paleomagnetic study of plio pleistocene sediments in the concentrated deformation zone along the eastern margin of the japan sea abstract paleomagnetic results are presented for a concentrated deformation zone cdz in a convergent plate boundary region along the eastern eurasian margin we sampled late pliocene early pleistocene tuffs and clastic sediments of the sasaoka formation 750 m thick in northeastern honshu japan to test whether the late pliocene quaternary crustal deformation within the cdz along the eastern margin of the japan sea was accompanied by rotation about a vertical axis rock magnetic experiments suggest that the principal magnetic carrier is magnetite in the fine tuffs and magnetic iron sulfide in the fine sandstones pre folding characteristic remanent magnetization was confirmed using a positive bootstrap fold test we obtained 21 acceptable site mean characteristic directions that include our preliminary published results and which cover an interval from ca 2 7 to 1 7 ma on the basis of magnetostratigraphic correlations an updated age depth model is given and this allowed us to make numerical age estimates for key interbedded tuff beds tephras a positive fold test also suggests that the gojome syncline began to develop after 1 7 ma which means the folding began long after the initiation of late pliocene crustal shortening in northeastern honshu after 100 unfolding the overall mean direction d 359 7 i 54 9 95 6 7 is indistinguishable from the geocentric axial dipole field direction indicating that the gojome syncline the most prominent structural element in the study area developed without vertical axis rotation a comparison of our results with plio pleistocene directions reported from other areas reveals no paleomagnetically detectable rotation in or adjacent to the cdz except for local rotation near strike slip faults in central honshu

tectonic plate generation and two phase damage void growth versus grain size reduction 1 the generation of plate tectonics from mantle convection requires shear localization in order to yield narrow weak plate boundaries separating broad strong plates a plausible shear localizing mechanism involves damage e g distributed microcracking one theoretical model of which involves two phase mechanics two phase damage theory employs a nonequilibrium relation between interfacial surface energy pressure and viscous deformation thereby providing a description of void generation and microcracking and hence weakening failure and shear localization here we examine the application of this theory to the problem of generating plate like behavior from convective type divergent convergent poloidal motion through a source sink formulation we extend the previous damage theory to consider two possible damage effects 1 growth and nucleation of voids associated with dilation of the host matrix and 2 increasing fineness i e reducing coarseness of the mixture by for example grain size reduction void generating damage is found to be poor at plate generation because of the predominance of dilational motion that is adverse to the development of plate like flow fineness generating damage is found to be very efficient at generating plate like behavior if we assume that the matrix viscosity is a simple function of grain void size as is typical for diffusion creep the implied grain size reduction mechanism is different from that of dynamic recrystallization and appears to be more capable of generating the requisite shear localization for forming tectonic plates from mantle flow

bookshelf tectonics rotated crustal blocks within the sovanco fracture zone the 15 kilometer wide sovanco fracture zone is a dextral slip transform fault linking the juan de fuca and explorer ridges in the n e pacific seabeam bathymetry shows that the sovanco comprises several rhomb shaped elevated blocks of oceanic crust bounded by northeast and northwest trending lineaments we hypothesize that the northeast trending lineaments are sinistral strike slip faults that are reactivated ridge parallel normal faults both the sinistral block bounding faults and the blocks themselves have rotated clockwise about 30 degrees in response to dextral shear within the sovanco zone

estimation of total lateral displacement including strike slip offset and broader drag deformation on an active fault tectonic geomorphic and paleomagnetic evidence on the tanna fault zone in central japan abstract when determining deformation along an active strike slip fault it is desirable to include the cumulative distributed deformation due to drag away from the fault trace in addition to offset on the fault we achieve this by integrating geomorphologic paleomagnetic and geologic data for the active left lateral strike slip tanna fault zone in central japan which previous studies suggest is slipping at about 2 mm yr we combine new detailed mapping of multiple quaternary strands of the fault zone with paleomagnetic measurements from volcanic rocks extruded across the faults from the taga volcano at about 0 6 ma from these data we determine differential counterclockwise rotations from which we infer cumulative strike slip drag deformation at distances of about 1 3 km from the faults these results suggest that the total strike slip displacement accompanying cumulative drag deformation along the fault zone from approximately 0 6 ma to the present is more than 2 3 2 7 km based on a kinematic model or about 6 0 km based on a power law rheology model after adding 1 km of offset along the fault trace thus depending on the model applied the total rate of strike slip deformation along the tanna fault zone is either more than 3 8 4 5 mm yr or about 10 mm yr respectively both of these rates are considerably higher than a previous estimate of about 2 mm yr based solely on strike slip offset without accommodating the drag deformation over the broader zone on either side of the fault break furthermore the deformation rate based on the power law rheology model is comparable to the rate detected by past gps observations

deformation processes adjacent to active faults examples from eastern california 1 major seismogenic faults are embedded within narrow zones of inelastic off fault deformation ofd where both distributed displacement and modification of rock properties occur active distributed displacement may affect slip rate estimates seismic energy radiation and geodynamic models this study addresses the role of ofd in the displacement history and mechanical behavior of seismogenic faults by multisite study of deformed geologic features adjacent to 30 60 km long active strike slip faults of 10 km of dextral displacement in the mojave desert eastern california we find that distributed displacement accommodates 0 to 25 of the total displacement over zones of one to two kilometers width displacement occurs mostly within 100 200 m of faults and decreases nonlinearly away from the main fault we show evidence for distributed displacement through simple shear in the form of parallel secondary faults and progressive deformation of linear markers adjacent to the calico fault we also find evidence for shear via rotation and progressive fragmentation adjacent to the harper lake fault analysis of block dimensions show that blocks tend to decrease in size toward faults and that cumulative length of secondary faults is longer than the main fault by at least a factor of 10 based on crosscutting relationships and the relationship of ofd to geophysically imaged compliant zones around active faults we argue that distributed displacement is an active process and suggest that zones of diminished rigidity near faults may be at least in part driven by secondary faulting during the rupture propagation along the main fault

paleomagnetic evidence for 25 15 ma crust fragmentation of north indochina 23 26 n consequence of collision with greater india ne corner

intraplate rotational deformation induced by faults vertical axis rotations provide important constraints on the tectonic history of plate boundaries geodetic measurements can be used to calculate interseismic rotations whereas paleomagnetic remanence directions provide constraints on the long term rotations accumulated over geological timescales here we present a new mechanical modeling approach that links between intraplate deformational patterns of these timescales we construct mechanical models of active faults at their locked state to simulate the presumed to be elastic interseismic deformation rate observed by gps measurements we then apply a slip to the faults above the locking depth to simulate the long term deformation of the crust from which we derive the accumulated rotations we test this approach in northern israel along the dead sea fault and carmel gilboa fault system we use 12 years of interseismic gps measurements to constrain a slip model of the major faults found in this region next we compare the modeled rotations against long term rotations determined based on new primary magnetic remanence directions from 29 sites with known age the distributional pattern of site mean declinations is in general agreement with the vertical axis rotations predicted by the mechanical model both showing anomalously high rotations near fault tips and bending points overall the results from northern israel validate the effectiveness of our approach and indicate that rotations induced by motion along faults may act in parallel or alone to rigid block rotations finally the new suggested method unravels important insights on the evolution timing magnitude and style of deformation along major faults

quantitative evaluation of quaternary crustal deformation around the takayama basin central japan a paleomagnetic and numerical modeling approach abstract neotectonic crustal deformation in central japan is described quantitatively on the basis of paleomagnetic measurements and numerical modeling the welded part of the earliest quaternary nyukawa pyroclastic flow deposit npfd preserves stable remanent magnetization detailed paleo rock magnetic experiments reveal that remanence of the npfd near the takayama basin resides in unimodal titanomagnetite and comprises a component of thermoremanent magnetization trm and three components of thermoviscous remanent magnetization tvrm scatter in the untilted declinations of the syn depositional trm component represents differential rotation about vertical axes related to quaternary activity of three faults enako makigahora and harayama associated with the takayama basin the normal and reversed tvrm components probably acquired by warm water circulation near the active faults during the jaramillo subchron record a complicated rotational sequence since ca 1 ma dislocation modeling successfully simulates the spatial distribution of rotation and the uplift subsidence pattern around the takayama basin assuming strike slip motion on the enako and makigahora faults along the basin margin and vertical displacements on the harayama fault within the basin temporal changes in rotational motions recorded in the tvrms of near fault sites can be modeled by considering transition of active segments of the three faults which is geologically constrained

the block structure and quaternary strike slip block rotation of central japan central japan is situated on the inflection point of the bow shaped japanese islands numerous nw se trending active faults arranged in parallel at intervals of 20 to 80 km are found in this area these active faults are more than 30 km long with shattered zones from 30 to 300 m wide several active faults constitute a given block boundary which serves as the dividing line for one of the four blocks that make up central japan the block boundaries require careful study since numerous historical earth quakes have occurred along these lines offset measurements of basement rocks created during the quaternary period due to left lateral faulting amount to 1 to 7 km gravity lineaments which link points of sudden change and saddles of bouguer anomalies are clearly found along the block boundaries the nw se trending active faults appearing on the ground surface are associated with motions of the block boundaries block rotational movement caused by left lateral faulting plays an important role in the crustal deformation of central japan rotational angles of the blocks calculated from the amount of displacement of basement rocks initiated during the quaternary period are estimated to be 3 to 7 in a clockwise manner

tectonic deformation by rotating parallel faults the bookshelf mechanism abstract in various tectonic environments extension of crustal parts and shear distortion has been accommodated by the rotation of an array of parallel faults because of its kinematic resemblance to the tilting of a row of books on a shelf the tectonic process may be referred to as a bookshelf mechanism its most important manifestions are cross faulting between normal faults or parallel wrench faults the extension of deltaic slope deposits and all forms of tilted block tectonics kinematically there are two basic modes of the mechanism a the dilational mode where rotating faults tend to open up and possibly become paths for fluid migration and b the domino style where reclining faults remain closed in both cases formation and rotation of the faults may take place in one tectonic event fault displacements may therefore often remain small and difficult to detect from the mechanical point of view bookshelf operations that accommodate shearing between parallel and predominantly parallel moving rock boundaries bookshelf mechanisms proper have to be differentiated from those operations responding to an imposed crustal extension or shortening after a review of geological evidence the process is addressed from a geomechanical point of view in order to determine the geological operating conditions and controlling parameters the crucial mechanical factor in the bookshelf mechanism is the component of normal stress that acts in the direction of the imposed displacement component parallel to the driving boundary plates in contrast to the usual assumption the driving shear stress on the boundary plates not only depends on the normal stress on the plates but it also varies with the value of the normal stress that acts inside the sheared material in the direction of the plate parallel displacement component it is the relationship between the two normal stresses that also determines the type of rotating parallel faults large scale rotation of parallel normal faults in domino style tilted block tectonics is primarily associated with the extension of ductile substrata from mechanical arguments and sand box experiments it has been inferred how the process and in particular the dip direction of the parallel faults is controlled by the way substratal extension progresses by means of the direction of a substratal squeeze flow the presence of a surface slope the strength anisotropy associated with fore set beds and by the configuration of competent boundaries of the extending overburden

generation of plate like behavior and mantle heterogeneity from a spherical viscoplastic convection model 1 how plate tectonics arises from mantle convection is a question that has only very recently become feasible to address with spherical viscoplastic computations we present mainly internally heated convection results with temperature dependent viscosity and explore parts of the rayleigh number ra yield stress y phase space as well as the effects of depth dependent y bottom heating and a low viscosity asthenosphere convective planform and toroidal poloidal velocity field ratio tpr are affected by near surface viscosity variations and tpr values are close to observed values for our most plate like models at the relatively low convective vigor that is accessible at present most models favor spherical harmonic degree one convection though models with a weaker surface viscosity form degree two patterns and reproduce tomographically observed power spectra an asthenospheric viscosity reduction improves plate like nature as expected for our incompressible computations pure bottom heating produces strong plumes that tend to destroy plates at the surface this implies that significant internal heating may be required both to reduce the role of active upwellings and to form a low viscosity zone beneath the upper boundary layer

orogen parallel transition from a decoupled fore arc sliver to andean type mountain chain paleomagnetic and geologic evidence from southern chile 37 39 s

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

paleomagnetic rotation pattern of the southern chile fore arc sliver 38 s 42 s a new tool to evaluate plate locking along subduction zones the chile fore arc at 37 s 47 s represents the coseismic deformation zone of the 1960 mw 9 5 valdivia earthquake here we report on the paleomagnetism of 43 oligocene pleistocene volcanic sites from the fore arc sliver between 38 s and 42 s sites were gathered west of the 1000 km long liquine ofqui dextral fault zone lofz that represents the eastern fore arc sliver boundary nineteen reliable sites reveal that the fore arc is characterized by counterclockwise ccw rotations of variable magnitude except at 40 s 41 s where ultrafast 50 myr clockwise cw rotations occur within a 30 km wide zone adjacent to the lofz ccw rotation variability even at close sites and rapidity 10 myr suggest that the observed block rotation pattern is related to nw se seismically active sinistral faults crosscutting the whole fore arc according to previously published data cw rotations up to 170 also occur east of the lofz and have been related to ongoing lofz shear we suggest that the occurrence and width of the eastern fore arc sliver undergoing cw rotations is a function of plate coupling along the subduction zone interface zones of high coupling enhance stress normal to the lofz induce high lofz strength and yield a wide deformation zone characterized by cw rotations conversely low coupling imply a weak lofz a lack of cw rotations and a fore arc entirely dominated by ccw rotations related to sinistral fault kinematics our locking inferences are in good agreement with those recently derived by gps analysis and indicate that seismotectonic segment coupling has remained virtually unchanged during the last 5 ma

paleomagnetism and crustal rotations along a shear zone las vegas range southern nevada in southern nevada paleozoic isopachs mesozoic structures and mountain ranges trend north south but as they approach the right lateral west northwest trending las vegas valley shear zone lvvsz they are bent clockwise up to 90 in oroflexes 30 km long in the las vegas range the declination of the characteristic magnetization of the cambrian bonanza king formation has likewise been rotated clockwise more than 50 for samples from eight sites 13 23 samples per site in the las vegas range and in its extension south of the lvvsz stepwise thermal demagnetization to 600 c removed recent and tertiary overprints revealing a nearly horizontal late paleozoic viscous partial thermoremanent magnetization vptrm which predates both the tertiary oroflexural bending and the sevier thrusting in the area the declination of the characteristic magnetization after correcting for the dip of bedding varies from 133 2 at a site 24 km north of the shear zone to 196 4 13 km north of it and 204 4 11 km south of the shear zone this parallels a similar change in the structural trend the paleomagnetic data indicate that the las vegas range is broken into rather small blocks 5 km which rotate in response to more continuous deformation at depth this deformation of the upper crust can be modelled using a thin non newtonian viscous plate model which when applied to the las vegas valley shear zone predicts rotations similar to those seen in the las vegas range

mechanisms for the generation of plate tectonics by two phase grain damage and pinning abstract weakening and shear localization in the lithosphere are essential ingredients for understanding how and whether plate tectonics is generated from mantle convection on terrestrial planets we present a new theoretical model for the mechanism of lithospheric weakening and shear localization and hence plate generation through damage grain evolution and zener pinning in two phase polycrystalline lithospheric rocks grain size evolves through the competition of coarsening which drives grain growth with damage which drives grain reduction however in a two phase medium the interface between phases induces zener pinning which impedes grain growth and facilitates damage the size of the pinning surfaces is given by the roughness of the interface and damage to the interface causes smaller pinning surfaces which in turn drive down the grain size forcing the rheology into the grain size dependent diffusion creep regime this process allows damage and rheological weakening to co exist which is normally considered impossible in single phase assemblages moreover pinning greatly inhibits grain growth and shear zone healing which is much faster in single phase materials hence the resulting shear localization is rapid less than 1 myr but the healing time for a dormant weak zone is very slow greater than 100 myrs these effects therefore permit rapidly forming and long lived plate boundaries the model therefore provides a key ingredient and predictive theory for the generation of plate tectonics on earth and other planets

magnetic and plagioclase linear fabric discrepancy in dykes a new way to define the flow vector using magnetic foliation in basaltic dykes the magnetic lineation k1 maximum magnetic susceptibility axis is generally taken to indicate the flow direction during solidification of the magma this assumption was tested in tertiary basaltic dykes from greenland displaying independent evidence of subhorizontal flow the digital processing of microphotographs from thin sections cut in k1 k2 planes yields the preferred linear orientation of plagioclase which apparently marks the magma flow lineation in up to 60 of cases the angular separation between k1 and the assumed flow direction is greater than 45 this suggests that the uncorroborated use of magnetic lineations in dykes is risky a simple geometrical method is proposed to infer the flow vector from ams in dykes based solely on magnetic foliations

quaternary strike slip crustal deformation around an active fault based on paleomagnetic analysis a case study of the enako fault in central japan abstract to evaluate cumulative strike slip deformation around an active fault we carried out tectonic geomorphic investigations of the active right lateral strike slip enako fault in central japan and paleomagnetic investigations of the kamitakara pyroclastic flow deposit kpfd 0 6 ma welded tuff distributed around the fault tectonic geomorphic study revealed that the strike slip displacement on the fault is ca 150 m during the past 600 ka we carried out measurements of paleomagnetic directions and anisotropy of magnetic susceptibility ams within the pyroclastic flow deposit stable primary magnetic directions at each sampling site are well clustered and the ams fabric is very oblate we then applied tilt correction of paleomagnetic directions at 15 sites using tilting data obtained by the ams property and orientations of eutaxitic structures within a distance of about 500 m from the fault trace differential clockwise rotations were detected the rotation angle is larger for zones closer to the fault because of this relation and absence of block boundary faults a continuous deformation model explains the crustal deformation in the study area the calculated minimum value of strike slip displacement associated with this deformation detected within the shear zone is 210 m the sum of this and offset on the enako fault is 360 m and the slip rate is estimated at 0 6 mm year

near surface thermal chemical boundary layer convection at infinite prandtl number two dimensional numerical experiments chemical differentiation and convective removal of internal heat make the earth s lithosphere a thermal and a chemical boundary layer thin layers of chemically light material form near the earth s surface and become embedded within the cold thermal boundary layer associated with interior heat removal the likelihood of near surface thermal and chemical boundary layer interactions influencing the earth s thermotectonic evolution prompts the models presented herein a simplified system consisting of a chemically light layer within the upper thermal boundary layer of a denser thermally convecting layer is explored through a suite of numerical experiments to see how its dynamic behaviour differs from similar well studied thermal boundary layer systems a major cause of differences between the two systems resides in the ability of the deformable near surface chemical layer to alter the effective upper thermal boundary condition imposed on the convectively unstable layer below in thermal equilibrium regions of chemical boundary layer accumulation locally enforce an effectively near constant heat flux condition on the thermally convecting layer due to the finite thermal conductivity of chemical boundary layer material for cases in which chemical accumulations translate laterally above the unstable layer the thermal coupling condition between chemical boundary layer material and the unstable layer below is one of non equilibrium type i e the thermal condition at the top of the convectively unstable layer is time as well as space variable a second major cause of differences is that for the thermal chemical system chemically induced rheologic variations can offset or compete with those due to temperature more specifically the presence of chemically weak material can lubricate convective downwellings allowing for enhanced overturn of an on average strong upper thermal boundary layer both of these factors have low order effects on internal flow structure and heat loss and lead to dynamic behaviour in which chemical boundary layer deformation is not only driven by flow in the thermally convecting interior layer but also feeds back and alters this flow some implications of this in regard to elucidating how near surface chemical boundary layer deformation e g continental tectonics might interact with and influence mantle convection are discussed

the use of paleomagnetic analysis to assess nonbrittle deformation within the san andreas fault zone a recently developed paleomagnetic extraction technique successfully permits sample collection from unconsolidated sediments traditional measurement and demagnetization procedures can subsequently be performed and several studies have already shown that soft sediment samples yield reliable magnetic polarity information to test the robustness of the extraction technique as well as the resolution limits of the resultant magnetic vector directions a total of 238 paleomagnetic samples were taken from unconsolidated strata exposed in an excavation across the san andreas fault zone in the carrizo plain california variable fault offset values for the most recent earthquakes at this locality favored the likelihood of rotational nonbrittle deformation such deformation could possibly be recorded in the drm detrital remanent magnetization of sediment deposited across the zone declination directions of sample groups taken from presumably unrotated strata show general agreement with the most recent secular variation curve constructed for southern california supporting the assumption that the stratigraphic units sampled do record an accurate drm however significant variations in declination directions are found between magnetically stable samples within sample groups i e taken as close as 1 cm apart within the same stratigraphic horizon probable causes of such declination variations include postdepositional physical disturbances associated with rupture events and errors generated by the sampling technique inadvertent sample rotation about the axis of the glass holders is one of the most evident sources of error found in this study although only samples which underwent large rotations 60 could be identified regardless of its origin the variability of the magnetic declination directions found for the 29 magnetically stable groups forces us to conclude that paleomagnetic results calculated in this study are not precise enough to discern reasonable 20 amounts of rotation these results question a similar soft sediment study upon which this study was modeled which claims to have successfully detected less than 20 in rotational deformation using an identical sampling method additional studies are needed preferably not within active fault zones to better define sources of error for this relatively new soft sediment sampling technique and to determine its resolution limits for discerning small changes in paleomagnetic vector directions

paleomagnetic measurement of nonbrittle coseismic deformation across the san andreas fault at pallett creek paleomagnetic data have been obtained to address a problem at the pallett creek paleoseismological site the 9 mm yr slip rate determined from three dimensional mapping of late holocene offsets across discrete faults is only a quarter of the expected value we suspected that nonbrittle deformation adjacent to the faults might account for the 26 mm yr discrepancy in our search for the missing slip we collected and analyzed 264 paleomagnetic samples from a 53 m wide transect across the fault zone half the samples came from a unit deposited immediately after a large earthquake of about a d 1480 these samples were affected by two large earthquakes that involved rupture at the site in 1812 and 1857 we collected the other half of the samples from a slightly older bed one that was deposited before the earthquake of about a d 1480 relative to control groups composed of 10 samples and collected 50 m from the fault samples closer to the fault display clockwise rotations of 30 or less if interpreted as block rotations the data from the older unit imply that it has sustained a total of 14 0 2 9 m of dextral warp during the past three major earthquakes and that the younger unit has experienced a total of 8 5 1 0 m of warp during the most recent two combining these values with the amounts of dextral slip across the mapped fault planes yields dextral offsets of 5 5 6 25 and 6 25 m for the events of a d 1480 1812 and 1857 and a slip rate of 35 6 6 7 mm yr this slip rate averaged over the past three complete seismic cycles is consistent with published rates from other sites offsets associated with the past three events are remarkably similar these amounts however appear independent of the length of interseismic cycles these observations suggest 1 that this part of the san andreas fault has a characteristic strength and 2 that conventional concepts of strain accumulation and relief for example time and slip predictable models of earthquake occurrence are unrealistic

understanding kinematics of intra arc transcurrent deformation paleomagnetic evidence from the liquine ofqui fault zone chile 38 41 s the liquine ofqui fault zone lofz is a major 1000 km long dextral shear zone of southern chile likely related to strain partitioning of nazca plate oblique convergence with south america to understand block rotation pattern along the lofz we paleomagnetically sampled 55 sites 553 samples between 38 s and 41 s we gathered oligocene to pleistocene volcanics and miocene granites at a maximum distance of 20 km from the lofz and at both sides of it rotations with respect to south america evaluated for 36 successful sites show that crust around the lofz is fragmented in small blocks 1 to 10 km in size while some blocks at both fault edges undergo very large 150 170 rotations others do not rotate even adjacent to fault walls we infer that rotations affected equidimensional blocks while elongated crust slivers were translated subparallel to the lofz without rotating rotation pattern across the lofz is markedly asymmetric east of the fault and adjacent to it rotations are up to 150 170 clockwise and fade out 10 km east of fault these data support a quasi continuous crust kinematics characterized by small rigid blocks drag by the underlying ductile crust flow and imply 120 km of total fault offset conversely crust west of the lofz is cut by seismically active nw se sinistral antithetic faults and yields counterclockwise rotations up to 170 at 8 10 km from lofz besides the unrotated blocks further data from the chile fore arc are needed to understand block rotation kinematics and plate dynamics west of the lofz

quantifying near field and off fault deformation patterns of the 1992 mw 7 3 landers earthquake coseismic surface deformation in large earthquakes is typically measured using field mapping and with a range of geodetic methods e g insar lidar differencing and gps current methods however either fail to capture patterns of near field coseismic surface deformation or lack preevent data consequently the characteristics of off fault deformation and the parameters that control it remain poorly understood we develop a standardized method to fully measure the surface near field coseismic deformation patterns at high resolution using the cosi corr program by correlating pairs of aerial photographs taken before and after the 1992 m w 7 3 landers earthquake cosi corr offers the advantage of measuring displacement across the entire zone of surface deformation and over a wider aperture than that available to field geologists for the landers earthquake our measured displacements are systematically larger than the field measurements indicating the presence of off fault deformation we show that 46 of the total surface displacement occurred as off fault deformation over a mean deformation width of 154 m the magnitude and width of off fault deformation along the rupture is primarily controlled by the macroscopic structural complexity of the fault system with a weak correlation with the type of near surface materials through which the rupture propagated both the magnitude and width of distributed deformation are largest in stepovers bends and at the southern termination of the surface rupture we find that slip along the surface rupture exhibits a consistent degree of variability at all observable length scales and that the slip distribution is self affine fractal with dimension of 1 56

vertical axis rotations and deformation along the active strike slip el tigre fault precordillera of san juan argentina assessed through palaeomagnetism and anisotropy of magnetic susceptibility palaeomagnetic data from poorly consolidated to non consolidated late cenozoic sediments along the central segment of the active el tigre fault central western precordillera of the san juan province argentina demonstrate broad cumulative deformation up to 450 m from the fault trace and reveal clockwise and anticlockwise vertical axis rotations of variable magnitude this deformation has affected in different amounts miocene to late pleistocene samples and indicates a complex kinematic pattern several inherited linear structures in the shear zone that are oblique to the el tigre fault may have acted as block boundary faults displacement along these faults may have resulted in a complex pattern of rotations the maximum magnitude of rotation is a function of the age of the sediments sampled with largest values corresponding to middle miocene lower pliocene deposits and minimum values obtained from late pleistocene deposits the kinematic study is complemented by low field anisotropy of magnetic susceptibility data to show that the local strain regime suggests a n s stretching direction subparallel to the strike of the main fault

a nested fault system with block rotation caused by left lateral faulting the neodani and atera faults central japan abstract a detailed study of outcrops existing around the neodani and atera faults which are large scale left lateral faults oriented nw se in central japan revealed they were accompanied by two distinct fault systems of different scale and slip sense intermediate scale parallel right lateral faults and small scale parallel left lateral kink bands or faults a nested fault model with different geometric scales is proposed to explain the hierarchical occurrence of the fault systems in this model the secondary fault system is contained within the primary fault system as a mirror image of it left lateral movement of the atera or neodani fault induces right lateral movement of intermediate scale faults and results in counterclockwise rotation of the blocks between the faults this right lateral movement in turn induces left lateral movement of small scale faults or kink bands which causes clockwise rotation of the small blocks between them since the angle of the counterclockwise rotation of the primary fault systems is the same as that of the clockwise rotation of the secondary fault system these rotations cancel each other while the large scale fault movements cause block rotation the small blocks eventually show no rotation

tectonics and paleomagnetic rotation pattern of yunnan 24 n 25 n china gaoligong fault shear versus megablock drift

active strike slip faulting and macroscopically nonrigid deformation of volcanic rocks in central japan inferred from a paleomagnetic study abstract detailed paleomagnetic investigation of a pyroclastic flow deposit has clarified the deformation mode around an active fault in central japan the early quaternary nyukawa pyroclastic flow deposit is cut by the active dextral enako fault activity level of the fault is evaluated on the basis of geological and geomorphological surveys then paleomagnetic samples are collected from 22 sites at exposures located on a lineament that is adjoining and parallel to the enako fault stable thermoremanent magnetization trm of the pyroclastic deposit is isolated through progressive thermal and or alternating field demagnetization tests untilted site mean directions of the trms simultaneously acquired during initial cooling indicate significant clockwise vertical axis rotation the lineament was then activated with right lateral motions through the early quaternary together with the late quaternary activities along the adjoining enako fault evaluated by our study the present result exemplifies a migration of active segments within a fault system during the quaternary paleomagnetic directions on the strike slip fault are not concordant with uniform deformation predicted by the model of rotation of rigid blocks aligned on a master fault but suggestive of a periodic deformation as a result of intense fracturing and differential rotation of blocks bounded by nested parallel faults

self lubricated mantle convection two dimensional models we present results from convection models allowing for self lubrication of downflows models impose a line source of chemically light low viscosity material at the top of a convecting layer of temperature dependent viscosity material low viscosity surface material serves as an analog to hydrated sediment crust and the high viscosity upper portion of the convecting layer as an analog to mantle lithosphere slow near surface motion in the convecting layer entrains low viscosity material into zones of downflow which has a lubricating effect once entrained lubricant is deeper than the cold high viscosity portion of the convecting layer rapid upper boundary layer overturn occurs and system properties change e g heat flux doubles this marks transition to a lubricated state before and after transition transport properties are dominantly determined by respectively the viscosity of mantle lithosphere and that of interior mantle lubricated and nonlubricated states appear as distinct regions in system output space suggesting that exchange between them is akin to a phase transition that such exchange depends on a near surface lubricant implies that the geodynamics of planets lacking such lubricants may fundamentally differ from that of planets possessing them

an urban model for dolomite precipitation authigenic dolomite on weathered building stones abstract formation of authigenic dolomite within alteration crusts developing on limestone surfaces of a historical building is confirmed by xrd polarising microscopy and sem with edx data two different types of authigenic dolomite occur limpid stoichiometric dolomite and ca rich protodolomite the presence of gypsum calcite pollution derived particles clay minerals and organic material within the crusts confirms their recent formation together with that of dolomite in a micro environment of high evaporation and ionic concentrations such environments are typically found in many urban centres on the basis of these findings an urban model for dolomite precipitation is proposed there are two sources of mg 1 dissolution of nearby dolostones overlying the limestones as a result of leaching by atmospheric so2 oxidised and hydrolysed as h2so4 and 2 mg rich metallic atmospheric particles elevated mg ca values are achieved by precipitation of gypsum which removes ca from the solution protodolomite then precipitates and later recrystallises as limpid dolomite due to changes in the pore fluids related with the environmental conditions co32 and co3h are provided by leaching of both the limestone support and the nearby dolostones additional sources of co2 are provided both by the polluted urban atmosphere rain water and the degradation of organic material within the crust organic matter fungi and bacteria pollution derived particulate matter and clays seem to play a key role in promoting dolomite precipitation in this micro environment by altering kinetic barriers and providing active sites for dolomite nucleation finally the formation of urban dolomite is compared with recent dolomites forming in natural environments with alternating evaporative fresh water conditions