lithostratigraphy of a cenozoic intra continental basin guadiana basin sw spain by using clay mineral assemblages and geophysical properties in the iberian peninsula alpine tectonics built several cenozoic basins that were mainly filled with continental deposits the guadiana basin is located halfway between two of the most important cenozoic basins of the sw of spain the tajo and the guadalquivir basins in this paper both geophysical and mineralogical studies have been carried out in order to establish the lithostratigraphy of the guadiana basin a combination of electric resistivity properties and variations in clay mineral assemblage content of the basin infill was used to identify several depositional sequences within the cenozoic deposits of the basin three depositional sequences ds1 ds2 and ds3 characterized by differentiated clay content and mineral assemblages were distinguished the lower depositional sequence ds1 consists of reddish siltstones and clays that scarcely crop out in the basin clay content of the 2 m fraction is dominated by illite averaging 60 of the total clay content with kaolinite and a few amount of smectite ds2 deposits lie unconformably over ds1 and the variscan basement and consist of a siliciclastic succession where carbonate units occur at bottom and at the top of the depositional sequence smectite dominates throughout the entire succession except in the basal carbonate unit where up to 70 of palygorskite is found in the younger sequence ds3 kaolinite is the dominant clay mineral electrical resistivity imaging helped in the physical characterization and horizontal and vertical distribution of each unit and provided good insight on the structure of the guadiana basin allowing to infer the basin structure due to high resistivity contrast between the basement and the sedimentary rocks in addition in areas where the lower sedimentary units do not crop out and borehole information is not available the geophysical response of the resistivity units imaged can be used to infer the corresponding depositional sequence the joint interpretation of the clay mineral assemblages and geophysical properties of the sedimentary units showed to be a useful tool to gather a reliable identification of depositional sequences in basins characterized by scarcity of good outcrops lack of borehole information and similarity of sedimentary rocks this is very important to properly correlate the different sedimentary units mapped as well as to infer the basin structure and its evolution through time

crack fusion dynamics a model for large earthquakes the physical processes of the fusion of small cracks into larger ones are nonlinear in character a study of the nonlinear properties of fusion may lead to an understanding of the instabilities that give rise to clustering of large earthquakes we have investigated the properties of simple versions of fusion processes to see if instabilities culminating in repetitive massive earthquakes are possible we have taken into account such diverse phenomena as the production of aftershocks the rapid extension of large cracks to overwhelm and absorb smaller cracks the influence of anelastic creep induced time delays healing the genesis of juvenile cracks due to plate motions and others a preliminary conclusion is that the time delays introduced by anelastic creep may be responsible for producing catastrophic instabilities characteristic of large earthquakes as well as aftershock sequences however it seems that nonlocal influences i e the spatial diffusion of cracks may play a dominant role in producing episodes of seismicity and clustering

a fractal model for crustal deformation abstract we hypothesize that crustal deformation occurs on a scale invariant matrix of faults for simplicity we consider a two dimensional pattern of hexagons on which strike slip faulting occurs the behavior of the system is controlled by a single parameter the fractal dimension deformation occurs on all scales of faults the fractal dimension determines the fraction of the total displacement that occurs on the first order or primary faults the value of the fractal dimension can be obtained from the frequency magnitude relation for earthquakes our results are applied to the san andreas fault system in central california earthquake studies give d 1 90 we associate the main strand of the san andreas fault with the primary faults of our fractal system we predict that the relative velocity across the main strand is 2 93 cm yr the remainder of the relative velocity of 5 5 cm yr between the pacific and north american plates occurs on higher order faults the predicted value is in reasonably good agreement with the value 3 39 0 29 cm yr obtained from geological studies

the role of porosity in the development of authigenic dolomite and palygorskite an example in siliceous sandstones of continental origin in western spain during the tertiary the hercynian basement of the iberian peninsula was uneven due to alpine tectonism which led to the development of a set of horsts and grabens forming its main geological structure one of these grabens is the ciudad rodrigo basin located close to the portuguese border the south western margin of this graben is filled with arkosic sandstones of continental origin that once deposited underwent important low grade diagenetic processes related to the surface processes the main diagenetic processes were hydrolysis replacement by carbonate and argillization to palygorskite these three processes led to the differentiation of three main levels within the outcrops studied 1 the lower level where the original clayey sandstone outcrops displaying fairly hydromorphic traits 2 the middle level where part of the clayey matrix has been replaced by dolomitic carbonate and 3 the upper level where palygorskite is the new neoformed clay the change in porosity seems to have been the controlling factor since it governs the dynamics of the solutions inside the rocks these conditions changed from being diffusion driven at the start of the diagenesis to flow driven as porosity increased

the origin of the sierra de aracena hollows in the sierra morena huelva andalucia spain hollows in the sierra de aracena part of western sector of sierra morena region huelva spain are geoecologically unusual macroforms they are underlain by deeply weathered bedrock but have eutrophic soils with distinctive vegetation paleosols with very dark colours a predominance of smectites and large amounts of total and free iron occur on the floors on the hollows an evolutionary model is proposed for the hollows involving differential weathering during the mesozoic on plutonic and amphibolitic rocks alpine tectonic activity followed by quaternary erosion and exhumation leading to formation of erosional terraces

the fluid dynamics of a basaltic magma chamber replenished by influx of hot dense ultrabasic magma this paper describes a fluid dynamical investigation of the influx of hot dense ultrabasic magma into a reservoir containing lighter fractionated basaltic magma this situation is compared with that which develops when hot salty water is introduced under cold fresh water theoretical and empirical models for salt water systems are adapted to develop a model for magmatic systems a feature of the model is that the ultrabasic melt does not immediately mix with the basalt but spreads out over the floor of the chamber forming an independent layer a non turbulent interface forms between this layer and the overlying magma layer across which heat and mass are transferred by the process of molecular diffusion both layers convect vigorously as heat is transferred to the upper layer at a rate which greatly exceeds the heat lost to the surrounding country rock the convection continues until the two layers have almost the same temperature the compositions of the layers remain distinct due to the low diffusivity of mass compared to heat the temperatures of the layers as functions of time and their cooling rate depend on their viscosities their thermal properties the density difference between the layers and their thicknesses for a layer of ultrabasic melt 18 mgo a few tens of metres thick at the base of a basaltic 10 mgo magma chamber a few kilometres thick the temperature of the layers will become nearly identical over a period of between a few months and a few years during this time the turbulent convective velocities in the ultrabasic layer are far larger than the settling velocity of olivines which crystallise within the layer during cooling olivines only settle after the two layers have nearly reached thermal equilibrium at this stage residual basaltic melt segregates as the olivines sediment in the lower layer depending on its density the released basalt can either mix convectively with the overlying basalt layer or can continue as a separate layer the model provides an explanation for large scale cyclic layering in basic and ultrabasic intrusions the model also suggests reasons for the restriction of erupted basaltic liquids to compositions with mgo 10 and the formation of some quench textures in layered igneous rocks

fractal reconstruction of sea floor topography sea floor bathymetric profiles exhibit features at many different scales of length this suggests that they could be described as fractals an algorithm interpolating a fractal line between points has been used to reconstruct bathymetric profiles from a few data points in general this fractal line has the same fourier amplitude spectrum as real bathymetry and if the parameters of the interpolation are suitably chosen it has a very similar appearance the success of this fractal reconstruction algorithm for the sea floor raises the possibility that it could be used to extrapolate from data collected at one scale the properties of the sea floor at finer scales and that similar techniques could be used to interpolate a surface between bathymetric profiles the fractal character is a sign that the processes that shape the sea floor are scale invariant and suggests that the renormalization group technique could be used to model these processes

along strike magma mixing beneath mid ocean ridges effects on isotopic ratios abstract the effects of mixing processes on the isotopic variability of mid ocean ridge basalts are studied the processes considered are porous flow dispersion and convective mixing in magma chambers porous flow dispersion is capable of mixing magmas over distances of only a few tens of meters convective mixing on the other hand is found to produce mixing over scales of kilometers to hundreds of kilometers calculations of convective mixing are carried out for continuous magma chambers where mixing is limited by convective processes and for discontinuous chambers where mixing is limited by chamber size preliminary comparison of our calculations with observations along the mid ocean ridges shows that the calculations are consistent with the existence of a correlation between bathymetry and isotopic ratio at long but not at short wavelengths they are also capable of explaining a decrease in isotopic variability with increasing spreading rate

mid ocean ridges fine scale tectonic volcanic and hydrothermal processes within the plate boundary zone a first order model of spreading centers as idealized linear boundaries of crustal and lithospheric generation provides only a gross understanding of global scale plate kinematics as we attempt to understand the complexity of crustal and lithospheric structure of two thirds of the earth s surface it is becoming increasingly necessary to study the tectonic volcanic and hydro thermal processes within the spreading center plate boundary zone all ocean ic crust bears the imprint of these processes this review focuses on a few selected topics concernining the fine scale tectonics and geophysics of the active axial zone of mid ocean ridges with reference to associated volcanic and hydrothermal processes it draws heavily on recent studies that use deeply towed instrument packages multi beam bathymetric mapping ocean bottom instruments and alvin e g the famous amar rise and galapagos expeditions we begin with a review of the large scale structure of spreading centers we then take a close look at the axial neovolcanic zone and progress away from the axis through the active tectonic zones next we consider the characteristics of the axial magma chamber and associated hydrothermal actvity as well as the generation of magnetic anomaly stripes and their implications for crustal generation one of our findings is that the initial two dimensional model of volcanic and tectonic zones must be expanded upon to allow for variations

the statistical mechanics of earthquakes abstract we review recent theoretical developments on the physics of earthquakes in particular we focus on the rise of the statistical mechanical view of earthquakes as a kind of phase transition this view is appealing in light of the well known scaling relations such as the gutenberg richter magnitude frequency and omori s law of aftershock decay scaling relations such as these which are in reality power laws are known to be associated with dynamical systems residing near a critical point in the state space of the system these second order critical points are associated with second order transitions which are a result of gradual changes of the controlling parameters at the same time characteristic earthquakes which involve the entire fault segment sliding nearly at once are more reminiscent of a first order transition which is characterized by sudden widespread changes in the physical state of the system in this paper we review these ideas and show how recent developments are leading to a view of earthquake fault systems based on modern statistical mechanics

a model for repetitive cycles of large earthquakes the theory of the fusion of small cracks into large ones reproduces certain features also observed in the clustering of earthquake sequences by modifying our earlier model to take into account the stress release associated with the occurrence of large earthquakes we obtain repetitive periodic cycles of large earthquakes a preliminary conclusion is that a combination of the stress release or elastic rebound mechanism plus time delays in the fusion process are sufficient to destabilize the crack populations and ultimately give rise to repetitive episodes of seismicity

premonitory transformation of steel fracturing and seismicity abstract transformation of microfracturing preceding the break up of steel and rock samples is similar to transformation of earthquakes flow prior to strong earthquakes in southern california the break up in a sample is preceded by transition from formation of new microcracks to coalescence or expansion of existing cracks this is reflected in the relation between the length and the number of the cracks similar transformation of seismicity precedes southern california earthquakes with magnitude m 6 6 1935 1994 specifically magnitude frequency relation bends downward for magnitudes from 3 to 4 5 and upward for magnitudes from about 4 5 to 6 in the usual notations the b value becomes larger in the first interval and smaller in the second one this transformation is accompanied by the increased share of aftershocks in the earthquakes flow in such a way the approach of a strong earthquake is reflected in both major traits of seismicity magnitude frequency relation and earthquake clustering imprecision of the earthquake catalog and reasonable variations in its analysis do not change our conclusions this phenomenon explains so far qualitatively a wide set of premonitory seismicity patterns we give it a formal definition allowing to test whether it takes place in other seismic regions

convective thinning of the lithosphere a model constrained by geoid observations abstract geoid observations in the oceans suggest that lithospheric thinning is effected by small scale convection within hot spot material trapped in dimples a few tens of kilometers deep at the base of the lithosphere significant thinning can occur within 5 ma if the viscosity of the convecting material is 10 16 pa s partial melting can enhance considerably the vigour of convection and the same rate of lithospheric thinning is obtained for a viscosity about five times higher these results are derived from convection models with a realistic temperature dependent rheology using the mean field approximation

premonitory seismicity changes prior to the parkfield and coalinga earthquakes in southern california abstract in this work we apply the pattern informatics technique for evaluating one surface expression of the underlying stress field the seismicity in order to study the parkfield coalinga interaction over the years preceding the 1983 coalinga earthquake we find that significant anomalous seismicity changes occur during the mid 1970s in this region prior to the coalinga earthquake that illustrate a reduction in the probability of an event at parkfield while the probability of an event at coalinga is seen to increase this suggests that the one event did not trigger or hinder the other rather that the dynamics of the earthquake system are a function of stress field changes on a larger spatial and temporal scale

global change and long term geomorphology landscape evolution is on the same time scale as global tectonics biological evolution and major climatic change some features of global change reflected in landscape evolution result from the breakup of pangaea others relate to major climatic changes and yet others to a major change from a dominantly plains landscape of the mesozoic to an increasingly mountainous landscape in the tertiary worldwide deep weathering profiles of cretaceous and early tertiary age suggest widespread planation and warm moist climates erosion of deeply weathered regolith following the formation of new continental margins and tectonic uplift led to the deposition of unusual mature sediments many river patterns can be traced to early tertiary or older antecedents some climatic changes are due to orbital forcing but others may be related to changing positions of continents creation of new seaways or to mountain building the timing of mountain uplift climatic changes and biological changes must be resolved to test models of their mutual interaction geomorphic input on tectonics drainage evolution and deep weathering will be an essential component in dealing with these problems

earthquake recurrence models and historical seismicity in the mexicali imperial valley abstract we have examined the historical seismicity of the mexicali imperial valley since about 1850 the largest observed earthquake in the area has been the magnitude m w 7 1 december 1934 event the magnitude distribution for large plate boundary rupturing earthquakes m 5 8 is not well fit by the gutenberg richter type b value model models which better fit the observed magnitude distribution are derived from a lognormal distribution of stress drops on faults of constant size and from an exponential distribution of rupture lengths as might be expected from randomly distributed rupture stopping asperities along the length of the fault this may be among the best data in the world for testing earthquake recurrence models e g time predictability slip predictability on a strike slip fault but the uncertainties are still too great to permit a unique interpretation

an observational test of the origin of accelerating moment release before large earthquakes 1 a progressive increase of seismic activity distributed over a wide region around a future earthquake epicenter is termed accelerating moment release amr this phenomenon has been observed in several studies over the last 15 years although there is no consensus about the physical origin of the effect in a recent hypothesis known as the stress accumulation sa model the amr is thought to result from the last stage of loading in the earthquake cycle in this view the increasing seismicity is due to minor stress release as the whole region becomes sufficiently stressed for the major event to occur the stress accumulation model makes specific predictions about the distribution of events in an amr sequence because the amr is predicted to be a result of loading on the main fault the precursory activity should be concentrated in the positive lobes of the far field stresses calculated by a backslip dislocation model of the main shock to test this model amr is first found in optimal circular regions around the epicenters of each of the m w 6 5 earthquakes in central and southern california since 1950 a backslip dislocation model is then used to determine which of the precursory events occur in the regions predicted by stress accumulation amr is shown to occur preferentially in the lobes of the backslip stress field predicted by the stress accumulation model

mechanisms of crustal deformation thirty sixthwilliam smith lecture the energy source for crustal deformation is isotopic heating and secular cooling of the mantle in a true solid heat would be lost to the surface by conduction however solid state creep processes allow the earth s solid mantle to exhibit a fluid behaviour thus thermal convection can convert heating into directed motion variations in temperature lead to variations in densitythrough thermal expansion and contraction although the resultant body forces are vertical horizontal variations in temperature lead to horizontal body forces at an ocean ridge the variations in the thickness of the lithosphere lead to the elevation of the ridge the result is a substantial horizontal ridge push force this force along with the trench pull force on the descending lithosphere is the primary force driving plate tectonics lithospheric thinning must occur beneath continental rifts and plateau uplifts i suggest that lithospheric thinning is caused by the diapiric penetration of hot asthenospheric rock to the crust mantle boundary this penetration may also cause lithospheric stoping and plateau uplifts lithospheric thinning leads to large tensional stresses above the zone of thinning these forces are generally much larger than the compressional forces generated by crustal thinning the forces generated by lithospheric thinning are quite large and may be responsible for the propagation of continental rifts in island arcs and andean type orogenic belts both lithospheric thinning and crustal thickening result in large tensional forces probably the most complex zone of crustal deformation is the continental collision variations in types of continental collisions are discussed

towards a new view of earthquake phenomena recent advances in the theory of fracture and fragmentation are reviewed empirical laws in seismology are interpreted from a fractal perspective and earthquakes are viewed as a self organized critical phenomenon soc earthquakes occur as an energy dissipation process in the earth s crust to which the tectonic energy is continuously input the crust self organizes into the critical state and the temporal and spatial fractal structure emerges naturally power law relations known in seismology are the expression of the critical state of the crust an soc model for earthquakes which explains the gutenberg richter relation the omori s formula of aftershocks and the fractal distribution of hypocenters is presented a new view of earthquake phenomena shares a common standpoint with other disciplines to study natural complex phenomena with a unified theory

axial depth anomalies from 10 to 50 north along the mid atlantic ridge correlation with other mantle properties abstract we present an analysis of intermediate to long wavelength a few hundred to a few thousand kilometers axial depth anomalies along the mid atlantic ridge between 10 and 50 n the maximum depth of the rift valley is chosen as the elevation datum for oceanic crust of zero age the large depth anomalies are correlated for short wavelengths less than a few hundred kilometers with some fracture zones irrespective of their offset and for intermediate to long wavelengths with mantle properties expressed in 1 excess elevation near triple junctions 2 trace element and isotope geochemistry of the basaltic liquids emplaced at the ridge axis and 3 anomalies in the earth s gravity field we suggest that the correlations may be explained in two ways the depth anomalies of intermediate to long wavelength may represent the sites of upwelling and downwelling of the deep mantle alternatively the depth anomalies could be due to a regionalization in temperature or mineralogy in the asthenosphere

extreme isotopic homogeneity among basalts from the southern east pacific rise mantle or mixing effect basaltic lavas which have erupted along the great oceanic ridge system are characterized by their overall chemical and isotopic homogeneity nevertheless they show evidence for variability in the chemical and isotopic composition of the ocean ridge basalt orb source whose scale and distribution remain uncertain isotopic compositions of sr nd pb and hf and ratios of some highly incompatible elements have been used as tracers of orb source compositions usually permitting source characteristics to be distinguished from petrogenetic effects the mid atlantic ridge mar in particular shows correlations in the isotopic compositions of several elements between isotopic compositions and topography and between these parameters and incompatible element concentrations and ratios1 3 we report here isotopic measurements for basalts dredged between approximately 30 and 34 s on the east pacific rise and adjacent maddingly rise which show highly uniform sr and nd isotopic compositions possibly resulting in part from mixing associated with a high rate of magma generation and rapid spreading 170 mm yr 1 however a ridge segment of comparable length between 18 and 22 s and with only a slightly lower spreading rate shows much greater isotopic variability hence we are apparently sampling small but detectable regional differences in mantle composition the isotopic homogeneity among the basalts from 30 to 34 s implies that any heterogeneity in the underlying upper mantle is uniformly distributed on a scale much smaller than the volume sampled in individual magma batches and is thus averaged out in the resulting lavas

fractal dimension of fault systems in japan fractal structure in rock fracture geometry at various scales based on fault maps whether or not the fracture geometry of rocks is self similar was examined by using a box counting algorithm the statistical self similarity fractal structure of the fault fracture systems holds well at the scale of about 2 to 20 km the fractal dimension in japan varied from 1 05 to 1 60 the fractal dimension is about 1 5 1 6 at the central part of the japan arc and decreases with distance from the center at a smaller scale the fractal structure also holds well in the rock fracture geometry the fractal dimension of the north izu peninsula fault system branching faults is 1 49 at the scale of 0 625 to 10 km the fractal dimension of rock fracture geometry at the scale order of 10 1 to 10 2 meters is about 1 49 1 61 the upper limit of the fractal dimension of rock fracture geometry is about 1 6 judging from the estimation of fractal dimension on actual fracture geometry of rocks this value may impose a restraint on modeling of faulting and the fracture process of rocks

persistent widespread pulsating aurora a case study 1 observations of a pulsating aurora event occurring on 11 february 2008 using the time history of events and macroscale interactions during substorms themis all sky imager asi array indicate a spatially and temporally continuous event with a duration of greater than 15 h and covering a region with a maximum size of greater than 10 h magnetic local time the optical pulsations are at times locally interrupted or drowned out by auroral substorm activity but are observed in the same location once the discrete aurora recedes the pulsations following the auroral breakup appear to be brighter and have a larger patch size than before breakup this suggests that while the onset of pulsating aurora is not necessarily dependent upon a substorm precursor the pulsations are affected and possibly enhanced by the substorm process the long duration of this pulsating aurora event lasting approximately 8 h without interruption as imaged from gillam station is significantly longer than the typical 2 3 h substorm recovery phase suggesting that pulsating aurora is not strictly a recovery phase phenomenon this paper is accompanied by a movie of the themis asi array data from 0000 to 1715 ut plotted in mosaic and superimposed onto a map of north america

sliding with cavity formation we present a model for the determination of a sliding law in the presence of sub glacial cavitation this law determines the basal stress at a clean ice bedrock interf ace in terms of the velocity and effective pressure the method is based on an exact solut ion of the nye kamb linearly viscous sliding problem with cavities and uses ideas of lliboutry 979 to construct via re norma lization methods an approximate law for gene ral bedrock form we show that for a bedrock whose spectrum has a power law behaviour one obtains a sliding law which gives the basal shear stress proportional to a power of the velocity and to a power of the effective pressure the effect of subgl acial cavitation on the drainage system is exam ined using recent ideas of kamb for sufficiently high velocities drainage through a r6thlisberger tunnel system is unstable and drai nage takes place through the linked system of cavities this leads to a reduction of the effective pressure and by taking account of this one can rewrite the sliding law in terms of st ress and velocity only this sliding law can be multi v alued and it is suggested that this unde rlies the dynamic phenomenon of surges

statistical model for the stick slip behaviour of faults summary inspired by an earlier work by smalley turcotte solla 1985 in this paper we consider a fault consisting of large sets of asperities with a statistical distribution of strength it is argued that the principle of equal load sharing between asperities inside a segment is necessary to account for the stick slip behaviour this principle is responsible for amplifying or damping the effective probability for the displacement of crustal blocks the antecedents of this idea in the seismological literature are commented on

a model of propagating brittle failure in heterogeneous media i consider a nonelastodynamic model for the propagation of brittle failure in a heterogeneously stressed medium numerical simulation shows a power law distribution of failure sizes with a slope not far different from the size distribution of seismic events the time history of calculated failure activity is not consistent with observed seismic behavior and some explanations and implications are discussed

the interpretation of the b and the b0 values and its implications on the regional deformation of the crust summary after reviewing the model and the interpretation of the negative power laws which represent the statistical distributions of the linear dimension of faults l and of the stress drops p of the earthquakes it is seen that the coefficient of the law log m0 m increases with m for smaller m it is verified that the parameters l and p of california earthquakes are independent and also it is suggested that one may consider a fractal dimension of earthquakes associated with p it is shown how these statistical distributions may allow distribution of slips in the seismic regions to be inferred where all the slips occur approximately in the same horizontal direction from the density distribution of the length of the faults it is found that in california 50 per cent of the regional displacement is due to the faults with linear lengths larger than 63 per cent of the maximum linear length of the faults similar results are obtained using the seismic moment m0 or the magnitude m instead of l in these cases however the density distribution of p is also needed for the exact computation of the displacement assuming that in california the regional displacement has been 5 cm yr 1 as measured with ground observations and space techniques it is tentatively estimated that the displacement due to earthquakes with m0 larger than 1027 1 may be as large as 4 2 cm yr 1 and that a cumulative displacement of at least 170 cm due to earthquakes with m0 larger than 1027 1 may have not been released since the great 1906 san francisco earthquake it is finally discussed how the variation in the density distribution of stress drops may be a precursor to earthquakes

the 2009 l aquila central italy seismic sequence as a chaotic process abstract in this paper we demonstrate that the seismic sequence of foreshocks culminating with the recent m w 6 3 main shock on april 6 2009 in l aquila central italy evolved as a chaotic process to do this we apply a nonlinear retrospective prediction to this seismic sequence and look at the temporal behaviour of the error between predicted and actual occurrence of the main shock when gradually increasing parts of the sequence are considered this is a generalisation of the typical nonlinear approach which is quite powerful to detect chaos in relatively short time series the method of prediction is based on the accelerated strain release asr analysis in time and on the nonlinear forecasting approach in a reconstructed phase space we find that i the temporal decay of the prediction error is consistent with an exponential function with a time constant of about 10 days and ii at around 6 days before the main shock asr analysis is quite powerful for anticipating the time of occurrence with an uncertainty of about a day due to its retrospective characteristics the latter result could be affected by changes on some a priori parameters used in the application of the asr technique however we consider these findings together with those obtained from the phase space analysis to be strong evidence that the studied sequence of foreshocks was produced by a physical process dominated by a significant chaotic component characterised by a k entropy 1 of about 0 1 day 1 this result could have important implications for the predictability of the possible main shock for those seismic sequences showing analogous nonlinear chaotic properties

convection in a two layer mantle with a strongly temperature dependent viscosity recent geochemical and isotopic data support the hypothesis that the earth s mantle convects in two separate layers with an interface at the 650 km seismic discontinuity this paper studies the implications of this hypothesis with regard to the thermal boundary layers that are expected to develop adjacent to the interface between the convecting layers we are particularly concerned with a possible decrease in the mantle viscosity across this interface in order to study the structure of the thermal boundary layers in a fluid with a strongly temperature dependent viscosity we utilize an approximate method developed by howard 1966 if the upper and lower mantle have the same viscosity law we find that stratified convection requires a lower mantle viscosity which is several orders of magnitude lower than the upper mantle viscosity this is not consistent with studies of postglacial rebound it is possible to obtain a viscosity law for the lower mantle that gives a viscosity nearly equal to that of the upper mantle and reasonable temperatures however the required law is not consistent with the currently available experimental data on lower mantle materials therefore we conclude that thermal arguments favor whole mantle convection

premonitory spreading of seismicity over the faults network in southern california precursor accord 1 we establish a connection between geometry of the faults network in a region and seismicity preceding the strong earthquakes in the intermediate term timescale of years previous studies of observed and computer simulated seismicity demonstrated that strong earthquakes are preceded in that timescale by the rise of seismic activity in a lower magnitude range here we explore a complementary phenomenon spreading of activity over the fault network this phenomenon is depicted by the seismicity pattern accord defined as a simultaneous rise of seismicity in a sufficiently large number of fault zones hence its name pattern accord has been found recently in synthetic seismicity generated by the colliding cascades cc model the present study demonstrates this pattern in observed seismicity of southern california we applied to observations a prediction algorithm based on the pattern accord scaled to the target magnitude 7 5 the pattern accord emerges within a few years before each of the three largest earthquakes in southern california kern county 1952 landers 1992 and hector mine 1999 and at no other time scaled to the target magnitude interval from 6 5 to 7 4 the pattern accord precedes six out of nine earthquakes the duration of alarms in both cases is about 30 of the time considered we repeated prediction with different combinations of adjustable numerical parameters of the algorithm summing up the success and error scores on an error diagram this numerical experiment shows that the prediction results are stable under moderate variations of adjustable parameters the final test would be as always an advance prediction the pattern accord has a simple physical explanation connected with equilibrium of the crustal blocks system under the impact of tectonic driving forces at the same time accord is a manifestation of a broader phenomenon premonitory increase of earthquakes correlation range the latter phenomenon was found for the first time in the cc model although it was hypothesized by one of the authors much earlier

the flow of hot brines in cracks and the formation of ore deposits we examined the thermal evolution of solutions transported vertically by turbulent flow in fractures and its implications for mississippi valley type ore deposition the main parameter governing the flow is fracture width which determines the flow rate volume and thermal evolution of the transported fluid we assumed local equilibrium and traced the chemical evolution of the transported solutions the mineral deposits associated with the cooling of these solutions and the limits of fracture clogging the volume of fluid expelled and the fracture width determine the location of the deposit and hence the deposit type i e carbonate hosted or vein we show that a network of thin cracks can indeed transport the volume of brines needed for the genesis of large mississippi valley type ore deposits such as the southeast missouri lead district

galapagos hot spot spreading center system 2 87sr 86 sr and large ion lithophile element variations 85 w 101 w thirty eight samples of basalts dredged from the galapagos spreading center gsc between 85 w and 101 5 w longitudes have been analyzed for k rb cs ba and sr contents as well as for 87sr 86sr ratios basalts between 85 w and 89 w segment of the gsc range from 0 7025 to 0 7028 in 87sr 86sr and those between 95 5 w and 101 5 w range from 0 7026 to 0 7027 these basalts are characterized by lree depleted patterns basalts from 89 w to 95 5 w segment having slightly lree depleted to lree enriched patterns la sm e f between 0 8 and 2 4 range from 0 7027 to 0 7031 in 87sr 86sr the longitudinal 87sr 86sr variation shows a maximum at about 92 w where the gsc is nearest to darwin island the alkali and alkaline earth elements as well as several element ratios also show maxima in their longitudinal profiles but these occur at about 91 w the apparent shift of 87sr 86sr maximum with respect to that of the trace elements may be related to differences in the degree of partial melting the highest 87sr 86sr from the gsc is only slightly lower than the highest 87sr 86sr for tholeiitic basalts from the galapagos archipelago several possible hypotheses have been examined to account for these geochemical and sr isotopic variations in the light of the presently available data the most promising explanation seems to be a binary mixing of hot spot or plume type material with the source of normal mid ocean ridge basalts and resulting rift propagation both end members seem to be heterogeneous and therefore it is at present difficult to put severe constraints on this binary mixing nevertheless the flow pattern of mantle material from the hot spot does not appear to be radial but is preferentially channeled along the 91 w and 92 5 w fracture zones toward the rift

large scale aspects and temporal evolution of pulsating aurora 1 pulsating aurora is a common phenomenon generally believed to occur mainly in the aftermath of a substorm where dim long period pulsating patches appear the study determines the temporal and spatial evolution of pulsating events using two themis all sky imager stations at gillam 66 18 magnetic latitude 332 78 magnetic longitude magnetic midnight at 0634 ut and fort smith 67 38 magnetic latitude 306 64 magnetic longitude magnetic midnight at 0806 ut along roughly the same invariant latitude parameters have been calculated from a database of 74 pulsating aurora events from 119 days of good optical data within the period from september 2007 through march 2008 as identified with the gillam camera it is shown that the source region of pulsating aurora drifts or expands eastward away from magnetic midnight for premidnight onsets and that the spatial evolution is more complicated for postmidnight onsets which has implications for the source mechanism the most probable duration of a pulsating aurora event is roughly 1 5 h while the distribution of possible event durations includes many long several hours events this may suggest that pulsating aurora is not strictly a substorm recovery phase phenomenon but rather a persistent long lived phenomenon that may be temporarily disrupted by auroral substorms observations from the gillam station show that in fact pulsating aurora is quite common with the occurrence rate increasing to around 60 for morning hours with 69 of pulsating aurora onsets occurring after substorm breakup

variations in architecture and cyclicity in fault bounded carbonate platforms early miocene red sea rift nw saudi arabia abstract the early miocene was a period of active rifting and carbonate platform development in the midyan peninsula nw saudi arabia however there is no published literature available dealing with the detailed characterization of the different carbonate platforms in this study area therefore this study aims to present new stratigraphic architectural models that illustrate the formation of different carbonate platforms in the region and the forcing mechanisms that likely drove their formation this study identified the following features formed during active rifting a a late aquitanian n4 fault block hangingwall dipslope carbonate ramp b a late burdigalian n7 n8 isolated normal fault controlled carbonate platform with associated slope deposits and c a late burdigalian n7 n8 attached fault bounded platform with reef buildups rimmed shelf developed on a footwall fault tip within a basin margin structural relay zone that formed coinciding with the second stage of rifting variations in cyclicity have been observed within the internal stratigraphic architecture of each platform and also between platforms high resolution sequence stratigraphic analysis shows to be parasequences the smallest depositional packages metre scale cycles within the platforms the hangingwall dipslope carbonate ramp and the attached platform demonstrate aggradational progradational parasequence stacking patterns these locations appear to have been more sensitive to eustatic cyclicities despite the active tectonic setting the isolated fault controlled carbonate platform reveals disorganized stratal geometries in both platform top and slope facies suggesting a more complex interplay of rates of tectonic uplift and subsidence variation in carbonate productivity and resedimentation of carbonates such that any sea level cyclicity is obscure this study explores the interplay between different forcing mechanisms in the evolution of carbonate platforms in active extensional tectonic regions characterization of detailed parasequence scale internal architecture allows the spatial variation in syn depositional relative base level changes to be inferred and is critical for understanding the development of rift basin carbonate platforms such concepts may be useful for the prediction of subsurface facies relationships beyond interwell areas in hydrocarbon exploration and reservoir modeling activities

asperity distribution and percolation as fundamentals of an earthquake cycle abstract a seismic cycle model is proposed based on the existence of an asperity space strength distribution along the fault plane and the applicability of the percolation theory to earthquakes as suggested by vrancea seismotectonic data two seismic regions somewhat decoupled are emphasized in the lower lithosphere roughly between 80 and 110 km and between 120 and 170 km depth and an asperity magnitude quasi independent dimension of 0 3 0 4 km is determined for small to moderate earthquakes accordingly two concepts are introduced 1 the active zone a distinct fault region able to generate a major earthquake by percolation and characterized by a specific background seismicity total area and maximum possible magnitude 2 the asperity cell an elementary local stress inhomogeneity of an active zone generating weak to moderate events percolation requires the presence of a critical stress free surface 44 of the active zone area the model explains the non linearity of the frequency magnitude relationship and enables the estimation of the major earthquake magnitude domain in each zone the computed maximum possible magnitudes are mw 7 6 and mw 7 8 respectively in agreement with historical data a complex form of the recurrence period of earthquakes in the major magnitude domain is determined ranging from about 40 to 100 years irrespective of the seismic zone it follows that the seismic activity per unit area is invariant in both zones this result is considered to be a consequence of an intrinsic material property the scale invariance of the fragmentation process in the lithospheric material different aspects related to the discrete structure of the active zone and the fractal dimension of faulting are also discussed from the point of view of this model

importance of porosity and transfer of matter in the rock weathering processes two examples in central spain some physical properties bulk and free porosity pore size distribution and the chemical composition and mass balance of two deeply weathered profiles one developed on hercynian granodiorite and the other on pre cambrian slates were studied hydric and mercury porosimetry nitrogen adsorption techniques chemical analyses and xrd techniques were used on granodiorite weathering has created increased porosity with a pore diameter 5 m whereas on slates the weathering has produced of ca 1 m in diameter these pore sizes have played an important role in the weathering processes assuming that weathering preserves volumes except in the uppermost part of the profiles it brought about a loss of matter of more than 12 300 kg m3 on granodiorite and ca 30 800 kg m3 on slates these changes are related to shifts in the mineralogical evolution with the appearance of new 2 1 and 1 1 phyllosilicates and fe oxy hydroxides as the main authigenic minerals the release of matter at least since the upper neogene until the present has led to the lowering of relief in a more or less homogeneous way giving rise to gentle hillsides and flat surfaces below which the current river networks are incised porosity studies have the potential to explain several specific landforms as well as affecting landscape development in general

on the distribution and separation of crystals in convecting magma abstract fractionation of crystals from magma stands squarely as the central principle of igneous petrology and the critical balance is the competition between crystal settling or rising velocity and magmatic convective velocity a ratio we call s the convective velocity is intimately related to the rate of heat transfer from the system although the theory of sediment distribution in rivers establishes the critical parametric balance and it has been often applied to igneous systems this method turns out to be valid only for small concentrations of crystals and it is not clear if it is accurate for other than turbulent flows where the prandtl number is near unity a generalized theory of particle crystal or bubble behavior is presented scaling of the generalized result shows for the magmatic conditions of small crystallinities small particle reynolds number and newtonian viscosity that the exact distribution of crystals in a convecting magma can be found analytically regardless of the flow field critical retention occurs only for 0 s s 0 for sinking crystals retention is centered in the region of maximum updraft for floating particles retention occurs in regions of downflow which for a simple cellular convective pattern produces a torus shaped retention region against the walls about the midsection of the body for a stack of flattened convective cells which in the crudest sense is analogous to double diffusive convection the zones of retention form depending on the exact flow field either a stack or staggered stack of pillows through the central region crystals settling from top to bottom around this stack take a tortuous path and may exhibit a complex but regular compositional zoning additional effects of fluids possessing a yield strength turbulence particle shape and wall and particle dispersive effects are more qualitatively evaluated for each flow field the amount of retention and the effective settling velocity of all crystals is found as a function of s the critical parameter s controlling retention can be estimated from a parametric representation involving stokes s law and the rayleigh number this shows that some retention probably occurs in all magmas and it increases with approach of the magma to the earth s surface although both crystal settling rate and convection decrease with increasing magmatic viscosity the overall effect is to increase retention decrease s magmas having a viscosity near and beyond about 10 4 poise and chambered in the nearsurface environment should show large degrees of crystal retention retention is however never complete for magmas and the flux of settling crystals leading to differentiation varies as a function of crystallinity this flux or flux probability p f is zero both at the liquidus and the point of maximum packing of crystals which for basalts is about 60 the importance of differentiation is regulated by the amount of time spent in the high crystal flux state and a relative measure of this time is given by the thermal probability p t introduced previously thus the probability of differentiation p d is given by the product p f p t which shows that differentiation must occur over a restricted range of crystallinities from about 20 to 45 for basalts and from about 10 to 30 for rhyolitic magmas the most basic lessons learned here are that the full range of crystallinities is not equally accessible to crystal fractionation and the most fundamental information describing the dynamic state and behavior of magma may well be the distribution of crystal sizes found in lavas

high frequency spectral falloff of earthquakes fractal dimension of complex rupture b value and the scaling of strength on faults the high frequency falloff omega sup minus gamma of earthquake displacement spectra and the b value of aftershock sequences are attributed to the character of spatially varying strength along fault zones the author assumes that the high frequency energy of a main shock is produced by a self similar distribution of subevents where the number of subevents with radii greated than r is proportional to r sup minus d d being the fractal dimension in this model an earthquake is composed of a hierarchical set of smaller earthquakes the static stress drop is parameterized to be proportional to r sup eta and strength is assumed to be proportional to static stress drop he finds that a distribution of subevents with d 2 and stress drop independent of seismic moment eta 0 produces a main shock with an omega sup minus 2 falloff if the subevent areas fill the rupture area of the main shock by equating subevents to islands of high stress of a random self similar stress field on a fault he relates d to the scaling of strength on a fault such that d 2 minus eta thus d 2 corresponds to constant stress drop scaling eta 0 and scale invariant fault strength amore self similar model of aftershock rupture zones on a fault is used to determine the relationship between the b value the size distribution of aftershock rupture zones and the scaling of strength on a fault the b value for aftershock sequences on a fault is found to equal 3 minus 1 5 eta 3 eta therefore this model indicates that the typically observed spectral falloffs of omega sup minus 2 and b values of 1 can be entirely caused by scale invariant strength eta 0 along fault zones less

nonconjugacy of pulsating auroral patches near l 6 simultaneous tv data of pulsating auroras were obtained at two nearly conjugate stations husafell in iceland and syowa in antarctica on september 9 10 1994 an investigation of the spatial and temporal coherence of pulsating patches revealed the following characteristics 1 the overall dynamic variations and activities of the pulsating features were very similar at both stations 2 most of the individual pulsating patches did not have clear counterparts in the opposite hemisphere that is individual pulsating patches appeared to be nonconjugate 3 even when the shape and type of pulsating aurora suggested a conjugate like relationship the pulsation periods were clearly different these interesting results indicate an asymmetry in the generation or precipitation mechanism of the particles producing pulsating auroras active ionospheric processes probably play an important role in causing or modifying auroras of this type

earthquake size frequency relations from an analytical stochastic rupture model an analytical stochastic model of earthquake rupture is presented although the general formulation makes no a priori self similarity assumption scale independent earthquake size frequency esf statistics emerge from the interaction between fault strength heterogeneity and rupture mechanics the model also gives theoretical derivations for scale dependent esf statistics including gradual frequency saturation for small earthquakes and a continuum of possible transitions in the statistics of large earthquakes a model fault is characterized as a surface composed of a large number of asperities defined as small discrete contact surfaces of finite strength an earthquake rupture grows via successive asperity breaking subevents the probability of rupture to a certain size earthquake or greater is the total product of incremental rupture growth probabilities these are governed by a new asperity failure probability distribution derived as a mixture of weibull distributions by including fracture mechanics the resulting mixture distribution characterized by the scale and shape parameters and is written in terms of the rupture size the important difference between the mixture distribution and the weibull distribution is that the mixture results in power law esf statistics self similarity occurs when material heterogeneity and rupture mechanics are mutually tuned to give 1 frequency saturation for small earthquakes is shown to be a simple consequence of a general aseismic nucleation process the nucleation magnitude m defines the roll off point in esf statistics that occurs when the area of seismic rupture equals the area of precursory aseismic rupture growth by fitting the model to the parkfield earthquake data set m 0 9 is obtained the change in esf scaling for the transition from moderate to large earthquakes depends on the changes in stress at the growing rupture front the northern california earthquake data center seismicity data set is fitted for a transition at magnitude m 5 with 0 4 and 0 75 this result indicates that the change in the esf relation associated with the transition from moderate to large earthquakes in california and nevada is caused by surface rupture accompanied by partial width and slip saturation

silcrete and alunite genesis in alluvial palaeosols late cretaceous to early palaeocene duero basin spain abstract an extensive formation of silcretes occurs in the upper half of a late cretaceous to palaeocene siderolithic unit consisting of conglomerates sandstones and sandy mudstones along the western margin of the tertiary duero basin spain the unit is arranged in fining upward sequences that were deposited in a fluvial braided system with floodplains subject to periodic events of exposure and drying out the original mineralogy of the siderolithic unit is seen in the less altered levels where it consists of quartz illite white mica kaolinite and at the top of the unit k feldspar all coming from the palaeoalteration mantles developed on the metasediments of the variscan basement the unit is characterized by a marked development of alluvial palaeosols at the uppermost part of each sequence at field scale the pedogenic structures and features are evident from the mottled pattern burrowing cracking planes and root traces at micromorphological scale an intense development of birefringent fabrics is seen in clays micas and feldspars show evidence of alteration due to hydrolysis while the more resistant quartz grains show common corrosion gulfs and have become the only surviving elements in the most silicified beds the neoformed minerals are related to the pedodiagenetic processes developed on the floodplains the main neoformed phase is opal probably amorphous silica in origin that aged to opal ct which ranges from local cementations in pores to an almost complete replacement of the rock specially the finest components matrix kaolinite is the most abundant neoformed clay locally veinlets of alunite accompany the opalized levels all the processes described occurred in a seasonal tropical climate during dry episodes strong evaporation resulted in an increase in ph favouring the hydrolysis of the original silicates the paucity of mg2 and ca2 in the groundwater would have favoured the increase in ph in ensuing wetter periods phs fell rapidly resulting in the precipitation of kaolinite and also favouring the precipitation of opal and alunite the alunite could have formed either by oxidation of the iron sulphides developed in reducing areas of the flood plains or by evaporitic concentration of sulphate in ca2 and mg2 free groundwaters

statistical physics approach to understanding the multiscale dynamics of earthquake fault systems 1 earthquakes and the faults upon which they occur interact over a wide range of spatial and temporal scales in addition many aspects of regional seismicity appear to be stochastic both in space and time however within this complexity there is considerable self organization we argue that the occurrence of earthquakes is a problem that can be attacked using the fundamentals of statistical physics concepts of statistical physics associated with phase changes and critical points have been successfully applied to a variety of cellular automata models examples include sandpile models forest fire models and particularly slider block models these models exhibit avalanche behavior very similar to observed seismicity a fundamental question is whether variations in seismicity can be used to successfully forecast the occurrence of earthquakes several attempts have been made to utilize precursory seismic activation and quiescence to make earthquake forecasts some of which show promise

seismicity based earthquake forecasting techniques ten years of progress abstract earthquake fault systems interact over a broad spectrum of spatial and temporal scales and in recent years studies of the regional seismicity in a variety of regions have produced a number of new techniques for seismicity based earthquake forecasting while a wide variety of physical assumptions and statistical approaches are incorporated into the various methodologies they all endeavor to accurately replicate the statistics and properties of both the historic and instrumental seismic records as a result the last ten years have seen significant progress in the field of intermediate and short term seismicity based earthquake forecasting these include general agreement on the need for prospective testing and successful attempts to standardize both evaluation methods and the appropriate null hypotheses here we differentiate the predominant approaches into models based upon techniques for identifying particular physical processes and those that filter or smooth the seismicity comparison of the methods suggests that while smoothed seismicity models provide improved forecast capability over longer time periods higher probability gain over shorter time periods is achieved with methods that integrate statistical techniques with our knowledge of the physical process such as the epidemic type aftershock sequence etas model or those related to changes in the b value for example in general while both classes of seismicity based forecasts are limited by the relatively short time period available for the instrumental catalog significant advances have been made in our understanding of both the limitations and potential of seismicity based earthquake forecasting there is general agreement that both short term forecasting on the order of days to weeks and longer term forecasting over five to ten year periods is within reach this recent progress serves to illuminate both the critical nature of the different temporal scales intrinsic to the earthquake process and the importance of high quality seismic data for the accurate quantification of time dependent earthquake hazard

some aspects of paleoweathering in the iberian hercynian massif summary the iberian hercynian massif occupies most of the western half of the iberian perninsula and forms the basement over which mesozoic cenozoic and quaternary materials rest unconformably over it can be found remains of weathering profiles that are fossilized by marine and or continental sediments of different ages on the southwestern border of the tertiary basin of the duero and below the series attributed to the lower tertiary palaeocene lies a weathering mantle that has been displaced by the effects of alpine tectonics accordingly its remains may appear truncated and or covered by other more recent deposits the present work studies this ancient weathering mantle in the zones in which it appears developed over the slaty series of the basement in the province of salamanca central west spain the profiles chosen reveal the existence of a strong chemical weathering that involves the destruction of some primary materials fe bearing chlorites and feldspars and the formation of kaolinites and fe oxihydroxides the start of the degradation of chlorite occurred during the first weathering phases this evolved towards an expandible smectite like mineral this first phase reflects the disappearance of albite and chemical analysis points to a pronounced loss of na in the most advanced stage the chlorites and smectites have disappeared giving way to the presence of kaolinite goethite and hematites this weathering phase is associated with a strong loss of mg the main processes occurring in these profiles are monosiallitisation and ferruginisation

fractal geometry in the san andreas fault system it has been noted that the spatial distribution of earthquakes and the mode of strain release in the san andreas fault system is related to the complexity of fault geometry because of their rough appearance over many length scales faults can be regarded as fractal surfaces direct estimates of fractal dimension d of portions of the san andreas fault system between the northern gabilan range and the salton sea including the postulated extent of the great 1857 fort tejon earthquake are obtained from measured fault lengths analogous to the lengths of coastlines as discussed by mandelbrot regions characterized by complicated fault geometry are associated with larger values of d based on fault traces mapped at a scale of 1 750 000 d is 1 3 for this reach of the fault defined as a 30 km wide band about a main fault trace for that part near parkfield which could be associated with the nucleation of the 1857 earthquake d is 1 1 at this same scale d is 1 4 for the san andreas and related faults near san bernardino where the 1857 rupture stopped compared to 1 2 for the san andreas san juan fault segments near the point of arrest of the 1966 parkfield earthquake at finer map scales 1 24 000 and 1 62 500 critical lengths of 500 m and 1 km are identified which might relate to the extent of off san andreas fault offsets the critical lengths also suggest that fault geometry is not self similar if this fractal geometry persists through the seismic cycle it may be possible to use a quantitative measure of complexity to explain the occurrence of great and characteristic earthquakes along a given reach of fault

a renormalization group approach to the stick slip behavior of faults we treat a fault as an array of asperities with a prescribed statistical distribution of strengths when an asperity fails the stress on the failed asperity is transferred to one or more adjacent asperities for a linear array the stress is transferred to a single adjacent asperity and for a two dimensional array to three adjacent asperities using a renormalization group rg method we investigate the properties of a scale invariant hierarchical model for the stochastic growth of fault breaks through induced failure by stress transfer an extrapolation to arbitrarily large scales shows the existence of a critical applied stress at which the solutions bifurcate at stresses less than the critical stress virtually no asperities fail on a large scale and the fault is locked above the critical stress asperity failure cascades away from the nucleus of failure we interpret this catastrophic failure as an earthquake and it corresponds to the transition from stick to slip behavior on the fault thus the stick slip behavior of most faults can be attributed to the distribution of asperities on the fault we propose our stochastic mechanism as an alternative to the traditional hypotheses for the stick slip behavior of faults a major advantage of our approach is the inclusion of scale invariance thus the observed frequency magnitude relation for seismicity is a natural consequence of our basic hypothesis

aseismic slip in earthquake nucleation and self similarity evidence from parkfield california aseismic slip microearthquakes and moderate earthquakes all take place along the san andreas fault at parkfield california in this letter we discuss the relationship of these slip mechanisms by establishing and modelling the local microearthquake size frequency distribution by examining the effect of background noise on earthquake event detection we show that the distribution is complete for m 0 3 unlike the gutenberg richter law the distribution begins with a relatively small number of very small events further the scaling relation of the distribution changes continuously with event size noting that many parkfield aseismic slip or creep events have moments equivalent to the smaller microearthquakes we show that the nucleation of microearthquakes by this type of slip can account for the size frequency distribution such a model does not require a lower limit to either earthquake or creep event size rather it suggests that at parkfield a transition from creep dominated slip to earthquake dominated slip takes place in the range of moments equivalent to magnitudes close to m 0 9 this is well above the m 0 3 detection limit of the seismic network but right at the limit of current near surface strain instruments

a physical model predicting instability of rock slopes with locked segments along a potential slip surface abstract better understanding the evolutionary mechanism of landslides is very important to predict their occurrence based on firm scientific grounds the stability of a rock slope is often dominated by one or more locked segments along a potential slip surface with a large bearing capacity to resist instability we propose three preliminary categories for locked segments and develop a physical model for predicting the instability of rock slopes with locked segments by coupling a one dimensional renormalization group model with a strain softening constitutive model based on the weibull distribution we found that the ratio of the strain at the peak strength point of a locked segment to the strain at its volume dilation point is exclusively dependent on the weibull shape parameter m and is approximately constant at 1 48 the accelerating displacement of the slope can be observed from the volume dilation point of the locked segment due to unstable fracture propagation the physical model for slopes with multiple locked segments is only related to the displacement corresponding to the volume dilation point of the first locked segment and the number of locked segments applying this model to two typical cases the yanchihe rockslide in china and the wedge rockslide in libby dam usa the results are in agreement with field records this work will help to better understand the failure mechanism of slopes with locked segments and may provide guidelines for disaster mitigation and prevention

study of paleoweathering on the spanish hercynian basement montes de toledo central spain summary the hercynian basement of the iberian peninsula consists of a series of late hercynian blocks that were unleveled by the alpine orogeny the montes de toledo range is found in one of the elevated blocks of the central zone and shows ancient alterations affecting different rocks which are fossilized by sediments of different ages two of these weathering profiles under the plio pleistocene sediments of rana formations are studied one is developed on granodiorite with some intercalated metamorphic rocks and the other on a slaty series in both profiles smectite is formed in a first weathering process a second weathering process yielding kaolinite and affecting rana sediments is superimposed on older one both processes seem to be widely spread in the western part of the iberian peninsula

strong motion seismology strong motion seismology is concerned with earthquake ground motion in the amplitude range that poses the threat of human injury or property damage because the occurrence of strong motion cannot be predicted in advance and because the time between significant events at any one place may range from tens to thousands of years strong motion data is recorded on triggered instruments that typically must be maintained in readiness for years between periods of significant recording as a consequence the strong motion data set is sparse because of the engineering need for estimates of future ground motion the scope of the field of strong motion seismology encompasses seismic source theory and any other aspect of seismology that can provide insights helpful in making the best possible estimates given the limited data this relationship with the rest of seismology is a reciprocal one in that strong motion data gives perhaps the best information available on earthquake source processes

introduction to special section on physical processes in geodynamics on may 16 and 17 1992 a meeting was held at cornell university as part of activities to honor donald l turcotte on the occasion of his 60th birthday which actually occurred on april 22 1992 the papers in the following special section are a result of that meeting which included invited presentations and posters representing the diverse areas of geology and geophysics to which donald turcotte has contributed three of the papers deal with aspects of mantle convection a c fowler addresses the problem of initiation of subduction by extending boundary layer theory to a viscoplastic rheology turcotte and oxburgh 1967 pioneered such studies by showing how boundary layer theory could be used to describe the dependence of geophysical observables such as heat flux on distance from a midocean ridge or age of the oceanic crust d w sparks et al use a model of three dimensional convection beneath a segmented ridge to explore how buoyancy effects and melt production beneath a spreading center influence ridge parallel variations in crustal thickness and gravity magma migration and the dynamics of midocean ridges have been major focuses of donald turcotte s research in papers dating back to 1978 e g turcotte and ahern 1978 ahern and turcotte 1979 turcotte 1982a kenyon and turcotte 1987 g a glatzmaier and g schubert calculate models of three dimensional two layer mantle convection in a spherical shell and compare with whole layer spherical shell three dimensional convection models these models represent the end member states of a spectrum of possible modes of mantle convection turcotte and oxburgh 1972 oxburgh and turcotte 1978 turcotte 1979a silver et al 1988

earthquake rupture as a critical point consequences for telluric precursors abstract earthquakes are related to rupture phenomena in complex statistical systems of cracks we first review some available information suggesting that rupture in earthquakes is a critical point the consequences of this hypothesis on several phenomena are then discussed in particular we focus our attention on a simple theory of electroseismic activity based on mechano electrical transduction effects such as the piezoelectric or the pressure induced polarization effect the neighbourhood of the rupture threshold is characterized by a specific response which could correspond to telluric wave activity observed as precursors of earthquakes

intensive kaolinization during a lateritic weathering event in south west spain mineralogical and geochemical inferences from a relict paleosol abstract this study documents the mineralogical and geochemical record of a lateritic weathering event during the pliocene in south west spain the paleoweathering profile derived from arkosic sands and comprises a white sandy clayey saprolite a red mottled clay zone overlain by a thick soft layer and a ferruginous pisolitic hardcap partially dismantled by erosive processes kaolinite quartz and degraded k feldspars are the major minerals forming the saprolite along with al goethite mottled zone as well as gibbsite and boehmite soft layer while the pisolitic duricrust is essentially composed of quartz grains embedded in a matrix of fe oxy hydroxides hematite goethite and or maghemite besides quartz the phases most resistant to alteration were a variety of heavy minerals mostly titanium oxides that are present as minor impurities in the residual kaolin deposit the dominant weathering process of kaolinization is geochemically characterized by striking losses of na k ca mg and large ion lithophile elements rb sr cs ba and u because of the almost entirely breakdown of primary minerals mainly feldspars and 2 1 phyllosilicates the ti normalized distribution patterns of trace elements also reveals remobilization and redistribution processes within the profile involving high field strength elements classically regarded as immobile like zr and hf iron showed a contrasted behaviour with depletion in the saprolite zone and strong accumulation in the pisolitic duricrust various transition trace metals cr v sc th nb and ta remained relatively immobile during the weathering and were residually concentrated in the duricrust linked to the fe oxy hydroxides the geochemical and mineralogical evolution of the paleosol studied is consistent with a laterization process evolved under humid subtropical conditions and driven by morphodynamic and hydrodynamic factors gently sloping coastal area with fluctuating water table and rapid water percolation favourable for the development of a deeply kaolinized paleosurface

omori s power law aftershock sequences of microfracturing in rock fracture experiment a time series of acoustic emissions ae in basalt was measured under constant uniaxial compression some bursts of ae events considered to be the main shock and aftershock sequences were observed two models describing the aftershock sequences the exponential decay model n t k exp pt and the omori s power law model n t k c t p where n t denotes the occurrence rate of aftershocks at time t were examined with the progress of the fracturing process the bursts changed from the exponential decay type to omori s power law type and the p value of omori s power law aftershock sequences decreased these results indicate that microfracturing gains a longer tail with the evolution of the fracture process the reproduction of omori s power law aftershock sequences of ae events suggests that the self similarity of rock fracturing holds good over a range from microfracturing to large earthquakes

geochemical constraints on magma sources and mixing processes in easter microplate morb se pacific a case study of plume ridge interaction the easter microplate is bounded in the east and west by two large overlapping spreading centres called the east and west rift respectively the east rift is located close to the easter hotspot the site of young intraplate volcanism above a mantle plume easter hotspot material creates a geochemical anomaly on the east rift spreading axis of the microplate and mainly northward directed material flow occurs beneath the propagating east rift the incompatible element depleted mantle of the easter microplate consists of two different sources one of which mixes with enriched easter hotspot material forming the east rift mid ocean ridge basalt morb the other depleted mantle source is present beneath the west rift and mixes with an enriched endmember apparently distinct from the easter hotspot source while the easter hotspot material leads to a bathymetric anomaly on the east rift no increased degree of melting is observed at the point of maximum inflow of enriched plume material implying low excess temperatures 50 c of the mantle the mixing processes between the easter hotspot and morb material probably take place in the partially molten asthenosphere during the horizontal flow of the plume material melting above the plume and at the spreading axes in the easter microplate region occurs over a range of pressures but there is no sign of melts from enriched garnet pyroxenite

effect of lateral migration of melt on chemical compositions implications for the local variations of mid ocean ridge basalts the decompressional melting process involving dynamically induced migration of melt in the residual country rock is analyzed to formulate the effects of melt migration on the chemical compositions of mid ocean ridge basalt morb it is rigorously proved that if the relative motion between melt and solid is unidirectional and steady the composition of the melt is the same as that expected from the batch melting because it is determined by equations that are separable from those concerning the relative melt motion the present proof is more general than the previous treatments and is applicable to any system consisting of arbitrary numbers of phases and components the effect of lateral melt motion on the concentration of a minor component is formulated more specifically using two parameters one of the parameters is the lateral gradient of melt flux that represents degree of convergence or divergence of melt in the flow the other parameter that specifies the gradient of the chemical composition is introduced to evaluate the so called chromatographic effect that separates the minor component migration paths in the flow by their partition coefficients the parameterization gives a good tool to predict the flow field from the known chemical variations it is shown that some local variations of morb compositions observed in individual mid ocean ridges can be modeled as a result of lateral melt migration convergent in some places and divergent in others

a geodetic sign of the critical point of stress strain state at a plate boundary i found a curious oscillating behavior in secular variations of relative ground level in the tokai district central japan the period of the oscillation is becoming shorter acceleratedly with time which thereby predicts the existence of a critical point in near future the data variations can successfully be expressed by the general equation describing the near critical point behavior based on the discrete scale invariance theory the critical point may be interpreted as the occurrence of the maximum sized fracture i e the biggest earthquake in a given tectonic environment the time predicted is 2004 7 1 7 year

new quantitative displacement criteria for slope deformation process from the onset of the accelerating creep to brittle rupture and final failure abstract two quantitative displacement criteria for slope deformation were deduced through the combination of a one dimensional renormalization group model and the strain softening constitutive model of geological materials the criteria can be used to understand the mechanical process from the onset of the accelerating creep on a slope through brittle rupture to the final failure and landslides the study showed that according to the first criterion the displacement ratio between the brittle rupture and the onset of the accelerating creep is approximately 1 48 which can be used to predict the brittle rupture of a slope with continuous progressive deformation the second displacement criterion shows that the displacement ratio between the final failure and the onset of the accelerating creep is approximately 2 59 which can be used to predict the occurrence of the ultimate disaster thus the critical displacement prior to the failure of the slope can be predicted using a time series of monitoring displacement data the methodology proposed in this study was validated using data from two well known landslides the vajont landslide in italy and the xintan landslide in china the results verify the applicability of this method

search for direct empirical spatial correlation signatures of the critical triggering earthquake model summary we propose a new test of the critical earthquake model based on the hypothesis that precursory earthquakes are actors that create fluctuations in the stress field which exhibit an increasing correlation length as the critical large event becomes imminent our approach constitutes an attempt to build a more physically based time dependent indicator cumulative scalar stress function in the spirit of but improving on the cumulative benioff strain used in previous works documenting the phenomenon of accelerating seismicity using a simplified scalar space and time dependent viscoelastic green s function in a two layer model of the earth s lithosphere we compute spatiotemporal pseudo stress fluctuations induced by a series of events before four of the largest recent shocks in southern california through an appropriate spatial wavelet transform we then estimate the contribution of each event in the series to the correlation properties of the simplified pseudo stress field around the location of the mainshock at different scales this allows us to define a cumulative scalar pseudo stress function which reveals neither an acceleration of stress storage at the epicentre of the mainshock nor an increase of the spatial stress stress correlation length similar to those observed previously for the cumulative benioff strain the earthquakes we studied are thus either simple witnesses of a large scale tectonic organization or are simply unrelated and or the green s function describing interactions between earthquakes has a significantly longer range than predicted for standard viscoelastic media used here