spinels and mg ilmenites from the noril sk 1 and talnakh intrusions and other mafic rocks of the siberian flood basalt province spinels from the mineralized noril sk 1 and talnakh intrusions show a broad and distinctive compositional spectrum from normal chromite to ti enriched aluminous magnetite in the talnakh intrusion in particular the range of spinel compositions extends across a compositional space where spinels are rare in other layered intrusions spinel compositions vary widely on a scale of individual thin sections and are influenced by the nature of the enclosing silicate phase spinels enclosed in olivines are less ti enriched than those outside olivine grains compositional variance in the spinels is attributed to variable but generally advanced reaction between cumulus chromite grains and solidifying trapped intercumulus liquid the advanced nature of the process is attributed to the open nature of the intrusions continuous prolonged flow through of hot magma enabled cumulates within the intrusions to remain above their solidus temperature for longer than would be normal for sills of comparable thickness the barren chibacheka river intrusion shows some of the same features but differs from talnakh in that spinel olivine pairs record equilibration temperatures higher than those at talnakh temperatures recorded by spinel olivine pairs at talnakh are anomalously low for such a small intrusion again indicating prolonged slow cooling consistent with a flow through model for the sill spinel compositions support a hypothesized comagmatic relationship between the chibacheka river intrusion and the ti cr rich gudchichinsky picritic basalts spinels in the noril sk and talnakh intrusions imply a parent magma with a lower cr al ratio than the gudchichinsky picritic basalts spinels from the siberian intrusions show a similar range in compositions to the feeder intrusions of the karoo flood basalt province jinchuan spinels share the features of high ti contents and anomalously low equilibration temperatures with the noril sk talnakh spinels mg ilmenites are a feature of the siberian and jinchuan intrusions they are attributed to crystallization of ilmenite from evolved trapped intercumulus liquid buffered by surrounding mg rich cumulus phases their existence implies moderately but not unusually ti rich parent magmas consistent with compositions of the siberian traps lavas

redistribution of dynamic stress during coseismic ruptures evidence for fault interaction and earthquake triggering we investigate the spatiotemporal evolution of dynamic stress outside a rupturing extended fault the dynamic stress variations caused by a coseismic rupture in a half space are computed by using the discrete wavenumber and reflectivity methods after a transient phase the stress time history evolves to the final static stress value we compare the static stress changes resulting from this model with those computed from a static dislocation model we have applied this method to study the interactions between the first two normal faults which ruptured during the 1980 ms 6 9 irpinia earthquake these two subevents are separated in time by nearly 20 s while the third and last subevent occurred 40 s after the rupture onset we compute the dynamic stress changes caused by the rupture of the first subevent our modeling results show that the dynamic stress peak on the second subevent fault plane is reached between 7 s and 8 s after the rupture initiation on the main fault on the average the static stress level on the second subevent 20 s fault plane is reached nearly after 14 s the dynamic rupture did not jump from a rupturing segment to the adjacent one immediately but the triggering of the 20 s subevent is delayed by roughly 10 s with respect to the instant of occurrence of the dynamic stress peak induced by the 0 s event the dynamic stress pulse propagates along the strike direction of the second subevent fault plane at an average velocity of nearly 3 4 km s the delayed triggering of the second subevent can be interpreted in terms of the frictional properties of the faults in particular rate and state dependent frictional law can explain a delayed instability after a sudden change in stress using the estimated values of the subevent triggering delay and the shear stress change we attempt to constrain the parameter a on the 20 s fault the values here inferred agree well with those resulting from previous studies

some properties of unstable slip on rough surfaces in this paper we report results obtained from various friction experiments under direct and oblique shear loading conditions we used four rock types of varying brittleness quartzite anhydrite limestone pyrophyllite with different surface roughness the observations concentrate on the time span several milliseconds before dynamic failure occurs during this period a premonitory unstable phase of slip slip 2 occurs this differs importantly from a premonitory stable process slip 1 with durations of hundreds of seconds on smooth surfaces slip 2 is usually observed with ductile rocks and less reliably with brittle rocks slip 2 is mostly accompanied by acoustic emissions which increase in rate of occurrence and in magnitude until the stick slip event foreshocks are observed during approximately 50 of the slip 2 events on rough surfaces foreshocks far exceed the acoustic noise level which is also prevalent before stick slip events on rough surfaces in the direct shear experiment where two faults are being loaded simultaneously in about 20 of the cases precursory slip 2 was observed on the opposite side on which the final stick slip event occurred

topographic characteristics of laboratory induced shear fractures the topography of laboratory induced shear fracture surfaces of westerly granite was studied three types of fracture surfaces were examined 1 a fresh fracture from the shear failure of an intact sample under polyaxial loading 2 40 mpa 3 15 mpa 2 a shear fracture subjected to frictional sliding of 100 m under polyaxial loading 3 a shear fracture subjected to frictional sliding of 800 m under conventional triaxial loading 1 2 3 40 mpa both sliding distances are within the range of the grain size of westerly granite the results are represented by a power spectral method

comparison of sediment plate methods to measure accretion rates in an estuarine mangrove forest new zealand abstract sedimentation is a fundamental process in aquatic receiving environments including vegetated habitats such as mangroves selection of appropriate methods to measure sedimentation depends on time scales of interest due to the variable nature of this process our study considers the appropriateness of methods to measure sediment accretion over time scales of months to years in estuarine mangroves sediment accretion has commonly been measured using marker horizons sediment erosion pins and buried plates bioturbation and erosion can make application of these methods problematic here sediment accretion rates for porous plastic mesh and impervious ceramic plates of two sizes 0 023 and 0 16 m2 were compared replicate plates of each type were installed on the substrate surface at nine rod surface elevation table rset sites distributed along a shore normal sedimentation gradient the plates were progressively buried by sedimentation 17 41 mm yr 1 measurements were made at seasonal to annual intervals over a seven year period 2012 2019 comparison of accretion rates on the plastic mesh with both types of ceramic plates showed strong positive correlations r2 0 96 with slopes close to unity mean 0 95 range 0 68 1 09 sediment accretion rates measured on the large and small ceramic plates were not measurably different from rates for the plastic mesh these results show that sediment accretion rates were spatially homogenous at sub metre to metre scales in the mangroves and sediment accretion rates did not measurably vary between different sediment plate methods the sediment plate method has a number of advantages over marker horizons for long term measurements of sediment accretion particularly where bioturbation alters the sediment profile mesh plates are easily maintained and provide a cost effective flexible precise and reproducible alternative to sediment marker horizons and solid plates for long term monitoring sediment accretion in mangroves and unvegetated intertidal habitats future studies including those employing rset should consider incorporating mesh plate measurements of sediment accretion

compositional variations in the mesoarchean chromites of the nuggihalli schist belt western dharwar craton india potential parental melts and implications for tectonic setting the chromite deposits in the archean nuggihalli schist belt are part of a layered ultramafic mafic sequence within the western dharwar craton of the indian shield the 3 1 ga ultramafic mafic units occur as sill like intrusions within the volcano sedimentary sequences of the nuggihalli greenstone belt that are surrounded by the tonalite trondhjemite granodiorite ttg suite of rocks the entire succession is exposed in the tagdur mining district the succession has been divided into the lower and the upper ultramafic units separated by a middle gabbro unit the ultramafic units comprise of deformed massive chromitite bodies that are hosted within chromite bearing serpentinites the chromitite bodies occur in the form of pods and elongated lenses 60 500 m by 15 m detailed electron microprobe studies reveal intense compositional variability of the chromite grains in silicate rich chromitite 50 modal chromite and serpentinite 2 modal chromite throughout the entire ultramafic sequence however the primary composition of chromite is preserved in the massive chromitites 60 75 modal chromite from the byrapur and the bhaktarhalli mining district of the nuggihalli schist belt these are characterized by high cr ratios cr cr al 0 78 0 86 and moderate mg ratios mg mg fe2 0 38 0 58 the compositional variability occurs due to sub solidus re equilibration in the accessory chromite in the serpentinite mg ratio 0 01 0 38 cr ratio 0 02 0 99 and in silicate rich chromitite mg ratio 0 06 0 48 cr ratio 0 60 0 99 in the massive chromitites the sub solidus re equilibration for chromite is less or absent however the re equilibration is prominent in the co existing interstitial and included olivine fo96 98 and pyroxene grains mg numbers 97 99 compositional variability on the scale of a single chromite grain occurs in the form of zoning and it is common in the accessory chromite grains in serpentinite and in the altered grains in chromitite in the zoned grains the composition of the core is modified and the rim is ferritchromit in general ferritchromit occurs as irregular patches along the grain boundaries and fractures of the zoned grains in this case ferritchromit formation is not very extensive this indicates a secondary low temperature hydrothermal origin of ferritchromit during serpentinization in some occurrences the ferritchromit rim is very well developed and only a small relict core appears to remain in the chromite grain however complete alteration of the chromite grains to ferritchromit without any remnant core is also present the regular well developed and continuous occurrence of ferritchromit rims around the chromite grain boundaries the complete alteration of the chromite grains and the modification of the core composition indicate the alteration in the nuggihalli schist belt to be intense pervasive and affected by later low grade metamorphism the primary composition of chromite has been used to compute the nature of the parental melt the parental melt calculations indicate derivation from a high mg komatiitic basalt that is similar to the composition of the komatiitic rocks reported from the greenstone sequences of the western dharwar craton tectonic discrimination diagrams using the primary composition of chromites indicate a supra subduction zone setting ssz for the archean chromitites of nuggihalli and derivation from a boninitic magma the composition of the komatiitic basalts resembles those of boninites that occur in subduction zones and back arc rift settings formation of the massive chromitites in nuggihalli may be due to magma mixing process involving hydrous high mg magmas or may be related to intrusions of chromite crystal laden magma however there is little scope to test these models because the host rocks are highly altered serpentinized and deformed the present configurations of the chromitite bodies are related to the multistage deformation processes that are common in archean greenstone belts

sea level and turbidity controls on mangrove soil surface elevation change increases in sea level are a threat to seaward fringing mangrove forests if levels of inundation exceed the physiological tolerance of the trees however tidal wetlands can keep pace with sea level rise if soil surface elevations can increase at the same pace as sea level rise sediment accretion on the soil surface and belowground production of roots are proposed to increase with increasing sea level enabling intertidal habitats to maintain their position relative to mean sea level but there are few tests of these predictions in mangrove forests here we used variation in sea level and the availability of sediments caused by seasonal and inter annual variation in the intensity of la nina el nino to assess the effects of increasing sea level on surface elevation gains and contributing processes accretion on the surface subsidence and root growth in mangrove forests we found that soil surface elevation increased with mean sea level which varied over 250 mm during the study and with turbidity at sites where fine sediment in the water column is abundant in contrast where sediments were sandy rates of surface elevation gain were high but not significantly related to variation in turbidity and were likely to be influenced by other factors that deliver sand to the mangrove forest root growth was not linked to soil surface elevation gains although it was associated with reduced shallow subsidence and therefore may contribute to the capacity of mangroves to keep pace with sea level rise our results indicate both surface sedimentation and subsurface root growth processes can influence mangrove capacity to keep pace with sea level rise within the same geographic location and that current models of tidal marsh responses to sea level rise capture the major feature of the response of mangroves where fine but not coarse sediments are abundant

a constitutive law for the shear failure of rock under lithospheric conditions abstract this paper first reviews recent studies on constitutive formulations for shear failure which leads to the conclusion that revealing the constitutive property for not only frictional slip failure but also shear failure of intact rock in the brittle to brittle plastic transition regimes is critical to establish the constitutive law which governs earthquake shear failure that proceeds in the lithosphere to this end a unique high stiffness testing apparatus capable of applying polyaxial stress fields to rectangular rock specimens has been constructed for which a brief description is given the paper then presents new results of laboratory experiments on constitutive properties of shear fracture of intact granite at lithospheric conditions in view of the physical principles and constraints to be imposed on the constitutive law for shear failure the slip dependency is a more fundamental property than the time or rate dependency and hence the constitutive law for shear failure should primarily be slip dependent this slip dependent constitutive law which itself is self consistent can unifyingly and quantitatively treat the entire phases from stable quasistatic ruture growth to unstable dynamic fast speed rupture propagation for shear failure of any type whether it is frictional slip failure along a preexisting fault or shear fracture of intact materials the slip dependent constitutive law includes a scaling parameter dc critical slip displacement explicitly which in turn is scaled by a characteristic length c representing geometrical irregularities of the fault surfaces incorporation of dc or c enables this constitutive law to provide a common interpretation for shear failure of any size scale as an earthquake source from small scale in the laboratory to large scale in the earth the present experiments corroborate the slip dependent constitutive relation and other constitutive properties over the entire process from slip strengthening to slip weakening of intact granite under the conditions that confining pressure is in the range 440 to 500 mpa pore pressure is in the range 30 to 300 mpa temperature is in the range from room temperature to 456 c and strain rate is in the range 10 4 to 10 7 s it is found that some constitutive law parameters are not independent but mutually related the constitutive relation for shear failure and the parameters such as p breakdown stress drop and dc prescribing its relation are affected by ambient conditions such as temperature and strain rate

nucleation process of an m2 earthquake in a deep gold mine in south africa inferred from on fault foreshock activity using a network of sensitive high frequency acoustic emission sensors we observed foreshock activity of an mw 2 2 earthquake main shock in a deep gold mine in south africa foreshock activity which selectively occurred on a part of the rupture plane of the forthcoming main shock lasted for at least 6 months until the main shock rock samples recovered from the main shock source region showed evidence of ancient hydrothermal alteration on the main shock rupture plane suggesting that the foreshock activity occurred on a preexisting weakness the foreshocks during 3 months before the main shock were concentrated in three clusters f1 f3 which we interpret as representing localized preslip at multiple sites while the location of mining area the source of stress perturbations changed with time the locations of foreshock clusters did not change suggesting that the preslip patches were controlled by strength heterogeneity rather than stress distribution activity over the entire foreshock area was generally constant but the largest cluster f2 showed accelerated activity starting at least 7 days before the main shock while mining stress did not increase in this period the main shock initiated at a point close to f1 away from f2 all the six foreshocks during the final 41 h occurred in f1 and f2 and in between these suggest that in the last stage of the preparation process of the main shock preslip patches interacted with each other through the stress concentration ahead of the expanding preslip patch f2 which should be the only driving force of the preparation process under the constant external load

earthquake source nucleation a physical model for short term precursors abstract ohnaka m 1992 earthquake source nucleation a physical model for short term precursors in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 149 178 this paper deals with a quasistatic leading to a quasidynamic at a later time nucleation process that precedes the earthquake dynamic rupture and models of the earthquake source nucleation are put forward based on physical principles a quasistatic to quasidynamic rupture nucleation process is an intrinsic part of the ensuing earthquake dynamic rupture in other words the nucleation process itself is an short term or immediate precursor that occurs in a localized zone during the earthquake nucleation premonitory slip proceeds in the localized nucleation zone and shear stress also decreases gradually in the zone since slip weakening occurs during the nucleation immediate foreshock activity is a part of the nucleation process leading to the mainshock dynamic rupture therefore hypocentral locations of foreshocks are necessarily restricted to lie near the mainshock hypocentre onset of the mainshock rupture whether or not foreshocks occur during the mainshock nucleation depends on how the rupture growth resistance varies on a local to small scale since patches of greater rupture growth resistance are considered to prevail on a local to small scale in the fault zone carrying immediate foreshocks would be one of the major characteristics of earthquakes that nucleate within the brittle seismogenic layer when a mainshock earthquake nucleates within the brittle seismogenic layer and its hypocentre is located near the base of the seismogenic layer immediate foreshocks for this mainshock are necessarily restricted to lie within a localized region shallower than hypocentral depth of the mainshock by contrast the nucleation process below the base of the seismogenic layer is aseismic in nature so that carrying no conspicuous foreshocks would be a common characteristic of interplate earthquakes that nucleate below the base of the brittle seismogenic layer the breakdown strength p the breakdown stress drop b and the critical slip displacement dc are indicative of the rupture growth resistance to estimate depth variations of these parameters the effects of the normal stress n and temperature t on those parameters are examined using available data so far published the combined effects of n and t on p in the brittle to semibrittle regime are found to be represented empirically by p n t po n 1 cosh 50 t 40 sinh 50 t exp 2000 t where po n 135 7 0 750 n and t is measured in k and n in mpa it is found that dc increases sharply with t but is insensitive to n above 300 c while dc depends on n but is insensitive to t below 300 c on the basis of these results variations in p dc and b at mid crustal depths are estimated for quartzo feldspathic rocks for a given geothermal gradient

photo acoustic study of subshear and supershear ruptures in the laboratory abstract we report supershear ruptures observed in spontaneously nucleating laboratory microearthquakes and describe the signature of the associated mach wavefront radiation transducers detect the wavefield both close and at a distance from the fault the rupture velocities are inferred from either photoelastic high speed imaging or using the acoustic recordings both methods yield compatible estimates of sufficient accuracy to discriminate between sub shear and supershear ruptures the acoustic records allow to characterize the mach wavefront radiated from the supershear rupture front in particular its amplitude and decay velocity functions recovered by integrating high frequency accelerometer signals in the case of supershear ruptures consist in a double pulse function a first pulse traveling at supershear velocity followed by a second pulse traveling at the rayleigh wave velocity conversely the sub shear event is characterized by a single pulse finally we perform numerical simulations of our experiment using a prescribed supershear rupture velocity the synthetic waveforms obtained from these simulations including the mach wave amplitude and phase yield a satisfactory fit to the experimental results

strain rate effect on frictional strength and the slip nucleation process abstract kato n yamamoto k yamamoto h and hirasawa t 1992 strain rate effect on frictional strength and the slip nucleation process in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 269 282 the strain rate dependence of frictional strength is investigated in relation to sliding behaviour by biaxial compression tests of large scale granite samples frictional sliding is generated by increasing shear strain at a constant rate under a constant normal stress on the fault the ram displacement is held constant for a prescribed time interval between two successive sliding events so as to have the same time effect of stationary contact between sliding surfaces we obtained the following results as the strain rate increases 1 sliding becomes more unstable 2 the nucleation zone size of stick slip decreases and 3 frictional strength logarithmically increases result 3 is consistent with the previous study by dieterich 1979a and 1 and 3 are similar to the strain rate effects on failure characteristics of intact rocks reported in the literature result 3 can be explained by a rate and state dependent friction law our results suggest that the strain rate dependence of the fault strength plays an important role in controlling the nucleation process of faulting

characteristic features of local breakdown near a crack tip in the transition zone from nucleation to unstable rupture during stick slip shear failure abstract characteristic features of local breakdown near a propagating crack tip during slip failure nucleation and its transition process to unstable rupture under mode ii conditions are experimentally studied using a rock sample with a simulated fault the size of which is large compared with the size of the breakdown zone in addition distinctive features in the nucleation zone are compared with those in the zone of steady dynamic rupture propagation it is found that the local breakdown stress drop the local dynamic stress drop the local stress increase immediately before the slip weakening process the dimensionless parameter s defined by das and aki and the shear fracture energy are functions of crack length in the transition zone from nucleation to unstable rupture i e they all increase with crack growth in the nucleation zone this is contrasted with the observations in the zone of steady dynamic rupture propagation where these physical parameters do not depend on crack length an increase in the magnitudes of these parameters with crack growth in the nucleation zone results in increasing resistance to crack extension with crack growth in the nucleation zone the reason for the increase in crack growth resistance in this zone is that a slip failure nucleus is formed at a point or zone where the local strength and the shear fracture energy are at a minimum this basic physical information can provide the key to earthquake prediction since the nucleation itself is a precursory phenomenon the ratio of the size of the breakdown zone to the crack length decreases abruptly beyond the critical crack length rupture velocity v accelerates with crack growth and reaches the shear wave velocity or super shear and v is found to be expressed empirically as a function of crack length in the nucleation zone a positive correlation is found between s and v in the nucleation zone v increases with increasing s however no such correlation was observed in the zone of steady dynamic rupture propagation where v seems to have reached the shear wave velocity of super shear for s 0 5 this is consistent with das and aki s numerical result the interrelationships between shear stress slip displacement slip velocity and acceleration near the crack tip during the breakdown in the nucleation zone are revealed and they are compared with those in the zone of dynamic rupture propagation the present experiments suggest that the relationship between shear stress and slip displacement is more fundamental during the breakdown process than the relationship between shear stress and slip velocity a model is presented to describe the breakdown process in the nucleation zone

scaling relationships between sizes of nucleation regions and eventual sizes of microearthquakes abstract we investigate the initial rupture process of microearthquakes to reveal relationships between nucleation region sizes and eventual earthquake sizes in order to obtain high quality waveform data we installed a trigger recording system with a sampling frequency of 10 khz at the base of a deep borehole at the nojima fault japan we analyze waveform data of 31 events around the borehole with seismic moment ranging from 4 2 10 9 nm to 7 1 10 11 nm we use both a circular crack model with an accelerating rupture velocity sk model sato t kanamori h 1999 beginning of earthquakes modeled with the griffith s fracture criterion bull seism soc am 89 80 93 which generates a slow initial phase of velocity pulse and a circular crack model with a constant rupture velocity sh model sato t hirasawa t 1973 body wave spectra from propagating shear cracks j phys earth 21 415 431 which generates a ramp like velocity pulse source parameters of these two models are estimated by waveform inversion of the first half cycle of the observed velocity pulse applying both a grid search and a non linear least squares method 14 of 31 events are never reproduced by the sh model with a constant q operator but sk model with a constant q operator provides a size of the pre existing crack corresponding to the size of the nucleation regions and a size of the eventual crack we recognize that i the eventual seismic moment is approximately scaled as the cube of the size of pre existing cracks ii the eventual seismic moment is scaled as the cube of the size of eventual cracks and iii the size of eventual cracks is roughly proportional to the size of pre existing cracks we thus conclude that the size of eventual earthquakes is controlled by the size of the nucleation regions

constitutive relations between dynamic physical parameters near a tip of the propagating slip zone during stick slip shear failure abstract constitutive relations between physical parameters in the cohesive zone during stick slip shear failure are experimentally investigated stick slip was generated along a 40 cm long precut fault in tsukuba granite samples using a servocontrolled biaxial loading apparatus dynamic behavior during local breakdown processes near a tip of the slipping zone is revealed the slip velocity and acceleration are given as a function of the slip displacement and the cohesive or breakdown shear stress as a function of the slip velocity a cycle of the breakdown and restrengthening process of stick slip is composed of five phases characterized in terms of the cohesive strength and the slip velocity the cohesive strength can degrade regardless of the slip velocity during slip instabilities the maximum slip acceleration u max and the maximum slip velocity u max are obtained experimentally as u max 2 u c u max 2 and u max b g v where u c is the critical displacement b the breakdown stress drop g the rigidity and v the rupture velocity these relations are consistent with ida s theoretical estimation based on the cohesive zone model the above formula gives good estimates for the maximum slip acceleration of actual earthquakes the cutoff frequency max of the power spectral density of the slip acceleration increases with increasing normal stress in particular max is found to be directly proportional to the normal stress n within the normal stress range less than 17 mpa as max khz 4 0 n mpa n max increase with an increase in u max or u max all these results lead to the conclusion that u max u max and max increase with increasing normal stress this is consistent with a previous observation that b increases with increasing normal stress the above empirical linear relation between max and n can be explained by a linear dependence of b on n the size scale dependence of physical parameters is discussed and such size scale dependent parameters as u max and apparent fracture energy are scaled to the breakdown zone size regarded as a characteristic length to extend the results obtained in the laboratory to an earthquake failure in the earth

precursors to the shear failure of rock discontinuities active geophysical monitoring of potential failure along mechanical discontinuities in rock requires identification of precursory signatures to failure in geophysical signals active ultrasonic monitoring of shear failure along frictional discontinuities was performed to determine the signatures of potential failure an instrumented direct shear apparatus was used to apply a constant shearing rate to a discontinuity that was held under a constant normal stress transmitted and reflected compressional and shear waves were recorded during the shearing process ultrasonic precursors were identified as distinct maxima in the amplitude of transmitted shear waves as well as minima in the amplitude of reflected shear waves that occurred well before the peak shear strength of a frictional discontinuity the precursors are linked to changes in the local shear specific stiffness along the discontinuity while the discontinuity s macroscopic shear strength continues to increase prior to failure

currents and sediment transport in mangrove forests abstract a field study of the tidal currents cohesive sediment dynamics and transport of organic carbon in a highly vegetated mangrove swamp was carried out at middle creek cairns australia the interaction of tidal currents and the vegetation generated jets eddies and zones of stagnant waters which were numerically modelled a high value of the manning friction coefficient n 0 1 was derived by the dense vegetation about 80 of the suspended sediment brought in from coastal waters at spring flood tide was trapped in the mangroves corresponding to about 10 12 kg of sediment m 1creek length spring tide resulting in a rise of the substrate by about 0 1 cm year 1 the selective trapping of clay was caused by flocculation of the finer particles in the mangroves there was an indication of a slight inwelling of organic carbon creek water was readily differentiated from mangrove water by large differences in the molecular weight distribution of the dissolved organic carbon

evaluating deep subsidence in a rapidly accreting mangrove forest using gps monitoring of surface elevation benchmarks and sedimentary records abstract ultimately the fate of mangrove forests depends on substrate elevation gains keeping pace with relative sea level rise rslr some of the world s largest mangrove forests occur on tectonically active margins river deltas and sedimentary basins where sea level trends are largely controlled by vertical land motion i e subsidence so that rslr can be markedly higher than sea level rise induced by climate warming the rod surface elevation table marker horizon rset mh method has been applied globally to evaluate coastal wetland resilience to slr by quantifying net rates of elevation change relative to a benchmark a limitation of the rset method is that the stability of the benchmark i e vertical trend is unknown and rslr in wetlands is typically inferred from regional tide gauge records in the present study we evaluate rslr in a rapidly subsiding avicenna marina mangrove forest with a large terrigenous sediment supply firth of thames new zealand using independent and complimentary methods 1 campaign gps surveys of the stability of three rset benchmarks driven 18 m into unconsolidated sediment a tide gauge some 10 km distant and a reference station located on basement rock 2007 2016 that are tied to a network of satellite based geodetic sites and 2 137cs validated 210pb sediment accumulation rates sar measured in cores as a proxy for rslr the similarity of deep subsidence rates at the rset benchmarks located several hundred metres apart 7 7 0 5 to 9 4 0 5 mm yr 1 provides confidence in these results these subsidence rates are two to five fold higher than recorded at the nearby tide gauge 3 6 0 7 mm yr 1 and reference station 1 6 0 5 mm yr 1 weighted average 210pb sar of 9 9 mm and 9 3 mm yr 1 yield similar estimates of deep subsidence i e 8 4 and 6 9 mm yr 1 slr adjusted for vertical land motion indicating that this geological process is the major driver of the long term sea level trend in the mangrove forest our findings suggest that regional tide gauge records may not provide reliable estimates of rslr for all coastal wetlands due to local subsidence associated with natural processes and human activities subsidence rates and rslr within coastal wetlands can be evaluated using campaign gps surveys of rset benchmarks and independently from longer term sedimentary records finally evaluations of the resilience of coastal wetlands to rising sea levels over the coming decades must be based on measurements of rslr from these systems themselves

effects of mesoscopic scale fault structure on dynamic earthquake ruptures dynamic formation of geometrical complexity of earthquake faults 1 we develop a new hierarchical earthquake rupture model that takes into account mesoscopic scale fault structure shear branches nucleated on the main fault are specifically assumed as an example of mesoscopic scale fault structure we numerically investigate dynamic formation of fault geometry and its effects on dynamic earthquake rupture process based on this rupture model as long as the length of the main fault is below a certain threshold lm the growth of these branches is shown to be arrested spontaneously soon after their nucleation the spatial distribution of arrested branches is shown to form a self similar geometrical structure this suggests the existence of a simple scaling relationship between small and large events as long as the length of the main fault is below the threshold lm however once the length of the main fault exceeds lm a limited number of branches begin unstable growth and their sizes soon become comparable to that of the main fault in other words mesoscopic scale branches are spontaneously transformed into macroscopic scale ones this finding indicates the critical importance of the consideration of mesoscopic scale fault structure in understanding rupture dynamics once macroscopic scale branches are formed they change the fault geometry which will considerably affect the rupture dynamics the emergence of macroscopic branches suggests that the above mentioned simple scaling relation is never valid above a critical length lm our study thus indicates that relationship between small and large earthquakes is complicated by the spontaneous transformation of a mesoscopic scale fault structure into a macroscopic scale one

slip dependent friction law and nucleation processes in earthquake rupture abstract matsu ura m kataoka h and shibazaki b 1992 slip dependent friction law and nucleation processes in earthquake rupture in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 135 148 we developed a physical model that interprets slip strengthening and slip weakening processes in brittle shear fracture by considering the microscopic interaction between statistically self similar fault surfaces our model successfully describes general features of the constitutive behaviour observed in laboratory experiments of stick slip with the progress of fault slip frictional stress first increases rapidly up to a peak value and then decreases gradually to a constant level the first slip strengthening process can be explained by the increase of frictional resistance in transition from the in phase contact to the random phase contact of fault surfaces the latter slip weakening process can be explained by the decrease of frictional resistance due to the abrasion of surface asperities the trade off between these two processes determines the peak stress and the critical displacement over which the slip weakening proceeds we examined the nucleation process proceeding in a seismogenic zone with the increase of external shear stress through numerical simulations in our model the seismogenic zone is represented by a broad weak zone with a locally strong part asperity on a fault plane the basic equations governing the nucleation process are the equation of equilibrium and the constitutive relation between frictional stress and fault slip we obtained the following results the nucleation process first proceeds quasi statically at the weak portions with the increase of external shear stress then if the constitutive relation at the asperity has a high and narrow peak of stress brittle dynamic rupture occurs in a limited area around the asperity when the constitutive relation has a low and broad peak the dynamic rupture of the asperity does not occur the process is completely aseismic when the peak of stress is high and broad the dynamic rupture of the asperity leads to the catastrophic rupture which extends over the whole region from these results it is concluded that diversity in the nucleation process can be ascribed to difference in the variation of constitutive behaviour along the fault

archean komatiitic sill hosted chromite deposits in the zimbabwe craton lenticular chromite deposits of widely varying age metamorphic grade and strain rate as well as size shape and ore quality are widespread in greenschist to amphibolite grade greenstonegneiss terrain in the south central part of the zimbabwe craton and in granulite grade equivalents in the northern marginal zone of the limpopo belt in the far south in order of age and very approximately decreasing abundance they form three groups 1 early archean 3 5 3 2 ga deposits associated with amphibolite grade greenstone remnants in the 3 6 to 3 35 ga tokwe gneisses e g hornet valley and on the amphibolite grade eastern flank of the shurugwi greenstone belt and granulite grade greenstone remnants in the northern marginal zone e g inyala rhonda 2 mid archean deposits within the ca 3 0 ga shurugwi group in the main greenschist part of the shurugwi belt e g peak railway block and associated with the ca 3 0 ga belingwean supergroup in several other belts and 3 late archean ca 2 74 ga deposits mostly in the western segment of the masvingo belt e g prince with their host and country rocks the deposits together preserve geologic and chromite compositional evidence of formation within poorly differentiated komatiitic sills intruded into predominantly siliciclastic bif platformal sedimentary sequences associated with mafic and or ultramafic lavas unlike the thin laterally extensive chromitite layers associated with macrocyclic units of large layered intrusions the komatiitic sill associated deposits are the remnants of laterally discontinuous up to several tens of meters thick chromitite layers or dunite chromitite zones located at high stratigraphic levels of their host intrusions not far below the upper pyroxenite differentiates in at least some deposits for example at railway block where the chromitites form narrow elongate bodies at least 1 000 m long the lateral discontinuities are most likely primary in many others later deformation obscures the primary geometry chromitite formation may have been delayed by the late attainment of equilibrium crystallization and the reduced nature of the magma the crystallization of thick massive cyclically layered cr rich chromitites was most probably controlled by the stabilization of chromite relative to olivine by absorption of connate water derived from wet host sediments and by episodic flow through processes which at railway block may have been focused along narrow pathways across the magma chamber floor the remarkable abundance of such chromitites and their formation in repeated episodes over 1 000 m y cf other cratons can be attributed to generation of komatiitic magmas in a mantle source that was both cr rich and strongly reduced archean komatiitic sill hosted deposits constitute a third type of chromite deposit in addition to stratiform and podiform deposits in layered intrusions and ophiolites respectively the economically important variability of bulk ore compositions especially cr fe al mg is due to several factors magnetite introduction during serpentinization and talc carbonate alteration at greenschist grade subsolidus fluid related and other metamorphic cation exchange processes dependant on chromite body size and possibly exsolution of cr al and magnetite phase pairs both at midamphibolite to granulite grade as well as fluid related retrogression and partial conversion of chromite to mainly chlorite during amphibolite metamorphism

stress release process along an intraplate fault analogous to the plate boundary a case study of the 2017 m5 2 akita daisen earthquake ne japan stress accumulation and release in the crust remains poorly understood compared to that at the plate boundaries spatiotemporal variations in foreshock and aftershock activities can provide key con

premonitory acoustic emissions and stick slip in natural and smooth faulted westerly granite 1 a stick slip event was induced in a cylindrical sample of westerly granite containing a preexisting natural fault by loading at constant confining pressure of 150 mpa continuously recorded acoustic emission ae data and computer tomography ct generated images of the fault plane were combined to provide a detailed examination of microscale processes operating on the fault the dynamic stick slip event considered to be a laboratory analog of an earthquake generated an ultrasonic signal that was recorded as a large amplitude ae event first arrivals of this event were inverted to determine the nucleation site of slip which is associated with a geometric asperity on the fault surface ct images and ae locations suggest that a variety of asperities existed in the sample because of the intersection of branch or splay faults with the main fault this experiment is compared with a stick slip experiment on a sample prepared with a smooth artificial saw cut fault surface nearly a thousand times more ae were observed for the natural fault which has a higher friction coefficient 0 78 compared to 0 53 and larger shear stress drop 140 compared to 68 mpa however at the measured resolution the ultrasonic signal emitted during slip initiation does not vary significantly between the two experiments suggesting a similar dynamic rupture process we propose that the natural faulted sample under triaxial compression provides a good laboratory analogue for a field scale fault system in terms of the presence of asperities fault surface heterogeneity and interaction of branching faults

stability of ilmenite and titanomagnetite in the presence of carbon dioxide a thermodynamic evaluation the stability of ilmenite and titanomagnetite in the presence of co2 gas was evaluated thermodynamically ilmenite with a composition ilm90hm10 breaks down to the assemblage siderite hematite anatase below 270 c at 1 000 bars and below 300 c at 2 000 bars titanomagnetite with a composition usp50mt50 breaks down to the same assemblage below 345 c at 1 000 bars and below 385 c at 2 000 bars during the low grade metamorphism of basaltic rocks a co2 partial pressure of only a few hundreds bars is sufficient to alter ilmenite and titanomagnetite to the assemblage siderite hematite anatase

the origin of large or great thrust type earthquakes along subducting plate boundaries abstract seismicity deformation state of stress and abundance of fluids along subducting plate boundaries are reviewed and the origin of large or great thrust type earthquakes is discussed based on the recent experimental results on the slip behavior of halite and serpentine gouges shallow subducting plate boundaries above 20 25 km in depth are characterized by low seismicity low tectonic stress inter plate decoupling ductile deformation associated with the formation of metamorphic schistosity except at very shallow depths metamorphism suggesting solution processes on massive scale and presence of abundant h 2 o it is argued that these unique features are due to pressure solution processes to high fluid pressure to low strength and stable behavior of clayey sediments under wet environments and or to the deformation of soft unconsolidated sediments at very shallow depths the low seismicity in this zone is in marked contrast with major strike slip faults along which large earthquakes occur at depths shallower than 15 20 km it is emphasized that these unique features are expected only for restricted regions where there is constant supply of h 2 o due to progressive metamorphism or where fluids in the rocks are trapped and cannot escape to the surface large or great thrust type earthquakes in subduction zones initiate at depths of 30 50 km below the shallow decoupled zone in this focal depth range the supply of h 2 o during progressive metamorphism perhaps diminishes downwards the overriding and subducting plates are coupled and stick to each other during much of the inter seismic period and the resistance to slip or shear stress is presumably high it is suggested that these earthquakes begin to occur at a depth where the plate boundary zone becomes fairly dry deformation at these depths appears to be predominantly ductile so that the earthquakes cannot be regarded simply as a brittle phenomenon 1 creep instability i e instability associated with plastic deformation and 2 dehydration induced instability are the most likely mechanisms for initiating the earthquakes and both have some experimental support stick slip of halite gouge while undergoing ductile deformation primarily by intracrystalline gliding is described and discussed as a supporting evidence for 1 shear resistance of halite gouge increases with increasing confining pressure in stick slip regimes hence the observed stick slip may be a semi brittle phenomenon with respect to the pressure dependence of the shear resistance although the deformation texture cannot be distinguished from that formed by pressure insensitive flow serpentine gouge exhibits violent stick slip upon its decomposition under dry not wet environments supporting the mechanism 2 above exact mechanisms which lead to the unstable fault motion are poorly understood as yet but stick slip of both halite and serpentine gouges is recognized only when the slip rate dependence of friction is negative i e lower friction at faster slip rate consistent with the theoretical prediction of rice and ruina 1983 there is a possibility that the thrust type earthquakes can be explained essentially within the framework of fault constitutive laws developed by dieterich 1979 and ruina 1983

relationship between rupture process complexity and earthquake size 1 we studied the complexity of waveforms for two shallow crustal earthquake sequences in japan using 47 earthquakes of the 2003 northern miyagi sequence and 95 events of the 2004 mid niigata sequence we estimated the number of complex and simple p waveforms for events with magnitudes from m3 1 to m6 6 data were recorded at borehole and surface stations with minimal site responses for close hypocentral distances of less than 30 km the determination of complexity was done by counting the zero crossings of the accelerations waveforms our results show that for the smaller earthquakes there are both simple and complex events but that all of the larger earthquakes are complex there appears to be a threshold size over which the earthquakes always become complex for both data sets this threshold is m4 0 to m4 5 we attribute this difference in complexity with earthquake size as an indication that larger earthquake grow with a complex ruptures that may be indicative of stochastic processes there do not appear to be large earthquakes that grow smoothly to their final size

estimating shallow subsidence in microtidal salt marshes of the southeastern united states kaye and barghoorn revisited abstract simultaneous measurements of vertical accretion and change in surface elevation relative to a shallow 3 5 m subsurface datum were made in selected coastal salt marshes of louisiana florida and north carolina to quantitatively test kaye and barghoorn s contention that vertical accretion is not a good surrogate for surface elevation change because of autocompaction of the substrate rates of subsidence of the upper 3 5 m of marsh substrate were calculated for each marsh as the difference between vertical accretion and elevation change measured with feldspar marker horizons and a sedimentation erosion table surface elevation change was significantly lower than vertical accretion at each site after 2 years indicating a significant amount of shallow subsidence had occurred ranging from 0 45 to 4 90 cm the highest rate of shallow subsidence occurred in the mississippi delta results confirm kaye and barghoorn s contention that vertical accretion is not generally a good surrogate for elevation change because of processes occurring in the upper few meters of the substrate including not only compaction but also apparently shrink swell from water storage and or plant production decomposition at some sites indeed surface elevation change was completely decoupled from vertical accretion at the florida site the assumption of a 1 1 relationship between vertical accretion and surface elevation change is too simplistic a generalization of the complex interactions between accretionary and substrate processes consequently the potential for coastal marsh submergence should be expressed as an elevation deficit based on direct measures of surface elevation change rather than accretion deficits these findings also indicate the need for greater understanding of the influence of subsurface and small scale hydrologic processes on marsh surface elevation

high surface elevation gains and prediction of mangrove responses to sea level rise based on dynamic surface elevation changes at dongzhaigang bay china abstract mangrove forest responses to sea level rise slr are likely misestimated in many studies because current assessment methods often assume a constant rate of surface elevation change along the intertidal profile most studies also neglect the ecogeomorphic feedback process known to accelerate soil building with slr here an empirical dynamic model that accounts for the above processes is constructed for the intertidal zone of a mangrove bay in hainan china the model allows us to explore the response of a tide dominated mangrove forest to different rates of slr rod surface elevation table marker horizon rset mh data 2015 2018 indicate rather high rates of surface accretion 13 3 57 9 mm yr 1 and surface elevation changes 7 9 35 5 mm yr 1 surface accretion and surface elevation change decreased exponentially with increasing ground elevation our model showed that slr at rates of 4 and 16 mm yr 1 would not lead to the loss of mangrove cover but that it could alter mangrove species zonation along the intertidal profile by 2100 due to a rich sediment supply and ecogeomorphic feedback importantly rapid slr and landward barriers can pose a considerable threat to the high intertidal community by causing increased inundation of the high intertidal zone subsequent shifts in species zones and the loss of mangrove biological and structural diversity along the intertidal profile overall this study predicts probabilities of habitat suitability for mangrove species under slr and expands our current understanding of the impacts of slr on tide dominated mangrove forests in sediment rich systems incorporation of extensive long term rset data into this kind of dynamic model could contribute to the better prediction of mangrove responses to slr at large scales in the future

inferring rate and state friction parameters from a rupture model of the 1995 hyogo ken nanbu kobe japan earthquake we consider the applicability of laboratory derived rate and state variable friction laws to the dynamic rupture of the 1995 kobe earthquake we analyze the shear stress and slip evolution of ide and takeo s 1997 dislocation model fitting the inferred stress change time histories by calculating the dynamic load and the instantaneous friction at a series of points within the rupture area for points exhibiting a fast weakening behavior the dieterich ruina friction law with values of dc 0 01 0 05 m for critical slip fits the stress change time series well this range of dc is 10 20 times smaller than the slip distance over which the stress is released dc which previous studies have equated with the slip weakening distance the limited resolution and low pass character of the strong motion inversion degrades the resolution of the frictional parameters and suggests that the actual dc is less than this value stress time series at points characterized by a slow weakening behavior are well fitted by the dieterich ruina friction law with values of dc 0 01 0 05 m the apparent fracture energy gc can be estimated from waveform inversions more stably than the other friction parameters we obtain a gc 1 5 l06 j m 2 for the 1995 kobe earthquake in agreement with estimates for previous earthquakes from this estimate and a plausible upper bound for the local rock strength we infer a lower bound for dc of about 0 008 m

reaction relationships of chrome spinels in igneous rocks further evidence from the layered intrusions of rhum and mull inner hebrides scotland compositions of chrome spinels in peridotites from the layered igneous rocks of rhum and of the ben buie intrusion mull show evidence of post depositional reaction relationships with the cumulus olivine and or the intercumulus liquid some seam forming spinels in the ben buie intrusion are highly aluminous more so than those in the rhum intrusion occasional zoned spinels in both intrusions show enrichment in al towards their rims the evidence suggests that the spinel reaction trend involving cr al exchange proceeds in the direction of al enrichment equilibrium between chrome spinel and cumulus olivine appears to have been attained rarely thus limiting the application of the olivine spinel geothermometer

biophysical controls on accretion and elevation change in caribbean mangrove ecosystems abstract habitat stability of coastal ecosystems such as marshes and mangroves depends on maintenance of soil elevations relative to sea level many such systems are characterized by limited mineral sedimentation and or rapid subsidence and are consequently dependent upon accumulation of organic matter to maintain elevations however little field information exists regarding the contribution of specific biological processes to vertical accretion and elevation change this study used biogenic mangrove systems in carbonate settings in belize bz and southwest florida fl to examine biophysical controls on elevation change rates of elevation change vertical accretion benthic mat formation and belowground root accumulation were measured in fringe basin scrub and dwarf forest types plus a restored forest elevation change rates mm yr 1 measured with surface elevation tables varied widely bz dwarf 3 7 bz scrub 1 1 fl fringe 0 6 fl basin 2 1 bz fringe 4 1 and fl restored 9 9 root mass accumulation varied across sites 82 739 g m 2 yr 1 and was positively correlated with elevation change root volumetric contribution to vertical change mm yr 1 was lowest in bz dwarf 1 2 and fl fringe 2 4 intermediate in fl basin 4 1 and bz scrub 4 3 and highest in bz fringe 8 8 and fl restored 11 8 sites surface growth of turf forming algae microbial mats or accumulation of leaf litter and detritus also made significant contributions to vertical accretion turf algal mats in fringe and scrub forests accreted faster 2 7 mm yr 1 than leaf litter mats in basin forests 1 9 mm yr 1 but similarly to microbial mats in dwarf forests 2 1 mm yr 1 surface accretion of mineral material accounted for only 0 2 3 3 of total vertical change those sites with high root contributions and or rapid growth of living mats exhibited an elevation surplus 2 to 8 mm yr 1 whereas those with low root inputs and low or non living mat accumulation showed an elevation deficit 1 to 5 7 mm yr 1 this study indicates that biotic processes of root production and benthic mat formation are important controls on accretion and elevation change in mangrove ecosystems common to the caribbean region quantification of specific biological controls on elevation provides better insight into how sustainability of such systems might be influenced by global e g climate atmospheric co2 and local e g nutrients disturbance factors affecting organic matter accumulation in addition to relative sea level rise

effects of sea level rise and climatic changes on mangroves from southwestern littoral of puerto rico during the middle and late holocene abstract we evaluated the response to sea level rise and climatic changes of the northeastern caribbean by establishing a palaeoenvironmental reconstruction of the flamenco lagoon located in the coastal side of the guanica dry forest a mab unesco reserve in the semi arid southwestern coast of puerto rico 17 57 10 31 n 66 50 39 30 w the reconstruction was based on pollen records sediments analysis 13 c 15 n c n data and ams 14 c dating of one sediment core the geology of the area is rocky calcareous karst with rocky outcrops and canyons with intermittent streams that move water during periods of high run off conditions the present lagoon is surrounded by rocky outcrops where dry forest vegetation is present on the terrestrial sides and sand dunes on the coastal side we propose that the studied lagoon developed after the stabilization of sea level rise in the region following three main stages 1 before 5400 cal yr bp sediments were accumulated according to small channels dynamics and trees shrubs and herbs were present the sedimentary organic matter was mainly sourced from terrestrial c 3 and c 4 plants 2 between 5400 and 4400 cal yr bp tidal flats were established and mangroves mainly represented by rhizophora trees migrated landward with sea level rise and established in the area and the sedimentary organic matter was sourced from terrestrial c 3 plants 3 around 4400 cal yr bp sea level was near the stabilization the endorheic minibasin was closed when a coastal sand dune was established as a result of drier climatic conditions mangroves were eliminated from the system as a result of the closure of the area by sand dunes and increased salinity in water due to high evaporative demand of the climate the pollen dominance of herbaceous and shrubby vegetation prevails until present throughout the lagoon development sedimentary organic matter was sourced from c 3 and c 4 plants as well as phytoplankton organic matter the closure of the lagoon and the drier conditions prevalent in the region during the late holocene which lasts until the present day and increased the contribution of salinity tolerant phytoplankton that characterizes the current conditions of the flamenco lagoon

composition and textures of chromite and platinum group minerals in chromitites of the western ophiolitic belt from pampean ranges of cordoba argentina abstract chromitite bodies hosted in the neoproterozoic western ophiolitic belt of pampean ranges of cordoba argentina were studied at los congos and los guanacos ultramafic bodies with regard to the composition and textures of the chromite and platinum group minerals primary chromite composition is only preserved in some massive chromitites from the los guanacos ultramafic body and is similar to al rich ophiolitic chromitites suggesting that they crystallized from melts with back arc basin basalts babb affinity in the suprasubduction mantle subsequently these chromitites underwent a prograde metamorphism chromites from chromitites and associated metamorphosed ultramafic rocks show complex replacement and exsolution textures mineral chemistry and texture indicate that the chromite composition records two main metamorphic trends a first trend defined by chromite from massive chromitite in which there is an enrichment in fe3 and fe2 cr remain relatively constant and slightly depleted in al mg a second trend is defined by chromite from disseminated chromitite and metamorphosed dunite and harzburgite in which a fe rich phase is replacing the al rich chromite this alteration trend is characterized by enrichment in the total iron content fe3 fe2 and a strong depletion in al and mg the chemical composition of all analyzed spinels from los guanacos and los congos as plotted on the ternary fe3 cr al diagram correlates well with the cr spinels from the upper amphibolite to granulite facies metamorphism platinum group minerals pgm identified include native osmium laurite erlichmanite irarsite platinum and a number of inadequately identified phases such as an oxide or hydroxide of ru pt and ir ru pt telluride ir ru as se and ir ru ti compounds native osmium was the only pgm which remained unaltered other pgm underwent mineralogical reworking during metamorphism although it is difficult to establish the extent of platinum group element mobilization based on mineralogical observation our results suggest that the ru os ir pgm in the los guanacos and los congos chromitites were modified in situ producing re distribution of these pge on a small scale the presence of rare pt and pge as se minerals was possibly related to remobilization of pt as and se by fluids during the alteration processes

mechanics of normal fault networks subject to slip weakening friction summary we seek to understand how the stress interactions and the slip weakening process combine within a non coplanar normal fault network to allow a slip instability to develop and shape the final slip distribution on the system in a first part we perform a non linear spectral analysis to investigate the conditions of stability and the process of slip initiation in an antiplane non coplanar fault system subject to a slip dependent friction law that numerical model allows determining the zones that are able to slip within a fault network as well as the location of the stress singularities the resulting slip profiles on the faults show only a few different shapes some of them with long linear sections this leads to formulate a general classification of slip profiles that can be used to infer the degree of fault interaction within any non coplanar system in a second part of work we use our modelling to try reproducing the cumulative slip profiles measured on three real normal interacting faults forming a large scale en echelon system for that we assume that cumulative slip profiles can be compared to the first static modal solution of our conceptual model we succeed reproducing the profiles quite well using a variable weakening along the faults overall the weakening rate decreases in the direction of propagation of the fault system yet modelling the slip along the propagating isolated termination segment of the system requires an unlikely distribution of weakening this suggests that factors not considered in our analysis may contribute to slip profile shaping on isolated propagating faults

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

rupture preparation process controlled by surface roughness on meter scale laboratory fault abstract we investigate the effect of fault surface roughness on rupture preparation characteristics using meter scale metagabbro specimens we repeatedly conducted the experiments with the same pair of rock specimens to make the fault surface rough we obtained three experimental results under the same experimental conditions 6 7 mpa of normal stress and 0 01 mm s of loading rate but at different roughness conditions smooth moderately roughened and heavily roughened during each experiment we observed many stick slip events preceded by precursory slow slip we investigated when and where slow slip initiated by using the strain gauge data processed by the kalman filter algorithm the observed rupture preparation processes on the smooth fault i e the first experiment among the three showed high repeatability of the spatiotemporal distributions of slow slip initiation local stress measurements revealed that slow slip initiated around the region where the ratio of shear to normal stress was the highest as expected from finite element method fem modeling however the exact location of slow slip initiation was where became locally minimum probably due to the frictional heterogeneity in the experiment on the moderately roughened fault some irregular events were observed though the basic characteristics of other regular events were similar to those on the smooth fault local stress data revealed that the spatiotemporal characteristics of slow slip initiation and the resulting drop for irregular events were different from those for regular ones even under similar stress conditions on the heavily roughened fault the location of slow slip initiation was not consistent with anymore because of the highly heterogeneous static friction on the fault which also decreased the repeatability of spatiotemporal distributions of slow slip initiation these results suggest that fault surface roughness strongly controls the rupture preparation process and generally increases its complexity with the degree of roughness

slip pulse rupture behavior on a 2 m granite fault we describe observations of dynamic rupture events that spontaneously arise on meter scale laboratory earthquake experiments while low frequency slip of the granite sample occurs in a relatively uniform and crack like manner instruments capable of detecting high frequency motions show that some parts of the fault slip abruptly velocity 100 mm s 1 acceleration 20 km s 2 while the majority of the fault slips more slowly abruptly slipping regions propagate along the fault at nearly the shear wave speed we propose that the dramatic reduction in frictional strength implied by this pulse like rupture behavior has a common mechanism to the weakening reported in high velocity friction experiments performed on rotary machines the slip pulses can also be identified as migrating sources of high frequency seismic waves as observations from large earthquakes show similar propagating high frequency sources the pulses described here may have relevance to the mechanics of larger earthquakes

trace element fingerprints of chromite magnetite and sulfides from the 3 1 ga ultramafic mafic rocks of the nuggihalli greenstone belt western dharwar craton india the 3 1 ga nuggihalli greenstone belt in the western dharwar craton is comprised of chromitite bearing sill like ultramafic mafic rocks that are surrounded by metavolcanic schists compositionally komatiitic to komatiitic basalts and a suite of tonalite trondhjemite granodiorite gneissic rocks the sill like plutonic unit consists of a succession of serpentinite after dunite peridotite pyroxenite and gabbro with bands of titaniferous magnetite ore the chromitite ore bodies length 30 500 m width 2 15 m are hosted by the serpentinite peridotite unit unaltered chromites from massive chromitites 80 modal chromite of the byrapur and bhaktarhalli chromite mines in the greenstone belt are characterized by high cr 100cr cr al of 78 86 and moderate mg 100 mg mg fe2 of 45 55 in situ trace element analysis la icpms of unaltered chromites indicates that the parental magma of the chromitite ore bodies was a komatiite lacking nickel sulfide mineralization in the ga fe3 versus ti fe3 diagram the byrapur chromites plot in the field of suprasubduction zone ssz chromites while those from bhaktarhalli lie in the mor field the above results corroborate our previous results based on major element characteristics of the chromites where the calculated parental melt of the byrapur chromites was komatiitic to komatiitic basalt and the bhaktarhalli chromite was derived from archean high mg basalt the major element chromite data hinted at the possibility of a ssz environment existing in the archean altered and compositionally zoned chromite grains in our study show a decrease in ga v co zn mn and enrichments of ni and ti in the ferritchromit rims trace element heterogeneity in the altered chromites is attributed to serpentinization the trace element patterns of magnetite from the massive magnetite bands in the greenstone belt are similar to those from magmatic fe ti v rich magnetite bands in layered intrusions and magnetites from andesitic melts suggesting that magnetite crystallized from an evolved gabbroic melt enrichments of ni co te as and bi in disseminated millerite and niccolite occurring within chromitites and in disseminated bravoite within magnetites reflect element mobility during serpentinization monosulfide solid solution inclusions within pyroxenes altered to actinolite in pyroxenite and interstitial pyrites and chalcopyrites in magnetite retain primary characteristics except for fe enrichment in chalcopyrite probably due to sub solidus re equilibration with magnetite disseminated sulfides are depleted in platinum group elements pge due to late sulfide saturation and the pge depleted nature of the mantle source of the sill like ultramafic mafic plutonic rocks in the nuggihalli greenstone belt

stratigraphical and palynological appraisal of the late quaternary mangrove deposits of the west coast of india the organic deposits derived from the mangrove swamps form reliable stratigraphic markers within the late quaternary sequence of kerala konkan basin three generations of such deposits have been identified the older one is dated to around 43 000 40 000 14c yr b p with a few dates beyond the range of radiocarbon the younger ones date from the middle holocene to latest pleistocene 10 760 4540 14c yr b p and the late holocene 4000 14c yr b p pollen analyses confirm that the deposits are mostly derived from the mangrove vegetation peat accumulation during the period 40 000 28 000 14c yr b p can be correlated with the excess rainfall 40 100 greater than modern values of the asian summer monsoon the low occurrence of mangrove between 22 000 and 18 000 14c yr b p can be attributed to the prevailing aridity and or reduced precipitation associated worldwide with last glacial maximum because exposure surfaces and ferruginous layers are commonly found in intervals representing this period the high rainfall of 11 000 4000 14c yr b p is found to be the most significant as the mangrove reached an optimum growth around 11 000 14c yr b p but with periods of punctuated weaker monsoons from the present and previous studies it has been observed that after about 5000 or 4000 14c yr b p the monsoons became gradually reduced leading to drying up of many of the marginal marine mangrove ecosystems a case study of hadi profile provided an insight to the relevance of magnetic susceptibility to record the ecological shift in late holocene

a spatial analysis of the relationship between mangrove avicennia marinavar australasica physiognomy and sediment accretion in the hauraki plains new zealand the relationship between mangrove avicennia marina var australasica physiognomy and forest bed accretion was quantified using experimental and field measurements at the piako river mouth firth of thames new zealand sediment accretion under six densities of artificial pneumatophores was monitored for 13 weeks in an experimental plot while accretion was simultaneously monitored for 5 months at 102 locations along two parallel 500 m transects experimental results demonstrated that accretion increases with pneumatophore density this was supported by bivariate analyses of cumulative accretion and avicennia marina stem density basal area and pneumatophore density along the transects only the latter is significantly correlated with accretion geostatistical analyses showed that variation in sediment accretion occurs at the same spatial scale as pneumatophore density accretion and pneumatophore density are spatially autocorrelated over distances 70 m and have fractal dimensions of 1 5 1 6 it is proposed that avicennia marina grow pneumatophores at a density that balances the benefits of aeration with the drawbacks of sediment accretion these results are compared with the concept of positivefeedback switches in plant communities 1996 academic press limited

complex unmixed spinels in layered intrusions within an obducted ophiolite in the natal namaqua mobile belt spinellids showing unmixed intergrowths of chromite or chromian spinel sensu stricto and magnetite or chromian magnetite are not known in mafic or ultramafic igneous rocks they do occur within metamorphosed rocks that attained temperatures sufficiently high upper amphibolite facies for the formation of homogeneous al cr fe3 ti spinel phases with compositions not matched in slowly cooled igneous rocks in the tugela rand intrusion complex intergrowths of chromian spinel chromian magnetite ulvospinel ilmenite and a transparent aluminous spinel are observed and interpreted in terms of the thermal history of the rocks compositional differences between the separate areas of chromian spinel and chromian magnetite in complex intergrowths exhibited by the metamorphosed tugela rand and mambulu complexes confirm the extension of the magnetite hercynite solvus turnock and eugster 1962 towards magnesium and chromium rich compositions the tugela rand spinellids are compared with those from the carr boyd complex purvis et al 1972 and the ultramafic rocks of the giant nickel mine muir and naldrett 1973 and the red lodge district loferski and lipin 1983 significant differences between the spinels from the red lodge district compared to the other three occurrences may reflect the different metamorphic histories of these areas

accessory chromium spinels their coexistence and alteration in serpentinites abstract accessory chromium spinel occurring in serpentinites is usually altered the extent of this alteration and its relationship to alteration processes such as serpentinization and metamorphism is not defined complicating the use of altered spinel as a petrogenetic indicator here the relationship between different alteration processes and spinel alteration is evaluated in terms of accessory chromium spinel occurring in serpentinites of progressive metamorphism in the eastern central alps two coexisting cr spinels were identified i e an altered fe rich cr spinel i with cr al and an fe poor cr spinel ii with al cr which exsolved a cr fe 3 phase and which resisted alteration alteration of cr spinel i is evident from decreasing al mg and cr values with a trend leading to ferrite chromite trend a an enrichment in cr trend b related to co 2 in the serpentinizing fluid indicated by the presence of carbonate talc or tremolite is superimposed to a alteration is a decomposition of the spinel structure caused by the dissolution of mg al and cr during serpentinization dissolution of cr is favored in a reduced environment whereas reprecipitation occurs under locally oxidizing conditions indicated by the presence of co 2 sio 2 detected in spinel is a relative measure of the degree of alteration metamorphism up to amphibolite facies recrystallized and homogenized preexisting spinel phases to various degrees whether or not and to what extent a spinel alters depends on its fe content fe 2 stabilized in the octahedral site high cfse is responsible for an inverse and less stable spinel structure fe rich spinels cr spinel i are therefore readily subjected to alteration whereas fe poor spinels cr spinel ii are resistant to alteration during the serpentinization processes

rupture nucleations in the 1995 hyogo ken nanbu earthquake and its large aftershocks summary local seismograms of the hyogo ken nanbu earthquake m 7 2 and its largest aftershocks show that a slow rising initial phase precedes the main p phase high dynamic range short period seismograms of the foreshocks mainshock and aftershocks were recorded by the japan meteorological agency jma network and the net hyogo using these seismograms we investigate the initial rupture process of the mainshock and large aftershocks using an empirical green s function method the deconvolved moment rate function of the mainshock shows that it begins with a small pre event mw 4 0 then the moment releases gradually and after about 0 6 s it increases rapidly the first 0 7 s of the deconvolved moment rate functions are inverted to obtain the spatio temporal images of the initial rupture process the results show that at the hypocentral area less than 1 km from the hypocentre slip velocity rises slowly with a low peak in the surrounding area 1 km east and downward from the hypocentre slip velocity rises rapidly with a high peak it is also found that during the initial rupture process the slip velocity pulse grows continuously these observations are in accord with a theoretical model of the transition process from nucleation to high speed dynamic rupture in which slip velocity rises slowly at the nucleation zone we also analyse the initiation and the main dynamic rupture of large aftershocks spatio temporal images of the largest aftershocks m 5 1 and m 4 8 show that there is a clear initial rupture process with a low moment release and after about 0 2 s slip velocity increases rapidly we compare the initial rupture process of the mainshock with those of the large aftershocks m 4 0 5 1 the duration 0 6 s of the initial phase of the mainshock is longer than those 0 02 0 3 s of the large aftershocks furthermore the slip velocity of the initial rupture process of the mainshock is several times larger than those of the two largest aftershocks these results suggest that the mainshock starts in the region where the stress drop and fracture energy is higher

modeling dynamic rupture in a 3d earthquake fault model we propose a fourth order staggered grid finite difference method to study dynamic faulting in three dimensions the method uses an implementation of the boundary conditions on the fault that allows the use of general friction models including slip weakening and rate dependence because the staggered grid method defines stresses and particle velocities at different grid points we preserve symmetry by implementing a two grid row thick fault zone slip is computed between points located at the borders of the fault zone while the two components of shear traction on the fault are forced to be symmetric inside the fault zone we study the properties of the numerical method comparing our simulations with well known properties of seismic ruptures in 3d among the properties that are well modeled by our method are full elastic wave interactions frictional instability rupture initiation from a finite initial patch spontaneous rupture growth at subsonic and supersonic speeds as well as healing by either stopping phases or rate dependent friction we use this method for simulating spontaneous rupture propagation along an arbitrarily loaded planar fault starting from a localized asperity on circular and rectangular faults the shape of the rupture front is close to elliptical and is systematically elongated in the in plane direction of traction drop this elongation is due to the presence of a strong shear stress peak that moves ahead of the rupture in the in plane direction at high initial stresses the rupture front becomes unstable and jumps to super shear speeds in the direction of in plane shear another interesting effect is the development of relatively narrow rupture fronts due to the presence of rate weakening friction the solutions for the thick fault boundary conditions scale with the slip weakening distance do and are stable and reproducible for do greater than about 4 in terms of 2t t ax finally a comparison of scalar and vector boundary conditions for the friction shows that slip is dominant along the direction of the prestress with the largest deviations in slip rate direction occurring near the rupture front and the edges of the fault

diffusion pathways of fe 2 and fe 3 during the formation of ferrian chromite a µxanes study the alteration of chromian spinel is a key process during serpentinization and metamorphism of ultramafic rocks controlled by oxygen fugacity fo2 and fe2 fe3 exchange during fluid rock interaction chromian spinel alteration is better recorded in less permeable chromitite than in peridotites where extensive fluid rock interaction frequently overprints the record of earlier stages of alteration to shed light on that process we have studied the distribution of fe2 and fe3 in variably altered chromian spinel grains from a set of chromitite samples from the same mining district using synchrotron based microscopic chemical imaging and spatially resolved x ray absorption near edge structure spectroscopy our results show that early stages of alteration do not involve changes in cr3 and fe2 contents or in fe speciation but only depletion in al3 and mg2 resulting in the formation of porous chromite with ongoing alteration fe3 migrates into porous chromite mainly along fracture walls and fracture zones as well as along grain boundaries sheared type chromitites record the maximum rates of fluid rock interaction because in these chromitite types the accommodation of deformation on porous chromite allowed higher rates of diffusion of fe3 and fe2 a magnetite component with fe3 fetotal 0 66 into the newly formed neoblasts in porous chromite type texture all the original chromite grains fully transformed to porous chromite the deformation and accompanying diffusion processes result in the formation of homogenous ferrian chromite grains in contrast in partly altered type texture chromite grains with original cores surrounded by porous chromite such processes are only restricted to the porous rims giving rise to zoned chromian spinel ferrian chromite grains

the 1995 off etorofu earthquake joint relocation of foreshocks the mainshock and aftershocks and implications for the earthquake nucleation process abstract prominent foreshock activity preceded the mw 7 9 off etorofu earthquake in the kurile islands on 3 december 1995 using a modified joint hypocenter determination method hurukawa 1995 we simultaneously relocated foreshocks the mainshock and aftershocks to study the foreshock activity in detail in view of the nucleation process of a large earthquake the distribution of relocated earthquakes and their focal mechanisms suggest that the 1995 off etorofu earthquake was an interplate earthquake at the boundary between the north american and pacific plates its source area overlaps with those of the 1958 off etorofu mw 8 3 and the 1963 off urup mw 8 5 earthquakes nine days before the occurrence of the mainshock a first immediate foreshock of magnitude 6 4 occurred at the deepest point of the foreshock area this event was followed by many foreshocks including three additional m 6 events which occurred east and southeast of the first foreshock the foreshock area expanded toward the trench axis with a velocity of several to several tens centimeters per second the number of events per day increased daily and the final size of the foreshock area was about 80 30 km eventually the rupture of the mainshock started at the deepest point of the foreshock area these observational facts are consistent with recent theoretical studies and laboratory experiments in which foreshocks are regarded as the rupture of localized asperities in a broad weak zone where the nucleation of the large earthquake started

dynamic stress changes during earthquake rupture we assess two competing dynamic interpretations that have been pro posed for the short slip durations characteristic of kinematic earthquake models de rived by inversion of earthquake waveform and geodetic data the first interpretation would require a fault constitutive relationship in which rapid dynamic restrengthen ing of the fault surface occurs after passage of the rupture front a hypothesized mechanical behavior that has been referred to as self healing the second inter pretation would require sufficient spatial heterogeneity of stress drop to permit rapid equilibration of elastic stresses with the residual dynamic friction level a condition we refer to as geometrical constraint these interpretations imply contrasting pre dictions for the time dependence of the fault plane shear stresses we compare these predictions with dynamic shear stress changes for the 1992 landers m 7 3 1994 northridge m 6 7 and 1995 kobe m 6 9 earthquakes stress changes are com puted from kinematic slip models of these earthquakes using a finite difference method for each event static stress drop is highly variable spatially with high stress drop patches embedded in a background of low and largely negative stress drop the time histories of stress change show predominantly monotonic stress change after passage of the rupture front settling to a residual level without significant evidence for dynamic restrengthening the stress change at the rupture front is usu ally gradual rather than abrupt probably reflecting the limited resolution inherent in the underlying kinematic inversions on the basis of this analysis as well as recent similar results obtained independently for the kobe and morgan hill earthquakes we conclude that at the present time the self healing hypothesis is unnecessary to explain earthquake kinematics

nucleation of stick slip instability within a large scale experimental fault effects of stress heterogeneities due to loading and gouge layer compaction geodetic observations and large scale laboratory experiments show that seismic instability is preceded by slow slip within a finite nucleation zone in laboratory experiments rupture nucleation is studied mostly using bare rock interfaces whereas upper crustal faults are typically filled with gouge to investigate effects of gouge on rupture nucleation we performed a biaxial shearing experiment on a 350 mm long saw cut fault filled with gypsum gouge at room temperature and a minimum horizontal stress 2 0 3 5 mpa the gouge layer was sandwiched between polymethylmethacrylate pmma plates for reference also a fault without gouge was deformed strain gauges and digital image correlation were used to monitor the deformation field along the fault zone margins stick slip behavior occurred on both the gouge filled fault and the pmma fault nucleation of instability on the pmma fault persistently occurred from one location 2 3 to 3 4 along the fault adjacent to a slow slip zone at the fault end but nucleation on the gouge filled fault was more variable nucleating at the ends and or at approximately 2 3 along the fault with precursory slip occurring over a large fraction of the fault nucleation correlated to regions of high average fault stress ratio n which was more variable for the gouge filled fault due to small length scale variations in normal stress caused by heterogeneous gouge compaction rupture velocities and slip rates were lower for the gouge filled fault than for the bare pmma fault stick slip persisted when 2 was lowered and the nucleation zone length increased expanding from the center to the sample ends before transitioning into instability

dynamic high speed rupture from the onset of the 2004 parkfield california earthquake 1 we investigated the 2004 parkfield earthquake using a multiscale slip inversion the multiscale approach allows us to both focus on the details of the early stages of the rupture process and to model the entire earthquake at a larger scale our model indicates that the parkfield earthquake began with bilateral high speed rupture with fast slip rate up to 4 m s and fast propagation velocity of about 3 0 km s rupture propagation to the southeast was arrested 3 s after onset while propagation to the northwest continued generated a large slip patch at 5 s and ceased within 10 s a similar rapid initiation was observed for the 2004 mid niigata prefecture japan earthquake in a previous study high speed initial rupture suggests that large earthquakes may initiate and grow in the same way as small earthquakes and that the final size is difficult to predict from the early stages of an earthquake

effects of physical fault properties on frictional instabilities produced on simulated faults laboratory studies of large scale simulated faults show that physical properties of the fault specifically normal stress and fault roughness significantly influence the unstable shear failure behavior of the fault in addition the experiments provide insights into important length scaling effects that are useful for assessing concepts such as critical crack length or rupture nucleation dimension stick slip shear failures have been generated along a 2 m long simulated fault in a block of sierra white granite experiments were conducted at normal stresses between 0 6 and 4 mpa with two different prepared roughnesses of the simulated fault a smooth fault with a profilometer measured roughness of 0 2 m and a rough fault with a measured roughness of 80 m high speed records of shear strains and slip velocities clearly show both the propagation of the stick slip failures and details of the local deformations and motions from which slip weakening of the fault at the onset of sliding can be resolved both the dynamic stress drops of the stick slip events and the apparent fracture energies of the events determined from the records of the fault slip weakening increase with increasing normal stress although critical slip weakening displacements are insensitive to normal stress they increase with increased fault roughness such that the apparent fracture energies are also larger on the rough fault than on the smooth fault slip velocities in these experiments are influenced by roughness and are proportional to stress drop although the onset of slip is sharply defined the termination of slip is more gradual without a clear stopping phase measured rupture velocities on the rough fault are lower than those on the smooth fault when a length scale based on rupture nucleation dimensions directly proportional to critical displacements is introduced the data suggest that at fault lengths close to the nucleation lengths rupture velocity and slip velocity increase with increasing fault length

observations of premonitory acoustic emission and slip nucleation during a stick slip experiment in smooth faulted westerly granite 1 to investigate laboratory earthquakes stick slip events were induced on a saw cut westerly granite sample by triaxial loading at 150 mpa confining pressure acoustic emissions ae were monitored using an innovative continuous waveform recorder the first motion of each stick slip was recorded as a large amplitude ae signal these events source locate onto the saw cut fault plane implying that they represent the nucleation sites of the dynamic failure stick slip events the precise location of nucleation varied between events and was probably controlled by heterogeneity of stress or surface conditions on the fault the initial nucleation diameter of each dynamic instability was inferred to be less than 3 mm a small number of ae were recorded prior to each macro slip event for the second and third slip events premonitory ae source mechanisms mimic the large scale fault plane geometry

earthquake nucleation size evidence of loading rate dependence in laboratory faults recent gps observations of major earthquakes such as the 2014 chile megathrust show a slow pre slip phase releasing a significant portion of the total moment ruiz et al 2014 despite advances from theoretical stability analysis rubin ampuero 2005 ruina 1983 and modeling kaneko carpenter nielsen 2017 it is not fully understood what controls the prevalence and the amount of slip in the nucleation process here we present laboratory observations of slow slip preceding dynamic rupture where we observe a dependence of nucleation size and position on the loading rate laboratory equivalent of tectonic loading rate the setup is composed of two polycarbonate plates under direct shear with a 30 centimeters long slip interface the results of our laboratory experiments are in agreement with the pre slip model outlined by ellsworth and beroza 1995 and observed in laboratory experiments latour schubnel nielsen madariaga vinciguerra 2013 nielsen taddeucci vinciguerra 2010 ohnaka kuwahara 1990 which show a slow slip followed by an acceleration up to dynamic rupture velocity however further complexity arises from the effect of 1 rate of shear loading and 2 inhomogeneities on the fault surface in particular we show that when the loading rate is increased from 10 2 mpa s 1 to 6 mpa s 1 the nucleation length can shrink by a factor of three and the rupture nucleates consistently on higher shear stress areas the nucleation lengths measured fall within the range of the theoretical limits lb and l derived by rubin and ampuero 2005 for rate and state friction laws

dynamic fault rupture and stress recovery processes in continental crust under depth dependent shear strength and frictional parameters abstract mikumo t 1992 dynamic fault rupture and stress recovery processes in continental crust under depth dependent shear strength and frictional parameters in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 201 222 the dynamic rupture process of large earthquakes in continental crust and the post seismic stress recovery process due to visco plastic behaviour are investigated by three and two dimensional numerical modelling taking into account the possible depth variations of the shear strength tectonic stress expected stress drop and of the critical weakening slip which are suggested by recent laboratory experiments on frictional parameters it was found that dynamic rupture can initiate at any depth in a brittle zone if high stress is concentrated with a dimensionless stress ratio s less than a certain limit but that the rupture cannot nucleate in a semi brittle zone with negative stress drop this suggests that the boundary between the fully brittle and semi brittle zones delineates the base of the seismogenic zone of background seismicity and aftershock distribution however the dynamic rupture of large earthquakes originating from the brittle zone can propagate into the semi brittle zone after some temporary arrest or with decelerated velocities which could generate low frequency seismic waves the depth extent of dynamic faulting and the maximum fault displacement are affected by the depth to the brittle semi brittle boundary and hence by the geothermal state within the crust the stress recovery due to visco plastic behaviour in the semi brittle and plastic regimes suggests that the rupture for eventual earthquakes tends to be nucleated near the upper boundary of the semi brittle zone

chromite from the swartkop chrome mine an estimate of the effects of subsolidus reequilibration chromites from the lg 3 lg 4 and lg 6 chromitite layers at the zwartkop mine are investigated and subsolidus behavior of chromite in olivine and orthopyroxene hosted environments is compared chromitite layers lg 3 and lg 6 are orthopyroxene hosted but layer lg 4 is olivine hosted with abundant orthopyroxene formed by a reaction relation between olivine and liquid chromite has reequilibrated with host silicate to a degree dependent on the nature of the host silicate and the modal amounts of chromite present in an olivine environment reequilibration between chromite and silicate proceeds to lower temperatures with consequently more iron rich chromite than in an orthopyroxene hosted chromite in a given environment the closure temperature for silicate chromite reequilibration decreases systematically as the modal amount of chromite decreases from this systematic relation the solidus temperature can be estimated and some inferences about the original chromite composition can be made in the lg 6 layer chromite compositions can be projected back to solidus compositions along a trajectory of constant activity of the mga1204 component and at the solidus temperature chromite composition within and adjacent to the chromitite layer is essentially the same the activity of mga1204 remained constant because chromite was in equilibrium with the host orthopyroxene throughout the temperature range in which reequilibration took place in layer lg 4 the activity of mga1204 increased during cooling because the solidus chromite was not in equilibrium with orthopyroxene formed by reaction between olivine and liquid because the liquid which reacted with olivine was more aluminous than the liquid from which the olivine originally crystallized subsolidus reequilibration between orthopyroxene and chromite led to an increase in the concentration of alcoa in chromite consequently the decrease in mg content of chromite during cooling is accompanied by an increase in a1 content in contrast to the more common decrease in a1 content observed in layer lg 6 which results from the higher stability of

chromite in komatiites ii modification during greenschist to mid amphibolite facies metamorphism chromite compositions in komatiites are influenced by metamorphic chromite is highly susceptible to modification during processes particularly above 500 c metamorphosed chromite is early hydrous alteration and subsequent prograde metasubstantially more iron rich than igneous precursors as a result of morphism of host rocks this modification is the subject mg fe exchange with silicates and carbonates chromite metaof this paper morphosed to amphibolite facies is enriched in zn and fe and metamorphic modification of chromite has been disdepleted in ni relative to lower metamorphic grades relative cussed extensively in the literature in the context mainly of proportions of the trivalent ions cr al and fe are not ophiolitic or alpine ultramafic complexes onyeagocha greatly modified by metamorphism up to lower amphibolite facies 1974 ulmer 1974 evans frost 1975 hoffman although minor fe depletion occurs during talc carbonate alwalker 1978 loferski lipin 1983 kimball 1990 teration at low temperature significant al is lost from chromite burkhard 1993 and in a few studies of komatiitic rocks cores above 550 c as a result of equilibration with fluids in bliss maclean 1975 donaldson 1983 gole hill equilibrium with chlorite elevated zn content in chromite is 1990 and in a detailed study of the pechenga intrusions restricted to rocks with low metamorphic mg fe ratios and is abzalov 1998 these studies have highlighted two the result of introduction of zn during low temperature alteration important effects first chromites become rimmed and with further concentration and homogenization during prograde progressively replaced by chromian magnetite or fermetamorphism cobalt and mn also behave similarly except where ritchromit second chromite core compositions become carbonate minerals are predominant in the metamorphic assemblage progressively modified during prograde metamorphism chromite at amphibolite facies is typically extensively replaced by as a result of exchange of components with surrounding magnetite this is the result of incomplete metamorphic reaction silicate minerals evans frost 1975 abzalov 1998 between chromite and chlorite bearing silicate assemblages magthis paper examines the nature and magnitude of these netite compositions at the inner chromite magnetite boundary are effects in komatiites from a variety of localities in the indicators of metamorphic grade eastern goldfields province of the archaean yilgarn block in western australia fig 1 brief locality descriptions are given in appendix b

elongated prismatic magnetite crystals in alh84001 carbonate globules potential martian magnetofossils using transmission electron microscopy tem we have analyzed magnetite fe 3o 4 crystals acid extracted from carbonate globules in martian meteorite alh84001 we studied 594 magnetites from alh84001 and grouped them into three populations on the basis of morphology 389 were irregularly shaped 164 were elongated prisms and 41 were whisker like as a possible terrestrial analog for the alh84001 elongated prisms we compared these magnetites with those produced by the terrestrial magnetotactic bacteria strain mv 1 by tem again we examined 206 magnetites recovered from strain mv 1 cells natural darwinian selection in terrestrial magnetotactic bacteria appears to have resulted in the formation of intracellular magnetite crystals having the physical and chemical properties that optimize their magnetic moment in this study we describe six properties of magnetite produced by biologically controlled mechanisms e g magnetotactic bacteria properties that collectively are not observed in any known population of inorganic magnetites these criteria can be used to distinguish one of the modes of origin for magnetites from samples with complex or unknown histories of the alh84001 magnetites that we have examined the elongated prismatic magnetite particles 27 of the total are indistinguishable from the mv 1 magnetites in five of these six characteristics observed for biogenically controlled mineralization of magnetite crystals

fracture energy of stick slip events in a large scale biaxial experiment the concept of apparent fracture energy for the shear failure process is employed by many authors in modeling earthquake sources as dynamically extending shear cracks using records of shear strain and relative displacement from stick slip events generated along a simulated prepared fault surface in a large 1 5m x 1 5m x 0 4m granite block and a slip weakening model for the fault direct estimates of the apparent shear fracture energy of the stick slip events have been obtained for events generated on a finely ground fault surface apparent fracture energy ranges from 0 06 j m sup 2 at a normal stress of 1 1 mpa to 0 8 j m sup 2 at a normal stress of 4 6 mpa in contrast to estimates for tensile crack formation we find that the apparent fracture energy of stick slip events increases linearly with normal stress the results for the slip weakening model for the stick slip events are generally consistent with constitutive fault models suggested by observations of stable sliding in smaller scale experiments

differential rates of vertical accretion and elevation change among aerial root types in micronesian mangrove forests abstract root systems in mangrove swamps have captured the attention of scientists for decades among the postulated roles of root structures include a contribution to the geomorphological stability of mangrove soils through sediment trapping and binding in this study we used feldspar marker horizons and sediment pins to investigate the influence of three different functional root types prop roots in rhizophora spp root knees in bruguiera gymnorrhiza and pneumatophores in sonneratia alba on vertical accretion and elevation change in three mangrove forests in the federated states of micronesia prop roots facilitated vertical accretion 11 0 mm year 1 more than pneumatophores or bare soil controls mean 8 3 mm year 1 sediment elevation on the other hand increased at an average rate of only 1 3 mm year 1 across all root types with rate differences by root type ranging from 0 2 to 3 4 mm year 1 being detected within river basins this investigation demonstrates that prop roots can assist in the settling of suspended sediments from estuarine waters yet prop root structures are not as successful as pneumatophores in maintaining sediment elevation over 2 5 years as root densities increase over time an increase in turbulence induced erosion and in shallow subsidence as organic peat layers form is expected in micronesian mangrove forests

microfracture processes in the breakdown zone during dynamic shear rupture inferred from laboratory observation of near fault high frequency strong motion high frequency velocities are measured during stick slip motion in the immediate vicinity of a fault in a granite sample to reveal the microscopic process taking place in the breakdown zone defined in the slip weakening model it is found that 1 the onset time of the observed strong motion approximately coincides with the local rupture onset time 2 the observed near fault high frequency strong motion duration is approximately proportional to the local breakdown time and 3 the power spectra of strong motions exhibit significant amplitudes at frequencies above the value offmax wherefmax is a cut off frequency relevant to rupturing the breakdown zone these observations suggest that the high frequency motion would be due to the incoherent brittle microfracture whose characteristic scale is much shorter than the breakdown zone size we present a stochastic fault model to synthesize the near fault high frequency velocity waveforms in the model a number of small circular subfaults are distributed randomly on the fault and the rupture onset time of an individual subfault is assumed to be random the main features of the observed velocity waveforms are well explained by this numerical modeling it is concluded that approximately half of the total energy of high frequency elastic waves observed at a point is radiated from the propagating breakdown zone we emphasize the importance of the observation of near fault high frequency strong motions for large shallow earthquakes

nucleation process of magnitude 2 repeating earthquakes on the san andreas fault predicted by rate and state fault models with safod drill core data recent laboratory shear slip experiments conducted on a nominally flat frictional interface reported the intriguing details of a two phase nucleation of stick slip motion that precedes the dynamic rupture propagation this behavior was subsequently reproduced by a physics based model incorporating laboratory derived rate and state friction laws however applying the laboratory and theoretical results to the nucleation of crustal earthquakes remains challenging due to poorly constrained physical and friction properties of fault zone rocks at seismogenic depths here we apply the same physics based model to simulate the nucleation process of crustal earthquakes using unique data acquired during the san andreas fault observatory at depth safod experiment and new and existing measurements of friction properties of safod drill core samples using this well constrained model we predict what the nucleation phase will look like for magnitude 2 repeating earthquakes on segments of the san andreas fault at a 2 8 km depth we find that despite up to three orders of magnitude difference in the physical and friction parameters and stress conditions the behavior of the modeled nucleation is qualitatively similar to that of laboratory earthquakes with the nucleation consisting of two distinct phases our results further suggest that precursory slow slip associated with the earthquake nucleation phase may be observable in the hours before the occurrence of the magnitude 2 earthquakes by strain measurements close a few hundreds meters to the hypocenter in a position reached by the existing borehole

fault structure wear mechanisms and rupture processes in pseudotachylyte generation abstract fault generated pseudotachylyte is found within both cataclastic and mylonitic host rocks suggesting that rapid catastrophic displacements have occurred at a variety of depths within paleoseismogenic zones pseudotachylyte bearing fault zones represent a composite of structural features associated with the process of earthquake rupture propagation and coseismic slip the development of multiple pseudotachylyte veins in fault linkages duplexes sidewall ripouts en echelon arrays and brittle zones suggests repeated rupturing during a series of characteristic earthquakes each earthquake as a coseismic slip event can be subdivided into initial rupture acceleration stable sliding and final deceleration stages these evolve through distinctive sequences of wear and deformation mechanisms that vary with sliding velocity duration of slip total displacement and the hydrodynamics of the developing fault zone slip is thought to proceed toward surface refinement and possible frictional melting following the propagation of leading shear fracture process zones the passage of the initial process zone of oblique fracturing would be followed by linkage to a throughgoing structure with asperity reduction through brecciation comminution and refined cataclastic flow for frictional melting in an abrasive wear dominant model at greater depths in the presence of mylonitic anisotropy slip would proceed through initial layer parallel surfaces and duplex linkages with rapid surface refinement through plastic smearing and laminar flow for frictional melting in an adhesive wear dominant model

compositional effects on the solubility of minor and trace elements in oxide spinel minerals insights from crystal crystal partition coefficients in chromite exsolution chromite from los congos and los guanacos in the eastern pampean ranges of cordoba argentinian central andes shows homogenous and exsolution textures the composition of the exsolved phases in chromite approaches the end members of spinel mgal 2 o 4 spl and magnetite fe 2 fe 2 3 o 4 mag that define the corners of the spinel prism at relatively constant cr 3 r 3 ratio where r 3 is cr al fe 3 the exsolution of these phases from the original chromite is estimated to have accounted at 600 c on the basis of the major element compositions of chromite with homogenous and exsolution textures that are in equilibrium with forsterite rich olivine fo 95 the relatively large size of the exsolved phases in chromite up to ca 200 m provided for the first time the ability to conduct in situ analysis with laser ablation inductively coupled plasma mass spectrometry for a suite of minor and trace elements to constrain their crystal crystal partition coefficient between the spinel rich and magnetite rich phases d i spl mag minor and trace elements listed in increasing order of compatibility with the spinel rich phase are ti sc ni v ge mn cu sn co ga and zn d i spl mag values span more than an order of magnitude from d ti spl mag 0 30 0 06 to d zn spl mag 5 48 0 63 our results are in remarkable agreement with data available for exsolutions of spinel rich and magnetite rich phases in other chromite from nature despite their different cr 3 r 3 ratio the estimated crystal crystal partitioning coefficients reflect the effect that crystal chemistry of the exsolved phases from chromite imposes on all investigated elements excepting cu and sc and only slightly for mn the observed preferential partitioning of ti and sc into the magnetite rich phase is consistent with high temperature chromite melt experiments and suggests a significant dependence on fe 3 substitution in the spinel structure a compositional effect of major elements on ga co and zn is observed in the exsolved phases from chromite but not in the experiments this might be due to crystal chemistry differences along the mgfe 1 al 2 fe 2 3 exchange vector which is poorly covered experimentally this inference is supported by the strong covariance of ga co and zn observed only in chromite from layered intrusions where this exchange vector is important a systematic increase of zn and co coupled with a net decrease in ga during hydrous metamorphism of chromitite bodies cannot be explained exclusively by compositional changes of major elements in the chromite which are enriched in the magnetite component the most likely explanation is that the contents of minor and trace elements in chromite from metamorphosed chromitites are controlled by interactions with metamorphic fluids involved in the formation of chlorite

earthquake nucleation on faults with rate and state dependent strength abstract dieterich j h 1992 earthquake nucleation on faults with rate and state dependent strength in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 115 134 faults with rate and state dependent constitutive properties reproduce a range of observed fault slip phenomena including spontaneous nucleation of slip instabilities at stresses above some critical stress level and recovery of strength following slip instability calculations with a plane strain fault model with spatially varying properties demonstrate that accelerating slip precedes instability and becomes localized to a fault patch the dimensions of the fault patch follow scaling relations for the minimum critical length for unstable fault slip the critical length is a function of normal stress loading conditions and constitutive parameters which include dc the characteristic slip distance if slip starts on a patch that exceeds the critical size the length of the rapidly accelerating zone tends to shrink to the characteristic size as the time of instability approaches solutions have been obtained for a uniform fixed patch model that are in good agreement with results from the plane strain model over a wide range of conditions above the steady state stress the logarithm of the time to instability linearly decreases as the initial stress increases because nucleation patch length and premonitory displacement are proportional to dc the moment of premonitory slip scales by d3c the scaling of dc is currently an open question unless dc for earthquake faults is significantly greater than that observed on laboratory faults premonitory strain arising from the nucleation process for earthquakes may by too small to detect using current observation methods excluding the possibility that dc in the nucleation zone controls the magnitude of the subsequent earthquake then the source dimensions of the smallest earthquakes in a region provide an upper limit for the size of the nucleation patch

tidal scale flow routing and sedimentation in mangrove forests combining field data and numerical modelling tidal scale biophysical interactions establish particular flow routing and sedimentation patterns in coastal mangroves sluggish water flows through the mangrove vegetation and enhanced sediment deposition are essential to maintain these valuable ecosystems thereby enabling their contribution to coastal protection and stabilization spatially explicit field observations of tidal scale flow routing and sediment deposition were obtained in an elevated mangrove stand dissected by tidal creeks located in the trang river estuary at the thai andaman coast an accurate and efficient depth averaged process based numerical model of this field site was developed in delft3d to study the contributions of various biogeophysical mangrove settings to the observed tidal dynamics and to study the impacts of changes of these environmental conditions the creeks are found to form the major pathway for the tidal inflow during the lower tides while the sheltered interior of the forest is an effective sediment sink during the higher tides a numerical sensitivity analysis of the initial response or adaptive capacity of the studied mangrove system to instantaneous environmental changes reveals the stable state of the study site deposition rates are largely imposed by the topography and relative elevation while they are rather independent of the vegetation density deeper inundations of the mangroves favor sheet flows through the forest and spatially averaged deposition rates decrease particularly when this coincides with decreasing vegetation densities moreover the sediment trapping efficiency is found to reduce significantly with diminishing sediment inputs and with mangrove area losses these results clearly indicate the sensitivity of mangroves ecosystem engineering ability in terms of sedimentation to climate change and anthropogenic threats

chrome spinels in gabbro wehrlite intrusions of the pechenga area kola peninsula russia emphasis on alteration features abstract chrome spinels are common accessory minerals of the pechenga ultramafic rocks in nw russia varying in metamorphic grade from sub greenschist to amphibolite facies magmatic chrome spinels can be grouped into two main types spinel 1 which crystallized first is represented by al ti chromite it occurs mainly as inclusions in olivine and rather less commonly enclosed within interstitial minerals spinel 2 crystallized after spinel 1 and has composition varying from ti rich chromite to ti rich chrome magnetite spinel 2 occurs in the interstitial spaces between olivine crystals and enclosed within intercumulus silicates zoned crystals with spinel 1 in the core overgrown by spinel 2 are also common cr poor titanomagnetite occurring in pyroxenites and gabbro apparently represents further evolution of spinel 2 phases metamorphic chrome spinels are represented by ferritchromit and cr magnetite which are the dominant chrome spinel phases in the amphibolite facies rocks the continuous trend of the magmatic chrome spinels composition is indicative of their intensive post cumulus alteration by reaction with evolving intercumulus liquid this reaction led to depletion of the earlier crystallized chrome spinels in mg cr and al and their enrichment in ti and fe 3 oxidation exsolution of ilmenite from ti rich chrome spinels is another common process of post crystallization alterations serpentinization of olivine led to formation of magnetite which overgrew and cut chrome spinel grains low temperature hydrothermal processes in particular talc carbonate alterations could cause a local loss of ti and further redistribution of mg mn and zn prograde metamorphic reactions led to formation of ferritchromit and magnetite replacing primary chrome spinels another common process affecting ti rich chrome spinels is a prograde metamorphic recrystallization of exsolved ilmenite which changes from submicron lamellae through a regular grid of coarse ilmenite crystals and further to their irregular blebs and rims metamorphism of epidote amphibolite and amphibolite facies has led to the liberation of most of the elements metamorphically liberated cr was captured by antigorite

scaling of the shear rupture process from nucleation to dynamic propagation implications of geometric irregularity of the rupturing surfaces a series of systematic high resolution laboratory experiments have been performed on the nucleation of propagating slip failure on preexisting faults having different surface roughnesses to demonstrate how the size scale and duration of shear rupture nucleation are affected by geometric irregularity of the rupturing surfaces on the basis of the experimental results it has been discussed theoretically how consistently scale dependent physical quantities inherent in shear rupture are scaled the experiments led to conclusive results that the nucleation process consists of two phases phase i an initial quasi static phase and phase ii a subsequent accelerating phase and that the nucleation process is greatly affected by geometric irregularities on the rupturing surfaces in phase i the rupture grows at a slow steady speed which is independent of the rupture growth length l in contrast during phase ii the rupture develops at accelerating speeds v which increase with an increase in l obeying a power law v vs l c n where vs is the shear wave velocity c is the characteristic length representing the geometric irregularity of the fault surfaces and and n are constants 8 87 10 29 and n 7 31 scale dependency of scale dependent physical quantities including the nucleation zone size and its duration is commonly ascribed to scale dependency of the slip dependent constitutive law parameter dc which is in turn governed by c it has been discussed that a unified comprehension can be provided for shear rupture of any size scale if the constitutive law for shear rupture is formulated as a slip dependent law

foreshocks during the nucleation of stick slip instability 1 we report on laboratory experiments which investigate interactions between aseismic slip stress changes and seismicity on a critically stressed fault during the nucleation of stick slip instability we monitor quasi static and dynamic changes in local shear stress and fault slip with arrays of gages deployed along a simulated strike slip fault 2 m long and 0 4 m deep in a saw cut sample of sierra white granite with 14 piezoelectric sensors we simultaneously monitor seismic signals produced during the nucleation phase and subsequent dynamic rupture we observe localized aseismic fault slip in an approximately meter sized zone in the center of the fault while the ends of the fault remain locked clusters of high frequency foreshocks mw 6 5 to 5 0 can occur in this slowly slipping zone 5 50 ms prior to the initiation of dynamic rupture their occurrence appears to be dependent on the rate at which local shear stress is applied to the fault the meter sized nucleation zone is generally consistent with theoretical estimates but source radii of the foreshocks 2 to 70 mm are 1 to 2 orders of magnitude smaller than the theoretical minimum length scale over which earthquake nucleation can occur we propose that frictional stability and the transition between seismic and aseismic slip are modulated by local stressing rate and that fault sections which would typically slip aseismically may radiate seismic waves if they are rapidly stressed fault behavior of this type may provide physical insight into the mechanics of foreshocks tremor repeating earthquake sequences and a minimum earthquake source dimension

scaling relationship of initiations for moderate to large earthquakes 1 we investigate the initiation sizes of earthquakes over a wide range of moderate to large events using the model of sato and kanamori which is based on griffith crack theory for a circular fault we estimate the initial crack sizes of earthquakes using high quality data recorded at close hypocentral distances taking into account the local attenuation and the dynamic stress drop of the earthquakes we estimate trigger factors and initial crack radii for 35 events in japan and taiwan with magnitudes of 3 5 to 7 9 our results show that all of the earthquakes can be explained with a small trigger factor and initial crack sizes of 12 96 m for the large range of earthquake sizes this is a small range of initial crack sizes there does not appear to be a clear scaling relationship between initial crack size and final earthquake size instead our results show that all the moderate to large earthquakes initiate with initial crack radii on the order of tens of meters

a window into the complexity of the dynamic rupture of the 2011 mw 9 tohoku oki earthquake the 2011 mw 9 tohoku oki earthquake recorded by over 1000 near field stations and multiple large aperture arrays is by far the best recorded earthquake in the history of seismology and provides unique opportunities to address fundamental issues in earthquake source dynamics here we conduct a high resolution array analysis based on recordings from the usarray and the european network the mutually consistent results from both arrays reveal rupture complexity with unprecedented resolution involving phases of diverse rupture speed and intermittent high frequency bursts within slow speed phases which suggests spatially heterogeneous material properties the earthquake initially propagates down dip with a slow initiation phase followed by sustained propagation at speeds of 3 km s the rupture then slows down to 1 5 km s for 60 seconds a rich sequence of bursts is generated along the down dip rim of this slow and roughly circular rupture front before the end of the slow phase an extremely fast rupture front detaches at about 5 km s towards the north finally a rupture front propagates towards the south running at about 2 5 km s for over 100 km key features of the rupture process are confirmed by the strong motion data recorded by k net and kik net the energetic high frequency radiation episodes within a slow rupture phase suggests a patchy image of the brittle ductile transition zone composed of discrete brittle asperities within a ductile matrix the high frequency is generated mainly at the down dip edge of the principal slip regions constrained by geodesy suggesting a variation along dip of the mechanical properties of the mega thrust fault or their spatial heterogeneity that affects rise time

slow and fast ruptures on a laboratory fault controlled by loading characteristics recent geodetic observations indicate that a single fault may slip slowly and silently or fast and seismically in different circumstances we report laboratory experiments that demonstrate how the mode of faulting can alternate between fast stick slip events 70 to 500 mm s sliding rates and slow silent events 0 001 to 30 mm s as a result of loading conditions rather than friction properties or stiffness of the loading machine the 760 mm long granite sample is close to the critical nucleation length scale for unstable slip so small variations in nucleation properties result in measurable differences in slip events slow events occur when instability cannot fully nucleate before reaching the sample ends dynamic events occur after long healing times or abrupt increases in loading rate which suggests that these factors shrink the spatial and temporal extents of the nucleation zone arrays of slip strain and ground motion sensors installed on the sample allow us to quantify seismic coupling and study details of premonitory slip and afterslip we find that seismic coupling decreases when slip rates fall below about 70 mm s the slow slip events we observe are primarily aseismic less than 1 of the seismic coupling of faster events and produce swarms of very small m 6 to m 8 events these mechanical and seismic interactions suggest that faults with transitional behavior where creep small earthquakes and tremor are often observed could become seismically coupled if loaded rapidly either by a slow slip front or dynamic rupture of an earthquake that nucleated elsewhere

earthquake aftereffects and triggered seismic phenomena the physical basis for delayed aftereffects of large crustal earthquakes is analyzed these effects apparently range in scale from typical aftershocks near the source region of a prior earthquake to the triggering of groundwater and deformation related anomalies possibly including other large earthquakes at locations as much as a few hundred kilometers from the source of a great earthquake observational reports of such aftereffects are reviewed and possible mechanisms for their occurrence are discussed

testing a model of earthquake nucleation abstract some laboratory models of slip find that a critical amount or velocity of slow slip is required over a nucleation patch before dynamic failure begins typically such patch sizes when extrapolated to earthquakes have been thought to be very small and the precursory slip undetectable ohnaka 1992 1993 has proposed a model in which foreshocks delineate a growing zone of quasi static slip that nucleates the dynamic rupture and suggests that it could be large enough 10 km across to be detectable and thus useful for short term earthquake prediction the 1992 landers earthquake m 7 3 had a distinctive foreshock sequence and initiated only 70 km from the strain meters at the pinon flat observatory pfo we use this earthquake to investigate the validity and usefulness of ohnaka9s model the accurate relocations of dodge et al 1995 show that the foreshock zone can be interpreted as expanding from an area of 800 m along strike by 900 m in depth to 2000 by 3200 m in the 6 5 hr before the mainshock we have calculated the deformation signals expected both at pfo and 20 km from the foreshock zone assuming either constant slip or constant stress drop on a circular patch expanding at 5 cm sec over 6 5 hr we find the slips or stress drops would have to have been implausibly high meters or kilobars to have been detectable on the strain meters at pfo slightly better limits are possible only 20 km from the source even though the distance from landers to pfo is small compared with the average spacing of strain meters in california we are unable to prove or disprove ohnaka9s model of earthquake nucleation this suggests that even if the model is valid it will not be useful for short term prediction

the petrology of some picrites from mauna loa and kilauea volcanoes hawaii the mineralogy and chemistry of picrites from mauna loa and kilauea have been investigated to evaluate for hawaiian tholeiitic picrites the contrasting genetic models which have been proposed for these mg rich volcanics namely products of direct crystallization of high mg melts 20 25 mgo or the result of accumulation of olivine phenocrysts into less mg rich melts genetic interpretations rely heavily on mg fe partitioning relations between olivines and their picrite hosts although the 100 mg mg fe2 ratios m of picrites are wide ranging m 73 6 82 9 for fe2o3 feo 0 15 with mgo as high as 27 8 the average 100 mg mg fe ratios mg of the cores of olivine phenocrysts megacrysts show only restricted compositional variation mg 87 2 89 0 successive olivine generations are progressively more fe rich olivine liquid mg fe partitioning data and the mn and ni abundances in olivine phenocrysts collectively indicate that they were precipitated by mg rich basaltic melts with 12 14 mgo spinel compositions range from liquidus magnesiochromites occurring mainly as inclusions in olivine phenocrysts to groundmass titanomagnetites which crystallized at nearsolidus temperatures the cr2o3 contents and m values of liquidus magnesiochromites suggest that their parent melts were neither mg rich picritic mgo 20 nor relatively mg poor basaltic types