magnetic susceptibility variations in carbonates of the la vid group cantabrian zone nw spain related to burial diagenesis abstract the carbonates of the lower devonian la vid group in the cantabrian zone nw spain reveal distinct variations in low field magnetic susceptibility ms from base to top there is good correlation between ms variations and bulk fe content a predominance of paramagnetic minerals fe carbonate cements pyrite fe chlorite mainly responsible for these ms variations is evidenced by optical methods temperature dependent ms measurements and high field magnetisation behaviour these minerals are members of the diagenetic mineral assemblage formed during migration of a reducing fe bearing fluid we interpret the variation in ms to reflect two stages of fe bearing mineral precipitation with an earlier fe carbonate and a later fe chlorite crystallisation the latter restricted to interbedded carbonates and shales furthermore porosity has an additional influence on the ms signature with high values in coarse grained sandstones and carbonates and lower values in fine grained dolostones and limestones this study highlights the influence of diagenetic mineral formation on ms variations in carbonate bearing successions

the earthquake prediction experiment at parkfield california since 1985 a focused earthquake prediction experiment has been in progress along the san andreas fault near the town of parkfield in central california parkfield has experienced six moderate earthquakes since 1857 at average intervals of 22 years the most recent a magnitude 6 event in 1966 the probability of another moderate earthquake soon appears high but studies assigning it a 95 chance of occurring before 1993 now appear to have been over simplified the identification of a parkfield fault segment was initially based on geometric features in the surface trace of the san andreas fault but more recent microearthquake studies have demonstrated that those features do not extend to seismogenic depths on the other hand geodetic measurements are consistent with the existence of a locked patch on the fault beneath parkfield that has presently accumulated a slip deficit equal to the slip in the 1966 earthquake a magnitude 4 7 earthquake in october 1992 brought the parkfield experiment to its highest level of alert with a 72 hour public warning that there was a 37 chance of a magnitude 6 event however this warning proved to be a false alarm most data collected at parkfield indicate that strain is accumulating at a constant rate on this part of the san andreas fault but some interesting departures from this behavior have been recorded here we outline the scientific arguments bearing on when the next parkfield earthquake is likely to occur and summarize geophysical observations to date

statistical physics seismogenesis and seismic hazard the scaling properties of earthquake populations show remarkable similarities to those observed at or near the critical point of other composite systems in statistical physics this has led to the development of a variety of different physical models of seismogenesis as a critical phenomenon involving locally nonlinear dynamics with simplified rheologies exhibiting instability or avalanche type behavior in a material composed of a large number of discrete elements in particular it has been suggested that earthquakes are an example of a self organized critical phenomenon analogous to a sandpile that spontaneously evolves to a critical angle of repose in response to the steady supply of new grains at the summit in this stationary state of marginal stability the distribution of avalanche energies is a power law equivalent to the gutenberg richter frequency magnitude law and the behavior is relatively insensitive to the details of the dynamics here we review the results of some of the composite physical models that have been developed to simulate seismogenesis on different scales during 1 dynamic slip on a preexisting fault 2 fault growth and 3 fault nucleation the individual physical models share some generic features such as a dynamic energy flux applied by tectonic loading at a constant strain rate strong local interactions and fluctuations generated either dynamically or by fixed material heterogeneity but they differ significantly in the details of the assumed dynamics and in the methods of numerical solution however all exhibit critical or near critical behavior with behavior quantitatively consistent with many of the observed fractal or multifractal scaling laws of brittle faulting and earthquakes including the gutenberg richter law some of the results are sensitive to the details of the dynamics and hence are not strict examples of self organized criticality nevertheless the results of these different physical models share some generic statistical properties similar to the universal behavior seen in a wide variety of critical phenomena with significant implications for practical problems in probabilistic seismic hazard evaluation in particular the notion of self organized criticality or near criticality gives a scientific rationale for the a priori assumption of stationarity used as a first step in the prediction of the future level of hazard the gutenberg richter law a power law in energy or seismic moment is found to apply only within a finite scale range both in model and natural seismicity accordingly the frequency magnitude distribution can be generalized to a gamma distribution in energy or seismic moment a power law with an exponential tail this allows extrapolations of the frequency magnitude distribution and the maximum credible magnitude to be constrained by observed seismic or tectonic moment release rates the answers to other questions raised are less clear for example the effect of the a priori assumption of a poisson process in a system with strong local interactions and the impact of zoning a potentially multifractal distribution of epicentres with smooth polygons the results of some models show premonitory patterns of seismicity which could in principle be used as mainshock precursors however there remains no consensus on both theoretical and practical grounds on the possibility or otherwise of reliable intermediate term earthquake prediction

magnetostratigraphy susceptibility of the přidolian lochkovian silurian devonian gssp klonk czech republic and a coeval sequence in anti atlas morocco abstract the magnetosusceptibility event and cyclostratigraphy msec record for the p idolian lochkovian silurian devonian global boundary stratotype section and point gssp klonk prague basin czech republic is described and used to establish a magnetostratigraphy susceptibility profile for the gssp gssp msec data are summarized into three magnetozones msz the tma msz late p idolian with 13 msszs mssz the klonk msz latest p idolian and earliest lochkovian with 17 msszs and the voskop msz early lochkovian with 7 msszs the base of klonk mssz 2 is coincident with the base of lochkovian and the devonian the proposed magnetostratotype for the p idolian lochkovian boundary is supported by ms data from a nearby core through the gssp sequence and into the upper ludlow three additional mszs are recognized for the portion of the core sequence older than the gssp boundary sequence the extension of the mszs and msszs away from the proposed magnetostratotype is tested by comparison with a lochkovian sequence in the western sahara of southeastern morocco mszs are the result of global sea level fluctuations that alter base level and the pattern of erosion and influx of detrital paramagnetic mineral components into the marine environment large scale transgressive and regressive patterns interpreted from the msec data establish that the silurian devonian boundary in the barrandian region falls between a short lived transgressive pulse in the latest p idolian and an equally short lived regressive pulse in the earliest lochkovian msszs identified in the gssp and core sequences are the result of variation in climate cycles and the resulting periodicity can explained by either the 38 9 ka silurian and devonian equivalent of the modern 54 ka obliquity cycle or the eccentricity cycle of 106 ka periodicity use of the obliquity periodicity gives a duration for the barrandian lochkovian of 4 46 ma which agrees with the most recent geochronometric estimate of 4 5 ma for the lochkovian use of the eccentricity periodicity gives a duration for the barrandian lochkovian of 12 16 ma which agrees with the previous geochronometric estimates of 12 2 and 12 5 ma for the lochkovian in any case the cyclic nature of the msec data established by the msszs can be explained by variations in the rate of supply of weathered terrigenous paramagnetic grains to the marine system these variations in supply occurred due to climate changes resulting from the either the obliquity or eccentricity of the earth s orbit knowledge of the periodicity of lochkovian cycles in the barrandian area allows estimation of the rates of sediment accumulation the duration of fossil ranges and the rates of evolution depending on the choice of obliquity or eccentricity to explain the cyclicity in the barrandian lochkovian the estimated rate of sediment accumulation in the gssp outcrop averaged either 51 or 140 ka m the range of the graptoloid monograptus uniformis angustidens wholly contained within the lochkovian sequence at the gssp is also estimated at either 51 or 140 ka

space time distribution patterns of destructive earthquakes in the inner belt of central japan part 2 moment release rates and earthquake prediction the inner belt of central japan between the itoigawa shizuoka tectonic line istl and tsurugawan isewan tectonic line titl can be divided into four blocks by boundaries linking major nw se trending left lateral active faults historical earthquakes of magnitude 6 4 or greater which caused significant damage mainly occurred along the four block boundaries and have been recorded or documented since 715 a d the average rates of seismic moments released along the block boundaries in the inner belt of central japan have been estimated since no destructive earthquakes were recorded or documented between 888 a d and 1585 a d this period is regarded as a time of seismic quiescence the average rates re of the seismic moments released by destructive earthquakes since 1586 a d the present active period were estimated from the amount of the released moment inferred from the magnitude of the earthquakes average rates rs of seismic moments are also calculated from the average rates of quaternary displacements along the major active faults constituting the block boundaries the average rates re during the active period were found to be0 031 1026dyne cm yr for the istl those for the other three boundaries ranged from 0 087 to0 095 1026dyne cm yr the average release rate re through the quiet and active periods since 888 a d ranged from 0 023 to0 031 1026dyne yr with exception of0 008 1026dyne cm yr for the istl these values were found to be in good agreement with the estimation ofs this suggests that destructive earthquakes are a manifestation of the movement of the block boundary thus it is important to assess the block boundary movements when designing large earthquake resistant structures regions having no incidences of earthquakes seismic gaps during the present active period since 1586 a d have already been detected by us in previous work destructive earthquakes are predicted to occur in these seismic gaps the dates of the future earthquakes are then estimated assuming that the moment accumulated since the last earthquake exceeds the moment inferred from the possible magnitude in the region of the seismic gap future earthquakes are predicted to occur between 2007 and 2076 a d

earthquake cycles in a model of interacting fault patches complex behavior at transition from seismic to aseismic slip numerical simulations of complex earthquake cycles are conducted using a model with two patches asperities on a fault where friction obeys a rate and state dependent law the patches are represented by regions of steady state velocity weakening friction and are in contact with each other or are separated by a region of steady state velocity strengthening friction simulated earthquake cycles are examined by changing the characteristic slip distance of friction in one patch while that in the other patch is maintained at a constant as the characteristic slip distance in a patch increases the slip at the patch tends to be aseismic and rupture tends to be delayed as compared to rupture at the other patch or arrested due to an increase in fracture energy as a result the slip pattern changes in a complicated manner with the change of the parameter a complex multiperiodic or aperiodic slip pattern occurs in the simulation and this pattern tends to occur near the boundaries between regions of different slip behavior characteristics such as the boundary between seismic and aseismic slip in the patch with a larger characteristic slip distance iteration maps of the recurrence intervals of simulated earthquakes for an aperiodic sequence are sometimes expressed by simple curves suggesting that the simulated earthquake cycles exhibit deterministic chaos in the two patch models of the present study an aperiodic slip pattern is observed for narrower parameter ranges than in a model of a two degree of freedom spring block system which is usually regarded as a simplified model of a fault with two patches online material simulated histories of moment release rate and recurrence interval of simulated slip events in the two patches and seismic coupling coefficients

populations of faults and fault displacements and their effects on estimates of fault related regional extension abstract measured populations of fault displacements derived from regional seismic oilfield seismic coalmine plans and outcrop data show a power law distribution with exponents s of 0 45 to 0 95 for singleline samples across an array of faults the more negative values indicate relatively larger numbers of smaller faults an expression for a population of active faults derived from the gutenberg richter magnitude frequency relation for earthquakes is log n a b d log d where d maximum displacement of a fault n number of faults of maximum displacement d or greater and b d 1 0 and has the same value as b for the corresponding earthquake population populations of dead faults existing at the end of a tectonic episode have been numerically derived using a fault growth model and satisfy the relation log n a e log d where e has a value between 1 6 and 2 0 numerically derived populations of fault displacements in a dead fault population have slopes of s where s e 1 the contribution of an individual fault to the regional strain varies with the lifetime seismic moment of the fault and is proportional to d 2 estimation of fault related extension by summing heaves on faults of a limited size range is valid only if the measured size range of faults accommodates most of the extension correction can be made if the s value of the fault displacement population is known

temporally unstable recurrence of earthquakes due to breaks in fractal scaling observed sequences of large earthquakes are not consistent in either recurrence time or energy release long term prediction has been impossible even in areas such as parkfield with well defined recurrence intervals the seismic gap hypothesis which predicts characteristic earthquakes in areas of the circum pacific belt that have not produced recent great earthquakes has also failed to predict the observed clustering of high energy events models in which fractal scaling is broken at high magnitude predict that characteristic events and recurrence behavior will be unstable in time the central predictions of these models are supported by recent observations at landers and big bear in california

control of asperities size and spacing on seismic behavior of subduction megathrusts the majority of the largest subduction megathrust earthquakes share the common characteristic of rupturing more than one asperity along strike of the margin understanding the factors that control coseismic failure of multiple asperities and thus maximum magnitude is central for seismic hazard assessment to investigate the role of asperities size and spacing on maximum magnitude seismicity rate and percentage of synchronized ruptures we use analog models simulating along strike rupture behavior of megathrust earthquakes we found negative correlations between the barrier to asperity length ratio db da and maximum magnitude and seismicity rate db da also controls the process of asperities synchronization along the megathrust a permanent barrier behavior is observed for db da 0 5 comparing our experimental results to the nankai trough historical seismicity we propose that the distribution of megathrust frictional heterogeneities likely explains the diversity of earthquakes which occurred there

simple spring mass model simulation of earthquake cycle along the nankai trough in southwest japan along the nankai trough in southwest japan due to the subduction of the philippine sea plate great earthquakes have occurred repeatedly the rupture zone is divided into five segments historical documents show the characteristic features of the past several earthquake cycles such as almost simultaneous rupture occurrence in segments in spite of different convergence rates the recurrence time of 90 to 150 years the existence of segment pairing in earthquake ruptures and the different coseismic slip behaviors in respective segments

magnetosusceptibility event and cyclostratigraphy method applied to marine rocks detrital input versus carbonate productivity magnetic susceptibility data from marine rocks can be used for global correlation due to synchronous variations in global erosion we show here that the magnetic susceptibility signature found in two forms resides mainly in paramagnetic and other detrital constituents in most marine rocks the first form is a short term low magnitude high frequency cyclic climate signature that is often useful for regional correlation the second form is a longer term higher magnitude low frequency signature resulting from transgressive and regressive events that can be used for global correlation fluctuations in detrital input due to eustatic based erosion are the primary cause of events these fluctuations are driven by large scale processes such as global orogenic cycles however variations in carbonate productivity cannot be ruled out when explaining the low magnitude climate driven cyclicity also observed in magnetic susceptibility data sets

long term dynamics of a fault with two asperities of different strengths summary a fault made of two segments or asperities having different strengths and subject to a constant strain rate is considered the fault is modelled by a discrete dynamical system made of two blockscoupledbyaspringandpulledatconstantvelocityonaroughplane wegiveacomplete analytical solution for the evolution of the system the long term behaviour of the fault is studied by calculating the orbits of the system in the phase space the dynamics of the system has four different modes and produces a variety of behaviours the asperities may slip one at a time originating a medium size earthquake or simultaneously originating a large earthquake in the latter case the focus may be at one asperity or at the other in some cases the weaker asperity may slip twice both before and after the failure of the stronger asperity the time pattern of the seismic events generated by the fault is controlled by the stress distribution on the asperities and may include many different behaviours we devise suitable correspondence rules allowing application of the discrete model to real fault systems as an example the model is applied to the 1964 great alaska earthquake which was originated by the failure of two asperities and a possible evolution of this fault system is discussed

a sequence of destructive earthquakes and the coupling of fault systems in central japan abstract in the western part of central japan large successive inland earthquakes have occurred causing serious damage the 1891 m 8 0 nobi earthquake was followed by the 1909 m 6 8 anegawa the 1945 m 6 8 mikawa and the 1948 m 7 1 fukui earthquakes the two major fault systems termed the tsurugawan isewan tectonic line titl and the fukui neodani block boundary line fnbb have been identified as lines linking nw se oriented active faults in the study area an examination of the vertical displacement of ground surfaces indicates that tilting of the central part of the fnbb caused by the nobi earthquake begins around the sekigahara fault on the central part of the titl ruptures and vertical displacements can also be found along the ogaki kisozaki fault close to the titl therefore it was concluded that the influence of the nobi earthquake extended to a part of the titl eighteen years after the nobi earthquake the anegawa earthquake occurred along the sekigahara fault these features and the earthquake sequence can be explained by a block rotation model with strike slip faulting the nobi earthquake created en echelon ruptures over an 80 km long line with a left lateral slip of up to 8 m along the neodani fault according to the model this left lateral slip must be accompanied by a clockwise rotation of the block between the fnbb and titl the block rotation should in turn induce a left lateral slip on the titl since the titl exhibits a sharp bend along the sekigahara fault a transtensional region should appear along the fault owing to the left lateral slip of the titl the expected transtensional region is consistent with areas damaged by the anegawa earthquake suggesting that the earthquake occurred in the transtensional regime about 40 years after the anegawa earthquake the mikawa and fukui earthquakes were generated on the southern and northern ends of the fnbb respectively this implies that the fault movement of the nobi and anegawa earthquakes created a concentration of stress at both ends of the fnbb resulting in the mikawa and fukui earthquakes approximately two years prior to the nobi earthquake seismic activity was initiated over a wide zone along the fnbb also notable earthquakes aligned along the titl were observed ten years prior to the anegawa earthquake the onset of seismicity along a fault system can be used in predicting destructive inland earthquakes which eventually occur along the fault

dynamics of a zone of four parallel faults a deterministic model we consider a two dimensional model for quasi static evolution of four parallel faults the model is based on the physics of continuum with slips along the faults long range interactions a distribution of barriers and asperities a velocity dependent friction healing and reactivation of cohesive forces and a mutual causality between faulting and tectonic forces all taken into account both the long term time series of seismic activity and details of seismic and aseismic crustal deformations during each phase of the earthquake cycle are produced by the model it is shown that the system whose evolution is described by a set of deterministic differential equations may exhibit periodic or quite irregular despite its assumed symmetry behavior depending on model parameters

evidence for chaotic fault interactions in the seismicity of the san andreas fault and nankai trough interactions between fault segments are one of the main sources of complexity in the seismicity of active tectonic regions such interactions are likely to influence the spatial and temporal patterns of earthquakes here we examine the dynamical behaviour introduced by fault interactions using a simple spring loaded slider block model with velocity weakening friction the model consists of two slider blocks coupled to each other and to a constant velocity driver by elastic springs for an asymmetric system in which the frictional forces on the two blocks are not equal the solutions exhibit chaotic behaviour the system s behaviour over a range of parameter values seems to be generally analogous to that of weakly coupled segments of an active fault we see similarities between our model simulations and observed patterns of seismicity on the south central san andreas fault in california and in the nankai trough along the coast of southwestern japan

cross basin variations in magnetic susceptibility influenced by changing sea level paleogeography and paleoclimate upper devonian western canada sedimentary basin abstract upper devonian rocks in western canada were deposited as carbonate platform and surrounding slope and basinal rocks during a second order sea level cycle characterized by long term climatic warming that ended with cooling associated with the frasnian famennian mass extinction event in this contribution we assess the hypothesis that high resolution magnetic susceptibility ms data records cross basin variations that are intimately tied to sea level and associated climatic change the depositional environment and the paleogeographic location of siliciclastic sediment sources four main trends are apparent in the ms data 1 the magnitude of the ms signature increases from west to east across western canada 2 platform facies generally have low ms signatures compared with off platform facies 3 the overall ms signature increases and then decreases throughout the stratigraphic profile largely in response to changes in depositional setting i e item 2 4 ms is generally high during third and fourth order sea level lowstand and early transgression and lower during late transgression and highstand during the late middle givetian to early late frasnian devonian siliciclastic sediments silt and fine sand size sourced from the west alberta arch and peace river arch contributed to relatively high ms signatures in facies deposited proximal to these source areas other important detrital sediment sources were the ellesmerian orogenic belt in northern canada and the laurussian continental landmass to the east these latter sources supplied fine grained sediments that were dispersed basinwide and resulted in a nearly order of magnitude increase in ms values to the east this trend and fine grain size implies that some detrital sediment was delivered from the east as eolian dust from the old red continent by the early frasnian the west alberta arch was submerged and by middle to late frasnian time the peace river arch was largely covered during the late middle frasnian a pronounced rise in ms signatures can be tied directly to deposition of the clay and locally silt rich mount hawk formation during the late middle to late frasnian carbonate ramp facies prograded from east to west resulting in seaward migration of the shoreline and increased siliciclastic input to the ramp slope that influenced the pronounced increase in ms signatures to the east by the late frasnian cross basin ms profiles record uniformly low susceptibilities indicating that high ms siliciclastic detritus was either bypassed seaward was swamped by carbonate input or was dominated by diamagnetic quartz individual ms events can be accurately correlated across much of the basin at a resolution that is higher than single conodont zones despite the local influences on variability of the signature variations in the ms signature can thus be explained partly by depositional environment platforms with low ms basins with higher ms and partly by third and fourth order sea level and associated climatic changes fourth order changes in sea level are routinely interpreted to result from variations in paleoclimate in the milankovitch band and recent work indicates that third order sea level changes may be linked to longer term modulation of milankovitch band orbital variations the increase in ms during prolonged frasnian warming thus appears to be directly linked to paleoclimatic change and comparison of the ms signature with more direct measures like oxygen isotopes would serve as a test of its utility as a paleoclimate proxy

fractals chaos self organized criticality and tectonics some geological structures have simple geometrical forms and can be analysed using deterministic equations examples include alluvial fans and many sedimentary basins but most geological structures are complex and appear to defy mathematical analyses yet in the complexity there is an order complex geological structures generally obey fractal statistics examples include topography distributions of earthquakes and faults and mineral deposits an unresolved question is whether the fractal order is simply the result of scale invariance or the result of governing equations that yield deterministic chaos in order to try to answer this question a variety of slider block models have been considered the stick slip behaviour of slider block models is a simple analogy to earthquakes a pair of slider blocks has been shown to behave chaotically models that use many slider blocks exhibit self organized criticality and generate fractal statistics similar to the statistics of regional seismicity

introduction to special section paleoseismology a proverb of confucius states study the past if you would divine the future if we could learn about the past history of earthquakes on a specific fault then we could serve society well by better forecasting the future earthquake behavior of that fault for most of the world the period of historical records is short about 200 years in california and less than that in new zealand oregon and other parts of the world and even where the historical record is thousands of years long such as in north central china or the eastern mediterranean region it is commonly difficult to correlate a major historical earthquake with a specific active fault even if this correlation could be made without ambiguity the recurrence intervals for many faults are longer than even a historical record of several thousand years for these reasons the history of large earthquakes on faults must for the most part be learned from the geological record

recurrence models and parkfield california earthquakes main shocks of the earthquake sequences that occurred on the parkfield section of the san andreas fault in central california in 1922 1934 and 1966 are characterized by southeast rupture expansion over the same 20 to 30 km long section of the fault whereas the seismic moments for the 1922 and 1934 events are identical to within a precision of 10 the seismic moment for 1966 is 20 greater than for the earlier events to within a precision of 20 the parkfield area seismicity in general seems well described by a recurring moderate size characteristic earthquake repeating the same epicenter magnitude seismic moment rupture area and southeast direction of rupture expansion an unexplained 10 year advance of the 1934 event is the only discrepancy in the hypothesis that the parkfield earthquakes in 1857 1881 1901 1922 1934 and 1966 represent a strictly periodic process assuming the strictly periodic model and the absence since 1966 of the perturbations hypothesized for the 1922 to 1934 period the next characteristic parkfield earthquake should occur between 1983 and 1993

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

periodic chaotic and doubled earthquake recurrence intervals on the deep san andreas fault earthquake recurrence histories may provide clues to the timing of future events but long intervals between large events obscure full recurrence variability in contrast small earthquakes occur frequently and recurrence intervals are quantifiable on a much shorter time scale in this work i examine an 8 5 year sequence of more than 900 recurring low frequency earthquake bursts composing tremor beneath the san andreas fault near parkfield california these events exhibit tightly clustered recurrence intervals that at times oscillate between 3 and 6 days but the patterns sometimes change abruptly although the environments of large and low frequency earthquakes are different these observations suggest that similar complexity might underlie sequences of large earthquakes

stratigraphic evidence for seven meters of dextral slip on the san andreas fault during the 1857 earthquake in the carrizo plain the smallest geomorphic offsets along a 35 km section of the san andreas fault in the carrizo plain vary from 7 to 10 m our three dimensional excavation of alluvial deposits a few km southeast of wallace creek confirms that at least 6 6 to 6 9 m of dextral slip occurred there during the latest large earthquake in 1857 dates on detrital charcoal suggest that the last event prior to the 1857 earthquake occurred before a date within the range a d 1305 to 1623 the 3 m range in smallest offsets along this portion of the fault may reflect either a 3 m variation in slip along the san andreas in 1857 or 2 to 3 m of slip during an event prior to 1857 observations made after the recent landers earthquake are compatible with the hypothesis of large local variations in slip during a single earthquake but do not explain the cause of such variations off fault dextral rotations would be one plausible explanation however paleoseismic data in the carrizo plain are too sparse to allow rejection of the alternative hypothesis that slip in the event prior to 1857 was only 2 to 3 m an amount of slip which would be several times too small to fit a time predictable model

constitutive behavior and stability of frictional sliding of granite an understanding of the frictional sliding on faults that can lead to earthquakes requires a knowledge of both constitutive behavior of the sliding surfaces and its mechanical interaction with the loading system we have determined the constitutive parameters for frictional sliding of initially bare surfaces of westerly granite using a recently developed high pressure rotary shear apparatus that allows long distances of sliding and therefore a greater assurance of attaining steady state behavior from experiments conducted at room temperature and normal stresses of 27 84 mpa several important results have been found 1 a gouge layer 100 to 200 m thick was developed from the initially bare rock surfaces after 18 to 70 mm of sliding 2 the steady state frictional resistance attained after about 10 mm of sliding is proportional to the negative of the logarithm of the sliding velocity 3 abrup changes in the velocity of sliding result in initial changes in the frictional resistance which have the same sign as the velocity change and are followed by a gradual decay to a new steady state value over a characteristic distance of sliding this velocity weakening behavior is essentially identical with that found by several previous workers on the same material at lower normal stress 4 our results are well described by a two state variable constitutive law the values of the constitutive parameters are quite similar to those found previously at low normal stress but the characteristic distance is about an order of magnitude smaller than that found at 10 mpa normal stress with thicker layers of coarser gouge 5 we have approximated our results with a one state variable constitutive law and compared the results with the predictions of existing nonlinear stability analysis in addition we have extended the stability analysis to systems possessing two state variables with such formulations good agreement is found between the experimentally observed and theoretically predicted transitions between stable and unstable sliding these results allow a better understanding of the instabilities that lead to earthquakes

seismicity seismotectonics and seismic hazard of italy abstract a first generation of probabilistic seismic hazard maps of the italian country are presented they are based on seismogenic zoning deriving from a kinematic model of the structural tectonic units and on an earthquake catalogue with the foreshock and aftershock events filtered out the following ground motion parameters have been investigated and mapped using attenuation equations based on strong motion recordings of italian earthquakes peak ground acceleration and velocity arias intensity strong motion duration and the pseudovelocity and pseudoacceleration spectral values at 14 fixed frequencies both for the vertical and the largest horizontal component a poissonian model of earthquake occurrence is assumed as a default and the hazard maps are presented in terms of ground motion values expected to be exceeded at a 10 probability level in 50 years return period 475 years according to the requirement of eurocode 8 for the seismic classification of national territories as well as in terms of exceedance probabilities of selected ground motion values finally as a tentative study the use of hybrid methods implementing both seismogenic zones and structures renewal processes including earthquake forecasting and the influence of site effects as the basis for the planning of earthquake scenarios were explored

space time distribution patterns of destructive earthquakes in the inner belt of central japan activity intervals and locations of earthquakes abstract based on a block structure model of the inner belt of central japan an examination was conducted of the space time distribution patterns of destructiv magnitudes m 6 4 or greater m japan meteorological agency scale the distribution patterns revealed a periodicity in earthquake activit seismic gaps major nw se trending left lateral active faults divide the inner belt of central japan into four blocks 20 80 km wide the occurrenc a d with m 6 4 which have caused significant damage were documented in the inner belt of central japan the epicenters of these earthquakes close to the block boundaries using the relationship between the magnitude of earthquakes which occurred in the japanese islands and the active length of faults that generated them movement is calculated for each historical earthquake space time distributions of earthquakes were obtained from the calculated lengths the latitud of generation when an active period begins a portion or segment of the block boundary creates an earthquake which in turn appears on the ground surf active period ends when the block boundary generates earthquakes over the entire length of the block boundary without overlapping five seismic gaps with fault lengths of 20 km or longer can be found in the inner belt of central japan it is predicted that the gaps will generate ea magnitudes of 7 0 these data are of significance for estimating a regional earthquake risk over central japan in the design of large earthquake resist the time sequences of earthquakes on the block boundaries reveal a similar tendency with alternating active periods with seismic activity and quiet pe activity the inner belt of central japan is now in the last stage of an active period the next active period is predicted to occur around 2500 a d

distinct sea level fluctuations and deposition of a megaclast horizon in the neritic rauchkofel limestone wolayer area carnic alps correlate with the lochkov prag event

application of fracture mechanics to the simulation of seismicity and recurrence of characteristic earthquakes on a fault we present a fault model consisting of a large number of collinear cracks and intervening asperities for the simulation of seismicity and recurrence of large earthquakes on a fault we apply fracture mechanics to the analysis of the interaction of cracks and to the consideration of fracture condition our fault model gives rise to a complex frequency distribution of event sizes even if no externally imposed spatial inhomogeneity is assumed for the distribution of cracks and asperities and a homogeneous statistical distribution is assumed for fracture strengths the frequency distribution of event sizes is found to be bimodal with no intermediate size event in all the calculations for the smaller events the frequency distribution shows a power law behavior whereas the larger size events denote ones that rupture the whole fault statistically the same frequency distributions are obtained for inhomogeneous distributions of crack lengths and fracture strengths the occurrence of events that rupture the whole fault is shown to be periodic when the fault is isolated the magnitudes of these large events generally increase with increasing recurrence period for given fault length and rate of remote loading the events having a longer recurrence period have a shorter fault length for given magnitude and rate of remote loading if there are fault interactions the periodicity in the recurrence of the large events that would be observed for the isolated fault disappears and the recurrence of the large events becomes complex

visual identification and quantification of milankovitch climate cycles in outcrop an example from the upper ordovician kope formation northern kentucky

magnetostratigraphy susceptibility of the frasnian famennian boundary magnetosusceptibility event and cyclostratigraphy msec is used to establish a non polarity based magnetostratigraphy susceptibility mss between the stratotype region for the frasnian famennian f f boundary sequence in the montagne noire of southern france the eastern rheinisches schiefergebirge of germany belgium the eastern anti atlas of morocco and the arbuckle mountains of southern oklahoma usa despite differences of depositional environment the mss is remarkably consistent and can be described in the context of a hierarchy of magnetozones that allow the extension of correlation away from the montagne noire reference section the nature of the controls on the influx of iron into the marine system produces a natural hierarchy of at least seven orders or magnetozones designated msz1 msz2 msz3 msz4 msz5 msz6 and msz7 these are characterized in terms of the magnitude of their duration the mss reference section of choice for the f f boundary is the well known trench c at la serre lsc in the northeastern montagne noire of southern france the f f boundary is located at the lower boundary of magnetozone la serre i 3b at la serre as well as in all other sections studied msz4 and msz5 magnetozones are used to establish intra and inter regional correlation between the reference sequence and the other regions the base of the upper kellwasser event is as variable within the mss zonation as it is within the biostratigraphic zonation as is the position of the lower kellwasser event

an earthquake model with magnitude sensitive dynamics considerations of the dimensionality of earthquake generating mechanisms as assessed by prediction regression analysis show that complete earthquake populations are best described by complex high dimensional dynamics cellular automata which allow individual degrees of freedom to many small areal increments of a fault face reproduce realistic event sequences which follow the gutenberg richter relation simple spring block models with as few as two blocks have been shown however to neatly explain the coupling between adjacent segments of transform faults which has been observed in the stratigraphic record here we propose a hierarchical earthquake model in which there is an explicit change in the generating dynamics with magnitude and which may be appropriate for seismicity on a section of a transform fault which includes more than one active segment in the model a high dimensional cellular automaton is responsible for the production of low energy events and a low dimensional double block model represents the dynamics of events in which an entire fault face slips frequency magnitude distributions of the model seismicity show a change in b value with magnitude which is the result of the change in universality class of the underlying dynamics similar changes in b value related to the finite width of the seismogenic layer have been reported in the literature

high resolution paleoclimatic trends for the holocene identified using magnetic susceptibility data from archaeological excavations in caves abstract a proxy paleoclimatic curve has been produced for the holocene c 9000 3500 bp from magnetic susceptibility ms measurements of sediment samples collected from two dated archaeological excavation trenches in konispol cave albania the resulting ms data provide paleoclimate estimates that are in excellent agreement with independently published paleoclimatic trends for early middle holocene time basically ms variations are attributed to variations in climate controlled pedogenesis and the production of magnetic mineral phases including maghemite outside the cave these soils are then washed blown or tracked into the cave where they accumulate creating the ms changes observed in the samples recovered low ms magnitudes indicate times of cooler drier climate resulting from reduced pedogenesis while warmer wetter times yield higher pedogenetic rates and thus higher ms magnitudes it is clear from the konispol cave results that some caves provide ideal protected environments from which high resolution paleoclimatic records can be extracted composite sections from excavations within a single region can yield a relatively continuous long term climatic proxy that can be routinely correlated to artefacts recovered from these or other protected excavations within the same region

space time correlations between inland earthquakes in central japan and great offshore earthquakes along the nankai trough implication for destructive earthquake prediction abstract based on the tectonic framework of central japan including the surrounding submarine areas the space time relationship between destructive inland earthquakes of magnitudesm 6 4 or greater and great offshore earthquakes along the nankai trough was examined from east to west four tectonic lines are defined as lines linking active faults the itoigawa shizuoka tectonic line istl the tsurugawan isewan tectonic line titl the hanaore kongo fault line hkfl and the arima takatsuki tectonic line attl the titl divides central japan into the chubu and kinki districts and probably extends southward to the nankai trough the chubu district is subdivided into four blocks by boundary lines linking nw se trending active faults having left lateral strike slip in the kinki district n s trending active reverse steep dip faults are dominant in the triangular region north of the median tectonic line between the titl and hkfl forming a basin and range province starting from 1586 a d a seismic space time sequence of high seismic activity in the chubu district in which earthquake occurrence migrates from the eastern to western tectonic lines of central japan was identified the sequence also revealed that inland earthquakes preceded great offshore earthquakes which occurred along the nankai trough it was also found that a destructive earthquake tends to occur on the hkfl within 30 years after the occurrence on the titl and that the western nankai trough generated great earthquakes ofm 7 0 at intervals ranging from 8 to 49 years after the hkfl earthquakes if the eastern nankai trough is coupled with the western nankai trough a forthcoming greater earthquake measuringm 8 5 may be expected since such great earthquakes are always accompanied by large tsunamis much attention should be focussed on possible tsunami disasters along the pacific coast of central japan based on its tectonic structure a tectonic model of central japan is proposed the seismic space time sequence which attempts to explain the cause of the sequential earthquake generation is also discussed

evidence for chaotic behaviour in seismic wave scattering scattering of seismic waves by lithospheric heterogeneities produces seismic coda which typically look random consequently stochastic modelling methods are usually applied to these coda 1 6 here we introduce a technique based on previous work 7 for evaluating the predictability of time series data as an indicator of underlying determinism when analyzed using this method both earthquake and explosive source seismic coda display strong short term predictability which is not consistent with a random generation mechanism

seismicity simulation with a rate and state dependent friction law the dynamic motions and stabilities of a single degree of freedom elastic system controlled by different friction laws are compared the system consists of a sliding block connected to an elastic spring driven at a constant velocity the friction laws are a laboratory inferred friction law called the rate and state dependent friction law proposed by dieterich and ruina and a simple friction law described by dynamic and static frictions we further extend the solution to a one dimensional mass spring model which is an analog of a fault controlled by the rate and state dependent friction law this model predicts non uniform slip and stress drop along the rupture length of a heterogeneous fault this result is very different from some earlier modelings based on the simple friction law and a slip weakening friction law in those earlier modelings the stress and slip functions become smoother with time along the length of the fault rupture owing to the interactions between fault segments during slip because of this smoothing process the number of small events will decrease with time and the universilly observed stationary magnitude frequency relation cannot be explained the interaction between a fault segment and its neighboring segments can be measured when the post slip stress on this segment is compared with the stress on an identical segment represented by a block in this modeling without neighboring segments if the post slip stress of the former is much higher than that of the latter strong interaction exists if the two are close only weak interaction exists the interaction is determined by the relative motion between fault segments and the time duration of interaction our new modeling with the rate and state dependent friction law appears to show no such smoothing effect and provides a physical mechanism for the roughening process in the difference between the fault strength and stress that is necessary to explain the observed stationary magnitude frequency relation the noninstantaneous healing predicted by the rate and state dependent friction law may be repsonsible for the recurring nonuniform slip and stress drop and may be explained by the reduction of interaction among fault segments due to the low frictional strength during the fault stopping the very low friction during slip stopping allows much longer times than does the higher friction due to instantaneous healing for the fault segments to adjust their motions from an upper limit slip velocity to almost rest according to newton s second law a process with fixed masses and constant velocity changes involves low forces and weak interactions if it is accomplished in a long time period and vice versa our modeling also indicates that the existence of strong patches with higher effective stress on a fault is needed for the occurrence of major events the creeping section of a fault such as the one along the san andreas fault in central california on the other hand can be simulated with the rate and state dependent friction law by certain model parameters which however must not include strong patches in this case small earthquakes and aseismic creep relieve the accumulating strain without any large events

a more precise chronology of earthquakes produced by the san andreas fault in southern california improved methods of radiocarbon analysis have enabled us to date more precisely the earthquake ruptures of the san andreas fault that are recorded in the sediments at pallett creek previous dates of these events had 95 confidence errors of 50 100 calendar years new error limits are less than 23 calendar years for all but two of the dated events this greater precision is due to larger sample size longer counting time lower background noise levels more precise conversion of radiocarbon ages to calendric dates and better stratigraphic constraints and statistical techniques the new date ranges with one exception fall within the broader ranges estimated previously but our estimate of the average interval between the latest 10 episodes of faulting is now about 132 years variability about the mean interval is much greater than was suspected previously five of the nine intervals are shorter than a century three of the remaining four intervals are about two to three centuries long despite the wide range of these intervals a pattern in the occurrence of large earthquakes at pallett creek is apparent in the new data the past 10 earthquakes occur in four clusters each of which consists of two or three events earthquakes within the clusters are separated by periods of several decades but the clusters are separated by dormant periods of two to three centuries this pattern may reflect important mechanical aspects of the fault s behavior if this pattern continues into the future the current period of dormancy will probably be greater than two centuries this would mean that the section of the fault represented by the pallett creek site is currently in the middle of one of its longer periods of repose between clusters and sections of the fault farther to the southeast are much more likely to produce the next great earthquake in california the greater precision of dates now available for large earthquakes recorded at the pallett creek site enables speculative correlation of events between paleoseismic sites along the southern half of the san andreas fault a history of great earthquakes with overlapping rupture zones along the mojave section of the fault remains one of the more attractive possibilities

magnetostratigraphy susceptibility of the upper ordovician kope formation northern kentucky abstract as a test of the utility of magnetic susceptibility ms measurements for correlation among lithified marine sequences samples were collected from well studied shale and limestone outcrops of the upper ordovician kope formation northern kentucky the bulk initial low field ms of these samples is compared among two litho and biostratigraphically correlated sections containing the same beds the results of this comparison demonstrated an excellent correlation among equivalent beds thermomagnetic susceptibility analysis supports previous xrd work indicating that illite is primary and is the main paramagnetic mineral responsible for the ms variations observed in this study a composite of ms results for a sequence of 31 named shale limestone couplets is used to build a composite section of kope sequences for the area these ms variations permit division of the various sections into a set of 28 ms cycles within the kope formation covering 50 m of section these cycles suggest a systematic control by climate on the influx of detrital material that formed these sedimentary sequences and support other work indicating kope climate cyclicity

effect of a large outer rise earthquake on seismic cycles of interplate earthquakes a model study a numerical simulation of the sliding process of a plate interface is performed to investigate the effect of stress perturbation due to a large outer rise earthquake on seismic cycles of large interplate earthquakes in a subduction zone a two dimensional model of uniform elastic half space is set up for repeatedly occurring large interplate earthquakes by assuming that the frictional stress on the plate interface obeys a rate and state dependent friction law derived from laboratory experiments an increase in shear stress on a shallow part of the plate interface due to a tensional outer rise earthquake promotes aseismic sliding on the shallower aseismic zone of the plate interface this aseismic sliding advances the occurrence time of the next interplate earthquake on the other hand a compressional outer rise earthquake tends to delay the occurrence time of the next interplate earthquake the magnitude of time advance or delay of the next interplate earthquake depends on the time of the outer rise earthquake in a seismic cycle due mainly to the complex behavior in propagation of aseismic sliding governed by the rate and state dependent friction law

interactive dynamics of faults abstract seismic activity may be treated as a process of slip movements along a complex system of interacting faults numerical simulations of quasi static faulting process were carried out by using two dimensional model of four parallel faults we may observe a variety of possible fault zone behaviour which results from the interactive and dynamical nature of the system some preliminary results of three dimensional modelling are also presented

precise timing of the upper taghanic biocrisis geneseo bioevent in the middle upper givetian middle devonian boundary in northern spain using biostratigraphic and magnetic susceptibility data sets abstract the ability to correlate with high precision among geological successions is critical in evaluating the global coincidence and therefore magnitude and duration of geological events this is a difficult problem given resolution uncertainties and ambiguities in biostratigraphic data sets the magnetostratigraphy susceptibility mss method based on low field bulk magnetic susceptibility ms measurements of closely spaced samples provides a well established abiotic high resolution correlation tool in stratigraphy that when combined with bio chemostratigraphic and other geophysical techniques offers ways to resolve correlation problems in addition such data sets lend themselves to time series analysis where developing high resolution timing of events becomes possible this paper examines the final episode equivalent to the geneseo bioevent in the appalachian basin of the important taghanic biocrisis known from globally distributed middle devonian geological sections the geneseo bioevent is important because the extinction of some major fossil groups occurred during this time while other groups declined significantly including many benthonic groups however the maxima of extinctions does not appear to have occurred everywhere simultaneously to help resolve timing of this bioevent results are reported for two middle devonian successions from northern spain the s huergas de gordon and punta boletos sections both showing the final taghanic biocrisis geneseo interval and correlate these successions to the same interval within an independent global database time series analyses of the mss data sets from the spanish sections was performed using multi taper mtm and fourier transform ft methods and have extracted well defined milankovitch bands from the primary ms data from each section using ft and mtm values for eccentricity at 400 kyr and 100 kyr a floating point time scale was developed for the two spanish sections that provides age resolution to 50 kyr for these successions the results show that the geneseo bioevent in northern spain occurred within a narrow time window estimated to have lasted for 70 kyr this time window fall s within the polygnathus ansatus uppermost part ozarkodina semialternans conodont zones just at the middle upper givetian boundary of the middle devonian in what appears to be the upper regressive phase of t r cycle iia

radiocarbon dating of late quaternary fault segments and systems recent developments in radiocarbon dating contribute to the analysis of fault evolution both at the level of individual fault segments and with regard to entire fault systems 14 c assay by accelerator mass spectrometry and the use of high precision radiometric counting systems have both improved the resolution of fault chronologies in conjunction with other sources of numerical ages they make it possible to trace fault related folding warping and regional deformation and thus to analyse a fault assemblage in its geodynamic context at dungeness se england 14 c dating of redeposited shells gives a minimum age for a planation surface and a fault that predates it in the gulf of corinth greece dating of lithophaga shells in their borings reveals 2 3m of differential holocene uplift of the south shore of gulf relative to the north improved chronologies should make it possible to complement the search for seismic recurrence intervals with analysis of deformation processes

slip along the san andreas fault associated with the great 1857 earthquake historical records indicate that several meters of lateral slip along the san andreas fault accompanied the great 1857 earthquake in central and southern california these records together with dendrochronological evidence suggest that the rupture occurred along 360 to 400 km of the fault including several tens of kilometers of the currently creeping reach in central california geomorphic expressions of late holocene right lateral offsets are abundant along the 1857 rupture along 300 kilometers of the 1857 rupture between cholame and wrightwood the youngest discernible offset ranges from 3 to 9 1 2 meters dormancy of the fault since 1857 almost certainly indicates that this latest offset was created in 1857 fault slip apparently associated with the 1857 earthquake varies in a broadly systematic way along the trace of the fault it is relatively uniform along each of several long segments but changes rather abruptly in value between these segments this nonuniform displacement pattern may imply that some segments of the fault rupture more frequently or experience a slower long term slip rate than others the 1857 offsets indicate a seismic moment m o between 5 3 and 8 7 10 27 dyne cm assuming a 10 to 15 km depth of rupture and relatively uniform slip as a function of depth a comparison with the rupture length average slip value and tectonic setting of the california earthquake of 1906 m s 8 1 4 indicates a value of m 8 1 4 for the 1857 event

the 1995 kobe earthquake and problems of evaluation of active faults in japan abstract the kobe earthquake m 7 2 of january 17 1995 which was the most damaging earthquake in recent japanese history made manifest the need for reconsidering the method of evaluating active faults an earthquake of this magnitude at this time was unexpected according to conventional evaluation in which the potential magnitude of earthquakes at a certain site is estimated by considering the greatest earthquake in the past 400 years and the length of the active fault the following characteristics of this earthquake made it appear unlikely by conventional understanding 1 the kobe earthquake involved several neighboring faults which had been previously been identified as separate fault systems 2 the surface rupture of about 10 km length was much shorter than the 50 km seismic faulting 3 the interval of 400 years between the kobe and penultimate keicho earthquake of 1596 ad m 7 5 which has been revealed by historical documents and some excavations is much shorter than the 2000 years estimated by calculating the average slip rate of displaced landforms these shortcomings imply that active fault evaluation with the traditional characteristic earthquake model which deals with each fault separately is not adequate for an area like japan where active faults swarm new concepts such as the block rotation model kanaori 1990 late mesozoic cenozoic strike slip and block rotation in the inner belt of southwest japan tectonophysics 177 381 399 considering the macroscopic tectonic framework for fault interactions are needed furthermore fault dynamics cannot be ignored physical and temporal parameters associated with faulting such as moment release rate must be considered for realistic and precise evaluation

the permian triassic boundary at nhi tao vietnam evidence for recurrent influx of sulfidic watermasses to a shallow marine carbonate platform the permian triassic boundary at nhi tao cao bang province vietnam was sampled in a 7 5 m thick outcrop section at high resolution 5 cm intervals for chemostratigraphic and magnetic susceptibility analysis the section consists entirely of slightly argillaceous limestone representing shallow marine facies of the jinxi platform one of several large carbonate platforms within the nanpanjiang basin located on the southern margin of the south china craton upper permian strata beds 1 7 are mainly dark gray cherty fossiliferous wackestones and packstones containing a diverse open marine fauna whereas uppermost permian and lower triassic strata beds 9 and higher are medium gray calcimicrobial framestones containing rare macrofossils these facies are separated by a 12 cm thick oolitic pisolitic grainstone bed 8 that coincides with the disappearance of most late permian faunal elements as well as with the first appearance of various geochemical anomalies that continue into the lower triassic part of the section this late permian event horizon is characterized by 1 an abrupt decline in total organic carbon to near zero values 2 the onset of a sustained decline in carbonate 13c and 3 the first of eight concentration peaks in pyrite sulfur significantly each sulfide peak is associated with lower pyrite 34s values as well as with the onset of a negative carbonate 13c excursion or the acceleration of an excursion already in progress these chemostratigraphic relationships are consistent with multiple episodes of upwelling of sulfidic 34s and 13c depleted deep ocean waters onto the jinxi platform the first upwelling event was the most intense and caused a drastic reduction in primary productivity and the demise of the late permian fauna subsequent episodes were less intense but may have contributed to a delay in recovery of early triassic marine ecosystems a ten fold increase in magnetic susceptibility in bed 9 may record the influx of fine detrital particles following destruction of terrestrial ecosystems and massive soil erosion the terrestrial signal of the end permian catastrophe thus follows the marine signal with a 12 cm lag which may reflect the time of transit of soil derived particles across the nanpanjiang basin suggesting that the marine and terrestrial crises in the nhi tao region occurred more or less synchronously these observations suggest a model in which renewal of global ocean overturn followed a prolonged interval of deep ocean stagnation during the late permian with upwelling intensity modulated by short term 20 kyr climate cyclicity

global correlation using magnetic susceptibility data from lower devonian rocks magnetic susceptibility data from marine rocks can be used for global correlation because of synchronous variations in global erosion we show here correlations between magnetic susceptibility data from two lower devonian biostratigraphically well defined sections one in northwestern spain and one from the anti atlas region of morocco using the moroccan outcrop section we correlate to cuttings from a bolivian well with minimal biostratigraphic control using the magnetic susceptibility data we identify the lower devonian pragian emsian and lower upper emsian stage boundaries in the bolivian well samples

modeling of the interaction between destructive inland earthquakes and large off coast earthquakes in central and south west japan abstract a one dimensional stick slip model which is introduced to explain the fractal features of earthquake phenomena is applied to describe he destructive earthquake occurrences in central and south west japan space time patterns of events are simulated and the predictablity is discussed on the basis of the block rotation model epicenters of historical destructive earthquakes with magnitude 6 4 or greater are relocated to the tectonic or block boundary lines this model has revealed that these events show a periodicity of about 1000 years of active and quiet alternative intervals in each active period individual block boundary lines generate several large earthquakes without overlapping rupture areas the space time pattern and moment release rate for the hanaore kongo fault line hkfl can be represented well with the one dimensional stick slip model the seismic coupling of large offshore earthquakes along the nankai trough is also found to be well modeled by this model this model may be useful for estimation of seismic risk in this region further this model can be applied to see the situation of the m7 2 kobe earthquake and interpret this earthquake to be the event that comes from the block structure in later section

stratigraphy of the middle devonian boundary formal definition of the susceptibility magnetostratotype in germany with comparisons to sections in the czech republic morocco and spain abstract one major difficulty in geology is high resolution correlation among widely separated sections especially in the paleozoic where magnetostratigraphy polarity is not well established because rocks are often remagnetized where critical biostratigraphic zonation may be poor or lacking or where structural complexities make correlations very difficult to address this problem we have been using magnetostratigraphy susceptibility measurements here we report our work from the middle devonian in europe and north africa the middle devonian emsian eifelian global boundary stratotype section and point gssp located in the eifel hills western germany was ratified by the international subcommission on stratigraphy in 1985 after careful evaluation of the biostratigraphy for this and many other sections the boundary interval has been characterized using biostratigraphy and the beginning of the eifelian stage has been specifically defined by the first occurrence of the conodont polygnathus costatus partitus we have collected the eifel hills section for magnetic susceptibility ms measurement and here we establish it as the magnetostratotype for the emsian eifelian stage boundary by formally defining the magnetostratigraphy susceptibility for the section we then collected measured and compared the magnetostratotype to four other sections for which conodont biostratigraphy has been studied and where p costatus partitus is present two emsian eifelian sections in morocco and two sections in the czech republic including the emsian eifelian parastratotype finally we have measured the ms for the el puerto creek section in the cantabrian mountains of spain and identified the location of the emsian eifelian boundary within the section based on ms comparison to the gssp in conjunction with excellent biostratigraphic indicators primarily brachiopods while the conodont zonation in the el puerto creek section is poorly defined we believe that the correspondence between the ms and biostratigraphy in the section allows the identification of the emsian eifelian boundary these results indicate that this method can be successfully applied to marine sequences where ambiguities in correlation exist

diagenesis of magnetic minerals in recent haemipelagic sediments rapidly deposited sediments from marine and lake environments are being used increasingly to study decadal to millennial fluctuations in the earth s magnetic field the objectives are to gain more fundamental understanding of the geodynamo and to establish a new dating technique for sediments while lacustrine sections are generally restricted to temperate latitude glacial lakes 20 000 yr old rapidly deposited marine sediments along continental margins potentially offer continuous high resolution yet long term records of geomagnetic secular variation however to interpret the sedimentary magnetic record accurately geochemical processes that affect the reliability of the magnetic signal must be understood we now report downcore magnetic profiles from undisturbed kasten cores taken in rapidly deposited laminated sediments from the gulf of california and in bioturbated haemipelagic muds on the oregon continental slope which give apparently reliable directions but show dramatic decreases in the intensities of natural nrm and artificial arm irm remanences with depth downcore porewater and solid sulphur analyses show concave down decreases in porewater sulphate and systematic increases in pyrite and metastable monosulphides the maximum curvature of the sulphide profile occurs directly below the high magnetization zone combined with other compositional and mineralogical analyses these data suggest that due to oxidative decomposition of organic matter magnetites and other iron oxides become progressively reduced and subsequently sulphidized and pyritized with depth iron reduction seems to occur before sulphide formation changes in magnetic stability parameters are consistent with selective dissolution of the finer sized grains causing downcore coarsening of the magnetic fraction

paleoseismic evidence of clustered earthquakes on the san andreas fault in the carrizo plain california exposures we have excavated across the san andreas fault contradict the hypothesis that part of the fault in the carrizo plain is unusually strong and experiences relatively infrequent rupture the exposures record evidence of at least seven surface rupturing earthquakes which have been approximately dated by accelerated mass spectrometry radiocarbon analysis of detrital charcoal and buried in situ plants five large earthquakes have occurred since 1218 a d the most recent earthquake event a was the 1857 fort tejon earthquake which we have associated with 6 6 10 m of dextral slip along the main fault trace the penultimate earthquake event b most likely occurred within the period a d 1405 1510 slip from either events b and c combined or from event b alone totals 7 11 m three earthquakes events c d and e occurred in a temporal cluster prior to event b and after approximately a d 1218 the average recurrence interval within this cluster is 73 116 years depending on assumptions events f and g occurred after 200 years b c a depositional hiatus between events e and f may hide evidence of additional earthquakes events b and d within the carrizo cluster of a d 1218 1510 may correlate with events t a d 1329 1363 and v a d 1465 1495 at pallett creek on the mojave segment of the fault this suggests two fault ruptures similar in length to that of 1857 events c and e apparently did not rupture the mojave section which suggests that the carrizo segment has ruptured independently or in combination with segments to the north irregular repeat times of large earthquakes suggest a pattern of clustered events at the end of seismic supercycles

chaotic fault interactions implications for seismic hazard in new zealand a chaotic fault interaction model previously developed for the san andreas fault system and the nankai trough examples of transform fault and subduction dominated tectonic regimes respectively is here applied to the large event seismicity in the new zealand region where the interacting blocks of the model are taken to be those parts of the indo australian plate boundary that are from north east to southwest subduction dominated transpressional and transform fault dominated the model suggests a shorter term recurrence of large events than do simple seismic cycle approaches

power law random behaviour of seismic reflectivity in boreholes and its relationship to crustal deformation models abstract there is good evidence for the fractal nature of some fault systems both from field observations and the frequency magnitude distribution of earthquakes recently two models with fundamentally different dynamics have been employed to explain seismicity low order non linear slider block models have successfully explained activity on part of the san andreas fault system and in the nankai trough while high dimensional self organised critical cellular automaton models convincingly reproduce the gutenberg richter frequency magnitude relationship output variables from these two models fall respectively into two distinct data classes chaotic deterministic and random using a predictability algorithm which can distinguish between random and chaotic datasets we examine the distribution class of in situ fractures as inferred from borehole seismic reflectivity logs in three chalk layers off the south coast of ireland we find that fractures are distributed in a non deterministic manner consistent with self organised critical dynamics therefore we may infer that deterministic seismicity should not occur on structures over the scale range covered by the logs at least in the end member case where the frequency magnitude distribution of earthquakes is controlled by the fractal distribution of faults

mid ludfordian coeval carbon isotope natural gamma ray and magnetic susceptibility excursions in the mielnik ig 1 borehole eastern poland dustiness as a possible link between global climate and the silurian carbon isotope record abstract the graptolite bearing upper silurian succession of the mielnik ig 1 borehole eastern poland represents a periplatform setting on a neritic carbonate platform located on the palaeocontinent of baltica and records widely recorded positive mid ludfordian carbon isotope excursion cie the initial increase of 13 c values occurs in the uppermost part of the neocucullograptus kozlowskii zone whereas pronounced increase and maximal values 6 74 are noted in the n kozlowskii pseudomonoclimacis latilobus interzone pristiograptus dubius bloom interval the thickness time relation in the section indicates that the main initial shift in carbon isotope ratio of 2 7 occurred over a very short time estimated to be around 4000 years and is coeval with a rapid initiation of deposition of rock forming silt sized detrital dolomite and quartz the cie decline is interpreted as steeper than in inner shelf sections and is coincident with a flooding event in the ps latilobus slovinograptus balticus zone whereas the end of the excursion is coeval with the next flooding surface marked by the ps latilobus uncinatograptus acer graptolite assemblage combined sgr spectral gamma ray facies and faunal records during the cie suggest prolonged sea level lowstand conditions the abundant detrital material dolomite siltstone facies occurring exclusively in the cie interval is noted in microfacies as well as in the geophysics record as pronounced negative excursions in total natural gamma ray and magnetic susceptibility both resulting from dilution by diamagnetic and low radioactivity minerals the perfectly sorted vertically equally sized silt material contains unique constant and low diversified grain assemblage euhedral dolomite quartz minute ooids suggesting its provenance exclusively from the shallower and or emerged parts of the carbonate platform interior the spot findings of graptolites and nautiloids along with delicate parallel lamination of sediments indicates relatively deep environment with absence of traction processes these features along with the lack of dolomite detritus in accompanying redeposited carbonates suggest its derivation by wind with regard to the earlier noted presence of aeolian detritus in the middle ludfordian we suggest dustiness as a plausible driving force of the cie in the hypothesis proposed bioavailable fe bearing dust inflow in concert with antiestuarine circulation on shelfs caused nutrient n p ratio disturbances resulting in methanogenesis in surface layer of the seas the surface layer methanogenesis should resulting in bathymetric gradient of isotope fractionation what is consistent with the cie record coincidence of sea level lowstand low latitude aridity and gustiness of the global climate are in accordance with the hypothetical short lived glaciation in mid ludfordian time

the magneto susceptibility event and cyclostratigraphy msec method used in geological correlation of devonian rocks from anti atlas morocco magneto susceptibility event and cyclostratigraphy msec is used here as a means of establishing sensitive chronostratigraphic markers and chronohorizons useful for high resolution correlation msec is a composite of the magnetic susceptibility ms record of marine strata and the coeval biostratigraphic record and similar to chronozones zones based on msec data have boundaries that are isochronous ms a measure of the concentration of magnetic grains in sediments proxies for the ratio of lithogenic to biogenic components controls on the detrital input of lithogenic material include eustasy and climate however induced and sea floor basin subsidence the development of an initial msec composite reference curve for the middle upper devonian of the anti atlas region of southern morocco is presented and discussed in the context of global sea level transgressive and regressive cycles msec trends composed of increasing ms magnitudes correlate well with episodes of regression whereas trends of decreasing ms magnitudes correlate with episodes of transgression