short term and intermediate term geochemical precursors detection of precursory phenomena in observation data is essential to earthquake prediction studies continuous monitoring of radon concentration in groundwater in japan in one case showed a short term anomaly related to a nearby earthquake with the exception of the 1978 izu oshimakinkai earthquake m7 0 however no abnormal change has been noted this may be due partially to difficulty in detecting insignificant precursory signals from observation data which ordinarily contains a noise induced fluctuations and partially to lack of understanding of the mechanism controlling the appearance of precursory phenomena in order to increase our knowledge of the variation pattern of precursory changes in radon concentration of groundwater hydrologic precursors with significant features are examined in this paper complexity of appearance of precursory phenomena and problems in assignment of the specific earthquake are discussed

magmatic metasomatism and formation of the merensky reef bushveld complex the rare earth element ree contents of pyroxenes and other minerals from the merensky reef and stratigraphically adjacent rocks of the atok section bushveld complex have been determined with the ion microprobe merensky reef clinopyroxene and orthopyroxene contain much higher and more variable concentrations of the ree than their cumulus counterparts in rocks several meters below the reef chondrite normalized merensky clinopyroxene ce contents vary from 10 to 90 for ce and from 4 to 17 for yb they also possess deep negative eu anomalies the eu anomalics being deeper for crystals having high ree contents and relatively shallow for pyroxenes with low ree contents similar compositional characteristics are displayed by cl rich apatite which is an accessory phase in the rocks interstitial pyroxene in cumulates above and below the reef also tends to have elevated ree contents and in general is not in equilibrium with coexisting cumulus minerals the melt from which the cumulus minerals crystallized falls within the compositional range of continental basalts that from which merensky and postcumulus pyroxenes crystallized is inferred to be much more highly enriched in ree than any normal tholeiitic or alkalic basalt despite their highly evolved nature in terms of the ree the merensky reef pyroxenes are not evolved in terms of major elements the decoupling of incompatible trace and major elements is best explained by a metasomatic process it is speculated that metasomatism involved upward percolation of hydrated silicate melt through and its reaction with the crystalline cumulate pile the fact that the rocks enriched in the platinum group elements are also those that show evidence for metasomatism suggests that these elements were also metasomatically redistributed

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

high temperature elasticity of iron bearing olivines the first high temperature data on the nine adiabatic elastic moduli for iron bearing olivine are reported these measurements are on two single crystal specimens of natural olivine at ambient pressure and from room temperature to a maximum of 1500 k the two specimens contain 8 and 9 modal percent fayalite which required the oxygen fugacity be controlled at high temperature to preserve their chemical stability the rectangular parallelepiped resonance apparatus was adapted to buffer the specimens from the atmosphere with a mixture of co and co2 gas a small increase 1 2 gpa in the adiabatic bulk modulus of each specimen over that of end member forsterite was found the data are high quality to extreme temperatures with good agreement found when comparing the temperature derivatives of the elastic moduli of the two specimens neither specimen exhibits measurable nonlinear temperature dependence in the computed isotropic bulk and shear moduli which is in contrast to published forsterite data the temperature derivatives of the isotropic bulk modulus ks are 1 69 1 80 10 2 gpa k 1 for the two olivine specimens and the shear modulus g derivatives are 1 38 1 36 10 2 gpa k 1 these derivatives are only slightly larger in magnitude than ks t p 1 56 10 2 and g t p 1 30 10 2 gpa k 1 found previously for iron bearing olivine over a very small temperature range there are also no significant differences between the temperature derivatives found here and the average derivatives of end member forsterite from data retrieved over a slightly larger temperature range several dimensionless parameters have been calculated from these results and are discussed in view of systematics which bear on high pressure phases in earth s transition zone one result from these systematics related to the seismic velocities in the earth and especially the shear wave velocities is that an olivine content of less than 50 is implied at the 400 km discontinuity if earth s upper mantle is isochemical furthermore the substitution of almost 10 iron for magnesium at the forsterite end of the olivine solid solution series has little effect on the dimensionless parameters or on the temperature derivatives of the elastic moduli at high temperature

the hierarchical rupture process of a fault an experimental study abstract we describe the detailed faulting process of a naturally healed fault containing geometric and mechanical asperities in a granitic porphyry sample based on data collected with a high speed acoustic emission ae waveform recording system asperity failure is examined using the detailed spatio temporal distribution of ae hypocenters the initial phase of ae activity is also examined using high dynamic range waveforms our experimental results indicate that quasi static nucleation of the heterogeneous fault is associated with the failure of asperities on the fault plane the fracturing of an asperity is characterized by a dense spatial clustering of ae events and a changing b value b hereinafter which is manifest in three typical stages of failure as follows 1 foreshocks exhibiting a decrease in b 2 a period of mainshocks corresponding to a minimum in b and 3 aftershocks of increasing b the progressive fracture of several coupled asperities results in short term precursory fluctuations in both b and ae rate furthermore some ae events possess similar dynamic rupture features to those of earthquakes having an initial phase associated with the transition from quasi dynamic to dynamic rupture we conclude based on these experimental observations that fault rupture has hierarchical characteristics quasi static nucleation of fault rupture represents dynamic fracture of the asperities on the fault plane likewise a quasi static nucleation process characterized by dynamic microfracturing precedes the fracture of an asperity since dynamic motions are easier to detect remotely than static deformations understanding the hierarchical processes underlying fault rupture may thus be helpful for elucidating quasi static nucleation at larger scales in terms of the dynamic rupture of the asperities at smaller scales careful studies of asperity failure in the lab may guide future seismic studies of large asperities on natural faults potentially making it possible to recognize the final preparation stage before a large earthquake

viscoplasticity of polycrystalline olivine experimentally deformed at high pressure and 900 c abstract we have performed tri axial compression experiments on olivine aggregates at 900 c and at a confining pressure of 300 mpa in a high resolution gas medium mechanical testing apparatus deformation at two different constant strain rates 1 1 10 5 s 1 and 3 4 10 4 s 1 yields continuous hardening reaching maximal differential stresses of 930 and 1076 mpa respectively before sample failure at ca 10 strain the deformed samples were characterized by electron backscatter diffraction ebsd and transmission electron microscopy tem crystallographic preferred orientations cpo are weak but reveal an alignment of the 010 axes around the compression direction and some concentration of 001 and 100 axes normal to it tem observations confirm plastic deformation by dislocation glide with both 001 and 100 burgers vectors electron tomography performed for the first time on deformed fined grained olivine shows that 001 dislocations glide extensively on 110 and 130 planes in complement to the 010 and 100 glide planes often reported at high temperatures 100 dislocations glide mostly on 010 but 011 and 041 planes are also activated the experimental cpo and relative activity of slip systems are well reproduced by viscoplastic self consistent simulations in which all 100 and 001 slip systems have similar strengths they are also consistent with olivine cpo from natural samples deformed at low temperature comparison of the present mechanical results to those obtained for olivine single crystals at similar conditions shows that at low temperature below 1100 c and high stress 300 mpa polycrystalline olivine has a more complex mechanical behavior than single crystals however both datasets advocate for a much weaker dry mantle lithosphere than previously thought

post deposition structures in the bushveld complex mafic sequence the stratigraphy of the bushveld complex is characterized by laterally continuous horizontal layering at the interface of some of these layers there are phenomena analogous to flame load cast ball and pillow and liquid escape structures of sedimentary rocks three plastic deformation styles recognized in the complex are i vertical ii vertical followed by horizontal and iii vertical fluid movement with brittle failure these post deposition structures are used to estimate viscosity and density of adjacent layers during consolidation the distribution of the structures through the mafic sequence provides some information on magma movement and rates of crystal accumulation

potholes of the merensky reef at brakspruit shaft rustenburg platinum mines primary disturbances in the magmatic stratigraphy potholes are locations where parts of the magmatic stratigraphy are missing in the foot wall sequence of the merensky reef in general potholes are circular to elliptical in plan and funnel shaped in cross section within narrow limits most potholes reveal the same three dimensional orientation to the strike and dip of the magmatic layering the updip pothole flank is steep to vertical the downdip flank is horizontal the pothole bottom generally coincides with one of the marker horizons of the footwall stratigraphy and is conformable with layering where the merensky reef fills potholes it is more variable in thickness than it is at its normal stratigraphic level in the potholes it changes over short distances from an unusually thin chromite rich contact phase of the reef to thick unlayered lenses of harzburgite pegmatite in deep seated parts of the potholes when the bastard reef is observed in potholes it sometimes grades into massive graphite rich transgressive gabbroic pegmatite the marker horizons in the anorthositic footwall units around potholes are often intensely mineralized with stratiform and crosscutting sulfides such marginal footwall mineralization is absent in the undisturbed footwall sequence away from potholes potholes are traditionally considered to be resorption pits due to the influx of a new hot primitive magma at the merensky reef level or to represent scars of a late magmatic fumarole activity the present study suggests that cumulate resorption played a minor role only potholes are sites of nondeposition where the missing rock units did not crystallize they formed where locally high concentrations of dissolved c h o s volatiles lowered the liquidus temperature of the magma and suppressed the crystallization of cumulus plagioclase potholes seem to be concentrated above anticlines of the metasedimentary basement rocks in the footwall of the bushveld complex volatiles derived by pyrometamorphism were focused upward into the overlying melt above such topographic highs and were accumulated at the level of the merensky reef

relationships between dynamically recrystallized grain size and deformation conditions in experimentally deformed olivine rocks new microstructural data on experimentally deformed wet and dry natural olivine rocks anita bay and aheim dunite together with the other reliable experimental data indicate that the experimental stress recrystallized grain size relationship in olivine rocks is largely independent of water content and temperature and is only slightly dependent on the flow properties of the material the experimental data cover a stress range of 30 300 mpa water contents from 30 ppm to 300 ppm and temperatures in the range 1100 1650 c local melt contents of up to 10 volume cannot be demonstrated to have a significant effect on the stress grain size relationship

constraints on the formation of platinum group element deposits in igneous rocks mechanisms of concentration of the platinmn group and other chalcophile elements iu several platinum group element deposits in layered intrusions are evaluated in light of recently published data on element partitioning between immiscible sulfide and silicate melts the similarity of the partition coefficieut d super sulfide melt silicate melt of ir to that of pd indicates that the observed fractionation of these elements in nature resulted from a process other than or in addition to sulfide liquid immiscibility in experiments designed to test the possibility that this fractionation was due to the presence of os ir alloy sulfide and silicate melts were equilibrated with ir metal at 1 450 degrees c 8 kbars total pressure and under sulfur and oxygen fugacity conditions appropriate for nature the ir content of the sulfide liquid was found to be or 3 7 wt percent and that of the coexisting silicate melt inferred to be or 1 000 ppb these concentrations are far in excess of the ir contents of natural sulfides or rocks and indicate that os ir alloys are not stable in the presence of sulfide or silicate melts in nature using our preferred values of d super sulfide melt silicate melt for the chalcophile elements and their estimated concentrations in the mantle limits are determined for the possible ranges of concentrations and relative abundances of these elements in immiscible sulfide liquid formed in magma derived by partial melting of the mantle the ratios of highly chalcophile to moderately chalcophile elements and of metal to sulfur of several deposits including the j m reef stillwater complex the ug 2 bushveld complex and the lac des isles complex are inconsistent with concentration solely by segregation of sulfide liquid in contrast the merensky reef fits the geochemical criteria for formation by accumulation of magmatic sulfide stratigraphic variations in chalcophile element concentrations through the ug 2 and the main sulfide zone of the great dyke also indicate that metals must have been redistributed on at least the meter scale our analysis implies either different relative mobilities of the chalcophile elements relative to one another in a process postdating initial sulfide liquid deposition or concentration by a different mechanism

three dimensional location and waveform analysis of microseismicity in multi anvil experiments we present an acoustic emission ae monitoring technique to study high pressure p 1 gpa microseismicity in multi anvil rock deformation experiments the application of this technique is aimed at studying fault mechanisms of deep focus earthquakes that occur during subduction at depths up to 650 km ae monitoring in multi anvil experiments is challenging because source locations need to be resolved to a submillimetre scale due to the small size of the experimental assembly aes were collected using an 8 receiver array located on the back truncations of the tungsten carbide anvils each receiver consists of a 150 1000 khz bandwidth pzt transducer assembly data were recorded and processed using a high speed amsy 5 acquisition system from vallen systems allowing waveform collection at a 10 mhz sampling rate for each event signal 3 d hypocentre locations in the assembly are calculated using standard seismological algorithms the technique was used to monitor fault development in 3 mm long x 1 5 mm diameter olivine cores during axisymmetric compression and extension the faults were generated during cold compression to similar to 2 gpa confining pressure subsequent aes at 2 6 gpa and 900 degrees c were found to locate near these pre existing faults and exhibit high pressure stick slip behaviour

switching from seismic faulting to silent slips in harzburgite induced by h2o fluid at upper mantle pressures slow slip events frequently occur but regular earthquakes are much less active on the h2o fluid rich subduction interface at depths of 40 km the characteristic duration for silent earthquakes which are categorized as the great slow slip events is more than five orders of magnitude longer than that for regular earthquakes such phenomena are often attributed to the slippage of the softer part of the subduction interface but the impact of h2o fluid on aseismic slip is still unsolved here we conduct deformation experiments on water saturated harzburgite at pressures of 1 2 to 3 0 gpa and temperatures of 770 to 1250 k corresponding to the conditions of the lower part of the overriding plate just above the subduction interface we observe deformation of the harzburgite followed by silent faulting at a significantly low stress level down to 0 3 gpa under fluid bearing conditions even though many acoustic emissions are generated at the onset of faulting in fluid free harzburgite we find that the observed silent faulting is caused by the detachment of asperity contacts by high pore pressures and lubrication of the fault plane by a hydration reaction we therefore propose that h2o fluid may prevent the occurrence of regular intraslab earthquakes but trigger silent earthquakes

thermal diffusivity and conductivity of olivine wadsleyite and ringwoodite to 20 gpa and 1373 k abstract we present results of lattice thermal diffusivity measurements on mg0 9fe0 1 2sio4 olivine and its high pressure polymorphs wadsleyite and ringwoodite under mantle conditions we used the angstrom method on cylindrical samples in multianvil apparatus at pressures up to 20 gpa and temperatures up to 1373 k because of the fine polycrystallinity of the specimens 30 40 m or less there is strong scattering absorption of light and suppression of radiative transport so that the lattice vibrational component is the dominant heat transfer mode lattice thermal conductivities were calculated from the thermal diffusivity results using heat capacity and equation of state data olivine thermal conductivities are consistent with previous results obtained at 1 atm e g j am ceramic soc 38 1954 107 j geophys res 77 1972 6966 science 283 1999 1699 thermal conductivity increases by approximately 30 at the transition from olivine to wadsleyite corresponding to the 410 km discontinuity and a further but smaller increase may occur at the transition from wadsleyite to ringwoodite for each of these phases lattice conductivity closely follows a t 1 2 dependence on temperature t phys rev 119 1960 507 j geophys res 79 1974 703 brown 2002 if such a dependence applies to other silicates and complex crystals there should be a useful way to estimate conductivities at high temperatures from room temperature measurements

indicators of critical point behavior prior to rock failure inferred from pre failure damage abstract to investigate possible indicators of critical point behavior prior to rock failure the statistical properties of pre failure damage were analyzed based on acoustic emission events ae recorded during the catastrophic fracture of typical rock samples under differential compression aes were monitored using a high speed 32 channel waveform recording system time dependent statistics including the energy release rate b value of the magnitude frequency distribution fractal dimension and spatial correlation length scl of the ae hypocenters were calculated for each data set each parameter is a function of the time to failure and thus can be treated as an indicator of the critical point it is clear that the pre failure damage evolution prior to catastrophic failures in several common rock types is generally characterized by 1 accelerated energy release 2 a decrease in fractal dimension and scl with a subsequent precursory increase and 3 a decrease in b value from 1 5 to 0 5 for hard rocks and from 1 1 to 0 8 for soft rocks such s c cataclasite however each parameter also reveals more complicated temporal evolution due to either the heterogeneity of the rock mass or the micro mechanics of shear fracturing this confirms the potential importance of integrated analysis of two or more parameters for successfully predicting the critical point the decreasing b value and increasing energy release may prove meaningful for intermediate term prediction while the precursory increase in fractal dimension and scl may facilitate short term prediction

significance of 87 sr 86 sr ratios in the merensky cyclic unit of the bushveld complex in a number of mafic layered intrusions layers with platinum group element pge mineralization coincide with breaks in cumulus mineral composition and isotopic variation trends through the layered sequence1 2 for example in the bushveld complex in south africa abrupt increases in initial 87sr 86sr ratios occur at the ug 2 and merensky pegmatoid or reef horizons both of which are exploited for pges we report here the results of a detailed sr isotope study across the merensky unit and its immediate foot and hangingwall rocks which when considered together with new ideas on processes operating in magma chambers3 5 suggest that magma mixing and post cumulus infiltration of liquids displaced from below were important during crystallization of the merensky pegmatoid

genesis of compositional characteristics of stillwater an i and an ii thick anorthosite units a single 10 m 10 m outcrop of stillwater anorthosite unit an ii was mapped for pyroxene mode on a decimeter scale and samples from each range of pyroxene proportion were analyzed for major and trace elements distinct one to several square meter regions of different pyroxene mode were observed samples from regions with 10 pyroxene showed strong elemental correlations and anticorrelations with mgo concentrations that can be interpreted in terms of the following scheme for development of the stillwater anorthosites aggregates containing 50 to 80 cumulus plagioclase average 67 formed stable frameworks in a crystal mush of complexly zoned plagioclase the interstices among the plagioclase grains in these frameworks filled in part with pyroxene and plagioclase that were produced in equilibrium with the bulk melt and in part with pyroxene and plagioclase derived by crystallization of trapped intercumulus liquid the proportions of these three types of materials were mutually constrained in a manner that gave rise to lines instead of fields on two element variation diagrams samples richest in cumulus plagioclase are also richest in intercumulus plagioclase and pyroxene regions of the outcrop with 10 original pyroxene underwent substantial alteration by hydrous fluids that produced variations in fe2o3 tio2 loi and most incompatible trace elements

the compaction of igneous and sedimentary rocks in many problems of interest to geology and soil mechanics a fluid moves through a solid matrix which is also being deformed in most cases of interest the effective viscosity of the matrix is many orders of magnitude greater than that of the percolating fluid and both form interconnected networks in three dimensions the partial differential equations governing such behaviour can now be obtained and a variety of simple model problems have been investigated some of the more surprising solutions contain solitary waves and compaction fronts some of the less exotic solutions are presently of more geological interest the mobility of volatile rich melts at melt fractions as small as 0 1 has important consequences for trace element geochemistry the geometry of layered intrusives appears to result from differential compaction of the crystal mush and the rates required can be used to estimate a viscosity of 3 x 10 18 pa s for an olivine matrix this value agrees excellently with laboratory experiments when proper account is taken of the grain size dependence compaction in sedimentary rocks results in overpressure when the porosity becomes sufficiently small and can also lead to the development of secondary porosity

concentration of platinum group elements by magmatic fluids in layered intrusions evidence leading to a model which supports the formation of pt pd reefs in a layered intrusion by the action of magmatic fluids is presented as well as some of the constraints imposed on such a model the stillwater complex is used as an example of this model within the stillwater complex no laterally continuous sulfide enriched cumulates occur above the lowermost parts of the ultramafic series until one reaches the platiniferous j m reef this sulfide poor stratigraphic interval beneath the j m reef is characterized by unusually cl rich apatite although reported sulfide modes and whole rock sulfur contents in the cumulates below the j m reef are approximately an order of magnitude lower than that expected for a sulfide saturated magma sulfide saturation prior to the formation of the j m reef is suggested by relatively high pd and pt concentrations reported in the cumulates below the j m reef as well as by the presence of sulfide as inclusions in silicate and oxide cumulus minerals hence it is suggested that the footwall cumulates to the j m reef were originally sulfide saturated but later lost sulfur to a fluid phase exsolving from inter cumulus liquid sporadic sulfide bearing pegmatoids in some of these rocks are additional evidence for late loss of sulfur these observations as well as the association of the j m reef at the first significant stratigraphic break in the cl cl f ratio of apatite and the relatively high solubility of pt and pd as aqueous cl complexes are consistent with the formation of the j m reef by exsolution of cl and volatile rich fluids from footwall intercumulus liquids which leached and transported ore components both the pge and s upward to the level of the reef using published whole rock platinum group element pge concentrations for the ultramafic and lower banded series the cumulates below the j m reef must have been enriched by a factor of at most 1 24 for pt and 1 75 for pd if these rocks were to be the source for the metals in the j m reef model raleigh fractionation calculations suggest that the cumulates beneath the j m reef could have had the required metal concentrations if during the crystallization of a parent magma containing no more than 15 ppb of either metal the average bulk solid liquid distribution coefficients for pt and pd were no more than 5 these values are consistent with assumption of sulfide saturation prior to the formation of the j m reef during solidification of intercumulus liquid the separation and loss of a cl rich fluid will deplete the residual assemblage of s and pge if 0 1 to 0 5 wt percent fluid containing 5 percent s evolved during solidification of the footwall cumulates the amount of fluid expected to be exsolved by the crystallization of approximately 2 to 10 percent fluid saturated intercumulus liquid the fluid liquid distribution coefficients for pt and pd would need to be almost as large as the sulfide liquid silicate liquid distribution coefficients to remove significant amounts of pt and pd much smaller distribution coefficients are needed if sulfide is completely lost to fluid during degassing the latter possibility is consistent with the low s contents of the footwall cumulates beneath the j m reef numerical models of the degassing of intercumulus liquids suggest that thick cumulus sequences can act as chromatographic columns to separate the pge and s during the degassing of intercumulus silicate liquids the pge being enriched at a sulfide dissolution front as upward migrating sulfide undersaturated fluids resorb cumulus sulfides zones of pge and s enrichment can occur where degassing fronts encounter stratigraphic physical chemical discontinuities such as changes in the fluid saturation temperature of the intercumulus silicate liquids

petrologic evolution of partially molten cumulate the atok section of the bushveld complex the postcumulus evolution of a portion of the bushveld complex that includes the merensky reef is inferred from the study of a continuous 56 m drill core the core penetrated the basal orthopyroxenites of the merensky and bastard units the massive anorthosites overlying the two pyroxenites and about 10 m of norite underlying the merensky pyroxenite detailed profiles of major minor and rare earth element ree contents of clinopyroxene and orthopyroxene were determined by electron and ion probe good correlations exist between textural and lithological variations and the ree contents of the pyroxenes specifically enrichments in pyroxene ree abundances are observed in the basal pyroxenites of the merensky and bastard units relative to the underlying and overlying rocks in the pyroxenites the nd content of clinopyroxene is typically over 12 ppm and reaches nearly 40 ppm 90 chondrite and nd yb ratio is in the range 8 to 25 these extreme enrichments in ree are not accompanied by large variations in major element contents computations of the compaction parameters relevant to the conditions of crystallization of the bushveld complex combined with a consideration of cooling history confirm the importance of compaction as a post cumulus process this analysis indicates that the geochemical variability is a result of redistribution of interstitial melt driven by compaction and cannot reflect variations in the initial porosity of the accumulating crystal pile a model for the development of the atok section is developed the merensky anorthosite is interpreted to have served as a barrier to the upward porous flow of late stage hydrous and incompatible element enriched melt which was thus trapped in the underlying merensky pyroxenite the flow was driven by compaction of the 350 meter thick section of predominantly norite beneath the anorthosite the introduction and accumulation of this melt in the pyroxenite and subsequent cooling resulted in partial dissolution recrystallization and ree enrichment of the rock forming minerals and in the formation of the main lithologic features of the merensky pyroxenite further upward percolation of the interstitial melt through the merensky anorthosite was restricted to channels due to the relatively impermeable nature of the cemented anorthosite this melt accumulated in and metasomatized the bastard pyroxenite in the same manner as the merensky pyroxenite having again been trapped by the overlying bastard anorthosite

testing the pattern informatics index on synthetic seismicity catalogs based on the non critical past abstract the non critical precursory accelerating seismicity theory or non critical past has recently been proposed to explain the formation of accelerating seismicity that may be observed before large earthquakes it has led to the possibility of constructing synthetic seismicity catalogs where patterns of accelerating seismicity activation and quiescence which occur in the same space time window can be evaluated by existing forecasting techniques in this study the pattern informatics or pi index is tested on synthetic catalogs where a realistic spatiotemporal clustering has been added on top of the theoretical precursory seismicity we show that the pi index is successful at identifying the precursory quiescent signal but fails in identifying precursory accelerating seismicity directly being more sensitive to aftershock sequences of background events than to the activation like behavior of the acceleration formed by background events alone we also show that the pi index has a high success rate in finding precursory quiescence even for a low signal to noise ratio as for the few false negatives they are usually due to interfering aftershocks as well which skew seismicity rates to higher means the non critical past by helping to better understand the behavior of the pi algorithm in synthetic catalogs gives new perspectives on how to improve it and on how to use it in real catalogs

simultaneous acoustic emissions monitoring and synchrotron x ray diffraction at high pressure and temperature calibration and application to serpentinite dehydration abstract we have successfully developed an experimental setup that allows collecting in situ x ray powder diffraction and simultaneously recording full waveform acoustic emissions ae at high pressure and temperature pt in a dia multi anvil device this setup is a powerful tool for investigating rock embrittlement at high pt due to phase transitions and or mineral reactions since both reaction progress and kinetics and ae triggering can be simultaneously monitored the dehydration of natural serpentinite samples antigorite rich under deviatoric stress has been investigated by this method since antigorite dehydration is believed to trigger intermediate depth earthquakes through dehydration embrittlement we performed beforehand a series of tests on the cold compression of reference materials with contrasted mechanical behaviors quartz beads and kaolinite powder due to grain crushing cold compression of quartz gave rise to numerous ae events several hundreds which were located within the sample cold compression and heating of kaolinite a ductile material yielded no aes demonstrating that the pressure assembly is noiseless unexpectedly antigorite rich serpentinite samples produced no detectable aes in the course of their dehydration under the differential stress imposed by alumina waveguides the only aes that were recorded occurred during cold compression sample microstructures indicate that conjugate faults inherited from the cold compression stage are activated during or after dehydration of the sample the aseismic slip along these faults could be attributed to the presence of talc or a talc like phase or of fine grained materials dehydration reaction products in the fault gouge furthermore ae triggering can also be influenced by hydraulic diffusivity and the differential stress level on the sample two parameters that are not controlled in conventional multi anvil experiments our results highlight the fact that coupling between dehydration reactions and seismicity might not be as straightforward as previously thought in fact fast reaction kinetics or high reaction extent may inhibit the nucleation of mechanical instabilities through rapid stress relaxation of the solid matrix

foreshock patterns preceding great earthquakes in the subduction zone of chile foreshock activity is considered as one of the most promising precursory changes for the main shock prediction in the short term averaging over several foreshock sequences has shown that foreshocks are characterized by distinct 3d patterns their epicenters move towards the main shock epicenter event count accelerates and b value drops however these space time size patterns were verified so far only in a very few individual cases mainly due to inadequate seismicity catalogue data we have investigated 3d foreshock patterns before the mw 8 8 maule in 27 february 2010 mw 8 1 iquique in 1 april 2014 and mw 8 4 illapel in 16 september 2015 great earthquakes in the chile subduction zone to avoid biased results no a priori spatiotemporal definitions of foreshocks were inserted the procedure was based on pattern recognition from statistically significant seismicity changes in the three domains the pattern recognition in one domain was independent of the pattern recognition in another domain we found and verified with two independent catalogue data sets csn ipoc that within a critical area of ca 65 km from the main shock epicenter the 2014 event was preceded by distinct foreshock 3d patterns a nearly weak foreshock stage 20 january 14 march 2014 was followed by a main strong stage 15 march 1 april 2014 highly significant in all domains although foreshock activity slightly decreased in about the last 5 days seismic moment release also accelerated in the last stage due to the occurrence of a cluster of very strong foreshock events foreshock activity very likely occurred in the hanging wall fault domain on the south american plate overriding nazca plate the 2014 foreshock activity was quite similar to the one preceding the 6 apr 2009 l aquila italy mw 6 3 earthquake associated with normal faulting using the 2014 earthquake as a reference event we observed that similar foreshock 3d patterns preceded the 2010 and 2015 earthquakes within critical distances of about 170 and 50 km respectively however the foreshock activities were only weak in both the cases likely because of poor catalogue completeness

bulk flow strength of forsterite enstatite composites as a function of forsterite content creep experiments have been conducted to investigate the effect of varying forsterite content vfo on the bulk flow strength of dry forsterite enstatite fo en aggregates in order to evaluate the applicability of existing theoretical models to two phase rocks as well as to understand the rheology of polyphase systems in general the experiments were performed at temperatures of 1423 1593 k stresses of 18 100 mpa oxygen fugacities of 10 14 10 2 5 mpa and 0 1 mpa total pressure the fine grained fo 10 17 mm en 14 31 mm composites of various fo volume fractions vfo 0 0 2 0 4 0 5 0 6 0 8 and 1 were synthesized by isostatically hot pressing in a gas medium apparatus at 1523 and 350 mpa our experiments show that flow strength contrasts between fo and en are in the range of 3 8 at the given experimental conditions with fo as the stronger phase the measured stress exponent n and activation energy q values of the fo en composites fall between those of the endmembers the n values show a nearly linear increase from 1 3 to 2 0 while the q values display a non linear increase from 472 to 584 kj mol with en volume fraction from 0 to 1 0 there is no clear dependence of creep rates on oxygen fugacity for the fo en composites the mechanical data and tem microstructural observations suggest no change in deformation mechanism of each phase when in the composites compared to when in a single phase aggregate the en deformed mainly by dislocation creep while the fo deformed by dislocation accommodated diffusion creep for our grain sizes and experimental conditions comparisons between the measured composite strengths and various theoretical models indicate that none of the existing theoretical models can give a precise predication over the entire vfo range from 0 to 1 however the theoretical models based on weak phase supported structures wps yield a good prediction for the flow strengths of the composites with vfo 0 6 no model gives a good prediction for the bulk strength of two phase composites in the transitional regime vfo 0 4 0 6 applications of the wps and sps based models in the transitional regime result in under and over estimations for the composite flow strength respectively thus the effect of rock microstructure should be taken into consideration in modeling the bulk flow strengths of the crust and upper mantle using laboratory determined flow laws of single phase aggregates d 2001 elsevier science b v all rights reserved

earthquake prediction a critical review summary earthquake prediction research has been conducted for over 100 years with no obvious successes claims of breakthroughs have failed to withstand scrutiny extensive searches have failed to find reliable precursors theoretical work suggests that faulting is a non linear process which is highly sensitive to unmeasurably fine details of the state of the earth in a large volume not just in the immediate vicinity of the hypocentre any small earthquake thus has some probability of cascading into a large event reliable issuing of alarms of imminent large earthquakes appears to be effectively impossible key word earthquake prediction

frictional sliding in serpentine at very high pressure abstract using a new four channel system for detecting acoustic emissions in a multianvil apparatus we have assessed the pressure temperature range for such emissions as well as the role of dehydration by deforming samples of extensively serpentinized peridotite we show that in the absence of dehydration and for samples initially faulted at low pressure acoustic emissions occurred well outside the expected pressure temperature field of unassisted brittle failure emissions were also detected during and after dehydration of serpentine microstructures of post run specimens revealed fault slip with offsets up to 500 m regardless of whether or not dehydration took place dehydration appears to effectively stop slip on pre existing faults and create new ones analysis of p wave travel times from the four sensors confirmed that the acoustic emissions originated within the specimen during fault slip these observations suggest that earthquakes can be triggered by slip along an existing fault containing serpentine under significantly higher pressure and temperature conditions than previously thought possible without dehydration

strontium isotope evidence for preserved density stratification in the main zone of the bushveld complex south africa the bushveld complex formed from two isotopically distinct magmas magma addition and mixing can be tracked by measuring initial strontium isotope ratios of cumulates rocks with ratios of 0 7065 lie below the lower 2 2 km of the main zone ratio 0 7085 whereas those with ratios of 0 7073 lie above it this unit represents a liquid layer intruded into the density stratified magma pile near the base of the chamber the merensky reef was produced by mixing of the pile with underlying trapped liquid enriched in precious metals

a study on the variations of recent seismicity in and around the central anatolian region of turkey abstract variations of the recent seismicity in and around the central anatolian region of turkey were evaluated based on the seismic b value standard normal deviate z value genas modelling annual probabilities and return periods of the earthquakes the catalog includes 16 702 earthquakes between 1974 and 2019 with magnitudes from 1 0 to 6 3 time distribution of b value shows that there is a tendency to decrease after the year of 2002 and b value decreased from 1 58 0 03 to 1 25 0 05 at the beginning of 2019 annual probabilities for magnitude ranges of 3 0 4 0 have the values between 3 and 30 return periods for magnitude levels of 5 0 5 5 have the values from 5 to 20 years and a value of 80 years for magnitude level of 6 0 the genas results show the significant temporal variations in the number of earthquakes smaller and larger than specific magnitude intervals by supplying the beginning periods of increases and decreases in the earthquake activity rate remarkable reductions in region time distribution of b value at the beginning of 2019 were detected in the regions covering nigde fault and its vicinity along the south west northwest and southwest directions among the mut fault zone karsanti karaisali fault zone and karatas osmaniye fault zone in and around surgu fault and along its northwest direction between surgu fault and east anatolian fault zone significant seismic quiescence areas in z value distribution include the northwest ends of the tuzgolu fault zone and study area including akpinar fault the northeast of salanda fault between salanda fault and the central anatolian fault zone the northeast parts of the central anatolian fault zone the west of malatya fault between surgu fault and the east anatolian fault zone the southeast end of the tuzgolu fault zone karsanti karaisali fault zone and its vicinity the southwest of tuzgolu thus these anomaly areas observed in the central anatolian region and its vicinity at the beginning of 2019 may be one of the most likely zones for the next strong large earthquake occurrences

testing earthquake prediction methods the west pacific short term forecast of earthquakes with magnitude mwhrv 5 8 in his paper kossobokov investigates the e ciency of our short term forecast for two western paciflc regions although we agree with the basic results of his evaluation that the forecast statistics is much better than a random guess we have reservations about his deflnition of earthquake prediction some of his tests and his interpretation of the test results we distinguish between deterministic earthquake predictions and statistical forecasts we argue that some techniques used by kossobokov may not be appropriate for testing our forecasts and discuss other testing methods based on the likelihood function we demonstrate that kossobokov s null hypothesis may be biased and this bias can in uence some of his conclusions we show that contrary to kossobokov s statement our algorithm predicts mainshocks when they are preceded by foreshocks

the effect of trapped liquid crystallization on cumulus mineral compositions in layered intrusions a series of calculations have been carried out to evaluate the effect on cumulus mineral compositions of solidification of trapped intercumulus liquid in orthocumulates the calculation assumes local equilibrium between phases and that the system remains chemically closed during crystallization of the trapped liquid the latter assumption is held to be valid on a scale of tens to hundreds of centimeters it is not necessary to know the composition of the trapped liquid as the calculation only requires an estimate of feo content and trapping temperature the change in composition of a mineral from that of the initially precipitated cumulus crystals to the final composition after complete solidification is termed the trapped liquid shift its magnitude depends on the modal proportions of cumulus phases and the initial porosity and is only weakly dependent on initial phase compositions trapped liquid shifts are significant when compared with mineral composition changes occurring during fractional crystallization crystallization of 30 trapped liquid gives rise to shifts of up to 10 mol percent in mg number of olivine or pyroxene the size of the shift becomes greater when the initial cumulus assemblage has a lower total feo mgo content and vice versa as a result of the relationship between trapped liquid shift and cumulus mode mineral composition variations and trends may be generated in sequences of cumulates which originally had constant compositions of cumulus minerals for example in a cyclic unit grading from a pyroxenitic base to an anorthositic top crystallization of a uniform proportion of trapped liquid will result in an apparent iron enrichment trend from bottom to top of the cycle as has been observed in the upper critical zone of the bushveld complex

semi brittle behavior of wet olivine aggregates the role of aqueous fluid in faulting at upper mantle pressures the role of aqueous fluid in fracturing in subducting slabs was investigated through a series of deformation experiments on dunite that was undersaturated i e fluid free or saturated with water i e aqueous fluid bearing at pressures of 1 0 1 8 gpa and temperatures of 670 1250 k corresponding to the conditions of the shallower regions of the double seismic zone in slabs in situ x ray diffraction radiography and acoustic emissions aes monitoring demonstrated that semi brittle flow associated with aes was dominant and the creep failure strength of dunite was insensitive to the dissolved water content in olivine in contrast aqueous fluid drastically decreased the creep failure strength of dunite up to 1 gpa of weakening over a wide range of temperatures in the semi brittle regime weakening of the dunite by the aqueous fluid resulted in the reduction of the number of ae events i e suppression of microcracking and shortening of time to failure the ae hypocenters were located at the margin of the deforming sample while the interior of the faulted sample was aseismic i e aseismic semi brittle flow under water saturated conditions a faulting slip rate of 10 3 to 10 4 s 1 associated with a large drop of stress 0 5 to 1 gpa and or pressure p 0 5 gpa was dominant in fluid free dunite while a slow faulting slip rate 8 10 5 s 1 without any stress pressure drop was common in water saturated dunite aseismic semi brittle flow may mimic silent ductile flow under water saturated conditions in subducting slabs

deformation of antigorite serpentinite at high temperature and pressure abstract deformation experiments were conducted in a griggs type apparatus to constrain the rheology of antigorite serpentinite at high temperatures and pressures samples deformed at temperatures of 400 625 c and pressures of 0 85 1 5 gpa experienced semi brittle deformation resulting in localization on faults at 5 to 25 strain samples deformed at 300 c exhibited transitional behavior the stresses measured for our samples are in good agreement with recent experiments conducted in the deformation dia apparatus however our results indicate that steady state ductile flow is not achieved in contrast with interpretations based on the deformation dia experiments extrapolation of our data to geologic conditions suggests that serpentinites may be weak enough during localized frictional sliding to account for slab wedge decoupling inferred from geologic observations experiments conducted above the thermal stability of antigorite at 700 c and 1 5 gpa show evidence for distributed deformation this observation does not support the hypothesis that intermediate depth earthquakes result directly from dehydration embrittlement in addition samples exhibit velocity strengthening from 300 to 700 c a frictional behavior that inhibits earthquake nucleation

superplasticity in hydrous melt bearing dunite implications for shear localization in earth s upper mantle abstract deformation experiments on hydrous melt bearing dunite olivine 4 vol orthopyroxene 4 vol clinopyroxene with less than 2 5 vol of the melt phase were conducted at pressures of 1 3 5 7 gpa and temperatures of 1270 1490 k in order to explore the effect of intergranular fluids on the plastic flow of olivine in earth s upper mantle the strain rate was proportional to steady state creep strength to the 2 1 power and the creep strength markedly increased with increase in grain size developments of the crystallographic preferred orientation of olivine and flattening of olivine grains were hardly observed even after 33 55 shortening of the samples these observations show that grain boundary sliding gbs dominated the deformation of olivine i e superplasticity the creep strength of hydrous melt bearing dunite was 2 5 times lower than that of melt free dunite the dependence of creep rate on melt fraction is known to be expressed empirically as e e 0 exp where is a constant and is the melt fraction the experimentally obtained value of was in the range of 150 230 corresponding to 5 7 times the reported values for the olivine basalt system at 0 3 gpa i e creep strength of dunite was efficiently reduced by the hydrous melt superplasticity is the dominant creep mechanism of olivine in fluid bearing fine grained peridotites under low temperature and high stress conditions i e peridotite shear zones in the upper mantle superplasticity induced by geological fluids would play an important role in the shear localization and thus initiation of subduction in the upper mantle

viscoplastic self consistent and equilibrium based modeling of olivine lattice preferred orientations implications for the upper mantle seismic anisotropy anisotropy of upper mantle physical properties results from lattice preferred orientation lpo of upper mantle minerals in particular olivine we use an anisotropic viscoplastic self consistent vpsc and an equilibrium based model to simulate the development of olivine lpo and hence of seismic anisotropy during deformation comparison of model predictions with olivine lpo of naturally and experimentally deformed peridotites shows that the best fit is obtained for vpsc models with relaxed strain compatibility slight differences between modeled and measured lpo may be ascribed to activation of dynamic recrystallization during experimental and natural deformation in simple shear for instance experimental results suggest that dynamic re crystallization results in further reorientation of the lpo leading to parallelism between the main 010 100 slip system and the macroscopic shear thus modeled simple shear lpos are slightly misoriented relative to lpos measured in natural and experimentally sheared peridotites this misorientation is higher for equilibrium based models yet seismic properties calculated using lpo simulated using either anisotropic vpsc or equilibrium based models are similar to those of naturally deformed peridotites errors in the prediction of the polarization direction of the fast s wave and of the fast propagation direction for p waves are usually 15 moreover overestimation of lpo intensities in equilibrium based and vpsc simulations at high strains does not affect seismic anisotropy estimates because these latter are weakly dependent on the lpo intensity once a distinct lpo pattern has been developed thus both methods yield good predictions of development of upper mantle seismic anisotropy in response to plastic flow two notes of caution have nevertheless to be observed in using these results 1 the dilution effect of other upper mantle mineral phases in particular enstatite has to be taken into account in quantitative predictions of upper mantle seismic anisotropy and 2 lpo patterns from a few naturally deformed peridotites cannot be reproduced in simulations these abnormal lpos represent a small percent of the measured natural lpos but the present sampling may not be representative of their abundance in the earth s upper mantle

compositional convection in a reactive crystalline mush and melt differentiation fractional crystallization and partial melting involve relative motion of liquid and solid phases and chemical and thermal interactions between them to elucidate some physical principles of thermosolutal convection in a reactive porous medium we describe experiments on the directional solidification of aqueous ammonium chloride solutions the addition of small amounts of a polymerizing agent permits variation of the solution viscosity independently of thermal conditions the phase diagram and permeability solutions were cooled from below and crystallization developed at the base of the tank generating at first a field of thin plumes of light residual fluid released from the boundary layer at the top of the mush the interstitial fluid within the mush also became unstable eventually the onset of convection occurring when the porous medium rayleigh number of the mush reached a critical value this threshold value was found to be 25 at low initial superheat and to decrease with increasing superheat local thermodynamic equilibrium between crystals and liquid within the mush coupled the evolution of temperature composition and porosity convective motions locally caused dissolution and precipitation and hence fluctuations of porosity developed dissolution occurred preferentially in the central parts of upwellings and the upflow gradually focused being ultimately channelized into narrow chimneys devoid of crystals all else being equal the areal density of chimneys was greater the lower the viscosity chimney diameter increased with increasing solution viscosity in the liquid above the growing mush the convective plumes were very similar to salt fingers depending on solution viscosity and temperature gradient they exhibited a phenomenon of collective instability such that vertical motion was disrupted by wave instabilities the base plate temperature chosen was above the eutectic and hence the total amount of crystals at the end of experiments with the same initial composition and the same final temperature was a constant fixed by the phase diagram the spatial distribution of crystals and the final porosity of the mush were however determined by the strength of compositional convection as measured by the porous medium rayleigh number when no convection occurred mush thickness finally became equal to the initial layer thickness and the system was homogeneous when compositional convection occurred the overlying reservoir underwent chemical evolution and mush growth slowed dramatically in experiments with progressively lower solution viscosity and hence more vigorous convection final mush thickness was progressively less and final porosity lower final mush thickness was found to scale with solution viscosity to the power 0 33 during fractional crystallization of magma the effects of compositional convection can be recorded in the chemical and mineralogical features of cumulate rocks we speculate that fossil chimney structures can be found in the lower zone of the bushveld ultramafic complex in the form of iron rich platinum bearing dunite pipes this could explain the adcumulate nature of the lower zone rocks and the chemical and mineralogical similarities between the pipes and the overlying merensky reef the merensky reef would be interpreted as a hiatus in mush growth the results may also have applications to the flow structure in regions of partial melting and in the earth s core

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

role of orthopyroxene in rheological weakening of the lithosphere via dynamic recrystallization for plate tectonics to operate on a terrestrial planet the surface layer the lithosphere must have a modest strength earth 200 mpa but a standard strength profile based on olivine far exceeds this threshold value consequently it is essential to identify mechanisms that reduce the strength of the lithosphere on earth here we report results of high strain laboratory deformation experiments on a representative olivine orthopyroxene composition that show the addition of orthopyroxene substantially reduces the strength in the ductile regime within a certain temperature window the reduction in strength is associated with the formation of small orthopyroxene and olivine grains our samples show heterogeneous microstructures similar to those observed in natural peridotites in shear zones fine grained regions containing both orthopyroxene and olivine that form interconnected bands where a large fraction of strain is accommodated a model is developed to apply these results to geological conditions such a model combined with our experimental observations suggests that orthopyroxene may play a key role in the plastic deformation of the lithosphere in a critical temperature range leading to long term weakening associated with strain localization in the lithosphere

are the lower planes of double seismic zones caused by serpentine dehydration in subducting oceanic mantle in a number of subduction zones earthquakes at 50 200 km depth define two dipping planes separated by 20 40 km that appear to merge downdip upper plane earthquakes are inferred to occur within the subducting oceanic crust whereas lower plane earthquakes occur in the subducting oceanic mantle beneath northeast japan the results of a new finite element heat transfer model suggest that the lower seismic plane cuts across isotherms at a shallow angle lower plane earthquakes occur at 550 800 c at 100 km depth and at 350 600 c at 160 km depth these conditions coincide with the dehydration reaction antigorite serpentine forsterite enstatite h 2 o which suggests that lower plane earthquakes may be triggered by dehydration embrittlement which in turn suggests that the subducting oceanic mantle is partially hydrated serpentinization may occur in the trench outer rise region where faulting may promote infiltration of seawater several tens of kilometers into the oceanic lithosphere if this hypothesis is correct current subduction zone h 2 o budgets may significantly underestimate the amount of bound h 2 o entering the subduction factory

earthquake prediction by animals evolution and sensory perception animals living within seismically active regions are subjected episod ically to intense ground shaking that can kill individuals through burrow collapse egg destruction and tsunami action although anecdotal and retrospective reports of animal behavior suggest that although many organisms may be able to detect an impending seismic event no plausible scenario has been presented yet through which accounts for the evolution of such behaviors the evolutionary mechanism of ex aptation can do this in a two step process the first step is to evolve a vibration triggered early warning response which would act in the short time interval between the arrival of p and s waves anecdotal evidence suggests this response already exists then if precursory stimuli also exist similar evolutionary processes can link an animal s perception of these stimuli to its p wave triggered response yielding an earthquake predictive behavior a population genetic model indicates that such a seismic escape response system can be maintained against random mutations as a result of episodic selection that operates with time scales comparable to that of strong seismic events hence additional understanding of possible earthquake precursors that are presently outside the realm of seismology might be gleaned from the study of animal behavior sensory physiology and genetics a brief review of possible seismic precursors suggests that tilt hygroreception humidity electric and mag netic sensory systems in animals could be linked into a seismic escape behavioral system several testable predictions of this analysis are discussed and it is recom mended that additional magnetic electrical tilt and hygro sensors be incorporated into dense monitoring networks in seismically active regions

intermediate depth earthquakes linked to localized heating in dunite and harzburgite earthquakes can occur at great depths in the earth within subducting tectonic plates deformation experiments suggest these deep earthquakes can be triggered by localized heating of the slabs under high pressures

melt segregation from partially molten source regions the importance of melt density and source region size the compressibility of basic melt at 1 atmosphere is about an order of magnitude higher than that of mantle minerals consequently the density contrast between melt and the principal residual crystals in mantle source regions is expected to decrease with increasing source region depth the increasingly olivine normative character of primary melts produced at greater depths is also expected to result in a decrease in this density contrast with increasing source region depth once vertical permeability is established by melt generated during partial melting buoyancy driven melt percolation can under some circumstances segregate melt from the residual crystals in its source region on a geologically rapid time scale limits to this process are provided by cooling of the source region freezing melt in and rigidity of the crystalline matrix mechanically trapping melt source region size influences these limits strongly consequently small partially molten diapirs km in diameter may be able to trap large melt fractions 30 but larger source regions would be unable to do so the reduction in density contrast with pressure reduces the buoyant force driving melt percolation and provides another limit to melt segregation diapirs at depth may thus stably contain large fractions of melt but may decompress and unload their melt during ascent this effect would be enhanced in small diapirs and may be relevant to the genesis of komatiitic magma melt compression may also be a factor in explaining why the very different maximum depths inferred for typical basic melt segregation from source regions on different planets 500 km on the moon 250 km on mars 100 km on earth correspond to similar pressures 25 35 kbar at greater pressures melt may no longer be capable under ordinary conditions of segregating upwards by buoyancy this may also help to explain why depleted peridotites overlie more fertile peridotites and how deep regions of the mantle are able to remain fertile over geologic time

temporal change in scattering and attenuation associated with the earthquake occurrence a review of recent studies on coda waves the study of coda waves has recently attracted increasing attention from seismologists this is due to the fact that it is viewed as a new means by which the stress accumulation stage preceding a large earthquake can be measured since the scattering paths nearly uniformly cover a fairly large region around the focus and observation stations compared with the direct ray paths to date we have had many reports on the temporal variation of the relation between coda duration and amplitude magnitude and that of the coda attenuationq 1 which is estimated from coda amplitude decay some of these have shown a precursor like behavior however others seem to have shown a coseismic change we have critically reviewed these reports and discussed what these observational facts tell us about the change in the heterogeneous crust we found significant temporal variations not only in the mean but also in the scatter ofq 1 associated with the mainshock occurrence the formation of new cracks the reopening and growing of existing cracks the interaction of these cracks and the pore water movement through these cracks might correspond to such variations in addition we may expect an inhomogeneous distribution of crack clusters in a fairly large region compared with the aftershock region the gradual appearance of such crack clusters seems to be the most plausible mechanism by which coda decay gradients are caused to largely scatter in the stress accumulation stage

earthquakes and plastic deformation of anhydrous slab mantle in double wadati benioff zones double wadati benioff seismic zones dsz with two parallel planes of seismicity separated by 15 30 km are a global feature of subduction zones in the 50 200 km depth range upper plane seismicity is generally attributed to dehydration of the oceanic crust but the origin of the lower seismicity plane is debated serpentine or hydrous phase dehydration embrittlement is a commonly advocated mechanism that implies significant slab mantle hydration high resolution seismic tomography revealed low seismic velocities in the lower seismicity plane that are better explained by seismic anisotropy of anhydrous deformed peridotites than by serpentinization earthquakes correlate with anisotropic planar shear zones and favor a shear instability mechanism as the cause of lower plane seismicity without requiring the presence of water in the center of subducting slabs the contribution of the subducted lithospheric mantle to the water budget of subduction zones is thus likely limited to the first 2 3 kilometers beneath oceanic crust

why is earthquake prediction research not progressing faster abstract as a physical phenomenon earthquakes must be predictable to a certain degree however the problem is difficult because the source volume inside the earth is inaccessible to direct observation and because the most important parameter the stress level cannot be measured directly also seismology is such a young science that the cause of earthquakes was discovered in the 1960s only advanced seismograph networks as well as modern techniques to measure crustal deformations such as the global positioning system gps and the synthetic aperture radar interferometry technique insar have come on line only recently and only in japan are they deployed with the densities necessary for significant advances in the understanding of the rupture initiation process in addition no real program for earthquake prediction research exists in the united states largely because funding agencies and peer reviewers shy away from a field in which unprofessional but motivated individuals are active although claims of successful predictions are often not justified a few correct predictions have been made most of these had time windows of years but some were accurate to days and allowed preparatory actions to make significant progress we must learn how to conduct rigorous science in a field where amateurs cannot be discouraged to venture leadership is necessary to raise the funding to an adequate level and to involve the best minds in this promising potentially extremely rewarding but controversial research topic

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

existence of a seismic belt in the upper plane of the double seismic zone extending in the along arc direction at depths of 70 100 km beneath ne japan 1 we relocated microearthquakes using data obtained via a dense seismic network and systematically detected the characteristic distribution of the upper seismic plane seismicity within the pacific slab beneath ne japan we found a seismic belt parallel to the iso depth contour of the plate interface that is beneath the forearc area at depths of 70 100 km indicating that the distribution of the upper plane earthquakes is non uniform the location of the deeper limits of this belt and seismicity of the upper seismic plane appear to correspond respectively to two facies boundaries where h2o contents change in the slab crust events in the upper seismic plane have mainly down dip compression type focal mechanisms but several events have normal fault type nf type versions whose spatial distribution appears to correspond to these boundaries these nf events might be induced by the tensional stress field that is caused by volume reduction due to dehydration reactions

dehydration of lawsonite could directly trigger earthquakes in subducting oceanic crust intermediate depth earthquakes in cold subduction zones are observed within the subducting oceanic crust as well as the mantle in contrast intermediate depth earthquakes in hot subduction zones predominantly occur just below the mohorovicic discontinuity these observations have stimulated interest in relationships between blueschist facies metamorphism and seismicity particularly through dehydration reactions involving the mineral lawsonite here we conducted deformation experiments on lawsonite while monitoring acoustic emissions in a griggs type deformation apparatus the temperature was increased above the thermal stability of lawsonite while the sample was deforming to test whether the lawsonite dehydration reaction induces unstable fault slip in contrast to similar tests on antigorite unstable fault slip that is stick slip occurred during dehydration reactions in the lawsonite and acoustic emission signals were continuously observed microstructural observations indicate that strain is highly localized along the fault r1 and b shears and that the fault surface develops slickensides very smooth fault surfaces polished by frictional sliding the unloading slope during the unstable slip follows the stiffness of the apparatus at all experimental conditions regardless of the strain rate and temperature ramping rate a thermomechanical scaling factor for the experiments is within the range estimated for natural subduction zones indicating the potential for unstable frictional sliding within natural lawsonite layers

ductile to brittle transition in thermally stable antigorite gouge at mantle pressures general shear experiments on antigorite rich serpentinite show a transition from ductile distributed to brittle localized deformation with increasing temperature from 300 c to 500 c at confining pressures from 1 to 2 gpa the coefficient of friction associated with slip along fractures decreases from 0 23 to 0 07 with an increase in temperature from 300 c to 500 c velocity stepping experiments exhibit a positive rate dependence as parameterized by a b values that decrease modestly with increasing temperature from 0 015 at 300 c to 0 01 at 500 c fractures contain fine grained foliated antigorite and there is no evidence of dehydration all samples have a moderate foliation and show microstructural evidence for both plastic and brittle deformation mechanisms under certain conditions the transition to brittle deformation at high pressures and temperatures in antigorite might generate earthquakes which could explain the occurrence of some intermediate depth seismicity within subduction zones in serpentinized regions that are too cold to induce dehydration

petrogenesis of the merensky reef in the rustenburg section of the bushveld complex a petrogenetic model for the merensky reef in the rustenburg section of the bushveld complex has been developed based on detailed field and petrographic observations and electron microprobe data the model maintains that the reef formed by reaction of hydrous melt and a partially molten cumulate assemblage the model is devised to account for several key observations 1 although the dominant rock type in the rusterburg sections is pegmatoidal feldspathic pyroxenite there is a continous range of reef lithology from pyroxenite to pegmatoidal harzburgite and dunite and small amounts of olivine are present in nearly all pegmatoids 2 the pegmatoid is usually bounded above and below by chromitite seams and the basal chromitite separated from underlying norite by a centimeter thick layer of anorthosite the thicknesses of the two layers exhibit a well defined positive correlation 3 inclusion of pyroxenite identical to the hanging wall and of leuconorite identical to the footwall are present in the pegmatoid the leuconorite inclusions are surrounded by thin anorthosite and chromitite layers in the same sequence as that at the base of the reef 4 chromite in seams adjacent to plagioclase rich rocks is characterized by higher mg mg fe and al r3 and lower cr r3 than that in seams adjacent to pyroxene rich rocks similar variations in mineral compositions are observed across individual chromitite seams where the underlying and overlying rock types differ the chromite compositional variations cannot be rationalized in terms of either fractional crystallization or reequilibration with surrounding silicates it is proposed that the present reef was originally a melt rich horizon in norite immediately overlain by relatively crystallized pyroxenite magmatic vapor generated by crystallization of intercumulus melt migrated upward through fractures in the cumulate pile below the protoreef the melt rich protoreef became hydrated because fractures were unable to propagate through it and because the melt itself was water undersaturated hydration of the intercumulus melt was accompanied by melting and the hydration melting front migrated downward into the footwall and upward into the hanging wall in the footwall melting resulted first in the dissolution of orthopyroxene and then of plagioclase with continued hydration chromite was stabilized as melt alumina content increased the regular variations in chromite compositions reflect the original gradients in melt composition at the hydration front the stratigraphic sequence downward through the base of the reef or pegmatoid melt chromitite anorthosite norite represents the sequence of stable mineral assemblages across the hydration melting front the sequence is shown to be consistent with knowledge gained from experiments on melting of hydrous mafic systems at crustal pressures with cooling the hydrated mixture from partial melting of norite footwall and more mafic hanging wall crystallized in the sequence chromite olivine pyroxene plagioclase with peritectic loss of some olivine calculations of mass balance indicate that a significant proportion of the melt was lost from the melt rich horizon variations in the development of the pegmatoid and associated lithologies and amount of modal olivine in the pegmatoids along the strike of the merensky reef resulted because the processes of hydration melting and melt loss operated to varying extents

fractal analysis for natural hazards in the earth sciences the concept of fractals and scale invariance is well recognized in many natural objects however the use of fractals for spatial and temporal analyses of natural hazards has been less used and accepted in the earth sciences this book brings together 12 contributions that emphasize the role of fractal analyses in natural hazard research including andslides wildfires floods catastrophic rock fractures and earthquakes a wide variety of spatial and temporal fractal related approaches and techniques are applied to natural data experimental data and computer simulations these approaches include probabilistic hazard analysis cellular automata models spatial analyses temporal variability prediction and self organizing behaviour the main aims of this volume are a to present current research on fractal analyses as applied to natural hazards and b to stimulate the curiosity of advanced earth science students and researchers in the use of fractals analyses for the better understanding of natural hazards

high stress creep preceding coseismic rupturing in amphibolite facies ultramylonites abstract coeval pseudotachylytes solidified melts produced during seismic slip and mylonites are generally regarded as the geological record of transient seismic events during dominant ductile flow thermal runaway has been proposed as a model to explain the pseudotachylyte mylonite association in the mont mary unit western alps pseudotachylyte fault veins occur along the amphibolite facies ca 550 c 0 35 gpa ultramylonitic foliation of paragneisses these veins formed at the same metamorphic conditions of the ultramylonites thus potentially recording thermal runaway we analysed the microstructure of quartz in ultramylonite and of ultramylonite clasts in pseudotachylyte to investigate the possible occurrence of thermal runaway quartz aggregates show an evolution under constant temperature to ultrafine grained recrystallised grain size 2 5 m reflecting creep under high differential stresses 200 mpa and high strain rates 10 9 s 1 along very narrow foliation parallel layers in the ultrafine aggregates viscous grain boundary sliding became dominant and promoted cavitation leading to disintegration of quartz aggregates and precipitation in the pore space of biotite oriented parallel to the main ultramylonitic foliation the strain rate limiting process was aseismic fluid assisted precipitation of biotite the potential occurrence at the deformation conditions of the mont mary ultramylonites of thermal runaway in pure quartz layers was investigated by numerical modelling the models predict a switch from stable flow to thermal runaway at background strain rates faster than 10 9 s 1 for critical differential stresses that are comparable to the brittle strength of rocks deformation of ultramylonites occurred close to the conditions for thermal runaway to occur but based on the microstructural record we conclude that the mont mary pseudotachylyte mylonite association is best explained by brittle failure triggered by transients of high differential stress and strain rate causing a downward deflection of the brittle ductile transition

the 2012 mw 8 6 indian ocean earthquake deep nucleation on a listric like fault abstract the 2012 mw 8 6 indian ocean earthquake the largest instrumentally recorded strike slip event has been described as a westward rupture on orthogonal faults that are part of the original oceanic fabric of the region reported estimates of its depth vary from 10 to 45 km while the maximum depth of its inferred rupture extends to 50 60 km the complexity of the earthquake is undeniable both in terms of fault geometry and rupture propagation with debates on the geometry of the causative faults results from recent seismic surveys enable a fresh look at the earthquake fault geometry nucleation depths and lithospheric rheology in the present study these new findings are incorporated into 22 forward models using a revised velocity structure and n s geometries that flatten with depth the rupture initiation is modeled in the uppermost mantle 25 30 km as well as in the upper mantle at 45 km the latter of which is 15 20 km below the commonly accepted values of maximum depth for frictional failure our study shows that the westward directionality of wave propagation is achieved for strike slip failure on a listric like fault in contrast to subvertical geometries as previously suggested this propagation is persistent for a strike slip failure only for events nucleating at upper mantle depths 45 km rather than for those set to originate at depths between 25 and 30 km however for a dip slip failure the westward propagation is found to be consistent at both nucleation depths on a listric like fault this study highlights a deep nucleation within the lithospheric mantle for the 2012 mw 8 6 earthquake that could be due to strain localization induced by fluid rock interaction and or mineral transformation crystallization near the 680 c isotherm at 45 km depth 1 4 gpa which correlates with deep serpentinization on faults

origin of pseudotachylites in slow creep experiments we conducted a series of experiments on granitoid cataclasites under mid crustal conditions pc 500 mpa t 300 c and slow displacement rates 10 8 ms 1 d 10 7 ms 1 i e within an order of magnitude of plate tectonic velocities the samples reach high peak strength 1250 1375 mpa then weaken slightly by 40 mpa and continue to deform without any abrupt stress drops up to a of 4 microstructural observations show that at peak strength nanocrystalline mean grain size 34 nm smallest crystalline particles 8 nm to partly amorphous material develops weakening occurs once this material is abundant enough to form through going anastomozing slip zones where the strain partitions during higher strain deformation deformation localizes further and 1 to 2 multiply connected layers of fragment loaded amorphous material develop this material shares many similarities with naturally occurring pseudotachylites however was formed at velocities up to 8 orders of magnitude slower than those calculated for earthquakes 1 ms 1 we conclude that the use of pseudotachylites as indicators for paleoseismic events should be reconsidered

physical modeling of the formation and evolution of seismically active fault zones acoustic emission ae in rocks is studied as a model of natural seismicity a special technique for rock loading has been used to help study the processes that control the development of ae during brittle deformation this technique allows us to extend to hours fault growth which would normally occur very rapidly in this way the period of most intense interaction of acoustic events can be studied in detail characteristics of the acoustic regime ar include the gutenberg richter b value spatial distribution of hypocenters with characteristic fractal correlation dimension d hurst exponent h and crack concentration parameter pc the fractal structure of ar changes with the onset of the drop in differential stress during sample deformation the change results from the active interaction of microcracks this transition of the spatial distribution of ae hypocenters is accompanied by a corresponding change in the temporal correlation of events and in the distribution of event amplitudes as signified by a decrease of b value the characteristic structure that develops in the low energy background ae is similar to the sequence of the strongest microfracture events when the ar fractal structure develops the variations of d and b are synchronous and d 3b this relation which occurs once the fractal structure is formed only holds for average values of d and b time variations of d and b are anticorrelated the degree of temporal correlation of ar has time variations that are similar to d and b variations the observed variations in laboratory ae experiments are compared with natural seismicity parameters the close correspondence between laboratory scale observations and naturally occurring seismicity suggests a possible new approach for understanding the evolution of complex seismicity patterns in nature

earthquake prediction using extinct monogenetic volcanoes a possible new research strategy abstract volcanoes are extremely effective transmitters of matter energy and information from the deep earth towards its surface their capacities as information carriers are far to be fully exploited so far volcanic conduits can be viewed in general as rod like or sheet like vertical features with relatively homogenous composition and structure crosscutting geological structures of far more complexity and compositional heterogeneity information carrying signals such as earthquake precursor signals originating deep below the earth surface are transmitted with much less loss of information through homogenous vertically extended structures than through the horizontally segmented heterogeneous lithosphere or crust volcanic conduits can thus be viewed as upside down antennas or waveguides which can be used as privileged pathways of any possible earthquake precursor signal in particular conduits of monogenetic volcanoes are promising transmitters of deep earth information to be received and decoded at surface monitoring stations because the expected more homogenous nature of their rock fill as compared to polygenetic volcanoes among monogenetic volcanoes those with dominantly effusive activity appear as the best candidates for privileged earthquake monitoring sites in more details effusive monogenetic volcanic conduits filled with rocks of primitive parental magma composition indicating direct ascent from sub lithospheric magma generating areas are the most suitable further selection criteria may include age of the volcanism considered and the presence of mantle xenoliths in surface volcanic products indicating direct and straightforward link between the deep lithospheric mantle and surface through the conduit innovative earthquake prediction research strategies can be based and developed on these grounds by considering conduits of selected extinct monogenetic volcanoes and deep trans crustal fractures as privileged emplacement sites of seismic monitoring stations using an assemblage of physical chemical and biological sensors devised to detect precursory signals earthquake prediction systems can be built up based on the concept of a signal emission transmission reception system in which volcanic conduits and or deep fractures play the role of the most effective signal transmission paths through the lithosphere unique precursory fingerprints of individual seismic structures are expected to be pointed out as an outcome of target oriented strategic prediction research intelligent pattern recognition systems are to be included for evaluation of the signal assemblages recorded by complex sensor arrays such strategies are expected however to be limited to intermediate depth and deep seismic structures due to its particular features and geotectonic setting the vrancea seismic structure in romania appears to be an excellent experimental target for prediction research

natural and experimental evidence of melt lubrication of faults during earthquakes melt produced by friction during earthquakes may act either as a coseismic fault lubricant or as a viscous brake here we estimate the dynamic shear resistance f in the presence of friction induced melts from both exhumed faults and high velocity 1 28 meters per second frictional experiments exhumed faults within granitoids tonalites indicate low f at 10 kilometers in depth friction experiments on tonalite samples show that f depends weakly on normal stress extrapolation of experimental data yields f values consistent with the field estimates and well below the byerlee strength we conclude that friction induced melts can lubricate faults at intermediate crustal depths

pseudotachylytes generated during seismic faulting and eclogitization of the deep crust pseudotachylytes are typically interpreted to have formed by frictional melting during coseismic faulting within the upper to middle crust pseudotachylytes in the bergen arcs of western norway contain microlites including omphacite garnet plagioclase and quartz this eclogite facies assemblage is stable at temperatures of about 800 c and pressures of 18 to 19 kilobars corresponding to depths of 60 kilometers or more the pseudotachylytes are exposed in grenvillian granulites that locally underwent fluid induced eclogitization and corresponding volume reduction of approximately 10 percent during the caledonian continental collision the pseudotachylytes may have formed as a result of the rapid relaxation of stresses caused by the eclogitization process

two stage red sea rifting inferred from mantle earthquakes in neoproterozoic lithosphere abstract we use earthquake geothermometry measured heat flow and structural constraints from p wave receiver functions to model the thermal evolution of the lithosphere beneath harrat lunayyir we suggest that the lithosphere thinned to its present 60 km thickness in a second stage of lithospheric thinning at 15 12 ma following initial red sea extension at 27 ma harrat lunayyir is an active volcanic field located in the arabian shield 150 km east of the red sea rift axis in the lithospheric mantle beneath harrat lunayyir we locate 64 high frequency earthquakes at depths of 42 48 km all with m l 2 5 these brittle failure earthquakes must have nucleated at relatively low temperatures based upon global maximum nucleation depths and temperature dependent deformation experimental results therefore the mantle earthquakes show that the upper mantle lithosphere is not in thermal equilibrium with the shallow 60 km underlying asthenosphere our thermal modeling indicates that the lithosphere beneath harrat lunayyir thinned to its current 60 km thickness at 12 2 ma as constrained by thermal modeling of 1 surface heat flow 2 the depth to the mid crustal brittle ductile transition and 3 the depth to the upper mantle brittle ductile transition