the evolution of regional seismicity between large earthquakes 1 we describe a simple model that links static stress coulomb modeling to the regional seismicity around a major fault unlike conventional coulomb stress techniques which calculate stress changes we model the evolution of the stress field relative to the failure stress background seismicity is attributed to inhomogeneities in the stress field which are created by adding a random field that creates local regions above the failure stress the inhomogeneous field is chosen such that when these patches fail the resulting earthquake size distribution follows a gutenburg richter law immediately following a large event the model produces regions of increased seismicity aftershocks where the overall stress field has been elevated and regions of reduced seismicity where the stress field has been reduced stress shadows the high stress levels in the aftershock regions decrease due to loading following the main event combined with the stress shadow from the main event this results in a broad seismically quiet region of lowered stress around the epicenter pre event seismicity appears as the original stress shadows finally fill as a result of loading the increase in seismicity initially occurs several fault lengths away from the main fault and moves inward as the event approaches as a result of this effect the seismic moment release in the region around the future epicenter increases as the event approaches synthetic catalogues generated by this model are virtually indistinguishable from real earthquake sequences in california and washington

mantle flow drives the subsidence of oceanic plates the subsidence of the sea floor is generally considered a consequence of its passive cooling and densifying since its formation at the ridge and is therefore regarded as a function of lithospheric age only however the lithosphere is defined as the thermal boundary layer of mantle convection which should thus determine its structure we examined the evolution of the lithosphere structure and depth along trajectories representative of the underlying mantle flow we show that along these flow lines the sea floor depth varies as the square root of the distance from the ridge as given by the boundary layer equation along the entire plate without any flattening contrary to previous models no additional heat supply is required at the base of the lithosphere

the age and origin of the central scotia sea summary opening of the drake passage gateway between the pacific and atlantic oceans has been linked in various ways to cenozoic climate changes from the oceanic floor of drake passage the largest of the remaining uncertainties in understanding this opening is in the timing and process of the opening of the central scotia sea all but one of the available constraints on the age of the central scotia sea is diagnostic of or consistent with a mesozoic age comparison of tectonic and magnetic features on the seafloor with plate kinematic models shows that it is likely to have accreted to a mid ocean ridge between the south american and antarctic plates following their separation in jurassic times subsequent regional shallowing may be related to subduction related processes that preceded backarc extension in the east scotia sea the presence of a fragment of jurassic cretaceous ocean floor in the gateway implies that deep water connections through the scotia sea basin complex may have been possible since eocene times when the continental tips of south america and the antarctic peninsula first passed each other

how do asperities fracture an experimental study of unbroken asperities abstract the fracture of a shear fault containing several unbroken asperities in a granitic porphyry is examined in detail via acoustic emission ae data collected by a high speed multi channel waveform recording system the experimental results reveal that a quasi static nucleation of the shear faulting corresponds to the fracture of coupled asperities on the fault plan aes caused by the fracture of individual asperities exhibit similar characteristics to the sequence for natural earthquakes including foreshock mainshock and aftershock events foreshocks initiated at the edge of the asperity occur with an event rate that increases according to a power law of the temporal distance to the mainshock and with a decreasing b value from 1 1 to 0 5 one or a few mainshocks then initiate at the edge of the asperity or the front of the foreshocks the aftershock period is characterized by a remarkable increase and subsequent gradual decrease in b value and a decreasing event rate obeying the modified omori law which has been well established for earthquakes the fracture of neighboring asperities is then initiated after the mainshock of a particular asperity presumably due to redistribution of the strain energy accumulated within an asperity which is released by the mainshock resulting in enhancement of the stress concentration around the nearest neighboring intact asperities the progressive fracturing of multiple coupled asperities during the nucleation of shear faulting results in short term precursory fluctuations in both b value and event rate which may prove useful information in the prediction of failure of the main fault plane of seismic earthquakes

50 ma initiation of hawaiian emperor bend records major change in pacific plate motion the hawaiian emperor bend has played a prominent yet controversial role in deciphering past pacific plate motions and the tempo of plate motion change new ages for volcanoes of the central and southern emperor chain define large changes in volcanic migration rate with little associated change in the chain s trend which suggests that the bend did not form by slowing of the hawaiian hot spot initiation of the bend near kimmei seamount about 50 million years ago ma was coincident with realignment of pacific spreading centers and early magmatism in western pacific arcs consistent with formation of the bend by changed pacific plate motion

spatial and temporal variations of subsidence of the east pacific rise 0 23 s abstract the distributions of crustal depths as a function of age have been analysed for the southeast pacific region along the east pacific rise between the equator and the easter microplate 23 s using age data and a new compilation of bathymetric data subsidence rates for both eastern and western flanks asymmetry of subsidence and zero age depths are computed within flow line corridors on the nazca and pacific plates variations of subsidence rates axial depths and subsidence asymmetry are examined both in space within corridors and time within several age intervals the variability in these parameters along the strike of the east pacific rise is systematic and serves to define several orders of ridge segmentation the largest variations of these parameters are correlated with the large scale segmentation of the ridge axis i e transform faults and very large overlapping spreading centres and are interpreted as related to variations in mantle heterogeneities mainly dependent upon temperature smaller variations of subsidence parameters are correlated with second and sometimes third order segmentation of the ridge axis which could be related to variations in axial magmatic supply across strike variations of subsidence suggest the existence of small lateral temperature and density variations in the mantle when analysing the slope of the distribution of depth versus square root of age within corridors we have observed the existence of changes in the slope which occur at specific age limits we have estimated the subsidence over different age ranges in order to determine the temporal evolution of subsidence parameters rates and asymmetry such an analysis may inform on the past axial segmentation and on the persistence of axial discontinuities in time a linear relationship between subsidence rates and axial depths is determined for each age range and suggests that shallower segments subside faster than deeper segments although a similar statistically defined linear relationship exists for any mid ocean spreading ridge both for intermediate or fast ultrafast spreading the resultant slopes of this relationship vary from ocean to ocean and show that this relationship is not universal over all oceans

the pacific lithosphere asthenosphere boundary seismic imaging and anisotropic constraints from ss waveforms 1 the lithosphere asthenosphere boundary lab separating the rigid lid from the underlying weaker convecting asthenosphere is a fundamental interface in mantle dynamics and plate tectonics however the exact depth and defining mechanism of the lab interface remain poorly understood the ocean plates are ideal for testing hypotheses regarding the nature of a plate since they make up 70 of earth s surface area and have a relatively simple geological history seismically imaging the oceanic lab at high resolution has proved challenging yet several studies have recently increased resolution with provocative results we summarize recent imaging of discontinuity structure beneath much of the pacific using receiver functions from ocean floor borehole seismometers and land stations located at ocean continent margins ss precursors and waveform modeling of multiple phases including multiple bounce s waves scs reverberations and surface waves overall there is much agreement among these different approaches about the reported depth of a negative discontinuity that occurs near the expected depth of the lab some of the apparent discrepancies in depth are explained by the variation in sensitivity of seismic waves that sample structure at different wavelengths yet when the results are considered together no single age depth relationship is illuminated there are also puzzling discrepancies in where the discontinuity is detected which again suggests greater complexity here we test the possibility that discrepant detection of a strong sharp discontinuity is caused by anisotropic structure we stack ss waveforms with bounce points in the central pacific into azimuthal bins we use two methods one that inverts for discontinuity structure based on subtle variations in the character of the ss waveform and another that considers ss at higher frequency we find azimuthal variation in the amplitude of the waveform including a polarity reversal we suggest that anisotropy is an important factor in imaging and constraining discontinuity structure of the oceanic plate and must be carefully considered to constrain the age depth dependence and defining mechanism of the oceanic lithosphere

the relationship between depth age and gravity in the oceans we reassess the applicability of the thermal plate cooling model to the subsidence of the north pacific atlantic and north indian ocean basins we use a new numerical plate model in which the thermophysical parameters of the lithosphere vary with temperature according to the results of laboratory experiments and the ridge temperature structure is consistent with the thickness of the oceanic crust we first attempt to exclude thickened crust from our data set and then to exclude swells and downwellings by masking regions of the data that remains that have significant gravity anomalies when there exists a clear regional correlation between intermediate wavelength gravity and topography we find that the average variation of depth with age is consistent with conventional half space models until about 90 myr thereafter the departure from the half space cooling curve is more rapid than predicted using simple conductive plate cooling models the depth age curves in the pacific and atlantic show 250 m of temporary shallowing between the ages of 90 130 myr a result consistent with the outcome of experiments on the initiation of small scale boundary layer convection the results do not change significantly if the estimated component of the gravity arising from plate cooling is subtracted prior to calculation of the correlation between gravity and topography a 90 km thick conductive plate is nevertheless a reasonable model for the average temperature structure of the oldest part of the pacific ocean lithosphere in the pacific the broad topographic undulations associated with the line island swell the hawaiian swell and surrounding basins have correlated gravity anomalies and an admittance of approximately 30 mgal km 1 and are likely to result from convective circulation in the upper mantle in the northeast atlantic the intermediate wavelength admittance over the cape verde swell is similar in the northwest atlantic over the bermuda swell it is slightly larger but not as well constrained

the empirical age depth relation and depth anomalies in the pacific ocean basin this paper presents a new age depth relation and a comprehensive depth anomaly map for the pacific ocean age depth and sediment thickness were averaged for each 1 1 area bathymetry was corrected for isostatic effects due to sediment and water load and for the variation of sound velocity in water seafloor existing at extreme distance from hot spot tracks is found to be anomalously deep hot spots were treated as thermal anomalies and data within 800 km of them were eliminated from further analysis an age depth equation was determined by fitting a least squares line to the remaining data the resulting depth versus age distribution confirms the linear dependence of depth on age up to 80 ma all older seafloor is within 800 km of hot spots or hot spot tracks and is shallower than predicted this flattening of the age depth distribution requires that a separate function be fit to data older than 80 ma as a result data representing the deepest seafloor older than 80 ma were selected for curve fitting and the age depth distribution was approximated by an exponential function it is impossible to distinguish between the infinite half space and cooling plate models of the lithopshere using the age depth data from the pacific ocean a depth anomaly map prepared by comparing observed depth with the depth predicted by the new age depth formula shows several newly recognized features including swells over the louisville ridge in the south pacific and in the gulf of alaska seamounts

the many surface expressions of mantle dynamics plate tectonic theory suggests that present day topography can be explained by the repeated interactions between the tectonic plates moving along earth s surface however mounting evidence indicates that a significant proportion of earth s topography results from the viscous stresses created by flow within the underlying mantle rather than by the moving plates this dynamic topography is transient varying as mantle flow changes and is characterized by small amplitudes and long wavelengths it is therefore often hidden by or confused with the more obvious topographic anomalies resulting from horizontal tectonic movements however dynamic topography can influence surface processes and thus enter the geological record it has for example played a role in the establishment of amazon drainage patterns in turn surface processes such as the erosion of topographical anomalies could affect mantle flow this emerging view of dynamic topography suggests that the concept of plate tectonics as the driver of surface deformation needs to be extended to include the vertical coupling between the mantle and the surface unravelling this coupling back in time with the help of models and the geological record can potentially provide unprecedented insights into past mantle dynamics

origins of hydrocarbon gas seeping out from offshore mud volcanoes in the nile delta abstract this paper discusses the origin of gas seepages free gas or dissolved gas in ground water or brine sampled with the nautile submarine during the nautinil cruise at the seafloor of the deep water area of the nile turbiditic system on different mud volcanoes and brine pools generally the gas is wet and includes c1 c2 c3 ic4 nc4 co 2 these gas samples show no evidence of biodegradation which is not the case of the gas present in the deep hydrocarbon accumulations at depth it indicates that the gas expelled by the mud volcanoes is not issued from direct leakages from deep gas fields the collected gas samples mainly have a thermogenic origin and show different maturities some samples show very high maturities indicating that these seepages are sourced from great depths below the messinian salt moreover the different chemical compositions of the gas samples reflect not only differences in maturity but also the fact that the gas finds its origin in different deep source rocks carbon dioxide has an organic signature and cannot result from carbonate decomposition or mantle fluids the crustal derived radiogenic isotopes show that the analyzed gas samples have suffered a fractionation processes after the production of the radiogenic isotopes due either to oil occurrence at depth interacting with the flux of gas and or fractionation during the fluid migration

regional viscosity variations small scale convection and slope of the depth age1 2 curve cooling plate and cooling half space models are commonly employed to describe the depth age1 2 curve of seafloor these conductive models are not able to reproduce the large range of subsidence rates that are observed with reasonable changes in the physical parameters we examine the influence of small scale convection in the mantle on subsidence rates with a one dimensional parameterized convection model the parameterization is based on a recent experimental study of thermal convection in a fluid with temperature dependent viscosity in our model convection in the asthenosphere begins at the ridge axis enhancing heat transfer out of the asthenosphere and increasing the subsidence rate above that for simple conductive cooling variations in deformation mechanism temperature and water content of the mantle cause changes in viscosity that affect the vigor of convection and may be responsible for large variations in subsidence rates average subsidence rates can range from 250 500 m ma1 2 when small scale convection is considered

subsidence of the seafloor in the atlantic and pacific oceans regional and large scale variations we present a deteiled survey of seafloor subsidence over the entire atlantic ocean and in the pacific ocean we examine the evolution of depth as age increases within narrow 200 km wide tectonic corridors elongate in the direction of spreading over the part of the young seafloor where the depth age12 relationship is valid we estimate the subsidence rate by a least squares adjustment in the three oceanic regions west atlantic east atlantic and pacific the subsidence rate shows regional 1000 2000 km and basin scale fluctuations of the order of 100 150 m m y 12 we also note that in some regions subsidence rate and axial depth are correlated with shallow ridges showing fast subsidence and deep ridges slow subsidence on the basis of published models we infer that regional variations in subsidence rate reflect temperature changes in the subaxial mantle of 100 c asymmetrical subsidence is observed in the atlantic especially in the south atlantic the age of departure from the depth age12 linear trend is highly variable with values larger than 100 m y reported in several instances but very low values 20 m y or less characterizing the central pacific flattening predicted by the plate model occurs in some areas in a number of cases however quite distinct behaviour is observed with a sudden depth increase where the depth age12 relationship breaks down and a slow rise of the seafloor at older ages our results suggest that the subsidence behaviour of the seafloor is much more complex than global plate or half space cooling models predict

comment on mantle flow drives the subsidence of oceanic plates adam and vidal reports 2 april 2010 p 83 reported sea floor depth increasing as the square root of distance from the ridge along mantle flow lines however their data actually support a depth age relationship and flattening at older ages we argue that no plausible physical mechanism supports their proposal that mantle flow drives subsidence

regional variations in subsidence rate of oceanic plates a global analysis a global analysis of the dependence of seafloor depth on crustal age has been performed for each large oceanic plate independently each plate has been divided into regions bounded by major tectonic features a total of 32 regions have been considered bathymetry corrected for sediment loading has been plotted as a function of crustal age for each region except for three regions western pacific between 10 s and 40 n north american plate between 24 n and 38 n and african plate between 10 n and 24 n where ocean floor older than 80 100 ma flattens with age in other regions depth increases linearly with age1 2 subsidence rate over each region has been computed by linear regression large variations up to a factor 2 are reported from one region to another asymmetrical subsidence is also observed in a number of areas however the largest asymmetries are less than the regional variations in subsidence rate occurring on individual plates regional variations in subsidence rate appear linearly related to regional variations in ridge crest topography shallow ridge subsiding quickly and deep ridge subsiding slowly hence seafloor depth subsides at a rate modulated by the value of the initial axial depth this observation suggests that regional variations in subsidence rate reflect the thermal regime of the mantle beneath mid ocean ridges rather than lateral temperature variations inside the asthenosphere involving small scale convection

seismicity patterns before the m 5 8 2002 palermo italy earthquake seismic quiescence and accelerating seismicity abstract seismic quiescence and accelerating seismic energy release are considered as possible spatio temporal patterns of the preparation process of the 6 september 2002 palermo italy earthquake m 5 8 the detailed properties of the quiescence are analyzed applying the rtl algorithm the rtl algorithm is based on the analysis of the rtl prognostic parameter which is designed in such a way that it has a negative value if in comparison with long term background there is a deficiency of events in the time space vicinity of the tested point the rtl parameter increases if activation of seismicity takes place the rtl algorithm identified that a seismic quiescence started from the beginning of november 2001 and reached its minimum at the end of may 2002 the palermo 2002 earthquake occurred 2 months after the rtl parameter restored its long term background level the application of a log periodic time to failure model gives a predicted in retrospect magnitude m 6 2 main shock on 5 may 2002

digital isochrons of the world s ocean floor we have created a digital age grid of the ocean floor with a grid node interval of 6 arc min using a self consistent set of global isochrons and associated plate reconstruction poles the age at each grid node was determined by linear interpolation between adjacent isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust were interpolated by estimating the ages of passive continental margin segments from geological data and published plate models we have constructed an age grid with error estimates for each grid cell as a function of 1 the error of ocean floor ages identified from magnetic anomalies along ship tracks and the age of the corresponding grid cells in our age grid 2 the distance of a given grid cell to the nearest magnetic anomaly identification and 3 the gradient of the age grid i e larger errors are associated with high age gradients at fracture zones or other age discontinuities future applications of this digital grid include studies of the thermal and elastic structure of the lithosphere the heat loss of the earth ridge push forces through time asymmetry of spreading and providing constraints for seismic tomography and mantle convection models

near axis subsidence rates hydrothermal circulation and thermal structure of mid ocean ridge crests we systematically investigated near axis subsidence on the ridge flanks of intermediate and fast spreading mid ocean ridges using bathymetric data from well surveyed portions of the southeast indian ridge spreading at 72 76 mm yr the northern east pacific rise 91 96 mm yr and the southern east pacific rise 144 mm yr in all three regions the mean subsidence rate of young 1 1 4 ma seafloor is less than 220 m m y 1 2 the distribution of individual estimates shows a distinct peak at 180 220 m m y 1 2 with few profiles having subsidence rates greater than 275 m m y 1 2 the observed subsidence rates are significantly lower than both the worldwide average 350 m m y 1 2 and subsidence rates observed for older lithosphere at the same ridge segments intense hydrothermal circulation at the ridge axis can result in low subsidence rates on the adjacent ridge flanks provided the vigorous flow is confined to the immediate vicinity 5 km of the axis according to our model the extremely vigorous hydrothermal circulation ceases off axis and conductive heat flow becomes a primary mechanism of vertical heat transport on the ridge flanks the very low geothermal gradient within the cooled portion of the uppermost lithosphere retards conductive cooling and the cooled area needs to be heated from below before a geothermal gradient can be established which permits significant heat to be conducted out of the lithosphere as a result subsidence in very young 0 1 1 ma lithosphere is suppressed a simple one dimensional thermal model with a nusselt number parameterization was used to estimate the effect of hydrothermal circulation an upper layer with a high nusselt number and the half space that it overlies are initially at a temperature of 1300 c and the surface is maintained at 0 c after 0 1 m y of cooling about 3 5 to 7 km from the spreading axis the nusselt number of the top layer is set to 1 so that normal conduction is simulated in the cooled layer we used an explicit finite difference method to solve for the temporal changes in temperature with depth this model produces subsidence rates in the range that we observe for nu in the range of 15 30 isotherms resulting from the modeling imply rapid lithospheric thickening very near the axis which is incompatible with most current models for the formation of the bathymetric axial high observed at fast spreading mid ocean ridges

lithospheric control on asthenospheric flow from the iceland plume 3 d density modeling of the jan mayen east greenland region ne atlantic

earthquakes induced by water injection at 3 km depth within the rongchang gas field chongqing china 1 unwanted water amounting more than 1 million m 3 has been injected intermittently at a pumping pressure of 2 1 2 9 mpa over hydrostatic at 2 6 2 9 km depth within the rongchang gas field western chongqing china since july 1988 the injections have induced more than 32 000 surface recorded earthquakes including 2 of m l 5 14 of m l 4 and more than 100 of m l 3 up until the end of 2006 we examined the epidemic type aftershock sequence etas model and the temporal evolution of several statistics of the earthquake sequence the random component in the etas model can be considered as an indicator of fluid driven activity while the rate of omori law type aftershocks indicates stress triggering of the preceding earthquakes we observed three distinct seismic activity phases that were coincident with different injection periods phase i corresponds to initial injections with low injection rate long time interval and shows a vast majority of omori type events and only 8 externally forced activity phase ii corresponds to a period of high injection rates and shows intense earthquake activity characterized by a high percentage 45 of fluid driven earthquakes phase iii demonstrates decreasing seismicity as a result of a lowering in the injection rate more than 70 of earthquakes occurred randomly over time indicating the dominance of external triggering the physical mechanism that induced the rongchang earthquake sequence was a change in coulomb s failure stress caused by pore pressure diffusion and transformed from seismic slip of preceding earthquakes a pressure increase of 2 1 2 9 mpa at the injection well is more than sufficient to induce failure within the local formations

indicators of critical point behavior prior to rock failure inferred from pre failure damage abstract to investigate possible indicators of critical point behavior prior to rock failure the statistical properties of pre failure damage were analyzed based on acoustic emission events ae recorded during the catastrophic fracture of typical rock samples under differential compression aes were monitored using a high speed 32 channel waveform recording system time dependent statistics including the energy release rate b value of the magnitude frequency distribution fractal dimension and spatial correlation length scl of the ae hypocenters were calculated for each data set each parameter is a function of the time to failure and thus can be treated as an indicator of the critical point it is clear that the pre failure damage evolution prior to catastrophic failures in several common rock types is generally characterized by 1 accelerated energy release 2 a decrease in fractal dimension and scl with a subsequent precursory increase and 3 a decrease in b value from 1 5 to 0 5 for hard rocks and from 1 1 to 0 8 for soft rocks such s c cataclasite however each parameter also reveals more complicated temporal evolution due to either the heterogeneity of the rock mass or the micro mechanics of shear fracturing this confirms the potential importance of integrated analysis of two or more parameters for successfully predicting the critical point the decreasing b value and increasing energy release may prove meaningful for intermediate term prediction while the precursory increase in fractal dimension and scl may facilitate short term prediction

depth versus age new perspectives from the chemical compositions of ancient crust petrological data provide a new approach to an evaluation of the depth age problem for ancient seafloor the correlations among basalt chemical composition axial depth and mantle temperature at current ocean ridges allow the determination of initial depth and mantle temperature for any portion of ancient seafloor that was created at a spreading center provided the chemical composition of the ancient crust is determined it is then possible to calculate a petrologically constrained depth at any age which can be compared to observed depths and depths from the classical half space models we evaluate data from dsdp and odp drill holes on crust older than 80 ma considering chemical composition back tracked depth and crustal thickness the data are complex and interpretation of their chemical composition requires consideration of alteration absence of glass compositions data quality and the influence of off axis volcanism and near ridge hot spots to check and expand the data set we develop and use trace element proxies for major element compositions since many trace element ratios are less influenced by alteration and by variable proportions of phenocrysts the twenty drill holes for which reliable data can be obtained are well distributed around the globe and include multiple sites on old crust in the atlantic pacific and indian ocean basins comparison of the chemical and crustal distributions between ancient and current n morb show that the oceanic crust older than 80 ma has significantly lower na 8 0 z r y sm ybn and higher cao al2o3 f e 8 0 and crustal thickness quantitative modeling of these results suggests that the mantle was hotter in this time period by about 50oc that the crust was several hundred meters shallower and 1 2 km thicker these observations show that half to two thirds of the observed flattening relative to a half space model is due to the change in mantle temperature and crustal composition thus only a few hundred meters of flattening by plate reheating by hot spots or by other mechanisms is required these results are consistent with the existence of abundant oceanic plateaus even at fast spreading rates in the mesozoic and with the apparent thickening of ocean crust with time 1999 elsevier science b v all rights reserved

earthquake source nucleation as self organization process abstract the theory of an earthquake source nucleation is discussed based on the assumption that self organization of damage process takes place in the zone of an earthquake source nucleation the theory incorporates the damage rheology framework of lyakhovsky et al and the approach of phenomenology theory of second order phase transition namely the free energy governing the process of an earthquake source nucleation depends on two collective variables and in addition to the strain tensor eij the variable quantifies the fracture of the medium and the variable quantifies the interaction effect of cracks the region s is associated with a potential source of an earthquake if the damage variable exceeds the critical value cr 1 inside s the important feature of a potential source is that interaction of fractures causes acceleration of damage process inside the region of potential source and the material should lose stability primarily in this region interaction of fractures results also in occurrence of a residual stress caused by nonuniformity of fracture density the appearance and development of the potential source result in increase of intensity of damage process not only in the region of potential source but also in a certain neighborhood of the last it is compatible with such observed effects as acceleration of seismic energy release and growth of correlation length of weak seismicity before large earthquake transition of potential source to the stage of avalanche unstable fracturing is associated with instability generated by explosive increase of interaction of fractures when the damage variable exceeds the second critical value cr 2 inside s

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

visibility graph analysis of the 2003 2012 earthquake sequence in the kachchh region of western india a visibility graph vg is a rather novel statistical method in earthquake sequence analysis it maps a time series into networks or graphs converting dynamical properties of the time series into topological properties of networks by using the vg approach we defined the parameter window mean interval connectivity time that informs about the mean linkage time between earthquakes we analysed the time variation of in the aftershock depleted catalogue of kachchh gujarat western india seismicity from 2003 to 2012 and we found that i changes through time indicating that the topological properties of the earthquake network are not stationary and ii appeared to significantly decrease before the largest shock m5 7 that occurred on march 7 2006 near the gedi fault an active fault in the kachchh region

correlation length as an indicator of critical point behavior prior to a large earthquake abstract a large earthquake preparation is often manifested in correlation of seismicity in an area whose characteristic dimension greatly exceeds a dimension of source of main shock zoller et al g zoller s hainzl j kurths observation of growing correlation length as an indicator for critical point behavior prior to large earthquakes j geophys res 106 2001 2167 2176 show the growth of correlation length of earthquakes prior to nine large earthquakes in california according to a power low we argue that the algorithm of correlation length estimation proposed by zoller et al g zoller s hainzl j kurths observation of growing correlation length as an indicator for critical point behavior prior to large earthquakes j geophys res 106 2001 2167 2176 can result in a decrease of correlation length preceding its precursory growth before large earthquakes if the area in which earthquake activity is correlated grows with time during a main shock preparation the correlation length analysis of acoustic emission events recorded in laboratory experiments on destruction of rocks and correlation length analysis of intermediate magnitude earthquakes in the area of large earthquakes preparation on kamchatka and in italy confirms the theoretical argument this effect can be considered as an additional premonitory pattern of large earthquake preparation

regional variations in subsidence rate of lithospheric plates implication for thermal cooling models abstract although simple thermal models of lithospheric cooling predict to first order the general behaviour of observed seafloor depth with increasing age important regional variations in seafloor subsidence in the range 250 400 m ma 1 2 are reported for several lithospheric plates such variations cannot be accounted for by classical cooling models unless implausible variations in asthenospheric temperature of 550 c are assumed here we present an alternative cooling model which assumes that at the ridge axis the temperature may deviate from the mean asthenospheric temperature such a model satisfactorily explains the data provided that the temperature deviation is 100 c only

sublithospheric small scale convection and its implications for the residual topography at old ocean basins and the plate model 1 the seafloor topography and heat flux differ significantly from the predictions of the half space cooling hsc model at old ocean basins understanding the deviations has important implications for thermal evolution of oceanic lithosphere and large scale mantle dynamics a widely used model that explains significant fraction of the deviations is the plate model but the dynamical feasibility of the plate model has never been demonstrated in this study we investigated the effects of sublithospheric small scale convection ssc and of internal heating on seafloor heat flux and topography and mantle thermal structure and we examined the dynamic feasibility of the plate model by formulating high resolution two dimensional numerical models of mantle convection with strongly temperature and depth dependent rheology we found that mantle convection with tectonic plates often leads to formation of a broad thermal anomaly below old lithosphere where the mantle is not cooled by subducted slabs and heat transfer is less efficient because of thick lithosphere especially when significant internal heating is present this trapped heat may exist in the middle mantle when the ssc is absent and it may also be redistributed by the ssc to shallow depths to reheat the lithosphere and to homogenize mantle temperature when internal heating accounts for 60 of the total heat output the trapped heat may provide sufficient heat supply to preferentially reheat old lithosphere via ssc while maintaining uniform mantle temperature we suggest that the trapped heat and the ssc are responsible for the residual heat flux and topography at old ocean basins relative to the hsc model predictions our models also show that for the plate model to be dynamically viable both the ssc and significant internal heating 60 are necessary this is because only the ssc in a mantle with significant internal heating can erode and reheat the lithosphere while maintaining a nearly constant mantle temperature below lithosphere which is the basic assumption of the plate model with the viscosity structure and internal heating rate for the present day mantle we think that the plate model is dynamically viable

response to comment on mantle flow drives the subsidence of oceanic plates croon et al challenge our conclusion that sea floor depth variations are driven by the underlying mantle convection we point out that contrary to their claim our data analysis is pertinent and that the sea floor linear trend as the square root of the distance from the ridge is a robust observation the mechanism responsible for this trend is an asthenospheric flow faster than the overlying plate which shapes the lithosphere structure

distributed damage faulting and friction we present a formulation for mechanical modeling of geological processes in the seismogenic crust using damage rheology the seismogenic layer is treated as an elastic medium where distributed damage modifying the elastic stiffness evolves as a function of the deformation history the model damage rheology is based on thermodynamic principles and fundamental observations of rock deformation the theoretical analysis leads to a kinetic equation for damage evolution having two principal coefficients the first is a criterion for the transition between strength degradation and recovering healing and is related to friction the second is a rate coefficient of damage evolution which can have different values or functional forms for positive degradation and negative healing evolution we constrain these coefficients by fitting model predictions to laboratory data including coefficient of friction in sawcut setting intact strength in fracture experiments first yielding in faulting experiments under three dimensional strain onset and evolution of acoustic emission and dynamic instability the model damage rheology accounts for many realistic features of three dimensional deformation fields associated with an earthquake cycle these include aseismic deformation gradual strength degradation development of process zones and branching faults around high damage areas strain localization brittle failure and state dependent friction some properties of the model damage rheology e g cyclic stick slip behavior with possible accompanying creep are illustrated with simplified analytical results the developments of the paper provide an internally consistent framework for simulating long histories of crustal deformation and studying the coupled evolution of regional earthquakes and faults this is done in a follow up work

implications of a statistical physics approach for earthquake hazard assessment and forecasting there is accumulating evidence that distributed seismicity is a problem in statistical physics seismicity is taken to be a type example of self organized criticality this association has important implications regarding earthquake hazard assessment and forecasting a characteristic of a thermodynamic system is that it exhibits a background noise that is self organized in the case of a dilute gas this self organization is the maxwell boltzmann distribution of molecular velocities in seismicity it is the gutenberg richter frequency magnitude scaling this scaling is fractal observations favor the hypothesis that smaller earthquakes in moderate sized regions occur at rates that are only weakly dependent on time thus the rate of occurrence of smaller earthquakes can be extrapolated to assess the hazard of larger earthquakes in a region we obtain the rate of occurrence of earthquakes with m 4 in 1 1 areas from the neic catalog using only this data we produce global maps of the seismic hazard observations also favor the hypothesis that the stress level at which an earthquake occurs is a second order critical point as a critical point is approached correlations extend over increasingly larger distances in terms of seismicity the approach to a critical point is associated with an increase in the rate of occurrence of intermediate sized earthquakes prior to a large earthquake this precursory activation has been shown to exhibit power law scaling and to occur over a region about ten times larger than the rupture length of the large earthquake analyses of the spinoidal behavior associated with second order critical points predict the power law increase in seismic activity prior to a characteristic earthquake this precursory activation provides the basis for intermediate range earthquake forecasting

flattening of the oceanic topography and geoid thermal versus dynamic origin summary the origin of the flattening of the seafloor bathymetry and geoid at old ages is still a matter of debate is this departure from the square root of age law induced by dynamic uplift of the lithosphere linked to the flow in the mantle or by cooling of the lithosphere different from that predicted for an infinite half space the amplitude of the dynamic uplift should strongly decrease at short wavelengths and should not be correlated with the seafloor age on a local scale therefore in order to eliminate the dynamic signal the cooling of the lithosphere is studied here by means of depth age and geoid age relationships computed from high pass filtered bathymetric geoid and age fields or from local dtopography d and dgeoid dage slopes the geoid age and depth age relationships obtained here are in good agreement with those previously deduced from global non filtered data at all observation scales a significant departure from the half space solution is found however the data are not sufficiently accurate to discriminate between the plate and chablis constant heat flow at the base of the lithospheric isotherm models our results support the existence of small scale convection supplying heat at the base of the old oceanic lithosphere

thermal evolution of the oceanic lithosphere an alternative view abstract the most common model used for representing the evolution with age of the oceanic lithosphere is the plate model where the temperature is set at a fixed depth called the base of the plate this base of the plate has no physical meaning but this model provides a mathematical substitute for a system where small scale convection occurs through instabilities growing at the base of the cooling lithosphere and becomes effective only below old ocean another possible view is that convection provides heat at the base of the lithosphere whatever the age of the overlying plate this last process can be modeled by a constant heat flow applied on the bottom lithospheric isotherm chablis model a good fit to the observables bathymetry and geoid as function of age and old age heat flow can be obtained both for plate and chablis models in spite of an experimentally determined thermal expansion coefficient much larger than assumed in previous plate models these models have important consequences for several geodynamic processes the plate at an age of 100 ma is only 80 km thick for both models melting above a hot spot can then occur in the garnet spinel transition field without much plate thinning in the plate model the subsidence is stopped at an age of about 80 ma while according to the chablis model several hundred meters of subsidence are expected after 100 ma thus the two models predict quite a different long term pattern of subsidence in the sedimentary basins finally in the chablis model the global cooling of the mantle coming from cold material eroded by secondary convection at the base of the plates is considerably larger than in plate models it amounts to 40 the remaining 60 being due to the subduction process

what lies beneath since archimedes shouted eureka more than 2200 years ago eurasia and north america have moved 55 m further away from each other as the sea floor has spread at the mid atlantic ridge the slow but steady process of sea floor spreading takes hot young lithosphere at the ridge axis and gradually moves it away as it cools thickens and sinks archimedes principle of buoyancy rules much of these plate tectonic processes on page 83 of this issue adam and vidal 1 remind us that it is not just what sits atop that matters but also what lies beneath they show that mantle flow beneath the oceanic crust influences the depth of the pacific ocean taking advantage of new easily accessible global geophysical data sets the authors offer a new explanation for a long standing mystery in the variation of sea floor depth with crustal age

studies on temporal and spatial variation of microseismic activities in a deep metal mine abstract aiming at forecasting techniques of ground pressure hazards in deep metal mines a microseismic monitoring system was established at a deep stope in hongtoushan copper mine in china based on theories of geophysics and rock mechanics a forecasting approach was introduced using microseismic multi parameters including cumulative apparent volume energy index spatial correlation length fractal dimension and b value the approach was used to predict large scale fractures and ground pressure hazards in rock masses the results showed that microseismic activities were very weak before mining commenced however activities became significant when mining started when mining finished microseismic activities remained at a higher level for about one week then became weakened before large scale fractures occurred all microseismic multi parameters behaved differently the apparent volume and spatial correlation length were continually increasing while energy index fractal dimension and b value were gradually dropping to their minimum values therefore these parameters could be used as precursory indicators for great ground pressure hazards comprehensive analysis on microseismic multi parameters changes could improve reliability of forecasting which is of great significance to deep metal mines in managing ground pressure failure risks

variation of the subsidence parameters effective thermal conductivity and mantle dynamics abstract the subsidence of young seafloor is generally considered to be a passive phenomenon related to the conductive cooling of the lithosphere after its creation at mid oceanic ridges recent alternative theories suggest that the mantle dynamics plays an important role in the structure and depth of the oceanic lithosphere however the link between mantle dynamics and seafloor subsidence has still to be quantitatively assessed here we provide a statistical study of the subsidence parameters subsidence rate and ridge depth for all the oceans these parameters are retrieved through two independent methods the positive outliers method a classical method used in signal processing and through the mifil method from the subsidence rate we compute the effective thermal conductivity k eff which ranges between 1 and 7 w m 1 k 1 we also model the mantle flow pattern from the s40rts tomography model the density anomalies derived from s40rts are used to compute the instantaneous flow in a global 3d spherical geometry we show that departures from the k eff 3 w m 1 k 1 standard value are systematically related to mantle processes and not to lithospheric structure regions characterized by k eff 3 w m 1 k 1 are associated with mantle uplifts mantle plumes or other local anomalies regions characterized by k eff 3 w m 1 k 1 are related to large scale mantle downwellings such as the australia antarctic discordance aad or the return flow from the south pacific superswell to the east pacific rise this demonstrates that mantle dynamics plays a major role in the shaping of the oceanic seafloor in particular the parameters generally considered to quantify the lithosphere structure such as the thermal conductivity are not only representative of this structure but also incorporate signals from the mantle convection occurring beneath the lithosphere the dynamic topography computed from the s40rts tomography model reproduces the subsidence pattern observed in the bathymetry overall we find a good correlation between the subsidence parameters derived from the bathymetry and the dynamic topography this demonstrates that these parameters are strongly dependent on mantle dynamics

maturation history of neogene quaternary sediments nile delta basin egypt geologic note the present nile delta area covers approximately 60 000 sq km fields in this area provide two thirds of the gas production in egypt geological knowledge of the nile delta is still limited because of insufficient subsurface data gas is generated and accumulates at stratigraphic levels ranging from the lower miocene to the lower pliocene the highest levels of organic maturation in the neogene quaternary section are in the northern part of the onshore area such as in the abu madi well and in the eastern part of the offshore area such as in the el temsah well where gas reservoirs occur in the lower pliocene sandstones abu madi formation and in the underlying sidi salem formation and lower miocene rocks here the sidi salem formation is probably generative having n r o of approximately 0 65 lom levels of organic metamorphism of 9 5 to 9 7 and tti time temperature index of 9 7 to 15 2 by contrast a different thermal history clearly existed in the western and eastern parts of the onshore area such as in the monaga and damanhur wells where the organic maturities are significantly lower than maturities elsewhere in the basin r o 0 38 and 0 29 respectively the predicted maturities obtained by using the lom method seem to fit much closer to the observed maturities than the predicted maturities obtained by using the lopatin tti method

pulsations in seafloor spreading rates and transit time dynamics correlation studies and theoretical models suggest the major plate driving forces slab pull and ridge push are closely linked to seafloor age at subduction zones transit time and hereafter denoted based on this fact it has been proposed that seafloor spreading rate fluctuations should be stably damped because a speedup should lead to rejuvenation of and hence a weakening of driving forces if true such stability could imply the first order cycle in pacific spreading rates during the mesozoic cenozoic the pulse of the earth was externally forced by mantle dynamics however we show that a crucial assumption in this stability argument is invalid increasing spreading rates do not necessarily cause transit time to decrease the transit time dynamics of seafloor are complex simple plate models suggest that rather than stabilizing spreading rate dependent plate driving forces may be destabilizing leading to self sustained and aperiodic oscillations these results raise questions about the cause of spreading rate cycles most importantly are the plates themselves through age dynamics actively contributing to the pulse of the earth

colliding cascades model for earthquake prediction a wide set of premonitory seismicity patterns is reproduced on a numerical model of seismicity and their performance in the prediction of major model earthquakes is evaluated seismicity is generated by the colliding cascades model recently developed by the authors the model has a hierarchical structure it describes the interaction of two cascades a direct cascade of loading which is applied to the top largest element and transfers down the hierarchy and an inverse cascade of failures which goes up the hierarchy from the smaller to the larger elements these cascades collide and interact loading leads to failures while failures release and redistribute the loading three basic types of earthquake precursors are considered i the clustering of earthquakes in space and time ii the intensity of earthquake sequences and iii the correlation distance between earthquakes patterns of the first two types are used in intermediate term earthquake prediction algorithms patterns of the third type are found in the colliding cascades model although they were hypothesized previously they have not been validated by observations for each precursor we explore what is called an error diagram showing the total duration of alarms the rate of failures to predict and the rate of false alarms

ocean bottom geophysical array studies may reveal the cause of seafloor flattening abstract flattening of old seafloor as a result of the time evolution of oceanic lithosphere and asthenosphere has been studied for several decades and remains one of the unresolved fundamental problems of geodynamics the phenomenon of seafloor flattening at ages greater than 70 80 ma can be explained by a simple model of a cooling plate with a fixed thickness but the physical cause of flattening is not fully understood here a simple model of lithosphere rejuvenation is considered as an alternative mechanism and is also shown to represent similar features of seafloor flattening we suggest that constraints on mantle structure from use of data such as variations of seafloor depth and heat flow are weak but that first order differences in mantle thermal structure are introduced by these two models this suggests that probing of the mantle by geophysical arrays on the seafloor particularly those sensitive to mantle temperature such as magnetotelluric imaging should be able to constrain the cause of seafloor flattening in the present study recent results of seafloor electromagnetic explorations are compiled and estimated depths to the high conductivity layer hcl are used as a proxy for 1 300 c isotherm depths for the data obtained at sites well away from plate boundaries in the pacific ocean a model of lithosphere rejuvenation was found to better explain the correlation between hcl depths and seafloor depths than a standard plate cooling model

role of temperature and time on organic metamorphism geologic notes organic metamorphism kerogen to hydrocarbon transformation is a function of both temperature and exposure time the effect of temperature is exponential of that of time linear at very low temperatures 266 f 130 c the reaction proceeds at such a high rate that time also plays no important role the effect of time is noticeable in the range of 158 to 212 f 70 to 100 c where intermediate conversion rates prevail stopping the heating process termination of burial freezes the rate constant of the reaction and allows organic metamorphism to continue at a linear rather than exponential rate this effect is demonstrated with the help of a simple geologic model for the first example a source rock was subjected to continuous linear heating whereas for the second the heating was terminated at a certain temperature level the model was analyzed by using the oleum scale a modified lopatin approach

non uniform scaling features in central italy seismicity a non linear approach in investigating seismic patterns and detection of possible earthquake precursors 1 the detrended fluctuation analysis dfa is a powerful method for capturing scaling behavior in nonstationary time series using an appropriate instability index it is possible to identify and quantify deviations from uniform power law scaling which suggest the presence of changing dynamics in the system under study in this context the scaling behavior of the 1981 2007 seismicity in umbria marche central italy which is one of the most seismically active areas in italy was investigated significant deviations from uniform power law scaling in the seismic temporal fluctuations were revealed mostly linked with the occurrence of rather large earthquakes or seismic clusters

single link cluster analysis as a method to evaluate spatial and temporal properties of earthquake catalogues summary single link cluster analysis is a straightforward method to quantitatively measure the degree of clustering or isolation of groups of elements in a set such as a catalogue of earthquakes to apply single link cluster analysis to a set of n earthquakes individual earthquakes are first linked to their nearest neighbours to form event sub groups the process is then repeated and each sub group linked to its nearest neighbour recursively until n 1 links are found to join all the earthquakes this paper shows how knowledge of these links can be used to divide a group of earthquakes into any number of spatial clusters with various modifications this analysis can identify earthquake nests isolated events aftershock sequences and zones of seismic quiescence to illustrate this method we apply it to i a global data set of 2178 earthquakes having mb of 5 8 or greater reported by the international seismological centre isc between 1964 and february 1986 and ii sets of earthquakes having mb of 4 9 and greater as reported by the isc occurring in central america and in the aleutians to facilitate comparison with real data this study also investigates the distribution of link lengths for synthetic events placed randomly on 1 d circular line 2 d circular area and 3 d spherical volume geometries if we remove links between nuclear explosions from the isc data the resulting link distribution is quite similar to that for synthetic events placed along a 1 d fault for the shortest links the similarity improves markedly if the synthetic fault has a finite width or if relative location errors cause events to be located away from the fault trace with a standard deviation of about 15 km

the gutenberg discontinuity melt at the lithosphere asthenosphere boundary the lithosphere asthenosphere boundary lab beneath ocean basins separates the upper thermal boundary layer of rigid conductively cooling plates from the underlying ductile convecting mantle the origin of a seismic discontinuity associated with this interface known as the gutenberg discontinuity g remains enigmatic high frequency ss precursors sampling below the pacific plate intermittently detect the g as a sharp negative velocity contrast at 40 to 75 kilometer depth these observations lie near the depth of the lab in regions associated with recent surface volcanism and mantle melt production and are consistent with an intermittent layer of asthenospheric partial melt residing at the lithospheric base i propose that the g reflectivity is regionally enhanced by dynamical processes that produce melt including hot mantle upwellings small scale convection and fluid release during subduction