high efficiency of natural lamellar remanent magnetisation in single grains of ilmeno hematite calculated using mossbauer spectroscopy rocks from large remanent magnetic anomalies on earth have been found to contain exsolved rhombohedral oxides which also have been proposed as earth analogues for the rocks creating the observed large remanent anomalies on mars theoretical considerations and previous case studies of natural rocks have shown that the natural magnetisation is carried by lamellar magnetism due to uncompensated moments at the interface between antiferromagnetic hematite and paramagnetic ilmenite here single grains 250 m of titanohematite with ferri ilmenite exsolution lamellae from mesoproterozoic metamorphic rock samples in southwest sweden and the adirondack mountains usa are studied using room temperature mossbauer spectroscopy to identify possible characteristic magnetic signatures of lamellar magnetism mossbauer spectra of synthetic samples of titanohematite fe0 95ti0 05o3 and fe0 9ti0 1o3 were collected for comparison and showed a dominant six line magnetic spectrum due to fe3 in titanohematite with a weak sextet due to fe2 fe3 charge transfer mossbauer spectra of the natural ilmeno hematite grains are similar to those for synthetic titanohematite but contain additionally two paramagnetic doublets corresponding to fe2 and fe3 in ilmenite however several grains also contain an additional weak broad magnetic component that we assign to iron in contact layers according to the lamellar magnetism model similar to the previous mossbauer results for natural hemo ilmenite there is no evidence for superparamagnetic behaviour of the nanoscale titanohematite lamellae contained within coarser ferri ilmenite lamellae and no evidence for single domain or superparamagnetic magnetite the compositions of titanohematite and ferri ilmenite in the individual ilmeno hematite grains calculated from the mossbauer area ratios show that compositions are closer to end member values than the compositions inferred from electron microprobe and transmission electron microscopy on the same grains consistent with observations that lamella thicknesses are as small as a few nm bulk compositions of ilmeno hematite grains calculated from the mossbauer data confirm that the swedish samples are significantly more ilmenite rich than the adirondack samples and agree with an estimation of bulk composition through point counting of electron backscatter images the mossbauer data allow a quantitative estimation of contact layer abundance which is used to determine the efficiency of lamellar natural remanent magnetisation acquisition because minerals with a high natural remanent magnetisation efficiency are expected to create larger remanent magnetic anomalies contact layer abundance determination by mossbauer spectroscopy provides a valuable new tool for mineral based magnetic anomaly interpretation on earth and other planetary bodies

thermodynamic analysis of ocean circulation abstract calculating a streamfunction as function of depth and density is proposed as a new way of analyzing the thermodynamic character of the overturning circulation in the global ocean the sign of an overturning cell in this streamfunction directly shows whether it is driven mechanically by large scale wind stress or thermally by heat conduction and small scale mixing it is also shown that the integral of this streamfunction gives the thermodynamic work performed by the fluid the analysis is also valid for the boussinesq equations although formally there is no thermodynamic work in an incompressible fluid the proposed method is applied both to an idealized coarse resolution three dimensional numerical ocean model and to the realistic high resolution ocean circulation and climate advanced model occam it is shown that the overturning circulation in occam between the 200 and 1000 m depth is dominated by a thermally indirect cell of 24 sverdrups 1 sv 106 m3 s 1 forced by ekman pumping in th

the passive and active nature of ocean heat uptake in idealized climate change experiments the influence of ocean circulation changes on heat uptake is explored using a simply configured primitive equation ocean model resembling a very idealized atlantic ocean we focus on the relative importance of the redistribution of the existing heat reservoir due to changes in the circulation and the contribution from anomalous surface heat flux in experiments in which the surface boundary conditions are changed we perform and analyze numerical experiments over a wide range of parameters including experiments that simulate global warming and others that explore the robustness of our results to more general changes in surface boundary conditions we find that over a wide range of values of diapycnal diffusivity and southern ocean winds and with a variety of changes in surface boundary conditions the spatial patterns of ocean temperature anomaly are nearly always determined as much or more by the existing heat reservoir redistribution than by the nearly passive uptake of temperature due to changes in the surface boundary conditions calculating heat uptake by neglecting the existing reservoir redistribution which is similar to treating temperature as a passive tracer leads to significant quantitative errors notably at high latitudes and secondarily in parts of the main thermocline experiments with larger circulation changes tend to produce a relatively larger magnitude of existing reservoir redistribution and a faster growing effective heat capacity of the system the effective heat capacity is found to be sensitive to both vertical diffusivity and southern ocean wind

characterization of hydraulic properties of rocks using probability of fluid induced microearthquakes the use of borehole fluid injections is typical for exploration and development of hydrocarbon or geothermal reservoirs such injections often induce small magnitude earthquakes the nature of processes leading to triggering of such microseismicity is still not completely understood here we consider induced microseismicity using as examples two case studies of geothermal reservoirs in crystalline rocks and one case study of a tight gas sandstone reservoir in all three cases we found that the probability of induced earthquakes occurring is very well described by the relaxation law of pressure perturbation in fluids filling the pore space in rocks this strongly supports the hypothesis of seismicity triggered by pore pressure moreover this opens additional possibilities of using passive seismic monitoring to characterize hydraulic properties of rocks on the reservoir scale with high precision

lamellar magnetism and exchange bias in billion year old titanohematite with nanoscale ilmenite exsolution lamellae i mineral and magnetic characterization

the role of vertical eddy flux in southern ocean heat uptake 1 the role of changing vertical eddy heat flux on southern ocean heat uptake is investigated in an idealized eddy permitting ocean model enhanced air sea heat flux drives deep reaching southern warming due to a reduction in the isopycnal meridional temperature gradient and therefore decreased upward eddy heat flux this mechanism is qualitatively similar in models with either permitted or parameterized eddies due to its dependence on the isopycnal temperature gradient rather than the dynamical response of the eddy field in contrast increased wind stress drives mid depth southern ocean cooling through an enhancement of the eddy field and resultant eddy heat divergence the transient cooling extends over multiple decades while the mean flow adjusts to balance the faster eddy response this wind driven cooling mechanism has not been captured by coarse resolution models with fixed eddy parameterizations and is a possible candidate for the recent cooling observed in the southern ocean

vertical heat transport by ocean circulation and the role of mechanical and haline forcing abstractvertical transport of heat by ocean circulation is investigated using a coupled climate model and novel thermodynamic methods using a streamfunction in temperature depth coordinates cells are identified by whether they are thermally direct flux heat upward or indirect flux heat downward these cells are then projected into geographical and other thermodynamic coordinates three cells are identified in the model a thermally direct cell coincident with antarctic bottom water a thermally indirect deep cell coincident with the upper limb of the meridional overturning circulation and a thermally direct shallow cell coincident with the subtropical gyres at the surface the mechanisms maintaining the thermally indirect deep cell are investigated sinking water within the deep cell is more saline than that which upwells because of the coupling between the upper limb and the subtropical gyres in a broader thermohaline circulation despite the higher salinity of its sinking water the deep cell tr

heterogeneous fault stresses from previous earthquakes and the effect on dynamics of parallel strike slip faults 1 we combine a viscoelastic model for the interseismic process and an elastodynamic model for the coseismic process to explore the dynamics over multiple earthquake cycles of two parallel strike slip faults embedded in a two dimensional full space the step over fault geometry results in a buildup of heterogeneous fault stress near the step over this heterogeneous stress accumulates at the early stage of the evolution of the fault system and finally stabilizes after a number of earthquake cycles the heterogeneity in fault stress varies with the geometrical parameters e g width and along strike overlap gap of the step over as well as the rupture history of the fault system this heterogeneous fault stress from previous earthquakes has significant effects on earthquake rupture initiation propagation and termination the locations with a low normal stress level near a step over are favorable points for earthquake initiation rupture can jump a 4 km wide compressional step over and a 8 km or wider dilational step over if the fault system has historically experienced many earthquakes a young step over with less induced heterogeneity allows rupture to jump only smaller step over widths these results may have important implications for seismic hazard analysis in areas where segmented strikeslip faults predominate particularly for estimating maximum earthquake potential citation duan b and d d oglesby 2006 heterogeneous fault stresses from previous earthquakes and the effect on dynamics of parallel strike slip faults j geophys res 111 b05309 doi 10 1029 2005jb004138

control of lower limb overturning circulation in the southern ocean by diapycnal mixing and mesoscale eddy transfer a simple model is developed of the lower limb of the meridional overturning circulation in the southern ocean based on residual mean theory it is hypothesized that the strength of the lower limb overturning is strongly controlled by the magnitude of abyssal diapycnal mixing and that of mesoscale eddy transfer k in particular it is argued that k the scaling and associated theory find support in a suite of sensitivity experiments with an idealized ocean general circulation model this study shows that intense diapycnal mixing is required to close the buoyancy budget of the lower limb overturning circulation in contrast to the upper limb where air sea buoyancy fluxes can provide the required diabatic forcing

induced seismicity associated with fluid injection into a deep well in youngstown ohio 1 over 109 small earthquakes mw 0 4 3 9 were detected during january 2011 to february 2012 in the youngstown ohio area where there were no known earthquakes in the past these shocks were close to a deep fluid injection well the 14 month seismicity included six felt earthquakes and culminated with a mw 3 9 shock on 31 december 2011 among the 109 shocks 12 events greater than mw 1 8 were detected by regional network and accurately relocated whereas 97 small earthquakes 0 4 mw 1 8 were detected by the waveform correlation detector accurately located earthquakes were along a subsurface fault trending ene wsw consistent with the focal mechanism of the main shock and occurred at depths 3 5 4 0 km in the precambrian basement we conclude that the recent earthquakes in youngstown ohio were induced by the fluid injection at a deep injection well due to increased pore pressure along the preexisting subsurface faults located close to the wellbore we found that the seismicity initiated at the eastern end of the subsurface fault close to the injection point and migrated toward the west away from the wellbore indicating that the expanding high fluid pressure front increased the pore pressure along its path and progressively triggered the earthquakes we observe that several periods of quiescence of seismicity follow the minima in injection volumes and pressure which may indicate that the earthquakes were directly caused by the pressure buildup and stopped when pressure dropped

the energetics of southern ocean upwelling abstractthe ocean s meridional overturning circulation is closed by the upwelling of dense carbon rich waters to the surface of the southern ocean it has been proposed that upwelling in this region is driven by strong westerly winds implying that the intensification of southern ocean winds in recent decades may have enhanced the rate of upwelling potentially affecting the global overturning circulation however there is no consensus on the sensitivity of upwelling to winds or on the nature of the connection between southern ocean processes and the global overturning circulation in this study the sensitivity of the overturning circulation to changes in southern ocean westerly wind stress is investigated using an eddy permitting ocean sea ice model in addition to a suite of standard circulation metrics an energy analysis is used to aid dynamical interpretation of the model response increased southern ocean wind stress enhances the upper cell of the overturning circulation through creation of avail

oceanic isopycnal mixing by coordinate rotation abstract current numerical models of oceanic circulation differentiate between the eddy diffusion and viscosity transport along the geopotential horizontal and vertical directions only in order to model the effect of anisotropic turbulence as diffusive transport along and across density surfaces the isopycnal mixing tensor has been transformed from a diagonal second rank tensor in the isopycnal coordinate system to a tensor containing off diagonal elements in the geopotential coordinate system

vertical heat flux in the ocean estimates from observations and from a coupled general circulation model the net heat uptake by the ocean in a changing climate involves small imbalances between the advective and diffusive processes that transport heat vertically generally it is necessary to rely on global climate models to study these processes in detail in the present study it is shown that a key component of the vertical heat flux namely that associated with the large scale mean vertical circulation can be diagnosed over extra tropical regions from global observational data sets this component is estimated based on the vertical velocity obtained from the geostrophic vorticity balance combined with estimates of absolute geostrophic flow results are compared with the output of a non eddy resolving coupled atmosphere ocean general circulation model reasonable agreement is found in the latitudinal distribution of the vertical heat flux as well as in the area integrated flux below about 250 m depth the correspondence with the coupled model deteriorates sharply at depths shallower than 250 m due to the omission of equatorial regions from the calculation the vertical heat flux due to the mean circulation is found to be dominated globally by the downward contribution from the southern hemisphere in particular the southern ocean this is driven by the ekman vertical velocity which induces an upward transport of seawater that is cold relative to the horizontal average at a given depth the results indicate that the dominant characteristics of the vertical transport of heat due to the mean circulation can be inferred from simple linear vorticity dynamics over much of the ocean

the dallas fort worth earthquake sequence october 2008 through may 2009 this paper describes a sequence of small earthquakes m b 3 3 that occurred at the dallas fort worth airport texas between 30 october 2008 and 31 may 2009 analysis of records at regional station wmok identified more than 180 earthquakes in the sequence about 90 percent occurred in four clusters on 30 october 1 november 20 november 26 december and 15 17 may after the sequence began a six station temporary local network obtained high quality three component records for 11 earthquakes occurring between 20 november and 1 december analysis of these data demonstrated that all 11 earthquakes originated from a focus near 32 855 n 97 051 w with an estimated depth 4 4 km this location is less than 0 5 km from a well completed in august 2008 that extends to a depth of 4 2 km drilled to dispose of brines collected during flowback of hydraulic fracturing fluids associated with the production of natural gas brine disposal commenced at the well on 12 september 2008 seismograms and s p intervals for the earthquakes are similar though not identical and relative locations indicate they occurred along a north northeast south southwest trend with horizontal and vertical dimensions of 1 1 km and 0 2 km respectively this trend is approximately coincident with that of a mapped normal fault in the subsurface and consistent with the maximum horizontal in situ stress direction because of the absence of previous historical earthquakes the proximity of the brine disposal well and the similarity with other documented cases of induced seismicity it seems likely that fluid injection induced the 2008 2009 sequence

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

injection induced seismicity poroelastic and earthquake nucleation effects the standard model of injection induced seismicity considers changes in coulomb strength due solely to changes in pore pressure we consider two additional effects full poroelastic coupling of stress and pore pressure and time dependent earthquake nucleation we model stress and pore pressure due to specified injection rate in a homogeneous poroelastic medium stress and pore pressure are used to compute seismicity rate through the dieterich 1994 model for constant injection rate the time to reach a critical seismicity rate scales with t r2 cfc where r is distance from the injector c is hydraulic diffusivity and fc is a factor that depends on mechanical properties and weakly on r the seismicity rate decays following a peak consistent with some observations during injection poroelastic coupling may increase or decrease the seismicity rate depending on the orientation of the faults relative to the injector if injection induced stresses inhibit slip abrupt shut in can lead to locally sharp increases in seismicity rate tapering the flux mitigates this effect the maximum magnitude event has been observed to occur postinjection we suggest the seismicity rate at a given magnitude depends on the nucleation rate the size distribution of fault segments and if the background shear stress is low the time varying volume of perturbed crust this leads to a rollover in frequency magnitude distribution for larger events with a corner that increases with time larger events are absent at short times but approach the background frequency with time larger events occurring post shut in are thus not unexpected

impact of mesoscale eddy transfer on heat uptake in an eddy parameterizing ocean model abstractusing a set of experiments with an eddy parameterizing ocean model it is found that the strength of the atlantic meridional overturning circulation amoc intensifies with the decrease of

exchange bias identifies lamellar magnetism as the origin of the natural remanent magnetization in titanohematite with ilmenite exsolution from modum norway abstract large and stable negative magnetic anomalies in southwestern sweden southern norway the adirondacks usa and quebec canada are related to rock units with a magnetic fraction consisting primarily of ilmeno hematite or hemo ilmenite it has been suggested that the unusual magnetic stability of these rocks results from lamellar magnetism this is a type of magnetic remanence carried by uncompensated magnetic layers at interfaces between nanoscale exsolution structures of antiferromagnetic afm hematite and paramagnetic ilmenite here we present the first direct proof that this lamellar magnetism indeed is responsible for the natural remanent magnetization nrm of a rock from modum norway our argument expands a previous observation that in mineral grains from this rock the cooling of a positive induced remanence from room temperature to 5 k which is well below the ordering temperature of ilmenite 57 k leads to a large negative shift of the low temperature lt hysteresis loop this can only be explained by exchange bias due to exchange coupling across the hematite ilmenite interfaces in a different experiment we now have cooled the original nrm of untreated grains to 5 k and then measured the hysteresis loop again in several separate grains we observed large shifts of the hysteresis curves this shows that exchange bias develops also from the untreated nrm this observation proves that the moments which carry the nrm also participate in the exchange coupling at the hematite ilmenite interfaces therefore the nrm is not carried by defect moments or stress induced moments which occur in normal bulk hematite a closer look at the nrm induced lt loops shows that exchange bias acts in both field directions though one direction is clearly predominant this observation can be interpreted as a frozen equilibrium of different proportions of oppositely directed lamellar moments a key feature of the original lamellar magnetism hypothesis we discuss lamellar aggregation and the formation of exchange coupled clusters to explain the observed high efficiency of lamellar nrm we also conclude that remanence carried by lamellar moments should not be used for paleointensity estimates of terrestrial or extraterrestrial material

a conceptual model of ocean heat uptake under climate change abstracta conceptual model of ocean heat uptake is developed as a multilayer generalization of gnanadesikan the roles of southern ocean ekman and eddy transports north atlantic deep water nadw formation and diapycnal mixing in controlling ocean stratification and transient heat uptake are investigated under climate change scenarios including imposed surface warming increased southern ocean wind forcing with or without eddy compensation and weakened meridional overturning circulation moc induced by reduced nadw formation with realistic profiles of diapycnal mixing ocean heat uptake is dominated by southern ocean ekman transport and its long term adjustment controlled by the southern ocean eddy transport the time scale of adjustment setting the rate of ocean heat uptake increases with depth for scenarios with increased southern ocean wind forcing or weakened moc deepened stratification results in enhanced ocean heat uptake in each of these experiments the role of diapycnal mixing in settin

lamellar magnetism and exchange bias in billion year old metamorphic titanohematite with nanoscale ilmenite exsolution lamellae ii exchange bias at 5 k after field free cooling of nrm and after cooling in a 5 t field

vertical heat transport in eddying ocean models 1 the effect of mesoscale eddies on the vertical heat transport of the ocean is examined using two eddy resolving numerical models the global heat transport by the mean flow and diffusion are both downwards and are balanced by an upward eddy heat flux mean and eddy advective heat fluxes dominate the subpolar regions while diffusive flux is important primarily in the subtropics in the subtropical abyss the mean advective heat flux is balanced by a combination of eddy and diffusive fluxes and the classical munk type advective diffusive heat balance must be modified the munk and wunsch 1998 expression for the vertical turbulent diffusivity over estimates the diffusivity by as much as a factor of four near the base of the main thermocline this implies that the mixing required to close the meridional overturning circulation determined by munk and wunsch 1998 may be an over estimate due to the neglect of mesoscale eddies

bottom enhanced diapycnal mixing driven by mesoscale eddies sensitivity to wind energy supply abstractit has been estimated that much of the wind energy input to the ocean general circulation is removed by mesoscale eddies via baroclinic instability while the fate of this energy remains a subject of research arguments have been presented suggesting that a fraction of it may get transferred to lee waves that upon breaking result in bottom enhanced diapycnal mixing here the authors propose several parameterizations of this process and explore their impact in a low resolution ocean climate model focusing on their impact on the abyssal meridional overturning circulation moc of antarctic bottom water this study shows that when the eddy energy is allowed to maintain diapycnal mixing the abyssal moc generally intensifies with increasing wind energy input to the ocean in such a case the whole system is driven by the wind wind steepens isopycnals and generates eddies and the parameterized eddies generate small scale mixing driving the moc it is also demonstrated that if the model diapycn

a process based analysis of ocean heat uptake in an aogcm with an eddy permitting ocean component about 90 of the anthropogenic increase in heat stored in the climate system is found in the oceans therefore it is relevant to understand the details of ocean heat uptake here we present a detailed process based analysis of ocean heat uptake ohu processes in higem1 2 an atmosphere ocean general circulation model with an eddy permitting ocean component of 1 3 resolution similarly to various other models higem1 2 shows that the global heat budget is dominated by a downward advection of heat compensated by upward isopycnal diffusion only in the upper tropical ocean do we find the classical balance between downward diapycnal diffusion and upward advection of heat the upward isopycnal diffusion of heat is located mostly in the southern ocean which thus dominates the global heat budget we compare the responses to a 4xco2 forcing and an enhancement of the windstress forcing in the southern ocean this highlights the importance of regional processes for the global ocean heat uptake these are mainly surface fluxes and convection in the high latitudes and advection in the southern ocean mid latitudes changes in diffusion are less important in line with the cmip5 models higem1 2 shows a band of strong ohu in the mid latitude southern ocean in the 4xco2 run which is mostly advective by contrast in the high latitude southern ocean regions it is the suppression of convection that leads to ohu in the enhanced windstress run convection is strengthened at high southern latitudes leading to heat loss while the magnitude of the ohu in the southern mid latitudes is very similar to the 4xco2 results remarkably there is only very small global ohu in the enhanced windstress run the wind stress forcing just leads to a redistribution of heat we relate the ocean changes at high southern latitudes to the effect of climate change on the antarctic circumpolar current acc it weakens in the 4xco2 run and strengthens in the wind stress run the weakening is due to a narrowing of the acc caused by an expansion of the weddell gyre and a flattening of the isopycnals which are explained by a combination of the wind stress forcing and increased precipitation

magnetization of exsolution intergrowths of hematite and ilmenite mineral chemistry phase relations and magnetic properties of hemo ilmenite ores with micron to nanometer scale lamellae from allard lake quebec hemo ilmenite ores from allard lake quebec were first studied over 50 years ago interest was renewed in these coarsely exsolved oxides based on the theory of lamellar magnetism as an explanation for the high and stable natural remanent magnetizations nrms 32 to 120 a m reported here to understand the magnetism and evolution of the exsolution lamellae the microstructures and nanostructures were studied using scanning electron microscopy and transmission electron microscopy tem phase chemistry and relations between mineral chemistry and the hematite ilmenite phase diagram cycles of exsolution during slow cooling resulted in lamellae down to 1 2 nm thick combined electron microprobe tem and x ray diffraction xrd results indicate that hematite hosts reached a composition approximately ilmenite ilm 14 4 and ilmenite hosts ilm 98 the bulk of the very stable nrm which shows thermal unblocking 595 620 c was acquired during final exsolution in the two phase region canted antiferromagnetic r3c hematite r3 ilmenite hysteresis measurements show a very strong anisotropy with a stronger coercivity normal to than parallel to the basal plane orientation of the lamellae magnetic saturation m s values are up to 914 a m compared to 564 a m predicted for a modally equivalent spin canted hematite corrected for 15 r 2 tio 3 substitution low temperature hysteresis ac susceptibility measurements and mossbauer results indicate a neel temperature t n of the geikielite substituted ilmenite at 43 k the low temperature hysteresis and ac susceptibility measurements also show a cluster spin glass like transition near 20 k below t n of ilmenite an exchange bias occurs with a 40 mt shift at 10 k

nature and origin of lamellar magnetism in the hematite ilmenite series grains consisting of finely exsolved members of the hematite ilmenite solid solution series such as are present in some slowly cooled middle proterozoic igneous and metamorphic rocks impart unusually strong and stable remanent magnetization tem analysis shows multiple generations of ilmenite and hematite exsolution lamellae with lamellar widths ranging from millimeters to nanometers rock magnetic experiments suggest remanence is thermally locked to the antiferromagnetism of the hematite component of the intergrowths yet is stronger than can be explained by canted antiferromagnetic caf hematite or coexisting paramagnetic pm fe ti ordered r 3 ilmenite alone in alternating field demagnetization to 100 mt many samples lose little remanence indicating that the nrm is stable over billions of years this feature has implications for understanding magnetism of deep rocks on earth or on planets like mars that no longer have a magnetic field atomic scale simulations of an r 3 ilmenite lamella in a caf hematite host based on empirical cation cation and spin spin pair interaction parameters show that contacts of the lamella are occupied by contact layers with a hybrid composition of fe ions intermediate between fe2 rich layers in ilmenite and fe3 rich layers in hematite structural configurations dictate that each lamella has two contact layers magnetically in phase with each other and out of phase with the magnetic moment of an odd non self canceling fe3 rich layer in the hematite host the two contact layers and the odd hematite layer form a magnetic substructure with opposite but unequal magnetic moments a lamellar ferrimagnetism made possible by the exsolution because it is confined to magnetic interaction involving the moments of just three ionic layers associated with each individual exsolution lamella lamellar magnetism is unique and quite distinct from conventional ferrimagnetism simulation cells indicate that the magnetic moments of contact layers are locked to the magnetic moments of adjacent af hematite layers and are parallel to the basal plane 001 thus lamellar magnetism is created at the temperature of chemical exsolution and is a chemical remanent rather than thermal remanent magnetization however in thermal demagnetization experiments too short for lamellar resorption demagnetization temperatures are those of the caf hematite considerably higher than temperatures of original lamellae formation internal crystal structure cannot dictate that the contact layers of different lamellae will form magnetically in phase with each other to give the highest net magnetic moment but magnetic moments of lamellae can be made to form in phase by the external force of the magnetizing field at the time of exsolution a thesis of this paper is that an external magnetic field can dictate the magnetic moments and hence the chemical location of ilmenite lamellae in a hematite host and that once in place neither the location nor the magnetic moment will be easily disturbed in an ilmenite host the external magnetic field cannot control the chemical location of a hematite lamella which is dictated by the enclosing ilmenite but once lamellae have formed the field can dictate their magnetic moments these moments however are not locked chemically to the host resulting in lower coercivity the effectiveness of the external force in single crystals is dictated by their orientation with respect to the magnetizing field in grains with 001 oriented parallel to the field it would be effective in producing in phase magnetic moments and very strong remanence in grains with 001 normal to the field the field would be less effective in producing in phase magnetic moments hence producing weak remanence the most intense lamellar magnetism per formula unit occurs with in phase magnetization high lamellar yields and the largest number of lamellae per unit volume i e smallest lamellar size compared to the magnetic moment per formula unit m pfu and magnetic moment per unit volume m v of end member magnetite m pfu 4 b m v 480 ka m and hematite m pfu 0 0115 b m v 2 1 ka m results for some atomic models reasonably tied to natural conditions are m pfu 0 46 1 36 b and m v 84 250 ka m

stress and aftershock constrained joint inversions for coseismic and postseismic slip applied to the 2004 m6 0 parkfield earthquake 1 both aftershocks and geodetically measured postseismic displacements are important markers of the stress relaxation process following large earthquakes postseismic displacements can be related to creep like relaxation in the vicinity of the coseismic rupture by means of inversion methods however the results of slip inversions are typically non unique and subject to large uncertainties therefore we explore the possibility to improve inversions by mechanical constraints in particular we take into account the physical understanding that postseismic deformation is stress driven and occurs in the coseismically stressed zone we do joint inversions for coseismic and postseismic slip in a bayesian framework in the case of the 2004 m6 0 parkfield earthquake we perform a number of inversions with different constraints and calculate their statistical significance according to information criteria the best result is preferably related to a physically reasonable model constrained by the stress condition namely postseismic creep is driven by coseismic stress and the condition that coseismic slip and large aftershocks are disjunct this model explains 97 of the coseismic displacements and 91 of the postseismic displacements during day 1 5 following the parkfield event respectively it indicates that the major postseismic deformation can be generally explained by a stress relaxation process for the parkfield case this result also indicates that the data to constrain the coseismic slip model could be enriched postseismically for the 2004 parkfield event we additionally observe asymmetric relaxation process at the two sides of the fault which can be explained by material contrast ratio across the fault of 1 15 in seismic velocity

three dimensional boundary integral modeling of spontaneous earthquake sequences and aseismic slip 1 fault processes involve complex patterns of seismic events and aseismic slip this work develops a three dimensional 3 d methodology for simulating long term history of spontaneous seismic and aseismic slip on a vertical planar strike slip fault subjected to slow tectonic loading our approach reproduces all stages of earthquake cycles from accelerating slip before dynamic instability to rapid dynamic propagation of earthquake rupture to postseismic slip and to interseismic creep including aseismic transients we use the developed 3 d methodology to study interaction of fault slip with a small patch of higher normal stress over long term slip history for uniform initial prestress dynamic rupture is significantly affected by the stronger patch in the first simulated event but not in subsequent ones the change in behavior is due to redistribution of shear stress by prior slip which demonstrates that distributions of fault strength and stress are related and illustrates the importance of simulating long slip histories even in studies of dynamic rupture despite no long term effect on dynamic rupture the small patch of higher normal stress influences nucleation processes and hence long term slip patterns in the model comparison of the fully dynamic simulations and a widely used quasi dynamic approach shows that the quasi dynamic approach modifies long term slip patterns in addition to resulting in much smaller slip velocities and rupture speeds during dynamic events we show that the response of quasi dynamic formulations with reduced radiation damping terms can be scaled to match the results of the standard quasi dynamic formulation and hence cannot improve the comparison