syntectonic development of a strain independent steady state grain size during mylonitization abstract michibayashi k 1993 syntectonic development of a strain independent steady state grain size during mylonitization tectonophysics 222 151 164 for a distance of greater than 50 km along the median tectonic line japan syntectonic recrystallization of quartz has resulted in the development of a strain independent steady state grain size within the core of the kashio shear zone that is also independent of rock type the mean grain size of quartz in recrystallized aggregates progressively decreases towards the shear zone core becoming stable at around approximately 37 m even though the strain increases within more strongly mylonitized rocks some variation of mean grain sizes may result from secondary effects due to hydrothermal activity associated with the median tectonic line despite the development of a steady state mean grain size individual grains were not stable as revealed by log normal grain size distributions consequently dynamic recrystallization and grain growth were competing processes that achieved a balance and hence resulted in the development of the steady state grain size the actual grain size that resulted probably depended on both the water content and strain rate as well as the flow stress approaching the centre of the shear zone mylonitic fabrics e g s c fabrics mica fish were established well before a steady state grain size was reached a steady state grain shape shape orientation and crystallographic fabrics may not be developed until even more mylonitization had occurred variable grain sizes result from heterogeneous deformation as a consequence of deformation partitioning even under a stable stress prior to the development of a steady state grain size consequently it should be determined whether a steady state grain size has been achieved within a shear zone before the grain size is used as a paleopiezometer

geochemistry of shales from the archean 3 0 ga buhwa greenstone belt zimbabwe implications for provenance and source area weathering abstract phyllites from the archean 3 0 ga buhwa greenstone belt zimbabwe were deposited on a stable cratonic platform analyses of the phyllites generally define a single geochemical group based on major and trace element abundances the phyllites are strongly depleted in cao na2o and sr with respect to average archean upper crust by contrast k2o ba and rb are enriched several times relative to average archean upper crust reflecting basin scale k metasomatism transition metals are somewhat depleted whereas high field strength elements are typically enriched relative to average archean upper crust samples generally have fractionated lree patterns average cen smn 2 4 with small negative eu anomalies average eu eu 0 78 and generally flat hrees average gdn ybn 1 3 such geochemical characteristics suggest that the source dominantly consisted of tonalite with less common occurrences mafic volcanic rocks and granite mixing calculations which massbalance the rees and th sc suggest 70 tonalite 15 mafic volcanic rocks and 15 granite as possible proportions for the source of the phyllites a nearby early archean 3 5 ga continental nucleus preserves similar lithologies and is the probable source intense chemical weathering of the source terrane is indicated by premetasomatized chemical index of alteration values of 95 100 nearly complete depletion of cao and na2o and high al2o3 na2o ratios fine grained sediments of comparable age and presumed tectonic setting elsewhere in southern africa show similar geochemical characteristics implying that source area compositions and weathering intensities were similar these mature platformal deposits suggest a tectonically stable environment where intense chemical weathering took place at 3 0 ga across southern africa

use of extension testing to investigate the influence of finite strain on the theological behaviour of marble most mechanical testing of rocks at high temperatures is carried out under axisymmetric triaxial shortening to small 20 strains however the most significant geological deformations involve much higher strains especially in plastic shear zones where there has been strain localization highly strained rocks commonly are microstructurally modified by dynamic recrystallization so that the sheared rock is microstructurally quite different from its protolith high strain deformation in experiments can be induced by direct shear or through torsion or by taking advantage of the tendency for extensional deformations to result in necking it is important to be able to separate out the geometrical factors favouring localization from those arising from strain dependent microstructural changes here we present the results of high strain 1000 axisymmetric extension tests on carrara marble at 700 c and 800 c in the form of strain time plots for the evolution of material sections through the sample at different distances from the neck at 800 c it is clear that total dynamic recrystallization by grain boundary migration is accompanied by substantial mechanical weakening but sufficient strain could not be applied to reach the steady state condition for the recrystallized material the recrystallization is interpreted to produce weakening because the migration of grain boundaries sweeps grains clear of accumulating dislocation density faster than recovery by dislocation climb in nature such mechanical weakening would be expected to favour the stable development of a localized zone of deformation

simple shear experiments on calcite rocks rheology and microfabric ideal simple shearing of carrara marble and solnhofen limestone was achieved by inserting calcite rock slices into sandstone cylinders precut at 35 the experiments covered a wide range in temperatures 25 900 c at confining pressures of 200 and 250 mpa and at strain rates between 10 3 and 10 5 s 1 shear strains of up 2 7 were achieved the stress strain data for simple shear favourably compare with predictions on the basis of existing flow laws established in coaxial testing this comparison demonstrates that the simple shear experiments covered most of the previously established flow regimes for calcite rocks at the highest temperatures carrara marble exhibited substantial work softening after high shear strains a complete texture analysis was carried out with the u stage and a texture goniometer the following four distinct microfabric regimes were found 1 twinning regime an oblique c axis maximum deflected from the pole to the flattening plane towards 1 and against the imposed sense of shear results directly from e twinning extensive twinning some grains are completely twinned rapidly rotates the c axes into near parallelism with 1 this regime was observed for carrara marble deformed at temperatures below 700 c and for solnhofen limestone at room temperature 2 intracrystalline slip regime three c axis maxima were observed in both rock types at more elevated temperatures and in the absence of twinning these c axis orientations result from an alignment of slip planes and slip directions into parallelism with the shear zone boundary and the shear direction respectively this finding supports the idea of an orientation for easy slip resulting from simple shearing in addition to r and f glide basal glide is inferred to have been operative 3 grain boundary sliding regime a great circle distribution of c axes approximately perpendicular to the direction of finite shortening is observed this texture is weaker compared to the other regimes it is interpreted to result from minor contributions of f slip towards total strain this regime is restricted to fine grained solnhofen limestone deformed at the highest temperatures 4 grain boundary migration regime only in carrara marble deformed at the highest temperatures is there substantial grain boundary migration recrystallization the texture consists of a dominant c axis maximum oriented perpendicular to the shear zone boundary this single maximum corresponds to an orientation for easy slip for basal slip grain boundary migration assists rapid lattice reorientation and leads to geometrical work softening quantitative analysis of grain boundary surface orientations gave the following results within the twinning and the intracrystalline slip regimes the characteristic grain shape is elliptical for both rock types the strain ellipses derived from this analysis closely correspond to the known finite strain at the lowest temperatures at intermediate temperatures and especially in carrara marble there is a consistent trend for the aspect ratios to indicate too little flattening and for the angles between the long axis of the strain ellipse and the shear zone boundary to be too small in the absence of grain boundary migration recrystallization this finding indicates minor translations of grains with respect to one another grain boundary sliding or translations accommodated in the mantle regions of grains at the highest temperatures where extensive grain boundary migration occurs in carrara marble grain boundary migration regime two preferred orientations of grain boundaries are observed 1 parallel to the shear zone boundary and 2 parallel to an oblique direction deflected 20 away from the normal to the shear zone boundary in the sense of the imposed shear the same pattern of grain boundary alignment is observed in solnhofen limestone deformed in the grain boundary sliding regime the geological applications of this experimental work are discussed in terms of calcite tectonites in particular and sheared rocks in general

the role of recrystallisation on the deformation behaviour of calcite rocks large strain torsion experiments on carrara marble abstract the rheological microstructural and textural evolution of carrara marble was studied during experimental deformation in torsion up to very large shear strains 0 4 50 experiments were performed at constant angular displacement rates corresponding to shear strain rates of 6 10 5 3 10 3 s 1 a confining pressure of 300 mpa and temperatures of 500 600 and 727 c microstructures and crystallographic preferred orientations cpo were analysed using light microscopy and electron backscatter diffraction ebsd at all conditions deformation occurred dominantly by dislocation creep even up to very large shear strains after peak stresses 2 recrystallisation mostly by subgrain rotation caused weakening 5 20 grain size reduction and a change in the cpo a monoclinic cpo that formed at small strains at all temperatures evolved into two different large strain cpos at different temperatures at large strains even after complete recrystallisation the cpo continued to strengthen and a secondary foliation was formed at a steep angle to the shear zone boundary this secondary foliation was continuously reset by both subgrain rotation and grain boundary migration recrystallisation and eventually overprinted the primary foliation misidentifying the primary and secondary foliations could result in misinterpretation of the applied strain field more generally information about the amount of strain is lacking for microstructures and cpos of highly deformed ultramylonites

image based mapping of surface fissures for the investigation of landslide dynamics abstract the development of surface fissures is an important indicator for understanding and forecasting slope movements landslide investigations therefore frequently include the elaboration and interpretation of maps representing their spatial distribution typically comprising intensive field work and instrumentation it is only recently that aerial photography with sub decimetre spatial resolution is becoming more commonly available and opens a window to analyse such features from a remote sensing perspective while these data are in principle helpful to elaborate maps from image interpretation techniques there is still no image processing technique available to extract efficiently these geomorphological features this work proposes a largely automated technique for the mapping of landslide surface fissures from very high resolution aerial images the processing chain includes the use of filtering algorithms and post processing of the filtered images using object oriented analysis the accuracy of the resulting maps is assessed by comparisons with several expert maps in terms of affected area fissure density and fissure orientation under homogenous illumination conditions true positive rates up to 65 and false positive rates generally below 10 are achieved the resulting fissure maps provide sufficient detail to infer mechanical processes at the slope scale and to prioritize areas for more detailed ground investigations or monitoring

a new type of numerical experiment on the spatial and temporal patterns of localization of deformation in a material with a coupling of grain size and rheology abstract the patterns of localization of deformation in recrystallising materials are investigated via a series of two dimensional grain scale numerical simulations these simulations couple a grain size and strain dependant viscous rheology with grain size reduction and grain growth processes the simulations are able to predict the mechanical microstructural and strain evolution of the polycrystals to moderate strain and allow us to examine the nature of the time dependent feedback between mechanical and microstructural behavior it was found that significant strain localization occurred only when the grain size dependence of the viscosity was non linear and was greatly enhanced by the activity of the grain size modifying processes the intensity and location of the zone of strain localization varied spatially and temporally and displayed two length and time scales with the result that the finite strain state showed a much broader and hence less intense zone of localized deformation than the instantaneous state

inversion of field data in fault tectonics to obtain the regional stress i single phase fault populations a new method of computing the stress tensor summary we attempt a general definition of the inverse problem of computing the components of the regional stress tensor from a set of field data including the measurements of the strike and dip of several faults and the directions and senses of relative motion along these faults as indicated by slickenslides in previous treatments of this problem no experimental errors could be taken into account except those in measuring the pitch of slickenslides thus errors in the orientation of the fault strike and dip which have considerable practical importance were neglected in our work all experimental errors in the field measurements are taken into account so that the agreement between the computed stress tensor and the set of field measurements can be rigorously checked

classic and new dating methods for assessing the temporal occurrence of mass movements abstract establishing landslide chronologies is essential both for understanding causes of mass movements as part of fundamental geomorphological research and for the assessment of landslide hazards as part of applied geomorphology we discuss the applicability of different methods for determining landslide chronologies frequencies and dynamics in relation to the type of material being dated sampling location and type of mass movement the emphasis is on the possibilities and limitations of the different dating methods established methods such as radiocarbon dating lichenometry and dendrochronology are briefly discussed the paper focuses however on 1 new analytical techniques like accelerator mass spectrometry ams thermally ionising mass spectrometry tims and laser fusion which have led to significant improvements of established dating methods and on 2 new dating methods like optically stimulated luminescence osl dating and alpha recoil track art dating

tectonic control of complex slope failures in the ameka river valley lower gibe area central ethiopia implications for landslide formation abstract even though major faults represent important landslide controlling factors the role the tectonic setting in actively spreading rifts plays in the development of large complex landslides is seldom discussed the ameka complex landslide area is located on the eastern scarp of the gibe gorge approximately 45 km to the west of the main ethiopian rift and 175 km to the southwest of addis ababa investigation of the complex landslide failures required a combination of satellite and airborne data based geomorphology geological field survey complemented with structural analysis radiocarbon geochronology and vertical electric sounding the obtained observations confirmed the multiphase evolution of the landslide area we have documented that apart from climatic and lithological conditions the main triggering factor of the ameka complex landslide is the tectonic development of this area the e w extension along the nne ssw trending main ethiopian rift is associated with the formation of numerous parallel normal faults such as the gibe gorge fault and the almost perpendicular scissor faults the geometry of the slid blocks of coherent lithology have inherited the original tectonic framework which suggests the crucial role tectonics play in the fragmentation of the compact rock masses and the origin and development of the ameka complex landslide area similarly the main scarps were also parallel to the principal tectonic features the local tectonic framework is dominated by faults of the same orientation as the regional structures of the main ethiopian rift such parallel tectonic frameworks display clear links between the extension of the main ethiopian rift and the tectonic development of the landslide area the ameka complex landslide developed in several episodes over thousands of years according to the radiocarbon data the last of the larger displaced blocks representing only 2 of the total area most likely slid down in the seventh century ad the main scarps namely the high scarps in the western part are unstable over the long term and toppling and falling type slope movements can be expected here in the future

gravitational and tectonic stress states within a deep seated gravitational slope deformation near the seismogenic periadriatic line fault abstract the role of tectonic horizontal stresses in activating deep seated gravitational slope deformations dsgsd has rarely been studied we applied a new numerical technique for determining the present day stress states within a large dsgsd situated near the periadriatic line fault pal in the eastern alps the stress states were calculated from three dimensional displacements of the sinistral obir fault conjugated to the dextral pal fault which also forms the upper dsgsd detachment plane the analysed fault displacements occurred in two distinct activity phases associated with the elastic rebound along i the obir fault in the summer of 2014 and ii the core of the pal fault in the winter of 2014 2015 these periods were synchronous with the periods of increased local seismicity the results brought an insight into a possible causative link between horizontal tectonic stresses and dsgsds activation we observed that transient dextral transpressions and dextral transtensions opposing to the general fault kinematics associated to the elastic rebound had a potential to destabilize the dsgsd at the micrometre level the applied stress tensor calculation although restricted only to shallow near surface conditions is a reliable method that can reveal stress states almost in the real time

curie point depth geothermal gradient and heat flow estimation and geothermal anomaly exploration from integrated analysis of aeromagnetic and gravity data on the sabalan area nw iran prospecting the geothermal resources in northwest of iran conducted in 1975 revealed several promising areas and introduced the sabalan geothermal field as a priority for further studies the sabalan mt representing the sabalan geothermal field is a large stratovolcano which consists of an extensive central edifice built on a probable tectonic horst of underlying intrusive and effusive volcanic rocks in this study curie point depth cpd geothermal gradient and heat flow map were constituted from spectral analysis of the aeromagnetic data for the nw of iran the top of the geothermal resource i e the thickness of the overburden was evaluated by applying the euler deconvolution method on the residual gravity data the thickness of the geothermal resource was calculated by subtracting the euler depths obtained from the cpds in the geothermal anomalous region the geothermal anomalous region was defined by the heat flow value greater than 150 mw m2 cpds in the investigated area are found between 8 8 km in the sabalan geothermal field and 14 1 in the northeast the results showed that the geothermal gradient is higher than 62 c km and the heat flow is higher than 152 mw m2 for the geothermal manifestation region the thickness of the geothermal resource was also estimated to vary between 5 4 and 9 1 km these results are consistent with the drilling and other geological information findings indicate that the cdps agree with earthquake distribution and the type of thermal spring is related to the depth of the top of the geothermal resource

deformation fields around a fault embedded in a non linear ductile medium summary the geological record of deformation is often characterized by a combination of discontinuous deformation in which strain is concentrated in faults and continuous deformation in which strain is distributed through the material where slip occurs on a fault that terminates the surrounding material is deformed in the lower crust and in cases where large strains occur over long geological time scales it is appropriate to model the deformation using a viscous probably non linear viscous rheology we describe a method for practical finite element solution of this problem using a dynamically self consistent formulation for stress and displacement on a fault of arbitrary geometry the accuracy of the method is tested by comparison with an analytical solution for the linear rheology we describe here the instantaneous deformation fields around a mode ii fault under both plane strain and plane stress conditions and a range of rheological exponents n where strain rate is proportional to deviatoric stress to the nth power the distributions of stress and strain rate around the fault tip are controlled primarily by the rheological exponent n a localized zone of high strain rate projects beyond the end of the fault if n is about 3 or greater and the degree of localization of deformation increases with the value of n the zone of high shear strain rate can be defined in practical terms by considering 1 the region in which the creep velocity differs by more than 20 per cent from the velocity on the nearby external boundary and 2 the region in which the maximum shear strain rate is greater than about twice the externally imposed shear strain rate for n 1 the volumes so defined differ considerably but for large values of n the two definitions both describe the same narrow zone of deformation beyond the end of the fault evaluation of the navier coulomb criterion for brittle failure of the medium surrounding the fault tip shows first that brittle failure is much more likely on the extensional side of the fault than the compressional side it also shows that the volume of material subject to brittle failure decreases rapidly with increasing n because of the relatively weaker stress singularity we analyse previously published displacement versus distance data for faults terminating in sedimentary rocks at 0 1 to 100 m length scales under different tectonic conditions in order to determine the rheological exponent n these analyses result in n values between approximately 0 85 and 5 for the different faults with error bounds on n typically pl 1 the variation in n values may result from differences in pressure temperature and fluid conditions at the time of faulting more importantly the analysis demonstrates a new method for the determination of the effective rheological exponent under in situ geological conditions

seismic and geodetic signatures of fault slip at the slumgullion landslide natural laboratory 1 we tested the hypothesis that the slumgullion landslide is a useful natural laboratory for observing fault slip specifically that slip along its basal surface and side bounding strike slip faults occurs with comparable richness of aseismic and seismic modes as along crustal and plate scale boundaries our study provides new constraints on models governing landslide motion we monitored landslide deformation with temporary deployments of a 29 element prism array surveyed by a robotic theodolite and an 88 station seismic network that complemented permanent extensometers and environmental instrumentation aseismic deformation observations show that large blocks of the landslide move steadily at approximately centimeters per day possibly punctuated by variations of a few millimeters while localized transient slip episodes of blocks less than a few tens of meters across occur frequently we recorded a rich variety of seismic signals nearly all of which originated outside the monitoring network boundaries or from the side bounding strike slip faults the landslide basal surface beneath our seismic network likely slipped almost completely aseismically our results provide independent corroboration of previous inferences that dilatant strengthening along sections of the side bounding strike slip faults controls the overall landslide motion acting as seismically radiating brakes that limit acceleration of the aseismically slipping basal surface dilatant strengthening has also been invoked in recent models of transient slip and tremor sources along crustal and plate scale faults suggesting that the landslide may indeed be a useful natural laboratory for testing predictions of specific mechanisms that control fault slip at all scales

landslide faults and tectonic faults analogs the slumgullion earthflow colorado recent geophysical observations of landslide movement support the hypothesis that processes involved in landslide faulting are analogous to those that operate in crustal scale faulting relative to crustal faulting studies quantitative seismic geodetic and creep measurements of landslide deformation may be made in a very short time with readily available instrumentation and at relatively minimal expense our results indicate that the displacement of landslide material occurs along discrete faults exhibiting a combination of brittle failure indicated by slide quakes and creep events and as stable sliding observed as steady state creep although slide quakes were observed a more steady state failure process of relieving accumulating strain is indicated

present day stress inversion from a single near surface fault a novel mathematical approach abstract a novel numerical approach enables determining contemporary stress states at a single fault near the ground surface using three dimensional fault displacement data i e displacements that include movement component perpendicular to the fault surface this approach is restricted to specific near surface conditions and is based on three assumptions i the near surface faults contain apertures and the blocks can move in all directions at a sub millimetric scale so the movement is not restricted only to the fault plane thus the stress vector traction acting on the fault surface has the same direction as the fault displacement vector ii the isotropic component of the stress tensor near the ground surface is negligible and iii one of the principal stress orientations must be vertical as being close to the ground surface these generalizations enable distinct formula simplification and the reduced stress tensor calculation input data for the mathematical solution are the orientation of the fault surface i e the down directed fault surface normal and the fault displacement i e the vector of the hanging wall displacement the orientation of the principal stresses and the shape parameter of the stress ellipsoid are the outputs of the method we demonstrate the approach on a single fault reactivation event on 7 november 2014 in obir cave near the periadriatic fault in the eastern alps

experimental study of the influence of stress temperature and strain on the dynamic recrystallization of carrara marble carrara marble has been deformed experimentally at temperatures ranging between 500 and 1000 c at confining pressures of 200 and 300 mpa and up to very large strains in extension and compression in order to study the microstructural and mechanical property changes associated with dynamic recrystallization microstructural studies were made by optical microscopy on ultrathin sections and automatic grain size measurement techniques were used when the temperature is sufficiently high 600 c and the stresses are high enough for deformation twinning to occur twin boundary migration is a powerful recrystallization mechanism that does not modify the grain size at stress levels too low to activate twinning recrystallization occurs in two stages the formation of nuclei by grain boundary bulging and subgrain rotation recrystallization in the grain boundary regions followed by a second stage of grain boundary migration recrystallization to a larger grain size that eventually overprints the entire rock volume the recrystallization process requires larger prestrains at the lower temperatures the size to which migration recrystallized grains grow seems to be limited by the stress and grain size dependent twinning field boundary or by the boundary between the dislocation creep and grain size sensitive flow mechanisms within the range of experimental observations dynamically recrystallized grain size does not depend on strain rate or temperature separate empirical stress versus grain size relations are presented for rotation and migration recrystallization that may be used for palaeopiezometry no unequivocal experimental evidence of weakening resulting from recrystallization to finer grain sizes at laboratory strain rates was found however extrapolation of the experimental data to low natural strain rates suggests that weakening following recrystallization may occur in nature

a few remarks on the kinetics of static grain growth in rocks static grain growth is a relatively simple transformation in which grain size increases under driving forces caused by grain and interphase boundary curvature given the relative simplicity of the protocol for grain growth experiments measurements of grain boundary mobility show surprising variations boundary mobilities during grain growth are affected by solute and impurity chemistry chemical fugacity of trace and major elements pore size and number pore fluid chemistry the presence of melts and the presence of solid second phases as well as temperature and pressure all of these factors may exert influence on grain growth of rocks in natural situations and many are also present during the laboratory experiments provided that the necessary kinetics parameters are known bounds may be placed on the interface mobility when pores partial melts or solutes are present to predict the rate of grain growth in natural situations will require improved laboratory data and careful consideration of the thermodynamic conditions likely to be encountered in nature

estimating slip rates and recurrence intervals for strong earthquakes along an intracontinental fault example of the pambak sevan sunik fault armenia north of the arabian plate active tectonics is characterised by both n s compression and e w extension associated with strike slip faults the pambak sevan sunik fault pssf zone in armenia is one of the major active structures of the region the fault is comprised of four main segments and it displays morphological evidence for dextral movement during the holocene however no large earthquake m 7 has occurred in the northern or central parts of the fault during the last 2000 years we undertook a geomorphological and paleoseismological investigation along the pambak sevan sunik fault with the aim of estimating the long term slip rate and recurrence interval of strong earthquakes trenches were excavated at three sites detailed studies of trench cross sections and dating radiocarbon and ceramics show three faulting events that occurred in the vanadzor artanih segment fioletovo and semionovka areas whereas a single event took place in the artanish sunik segment khonarhasar area in both areas we estimated the average slip rate using i the offset of rivers along the vanadzor artanish segment 2 24 0 96 mm year over an interval of 120 300 ka and ii the offset of volcanic cones along the artanish sunik segment 0 53 0 04 mm year over an interval of 1 4 ma these results suggest that a greater slip rate characterises the vanadzor artanish segment fioletovo site from the artanish sunik khonarhasar site segment division of the pambak sevan sunik fault zone into two main branches east of the artanish peninsula sevan lake could explain the difference in slip rate in addition to its segmented seismic behaviour the pambak sevan sunik fault is a well documented example of a fault that generates strong earthquakes with long recurrence time intervals about 3000 4000 years d 2001 elsevier science b v all rights reserved

flow behavior of fine grained synthetic dunite in the presence of 0 5 wt h2o the deformation behavior of synthetic dunite mg forsterite plus 2 5 vol enstatite with a grain size of 1 m has been investigated in combined constant displacement rate and temperature stepping experiments at temperatures of 850 to 1000 c strain rates of 10 7 to 10 5 s 1 and a confining pressure of 600 mpa nominally dry material behaved purely elastically in contrast samples with 0 5 wt added water flowed at stresses between 9 and 81 mpa reaching strains up to 12 fitting a dorn type power law to the wet data yielded stress exponents n of 1 7 0 4 and apparent activation energies in the range 302 22 kj mol 1 the wet deformed samples showed polygonal grains no crystallographic preferred orientation no subgrains low dislocation densities and evidence for grain boundary cavitation grain growth was minor it is concluded that the wet samples probably deformed by a grain size sensitive grain boundary sliding dominated mechanism though the nature of the accommodation process remains unclear and the possibility of transitional behavior between dislocation creep and diffusion creep cannot be eliminated application of the results to upper mantle shear zones supports previous speculation that the presence of such zones can lead to a significant weakening of the top 10 to 20 km of the upper mantle during extension of the continental lithosphere

syndeformational grain growth microstructures and kinetics abstract grain growth can be an important high temperature process in fine grained polycrystalline materials we studied its effect on texture during deformation using a two dimensional computer model and a see through experiment with octachloropropane syndeformational grain growth in geological materials can slow down the development of a grain shape preferred orientation or even obliterate it important processes are preferentially oriented deformation induced neighbour switches the presence of a grain shape preferred orientation slows down the increase in grain size due to grain growth

extension in nw iran driven by the motion of the south caspian basin contrasted tectonic styles occur in northern iran west of kopet dagh the south caspian basin is an aseismic and possibly rigid blockinvolved inthecollisionzonebetweeneurasiaandarabia tothenw largescalevelocityfield ofirangivenbyrecentrepeated gps surveys suggests 8 mm yr of right lateral displacement for the wnw ese faults in the tabriz region more surprisingly geodetic motion also suggests a prominent n 30 extension north to the tabriz fault where compression would be expected in order to quantify more precisely the right lateral movement of the tabriz region the extension of nw iran and the motion of the south caspian basin we deployed a dense gps network in nw iran from central iran to the turkish armenian and azerbaijan borders three repeated surveys from 2002 to 2004 assess that the tabriz fault concentrates entirely the 8 mm yr of right lateral movement observed in nw iran this rate is in good agreement with a recurrence interval time of 250 300 yr proposed from historical seismicity studies we found also two zones of extension one just north of the tabriz fault in the south of the talesh plateau and another close from the azerbaijan border north of the talesh plateau we suggest that the existence of a northward subduction of the south caspian basin could explain such an extension in the core of the arabia eurasia collision increasing evidences of quaternary extensional tectonics in the region from armenia to alborz may lead to significantly alter our understanding of the northern iran tectonics and challenge the traditional arabian indenter plate tectonics

palaeostress analysis of a giant holocene rockslide near boaco and santa lucia nicaragua central america a giant rockslide occurred on the southern side of an upper tertiary shield volcano in central nicaragua in the holocene the failure caused tectonic like deformation of rock masses and changed the local stress regime the article describes this stress state

are sackungen diagnostic features of de glaciated mountains abstract deep seated gravitational slope deformations dsgsds with characteristic sackung landforms e g double crests trenches uphill facing scarps and toe bulging are considered by some researchers to be diagnostic features indicating past mountain glaciations however an extensive literature review on sackung features throughout the world reveals that in some regions paraglacial processes are not the causes of such phenomena sackungen occur across a diverse spectrum of mountain types with different morphoclimatic histories including regions that have never experienced glaciation to reinforce that sackungen may originate independently of glaciation we also include two case studies from the western carpathians czech republic and slovakia which are supported by detailed geomorphic mapping trenching and absolute dating 10 be 14 c and osl on the ond ejnik ridge outer western carpathians czech republic sackungen occur in the mid holocene in the medium high mountains which are beyond the pleistocene glacial limits on the salatin mt tatra mts slovakia the sackungen which occur in formerly glaciated terrain date between 7 5 and 4 2 ka bp representing a 4 ka time lag after the disappearance of glaciers this suggests that the direct link between the ice retreat and the onset of sackung formation is not obvious even in the case of the once glaciated mountain range although paraglacial stress release is undoubtedly one of the crucial causes of sackung genesis in many mountain regions it is not the only important mechanism therefore despite occurring in numerous de glaciated mountains sackung features cannot be considered as proof of past mountain glaciations e g during analysis of extra terrestrial settings

the development of δ clasts in non linear viscous materials a numerical approach abstract winged porphyroclasts are often used as kinematic or strain indicators in shear zones in particular it has been suggested that the geometry of clasts in mylonites can give information about the rheological behaviour of the matrix around the clast passchier et al 1993 we tested this hypothesis with a numerical finite element simulation of the flow field of a viscous matrix around a relatively rigid clast power law viscous flow properties of the matrix with stress exponents of 1 linear viscous 3 and 5 were tested as well as three different sets of approximately simple shear boundary conditions which are relevant to experimental and or natural situations the simulations show that the flow field is primarily determined by the boundary conditions the stress exponent is of secondary importance in general the different boundary conditions produce two types of flow fields about the rigid clast an eye shaped flow field and a bow tie shaped flow field the former is produced by boundary conditions that approximate simple shear applied at an infinite distance from the rigid clast and the latter is produced by boundary conditions which are equivalent to a shear box or ring shear apparatus although both the shear box and ring shear boundary conditions produce bow tie flow patterns the wing geometries which result from the flow patterns for these two cases can be significantly different the geometry of the wings that develop on a clast is a direct function of the flow field around the clast for linear and non linear rheologies only the ring shear boundary conditions produce wings that show stair stepping i e wings that are parallel but not in the same plane in natural shear zones clasts both with and without stair stepping are observed in comparing geologic observations with experimental or numerical modelling it is essential to understand which boundary conditions are appropriate

stress field reconstruction in an active mudslide abstract meso scale structures from gravitational slope deformation observed in landslides and deep seated gravitational slope failures are very similar to those of endogenous ones therefore we applied palaeostress analysis of fault slip data for reconstructing the stress field of an active mudslide in pechgraben austria this complex compound landslide has developed in clayey colluvium and shale and was activated after a certain period of dormancy in june 2013 during the active motion on june 12 2013 73 fault slip traces at 9 locations were measured within the landslide body the heterogeneous fault slip data were processed in term of palaeostresses the reconstructed palaeostress tensor being characterized by the orientations of the three principal stress axes and the stress ratio which provides the shape of the stress ellipsoid the results of the palaeostress analysis were compared to airborne laser scan digital terrain models that revealed dynamics and superficial displacements of the moving mass prior and after our survey the results were generally in good agreement with the observed landslide displacement pattern and with the anticipated stress regime according to mohr coulomb failure criteria and anderson s theory the compressional regime was mostly registered at the toe in areas where a compressional stress field is expected during previous mass movement stages or at margins loaded by subsequent landslide bodies from above on the other hand extension regimes were identified at the head scarps of secondary slides subsequently on bulged ridges at the toe and in the zone of horst and graben structures in the lower central part of the main landslide body where the basal slip surface probably had locally convex character strike slip regimes as well as oblique normal or oblique reverse regimes were observed at the lateral margins of the landslide bodies the directions of principal stresses could be used as markers of landslide movement directions although the multiphase strain indicators were in general relatively poorly preserved the palaeostress analysis revealed several different deformation phases at some landslide parts related to different evolution episodes of the complex landslide palaeostress analysis based on the multiple inversion method is an affordable approach for reconstructing stress fields within landslides in soft material this method is an inexpensive and objective tool for stress field reconstruction even in heterogeneous stress field conditions where the distinction of different faults generations may be impossible

temporal behavior of deep seated gravitational slope deformations a review abstract deep seated gravitational slope deformations dsgsds are slow moving hillslope scale mass movements featuring characteristic landforms such as double crested ridges and upslope facing scarps that occur in diverse landscapes throughout the world although these deformations have been studied since the 1960s significant insights to the rates of dsgsds have only been gained within the last two decades owing to progress in geochronology remote sensing and instrumental monitoring absolute age and monitoring data indicate that dsgsd movements are observable over long term 102 years and short term future research directions include constraining the lifespan of dsgsds with absolute age dating and precise high resolution monitoring of spatio temporal displacement across dsgsd bodies it is of great importance to include absolute time scales in the numerical models of dsgsds furthermore combining remote sensing techniques such as synthetic aperture radar interferometry with high resolution lidar scanning and near surface geophysics offers a promising toolkit for collecting very detailed and accurate data on the short term deformation rates of dsgsds

localized rheological weakening by grain size reduction during lithospheric extension abstract grain size reduction may be a possible mechanism for the origin of localized deformation in the ductile regime i investigated the effects of grain size reduction due to dynamic recrystallization cataclasis and syntectonic metamorphic reaction on the stress envelope in the lithospheric mantle during extension by using a simple one dimensional model in this model the lithosphere extends uniformly with a constant strain rate and a fall in rock strength appears as a decrease in stress because grain size distribution at the onset of extension is unknown i regarded the steady state grain size due to dynamic recrystallization as the initial size then i evaluated the maximum effects of grain size reduction by dynamic recrystallization during extension and consequently examined the effects of grain size reduction by cataclasis and metamorphic reaction under conditions when dynamic recrystallization occurs significantly i find that it is difficult to bring about localized rheological weakening by grain size reduction owing to dynamic recrystallization in contrast grain size reduction by cataclasis can cause localized weakening during extension there is a wide ranging rate of grain size reduction by means of cataclasis that causes localized weakening just below the moho i specified the reaction from spinel lherzolite to plagioclase lherzolite that plays a role in grain size reduction by syntectonic metamorphism the reaction occurs at depths less than 35 km which is independent of the initial thermal state of the lithosphere localized rheological weakening can occur if the following conditions are satisfied 1 grain size before the reaction is greater than 0 7 mm under dry conditions and greater than 0 5 mm under wet conditions and it decreases down to those values by the reaction 2 grain size decreases down to less than initial grain size when the dominant deformation mechanism is gss creep at the onset of extension it is also noted that dry conditions are more favourable for localized weakening

composite flow laws for crystalline materials with log normally distributed grain size theory and application to olivine abstract conventional steady state flow laws describing combined grain size insensitive dislocation creep and grain size sensitive diffusion creep incorporate grain size as a single mean value however rocks exhibit distributed grain size and variations in the shape of the distribution such as its width will accordingly affect rheological behavior to evaluate this effect we have derived composite dislocation diffusion flow laws describing upper and lower bounds on the rate of deformation of materials showing a grain size distribution of the commonly observed log normal type the upper and lower bound flow laws obtained allow systematic investigation of the influence of the grain size distribution parameters i e the median and standard deviation on composite rheology the results demonstrate major effects of distribution width as well as median value application to polycrystalline olivine deforming by coble creep and power law dislocation creep reveals significant implications for interpreting deformation experiments and modeling flow in the earth s mantle the flow laws also provide an improved basis for modeling the deformation of rocks during geological processes in the crust and mantle

geological controls on the topological properties of some trellis channel networks it has been traditionally assumed but never quantitatively demonstrated that the topological properties of trellis channel networks are strongly influenced by the underlying geology in this study the topological properties of seven trellis networks underlain by a plunging syncline are analyzed and compared with those of 45 dendritic networks the analysis of the trellis networks reveals 1 that tributaries flowing both downplunge and downdip are preferentially developed 2 that there is an excess of obtuse over acute tributaries and chains because the general alignment of the networks is such that most of the tributaries flowing downplunge are obtuse 3 that cis links outnumber trans links as far downstream as diameter 7 links owing to the preferential development of tributaries flowing downdip 4 that because the spacing of along strike streams and ridges constrains the development of across strike tributaries there are strong spatial regularities in tributary size and 5 that for the same reason the trellis networks contain a higher proportion of small tributaries and a lower proportion of large tributaries than do dendritic networks thus this study not only establishes that geological controls have a pronounced effect on the topological properties of trellis networks but it shows how particular topological properties are affected by specific controls as these controls vary from one area of trellis drainage to another the topological properties of the channel networks might also be expected to vary consequently no one set of topological properties can be considered typical of trellis networks

relict landslide development as inferred from speleothem deformation tectonic data and geoelectrics abstract the direct dating of pre and postfaulting dislocated calcite speleothems afforded new insight into slope failure in the tatra mountains in southern poland a multi approach study of the karstic kalacka cave non crevasse type enabled us to infer the slope deformation structure which had been poorly preserved in ground surface topography using combined methods including geomorphological and structural mapping of cave and ground surfaces paleostress analysis near surface electrical resistivity tomography ert and induced polarization methods ip uranium series dating 234u 230th calcite microtexture analysis and stable isotope 18o and 13c analysis here slope deformation began with dilation between 280 7 ka and 265 8 ka and proceeded as deep seated gravitational slope deformations the final stage consisted of dilation rejuvenation and rockfall during the latest pleistocene or holocene post 35 4 ka additionally some dilations are evident beyond the extent of the landslide detected by ert indicating further progradation of slope failure since this failure was initiated during the climatic transition from mis 9 to mis 8 stable isotope analysis of calcite flowstone layers was applied to test climate factors the correlation of calcite microtexture and 18o and 13c compositional changes with the interval of dilation activity indicates that regional environment factors chiefly an increase in precipitation probably contributed to slope destabilization

on the role of grain topology in dynamic grain growth 2d microstructural modeling abstract microstructural modification processes like dynamic recrystallization and grain growth can have a major effect on the transient and semi steady state flow behaviour of deforming materials work on metals and ceramics suggests that deformation enhanced changes in grain topology and the corresponding increase in fraction of non hexagonal grains called cellular defect fraction can promote grain growth during deformation the present study tests this hypothesis by investigating the evolution of the cellular defect fraction during deformation accompanied by grain growth of aggregates with distributed grain sizes for this purpose we made use of the elle 2d microstructural modeling package we simulated and quantified microstructural evolution under conditions where both surface energy driven grain boundary migration gbm and homogeneous deformation or grain size sensitive gss straining were allowed to occur the simulations show that contemporaneous gbm and simple geometrical straining of grain aggregates with distributed grain size and coordination number lead to extra grain neighbor switching an increase in defect fraction and enhanced grain growth an increase in defect fraction was also found in a selected set of natural calcite mylonites that with increasing temperature show an increase in grain size and contribution of gss creep analysis of defect fraction thus appears to be a good microstructural tool to establish whether or not a material has experienced normal static defect fraction 0 7 or dynamic grain growth defect fraction 0 8

dynamic recrystallization of wet synthetic polycrystalline halite dependence of grain size distribution on flow stress temperature and strain abstract it is often observed that dynamic recrystallization results in a recrystallized grain size distribution with a mean grain size that is inversely related to the flow stress however it is still open to discussion if theoretical models that underpin recrystallized grain size stress relations offer a satisfactorily microphysical basis the temperature dependence of recrystallized grain size predicted by most of these models is rarely observed possibly because it is usually not systematically investigated in this study samples of wet halite containing 10 ppm water by weight were deformed in axial compression at 50 mpa confining pressure the evolution of the recrystallized grain size distribution with strain was investigated using experiments achieving natural strains of 0 07 0 12 and 0 25 at a strain rate of 5 10 7 s 1 and a temperature of 125 c the stress and temperature dependence of recrystallized grain size was systematically investigated using experiments achieving fixed strains of 0 29 0 46 and one to a strain of 0 68 at constant strain rates of 5 10 7 1 10 4 s 1 and temperatures of 75 240 c yielding stresses of 7 22 mpa the microstructures and full grain size distributions of all samples were analyzed the results showed that deformation occurred by a combination of dislocation creep and solution precipitation creep dynamic recrystallization occurred in all samples and was dominated by fluid assisted grain boundary migration during deformation grain boundary migration results in a competition between grain growth due to the removal of grains with high internal strain energy and grain size reduction due to grain dissection i e moving boundaries that crosscut or consume parts of neighbouring grains at steady state grain growth and grain size reduction processes balance yielding constant flow stress and recrystallized grain size that is inversely related to stress and temperature evaluation of the recrystallized grain size data against the different models for the development of mean steady state recrystallized grain size revealed that the data are best described by a model based on the hypothesis that recrystallized grain size organizes itself in the boundary between the grain size sensitive solution precipitation and grain size insensitive dislocation creep fields application of a piezometer calibrated using the recrystallized grain size data to natural halite rock revealed that paleostresses can vary significantly with temperature up to a factor of 2 5 for t 50 200 c and that the existing temperature independent recrystallized grain size stress piezometer may significantly underestimate flow stresses in natural halite rock

an introductory review on gravitational deformation induced structures fabrics and modeling abstract recent studies have pointed out a similarity between tectonics and slope tectonic induced structures numerous studies have demonstrated that structures and fabrics previously interpreted as of purely geodynamical origin are instead the result of large slope deformation and this led in the past to erroneous interpretations nevertheless their limit seems not clearly defined but it is somehow transitional some studies point out continuity between failures developing at surface with upper crust movements in this contribution the main studies which examine the link between rock structures and slope movements are reviewed the aspects regarding model and scale of observation are discussed together with the role of pre existing weaknesses in the rock mass as slope failures can develop through progressive failure structures and their changes in time and space can be recognized furthermore recognition of the origin of these structures can help in avoiding misinterpretations of regional geology this also suggests the importance of integrating different slope movement classifications based on distribution and pattern of deformation and the application of structural geology techniques a structural geology approach in the landslide community is a tool that can greatly support the hazard quantification and related risks because most of the physical parameters which are used for landslide modeling are derived from geotechnical tests or the emerging geophysical approaches

paleostress analysis of a gigantic gravitational mass movement in active tectonic setting the qoshadagh slope failure ahar nw iran abstract for better understanding of the dynamics of large slope failures the slope scale stress field reconstructions are eligible a new approach of paleostress analysis of large gravitational mass movements based on the multiple inverse method in 9d space and processed by a non commercial code mark2010 is demonstrated on the case of a gigantic gravitational slope failure in active tectonic setting at mount qoshadagh in nw iran the entire slope failure represents a very deep seated gravitational slope deformation with relatively short displacement roto translational base and an estimated volume of about 83 110 km3 which is of the last glacial age this gigantic slope failure has developed in an active tectonic setting along the qoshadagh fault system or called south ahar fault which caused fast uplift of the entire mountain range of qoshadagh and it was probably seismically triggered using this paleostress approach we were able to distinguish the mass movement stress phase of nw compression in the rockslide s zone of compression and nw se extension in the upper part from a variety of other 8 regional tectonic and 2 subsequent gravitational phases maximum principal stress of the slope failure phase was in its compression zone sub parallel to the estimated displacement vector in the head it was sub vertical the paleostress analysis has been proved as a useful tool for reconstructing the stress field evolution of large slope failures

recent tectonic stress evolution in the lesser caucasus and adjacent regions the stress indicators describing the recent provided by active tectonics framework and palaeo stress provided by micro fault kinematics and volcanic cluster patterns show the scale and temporal changes in stress states since the beginning of arabian eurasian collision the recent stress derived from the active fault kinematics in the lesser caucasus and adjacent area corresponds to a strike slip regime with both transtension and transpression characteristics the kinematics of active structures of various scale are conditioned by tectonic stress field with general north south compression and east west extension the distribution of neogene to quaternary volcanic cluster geometries and micro fault kinematic data evidence the time and orientation variability of the stress field since the beginning of the arabian eurasian collision in addition to the general north south compression orientation two other nw se and ne sw secondary orientations are observed the first one was dominant between the palaeogene and the late early miocene and the second one has prevailed between the late miocene and the quaternary since the continental collision of arabia with eurasia the tectonic stress regime in the lesser caucasus and adjacent area changed from compression thrusting and reverse faulting to transtension transpression strike slip faulting with various vertical components

active tectonics in the lesser caucasus coexistence of compressive and extensional structures detailed spot image analysis which completed field data and a microseismicity study was done on the central caucasian mountain belt georgia armenia and eastern turkey north of the front of the arabian collision in order to clarify the relationships between compression extension and volcanism in fact this region is characterized by relatively complex active tectonics associating both n s compressive e w thrusts and folds and e w extensional n s normal faults and dikes structures accompanied by considerable neogene to quaternary volcanism and ne sw left lateral and nw se right lateral strike slip faults these different structures are all intricately imbricated and can be observed at different scales the general layout implies an important variation in the stress state for instance this passes from a n s compression in the spitak earthquake fault zone to an e w extension at the aboul samsar volcanic axis these results agree well with the n s convergence between arabia and eurasia and the e w lateral expulsion of the anatolian and iranian blocks a detailed cartographic network of active structures was drawn and their kinematic relationships were specified in places recent offsets on strike slip faults were estimated at about 500 to 1000 m suitable sites for future determination of fault velocity displacements were also selected this study shows that some strike slip faults behave partly like faults which transform the e w extension of the n s striking normal faults into a n s compression along the e w thrusts one of the characteristics of this region is the continuous important volcanic activity at least from the jurassic until now this persistence evidences a lithospheric thinning which remained in spite of the recent arabian eurasian collision because of the e w extension linked to the opposite lateral expulsion of the anatolian and iranian blocks this geodynamic evolution can explain the juxtaposition and superimposition of volcanic structures and thrusts in a general compressive context

grain size evolution and the rheology of ductile shear zones from laboratory experiments to postseismic creep abstract geologic experimental and geodetic studies indicate that ductile shear zones do not deform in steady state we present a theoretical model for an elastically loaded ductile shear zone deforming by combined dislocation and diffusion creep in which grain size is allowed to evolve toward its equilibrium recrystallized value several grain size evolution laws are considered simulations of laboratory experiments show that grain size evolution can lead to changes in the dominant deformation mechanism that are accompanied by transient strain weakening or strain strengthening episodes reminiscent of laboratory observations ductile shear zones can also produce postseismic creep as observed in geodetic data following large earthquakes non steady state ductile creep is difficult to differentiate from frictional sliding with velocity strengthening friction hence ductile creep may play a role in the transition from velocity weakening to velocity strengthening friction with increasing temperature

the effect of second phase particles on stable grain size in regionally metamorphosed polyphase calcite marbles samples of the calcite rich shelburne marble collected at the pfizer quarry in adams massachusetts show an order of magnitude variation in grain size calcite grain size ranges from 94 to 1101 m because these calcite marbles share the same pressure temperature and strain histories some other factor must be responsible for the grain size variation grain size appears to be controlled by the concentration of impurity or second phase particles large calcite grain size occurs where the volume fraction of second phase particles is low and grain size decreases as second phase volume fraction increases the relationship between calcite grain size d second phase grain size d and second phase volume fraction f can be described by the power law d d 1 4 f 0 36 a result that is consistent with models based upon short term hours or days laboratory experiments with metals and ceramics and computer simulations of grain growth grain growth appears to be greatly restricted by as little as a few per cent of second phase particles with a transition from highly restricted to almost unrestricted grain growth occurring at 5 volume of second phase particles these results indicate that second phase particles exercise an important control on grain size and can effectively inhibit grain growth in metamorphic rocks the behaviour of second phases in short term laboratory experiments may closely approximate the behaviour of second phases in grain growth lasting several orders of magnitude longer in the metamorphic environment

rheological and microstructural evolution of carrara marble with high shear strain results from high temperature torsion experiments abstract this study investigated the rheological and microstructural evolution of carrara marble deformed to large shear strain to understand how dynamic recrystallization and lattice preferred orientation lpo are related to strain softening processes solid cylinders of carrara marble were deformed in torsion up to a shear strain of 11 at constant twist rates which correspond to a shear strain rate of 3 10 4 s 1 at the outer surface and at temperatures of 1000 and 1200 k 727 and 927 c respectively for the initial grain size of 150 m these conditions are within the dislocation creep regime substantial changes in both rheology and microstructure were observed as the marble deformed to high shear strain at 1000 k 1200 k a peak stress was reached at about 1 0 5 followed by moderate strain weakening an apparent steady state flow stress was obtained at high shear strain of 5 2 the stress exponent n decreased slowly with strain from 10 1 to 6 9 at 1000 k but it remained approximately constant at 1200 k n around 10 at the maximum reached shear strain of 11 8 5 the marble had almost completely recrystallized to a fine grain size of about 10 m 20 m a secondary foliation developed in the recrystallized matrix which is at a large oblique angle to the shear zone boundary szb lpo was measured by electron backscatter diffraction ebsd for both temperatures the lpo evolved from an oblique deformation texture to a very sharp and symmetric single orientation component with r 1014 parallel to the shear plane and a 1210 parallel to the shear direction it is concluded that strain weakening was associated with the development of a strong lpo during dynamic recrystallization to a finer grain size mechanical and microstructural steady state is only reached at large shear strain the steady state lattice and grain shape fabrics can hardly be used as shear sense indicators in such recrystallized calcite mylonites

co seismic stress transfer and magnitude frequency distribution due to the 2012 varzaqan ahar earthquake doublets m w 6 5 and 6 4 nw iran abstract the coulomb stress changes imparted by the 2012 varzaqan ahar earthquake doublets to the surrounding area have been examined and correlated with the spatial distribution of the aftershocks the stress changes due to the first main shock show that the western half of the south ahar fault the southeastern half of the magnetic lineament ml1 the northeastern end of the ml2 the entire length of the ml3 a large part of the ml4 and the northeastern half of the ml5 were brought closer to failure whereas the entire length of the khajeh fault a part of the north tabriz fault the western half of the ml1 a large part of the ml2 the northwestern end of the ml4 and the southwestern half of the ml5 were moved away from failure along the length of the ml1 some aftershocks were clustered in the southeastern and central sections while around the western section there is no earthquake clustering the epicentral distributions of the aftershocks exhibit that most of the events were concentrated in the increased coulomb stress zones the b value distributions in the map view and in the cross sectional view have been investigated the map view shows that the low b value regions e g the north northwest east northeast and southeast of the main shock are in good agreement with the positive coulomb stress change zones the cross sectional view indicates that the high b value regions correlate with the areas of high co seismic slip release therefore surrounding the hypocenter and the western end of the first main shock fault have high b values more slip and positive stress drop while the central sections of the fault have low b values less slip and negative stress drop