 compared with other nakhlites and compositions of augite cores wo38 42en35 40fs22 28 and their hedenbergite rims we suggest that mil 03346 is part of the same or a similar martian cumulate rich lava flow as other nakhlites however mil 03346 has experienced less equilibration and faster cooling than other nakhlites discovered to date calculated trace element concentrations based upon modal abundances of mil 03346 and its constituent minerals are identical to whole rock trace element abundances parental melts for augite have ree patterns that are approximately parallel with whole rock and intercumulus melt using experimentally defined partition coefficients this parallelism reflects closed system crystallization for mil 03346 where the only significant petrogenetic process between formation of augite and eruption and emplacement of the nakhlite flow has been fractional crystallization a model for the petrogenesis of mil 03346 and the nakhlites nakhla governador valadares lafayette yamato 000593 northwest africa nwa 817 nwa 998 would include 1 partial melting and ascent of melt generated from a long term lree depleted mantle source 2 crystallization of cumulus augite olivine magnetite in a shallow level martian magma chamber 3 eruption of the crystal laden nakhlite magma onto the surface of mars 4 cooling crystal settling overgrowth and partial equilibration to different extents within the flow 5 secondary alteration through hydrothermal processes possibly immediately succeeding or during emplacement of the flow this model might apply to single or multiple flow models for the nakhlites ultimately mil 03346 and the other nakhlites preserve a record of magmatic processes in volcanic rocks on mars with analogous petrogenetic histories to pyroxene rich terrestrial lava flows and to komatiites

slab pull and the seismotectonics of subducting lithosphere this synthesis links many seismic and tectonic processes at subduction zones including great subduction earthquakes to the sinking of subducted plate earthquake data and tectonic modeling for subduction zones indicate that the slab pull force is much larger than the ridge push force interactions between the forces that drive and resist plate motions cause spatially and temporally localized stresses that lead to characteristic earthquake activity providing details on how subduction occurs compression is localized across a locked interface thrust zone because both the ridge push and the slab pull forces are resisted there the slab pull force increases with increasing plate age thus because the slab pull force tends to bend subducted plate downward and decrease the force acting normal to the interface thrust zone the characteristic maximum earthquake at a given interface thrust zone is inversely related to the age of the subducted plate the 1960 chile earthquake mw 9 5 the largest earthquake to occur in historic times began its rupture at an interface bounding oceanic plate 30 m y old however this rupture initiation was associated with the locally oldest subducting lithosphere weakest coupling the rupture propagated southward along an interface bounding progressively younger oceanic lithosphere terminating near the subducting chile rise prior to a great subduction earthquake the sinking subducted slab will cause increased tension at depths of 50 200 km with greatest tension near the shallow zone resisting plate subduction plate sinking not only leads to compressional stresses at a locked interface thrust zone but may load compressional stresses at plate depths of 260 350 km provided that the shallow sinking occurs faster than the relaxation time of the deeper mantle this explains k mogi s observations of m 7 thrust earthquakes at depths of 260 350 km immediately downdip and within 3 years prior to five great shallow earthquakes of northern japan the slab pull model explains the lower layer of double seismic zones as due to tension from the deeper sinking plate and the upper layer as due to localized in plate compression as plate motion is resisted by the bounding mantle just downdip of the interface thrust zone there occurs an aseismic 20 50 dip increase of subducted plate this slab bend reflects the summed slab pull force of deeper plate and probably is at the crustal basalt to eclogite phase change resistance to subduction provided by a continually developing slab bend may be an important factor in the size of slab pull force delivered to an interface thrust zone

application of a textural geospeedometer to the late stage magmatic history of mil 03346 dynamic crystallization experiments performed on fe rich al poor basalt are employed as a textural calibration set to quantify the late stage igneous history of nakhlite miller range mil 03346 the ratio of crystal melt surface area to volume typifying morphologically distinct populations of ca pyroxene has been shown to vary as a strong function of cooling rate hammer 2006 furthermore a texture of phenocrysts surrounded by finer grained groundmass crystals arises by sequential nucleation events during constant rate cooling but multiple populations nucleate only if the cooling rate is 72 c h 1 textural analysis of meteorite mil 03346 reveals at least two distinct populations the ca pyroxene phenocryst and microphenocryst three dimensional 3d aspect ratios are 112 8 3 and 1530 160 mm 1 respectively by comparison with the calibration set the range of cooling rates consistent with 3d aspect ratios of both populations in mil 03346 is 20 c h 1 an additional experiment was performed approximating a conductive heat transfer profile in order to interpret and apply results of constant rate cooling experiments to the natural cooling of magma results suggest that the textures of constant rate experiments parallel the initial period of rapid cooling in natural magma initial cooling rates of 20 c h 1 in the lava hosting mil 03346 occur in conductively solidifying lava at depths of 0 4 m constraining the minimum total thickness to 0 8 m crystal accumulation beginning in a subsurface reservoir and continuing after lava emplacement as an inflated pahoehoe sheet satisfies all textural constraints on the late stage igneous history of mil 03346

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

methods of determining the rheological properties of magmas at sub liquidus temperatures non vesicular basaltic melts behave as newtonian fluids at temperatures above their liquidus and their viscosities can be calculated using a method developed by shaw 1972 and bottinga and weill 1972 because many igneous processes involve the flow of silicates at sub liquidus temperatures numerous attempts have been made to calculate the interactive effects of the crystal phase however current methods are appropriate only for relatively low crystal concentrations and they assume newtonian behaviour we argue that this assumption is invalid when bubble or crystal concentrations exceed 30 at higher concentrations factors other than concentration become increasingly important these include particle shape and size distribution a method which takes these factors into account is tested on a range of suspensions including magmas at sub liquidus temperatures and rheological properties calculated using this method agree closely with the measured values we also demonstrate that an equation which was introduced to explain large differences in measured apparent viscosities during the cooling and crystallisation of mount st helens dacite murase et al 1985 and which is currently used to calculate the rheological properties of crystallising lavas generates viscosities which may be in error by several orders of magnitude this difference is argued to be caused by a combination of factors including the ten orders of magnitude range in the strain rates utilised during the mount st helens measurements causing orders of magnitude difference in the resulting apparent viscosities rheological data on crystallising silicic melts are reinterpreted taking into account the non newtonian rheology of the magmas and changes in activation energy of flow during crystallisation

the large normal faulting mariana earthquake of april 5 1990 in uncoupled subduction zone a large ms 7 5 shallow earthquake occurred beneath the mariana trench on april 5 1990 from the relocated aftershock distribution the fault area is estimated to be 70 40 km2 a tsunami observed on the japanese islands verifies that the depth of the main shock is shallow for waveform analysis we use long period surface waves and body waves recorded at global networks of gdsn iris geoscope and erios the centroid moment tensor cmt solution from surface waves indicates normal faulting on a fault whose strike is parallel to the local axis of the mariana trench with the tension axis perpendicular to it the seismic moment is 1 4 1020 nm 1027 dyn cm which gives mw 7 3 far field p and sh waves from 13 stations are used to determine the source time function since the sea around the epicentral region is about 5 km deep body waveforms are contaminated with water reverberations the inversion results in a source time function with a predominantly single event with a duration of 10 sec a seismic moment of 2 1 1020 nm and a focal mechanism given by strike 198 dip 48 slip 90 the short duration indicates a small area of the rupture the location of the main shock with respect to the aftershock area suggests that the nodal plane dipping to the west is preferred for the fault plane the local stress drop of the single subevent is estimated to be 150 mpa 1 5 kbars the mariana earthquake is considered to have occurred in an uncoupled region in response to the gravitational pull caused by the downgoing pacific plate

analysis of a crater forming meteorite impact in peru 1 the fireball producing a crater forming meteorite fall near carancas peru on 15 september 2007 has been analyzed using eyewitness seismic and infrasound records the meteorite impact which produced a crater of 13 5 m diameter is found to have released of order 1010 j of energy equivalent to 2 3 tons of tnt high explosives based on infrasonic measurements our best fit trajectory solution places the fireball radiant at an azimuth of 82 relative to the crater with an entry angle from the horizontal of 63 from entry modeling and infrasonic energetics constraints we find an initial energy for the fireball to be in the 0 06 0 32 kton tnt equivalent the initial velocity for the meteoroid is restricted to be below 17 km s from orbit considerations alone while modeling suggests an even lower best fit velocity close to 12 km s the initial mass of the meteoroid is in the range of 3 9 tons at impact modeling suggests a final end mass of order a few metric tons and impact velocity in the 1 5 4 km s range we suggest that the formation of such a substantial crater from a chondritic mass was the result of the unusually high strength and corresponding low degree of fragmentation in the atmosphere of the meteoritic body additionally the high altitude of the impact site 3800 m a s l resulted in an almost one order of magnitude higher impact speed than would have been the case for the same body impacting close to sea level

present day crustal deformation along the el salvador fault zone from zfesnet gps network abstract this paper presents the results and conclusions obtained from new gps data compiled along the el salvador fault zone esfz we calculated a gps derived horizontal velocity field representing the present day crustal deformation rates in the esfz based on the analysis of 30 gps campaign stations of the zfesnet network measured over a 4 5 year period from 2007 to 2012 the velocity field and subsequent strain rate analysis clearly indicate dextral strike slip tectonics with extensional component throughout the esfz our results suggest that the boundary between the salvadoran forearc and caribbean blocks is a deformation zone which varies along the fault zone we estimate that the movement between the two blocks is at least 12 mm yr 1 from west to east this movement is variably distributed between faults or segments of the esfz we propose a kinematic model with three main blocks the western central and eastern blocks delimited by major faults for the first time we were able to provide a quantitative measure of the present day horizontal geodetic slip rate of the main segments of esfz ranging from 2 mm yr 1 in the east segment to 8 mm yr 1 in the west and central segments this study contributes new kinematic and slip rate data that should be used to update and improve the seismic hazard assessments in northern central america

source process of the great 1977 sumba earthquake in order to investigate the applicability of the asperity model to intraplate earthquakes we have studied the rupture process of the great 1977 sumba normal faulting earthquake mw 8 2 8 3 one of the largest earthquakes since 1963 this event has been variously interpreted as a plate detachment event i e rupture through the entire lithosphere or a shallow plate bending event we have analyzed long period body waves in order to determine the spatiotemporal rupture characteristics including the depth extent of the rupture area visible depth phases in the initial stage of weak radiation beginning about 15 s before the main pulse suggest that the earthquake nucleated near 29 km depth which corresponds to the maximum depth of the aftershock sequence the excitation of a strong tsunami implies that rupture extends to the surface while deconvolutions of long period p waves suggest a relatively shallow 50 km maximum depth extent however the existence of slip below this depth cannot be ruled out particularly if it preferentially radiates frequencies below the passband of the body waves used 0 02 hz for undiffracted phases the source time function of the principal rupture which initiated 30 km west of the epicenter of the precursor comprises a dominant initial short duration 24 s triangular pulse followed by several smaller pulses however slightly diffracted phases indicate a simple basic underlying character for the rupture consisting of the initial 24 s triangle superimposed on a longer duration 42 44 s trapezoid the absence of observable directivity in the deconvolved source time functions suggests a bilateral rupture mode although the body waves do not require a fault length greater than 80 km the aftershock area and surface wave results of zhang and kanamori 1988 imply a total length of at least 200 km the body wave source functions are well modeled by a 200 km long fault extending to 30 50 km depth on which slip nucleates at the center of the fault and has variable displacement along strike the peak moment release of the deconvolved source functions indicates higher displacement in the hypocentral area than in other areas of the fault the spatial relationship of the precursor and the main pulse is suggestive of rupture initiating at and propagating along the edge of an asperity prior to the rupture of the asperity itself the large size of the event may be due to an unusual stress environment arising from strong lateral gradients in seismic interplate coupling along the java timor arc

on the deformation cycle of a strongly coupled plate interface the triple earthquakes of 16 march 1963 15 november 2006 and 13 january 2007 along the kurile subduction zone 1 the great plate interface kurile earthquake of 15 november 2006 mw 8 3 was immediately followed by normal aftershocks in the outer rise of the central kurile subduction zone two months later at a distance 50 km from this event the 13 january 2007 mw 8 1 earthquake with a pure normal mechanism occurred in the outer rise of the central kurile the 15 november 2006 earthquake ruptured an area of 280 150 km2 with maximum slip of almost 7 m while the 13 january 2007 earthquake ruptured an area of 240 40 km2 with a maximum slip of almost 14 m these two significant events were preceded by a major reverse earthquake on 16 march 1963 mw 7 7 that took place close to the location of the 13 january 2007 earthquake these very different earthquakes demonstrate the different stages of the deformation cycle along strongly coupled plates at the central kurile arc and present a rare case of stress regime reversal over a short time span in order to understand the details of these three earthquakes we inverted for the source rupture processes of the earthquakes and delineated the location and dimension of asperities the role of gravity and topography anomalies and their correlation to the asperity distribution as well as the long term seismicity is studied in detail using trench parallel bouguer anomaly we have identified the differences in the asperities and the location of larger normal outer rise aftershocks as well as the location of 13 january 2007 earthquake we also show that the long term seismicity of the central kurile arc is confined to the intraslab and not the plate interface the static stress transfer for these earthquakes showed that the stress on optimally oriented thrust faults is increased in the northeastern part of the rupture area of the 15 november 2006 earthquake absence of major and great earthquakes to the northeastern immediate vicinity of the rupture area of the 15 november 2006 earthquake supports the hypothesis that this area is mature for the next strong earthquake along the kurile arc

environments of crystallization and compositional diversity of mauna loa xenoliths two picrite flows from the sw rift zone of mauna loa contain introduction xenoliths of dunite harzburgite lherzolite plagioclase bearing xenoliths hosted in mauna loa s tholeiitic stage lavas lherzolite and harzburgite troctolite gabbro olivine gabbro and provide a rare opportunity to glimpse into the volcano s gabbronorite textures and olivine compositions preclude a mantle magma chambers and plumbing system in hawaii source for the xenoliths and rare earth element concentrations of xenoliths are much more abundant in alkalic lavas than xenoliths and clinopyroxene indicate that the xenolith source is in tholeiitic lavas as a result of reconfiguration of the not old oceanic crust but rather a hawaiian tholeiitic stage conduit and storage system as magma supply rate demagma pyroxene compositions phase assemblages and textural creases clague 1987 each xenolith records the chemrelationships in xenoliths indicate at least two different crys ical and physical environment in a small part of the tallization sequences calculations using the pmelts algorithm magma chamber at a particular time similarly the show that the two sequences result from crystallization of primitive individual crystals that compose xenoliths hosted in a mauna loa magmas at 6 kbar and 2 kbar independent single flow or series of flows may reflect the changes in calculations of olivine ni fo compositional variability in the magma composition over time textural and complagioclase bearing xenoliths over these crystallization sequences positional features of xenoliths preserve evidence for are consistent with observed olivine compositional variability variation in geochemical petrological and physical contwo parents of similar bulk composition but which vary in ni ditions within the magma system content are necessary to explain the olivine compositional compositions of mauna loa xenoliths range widely variability in the dunite and plagioclase free peridotitic xenoliths and include pyroxenite peridotite troctolite and dunite xenoliths probably crystallized in a small magma storage area as well as gabbroic lithologies many exhibit distinctive beneath the rift zone rather than the large sub caldera magma cumulate or laminated textures previous studies of reservoir primitive picritic magmas are introduced to isolated mauna loa xenoliths are few white 1966 jackson et rift zone storage areas during periods of high magma flux al 1982 so the initial objective of this study is to subsequent eruptions reoccupy these areas and entrain and characterize the petrography and geochemistry of a reptransport xenoliths to the surface resentative collection of samples the second objective is to analyze textures mineral assemblages phase relationships and compositions to identify genetic relationships among the xenoliths as well as with the host to construct a crystallization history of the magmas that are parental to the xenoliths and ultimately to model the

formation of a martian pyroxenite a comparative study of the nakhlite meteorites and theo s flow the unusual composition of the nakhlites a group of pyroxenitic martian meteorites with young ages presents an opportunity to learn about nonbasaltic magmatic activity on another planet however the limited number of these meteorites makes unraveling their history difficult a promising terrestrial analog for the formation of the nakhlites is theo s flow in ontario canada this atypical 120 m thick flow differentiated in place forming distinct layered lithologies of peridotite pyroxenite and gabbro theo s pyroxenite and the nakhlites share strikingly similar petrographies with concentrated euhedral to subhedral augite grains set in a plagioclase rich matrix these two suites of rocks also share specific petrologic features mineral and whole rock compositional features and size and spatial distributions of cumulus grains the numerous similarities suggest that the nakhlites formed by a similar mechanism in a surface lava flow or shallow intrusion their formation could have involved settling of crystals in a phenocryst laden flow or in situ nucleation and growth of pyroxenes in an ultramafic lava flow the latter case is more likely and requires steady state nucleation and growth of clusters of pyroxene grains and olivine in the nakhlites circulating in a strongly convecting melt pool followed by settling and continued growth in a thickening cumulate pile trapped pockets of intercumulus liquid in the pile gradually evolved finally growing fe enriched rims on cumulus grains with sufficient evolution the melt reached plagioclase supersaturation causing rapid growth of plagioclase sprays and late stage mesostasis growth

seismic strain rate along the middle america trench reveals significant differences between cocos north america and cocos caribbean convergence summary centroid moment tensor solutions for thrust faulting earthquakes in the last 27 yr are used to obtain and compare seismic strain rate associated to the subduction process along the cocos north america and along the cocos caribbean convergent margins in both cases the eigenvectors of the strain rate tensor align along radial and tangential directions with respect to their respective euler pole seismic strain rate along the cocos north america plate boundary is about 2 8 10 7 yr 1 a value close to those previously found along the japan and aegean convergent margins strain rate along the cocos caribbean margin is one order of magnitude smaller namely 3 7 10 8 yr 1 the relative plate velocity is also calculated using seismic moment tensors we find a relative plate convergence of 1 13 myr 1 for the cocos north america plate margin and 0 13 myr 1 for cocos caribbean this means that 80 per cent of the plate motion along the cocos north america plate margin is expressed as thrust faulting earthquakes as compared to the velocity given by global plate motion models in contrast only about 10 per cent of the cocos caribbean relative motion is translated into thrusting events similar results are obtained when a 102 yr earthquake database is used we suggest that differences in strain rate and percentage of plate motion are due to differences in the behaviour of the overriding plate and or the central america forearc sliver being detached from the caribbean plate and being incorporated into the cocos plate

the parent magma of the nakhla snc meteorite inferred from magmatic inclusions abstract the nakhla meteorite one of the snc group of putative martian origin is an igneous rock a cumulate of augite and olivine that does not represent a magma composition samples of its parent magma were trapped as magmatic inclusions in its cumulus olivine crystals the inclusions range from 10 350 m in diameter and consist of augite rich in ti and al silica rich glass iron oxides ilmenite apatite and rare amphibole each inclusion has a rind of augite and chromite against its host olivine and a core of radiating sprays of augite set in glass and feldspar these textures are consistent with an origin as trapped silicate liquid twenty four inclusions were analyzed by electron microprobe by averaging series of rastered beam analyses on average the analyses are independent of the size of the inclusion most clearly for inclusions larger than 70 m diameter and variations among analyses are consistent with small differences in the proportions of augite glass and iron oxides exposed on thin section surfaces the average inclusion analysis is calculated to represent 28 host olivine and 72 inclusion composition the inclusion rinds are calculated to be 13 of the inclusion composition for which a small correction is made the inclusion composition is then corrected for mg fe exchange with the host olivine to chemical equilibrium with the cumulus augite cores and crystallization of 13 olivine onto the host crystal to yield a magma composition with the proper mgo feo ratio and with olivine and augite on its liquidus this composition nk93 is an estimate of nakhla s parent magma originally trapped in the inclusions nk93 is basaltic rich in iron and poor in aluminum compared to terrestrial basalts its abundances of al ti and na are consistent with the geochemistry of the snc meteorites as a whole nk93 is similar to the parent magmas proposed in an independent study of magmatic inclusions in nakhla but unlike other proposed compositions one proposed parent magma based on mass balance and the assumption that nakhla was a closed system after crystal accumulation is inconsistent with the magmatic inclusion studies and nakhla s petrography this suggests that nakhla was not a closed system but was infiltrated by post cumulus basaltic magmas another suggested parent magma was derived from element distribution between augite and basaltic magma but that calculation relied on an incorrect augite composition using a correct augite composition in that calculation yields a parent magma much closer in composition to nk93 thus three independent approaches converge in requiring that nakhla originally formed from a low al low mgo feo basalt like nk93

runup of solitary waves on a circular island this is a study of the interactions of solitary waves climbing up a circular island a series of large scale laboratory experiments with waves of different incident height to depth ratios and different crest lengths is described detailed two dimensional run up height measurements and time histories of surface elevations around the island are presented a numerical model based on the two dimensional shallow water wave equations including runup calculations was developed numerical model predictions agreed very well with the laboratory data and the model was used to study wave trapping and the effect of slope under certain conditions enhanced runup and wave trapping on the lee side of the island were observed suggesting a possible explanation for the devastation reported by field surveys in babi island off flores indonesia and in okushiri island japan

tsunami sources of the november 2006 and january 2007 great kuril earthquakes abstract along the northern kuril trench a great interplate earthquake occurred in november 2006 followed by an outer rise normal fault event in january 2007 surface wave magnitudes m s 7 8 and 8 2 indicate that the 2007 event was larger while the global cmt solutions m w 8 3 and 8 1 indicate that the 2006 event was larger tsunamis from both events were recorded at tide gauge stations in japan russia and the united states as well as deep ocean assessment and reporting of tsunamis dart systems and cabled tsunami sensors installed on deep ocean bottom inversion of 52 tsunami waveforms indicates that the 2006 tsunami source was about 200 km long extending from the epicenter to northeast the largest slips of 4 7 m are estimated on the northeastern subfaults for the 2007 event inversion of 32 waveforms shows that the tsunami source was about 120 km long with the largest slip of 3 5 m on the northeastern subfault the agreements between the observed and synthetic tsunami waveforms are generally good for both events not only within the inversion time windows but also for the later phases which were not used in inversions the slip distributions yield the seismic moment of m w 8 1 for the 2006 event and m w 7 9 for the 2007 event the seismic moment of the 2006 event was larger than the 2007 event from comparison of tsunami data regardless of fault model

stress triggering in thrust and subduction earthquakes and stress interaction between the southern san andreas and nearby thrust and strike slip faults 1 we argue that key features of thrust earthquake triggering inhibition and clustering can be explained by coulomb stress changes which we illustrate by a suite of representative models and by detailed examples whereas slip on surface cutting thrust faults drops the stress in most of the adjacent crust slip on blind thrust faults increases the stress on some nearby zones particularly above the source fault blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults we calculate that during a progressive thrust sequence in central california the 1983 mw 6 7 coalinga earthquake brought the subsequent 1983 mw 6 0 nunez and 1985 mw 6 0 kettleman hills ruptures 10 bars and 1 bar closer to coulomb failure the idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events in agreement with findings of prior investigations subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust faulting events on the periphery of the seismic rupture and its downdip extension these features are evident in aftershocks of the 1957 mw 9 1 aleutian and other large subduction earthquakes we further examine stress changes on the rupture surface imparted by the 1960 mw 9 5 and 1995 mw 8 1 chile earthquakes for which detailed slip models are available calculated coulomb stress increases of 2 20 bars correspond closely to sites of aftershocks and postseismic slip whereas aftershocks are absent where the stress drops by more than 10 bars we also argue that slip on major strike slip systems modulates the stress acting on nearby thrust and strike slip faults we calculate that the 1857 mw 7 9 fort tejon earthquake on the san andreas fault and subsequent interseismic slip brought the coalinga fault 1 bar closer to failure but inhibited failure elsewhere on the coast ranges thrust faults the 1857 earthquake also promoted failure on the white wolf reverse fault by 8 bars which ruptured in the 1952 mw 7 3 kern county shock but inhibited slip on the left lateral garlock fault which has not ruptured since 1857 we thus contend that stress transfer exerts a control on the seismicity of thrust faults across a broad spectrum of spatial and temporal scales

petrogenesis of the nakhlite meteorites evidence from cumulate mineral zoning abstract a simple igneous petrogenesis for the meteorite nakhla has previously been called into question because mg fe ratios in olivine indicate substantial disequilibrium between the predominant cumulus minerals olivine and augite comparative analyses of simulated diffusive zoning and the observed cumulus mineral zoning for all three nakhlites nakhla governador valadares and lafayette show that their current compositions do not necessarily reflect parental magma compositions instead diffusion has altered primary cumulus compositions to varying degrees nakhla being the least affected and lafayette being almost completely re equilibrated only the cores of augite grains in nakhla and governador valadares appear to have preserved their original compositions mineral zoning in each meteorite is strongly concentric around mesostasis areas suggesting that reaction with intercumulus liquid has controlled the observed zoning the presence of pigeonite and orthopyroxene overgrowths in nakhla and governador valadares and of poikilitic orthopyroxene enclosing olivine relicts in lafayette indicate substantial late magmatic reactions two pyroxene geothermometry for lafayette indicates temperatures around 950 c suggesting subsolidus equilibration as well the nakhlites appear to be a series of relatively simple cumulate rocks which have undergone various amounts of late magmatic and subsolidus diffusion possibly reflecting their relative positions in a cooling cumulate pile

imaging a slow bilateral rupture with broadband seismic waves the september 2 1992 nicaraguan tsunami earthquake the spatio temporal rupture history of the september 2 1992 nicaragua tsunami earthquake ms 7 2 mw 7 6 is analyzed using long period 157 288 s rayleigh and love wave spectral inversions and an empirical green function analysis of very broadband 10 250 s body and surface waves the event has a rupture duration exceeding 110 s with a slow 0 6 2 3 km s rupture velocity and involves shallow dipping 6 10 thrust faulting at a shallow depth 10 km with the latter being primarily responsible for the strong tsunami excitation two subevents dominate the source radiation resulting from a slow asymmetric bilateral 100 160 km long rupture long period surface wave directivity reveals a predominant rupture azimuth of 140 30 consistent with asymmetric extension of the bilateral rupture at an azimuth of 125 30 resolved by the source time function analysis an inverse radon transform of the source time functions confirms the asymmetric bilateral rupture characteristics

petrology of the miller range 03346 nakhlite in comparison with the yamato 000593 nakhlite we petrologically examined the miller range mil 03346 nakhlite the main phase modal abundances are 67 7 vol augite 0 8 vol olivine and 31 5 vol mesostasis among all known nakhlites mil 03346 s modal abundance of olivine is the smallest and of mesostasis is the largest augite occurs as cumulus phenocrysts having a homogeneous core composition en36 38fs24 22wo40 which is identical with other nakhlites they accompany thin ferroan rims divided into inner and outer rims with a compositional gap at the boundary between the two rims olivine grains have magnesian cores fa 55 and show normal zoning toward ferroan rims fa 84 mesostasis consists mostly of glass 26 0 vol with minor skeletal fayalites skeletal titanomagnetites acicular phosphate massive cristobalite and sulfides we conclude that mil 03346 is the most rapidly cooled nakhlite among all known nakhlites based on the petrography we obtain the intercumulus melt composition for mil 03346 from the mass balance calculation using the modal abundances and discuss the crystallization sequence of mil 03346 in comparison with that of yamato y 000593 although magnesian olivines of y 000593 are phenocrystic magnesian olivine grains of mil 03346 seem to have texturally crystallized from the intercumulus melt after the mil 03346 magma intruded upward to the martian surficial zone the magnesian olivine crystallized and then the ferroan inner rim formed on phenocrystic core augite the outer rim of phenocrystic augites formed after the crystallization of skeletal fayalites and skeletal titanomagnetites resulting in a compositional gap between the inner and outer rims finally glassy mesostasis formed from the residual melt this crystallization sequence of mil 03346 is different from those of other nakhlites including y 000593

fault parameters of the 1896 sanriku tsunami earthquake estimated from tsunami numerical modeling the june 15 1896 sanriku earthquake generated devastating tsunamis with the maximum run up of 25 m and caused the worst tsunami disaster in the history of japan despite its moderate surface wave magnitude ms 7 2 and weak seismic intensity this is a typical tsunami earthquake which generates anomalously larger tsunamis than expected from its seismic waves previously proposed mechanisms of tsunami earthquakes include submarine slumping and slow rupture in the accretionary wedge or in the subducted sediments in this paper we estimate the fault parameters of the 1896 tsunami earthquake by numerically computing the tsunami and comparing the waveforms with those recorded at three tide gauge stations in japan the result indicates that the tsunami source is very close to the japan trench and the fault strike is parallel to the trench axis the fault width is about 50 km suggesting that the tsunami earthquake is a slow rupture in the subducted sediments beneath the accretionary wedge

near simultaneous great earthquakes at tongan megathrust and outer rise in september 2009 the tsunami that struck the samoan and northern tongan islands in september 2009 was preceded by a magnitude 8 earthquake on the outer slope of the oceanic trench where the pacific plate bends as it enters the subduction zone this was initially thought to be the sole source of the tsunami but a more complex picture is emerging two groups report the occurrence of two earthquakes a triggered doublet at nearly the same time and place what is not clear is which triggered the other beavan et al use an analysis of global positioning system station displacements and tsunami models to show that the outer rise earthquake was accompanied possibly triggered by a near simultaneous mega thrust earthquake in the adjacent tonga subduction zone lay et al analyse the available seismic data and their model suggests that the outer rise event triggered megathrust faulting either way this dual strike suggests a mechanism for the occasional large tsunamis generated at the tonga subduction zone on 29 september 2009 a tsunami devastated the samoan and northern tongan islands it is shown here that an unusual earthquake sequence preceded this tsunami a magnitude 8 earthquake in the outer rise intraplate region occurred almost simultaneously with rupture of the shallow subduction interplate interface equivalent to a magnitude 8 earthquake the findings provide information on strain release mechanisms at subduction zones and a possible mechanism for the occasional large tsunamis generated at the tonga subduction zone the earth s largest earthquakes and tsunamis are usually caused by thrust faulting earthquakes on the shallow part of the subduction interface between two tectonic plates where stored elastic energy due to convergence between the plates is rapidly released1 2 the tsunami that devastated the samoan and northern tongan islands on 29 september 2009 was preceded by a globally recorded magnitude 8 normal faulting earthquake in the outer rise region where the pacific plate bends before entering the subduction zone preliminary interpretation suggested that this earthquake was the source of the tsunami3 here we show that the outer rise earthquake was accompanied by a nearly simultaneous rupture of the shallow subduction interface equivalent to a magnitude 8 earthquake that also contributed significantly to the tsunami the subduction interface event was probably a slow earthquake with a rise time of several minutes that triggered the outer rise event several minutes later however we cannot rule out the possibility that the normal fault ruptured first and dynamically triggered the subduction interface event our evidence comes from displacements of global positioning system stations and modelling of tsunami waves recorded by ocean bottom pressure sensors with support from seismic data and tsunami field observations evidence of the subduction earthquake in global seismic data is largely hidden because of the earthquake s slow rise time or because its ground motion is disguised by that of the normal faulting event earthquake doublets where subduction interface events trigger large outer rise earthquakes have been recorded previously4 but this is the first well documented example where the two events occur so closely in time and the triggering event might be a slow earthquake as well as providing information on strain release mechanisms at subduction zones earthquakes such as this provide a possible mechanism for the occasional large tsunamis generated at the tonga subduction zone5 where slip between the plates is predominantly aseismic6

the parent magma of the nakhlite meteorites clues from melt inclusions abstract several forms of trapped liquid found within nakhlite meteorites have been examined including interstitial melt and magmatic inclusions within the cores of large olivine grains differences in the mineralogy and texture between two types of trapped melt inclusions and between these inclusions and the mesostasis indicate that vitrophyric inclusions are most appropriate for estimating the composition of a nakhlite parental magma in equilibrium with early forming olivine and augite parent liquids were calculated from the mineralogy of large inclusions in nakhla and governador valadares using a system of mass balance equations solved by linear regression methods the chosen parental liquids were cosaturated in olivine and augite and had mg fe values consistent with measured augite liquid kd s these parental magma compositions are similar to other published compositions for nakhla chassigny and shergotty parental melts and may correspond to a significant magma type on mars

relations between earthquake magnitude and fault rupture dimensions how regionally variable are they data on subsurface rupture dimensions and seismic moments have been gathered for earthquakes in new zealand screened for data quality and analyzed along with the multiregion rupture area data of hanks and bakun 2002 regression analyses have been carried out for relations among magnitude and rupture length subsurface width area slip and aspect ratio statistical comparisons show that there are significant differences between the regressions of new zealand and multiregion data the new zealand relations among magnitude area and displacement are linear those among magnitude subsurface rupture length and width are bilinear whereas those between magnitude and rupture aspect ratio l w are trilinear the magnitudes predicted from rupture subsurface lengths widths or areas by multiregion relations are about 0 4 units smaller than those obtained from relations based on new zealand data the multiregion relations predict ruptures that are untenably large for new zealand on the basis of structural and other evidence separate regressions were carried out for the california china and japan subsets of the multiregion data and it was found that there were statistically significant differences between new zealand and california new zealand and japan new zealand and china and japan and california the respective contributions of rupture area and mean displacement to seismic moment are very different in new zealand from those in california japan and china suggesting that rupture styles differ with geological region in a manner yet to be appropriately defined thus multiregion relations are a poor approximation of the new zealand data and perhaps also of the data of other regions where geological conditions differ substantially from the multiregion average

an integrated global model of present day plate motions and plate boundary deformation summary in this paper we present a global model gsrm 1 of both horizontal velocities on the earth s surface and horizontal strain rates for almost all deforming plate boundary zones a model strain rate field is obtained jointly with a global velocity field in the process of solving for a global velocity gradient tensor field in our model we perform a least squares fit between model velocities and observed geodetic velocities as well as between model strain rates and observed geological strain rates model velocities and strain rates are interpolated over a spherical earth using bi cubic bessel splines we include 3000 geodetic velocities from 50 different mostly published studies geological strain rates are obtained for central asia only and they are inferred from quaternary fault slip rates for all areas where no geological information is included a priori constraints are placed on the style and direction but not magnitude of the model strain rate field these constraints are taken from a seismic strain rate field inferred from normalized focal mechanisms of shallow earthquakes we present a global solution of the second invariant of the model strain rate field as well as strain rate solutions for a few selected plate boundary zones generally the strain rate tensor field is consistent with geological and seismological data with the assumption of plate rigidity for all areas other than the plate boundary zones we also present relative angular velocities for most plate pairs we find that in general there is a good agreement between the present day plate motions we obtain and longterm plate motions but a few significant differences exist the rotation rates for the indian arabian and nubian plates relative to eurasia are 30 13 and 50 per cent slower than the nuvel1a estimate respectively and the rotation rate for the nazca plate relative to south america is 17 per cent slower on the other hand caribbean north america motion is 76 per cent faster than the nuvel 1a estimate while crustal blocks in the india eurasia collision zone move significantly and self consistently with respect to bounding plates only a very small motion is predicted between the nubian and somalian plates by integrating plate boundary zone deformation with the traditional modelling of angular velocities of rigid plates we have obtained a model that has already been proven valuable in for instance redefining a no net rotation model of surface motions and by confirming a global correlation between seismicity rates and tectonic moment rates along subduction zones and within zones of continental deformation

petrology of the yamato nakhlites the yamato nakhlites y 000593 y 000749 and y 000802 were recovered in 2000 from the bare icefield around the yamato mountains in antarctica consisting of three independent specimens with black fusion crusts they are paired cumulate clinopyroxenites we obtained the intercumulus melt composition of the yamato nakhlites and here call it the yamato intercumulus melt yim the yim crystallized to form the augite rims the olivine rims and the mesostasis phases in the cumulates the augite rims consist of two layers inner and outer the crystallization of the inner rim drove the interstitial melt into the plagioclase liquidus field subsequently the residual melt crystallized pigeonites and plagioclase to form the outer rims and the mesostasis three types of inclusions were identified in olivine phenocrysts rounded vitrophyric angular vitrophyric and monomineralic augite inclusions the monomineralic augite inclusions are common and may have been captured by growing olivine phenocrysts the rounded vitrophyric inclusions are rare and may represent the composition of middle stage melts whereas the angular vitrophyric inclusions seem to have been derived from fractionated late stage melts glass inclusions occur in close association with titanomagnetite and ferroan augite halo in phenocryst core augites and the assemblages may be magmatic inclusions in augites we compared the yim with compositions of magmatic inclusions in olivine and augite the composition of magmatic inclusions in augite is similar to the yim phenocrystic olivines contain exsolution lamellae augite magnetite aggregates and symplectites in the cores the symplectites often occur at the boundaries between olivine and augite grains the aggregates symplectite and lamellae formed by exsolution from the host olivine at magmatic temperatures we present a formational scenario for nakhlites as follows 1 accumulation of augite olivine and titanomagnetite phenocrysts took place on the floor of a magma chamber 2 olivine exsolved augite and magnetite as augite magnetite aggregates symplectites and lamellae 3 the overgrowth on olivine phenocrysts formed their rims and the inner rims crystallized on augite phenocryst cores and finally 4 the outer rim formed surrounding the inner rims of augite phenocrysts and plagioclase and minor minerals crystallized to form mesostasis under a rapid cooling condition probably in a lava flow or a sill

temperature constraints on the ginkgo flow of the columbia river basalt group this study provides the first quantitative estimate of heat loss for a columbia river basalt group flow a glass composition based geothermometer was experimentally calibrated for a composition representative of the 500 km long ginkgo flow of the columbia river basalt group to measure temperature change during transport melting experiments were conducted on a bulk sample at 1 atm between 1200 and 1050 c natural glass was sampled from the margin of a feeder dike near kahlotus washington and from pillow basalt at distances of 120 km vantage washington 350 km molalla oregon and 370 km portland oregon ginkgo basalt was also sampled at its distal end at yaquina head oregon 500 km comparison of the glass mgo content k 2 o in plagioclase and measured crystallinities in the experimental charges and natural samples tightly constrains the minimum flow temperature to 1085 5 c glass and plagioclase compositions indicate an upper temperature of 1095 5 c thus the maximum temperature decrease along the flow axis of the ginkgo is 20 c suggesting cooling rates of 0 02 0 04 c km these cooling rates substantially lower than rates observed in active and historic flows are inconsistent with turbulent flow models calculated melt temperatures and viscosities of 240 750 pa s allow emplacement either as a fast laminar flow under an insulating crust or as a slower inflated flow

cooling and crystallization of lava in open channels and the transition of pāhoehoe lava to a ā samples collected from a lava channel active at kilauea volcano during may 1997 are used to con strain rates of lava cooling and crystallization during early stages of flow lava erupted at near liquidus tem peratures f1150 7c cooled and crystallized rapidly in upper parts of the channel glass geothermometry indi cates cooling by 12 14 7c over the first 2 km of trans port at flow velocities of 1 2 m s this translates to cooling rates of 22 50 7c h cooling rates this high can be explained by radiative cooling of a well stirred flow consistent with observations of non steady flow in proximal regions of the channel crystallization of plag ioclase and pyroxene microlites occurred in response to cooling with crystallization rates of 20 50 per hour crystallization proceeded primarily by nucleation of new crystals and nucleation rates of f10 4 cm 3 s are similar to those measured in the 1984 open channel flow from mauna loa volcano there is no evidence for the large nucleation delays commonly assumed for plagioclase crystallization in basaltic melts possibly a reflection of enhanced nucleation due to stirring of the flow the transition of the flow surface morphology from pahoehoe to a aoccurred at a distance of 1 9 km from the vent at this point the flow was thermally stratified with an interior temperature of f1137 7c and crystallinity of f15 and a flow surface tempera ture of f1100 7c and crystallinity of f45 a afor mation initiated along channel margins where crust was continuously disrupted and involved tearing and clotting of the flow surface both observations suggest that the transition involved crossing of a rheological threshold we suggest this threshold to be the develop ment of a lava yield strength sufficient to prevent vis cous flow of lava at the channel margin we use this concept to propose that a aformation in open chan nels requires both sufficiently high strain rates for con tinued disruption of surface crusts and sufficient groundmass crystallinity to generate a yield strength equivalent to the imposed stress in hawai i where lava is typically microlite poor on eruption these combined requirements help to explain two common observations on a aformation a a aflow fields are generated when effusion rates are high thus promoting crustal disruption and b under most eruption conditions lava issues from the vent as pahoehoe and changes to a aonly after flowing some distance thus permitting sufficient crystallization

effects of martian conditions on numerically modeled cooling limited channelized lava flows 1 we used the flowgo thermorheological model to examine the effects of martian gravitational and environmental conditions on the cooling limited behavior of lava flowing in a channel the largest effect is due to the lower gravity on mars as compared to earth which causes lava to flow more slowly the lower velocity means that heat loss per distance down a mars channel is greater even though the lower velocity also produces a higher percentage cover of insulating crust gravity alone causes the mars flow to be 65 km shorter than an earth flow with an equivalent volumetric flow rate the cooler ambient mars atmosphere causes a slight increase in heat loss by forced convection this slows the flow a bit more resulting in a very slight increase in heat loss per distance by all mechanisms and decreases the modeled flow length by 1 km a difference well below our model uncertainty replacing terrestrial values of atmospheric density viscosity thermal conductivity heat capacity and cubic expansivity makes convection less efficient and increases flow length by 15 km nevertheless at the same volumetric flow rate lava flows 50 km less far under martian conditions than under terrestrial conditions our specific model flow has a volumetric flow rate of 5000 m3 s 1 and traveled 190 km down a channel on a constant 7 slope this volumetric flow rate is slightly less than the maximum rates during the 1783 1785 laki eruption and is 5 10 times greater than those of typical mauna loa eruptions

seismicity and tectonics of the subducted cocos plate we have examined teleseismic earthquake locations reported by the international seismological centre isc for the middle america region and selected 220 as the most reliable these hypocenters and other data are used to delineate the deep structure of the subducted cocos plate the results indicate that the subducted plate consists of three major segments segment i extends from the panama fracture zone to the nicoya peninsula the structure of this segment is poorly defined segment ii is the largest and best defined segment this segment consists of two parts iia and iib part iia extends from the nicoya peninsula to western guatemala and is very well defined and continuous in structure its strike follows the curvature of the trench and dips at about 60 part iib extends from western guatemala to orizaba mexico the dip of this part of the segment decreases slightly toward the northwest and its strike is more northward than that of the trench segment iii extends from orizaba to the rivera fracture zone and is not well defined due to a lack of earthquake activity beneath about 100 km its orientation differs markedly from segment ii and strikes somewhat more westward than the trench between parts iia and iib of segment ii the subducted plate seems to be continuous bending smoothly to accommodate the change in geometry local network data from costa rica suggest there may be a tear between segments i and ii between segments ii and iii there is a gap in the hypocenters which makes it difficult to define the boundary the change in geometry between these two segments indicates that there may be a tear and two strike slip focal mechanisms in the region support this conclusion we find no convincing evidence supporting the existence of segments smaller than the three described above if there is smaller scale segmentation in the shallow part of the subducting plate the plate must still maintain enough continuity to appear continuous at greater depths there is no evidence for any major tear in the subducted plate associated directly with either the tehuantepec ridge or the orozco fracture zone the shallow subduction at the northwestern end of segment ii may be related to the bouyancy of the tehuantepec ridge the cocos ridge is probably directly responsible for the change in geometry between segments i and ii and may even be slowing or stopping subduction in segment i the structure of the subducted plate in segment ii and the changes in the character of volcanism along the arc can be related to the relative motion of the north american and caribbean plates the present geometry of part iib of segment ii is more consistent with the probable configuration of the trench about 7 ma ago than with the present configuration indicating that the north american plate is overriding the subduction zone appendices 2 3 and 4 are available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b84 009 2 50

constraints from finite element modeling on the active tectonics of northern central america and the middle america trench 1 we have developed an elastic finite element model in order to study the role of the different forces acting on the northwestern part of the central american volcanic arc and the chortis block we present synthetic focal mechanisms maps of tectonic regime and strain crosses to analyze the results the models show that to achieve the observed state of stress on the volcanic arc the arc must be modeled as a lithospheric weak zone also the forces related to the eastward drift of the caribbean plate must be higher than those related to the subduction of the cocos plate the coupling on the subduction interface must be low with or without slip partitioning due to the obliquity of the subduction at the trench at guatemala the western edge of the chortis block is pinned against north america even with low trench normal forces making the triple junction between the cocos north american and caribbean plates a zone of diffuse deformation the extension in the western part of the chortis block from guatemala to the honduras depression is explained by the geometry of the north american caribbean plate boundary and the direction of motion of the caribbean plate with respect to north america the direction of extension in the chortis block is always e w regardless of the magnitude of the applied forces and the main part of the deformation is absorbed between the ipala graben and the honduras depression both features being consistent with our models

chemical stratigraphy iceland research drilling project reydarfjordur eastern iceland major element data are reported for lavas and dikes from a 3 2 km section through the eastern iceland lava pile the section includes a 1 2 km subaerial exposure and a 1 9 km sequence drilled by the iceland research drilling project irdp alteration increases down section although primary magma chemistry may be interpreted from feo al2o3 tio2 p2o5 and to a lesser extent sio2 in addition to immobile trace elements lava compositions range from mgo rich tholeiite to sio2 rich icelandite while dikes range from tholeiite to tholeiitic andesite three stratigraphic divisions based on volcanologic and trace element criteria e g ce yb and zr y are confirmed by major elements upper and lower groups are predominantly basaltic while the middle group includes a high proportion of silicic lavas variation within groups conforms to simple models combining fractional crystallization and accumulation of phenocryst plagioclase during build up of the pile eruptive phases commenced with silica rich magma and frequently terminated with basaltic or intermediate plagioclase cumulates dike chemistry resembles that of upper group lavas and also the nearby breiddalur volcano middle group lavas probably derive from a buried silicic complex while the lower group may represent the flank of a more deeply buried complex chemical stratigrapy is consistent with iterative burial with spreading of lenticular basaltic silicic complexes magma supply fractionation and mixing are considered in the framework of such kinematic models although it is premature to draw direct analogies to the active neogene zone of iceland

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

the importance of pahoehoe abstract pahoehoe lava flows are common in every basaltic province and their submarine variants pillow lavas and sheet flows cover the bulk of the earth pahoehoe flows are emplaced by inflation the injection of molten lava underneath a solidified crust only in the past few years has an understanding of the inflation process and the ability to recognize ancient inflated lava flows been achieved all large terrestrial basaltic flow fields studied to date including flood basalts were emplaced as thermally efficient inflated compound pahoehoe sheet flows this leads us to propose that this is the standard way of emplacing large lavas the swell hypothesis the atmospheric impact of such flood basalt eruptions could have been protracted and severe providing a plausible link between flood basalt eruptions and mass extinctions

the yield strength of subliquidus basalts experimental results yield strength is an important property of particle fluid suspensions in basaltic lavas that crystallize during flow emplacement the onset of yield strength may result in threshold transitions in flow behavior and flow surface morphology however yield strength crystallinity relations are poorly known particularly in geologic suspensions where difficulties of experimental and field measurements have limited data acquisition in the subliquidus temperature range here we describe two complementary experimental approaches designed to examine the effect of particle shape on the low shear yield strength of subliquidus basalts the first involves melting cubes of holocrystalline basalt samples with different initial textures to determine the temperature crystallinity at which these samples lose their cubic form these experiments provide information on the minimum crystal volume fractions 0 20 0 35 required to maintain the structual integrity of the cube the second set of experiments uses suspensions of corn syrup and neutrally buoyant particles to isolate the effect of particle shape on yield strength development from these experiments we conclude that the shape is important in determining the volume fraction range over which suspensions exhibit a finite yield strength as anisotropic particles may orient during flow the effect of particle shape will be controlled by the orientation distribution of the constituent particles we find that the so called excluded volume can be used to relate results of experiments on anisotropic particles to those of suspensions of spherical particles recent measurements of yield strength onset in basaltic melts at crystal volume fractions near 0 25 are consistent with our observations that crystal frameworks develop at low to moderate crystal volume fractions when crystals are anisotropic e g plagioclase we further suggest that conditions leading to yield strength onset at low crystallinities include rapid cooling increased crystal anisotropy heterogeneous nucleation which promotes extensive crystal clustering and large cluster anisotropy and static conditions random crystal orientations

great earthquakes and slab pull interaction between seismic coupling and plate slab coupling great earthquakes the few largest earthquakes that account for most of the earth s seismic energy release have occurred at only a few subduction zones around the world strong locking or seismic coupling of the interface between plates at certain subduction zones is often invoked to explain these great earthquakes although past studies have correlated strong seismic coupling with a compressional stress environment that is characterized by back arc compression and caused by trenchward motion of the overriding plate the consequences of this compressional environment for the tectonic forces that drive global plate motions are not yet clear to examine these consequences we compared subduction zone earthquake magnitudes to tectonically constrained estimates of the degree to which each slab transmits its excess weight as a direct pull force on a subducting plate at seismically uncoupled subduction zones that generate only moderate sized earthquakes we find that slabs must transmit nearly their entire upper mantle weight as a pull force on the subducting plate at seismically coupled subduction zones that produce great earthquakes however we find that slabs must be nearly completely detached from their subducting plates this suggests that slabs subducting in a compressional environment experience stress induced weakening that prevents the effective transmission of the slab pull force convergent mantle flow above a descending slab that becomes decoupled from its surface plate may induce additional surface compression that further locks the subduction zone and leads to additional slab decoupling and detachment the resulting redistribution of plate driving forces may be responsible for rapid changes in plate motion c 2003 elsevier b v all rights reserved

rupture process of the february 4 1965 rat islands earthquake the great rat islands underthrusting earthquake mw 8 7 of february 4 1965 represents subduction of the pacific plate beneath the north american plate along a 600 km segment of the western end of the aleutian islands body wave inversion techniques are used to determine the spatial and temporal heterogeneities associated with the rat islands earthquake we have deconvolved world wide standard seismograph network long period teleseismic p wave seismograms to obtain source time functions directivity associated with the three major pulses of moment release in the source time functions indicates a total source duration of 160 s unilateral rupture in the direction 300 fault length of 420 km and average rupture velocity of 2 5 km s the three pulses of moment release are located along the fault and these regions of high moment release are interpreted as asperities the first asperity extends from the epicenter to 100 km to the wnw this is the largest asperity and corresponds to a smooth pulse of moment release in the source time function with a duration of 50 s the second pulse of moment release is very jagged is less coherent between stations and is centered 200 km wnw of the epicenter the third pulse of moment release extends from 360 to 420 km wnw of the epicenter although the aftershock area is 600 km in length we can not resolve any moment release from the p waves beyond 420 km wnw of the epicenter the rat islands event was closely followed by a large tensional outer rise event on march 30 1965 ms 7 5 which is located oceanward of the largest moment release associated with the rat islands mainshock rupture detailed analysis of the p waves for this large outer rise event confine the depth extent to the upper 30 5 km of the crust the spatial and temporal association between the february 4 mainshock and the march 30 tensional outer rise event suggests the tensional event may have been triggered by the large displacement near the mainshock epicenter the overriding plate along the western aleutian subduction zone is laterally segmented into a series of rigid tectonic blocks separated by fault controlled canyons and extensional basins geist et al 1988 we suggest that the central undeformed parts of the blocks have the strongest coupling with the down going plate and hence are the sites of the largest moment release during an underthrusting earthquake the three asperities determined from the p waves correspond to the rat buldir and near tectonic blocks respectively hence the p wave seismic moment release of the rat islands earthquake is controlled by the lateral segmentation of the overriding plate

tsunami earthquakes slow thrust faulting events in the accretionary wedge the november 20 1960 peru october 20 1963 kurile and june 10 1975 kurile earthquakes are classified as tsunami earthquakes based on anomalously large tsunami excitation relative to earthquake magnitude long period surface wave analysis indicates double couple faulting mechanisms for all three events rather than single force mechanisms indicative of submarine landslides the earthquakes have shallow depths 15 km and are located near the trench axis and seaward of most other thrust zone events beneath the accretionary prism body waveform inversion indicates very shallowly dipping thrust faulting mechanisms for the three events with dip angles of 6 8 surface wave spectral amplitudes and deconvolution of sh waveforms suggests anomalously long source durations and large seismic moments relative to ms specifically the 1963 kurile event ms 7 2 shows a duration of 85 s and a moment of 6 0 1027 dyn cm mw 7 8 the 1975 kurile event ms 7 0 shows a duration of 60 s and a moment of 2 0 1027 dyn cm mw 7 5 and the 1960 peru event ms 6 75 shows a time function consisting of four subevents with a total duration of 110 130 s and a seismic moment of 3 4 1027 dyn cm mw 7 6 estimated rupture velocities are about 1 km s or less but there is no evidence of unusually low stress drops the august 1 1968 philippines event previously classified as a tsunami earthquake shows none of the anomalous source properties and teleseismic tsunami height measurements are sparse we do not consider this event a tsunami earthquake most of the anomalous tsunami excitation results from underestimation of earthquake size by ms due to the long source duration the tsunami heights are not significantly anomalous relative to seismic moment the slow nature of these events may result from rupture through the sedimentary rock along the basal decollement of the accretionary prism standard scaling laws when adjusted for the slow seismic velocity in the source region show an mw ms relationship similar to that observed for the tsunami earthquakes and predict ms saturation at about 7 3 rather than 8 0 for typical events

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

crystallization history of the 1984 mauna loa lava flow during a 3 week eruption in 1984 mauna loa produced vent lavas that increased in crystallinity from 1 to 30 and 27 km long flows that increased in crystallinity as they moved downstream we examined the crystallization history of these lavas using crystal size distribution csd analysis to study the rates of crystallization viscosity increase and latent heating typical average growth and nucleation rates were 5 10 9 cm s 1 and 5 cm 3 s 1 for microphenocrysts 20 to 500 m size crystals nucleated in the rift zone and 5 10 8 cm s 1 and 5 104 cm 3 s 1 for microlites 1 to 20 m size crystals nucleated in the channel these crystallization rates are high compared with those found in other csd studies of igneous rocks probably due to highly nonequilibrium conditions brought on by rapid degassing in the rift zone and cooling in the lava channel growth and nucleation rates decreased with time at the vent and with distance downstream the maximum downstream total crystallinity measured is 39 25 microlites 14 microphenocrysts in a quenched sample 14 km from the vent growth and nucleation rates cannot be calculated for postemplacement samples but they place upper limits of 53 58 on the amount of crystallization in the channel 9 20 km from the vent crystallization could have been mostly responsible for the 105 fold downstream increase in apparent viscosity although degassing and increasing incorporation of solid lava fragments also contributed another effect of crystallization on the lava flow was the sizeable latent heating 0 01 j g 1 s 1 over the first half of the flow length if the crystallinity of downstream quench samples is representative of the hot fluid core which may have been counteracted by entrainment of cooler material measurements of crystallization are shown to be crucial in the study of lava flow emplacement dynamics

the initial cooling of pahoehoe flow lobes in this paper we describe a new thermal model for the initial cooling of pahoehoe lava flows the accurate modeling of this initial cooling is important for understanding the formation of the distinctive surface textures on pahoehoe lava flows as well as being the first step in modeling such key pahoehoe emplacement processes as lava flow inflation and lava tube formation this model is constructed from the physical phenomena observed to control the initial cooling of pahoehoe flows and is not an empirical fit to field data we find that the only significant processes are a heat loss by thermal radiation b heat loss by atmospheric convection c heat transport within the flow by conduction with temperature and porosity dependent thermal properties and d the release of latent heat during crystallization the numerical model is better able to reproduce field measurements made in hawai i between 1989 and 1993 than other published thermal models by adjusting one parameter at a time the effect of each of the input parameters on the cooling rate was determined we show that a the surfaces of porous flows cool more quickly than the surfaces of dense flows b the surface cooling is very sensitive to the efficiency of atmospheric convective cooling and c changes in the glass forming tendency of the lava may have observable petrographic and thermal signatures these model results provide a quantitative explanation for the recently observed relationship between the surface cooling rate of pahoehoe lobes and the porosity of those lobes jones 1992 1993 the predicted sensitivity of cooling to atmospheric convection suggests a simple field experiment for verification and the model provides a tool to begin studies of the dynamic crystallization of real lavas future versions of the model can also be made applicable to extraterrestrial submarine silicic and pyroclastic flows

non newtonian rheological law for highly crystalline dome lavas volcanic eruption models are hampered by the lack of multiphase magmatic flow laws most rheological models estimate the viscosity of multiphase lavas via the einstein roscoe equation but this simplification cannot be used for high crystallinity and it does not consider the non newtonian strain rate dependence of viscosity we carried out parallel plate experiments on natural samples to simulate multiphase lava deformation under various stresses and strain rates multiphase lavas exhibit an important component of shear thinning and appear to invalidate the adequacy of einstein roscoe based formulations for highly crystalline lava rheology the remarkable singular dependence of viscosity on strain rate yields a novel universal rheology law at eruptive temperatures t i e log 0 993 8974 t 0 543 log our work reveals the importance of considering microcracking and viscous dissipation at very high strain rate 10 3 s 1 explaining the occurrence of seismic swarms along the conduit margins and consequently supporting plug like magma ascent models

hawaiian lava flows in the third dimension identification and interpretation of pahoehoe and a a distribution in the kp 1 and soh 4 cores 1 hawaiian lava flows are classified as pahoehoe or a a by their surface morphology as surface morphology reflects flow emplacement conditions the surface distribution of morphologic flow types has been used to study the evolution and eruptive history of basaltic volcanoes we extend this analysis to the third dimension by determining the distribution of flow types in two deep drill cores the scientific observation hole 4 soh 4 core drilled near kilauea s east rift zone erz and the pilot hole kahi puka 1 kp 1 for the hawaiian scientific drilling project hsdp drilled through distal flows from mauna loa and mauna kea flows are classified using both internal structures and groundmass textures with the latter useful when identification based on mesoscopic flow features e g surface morphology and vesicle content and distribution is ambiguous we then examine the temporal distribution of pahoehoe and a a flows in proximal soh 4 and distal kp 1 settings sequence analysis shows that the two flow types are not randomly distributed in either core but instead are strongly clustered the proximal soh 4 core is dominated by thin pahoehoe flows 60 by volume consistent with the common occurrence of surface fed pahoehoe flows in near vent settings the distal kp 1 core has a high proportion of a a 58 by volume although the proportion of pahoehoe and a a varies dramatically throughout the mauna kea sequence thick inflated pahoehoe flows dominate when the drill site was near sea level consistent with the numerous inflated pahoehoe fields on the current coastal plains of kilauea and mauna loa a a flows are abundant when the site was far above sea level as slope increases from the coastal plains to mauna kea s flank this correlation may reflect the combined effect of long transport distances and increased slopes on flow emplacement these results demonstrate that flow type and thickness variations in cores provide valuable information about both vent location and local site environment observed variations in flow type within the kp 1 core raise interesting questions about feedback between volcano evolution and flow morphology and suggest that flow type is an important variable in models of volcano growth and related models for lava flow hazard assessment

observations on basaltic lava streams in tubes from kilauea volcano island of hawai i from 1986 to 1997 the pu u o o kupaianaha eruption of kilauea produced a vast pahoehoe flow field fed by lava tubes that extended 10 12 km from vents on the volcano s east rift zone to the ocean within a kilometer of the vent tubes were as much as 20 m high and 10 25 m wide on steep slopes 4 10 a little farther away from the vent some tubes formed by roofing over of lava channels lava streams were typically 1 2 m deep flowing within a tube that here was typically 5 m high and 3 m wide on the coastal plain 1 tubes within inflated sheet flows were completely filled typically 1 2 m high and several tens of meters wide tubes develop as a flow s crust grows on the top bottom and sides of the tubes restricting the size of the fluid core the tubes start out with nearly elliptical cross sectional shapes many times wider than high broad flat sheet flows evolve into elongate tumuli with an axial crack as the flanks of the original flow were progressively buried by breakouts temperature measurements and the presence of stalactites in active tubes confirmed that the tube walls were above the solidus and subject to melting sometimes the tubes began downcutting progressive downcutting was frequently observed through skylights a rate of 10 cm d was measured at one skylight for nearly 2 months

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

estimate of the tsunami source of the 1992 nicaraguan earthquake from tsunami data the nicaraguan earthquake of september 2 1992 excited large tsunamis which caused significant damage along the nicaraguan coasts some of the inhabitants felt only minimal shock before the tsunami arrived indicating that excitation of short period seismic waves was very small numerical simulation with the initial tsunami source estimated by the seismic data is carried out to study the characteristics of the tsunami source by comparing the calculated data with the measured data along the nicaraguan coast finding of the comparison shows that the dislocation of the fault estimated from the measured data is 5 6 to 10 0 times larger than that from seismic data the tsunami source area which is 200km in length 100km in width is used to explain the distribution of measured tsunami heights along the coast and the wave period as shown in the tide record at corinto the effect of rise time on tsunami excitation indicates a slow process which corresponds with the seismic waves this event falls under the tsunami earthquake category to produces anomalously large tsunamis relative to earthquake magnitude

stress interaction between subduction earthquakes and forearc strike slip faults modeling and application to the northern caribbean plate boundary 1 strike slip faults in the forearc region of a subduction zone often present significant seismic hazard because of their proximity to population centers we explore the interaction between thrust events on the subduction interface and strike slip faults within the forearc region using three dimensional models of static coulomb stress change model results reveal that subduction earthquakes with slip vectors subparallel to the trench axis enhance the coulomb stress on strike slip faults adjacent to the trench but reduce the stress on faults farther back in the forearc region in contrast subduction events with slip vectors perpendicular to the trench axis enhance the coulomb stress on strike slip faults farther back in the forearc while reducing the stress adjacent to the trench a significant contribution to coulomb stress increase on strike slip faults in the back region of the forearc comes from unclamping of the fault i e reduction in normal stress due to thrust motion on the subduction interface we argue that although coulomb stress changes from individual subduction earthquakes are ephemeral their cumulative effects on the pattern of lithosphere deformation in the forearc region are significant we use the coulomb stress models to explain the contrasting deformation pattern between two adjacent segments of the caribbean subduction zone subduction earthquakes with slip vectors nearly perpendicular to the caribbean trench axis is dominant in the hispaniola segment where the strike slip faults are more than 60 km inland from the trench in contrast subduction slip motion is nearly parallel to the caribbean trench axis along the puerto rico segment where the strike slip fault is less than 15 km from the trench this observed jump from a strike slip fault close to the trench axis in the puerto rico segment to the inland faults in hispaniola is explained by different distributions of coulomb stress in the forearc region of the two segments as a result of the change from the nearly trench parallel slip on the puerto rico subduction interface to the more perpendicular subduction slip beneath hispaniola the observations and modeling suggest that subduction induced strike slip seismic hazard to puerto rico may be smaller than previously assumed but the hazard to hispaniola remains high

comparison of earthquake scaling relations derived from data of the instrumental and preinstrumental era estimates of surface rupture displacement and magnitude for crustal earthquakes from the preinstrumental era pre 1900 tend to be greater than the corresponding estimates derived from modern scaling relations we investigate this tendency using an expanded and updated version of the earthquake dataset of wells and coppersmith 1994 to fit regression relations of moment magnitude on surface rupture length and rupture area and average surface displacement on surface rupture length separate relations are fitted to preinstrumental and instrumental data and the results compared to the equivalent relations of wells and coppersmith we find that our relations for instrumental data remove some but not all of the differences between the preinstrumental data and the relations of wells and coppersmith we attribute the remaining differences largely to natural censoring of surface displacements less than about 1 m and surface rupture lengths less than about 5 km from the dataset for the preinstrumental era because regressions constructed from similarly censored instrumental data are indistinguishable from the preinstrumental regressions since the regressions for our censored instrumental data i e restricted to moderate to large earthquakes are different from regressions for our complete dataset of instrumental earthquakes and from the regressions of wells and coppersmith both with a larger proportion of small to moderate earthquakes the results may indicate that large earthquakes have different scaling relationships from those of smaller earthquakes

mechanism of the 1992 nicaragua tsunami earthquake the 1992 nicaragua earthquake generated larger tsunamis than expected from its surface wave magnitude ms 7 2 and is known as a tsunami earthquake seismological studies showed that the duration was very long for its size about 100 s other studies have shown that the seismic moment estimated from tsunamis is an order of magnitude larger than that from seismic waves even after the long duration is accounted for numerical computations of tsunamis from various fault models are made to reconcile this discrepancy comparison of calculated waveforms with tide gauge records shows that the fault width is 40 km much narrower than the aftershock area and extends only into the upper 10 km of the ocean bottom slip amount on the fault is estimated to be 3 m from amplitude comparisons the fault length is estimated to be 250 km slightly longer than the aftershock area from comparison of the tsunami height distribution the rigidity around the shallow fault may be smaller than that of a standard underthrust fault and the seismic moment is estimated as 3 1020 nm consistent with the seismic observations a slow rupture on the shallow fault presumably in the subducted sediments is responsible to the unusually large tsunami excitation

basalts of the northeastern deccan traps india isotopic and elemental geochemistry and relation to southwestern deccan stratigraphy the northeastern deccan traps include flows with strong isotopic and elemental affinities to lavas in the southwest as far as 900 km away however many of the northeastern flows show a negative correlation of 206pb 204pb with end t and positive correlation of 206pb 204pb with 87sr 86sr t distinct from any of the isotopic fields for the southwestern formations this array from end t 5 87sr 86sr t 0 7041 206pb 204pb 17 9 to end t 0 87sr 86sr 0 7068 206pb 204pb 20 5 overlaps the ambenali formation fm field and runs toward that of the common signature peng et al 1994 that appears to have been an important magma type in several of the lower formations of the southwest this array appears to represent mixing between an ambenali type and 1 a common signature end member or 2 an end member with even higher 206pb 204pb and 87sr 86sr and lower end than the common signature such mixing has been postulated but not documented previously for the deccan lavas isotopically and chemically indistinguishable from the ambenali fm form the tops of sections near jabalpur and chikaldara beneath them are flows that chemically resemble the poladpur fm which sits immediately below the ambenali in the southwest and several lavas similar to the khandala fm beneath the poladpur and intervening bushe fm in the southwest given the general stratigraphic correspondence with the southwestern sequence many of these northeastern flows may be petrogenetically related to the respective southwestern formations lavas with broadly poladpurand khandala like elemental compositions are also abundant in a thick section south of mhow several other mhow area flows resemble the distinctive bushe fm however nearly all of the poladpur and khandala like northeastern deccan lavas analyzed have higher 206pb 204pb man any southwestern poladpur or khandala fm basalts if they indeed are related petrogenetically to these formations many of the northeastern magmas interacted less with low 206pb 204pb continental material and thus must have erupted from different feeder systems

a developmental model of olivine morphology as a function of the cooling rate and the degree of undercooling we performed dynamic crystallization experiments in the cmas system at 1 atm to investigate the evolution of the morphology of forsterite crystals as a function of cooling rate and degree of undercooling in sections parallel to the 010 plane we observed the evolution of the forsterite morphology from tablets to hopper skeletal crystals and then to swallowtail shapes dendritic morphology for increased degree of undercooling the other shapes described in the literature can be interpreted as particular sections of those three shapes the onset of dendritic growth is due to a competition between the growth of the faces of the initial hopper crystal and dendrite overgrowths the forsterite dendrites are formed by a succession of units which look like hopper shapes this result has been tested by an additional set of experiments