convection within the inner core and thermal implications estimation of the rayleigh numbers of the inner core leads to the conclusion that even with low internal heating rates this region of the earth is convecting this work presents an axisymmetrical model able to investigate convection in a sphere and its applications to the earth s inner core rayleigh numbers ranging from the critical onset of the convection to ten thousand times the critical have been explored the thermal implications of a convecting inner core have been pointed out in all the cases the temperature profiles are very close to the adiabat leading to the possibility of a partially molten regions in the inner core indeed the most important effects appear in the first tens of kilometers just below the inner core surface and could be at the origin of the low quality factors q and q revealed by seismological studies

distinct layering in the hemispherical seismic velocity structure of earth s upper inner core the existence of hemispherical variation in the earth s inner core is well documented but consensus has not yet been reached on its detailed structure the uppermost layers are a region of particular importance as they are directly linked to the growth processes and post solidification mechanisms of the inner core here we use a large pkikp pkikp differential travel time residual data set to derive a model for the upper inner core providing new constraints on its isotropic and anisotropic velocity and the amount of scattering we find that the eastern and western hemisphere are separated by sharp boundaries this is incompatible with the recently proposed inner core translation model but might be explained by differences in outer core convection and inner core solidification rates the eastern hemisphere displays weak anisotropy of 0 5 1 0 the western hemisphere on the other hand is characterized by the presence of an isotropic upper layer with a thickness of 57 5 km with anisotropy of 2 8 appearing at deeper depths the boundary between the isotropic layer and the deeper anisotropy appears sharp we also detect for the first time a high velocity layer at the top of the eastern hemisphere with a thickness of 30 km which we interpret as being due to an increased amount of light elements there appears to be no relationship between the layered structure in the two hemispheres with abrupt changes in velocity with depth in one hemisphere without any significant change at the same depth in the other hemisphere our results indicate that there is a difference in composition and mineral structure between the hemispheres resulting in differing responses to external processes

geological implications of the 0212 earthquake in 2014 at the tatun volcano group of taiwan synergistic effects of volcanic and faulting activities abstract on february 12 2014 an ml 4 2 earthquake named 0212 eq occurred at the tatun volcano group tvg in northern taiwan seismic data from both the regional broadband array in taiwan and a local dense seismic network in the tvg indicate that the 0212 eq was located at a depth of 4 3 km near shamoshan one of the latest eruptive units in the tvg referring to the aftershocks surrounding the 0212 eq we further found that 1 they formed a linear seismic zone dipping 50 towards the southeast to reach the shanchiao fault that cuts through the tvg 2 focal mechanism of more than half of the larger aftershocks md 1 5 matched this linear seismic zone for a normal faulting and 3 the seismic b value was calculated to be 3 55 they are used to delineate the geometry of the shanchiao fault at the upper crust and to infer that localized geothermal fluid might have affected the activity of aftershocks as manifested by the very high seismic b value the strongly compensated linear vector dipole of the centroid moment tensor suggests the 0212 eq had a non double couple source resulted from the gravitational collapse thus we conclude that the 0212 eq was a combined synergistic effect of a collapsed reservoir filled with volcanic fluids and faulting activities along the shanchiao fault

imaging the inner core under africa and europe abstract the inner core under africa is thought to be a region where the nature of inner core texture changes from the strongly anisotropic western part of the inner core to the weakly anisotropic or isotropic eastern part of the inner core additionally observations of a difference in isotropic velocity between the two hemispheres have been made a very large new dataset of simultaneous pkpdf and pkpbc observations on which differential travel times have been measured is used to examine the upper 360 km of the inner core under europe africa and the surrounding oceans inversion of the differential travel time data for laterally varying inner core anisotropy reveals that inner core anisotropy is stronger under central africa and the atlantic ocean than under the western indian ocean no hemispherical pattern is present in voigt isotropic velocities indicating that the variation in anisotropy is due to differing degrees of crystal alignment in the inner core not material differences when anisotropy is permitted to change with depth the upper east most part of the study region shows weaker anisotropy than the central and western regions when depth dependence in the inner core is neglected the hemisphere boundary is better represented as a line at 40 e than one at 10 e however it is apparent that the variation of anisotropy as a function of depth means that one line of longitude cannot truly separate the more and less anisotropic regions of the inner core the anisotropy observed in the part of the inner core under africa which lies in the western hemisphere is much weaker than that under central america showing that the western hemisphere is not uniformly anisotropic as the region of low anisotropy spans a significant depth extent it is likely that heterogeneous heat fluxes in the core which may cause variations in inner core anisotropy have persisted for several hundred million years

texture of the uppermost inner core from forward and back scattered seismic waves body waves interacting with the boundary of the solid inner core at narrow and wide angles of incidence provide independent constraints on a heterogeneous texture that may originate from the process of solidification the equatorial quasi eastern hemisphere of the uppermost 50 100 km of the inner core is characterized by a higher isotropic p wave velocity lower q s inferred from pkikp and simpler pkikp pulses compared to adjacent regions in the western hemisphere and polar latitudes compared to this region the adjacent western primarily pacific equatorial region is characterized by higher q s and a higher level of coda excitation following pkikp lateral variations in both inner core q inferred from transmitted pkikp and inner core heterogeneity inferred from the coda of reflected pkikp can be modeled by lateral variations in a solidification fabric in an actively crystallizing eastern equatorial region characterized by upwelling flow in the outer core fabrics that explain strong attenuation and the absence of attenuation and velocity anisotropy in short range 120 140 pkikp and weak pkikp codas have an anisotropy of scale lengths with longer scale lengths in the vertical direction perpendicular to the inner core boundary in less actively solidifying regions in the equatorial western hemisphere longer scale lengths tend to be more parallel to the inner core boundary consistent with outer core flow tangent to the inner core boundary or viscous shearing and recrystallization in the horizontal direction away from more actively crystallizing regions in the eastern hemisphere this texture is less effective in attenuating pkikp by forward scattering lateral variation in the equatorial western hemisphere between vertical versus horizontal oriented plate like textures may explain lateral variations from weak to strongly back scattered pkikp coda and from strong to weak velocity and attenuation anisotropy in short range pkikp 2007 elsevier b v all rights reserved

growyouric a step toward a coherent model of the earth s inner core seismic structure a complex inner core structure has been well established from seismic studies showing radial and lateral heterogeneities at various length scales yet no geodynamic model is able to explain all the features observed one of the main limits for this is the lack of tools to compare seismic observations and numerical models successfully we use here a new python tool called growyouric to compare models of inner core structure we calculate properties of geodynamic models of the inner core along seismic ray paths for random or user specified datasets we test kinematic models which simulate fast lateral translation super rotation and differential growth we explore first the influence on a real inner core data set which has a sparse coverage of the inner core boundary such a data set is however able to successfully constrain the hemispherical boundaries due to a good sampling of latitudes combining translation and rotation could explain some of the features of the boundaries separating the inner core hemispheres the depth shift of the boundaries observed by some authors seems unlikely to be modelled by a fast translation but could be produced by slow translation associated to super rotation

detection of small scale heterogeneities at the inner core boundary 2018 elsevier b v the hemispherical pattern of seismic velocities in the uppermost inner core has been described at the global scale in many studies in this paper we investigate shorter scale heterogeneities in the vicinity of the inner core boundary icb using differential travel time and amplitude measurements between the pair of core phases pkp df and pkikp seismic events occurring close to sumatra and recorded at usarray stations in the distance range 132 142 are used to investigate the velocity and attenuation structure at the icb and in the uppermost 100 km of the inner core beneath eastern russia in this distance range pkp df and pkikp are difficult to separate due to their proximity in travel time we present a new method based on the envelope of the seismic signal to identify them following which we measure differential travel time residuals and amplitude ratios by comparison with synthetics computed using the direct solution method which allows us to take into account the correct phase shift of the pkikp we found that in our region of study the compressional velocity is slower in the uppermost inner core than the ak135 model however the sampled region is located in the eastern hemisphere generally considered as faster and more attenuating than the ak135 model this suggests significant regional departures from the simple hemispherical pattern reported in the literature we also deduce from the amplitude ratios that the attenuation is stronger than the global average at the top of the inner core in this region as expected from its location in the eastern hemisphere our results confirm the presence of a low attenuation zone at the top of the inner core followed by a highly attenuating layer centered around 35 km depth in the inner core as found in the eastern hemisphere in previous studies this zone is however thinner 15 km and more attenuating q reaching values less than 50

seismic tomography of the uppermost inner core abstract seismic body wave and normal mode analyses have revealed that the inner core is solid strongly anisotropic and characterized by dramatic quasi hemispherical differences in elastic structure and attenuation yet despite these discoveries the highly heterogeneous and incomplete data coverage of the inner core has impeded the development of tomographic models even at the longest wavelengths here we use a probabilistic and transdimensional tomographic approach tbi on a newly expanded dataset of p wave travel times sensitive to the upper 120 km of the inner core the tbi approach yields a ensemble of parsimonious models that simultaneously capture both the dominant hemispheric dichotomy and laterally abrupt velocity variations analysis of the model ensemble allows us to determine the locations of the hemisphere boundaries and rule out the presence of hemispheric dichotomy in anisotropy instead we robustly map regional variations in anisotropy beneath africa and the eastern pacific and detect variations at high latitudes suggesting that cylindrical anisotropy may not be adequate for describing the uppermost inner core

temporal variations of gas compositions of fumaroles in the tatun volcano group northern taiwan article i nfo he 4 he geochemical monitoring hydrothermal activity is common in the tatun volcano group of northern taiwan helium isotopic compositions of fumarolic samples show that mantle component occupies more than 60 in the previous study along with recent seismic results a magma reservoir is inferred to have existed beneath the area of da you keng where fumarolic venting is the most active in tatun volcano group progressive increases of hcl concentrations and so2 h2s ratio in fumaroles from da you keng have been observed since august 2004 the hcl concentration changed from almost the detection limit to thousands of ppm even up to 30 000 ppm so2 h2s ratios varied from almost 0 to 3 hence so2 became the dominated s species in this area these variations were accompanied by rising temperature of fumaroles in the tatun volcano group especially in the area of da you keng from boiling point to 131 c meanwhile 3

volcano hydrothermal inflation revealed through spatial variation in stress field in tatun volcano group northern taiwan abstract to investigate the inflation characteristics of subsurface volcano hydrothermal activity we examine the spatial variability of the stress field in the tatun volcano group tvg of northern taiwan using 1016 earthquake focal mechanisms at depths shallower than 5 km from 2012 to 2017 we determine these focal mechanisms using the data from a dense seismic network composed of 40 seismic stations in an area of approximately 10 10 km2 in the tvg we find that this area is subject to the northwest southeast trended extension and subvertical compression the stress magnitude ratios near the dayoukeng area are significantly lower than that in the other areas this feature is likely related to an inflating source buried underneath the dayoukeng area our model shows good agreement between the observed and predicted values when the inflating pressure source located at a depth of approximately 2 km and with the average potency ranging from 1 4 105 to 7 105 m3 near the dayoukeng area we suggest that this inflation is associated with the local volcano hydrothermal activity this inflation is the principal pressure source in the shallow crust 5 km at depth in the tvg and may persist for at least a decade

gully incision as a key factor in desertification in an arid environment the negev highlands israel abstract gully incision has been eroding the alluvial sediments and loess soils deposited and developed along the valleys in the arid and semiarid regions of israel this phenomenon is critical in the arid regions of the negev highlands where the agricultural fields the main floral biomass and the areas which have the highest grazing value are limited to narrow valleys filled with redeposited loessial sediments the headcut migration and gully development in the region were studied between 1990 and 2001 in three representative drainage basins zipporim revivim and sekher during flood events the runoff penetrates the alluvial cover of the valleys forming vertical headcuts which gradually retreat up the valley the runoff is channeled into narrow gullies preventing the floodwater from spreading over the whole width of the valley the change in irrigation efficiency along the valleys is reflected in a sharp estimated drop of 70 90 in the floral biomass causing the reduction of the range value by 83 99 during the monitoring time interval 1990 2001 the linear gully retreat in the study area ranged between 12 3 and 250 m an average rate of 1 12 22 7 m year 1 for each gully head the process is accompanied by erosion of soil which has high agricultural and range value the total soil losses in these sites ranged between 800 and 9000 m3 at an average rate of 81 818 m3 year 1 for each gully head which is equivalent to 121 1227 mg year 1 during the monitoring period approximately 0 11 0 87 ha of land lost its agricultural and range value in each basin under study at an average rate of 0 01 0 079 ha year 1 since the byzantine period 1400 bp approximately 6 5 ha which is 10 of the land that had high agricultural and range value in the zipporim valley lost its value due to gully erosion no recovery effects of the gully channels were found in the nearby region the soil erosion is generated by a long term natural dynamic change in the soil rock ratio evolving within the drainage basins through time since the termination of the last glacial phase the loessic sediments originally deposited within the drainage basins during the late pleistocene glacial stage are being removed under the present holocene climate in several erosion stages this ongoing phenomenon is causing degradation of soil and biomass and is severely reducing the agricultural and range potential of the region these parameters indicate that an ongoing process of desertification is active in the arid environment of the negev highlands and is advancing in proportion to the headcut retreat rates in the region the soil erosion and headcut retreat have been active in the negev highlands for the last few millennia if these processes continue in the future the negev highlands region will lose its agricultural potential within a few millennia however the fact that the ancient inhabitants of the region implemented successful long term land conservation techniques already 3000 years ago implies that a sustainable land management policy can be adapted to the negev highlands as well as to other semi arid regions in the middle east

an empirical relationship between seismic attenuation and velocity anomalies in the upper mantle we use recent p wave attenuation q 1 and velocity vp tomographic models of the tonga fiji region to obtain an empirical relation between attenuation and velocity for the upper mantle the attenuation and velocity anomalies show a strong inverse correlation allowing the determination of an empirical relationship the relationship is similar to a predicted relation derived from laboratory experiments on peridotite and dunite assuming the observed anomalies result from temperature variations the results here suggest that the observed anomalies are generally consistent with the effect of temperature and demonstrate that the combination of velocity and attenuation data provides powerful constraints on the physical state of upper mantle materials we find that the chosen geotherm and activation energy has a strong effect on the position of the solidus within the seismic data

prehistoric earthquakes along the shanchiao fault taipei basin northern taiwan abstract stratigraphic relations recorded in boreholes drilled along the shanchiao fault a normal fault that bounds the western margin of metropolitan taipei reveal evidence of early mid holocene subsidence and active extension of the taipei basin paleoseismic data suggest that the maximum displacement for each subsidence event ranges from 2 3 to 4 5 m despite large uncertainties the large offsets imply earthquake magnitudes that range in size from 6 9 to 7 1 our results suggest that large magnitude earthquakes along the shanchiao fault are one of the major seismic hazards in the metropolitan taipei area

seismogenic stress field beneath the tatun volcano group northern taiwan article i nfo the tatun volcano group tvg represents the main volcanic center in northern taiwan and based on various observations it is considered a potentially active volcano tvg has been monitored since 2003 by a seismic network that consists of eight stations equipped with three component short period and broadband seismometers in this study we use waveform data of high frequency earthquakes in order to investigate the stress field orientation beneath the tvg area the focal mechanisms of 35 selected events have been derived using p wave polarities and amplitude ratios assuming a double couple source these fault plane solutions and various subsamples derived from them were subsequently inverted for the best fitting stress tensor using a linear inversion method the results show stress homogeneity beneath tvg for depths larger than 3 km while the stress tensor is characterized by a subvertical 1 and a subhorizontal nw se trending 3 axis consistent with the regional stress field in northern taiwan on the other hand chihsinshan which is an area of vigorous hydrothermal activity exhibits a localized stress field with horizontal nw se trending 3 axis and ne sw trending horizontal 1 such an axes orientation is likely to be causing opening of microcracks and thus favour the ascent and circulation of fluids in the upper crust shear wave splitting measurements seem to confirm these results showing fast polarization directions along nne ne subparallel to the main fracture system in tvg shear wave anisotropy averages about 2 9 and is probably caused by an anisotropic volume of fluid saturated cracks within the upper 2 5 km of the crust

the inner core hemispheric boundary near 180 w abstract the inner core ic east west hemispheric dichotomy is widely recognized but the reported position of the hemispheric boundary varies among studies due to uneven sampling coverage and the data analyzed this study investigates the sharpness of the western hemispheric boundary whb near 180 w by analyzing differential time residuals of pkikp pkpdf and pkp bc df for pkpdf phases that sample 155 e 130 w in various azimuthal directions using pkikp pkpdf observations the whb is located at 175 e 180 w in the southern hemisphere based mainly on the lateral isotropy anisotropy transition however based on the lateral isotropic velocity contrast and this isotropy anisotropy transition between the two hemispheres its location is 170 160 w in the northern hemisphere these findings indicate that the whb is sharp and exhibits a latitudinal dependence with a 10 20 kink as well as 1 75 anisotropy in the uppermost ic across the 180 155 w range of the western hemisphere as suggested by pkp bc df the whb could remain at 160 w at depth the isotropic velocity contrast near the whb 160 w between the eastern and western hemispheres is lower than previous estimates using pkpdf phases sampling the bulk part of each hemisphere

preliminary analysis of volcanoseismic signals recorded at the tatun volcano group northern taiwan 1 the tatun volcano group lies at the northern tip of taiwan only 15 km north of the capital taipei a seismic array consisting of 5 stations equipped with both broadband and short period sensors was installed in 2003 in order to monitor the seismic activity of the area it recorded a variety of events including common volcano tectonic earthquakes and volcanoseismic signals like tornillos short duration monochromatic events 10 15 s and long duration spasmodic bursts 15 min an analysis of the complex frequencies of the tornillo monochromatic signals shows that q values are of the order of several hundreds based on the model of a fluid filled crack such q values can result from the oscillations of a crack containing a misty or dusty gas these observations put into doubt the long standing suggestion that the tatun volcanoes are extinct and prompt for a thorough assessment of the volcanic hazard for this area

very long period seismic signals at the tatun volcano group northern taiwan abstract very long period vlp seismic events have been detected in the tatun volcano group tvg located around the border between taipei city and new taipei city in northern taiwan in which has 7 million residents by using both analyses of particle motions and travel time delay one vlp volcanic earthquake s source is estimated to be at a shallow depth 800 m beneath mt chihsin which is the highest and youngest volcano in the tvg the significant variation of seismic energy at different azimuths provides strong evidence to distinguish a crack source from other kinds of sources such as a sphere vertical pipe or even double couple source this is further confirmed by synthetic modeling of the seismograms recorded at two stations as well as the compressional first motion at three seismic stations thus a deeper plumping system with high pressure fluid is required to generate the vlp signals and other volcanic earthquakes in the tvg combining this result with those of previous studies we conclude that the tvg might not be totally extinct and some further investigations must be carried out to improve understanding of the volcanic characteristics of the tvg

the feasibility of thermal and compositional convection in earth s inner core inner core convection and the corresponding variations in grain size and alignment has been proposed to explain the complex seismic structure of the inner core including its anisotropy lateral variations and the f layer at the base of the outer core we develop a parametrized convection model to investigate the possibility of convection in the inner core focusing on the dominance of the plume mode of convection versus the translation mode we investigate thermal and compositional convection separately so as to study the end members of the system in the thermal case the dominant mode of convection is strongly dependent on the viscosity of the inner core the magnitude of which is poorly constrained furthermore recent estimates of a large core thermal conductivity result in stable thermal stratification hindering convection however an unstable density stratification may arise due to the pressure dependant partition coefficient of certain light elements we show that this unstable stratification leads to compositionally driven convection and that inner core translation is likely to be the dominant convective mode due to the low compositional diffusivity the style of convection resulting from a combination of both thermal and compositional effects is not easy to understand for reasonable parameter estimates the stabilizing thermal buoyancy is greater than the destabilizing compositional buoyancy however we anticipate complex double diffusive processes to occur given the very different thermal and compositional diffusivities

seismic quiescence before the 1999 chi chi taiwan mw 7 6 earthquake the chi chi taiwan earthquake of 20 september 1999 was preceded by a notable decrease of the regional seismicity rate the anomalous period started in january 1999 and lasted about 9 months up to the occurrence of the mainshock as revealed from analyzing the taiwan catalog data from 1 january 1994 to 20 september 1999 our results indicate that the mean seismicity rate is 435 events per month with a standard deviation of 78 events for earthquakes with magnitude above 2 0 during the anomalous period seismicity rates fell outside the range of one standard deviation with a mean value of 314 events per month there was also a consistent trend of decreasing regional b value as well as notable increases of seismic activity in areas surrounding the chi chi earthquake source region via the z test map zmap analysis

seismic velocity and attenuation structures in the top of the earth s inner core 1 we collect a global data set of pkikp and pkikp phases recorded by the global seismic network and many regional seismic arrays to study seismic structure in the top of the earth s inner core the pkikp and pkikp observations show different characteristics between those sampling the eastern hemisphere 40 e 180 e of the inner core and those sampling the western hemisphere 180 w 40 e pkikp phases 1 arrive about 0 4 s earlier than the theoretical arrivals based on preliminary reference earth model prem for those sampling the eastern hemisphere of the inner core and about 0 3 s later for those sampling the western hemisphere 131 141 2 bifurcate at smaller epicentral distances for those sampling the eastern hemisphere compared to those sampling the western hemisphere and 3 have smaller amplitudes for those sampling the eastern hemisphere waveform modeling of these observations suggests two different types of models for the two hemispheres of the top of the inner core with a model in the eastern hemisphere having a p velocity increase of 0 765 km s across the inner core boundary a small radial velocity gradient of 0 000055 km s km and an average q value of 250 and a model in the western hemisphere with a p velocity increase of 0 633 km s across the inner core boundary a radial velocity gradient of 0 000533 km s km and an average q value of 600 the hemispherical difference of seismic structures may be explained by different geometric inclusions of melt and or different alignments of iron crystals with anisotropic properties in both velocity and attenuation we speculate that this large scale pattern of seismic heterogeneities may be caused by a large scale heat flow anomaly at the bottom of the outer core and or different vigorousness of convection in the top of the inner core between the two hemispheres

anomalously strong observations of pkikp pcp amplitude ratios on a global scale the inner core boundary marks the phase transition between the solid inner core and the fluid outer core as the site of inner core solidification the boundary provides insight into the processes generating the seismic structures of the inner core in particular it may hold the key to understanding the previously observed hemispherical asymmetry in inner core seismic velocity anisotropy and attenuation here we use a large pkikp pcp amplitude ratio and travel time residual data set to investigate velocity and density contrast properties near the inner core boundary although hemispherical structure at the boundary has been proposed by previous inner core studies we find no evidence for hemispheres in the amplitude ratios or travel time residuals in addition we find that the amplitude ratios are much larger than can be explained by variations in density contrast at the inner core boundary or core mantle boundary this indicates that pkikp is primarily observed when it is anomalously large due to focusing along its raypath using data in which pkikp is not detected above the noise level we calculate an upper estimate for the inner core boundary icb density contrast of 1 2 kg m 3 the travel time residuals display large regional variations which differ on long and short length scales these regions may be explained by large scale velocity variations in the f layer just above the inner core boundary and or small scale topography of varying magnitude on the icb which also causes the large amplitudes such differences could arise from localized freezing and melting of the inner core

melting induced stratification above the earth s inner core due to convective translation several observed properties of earth s solid inner core and liquid outer core remain enigmatic including an east west seismic asymmetry and the presence of a roughly 250 kilometre thick layer of reduced seismic velocity at the base of the outer core alboussiere et al now suggest a model that can produce both of these features based on experiment and numerical modelling they propose that simultaneous crystallization and melting at opposite sides of earth s inner core surface can result in a translational mode of thermal convection within the inner core which also introduces an asymmetry between hemispheres these authors show that simultaneous crystallization and melting at the surface of the earth s inner core can result in a translational mode of thermal convection within the inner core producing the observed stratified layer of reduced seismic velocity at the base of the outer core the dynamical model they propose also introduces an asymmetry between hemispheres that may explain the enigmatic east west asymmetry in seismic properties of the inner core in addition to its global north south anisotropy1 there are two other enigmatic seismological observations related to the earth s inner core asymmetry between its eastern and western hemispheres2 3 4 5 6 and the presence of a layer of reduced seismic velocity at the base of the outer core6 7 8 9 10 11 12 this 250 km thick layer has been interpreted as a stably stratified region of reduced composition in light elements13 here we show that this layer can be generated by simultaneous crystallization and melting at the surface of the inner core and that a translational mode of thermal convection in the inner core can produce enough melting and crystallization on each hemisphere respectively for the dense layer to develop the dynamical model we propose introduces a clear asymmetry between a melting and a crystallizing hemisphere which forms a basis for also explaining the east west asymmetry the present translation rate is found to be typically 100 million years for the inner core to be entirely renewed which is one to two orders of magnitude faster than the growth rate of the inner core s radius the resulting strong asymmetry of buoyancy flux caused by light elements is anticipated to have an impact on the dynamics of the outer core and on the geodynamo

b values of shallow earthquakes in taiwan abstract in taiwan the b values of earthquakes with focal depths of less than 35 km are smaller offshore than on land on land except for the coastal range the b value correlates to the degree of metamorphism of rocks which decreases inland from east to west small b values appear at the leading edge of the subducting slab of the philippine sea plate that plunges underneath northern taiwan possibly indicating high stress due to a bending of the slab large b values in an area including the volcano groups in northern taiwan may be due to the remnant geothermal effect after past volcanic activities besides small b values on land are mainly associated with low bouguer gravity anomalies offshore small b values are related to high bouguer gravity anomalies particularly in regions with a large gravity gradient

seismic anisotropy of the earth s inner core resulting from flow induced by maxwell stresses seismological observations indicate that the inner core of the earth is elastically anisotropic1 anisotropic structures are likely to be formed by dynamic processes and therefore such observations have the potential to provide constraints on flow in the inner core and on the geodynamo itself but in addition to the difficulties in estimating the relevant physical properties of iron under inner core conditions2 3 4 even the macroscopic processes responsible for generating seismic anisotropy in this region have yet to be determined5 6 7 8 9 as a result the geodynamic significance of seismic anisotropy in the inner core has remained unknown here i propose based on geodynamic and mineral physics considerations that flow induced by the stress due to the magnetic field the maxwell stress near the inner core boundary produces an axisymmetric fabric responsible for the observed seismic anisotropy the resultant seismic anisotropy reflects the geometry of the magnetic field near the inner core boundary and therefore seismological observations might provide constraints on the geodynamo this flow also causes non uniform release of energy at the inner core boundary associated with solidification and melting which may affect the pattern of convection in the outer core

production storage and output of particulate organic carbon waipaoa river basin new zealand 1 we compute the particulate organic carbon poc yield of the waipaoa river new zealand using sediment rating curves in conjunction with measurements of the carbon content of the suspended sediment to ascertain the source of the carbon and the extent to which the poc flux is tied to different erosion processes we determined the stable isotopic carbon composition 13c and carbon to nitrogen c n ratio of weathered bedrock soil and regolith most poc is derived from suspended sediment generated by gully erosion incision into weathered bedrock supplemented by landsliding during extreme events the specific yield of poc from the headwaters drainage area 1580 km2 is 55 g m 2 yr 1 which is very high by global standards and by comparison with other turbid steep land rivers the annual loss to floodplain storage is 4 3 6 kt of the mean annual poc yield 86 7 kt thus the waipaoa river is a very effective conduit for transporting poc to the ocean

eccentricity of the geomagnetic dipole caused by lopsided inner core growth the axis of the geomagnetic field is offset eastwards from earth s centre by more than 500 km simulations of earth s geomagnetic field using a numerical dynamo model show that lopsided growth of the inner core with faster solidification occurring in one hemisphere could cause the offset

human impact on the environment in the ethiopian and eritrean highlands a state of the art abstract this review analyses the environmental evolution of the ethiopian highlands in the late quaternary the late pleistocene 20 000 12 000 14c years bp was cold and dry with 1 low lake levels in the rift valley 2 large debris fans on the flanks of lake abhe basin and 3 the blue nile transporting coarse bedload then a period with abundant and less seasonal rains existed between 11 500 and 4800 14c years bp as suggested by increased arboreal pollen high river and lake levels low river turbidities and soil formation around 5000 4800 14c years bp there was a shift to more arid conditions and more soil erosion many phenomena that were previously interpreted as climate driven might however well be of anthropic origin thick sediment deposits on pediments as well as an increase of secondary forest scrub and ruderal species in pollen diagrams are witnesses of this human impact one important aspect of the late quaternary palaeoenvironment is unclear changes in nile flow discharges and rift valley lake levels have been linked to changes in precipitation depth most authors do not take into account changes in land use in the highlands nor changes in the seasonality of rain both of which can lead to a change in runoff coefficients tufa and speleothem deposition around 14 000 years ago tend to indicate that at the end of the last glacial maximum lgm conditions might have been wetter than generally accepted the most important present day geomorphic processes are sheet and rill erosion throughout the country gullying in the highlands and wind erosion in the rift valley and the peripheral lowlands based on existing sediment yield data for catchments draining the central and northern ethiopian highlands an equation was developed allowing to assess area specific sediment yields sy 2595a 0 29 n 20 r 2 0 59 where sy area specific sediment yield t km 2 year 1 and a drainage area km2 with respect to recent environmental changes temporal rain patterns apart from the catastrophic impact of dry years on the degraded environment cannot explain the current desertification in the driest parts of the country and the accompanying land degradation elsewhere causes are changing land use and land cover which are expressions of human impact on the environment deforestation over the last 2000 3000 years was probably not a linear process in ethiopia studies on land use and land cover change show however a tendency over the last decades of increasing removal of remnant vegetation which is slowed down or reversed in northern ethiopia by a set aside policy ongoing land degradation requires urgent action at different levels of society soil and water conservation swc structures are now widely implemented local knowledge and farmer s initiatives are integrated with introduced swc techniques at various degrees impact assessments show clear benefits of the soil conservation measures in controlling runoff and soil erosion in high rain areas runoff management requires greater emphasis during the design of soil conservation structures in such areas investment in swc might not be profitable at farm level although benefits for society are positive this pleads in favour of public support the present land degradation in the ethiopian highlands has a particular origin which includes poverty and lack of agricultural intensification causes of these are to be found in the nature of past and present regional social relations as well as in international unequal development this review strengthens our belief that under improved socio economic conditions land husbandry can be made sustainable leading to a reversal of the present desertification and land degradation of the ethiopian highlands

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

measuring the seismic velocity in the top 15 km of earth s inner core abstract we present seismic observations of the uppermost layer of the inner core this was formed most recently thus its seismic features are related to current solidification processes previous studies have only constrained the east west hemispherical seismic velocity structure in the earth s inner core at depths greater than 15 km below the inner core boundary the properties of shallower structure have not yet been determined because the seismic waves pkikp and pkikp used for differential travel time analysis arrive close together and start to interfere here we present a method to make differential travel time measurements for waves that turn in the top 15 km of the inner core and measure the corresponding seismic velocity anomalies we achieve this by generating synthetic seismograms to model the overlapping signals of the inner core phase pkikp and the inner core boundary phase pkikp we then use a waveform comparison to attribute different parts of the signal to each phase by measuring the same parts of the signal in both observed and synthetic data we are able to calculate differential travel time residuals we apply our method to data with ray paths which traverse the pacific hemisphere boundary we generate a velocity model for this region finding lower velocity for deeper more easterly ray paths forward modelling suggests that this region contains either a high velocity upper layer or variation in the location of the hemisphere boundary with depth and or latitude our study presents the first direct seismic observation of the uppermost 15 km of the inner core opening new possibilities for further investigating the inner core boundary region

the innermost inner core of the earth evidence for a change in anisotropic behavior at the radius of about 300 km since the discovery of the inner core in 1936 no additional spherical subshell of the earth has been observed based on an extensive seismic data set we propose the existence of an innermost inner core with a radius of 300 km that exhibits a distinct transverse isotropy relative to the bulk inner core specifically within the innermost inner core the slowest direction of wave propagation is 45 from the east west direction in contrast the direction of the slowest wave propagation in the overlying inner core is east west the distinct anisotropy at the center of the earth may represent fossil evidence of a unique early history of inner core evolution

historical evolution of permanent gullies in the myjava hill land slovakia abstract the myjava hill land is part of the area with the highest density of permanent gullies in slovakia up to 11 km km 2 gullies are often 10 15 m deep and occasionally extend 20 m the pattern and density of gullies have been controlled primarily by the original land use from the pre collectivization era old maps and historical sources indicate two to three periods of gully formation the central part of the area settled between the second half of the 16th and the beginning of the 19th centuries was affected by gully formation in two periods the first between the end of the 16th century and the 1730s and the second roughly between the 1780s and 1840s marginal parts of the study area to the west and south west which were settled earlier may have been affected by disastrous gullying as early as the 14th century gullies were formed during periods of extensive forest clearance and expansion of farmland but the triggering mechanism of gullying was extreme rainfalls during the little ice age however periods of gully formation in the myjava hill land were not fully synchronous with the well known phases of gullying in other central european countries

structure and dynamics of earth s inner core abstract the seismological exploration of the earth s inner core has revealed unexpected and puzzling structural complexities its elastic anisotropy is now well established and has been shown to vary spatially there is a well defined hemispherical dichotomy in anisotropy and attenuation and significant variations in the radial direction with weaker anisotropy in the uppermost regions and possibly different properties in an innermost inner core of radius 300 600 km perhaps even more puzzling is the observation of a stably stratified layer at the base of the outer core which has recently been proposed to result from melting of inner core material if confirmed the presence of this layer has major implications for our understanding of convection in the outer core inner core differential rotation with respect to the mantle remains controversial we will review here recent progress in understanding the dynamics of the inner core a number of different models have been proposed for the development of the inner core s structure and formation of the stable layer at the base of the outer core and particular care will be taken to clarify under which conditions the proposed mechanisms can be active

hemispherical transition of seismic attenuation at the top of the earth s inner core in contrast to the liquid outer core the earth s inner core is mostly solid and its composition is more pure iron based on dynamic arguments related to the freezing process of the inner core and the observation of much lower p wave quality factor in the inner core q 10 000 it has been suggested that a mushy layer with liquid inclusions may exist at the top of the inner core on the other hand seismic measurements indicate that q increases towards the center of the inner core we here present estimates of q in the depth range 32 110 km beneath the inner core boundary icb based on the measurement of pkikp pkikp amplitude ratios after a narrow band pass filtering 0 7 2 0 hz our measurements indicate that there are pronounced hemispherical differences in the values of q 335 and 160 in the western 180 w to 40 e and eastern 40 e to 180 e hemispheres respectively and in the depth of transition from decreasing to increasing q 32 km beneath the icb in the eastern hemisphere and 85 km in the western hemisphere below 85 km the hemispherical pattern disappears we also confirm the existence of a correlated hemispherical pattern in p velocity down to 85 km the p velocity and q variations are compatible with an interpretation in terms of small hemispherical variations of temperature at the top of the inner core and their influence on the morphology of porosity and connectivity of liquid inclusions in the mushy zone the disappearance of the differences in q beneath 85 km provide constraints on the likely depth extent of the mushy zone

sharp hemisphere boundaries in a translating inner core 1 geodynamic models of a convectively translating inner core have recently been proposed that would account for the seismically observed differences in isotropic velocity between the eastern and western hemispheres of the inner core these models however have previously been thought to be incompatible with seismic observations of a 1 5 p wave velocity change occurring over an 800 km wide region at the boundary between hemispheres of the inner core here we show that if rigid translation occurs the age of material in the 100 km below the inner core boundary changes quickly as it crosses the boundary between the western and eastern hemispheres we then forward model seismic traveltimes to show that the sharp transition in vp between hemispheres may be explained by a random distribution of highly oriented crystalline domains that grow during translation and are composed of material with relatively high elastic anisotropy up to 12

sharpness of the hemispherical boundary in the inner core beneath the northern pacific abstract the hemispherical nature of heterogeneities of the isotropic velocity and attenuation of the inner core has been extensively studied by seismic observations but consensus on the character of the boundary between two hemispheres has not yet been achieved to investigate the hemispherical boundary in detail we analyze core phase data whose ray paths propagate beneath the northern pacific we employ a waveform inversion approach based on simulated annealing to measure the differential traveltime and the attenuation parameter of the core phases measured differential traveltimes for data from european stations for events in the fiji tonga region show positive anomalies consistent with the eastern hemisphere model while those from usarray for events in indonesia show relatively small values ray theory based forward modeling of the differential traveltimes is conducted by varying the shape and the transition width of the boundary an arc like shape boundary that connects points 0 n 159 w on the equator and 79 n 110 e in far north with a transition width of 600 km best explains the observed differential traveltimes rather than a sharp boundary this model also accounts for the observed variation of attenuation parameters

monitoring of gully erosion on the loess plateau of china using a global positioning system abstract with the development of a technique global positioning system gps has become progressively less expensive lighter and easier to use the accuracy of gps has been improved and it appears applicable to the continuously monitoring morphology changes on the earth surface with small and slow change the objective of this study is to use gps to measure the morphology of gullies in a small catchment near suide shaanxi province china there are three main gully types in the study area bank gullies floor gullies and hill slope gullies and this study mainly focuses on the hill slope gullies the hill slope gullies in the study area are mainly discontinuous and are developing rapidly the gully density in the study area is very large the retreat rate of hill slope gullies is 0 16 2 02 m year 1 the relationships between the upslope drainage area a and the critical slope gradient s for hill slope gullies is s 0 1839a 0 2385 the values of as2 range from 41 to 814 m2 for the hill slope gully headcuts and most of them fell into the range of 100 300 m2 both of these relationships are suggested as indexes for estimating the location of gully headcuts

elucidating the geometry of the active shanchiao fault in the taipei metropolis northern taiwan and the reactivation relationship with preexisting orogen structures the shanchiao fault is an active normal fault with documented paleoearthquakes in the taipei metropolis taiwan while posing direct seismic threat on the multimillion population its crustal scale fault plane configuration has not been constrained this study presents the first attempt to resolve the fault plane dip changes of the shanchiao fault within the upper crust by forward modeling late quaternary deformation tectonic subsidence over the last 23 ka is estimated from vertical displacements of a rapidly formed alluvial fan horizon deformed into a dramatic rollover monocline a 2 d profile across the shanchiao fault is chosen for elastic half space dislocation modeling and the results suggest that the fault is listric in the shallow crust with an abrupt change from subvertical ramp 85 75 to near horizontal flat 10 15 at 3 4 km depth consistent with an origin from the inversion of an orogen related thrust detachment given the presence of rift related fabrics in the underthrust chinese continental margin basement beneath the taiwanese orogenic wedge listric ramp flat ramp models with a second deeper bend to 60 dip are also tested reasonable fits with the geological observations are produced when the lower ramp is located at greater than 8 km depth which correlates with the hypocentral location of a moderate earthquake in 2004 joint reactivation of preexisting thrust and rift faults by the shanchiao fault is therefore plausible with implications for seismic hazard in the taipei area

hemispherical structure in inner core velocity anisotropy 1 we investigate the hemispherical pattern in inner core velocity anisotropy using a new and independent high quality data set of pkpbc pkpdf and pkpab pkpdf body wave observations our data show no evidence for a tilted anisotropy axis with respect to the earth s rotation axis and is significantly better fit by a model with 4 4 anisotropy in the western hemisphere and only 1 0 in the eastern hemisphere than by a model of uniform anisotropy we carry out variance minimization and find the boundaries between the hemispheres at lines of constant longitude at 14 e and 151 w variance minimization enables us to extract the imprint of hemispherical structure from all of the data and not just polar paths resulting in boundaries which are nearly 30 from the results of previous studies the high quality of the data allows us to provide robust evidence that the isotropic velocity in the eastern hemisphere is 0 2 lower than in the western hemisphere in the top 660 km of the inner core our data set also suggests an increase in inner core anisotropy in the eastern hemisphere from 1 to around 6 at depths deeper than 660 km indicating that the hemispherical pattern in anisotropy may disappear at greater depths the presence of hemispherical structure rules out mechanisms for creating anisotropy which are unable to sustain longitudinal variations in the inner core furthermore steady inner core superrotation of the order of 0 1 year would eradicate the hemispherical differences though inner core oscillation would still be permissible

volcano hydrothermal activity detected by precise levelling surveys at the tatun volcano group in northern taiwan during 2006 2013 abstract precise levelling surveys were conducted from 2006 to 2013 on three levelling routes in the tatun volcano group tvg located approximately 15 km northeast of taipei to detect deformation in relation to the volcano hydrothermal activities of the tvg uplift was detected around the most active fumarole tayoukeng fumarole throughout the period 2007 to 2011 the uplift rate throughout the period from march 2009 to march 2011 was reduced in comparison to the rate between 2007 and 2009 following this a dormant state or a small amount of subsidence was detected in the period march 2011 to march 2013 and throughout the period from june 2006 to march 2013 subsidence was centred on an area 0 5 km east of the summit of mt cising the highest peak in the tvg a model of two spherical sources was therefore estimated from the deformation recorded from august 2007 to march 2011 using a genetic algorithm a deflation source was obtained about 0 5 km northeast of mt cising at a depth of 2 km and an inflation source was situated approximately 1 km south of the tayoukeng fumarole at a depth of 0 7 km based on previous seismic and amt studies the estimated sources are interpreted as being hydrothermal reservoirs because almost all the benchmarks around mt cising show subsidence at a constant speed we conclude that the deeper hydrothermal reservoir at a depth of 2 km may have been releasing hydrothermal fluid at a constant rate throughout the period from 2006 to 2013 however it was suggested that in 2011 the shallower hydrothermal reservoir at a depth of 0 7 km changed from an inflation state to a dormant state or small deflation based on temporal vertical changes around tayoukeng fumarole a possible model for the volcano hydrothermal system is therefore proposed it is considered that the hydrothermal fluid may be supplied intermittently from the magma chamber to the deeper hydrothermal reservoir at a depth of 2 km although this type of fluid input event may not have occurred during our research period and that the hydrothermal fluid upwelling between mt cising and tayoukeng fumarole flows transversally into a highly cracked and fluid saturated area that continues to tayoukeng fumarole the existence of a shallower hydrothermal reservoir at a depth of 0 7 km in the highly cracked and fluid saturated area is therefore plausible

study of infiltration in a sahelian gully erosion area using time lapse resistivity mapping abstract observing that concentrated runoff destroys indurate and impermeable surface horizons to form gullies on sahelian slopes we investigated whether these gullies are preferential places for deep infiltration and groundwater recharge processes the primary aim of this study is to determine if resistivity mapping is an appropriate method to use for locating recharge zones from the surface the study area in northern burkina faso is a typical 1 ha gully erosion area located at the outlet of an 82 ha catchment with solonetz soils and a crystalline basement taking advantage of a long dry season followed by a short rainy season we made use of a time lapse approach to carry out electrical resistivity mapping and monitor apparent resistivity variations that occurred in the soils during the rainy season between june and september we made nine apparent resistivity maps in the year 2000 and two in january and march 2001 to monitor expected infiltration and percolation to depths of 5 m or more we laid out wenner array profiles with an inter electrode spacing of 5 m the time lapse mapping was also controlled with i neutron probe measurements ii resistivity measurements on outcrops during infiltration tests iii electrical resistivity logging in auger holes geophysical results showed that the apparent resistivity parameter can either decrease typical case or increase unexpected case after a rain neutron probe measurements indicated that infiltration varies within a few decimeters even at the centre of the main gully using one dimensional 1d modelling based on resistivity variations monitored during infiltration tests we concluded that apparent resistivity variations are linked to the presence of carbonate in the soils when soluble carbonates are present the resistivity of the infiltrated layer varies from 220 m dry state to less than 5 m wet state bringing about a decrease in apparent resistivity value for the 5m spacing in the absence of carbonate resistivity varies from 1500 to 180 m but produces an increase of the apparent resistivity value for the same spacing consequently we found time lapse apparent resistivity mapping to be an efficient way to delineate certain soil properties it also provided additional information about punctual observations however our results have led us to conclude that the 5 m inter electrode spacing is too large to monitor this type of shallow infiltration phenomenon and that the effect of temperature on resistivity should be considered when comparing maps over the period of a few months furthermore this type of survey should be controlled using electrical loggings in auger holes or electrical soundings in order to get a better understanding of in depth resistivity variations finally this survey indicated that deep infiltration processes are not occurring below the gully situated on the slope further studies are required downstream to identify the location of groundwater recharge in sahelian crystalline contexts

medium term evolution of a gully developed in a loess derived soil field surveys in the belgian loess belt revealed the presence in many forested areas of large permanent gully systems most of which are currently inactive in cultivated areas such gullies can only be observed in cross sectional soil profiles through hollows as virtually all such large gullies are currently infilled with colluvium little is known about the spatial distribution initiation and temporal evolution of these large permanent gully systems on loess derived soils therefore the medium term evolution of a gully initiated in a cultivated area on loess derived soils southwest of leuven belgium in may june 1986 was studied over 13 years two intense rainfall events created this ephemeral gully which was not erased by subsequent tillage between june 1986 and the december 1999 eight field surveys were conducted to measure gully dimensions during two surveys topographic indices e g slope and drainage area were also measured daily rainfall for the measuring period were obtained from a rainfall station located some 10 km southwest of the gully analysis of rainfall data showed that no extreme rainfall event was required to initiate such large permanent gullies as observed in forested areas and through cross sectional profiles in cultivated fields in the belgian loess belt return periods of the event that caused the gully varied between 1 year and 25 years depending on the assumptions used for defining event rain intensity once established length surface area and volume of the studied gully evolved with time cumulative rainfall or cumulative runoff following a negative exponential relation this accords with observations reported for gullies in australia and the usa this study shows that a degressive increase of gully extension can be largely explained by the evolution of a slope drainage area factor s a which is proportional to stream power with time while gully length and gully surface area asymptotically evolve towards a final value gully volume decreased at a given point in time from this it is inferred that sediment deposition will potentially infill the gully to such an extent that the farmer can drive across it from this moment on the combined effect of water and tillage erosion in the gully drainage area will lead towards rapid infilling this expected evolution of a gully in cultivated fields accords with observations of large infilled gully systems in cultivated areas in eastern belgium the permanent gullies observed under forest are attributed to the fact that after severe gully erosion this area was reforested or abandoned therefore the sediment source was cut off and the gully was not filled in by sediment deposition

gully erosion impacts factors and control gully erosion attracts increasing attention from scientists as reflected by two recent international meetings poesen and valentin eds catena 50 2 4 87 564 li et al 2004 gully erosion under global change sichuan science technology press chengu china 354 pp this growing interest is associated with the increasing concern over off site impacts caused by soil erosion at larger spatial scales than the cultivated plots the objective of this paper is to review recent studies on impacts factors and control of gully erosion and update the review on dgully erosion and environmental change importance and research needst poesen et al 2003 catena 50 2 4 91 134 for the farmers the development of gullies leads to a loss of crop yields and available land as well as an increase of workload i e labour necessary to cultivate the land gullies can also change the mosaic patterns between fallow and cultivated fields enhancing hillslope erosion in a feedback loop in addition gullies tend to enhance drainage and accelerate aridification processes in the semi arid zones fingerprinting the origin of sediments within catchments to determine the relative contributions of potential sediment sources has become essential to identify sources of potential pollution and to develop management strategies to combat soil erosion in this respect tracers such as carbon nitrogen the nuclear bomb derived radionuclide 137 cs magnetics and the strontium isotopic ratio are increasingly used to fingerprint sediment recent studies conducted in australia china ethiopia and usa showed that the major part of the sediment in reservoirs might have come from gully erosion gullies not only occur in marly badlands and mountainous or hilly regions but also more globally in soils subjected to soil crusting such as loess european belt chinese loess plateau north america and sandy soils sahelian zone north east thailand or in soils prone to piping and tunnelling such as dispersive soils most of the time the gullying processes are triggered by

convection and anisotropy of the inner core estimation of the rayleigh number of the inner core suggests that this region is convecting the flow pattern is likely to produce crystallographic preferred orientation of the elastically anisotropic hexagonal closest packed phase of iron such that compressional wave velocities would be greater in the axial relative to the equatorial direction by roughly 1 percent this result is in agreement with seismological evidence that the inner core is elastically anisotropic

reconciling the hemispherical structure of earth s inner core with its super rotation earth s solid inner core grows through solidification of material from the fluid outer core onto its surface at rates of about 1 mm per year1 freezing in core properties over time and generating an age depth relation for the inner core a hemispherical structure of the inner core is well documented an isotropic eastern hemisphere with fast seismic velocities contrasts with a slower anisotropic western hemisphere2 3 4 independently the inner core is reported to super rotate at rates of up to 1 per year5 6 7 considering the slow growth steady rotation rates of this magnitude would erase frozen in regional variation and cannot coexist with hemispherical structure here we exploit the age depth relation using the largest available pkikp pkikp seismic travel time data set to confirm hemispherical structure in the uppermost inner core and to constrain the locations of the hemisphere boundaries we find consistent eastward displacement of these boundaries with depth from which we infer extremely slow steady inner core super rotation of 0 1 1 per million years our estimate of long term super rotation reconciles inner core rotation with hemispherical structure two properties previously thought incompatible it is in excellent agreement with geodynamo simulations8 9 while not excluding the possibility that the much larger rotation rates inferred earlier5 6 7 correspond to fluctuations in inner core rotation on shorter timescales10

seismicity characteristics of a potentially active quaternary volcano the tatun volcano group northern taiwan the tatun volcano group tvg is located at the northern tip of taiwan near the capital taipei and close to two nuclear power plants because of lack of any activity in historical times it has been classified as an extinct volcano even though more recent studies suggestthattvgmighthavebeenactiveduringthelast20ka inmay2003aseismicmonitoringprojectatthetvgareawasinitiated by deploying eight three component seismic stations some of them equipped with both short period and broadband sensors during the 18 months observation period local seismicity mainly consisted of high frequency earthquakes either occurring as isolated events or as a continuous sequence in the form of spasmodic bursts mixed and low frequency events were also present during the same period eventhoughtheyoccurredonlyrarely arrivaltimesfromeventswithclearp s wavephaseswereinvertedinordertoobtaina minimum 1dvelocity modelwithstation corrections probabilistic nonlinear earthquakelocationswere calculated for allthese events using the newly derived velocity model most high frequency seismicity appeared to be concentrated near the areas of hydrothermal activity forming tight clusters at depths shallower than 4 km relative locations calculated using the double difference method and utilising catalogue and cross correlation differential traveltimes showed insignificant differences when compared to the nonlinear probabilistic locations in general seismicity in the tvg area seems to be primarily driven by circulation of hydrothermal fluids as indicated by the occurrence of spasmodic bursts mixed low frequency events and a b value 1 17 0 1 higher than in any other part of taiwan these observations that are similar to those reported in other dormant quaternary volcanoes indicate that a magma chamber may still exist beneath tvg and that a future eruption or period of unrest should not be considered unlikely

hemispherical variations in seismic velocity at the top of the earth s inner core knowledge of the seismic velocity structure at the top of the earth s inner core is important for deciphering the physical processes responsible for inner core growth1 2 3 previous global seismic studies4 5 6 7 8 9 have focused on structures found 100 km or deeper within the inner core with results for the uppermost 100 km available for only isolated regions10 11 12 here we present constraints on seismic velocity variations just beneath the inner core boundary determined from the difference in travel time between waves reflected at the inner core boundary and those transmitted through the inner core we found that these travel time residuals observed on both global seismograph stations and several regional seismic networks are systematically larger by about 0 8 s for waves that sample the eastern hemisphere of the inner core 40 e to 180 e compared to those that sample the western hemisphere 180 w to 40 e these residuals show no correlation with the angle at which the waves traverse the inner core this indicates that seismic anisotropy is not strong in this region and that the isotropic seismic velocity of the eastern hemisphere is about 0 8 higher than that of the western hemisphere

non double couple earthquake mechanisms at the hengill grensdalur volcanic complex southwest iceland the hengill grensdalur area in iceland generates frequent small non double couple earthquakes with explosive volumetric components we collected high quality three component digital recordings of 4 000 earthquakes on a purpose designed 32 station network in 1991 and determined focal mechanisms for 100 of the best recorded earthquakes by inverting amplitude ratios many of the mechanisms are consistent within the errors with simultaneous shear and tensile faulting with tensile faults parallel to the local spreading ridge and shear faulting similar to that in the south iceland transform fault zone some events cannot be explained by this model however and require other processes such as crack closing and partial compensation of tensile cracks by fluid flow

constraints on grain size and stable iron phases in the uppermost inner core from multiple scattering modeling of seismic velocity and attenuation we propose to model the uppermost inner core as an aggregate of randomly oriented anisotropic patches a patch is defined as an assemblage of a possibly large number of crystals with identically oriented crystallographic axes this simple model accounts for the observed velocity isotropy of short period body waves and offers a reasonable physical interpretation for the scatterers detected at the top of the inner core from rigorous multiple scattering modeling of seismic wave propagation through the aggregate we obtain strong constraints on both the size and the elastic constants of iron patches we perform a systematic search for iron models compatible with measured seismic velocities and attenuations an iron model is characterized by its symmetry cubic or hexagonal elastic constants and patch size independent of the crystal symmetry we infer a most likely size of patch of the order of 400 m recent it bcc iron models from the literature are in very good agreement with the most probable elastic constants of cubic crystals found in our inversion our study 1 suggests that the presence of melt may not be required to explain the low shear wavespeeds in the inner core and 2 supports the recent experimental results on the stability of cubic iron in the inner core at least in its upper part

heterogeneity and anisotropy of earth s inner core seismic observations provide strong evidence that earth s inner core is anisotropic with larger velocity in the polar than in the equatorial direction the top 60 80 km of the inner core is isotropic evidence for an innermost inner core is less compelling the anisotropy is most likely due to alignment of hcp hexagonal close packed iron crystals aligned either during solidification or by deformation afterward the existence of hemispherical variations used to be controversial but there is now strong evidence from both seismic body wave and normal mode observations showing stronger anisotropy less attenuation and a lower isotropic velocity in the western hemisphere two mechanisms have been proposed to explain the hemispherical pattern either a inner core translation wherein one hemisphere is melting and the other is solidifying or b thermochemical convection in the outer core leading to different solidification conditions at the inner core boundary neither is yet able to explain all se

gully erosion and sediment production te weraroa stream new zealand conversion to pasture early in the twentieth century was ameliorated by reforestation that commenced in 1962 estimates of sediment production were made using the change in gully area observed in sequential aerial photographs channel storage was assessed from stream cross section surveys at its peak gully erosion affected 6 of the total catchment area the amount of sediment contributed from gullies declined by 62 as the forest became established but of the 28 7 mt of sediment generated by gully erosion between 1950 and 1988 48 was stored in the channel along the lower 8 km of te weraroa stream even if the amount of sediment generated by gully erosion continues to decline it likely will be many decades before the gravel is released from storage index terms 1815 hydrology erosion and sedimentation 1824 hydrology geomorphology 1625 1878 hydrology water energy interactions keywords channel storage gully erosion sediment production citation gomez b k banbury m marden n a trustrum d h peacock and p j hoskin gully erosion and sediment production te weraroa stream new zealand water resour res 39 7 1187 doi 10 1029 2002wr001342 2003