high silicon self diffusion coefficient in dry forsterite silicon self diffusion coefficients dsi in dry synthetic forsterite single crystals were measured at temperatures of 1600 and 1800 k from ambient pressure up to 13 gpa using an ambient pressure furnace and kawai type multi anvil apparatus the water contents in the samples were carefully controlled at 1 g g diffusion profiles were obtained by secondary ion mass spectrometry sims in depth profiling mode small negative pressure dependence of dsi is determined with an activation volume of 1 7 0 4 cm3 mol the activation energy is found to be 410 30 kj mol logdsi values dsi in m2 s at 1600 and 1800 k at ambient pressure are determined to be 19 7 0 4 and 18 1 0 3 respectively these values are 2 4 orders of magnitude higher than those reported by jaoul et al 1981 we speculate that their low dsi might reflect the effects of a horizontal migration of the isotopically enriched thin films applied on the sample surfaces which may inhibit diffusion into the substrate during annealing our results for dsi resolve the inconsistency between dsi measured in diffusion experiments and those deduced from creep rates measured in deformation experiments

creep strength of ringwoodite measured at pressure temperature conditions of the lower part of the mantle transition zone using a deformation dia apparatus abstract creep strength of ringwoodite is important for understanding complicated patterns of the mantle convection in and around the mantle transition zone to determine the creep strength of ringwoodite we expanded pressure temperature conditions of in situ stress strain measurements in a deformation dia apparatus combined with synchrotron x ray to those of the lower part of the mantle transition zone the expansion of the pressure temperature conditions was made by shrinking anvil truncation to 2 0 mm and the development of a cell assembly for in situ deformation experiments up to 1700 k utilizing the developed technique creep strength measurements on polycrystalline ringwoodite were performed at 16 9 18 0 gpa and 1300 1700 k during axial deformation with strain rates of 1 48 3 59 10 5 s 1 to strains of 13 2 24 9 based on mechanical and microstructural observations we infer that ringwoodite deformed by exponential dislocation creep through the peierls mechanism at 1300 1400 k and power law dislocation creep at 1500 1700 k the creep strength of ringwoodite is apparently lower than that of bridgmanite wadsleyite and olivine the present result implies the possibility that the lower mantle transition zone is a low viscosity layer further creep strength data of these minerals are necessary to be determined above 13 5 gpa and high temperatures to determine viscosity structure in and around the lower mantle transition zone at strain rates relevant to the mantle convection

an interpretation of the active deformation of southern taiwan based on numerical simulation and gps studies abstract the fold and thrust belt of taiwan results from oblique convergence between the eurasia and the philippine sea plate and its front structures are strongly influenced by the presence of large horsts and basins in the foreland using a 2 d numerical modelling finite element and distinct element methods we evaluate the influences on the active deformation of southern taiwan of 1 the foreland structural highs 2 the major fault zones in the belt and 3 the presence of a subduction zone to the south to constrain our models we take into account for the first time the present day velocity field of southern taiwan estimated based on new geodetic data obtained through the global positioning system gps particular attention is paid to the role of geological discontinuities through an evaluation of the presence and role of mechanical decoupling along major faults which plays an important role in the distribution of the regional and local velocity and stress patterns this particular analysis of the behaviour and influence of weak shear zones in taiwan is carried out by using for the first time the distinct element method additional 3 d distinct element modelling allows better consideration of oblique shearing such as for the longitudinal valley fault of eastern taiwan we conclude that the active velocity field and tectonic stress pattern in southwestern taiwan strongly depend on 1 the presence and shape of the peikang high 2 the presence of the major active regional discontinuities the longitudinal valley fault and the major thrusts of western taiwan and 3 the neighbouring weakness zone of the accretionary prism of the northern manila subduction zone and cannot be explained by any of these factors taken solely

fe mg interdiffusion in wadsleyite the role of pressure temperature and composition and the magnitude of jump in diffusion rates at the 410 km discontinuity abstract the limited stability range of wadsleyite seriously impedes our ability to constrain kinetic parameters e g activation energy activation volume using experiments carried out over a wide range of temperature and pressure we have carried out a new measurement to extend the experimental temperature range of the dataset of chakraborty et al chakraborty s knoche r schulze h rubie d c dobson d ross n l angel r j 1999 enhancement of cation diffusion rates across the 410 kilometer discontinuity in earth s mantle science 283 362 365 to the maximum possible limit for that experimental setup this result allows us to i obtain a better constrained value for activation energy for fe mg diffusion in wadsleyite at 15 gpa 230 kj mol and ii characterize the compositional dependence of fe mg diffusion in wadsleyite evaluation of all data available in the literature i e this study chakraborty et al 1999 farber d l williams q ryerson f j 2000 divalent cation diffusion in mg2sio4 spinel ringwoodite phase wadsleyite and olivine implications for the electrical conductivity of the mantle j geophys res 105 513 529 kubo t shimojuko a ohtani e 2004 fe mg interdiffusion rates in wadsleyite and the diffusivity jump at the 410 km discontinuity phys chem miner 31 456 464 reveals that there is a strong pressure dependence of the diffusion coefficient activation volume 14 cm3 mol the expression d m 2 s 1 24 10 6 exp 11 8 0 86 x mg exp 229 000 p 15 13 9 10 3 j mol r t is an excellent description of all experimentally measured diffusion coefficients in wadsleyite and points to consistency between the various studies from different laboratories that used different methods this expression should provide a robust basis for extrapolation of diffusion data for wadsleyite to conditions removed from the experimental ones e g for modeling processes in the interiors of cold subducting slabs moreover characterization of fo2 and water contents of wadsleyites in the current study and consideration of the pressure dependence of diffusion rates in olivines confirms that the jump in diffusion rates at the olivine wadsleyite boundary in the transition zone is at least six orders of magnitude increased water contents in wadsleyite can cause the actual enhancement kubo et al 2004 to be as much as seven orders of magnitude taken together with the observation that diffusive mixing is practically impossible in the lower mantle holzapfel c rubie d c frost d j langenhorst f 2005 fe mg interdiffusion in mg fe sio3 perovskite and lower mantle reequilibration science 309 1707 1710 has a maximum at the lithosphere asthenosphere boundary in the olivine bearing upper mantle holzapfel c chakraborty s rubie d c frost d j 2007 effect of pressure on fe mg ni and mn diffusion in fexmg1 x 2sio4 olivine phys earth planet int 162 186 198 and decreases with depth within the transition zone this work these results establish the base of the lithosphere and the top of the mantle transition zone as the key regions for mixing and erasure of chemical heterogeneities in the mantle

slab weakening during the olivine to ringwoodite transition in the mantle the strength of subducted slabs in the mantle transition zone influences the style of mantle convection intense deformation is observed particularly in relatively old subducted slabs in the deep mantle transition zone understanding the cause of this regional and depth variation in slab deformation requires constraint of the rheological properties of deep mantle materials here we report results of in situ deformation experiments during the olivine to ringwoodite phase transformation from which we infer the deformation process under the conditions of cold slabs deep in the mantle transition zone we find that newly transformed fine grained ringwoodite deforms by diffusion creep and that its strength is substantially smaller than that of coarser grained minerals but increases with time scaling analysis based on a model of transformation kinetics and grain size evolution during a phase transformation suggests that a cold slab will be made of a mixture of weak fine grained and strong coarse grained materials in the deep transition zone whereas a warm slab remains strong because of its large grain size we propose that this temperature dependence of grain size may explain extensive deformation of cold slabs in the deep transition zone but limited deformation of relatively warm slabs in relatively cold subducted slabs olivine may transform to finer grained weaker ringwoodite than in warm slabs according to deformation experiments under conditions analogous to those in the mantle transition zone and scaling analysis

the olivine spinel transformation and the rheology of subducting lithosphere during subduction relatively hot lithospheric slabs are expected to deform in a superplastic flow regime below a depth of 300 km if olivine reacts to fine grained spinel this process reduces the flow strength of such slabs below the phase boundary so that they become aseismic at about this depth in colder slabs temperatures are too low for superplastic deformation and a high flow strength and seismic activity are maintained to a depth of 600 700 km

si and o diffusion in mg fe 2sio4 wadsleyite and ringwoodite and its implications for the rheology of the mantle transition zone si and o diffusion rates on polycrystalline mg fe 2 sio 4 wadsleyite and ringwoodite have been determined at pressures between 16 and 22 gpa and temperatures between 1400 and 1600 c using a kawai type multi anvil high pressure apparatus pre synthesized polycrystalline wadsleyite or ringwoodite was used as starting materials diffusing sources of 29 si and 18 o enriched mg fe 2 sio 4 thin film were deposited on the surface of wadsleyite and ringwoodite by pulsed laser deposition the diffusion profiles were obtained using secondary ion mass spectrometry in the depth profiling mode all measured diffusion profiles were composed of volume and grain boundary diffusion regimes arrhenius relations for volume and grain boundary diffusion rates of si and o in wadsleyite and ringwoodite have been determined the results show that si is the slowest diffusing element among the major elements in both wadsleyite and ringwoodite under mantle transition zone as well as slab conditions therefore si should be the rate controlling species for high temperature creep in wadsleyite and ringwoodite comparisons with si and o diffusion rates obtained in this study and those in olivine and silicate perovskite suggest that si and o diffusion rates are enhanced at both 410 and 660 km seismic discontinuities the deformation mechanism maps constructed from si diffusion data in wadsleyite and ringwoodite suggest that the dominant deformation mechanism operating in the mantle transition zone is dislocation creep which may be the origin of the observed global seismic anisotropy under cold subduction zone conditions grain size sensitive diffusion creep becomes dominant when the grain size is reduced to less than 10 100 m below the metastable olivine wedge

2003 mw6 8 chengkung earthquake and its related seismogenic structures abstract the mw 6 8 chengkung earthquake on december 10 2003 in eastern taiwan was associated with abundant aftershocks to explore the seismogenic mechanism and its causative fault system we relocated the aftershocks determined the focal mechanisms from p wave polarities and used the finite dimension source model method to identify the fault plane based on our results the earthquake can be divided into three seismic clusters one is located in the east of the southern longitudinal valley one on the chihshang fault and the other on the western side of the luyeh fault to the south both the seismic distribution and finite dimension source model method show that east dipping fault planes with thrust mechanisms coincide with previous studies based on background seismicity the third seismic cluster suggests thrust mechanism along west dipping fault plane that was not recognized by background seismicity this seismic cluster occurred along the central range fault previously proposed as active by geomorphic and geologic evidence

growth kinetics of forsterite reaction rims at high pressure abstract growth kinetics of forsterite fo reaction rims between periclase per and enstatite en were studied experimentally at pressure p and temperature t conditions of 3 0 11 1 gpa and 1473 1873 k respectively pt markers originally placed at the per en interface were always observed at the per fo interface which indicates that mg and o are the diffusing species in fo rim growth mg o coupled diffusion the presence of some en inclusions in fo grains and the growth rate of the fo rim suggests that grain boundary diffusion is dominant rather than lattice diffusion considering the very fast grain boundary diffusion of o in olivine the mg o coupled grain boundary diffusion in fo is deduced to be rate limited by the diffusivity of mg based on an analysis of data collected under dry conditions the product of the mg grain boundary diffusion coefficient d gb and the effective grain boundary width was determined to be d gb d gb 0 exp e pv rt with d gb 0 10 9 68 1 51 m 3 s e 379 44 kj mol and v 1 9 1 4 cm 3 mol our results combined with previously reported data on mg lattice diffusion in fo suggest that for mg the significance of grain boundary diffusion increases with depth in the earth s upper mantle although lattice diffusion is still dominant for typical mantle grain sizes of 1 10 mm

seismogenic structure in a tectonic suture zone with new constraints from 2006 mw6 1 taitung earthquake 1 a mw 6 1 earthquake occurred on april 1st 2006 near taitung eastern taiwan it produced significant coseismic ground displacements and a large number of aftershocks in the ensuing month this event provides an opportunity to diagnose the seismogenic structure in the southern longitudinal valley lv of eastern taiwan long viewed as one of the collision sutures between the philippine sea and the eurasian plates with precisely relocated main and aftershock hypocenters focal mechanisms for m 3 8 events and coseismic ground displacements from strong motion records we determine a main shock dislocation model our results indicate that the main shock occurred on a high angle fault azimuth 198 dip 77 the model comprises a fault with two segments the main shock and a large number of aftershocks are associated with the northern segment that exhibited predominantly left lateral strike slip motion in agreement with p wave first motions and waveform usgs solutions the southern segment exhibits a slightly larger thrust component in agreement with cmt solutions tectonically this event highlights a nne trending fault on the west side of the lv which is predominantly strike slip the aftershocks clustered to the east of the main shock which exhibit mainly thrust mechanisms indicate that shortening is still acting on the sedimentary materials deposited between the coastal and central ranges prior to collision as a result the southern lv is undergoing slip partitioning along different faults which has never been specified before

plastic deformation experiments to high strain on mantle transition zone minerals wadsleyite and ringwoodite in the rotational drickamer apparatus we report the results of plastic deformation experiments on polycrystalline wadsleyite and ringwoodite performed at 15 23 gpa and 1300 2100 k conducted using the rotational drickamer apparatus rda wadsleyite was synthesized from fine grained 2 mm san carlos olivine in a kawai type multianvil apparatus the average grain size of the resulting wadsleyite was 1 2 mm the initial water content of the undeformed wadsleyite was 24 000 26 000 h 10 6 si but the final water content is variable and less than the initial water content ringwoodite was synthesized from wadsleyite in situ in the rda both strain and stress were measured in situ using a synchrotron x ray facility determinations of strains and strain rates were made from x ray radiographs of the sample using a mo foil strain marker in the sample assembly the state of stress was determined from the observed d spacing of multiple lattice planes as a function of azimuth angle samples were deformed at various strain rates at around 10 4 10 5 s 1 deformation mechanisms were inferred from the stress exponent and the microstructures we determined the stress exponent n for wadsleyite to be 673 suggesting dislocation creep was the dominant deformation mechanism in wadsleyite at grain sizes of 1 mm our samples were still deforming primarily by dislocation creep however small dislocation free grains are also observed suggesting that diffusion creep may operate in some parts of our samples 2012 published by elsevier b v

seismogenic patterns in the taiwan region insights from source parameter inversion of bats data abstract we systematically invert source parameters of 96 earthquakes that occurred in the taiwan region between july 1995 and june 1998 using waveforms recorded by the newly established broadband array in taiwan for seismology bats the results are utilized to delineate the seismogenic patterns associated with the regional tectonic processes between the eurasia and philippine sea plates in general high seismicity is observed at five locations including the nan ao basin 24 n 122 4 e near the hualien area 24 2 n 121 7 e east of the longitudinal valley and within the philippine sea plate the forearc region to the west of lanshu and the okinawa trough events with focal depths less than 25 km scatter across a wide region from the taiwan strait to the ryukyu and luzon arcs whereas events between 25 and 50 km concentrate offshore east of taiwan most earthquakes that occurred beneath the nan ao basin are consistent with the northward subduction of the philippine sea plate along the plate interface events offshore east of the longitudinal valley and within the philippine sea plate are dominated by a compressional regime along the nw nww directions whereas the lanshu lutao forearc is characterized by e w compression normal faults showing n s extension are observed in the okinawa trough where we observed a successive rotation of t axes from n s to nw se as the epicenters approach taiwan indicating a possible interaction between the extensional and compressional strain regimes there most events between 50 and 65 km depth within the subducted philippine sea plate beneath ryukyu are in downdip extension with lateral compression approximately parallel to the strike of the slab the depth where the state of strain switches from downdip extension to downdip compression is constrained at 110 125 km for the southernmost ryukyu slab based on our results we propose that the subducted philippine sea plate beneath ne taiwan plays a significant role in the overall orogenic process of taiwan the lithospheric collision in taiwan should consist of two major components one is the well recognized arc continent collision that dominates the central and southern taiwan and another the slab continent collision that reigns in northern taiwan a cluster of earthquakes near hualien suggests that an incipient west or northwestward subduction of the philippine sea plate is currently taking place there alternatively they can be interpreted to suggest that the steeply east dipping longitudinal valley fault may have transformed near hualien into a diffuse thrust zone which eventually connects itself to the plate interplate beneath the southernmost ryukyu arc earthquakes beneath taiwan and the taiwan strait are compatible with the overall collision convergence and lateral extrusion nonetheless the lateral extrusion is probably only a secondary feature in the tectonic processes of taiwan

seismogenic faults along the major suture of the plate boundary deduced by dislocation modeling of coseismic displacements of the 1951 m7 3 hualien taitung earthquake sequence in eastern taiwan abstract research at plate boundaries generally focuses on the kinematics of plate motions the genesis of large earthquake and natural resources however often the present state of knowledge is still insufficient to reveal the details of such dynamic systems to define in more detail the dynamics of a major plate boundary fault the coastal range fault eastern taiwan we use seismologic and geodetic data to unravel its subsurface geometry and relevant fault behavior by recomputing the archive triangulation datasets 1917 1978 and using a dislocation algorithm we determine that it consists of three segments our model results are consistent with the observation of the 1951 m7 3 hualien taitung earthquake sequence that the southern two segments are both oblique slip faults with significant thrust components while the northern segment is a pure strike slip fault according to our model each segment has the potential to produce an earthquake larger than m7 however based on gps observations and seismic records slip on the southern segment may take the form of aseismic creep and multiple moderate earthquakes rather than large events with long recurrence interval as occur on the two more northerly segments with regard to the central segment the epicenter distribution of catalogued earthquakes occurring after 1951 reveals the presence of a seismic gap indicating that slip on this segment is predominantly coseismic with a correspondingly higher potential for large earthquakes in the future

re evaluation of the surface ruptures of the november 1951 earthquake series in eastern taiwan and its neotectonic implications the earthquakes of november 1951 constitute the most destructive seismic episode in the recorded history of the longitudinal valley eastern taiwan however information about their source parameters is sparse to understand the relationship between the 1951 ruptures and new interpretations of the regional neotectonic architecture of the longitudinal valley we re evaluated the november 1951 ruptures by analyzing old documents reports and photographs and by interviewing local residents who experienced the earthquake as a result we have revised significantly the rupture map previously published we divide the surface ruptures from south to north into the chihshang yuli and rueisuei sections the first shock of the 1951 series probably resulted from the chihshang rupture and the second shock probably resulted from the yuli and rueisuei ruptures the lengths of these ruptures indicate that the two shocks had similar magnitudes the chihshang and rueisuei ruptures are along segments of the longitudinal valley fault a left lateral oblique fault along which the coastal range thrusts westward over the longitudinal valley the yuli rupture on the other hand appears to be part of a separate left lateral strike slip yuli fault which traverses the middle of the longitudinal valley the complex behavior of these structures and interaction between them are important in understanding the future seismic hazard of the area

deformation across the mantle transition zone a theoretical mineral physics view abstract the dynamics of the earth s mantle is still poorly constrained due to the lack of understanding the transfer of matter between the upper and the lower mantle and their convective vigor the transition zone tz might play a crucial role as the interface connecting the upper to the lower mantle here we examine the rheology of the main tz minerals wadsleyite ringwoodite and majorite garnet based on a mineral physics approach using the results of lattice friction modeling and dislocation glide mobilities together with the available data on self diffusion in the tz minerals we quantify their plastic deformation by diffusion and dislocation creep from theoretical plasticity models we show that pure climb creep is expected to contribute to the plasticity of the tz without the need of significant diffusion related hydrolytic weakening matching well the geophysical observations our model results predict that crystallographic preferred orientations cpo might only develop along with stress concentrations as present around cold subducting slabs which can be locally weaker than the surrounding tz despite their lower temperatures

coupled effects of phase transitions and rheology in 2 d dynamical models of subduction author s arredondo km billen mi abstract 2017 american geophysical union all rights reserved observations of seismicity and seismic tomography provide a present day constraint on the geometry of slabs within the mantle however it is challenging to directly relate the observed shape of slabs to their time evolution phase transitions modify the buoyancy forces within slabs affecting how slabs deform as they sink into the lower mantle and how forces are transmitted to the surface plates here we show that if the crustal shear zone is sufficiently weak 1020 pa s then the coupled effects of a compositionally dependent phase transition model and a stress dependent rheology lead to oscillatory plate speeds and trench motion in response to buckling and folding of the slab on average subducting plate velocity is 4 cm yr and trench motion is 0 7 cm yr however during folding subducting plate speed and trench motion increases by a factor of 3 and trench motion switches from advance to retreat in models with a higher viscosity shear zone 1021 pa s average plate speed is lower 2 cm yr and there is only trench advance stress dependent weakening due to increasing driving stresses can also cause unexpected changes in plate velocity i e decrease or no change in addition due to the added negative buoyancy from the phase transitions slab breakoff occurs in models with a yield stress 500 mpa because of the oscillatory motion of the trench long flat slabs do not form in the transition zone this suggests that other factors such as interaction of the slab with deep mantle flow may be required to create long flat slabs

numerical modelling of entrainment deposition in rock and debris avalanches abstract rock and debris avalanches as well as debris flows are characterized by peculiar behaviour influenced by geometry of the initial failure surface topography involved materials involved and water content during their motion rock avalanches can entrain large volumes of sediments both in a dry and in a saturated state entrained dry material has generally the consequence to reduce the total landslide runout whereas entrainment of almost saturated material can have more complex consequences we use a finite element code to simulate the motion of a moving landslide mass on materials with different properties and along very sharp topographies erosion and deposition can be modelled as well as interaction with obstacles of different characteristics we present two examples of the modelling problems and capabilities we simulated the runout of a rock avalanche on a ground formed by alluvial material under dry and saturated conditions this material can be entrained and plowed by the impacting and running rock avalanche material sensitivity of the erosion and transport mechanisms has been analysed by performing different analyses the simulated case study is the 6 10 5 m 3 arvel rock avalanche 1922 switzerland for which a reliable set of pre and post failure observations is available final geometry mass redistribution velocities and runup are used to validate the model capabilities and study the effects of different material properties

grain size evolution in subducted oceanic lithosphere associated with the olivine spinel transformation and its effects on rheology we investigate the role of grain size reduction during the olivine spinel transformation on rheological properties of subducting slabs on the basis of a scaling model for microstructural development during nucleation and growth in this model the size of spinel grains nucleating at olivine grain boundaries is controlled by the relative rates of nucleation and growth taking into account the impingement through the collision of grains due to growth when the volume fraction of spinel reaches a certain threshold value critical volume fraction 1 10 depending on the p t conditions in the slab the new phase will form a continuous film and will significantly reduce the strength of the two phase aggregate if spinel grain size is small the size of spinel grains d at this stage is calculated and is shown to be highly sensitive to 0 size and 2 a subducting slab has a complicated rheological structure containing a weak region below the tip of a metastable olivine bearing wedge in a cold slab possible implications of these anomalous rheological structures of slabs on the dynamics of subduction are discussed including the mechanisms of deep earthquakes

effects of pressure and temperature on the silicon diffusivity of pyrope rich garnet abstract we have determined the pressure and temperature dependencies of si volume diffusion rates in a single crystal of pyp75alm15gr10 garnet at 6 25 gpa and 1400 1800 c by the 29si tracer diffusion method high pressure experiments were conducted using the kawai type multi anvil high pressure apparatus diffusion profiles were obtained using secondary ion mass spectrometry in the depth profiling mode the si diffusion coefficient in garnet dgt is expressed by the arrhenius equation dgt d0 exp e pv rt with log10d0 7 1 1 7 m2 s e 345 56 kj mol and v 4 7 0 5 cm3 mol si diffusion seems to be the slowest in the major constituent elements in a pyrope rich garnet and control rates of plastic deformation the comparison between si diffusion rates in garnet and wadsleyite ringwoodite suggests that garnet has similar or slightly lower strength at most 2 times compared with wadsleyite and has similar or slightly higher strength at most 3 times compared with ringwoodite at temperatures ranging from 900 to 1300 c thus strength contrast between subducted oceanic crust and underlying peridotite layer may be small at the mantle transition zone conditions this result suggests that the separation of subducted oceanic crust from an underlying peridotite layer may not occur

evolution of grain sizes and orientations during phase transitions in hydrous mg2sio4 transformation microstructures in mantle minerals such as mg fe 2sio4 are critical for predicting the rheological properties of rocks and the interpretation of seismic observations we present in situ multi grain x ray diffraction experiments on hydrous mg2sio4 at the p t conditions relevant for deep cold subducting slabs up to 40 gpa and 850 c at a low experimental strain rate 4 10 6s 1 we monitor the orientations of hundreds of grains and grain size variations during the series of forsterite wadsleyite ringwoodite phase transformations microtextural results indicate that the and an intermediate phase grow incoherently relatively to the host phase consistent with a nucleation and growth model the and phase exhibit orientation relationships which are in agreement with previous ex situ observations the and intermediate show texturing due to moderate differential stress in the sample both the and transformation induce significant reductions of the mean sample grain size of up to 90 that starts prior to the appearance of the daughter phase apart from the in the newly formed and phases the nucleation rate is faster than the growth rate inhibiting the formation of large grains these results on grain orientations and grain size reductions in relation to transformation kinetics should allow refining existing slab strength models

some mineral physics constraints on the rheology and geothermal structure of earth s lower mantle we explore the implications of recent mineral physics measurements of diffusion coefficients and melting temperatures of lower mantle materials on the rheological and geothermal structure of earth s lower mantle we show that mgsio3 perovskite is significantly stronger than mgo periclase and therefore the rheology of the lower mantle depends strongly on the geometry of a weaker phase periclase we calculate viscosities of the lower mantle for two cases 1 where periclase occurs as isolated grains and 2 where periclase occurs as continuous films using mineral physics data and models of two phase rheology we find that the effective viscosity for the former is about 10 1000 times higher than the latter we therefore suggest that the rheology of the lower mantle is structure and hence strain dependent leading to weakening at large strains due to the formation of continuous films of periclase overall depth variation of viscosity depends not only on the pressure dependence of creep but also on the geothermal gradient both mgsio3 perovskite and periclase have relatively small activation energies e g r t m with g 10 14 where r is the gas constant and t m is melting temperature and therefore the depth variation of viscosity is rather small even for a nearly adiabatic temperature gradient however the geothermal gradients consistent with the geodynamical inference of nearly depth independent viscosity are sensitive to the pressure dependence of viscosity which is only poorly understood a superadiabatic gradient of up to 0 6 k km is also consistent with mineral physics and geodynamical observations

non traditional and emerging methods for characterizing diffusion in minerals and mineral aggregates the data summarized in this rimg volume reflect the growing interest among geoscientists in the characterization of atomic transport in natural materials interest in diffusion dates back to the early 20th century e g bowen 1921 but the need for constraints on mobility of atoms became especially important in the 1950s and 60s with our increasing reliance upon radioactive decay for determination of mineral and rock ages the question of decay product retention in relevant phases became vitally important with a few notable exceptions however experimental geoscientists did not take up the cause of diffusion in solids until the 1970s and 80s by that time the motivation for acquiring diffusion data had spread to many areas of petrology mineralogy and geochemistry and experimental techniques began to blossom the result is very much in evidence in this volume all experiments aimed at measuring a diffusion coefficient have two things in common a technique to introduce the diffusant of interest to the sample and a method to determine the extent of diffusion traditionally diffusion experiments are designed to take advantage of an existing solution to the non steady state diffusion equation and experiments are conducted in such a way as to reproduce as well as possible the boundary conditions specified for the solution for ease of analysis and interpretation most experiments are set up to limit diffusion to just one dimension most researchers have further settled on one of three general experiment designs 1 the interdiffusion couple 2 the thin film geometry or 3 the constant surface concentration design fig 1 noble gas geochemists including those interested in k ar ar ar and u th he dating methods have exploited 3 d variants of this last approach by conducting bulk degassing studies of minerals in which radiogenic noble gases have accumulated over time in the natural environment baxter 2010

seismological and experimental constraints on metastable phase transformations and rheology of the mariana slab abstract a wedge with a low seismic wave velocity implying the presence of metastable olivine and the depression of the 660 km seismic discontinuity have been observed inside the mariana slab based on these seismic observations and numerical calculation of thermal structures of the slab we suggest that the phase transformations from olivine to ringwoodite and from ringwoodite to perovskite ferropericlase the post spinel transformation occur at the depth of 630 km and 550 c and at 690 km and 700 c respectively in the central coldest part of the mariana slab combining this information with recent experimental kinetic data we constrain the details of non equilibrium phase transformations and rheology of the mariana slab the observed depth of the metastable olivine inside the mariana slab can be explained by growth controlled olivine ringwoodite transformation under relatively dry condition such as the water content of about 150 wt ppm h2o on the other hand nucleation process controls the depth of the post spinel transformation in the mariana slab and therefore the observed depressions of the 660 km discontinuity should depend on both the overpressure needed for the nucleation and the negative clapeyron slope for the transformation when the overpressure for the nucleation is 0 5 gpa the observed depressions can be explained by the clapeyron slope of 0 7 mpa k grain size evolution and viscosity structures in the mariana slab are estimated based on these metastable phase transformations the slab weakening due to the grain size reduction is limited in about 40 km in width below the metastable olivine wedge at the depths from 630 to 690 km whereas the width of the weakened portion of the slab increases to more than 120 km at deeper than the 690 km depth after the post spinel transformation these viscosity structures are consistent with the behaviors of the mariana slab estimated from seismic tomography the slab vertically descends to the bottom of the transition zone and substantially deforms and thickens at the top of the lower mantle

global azimuthal anisotropy in the transition zone surface wave dispersion measurements for love wave overtones carry evidence of azimuthal anisotropy in the transition zone of earth s mantle 400 to 660 kilometers deep a backus gilbert inversion of anisotropic phase velocity maps with resolution kernels mainly sensitive to the transition zone shows a robust long wavelength azimuthally anisotropic velocity structure this observation puts new constraints on the mineralogy and dynamics of the transition zone because this anisotropy may result from aligned minerals tilted laminated structures or even organized pockets of fluid inclusions

crust mantle boundaries in the taiwan luzon arc continent collision system determined from local earthquake tomography and 1d models implications for the mode of subduction polarity reversal abstract in order to better understand the mode of subduction polarity reversal in the taiwan luzon arc continent collision zone we mapped its crust mantle boundaries using local earthquake tomography by contouring surfaces of constant vp 7 5 km s 1 we identified three moho discontinuities and the plate interface that juxtaposes eurasian lower crust against mantle lithosphere of the philippine sea plate the plate interface dips to the east under southeastern taiwan and steepens progressively towards north until it becomes vertical at 23 7 n from there it continues northward in a vertical orientation until the limit of the tomographic model inhibited further mapping for the moho additional depth constraints were derived from 1d models using p wave arrivals of local earthquakes the mohos of the eurasian and philippine sea plates are disconnected across the plate interface beneath southern taiwan the eurasian moho dips to the east at 50 60 following the orientation of the plate boundary and continuous with the benioff zone towards north the eurasian moho steepens into subvertical again together with the plate boundary the philippine sea plate moho exhibits a synform like crustal root interpreted as the base of the magmatic luzon arc towards the north this root deepens from 30 to 70 km underneath the ryukyu trench in northernmost taiwan the hinge of the vertically subducting eurasian slab steps westward out of the thrust belt leaving the deformation front to the east inactive and giving way to the north dipping philippine sea plate a subhorizontal moho at 30 35 km depth overlies the north dipping philippine sea slab and is interpreted as a newly formed moho established after westward rollback and delamination of the subducting eurasian slab in combination these data support a model of progressive subduction polarity reversal in which a tear within the eurasian lithosphere propagated southwestward deactivating the deformation front

coseismic deformation revealed by inversion of strong motion and gps data the 2003 chengkung earthquake in eastern taiwan summary a moderate earthquake of mw 6 8 occurred on 2003 december 10 it ruptured the chihshang fault in eastern taiwan which is the most active segment of the longitudinal fault as a plate suture fault between the luzon arc of the philippine sea plate and the eurasian plate the largest coseismic displacements were 13 cm horizontal and 26 cm vertical we analyse 40 strong motion and 91 gps data to model the fault geometry and coseismic dislocations the most realistic shape of the chihshang fault surface is listric in type the dipping angle of the seismic zone is steep about 60 70 at depths shallower than 10 km and then gradually decreases to 40 50 at depths of 20 30 km thus the polygonal elements in poly3d are well suited for modelling complex surfaces with curving boundaries using the strong motion data the displacement reaches 1 2 m dip slip on the chihshang fault and decreases to 0 1 m near surface the slip averages 0 34 m releasing a scalar moment of 1 6e26 dyne cm for gps data our model reveals that the maximal dislocation is 1 8 m dip slip the dislocations decrease to 0 1 m near the surface the average slip is 0 48 m giving a scalar moment of 2 2e26 dyne cm regarding post seismic deformation a displacements of 0 5 m were observed near the chihshang fault indicating the strain had not been totally released as a probable result of near surface locking of the fault zone

silicon and oxygen self diffusion in stishovite implications for stability of sio2 rich seismic reflectors in the mid mantle abstract diffusion of si and o in single crystal stishovite was examined at pressures of 14 0 21 5 gpa and temperatures of 1673 2073 k self diffusion coefficients of si dsi and o d o were determined as dsi m 2 s 2 4 10 12 exp 237 kj mol 6 0 cm 3 mol p r t and d o m 2 s 7 2 10 11 exp 263 kj mol 4 8 cm 3 mol p r t respectively where p is pressure in gpa t is absolute temperature in k and r is the ideal gas constant it was revealed that diffusion of si is approximately one order of magnitude slower than that of o and thus si is the rate controlling element for plastic deformation of stishovite si diffusion in stishovite is assessed to be at least three orders of magnitude slower than that in bridgmanite under mid mantle conditions therefore it is anticipated that highly viscous sio2 rich components subducted into the lower mantle persist as the seismic reflectors for long term without mixing up with the bridgmanite dominated surrounding mantle

structure and holocene evolution of an active creeping thrust fault the chihshang fault at chinyuan taiwan abstract we conducted a variety of measurements and analyses at chihshang active fault observatory in eastern taiwan including surface rupture mapping three shallow borehole core analysis and kinematic analysis of geodetic measurements we found that the chihshang fault exhibits a three branch fault system in the chinyuan alluvial fan which is composed of at least 100 m thick gravel deposits outside of the chinyuan river the chihshang fault shows a single fault system with a sharp lithological contact combining the leveling results and trench excavation we interpret that the three fault branches are coupled with a 50 60 m wide pop up structure in the hangingwall based on the ratio between vertical and horizontal displacements we obtained dip angles of 38 62 and 16 for two west vergent thrusts and an east vergent backthrust respectively this pop up was estimated to develop at the uppermost 30 40 m unconsolidated gravels during the last few thousand years above the main fault with a dip angle of 42 by compiling the available ages data we obtained an uplift rate of 2 3 cm yr of the chihshang fault and an alluvial sedimentation rate of 1 1 cm yr during the past thousands years consequently the individual uplift rate for each fault branch at the chihshang observatory was slightly less than the deposition rate of the chinyuan river no geomorphic fault scarp can thus be observed in the three branch fault system area

tectonic erosion and the removal of forearc lithosphere during arc continent collision evidence from recent earthquake sequences and tomography results in eastern taiwan a very common but important observation of collided and accreted volcanic arcs is that the forearc regions of these arcs are largely or even entirely missing the processes and mechanisms responsible for the removal and transport of the forearc materials from the collisional belts are thus important issues in understanding tectonics and crustal growth the young and ongoing collision between the luzon volcanic arc and the eurasian continental margin that forms the island of taiwan provides a rare opportunity to examine these processes and mechanisms as they occur from observations of a new detailed 3 d tomography combined with relocated hypocenters of two earthquake sequences occurred in 2003 and 2006 we found that the luzon forearc lithosphere initially underthrusts westward after the collision began as the collision proceeds the forearc basement then subducts eastward beneath the colliding and accreting luzon arc along a major fault system in eastern taiwan thus the luzon forearc lithosphere appears to be removed by tectonic erosion and is being transported eastward into the mantle our results from the active taiwan orogen will provide important insights for interpreting rock records from many old arc continent collisional belts in the world

subsurface imaging taiger experiments and tectonic models of taiwan abstract the seismicity deformation rates and associated erosion in the taiwan region clearly demonstrate that plate tectonic and orogenic activities are at a high level major geologic units can be neatly placed in the plate tectonic context albeit critical mapping in specific areas is still needed but the key processes involved in the building of the island remain under discussion of the two plates in the vicinity of taiwan the philippine sea plate psp is oceanic in its origin while the eurasian plate eup is comprised partly of the asian continental lithosphere and partly of the transitional lithosphere of the south china sea basin it is unanimously agreed that the collision of psp and eu is the cause of the taiwan orogeny but several models of the underlying geological processes have been proposed each with its own evolutionary history and implied subsurface tectonics taiger taiwan integrated geodynamics research crustal and mantle imaging experiments recently made possible a new round of testing and elucidation the new seismic tomography resolved structures under and offshore of taiwan to a depth of about 200 km in the upper mantle the steeply east dipping high velocity anomalies from southern to central taiwan are clear but only the extreme southern part is associated with seismicity toward the north the seismicity disappears the crustal root under the central range is strongly asymmetrical using 7 5 km s as a guide the steep west dipping face on the east stands in sharp contrast to a gradual east dipping face on the west a smaller root exists under the coastal range or slightly to the east of it between these two roots lies a well delineated high velocity rise spanning the length from hualien to taitung the 3 d variations in crustal and mantle structures parallel to the trend of the island are closely correlated with the plate tectonic framework of taiwan the crust is thickest in the central taiwan collision zone and although it thins toward the south the crust is over 30 km thick over the subduction in the south in northern taiwan the northward subducting psp collides with taiwan and the crust thins under northern taiwan where the subducting indenter reaches 50 km in depth the low vp vs ratio of around 1 6 at a mid crustal depth of 25 km in the central range indicates that current temperatures could exceed 700 c the remarkable thickening of the crust under the central range its rapid uplift without significant seismicity its deep exhumation and its thermal state contribute to make it the core of orogenic activities on taiwan island the expanded network during the taiger deployment captured broadband seismic data yielding enhanced s splitting results with mainly sks skks data the polarization directions of the fast s waves follow very closely the structural trends of the island supporting the concept of a vertically coherent taiwan orogeny in the outer few hundred kilometers of the earth

grain growth kinetics in wadsleyite effects of chemical environment abstract grain growth kinetics in wadsleyite was investigated using a multianvil high pressure apparatus fine grained wadsleyite aggregates were synthesized by isostatic hot pressing and were subsequently annealed under high pressure and temperature in a controlled chemical environment wadsleyite samples show normal grain growth characterized by a log normal grain size distribution following the relation l n l 0 n k t where n is a constant l the grain size at time t l0 the grain size at time t 0 and k is a rate constant that depends on temperature t and chemical environments f o 2 oxygen fugacity in pa coh water content in h 106si as k a d f o 2 r d exp h d r t a w f o 2 r w c oh q exp h w r t with a d 10 4 9 6 1 8 0 7 4 m n s 1 p a r d rd 0 12 0 11 0 20 0 14 h d 410 230 500 270 kj mol a w 10 18 2 1 4 24 0 1 7 m n s 1 p a r w rw 0 14 0 05 0 22 0 06 q 1 7 0 3 2 2 0 3 and h w 120 60 160 70 kj mol with assumed value of n 2 3 values in parentheses denote parameters for n 3 both water and oxygen fugacities significantly enhance grain growth kinetics the large value of the parameter describing the water fugacity dependence q 1 5 2 5 cannot be explained solely by a simple model in which grain growth is controlled by diffusion of atoms defects across the grain boundaries the interaction of grain boundaries with charged defects or the density of hydrated ledges may be important factors that control the grain growth kinetics of wadsleyite when compared at similar thermo chemical conditions grain growth of wadsleyite is found to be more sluggish than grain growth of olivine the present results show that a small wadsleyite grain size 100 000 h 106si is present a small grain size

slab dynamics in the transition zone abstract seismic images of horizontal slab segments in across or below the transition zone invoke scenarios in which slabs are laid down in the mantle through progressive trench retreat however observations of subduction characteristics do not exhibit a clear correlation between trench retreat and slab dip in the transition zone instead analysis of a range of subduction characteristics demonstrates that while transition zone slabs include slabs of many ages and subduction velocities with both retreating and advancing trench motion they also have several enigmatic characteristics such as faster sinking rates and a larger range in slab dip than slabs that extend to either shallower or deeper depths comparison of subduction characteristics with several analytical and numerical models of subduction dynamics suggests that many of the possible mechanisms for trapping slabs in the transition zone e g positive buoyancy sources viscous resistance slab weakening are only viable if the slab is already shallow dipping two scenarios for the formation of stagnant slabs are proposed 1 trench retreat prior to slabs entering the transition zone or caused by the negative buoyancy forces associated with the wadsleyite and ringwoodite phase transitions and 2 slow lateral migration of slabs in stable subduction zones

fmnear determination of focal mechanism and first estimate of rupture directivity using near source records and a linear distribution of point sources abstract the fmnear method is based on both the waveform inversion of near source seismic records and on a linear finite source model the primary source parameters that are determined are the moment magnitude m w the double couple focal mechanism strike dip and rake and the distribution of seismic moment along strike which provides a first order estimate of rupture length and directivity source depth is also explored an advantage of the approach is the use of the finite source model directly within the search of the focal mechanism this strategy allows the inclusion of strong motion records at short distances for moderate to very large earthquakes m w 5 5 however for moderate to small earthquakes m w m w 4 5 to 9 0 test cases incorporate continental events recorded by a large number of well distributed stations and less favorable cases in its present form the fmnear approach is very well adapted to continental earthquakes surrounded by seismic stations but it can also give informative results in more difficult configurations the fmnear method is now ready for fully automated determinations and is already implemented in near real time online material details on inversion parameters flow charts of the fmnear method figures of waveform modeling and sensitivity for selected events and table of velocity models

intraplate volcanism due to convective instability of stagnant slabs in the mantle transition zone the study of volcanism can further our understanding of earth s mantle processes and composition continental intraplate volcanism commonly occurs above subducted slabs that stagnate in the mantle transition zone mtz such as in europe eastern china and western north america here we use two dimensional numerical models to explore the evolution of stagnant slabs in the mtz and their potential to sustain mantle upwellings that can support volcanism we find that weak slabs may go convectively unstable within tens of million years upwellings rise out of the relatively warm underbelly of the slab are entrained by ambient mantle flow and reach the base of the lithosphere the first and most vigorous upwellings rise adjacent to lateral heterogeneity within the slab ultimately convective instability also acts to separate the compositional components of the slab harzburgite and eclogite from each other with harzburgite rising into the upper mantle and eclogite sinking into the lower mantle such a physical filtering process may sustain a long term compositional gradient across the mtz

divalent cation diffusion in mg2sio4 spinel ringwoodite β phase wadsleyite and olivine implications for the electrical conductivity of the mantle mg fe and mg ni interdiffusion coefficients have been measured in single crystal olivine alpha mg ni fe sub 2 sio sub 4 polycrystalline beta phase beta mg ni fe sub 2 sio sub 4 and silicate spinel gamma mg ni fe sub 2 sio sub 4 at 1473 k between 1 and 14 gpa under controlled thermodynamic conditions in olivine d sub mg ni sup alpha ranges from 10 sup 17 m sup 2 s sup 1 at 1 gpa to 4x10 sup 18 m sup 2 s sup 1 at 9 gpa and d sub mg fe sup alpha ranges from 3x10 sup 15 m sup 2 s sup 1 at 1 gpa to 10 sup 15 m sup 2 s sup 1 at 4 gpa at 9 gpa the cation diffusion rates in gamma spinel are approx 3 orders of magnitude higher than those in olivine between 9 and 14 gpa d sub mg ni sup gamma decreases from 8x10 sup 15 to 9x10 sup 16 m sup 2 s sup 1 and d sub mg fe sup gamma decreases from 2x10 sup 13 to 5x10 sup 14 m sup 2 s sup 1 between 10 and 14 gpa the diffusion coefficients for both fe and ni are similar in magnitude and pressure dependence between beta phase and gamma spinel the activation volumes for mg ni diffusion are 3 2 and 6 7 cm3 mol 1 in the alpha and gamma beta phases respectively and for mg fe diffusion are 5 4more and 6 1 cm3 mol 1 in the alpha and gamma beta phases respectively our results demonstrate that extreme differences in transport properties are expected to occur across the 400 km discontinuity a model for electrical conductivity in the upper mantle involving two mechanisms for electrical conduction with one mechanism being associated with a hydrogen or defect related conduction process and the other involving a straightforward application of the nernst einstein equation to our cationic diffusion data reproduces geomagnetic sounding results for the upper mantle and shallow transition zone this modeling yields an order of magnitude increase in electrical conductivity across the 400 km discontinuity with little or no change in conductivity occurring near 520 km depth our modeling suggests that divalent cation diffusion is the dominant mechanism of charge transport between 400 and 670 km depth and that the high pressure olivine polymorphs dominate the electrical behavior of the deep upper mantle comparison between field based deep mantle conductivity profiles derived from magnetotelluric studies and extrapolation of our model suggests that a discontinuity in electrical transport properties exists at the base of the transition zone as well similarly given the dramatic differences in chemical diffusion between different polymorphs of olivine it is possible that other transport property mediated processes such as viscous flow could dramatically change across the 400 and 670 km discontinuities such changes are less likely to occur at 520 km depth c 2000 american geophysical union less

shear concentration in a collision zone kinematics of the chihshang fault as revealed by outcrop scale quantification of active faulting longitudinal valley eastern taiwan abstract repeated measurements of active deformation were carried out at three sites along the active chihshang fault a segment of the longitudinal valley fault zone of eastern taiwan the present day plate boundary between the philippine sea plate and eurasia reliable annual records of displacement along an active fault were obtained based on detailed surveys of faulted concrete structures along the active chihshang fault striking n18 e we determined average motion vectors trending n37 w with an average shortening of 2 2 cm yr thus the transverse component of motion related to westward thrusting is 1 8 cm yr whereas the left lateral strike slip component of motion is 1 3 cm yr the fault dips 39 45 to the east so that the vertical displacement is 1 5 3 cm yr and the actual oblique offset of the fault increases at a rate of 2 7 3 7 cm yr this is in good agreement with the results of regional geodetic and tectonic analyses in taiwan and consistent with the n54 w trend of convergence between the northernmost luzon arc and south china revealed by gps studies our study provides an example of extreme shear concentration in an oblique collision zone at chihshang the whole horizontal shortening of the longitudinal valley fault 2 2 cm yr on average occurs across a single narrow fault zone so that the whole reverse slip about 2 7 3 7 cm yr depending on fault dip was entirely recorded by walls 20 200 m long where faults are tightly localized this active faulting accounts for more than one fourth 27 of the total shortening between the luzon arc and south china recorded through gps analyses further surveys should indicate whether the decreasing shortening velocity across the fault is significant revealing increasing earthquake risk due to stress accumulation or not revealing continuing fault creep and weak behaviour of the chihshang fault

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

a new inference of mantle viscosity based upon joint inversion of convection and glacial isostatic adjustment data we present new profiles of mantle viscosity derived on the basis of non linear occam style joint inversions of an extensive set of data associated with mantle convection and glacial isostatic adjustment gia the convection related observables include satellite derived free air gravity harmonics the geodetically inferred excess ellipticity of the cmb and tectonic plate motions the gia constraints involve two classes of observables previously shown to be relatively insensitive to errors in the late pleistocene ice history the so called fennoscandian relaxation spectrum frs and a set of site specific decay times determined from the postglacial sea level history in hudson bay and sweden the inverted viscosity profiles show a significant three orders of magnitude increase from the upper mantle mean value of f4 10 20 pa s to a high viscosity 10 23 pa s peak at

dense network intense seismicity and tectonics of taiwan abstract a temporary seismic network consisting of 295 land stations was deployed in 2009 in taiwan to monitor airgun sources during an onshore offshore experiment in taiwan we exploit the continuously recorded dataset to detect and map seismicity in the seismically very active taiwan by combining recent automatic detection and phase picking techniques we successfully generate an initial earthquake catalog of over 8400 events the hypodd algorithm is used to relocate and filter these events this network recorded smaller events than the permanent regional network because of the many stations around the high mountain ranges and the generally high station density along 6 lines the results based on the 2009 data generally reproduce the dominant seismicity features from many years of earthquake monitoring in taiwan in addition we map hitherto unknown dipping zones under the foothills and the central range that may correspond to seismogenic structures

residual luminescence in modern debris flow deposits from western taiwan a single grain approach abstract in an active fold and thrust belt sediment is commonly transported in the form of debris and colluviums and the ages of such deposits can be important for seismic hazard assessment these sediments are mainly transported by high concentration flows that travel very short distances before burial and therefore have very few opportunities for daylight exposure and bleaching which limits the application of luminescence dating in such environments luminescence studies on modern debris flow deposits and channel sediments in central taiwan indicate a mixed population of bleached and unbleached grains the well bleached grains constitute a small proportion of the sediments and could only be identified using the single grain dating technique doing single aliquot analysis may result in overestimation of the age of such sediments by 3 25 ka the data reveal that outwash sediments are better bleached than debris flow sediments our results show that quartz that has experienced partial resetting can be used for luminescence dating only through the use of the single grain technique

a synthesis of the geologic evolution of taiwan abstract the island arc of taiwan is composed of cenozoic geosynclinal sediments more than 10 000 m thick lying on a pre tertiary metamorphic basement pleistocene to miocene andesitic islands surround the main island and are related mostly to arc magmatism the penghu island group in the taiwan strait is covered with pleistocene flood basalt neogene shallow marine clastic sediments are exposed mainly in the western foothills with pleistocene andesitic extrusives at the northern tip and the northeastern offshore islands a thick sequence of paleogene to miocene argillitic to slaty metaclastic rocks underlies the western central range and forms the immediate sedimentary cover on the pre tertiary metamorphic complex to the east which represents an older mesozoic arc trench system the coastal range in eastern taiwan is a neogene andesitic magmatic arc including also a large variety of volcaniclastic and turbiditic sediments cenozoic taiwan is the site of arc continent collision where the luzon arc on the philippine sea plate overrides the chinese continental margin on the eurasian plate east and northeast of taiwan the polarity of subduction changes whereby the oceanic philippine sea plate is subducting beneath the ryukyu arc system on the eurasian plate continent arc collision in taiwan island is anomalous and may occur in a broad belt of deformation rather than along a well defined plate boundary or subduction zone

hydrogen diffusivity in wadsleyite and water distribution in the mantle transition zone abstract the kinetics of the hydrogen diffusivity in synthesized polycrystalline wadsleyite was measured by ir spectroscopy in order to determine the diffusion coefficient of hydrogen in wadsleyite the major constituent mineral in the mantle transition zone with the composition of mg0 89fe0 11 2sio4 the hydration experiments were conducted at 15 16 gpa and temperature range from 900 to 1200 c with mg oh 2 as the water source by kawai type multi anvil apparatus the diffusion rate obtained here is considered to be an effective diffusion coefficient with the grain size of 9 m involving contributions both from the lattice diffusion and the grain boundary diffusion the temperature dependence of diffusion of hydrogen in polycrystalline wadsleyite was determined to be dh 9 6 10 6 exp 123 32 kj mol 1 rt at 15 gpa hydrogen diffusion rate in wadsleyite is roughly consistent with the average diffusivity of hydrogen in olivine in recent years several authors have suggested a possibility of the hydrous transition zone and the distribution and transport properties of water are still debated on the basis of water dependence of the electrical conductivity the water content in the mantle transition zone was estimated from the observed conductivity by using the nernst einstein relation the results obtained here show that the distribution of water should be quite heterogeneous throughout the mantle transition zone

active detachment of taiwan illuminated by small earthquakes and its control of first order topography we use 110 000 small earthquakes to locate and map active faults in three dimensions within the taiwan arc continent collision the structure is dominated by a nearly horizontal band of small earthquakes at 10 km depth that is interpreted to seismically illuminate the main detachment zone of the mountain belt with other illuminated fault zones abutting the detachment zone the zone steepens below eastern taiwan to 30 90 and reaches depths of 30 60 km the three dimensional shape of the detachment zone in relation to topography allows a new test of critical taper wedge mechanics and suggests that the reversal of topographic slope across taiwan is controlled by the shape of the detachment

insights into active tectonics of eastern taiwan from analyses of geodetic and geologic data 1 about 50 mm yr of convergence between the philippine sea and eurasian plates is absorbed in eastern taiwan and it remains unclear how the convergence is partitioned among active faults the longitudinal valley fault lvf the most seismically active fault in eastern taiwan creeps at the surface in the south and not in the north however it is unclear how much of the fault is locked or creeping at depth to address these problems we model holocene and interseismic deformation of elastic lithospheric blocks moving over a viscoelastic asthenosphere in eastern taiwan through a fully probabilistic scheme we invert gps interferometric synthetic aperture radar creepmeter and holocene marine terrace data for block motions fault slip rates and distribution of interseismic creep the data are explained with four blocks separated by three faults central range fault lvf and an offshore fault the model explains the essential features of interseismic and holocene deformation we find that 35 55 mm yr of slip on the offshore fault is necessary to fit marine terrace uplift rates which is a larger fraction of the plate convergence than previously recognized the lvf has a holocene slip rate of 20 30 mm yr with approximately equal magnitudes of reverse slip and left lateral strike slip components only about half of the surface area of the longitudinal valley fault appears to be locked the southern segment of the lvf creeps at a rate of 5 28 mm yr down to a depth of 15 20 km while the northern segment is locked from the surface to a depth of 20 km

determination of the fault plane using a single near field seismic station with a finite dimension source model summary we explore the possibility of determining the actual fault plane of an earthquake from the inversion of near source displacement seismograms of one station when a finitedimension source is used instead of a point source model and when the complete displacement is taken into account including near field waves tests on synthetic seismograms and real data recorded at local distances show that this is possible even with a single three component station a single accelerogram available for the erzincan turkey 1992 march 13 m s 6 8 earthquake is inverted and the solution found is compatible with other seismological studies and with the mechanism expected for the north anatolian fault

focal mechanisms and seismotectonic stress in north central taiwan in relation with the chi chi earthquake abstract the aftershock sequence of the 1999 chi chi earthquake mw 7 6 provided a large number of focal mechanisms recorded with bats centroide moment tensors cmt which allowed us to perform reliable stress tensor inversions in north central taiwan these inversions were done for three time periods corresponding to the post seismic phase of the 1999 chi chi earthquake mw 7 6 in the last period the 2003 chengkung earthquake mw 6 5 occurred on the vicinity of our study area and its influence is also examined for comparison between seismotectonic regimes of the pre and post chi chi periods we also carried out stress inversion using published focal mech of the pre chi chi period for each period we delineated seismogenic domains with relatively homogeneous stress regimes in agreement with the local structures the boundaries of these domains vary during the whole post chi chi period as seismic activity decays a 25 clockwise rotation of the main compressive stress 1 is observed between the pre and the post chi chi periods in the domain located near the northern termination of the chi chi rupture a stress perturbation related to the chengkung earthquake could be detected in the eastern part of the central range we present an interpretation of the determined stress regimes in terms of changes in mechanical behaviour of the sanyi puli transfer zone

an experimental study of grain scale microstructure evolution during the olivine wadsleyite phase transition under nominally dry conditions abstract the grain scale microstructure evolution during the phase transformation of olivine to wadsleyite was investigated using a multi anvil high pressure apparatus we identified three stages in the microstructure evolution during olivine to wadsleyite phase transformation 1 nucleation of wadsleyite along potential nucleation sites e g grain boundaries and grain corners inside of grains dislocations stacking faults 2 development of an interconnected network of fine grained wadsleyite along grain boundaries 3 growth of wadsleyite into olivine our observations suggest that at low over pressures 3 gpa intra crystalline nucleation makes a significant contribution to the volume fraction transformed the rheological properties of a sample undergoing the phase transformation are controlled by the grain size and the connectivity of newly formed grains based on the model of grain size evolution involving both nucleation and growth we show that the initial grain size of wadsleyite is controlled by the competition between nucleation rate and growth rate when phase transformation takes place near the equilibrium boundary at relatively higher temperatures 1200 k but mostly by critical size for nucleation when phase transformation takes place away from the equilibrium boundary at relatively low temperatures

interseismic deformation and earthquake hazard along the southernmost longitudinal valley fault eastern taiwan about half of the 8 cm yr of oblique convergence across the active convergent plate boundaries of taiwan occurs in eastern taiwan across the longitudinal valley significant shortening and left lateral slip occurs across the longitudinal valley fault there both as shallow fault creep and as seismogenic fault slip the southernmost longitudinal valley fault comprises an eastern peinan strand and a western luyeh strand we derive an interseismic block model for these two strands using data from a small aperture global positioning system gps campaign and leveling the model provides estimates of fault slip rates and quantifies slip partitioning between the two strands a 45 mm yr dip slip rate on the northern peinan strand diminishes southward whereas the left lateral component increases in contrast nearly pure dip slip motion of about 20 mm yr on the southern luyeh strand diminishes northward to about 8 mm yr and picks up a component of left lateral motion of about 15 mm yr before it dies out altogether at its northern terminus the luyeh and the northern peinan strands record near surface creep but the southern peinan strand appears locked the potential earthquake magnitude for the two strands may be as high as m w 6 5 we anticipate seismic rupture mainly on the locked portion of the peinan strand

application of the cbω model to the calculation of diffusion parameters of si in silicates silicon diffusion in major mantle minerals plays an important role in understanding a number of physical and chemical processes in the earth s interior inspection of existing experimental data reveals linear compensation law between the preexponential factors and the activation energies for si diffusion in various minerals by focusing on those of geophysical interest on the basis of the observed compensation relationship here we propose a thermodynamic model the so called cb model that interconnects point defect parameters with the bulk properties to reproduce the si self diffusion coefficients in different rock forming minerals when the uncertainties are considered the predicted results show that the temperature and pressure dependences of self diffusion coefficients concur with existing experimental data and theoretical calculations in most cases

modern vertical deformation rates and mountain building in taiwan from precise leveling and continuous gps observations 2000 2008 1 to characterize the present day vertical displacement field in the active taiwan orogenic belt 1843 precise leveling and 199 continuous gps measurements from 2000 to 2008 are collected and analyzed in this study vertical velocities derived from the leveling data are placed in a reference frame of the chinese continental margin using continuous gps observations at nearby sites the leveling and gps vertical velocities generally reveal a dome shaped pattern with uplift of 0 2 18 5 mm yr in the interior of the mountain range and subsidence on the flanks of the mountains and coastal plains modern uplift rates in the active fold and thrust belt are generally consistent with geologic uplift rates however present day uplift rates in the central range are faster than the million years averaged exhumation rates the modern subsidence rates are generally consistent with geologic rates except for the rates in western coastal areas due to groundwater pumping present day subsidence in the southern central range and northern coastal range is however inconsistent with long term uplift which may reflect interseismic elastic strain accumulation across faults present day subsidence in northern taiwan occurs in a region of postcollisional orogenic collapse we model the present day and geologic vertical velocities and published gps horizontal velocity data across southern taiwan using a 2 d lithospheric model the model suggests a combined slip rate of 40 mm yr on the frontal thrusts and 45 mm yr on the longitudinal valley fault the model requires an additional source of crustal thickening under the central range to match the observed present day uplift rates

geomorphic analysis of the central range fault the second major active structure of the longitudinal valley suture eastern taiwan numerous landforms along the longitudinal valley suture of eastern taiwan indicate that two opposing reverse faults currently dominate the suturing process between the luzon volcanic arc and the central range of taiwan the east dipping longitudinal valley fault on the eastern flank of the valley is well known the west dipping central range reverse fault on the western flank of the valley is more obscure nonetheless it has produced many uplifted lateritic fluvial terraces along the eastern flank of the central range in the central reach of the valley from just north of the wuhe tableland to near chihshang the fault appears to be active but blind south of chihshang and inactive along the northern part of the longitudinal valley the late quaternary slip rate of the fault is less than 12 8 mm yr this constraint means that the fault is absorbing far less than half of the horizontal shortening across the longitudinal valley suture however the late quaternary slip rate along the fault may be comparable to the uplift and exhumation rate of the central range this suggests that localized brittle slip along the central range fault is an important component of crustal thickening and uplift of the range even though additional shortening and crustal thickening may be occurring because of pervasive deformation beneath the range

grain growth kinetics of ringwoodite and its implication for rheology of the subducting slab abstract grain growth rates of mg2sio4 and mg0 9fe0 1 2sio4 ringwoodites have been studied under the conditions of the mantle transition zone at a pressure of 21 gpa and temperatures ranging from 1473 to 2023 k using a kawai type high pressure apparatus the grain growth rates were expressed by gn g0n k0texp h rt where g m is grain size at time t s and g0 is the initial grain size at t 0 with n 4 5 0 8 and h 414 kj mol and log k0 20 4 1 6 m4 5 s for mg0 9fe0 1 2sio4 ringwoodite and h 456 kj mol and logk0 20 2 1 4 m4 5 s for mg2sio4 ringwoodite using these kinetic parameters for grain growth we estimated the grain size of ringwoodite in the cold subducting slabs to be less than 100 m this suggests that the dominant deformation mechanism in the subducting slab is diffusion creep it is also likely that some cold slabs are softer than the warmer surrounding mantle

evaluation of approaches to calculate debris flow parameters for hazard assessment abstract many different runout prediction methods can be applied to estimate the mobility of future debris flows during hazard assessment the present article reviews the empirical analytical simple flow routing and numerical techniques all these techniques were applied to back calculate a debris flow which occurred in 1982 at la guingueta catchment in the eastern pyrenees a sensitivity analysis of input parameters was carried out while special attention was paid to the influence of rheological parameters we used the voellmy fluid rheology for our analytical and numerical modelling since this flow resistance law coincided best with field observations the simulation results indicated that the basal friction coefficients rather affect the runout distance while the turbulence terms mainly influence flow velocity a comparison of the velocity computed on the fan showed that the analytical model calculated values similar to the numerical ones the values of our rheological parameters calibrated at la guingueta agree with data back calculated for other debris flows empirical relationships represent another method to estimate total runout distance the results confirmed that they contain an important uncertainty and they are strictly valid only for the conditions which were the basis for their development with regards to the simple flow routing algorithm this methods could satisfactorily simulate the total area affected by the 1982 debris flow but it was not able to directly calculate total runout distance and velocity finally a suggestion on how different runout prediction methods can be applied to generate debris flow hazard maps is presented taking into account the definition of hazard and intensity the best choice would be to divide the resulting hazard maps into two types final hazard maps and preliminary hazard maps only the use of numerical models provided final hazard maps because they could incorporate different event magnitudes and they supplied output values for intensity calculation in contrast empirical relationships and flow routing algorithms or a combination of both could be applied to create preliminary hazard maps the present study only focussed on runout prediction methods other necessary tasks to complete the hazard assessment can be looked up in the guidelines for landslide susceptibility hazard and risk zoning included in this special issue

rheological structure and deformation of subducted slabs in the mantle transition zone implications for mantle circulation and deep earthquakes abstract rheological structure of subducted slabs of oceanic lithosphere in the mantle transition zone is investigated based on mineral physics observations incorporating grain size stress temperature and pressure dependence of rheology it is shown that the rheological structure of slabs depends strongly on subduction parameters through temperature that controls the grain size of spinel ringwoodite and the magnitude of forces acting on a slab we use a theoretical model of grain size evolution associated with the olivine spinel transformation plastic flow laws of olivine and spinel combined with a thermal model of subducting slab in which the effect of latent heat release is incorporated three deformation mechanisms for olivine and spinel diffusional creep power law dislocation creep and the peierls mechanism are considered due to the large variation in temperature stress and grain size a subducting slab is shown to have a complicated rheological structure which varies both laterally and with depth a cold slab in the deep transition zone is characterized by a weak fine grained spinel region surrounded by narrow but strong regions the flexural rigidity and the curvature of a slab are calculated using a new formulation in which the effects of stress dependent rheology is incorporated in a self consistent fashion although uncertainties in both the transformation kinetics and the rheology of high pressure phases are still large the general trend of dependence of slab flexural rigidity and the curvature on the subduction parameters is well constrained slabs with very low thermal parameters warm slabs are weak but slabs with large thermal parameters cold slabs are also weak due to small spinel grain size and large external force bending moment slabs with intermediate thermal parameters will have a relatively large flexural rigidity and could penetrate into the lower mantle without much deformation thus the 660 km discontinuity may work as a rheological filter for mantle convection this prediction provides a natural explanation for a paradoxical observation that significant deformation of slabs is observed exclusively in the western pacific where temperatures of the slabs are considered to be low our slab rheology models also have important implications for deep earthquakes overall rheological weakening of slabs in the deep transition zone results in high rates of deformation under relatively low temperatures providing a favorable environment for thermal runaway instability adiabatic shear instability our model predicts heterogeneous energy dissipation as a result of heterogeneous rheology energy dissipation in deep cold slabs is concentrated in high strength regions surrounding a weak fine grained spinel core the regions of high energy dissipation are prone to thermal runaway instability and are likely to be seismogenic the width of this seismogenic region is well constrained by our model and is predicted to be 40 60 km which is in excellent agreement with seismological observations other features of deep earthquakes including low seismic efficiency and low aftershock activities can also be explained by the thermal instability model

growth kinetics of mgsio3 perovskite reaction rim between stishovite and periclase up to 50 gpa and its implication for grain boundary diffusivity in the lower mantle abstract the growth rate of mgsio3 perovskite reaction rims between periclase and stishovite was investigated at 24 50 gpa and 1650 2150 k using a kawai type high pressure apparatus the textural observations of the recovered samples and rim growth kinetic data revealed that the reaction is controlled by coupled grain boundary diffusion of mgo and grain coarsening in the perovskite reaction layer assuming a high diffusivity of o compared with mg the grain boundary diffusivity of mg in the perovskite was determined to be d g b mg m 3 s 10 15 1 exp 176 000 p 24 3 8 10 3 rt which is 3 5 orders of magnitude faster than that of si we found that the bulk diffusivity of mg in polycrystalline perovskite is affected by the grain boundary when we consider the possible grain sizes and temperatures in the lower mantle accordingly grain boundary diffusion in perovskite may be an effective mechanism for chemical transportation of divalent cations in the lower mantle

plate boundary strain partitioning along the sinistral collision suture of the philippine and eurasian plates analysis of geodetic data and geological observation in southeastern taiwan crustal deformation and strain partitioning of oblique convergence between the philippine sea plate and the eurasian plate in the southern longitudinal valley of eastern taiwan were characterized based on geodetic analysis of trilateration network and geological field investigation the longitudinal valley fault one of the most active faults on taiwan branches into two individual faults in the southern longitudinal valley these two active faults bound the plio pleistocene pinanshan conglomerate massif between the coastal range the luzon island arc belonging to the philippine sea plate and the central range the metamorphic basement of the eurasian plate a geodetic trilateration network near the southern end of the valley shows a stable rate of the annual length changes during 1983 1990 the strain tensors for polygonal regions including triangular regions of the taitung trilateration network reveal that there are two distinct zones of deformation a zone of shortening thrusting between the pinanshan massif and the central range on the west and a strike slip movement between the pinanshan massif and the coastal range on the east the analysis of a discontinuity model consisting of three rigid blocks separated by two discontinuities has been carried out the results show that the deformation in this region can be characterized by two major faults a reverse fault is located between the plio pleistocene pinanshan massif and the metamorphic basement of the central range with a shortening rate of about 12 mm yr in the direction n280 e a strike slip fault is located principally along the river between the pinanshan massif and island arc system of the coastal range with a purely strike slip component of about 22 mm yr in the direction n353 e the analysis of the geodetic data further suggests that substantial deformation probably strike slip in type occurs within the pinanshan massif geological evidence of deformation in the plio pliestocene pinanshan conglomerate includes regional folding a conjugate set of strike slip fractures at the outcrop scale and morphological lineaments related to fracturing all indicating that the pinanshan massif is being deformed within a transpressive stress regime regional kinematic data indicate that a significant portion of the 82 mm yr of motion between the eurasian plate and the philippine sea plate is absorbed in the southern longitudinal valley by the decoupling of two distinct major faults the geometry of the oblique convergence and the rheology of the rock units the well consolidated plio pleistocene conglomerate and the sheared melange formation play the two important roles in the partitioning of crust deformation

neotectonic characteristics along the eastern flank of the central range in the active taiwan orogen inferred from fluvial channel morphology the tectonic activity of the taiwan orogenic belt has been studied by different methods over various timescales constraints on tectonic characteristics over timescales of 103 105 years however are rather limited to further understand the tectonic forcing over this timescale we analyzed 20 major river basins along the eastern flank of the central range the mountainous core of the orogen the results of river steepness index ksn values and the distribution patterns of knickpoints are consistent with the patterns of tectonic evolution in taiwan on both ends of the orogen the rivers have low ksn values that indicate low uplift rates throughout the area in the central part of the island where the orogen is under rapid collisional processes the rivers are steeper and are characterized by many tectonic knickpoints our results show different patterns from both short term and long term uplift and denudation rate patterns this suggests that these rates change temporally and spatially moreover the steepness indexes of rivers in the taiwan orogen show the same increasing trend with erosion rates as those in other active orogens but correspond to significantly higher erosion rates this is likely produced by the frequent debris flow and landslide events in taiwan a character that makes the island distinctive from other active orogens in the world

the kinetics of the reaction of majorite plus ferropericlase to ringwoodite implications for mantle upwellings crossing the 660 km discontinuity we have measured the kinetics of reaction between mgo and majoritic garnet at 20 gpa and 1773 2123 k as a proxy for the reaction between perovskite and ferropericlase during mantle upwelling across the 660 km seismic discontinuity ringwoodite forms a layer between mgo and garnet and in the case of aluminous garnets the interface between ringwoodite and garnet develops a fingering instability resulting in a complex intergrowth at this interface by contrast the mgo ringwoodite interface is always planar for an initial planar mgo garnet interface two thicknesses are therefore defined 1 a layer thickness x1x1 which is the maximum thickness of ringwoodite which forms a plane parallel bounded layer next to the mgo and 2 an interface thickness x2x2 which is the maximum extent of the intergrowth region away from the ringwoodite layer the growth of both of these regions can be described by apparent rate constants kiki which are arrhenius with view the mathml sourceln k10 6 36 0 25 m2 s and e1 456 40 kj mole1 456 40 kj mol for the ringwoodite layer and view the mathml sourceln k20 9 2 3 3 m2 s and e2 371 53 kj mole2 371 53 kj mol for the intergrowth region the fingering instability is caused by the incompatibility of aluminium in ringwoodite and its low chemical diffusivity in garnet which results in an increase of surface area at the ringwoodite garnet interface to minimise the aluminium concentration at the interface the intergrowth region contains a fine grained mixture of ringwoodite and garnet which coarsens very slowly with time this might result in a transient weakening of upwelling regions of mantle just above the 660 km seismic discontinuity allowing some viscous decoupling between the upper and lower mantle

stagnation of subducting slabs in the transition zone due to slow diffusion in majoritic garnet subducting slabs of oceanic lithosphere often stagnate before reaching the lower mantle laboratory experiments under high pressures and temperatures show that pyroxene a common mineral in such slabs is transformed to its dense high pressure counterpart majorite garnet at a very slow rate temporarily keeping the slabs buoyant compared to the surrounding mantle

computational experiments on the 1962 and 1970 landslide events at huascaran peru with r avaflow lessons learned for predictive mass flow simulations abstract mass flow simulations are considered important tools for hazard analysis for the simulation of single process mass flows such as debris flows robust tools and reasonable parameter range estimates are available however this is much less the case for more complex mass flows e g involving process chains and flow transformation we explore the challenges of simulating complex flow dominated landslides by back calculating the huascaran events of 1962 and 1970 with r avaflow a two phase mass flow model pudasaini 2012 in a gis based open source simulation framework both events started as rock ice falls on the western slope of the north summit of nevado huascaran cordillera blanca peru and entrained large volumes of glacial till at lower elevation resulting in highly mobile debris avalanches whereas the 1962 event badly affected the village of ranrahirca when spreading over a debris cone the 1970 event overtopped a ridge and led to the complete destruction of the town of yungay well documented in the literature these events provide an opportunity as a natural laboratory for testing innovative mass flow simulation tools and their features in a first step we consider i the 1962 event and ii the 1970 event separately for each of them optimizing the key input parameters in terms of empirical adequacy in a second step we apply the optimized parameter set for i to the 1970 event and the parameter set derived for ii to the 1962 event in a third step we explore the sensitivity of the model outcomes to selected key parameters basal friction angle and entrainment coefficient the results a demonstrate the general ability of r avaflow to reproduce the spatio temporal evolution of flow heights and velocities as well as travel times and volumes of these complex mass flow events reasonably well and b highlight the challenges and uncertainties involved in predictive simulations with parameter sets obtained from back calculations we suggest a strategy to appropriately deal with uncertain outcomes by superimposing the results of multiple simulations

active fault creep variations at chihshang taiwan revealed by creep meter monitoring 1998 2001 1 the daily creep meter data recorded at chihshang in 1998 2001 are presented the chihshang creep meter experiment was set up across the chihshang thrust fault the most active segment of the longitudinal valley fault which is the present day plate suture between the eurasian and the philippine sea plates in eastern taiwan near continuous data recording at two sites revealed different surface fault motions yet similar annual shortening rates 16 2 mm at the tapo site comprising two connected creep meters and 15 0 mm at the chinyuan site three creep meters straddling parallel fault branches four of the five creep meters showed a seasonal variation with the fault moving steadily during the rainy season from april to october and remaining quiescent during the rest of the year the only exception was recorded by the creep meter located on a melange composed hillslope where local gravitational landsliding played an additional role other than tectonic faulting through comparison with daily precipitation data we inferred that moderate rainfall suffices to trigger or facilitate slippage on the surface fault during the transition period of the dry wet season during the observation period from 1998 to 2001 the subsurface seismicity exhibited clusters of microearthquakes on the chihshang fault at depths of 10 25 km recurrent earthquakes occurred regardless of whether the season was wet or dry indicating that the stress relaxation associated with seismicity in the seismogenic zone did not transfer immediately up to the surface the accumulated strain on the chihshang fault at shallow surface levels was released through creep during the wet season in addition to these short term seasonal variations an apparent decrease in the annual slipping rate on the chihshang fault during the last few years deserves further investigation in order to mitigate against seismic hazard

rupture behavior of a moderate earthquake mw 5 9 april 2006 and its close relation with the 2003 chengkung earthquake mw 6 8 at the southern termination of the plate boundary southeast taiwan the taiwanese orogen is the result of the active and vigorous collision between the eurasian and the philippine sea plates in this strong convergence context a one month long earthquake sequence composed of two mainshocks of magnitude 6 occurred in april 2006 in the taitung area the first mainshock t1 mobilized a structure just west to the plate boundary while the second one t2 is located on the other side in order to retrieve the exact fault geometry of t2 we inverted waveforms from stations located at local and teleseismic distances we performed a grid search on strike and dip each strike dip couple defining a geometry considering the source as a point source then as an extended source in the last case a simple average over stations misfit failed to isolate a precise geometry to overcome this problem we used a more statistical approach on the distribution of misfits to define the best geometry comparing the best model to local structures it appears the generative fault was the plate boundary that rotates from a strike pointing at n20 e north of the event to n0 e in t2 area with an identical eastward dip of 35 for this model the fault slip inversion provides a critical slip of 3 5 cm above which slip rake and rupture time are constrained with uncertainties of 29 14 and 0 47 s respectively the average slip along the rupture was 20 cm with a maximum of 46 13 cm the movement was inverse with a minor left lateral component similar to the faulting behavior of the plate boundary in addition the slip pattern of t2 is contained within the southern portion of the deepest segment of the plate boundary and at the edge of the rupture area of the 2003 chengkung earthquake mw 6 8 a large event also generated by the plate boundary but 2 5 years earlier after 1 s of aseismic spreading the rupture propagated seismically and circularly outward before being stopped by the fault bending

slow si al interdiffusion in garnet and stagnation of subducting slabs abstract si 4 m 2 2al 3 m mg fe ca interdiffusion rates in majoritic garnet have been determined at pressure of 17 gpa and temperatures of 1550 1700 c using a kawai type high pressure apparatus the diffusion profiles were measured across the interface between pyropic garnet and majoritic garnet samples by an analytical transmission electron microscope and the rate of the si 4 m 2 2al 3 interdiffusion was determined to be a d si al m 2 s 1 2 10 10 exp 364 kj mol 1 rt we found that the diffusion rate is low compared to the si diffusion rate in other silicate minerals relevant to the deep mantle slow kinetics of the pyroxene garnet transformation due to the low diffusion rate indicates that large low density metastable regions may exist in the slab greatly contributing to the slab stagnation around the transition region stagnant slabs possibly stay in this region over 10 8 yr because of the sluggish pyroxene garnet transformation but may eventually fall into the lower mantle after the completion of the transformation

seismicity characteristics before the 2003 chengkung taiwan earthquake abstract we investigate the variations in seismicity pattern in the taiwan region before the 2003 chengkung taiwan earthquake m w 6 8 by calculating the standard normal deviate of the z values and b values from the gutenberg richter relation the mogi donut shaped variations in the seismicity can be identified in the z value map surrounding the chengkung earthquake source region noticeable decreases in the b values have also been found around the mainshock region before the chengkung event the relatively low seismicity rate and the decrease in the b values may be the precursory phenomena associated with the quiescence in overall seismicity and the activation of moderate sized events occurred around the mainshock region before the chengkung event

slip distribution on a thrust fault at a plate boundary the 2003 chengkung earthquake taiwan summary the 2003 chengkung earthquake mw 6 8 occurred on the east dipping chihshang fault of eastern taiwan a listric fault with dominant reverse motion a joint inversion taking into account geodetic gps and seismological accelerometric and teleseismic data is performed this modelling highlights the rupture process behaviour on the fault plane at depth the coseismic rupture developed essentially between 12 and 26 km depth expanding laterally by about 30 km towards the ssw two slip patches dominated with slip values exceeding 1 5 m during the 30 s of the whole process the rupture propagation decelerated with time starting at 3 4 0 3 km s 1 in the two main slip patches and ending with velocities below 1 6 0 1 km s 1 the 48 hr of aftershocks that followed the main shock are distributed essentially inside the coseismic slip patches on the fault surface except in the deepest southern part of the fault where slip is less resolved the results of our modelling illustrate the particular behaviour of the 2003 chengkung earthquake where the coseismic slip rapidly diminished towards the surface in good agreement with the observation of fast post seismic slip followed by interseismic creep along the chihshang fault

self diffusion of oxygen and silicon in mgsio3 perovskite abstract we present results of simultaneous measurements of self diffusion of oxygen and silicon in magnesium silicate perovskite oxygen diffusion is 2 orders of magnitude faster than si self diffusion and fe mg interdiffusion in perovskite with d0 9 16 10 4 0 16 9 2 10 6 m2 s and q 501 80 kj mol at 25 gpa despite this high o diffusivity however the electrical conductivity of the lower mantle will be dominated by electronic conduction and the present day core is likely to be out of redox equilibrium with the mantle

formation processes of compound chondrules in cv3 carbonaceous chondrites constraints from oxygen isotope ratios and major element concentrations abstract we found thirty compound chondrules in two cv3 carbonaceous chondrites the abundance in each meteorite relative to single chondrules is 29 1846 1 6 in allende and 1 230 0 4 in axtell we examined petrologic features major element concentrations and oxygen isotopic compositions textural compositional and isotopic evidence suggests that multiple different mechanisms are responsible for the formation of compound chondrules seven compound chondrules are composed of two conjoined porphyritic chondrules with a blurred boundary at the boundary region of this type of compounds a poikilitic texture is commonly observed this suggests that the two chondrules were melted when they came to be in contact on the other hand seventeen compound chondrules consist of two conjoined chondrules with a discrete boundary the preservation of spherical boundary planes of an earlier formed chondrule of this type implies that it already solidified before fusing with a later formed chondrule that was still melted six samples out of 17 compound chondrules of this type are composed of two bo chondrules the bo bo compound chondrules have a unique textural feature in common the directions of the barred olivines are mostly parallel between two chondrules this cannot be explained by a simple collision process and forces another mechanism to be taken into consideration the remaining six compound chondrules differ from the others they consist of an earlier formed chondrule enclosed by a later formed chondrule a large feo enrichment was observed in the later formed chondrules and the enrichment was much greater than that in the later formed chondrules of other types of compounds this is consistent with the relict chondrule model which envisages that the later formed chondrule was made by a flash melting of a porous feo rich dust clump on an earlier formed chondrule the textural evidence of this type of compound shows that the earlier formed chondrule has melted again to varying degrees at the second heating event this implies that feo concentrations in bulk chondrules increases during the second heating event if an earlier formed chondrule was totally melted together with the feo rich dust aggregates silicate minerals such as olivine and low ca pyroxene in compound chondrules have oxygen isotope compositions similar to those in single chondrules from cv3 chondrites the oxygen isotope composition of each part of the compound chondrule is basically similar to their chondrule pair but silicates in some chondrules show varying degrees of 16 o enrichment down to 15 in 18 o while those in their partners have 16 o poor invariable compositions near 0 in 18 o this implies that the two chondrules in individual compounds formed in the same environments before they became conjoined and the heterogeneous oxygen isotope compositions in some chondrules resulted from incomplete exchange of oxygen atoms between 16 o rich chondrule melts and 16 o poor nebular gas

coseismic versus interseismic ground deformations fault rupture inversion and segmentation revealed by 2003 mw 6 8 chengkung earthquake in eastern taiwan 1 the 2003 chengkung earthquake mw 6 8 provided diagnostic evidence for a source model showing the deformation process of the seismogenic chihshang fault in eastern taiwan the aftershocks show a fault bend at a depth of 18 km coseismic ground displacements recorded by strong motion records allow us to deduce instant rupturing of this event our resulting model shows a fault length of 33 km and dip slip dominant rupture on fault plane deeper than 18 km estimated coseismic displacements constrain two fault planes one at 5 18 km depth dipping 60 e and 18 36 km depth dipping 45 e the uppermost fault plane of the chihshang fault 0 5 km did not break immediately after the main shock however it may have a major role in after slip and even interseismic ground deformation the taiyuan basin developed in the hanging wall is a geomorphic feature consistent with and adequately explained by coseismic ground displacements

diffusion in polycrystalline materials grain boundaries mathematical models and experimental data geological relevance of grain boundary diffusion as a rule of thumb diffusion along grain boundaries is several orders of magnitude faster than within minerals and hence it could enable mass transport on much larger spatial scales within geological time scales therefore earth scientists are interested in the transport properties of grain and interphase boundaries and other short circuit diffusion paths such as dislocations or a fluid network since they may provide very efficient transport paths controlling a variety of processes operating on very different spatial scales for example on a micron scale corona formation around minerals is a common phenomenon that is typically controlled by grain boundary diffusion similarly element and isotopic exchange between a physically separated mineral pair used for example as a geothermometer requires transport along grain boundaries metasomatic reaction zones on the centimeter to meter scale are not always simply related to fluid flow but are also induced by fluid assisted diffusive fluxes between two different rock types imposed on each other due to tectonic processes e g miller et al 2009 it has been also argued that the observed strong gradual fractionation of li isotopes on the meter scale was a result of diffusion where a strong contribution comes from grain boundary diffusion within these rocks teng et al 2006 further new data on grain boundary diffusion of siderophile elements and carbon in polycrystalline mgo suggest that grain boundary diffusion provides an efficient mechanism to exchange these elements between the mantle and the core even on the kilometer scale within reasonable time scales hayden and watson 2007 2008 in addition to the significant role of grain boundary diffusion for element transfer in rocks grain boundary diffusion can also dominate the bulk physical properties of rocks e g their viscosity coble creep or electrical conductivity which is for example relevant for the interpretation of

spatial variation of seismogenic depths of crustal earthquakes in the taiwan region implications for seismic hazard assessment abstract this paper presents the first whole taiwan scale spatial variation of the seismogenic zone using a high quality crustal seismicity catalog the seismicity onset and cutoff depths i e seismogenic depths are determined by the earthquake depth moment distribution and used to define the upper and lower boundaries of the seismogenic zone respectively together with the published fault geometries and fault area moment magnitude relations the depth difference in the onset and cutoff depths i e seismogenic thickness is used as the fault width to determine the moment magnitudes of potential earthquakes for the major seismogenic faults results show that the largest mw7 9 8 0 potential earthquake may occur along the changhua fault in western taiwan where the seismic risk is relatively high and seismic hazard mitigation should be a matter of urgent concern in addition the first motion focal mechanism catalog is used to examine the relation between the seismogenic depths and earthquake source parameters for crustal earthquakes 50 km the shallowest onset and cutoff depths are observed for normal and strike slip events respectively this observation is different from the prediction of the conventional continental rheology model which states that thrust events have the shallowest cutoff depth thus a more sophisticated rheology model is necessary to explain our observed dependence of the seismogenic depths on faulting types meanwhile for intermediate to large crustal mw 4 depth 50 km earthquakes thrust events tend to occur at the bottom region of the seismogenic zone but normal and strike slip events distribute at a large depth range

creep mechanism in mg2geo4 effects of a phase transition we deformed polycrystalline mg2geo4 olivine and spinel in a griggs type solid medium apparatus flow of mg2geo4 olivine can be represented by 6 5 l07 3 5 exp 105 kcal mol rt where kbar is the differential stress and s 1 is the natural strain rate for mg2geo4 spinel the flow law is 2 6 104 2exp 73 kcal mol rt the low stress exponent and activation enthalpy coupled with fine grain size 3 m suggest that mg2geo4 spinel deformed by a superplastic mechanism flow parameters for the olivine phase suggest a dislocation creep mechanism comparison of theoretical superplastic flow laws for mg2geo4 olivine with the spinel phase data suggests that strain rates in mg2geo4 spinel are only about a factor of 3 lower than for mg2geo4 olivine of the same grain size a similar estimate holds for dislocation creep of the two phases if it is controlled by diffusion transformation from mg2geo4 olivine to spinel reduced grain size to approximately 3 m thus we might expect a similar reduction in grain size in the earth s transition zone which could result in superplastic deformation of the transformed phase and cause a weak decoupling zone at the transition boundary in the mantle superplasticity brought about by transformation induced reduction in grain size may also provide a mechanism for deep focus earthquakes and an explanation for the correlation observed between their distribution with depth and the depths of phase transitions within the mantle

three dimensional p velocity structures of the lithosphere beneath taiwan from the analysis of taiger and related seismic data sets 1 the convergence of the philippine sea and the eurasian plates in the taiwan region led to the formation of a young collisional mountain between two subduction zones of nearly orthogonal polarities the geological processes underlying the collision and its relation to subduction are the primary targets of taiger taiwan integrated geodynamic research project newly acquired passive and active sources data on land supplemented by ocean bottom as well as permanent seismic network data are used to derive a new 3 d tomographic velocity model using the 7 5 km sec contour as a marker for crustal deformation two trend parallel roots one under the central range with a maximum depth of 55 km and the other under the coastal range at 40 km are found to extend from southern to central 24 n taiwan between the two roots and lying approximately beneath the longitudinal valley the 7 5 km sec contour rises to 25 km depth in the upper mantle a high velocity zone east dipping and its upper surface coinciding with a wadati benioff zone in the south 22 8 n becomes near vertical and ill defined in the north 23 9 n the crustal deformation as defined by the roots and the along trend variations of the upper mantle structures under taiwan provide key information for the orogeny with the thickening of crust to 55 km or more processes such as eclogitization and delamination may come into play

silicon diffusion in forsterite aggregates implications for diffusion accommodated creep silicon diffusion rates were determined in fine grained 4 5 m hot pressed forsterite aggregates at 900 to 1200 c and 0 1 mpa using a 30si tracer and standard sims analysis there is no measurable difference in diffusion rates between samples buffered by excess mgo or sio2 nor samples run in dry n2 or h2 co2 the results yield the arrhenius parameters d0 bulk 5 4 10 9 m sec and q 203 36 kj mol at 1200 c the grain boundary diffusion rate of 30si is similar to 26mg si 10 times greater 10 less than fe and 105 less than o in addition the 30si grain boundary diffusion rate is 109 greater than the si volume diffusion rate and indicates that diffusional transport of si in forsterite aggregates is dominated by grain boundaries

sensitivity of the short to intermediate wavelength geoid to rheologic structure in subduction zones 1 the rheologic structure of subduction zones determines how the negative buoyancy of sinking lithosphere slabs couples to the surface to cause surface deformation and plate motion however the rheologic structures determined using different methods are inconsistent analysis of the geoid and some dynamical models conclude that slabs must be weak whereas other dynamical models and experimentally determined rheology predict that slabs are strong using idealized three dimensional models of a subduction zone we show that lateral variations in viscosity lvvs within a slab caused by yielding render the geoid insensitive to the viscosity structure outside of the bending region of the slab spectral analysis of the geoid up to harmonic degree 360 features at wavelengths down to 110 km shows that lvvs cause significant mode coupling with changes to the long wavelength geoid 1000 km caused by short wavelength 500 km changes to dynamic topography models with either a uniformly weak slab or a strong slab with yielding provide a good match to the observed geoid spectrum and characteristic features of the geoid over subduction zones therefore observations other than the geoid are needed to constrain the strength profile of subducting slabs

hydrogen self diffusivity in single crystal ringwoodite implications for water content and distribution in the mantle transition zone hydrogen lattice diffusion in fe bearing ringwoodite was investigated through hydrogen and deuterium interdiffusing in a pair of synthesized single crystals at various temperatures 1000 1300 k at 21 gpa diffusion profiles were investigated by secondary ion mass spectrometer to determine the hydrogen self diffusivity in ringwoodite temperature dependences of hydrogen diffusion in ringwoodite were determined to be dh 10 7 29 0 46 exp 101 10 kj mol 1 rt m2 s in ringwoodite at 21 gpa the proton conductivities of ringwoodite estimated from the present diffusion coefficients are similar to those of yoshino et al 2008 at the transition zone condition at low water content 1000 ppmw if the proton vacancy mechanism is assumed to be a main controlling mechanism contribution of water to the electrical conductivity of ringwoodite is insignificant due to large contribution of hopping conduction at the transition zone condition and global average water concentration in the lower part of transition zone is less than 1000 ppmw

routing debris flows with particle segregation a computer simulation method is developed to predict the temporal variations of debris flow discharge solids concentration and vertical mean particle size distribution a single finite step in the simulation is divided into two stages in the first stage a sediment bed composed of a well graded mixture is eroded by surface water introduced at the head of a channel thereby generating a debris flow in the second stage larger particles in the debris flow move upward because of dispersive force and are then transported forward faster than smaller particles which remain in the lower part of the flow because the velocity is slower in the lower layer another numerical simulation method is also developed to predict simultaneously the shape of the debris deposit area the distribution of the deposit thicknesses within the area and the three dimensional distribution of the mean diameters of the deposited particles both simulation methods are verified using laboratory experiments