seismicity normal faulting and the geomorphological development of the gulf of corinth greece the corinth earthquakes of february and march 1981 three major destructive earthquakes of m s 6 7 6 4 6 4 occurred in the eastern part of the gulf of corinth in february and march 1981 associated normal faulting was observed on both the north and the south sides of the gulf examination of teleseismic local seismic surface faulting and geomorpbological data suggests that the first and second of these shocks activated major north dipping normal faults these faults control the topography and bathymetry and are related to the recent uplift and subsidence of the coastline it is probable that the first earthquake occurred on a faultwhich outcrops underwater and the second on a fault which is visible on land it appears that the third shock activated an antithetic normal fault dipping southwards on the north side of the gulf and that the overall structure of the gulf of corinth graben is asymmetric the northern antithetic fault clearly demonstrates the geomorphological changes associated with developing young normal faulting in addition we suggest that observations of recent coastline movement provide a powerful tool for identifying major active fault systems and predicting their historical role in the paleogeography of an area

a composite record of late pleistocene relative geomagnetic paleointensity from the wilkes land basin antarctica abstract we report high resolution paleomagnetic records obtained from six piston cores recovered on the continental rise of the wilkes land basin wlb east antarctica in the frame of the italian australian wilkes land glacial history wega project the studied cores with a length of ca 4 m each were collected from the gentle and steep sides of sedimentary ridges present in the lower part of the continental rise and consist of very fine grained sediments paleomagnetic measurements were carried out on u channel samples apart from a low coercivity magnetic overprint removed after the first steps of alternating field demagnetization each core is characterized by a well defined characteristic remanent magnetization paleomagnetic inclinations fluctuate around the expected value of ca 77 for such high latitude sites and always indicate normal magnetic polarity short period oscillations to anomalously shallow paleomagnetic inclinations up to 20 were identified at different levels of the sampled sequences positive reverse inclination values were however not observed specific rock magnetic measurements indicate a substantial homogeneity of the magnetic mineralogy in the sampled sequences for each core we reconstructed curves of relative paleointensity rpi as computed by nrm 20 mt and nrm 20 mt arm 20 mt variation of the geomagnetic field an original age model was established by tuning the individual rpi curves with the available global and regional reference rpi stacks paleomagnetic results supported by other limited bio and chronostratigraphic constraints establish that all the cores are late pleistocene in age two provide an expanded record of the last ca 30 ka pc18 and pc19 three span the last ca 100 200 and 300 ka respectively pc25 pc27 and pc26 and one reaches back to ca 780 ka pc20 approaching the brunhes matuyama transition thus the wega paleomagnetic record provides the first experimental data documenting the dynamics and amplitude of the geomagnetic field variations at high southern latitudes during the brunhes chron the individual normalized rpi records were merged in a wega rpi stacking curve spanning the last 300 kyr the comparison of the wega rpi individual and stacked curves with the global references rpi stacks shows that geomagnetic paleointensity variations with periods longer than a few to tens kyr depending on the sedimentation rate can be safely recognized in this sector of the peri antarctic margins furthermore the stacking of the individual chrm inclination records indicates that the recurrent swings to shallow paleomagnetic inclinations may be correlated to the main known geomagnetic excursions of the brunhes chron supporting the validity of the age models the reconstructed average sediment accumulation rates for the individual cores range from 0 6 to 19 cm ka and are compatible with their position within the wlb with the lowest rates found close to the ridge of the sedimentary drifts moreover the high resolution age models obtained in this study provide original constraints to assess chronology rates and amplitudes of the climatic and environmental processes affecting this key area of the peri antarctic margins during the late pleistocene

the composition and evolution of the continental crust rare earth element evidence from sedimentary rocks the composition of the present day upper crust inferred from the uniformity of sedimentary rock r e e rare earth element patterns is close to that of granodiorite a revised andesite model is used to obtain total crustal composition the lower crust is the composition remaining assuming that the upper crust one third of the total is derived from intracrustal partial melting the upper crustal r e e pattern has pronounced eu depletion eu eu 0 64 the lower crustal pattern has eu enrichment eu eu 1 17 and the total crust has no eu anomaly relative to chondritic abundances the eu depletion in the upper crust is attributed to retention of eu in plagioclase in the lower crust because plagioclase is not stable below 40 km 10 kbar the anomaly is intracrustal in origin the archaean upper crust has a different r e e pattern to that of the present day upper crust being lower in total r e e and la yb ratios and lacking an eu anomaly these data are used to infer the archaean upper crustal composition which resembles that of the present day total crust except that ni and cr contents are higher the archaean crustal composition can be modelled by a mixture of tholeiites and tonalite trondhjemites the latter have steep light r e e enriched heavy r e e depleted patterns consistent with equilibration with garnet and hence probable mantle derivation there is little reason to suppose that the archaean lower crust was different in composition from the upper crust except locally where partial melting episodes occurred the r e e evidence is consistent with isotopic and geological evidence for a low continental growth rate in the early archaean a massive increase to about 70 of the total crust between about 3000 and 2500 ma b p and a slow increase until the present day the change from archaean to post archaean r e e patterns in the upper crust is not isochronous but is reflected in the sedimentary rock r e e patterns at differing times in different continents on the basis of a model composition for the mantle 36 of the potassium 30 of uranium 15 of lanthanum and 3 of ytterbium are concentrated in the present continental crust this enrichment is related to ionic size and valency differences from common mantle cations e g mg fe pre 3 9 ga b p crusts were obliterated by meteorite bombardment no geochemical evidence exists for primordial anorthositic sialic or mafic crusts

a new rock magnetic approach to selecting sediments for geomagnetic paleointensity studies application to paleointensity for the last 4000 years the hypothesis that the ratio of detrital remanent magnetization to anhysteretic remanent magnetization drm arm for sediment samples is a measure of relative geomagnetic paleointensity is critically evaluated by two distinct approaches one approach is a detailed rock magnetic examination of the implicit assumptions of the drm arm method and the construction of a selection process by which to identify sediments that conform to requirements satisfying these assumptions sediments are uniform with respect to drm arm ratio if they contain magnetite in the 1 15 ym particle size range as the predominant magnetic mineral and have variations in magnetite content of less than 20 30 times the minimum concentration the drm arm ratios of these sediments should provide estimates of relative geomagnetic paleointensity relative particle size variations in magnetite are detected with a plot of anhysteretic susceptibility xarm versus low field susceptibility x and the size range 1 15 m is approximately identified by high field hysteresis parameters a rock magnetic evaluation of leboeuf lake sediments with these techniques indicates that these sediments are suitable for a relative plaeointensity study the second approach to evaluating the drm arm ratio as a measure of relative paleointensity is direct comparison with absolute paleointensity data a comparison between the leboeuf lake estimates and thellier thellier results from the western united states supports the conclusion that suitable sediments can record geomagnetic paleointensity fluctuations

mode of strong earthquake recurrence in the central ionian islands greece possible triggering due to coulomb stress changes generated by the occurrence of previous strong shocks the spatiotemporal distribution of shallow strong m 6 3 earthquakes occurring in the area of central ionian islands is analyzed these shocks are generated on two adjacent fault segments with different strike but both segments are associated with strike slip faulting constituting the boundary between continental collision to the north and oceanic subduction to the south seismic activity is concentrated in short time intervals alternating with much longer relatively quiescent periods each active period consists of a relatively large event or series two to four of events occurring closely both in space and time this alteration was observed to happen four times since 1867 the period when complete data exist for the study area since the phenomenon is not strictly periodic and during each active period multiple events occurred i attempted to interpret the seismic behavior on the basis of possible trig gering i then investigated how changes in coulomb failure function dcff asso ciated with one or more earthquakes may trigger subsequent events both the co seismic slip due to the generation of the strong earthquakes and stress buildup associated with the two major fault segments were taken into account for the dcff calculation earthquakes can be modeled as static dislocations in elastic half space and the stress pattern has been calculated according to the geometry and slip of each of the faults that ruptured in the chain of events these calculations show that 13 out of 14 earthquakes of m 6 3 were preceded by a static stress change that encouraged failure the magnitude of the stress increases transferred from one earthquake to another ranged from 0 01 mpa 0 1 bar to over 0 1 mpa 1 bar showing that stress transfer adequately explains the occurrence pattern of these events maps of current dcff provide additional information to long term earthquake prediction areas of positive dcff have been identified at two sites in kefalonia and lefkada faults respectively where the next strong events are expected to occur a fact that will substantiate the hypothesis elaborated in this article

the age and duration of the matuyama brunhes transition from new k ar data from la palma canary islands and revisited 40ar 39ar ages abstract paleomagnetic investigations conducted on lava sequences from la palma canary islands yielded several independent records of the matuyama brunhes transition mbt seven k ar ages of flows sampled across the mbt suggest a duration between 0 and 11 kyr and provide a weighted mean age of 786 3 ka analytical uncertainty only for the transition this value is significantly older than the previously admitted age of 779 2 ka derived from volcanic or sedimentary sequences when the 1 uncertainty on the calibration standard used in the present study is considered our age for the transition recorded at la palma becomes 786 8 ka we have recalculated the 40ar 39ar determinations from the previous studies using recent revisited ages for 40ar 39ar standards this yields a global dataset of 23 k ar and 40ar 39ar determinations our best estimate for the mbt age derived from this compilation is 789 2 ka analytical error or 789 8 ka total error within this 8 kyr uncertainty which could be considered as a minimum estimate this age remains compatible with recent determinations made by the astronomical time scale however the present study suggests that better control of the lock in depth as well as better quantification of uncertainties involved in the tuning of 18o records to orbital forcing models are needed to improve further the astronomical polarity time scale derived from sedimentary records in addition absolute dating by k ar and 40ar 39ar will gain in accuracy when uncertainty determinations on standards will be significantly improved

a restricted linked stress release model lsrm for the corinth gulf greece abstract the earthquake occurrence in the corinth gulf greece is modeled by means of the linked stress release model which combines the gradual increase of the strain energy due to continuous tectonic loading and its sudden release when an event occurs the modeling is based on the theory of stochastic point processes and it is determined by the conditional intensity function the modeled time dependent seismicity incorporates stress transfer and interactions among the major fault segments that belong either to the western or to the eastern part of the study area static stress changes caused by the coseismic slip of eight characteristic events that occurred during the instrumental era were calculated their perturbations reveal that earthquakes occurring in the eastern part provoke excitation in the western part while the events that occurred in the western part do not affect the seismicity of the eastern part this result was taken into account and the values of the model parameters were constrained accordingly the analysis is also performed on synthetic earthquake catalogs developed by an earthquake simulator algorithm that can replicate the seismic activity in the study area and yields to comparable results

environmental magnetism of antarctic late pleistocene sediments and interhemispheric correlation of climatic events abstract recent developments in paleomagnetism and environmental magnetism provide new tools for the detailed correlation of climatically induced magnetic mineralogy changes in sedimentary sequences studies of these changes contribute to the reconstruction of climate history for the glacial interglacial cycles of the late pleistocene and to the delineation of the range of natural variability for global climate during the past hundred thousands years here we show that sharp coercivity minima observed in fine grained sediments from the continental rise of the western antarctic peninsula correlate to the major rapid cooling events of the northern atlantic heinrich layers we interpret such an environmental magnetic signal in terms of variations in deep sea diagenetic processes of sulfide formation which reflect changes in the input of detrital organic matter controlled by sea ice extent with the inherent uncertainties in age controls the sedimentary paleoclimatic markers of the two hemispheres are almost contemporaneous but interhemispheric time lags or leads of the order of 1 2 kyr such as those recently reported from the greenland and antarctic ice cores are also compatible with the data

relative changes of the geomagnetic field intensity during the last 280 kyear from piston cores in the acores area abstract relative changes in geomagnetic field intensity over the last 280 kyears have been recovered from the study of three marine cores from the acores area one core was precisely dated by oxygen isotope study and the other two records were linked to it using light reflectance analysis which allowed precise correlation rock magnetic analysis shows that the main magnetic mineral is magnetite with a very homogeneous grain size distribution in the pseudo single domain range for the three cores changes in the amount of magnetite do not exceed a factor of 10 therefore these cores appear to be suitable for relative palaeointensity determinations two mineral magnetic components with periodicities of 23 and 18 kyears are present in the records of bulk magnetic parameters and natural remanent magnetisation nrm but the power at these frequencies is not significant at the 95 level for the normalised remanence records for each core normalisation of the nrm using different normalising parameters yields virtually identical results using saturation isothermal remanent magnetisation sirm as the normalising parameter the results of the three cores were then combined into a stacked curve squared coherence analysis between this stacked curve and bulk mineral magnetic parameters reveals that the 18 kyear component is still present in the record but that the power spectrum is barely above noise level at this frequency some of the features of this north atlantic record are consistent with the main characteristics already documented in other sedimentary or volcanic records for instance distinct periods of low intensity are observed around 40 120 and 190 kyears and periods of high intensity at 50 and 80 kyears because of the uniformity of the mineral magnetic characteristics of the three cores we suggest that this record may be a suitable palaeointensity reference curve for the central north atlantic ocean region

a comparison of different techniques for relative paleointensity parallel relative paleointensity records that are supposed to display the same geomagnetic variations often show discrepancies we compared various techniques of normalization with different parameters involving alternating fields a f and thermal demagnetization of sediment samples spanning the same period from the indian and the pacific oceans the results are basically unchanged using any technique there is also no causal relationship between changes in rock magnetic properties and mismatch between the two records thus discrepancies between parallel records do not depend on methods for relative paleointensity and any technique can be used with confidence provided that the characteristic component has been properly isolated and the sediments are magnetically homogeneous complications are more likely due to subtle variations in the sediment remanent magnetization acquisition these results point to the importance of sedimentological lithology and physical properties factors in controling the process of magnetization

intermittent upwelling of asthenosphere beneath the gregory rift kenya k ar dates and chemical compositions of basalts in the gregory rift kenya demonstrate marked secular variation of lava chemistry two magmatic cycles characterized by incompatible element relative depletion are recognized both occurring immediately after the peak of basaltic volcanism and coeval with both trachyte phonolite volcanism and domal uplift of the region these cycles may be attributed to increasing degree of partial melting of mantle source material in association with thinning of the lithosphere by thermal erosion through contact with hot upwelling asthenospheric mantle cyclic variation in asthenosphere upwelling may be considered an important controlling process in the evolution of the gregory rift

detailed microseismicity study in the area of florina greece evidence for fluid driven seismicity abstract a local seismic network was installed and operated in the area of florina northern greece during july 2013 january 2014 for studying the high microseismic activity following the occurrence of an mw 4 1 event on 17 february 2013 the recordings of the local network along with the ones of the hellenic unified seismological network husn are used for obtaining accurate locations and defining the characteristics of the seismic activity a new velocity model is calculated for a broader area using the recordings of the husn stations relocation is performed for 1330 events recorded by the local network and 423 events recorded by husn using the double difference technique and cross correlation measurements fault plane solutions are determined for the two largest events mw 3 6 and mw 4 1 using waveform inversion technique the causative fault of the largest event mw 4 1 is striking almost e w and dipping to the north however most of the activity is concentrated in its south and forms an almost vertical south dipping plane striking almost e w this southern cluster consists of multiplets and is located in an area of positive coulomb stress changes due to the coseismic slip of the mw 4 1 earthquake the spatio temporal evolution of microseismicity is in most cases well explained by diffusion curves a signature of fluid induced seismicity however there are cases where a triggering front could not describe the evolution of the activity resulting to an earthquake earthquake triggering the dependent or independent poisson process earthquake occurrence was examined by searching their interevent time distribution these characteristics are interpreted as the consequence of co2 emission through faults which are used as pathways in an area enhanced by the coseismic coulomb stress changes

magnetostratigraphy of plio pleistocene sediments in a 1700 m core from osaka bay southwestern japan and short geomagnetic events in the middle matuyama and early brunhes chrons abstract a magnetic polarity stratigraphy spanning more than the past 3 2 myr was determined for a long 1545 m continuous sedimentary sequence of marine fluvial and lacustrine deposits from the osaka basin southwestern japan additionally two short geomagnetic reversal events were identified a short event at about 0 69 ma lasting for about 7 kyr in the early brunhes chron around the lower boundary of a marine clay deposited during a period of eustatic high sea level during the marine oxygen isotope stage 17 and another short matuyama event 1 60 1 58 ma correlated with stage 54 event and the early stage of the sangiran excursion accumulation rate was 0 3 0 4 mm yr from 3 to 2 ma and then increased by about 50 with a rate of 0 51 mm yr during the olduvai subchron high values of 0 59 mm yr were maintained from the upper olduvai boundary to the brunhes matuyama boundary from 1 77 to 0 78 ma with a peak at 0 74 mm yr during the jaramillo subchron these changes in accumulation rate probably reflect the history of tectonic subsidence of the drilling site the magnetic polarity stratigraphy provides a chronological framework for sedimentological paleoenvironmental tephrochronological and tectonic studies of the osaka basin

global changes in intensity of the earth s magnetic field during the past 800kyr recent advances in palaeomagnetic and dating techniques have led to increasingly precise records of the relative intensity of the earth s past magnetic field at numerous field sites the compilation and analysis of these records can provide important constraints on changes in global magnetic field intensity and therefore on the earth s geodynamo itself a previous compilation for the past 200 kyr integrated 17 marine records into a composite curve1 with the geomagnetic origin of the signal supported by an independent analysis of 10be production made on different cores2 the persistence of long term features in the earth s magnetic intensity or the existence of long term periodic changes cannot however be resolved in this relatively short time span here we present the integration of 33 records of relative palaeointensity3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 into a composite curve spanning the past 800 kyr we find that the intensity of the earth s dipole field has experienced large amplitude variations over this time period with pronounced intensity minima coinciding with known excursions in field direction reflecting the emergence of non dipole components no stable periodicity was found in our composite record and therefore our data set does not support the hypothesis that the earth s orbital parameters have a direct and strong influence on the geodynamo

coupled stress release model for time dependent seismicity based on the original stress release model of seismicity proposed by vere jones 1978 this paper has developed a stochastic coupled stress release model of time dependent seismicity which considers the earthquake interaction and stress transfer between different seismic subregions as an example the model is applied to a statistical analysis of the historical earthquake catalog with magnitude m 6 0 during the period from 1480 to 1996 in north china according to the akaike information criterion aic the results show that the coupled stress release model is better than the original model which demonstrates the existence of long range correlations between different seismic subregions we also apply both the stochastic original and developed coupled models to analyze the synthetic catalog produced by a cellular automata model which is based on mechanics of a slide spring damper system to model the fault network the stress release model provides a good fit to the synthetic regional stress and the coupled stress release model provides an improvement in fit to the synthetic catalog over the original model

a new multidimensional stress release statistical model based on coseismic stress transfer summary following the stress release model srm proposed by vere jones 1978 we developed a new multidimensional srm which is a space time magnitude version based on multidimensional point processes first we interpreted the exponential hazard functional of the srm as the mathematical expression of static fatigue failure caused by stress corrosion then we reconstructed the srm in multidimensions through incorporating four independent submodels the magnitude distribution function the space weighting function the loading rate function and the coseismic stress transfer model finally we applied the new model to analyse the historical earthquake catalogues in north china an expanded catalogue which contains the information of origin time epicentre magnitude strike dip angle rupture length rupture width and average dislocation is composed for the new model the estimated model can simulate the variations of seismicity with space time and magnitude compared with the previous srms with the same data the new model yields much smaller values of akaike information criterion and corrected akaike information criterion we compared the predicted rates of earthquakes at the epicentres just before the related earthquakes with the mean spatial seismic rate among all 37 earthquakes in the expanded catalogue the epicentres of 21 earthquakes are located in the regions of higher rates the map of predicted earthquake rates at the ending time 1997 january 1 suggests that the next destructive earthquake in north china is likely to occur in the regions south of datong north of beijing and east of hejian

petrology of the alkaline rocks of the macau volcanic field ne brazil the macau volcanic field mvf in the borborema province ne brazil contains multiple centres of volcanic activity of early to late cenozoic ages we present element and sr nd pb isotope geochemical data for four of the few most prominent basalt types of this volcanic field serrote preto type serra aguda type pico do cabugi type and serra preta type in order to assess their magmatic history from source to crystallization and the evolution of the mantle beneath the borborema province the basalts are basically sodic nephelinitic basanitic alkali olivine basalts enriched in lile and in nb ta the serra preta cabugi and serra aguda types demonstrate compositions close to primitive characteristics with 10 mgo 15 wt and 200 ppm ni 500 ppm and experienced limited fractional crystallization of olivine clinopyroxene plagioclase oxides with negligible wall rock assimilation rb sr and ba rb constraints support the generation of sio2 undersaturated magmas from mantle melting of amphibole bearing peridotites with minor phlogopite the source for the basanites and alkali basalts is estimated to be a garnet bearing domain around the lithosphere asthenosphere boundary 80 93 km deep while the nephelinites are derived from the adiabatic asthenosphere at 105 km with temperatures of 1480 c their incompatible trace element patterns and sr nd pb isotopic compositions are similar to fozo and em type oib magmas from the comparison of data with those of the ceara mirim dyke swarm we propose that there is a ubiquitous fozo reservoir in the sclm beneath the borborema province this fozo signature characterized the upwelling asthenosphere during the lithospheric extension and thinning at the opening of the equatorial atlantic and is clearly represented in the mesozoic olivine tholeiites of ceara mirim the upwelled asthenosphere cooled as a rigid sclm since the cretaceous and has preserved its fozo signature evident in the macau cenozoic basalts the em signatures in mvf lavas probably represent a deep component derived from metasomatizing fluid melts that have interacted with an originally old oib type mantle to produce metasomatic minerals such as k rich amphibole mica with highly incompatible trace elements contents which enhanced the generation of alkaline magmas through mantle melting

models of lithospheric thinning lithospheric thinning denotes a gcodynamieal process that is associated with extensional tectonic phenomena in plate tectonics the lithosphere is a layer of strength compared with the underlying asthenosphere its thick ness is commonly defined by the depth to a particular isothermal or by a fraction of the melting temperature of rocks a typical thickness is of the order 100 km and includes the earth s crust and parts of the upper mantle this definition is equivalent to that used in seismology but it does not necessarily correspond to the elastic thickness derived from flexural defor mations in response to loading according to its thermal regime state of stress and lithology we expect the lithosphere to contain layers of predominantly brittle and ductile deformation the oceanic and continental lithospheres have distinctive origins structures and compositions while the age of the oceanic litho sphere is only of order 108 myr the continental lithosphere contains the oldest rocks known on earth the latter has therefore the most com prehensive record of past geodynamical processes lithospheric thinning is expressed by a variety of tectonic and epeiro genic manifestations such as domal uplifts and hotspot swells crough 1983 continental rifts morgan baker 1983 platform basins sleep et ai 1980 and plateau uplifts on the other hand our understanding of the thinning mechanisms is based on physical concepts in association with observations reheating of the lithosphere b uoyantly driven diapiric pene tration or stretching under isostatic conditions are the most frequently discussed models they implicitly define the nature of the source of thin ning

geomagnetic field intensity north atlantic deep water circulation and atmospheric δ14c during the last 50 kyr we present simulated records of past changes in the atmospheric 14c for the last 50 kyr due to changes in geomagnetic field intensity and in the strength of the north atlantic deep water nadw a new geomagnetic record was used largely based on the napis 75 record laj et al phil trans r soc london a 358 2000 1009 1025 which has been extended for the 0 20 kyr interval using archeomagnetic and volcanic data past changes of the nadw were derived from a mineral magnetic study of the cores used in the construction of napis 75 two box models of different complexity 4 and 17 boxes were used to simulate the carbon cycle calculated records of 14c are consistent with experimental determinations for the last 24 kyr for older ages the records calculated with variable oceanic circulation conditions reach values as high as 600 with an average of 500 between 20 and 40 kyr with maxima around 21 30 and 38 kyr gisp2 age model while low values are observed prior to 42 kyr although large inconsistencies in experimental data preclude precise comparison the average record simulated with the 17 box model is overall consistent with the icelandic sea record voelker et al radiocarbon 40 1998 517 534 42 2000 437 452 except for the extremely high peak observed in this record at 40 5 kyr on the other hand the results recently reported from a stalagmite recovered from a submerged cave in the bahamas beck et al science 292 2001 2453 2458 are inconsistent with all our model simulations in the 20 45 kyr interval the improved geomagnetic record combined with the new nadw profile allows us to give a modeled evaluation of the relative contribution of these factors to changes in atmospheric 14c the average simulation provides a first order modeled correction for conventional radiocarbon ages older than 25 kyr for which no calibration curve is available as yet

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

physical changes in the lithosphere associated with thermal relaxation after rifting we define the terms modem rift and paleorift with respect to the thermal state of the lithosphere the former being rifted lithosphere not in thermal equilibrium and the latter being thermally stabilized rifted lithosphere a comparison of the physical characteristics of modern rifts with paleorifts shows that they share many of the same geomorphic structural and magmatic features but have important differences in their geophysical signatures using a simple model for the thermal relaxation of the lithosphere in the transition from modern rift to paleorift we show that differences in upper mantle seismic velocities and density surface heat flow thermal structure and curie point depth and magnetotelluric properties of the lithosphere between modern and paleorifts can be explained by lithospheric cooling cooling alone cannot explain the complex subsidence histories associated with and following rifting however nor the presence of high velocity crustal layers and sometimes thickened crust in paleorifts these features can be explained by consideration of lithospheric flexural strength and magmatic thickening of the crust associated with rifting we speculate that the anomalous upper mantle beneath many modern rifts may be associated with the process of magmatic thickening of the rifted crust

a microseismic study in the western part of the gulf of corinth greece implications for large scale normal faulting mechanisms summary we present the results of a dense seismological experiment in the western part of the gulf of corinth psathopyrgos aigion area one of the most active rifts in the aegean region for which we have precise tectonic information the network included 51 digital stations that operated during july and august 1991 covering a surface of 40 x 40 km2 among the 5000 recorded events with ml ranging between 1 0 and 3 0 we precisely located 774 events we obtained 148 well constrained focal mechanisms using p wave first motions of these 60 also have mechanisms obtained by combining the p wave first motions with the s wave polarization directions the observed seismicity is mainly located between 6 and 11 km depth most of the fault plane solutions correspond to e w striking normal faulting in agreement with the geological evidence most of the well determined mechanisms indicate a nodal plane dipping 10 25 due north and a steep south dipping plane a similar asymmetry is also seen in the seismicity distribution and in the overall geological structure of the corinth rift we discuss this evidence and the inference of a deep detachment zone a structure where the major faults seen at the surface appear to root a large part of the microseismic activity appears to cluster in regions near the junctions of the main faults with the proposed detachment zone this feature of the microseismicity is interpreted in terms of stress transfer and stress concentration in regions of probable nucleation of future large earthquakes

geomagnetic moment variation and paleomagnetic excursions since 400 kyr bp a stacked record from sedimentary sequences of the portuguese margin abstract a paleomagnetic study was performed in clayey carbonate sedimentary sequences deposited during the last 400 kyr on the portuguese margin northeast atlantic ocean declination and inclination of the stable remanent magnetization present recurrent deviations from the mean geomagnetic field direction the normalized intensity documents a series of relative paleointensity rpi lows recognized in other reference records three directional anomalies occurring during rpi lows chronologically correspond to the laschamp excursion 42 kyr bp the blake event 115 122 kyr bp and the icelandic basin excursion 190 kyr bp a fourth directional anomaly recorded at 290 kyr bp during another rpi low defines the portuguese margin excursion four non excursional rpi lows are recorded at the ages of the jamaica pringle falls mamaku calabrian ridge 1 and levantine excursions the rpi record is characterized by a periodicity of 100 kyr paleointensity lows often coinciding with the end of interglacial stages this record sets the basis of the construction of an authigenic 10be 9be record from the same sedimentary sequences carcaillet et al this issue

normal faulting in the upper continental crust observations from regions of active extension abstract observations of present day normal faulting in regions of active continental extension may be helpful when interpreting the geological record in older extensional basins the most obvious manifestation of active extension is normal faulting in earthquakes earthquake foci are mostly confined to the upper seismogenic continental crust whose thickness imposes a scale on the observed deformation large earthquakes move faults with lengths similar or large compared with the thickness of the seismogenic layer large seismogenic normal faults on the continents appear to be restricted to a dip range of around 30 60 dips significantly gentler than 20 have not been observed in fault plane solutions of large earthquakes large seismographic normal faults are approximately planar in cross section and cut through the base of the upper seismogenic layer rotating about a horizontal axis as they move a reasonable estimate of the regional extension can often be made from the dip of the large normal faults and the tilt of the blocks they bound the domino model such faults are rarely continuous for more than 15 20 km but commonly change strike or step in an en echelon fashion this segmentation may occur on a scale controlled by the thickness of the seismogenic layer and is an important influence on sedimentation and drainage these observations are common to large seismogenic normal faults from a variety of tectonic settings and suggest that the kinematics of normal faulting may not be strongly influenced by the forces responsible for the extension which can vary widely in nature and magnitude small earthquakes which move faults that are small compared with the seismogenic layer thickness show no simple pattern and often can be interpreted as internal deformation of blocks bounded by large faults in some places the seismogenic basement faults do not reach the surface but are decoupled from the sedimentary cover by layers of weak lithology faults in the sedimentary cover may be strongly curved in cross section requiring their hangingwalls to deform internally estimating extension from such faults is not straightforward and requires a knowledge of the hangingwall deformation estimates made in this way are often very non unique and prone to large errors we postulate that the thickness of the seismogenic upper crust controls both the maximum length of large normal fault segments along strike and the maximum size of blocks that can rotate coherently about a horizontal axis

an active thermoelastic rift mechanism finite element solutions for stresses and displacements during rift development are obtained for a variable thickness elastic lithosphere plate subjected to thermoelastic loading by conductive heating from an axial line source in the asthenosphere the asthenosphere is modelled as a fluid foundation the prerift lithosphere is modelled as an infinite continuous plate a semi infinite plate is used to characterize the rifted lithosphere horizontal restraints are removed at the rift axis to model the transition from a continuous to separated lithosphere plate during rifting lithosphere strength envelope curves derived from olivine flow laws are used to determine the elastic lithosphere depth in the solutions conductive heating of a variable thickness continuous lithosphere plate by a 2000 w m line source at 60 km depth produces high stresses oriented orthogonal to the forming rift axis and small vertical displacements the maximum uplift obtained in the continuous lithosphere plate models subjected to thermoelastic loading was 0 12 km at a distance of 120 km from the forming rift axis this small uplift is accompanied by shallow tensile stresses of 80 mpa at a distance of 5 km from forming rift axis which decrease to 6 mpa at a distance of 210 km shallow horizontal thermoelastic tensile stresses are over 5 times greater than the horizontal stresses produced by thermal buoyancy loads near the forming rift axis the transition from a continuous to rifted lithosphere is accompanied by an increase in lithosphere uplift at the rift axis from 0 11 to 0 42 km and a reduction in shallow horizontal stress magnitude by a factor of 30 thermoelastic loading may be a source of shallow tensile stress in the lithosphere and a contributing factor for the initiation of rifting thermal loading may also produce postrifting topography changes thermoelastic loading of the lithosphere is proposed as a possible driving mechanism for rift formation which produces separation and the transition from a continuous to rifted lithosphere plate

ar ar ages from transitionally magnetized lavas on la palma canary islands and the geomagnetic instability timescale 1 a detailed study of 43 lava flows comprising two stratigraphic sequences exposed along the north and south walls of barranco de los tilos on the island of la palma canary islands reveals a complex temporally segmented record of geodynamo behavior that contains no less than three distinct geomagnetic events the matuyama brunhes m b reversal is recorded in five transitionally magnetized lava flows from the north tn section the isochrons obtained from three of the lower four m b lavas are defined by 14 incremental heating experiments that together with a previous age determination yielded a weighted mean of 798 4 6 2 ka all uncertainties 2s in addition a 780 3 10 3 ka isochron was determined for the overlying transitionally magnetized flow indicating that it was erupted during a distinctly younger portion of the transition near the base of the south ts section one finds a sequence of weakly magnetized flows associated with virtual geomagnetic pole vgp positions in the southwest indian ocean between latitudes 56 s and 65 s suggesting instability of the geomagnetic field beyond that of typical secular variation 40 ar 39 ar isochrons from three of these flows defined by 11 separate incremental heating experiments gave a weighted mean of 822 2 8 7 ka this anomalous field behavior recorded 24 11 kyr prior to the m b reversal may coincide with an event featured in several marine sediment records directly above two normal polarity flows 40 ar 39 ar isochrons of 751 9 18 1 ka and 675 0 15 7 ka are nine transitionally magnetized lavas having magnetization directions associated with low to midlatitude vgps spanning 23 60 n these flows are then capped by a single flow possessing normal polarity based on 12 incremental heating experiments 40 ar 39 ar isochrons of five of these nine lavas along with the uppermost flow gave a weighted mean age of 580 2 7 8 ka for this period of transitional to normal field behavior from these same transitional lavas quidelleur et al 1999 reported three unspiked k ar ages with a weighted mean of 602 24 ka and proposed a new event called the la palma excursion however the 40 ar 39 ar age presented here is three times more precise than the k ar age and is indistinguishable at the 95 confidence level from the 40 ar 39 ar age of a lava from the snake river plain idaho that originally defined the big lost event transitional field behavior of similar age observed in astronomically dated marine cores further establishes that the big lost event recorded at la palma was indeed global in extent rigorous temporal and geomagnetic constraints for several additional periods of geomagnetic field instability during the last several million years will comprise a geomagnetic instability timescale that can be factored confidently into models of the dynamo process index terms 1560 geomagnetism and paleomagnetism time variations secular and long term 1520 geomagnetism and paleomagnetism magnetostratigraphy 1035 geochemistry geochronology 1513 geomagnetism and paleomagnetism geomagnetic excursions keywords argonargon dating lavas excursion paleomagnetism reversal

deconvolution of u channel paleomagnetic data near geomagnetic reversals and short events 1 the deconvolution scheme of oda and shibuya 1996 designed for half core data from the pass through magnetometer aboard the joides resolution has been adapted for treatment of u channel data the program was tested using u channels from ocean drilling program odp site 1090 a significant increase in resolution of the u channel data can be achieved by deconvolution resulting in data comparable with that obtained by continuous discrete sampling large amplitude changes of the magnetization vector revealed by the deconvolution treatment are in good agreement with the results obtained on discrete samples extracted from the same u channels application of this procedure to u channel data from odp sites 983 and 984 over a short time interval around 1 255 ma permitted enhanced definition of the so called bjorn geomagnetic event

the galaxidi earthquake of 18 november 1992 a possible asperity within the normal fault system of the gulf of corinth greece the galaxidi earthquake that occurred in the gulf of corinth on 18 november 1992 was not followed by a noticeable aftershock sequence a fact that was also observed for the 1965 eratini event in the same area the temporary network of 35 stations that we installed 5 days after the mainshock did not help to identify a cluster of activity related to the mainshock in a section across the epicentral zone the focal mechanism of the mainshock and the distribution of a few aftershocks define a plane dipping north consistent with the nearby helike fault we propose that the galaxidi earthquake was related to an asperity located between the helike and xilo kastro faults

renewal models and coseismic stress transfer in the corinth gulf greece fault system 1 we model interevent times and coulomb static stress transfer on the rupture segments along the corinth gulf extension zone a region with a wealth of observations on strong earthquake recurrence behavior from the available information on past seismic activity we have identified eight segments without significant overlapping that are aligned along the southern boundary of the corinth rift we aim to test if strong earthquakes on these segments are characterized by some kind of time predictable behavior rather than by complete randomness the rationale for time predictable behavior is based on the characteristic earthquake hypothesis the necessary ingredients of which are a known faulting geometry and slip rate the tectonic loading rate is characterized by slip of 6 mm yr on the westernmost fault segment diminishing to 4 mm yr on the easternmost segment based on the most reliable geodetic data in this study we employ statistical and physical modeling to account for stress transfer among these fault segments the statistical modeling is based on the definition of a probability density distribution of the interevent times for each segment both the brownian passage time bpt and weibull distributions are tested the time dependent hazard rate thus obtained is then modified by the inclusion of a permanent physical effect due to the coulomb static stress change caused by failure of neighboring faults since the latest characteristic earthquake on the fault of interest the validity of the renewal model is assessed retrospectively using the data of the last 300 years by comparison with a plain time independent poisson model by means of statistical tools including the relative operating characteristic diagram the r score the probability gain and the log likelihood ratio we treat the uncertainties in the parameters of each examined fault source such as linear dimensions depth of the fault center focal mechanism recurrence time coseismic slip and aperiodicity of the statistical distribution by a monte carlo technique the monte carlo samples for all these parameters are drawn from a uniform distribution within their uncertainty limits we find that the bpt and the weibull renewal models yield comparable results and both of them perform significantly better than the poisson hypothesis no clear performance enhancement is achieved by the introduction of the coulomb static stress change into the renewal model

relative paleointensity across the last geomagnetic reversal from sediments of the atlantic indian and pacific oceans paleointensity records from marine sediments at three locations in the atlantic indian and pacific oceans show coherent and reproducible signals across the brunhes matuyama reversal the low field susceptibility signals are predominantly anticorrelated between the indo pacific and the atlantic sites while the normalization of the natural remanent magnetization by any rock magnetic parameter yield identical results we deduce that in these cases climatic components do not induce first order effects in the determination of relative paleointensity the results establish the worldwide character of the triangular pattern displayed by the decay and recovery phases of the field intensity variations across the brunhes matuyama reversal

plio quaternary sedimentation on the wilkes land continental rise preliminary results abstract the wilkes land continental rise is characterised by mounds and channels with approximately a north south elongation perpendicular to the margin proximal mound relief is up to 1000 m decreasing to about 300 m in the central part during the geophysical and geological survey conducted on in february march 2000 by the joint italian and australian wega project onboard r v tangaroa 11 piston cores were collected along two transects crossing the channel mound system all cores were logged for physical magnetic susceptibility and density and acoustic properties p wave velocity split cores were x rayed and samples were analysed for clay mineral assemblages chemical and micropaleontological diatoms foraminifera and nannofossils content glacial and interglacial intervals have been recognised in the sediment cores the interglacial facies consists of massive mud distinguished by a bioturbated massive mud occasionally with fine grained ice rafted debris ird and b structureless massive mud with abundant fine to coarse grained ird containing well preserved open ocean diatoms the glacial facies is represented by laminated mud with planar and or cross laminations with occasional isolated dropstones and rare poorly preserved sea ice diatoms the sharp boundary characterizing the limit between massive to laminated facies is interpreted to indicate a fast glacial onset in contrast the smooth passage presents from laminated to massive sediments indicates a gradual glacial waning recent down slope gravity flows have been identified in a turbidite a normally graded coarse grained sand recovered in the thalweg of jussie canyon and probably also in the massive debris facies from the steep side of mound a the massive debris is characterised by structureless and unsorted gravel and pebbles within a muddy matrix clay mineral assemblages and grain lithologies indicate a hinterland wilkes basin and continental shelf provenance for the terrigenous fraction

stress release model and proxy measures of earthquake size application to italian seismogenic sources italian dipartimento della protezione civile in the framework of the 2007 2009 agreement with istituto nazionale di geofisica e vulcanologia ingv project s1 analysis of the seismic potential in italy for the evaluation of the seismic hazard

active continental deformation and regional metamorphism the vertical and horizontal distribution of present day continental deformation is examined to see how tectonic movements may be related to large wavelength perturbations to the temperature and pressure experienced by rocks in the crust earthquakes are generally restricted to the upper part of the continental crust the lower crust is usually aseismic and assumed to be weaker the uppermost mantle beneath continental regions has minor seismic activity that does not account for much deformation but probably indicates an important strength contrast between the lower continental crust and the upper mantle the maximum focal depth of earthquakes in any region appears to be limited by temperature with most restricted to material colder than 350 pm 100 degrees c in the crust and colder than 700 pm 100 degrees c in the mantle at length scales long compared with the thickness of the brittle upper crust the deformation in regions of continental extension or shortening appears to be continuous even though in reality discontinuous movement on faults occurs this probably indicates that the deformation is dominated by distributed flow in the ductile portion of the lithosphere and not by the behaviour of the thin brittle upper crust the distribution of seismicity elevation contrasts and vertical movements at the surface suggests that there is little spatial separation between the brittle deformation in the upper crust and the ductile deformation below on length scales larger than the lithosphere thickness for this reason and because of the short thermal time constant of the crust long wavelength perturbations to the thermal regime are more influenced by the behaviour of the lithosphere as a whole than by the precise geometry of deformation in the crust large scale regional metamorphism in zones of shortening may result from the re establishment of the initial geotherm in thickened crust when the lower part of the lithosphere detaches and falls into the asthenosphere in regions of extension an increased geothermal gradient is unlikely to result in regional metamorphism unless magmatic augmentation to the heat supply is important however if the stretched region is covered by thick sediments the basement may experience a small increase in temperature and remain significantly hotter than it would be if there were no sediment cover while unlikely to account for significant metamorphism this effect may strongly influence the rheological behaviour of the lithosphere in extending regions the rapid vertical movements associated with syn or post orogenic normal faulting in regions of large scale crustal thickening are probably at least as important in exhuming mid crustal metamorphosed rocks and in disrupting patterns of isograds as those associated with erosion

deconvolution of long core paleomagnetic data of ocean drilling program by akaike s bayesian information criterion minimization deconvolution of long core paleomagnetic data of the ocean drilling program odp was developed based on bayesian statistics samples of deep sea sediments obtained by drilling with an advanced piston corer are subjected to pass through measurements by a cryogenic magnetometer aboard the odp s research vessel joides resolution which provide continuous paleomagnetic records deconvolution of the magnetometer output was developed in order to obtain more detailed variations of the magnetization than permitted by the spatial resolution of the pickup coil approximately 11 cm the magnetization vector was modeled as a smoothly changing sequence parametrized by l2 norm of second order difference and then deconvolved using a matrix calculation as a smoothness constrained least squares method the optimum smoothness was obtained by minimizing akaike s bayesian information criterion which is a measure of the logarithm of the likelihood this deconvolution scheme was applied to pass through data artificially produced by convolving synthetic reversal record and adding a gaussian noise the amplitude of the noise was estimated and the variations shorter than the spatial resolution of the sensor were obtained the deconvolution also was applied to the real pass through data from holes 769a and 769b measured at intervals of 5 mm the deconvolution revealed variations of the magnetizations with a maximum spatial resolution of about 2 cm the magnetizations after deconvolution were in good agreement with magnetization values measured separately on cube samples taken at intervals of 5 or 10 cm

synthetic earthquake catalogs simulating seismic activity in the corinth gulf greece fault system the characteristic earthquake hypothesis is the basis of time dependent modeling of earthquake recurrence on major faults however the characteristic earthquake hypothesis is not strongly supported by observational data few fault segments have long historical or paleoseismic records of individually dated ruptures and when data and parameter uncertainties are allowed for the form of the recurrence distribution is difficult to establish this is the case for instance of the corinth gulf fault system cgfs for which documents about strong earthquakes exist for at least 2000 years although they can be considered complete for m 6 0 only for the latest 300 years during which only few characteristic earthquakes are reported for individual fault segments the use of a physics based earthquake simulator has allowed the production of catalogs lasting 100 000 years and containing more than 500 000 events of magnitudes 4 0 the main features of our simulation algorithm are 1 an average slip rate released by earthquakes for every single segment in the investigated fault system 2 heuristic procedures for rupture growth and stop leading to a self organized earthquake magnitude distribution 3 the interaction between earthquake sources and 4 the effect of minor earthquakes in redistributing stress the application of our simulation algorithm to the cgfs has shown realistic features in time space and magnitude behavior of the seismicity these features include long term periodicity of strong earthquakes short term clustering of both strong and smaller events and a realistic earthquake magnitude distribution departing from the gutenberg richter distribution in the higher magnitude range

significance of stress transfer in time dependent earthquake probability calculations 1 a sudden change in stress is seen to modify earthquake rates but should it also revise earthquake probability data used to derive input parameters permit an array of forecasts so how large a static stress change is required to cause a statistically significant earthquake probability change to answer that question effects of parameter and philosophical choices are examined through all phases of sample calculations drawing at random from distributions of recurrence aperiodicity pairs identifies many that recreate long paleoseismic and historic earthquake catalogs probability density functions built from the recurrence aperiodicity pairs give the range of possible earthquake forecasts under a point process renewal model consequences of choices made in stress transfer calculations such as different slip models fault rake dip and friction are tracked for interactions among large faults calculated peak stress changes may be localized with most of the receiving fault area changed less than the mean thus to avoid overstating probability change on segments stress change values should be drawn from a distribution reflecting the spatial pattern rather than using the segment mean disparity resulting from interaction probability methodology is also examined for a fault with a well understood earthquake history a minimum stress change to stressing rate ratio of 10 1 to 20 1 is required to significantly skew probabilities with 80 85 confidence that ratio must be closer to 50 1 to exceed 90 95 confidence levels thus revision to earthquake probability is achievable when a perturbing event is very close to the fault in question or the tectonic stressing rate is low

continental shelf drift deposit indicates non steady state antarctic bottom water production in the holocene a late quaternary current lain sediment drift deposit over 30 m in thickness has been discovered on the continental shelf of east antarctica in an 850 m deep glacial trough off george vth land radiocarbon dating indicates that a period of rapid deposition on the drift averaging 290 cm kyr occurred in the mid holocene between about 3000 and 5000 yr before present slower rates of around 10 cm kyr during the past 0 3000 yr and from 5000 to about 13000 yr bp coincides with deposition of bioturbated ice rafted debris ird rich sandy mud under an energetic bottom current regime in contrast the mid holocene 3000 5000 yr bp sediments are fine grained laminated to cross laminated with minimal ird content and are contemporaneous with a period of warmer marine conditions with less sea ice production this pattern suggests that bottom currents were weaker than present day in the mid holocene and that the rate of dense bottom water production was reduced at that time this scenario is consistent with the hypothesis of non steady state rates of antarctic bottom water production through the holocene as recently proposed by broecker and his colleagues

a sedimentary paleomagnetic record of the matuyama chron from the western antarctic margin odp site 1101 a high resolution paleomagnetic record for part of the matuyama chron 0 7 2 1 ma is reported for ocean drilling program site 1101 leg 178 off the antarctic peninsula pacific margin a rock magnetic investigation of 62 discrete samples revealed that the natural remanent magnetization nrm is carried by pseudo single domain magnetite progressive alternating field demagnetization of 83 m of u channels provided a polarity stratigraphy down to the olduvai subchron two geomagnetic events preceding the jaramillo subchron were identified including the cobb mountain polarity interval the bulk magnetic parameters vary by more than a factor of 20 over the entire time interval but by less than a factor of 6 over the 0 7 1 1 ma interval this latter interval was selected for paleointensity determinations which were carried out by normalizing the nrm by the anhysteretic remanent magnetization arm direct comparison of the site 1101 paleointensity record with other curves available for the same time interval suggests a geomagnetic origin for features present in the record a more quantitative comparison was achieved by means of a jackknife test performed on nine records of relative paleointensity over the 0 95 1 1 ma interval this test yielded no outlier for the period considered confirming the geomagnetic character of the records we have constructed a lowresolution stack revealing some of the characteristic paleointensity features of the jaramillo subchron fl 2001 elsevier science b v all rights reserved

quaternary evolution of the corinth rift and its implications for the late cenozoic evolution of the aegean summary we present geological and morphological observations at different scales to constrain rates of faulting and the distribution of deformation in the seismically active aegean region we focus first on the 130 km long corinth rift an asymmetric graben where a flight of terraces of marine origin are uplifted we show that the edges of the terraces lie in the footwall of the normal fault bounding the corinth rift and correspond to sea level highstands of laic pleistocene age using a detailed analysis of aerial and spot imagery supported by field observations we have mapped 10 terrace platforms and strandlines ranging in elevation from 10 to 400 m over distances of 2 to 20 km from the fault the elevation of the terraces inner edges was estimated at 172 sites with an error of 5m this data set contains a precise description of the uplift and flexure of 10 different palaeohorizontal lines with respect to the present sea level to date the deformation we correlate the corinth terraces with late pleistocene oxygen isotope stages of high sea level stands and with global sea level fluctuations using a thick elastic plate model consistent with our current understanding of the earthquake cycle and a boundary element technique we reproduce the geometry of the shorelines to constrain both mechanical parameters and the slip on the fault we show that the seismogenic layer behaves over the long term as if its elastic modulus were reduced by a factor of about 1000 all the terraces are fitted for fault slip increasing in proportion to terrace age and the component of regional uplift is found to be less than 0 3 mm yr 1 the best fits give a slip rate of 11 3 mm yr 1 on the main rift bounding fault over the last 350 kyr other geological and morphologic information allows us to estimate the total age of the main fault 1 ma and to examine the mechanical evolution of the corinth rift the minimum observed sediment thickness in the gulf places an extreme check on the results of the modelling and a lower bound on slip rate of 6 7 mm yr 1 40 per cent less than estimated with modelling even this slip rate is nearly 10 times higher than for comparable features in most of the aegean and elsewhere in the world at a larger scale the spacing and asymmetry of the rift systems in the aegean suggest strain localization in the upper mantle with slow extension starting 15 myr ago or earlier the more recent 1 myr rapid phase of rifting in corinth partly reactivated this earlier phase of extension the younger faulting in corinth appears to result from its present location in the inhomogeneous stress field process zone of the south westward propagating tip of the southern branch of the north anatolian fault we extend these relations to propose a mechanical model for the late cenozoic evolution of the aegean as the arabia europe collision progressed in eastern turkey it caused anatolia to move to the west and the north anatolian fault to propagate into the aegean where the early slow extension started to be modified about 5 ma ago the process of propagation dramatically increased the activity of some but not all of the earlier rifts the model we present is compatible with tectonic observations as well as with the seismicity the palaeomagnetic rotations and the displacement field now observed with gps and slr

a study on seismicity in the yunnan region by using the multidimensional stress release model abstract the long term seismic activity in the yunnan region has attracted much attention due to frequent occurrences of disastrous earthquakes we investigated the seismicity of the yunnan region using the multidimensional stress release model msrm to evaluate the long term seismic hazard msrm combines three factors that affect earthquake occurrence i e initial stress background tectonic loading and coseismic stress transfer and can simulate and forecast the spatiotemporal seismicity in this study a complete catalog comprising 28 strong earthquakes m 6 5 after 1900 in the yunnan region was investigated using msrm we calculated the spatiotemporal variations of seismicity rates and found that strong earthquakes occur at locations with higher seismic activity comparisons between the seismicity rates at the epicenter locations immediately before and after strong earthquakes show that the seismicity rates in the vicinity of the epicenters significantly decrease after strong earthquakes the estimated seismicity rates at the ending time january 1 2025 suggest that strong earthquake potential in the section between kunming and huaning of the xiaojiang fault and the northeastern section of the lijiang xiaojinhe fault should receive more attention while the seismicity in the southwestern part decreases and the seismicity in the middle segment of the red river fault remains low

crustal underplating and evolution in the red sea rift uplifted gabbro gneiss crustal complexes on zabargad and brothers islands the nature of the crust of the red sea outside the oceanic axial trough segments can be inferred from uplifted crustal sections exposed on the islands of zabargad and the brothers in the central and northern red sea zabargad exposes in addition to mantle derived peridotites a crustal section consisting of metagabbros and metapyroxenites associated with silicic gneisses and cut by doleritic dikes seismic velocities of samples from this section are compatible with crustal velocities obtained by seismic refraction experiments in the central and northern red sea the zabargad peridotitesilicic gneiss gabbroic association provides a sample of upper mantle lower crust in a continent before the inception of a major rifting event the petrology and mineral chemistry of the zabargad metagabbros suggest that they were originally part of a basic layered complex which crystallized at relatively high pressure 900 1000 mpa or 9 10 kbar i e over 30 km deep the gneisses have tonalitic trondhjemitic affinity and were originally equilibrated in the garnet granulite facies implying also high pressure and derivation from the lower continental crust this suggests that after the subcrustal continental lithosphere along the proto red sea rift had been consumed possibly by convective thinning but before any significant thinning of the crust basaltic melts intruded the base of the continental crust underplating it with gabbroic complexes thus crustal rifting was probably preceded by a thermal anomaly in the mantle which supports an active rifting hypothesis the gabbro pyroxenite complex and the gneisses underwent subsequently retrometamorphic events under decreasing pt conditions from granulite to amphibolite to greenschist facies implying decompression and uplift probably related to the gradual thinning of the continental crust during rifting during this stage additional gabbroic intrusions and basaltic dikes exemplified by the gabbros and dolerites from the brothers islands were emplaced at decreasing depths beneath the thinned continental crust the northern red sea crust is presently in this stage it is neither oceanic nor continental it lacks a continuous thick basaltic upper crustal layer and is made prevalently of gabbroic and doleritic intrusives with relicts of sialic continental crust subsequently basaltic injections became progressively focused in a narrow axial zone and seafloor spreading initiated at discrete equidistant hot points as observed presently in the central red sea which by axial propagation evolved into nearly continuous zones of oceanic crust accretion as observed presently in the southern red sea processes similar to those proposed here for the evolution of the red sea rift can be documented in passive margins of the atlantic and in some alpine ophiolite complexes

age of the mono lake excursion and associated tephra abstract the mono lake excursion mle is an important time marker that has been found in lake and marine sediments across much of the northern hemisphere dating of this event at its type locality the mono basin of california has yielded controversial results with the most recent effort concluding that the mle may actually be the laschamp excursion earth planet sci lett 197 2002 151 we show that a volcanic tephra ash 15 that occurs near the midpoint of the mle has a date not corrected for reservoir effect of 28 620 300 14c yr bp 32 400 gisp2 yr bp in the pyramid lake basin of nevada given the location of ash 15 and the duration of the mle in the mono basin the event occurred between 31 500 and 33 300 gisp2 yr bp an age range consistent with the position and age of the uppermost of two paleointensity minima in the napis 75 stack that has been associated with the mle philos trans r soc london ser a 358 2000 1009 the lower paleointensity minimum in the napis 75 stack is considered to be the laschamp excursion philos trans r soc london ser a 358 2000 1009

microseismicity and faulting geometry in the gulf of corinth greece summary during the summer of 1993 a network of seismological stations was installed over a period of 7 weeks around the eastern gulf of corinth where a sequence of strong earthquakes occurred during 1981 seismicity lies between the alepohori fault dipping north and the kaparelli fault dipping south and is related to both of these antithetic faults focal mechanisms show normal faulting with the active fault plane dipping at about 45 for both faults the aftershocks of the 1981 earthquake sequence recorded by king et al 1985 were processed again and show similar results in contrast the observations collected near the western end of the gulf of corinth during an experiment conducted in 1991 rigo et al 1996 and during the aftershock studies of the 1992 galaxidi and the 1995 aigion earthquakes hatzfeld et al 1996 bernard et al 1997 show seismicity dipping at a very low angle about 15 northwards and normal faulting mechanisms with the active fault plane dipping northwards at about 30 we suggest that the 8 12 km deep seismicity in the west is probably related to the seismic aseismic transition and not to a possible almost horizontal active fault dipping north as previously proposed the diverence in the seismicity and focal mechanisms between east and west of the gulf could be related to the diverence in the recent extension rate between the western gulf of corinth and the eastern gulf of corinth which rotated the faults dipping originally at 45 as in the east of the gulf to 30 as in the west of the gulf

further applications of the stochastic stress release model to historical earthquake data abstract the stochastic stress release model provides a stochastic version of the elastic rebound model which may be used to fit simulate and forecast occurrence of large earthquakes within a seismic region this paper reviews its applications to historical earthquakes from china iran and japan thereby extending and supporting earlier work on the chinese historical data the model generally provides an improvement in fit over poisson models with either constant rate or linear trend a crucial factor is the identification of suitable subregions which can act as largely independent seismic units in northern china divisions into two and four such units are considered based on recognized geophysical subdivisions in iran the best results are obtained from a subdivision into three such units the situation in japan seems more complex a preliminary model with two units gives a significant improvement of fit in one out of the two cases in all regions treating the subregions separately gives marked improvements over treating the whole region as a single unit however the quality of fit within subregions differs sharply from case to case pointing to substantial differences in the seismic regimes as reflected in the historical data

normalized remanence in sediments of the western equatorial pacific relative paleointensity of the geomagnetic field piston cores from the ontong java plateau collected during the eurydice expedition have been used to estimate regional geomagnetic paleointensity rock magnetic measurements of the sediments show that 1 the remanence is carried by stable pseudo single domain magnetite 2 the grain sizes and concentrations are relatively uniform with respect to the normalization technique and 3 susceptibility is an adequate parameter for normalizing remanent intensity in order to determine relative variations in the intensity of the paleomagnetic field we therefore have measured the remanent intensity both natural and demagnetized to 15 mt and susceptibility of archive quarters of three cores at centimeter intervals using an automated through bore magnetometer a further test of the normalized intensity records is provided by the coherence function between the normalized remanence and the susceptibility of the cores one of our cores displays high coherence over a broad range of frequencies while for two others coherence is insignificantly different from zero at the 95 level of confidence oxygen isotopic records paleontological datum levels and the brunhes matuyama boundary provide an independent temporal framework for inter core comparison when the two cores which pass our acceptance criteria are placed on a common time scale the coherence between the normalized intensity records is significantly different from zero at well above the 95 level of confidence suggesting some common input signal over the same band of frequencies furthermore there is a great deal of similarity between the records from the ontong java plateau and a record from core rc10 167 taken some 3000 km to the north the distribution of intensities obtained from these sedimentary records has the same shape as the absolute virtual dipole moment data obtained from lava flows 0 5 ma with a slightly smaller standard deviation the inter core agreement within a single region the similarity of records from 3000 km apart and the general correspondence of statistical character of these sediments with lava flow data all argue that the normalized intensity records presented here reflect variations in the intensity of the ancient geomagnetic field spectral analysis of the paleointensity time series shows that there a is significant enhancement of variance concentrated in frequencies around 33 thousand years over the period 0 350 ka this feature is however lacking for the period 350 700 ka

paleointensity of the geomagnetic field during the last 80 000 years high resolution records of the relative paleointensity of the geomagnetic field have been obtained from five marine cores three duplicate records were used to estimate the regional coherency of the data within a single area tyrrhrenian sea while the two others document the field variations in the eastern mediterranean and the southern indian ocean careful investigations of distinct rock magnetic parameters have established the downcore uniformity of the sediments in terms of magnetic mineralogy and grain sizes the time depth control was provided by oxygen isotopes and small scale variations in the deposition rates were constrained by means of tephrachronology the synthetic curve calculated from the mediterranean records provides a continuous record of the intensity variations during the last 80 000 years 80 kyr which correlates well with the sparse volcanic data available for the period 0 40 kyr the fact that identical behavior is seen in both data sets and that they also compare quite well with results from a core collected in the pacific ocean establishes the truly dipolar character of these variations the dipole field moment is characterized by large scale changes as shown by the existence of pronounced drops at 39 and 60 kyr alternating with periods of higher intensity the record suggests a periodic nature for these intensity variations however the period studied is not sufficiently long to state this conclusively these results demonstrate the potential of sediments for such studies and constitute a first step towards obtaining a global paleointensity record over a long period of time

a rapid method for magnetic granulometry with applications to environmental studies we have developed a rapid method of characterizing the fine scale variation sub micron to hundreds of microns m in the grain size of magnetite in long sediment cores this method is a new rock magnetic tool and can be readily applied to the following disciplines 1 environmental studies 2 hydrology 3 petrology and 4 geomagnetism the method consists of a comparative plot of the depth variation of two magnetic parameters the first parameter low field less than 0 1 millitesla mt or 1 oe susceptibility in a steady field is plotted on the abscissa the second parameter anhysteretic remanent magnetization arm imparted by a smoothly decreasing af of peak value 100 mt 1 000 oe in the presence of a weak steady field 0 01 0 1 mt or 0 1 1 oe is plotted on the ordinate for a sediment column in which the magnetic mineral is magnetite a plot of the two magnetic parameters shows transitions in the average magnetic grain size with depth as clearly discernible changes in the slope of a regression line fit to the individual points arm

application of linked stress release model to historical earthquake data comparison between two kinds of tectonic seismicity the linked stress release model incorporating a slow buildup of stress within a seismic region its stochastic release through earthquakes and transfer between seismic regions is applied to fit historical data from two typical kinds of seismicity earthquakes occurring in intraplate north china and plate boundary new zealand regions the best model among different modifications of the basic model which may reflect on a possible geophysical mechanism for earthquake occurrences is obtained in terms of akaike information criterion for both tectonic regions studied the linked stress release model fits the new zealand data better than a collection of independent simple models but is nearly indistinguishable from the simple stress release model in the case of north china the seismicity in a plate boundary region due to subduction is more active and complex than that in an intraplate region due to collision between tectonic plates the results highlight the major differences in tectonic seismicity especially the heterogeneities of tectonic stress fields and dynamic triggering mechanism with evidence that the crust may lie in a near critical state

evidence for a new geomagnetic reversal from lava flows in idaho discussion of short polarity reversals in the brunhes and late matuyama polarity chrons k ar ages and paleomagnetic data for basalt samples from a new core hole site e at the idaho national engineering laboratory inel indicate that the age of the reversed polarity event recorded in snake river plain lavas is older than 465 50 ka 1000 years before present reported previously by champion et al 1981 nine basalt flows eight with normal polarity and one with reversed polarity were recognized in the site e core hole the flows above and below the reversed flow have ages of 491 80 ka and 580 93 ka respectively the inclination of the paleomagnetic field direction of the reversed flow at site e agrees with the inclination of reversed flows elsewhere at inel which have an age of 565 14 ka these reversed flows were previously thought to be correlative with the emperor event we suggest that this polarity event is an older event which we name the big lost reversed polarity subchronozone and subchron a review of data documenting short reversal records from volcanic and sedimentary rocks shows that there is evidence for eight polarity subchrons in the brunhes and two besides the jaramillo in the late matuyama these 10 short subchrons begin to indicate the many short events that cox 1968 hypothesized must exist if polarity interval lengths have a poisson distribution these events are true subchrons not excursions and may or may not have low associated paleointensities although low field strengths might explain why the reversal process aborts the mean sustained polarity interval length since late matuyama chron time is 90 000 years the similarity of this number with the 105 year period of the earth s orbital eccentricity suggests anew that linkage between geomagnetic paleoclimatic and possible underlying earth orbital parameters should be evaluated

non poissonian earthquake occurrence in coupled stress release models and its effect on seismic hazard summary most seismic hazard estimations are based on the assumption of a poisson process for earthquake occurrence even though both observations and models indicate a departure of real seismic sequences from this simplistic assumption instrumental earthquake catalogues show earthquake clustering on regional scales while the elastic rebound theory predicts a periodic recurrence of characteristic earthquakes on longer timescales for individual events recent implementations of time dependent hazard calculations in california and japan are based on quasi periodic recurrences of fault ruptures according to renewal models such as the brownian passage time model however these renewal models neglect earthquake interactions and the dependence on the stressing history which might destroy any regularity of earthquake recurrences in reality to explore this we investigate the coupled stress release model a stochastic version of the elastic rebound hypothesis in particular we are interested in the time variability of the occurrence of large earthquakes and its sensitivity to the occurrence of gutenberg richter type earthquake activity and fault interactions our results show that in general large earthquakes occur quasi periodically in the model the occurrence probability of large earthquakes is strongly decreased shortly after a strong event and becomes constant on longer timescales although possible stress interaction between adjacent fault zones does not affect the recurrence time distributions in each zone significantly it leads to a temporal clustering of events on larger regional scales the non random characteristics especially the quasi periodic behaviour of large earthquakes are even more pronounced if stress changes due to small earthquakes are less important the recurrence time distribution for the largest events is characterized by a coefficient of variation from 0 6 to 0 84 depending on the relative importance of small earthquakes

link between excursions and paleointensity inferred from abnormal field directions recorded at la palma around 600 ka abstract an excursion of the geomagnetic field characterized by strongly abnormal directions associated with a field intensity as low as 7 t has been identified in a lava flow sequence from la palma canary islands the age of 602 12 ka obtained by k ar dating using the cassignol technique for a transitional flow represents our best estimate for the age of the occurrence of this episode of excursional directions this age is concordant with a minimum observed in the global sint800 composite record derived from worldwide deep sea records of relative paleointensity we show that a geomagnetic field model composed of a present day like non dipole field superimposed on an axial dipole reduced by a factor of 2 compared to its present value can account for excursional directions associated with low paleointensity in some areas while most other parts of the globe display apparently normal polarity directions we next generate through linear inversion a synthetic field model constrained by the actual la palma data and a set of directions at 30 sites distributed worldwide based on an axial dipole field with half present day intensity the energy spectrum of this synthetic field model is compatible with most of the non dipole part of the present day field and in that sense is earth like i e represents an acceptable configuration of the past geomagnetic field at 600 ka the model shows that very anomalous excursional directions covering 1 5 of the earth s surface may co exist with apparently normal directions elsewhere the new data and modeling strongly support the hypothesis that excursions are an integral aspect of secular variation there may be a continuum between normal sv and field reversals primarily controlled by the ratio of axial dipole field intensity relative to the remaining non axial dipole part

evolution of the stress field in southern california and triggering of moderate size earthquakes a 200 year perspective changes in stress in southern california are modeled from 1812 to 2025 using as input 1 stress drops associated with six large 7 0 7 5 earthquakes through 1995 and 2 stress buildup associated with major faults with slip rates 3 mm yr as constrained by geodetic paleoseismic and seismic measurements evolution of stress and the triggering of moderate to large earthquakes are treated in a tensoffal rather than a scalar manner we present snapshots of the cumulative coulomb failure function acff as a function of time for faults of various strike dip and rake throughout southern california we take acff to be zero everywhere just prior to the great shock of 1812 we find that about 95 of those well located m 6 earthquakes whose mechanisms involve either strike slip or reverse faulting are consistent with the coulomb stress evolutionary model that is they occurred in areas of positive acff the interaction between slow moving faults and stresses generated by faster moving faults significantly advanced the occurrence of the 1933 long beach and 1992 landers events in their earthquake cycles coulomb stresses near major thrust faults of the western and central transverse ranges have been accumulating for a long time future great earthquakes along the san andreas fault especially if the san bernardino and coachella valley segments rupture together can trigger moderate to large earthquakes in the transverse ranges as appears to have happened in the santa barbara earthquake that occurred 13 days after the great san andreas shock of 1812 maps of current acff provide additional guides to long term earthquake prediction

effects of variable sedimentation rates and age errors on the resolution of sedimentary paleointensity records 1 synthetic u channel records of relative paleointensity have been generated with a numerical model simulating the recording process in sediments variable quality age control and variable sedimentation rates over a time interval of 500 ky simulation results indicate that paleointensity records with mean sedimentation rates up to 15 cm ky can reflect geomagnetic dipole intensity fluctuations with some amplitude differences between individual records of nongeomagnetic origin this study confirms that relative paleointensity records have great potential as a stratigraphic tool and that a stratigraphic precision of a few thousand years can be achieved with records characterized by high sedimentation rates spectral analyses suggest that caution should be used when interpreting the power spectra of individual records and that stacked records should be favored stacked u channel records with mean sedimentation rates of 1 cm ky do not provide reliable spectral information on the dipole intensity for wavelengths shorter than 25 50 ky and their utility is limited to long term trends in paleointensity for higher sedimentation rates the range of spectral information depends on the stack resolution sedimentation rates and the age model the best results are predictably obtained with high sedimentation rates and excellent age control in these cases the power spectra are reliable for wavelengths as short as 4 ky

onto what planes should coulomb stress perturbations be resolved 1 coulomb stress maps are produced by computing the tensorial stress perturbation due to an earthquake rupture and resolving this tensor onto planes of a particular orientation it is often assumed that aftershock fault planes are optimally oriented in other words the regional stress and coseismic stress change are used to compute the orientation of planes most likely to fail and the coseismic stress is resolved onto these orientations this practice assumes that faults capable of sustaining aftershocks exist at all orientations an assumption contradicted by the observation that aftershock focal mechanisms have strong preferred orientations consistent with mapped structural trends here we systematically investigate the best planes onto which stress should be resolved for the landers hector mine loma prieta and northridge earthquakes by quantitatively comparing observed aftershock distributions with stress maps based on optimally oriented planes two and three dimensional main shock orientation and regional structural trend we find that the best model differs between different tectonic regions but that in all cases models that incorporate the regional stress field tend to produce stress maps that best fit the observed aftershock distributions although not all such models do so equally well our results suggest that when the regional stress field is poorly defined or in structurally complex areas the best model may be to fix the strike of the planes upon which the stress is to be resolved to that of the main shock but allow the dip and rake to vary

active lithospheric thinning abstract this paper starts with a discussion of the physical mechanisms capable of inducing a rapid upward migration of the lithosphere asthenosphere boundary two models based on a thermomechanical destabilization of the lower lithosphere are proposed first we consider the enhancement of small scale sublithospheric convection modes by a hot thermal plume a perturbation of a few hundred degrees is found to thin the lithosphere and generate uplift within a few tens of million years this efficient erosion from below only stops when it reaches a layer of low density such as the crust or some depleted mantle material second we show that passive lithospheric stretching leads to an unstable lithospheric configuration on the sides of the rift the denser unstretched lithosphere is subject to a lateral convective penetration by the hotter asthenospheric mantle material coming from the rift zone this lateral destabilization generates uplift of the shoulders natural examples can be found along passive continental margins a good example is given by the uplift of the scandinavian caledonides following the break up in the north atlantic

convective thinning of the lithosphere a mechanism for the initiation of continental rifting thinning of the lithosphere by heat carried convectively to its base is a possible mechanism for the initiation of continental rifting the lithosphere asthenosphere boundary marks the transition from a quasi rigid behavior of the mantle on geological time scales to a viscous one the boundary lies at or close to the solidus of the mantle material and its position is a function of temperature and pressure additional heat carried to the boundary will cause it to rise and the lithosphere to thin a one dimensional model is used to study the upward movement of the boundary from an initial equilibrium position as a consequence of an increase in the heat flux from the convecting mantle the ratio of the amount of thinning to the initial thickness is directly proportional to the increase in heat flux from the asthenosphere and inversely proportional to the difference between the final subcrustal geothermal gradient and the slope of the transition temperature profile the rate of thinning is determined by the initial and final equilibrium thicknesses the thermal diffusivity the transition temperature profile and the plume temperature profile it depends only slightly on any latent heat associated with the lithosphere asthenosphere transition during a large fraction of the time between the initial and final equilibrium states the lithosphere thins at a rate which is inversely proportional to the square root of time t even 300 km thick lithospheres may be thinned to 50 km or crustal thicknesses in tens of million years by the heat advected by mantle plumes this heat contributes to an enhanced surface heat flow because of the constant level of radioactive heat production in the crust the ratio of the final to the initial surface heat flow increases much less than the ratio of the final to the initial heat flow from the asthenosphere for large increases in asthenospheric heat flow the lithosphere is almost thinned to the crust before any significant change of surface heat flow occurs uplift due to thermal expansion upon lithospheric thinning is of the order of 102 103 m a rayleigh taylor instability acting on the thinning lithosphere may further increase thinning rates and cause magmatic intrusions of the lithosphere and surface volcanism

assessing the dipolar signal in stacked paleointensity records using a statistical error model and geodynamo simulations abstract stacks of globally distributed relative paleointensity records from sediment cores are used to study temporal variations in the strength of the geomagnetic dipole we assess the intrinsic accuracy and resolution of such stacks which may be limited by errors in paleointensity non dipole field contributions and the age scales assigned to each sediment core our approach employs two types of simulations numerical geodynamo models generate accurate predictions of time series of magnetic variations anywhere in the world the predicted variations are then degraded using an appropriate statistical model to simulate expected age and paleointensity errors a series of experiments identify the major contributors to error and loss of resolution in the resulting stacks the statistical model simulates rock magnetic and measurement errors in paleointensity and age errors due to finite sampling and approximations inherent in interpolation incomplete or inaccurate tie point information and sedimentation rate variations data sampling and interpolation to a designated age scale cause substantial decorrelation and control the maximum level of agreement attainable between completely accurate records the particular method of interpolation appears to have little effect on the coherence between accurate records but denser tie point data improve the agreement age errors decorrelate geomagnetic signals usually at shorter periods although they can destroy coherence over a broad range of periods the poor correlation between neighboring paleomagnetic records often observed in real data can be accounted for by age errors of moderate magnitude in a global dataset of 20 records modeled after the sint800 compilation and spanning 300 kyr our results show that dipole variations with periods longer than about 20 kyr can be recovered by the stacking process reasonable contributions to error in the paleointensity itself have a modest influence on the result as do non dipole field contributions whose effect is minor at periods longer than 10 kyr modest errors in the ages of tie points probably account for most of the degradation in geomagnetic signal stacked sedimentary paleomagnetic records can be improved by denser temporal sampling and careful selection of independent high quality tie points

predictive modeling of the seismic cycle of the greater san francisco bay region the seismic cycle for the san francisco bay region is synthesized by a model combining the pre and post 1906 seismic histories the long term acceleration of seismic release seismic moment benioff strain release or event count in the seismic cycle and the shorter term accelerations preceding the larger earthquakes within that cycle are modeled using an empirical predictive technique called time to failure analysis in which rate of seismic release is proportional to an inverse power of the remaining time to failure the exponent of time to failure in the accelerating sequences appears to be scale invariant and the length of the full cycle is estimated at 269 50 years the 1989 loma prieta earthquake which is the culmination of the first subcycle in the present long term seismic cycle should have been predictable with an uncertainty of 2 years in time and 0 5 in magnitude although the specific location at loma prieta was not predictable by this technique if our model is correct and if the loma prieta earthquake is the culmination of a subcycle the san francisco bay region should be entering a relatively long 20 50 years period of seismic quiescence above magnitude 6 a great earthquake such as the 1906 san francisco event would appear to be more than a century in the future

did rifting on australia s southern margin result from tectonic uplift subsidence analyses from australia s southern margin are used to investigate the idea that rifting on the margin was caused by an extensional lithospheric stress field induced by a hot thermal plume impinging on the base of the lithosphere from beneath the continental lithosphere is modelled as a thin sheet with depth dependent rheology the model does not explicitly include elastic flexural or thermal stresses the excess buoyancy of a thermal plume pushes the lithosphere upward by as much as 1 km thereby increasing its potential energy if the horizontal components of lithospheric stress are fixed at some distant plate boundary the lithosphere is a stress guide the lithospheric stress field above the plume will produce horizontal extension that may ultimately be followed by continental separation and seafloor spreading the uplift is modelled by a time dependent function which increases smoothly from zero to its peak value and then decreases back to zero using a plausible mantle rheology the amount of extension inferred at well sites on the margin typically 20 to 30 extension is explained by uplift of the lithosphere to approximately 900 m with a subsequent decay of the uplift over a period of approximately 60 m y the rise time of the uplift function is poorly constrained in the uplift model extension occurs in the subaerial environment during the late jurassic early cretaceous the initial stage of rapid subsidence observed at most well sites on the margin is due in large part to decrease of the vertical stress anomaly caused by the decay of the thermal plume or by the lithosphere moving away from above it the rapid subsidence is followed by very gradual continued subsidence attributed to cooling of the extended lithosphere as in previous studies

stress triggering and earthquake probability estimates 1 stress triggering and fault interaction concepts are beginning to be incorporated into quantitative earthquake probability estimates however the current methods are limited in their range of compatible earthquake nucleation models i introduce a new general method for translating stress changes into earthquake probability changes which can potentially be used with any physical fault model given the large uncertainties in earthquake probability calculations it is unclear whether the small probability changes resulting from stress transfer are significant and meaningful for the purposes of seismic hazard assessment i present a case study of the effect of the 1992 m7 3 landers california earthquake on the probability of a major earthquake on the san andreas fault in southern california this is a large event in a well studied region which should maximize the probability change signal and minimize the uncertainty even for this scenario the earthquake probability change for a 30 year period is not significant with respect to the initial uncertainty in the earthquake probability this example comparisons with other studies and exploration of parameter space imply that the probability changes due to stress triggering are significant only for time intervals which are short compared to the repeat time of the target fault therefore stress change calculations will be useful in long term seismic hazard assessment only for low slip rate faults otherwise stress triggering calculations are best utilized in the short term immediately following a major earthquake

revised tuning of ocean drilling program site 964 and kc01b mediterranean and implications for the δ18o tephra calcareous nannofossil and geomagnetic reversal chronologies of the past 1 1 myr 1 high resolution color reflectance records of kc01 and kc01b calabrian ridge ionian sea are presented and compared with a modified spliced high resolution color reflectance record of ocean drilling program odp site 964 this comparison revealed that kc01b is characterized by intensive deformation between 27 and 28 5 m piston depth and that some sapropels are tectonically reduced in thickness moreover the piston coring has caused considerable stretching in the top of kc01 and kc01b using a new splice of odp site 964 as guide previous astronomical tuned timescales of kc01b and odp site 964 were evaluated this evaluation resulted in a new sapropel based astronomical timescale for the last 1 1 myr the new timescale implies a much more uniform change in sedimentation rate for the ionian sea cores two prominent excursions to lighter values in the 18o record of the planktonic foraminiferal species globigerinoides ruber occur during marine isotopic stages 12 and 16 applying the new timescale these shifts correspond with maxima in obliquity and are punctuated by minima in the precession cycle they are absent in global ice volume records and are interpreted as reflecting a summer low salinity surface water lens that floats on top of extremely saline intermediate and deep waters at times of the very low sea levels during these glacial periods all biostratigraphic and magnetostratigraphic events found in kc01b and odp site 964 were re dated according to the new timescale and the ages of 33 tephra layers were reviewed the new ages for the calabrian ridge 2 and 3 magnetic events in the brunhes are concordant with minima in the global sint800 composite record derived from worldwide deep sea records of relative paleointensity and have been attributed to the big lost and la palma excursions respectively

the linked stress release model for spatio temporal seismicity formulations procedures and applications summary the linked stress release model is based on the build up of stress through elastic rebound and its dissipation in the form of earthquakes in addition stress can be transferred between large scale geological or seismic features the model can be statistically fitted to both historical and synthetic seismicity catalogues and through simulation can be used to create probabilistic forecasts of earthquake risk we review the genesis of the model provide some observations on forecasting using the model and follow with a comprehensive review of applications to date a systematic procedure for identification of the best model is illustrated by data from the persian region we then consider the evaluation of fitted models using residual point processes and information gains implications of the use of benioff strain rather than seismic moment are discussed the sensitivity of the model to regionalization magnitude errors catalogue incompleteness catalogue size and declustering magnitude cut off is then considered in detail with reference to data from north china the latter data are also used to illustrate the model evaluation techniques introduced earlier some technical material on numerical fitting simulation and calculation of the information gain is given in an appendix

lewisian gneiss geochemistry and archaean crustal development models abstract the geochemistry of lewisian amphibolite facies gneisses from northwest scotland is described with particular reference to the rare earth elements ree and compared with the geochemistry of lewisian granulite facies gneisses the results show that there are no significant differences between laxfordian amphibolite facies and scourian granulite facies gneisses in terms of ree and other immobile trace elements at equivalent silica levels although the mobile radioactive heat producing elements k rb th u are significantly lower in the granulites in both types the basic gneisses have moderately fractionated ree patterns while the intermediate and acid gneisses have strongly fractionated ree patterns with low heavy ree abundances and decreasing levels of total ree with increasing sio 2 the most silicic gneisses develop large positive europium anomalies these gross chemical similarities between gneisses from intermediate amphibolite facies and lower granulite facies crustal levels constrain models for the evolution of the archaean crust the depletion of k rb cs th and u in granulites but not other incompatible trace elements cannot be explained by magmatic processes the positive eu anomaly in the more siliceous gneisses of both facies is a function of the primary processes of crustal generation and not secondary processes such as intracrustal melting or fractional crystallisation fractionation of radioactive heat producing elements from other trace elements is a result of granulite facies metamorphism with these elements being removed by an active fluid phase the apparent lack of partial melting in lower crustal granulites suggests a model for archaean crustal growth largely through underplating by primary tonalitic magmas